b10-radio file tuning
TRANSCRIPT
Introduction to Radio Fine Tuning B10 - Page 1All Rights Reserved © Alcatel-Lucent 2008
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EVOLIUM Base Station SubsystemIntroduction to Radio Fine Tuning
B10
STUDENT GUIDE
3FL10493ADAAZZZZA Issue 01
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contents not permitted without written authorization from Alcatel-Lucent
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Terms of Use and Legal Notices
Switch to notes view!1. Safety WarningBoth lethal and dangerous voltages may be present within the products used herein. The user is strongly advised not to wear conductive jewelry while working on the products. Always observe all safety precautions and do not work on the equipment alone.
The equipment used during this course may be electrostatic sensitive. Please observe correct anti-static precautions.
2. Trade MarksAlcatel-Lucent and MainStreet are trademarks of Alcatel-Lucent.
All other trademarks, service marks and logos (“Marks”) are the property of their respective holders, including Alcatel-Lucent. Users are not permitted to use these Marks without the prior consent of Alcatel-Lucent or such third party owning the Mark. The absence of a Mark identifier is not a representation that a particular product or service name is not a Mark.
Alcatel-Lucent assumes no responsibility for the accuracy of the information presented herein, which may be subject to change without notice.
3. CopyrightThis document contains information that is proprietary to Alcatel-Lucent and may be used for training purposes only. No other use or transmission of all or any part of this document is permitted without Alcatel-Lucent’s written permission, and must include all copyright and other proprietary notices. No other use or transmission of all or any part of its contents may be used, copied, disclosed or conveyed to any party in any manner whatsoever without prior written permission from Alcatel-Lucent.
Use or transmission of all or any part of this document in violation of any applicable legislation is hereby expressly prohibited.
User obtains no rights in the information or in any product, process, technology or trademark which it includes or describes, and is expressly prohibited from modifying the information or creating derivative works without the express written consent of Alcatel-Lucent.
All rights reserved © Alcatel-Lucent 2008
4. DisclaimerIn no event will Alcatel-Lucent be liable for any direct, indirect, special, incidental or consequential damages, including lost profits, lost business or lost data, resulting from the use of or reliance upon the information, whether or not Alcatel-Lucent has been advised of the possibility of such damages.
Mention of non-Alcatel-Lucent products or services is for information purposes only and constitutes neither an endorsement, nor a recommendation.
This course is intended to train the student about the overall look, feel, and use of Alcatel-Lucent products. The information contained herein is representational only. In the interest of file size, simplicity, and compatibility and, in some cases, due to contractual limitations, certain compromises have been made and therefore some features are not entirely accurate.
Please refer to technical practices supplied by Alcatel-Lucent for current information concerning Alcatel-Lucent equipment and its operation, or contact your nearest Alcatel-Lucent representative for more information.
The Alcatel-Lucent products described or used herein are presented for demonstration and training purposes only. Alcatel-Lucent disclaims any warranties in connection with the products as used and described in the courses or the related documentation, whether express, implied, or statutory. Alcatel-Lucent specifically disclaims all implied warranties, including warranties of merchantability, non-infringement and fitness for a particular purpose, or arising from a course of dealing, usage or trade practice.
Alcatel-Lucent is not responsible for any failures caused by: server errors, misdirected or redirected transmissions, failed internet connections, interruptions, any computer virus or any other technical defect, whether human or technical in nature
5. Governing LawThe products, documentation and information contained herein, as well as these Terms of Use and Legal Notices are governed by the laws of France, excluding its conflict of law rules. If any provision of these Terms of Use and Legal Notices, or the application thereof to any person or circumstances, is held invalid for any reason, unenforceable including, but not limited to, the warranty disclaimers and liability limitations, then such provision shall be deemed superseded by a valid, enforceable provision that matches, as closely as possible, the original provision, and the other provisions of these Terms of Use and Legal Notices shall remain in full force and effect.
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Introduction to Radio Fine Tuning B10EVOLIUM Base Station Subsystem5
Course Outline
About This CourseCourse outlineTechnical supportCourse objectives
1. Topic/Section is Positioned HereXxxXxxXxx
2. Topic/Section is Positioned Here
3. Topic/Section is Positioned Here
4. Topic/Section is Positioned Here
5. Topic/Section is Positioned Here
6. Topic/Section is Positioned Here
7. Topic/Section is Positioned Here
1. Radio Fine Tuning
1. Typical Radio Problems
2. Algorithms and Associated Parameters
3. Other Algorithms
4. Algorithms Dynamic Behaviors
5. Case Studies
6. Annexes
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Course Outline [cont.]
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Introduction to Radio Fine Tuning B10EVOLIUM Base Station Subsystem7
Course Objectives
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Welcome to Introduction to Radio Fine Tuning B10
Upon completion of this course, you should be able to:
Characterize the usual radio problems and decide on the appropriate maintenance teamList and describe BSS radio algorithms and related parametersList radio parameters and verify conformity with Alcatel standardsEstimate the qualitative impact of an algorithm parameter changePropose algorithm parameter setup to solve typical radio problems for conventional networks
Hierarchical, dual-band, frequency hopping, concentric cell and GPRS networks are not covered.
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Course Objectives [cont.]
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About this Student Guide
Switch to notes view!Conventions used in this guide
Where you can get further information
If you want further information you can refer to the following:
Technical Practices for the specific product
Technical support page on the Alcatel website: http://www.alcatel-lucent.com
Note Provides you with additional information about the topic being discussed. Although this information is not required knowledge, you might find it useful or interesting.
Technical Reference (1) 24.348.98 – Points you to the exact section of Alcatel-Lucent Technical Practices where you can find more information on the topic being discussed.
WarningAlerts you to instances where non-compliance could result in equipment damage or personal injury.
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Introduction to Radio Fine Tuning B10EVOLIUM Base Station Subsystem10
About this Student Guide [cont.]
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Self-assessment of Objectives
At the end of each section you will be asked to fill this questionnairePlease, return this sheet to the trainer at the end of the training
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Instructional objectives Yes (or globally
yes)
No (or globally
no) Comments
1 To be able to XXX
2
Contract number :
Course title :
Client (Company, Center) :
Language : Dates from : to :
Number of trainees : Location :
Surname, First name :
Did you meet the following objectives ?Tick the corresponding box
Please, return this sheet to the trainer at the end of the training
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Self-assessment of Objectives [cont.]
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Instructional objectives Yes (or Globally
yes)
No (or globally
no) Comments
Thank you for your answers to this questionnaire
Other comments
Section 1 · Module 1 · Page 1
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Do not delete this graphic elements in here:
All Rights Reserved © Alcatel-Lucent 2008
Module 1Typical Radio Problems
3JK11052AAAAWBZZA Issue 01
Section 1Radio Fine Tuning
EVOLIUM Base Station SubsystemIntroduction to Radio Fine Tuning B10
3FL10493ADAAZZZZA Issue 01
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First editionLast name, first nameYYYY-MM-DD01
RemarksAuthorDateEdition
Document History
Section 1 · Module 1 · Page 3
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 3
Module Objectives
Upon completion of this module, you should be able to:
Characterize typical radio problems in order to trigger an intervention of the appropriate team
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Module Objectives [cont.]
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 5
Table of Contents
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1 Theoretical Presentation 72 Coverage Problem 93 Interference Problem 184 Unbalanced Power Budget Problem 325 TCH Congestion Problem 386 Deducing the Right Team for Intervention 43
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Table of Contents [cont.]
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Section 1 · Module 1 · Page 7
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 7
1 Theoretical Presentation
Section 1 · Module 1 · Page 8
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 8
1 Theoretical Presentation
Justification
Several sources of information can alert RFTM team: QoS indicatorsCustomers complaintsDrive testsOther teams information (NSS statistics)
As many symptoms are common to several causes, it can be necessary to:
Consolidate standard sources of informationCarry out specific examinationsDeduce the appropriate team for intervention
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2 Coverage Problem
Section 1 · Module 1 · Page 10
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 10
2 Coverage Problem
Definition and Symptoms
Definition: Bad coverageA network or cell facing coverage problems presents a bad RxLev and RxQualat the same time on some areas.
Symptoms:Customers complain about dropped calls or/and “no network”OMC QoS indicators
TCH failure rateCall drop rateLow proportion of better cell HOHigh rate of DL quality HO
A interface indicatorsHigh rate of Clear Request messages, cause radio interface failure
No information is available on non-covered parts of the network, as there are non-mobiles making calls over there!
Nevertheless, cells in border of non-covered zones do have a particular behavior:
Cell A will mainly perform Better Cell handovers towards its neighbors, whereas cell B, bordering the non-coverage area, will perform emergency handovers for MSs exiting the network.
For these MSs, mainly DL Quality HO will be triggered:
DL because MS antenna is less efficient than BTS one,
Quality rather than Level since Qual has a greater priority in Alcatel-Lucent HO causes.
AB
Section 1 · Module 1 · Page 11
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 11
2 Coverage Problem
Examination
Depending on the information sources you have:Radio Measurement Statistics (RMS) –
(RxLevel , RxQuality) matrixRadio Link Counter S vectorNumber of calls with DL/UL bad coverage (bad RxLev, bad RxQual)
Abis interface (for example with COMPASS)bad quality > 5%bad level RxLev < - 95 dBm and RxQual > 4
OMC-R or A interfaceunexpected high traffic, induced by call repetition
Billing informationHigh recall rate detected
RMS:
Provides statistics from any area in the network which are available at any time.
Cost-effective.
Easier and cheaper to perform than Drive test or Abis Trace.
The operator can tune 54 parameters (based on RxLev, BFI, C/I, Radio Link Counter S, Path Balance, etc.) to define up to 16 templates (depending on cell type – rural, urban, etc. – for example).
Trigger from the OMC-R.
NPO can save up to 15 days of RMS for the complete network.
Templates can be designed in NPO.
Default result reports are available in NPO.
Section 1 · Module 1 · Page 12
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 12
2 Coverage Problem
Typical Causes
If the actual coverage is not the one predicted by RNP tools:check antenna systemincrease or decrease antenna down-tiltcheck BS_TXPWR_MAX
to be increased if value different from RNP power budget
If the actual coverage is OK compared to the predicted ones:indoor traffic, to be handled by specific meansif black spot close to cell border, ease outgoing HO
Section 1 · Module 1 · Page 13
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 13
2 Coverage Problem
Investigation with Abis Trace
Example of an Abis trace analysis
TRX index RxLev_UL RxLev_DL RxQual_UL Path_loss_UL Path_loss_DL delta_Path_loss Delta_quality AV_MS_PWR Nb_of_samplesRxQual_DL
TRX index Qual0 Qual1 Qual2 Qual4 Qual5 Qual6 Qual7 Bad_QualityQual3
TRX index Qual0 Qual1 Qual2 Qual4 Qual5 Qual6 Qual7 Bad_QualityQual3
1 -89.29 -84.67 0.42 123.82 123.67 0.15 -0.01 34.53 30740.43
2 -89.77 -89.09 0.41 124.87 128.09 -3.21 0.03 35.11 10 2530.38
3 -83.15 -79.15 0.17 116.05 121.22 -5.16 -0.16 32.9 53390.33
DISTRIBUTION OF UPLINK QUALITY
1 86.50% 3.19% 2.50% 1.92% 2.08% 0.98% 0.26% 3.32%2.57%
2 88.11% 1.82% 1.91% 2.14% 2.17% 1.15% 0.19% 3.51%2.51%
3 77.70% 4.30% 4.30% 3.56% 3.56% 1.70% 0.17%4.36%
1 88.29% 1.82% 2.05% 1.30% 1.46% 1.76% 0.94% 4.16%2.37%
2 87.50% 2.98% 2.60% 2.11% 1.14% 0.74% 0.50% 2.38%2.43%
3 71.30% 3.82% 4.02% 4.16% 4.30% 4.23% 3.16%4.89%
DISTRIBUTION OF DOWNLINK QUALITY
5.43%
11.73%
It could have been coverage problems if this trace was made for 3 mono-TRX cells. In this case, the 3 lines are uncorrelated. Anyway, delta path loss of frequency 111 is greater than 5dB, showing a problem on this TRX.
If this is a 3-TRX cell, it cannot be a coverage problem as the three TRXs are not impacted. It will be either interference or malfunction of one TRE.
If the trace is done on 3 mono-TRX cells, in that case, it could be a coverage problem. Be careful when interpreting this result table: even if average levels in the UL and the DL are high and a lot of Quality problems are seen, nobody can say that samples with bad quality have a good level! The level seen is just an average…
One should have a look at the next slide…
Section 1 · Module 1 · Page 14
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 14
2 Coverage Problem
Investigation with Abis Trace [cont.]
Example of an Abis trace analysisThresholds
Bad Coverage
RxLev ≤ -95
RxQual > 4
InterferenceRxLev > -95
RxQual > 4
3-88.0063-95.3331-71.0031-80.0061-80.003 -80.003
57
111
1212
Number_UL: 10 253Number_DL: 10 253
Int_UL: 2BC_UL: 358Int_DL: 0%
0.02%3.49%
67-104.64
2048-
107.5051
Number_UL: 5339Number_DL: 5339
Int_UL: 0BC_UL: 290Int_DL: 0%BC_DL: 626
0.00%5.43%
Samples<Lev>BSIC63-101.542
Samples<Lev>BSICNeigh_Cell_Nb
Samples<Lev>BSICNeigh_Cell_Nb
<RxLev_Serving>= -102.17 dBm3.74%BC_DL: 115
57-100.532045-98.7121034-98.036533-98.6137
<RxLev_Serving>= -106.56 dBm
BC_DL: 244 2.38% <RxLev_Serving>= -106.17 dBm
Frequency: 92
Frequency: 111
11.73%Neigh_Cell_N
b10
All samples are Bad Coverage samples (BC). None is interference, showing that this cell is not facing any interference problem.
By the way, if the cell is:
mono-TRX, this is a coverage problem.
3 TRXs, this is a malfunction of the TRE (shown also by the high value of delta_path_loss).
Section 1 · Module 1 · Page 15
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 15
2 Coverage Problem
Investigation with RMS
Suspecting a cell coverage problemDistribution of samples per RxQual value and RxLev band
Distribution of samples per RxLev band
012
45
7
[-110,-104[
[-104,-98[
[-98,-92[
[-92,-86[
[-86,-80[
[-80,-74[
[-74,-68[
[-68,-62[
[-62,-56[
[-56,-47[
RxQuality (Nb)
RxLevel(dB)
[0, 14 793]]14 793, 23 446]]23 446, 29 586]]29 586, 34 348]]34 348, 38 239]]38 239, 41 529]]41 529, 44 378]]44 378, 46 892]
Out of RangeX
Interval of numberof samples
Downlink Samples Matrix in log scale
3
6
Not acceptable coverage limit:too low level
too bad quality
A coverage problem is observed when a significant amount of the traffic of a cell is suffering from both low level and bad quality (RxQual).
To confirm, distribution of samples per RXLEV band should be also considered to know the proportion of calls which are experiencing a low signal level.
If a lot of samples of low level and bad quality are observed for only a sub-part of the TRXs (can be one only) then a BTS hardware problem or a problem on the antenna should be suspected.
If all the TRXs are experiencing a lot of samples of low level and bad quality then a coverage problem must be suspected.
These RMS indicators are provided on the NPO tool per TRX, per Cell:
Matrix of Number of Measurement Results per DL RxQual value and per DL RxLev bandRMQLDSAM = RMS_DL_RxQuality_RxLevel_sample
Vector of Percentage of Samples per DL RxLev bandRMQLDLVDV = RMS_DL_RxLevel_distrib
Vector of Percentage of Samples per DL RxQual bandRMQLDQUDV = RMS_DL_RxQuality_distrib
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 16
2 Coverage Problem
Investigation with RMS [cont.]
Suspecting a cell coverage problemAverage TA values per RxQual value and RxLev band
16.00%14.00%12.00%10.00%8.00%6.00%4.00%2.00%0.00%
01/1
2/20
01
01/0
1/20
02
02/0
1/20
02
03/0
1/20
02
04/0
1/20
02
05/0
1/20
02
06/0
1/20
02
07/0
1/20
02
08/0
1/20
02
09/0
1/20
02
10/0
1/20
02
11/0
1/20
02
12/0
1/20
02
13/0
1/20
02
14/0
1/20
02
109876543210
%N > TA thres TA max
Maximum Timing Advance and TA > threshold
N > TA thresTA maxTA thresholdAcceptable
coverage limit:sufficient level and
good quality
Not acceptablecoverage limit:
too low level andtoo bad quality
% of TA valueover TA threshold
has also to beconsidered
012
45
7
[-110,-104[
[-104,-98[
[-98,-92[
[-92,-86[
[-86,-80[
[-80,-74[
[-74,-68[
[-68,-62[
[-62,-56[
[-56,-47[
RxQuality (Nb)
RxLevel(dB)
[0, 2]]2, 4]]4, 6]]6, 8]
Out of Range
Interval of averageTiming Advance
Uplink average TA Distribution
3
6
X
Down
In order to know if the coverage problem is due to a big amount of traffic at the cell border or rather to indoor calls, the average TA value per RXQUAL value and RXLEV band as well as the Percentage of TA values over TA threshold should be observed:
Matrix of Average TA per UL RxQual value and per UL RxLev bandRMQLUTAM = RMS_UL_RxQuality_RxLevel_TimingAdvance
Rate of Measurements Results whose TA is greater than the TA thresholdRMTAGTR = RMS_TimingAdvance_greater_threshold_rate
Maximum TA value of all values reported in Measurement Results RMTAMXN = RMS_TimingAdvance_max
Section 1 · Module 1 · Page 17
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 17
2 Coverage Problem
Investigation with RMS [cont.]
Suspecting a local cell coverage problemRxQual and RxLev per TA bands
5
4
3
2
0
1
2.5
[0,5[ [6,11[ [55,63[[49,54[[43,48[[37,42[[31,36[[25,30[[19,24[
[12,18[
-47
- 60
- 70
- 80
- 110
- 90
- 59
[0,5[ [6,11[ [55,63[[49,54[[43,48[[37,42[[31,36[[25,30[[19,24[
[12,18[
Bad qualityand bad Level
for a specific TA band
Coverage problem
In order to know if the coverage problem is due to a big amount of traffic at the cell border or rather to indoor calls, the average TA value per RXQUAL value and RXLEV band as well as the Percentage of TA values over TA threshold should be observed:
Matrix of Average TA per UL RxQual value and per UL RxLev bandRMQLUTAM = RMS_UL_RxQuality_RxLevel_TimingAdvance
Rate of Measurements Results whose TA is greater than the TA thresholdRMTAGTR = RMS_TimingAdvance_greater_threshold_rate
Maximum TA value of all values reported in Measurement Results RMTAMXN = RMS_TimingAdvance_max
Section 1 · Module 1 · Page 18
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 18
3 Interference Problem
Section 1 · Module 1 · Page 19
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 19
3 Interference Problem
Definition and Symptoms
Definition: InterferenceA network facing interference problems presents good RxLev and bad RxQualat the same time on some areas.
SymptomsCustomers complain about bad speech quality (noisy calls) and/or call dropsOMC QoS indicators:
SDCCH/TCH DropLow proportion of better cell HOHigh rate of DL/UL quality HO and interference HOLow HO success rate
A interface indicatorsHigh rate of Clear Request messages, cause radio interface failure
DL/UL depends on the way on which the interference is present.
Mainly, interferences are in the DL, due to bad frequency planning introducing interferences in the network. And this problem will not change till the frequency plan is not returned…
Sometimes, interference can be in the UL in very dense area (for example, microcell area), since MSs are very close.
Finally, sometimes interferences are not coming from BS or MS but from another radio equipment, either in the UL or the DL.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 20
3 Interference Problem
Examination with RMS
Radio Measurement Statistics (RMS)RxQual/RxLev matrix CFE/RxLev matrixC/I vectors for neighborsC/I vectors for MAFA frequencies
MAFA is a new standardized GSM feature for mobilesMAFA mobiles can provide C/I measurements from non-neighbor cells
Number of calls with DL/UL interference (good RxLev, bad RxQual)Number of noisy calls (bad RxQual) with bad voice quality (bad FER)A high rate use of the most robust AMR codecs also denounces interferences problems. But be careful, this can also be due to a pessimistic choice of the thresholds used for codec change.
The feature Radio Measurement Statistics (RMS) is designed to make far easier the work for planning and optimization of the network by providing the operator with useful statistics on reported radio measurements.
In fact these statistics give directly the real cell characteristics by taking into account the MS distribution.
Thanks to this feature, the operator is able to:
detect interfered frequencies.
assess the quality of the cell coverage.
detect and quantify cell unexpected propagation.
assess the traffic distribution in the cell from statistics on reported neighboring cells.
evaluate the voice quality in the cell.
etc.
In regards to the “RTCH Measurements Observation” (measurement type 11), the Radio Measurement Statistics feature (RMS) brings the following advantages:
smaller report files.
the report files always have the same maximum length no matter what the measurement duration is.
every measurement is taken into account (no sampling).
no more need for measurement post-processing tools for statistics. Directly available with NPO.
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3 Interference Problem
Examination with RMS [cont.]
Suspecting a cell interference problemNumber of samples per RxQual value and RxLev band
Quality problems are obvious at any level of RMS data
Interference highlighted
Network fine tuning needed
012
45
7
[-110,-104[
[-104,-98[
[-98,-92[
[-92,-86[
[-86,-80[
[-80,-74[
[-74,-68[
[-68,-62[
[-62,-56[
[-56,-47[
RxQuality (Nb)
RxLevel(dB)
[0, 14 793]]14 793, 23 446]]23 446, 29 586]]29 586, 34 348]]34 348, 38 239]]38 239, 41 529]]41 529, 44 378]]44 378, 46 892]
Out of RangeX
Interval of numberof samples
Downlink Samples Matrix in log scale
3
6
Average RxQual value per RXLev bandhas also to be considered
0123456
[-110,-104[
[-104,-98[
[-98,-92[
[-92,-86[
[-86,-80[
[-80,-74[
[-74,-68[
[-68,-62[
[-62,-56[
[-56,-47[
RxQuality (Nb)
RxLevel(dB)
Downlink average RxQuality per RxLevel
RxQualityAverage
5
Average DL RxQuality = 2.81
Section 1 · Module 1 · Page 22
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 22
3 Interference Problem
Examination with RMS [cont.]
Suspecting a Voice Quality problemNumber of samples per BFI band and RxLev band
0123456
[-110,-104[
[-104,-98[
[-98,-92[
[-92,-86[
[-86,-80[
[-80,-74[
[-74,-68[
[-68,-62[
[-62,-56[
[-56,-47[
Average CFE
RxLevel (dB)
Uplink average Consecutive Frame Erasure per RxLevel
78
Average RxQual
0
1
2
3
4
5
6CFEAverage
RxQualityAverage
Consecutive Frame Erasure (BFI) is a measurement based on loss of consecutive
speech frames over one SACCH mw.
It is directly linked to Voice Quality.
RxQual to be compared with CFE since Bad RxQual does not always mean bad VQ.
[0, 1[[1, 2[[2, 4[
[6, 8[[8, 10[
[14, 18[
[-110,-104[
[-104,-98[
[-98,-92[
[-92,-86[
[-86,-80[
[-80,-74[
[-74,-68[
[-68,-62[
[-62,-56[
[-56,-47[
CFE (Nb)
RxLevel(dB)
[0, 14 793]]14 793, 23 446]]23 446, 29 586]]29 586, 34 348]]34 348, 38 239]]38 239, 41 529]]41 529, 44 378]]44 378, 46 892]
Out of RangeX
Interval of numberof samples
Consecutive Frame Erasure Matrix in log scale
[4, 6[
[10, 14[
[14, 18[[14, 18[[22, 25[
[18, 22[
[14, 18[
These RMS indicators are provided on the NPO tool per TRX, per Cell:
Matrix of Number of Measurements Results per CFE band (or BFI band) and per UL RxLev band RMFEM = RMS_UL_ConsecutiveFrameErasure_RxLevel_sample
Vector of Average number of Consecutive Frame Erasure per UL RxLev bandRMFEBFAV = RMS_UL_ConsecutiveFrameErasure_avg_per_RxLevel
Vector of Average UL RxQual per RxLev bandRMQLUQUAV = RMS_UL_RxQuality_avg_per_RxLevel
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 23
3 Interference Problem
Examination with RMS [cont.]
Suspecting a local interference problemRxQual and RxLev per TA bands
5
4
3
2
0
1
2.5
[0,5[ [6,11[ [55,63[[49,54[[43,48[[37,42[[31,36[[25,30[[19,24[
[12,18[
Bad qualityand good Level
for a specific TA band
interference problem
-47
- 60
- 70
- 80
- 110
- 90
- 59
[0,5[ [6,11[ [55,63[[49,54[[43,48[[37,42[[31,36[[25,30[[19,24[
[12,18[
These RMS indicators are provided on the NPO tool per TRX, per Cell:
Matrix of Number of Measurements Results per CFE band (or BFI band) and per UL RxLev band RMFEM = RMS_UL_ConsecutiveFrameErasure_RxLevel_sample
Vector of Average number of Consecutive Frame Erasure per UL RxLev bandRMFEBFAV = RMS_UL_ConsecutiveFrameErasure_avg_per_RxLevel
Vector of Average UL RxQual per RxLev bandRMQLUQUAV = RMS_UL_RxQuality_avg_per_RxLevel
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 24
3 Interference Problem
Typical Causes
GSM interferenceco-channeladjacent
Non-GSM interferenceother Mobile Networksother RF sources
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3 Interference Problem
GSM Interference: Adjacent Channels
Adjacent channel interference+6dB are sufficient to interfere (9dB according to GSM)
Level
Frequency
F(BTS1)
6 dB
F(BTS2)F(BTS1) = F(BTS2)+1
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 26
3 Interference Problem
GSM Interference: Adjacent Channels [cont.]
Adjacent channel interference:Symptom
Usually downlink interferenceHigh rate of quality HO, call drop (due to HO but mainly due to radio) and TCH assignment failure
ExaminationNeighbor cells in Abis trace (only for BCCH)Non-neighbor cells in RMS (MAFA frequencies)Frequency planning C/(I adjacent) < -6dB
CorrectionDowntilt increase of interferer, or even change of antenna orientation Reduction of BS power if necessary, Change of frequency (best solution)Concentric cell implementation (1 extra TRX needed if traffic cannot be supported by Outer+Inner configuration)
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 27
3 Interference Problem
GSM Interference: Co-Channel
GSM InterferenceCo-Channel interference
-12dB are sufficient (-9dB according to GSM)by Outer+Inner configuration
Level
Frequency
F(BTS1)
-12 dB
F(BTS2)F(BTS1) = F(BTS2)
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 28
3 Interference Problem
GSM Interference: Co-Channel [cont.]
Co-channel interferenceSymptom
Usually downlink interferenceHigh rate of quality HO, call drop and call failure
ExaminationNeighbor cells in Abis trace (only for BCCH)Non-neighbor cells in RMS (MAFA frequencies)Frequency planning C/I < 12 dB
CorrectionDowntilt increase of interferer, or even change of antenna orientation Reduction of BS power, Change of frequencyConcentric cell implementation (1 extra TRX needed if traffic cannot be supported by Outer+Inner configuration)
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 29
3 Interference Problem
GSM Interference: µcellular
GSM interference: µcellular
BTS1: ARFCN 5BTS2: ARFCN 6
MS1 indoorRxLev_UL: - 90 dBm
MS2 outdoor, connected to BTS21: no level on BTS1(BTS 1 under-roof)2: - 80 dBm on BTS1:interferer UL/DL3: no level on BTS1µcell algo prevents BTS2->BTS1 HO
MS 1(indoor)
MS 2(outdoor) 1
2
3
BTS 1(Micro)
BTS 2
When interferences are created by frequency planning, it’s not so hard to detect them. But frequency planning tools mainly consider DL C/I and coverage.
Some problems are more difficult to predict. For example, let’s consider a microcell layer:
A and B are 2 microcells with the coverage described before in dense urban environment.
Even if both cells A & B are using adjacent frequencies (5 and 6), the overlapping area is far from cell A antenna. Thus, in this area C/I is lower than 6 dB.
A “red” MS is connected to cell A. When the MS starts its call, it transmits full power and a PC algorithm quickly reduces MS power as the received level is very good (microcell coverage). When MS A enters the building, it faces a loss of signal of 20 dB. Then, the MS power increases to MS_TXPWR_MAX.
A second mobile “B” is connected to cell B and moves down in the coverage area of cell B. The MS power of B decreases quickly down to MS_TXPWR_MIN as the MS is close to the antenna. But when MS B arrives outside the building where A is sitting, A and B are close and transmitting on adjacent frequencies… Then B has to increase its power to avoid dropping its call. By the way, global level of freq B is increased in all cell B… creating interference in the UL.
AB
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 30
3 Interference Problem
GSM Interference: Forced Directed Retry
GSM Interference: Forced Directed RetryThe MS should connect to cell2, but no TCH availableThe MS connects to cell 1 with forced directed retryThe MS is emitting at high level (far from BTS1)
UL interference for BTS 3BTS 1 is emitting at high level
DL interference at BTS 3
Cell 2: 45
C ell 3: 23
Ce
ll 1:
2
4
MS
BTS 2
BTS 1
BTS 3
Another more difficult case of interference: FDR
When examining the preceding situation of planning tool: no problem of C/I. No risk of interference.
The FDR algorithm allows an MS connected on an SDDCH on a cell without any free TCH to make an SDCCH-TCH handover (cause 20) so that it takes a TCH on its neighbor. As seen from the user, this is not a handover (call establishment phase, no impact on speech quality), and this algorithm is very efficient to avoid cell congestion cases.
This algorithm is mainly based on neighbor level compared to parameter L_RXLEV_NCELL_DR (n). If the level greater than this threshold, the TCH is to be seized on neighbor.
FDR is mandatory for dual layer or dual band networks (and very easy to configure in this case), since we have capture handovers. Capture handovers send traffic to lower or preferred band cells. In case these cells are congested, calls may not be established, even if upper or non-preferred band cells are free (due to MS idle mode selection, advantaging microcell for example). With the FDR algorithm, the MS takes an SDCCH in the preferred cell, and FDR is used to take a TCH on the non-preferred cell in case of congestion. This situation highlights a good network behavior, since the MS is at the same time in the coverage area of both cells (preferred and not preferred).
The situation described on the slide corresponds to the usage of FDR in a single layer network. This is in that case a heavy-to-tune algorithm presenting of lot of interference and bad quality call risks, since the mobile will be connected to a cell when being not in its service area.
umbrella
microcellFDRcapture
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 31
3 Interference Problem
Non-GSM Interference
Other mobile networks: TACS/AMPS/NMT900Inter-modulation with GSM BS/MS receiverSpurious RACH for AMPS (AMPS Tx bands close to GSM uplink band)Examination
TASC: coverage hole with 600 m from TASC BTSAMPS => 50% reduction of range if AMPS/GSM BTS collocated
Other RF interferers (Radar, shop anti-theft mechanisms, medical device, etc.)
Other RF interferers:
medical devices: GSM equipment disturb them more than the opposite!
anti-theft mechanisms.
Example:
The Microcell is showing a very high call drop rate. On one frequency, very small call duration.
No problem seen in the frequency plannig. No potential interferer.
Abis trace:
The Spectrum analyzer connected on the antenna feeder highlights a peak on GSM freq 6 in the UL…
Anti-theft mechanism turned off: no more problem…
shop
Microcellantenna
Qual
Level
Qual
Level
DL UL
interference
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 32
4 Unbalanced Power Budget Problem
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 33
4 Unbalanced Power Budget Problem
Definition and Symptoms
Definition: Unbalanced power budgetA cell facing unbalanced power budget problems presents a too high path-loss difference between UL and DL (often DL>UL)Rule: try to have delta as small as possible to avoid access network possible only in 1 direction (usually BTS->MS: OK and MS->BTS: NOK)
Symptoms:OMC QoS indicators
High rate of Uplink quality Handover causesLow incoming HO success rate (no HO Access triggered on the uplink)Degradation of TCH failures and OC call drop indicators
A interface indicatorsHigh rate of Clear Request messages, cause radio interface failure
O&M AlarmsVoltage Standing Wave Ratio BTS Alarm (VSWR)TMA Alarm (in case of G2 BTS or Evolium™ BTS with high power TRE)
UL Quality HO is triggered:
UL since the problem is in the UL.
Quality as Quality has greater priority than level.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 34
4 Unbalanced Power Budget Problem
Examination
RMS:Path Balance vector per TRXNumber of calls with abnormal bad FER (good RxQual & bad FER)
Abis monitoring:|delta path-loss| > 5dBCheck if problem is occurring for 1 TRX or all
Problem on 1 TRX: FU/CU or TRE problem or ANY problem or cables connected to this equipment.
All TRXs: problem on antenna, feeder, jumper or common equipment (e.g., ANX, ANC).
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 35
4 Unbalanced Power Budget Problem
Abis Trace
Example of an Abis trace analysis
106 -94.52 -87.19 0.43 127.55 130.19 -2.64 0.18 33.03 20660.25
Frequency Qual0 Qual1 Qual2 Qual4 Qual5 Qual6 Qual7 Bad_QualityQual3
Frequency Qual0 Qual1 Qual2 Qual4 Qual5 Qual6 Qual7 Bad_QualityQual3
89 -84.29 -75.17 0.65 115.32 118.17 -2.85 0.21 31.03 20010.44
118 -90.75 -83.36 0.46 123.22 126.36 -3.14 0.04 32.46 31930.41
124 -88.89 -85.30 0.29 120.48 128.30 -0.37 31.59 29310.67
DISTRIBUTION OF UPLINK QUALITY
106 84.75% 4.07% 3.68% 1.36% 1.50% 0.92% 0.53% 2.95%3.19%
89 81.41% 1.70% 2.95% 6.35% 2.55% 1.30% 0.10% 3.95%3.65%
118 83.62% 4.23% 4.23% 1.57% 1.79% 0.97% 0.25%3.35%
106 90.27% 3.44% 2.08% 0.92% 1.36% 0.34% 0.05% 1.74%1.55%
89 80.16% 6.45% 7.00% 1.50% 0.50% 0.45% 0.10% 1.05%3.85%
118 86.78% 2.72% 3.95% 1.41% 1.13% 1.19% 1.00%1.82%
DISTRIBUTION OF DOWNLINK QUALITY
3.01%
3.32%
Frequency RxLev_UL RxLev_DL RxQual_UL Path_loss_UL Path_loss_DL delta_Path_loss Delta_quality AV_MS_PWR Nb_of_samplesRxQual_DL
-7.82
124 90.79% 1.06% 2.18% 1.77% 1.30% 0.48% 0.07%2.35% 1.84%
124 77.14% 4.37% 5.87% 3.48% 1.36% 0.82% 1.02%5.94% 3.21%
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 36
4 Unbalanced Power Budget Problem
RMS Data
Suspecting a TRX hardware problemAverage Path Balance
A fair average Path Balance at Cell level can hide a bad value for one TRX
0500
10001500200025003000
[-110,-20[
[-20,-10[
[-10,-6[
[-6,-3[
[-3,0[
[0,3[
[3,6[
[6,10[
[10,20[
[20,110[
Nb Samples
PathBalance(dB)
NbSamples
PathBalance Distribution
Average Cell Path Balance = - 0.9 dB
These RMS indicators are provided on the NPO tool per TRX, per Cell:
Vector of the Number of Measurement Results per Path Balance bandRMPBV = RMS_PathBalance_sample
Average Path Balance valueRMPBAN = RMS_PathBalance_avg
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 37
4 Unbalanced Power Budget Problem
Typical Causes
Antennas or common RF components, TMA (pb common to all TRXs of the BTS)
TRX RF cables/LNA ... if problem located on only 1 FU
Every BTS has its proper architecture and the diagnosis must be adapted.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 38
5 TCH Congestion Problem
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 39
5 TCH Congestion Problem
Definition and Symptoms
Definition: TCH CongestionTCH Congestion rate (TCH Assignment Phase) is too high (more than 2%)Rule: try to meet the offered traffic (asked by users) by providing the right number of resources (TRX extension)
Symptoms:Customers complain about ‘Network busy’OMC QoS indicators
High “TCH Congestion rate”Low “incoming Intra/Inter BSC HO success rate” (no TCH available)High “Directed Retry rate” if activated
A interface indicator: “BSS Congestion failure in OC”High rate of Assignment Failure messages, No radio resource available
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 40
5 TCH Congestion Problem
Examination and Typical Causes
Examination: TCH CongestionOn a per cell basis examination, check the evolution of the TCH Congestion rate.
Typical causes:Special events:
Foreseeable: football match, important meeting Activate some TRXs already installed (and use Synthesized FH)Add special moving BTSs
Not foreseeable: car crash on the highway
Cells on wheel operational by several operators around the world for special events coverage & capacity:
IRMA (SFR) connected to Caen’s BSC.
Orange coverage / Football WC 1998 for Paris « Stade de France »:
Specific cells covering Paris Stadium. During games, only small capacity (using joker frequencies). During breaks, some TRX off-cells around are turned off, and frequencies are reused for stadium cells.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 41
5 TCH Congestion Problem
Typical Causes
Daily periodic problemsAt peak hour, the cell is not correctly dimensioned.
Hardware solution (refer to Annex)
Estimate the offered traffic: At OMC-R level: Traffic in Erlang/(1- TCH Congestion rate)
Use the B-Erlang law to estimate the number of TCHs required for a 2% blocking rate, thus the target configuration
Add TRXs to reach the new target configuration and find ‘joker frequencies’ and / or implement concentric cells
Warning: “offered traffic” is not the capacity delivered by the system but the traffic asked by the users.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 42
5 TCH Congestion Problem
Typical Causes [cont.]
Daily periodic problemsAt peak hour, the cell is not correctly dimensioned.
Software solutionUse specific densification features
Half RateForced Directed Retry Traffic handoverFast Traffic handover Candidate Cell Evaluation (FREEFACTOR / LOADFACTOR)
Half rate may not only mean “SW” solution. Need of G2 BSC/TC, Evolium TRE or G2 DRFU.
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6 Deducing the Right Team forIntervention
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6 Deducing the Right Team for Intervention
Process
Problem characterization
Make assumption causes
Check the tuning of default radio parameters
Consult the config. db Choose an (other) classical algo
Identify the tunable parameters
Impact estimation
Standard setting ?
No
Yes
Yes
No
No
Yes
Call expert
- Microcell, multiband- Concentric
=N
No
Yes
No
Yes
No
Yes
Parameters modificationDatabase updating
Impact simulation of aparameter modification
No
- Hopping- Marketing
Yes
QOS alarm on the network,on a BSC or some cells
- Indicators (% call drop)- Field measurements/planning- Subscriber complains
QOS team
DHCPEND
Drive test team
DHCPEND
Dimensionning team
OK
Correctionaction
Maintenance team
Planning team
NOK
Cell corrected ?Neighbor cell ?
RFT team - Interferences- Coverage (indoor)- Power budget- Congestion (TCH, SDCCH)- BSS problemInvestig problem ?
Planning/BSS causes
Standard parameters ?
Onpurpose
Systemproblem ? Simulation
OK ?
Recurrent problem ?
N timesCheck ?
With QOS ?
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6 Deducing the Right Team for Intervention
Coverage Problem
In case of coverage problem:If the field reality does not match the RNP prediction
Maintenance team to change physical configuration (tilt, azimuth, antenna height, etc.) and drive test team to check it
If the field reality matches the RNP predictionDeployment team to add sites (tri-sector, micro cellular, indoor cells)
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 46
6 Deducing the Right Team for Intervention
Other Problems
In case of interference problem:Planning team to identify the interference source and correct it (joker frequency, new frequency planning, etc.)
In case of unbalanced power budget problem:Maintenance team to check the impacted BTS (antennas, TMA, RF cables, LNA, diversity system, etc.)
In case of TCH congestion problem:Traffic team (theoretically always in relation with the marketing team) to manage the need of TRX extension, densification policy, etc.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Typical Radio Problems1 · 1 · 47
Exercise
Match the symptoms listed below with the corresponding problem.
High rate of UL QUAL HO causesGood RxLev and Bad RxQual
VSWR alarm (OMC-R) (Voltage Standing Wave Ratio)
Bad RxLev and Bad RxQual
OMC QOS indicators: % TCH ASS failure high % call drop high
% QUAL HO % call drop % call failure
Unbalanced Power Budget Bad coverage Interferences TCH
Congestion
High Path-loss difference between UL and DLLow incoming HO success rate
Time allowed: 10 minutes
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Self-assessment on the Objectives
Please be reminded to fill in the formSelf-Assessment on the Objectivesfor this moduleThe form can be found in the first partof this course documentation
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End of ModuleTypical Radio Problems
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Do not delete this graphic elements in here:
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Module 2Algorithms and Associated Parameters
3JK11053AAAAWBZZA Issue 01
Section 1Radio Fine Tuning
EVOLIUM Base Station SubsystemIntroduction to Radio Fine Tuning B10
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Module Objectives
Upon completion of this module, you should be able to:
Describe the Power control and Handover algorithmsList the associated parameters
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 4
Module Objectives [cont.]
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 5
Table of Contents
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1 Theoretical Presentation 72 Radio Measurement Principles 93 Radio Measurement Data Processing 164 Radio Link Supervision and Power Control 245 Handover Detection 476 Handover Candidate Cell Evaluation 1297 Exercise 139
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 6
Table of Contents [cont.]
Switch to notes view! Page
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 7
1 Theoretical Presentation
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 8
1 Theoretical Presentation
Justification
When the detected problem does not concern another team (Networkplanning and frequency planning, Dimensioning, Radio engineering, Maintenance) or when the other teams cannot give any solution (too tight frequency planning, no additional TRX available, no financial budget for new sites, etc.), the Radio Fine Tuning team has to find a compromise between:
High traffic density (Erl/km²/Hz)High quality of service (Call drop, CSSR, Speech quality, indoor, etc.)
Its role: take charge of radio resources management processThis process can be fully described by Power Control and Handover algorithms.
In-depth knowledge of these algorithms is required for tuning
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 9
2 Radio Measurement Principles
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 10
2 Radio Measurement Principles
Radio Measurement Mechanisms
MS connected (TCH or SDCCH)The serving cell gives the MS the list of the neighbor cells to listen toEvery SACCH, the MS reports to the serving cell via a measurement report message:
Received level of 6 best cells(which can change)DL level and qualityof serving cell
Best cellBest cell
Best cell Best c ellC ell
C ell
Best cell
Cell
Best cell
Se
rvin
g cell
SYS_INFO_5message (list)
MS reporting
The BTS sends a SYS_INFO_5 message that contains the list of neighbor cells for connected mode (The SYS_INFO_2 message contains the list of neighbor cells for idle mode).
Sys info 2bis, 2ter, 5bis and 5ter are also used for multiband networks.
MS reporting depends on EN_INTERBAND_NEIGH and on MULTIBAND_REPORTING parameters. The MS may report:
6 strongest cells of any band (MULTIBAND_REPORTING=0), or
5 strongest cells of the serving band + 1 strongest cell of another band (MULTIBAND_REPORTING=1), or
4+2 (MULTIBAND_REPORTING=2), or
3+3 (MULTIBAND_REPORTING=3).
RXLEVRange: [-110dBm, -47dBm]
Binary range: [0, 63]; 0=-110dBm, 63=-47dBm
The higher the physical or binary value, the higher the receiving level
RXQUALRange: [0.14%, 18.10%]
Binary range: [0, 7]; 0=0.14%, 7=18.10%
The lower the physical or binary value, the lower the bit error rate, the better the quality
0-2=excellent; 3=good; 4=ok; 5=bad; 6=very bad; 7=not acceptable
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 11
2 Radio Measurement Principles
Radio Measurement Mechanisms [cont.]
For each MS connected to the BTS(TCH or SDCCH)
UL received level and quality is measured every SACCHThe Timing Advance (TA) is computedThe UL information is gathered into the measurement reportThis is the message result sent by the BTS to the BSC
BSC
MS
DL measurements
UL+DL measurements
BTS
Measurementreport
Measurementresult
Candidate cellevaluation
Measurements Active channelpreprocessing
Candidate cellevaluationHO & PCdecision
Candidate cellevaluation
PC execution
HO execution
The BSC is computing algorithms usually using average value (sliding window) of these measurements
The BTS starts sending MEASUREMENT RESULT messages as soon as it receives the RL ESTABLISH INDICATION message from the MS.
The BTS stops sending MEASUREMENT RESULT messages upon receipt of one of the two following messages:
DEACTIVATE SACCH
RF CHANNEL RELEASE
Every SACCH multiframe, the BTS:
receives the MEASUREMENT REPORT message from the MS. For power control and handover algorithms, this message contains downlink measurements and, in the layer 1 header, the power used by the MS.
does uplink measurements.
reports the uplink and downlink measurements to the BSC in the MEASUREMENT RESULT message.
Input flows
Uplink radio signal: radio signal received on the Air interface.
BS_TXPWR_CONF: BS transmit power currently used by the BS.
DTX_DL: indicator of downlink DTX use.
Output flows: Abis MEASUREMENT RESULT message
Internal flows:
Radio measurements.
Air MEASUREMENT REPORT message (DL) containing DL MS radio measurements.
Uplink radio measurements (quality and level) and a flag indicating whether DTX was used in the downlink (DTX/DL).
Timing advance: last TA calculated by the BTS.
MS_TXPWR_CONF: last reported value of MS power (reported by the MS).
BS_TXPWR_CONF: value of the BS transmit power currently in use.
BFI_SACCH: bad frame indicator of the SACCH block produced every SACCH multiframe (# 480ms):
0 = SACCH frame successfully decoded
1 = SACCH frame not successfully decoded
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 12
2 Radio Measurement Principles
Structure of a Measurement Result
CHAN_NUMBER_IEID
FREQ(5) / BSIC(5) / RXLEV_NCELL(6)
Meas_result_number_IEIDMeas_result_numberElement IdentifierLength
{2} / RXLEV_UL_SUB_{2} / RXQUAL_UL_FULL / RXQUAL_UL_SUBBS_POWER_IEID{3} / BS_POWERElement IdentifierMS_TXPWR_CONF / R{3}TOA / R{2}Element IdentifierLengthLength
BA_USED / DTX_UL / RXLEV_DL_FULL0 / MEAS_VALID / RXLEV_DL_SUB0 / RXQUAL_DL_FULL / RXQUAL_DL_SUB / NO_NCELL_MNO_NCELL_M / RXLEV_NCELL(1)FREQ(1) / BSIC(1)BSIC(1) / RXLEV_NCELL(2)RXLEV_NCELL(2) / FREQ(2) / BSIC(2)BSIC(2) / RXLEV_NCELL(3)RXLEV_NCELL(3) / FREQ(3) / BSIC(3)BSIC(3) / RXLEV_NCELL(4)
0 / Message Type{7}
RXLEV_NCELL(5) / FREQ(5)
RXLEV_NCELL(4) / FREQ(4)
SACCH_BFI / DTX_DL{1} / RXLEV_UL_FULL
CHANNEL_NUMBER
RXLEV_NCELL(6) / FREQ(6)
MSG_TYPEMSG_DISK
TI {4} / Prot. Disc{4}
BSIC(4) / RXLEV_NCELL(5)
FREQ(6) / BSIC(6)
L1 Info
L3 Info:
Measurement report from
the MS
Basically, the MEASUREMENT RESULT message is composed of:
L1 info: SACCH Layer 1 header containing MS_TXPWR_CONF and TOA.
L3 info: MEASUREMENT REPORT from the MS. This message contains the downlink measurements andneighbor cell measurements.
Uplink measurements performed by the BTS.
BTS power level used.
SUB frames correspond to the use of DTX:
if the mobile is in DTX, the rxlevsub or rxqualsub is used to avoid measuring the TS where there is nothing to transmit in order not to distort measurements.
else rxlevfull is used that is to say all TSs are measured.
MS TXPOWER CONF: which is the actual power emitted by the MS.
TOA is timing advance.
SACCH BFI: bad frame indicator; 2 values 0 or 1; 0 means that the BTS succeeded in decoding the measurement report.
How the neighbor cells are coded:
BCCH1 index in BA list / BSIC1; BCCH2 index in BA list / BSIC2
why? because it does not receive LAC/CI (too long) but BCCH and replies with BCCH/BSIC
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 13
2 Radio Measurement Principles
EXtended Measurement Reporting (EMR)
Extended Measurement Reporting mechanismsExtended Measurement Order includes the MAFA frequencies the MS is asked to measureEMO sent once to the MS on SACCH after TCH seizureExtended Measurement Results include the average signal level measured on each MAFA frequency over one SACCH mf durationEMR received once per call on SACCH
Channel Activation Acknowledge
Assignment RequestPhysical Context Request
Physical Context Confirm
Channel Activation (TCH)(EMO included)
TCH ESTABLISHMENTTCH
Assignment CompleteAssignment Complete
Assignment CompleteSACCH
SACCH
SACCH
SACCH
SACCH (EMO)(MAFA Freq. List)
SACCH (EMR)(MAFA Freq. RxLev)
TCH ASSIGNMENT (OC or TC)
MS BTS BSC MSC
When the BTS receives a CHANNEL ACTIVATION with the Extended Measurement Order (EMO) included, it must send this information on the SACCH to the corresponding mobile only once.
When the BTS has to send this information, it must replace the sending of system information 5, 5bis, 5ter or 6 by this information. At the next SACCH multiframe, the BTS must resume the sending of this system information by the replaced one.
The EMO must be sent after 2 complete sets of SYS_INFO5 and 6, i.e. after the 2nd SYSINFO 6 after the reception of SABM. This guarantees the MS has received a complete set.
Then, the BTS normally receives from the MS an EXTENDED MEASUREMENT RESULT with the level of the frequencies to monitor. The BTS must make the correlation between these levels and the frequencies contained in the latest EMO information, after having decoded them, according to the order of the ARFCN. The ‘EXTENDED_MEASUREMENT_RESULT’ is NOT forwarded to the BSC, instead a ‘MEASUREMENT_RESULT’ with indication ‘no_MS_results’ is sent to the BSC.
In particular, the BTS must identify the level of the BCCH frequency of the serving cell (which must always be part of the frequencies to monitor) and apply it as the RXLEV_DL in the Radio Measurement Statistics. The other frequencies will be considered in the same way as the BCCH frequency of neighbor cells: they will be linked to the neighbor level and C/I statistics.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 14
2 Radio Measurement Principles
Exercise 1
(BSIC, BCCH index)/(LAC, CI) problem
As LAC and CI information take up too much space, the MS only reports the decoded BSIC and the BCCH index when it sends measurement on theadjacent cell.The BSC makes the correspondence between the couple (BSIC, BCCH index) and the real neighbor cell concerned [completely defined by (LAC,CI)].WHAT IS THE RISK?
Time allowed:
5 minutes
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 15
2 Radio Measurement Principles
Exercise 2
Explain why cell 2 has a very high outgoing HO unsuccessful rate and a high call drop.
Cell 2
Cell 1
Cell
(7, 62)
CI=1964GSM900
Cell 3
CI=6169GSM900
(7, 62)
(3, 46)
Cell
CI=6169GSM900
2006
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 16
3 Radio Measurement Data Processing
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 17
3 Radio Measurement Data Processing
Functional Entities
BSC
Active ChannelPre-processing
BTS
Radio LinkMeasurements
Assignment of radio measurements data processing functions in the ALCATEL BSS
The active channel pre-processing function calculates average values of signal levels, qualities and timing advance provided by the radio link measurements function.
The pre-processing is based on a sliding window averaging technique. The averaging is either weighted orunweighted depending on the type of the input parameters.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 18
3 Radio Measurement Data Processing
Active Channel Pre-Processing
Active channel pre-processing
ACTIVATED EACH TIME A MEASUREMENT IS RECEIVED
AVERAGING VALUES OF SIGNAL LEVELS, QUALITIES, TIMING ADVANCEUSING “SLIDING WINDOW” TECHNIQUE
BUILDING A BOOK-KEEPING LIST OF neighbor CELLSThe MS is reporting the 6 best cells at one timeThey can change from 1 measurement to anotherMaximum for 1 call: last 32 best ones (among 64 maximum declared as neighbor)
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 19
3 Radio Measurement Data Processing
Active Channel Pre-Processing - Principles
HANDLED by the BSCACTIVATED when the BSC receives:
ESTABLISH INDICATION from the MS on SAPI 0, orHANDOVER FAILURE from the MS, orASSIGNMENT FAILURE from the MS (in case of intracell handover)
STOPPED when a HANDOVER COMMAND is emitted in the serving BSC
AVERAGING VALUES OF SIGNAL LEVELS, QUALITIES, TIMING ADVANCEUSING “SLIDING WINDOW” TECHNIQUE
BUILDING A BOOK-KEEPING LIST OF neighbor CELLS
The pre-processing function is stopped when a HANDOVER COMMAND is emitted by the serving BSC. At this time, the MEASUREMENT RESULT messages are ignored by the pre-processing function and no update of the book-keeping tables or averaging is done anymore.
The pre-processing function is enabled again (in case of failure of an intracell or intercell handover) after reception of either messages listed above, and the old measurements are kept in the book-keeping list and taken into account in the new averaging.
The pre-processing function is completely handled by the BSC. The input parameters of this function are provided by the BTS every SACCH multiframe in the MEASUREMENT RESULT message.
The function calculates average values of levels, qualities and timing advance. The pre-processing method is based on a sliding window averaging technique. The pre-processing is done for every measurement sample, i.e. every SACCH multiframe. The averaging intervals are expressed in terms of SACCH multiframeperiods and their range is between 1 and 31.
The averaging process for any variable can start as soon as A_YYYY_XX (YYYY stands for “LEV”, “QUAL”, “PBGT” or “RANGE” and XX for “HO”, “DR”, “PC” or “MCHO”) samples, each with MEAS_VALID bit set to 0 (validity indicator reported by the MS in the MEASUREMENT REPORT message), are actually available except in case of the averaging of the received level from the neighbor cells and the averaging of AV_RXLEV_PBGT_HO, AV_BS_TXPWR_HO and AV_BS_TXPWR_DR.
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3 Radio Measurement Data Processing
Measurement Averaging
Avoid reacting too early to some “atypical” measurement(s)
75.00
80.00
85.00
90.00
95.00
100.00
105.00-------
The calculation of levels, qualities and timing advance (i.e. distance information) uses a variety of averaging window sizes as well as specific weighting factors for quality estimates.
One separate window exists for:
power control on the uplink and the downlink (A_LEV_PC , A_QUAL_PC),
emergency handover (A_LEV_HO , A_QUAL_HO , A_RANGE_HO),
fast emergency handover for microcells (A_LEV_MCHO),
better cell handover and better zone handover (A_PBGT_HO) for intra-layer, interlayer and interzonehandovers,
forced directed retry (A_PBGT_DR),
neighbor filtering and ranking for all HOs (A_PBGT_HO),
codec adaptation (A_QUAL_CA_HR_FR , A_QUAL_CA_FR_HR).
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 21
3 Radio Measurement Data Processing
Measurement Averaging [cont.]
Objective: average measurements to avoid reacting to transient degradation
Principle: sliding window: level/quality/distance values are averaged for N last samples
N = A_LEV_HO samples for uplink and downlink levelN = A_QUAL_HO samples for uplink and downlink qualityN = A_RANGE_HO samples for distanceN = A_PGBT_HO for level used in power budget equation
Example (A_LEV_HO=6, A_QUAL_HO=4, A_PBGT_HO=8)
Experiences• some experiments have shown that the number of HOs is very sensitive to
modification of these values
DL LevelAV-RxLev
AV-Lev-PGBTDL Qual
AV-RxQual
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24Meas
2 3 3 4
3
7
4
-95
7
5
-99-90 -92 -93 -98 -100 -98 -90 -80
-97 -96 -94
-95 -947 5 2
6 7 5
-75 -72 -71 -110 -70-90 -86 -81 -83 -80
-92 -89 -86 -87 -83
1 1 0 6 0
4 2 1 2 2
-69-78-80
0
2
-68 -78 -88 -95-77 -78 -81 -78
-77 -77 -78 -81
0 0 1 22 0 0 1
-98-83
-85
32
-100 -110 -110-88 -95 -100
-83 -88 -93
6 7 7
3 5 6
-110-104
-997
7
At BSC level,
Input flows
MEASUREMENT RESULT
Control flows
active channel pre-processing configuration parameters for PC:
A_LEV_PC, W_LEV_PC, A_QUAL_PC and W_QUAL_PC,
active channel pre-processing configuration parameters for HO:
A_LEV_HO, W_LEV_HO, A_PBGT_HO, W_PBGT_HO, A_QUAL_HO, W_QUAL_HO, A_RANGE_HO, A_LEV_MCHO, W_LEV_MCHO, A_PBGT_DR.
cells list for book-keeping:
BA_IND_SACCH: indicator of the change of the BA_allocation,
NBR_ADJ: number of declared adjacent cells of the serving cell denoted by n,
for n=1 to NBR_ADJ: BSIC(n) and FREQ(n).
Output flows
Averaged measurements for power control:
AV_RXQUAL_UL_PC ; AV_RXLEV_UL_PC: MS power control/threshold comparison,
AV_RXQUAL_DL_PC ; AV_RXLEV_DL_PC: BS power control/threshold comparison.
Averaged measurements for handover detection:
AV_RXQUAL_UL_HO, AV_RXQUAL_DL_HO, AV_RXLEV_UL_MCHO,
AV_RXLEV_UL_HO, AV_RXLEV_DL_HO, AV_RXLEV_DL_MCHO,
AV_LOAD , averaged traffic load
AV_BS_TXPWR_HO, AV_RANGE_HO,
AV_RXLEV_PBGT_HO, AV_RXLEV_NCELL(n), AV_RXLEV_NCELL_BIS(n).
AV_RXLEV_PBGT_DR,
AV_RXLEV_NCELL_DR(n), n=1..BTSnum.
BFI_SACCH
AV_RXQUAL_xx_CA_HR_FR, AV_RXQUAL_xx_CA_FR_HR
MS_TXPOWER_CONF / BS_POWER: last power level reported by the MS and transmit power currently used by the BS.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 22
3 Radio Measurement Data Processing
Neighbor Cell Measurement Book-Keeping
BUILDING A BOOK-KEEPING LIST OF neighbor CELLSThe MS reports the measurements of the NO_NCELL_M (≤ 6) best cells every multi-frameThe adjacent cells reported by the MS can change from one measurement to anotherThe book-keeping function keeps a table of the last 32 reported adjacent cellsClearing process of non-reported neighbors during 10s (signal level=0)
An MS is required to measure the BCCH power level of a number of BCCH frequencies. These measurements are used for the power budget computation in the BSC and the candidate cell evaluation in the BSC.
The MS reports to the BTS, in the MEASUREMENT REPORT message, the measurements of the NO_NCELL_M (NO_NCELL_M <= 6) best cells it receives (RXLEV_NCELL, BCCH frequency index and BSIC number) for eachmultiframe. In case of multiband capability, the mobile reports the best cells of each supported frequency band (if available). This reporting is allowed at BSS level by the flag EN_INTERBAND_NEIGH and it is specified by the parameter MULTIBAND_REPORTING.
The adjacent cells reported by an MS can change over the averaging interval. The book-keeping function keeps a table composed of the last 32 reported adjacent cells, the maximum number of which is NBR_ADJ. The total number of adjacent cells for which measurements reported by the MSs are available within the average interval is BTSnum.
The BSC G1 maintains a table of up to 150 cells, from which up to 64 can be declared as adjacent cells to a given cell.
The BSC G2 maintains a list of up to 1000 cells, from which up to 64 can be declared as adjacent cells to a given cell.
Because the maximum number of adjacent cells may be greater than 32, the number of adjacent BCCH frequencies is limited to 32. Moreover, a mechanism for overwriting obsolete entries in the book-keeping table, when new cells are reported, is provided.
When the variable BTSnum reaches its maximum value of 32 and at least one new cell has to be entered in the list, then the BSC sorts out all cells in the book-keeping list, which have been reported with signal level = 0 for the last 20 measurements (10 seconds).
This is done by summing the raw measurement values over the last 20 samples. All the corresponding cell entries are cleared from the bookkeeping list, BTSnum is decreased by the number of cleared entries and some of the vacant entries are used to include the new cells.
The end of the comment is on the next page...
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 23
3 Radio Measurement Data Processing
Exercise
Measurements averagingWith ‘averaging window’ excel sheet:
Compute averaging on quality,distance and levelMake charts with different slidingaveraging windows
Time allowed:
10 minutes
Raw measurements
Average measurements
AV_RXLEV_DL_HOA_LEV_HO=8
A_LEV_HO=2
2 3 4 5 6 7 8 9 10 11 12 13 14 151-75
-80
-85
-90
-95
Number ofmeasurements
Level
AV_RXQUAL_DL_HO
3
A_QUAL_HO=8
A_QUAL_HO=2
2 3 4 5 6 7 8 9 10 11 12 13 14 151
4
3
2
1
0
Quality
AV_RANGE_HO
10
12
15
A_RANGE_HO=8
A_RANGE_HO=2
2 3 4 5 6 7 8 9 10 11 12 13 14 151
25
20
15
10
5
Distance
DL LevelA_LEV_HO=8A_LEV_HO=4A_LEV_HO=2
DL LevelA_QUAL_HO=8A_QUAL_HO=4A_QUAL_HO=2
DL LevelA_RANGE_HO=8A_RANGE_HO=4A_RANGE_HO=2
-802
10
-78211
-8439
-873
11
-802
13
-75112
-77414
-944
15
-793
16
-77117
-782
18
-843
17
-89319
-90320
-914
19
DL LevelDL QualityDistance
-80-76
-82-82-86
-82-81-87
-82-82-78
-81-82-78
-81-80-81
-82-82-87
-84-85-90
-85-89-91-81
-82-86
-82-84
-82-78-79
A_LEV_HO=4
Number ofmeasurements
Number ofmeasurements
323
323
333
334
334
334
332
332
33
22
332 3
A_QUAL_HO=4 3
131416
131617
151718
151718
161818
171920
181920
1112
1113
1313
1411 10
A_RANGE_HO=4 10
Fill up the table with average function. The chart will be automatically processed
The fact that there may not be enough cleared entries to store new measurements is excluded, see justification below:
Because the MS must resynchronize at most every 10s with the neighbor cells it monitors, it is useless to keep cells in the book-keeping list which have not been reported for more than 10s, it will be impossible to make a handover towards these cells.
Therefore, the overwriting mechanism described above will function correctly if there are less than 32 cells reported in every 10s, which makes an average rate of 3 new cells per second.
The potentiality of overflow of the book-keeping list is therefore excluded.
The book-keeping is performed according to the BSIC and BCCH frequency couple. This function updates the table every multiframe except if the measurement report is missing or Measurement Valid Bit is set to not valid. When the level of a cell is not reported, a zero must be entered as measurement value. For eachmultiframe and for each of the NO_NCELL_M cell measurements it receives, the function has to check the BSIC number and the BCCH frequency index (FREQ(n)).
When the couple (BSIC, BCCH frequency) is not in the reference list (received from the OMC), the corresponding measurements should be discarded.
The BTSnum variable is updated every multiframe except if the measurement report from the MS is missing. It is incremented by the number of new couples (BSIC number, BCCH frequency index) registered as described above.
Remark: Two cells can have the same BSIC number or the same BCCH frequency index. Therefore, the couple of these parameters is needed to define a cell.
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4 Radio Link Supervision and PowerControl
Section 1 · Module 2 · Page 25
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4 Radio Link Supervision and Power Control
Functional Entities
BSCBTS
Radio LinkSupervision
PC CommandPC ThresholdComparison
Radio LinkCommand
Radio LinkMeasurements
Active ChannelPre-processing
Assignment of PC functions in the ALCATEL BSS
The two main functions specified in this document and implemented in the Alcatel-Lucent BSS are:
Radio link supervision and radio link command:
These functions handle the detection of the radio link failure so that calls which fail either from loss of radio coverage or unacceptable interference are satisfactorily handled by the network. The radio link supervision is responsible for detection of the loss of the radio link, based on incorrectly received SACCH frames. The radio link command is responsible for commanding to set the power at a maximum level for radio link recovery or to clear the call when the radio link has failed.
The radio link recovery can be activated or not, depending on a configuration flag (EN_RL_RECOV). The radio link failure procedure is always running and clears the call when the radio link has failed.
Power control:This function handles the adaptive control of the RF transmit power from the MS and the BS. The RF power control aims at minimizing the co-channel interference and also at reducing the DC power consumption of the MS. This function is in charge of detecting a need for a power command and then of applying this power command. Therefore it can be divided into two processes: PC threshold comparison and PC command. MS and BS power control are operating independently, they can be activated or not, depending on configuration flags (EN_MS_PC and EN_BS_PC).
All these functions require directly or indirectly input parameters provided by the function in charge of the radio link measurements.
Most of the input data required by the power control functions are provided by the Active channel pre-processing function.
The figure depicts in a general way:
the interconnections between all these functions,
the implementation of these functions in the Alcatel-Lucent BSS.
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4 Radio Link Supervision and Power Control
Radio Link Supervision
Principles
Detection (by BTS) of a radio link failure with an MSnotification to BSC for radio resource release
Try to recover an MS when radio becomes pooroptional mechanism “radio link recovery”by requiring BTS and MS to transmit at maximum power
Equivalent mechanism in MS for Radio Link Failure detection
The determination of the radio link failure is based on a counter. According to the GSM Technical Specification 05.08 for the BSS, the criterion for incrementing/decrementing this counter should be based:
either on the error rate on the uplink SACCH,
or on RXLEV/RXQUAL measurements of the MS.
In the Alcatel-Lucent BSS, it is based on the number of SACCH frames which cannot be decoded.
It must be stressed that this criterion is related to the first one recommended above but it is not exactly the same. The Alcatel-Lucent criterion is in fact the one recommended by the GSM Technical Specification 05.08 for the MS.
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4 Radio Link Supervision and Power Control
Principles of Radio Link Supervision
For each active radio channel, a counter “S” is:decremented by 1 each time an SACCH frame cannot be decoded (BFI=1)incremented by 2 each time a valid SACCH frame is received
The value of S gives a measure of the “quality” of uplink radio linkInitial value of S = BS_RADIO_LINK_TIMEOUT
if S reaches N_BSTXPWR_M, a radio link recovery is triggered (optional)if S reaches 0, a radio link failure is detected
RADIOLINK_TIMEOUT_BS(_AMR) ≥ RADIOLINK_TIMEOUT is important because the mobile must release the radio channel first
B10
M SBTS
C o u n te r S C o u n ter S '
R L T O _ B S(B S _ R A D IO _ L IN K _T IM E O U T ) 1 8
16 R L T O (T 1 0 0)(R A D IO _ L IN K _ T IM E O U T )
N _ B ST X P W R _ M 1 3 R a d io lin k
R ec o v e ry
S A C C H b lo c klo s t: - 1
S A C C H b lo c krec e iv ed : + 2
0 0R ad io lin kF a ilu re
The radio link supervision function is performed in the BTS and it uses three parameters given to the BTS in the TRX configuration data message:
EN_RL_RECOV: flag enabling/disabling the sending of CONNECTION FAILURE INDICATION by the BTS when the need for radio link recovery is detected.
N_BSTXPWR_M: threshold for the radio link recovery.
RADIOLINK_TIMEOUT_BS: threshold (number of SACCH messages) for the radio link failure.
RADIOLINK_TIMEOUT_BS_AMR: threshold (number of SACCH messages) for the radio link failure of calls using an AMR codec.
In addition, the function handles a counter named S. RADIOLINK_TIMEOUT_BS is the initial and maximum value of S.
For each SACCH not decoded, S is decremented by 1 while for each SACCH decoded, it is incremented by 2. The incrementation or decrementation is performed if the following condition is met: RADIOLINK_TIMEOUT_BS(_AMR) >= counter S >= 0.
As soon as the counter S is equal to the threshold N_BSTXPWR_M, the radio link recovery is triggered if EN_RL_RECOV = ENABLE. Therefore, in the case where the shadowing is so strong that all SACCH frames are lost, the radio link recovery will be triggered after (RADIOLINK_TIMEOUT_BS(_AMR) - N_BSTXPWR_M) SACCH periods.
The parameter N_BSTXPWR_M must be set according this simple behavior.
If the radio link recovery is not successful, as soon as S reaches 0, the radio link failure procedure is applied.
As soon as a radio link failure is detected, the radio link supervision must be started again in the BTS.
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4 Radio Link Supervision and Power Control
S Counter for Radio Link Supervision
SACCHnumber
S value
29282726252423222120191817161514131211109876543210
5
10
15
20
25
RADIO_LINK_TIMEOUT_BS
N_BSTXPWR_M
SBFI
S = f [ BFI(t) ]
1
Received Events
Activate supervision: activation of the radio link supervision from the BTS telecom layer 3,
SACCH, BFI = 1: not decoded SACCH frame,
SACCH, BFI = 0: decoded SACCH frame.
Note: the BFI flag is internal to the BTS and does not deal with the BFI flag defined by the GSM.
Deactivate supervision: deactivation of the radio link supervision by the BTS telecom layer 3.
Transmitted Events
Radio link recovery: indication sent to the radio link command function in order to set the BS and MS powers to the maximum.
Radio link failure: indication sent to the radio link command function in order to release the call.
These events are sent to the BSC in the CONNECTION FAILURE INDICATION message:
In case of Radio link recovery, the BTS sends only once (to avoid overload of the Abis interface) the CONNECTION FAILURE INDICATION message to the BSC with cause "set MS/BS-TXPWR-M” (value: '001 1111', reserved for National use). This action (message formatting) is performed by the GSM layer 3.
In case of Radio link failure, the BTS sends the CONNECTION FAILURE INDICATION message with cause 'Radio link Failure' to the BSC.
Thus, the CONNECTION FAILURE INDICATION message on Abis is not showing any call drop. One should look at the cause of CONFAIL.
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4 Radio Link Supervision and Power Control
Radio Link Recovery
The BTS sends a Connection Failure Indication messageCause ‘001 1111’ reserved for national usage (Alcatel-Lucent: RLR)On K1205: “set MS/BS_TXPWR_MAX (Alcatel-Lucent only)”
The BSC sends BS and MS POWER CONTROL messagesRequired for maximum possible valuesThe MS required level is embedded in the SACCH header in the downlink
Optional mechanismEN_RL_RECOV =ENABLEuseless without power control“master” vs. power control
The action consists in increasing the power of the MS and of the BTS to their maximum, in a single step, if the link is failing, i.e. the BTS is not able to decode the SACCH anymore for some period of time.
This functionality is performed upon reception of the CONNECTION FAILURE INDICATION message (cause “set MS/BS-TXPWR-M”) from the BTS. This message can be sent by the BTS only if EN_RL_RECOV = ENABLE. Upon reception of this message, the radio link command function:
1. sends to the BTS a power increase command up to BS_TXPWR_MAX (BS_TXPWR_MAX_INNER if the MS is on the inner zone of a concentric or multiband cell) in the BS POWER CONTROL message.
2. sends to the MS a power increase command up to min(MS_TXPWR_MAX,P) (min (MS_TXPWR_MAX_INNER,P) if the MS is in the inner zone of a concentric or multiband cell) in the message MS POWER CONTROL.
When a radio link recovery occurs, the radio link command function gives an indication to the power control function once the power increase has been commanded.
The maximum power increase of the MS is 2dB per 60 ms. Thus, if MS_TXPWR_MAX=33dBm and MS_TXPWR_MIN=13dBm, the MS coming from MIN to Max will take 600 ms.
Note: the BS Power Control process does not interfere with the recovery procedure since the former comes to a halt when no SACCH multiframe is received. Thus, the BS power control process does not take into account the radio link recovery event.
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4 Radio Link Supervision and Power Control
Radio Link Failure
The BTS sends a Connection Failure Indication messageCause ‘radio link failure’
The BSC notifies the loss to the MSCUsually Clear Request “radio interface failure”
The BSC releases locally the radio resource (TCH or SDCCH)Radio frequency Channel Release message sent to BTS
The call is dropped!
The task of the radio link command consists in informing the call control function to release the call.
Concentric Cell or Multiband CellThe power value BS_TXPWR_MAX_INNER is applied in case of radio link recovery for an MS in the inner zone. The power value BS_TXPWR_MAX is applied in case of radio link recovery for an MS on an outer zone channel.
Note: the radio link supervision procedure will function also if SACCH frames are not lost continuously, but with a longer reaction time.
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4 Radio Link Supervision and Power Control
Exercise: Radio Link Supervision
With the “RLS” excel sheet, taking into account the measurements with BFI and the parameter values (N_BSTXPWR_M and RADIOLINK_TIMEOUT_BS), indicate when:
A radio link recovery is triggeredA radio link failure is triggered
Time allowed:
5 minutes
0
1
1000
01111
1101
0111111101
1
1
0
1
0
1
1
1
1
1
18
5
17181818
1817161514
12111312
1211109876576
10
6
8
17
18
4
11
7
3
13 Radio Link Recovery
BFI S Action
Radio Link Supervision
N_NSTXPWR_MAXRLTO_BS
1318
Parameters:
N_BSTXPWR_M
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4 Radio Link Supervision and Power Control
Power Control
Aims of Power controlReduce emitted power to the minimum possibleMinimum power levels:
GSM: 11dBm, 9dBm, 7dBm and 5dBmDCS: 2dBm, 0dBm
Ensuring quality and received level of peer entityAdapted in real-timeFor Uplink PC: decrease UL interference and save MS batteryFor Downlink PC, decrease DL interference
Output Power (dBm)GSM-900
Output Power (dBm)DCS-1800
Powerlevel
14
15
16
17
18
19
15
13
11
9
7
5
2
0
-
-
-
-
BTS MS
Uplink
RXLEV_UL
MS_TXPWRDownlink
BS_TXPWR
RXLEV_DL
The main objective of the power control, in connection with handover algorithms, is to allow a maximum number of MSs to operate in the network while maintaining a minimum interference level.
The algorithms must ensure that any mobile is connected with the cell in which the output powers from the MS and the BS are as low as possible (to reduce MS power consumption and interference in the network) while keeping a satisfactory link quality.
When on a sufficient duration, the propagation conditions keep worsening, then action must be taken.
The first action is to increase the output power levels at the MS or the BS. When the maximum allowed value has been reached, a handover may become necessary.
To reflect this philosophy in macrocells (not in microcellular environment), the algorithm allows for handover on quality and strength reasons only when the last step of power control has been reached. If propagation conditions worsen rapidly when the MS is at low power, the power control algorithm allows to reach quickly the maximum power.
Nevertheless great care must be taken in choosing the relative values of the thresholds for power control and handover as well as the averaging window sizes (smaller window size and higher threshold for power control than for handover). It must be remembered that, although it is desired that the MS transmits with the lowest possible power, it is more important not to lose a call. Thus early triggering for the power control is possible by choosing small values for the averaging window sizes and higher comparison thresholds.
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4 Radio Link Supervision and Power Control
Power Control Principles
Based on a threshold comparison mechanism
Decrease emitted power when received level AND quality measured by peer entity are better than a given value
Increase emitted power when the received level OR quality is lower than a given value
Does not decrease power if the resulting level is below the low level threshold
FEATURE REAL FAST PC GIVES REACTIVITY TO THE ALGORITHMS
The threshold comparison process detects the need to change the MS power level. This detection is done by comparison between the averaged values produced by the active channel pre-processing function and thresholds.
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4 Radio Link Supervision and Power Control
Power Control Detection
MS Power control (for BS PC, replace MS by BS and UL by DL)
U_RXQUAL_UL_P
L_RXQUAL_UL_P
1
2
-95 -93 -85
L_RXLEV_UL_P
POW_RED_STEP_SIZE
U_RXLEV_UL_P
Quality
Level
-90 -75-86
3
2
A need for a PC command is detected when one of the conditions above is true. Then, the information for the execution of the PC command is given to the ‘PC command’ process.
The MS power control function can be disabled with a flag EN_MS_PC. This flag is changeable from the OMC-R.
Note: The GSM coding of quality is contra-intuitive, since the value 0 codes for the best quality and 7 for the worst. Thus, the comparison between two quality values must be understood in the opposite way in terms of quality.
Note: POW_RED_STEP_SIZE is used in two ways: for PC_COMMAND (decrease of MS power) and for PC_THRESHOD_COMPARISON (to avoid ping-pong effect).
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4 Radio Link Supervision and Power Control
MS PC Threshold Comparison
MS Power increase: IfAV_RXQUAL_UL_PC > L_RXQUAL_UL_P + OFFSET_RXQUAL_FHAV_RXQUAL_UL_PC ≤ L_RXQUAL_UL_P + OFFSET_RXQUAL_FHand AV_RXLEV_UL_PC < L_RXLEV_UL_P
Then PC_COMMAND(MS, INC, MS_P_INC dB, <min(MS_TXPWR_MAX, P))
Power decrease: IfAV_RXQUAL_UL_PC < U_RXQUAL_UL_Pand AV_RXLEV_UL_PC >= L_RXLEV_UL_P + POW_RED_STEP_SIZE
AV_RXQUAL_UL_PC ≤ L_RXQUAL_UL_P + OFFSET_RXQUAL_FHand AV_RXQUAL_UL_PC ≥ U_RXQUAL_UL_P and AV_RXLEV_UL_PC > U_RXLEV_UL_P
Then PC_COMMAND(MS, RED, MS_P_RED dB, >MS_TXPWR_MIN)
OFFSET_RXQUAL_FH is an internal variable that is equal to 0 in case of Non-Hopping cell and OFFSET_HOPPING_PC in case of BBH or RH.
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4 Radio Link Supervision and Power Control
MS Power Control Command
MS Power command philosophy:
Target received level TARGET_RXLEV_ULmiddle threshold between U_RXLEV_UL_P and L_RXLEV_UL_P
Adaptive power step sizeAccording to the average received levelLimited power step size to MAX_POW_INC and MAX_POW_REDIf only Quality problem: fixed power step size
POW_INC_STEP_SIZE and POW_RED_STEP_SIZE Two weighting factors to modify the algorithm reactivity when level problem
POW_INC_FACTOR for power increasePOW_RED_FACTOR for power decrease
Whenever any of the threshold conditions occurs, a PC command must be sent to the MS over the air interface.
In order to compute the adaptive power step size, the middle threshold between the upper threshold U_RXLEV_UL_P and the lower threshold L_RXLEV_UL_P is considered.
This threshold is regarded as the target received level around which the MS should always stay. The following algorithm tries to maintain and bring the MS power closer to this target threshold. The size of the power step is limited to MAX_POW_INC for an increase of the MS power and MAX_POW_RED for a decrease of the MS power.
When the received level is between the two thresholds U_RXLEV_UL_P and L_RXLEV_UL_P (i.e. no need to change the level) and a power control on quality cause is triggered, fixed power step sizes are applied: POW_INC_STEP_SIZE for power increase and POW_RED_STEP_SIZE for power decrease.
Two weighting factors POW_INC_FACTOR (for power increase) and POW_RED_FACTOR (for power decrease) allow to modify the reactivity of the algorithm (the more POW_INC_FACTOR is nearby 1, the greater the reactivity of the algorithm is and the larger the power step size is).
The target received level is TARGET_RXLEV_UL for the uplink path.
TARGET_RXLEV_UL corresponds to the next higher multiple of 1 dB from (U_RXLEV_UL_P + L_RXLEV_UL_P)/2.
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4 Radio Link Supervision and Power Control
Fast and Normal Comparison
Example:Example
4800 960 1440 1920 2400
-110
-100
-90
-80
20 dB
Time(ms)
Power level(dB)
6 dB (POW_INC_STEP_SIZE)
4 SACCH =1 Measurement Report (MR)
MR 2 MR 3 MR 4
Need for PC Command detected
PC Command
Normal Power Control
Fast Power Control
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4 Radio Link Supervision and Power Control
MS Power Increase Command Computation
PC_COMMAND (MS, INC, MS_P_INC dB, < power max)If MS_TXPWR < power maxthen increase MS_TXPWR by min(MS_P_INC, MAX_POW_INC, powermax-MS_TXPWR)Where MS_P_INC is evaluated by the following algorithm:
if (AV_RXLEV_UL_PC < L_RXLEV_UL_P) (problem of level)if (AV_RXQUAL_UL_PC ≤ L_RXQUAL_UL_P + OFFSET_RXQUAL_FH) (sufficient
quality)then MS_P_INC = roundup[ POW_INC_FACTOR* (TARGET_RXLEV_UL -
AV_RXLEV_UL_PC)]else MS_P_INC = roundup[ MAX ( POW_INC_FACTOR * (TARGET_RXLEV_UL -
AV_RXLEV_UL_PC ), POW_INC_STEP_SIZE )]else (problem of quality)
MS_P_INC = POW_INC_STEP_SIZE
In the equations:
MS_TXPWR is the last MS_TXPWR_CONF value reported by the BTS.
‘roundup’ means ‘round to its next higher multiple of 2 dB’.
‘rounddown’ means ‘round to its next lower multiple of 2 dB’.
The rate of change of MS power is required to be one nominal 2 dB step every 60 msec. Thus a 30 dB step change should be accomplished in 900 msec. The operator should be warned of this as it may impact on the choice of settings for MS_P_CON_ACK and MS_P_CON_INT.
Then the ordered value of the MS transmit power, called MS_TXPWR, is sent to the MS as follows:
The BSC sends the MS POWER CONTROL message to the BTS (i.e. to the TRX handling the relevant channel) which then forwards the PC command to the MS in the Layer 1 header.
The MS applies the PC command and confirms this action by transmitting the applied power value (MS_TXPWR_CONF) on the uplink SACCH in the layer 1 header.
On SACCH channel, the MS may not send the MEASUREMENT REPORT message (e.g. in case of transmission of Short Message).
In this case, the BSC receives a MEASUREMENT RESULT message which does not contain the MEASUREMENT REPORT. The BSC takes into account the MS_TXPWR_CONF variable.
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4 Radio Link Supervision and Power Control
MS Power Decrease Command Computation
PC_COMMAND (MS, RED, MS_P_RED dB, > power min)If MS_TXPWR > power minthen decrease MS_TXPWR by min(MS_P_RED, MAX_POW_RED, MS_TXPWR-power min)Where MS_P_RED is evaluated by the following algorithm:
if (AV_RXLEV_UL_PC > U_RXLEV_UL_P) (good level)if (AV_RXQUAL_UL_PC ≥ U_RXQUAL_UL_P) (sufficient quality)then MS_P_RED = roundup[ MAX(POW_RED_FACTOR* (AV_RXLEV_UL_PC-
TARGET_RXLEV_UL)), 2dB]else MS_P_RED = roundup[ MAX ( POW_RED_FACTOR * (AV_RXLEV_UL_PC-
TARGET_RXLEV_UL), POW_RED_STEP_SIZE )]else (good quality)
MS_P_RED = POW_RED_STEP_SIZE
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4 Radio Link Supervision and Power Control
Frequency Hopping Cases
OFFSET_RXQUAL_FH
This variable allows to take into account the frequency hopping in the RxQualevaluation (see Annex)
Defined on a per cell basis
Algorithm:If Frequency hopping applied
then OFFSET_RXQUAL_FH = Offset_hopping_PCElse OFFSET_RXQUAL_FH = 0
In order to take into account the frequency hopping in the RXQUAL evaluation, the variable OFFSET_RXQUAL_FH is introduced.
If Frequency hopping is applied on the corresponding channel then OFFSET_RXQUAL_FH = Offset_Hopping_PC otherwise OFFSET_RXQUAL_FH = 0
Offset_Hopping_PC is a parameter defined on a per cell basis.
PC Downlink in Frequency Hopping CaseIn this case, the BSC inhibits the BS power control on all the channels which use the BCCH carrier. The
entity performing the BS power control in the BSC gets all the information concerning a new channel and decides whether to activate the BS power control for this channel. The power control must be inhibited when the frequency used by the new channel is the same as the frequency used for the BCCH in the BTS (cell) in which the channel is activated.
For any channel which has the BCCH frequency in its hopping sequence (MA), the MS is measuring a very good downlink level each time it hops on the BCCH. To avoid that this results in a too optimistic average, it is possible to require from the MS not to include the BCCH measurement in the averages. This is achieved by setting the PWRC flag to 1 in the SYSTEM INFORMATION type 6 message sent by the BSS on the SACCH.
If the channel is hopping only on the BCCH frequency (after a transmitter failure), it is considered as a non-hopping channel and it is concerned by the non-frequency hopping case.
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4 Radio Link Supervision and Power Control
Power Control Timers
Timers
T_SDCCH_PC allows the inhibition of PC on SDCCH
When a new power is required, the confirmation is awaited: MS_P_CON_ACKBS_P_CON_ACK
As soon as the new power is acknowledged, a fixed duration is awaited to trigger a new change of power, if necessary:
MS_P_CON_INTBS_P_CON_INT
The timer T_SDCCH_PC allows to inhibit the MS and BS power control on SDCCH:
This timer is changeable at the OMC-R level on a per cell basis. It is triggered upon receipt of theESTABLISH INDICATION message after SDCCH activation for immediate assignment procedure. As long as the timer runs, the power control is inhibited on SDCCH.
If the timer expires, the power control will be enabled again on SDCCH.
If the timer is running at the sending of the RF CHANNEL RELEASE message, the timer is stopped.
T_SDCCH_PC is useful in case of long SDCCH phases.
During SDCCH for call establishment, PC disabled should be preferred with a view to secure call setup. Nevertheless, if SMS usage is very high, SDCCH phases may be long. In this case, to avoid interference, PC will be enabled after T_SDCCH_PC expiry (about 5s).
After any PC command is sent to the MS, some time must be expected before MS_TXPWR_CONF (power confirmation sent by the MS on the uplink SACCH) can reach the desired value. The timer MS_P_CON_ACK is triggered after any power modification command to monitor that the desired transmission power MS_TXPWR is reached.
If MS_P_CON_ACK elapses before the expected value of MS_TXPWR_CONF is received, the power control decision process is resumed immediately with the last MS_TXPWR_CONF received.
If the expected value of MS_TXPWR_CONF is received before the timer MS_P_CON_ACK is elapsed, the timer MS_P_CON_ACK is stopped and the timer MS_P_CON_INT is triggered. Then the MS PC threshold comparison process is resumed with MS_TXPWR_CONF for the same MS as soon as MS_P_CON_INT expires.
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4 Radio Link Supervision and Power Control
Power Control Timers [cont.]
IF xx_P_CON_ACK is expiring, it is a system problem: Wrong setting of xx_P_CON_ACK (too short)No reception of power command by the MS
a radio link recovery can be activatedProblem on Abis
repetition of BS power command
The expiry of P_CON_INT is a normal mechanism
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4 Radio Link Supervision and Power Control
Extra Information
LEVEL and QUALITY USED in EQUATION are average ones with window size A_QUAL_PC and A_LEV_PCBS POWER CONTROL INHIBITED ON BCCH frequency
BCCH must be emitted at the maximum levelMS dynamic constraint
minimum 2dB every 60 msEmitted power can be changed by radio link supervision algorithm
Radio link supervision has a greater priorityActivation of power control can slow down HO decision
some causes can be triggered only if the MS (BTS) is emitting at the maximum power
Interaction with Radio Link Command
The MS power control function is informed of a radio link recovery by the radio link command function. Once the indication is received, the PC command process is resumed immediately:
timer MS_P_CON_ACK is started (or reset and started if running),
If MS_P_CON_ACK elapses before the expected value of MS_TXPWR_CONF is received, the power control decision process is resumed immediately with MS_TXPWR_CONF = min(MS_TXPWR_MAX,P).
According to GSM Technical Specification 05.08 section 7.1, the BCCH carrier must be broadcast with a constant power in the cell. In this release of the Alcatel-Lucent BSS, this constant value is set to the maximum power allowed in the cell that is defined by the parameter BS_TXPWR_MAX.
This means that all dedicated channels (TCH, SDCCH) which are on the BCCH frequency must always be transmitted with the maximum power, i.e. the BCCH power must not be changed by the BS power control function.
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4 Radio Link Supervision and Power Control
Exercise: Power Control
Power control UL(Remark: Use the default parameters document)
What happens if we do not use Frequency Hopping?Why is it better to have A_LEV_PC=A_LEV_HO/2?Thresholds:
Lower QUAL of RX uplink = 3High QUAL of RX uplink = 2Lower LEV of RX uplink = -90dBmUpper LEV of RX uplink = -75dBmPOW_RED_STEP_SIZE= 4POW_INC_STEP_SIZE= 6
Put the right threshold in the next slide chart
Time allowed: 25 minutes
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4 Radio Link Supervision and Power Control
Exercise: Power Control [cont.]
Power control ULFor each case:
PC triggered?Step size value?
With POW_INC_FACTOR = 0,6and POW_RED_FACTOR = 0,6and MAX_POW_INC = MAX_POW_RED = 8
Quality
Level
Nb of case
AV RXQUAL UL PC
AV RXLEV UL PC
Power control
Delta value
1 2 3 4 5 6
0 1 2 6 3 4
-98 -80 -73 -69 -86 -91
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4 Radio Link Supervision and Power Control
Exercise: Power Control [cont.]
Power control DLThresholds:
L_RXLEV_DL_P = -85dBm POW_INC_FACTOR = 0.6U_RXLEV_DL_P = -75dBm POW_RED_FACTOR = 0.8L_RXQUAL_DL_P = 2.9 MAX_POW_INC = 16dBU_RXQUAL_DL_P = 1 MAX_POW_RED = 16dBA_QUAL_PC = 4 BS_P_CON_ACK = 3sA_LEV_PC = 4 BS_TXPWR_MIN = -16dB
Using the Trace Abis Excel file, find each parameter value:POW_INC_STEP_SIZE = ? BS_P_CON_INT = ?POW_RED_STEP_SIZE = ? OFFSET_RXQUAL_FH = 0 or 1 ?
Which phenomenon can you observe as regards the successive PC commands?
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 47
5 Handover Detection
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5 Handover Detection
Handover Main Objective
Send connected MS to another cellWhen needed: “rescue/emergency” handoverIf useful: “better cell” handover
Toward the “best” cellFrom a radio point of view
Power budgetLevel
From a traffic point of viewLess loaded target
From a dynamic point of viewMS speed“History” of the call
From an operator point of view
Emergency Intercell HandoversThese handovers are triggered when the call conditions deteriorate significantly in order to rescue the call. The causes are:
"too low quality" ,"too low level", " too long MS-BS distance", “too short MS-BS distance”, "consecutive bad SACCH frames", "level dropping under high threshold".
Better Cell HOThese handovers are triggered to improve the overall system traffic capacity. This spans: interference reduction, signaling load reduction, traffic unbalance smoothing. The basic assumption for these handovers is that they should respect the cell planning decided by the operator.The causes are:
"power budget", "high level in neighbor lower layer cell for slow mobile","high level in neighbor cell in the preferred band" ,“traffic handover”.
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5 Handover Detection
Principle
The BSC analyzes averaged measurement results:active channel pre-processing (measurements averaging and book-keeping)
To detect need/utility to handoverHandover detection process
To choose/rank target cells according to several criteriaCandidate cell evaluation process
To perform the handoverHandover management process
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5 Handover Detection
Functional Entities
BSCBTS
Radio LinkMeasurements
HO Detection
Active ChannelPre-processing
HO Preparation
HO CandidateCell Evaluation
HO Management
HO Protocol
MSC
Assignment of HO functions in the ALCATEL BSS
The HO Preparation function can also be named "handover algorithms" as the algorithms described are the "heart" of this function.
The Alcatel-Lucent handover preparation is derived from the basic algorithm found in Annex A of the GSM Technical Specification 05.08.
The handover preparation is in charge of detecting a need for handover and proposing a list of target cells. Therefore it can be divided into two processes: handover detection and handover candidate cell evaluation.
The handover detection process analyzes the radio measurements reported by the BTS and triggers the candidate cell evaluation process each time a handover cause (emergency or better cell type) is fulfilled.
The handover candidate cell evaluation works out a list of possible candidate cells for the handover. This list is sorted according to the evaluation of each cell as well as the layer they belong to (in a hierarchical network) and the frequency band they use (in a multiband network).Once the handover preparation is completed, the handover decision and execution (handover management entity) is performed under the MSC or BSC control. The directed retry preparation is performed by the handover preparation function. Once the directed retry preparation is completed, the directed retry is performed either under the BSC control (internal directed retry) or under the MSC control (external directed retry).
An example of implementation of these functions except for directed retry is given in the GSM Technical Specification 05.08.
The handover preparation requires indirectly input parameters provided by the function in charge of the radio link measurements.
Most of the input data required by the handover functions are provided by a function called: Active channel pre-processing.
The figure above depicts in a general way:
the interconnections between these functions,
the implementation of these functions in the Alcatel-Lucent BSS.
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5 Handover Detection
Handover Causes Detection
Based on the contents of the measurement results
The BSC is computing the need or utility to trigger a handover
25 HO causes, split into 2 main categories: Emergency handover
quality, level, distance, etc.Better cell handover
power budget, traffic, etc.
Some are specific to hierarchical and concentric architectures
The process is achieved in the BSC.
Each time a set of pre-processed (averaged) measurements is available, this process checks whether a handover is needed. If the need for a handover is detected, the target cell evaluation process is triggered.
In case of a handover alarm, the handover detection process gives to the cell evaluation process:
the preferred target cell layer: lower, upper or none.
the raw candidate cell list, which can be either all neighbors, or the subset which verifies the handover causes (plus other specific cells in particular cases). With each cell is given one of the handover causes which have been verified.
The cause of handover.
Four main handover categories are provided, depending on the cause of handover and the context of application. The context of application for a handover is either "intercell" (the handover is performed between two different cells) or "intracell" (the handover is performed in the same cell).
The detection of a need for handover is performed through handover causes which are going to be detailed.
The cause of handover is based either on a situation of emergency (this cause is therefore called "emergency cause") or on the existence of better conditions. In this last case, the name of the cause depends on the context of application: for intercell handovers, it is called "Better cell cause". For intracell handovers, it is called "Better zone cause", as it is applied only in the case of interzone handovers in concentric or multiband cells.
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5 Handover Detection
Handover Causes
16 HO causes for standard networks (26 on the whole)
B10
Emergency HO
Cause 2
Cause 3
Cause 4
Cause 5
Cause 6
Cause 15
Cause 16
Cause 26
Too low quality on the uplink
Too low level on the uplink
Too low quality on the downlink
Too low level on the downlink
Too long distance between theMS and the BTS
High interference on the uplink(intracell HO)High interference on the downlink(intracell HO)AMR channel adaptation HO(HR to FR)
Better conditions HO
Cause 12
Cause 20
Cause 23
Cause 24
Cause 27
Cause 28
Cause 29
Power budget evaluation
Forced directed retry
Traffic
General capture
AMR channel adaptationHO (FR to HR)
Fast traffic HO
TFO HO
30 Move from PS to CS zone
HO causes for Extended Cells:
Emergency causes:
cause 22: too short MS-BTS distance
HO causes for hierarchical or multiband network:
Emergency causes
cause 7: consecutive bad SACCH frames received in a microcell
cause 17: too low level on the uplink in a microcell compared to a high threshold
cause 18: too low level on the downlink in a microcell compared to a high threshold
Better causes
cause 14: high level in neighbor lower layer cell for slow mobile
cause 21: high level in neighbor cell in the preferred band
HO causes for Concentric cells:
Emergency causes
cause 10: too low level on the uplink in the inner zone
cause 11: too low level on the downlink in the inner zone
Better causes
cause 13: Outer zone level uplink and downlink
HO causes inter techno:
Cause 31: 2G to 3G HO
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5 Handover Detection
Handover Causes 2: UL Quality
CAUSE 2: too low quality on the Uplink
AV_RXQUAL_UL_HO > L_RXQUAL_UL_H + OFFSET_RXQUAL_FHand AV_RXLEV_UL_HO <= RXLEV_UL_IHand MS_TXPWR = min (P, MS_TXPWR_MAX)and EN_RXQUAL_UL= ENABLE
Size of window for averaging quality: A_QUAL_HOSize of window for averaging level: A_LEV_HO
Quality
Level
Quality and Level causes (2, 3, 4, 5, 15, 16)
The aim of these causes is to keep the call going when the radio link is degrading otherwise the radio link failure might be detected and the call released. These causes wait generally for the power control process to increase the BTS and MS power to their maximum values, except for the causes specific to microcellular environment.
Handover on "too low level" is used to avoid situations where the interference level is low, while the attenuation is quite high. These conditions may appear for example in big city streets which enable a line of sight propagation from the BTS antenna. There is in this case a risk of abrupt quality degradation, if the MS moves away from the line of sight street.
In case of simultaneous low-level and low-quality signals, an intercell handover is requested.
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5 Handover Detection
Handover Causes 3: UL Level
CAUSE 3: too low level on the uplink
AV_RXQUAL_UL_HO <= L_RXQUAL_UL_H + OFFSET_RXQUAL_FHand AV_RXLEV_UL_HO < L_RXLEV_UL_Hand MS_TXPWR = min (P, MS_TXPWR_MAX)and EN_RXLEV_UL= ENABLE
Size of window for averaging quality: A_QUAL_HOSize of window for averaging level: A_LEV_HO
Quality
Level
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5 Handover Detection
Handover Causes 4: DL Quality
CAUSE 4: too low quality on the downlink
AV_RXQUAL_DL_HO > L_RXQUAL_DL_H + OFFSET_RXQUAL_FHand AV_RXLEV_DL_HO <= RXLEV_DL_IHand BS_TXPWR = BS_TXPWR_MAXand EN_RXQUAL_DL= ENABLE
Size of window for averaging quality: A_QUAL_HOSize of window for averaging level: A_LEV_HO
Quality
Level
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5 Handover Detection
Handover Causes 5: DL Level
CAUSE 5: too low level on the downlink
AV_RXQUAL_DL_HO <= L_RXQUAL_DL_H + OFFSET_RXQUAL_FHAV_RXLEV_DL_HO < L_RXLEV_DL_HBS_TXPWR = BS_TXPWR_MAXand EN_RXLEV_DL= ENABLE
Size of window for averaging quality: A_QUAL_HOSize of window for averaging level: A_LEV_HO
Quality
Level
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5 Handover Detection
Handover Causes 6: Distance
CAUSE 6: Too long distance between the MS and the BTS
AV_RANGE_HO > U_TIME_ADVANCEand EN_DIST_HO= ENABLE
Size of window for distance averaging: A_RANGE_HO
Too long distanceBTSGood level but …
This cause is used when a dominant cell provides a lot of scattered coverages inside other cells, due to propagation conditions of the operational network. The consequence of these spurious coverages is the probable production of a high level of co-channel interference.
This cause is different from the others as it is more preventive. It does not make use of the propagation conditions of a call. It just does not allow an MS to talk to a BTS if it is too far away.
It may happen for example that some peculiar propagation conditions exist at one point in time that provide exceptional quality and level although the serving BTS is far and another is closer and should be the one the mobile should be connected to if the conditions were normal.
It may then happen that these exceptional conditions suddenly drop and the link is lost, which would not have happened if the mobile had been connected to the closest cell. So for these reasons, this cause does not wait for the power control to react.
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5 Handover Detection
Handover Causes 12: Power Budget
CAUSE 12: Power budgetDecision based mainly on comparison of serving and neighbor cells for:
downlink level of serving and neighbor cellsmaximum emitting level of MS
Aiming at decreasing UL & DL emitted power
Should be the “normal” handover typeno matter of emergency
In this case, there is another cell with a better power budget i.e., the link quality can be improved or maintained with a reduced transmit power of both the MS and the BTS. The radio link is not degraded but there is the opportunity to decrease the overall interference level by changing the serving cell of the given MS.
In conjunction with power control, it presents the advantage to keep the interference as low as possible, since it minimizes the path loss between the BTS and the MS.
This cause is especially designed to cope with the requirement that the mobile should be connected with the cell with which the lowest possible output powers are used. To assess which of the cells is this "best cell", the algorithm performs every measurement reporting period the comparison of the path loss in the current and in the neighbor cell. This is a feature special to GSM which is made possible because the mobile measures the adjacent cell signal levels and reports the six best ones.
This power budget gives the difference in path loss between the current cell and the adjacent cells reported by the mobile.
When PBGT(n) is greater than 0, then the path loss from cell n is less than the path loss from the serving cell and thus the radiated power in the downlink direction, and therefore in the uplink direction as well, will be lower in cell n than in the current cell.
However it would not be advisable to hand over the MS to another cell as soon as PBGT is greater than 0, because the MS would probably oscillate between the two adjacent cells as the propagation conditions vary. An hysteresis mechanism is implemented to avoid this undesirable effect.
No PBGT between different layers.
Ok between different bands if EN_INTERBAND_PBGT_HO = 1
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5 Handover Detection
Handover Causes 12: Power Budget [cont.]
CAUSE 12: Power budget equation
PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO - (BS_TXPWR_MAX – AV_BS_TXPWR_HO)- (MS_TXPWR_MAX(n) – MS_TXPWR_MAX)- PING_PONG_MARGIN(n, call_ref)
The MS may be handed over from the serving cell indexed 0 to a neighbor cell indexed n only if the power budget exceeds the handover Margin(0,n). The handover Margin(0,n) can be modified according to the traffic situation in the serving cell and the neighbor cell n. In this way, power budget handover can be delayed towards a loaded cell and traffic load handover can be triggered from a loaded cell. Once the MS is handed over, the same algorithm is applied in the new cell, and a new PBGT is computed (which will be close to the opposite value of PBGT in the old cell) and compared to a new HOMargin. (Thus, the global hysteresis (from cell 0 to cell n and back to cell 0) is the sum of the two HOMargins).
However, it is still possible that a ping-pong mechanism is created by different handover causes, for instance a handover may be triggered towards a neighbor cell for bad quality, but in the neighbor cell, a handover back may be triggered for power budget reasons. In order to avoid this, an additional anti-ping-pong mechanism is implemented in the power budget calculation. It enables to penalize for a certain time the cell on which the call has been before.
In case of handover from SDCCH to SDCCH, this cause does not take the traffic situation into account.
In multiband cell environment, the mobile can operate in a different band than the frequency band of the BCCHs. This can lead to circular ping-pong handovers from the inner zone if the new band is DCS 1800 or to the impossibility to trigger PBGT handovers from the inner zone if the preferred band is GSM 900.
To avoid this problem, when the MS is in the inner zone of a multiband cell, it may be handed over from the serving cell indexed 0 to a neighbor multiband cell indexed n only if the power budget exceeds the handover Margin(0,n) plus the offset handover margin which allows to handicap or favor the PBGT (In the inner zone, the cause “power budget” is only checked between multiband cells, in a way to maintain the MS in the preferred band).
The offset handover margin can possibly be used in concentric cells.
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5 Handover Detection
Handover Causes 12: Power Budget [cont.]
CAUSE 12: Power budget
AV_RXLEV_NCELLreceived level of BCCH of neighbor cell
AV_RXLEV_PBGT_HOreceived level of serving cell (BCCH or not)
AV_RXLEV_NCELL - AV_RXLEV_PBGT_HOthe highest is the best neighbor cellbut serving might not be at the maximum level (with DL power control)
necessity to have a corrective factor
PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO - (BS_TXPWR_MAX – AV_BS_TXPWR_HO)- (MS_TXPWR_MAX(n) – MS_TXPWR_MAX)- PING_PONG_MARGIN(n, call_ref)
Δ BCCH = AV_RXLEV_NCELL(n) - (AV_RXLEV_PBGT_HO + C)
with C = BS_TXPWR_MAX - AV_BS_TXPWR_HO.
This corresponds to the difference of received BCCH signal levels.
A correction factor C is taken into account for the serving cell, because the received signal level (i.e. AV_RXLEV_PBGT_HO) may not be measured on BCCH.
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5 Handover Detection
Handover Causes 12: Power Budget [cont.]
CAUSE 12: Power budget
BS_TXPWR_MAX – AV_BS_TXPWR_HO
BS_TXPWR_MAX are attenuations, not absolute level= (“bts_max_power”+BS_TXPWR_MAX) -(“bts_max_power”+AV_BS_TXPWR_HO)
AV_BS_TXPWR_HO: average of BS_POWER over A_PBGT_HO measurementscorrective factor used to compensate for the fact that the serving cell may not emit at the maximum level
AV_RXLEV_NCELL-[AV_RXLEV_PBGT_HO+(BS_TXPWR_MAX-AV_BS_TXPWR_HO)]
compare received level of neighbor and serving cells as if the serving one was emitting at the maximum level
PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO - (BS_TXPWR_MAX – AV_BS_TXPWR_HO)- (MS_TXPWR_MAX(n) – MS_TXPWR_MAX)- PING_PONG_MARGIN(n, call_ref)
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5 Handover Detection
Handover Causes 12: Power Budget [cont.]
CAUSE 12: Power budget
MS_TXPWR_MAX(n)maximum emitting power for the MS in neighbor cell n
MS_TXPWR_MAXmaximum emitting power for the MS in the serving cell
MS_TXPWR_MAX(n) - MS_TXPWR_MAXCorrective factor to compensate for the difference of maximum power of each cell
MS_TXPWR_MAX(n) - MS_TXPWR_MAX = bts_max_power(n) - bts_max_powerwhich should be the case if delta_path_loss is equilibratedif not exact, can be corrected with HO_MARGIN(0,n)
PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO - (BS_TXPWR_MAX – AV_BS_TXPWR_HO)- (MS_TXPWR_MAX(n) – MS_TXPWR_MAX)- PING_PONG_MARGIN(n, call_ref)
Then, another correction factor must be taken into account because the maximum BS powers of the serving and neighbor cells may be different:
Δ TXPWR= MS_TXPWR_MAX(n) - MS_TXPWR_MAX.
As the first step of calculation is based on the downlink parameters, this correction factor should be based on the maximum BS powers used in the serving and neighbor cells.
Two reasons (which are not completely de-correlated) for not using the BS powers can be envisaged:
for a given cell, the GSM does not specify formally the maximum BS power of the neighbor cells. Only BS_TXPWR_MAX is defined (it is sent on the air interface),
it is not easy for the evaluating BSC to know the maximum BS powers of the neighbor cells.
The use of the maximum MS powers requires that the difference of MS powers is equal to the difference of BS powers. This condition is met in most cases. If it is not the case, the difference can be corrected by the operator with the HO_MARGIN(0,n) parameter (HO hysteresis).
PBGT >0: the neighbor cell is more advantageous as the path loss is lower than in the current cell.
PBGT <0: the serving cell is more advantageous than the current cell.
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5 Handover Detection
Handover Causes 12: Power Budget [cont.]
CAUSE 12: Power budget
Hysteresis to avoid ping-pong HO
Static hysteresis defined for each couple of cells:HO_MARGIN (0,n)
can also be used to correct delta_path_loss
“Dynamic” penalty for call coming from cell n: ping_pong_margin(n,call_ref)penalty PING_PONG_HCPapplied during a limited duration: T_HCPnot used if call arrived with a forced directed retrypenalty defined on a cell basis
PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO - (BS_TXPWR_MAX – AV_BS_TXPWR_HO)- (MS_TXPWR_MAX(n) – MS_TXPWR_MAX)- PING_PONG_MARGIN(n, call_ref)
The main drawback of this handover category is the risk of "ping-pong " effect, which is an oscillating back and forth handover between two (or three) cells. As the "better cell" handovers are meant to find the "best cell", the variation of the radio conditions will trigger a big amount of better cell handovers, if the algorithms have a too sensitive reaction. Hence, some mechanisms are forecast, in order to prevent these oscillations from occurring repeatedly at given places.
PING_PONG_MARGIN(n,call_ref) is a penalty put on the cell n if:
it is the immediately precedent cell on which the call has been,
this cell belongs to the same BSC as the serving cell,
the call has not performed a forced directed retry towards the serving cell,
less than T_HCP seconds have elapsed since the last handover.
In this case PING_PONG_MARGIN(n,call_ref) = PING_PONG_HCP
If the call was not precedently on cell n, or if the preceding cell was external, or if the call has just performed a forced directed retry, or if the timer T_HCP has expired, then PING_PONG_MARGIN(n,call_ref) = 0
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5 Handover Detection
Handover Causes 12: Power Budget [cont.]
CAUSE 12: Power budgetping_pong_margin example
Cell Cell Cell
Case 1
Case 3
Case 2
OK1
Ping-pong case A OK with Static margin (HO_MARGIN)
Not a ping-pong case
OK due to T_HCP expiry
2
3 Ping-pong case B
This chart shows the efficiency of the anti-ping-pong mechanism.
But, never forget that the anti-ping-pong mechanism distorts the serving areas of the cells.
This is why interference problems might occur when enabling this mechanism. Tuning PING_PONG_HCP parameter is thus very important.
Warning: this mechanism is not applied for emergency handovers (new mechanism in B7 exists for capture HO, based on T_INHIBIT_CPT timer).
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5 Handover Detection
Handover Causes 12: Power Budget [cont.]
CAUSE 12: Power budget
If EN_TRAFFIC_HO(0,n)=ENABLEThen PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER
+ max(0, DELTA_HO_MARGIN(0,n))
(n=1…BTSnum)Else PBGT(n) > HO _MARGIN(0,n)
+OFFSET_HO_MARGIN_INNER
AND AV_RXLEV_PBGT_HO ≤ RXLEV_LIMIT_PBGT_HO
AND EN_PBGT_HO = ENABLE
Size of window for level averaging: A_PBGT_HO
Cause 12 HO is correlated with HO cause 23. This is why there are two equations according to the activation of HO cause 23 (EN_TRAFFIC_HO).
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5 Handover Detection
Handover Causes 12: Power Budget [cont.]
CAUSE 12: Power budget
Mechanism to avoid PBGT HO if the level from the serving cell is high enoughRXLEV_LIMIT_PBGT_HO: threshold above which it is not necessary to trigger a handover on power budgetAV_RXLEV_PBGT_HO: average of the received levels over A_PBGT_HOmeasurements
Specific to particular algorithms (not mentioned in this course)OFFSET_HO_MARGIN_INNER: offset which allows to take into account the radio differences between outer and inner zones (especially in case of multi-band cells)
RXLEV_LIMIT_PBGT_HO: Dense Network Handover Regulator features
The feature aims at optimizing the better cell handovers, especially in the microcellular environment.
In very dense networks, there is a lot of overlapping between adjacent cells: a better cell handover will be realized very often. Since B6, the Alcatel-Lucent BSS tunes the number of handovers performed to the accurate need by taking into account the level received by the serving cell.
Therefore, the best trade-off between quality of speech and intempestive handovers is achieved.
Why?Especially in microcellular environment (where cell radius is smaller), the better cell HO (based on Power
Budget) is likely to be performed at a high rate to the detriment of the quality.
But it is necessary to maintain the better cell HO.
How?
With a modification of the power budget triggering cause.
Principles
HO cause 12 (Power Budget HO) is modified and takes into account the received downlink level of the serving cell (new criterion): if the received level is high enough, there is no need to perform an HO.
Consequence
Less HOs when the number of overlapping cells is high.
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5 Handover Detection
Handover Causes 12: Power Budget [cont.]
CAUSE 12: Power budget
Specific to traffic considerationsDELTA_HO_MARGIN(0,n): evaluated according to the traffic situation of the serving cell and the neighbor cell n (Traffic_load(n)) in the following way:If Traffic_load(0) = high and Traffic_load(n) = low,
DELTA_HO_MARGIN(0,n) = - DELTA_DEC_HO_margin
If Traffic_load(0) = low and Traffic_load(n) = high,DELTA_HO_MARGIN(0,n) = DELTA_INC_HO_margin
Else DELTA_HO_MARGIN(0,n) = 0
PhilosophyThis mechanism aims at penalizing cause 12 detection when the traffic in the serving cell is low and is high in the cell n.
DELTA_HO_MARGIN(0,n) is evaluated according to the traffic situation of the serving cell and the neighbor cell n (Traffic_load(n)) in the following way:
If Traffic_load(0)=high and Traffic_load(n)=low
DELTA_HO_MARGIN(0,n)= -DELTA_DEC_HO_margin
If Traffic_load(0)=low and Traffic_load(n)=high
DELTA_HO_MARGIN(0,n)= DELTA_INC_HO_margin
else DELTA_HO_MARGIN(0,n)=0
where DELTA_DEC_HO_margin allows the cause 23 (traffic handover) detection.
When the traffic in the serving cell is high and is low in the cell n:
DELTA_INC_HO_margin allows to penalize the cause 12 detection when the traffic in the serving cell is low and is high in the cell n.
Note:In the case of concentric or multiband cells, if the channel is in the inner zone (ZONE_TYPE = INNER), BS_TXPWR_MAX and MS_TXPWR_MAX in equation must be replaced by BS_TXPWR_MAX_INNER and MS_TXPWR_MAX_INNER respectively.
If the channel is in the outer zone (ZONE_TYPE = OUTER), the formulation of equation is not changed.
Note: The value of PBGT(n) is calculated every SACCH period for each neighbor cell n whose measures are kept in the book-keeping list.
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5 Handover Detection
Handover Causes 12: Power Budget [cont.]
CAUSE 12: Power budget
Traffic_load() is a function managed for every cell of a BSCTraffic_load() can have three values:
high: cell is loadedlow: cell is unloadedindefinite: cell is neither loaded nor unloaded
Traffic_load() value is modified according to the long-term traffic evaluation algorithm using the following parameters:
A_TRAFFIC_LOAD, N_TRAFFIC_LOAD, HIGH_TRAFFIC_LOAD, IND_TRAFFIC_LOAD, LOW_TRAFFIC_LOAD: can be modified per cellTCH_INFO_PERIOD: cannot be modified
TCH_INFO_PERIOD = 5s period used by the BSC to count the number of free TCHs.
More details are provided in Annex.
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5 Handover Detection
Handover Causes 23: Traffic
CAUSE 23: Traffic Handover
DELTA_HO_MARGIN(0,n) < 0dB
AND PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGNIN_INNER + DELTA_HO_MARGI (0,n)
(n=1…BTSnum)
AND EN_TRAFFIC_HO(0,n) = ENABLE
Size of window for level averaging: A_PBGT_HO
The principle of this handover is to reduce the size of the serving cell when it is high-loaded relatively to a low-loaded cell.
When the mobile moves away from the BTS, the power budget will increase and a better cell handover will be triggered earlier.
It is recommended to inhibit Traffic handover towards 1-TRX cells. These cells do not have enough resources to receive incoming handovers due to congestion of neighbor cells. Moreover because of the great variation of traffic in the 1-TRX cells, traffic load is never considered as low.
This cause is inhibited for handover from SDCCH to SDCCH.
Cause 23 is checked over all the neighboring cells belonging to the same layer. It means that it is checked between cells whose CELL_LAYER_TYPE is single or upper, between cells whose CELL_LAYER_TYPE is lower, and between cells whose CELL_LAYER_TYPE is indoor.
In addition to the condition on the cell layer type, the cell frequency band condition for checking Cause 23 is as follows whether or not the MS is in the inner zone of a multi-band cell:
a) The MS is not in the inner zone of a multi-band cell:
If the flag EN_MULTI-BAND_PBGT_HO is set to “disabled”, Cause 23 must not be checked between cells which use different frequency bands (i.e cells having different CELL_BAND_TYPE).
If the flag EN_MULTI-BAND_PBGT_HO is set to “enabled”, Cause 23 will be checked over all the neighboring cells without any cell frequency band restriction.
b) The MS is in the inner zone of a multi-band cell:
If the flag EN_MULTI-BAND_PBGT_HO is set to “disabled”, Cause 23 is checked over all the neighboring cell multi-band cells (FREQUENCY_RANGE= PGSM-DCS1800 or EGSM-DCS1800) which belong to the same BSC as the serving cell.
If the flag EN_MULTI-BAND_PBGT_HO is set to “enabled”, Cause 23 will be checked over all the neighboring cells without any cell frequency band restriction.
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5 Handover Detection
Handover Causes 23: Traffic [cont.]
CAUSE 23: Traffic Handover
DELTA_HO_MARGIN(0,n) computation is already described in Cause 12 HO
DELTA_HO_MARGIN(0,n) < 0dB means that
The serving cell is loaded
The target cell is unloaded
PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER
+ DELTA_HO_MARGIN(0,n) (n=1…BTSnum)
This constraint is less discriminative than Cause 12
In specific traffic distribution, this cause is triggered before cause 12
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5 Handover Detection
Handover Causes 12 & 23 Interworking
Cause 12 & 23: A dynamic way to handle traffic loadPBGT (n2)
PBGT (n1)
Traffic_loadTraffic_load(n2)=highTraffic_load(n1)=low
Other cases Traffic_load(n2)=lowTraffic_load(n1)=high
HO_MARGING(n1, n2) + DELTA_INC_HO_margin
HO_MARGING(n1, n2)
HO_MARGING(n1, n2) - DELTA_DEC_HO_margin
HO_MARGING(n2, n1) - DELTA_DEC_HO_margin
HO_MARGING(n2, n1)
HO_MARGING(n2, n1) + DELTA_INC_HO_margin
PBGT Handover
PBGT Handover
2 x HO_MARGIN+ DELTA_INC_HO_margin- DELTA_DEC_HO_margin
2 x HO_MARGIN
PBGT Handover
Traffic Handover
PBGT Handover
Traffic Handover
Handover from n1 to n2
Handover from n2 to n1
N2 loaded
N1 loaded
The figure represents the triggering areas of PBGT and traffic handovers according to the traffic load in the serving cell and in the neighbor cell.
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5 Handover Detection
Directed Retry Principles
Directed Retry is:an SDCCH to TCH intercell handoverTriggered during call setup procedure
If the serving cell is completely congested, the MS is allocated an SDCCH
If no TCH is available, the MS is queuedUnder certain conditions, the MS obtains TCH in another cell
SDCCH-TCH handover on:better condition or emergency causes = Directed Retrycause 20 = Forced Directed Retry
Internal and External Directed Retries are possible (since B6.2)
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5 Handover Detection
Directed Retry
Directed Retry
Set on a per cell basis with parameter EN_DR
Same behavior as TCH HO
Intercell handover causes are checked (i.e. all HO causes except 10, 11 and 13 (concentric cells) and causes 15 and 16 (intracell HO))
Candidate cell evaluation process: same as for TCH HO
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5 Handover Detection
Forced Directed Retry: Cause 20
CAUSE 20: Forced Directed Retry
AV_RXLEV_NCELL_DR(n) > L_RXLEV_NCELL_DR(n)
And EN_FORCED_DR = ENABLE
EN_FORCED_DR value is only relevant if EN_DR = true
AV_RXLEV_NCELL_DR(n) is calculated with A_PBGT_DR window
if less than A_PBGT_DR samples are available, the average value is calculated with the available samples and the averaging window is filled in with -110 dBm
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5 Handover Detection
Forced Directed Retry: Cell Candidate Evaluation
Pre-rankingusing PREF_LAYER, PRIORITY(0,n), frequency band
Filtering processAV_RXLEV_NCELL_DR(n) > RXLEVmin(n)
+max(0,MS_TXPWR_MAX(n) - P)
Number of free TCHs t(n) > FREElevel_DR(n)
Remaining cells are sorted according totheir PBGT_DR(n) (averaging window A_PBGT_DR)
PBGT_DR(n) = AV_RXLEV_NCELL_DR(n) - AV_RXLEV_PBGT_DR - (BS_TXPWR_MAX - BS_TXPWR)
- (MS_TXPWR_MAX(n) - MS_TXPWR_MAX)
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5 Handover Detection
Forced Directed Retry: Parameters
L_RXLEV_NCELL_DR(n): level required in the neighbor cell nThe parameter considered is the one set in the neighbor cellThe default value depends on network architectureSee next slide
Freelevel_DR(n): number of free TCH channels required in theneighbor cell n
The parameter considered is the one set in the neighbor cellDefault value = 0 to 4 TCHs (linked to the nb of TRXs)
A_PBGT_DR: Averaging windowDefault value = 4 SACCHs
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5 Handover Detection
Cause 24: General Capture
CAUSE 24: general capture
Capture handoverModified in B8: Inhibition of capture handovers for “Single layer serving cell”
May be triggeredFrom all cellsTowards all cells except servingCan be used to capture traffic by any cell, whatever its type, band, etc.
Serving cellCell
Cell
Cell
Cell
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5 Handover Detection
Cause 24: General Capture [cont.]
CAUSE 24: general capture
AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n) + max (0, [MS_TXPWR_MAX(n) - P])
and Traffic_load(0) = CAPTURE_TRAFFIC_CONDITIONand Traffic_load(n) ≠ HIGHand EN_GENERAL_CAPTURE_HO = ENABLE
Size of window for averaging level: A_PBGT_HOCAPTURE_TRAFFIC_CONDITION can take 3 values: ANY_LOAD (default), HIGH, NOT_LOWAnti ping-pong: not checked if T_INHIBIT_CPT is running – new in B8 for single layer
Case the serving cell is in the upper or single layer (CELL_LAYER_TYPE(n0) = upper or single):
Condition 1:
The immediately preceding cell n-1 is in the indoor or lower layer, i.e. CELL_LAYER_TYPE(n–1) = lower or indoor, or the frequency band of the immediately preceding cell n-1 is different from the frequency band of the serving cell n0, i.e. CELL_BAND_TYPE(n–1) <> CELL_BAND_TYPE(n0).
Condition 2:
The call has previously performed i) an emergency internal handover on quality (Cause 2, 4, and 7) towards the serving cell or ii) an external handover with the A interface GSM cause “uplink quality or downlink quality” and there is a bi-directional adjacency link between the preceding external cell n-1and the serving cell n0.
If Conditions 1 and 2 are fulfilled the timer T_INHIBIT_CPT is started
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5 Handover Detection
Handover Cause 28: Fast Traffic HO
CAUSE 28: Fast Traffic HO
Push out of a cell a mobile in dedicated mode to allow a queued request to be served in the serving cell
Complement the current traffic HO (Cause 23), for sudden traffic peaks (no averaging window used)More efficient where the overlap of adjacent cells is reduced
Most appropriate MSto be pushed out
New call attempt
CongestedServing cell
Neighbor cell Cell
Neighbor cell Cell
Upper layer cell
HO
HOMost appropriate MSto be pushed out
New call attempt
CongestedServing cell
AV_RXLEV_NCELL( n) > L_RXLEV_NCELL_DR( n) + max(0,[MS_TXPWR_MAX( n)-P])
The threshold L_RXLEV_NCELL_DR(n) is the observed level from the neighbor cell n at the border of the area where fast traffic handovers are enabled. This threshold fixes the size of the overlapping area where fast traffic handovers can be performed. It should be greater than RXLEVmin(n).
And t(n) > FREElevel_DR(n)
FREElevel_DR(n) is the minimum threshold of free TCHs in the neighbor cell n for forced directed retry and fast traffic handover.
t(n) is the absolute number of free (dual rate) TCHs in the neighbor cell n.
For external cells, t( n) is fixed to the arbitrary value t(n) = 255. Therefore, setting FREElevel_DR(n) to 255 for an external cell inhibits outgoing external fast traffic handover towards this cell. Setting FREElevel_DR(n) to any other value will allow outgoing external fast traffic handover towards this cell.
EN_CAUSE_28 = enable
The flag EN_CAUSE_28 is not an OMC flag but a HOP flag.
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5 Handover Detection
Handover Cause 28: Fast Traffic HO [cont.]
CAUSE 28: Fast Traffic Handover
Cause 28 is only checked if the channel of the candidate MS can support the channel rate (HR or FR) required by the queued request:
HO is triggered when a request is queued at the top of the queue
FR FR (Whatever the TRX type)
HR , or FR on dual rate TRX
Queued Request Candidate MS
HR
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5 Handover Detection
Handover Cause 28: Fast Traffic HO [cont.]
CAUSE 28: Fast Traffic Handover equation
AV_RXLEV_NCELL(n) > L_RXLEV_NCELL_DR(n) + max(0,[MS_TXPWR_MAX(n)-P])
AND t(n) > FREElevel_DR(n)AND EN_CAUSE_28 = ENABLEAND EN_FAST_TRAFFIC_HO = ENABLE
Size of window for averaging level: A_PBGT_DR
Same thresholds and window as Cause 20 (Forced Directed Retry)EN_CAUSE_28 is an internal HOP process variable
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5 Handover Detection
Handover Cause 28: Fast Traffic HO [cont.]
CAUSE 28: Fast Traffic Handover process
DHCPEND
- Cause number 28- Reference of the call to handover(which corresponds to the firstcandidate MS received)
Start HO
Assignment request queued - Queued request reference- Channel rate of queued request
Fast Traffic HO Request
Yes
EN_CAUSE_28=enable
EN_CAUSE_28=disable
HO alarm:cause 28?
NOK
DHCPEND
Requeststill queued?
Resource AllocationManagement
HandoverPreparation
T_FILTERis started
HandoverManagement
OK
Check first2 conditions of cause 28
- Queued request reference- Reference of MS can perform HO
Fast Traffic HO Acknowledge
Yes
No
NO
HO cause 28 process:
If EN_FAST_TRAFFIC_HO = enable, when an assignment request (or external emergency HO request) is queued, the RAM process sends to the HOP process a Fast Traffic HO request which contains the queued request reference and its channel rate.
Then, HO cause 28 becomes checkable (EN_CAUSE_28=enable).
Once an HO alarm for cause 28 is triggered, the flag EN_CAUSE_28 is set to “disable” so as not to perform more than one handover. In the same time, the HOP process gets back to the RAM process a Fast Traffic HO Acknowledge which contains the queued request reference and the reference of the MS that can perform HO.
If several answers are sent to the RAM process, only the first one corresponding to the queued request is taken into account. The RAM process checks if the request is still queued. If that is so, the RAM process asks the HOP process to start HO for this mobile; otherwise the process is stopped.
Once the HOP process receives this message, the first two conditions of Cause 28 (good enough level, enough free resources in the target cell) are checked one more time. If the conditions are fulfilled, the HOP process sends an alarm to the HOM entity and the timer T_FILTER is started ; otherwise the process is stopped.
Note: the first two conditions of cause 28 are tested twice in order to be sure that the candidate cells are still valid when the « cause 28 start HO » message is received from the RAM process.
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5 Handover Detection
Handover Cause 15: UL Interference
CAUSE 15: High interference on the uplink Intracell HOAV_RXQUAL_UL_HO > THR_RXQUAL_CAUSE_15 +OFFSET_RXQUAL_FH
AND AV_RXLEV_UL_HO > RXLEV_UL_IHAND EN_CAUSE_15 = ENABLEAND [ no previous intracell handover for this connection failed
OR EN_INTRACELL_REPEATED = ENABLE ]Size of window for averaging quality: A_QUAL_HOSize of window for averaging level: A_LEV_HO
THR_RXQUAL_CAUSE_15 and EN_CAUSE_15 are not parameters but variables defined just after.
In B7:
New causes (26 & 27) introduced due to AMR support
Cause 26 is an emergency condition:
Intracell HO: speech codec from AMR-HR to AMR-FR
Cause 27 is a better condition
Intracell HO: speech codec from AMR-FR to AMR-HR
Causes 15 & 16 are modified due to AMR support
Specific enablers and thresholds for AMR calls
AMR emergency HO (cause 26) is triggered if cause 15 or 16 has already been triggered
Cause 29 is created for intracell handover due to TFO
Codec sharing and optimization for MTM calls
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5 Handover Detection
Handover Cause 16: DL Interference
CAUSE 16: High interference on the downlink
Intracell HOAV_RXQUAL_DL_HO > THR_RXQUAL_CAUSE_16 + OFFSET_RXQUAL_FH
AND AV_RXLEV_DL_HO > RXLEV_DL_IHAND EN_CAUSE_16 = ENABLEAND [ no previous intracell handover for this connection failed
OR EN_INTRACELL_REPEATED = ENABLE ]Size of window for averaging quality: A_QUAL_HOSize of window for averaging level: A_LEV_HO
THR_RXQUAL_CAUSE_16 and EN_CAUSE_16 are not parameters but variables defined after.
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5 Handover Detection
New Parameters for Causes 15 & 16
CAUSE 15 and CAUSE 16:THR_RXQUAL_CAUSE_15 (or 16) and EN_CAUSE_15 (or 16) are specific to HOPTHR_RXQUAL_CAUSE_15 (or 16) =
L_RXQUAL_XX_H for a non AMR call (same threshold as CAUSE 2 or CAUSE 4)L_RXQUAL_XX_H_AMR for an AMR call
EN_ CAUSE _15 (or 16) = EN_INTRA_XX for a non AMR callEN_INTRA_XX_AMR for an AMR call
XX = UL or DL
For a non-AMR call, the thresholds used are identical to the ones used for CAUSE 2 and CAUSE 4.
In this case and if EN_INTRACELL_REPEATED = DISABLE, when aN HO CAUSE 15 (or 16) fails, it can be modified as UPLINK (or DOWLINK) QUALITY, HO CAUSE 2 (respectively HO CAUSE 4).
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5 Handover Detection
Adaptive Multi-Rate Codec (AMR)
Principles:Two consecutive encodings: speech coding and channel codingWith current codecs, the share of each coding is FIXED (not optimized)
Speech protection"against degradation"
22.8 Kbit/s (FR TS)
Speech protection"against degradation"
11.4 Kbit/s (HR TS)
Channel coding
Channel coding
FIXEDFIXEDFIXED
Radio
Radio
Speech codingSpeech information "useful part"
13 Kbit/sou 12.2 Kbit/s
(FR)(EFR)
Speech information "useful part"
5.6 Kbit/s (HR)
Speech coding
Voice
Voice
Speech coding contains speech information (the “useful” part).
Channel coding protects speech information (against radio degradations).
The main speech codec currently used in GSM networks, speech Full Rate, is quite old. It has been specified more than 10 years ago. Around 1992, to increase network capacity, GSM has specified a half rate speech codec. But this codec showed strong limitations in terms of speech quality, especially for mobile to mobile calls (double transcoding degrades very much the speech quality of the half rate codec) and under poor radio conditions.
Recently, studies on AMR have been launched to provide a solution to:
Increase speech quality in full rate and half rate,
Increase network capacity by offering a good half rate solution,
Use a long-term solution, to avoid adding more and more codecs handled independently from the others.
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5 Handover Detection
AMR: Codec and Channel Adaptation
AMR uses a variable balance between speech coding and channel coding (CODEC Mode Adaptation)
Choice between FR and HR Codecs: Channel Mode Adaptation
Variable channelcoding rate
22.8 Kbit/s (FR TS)
Variable channelcoding rate
Channel coding
Channel coding
Radio
Speech codingVariable speech coding rate
Variable speech coding rate
Speech coding
Voice
Voice
FLEXIBLEFLEXIBLEFLEXIBLE4.75 Kbit/s5.15 Kbit/s5.9 Kbit/s
6.7 Kbit/s7.4 Kbit/s7.95 Kbit/s
10.2 Kbit/s12.2 Kbit/s
4.75 Kbit/s5.15 Kbit/s
5.9 Kbit/s6.7 Kbit/s
7.4 Kbit/s7.95 Kbit/s
11.4 Kbit/s (HR TS)(AMR HR 7.95 not supported)
Radio
In order to adapt the intermediate rate, a set of speech codecs has been defined by ETSI to be used by AMR:
When radio conditions are good, increases speech information.
When radio conditions are bad, protects speech information.
Full Rate: Alcatel-Lucent implementation is fully compliant with GSM recommendations. All these AMR FRcodec modes are supported. In particular, the Alcatel-Lucent BSS has implemented the 7.95, 5.9 and 4.75 codec modes which use polynomials of constraint length 7 to ensure a high protection.
Half Rate: Alcatel-Lucent implementation supports 5 out of 6 AMR HR codec modes (AMR HR 7.95 is not supported) which are fully compliant with GSM recommendations. In particular, the Alcatel-Lucent BSS has implemented the 4.75 codec mode which uses polynomials of constraint length 7 to ensure a high protection.
During a call, only a subset out of these 8 codecs is used. The subset can include from 1 to 4 codecs. It is up to the operator to define its own codec subset. In particular, he can define a codec subset limited to the common codec modes supported by all the BSSs of its network (some BSSs may not be able to support all of them due to implementability problems).The codec subset defined by the operator is the same in the uplink and in the downlink.
Codec Mode Adaptation:
dynamic change from one codec to another, using the same channel (FR or HR).
metric used: C/I (Carrier over interference ratio).
Channel Mode adaptation:
change from one FR channel to an HR one and vice-versa independently from the codec mode.
metric used: RX_QUAL uplink and downlink.
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AMR Codec Adaptation Objective
Based on adaptive trade-off between the share of throughput given to speech coding and the one given to channel coding (speech protection)Depends on radio conditions estimated in real-time
Mediumradio conditions
Badradio conditions
Goodradio conditions
Speech coding = speech information
Channel coding = speech protection
The AMR principle is to have a set of codecs and, for any radio conditions, to use the one with the best speech quality.
Under good radio conditions, a codec with a high bit rate is used. Speech is encoded with more information so the quality is better. In the channel coding, only little place is left for redundancy.
Under poor radio conditions, a codec with a low bit rate is chosen. Speech is encoded with less information, but this information can be well protected due to redundancy in the channel coding.
The BSS adapts dynamically the codec in uplink direction and in downlink direction, taking into account the C/I measured by the BTS (for uplink adaptation) and by the MS (for downlink adaptation).
The codec used in the uplink and used in the downlink can be different: the adaptation is independent in each direction.
This permits to use an optimal codec for each C/I value of each direction, as indicated in the figure below.
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5 Handover Detection
AMR: Codec Mode Adaptation
Codec mode adaptationOnly a subset out of these codecs can be usedThis subset may include from 1 to 4 codecsThe same codec subset is used for both the Uplink and the DownlinkUplink codec mode adaptation:
For each SACCH frame, the BTS compares C/I value to the threshold corresponding to the current codec (belonging to the codec subset defined by the operator)
Downlink codec mode adaptation:Same process as uplink adaptationNevertheless, the BTS remains the master
Unrelated processes ⇒ uplink and downlink codecs may be different at a given time
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5 Handover Detection
AMR: Codec Mode Adaptation [cont.]
The Codec mode can be modified on one frame out of two (CMI / CMC-CMR).Decision based on thresholds (OMC-R settable), for the uplink and the downlink.
CODEC_MODE_4(less robust)
CODEC_MODE_3
CODEC_MODE_2
CODEC_MODE_1(most robust)
High
Low
C/I norm
AMR_FR_THR_1 + AMR_FR_HYST
AMR_FR_THR_1
AMR_FR_THR_2 + AMR_FR_HYST
AMR_FR_THR_2
AMR_FR_THR_3 + AMR_FR_HYST
AMR_FR_THR_3
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5 Handover Detection
AMR: Codec Mode Adaptation [cont.]
Uplink adaptation
Downlink adaptation
Codec Mode Request(new codec mode)
Codec Mode Indication(new codec mode)
Codec Mode Request(new codec mode)
MS BTS TC
Codec Mode Indication(new codec mode)
C/I evaluation &thresholds comparison
Codec Mode Indication(new codec mode)
Codec Mode Command(new codec mode)
MS BTS TC
Codec Mode Indication(new codec mode)
C/I evaluation &thresholds comparison
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5 Handover Detection
AMR: Codec and Channel Mode Adaptation
Codec mode adaptation is dynamically performed through a set of pre-defined “codec modes”:
In FR mode:
In HR mode:
Choice between HR and FR (Channel mode adaptation) is done at call setup and during call through HO causes 26 & 27
Variable speech coding rate
Channel codingSpeech coding
Variable speech coding rate
To endof chain
Fromacoustic part
22.8 Kbit/s (FR TS)
12.2 Kbit/s10.2 Kbit/s7.95 Kbit/s7.4 Kbit/s
6.7 Kbit/s5.9 Kbit/s5.15 Kbit/s4.75 Kbit/s
12.2 Kbit/s10.2 Kbit/s7.95 Kbit/s7.4 Kbit/s
6.7 Kbit/s5.9 Kbit/s5.15 Kbit/s4.75 Kbit/s
Variable speech coding rate
Channel codingSpeech coding
Variable speech coding rate
Fromacoustic part
To endof chain
11.4 Kbit/s (HR TS)7.4 Kbit/s6.7 Kbit/s5.9 Kbit/s
5.15 Kbit/s4.75 Kbit/s
7.4 Kbit/s6.7 Kbit/s5.9 Kbit/s
5.15 Kbit/s4.75 Kbit/s
Codec mode adaptation:
The codec mode adaptation is the dynamic change from one codec to another codec, using the same channel (FR or HR). This adaptation is performed by the layer 1 of the BTS. It is transparent for the BSC and the layer 3 of the BTS.
The metric used for codec mode adaptation is the evaluation of the ratio: signal over noise.
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5 Handover Detection
AMR Gain
AMR: always gives end user the best satisfactionComparison between different codecs in terms of capacity and quality:
Speech quality requirement
AMR-FR + AMR-HR
AMR-HR
AMR-FR
HR
EFR
FR
Capacity requirement
The main speech codec currently used in GSM networks, speech Full Rate, is quite old. It has been specified more than 10 years ago.
Around 1992, to increase network capacity, GSM has specified a half-rate speech codec. But this codec showed strong limitations in terms of speech quality, especially for mobile-to-mobile calls (double transcoding degrades very much the speech quality of the half-rate codec) and under poor radio conditions.
A few years later, when GSM started to be introduced in North America, American operators asked for an improved speech codec for full rate channels. Indeed speech quality was a major argument for customers used to have a good speech quality with analog systems. For that issue, EFR was specified for GSM.
Recently, studies on AMR have been launched to provide a solution to:
Increase speech quality in full rate and half rate,
Increase network capacity by offering a good half rate solution,
Use a long-term solution, to avoid adding more and more codecs handled independently from the others,
Take into account Tandem Free Operation (TFO), especially between MSs on half rate on one side and on full rate on the other side.
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5 Handover Detection
AMR: TCH Allocation
FR / HR discriminationCell load AV_LOAD() computed from
load samples = NB_BUSY_TS / NB_TS * 100non sliding window (LOAD_EV_PERIOD) averaging process
THR_FR_LOAD_U_SV1=80%
THR_FR_LOAD_U_SV3=60%
THR_FR_LOAD_L_SV1=50%
THR_FR_LOAD_L_SV3=40%
AV_LOAD
Time
100%
FR for any MS
HR for AMR MSFR for other MS
HR for any MS
HR for AMR MSFR for other MS
FR for any MS
Load samples are computed by the BSC every TCH_INFO_PERIOD = 5 seconds.
LOAD_EV_PERIOD is the averaging window size for cell load computation. It is equal to 12 but can be changed at the OMC-R level on a per cell basis. Therefore cell load process has a periodicity of 1mn by default (TCH_INFO_PERIOD*LOAD_EV_PERIOD). The allocation of Half rate resources is decided upon the load evaluation in the serving cell.
AMR HR (HR SV3) offers a better speech quality than HR SV1. The Alcatel-Lucent BSS offers thus the possibility to define a set of thresholds specific for AMR. If the load increases, AMR HR capable MSs can be the first to be allocated in HR (HR SV3) for load reasons, and if the load still increases, then all the HR capable MSs can be allocated in HR (HR SV1 & HR SV3) for load reasons.
This is why two variables of load are defined: LOAD_SV3 and LOAD_SV1.
Each load variable is calculated through its own threshold set: the thresholds related to the variable LOAD_SV3 (THR_FR_LOAD_U_SV3 and THR_FR_LOAD_L_SV3) are less restrictive than the ones related to the variable LOAD_SV1 (THR_FR_LOAD_U_SV1 and THR_FR_LOAD_L_SV1).
As a consequence, if the load of the cell increases, then the variable LOAD_SV3 will first equal TRUE, and if the load still increases, the variable LOAD_SV1 will then equal TRUE.
The variable LOAD_SV1 corresponds to a level of load where it is important to put as many MSs on half rate TCH as possible: HR SV3 or HR SV1.
The same computation is done to compute LOAD_SV3 with the thresholds: THR_FR_LOAD_U_SV3 and THR_FR_LOAD_L_SV3 with the following relations:
THR_FR_LOAD_L_SV3 ≤ THR_FR_LOAD_U_SV3
THR_FR_LOAD_U_SV3 ≤ THR_FR_LOAD_U_SV1
THR_FR_LOAD_L_SV3 ≤ THR_FR_LOAD_L_SV1
Previous stateAV_LOAD
LOAD_SV1 = FALSE LOAD_SV1 = TRUE
AV_LOAD £ THR_FR_LOAD_L_SV1 LOAD_SV1 = FALSE LOAD_SV1 = FALSETHR_FR_LOAD_L_SV1 <
AV_LOAD £THR_FR_LOAD_U_SV1
LOAD_SV1 = FALSE LOAD_SV1 = TRUE
THR_FR_LOAD_U_SV1 < AV_LOAD LOAD_SV1 = TRUE LOAD_SV1 = TRUE
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5 Handover Detection
Cause 26: AMR HR to FR HO
CAUSE 26: AMR channel adaptation HO (HR to FR)
Cause 26 is triggered if :Current channel rate is HRCurrent channel is dual rate and changes are allowedAMR_FR speech codec is allowed:
EN_AMR_FR = ENABLE
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Cause 26: AMR HR to FR HO [cont.]
CAUSE 26: AMR channel adaptation HO (HR to FR) equation[ a previous intracell HO cause 15 or 16 has been triggered for this call in the serving cellOR
EN_INTRA_DL_AMR = DISABLE and EN_INTRA_UL_AMR = DISABLE] AND
AV_RXQUAL_UL_CA_HR_FR > THR_RXQUAL_CA + OFFSET_CA+ OFFSET_RXQUAL_FH and AV_RXLEV_UL_HO > RXLEV_UL_IH
ORAV_RXQUAL_DL_CA_HR_FR > THR_RXQUAL_CA + OFFSET_CA+ OFFSET_RXQUAL_FH and AV_RXLEV_DL_HO > RXLEV_DL_IH
AND EN_AMR_CA_HR_FR = ENABLE
Size of window for averaging quality: A_QUAL_CA_HR_FR
B10
2 different flags in order to activate cause 26 and cause 27 separately.
In B10, EN_AMR_CA has been removed and replaced by 2 parameters:
EN_AMR_CA_FR_HR EN_AMR_CA_HR_FR
HO algorithms in the BSC is modified so that cause 26 and cause 27 are enabled separately.
EN_AMR_CA_HR_FR: This flag enables/disables intracell HO for AMR channel adaptation (Handover Cause 26) (cell parameter)
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5 Handover Detection
Cause 26: AMR HR to FR HO [cont.]
CAUSE 26: AMR channel adaptation HO (HR to FR)
THR_RXQUAL_CA and OFFSET_CA are set as follows:if LOAD_SV3(0) = false then
THR_RXQUAL_CA = THR_RXQUAL_CA_NORMALOFFSET_CA = OFFSET_CA_NORMAL
if LOAD_SV3(0) = true thenTHR_RXQUAL_CA = THR_RXQUAL_CA_HIGHOFFSET_CA = OFFSET_CA_HIGH
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5 Handover Detection
Cause 26: AMR HR to FR HO [cont.]
CAUSE 26: AMR channel adaptation HO (HR to FR)
Calculation of LOAD_SV3(0):If previous value of LOAD_SV3 = false then
If AV_LOAD > THR_FR_LOAD_U_SV3 thenLOAD_SV3 = true
Else LOAD_SV3 = false
Else (if previous value of LOAD_SV3 = true then)If AV_LOAD <= THR_FR_LOAD_L_SV3 then
LOAD_SV3 = falseElse LOAD_SV3 = true
More details are provided in Annex.
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5 Handover Detection
Cause 27: AMR FR to HR HO
CAUSE 27: AMR channel adaptation HO (FR to HR)
Cause 27 is triggered if:
Current channel rate is FRCurrent channel is dual rate and changes are allowedAMR_HR speech codec is allowed:
EN_AMR_HR = ENABLE
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Cause 27: AMR FR to HR HO [cont.]
CAUSE 27: AMR channel adaptation HO (FR to HR) equationAV_RXQUAL_UL_CA_FR_HR <= THR_RXQUAL_CA+ OFFSET_RXQUAL_FH
ANDAV_RXQUAL_DL_CA_FR_HR <= THR_RXQUAL_CA+ OFFSET_RXQUAL_FH
AND EN_AMR_CA_FR_HR = ENABLE
Size of window for averaging quality: A_QUAL_CA_FR_HR
B10
2 different flags in order to activate cause 26 and cause 27 separately.
In B10, EN_AMR_CA has been removed and replaced by 2 parameters:
EN_AMR_CA_FR_HR EN_AMR_CA_HR_FR
HO algorithms in the BSC is modified so that cause 26 and cause 27 are enabled separately.
EN_AMR_CA_FR_HR: This flag enables/disables intracell HO for AMR channel adaptation (Handover Cause 27) (cell parameter)
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5 Handover Detection
Cause 26 & 27 Interworking
Cause 26 & 27 interaction
THR_RXQUAL_CA_NORMAL
Quality
THR_RXQUAL_CA_NORMAL +OFFSET_CA_NORMAL
THR_RXQUAL_CA_HIGH
THR_RXQUAL_CA_HIGH +OFFSET_CA_HIGH
Bad quality: 7
Bad quality: 7
Load = False Load = True
Half Rate
Full Rate
Half Rate
Full Rate
HO cause 26
HO cause 27
HO cause 26
HO cause 27
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Introduction to TFO
Tandem Free Operation (TFO) solution
TC TC
Codec GSM (A)(8 or 16 Kbit/s)
MS A MS B
Codec GSM (B)(8 or 16 Kbit/s)
A/µ law(64 Kbit/s)
Double transcoding without TFO
TC TC
Codec GSM (A)(8 or 16 Kbit/s)
MS A MS B
No transcoding withTFO
The Tandem Free Operation (TFO) feature is a way to avoid double transcoding in mobile to mobile speech calls.
Indeed, without TFO one GSM codec type is used between the first mobile and the first transcoder, then the speech is transcoded into A/μ law between transcoders and finally this speech is transcoded again into a second GSM codec type (which may be the same as the first one) between the second transcoder and the second mobile.
With TFO, after call establishment, both BSSs at each side are able to negotiate a common GSM codec type which is then used from one mobile to the other mobile. This negotiation is performed through in-bandsignaling between transcoders.
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Introduction to TFO [cont.]
Applicability: Only MS-to-MS speech callsTFO is based on information exchanged between transcoders
TRAU
MS MSBTS
64 Kbit/s Speech Sample carrying:
- TFO frames on the LSB containing: - compressed speech samples - control bits - TFO messages
- original PCM speech samples on the MSB
TRAU
BSC
IPE
MSC
IPE
MSC
BTS
BSC
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TFO Principles
In the case of first allocation (normal assignment at call setup, inter-BSS handover, intra-BSS handover where no TFO was previously on-going):
Exchange of Codec capabilities
New call setup
Match
Found
Yes No
Look for common codec
NoYes
Normal operationTFO mode ON
Intracell HO
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5 Handover Detection
Cause 29: TFO HO
CAUSE 29: TFO HO
Intracell HO used in case of codec mismatch between two MSs calling, in order to match their speech codecNo radio measurements needed No priority and may be triggered at any timeConditions:
HO_INTRACELL_ALLOWED = ENABLEAND
EN_TFO_MATCH = ENABLE
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Cause 29: TFO Parameters
EN_TFOenables/disables the feature, per cell
EN_TFO_MATCHenables/disables resolution of codec mismatch, per cell
EN_TFO_OPTenables/disables codec optimization, per cell
FORCE_TFO_VS_AMRenables/disables the basic functions of TFO for GSM EFR, FR and HR codec types when the current codec is AMR FR or AMR HR
FORCE_TFO_HR_WHEN_LOADEDcontrols the establishment of TFO in HR when the cell is loaded
KEEP_CODEC_HOindicates if the BSC tries to keep the same codec in case of internal intercell HO
Codec Mismatch
At call setup for a mobile-to-mobile speech call, when both BSSs do not use the same codec type, a codec mismatch occurs. If a common codec type can be found, either one or possibly both BSSs perform an intracell handover to use the common codec type found. Afterwards TFO can be started using this common codec type. Codec mismatch resolution is authorized in the BSC using an O&M flag: EN_TFO_MATCH. This flag is forwarded to the TC, via the BTS.
Codec Optimization
At call setup for a mobile-to-mobile speech call, it can occur that a first common codec type can be found but a better speech quality would be provided with another common codec type. Once both BSSs operate in Tandem Free, they exchange their complete codec capabilities, to try to find a better codec type than the current one. Codec optimization is authorized in the BSC using an O&M flag : EN_TFO_OPT. This flag is forwarded to the TC, via the BTS.
Classification of Codec Types
In all cases, TFO is considered better as any tandeming configuration. In TFO, EFR is considered as better than FR, considered as better than HR.Force TFO vs. AMRTFO + AMR is not supported in this implementation of TFO. In the normal operation, a call established with AMR will not initiate a TFO negotiation. The goal of the function Force TFO vs. AMR is to allow a call, established with AMR to initiate a TFO negotiation and, if possible, to change of codec type to FR, HR or EFR to establish TFO.
In-Path Equipment (IPE)
TFO can only be activated if TFO frames (at 8 or 16 Kbit/s) can be sent transparently through the public switching network. In-path equipments are equipments such as echo cancelers or A/μ law converters that modify the 64 Kbit/s speech signal. Such equipment need to be deactivated for TFO calls.
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5 Handover Detection
Cause 29: TFO Parameters [cont.]
EN_TFO_OPT: enables/disables codec optimization, per cellAllows new TFO negotiation on an on-going MTM call to find a better common codec
For example, HR is used on both sides, but FR is possible tooHO cause 29 will be triggered on both sides towards the best codec
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Cause 29: TFO Parameters [cont.]
FORCE_TFO_VS_AMR: TFO AMR not specified
Call setup in AMR is not followed by TFO negotiationFORCE_TFO_VS_AMR enables HO cause 29 after AMR call establishment towards the best TFO codec
ERF + TFOThe MS A can only use HR/EFR/FR
The MS B can use HR/EFR/FR
Cell cap:A MR/HR/EFR/F R Cell cap:HR/EFR/FR
The MS A using AMR, could use HR/EFR/FR
The MS B can use HR/EFR/FR
MS A MS B
TFO not possible
Enable (Alcatel patent)
FORCE_TFO_VS_AMR
Disabled(ETSI implementation)
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5 Handover Detection
Cause 29: TFO Parameters [cont.]
FORCE_TFO_HR_WHEN_LOADED: Gives control on load regulation precedence vs. TFO
3 values: TFO_HR_NOT_FORCED, TFO_HR_ONLY, TFO_HR_PREFERRED enable different behaviours in case of loaded cell
HR + TFOThe MS A can only use HR
The MS B can use HR/EFR/FR
Loaded cellMS/cell cap:
Unloaded cellMS/cell cap:
The MS A can use HR/EFR/FR
The MS B can use HR/EFR/FR
MS A MS B
EFR + TFO
Enable (Alcatel patent)
FORCE_TFO_HR_WHEN_LOADED
Disabled(ETSI implementation)
H/EFR/FR HR/EFR/FR
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5 Handover Detection
Cause 29: TFO Parameters [cont.]
KEEP_CODEC_HOkeeps the same codec type in the new cell in case of internal intercell HO in order to avoid resolving a new mismatch codec situationAvoids double speech quality transition:TFO --> non-TFO --> TFO3 possible behaviors:
TFO_CALLS_ONLY: codec is preferably kept in case of internal intercell HO for TFO calls onlyALL_CALLS: codec is preferably kept in case of internal intercell HO for all calls (whatever the TFO state)FREE: the choice of the codec type is free and depends on the situation in the target cell
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5 Handover Detection
Cause 30: Move from PS to CS Zone
If EN_RETURN_CS_ZONE_HO = enableAND a CS call is inside both
The Non pre-emptable zone andThe MAX_SPDCH_LIMIT_ZONE then
An intra cell HO cause 30 is triggered
TRX3 TRX1
BCCH SDCCHPS PS PS PSCS CS CS
Non pre-emptable zone
MAX_SPDCH_HIGH_LOAD zone
MAX_SPDCH_LIMIT zone
PS traffic zone
HO cause 30
PS PS
The enabling/disabling of Cause 30 is independent of the flag HO_INTRACELL_ALLOWED.
MAX_SPDCH_HIGH_LOAD zone: this zone corresponds to the MAX_SPDCH_HIGH_LOAD consecutive PS capable timeslots that are preferred for PS allocation. In this zone, allocated TBFs cannot be pre-empted. If the value of MAX_SPDCH_HIGH_LOAD is not modified, this zone remains unchanged.
Non pre-emptable PS zone: this zone is always inside the MAX_SPDCH_HIGH_LOAD zone. In this latter zone, we search for the rightest timeslot allocated to the MFS and used. Then, all timeslots situated at its left define this non pre-emptable PS zone.
MAX_SPDCH_LIMIT zone: this zone corresponds to the MAX_SPDCH_LIMIT consecutive PS capable timeslots that are preferred for PS allocation.
PS traffic zone: this zone corresponds to the larger zone between the non pre-emptable PS zone and the MAX_SPDCH_LIMIT zone.
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5 Handover Detection
Handover Causes Priorities
Emergency Handover
Uplink Quality Cause 2
Downlink Quality Cause 4
Uplink Level Cause 3
Downlink Level Cause 5
Distance Cause 6
Too Low Level UL Inner Cause 10
Too Low Level DL Inner Cause 11
HR to FR Channel Adaptation Cause 26 intracell
Uplink Interference Cause 15 intracell
Downlink Interference Cause 16 intracell
Better Condition Handover
Capture Handover Cause 24
Power Budget Cause 12
Traffic Cause 23
Outer UL/DL Level Cause 13
FR to HR Channel Adaptation Cause 27 intracell
Forced Directed Retry Cause 20
Fast Traffic HO Cause 28
HANDOVER PRIORITIES
The causes 24, 12 and 23 have the same priority. Nevertheless, if a cell is a candidate for both causes, triggered at the same time, it is kept only for cause 12.
Dealing with all available causes, we get the following list:
Emergency: 7 > 17 > 18 > 2 > 4 > 3 > 5 > 6 > 22 > 10 > 11 > 26 > 15 > 16
Better conditions: 21=14=24=12=23 > 13 > 27 > 20 > 28
29,30 and 31 has no priority (can be detected at any time)
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5 Handover Detection
Exercise 1
Emergency causesWhat is the HO cause 2?Which is the flag to activate the HO cause 2?
Time allowed:
45 minutes
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5 Handover Detection
Exercise 2
Emergency causesComplete the diagram below and fill in the chart with:
L_RXQUAL_UL_H = 3RXLEV_UL_IH = -70 dBmP=MS_TXPWR_MAX=33dBm
Quality
Level
Nb of case
AV_RXQUAL_UL_HO
AV_RXLEV_UL_HO
Current MS power
HO cause 2: YES/NO?
1 2 3 4 5 6
4 1 3 4 4 4
-81 -79 -75 -70 -69 -72
33 33 33 33 33 29(0.8 w)
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5 Handover Detection
Exercise 3
Better condition causes (simple case)There are only 2W cells and 2W MSEN_TRAFFIC_HO(0,n) =DisableNo Ping-Pong marginHO_MARGIN(0,n) =5 dBNO DL PC,RXLEV_LIMIT_PBGT_LIMIT=-47dBm,The serving is not a concentric cell.
Fill in the chart:
Nb of case
AV_RXLEV_NCELL(n)
AV_RXLEV_PBGT_HO
PBGT(n)
HO cause 12: YES/NO?
1 2 3 4 5 6
-70 -70 -80 -70 -70 -75
-80 -70 -75 -75 -79 -96
Serving cell N cell
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5 Handover Detection
Exercise 4
Better condition causes (ping-pong case)EN_TRAFFIC_HO(0,n) =DisablePing-Pong marginPING_PONG_HCP=15dbT_HCP =15sHO_MARGIN(0,n) =5 dBA_PBGT_HO = 8 SACCHA n to 0 HO has just been triggered, what happens after 4s?
N cellServing cell?
Nb of case
AV_RXLEV_NCELL(n)
AV_RXLEV_PBGT_HO
PBGT(n)
HO cause 12: YES/NO? PBGT>HO margin
PING_PONG_HCP=15 -> PBGT(n)
HO cause 12:YES/NO?
1 2 3 4 5 6
-70 -70 -80 -70 -70 -75
-80 -70 -75 -75 -79 -96
10 0 -5 5 9 21
YES NO NO NO YES YES
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5 Handover Detection
Exercise 5
Handover Detection Better condition causes (traffic case)EN_TRAFFIC_HO(0,n) =EnableNo Ping-Pong marginHO_MARGIN(0,n) =5 dBDELTA_DEC_HO_margin =5dBDELTA_INC_HO_margin =5dB
N cellServing cell
HO
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5 Handover Detection
Exercise 6
Better condition causes (traffic case)
Fill in the chart: N cellServing cell
HO ?
Nb of case
AV_RXLEV_NCELL(n)
AV_RXLEV_PBGT_HO
Traffic distribution
PBGT(n)
DELTA_HO_MARGIN (0, n)
Cause 12 HO: YES/NO?
Cause 23 HO: YES/NO?
1 2 3 4
-71 dBm -71 dBm -76 dBm -71 dBm
-80 dBm -80 dBm -80 dBm -80 dBm0: traffic lowN: traffic high
0: traffic highN: traffic low
0: traffic highN: traffic low
0: traffic lowN: traffic low
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5 Handover Detection
Exercise 7
Channel adaptation (cause 26 and cause 27)Why is it recommended to have A_QUAL_CA_FR_HR ≥ A_QUAL_CA_HR_FR?An operator may be willing to:- Under normal load, use only HR calls for quality 0- Under high load, use HR calls for qualities 0 to 3, with an hysteresis of 1Find the thresholds and offsets for normal and high load:THR_RXQUAL_CA_NORMAL = ? OFFSET_CA_NORMAL = ?THR_RXQUAL_CA_HIGH = ? OFFSET_CA_HIGH = ?
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5 Handover Detection
Exercise 8
Channel adaptation (cause 26 and cause 27)EN_INTRA_XX_AMR = DisableRXLEV_XX_IH = -110 dBmOFFSET_RXQUAL_FH = 0A_QUAL_CA_FR_HR =4 and A_QUAL_CA_HR_FR = 2
Use the previous thresholds and fill in the chart:
UL_QUAL 0 1 2 3 3 1 1 0 0 1
DL_QUAL 0 0 1 1 1 0 0 2 4 3
LOAD_SV3 False False False False True True True True True True
AV_RXQUAL_UL_CA_HR_FR
AV_RXQUAL_DL_CA_HR_FR
AV_RXQUAL_UL_CA_FR_HR
AV_RXQUAL_DL_CA_FR_HR
CHANNEL TYPE FR FR FR
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5 Handover Detection
Exercise 9
Capture HO (Cause 24 )There are only 2W cells and 2W MSL_RXLEV_CPT_HO(0,n) = -85dBmEN_GENERAL_CAPTURE_HO = ENABLE
Fill in the chart:
Nb of case 1 2 3 4 5 6
AV_RXLEV_NCELL(n) - 70 - 70 - 80 - 70 - 70 - 85
CAPTURE_TRAFFIC_CONDITION NOT_LOW HIGH ANY_LOAD HIGH HIGH HIGH
TRAFFIC_LOAD(0) HIGH LOW INDEFINITE HIGH LOW HIGH
TRAFFIC_LOAD(n) HIGH LOW INDEFINITE LOW LOW LOW
HO cause 24: YES/NO?
N cellServing cell
HO ?
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5 Handover Detection
Exercise 10
Fast Traffic HO (cause 28)Find the appropriate candidate MS for this queued request:
Channel rate required: HRL_RXLEV_NCELL_DR(n) = -85 dBm (whatever n)FREElevel_DR(n) = 1 (whatever n)Channel rate: MS1 FR on Full rate TRX, MS2 HR, MS3 FR on Dual rate TRXt(n) for neighbor cells: t(1)=1, t(2)=2, t(3)=2AV_RXLEV_NCELL(n) in dBm:
Neighbors
MS 1
MS 2
MS 3
1 2 3
- 82 dBM
- 79 dBM
- 90 dBM
- 85 dBM
- 86 dBM
- 82 dBM
- 78 dBM
- 92 dBM
- 89 dBM
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5 Handover Detection
Exercise 11
TFO HO (cause 29): after call setup
Find the 2 speech version types of the following MS-to-MS call:EN_TFO = enable, EN_TFO_MATCH = enableFORCE_TFO_HR_WHEN_LOADED = TFO_HR_NOT_FORCED
Loaded cellMS/cell cap:
Unloaded cellMS/cell cap:
MS A MS B
TCH = ? TCH = ?
TCH = ? TCH = ?
Aftercall setup
After TFOnegociation
HR/EFR/FR EFR/FR
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5 Handover Detection
Exercise 12
TFO HO (cause 29): after call setupFind the 2 speech version types of the following MS-to-MS call:
EN_TFO = enable, EN_TFO_MATCH = enableFORCE_TFO_HR_WHEN_LOADED = TFO_HR_ONLY
Loaded cellMS/cell cap:
Unloaded cellMS/cell cap:
MS A MS B
TCH = ? TCH = ?
TCH = ? TCH = ?
Aftercall setup
After TFOnegociation
HR/EFR/FR EFR/FR
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5 Handover Detection
Exercise 13
TFO HO (cause 29): after call setup
Find the 2 speech version types of the following MS-to-MS call:EN_TFO = enable, EN_TFO_MATCH = enableFORCE_TFO_HR_WHEN_LOADED = TFO_HR_PREFERRED
Loaded cellMS/cell cap:
Unloaded cellMS/cell cap:
MS A MS B
TCH = ? TCH = ?
TCH = ? TCH = ?
Aftercall setup
After TFOnegociation
HR/EFR/FR EFR/FR
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5 Handover Detection
Exercise 14
TFO HO (cause 29): after call setup
Find the 2 speech version types of the following MS-to-MS call:EN_TFO = enable, EN_TFO_MATCH = enableFORCE_TFO_HR_WHEN_LOADED = TFO_HR_ONLY
Loaded cellMS/cell cap:
Unloaded cellMS/cell cap:
MS A MS B
TCH = ? TCH = ?
TCH = ? TCH = ?
Aftercall setup
After TFOnegociation
HR/EFR/FR HR/EFR/FR
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5 Handover Detection
Exercise 15
TFO HO (cause 29): after handoverFind the speech version types of the following MS-to-MS call:
EN_TFO = enable, EN_TFO_MATCH = enableFORCE_TFO_HR_WHEN_LOADED = TFO_HR_ONLY
1. KEEP_CODEC_HO = TFO_CALLS_ONLY 2. KEEP_CODEC_HO = FREE
??
Loaded cellMS/cell cap:
Unloaded cellMS/cell cap:
MS 1
Unloaded cellMS/cell cap:
MS 2
HO
?
MS 2Call setup +
TFO negociationMS 2HO
?TFO
? TFO
HR/EFR/FR HR/EFR/FR HR/EFR/FR
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5 Handover Detection
Exercise 16
TFO HO (cause 29): after handoverFind the speech version types of the following MS-to-MS call:
EN_TFO = enable, EN_TFO_MATCH = enableFORCE_TFO_HR_WHEN_LOADED = TFO_HR_ONLYKEEP_CODEC_HO = TFO_CALLS_ONLY
1. EN_TFO_OPT = disable2. EN_TFO_OPT = enable
??
Unloaded cellMS/cell cap:
Loaded cellMS/cell cap:
MS 1
Unloaded cellMS/cell cap:
MS 2
HO
?
MS 2Call setup +
TFO negociationMS 2HO
?TFO
? TFO
HR/EFR/FR HR/EFR/FR HR/EFR/FR
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6 Handover Candidate Cell Evaluation
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6 Handover Candidate Cell Evaluation
Principles
Used to rank potential target cells:
Ranking based on radio characteristics
Ranking based on operator preferences
Ranking based on traffic intensity
Handover Candidate Cell Evaluation
The process is performed in the BSC.
Once a need for handover is detected, this process looks for possible target cells (except if it is an intracell handover or an interzone handover) and provides the BSC entity in charge of the HO decision and execution entity with a list of candidate cells and their respective HO cause.
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6 Handover Candidate Cell Evaluation
Evaluation Process
MeasurementPreprocessing
A_LEV_HOA_QUAL_HOA_PBGT_HOA_RANGE_HO
HO Detection
Cause 2: uplink qualityCause 3: uplink levelCause 4: downlink qualityCause 5: downlink levelCause 6: distanceCause 12: power budget
Performed every SACCHPerformed every SACCH
Pre-ranking
Priority (0, n) = 0Cell 2: cause C2Cell 3: cause C2Cell 4: cause C2
Priority (0, n) = 1Cell 1: cause C2
Priority (0, n) = 2Priority (0, n) = 3
Cell 5: cause C2Cell 6: cause C2Cell 7: cause C2Cell 8: cause C2
Priority (0, n) = 4Priority (0, n) = 5
Priority (0, n) = 0Cell 2: cause C2Cell 3: cause C2Cell 4: cause C2
Priority (0, n) = 1Priority (0, n) = 2Priority (0, n) = 3
Cell 6: cause C2Cell 8: cause C2
Priority (0, n) = 4Priority (0, n) = 5
PBGT filteringHO_MARGIN_XX(0,n)
Grade
Priority (0, n) = 0Cell 4: cause C2Cell 2: cause C2Cell 3: cause C2
Priority (0, n) = 1Priority (0, n) = 2Priority (0, n) = 3
Cell 6: cause C2Cell 8: cause C2
Priority (0, n) = 4Priority (0, n) = 5
Order
Priority (0, n) = 0Cell 4: cause C2Cell 3: cause C2Cell 2: cause C2
Priority (0, n) = 1Priority (0, n) = 2Priority (0, n) = 3
Cell 6: cause C2Cell 8: cause C2
Priority (0, n) = 4Priority (0, n) = 5
Cell evaluation process (Order or Grade)
HO Candidate Cells Evaluation
Maxevery SACCH
Preprocessmeasurement
Measurementresult
Raw cell list
Cell 1: cause C2Cell 2: cause C2Cell 3: cause C2Cell 4: cause C2Cell 5: cause C2Cell 6: cause C2Cell 7: cause C2Cell 8: cause C2... max 32 cells
The HO candidate evaluation process is run after all intercell handover alarms.
In case of intracell handover alarm (HO causes 10, 11, 13, 15, 16), the candidate cell evaluation process is skipped: the target cell is the serving cell.
The handover detection gives as indication the raw cell list (built from book-keeping list) and the preferred layer for the handover. In case of emergency handover alarms or cause 20 alarm, the cell evaluation will order the cells given in the raw list, putting in the first position the cells belonging to the preferred layer, having the highest priority (if EN_PRIORITY_ORDERING=ENABLE) and/or having the same frequency band type as the serving cell. In case of an intercell handover alarm, if the serving cell belongs to the raw cell list (emergency handover from the DCS 1800 inner zone of a multiband cell), this cell is put at the end of the candidate cell list with the MS zone indication OUTER.
In case of better condition handover alarms (except cause 20), the cell evaluation will order the cells given in the raw list, putting in the first position the cells belonging to the preferred layer and having the highest priority (if EN_PRIORITY_ORDERING=ENABLE).
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6 Handover Candidate Cell Evaluation
Pre-Ranking
Pre-ranking in hierarchical or multi-band networks:For emergency handover and causes 20 and 28 only.
Priority(0,n) = 0Cell_layer_type = Pref_layerCell_band_type = serving_cell
Priority(0,n) = 1
Priority(0,n) = 5
Cell_band_type = serving_cell
Priority(0,n) = 0Cell_layer_type = Pref_layer
Priority(0,n) = 1
Priority(0,n) = 5
List ofcandidate
cells n
Cell_band_typenot applicable
to comfort causes
!
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6 Handover Candidate Cell Evaluation
Pre-Ranking [cont.]
With priority(0,n) settings, the operator can, for each couple of cells:tag the target cell with a defined priority (from 0 = max to 5 = min)this definition has an higher priority than usual order/grade ranking
Especially useful for multi band/hierarchical architectures: a simple way to force a target cell whatever its RxLev level and PBGTnevertheless can be skipped over by filtering processeslow interest for standard networks
RxLev: - 90 dBmPBGT: + 5 dB
Serving cell
Candidate cell 1
Candidate cell 2
RxLev: - 70 dBmPBGT: + 10 dB
Priority
P1
P0
Cell Ordering according to Target Layer and Target Band
In hierarchical or multiband environment, cells are characterized by the layer they belong to or/and the frequency band they use. The candidate cell evaluation process takes into account these characteristics in the candidate cell ordering.
In hierarchical environment, the HO detection process can indicate a preferred layer where the handover must be directed to. If this indication is used, the candidate cell evaluation puts in the first places of the list, the candidate cells belonging to the preferred layer. They are followed by the cells of the other layer, providing they are also correct candidates.
After this possible distinction, in each part of the list, the candidate cell evaluation sorts the candidate cells according to the parameter PRIORITY(0,n) (parameter on line changeable from the OMC-R).
The cells having the highest priority are put in the first place of the list. They are followed by the cells having the lowest priorities. The PRIORITY(0,n) is only used when the flag EN_PRIORTY_ORDERING is set to “enable”.
In case of emergency handover, for each category (preferred layer and other layer) and between cells having the same priority, the candidate cell evaluation sorts the candidate cells according to the frequency band they use: the cells which use the same frequency band as the serving cell are put first and they are followed by the cells which use the other frequency band.
The cell evaluation function is then applied to the different candidate cell lists defined from the preferred layer indication, the PRIORITY(0,n) parameter and the frequency band of the serving cell (only in case of emergency handover).
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6 Handover Candidate Cell Evaluation
PBGT Filtering
Characteristics:optional, flag EN_PBGT_FILTERINGfilter out cells from the target listinhibited for better cell handoversbased on of cellspower budgetper couple was needed for multiband architecture
PBGT(n) > HO_MARGIN_XX (0,n) + OFFSET_HO_MARGIN_INNER
HO_MARGIN_XX (0,n) = HO_MARGIN_QUAL (0,n)for cause 2,4HO_MARGIN_XX (0,n) = HO_MARGIN_LEV (0,n) for cause 3,5HO_MARGIN_XX (0,n) = HO_MARGIN_DIST (0,n) for cause 6OFFSET_HO_MARGIN_INNER is only applied when the MS is in the inner zone of a concentric or multi band cellThe averaging window is A_PBGT_HO
The filtering process allows to filter out cells from the target list before sending them to the ORDER or GRADE evaluation process.
It can be enabled/disabled on-line on a per cell basis from the OMC-R with the flag EN_PBGT_FILTERING.
The candidate cells are filtered on their power budget in relation to a handover margin threshold based on the handover cause.
Note: the averaging window used for this process is A_PBGT_HO (even for emergency handovers, where a handover alarm could have been raised through A_LEV_HO or A_QUAL_HO samples)
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6 Handover Candidate Cell Evaluation
Order Evaluation
ORDER cell evaluation processCell "n" is ranked among other accordingly:If EN_LOAD_ORDER = ENABLE and cell n is internal to the BSC
ORDER (n) = PBGT(n) + LINK_FACTOR(0,n) + FREEfactor(n)- FREEfactor(0)- HO_MARGIN_XX(0,n)
· Link_factor (0,n) is an operator parameter to give a bonus/penalty to a cellex: avoid external HO, decrease incoming flow of HO to a cell from another
· FREEfactor is TCH traffic based bonus/penalty to rank cells
If EN_LOAD_ORDER = DISABLE or cell n is external to the BSCORDER (n) = PBGT(n) + LINK_FACTOR(0,n) - HO_MARGIN_XX(0,n)
Cell "n" is kept if:AV_RXLEV_NCELL (n) > RXLEVmin (n)+ max [0;(MS_TXPWR_MAX(n)-P)] [dBm]
Two types of cell evaluation algorithms can be used: ORDER and GRADE.
ORDER and GRADE are two different methods of cell ranking. They both consist in giving a mark or ’figure of merit’ to each candidate cell.
The basic differences between ORDER and GRADE are that:
with ORDER:
The candidate cell evaluation process interacts with the handover detection by use of cause-dependent handover margins.
The candidate cell evaluation process takes into account the number of free TCHs in the candidate cells.
with GRADE:
The candidate cell evaluation process does not interact with the handover detection.
The candidate cell evaluation process takes into account the relative load of traffic channels in the candidate cells.
The type of cell evaluation is chosen by the operator on a (serving) cell basis and is provided to the BSC with the parameter CELL_EV.
For any handover cause, the first cell in the list is taken as a target cell, i.e. the cell with the highest value of ORDER(n). The cells do not need to fulfill any other condition.
If no cell fulfills the condition and the serving cell does not belong to the target cell list, the target cell list is empty and no further action is carried out.
Note: the A_PBGT_HO averaging window is used for this process.
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6 Handover Candidate Cell Evaluation
GRADE Evaluation
GRADE cell evaluation processCell "n" is ranked among other accordingly:If EN_LOAD_ORDER = ENABLE and cell n is internal to the BSC
GRADE (n) = PBGT(n) + LINK_FACTOR(0,n) + LOADfactor(n)
· Link_factor (0,n) is an operator parameter to give a bonus/penalty to a cell· LOADfactor(n) is a weighting factor that takes into account the relative load of
traffic channels in a cell
If EN_LOAD_ORDER = DISABLE or cell n is external to the BSC
GRADE (n) = PBGT(n) + LINK_FACTOR(0,n)
Cell "n" is kept if:AV_RXLEV_NCELL (n) > RXLEVmin(n)+ max [0;(MS_TXPWR_MAX(n)-P)]
LINKfactor(0,n) is a parameter set by OMC command for each cell(n).
LINKfactor(n1,n2) allows the operator to handicap or to favor the cell n1 with respect to its neighbor cell n2. In particular, it can be used to disadvantage an external cell when an internal cell is also a possible candidate.
For any handover cause, the first cell in the list is taken as a target cell, i.e. the cell with the highest value of GRADE(n). If no cell fulfills the condition and the serving cell does not belong to the target cell list, the target cell list is empty and no further action is carried out.
Note: the A_PBGT_HO averaging window is used for this process.
More details are provided in Annex.
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7 Exercise
Exercise 1
Emergency HO detectedWith the “Candidate evaluation.xls” excel sheet...
Filtering simulation for a list of candidate cellsRanking simulation for a list ofcandidate cells
Candidate Cell Evaluation
Serving cell Cell 1 Cell 2 Cell 3 Cell 4 Cell 5 Cell 6RxLev_cell1Mk RxLev_DL Cell_Nb1 BSIC_cell1 Cell_Nb2 BSIC_cell2RxLev_cell2 Cell_Nb3 BSIC_cell3RxLev_cell3 Cell_Nb4 BSIC_cell4RxLev_cell4 Cell_Nb5 BSIC_cell5RxLev_cell5 Cell_Nb6 BSIC_cell6RxLev_cell6
-102** 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110-99** 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110-99** 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110-98AssCmd 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110
-110AssCmp 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110-76** 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110-96** 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110-95** 14 3 -91 0 0 -110 0 0 -110 0 0 -110 0 0 -110-93** 14 3 -92 0 0 -110 0 0 -110 0 0 -110 0 0 -110-93** 1 0 -89 14 3 -91 0 0 -110 0 0 -110 0 0 -110-93** 1 0 -90 14 3 -94 0 0 -110 0 0 -110 0 0 -110-93** 1 -0 -88 14 3 -94 3 1 -101 0 0 -110 0 0 -110-94** 8 7 -93 1 0 -93 14 3 -96 3 1 -103 0 0 -110-96** 1 0 -93 8 7 -95 14 3 -99 3 1 -106 0 0 -110-96** -1 0 -91 8 7 -95 14 3 -99 3 1 -104 0 0 -110-98** 1 0 -92 14 3 -98 8 7 -99 3 1 -107 0 0 -110
-101** 8 7 -97 1 0 -97 14 3 -102 3 1 -107 0 0 -110-101HOCMD 8 7 -96 1 0 -99 14 3 -103 3 1 -108 0 0 -110
0 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -110
HO CauseA_PBGT_HOGRADE EVALUATIONPriority(0,n)HO_MARGIN_LEV(0,n)RX_LEV_MIN(n)LINK_FACTOR(0,n)LoadFactor(n)
DL Level6
0 for all neighbor cell0-1000 for all neighbor cell0
Time allowed:
15 minutes
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Algorithms and Associated Parameters1 · 2 · 138
6 Handover Candidate Cell Evaluation
Exercise
Emergency HO detected
1 Book-keeping list
Book-keeping list(14;3) (1;0) (8;7) (3;1)
2 Averaging measurement
Averaged measurements and PBGT(n)AV_RXLEV_PBGT_HO
AV_RXLEV_PBGT_HO(14;3)(1;0)(8;7)(3;1)
-100-95-96
-106
PBGT(n)-232-8
3 PBGT Filtering
PBGT(n)(1;0)(8;7)
32
PBGT Filtering
4 GRADE evaluation process
GRADE(n)(1;0)(8;7)
32
GRADE evaluation process
5 Target Cell
(1;0)
? ?
?
?
?
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7 Exercise
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6 Handover Candidate Cell Evaluation
Exercise
List all the parameters involved in the detection of cause 23List all the causes impacted by the parameter DELTA_INC_HO_MARGINList all the causes impacted by the parameter L_RXQUAL_UL_HList all the causes impacted by the parameter BS_TXPWR_MAXList all the causes impacted by the parameter BS_P_CON_ACK
Time allowed:
10 minutes
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Self-assessment on the Objectives
Please be reminded to fill in the formSelf-Assessment on the Objectivesfor this moduleThe form can be found in the first partof this course documentation
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End of ModuleAlgorithms and Associated Parameters
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Section 1Radio Fine Tuning
EVOLIUM Base Station SubsystemIntroduction to Radio Fine Tuning B10
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First editionLast name, first nameYYYY-MM-DD01
RemarksAuthorDateEdition
Document History
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Module Objectives
Upon completion of this module, you should be able to:
Describe TCH resource allocation, MS reselection algorithmsList the associated parameters
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Module Objectives [cont.]
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Table of Contents
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1 TCH Resource Allocation Algorithm 72 MS Reselection Algorithms 25
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Table of Contents [cont.]
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1 TCH Resource Allocation Algorithm
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1 TCH Resource Allocation Algorithm
Radio Allocation and Management
Radio resource Allocation and Management (RAM) aims at: Managing pools of TCH radio resources by:
defining TCH radio timeslots as a function of the cell radio configuration from the operatorsorting these TCH TSs according to their radio capabilities (FR or DR, frequency band(G1 or GSM/DCS))
Allocating dedicated TCH radio resources by: selecting the TCH pool in which the TCH should be chosen according to:
the requested channel rate (FR or HR)the radio capability of the mobilethe TRE DR capability and the TRE band
selecting the best TCH resource among the available TCH channels of this pool according to several criteria
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1 TCH Resource Allocation Algorithm
Radio Timeslot of a Cell: Operator View
On the OMC-R the operator can configure the following Radio TS per cell:
Main BCCH timeslot (BCC): TS carrying FCCH + SCH + BCCH + CCCHMain combined BCCH timeslot (CBC): TS carrying FCCH + SCH + BCCH + CCCH + SDCCH/4 + SACCH/4Static SDCCH timeslot (SDC): TS carrying SDCCH/8 + SACCH/8Dynamic SDCCH/8 timeslot (SDD): TS carrying TCH + SACCH or SDCCH/8 + SACCH/8TCH timeslot (TCH): TS carrying TCH + SACCH or used as a PS timeslot (PDCH)
The operator has to choose between a Combined BCCH (CBC TS) or a Non-combined BCCH configuration (BCC TS).
A PDCH is a radio timeslot used for PS traffic or signaling.
It can carry either PS traffic or PS signaling but not both.
If it carries traffic it is called a Slave PDCH (SPDCH) TS and it carries the logical channels PDTCH+PACCH+PTTCH.
If it carries signaling it is called a Master PDCH (MPDCH) TS and it carries:
either the logical channels PBCCH+PPCH+PAGCH+PRACH: it is then called a Primary MPDCH
or only PPCH+PAGCH+PRACH: it is then called a Secondary MPDCH
SDD TS can carry either TCH or SDCCH channels but not both at the same time.
TCH TS can carry either CS traffic channel TCH or PS logical channels but not both at the same time.
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1 TCH Resource Allocation Algorithm
Radio Timeslot of a Cell: RAM View
In the BSS the RAM software module maps the OMC-R cell radio configuration to its own types of TS:
Pure BCCH timeslot: BCC TS carrying only common CS signaling (BCCH+CCCH)Pure SDCCH timeslot: CBC or SDC TS carrying only dedicated CS signaling(SDCCH)Pure TCH timeslot: TCH TS carrying only TCH trafficTCH/SDCCH timeslot: SDD TS carrying either CS traffic (TCH) or dedicated CSsignaling (SDCCH) TCH/SPDCH timeslot: TCH TS carrying either CS traffic (TCH) or PS traffic (SPDCH channels) MPDCH timeslot: TCH TS carrying common PS signalling (PBCCH+PCCCH or PCCCH only)
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1 TCH Resource Allocation Algorithm
Radio Timeslot: OMC-R / RAM Mapping
NB_TS_MPDCH MPDCH TS are defined on the BCCH TRX:on the timeslots configured as TCH TS on the OMC-R having the lowest timeslot index
TCH/SPDCH TS are defined as being part of an SPDCH group Pure TCH timeslots are OMC-R TCH TS neither defined as MPDCH TS nor in an SPDCH group
TCH
Pure BCCH
Pure SDCCH
TCH/SDCCH
TCH/SPDCH
MPDCH
Pure TCH
BCC
CBC
TCHSDC
SDD
TCH
OMC-Rradio TS
RAMradio TS
MPDCH TS are defined on the BCCH TRX even if the corresponding TRX_PREF_MARK is different from 0.
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1 TCH Resource Allocation Algorithm
Definition of a TCH/SPDCH TS
For PS traffic resource allocation, an SPDCH group is defined on a per TRX basis and is made up of consecutive timeslots:
mapped on OMC-R TCH TSlocated on a PS capable TRX (TRX_PREF_MARK = 0)not defined as MPDCH TShaving the same radio configuration (MA, MAIO)
If several SPDCH groups can be defined on a given TRX, the BSS chooses the SPDCH group of timeslots having the highest number of consecutive timeslots.
A radio timeslot belonging to one of the different SPDCH groups of the cell is identified in RAM as a TCH/SPDCH timeslot.
The timeslots shall be consecutive on a given TRX, which means that there shall be no hole in the SPDCH group.
If several SPDCH groups can be defined on the same TRX and having the same number of consecutive timeslots then the group that is located on the left side of the TRX (i.e. the timeslots having the lowest index) shall be chosen.
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1 TCH Resource Allocation Algorithm
Definition of a TCH/SPDCH TS [cont.]
A non-hopping cell is configured on the OMC-R
Find the radio TS configuration in RAM if NB_TS_MPDCH= 2
BCC TCH SDC TCH
SDD TCH SDC TCH
TCH TCH TCH TCH
TCH TCH TCH TCH
TCH TCH TCH TCH TCH TCH TCH TCH
TCH TCH TCH TCH TCH TCH TCH TCH
TRX1
TRX2
TRX3
TRX4
TRX_PREF_MARK
0
0
0
1
0 1 2 3 4 5 6 7
TRX1
TRX2
TRX3
TRX4
0 1 2 3 4 5 6 7MPDPBCPSDPTCTSDTSP
: MPDCH: Pure BCCH: Pure SDCCH: Pure TCH: TCH/SDCCH: TCH/SPDCH
The timeslots shall be consecutive on a given TRX, which means that there shall be no hole in the SPDCH group.
If several SPDCH groups can be defined on the same TRX and having the same number of consecutive timeslots then the group that is located on the left side of the TRX (i.e. the timeslots having the lowest index) shall be chosen.
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1 TCH Resource Allocation Algorithm
TCH Pools
3 pools of TCH resources are managed per cell: G1 pure TCH pool: contains all the free TCH sub-channels (FR or HR) free on the pure TCH TS of the G1 TRXsGSM/DCS pure TCH - TCH/SPDCH pool: contains all the free TCH sub-channels (FR or HR) free on the pure TCH TS and on the TCH/SPDCH TS of the GSM/DCS TRXsGSM/DCS TCH/SDCCH pool: contains all the free TCH sub-channels (FR or HR) free on the TCH/SDCCH TS of the GSM/DCS TRXs
Any pure TCH, TCH/SPDCH, TCH/SDCCH TS can be:Busy: if it is not free to serve an FR TCH requestFree: if it is free to serve an FR TCH request
A DR TS (timeslot on a DR TRX) is free if no FR TCH or HR TCH is allocated for a call on this timeslot.
A DR TS is busy if at least one TCH is allocated for a call on this timeslot:
1 FR TCH, or
1 HR TCH (HR 0 TCH or HR 1 TCH), or
2 HR TCHs (HR 0 TCH and HR 1 TCH).
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1 TCH Resource Allocation Algorithm
TCH Sub-Pools
FR TCH channels can be allocated on both FR and DR TRXs whereas HR TCH channels can only be allocated on DR TRXs
Each of the three TCH pools is divided in three sub-pools:FR sub-pool: contains all the free FR TCH sub-channels available on the FR TRXDR: sub-pool: contains all the free FR TCH sub-channels available on the DR TRXHR sub-pool: contains all the free HR TCH sub-channels whose mate HR TCH sub-channel is busy(always located on the DR TRX)
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1 TCH Resource Allocation Algorithm
TCH Allocation Process
TCH Request
TCH Allocation
- Radio capability of the mobile- Channel type (FR, HR, DR)- Speech version (FR, HR, EFR, AMR FR, AMR HR)- Request type (NA or HO)
- Cell channel type capability- Cell codec type capability- Cell load
TCH selected
TCH free?
Yes
Queuing?
Select a TCH sub-pool
Select a TCH in this sub-pool
TCH rejectedTCH queued
Yes No
No
Inputs for TCH allocation function:
radio capability of the MS:
The BSS knows the radio capability of the mobile from the MS CLASSMARK after the Radio Link Establishment procedure
requirements from the MSC:
Channel type (mandatory) is one of the following:
List of preferred speech version (optional):
GSM full rate speech version 1 = FR
GSM full rate speech version 2 = EFR
GSM full rate speech version 3 = AMR FR
GSM half rate speech version 1 = HR
GSM half rate speech version 3 = AMR HR
capabilities of the cell:
FR TCHs only if only FR TRXs / FR+HR TCHs if some DR TRXs
codec supported among: FR, EFR, AMR FR, HR, AMR HR
FR Full Rate onlyHR Half Rate onlyDR FR P NCA Dual Rate Full Rate Preferred No Changes Allowed after first channel allocation
as a result of the requestDR FR P CA Dual Rate Full Rate Preferred Changes Allowed after first channel allocation as a
result of the requestDR HR P NCA Dual Rate Half Rate Preferred No Changes Allowed after first channel allocation
as a result of the requestDR HR P CA Dual Rate Half Rate Preferred Changes Allowed after first channel allocation as a
result of the requestDR SV P NCA Dual Rate No Changes of channel rate Allowed after first channel allocation as a
result of the requestDR SV P CA Dual Rate Changes of channel rate Allowed after first channel allocation as a
result of the request
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Other Algorithms1 · 3 · 17
1 TCH Resource Allocation Algorithm
TCH Allocation Process [cont.]
TCH Allocation
TCH free?
Queuing?
TCH selected
Select a TCH sub-pool
Select a TCH in this sub-pool
TCH rejectedTCH queued
Yes No
Yes No
ALLOC_ANYWAYT11T11_FORCEDT_QHO
NUM_TCH_EGNCY_HO
The timer T11 corresponds to normal assignment with queuing authorised.
The timer T11_FORCED corresponds to normal assignment:
either when the queuing is not authorized by the MSC but forced by the BSC (QUEUE_ANYWAY = TRUE),
or when the queuing is not authorized but the request has its pre-emption indicator set and has already forced the release of a lower priority pre-emptable on-going call.
The QUEUE_ANYWAY flag is checked by the Normal Assignment (NASS) entity.
The timer T_QHO corresponds to an external channel change with queuing authorized or to an external channel change when the queuing is not authorized but the request has its pre-emption indicator set and has already forced the release of a lower priority pre-emptable on-going call.
NUM_TCH_EGNCY_HO: Number of RTCHs reserved for incoming HO. These RTCHs cannot be allocated for call establishment. (from the user point of view, it can be better to avoid a drop rather than to allow a new call).
ALLOC_ANYWAY: set to “TRUE”, it allows to use an RTS normally reserved for incoming HO (NUM_TCH_EGNCY_HO) for call establishment. But only after having passed by the queue.
3 queues: 3 different timers
T11: maximum time a request can be kept in queue.
T11_FORCED: maximum time a request can be kept in queue when the queue is forced.
T_QHO: maximum time an incoming HO request can be kept in queue.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Other Algorithms1 · 3 · 18
1 TCH Resource Allocation Algorithm
TCH Sub-Pool Selection
The BSS selects the TCH sub-pools in which a TCH channel can be allocated according to:
The requested channel rate and the cell load situationfavour HR if cell is loaded
A priority given to generic resources1. G1 pool (E-GSM mobile only) on non PS capable TRX2. GSM/DCS pure TCH - TCH/SPDCH pool on non PS capable TRX3. GSM/DCS pure TCH - TCH/SPDCH pool on PS capable TRX4. G1 pool (E-GSM mobile only) on PS capable TRX 5. GSM/DCS TCH/SDCCH poolAn optimisation of FR/HR resources
favour FR pool over DR pool for a FR TCH requestfavour HR pool over DR pool for an HR TCH request
The availability of a TCH channel in the sub-pool
TCH allocation without list of preferred speech versions:
FR request: FR pool DR pool
HR request: HR pool DR pool
DR FR preferred request:
cell load=False: FR pool DR pool HR pool
cell load=True: HR pool DR pool FR pool
DR HR Pref. request: HR pool DR pool FR pool
TCH allocation with a list of preferred speech versions:
FR SV then HR SV: FR pool DR pool HR
HR SV then FR SV: HR pool DR pool FR
FR SV only: FR pool DR pool
HR SV only: HR pool DR pool
From B9 and due to the new feature “Enhanced E-GSM band handling”, a new parameter has to be set:
EGSM_RR_Alloc_Strategy = 0 (default) (Different behavior for EGSM-capable MS):The BSS handles differently EGSM capable MS from PGSM only capable MS in EGSM cells; this means that not all GSM900 MS in the network are assumed to be E-GSM capable. G1 and PGSM TRX are not managed in the same way.
EGSM_RR_Alloc_Strategy = 1 (Same behavior for EGSM capable MS):The BSS handles in the same way PGSM capable only MS as EGSM-capable MS in EGSM cells; this means that all GSM900 MS in the network are assumed to be E-GSM capable. No difference made between a G1 TRX and a PGSM TRX.
So, if PGSM only capable MS have to be supported, the parameter must be set to the value 0. Otherwise 1.
As (E)GPRS service was not supported on G1 TRX (B7.2, B8). Consequently, new pools have to be taken into account:Capable or not capable PS TRX in G1 and in GSM/DCS bands.
Independently of the E-GSM preference, a TCH request is preferentially allocated firstly on TCH/VGCH timeslots, secondly on TCH/SPDCH/VGCH timeslots. Finally, TCH requests are served on TCH/SDCCH timeslots, which timeslots can also be used for SDCCH allocations (i.e. TCH requests are preferentially not served on TCH/SDCCH timeslots).VGCH: Voice Group Call Channel
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1 TCH Resource Allocation Algorithm
TCH Selection
PS traffic resources optimizationTCH allocated on TRX of highest TRX rank
and on TS of highest TS indexSPDCH allocated on TRX of lowest TRX rank
and on TS of lowest TS index
2 modes of TCH selectionOn pure TCH or TCH/SDCCH timeslotsOn TCH/SPDCH timeslots
TCH selection on pure TCH or TCH/SDCCH timeslots if:
there is at least one candidate TCH free on pure TCH TS
OR
there is no candidate TCH free on TCH/SPDCH TS: only the candidate TCH sub-channels available on pure TCH TS and on TCH/SDCCH TS are kept as candidate
TCH selection on TCH/SPDCH timeslots if:
there is at least one candidate TCH free on a TCH/SPDCH TS
AND
there is no candidate TCH free on pure TCH TS: only the candidate TCH sub-channels available on TCH/SPDCH TS are kept as candidate
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1 TCH Resource Allocation Algorithm
TCH Selection on Pure TCH or TCH/SDCCH TS
The TCH is chosen from the selected sub-pool according to the following criteria:
Non hopping cellBiggest Mobile AllocationEN_MA_SELECTION = true
TCH selected
Highest TS index
HR 0 TCH sub-channel
TCH candidates of the selectedTCH sub-pool
Highest TRX_PREF_MARK
FR allocation orHR allocation on busy TS
Best Interference Band
Highest TRX Identity
The BSS attempts to offer the best quality of service for TCH calls in accordance with the privileged order between the groups of TRXs (if any) defined by the operator. Among a group of TRXs, the BSS attempts to allocate traffic channels that have the best quality characteristics (channels using frequency with low reuse factor, large hopping frequency sets, low measured interference).
The benefits from this type of allocation are that the operator has the possibility to define groups of TRXs and to favor (or todisadvantage) them on the other if he wants to do so. Among a group of pure TCH or TCH/SDCCH timeslots, the overall interference is kept as low as possible, thus the user will perceive a better quality of service.
The BSS chooses the best TCH among the sub-channels of the selected TCH sub-pool applying criteria below in the specified order of priority:
1. TCH on TS with the highest TRX Preference Mark
According to the frequency plan, the coverage and interference probability of a cell (or according to measurements), the operator may know which TRX should be a priori favored for TCH selection. For that purpose, it is possible for operators to give a preference mark to each TRX of a cell. This mark is given through the parameters TRX_PREF_MARK (TPM) changeable at OMC-R side per TRX. The range of TRX_PREF_MARK will be from 0 (lowest priority) to 7 (highest priority). The TCH selection function favors the channels with the highest TPM.
Note that a few Pure TCH TS should be available in a cell on a TRX of TRX_PREF_MARK value of 0 since TCH/SPDCH TS may also be defined on this TRX according to PS radio resource configuration.
2. TCH on TS with the biggest Mobile Allocation (for hopping cell only)
Considering that the number of frequencies is a key factor for the average quality of channels, the TCH selection function favors the TS with the biggest MA (i.e. with the most frequencies in their frequency hopping sequence). This selection criterion is enabled/disabled via the flag EN_MA_SELECTION changeable at the OMC-R side on a per cell basis.
3. TCH on TS from the best Interference Band
Considering that the uplink received level measured by the BTS on an idle channel is a means to assess the quality when in connected mode, the TCH selection function favors the TS belonging to the best Interference Band (IB). Five IBs are defined through 5 parameters INTFBD1 to INTFBD5 where INTFBD(i)< INTFBD(i+1) and INTFBD5 = -47 all changeable at the OMC-R side on a per BTS basis.
4. TCH on TRX with the highest TRX identity
5. TCH on TS with the highest TS index
6. HR 0 TCH if the two sub-channels remaining candidates are the 2 HR TCHs of the same free TS
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Other Algorithms1 · 3 · 21
1 TCH Resource Allocation Algorithm
TCH selection on TCH/SPDCH TS
The TCH is chosen from the selected sub-pool according to the following criteria:
TRX rank is determined by the TRX Ranking algorithm described in the GPRS & EGPRS Radio Algorithms Description training course
Highest TRX Rank
TCH selected
FR allocation orHR allocation on busy TS
HR 0 TCH sub-channel
Highest TS index
TCH candidates of the selectedTCH sub-pool
The BSS tends to allocate to the MFS the TCH/SPDCH timeslots so as to avoid conflicts between CS and PS allocations on PS capable TRX.
In order to be able to allocate as much slave PDCHs as possible to a given TBF, it is important to avoid any mix of allocation between TCHs and SPDCHs (e.g. avoid on a TRX a configuration such as TCH – TCH – SPDCH – SPDCH – TCH – SPDCH – SPDCH – SPDCH). For that purpose, a TRX rank is assigned to each PS capable TRX. The TRX having the highest TRX rank is preferentially selected for TCH allocations, whereas TRX having the lowest TRX rank is preferentially selected for SPDCH allocations
This rule only applies on PS capable TRX. On a given PS capable TRX, TCH are preferentially allocated on the right side of the TRX (highest TS index), whereas SPDCH are preferentially allocated on the left side (lowest TS index).
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1 TCH Resource Allocation Algorithm
Exercise 1
A cell is configured on the OMC-R and TREs are mapped by BSS.
Time allowed:
10 minutes
BCC SDC TCH TCH
SDD TCH TCH TCH
TCH TCH TCH TCH
TCH TCH TCH TCH
SDC TCH TCH TCH TCH TCH TCH TCH
TCH TCH TCH TCH TCH TCH TCH TCH
TRX1
TRX2
TRX3
TRX4
TRX_PREF_MARK
0
0
1
0
0 1 2 3 4 5 6 7
TCH TCH TCH TCH TCH TCH TCH TCHTRX51
TRE
G4 MP FR
G4 MP DR
G3 DR
G4 MP FR
G3 DR
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1 TCH Resource Allocation Algorithm
Exercise [cont.]
Find the radio TS configuration in RAM if NB_TS_MPDCH= 2
MPD MPDCH
PBC Pure BCCH TS
PSD Pure SDCCH TS
PTC Pure TCH TS
TSD TCH/SDDCH TS
TSP TCH/SPDCH TS
TRX1
TRX2
TRX3
TRX4
TRX_PREF_MARK
0
0
1
0
0 1 2 3 4 5 6 7
TRX51
TRE
G4 MP FR
G4 MP DR
G3 DR
G4 MP FR
G3 DR
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1 TCH Resource Allocation Algorithm
Exercise [cont.]
Find which TCH sub-channel is allocated:1. For MS1: E-GSM, DR2. For MS2: GSM/DCS, DR3. For MS3: GSM, FR4. For MS4, MS5, …., MSn: E-GSM, DR
n = ?
TSD P P P
P P P
P F
F F F F F F
P P P P P P P
TRX1
TRX2
TRX3
TRX4
TRX_Rank
2
3
-
1
0 1 2 3 4 5 6 7
F FTRX5-
TRE
GSM/FR
GSM/DR
GSM/DR
GSM/FR
G1/DR
H
H HHHHHH
Pure TCH TS
TCH/SPDCH TS
TCH/SDDCH TSas TCH TS
FHP
Cell load = true
: FR TCH call: HR TCH call: SPDCH TS
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2 MS Reselection Algorithms
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2 MS Reselection Algorithms
Selection and Reselection Principles
At startup (IMSI Attach), the MS selects a cell with:best C1once “camped on” one cell (in idle mode)…
…the MS can decide to reselect on another one if:C1 criterion is too lowthe MS cannot decode downlink messages the current cell is becoming forbidden (e.g. barred)the MS cannot access the cellthere is a better cell, regarding C2 criterion
Idle Mode
Status null: the Mobile Station (MS) is off
Status search BCCH: the MS searches a broadcast channel with the best signal level (cell selection and reselection)
BCCH list: up to 36 BCCH frequencies plus BSIC can be saved on SIM per visited network.
Look if frequencies of the BCCH list can be used.
No entries in the BCCH list, or the location is completely different: scan frequency band.
Status BCCH: the MS is synchronized on a BCCH. The MS camps on a cell.
The BTS sends the neighbor cells list (BCCH allocation BA) on BCCH in System Information (SI) 2, 2bis and 2ter if BSS parameter EN_INTERBAND_NEIGH in dual band networks:
GSM900 serving cell
GSM900 neighbor cells put into SI 2
GSM1800 neighbor cells put into SI 2ter/2bis
GSM1800 serving cell
GSM900 neighbor cells put into SI 2ter
GSM1800 neighbor cells put into SI 2/2bis
The MS measures RXLEV from BCCH of the serving and neighbor cells.
Camping on a cell is performed using C1 criterion only (the chosen cell is the one with the best C1)
The MS needs to have access to the network.
The MS needs to be accessible by the network.
Reselection is done using the mechanisms referenced above.
‘handover algorithms’ in idle mode
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2 MS Reselection Algorithms
C1 Criteria
C1ensures that, if a call was attempted, it would be done with a sufficient downlink and uplink received levelbased on 2 parameters, broadcast on BCCH
RXLEV_ACCESS_MIN [dBm]minimum level to access the cell
MS_TXPWR_MAX_CCH [dBm]maximum level for MS emitting
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2 MS Reselection Algorithms
C2 Criteria
C2CELL_RESELECT_PARAM_IND= not present THEN C2=C1 else
C2 = C1 + CELL_RESELECT_OFFSET - TEMPORARY_OFFSET (T) (if PENALTY_TIME ≠ 31)
if T > PENALTY_TIME, TEMPORARY_OFFSET(T) = 0used to avoid locating on “transient cell”CELL_RESELECT_OFFSET used to favor cell among other (e.g. micro-cell vs. umbrella, once T > PENALTY_TIME)
Or C2 = C1 - CELL_RESELECT_OFFSET (if PENALTY_TIME = 31) CELL_RESELECT_OFFSET used to handicap some cells among others
One reselection criterion is compared to C2sC2neighbor > C2current if cells belong to same LAC2neighbor > C2current+Cell_Reselect_Hysteresis if cells from a different LA
Note:
CRO: from 0 to 126 dB, step 2dB
PENALTY_TIME: from 0=20s to 30=620s, step: 20s; 31=infinite
TEMPORARY_OFFSET: from 1=10dB to 6=60dB; 7 = infinite
The use of a second formula (Penalty_time = 31) is restricted to very special cases, as we do not like to penalize a cell. If a cell is parametered with PT=31, it will be penalized compared to ALL its neighbors. To penalize a cell compared to one neighbor, one should better boost the neighbor cell (using the first formula).
The first formula is very useful for favoring indoor cell or microcell.
Cell Selection and Cell Reselection Considering CELL_BAR_QUALIFYIn case of phase 2 MS and CELL_RESELECT_PARAM_IND=1, it is possible to set priorities to cells
CELL_BAR_QUALIFY
Two values:
0 = normal priority (default value)
1 = lower priority
CELL_BAR_QUALIFY Interacts with CELL_BAR_ACCESS (barring cell)
A phase 2 MS selects the suitable cell with the highest C2 (C1>0) belonging to the list of normal priority.
If no cell with normal priority is available then the MS would select the lower priority cell with the highest C2 (C1>0).
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2 MS Reselection Algorithms
Exercise 1
On this network exampleList the parameters involved in the selection / reselection process
Time allowed:
5 minutes
Cell
Sectorized cell
CI=6169GSM900
Concentric cell
(8564, 1964)
(8564, 6169)
(8557, 1823)
Cell
CI=6271GSM900
CI=6270, GSM900
CI=1823GSM900
CI=1964GSM900
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2 MS Reselection Algorithms
Exercise 2
Find the selected cell by the MS
Cell 1
Cell 2
CI=6169GSM900
Cell 3
(8564, 1964)
(8564, 6169)
(8557, 1823)
Cell
CI=6271GSM900
CI=6270, GSM900
CI=1823GSM900
CI=1964GSM900
Measurements RxLev (cell 1) RxLev (cell 2) RxLev (cell 3)12345
-80-84-88-88-89
-96-90-90-87-85
-104-100-87-82-78
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Self-assessment on the Objectives
Please be reminded to fill in the formSelf-Assessment on the Objectivesfor this moduleThe form can be found in the first partof this course documentation
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End of ModuleOther Algorithms
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Module 4Algorithms Dynamic Behaviors
3JK11055AAAAWBZZA Issue 01
Section 1Radio Fine Tuning
EVOLIUM Base Station SubsystemIntroduction to Radio Fine Tuning B10
3FL10493ADAAZZZZA Issue 01
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First editionLast name, first nameYYYY-MM-DD01
RemarksAuthorDateEdition
Document History
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Module Objectives
Upon completion of this module, you should be able to:
Estimate qualitatively the impact of parameters change
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Module Objectives [cont.]
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Table of Contents
Switch to notes view! Page
1 Theoretical Presentation 72 Examples and Exercises 9
2.1 Overview 102.2 Optimization of Handover Algorithms 112.3 Power Control Algorithms Optimization 162.4 Traffic Load Sharing 19
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Table of Contents [cont.]
Switch to notes view!
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1 Theoretical Presentation
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1 Theoretical Presentation
Justification
Tuning is not an exact scienceThe optimizer has to control every parameter change and predict qualitatively what the consequences will beNote: Each change of parameter and its justification have to be registered in a database for operation convenience
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2 Examples and Exercises
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2 Examples and Exercises
2.1 Overview
Example 1: Optimization of handover algorithmsSliding averaging window
Example 2: Optimization of power control algorithmsSliding averaging window
Example 3: Traffic load sharingParameters qualitative influence
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2 Examples and Exercises
2.2 Optimization of Handover Algorithms
Search for best tuning of HO parameters to decrease call drop
Call drop
HO/Call
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2 Examples and Exercises
2.2 Optimization of Handover Algorithms [cont.]
Main Objective: make the HO algorithm as efficient as possible
Minimize call drop ratetrigger HO soon enoughtoward the “best” neighbour
While keeping a good speech qualityavoid HO due to quality: “too late”avoid having HO/call rate too high
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2 Examples and Exercises
2.2 Optimization of Handover Algorithms [cont.]
MethodCollect Abis trace chartSearch for HO level to avoid quality lower than 4 (or even 3)
sufficient number of “bad quality” sampleslow standard deviationproblem when HO already activated
Then tune according to QoS indicators (OMC-R) by repetitive processA_PBGT_HO/A_LEV_HO/A_QUAL_HOL_RXLEV_UL_H, L_RXLEV_DL_H, L_RXLEV_UL_P, L_RXLEV_DL_P OK as soon as HO success rate stabilized
< R x Q u a l _ D L > = f ( A V _ R x L e v _ D L )
0
1
2
3
4
5
6
7
N b _ s a m p l e s
0
2 0 0
4 0 0
6 0 0
S t a n d a r d D e v i a t i o n
0
0 .5
1
1 .5
2
< R x Q u a l _ U L > = f ( A V _ R x L e v _ U L )
0
1
2
3
4
5
6
7
N b _ s a m p l e s
02 0 04 0 06 0 08 0 0
1 0 0 0
S t a n d a r d D e v i a t i o n
0
1
2
3
Never forget that Abis information takes into account the traffic distribution in the cell. Any parameter tuning done after an Abis study has to be checked periodically as the distribution in the cell can change from one week to another.
Use the pivot table function (Excel) to build this graph.
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2 Examples and Exercises
2.2 Optimization of Handover Algorithms [cont.]
Neighbouring relationship cleanupRemove useless relationships (A interface statistics, PM Type 180)Remove the common BCCH/BSIC coupleAdd new relationships when a new site is created
Finally, check the main QoS indicatorsCall drop rateHO failure rateHO/call rateRadio Link Failure rate(the strong rate of radio link failure can denounce a lack of vicinity relation between cells)
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2 Examples and Exercises
2.2 Optimization of Handover Algorithms [cont.]
According to the Abis results and some parametersalready set, tune qualitatively the sliding averaging windows:
A_QUAL_HOA_LEV_HO
Time allowed:
5 minutes
Level at RxQual=3 - 80 dBm - 96 dBm - 90 dBmL_RXLEV_DL_H
A_QUAL_HOA_LEV_HO
- 85 dBm6?
- 90 dBm6?
- 90 dBm?4
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2 Examples and Exercises
2.3 Power Control Algorithms Optimization
Optimization of Downlink Power ControlDecrease of downlink interferenceRisks of delay of HO (without fast power control)
Optimization of Uplink Power ControlDecrease of Uplink interferenceMS battery savingRisks of delay of HO (without fast power control)
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2 Examples and Exercises
2.3 Power Control Algorithms Optimization [cont.]
The main tuning problem is the interaction with handover, which can slow down HO decision, and debase call drop rate
Power control threshold must be within HO onesDynamic step size must be activated if possible
In the example below, a dynamic MS PC is activated. The MS power changes are really reactive and control the UL level between -80 and -90dBm. In this example, the HO threshold is -98 dBm.
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2 Examples and Exercises
2.3 Power Control Algorithms Optimization [cont.]
Explain qualitatively the impacts of some parameter changes
What happens if:we increase POW_INC_FACTOR?we increase MAX_POW_INC?We increase A_LEV_PC?
Time allowed:
5 minutes
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2 Examples and Exercises
2.4 Traffic Load Sharing
Used to unload cell with too high traffic, without HW extension Trade-off between traffic sharing/radio qualityDifferent algorithms
Fast Traffic Handover: Cause 28 Traffic Handover: Cause 23 and 12 with DELTA_HO_MARGIN(0,n)Static (couple of cells): HO_MARGIN, LINK_FACTOROn a local traffic basis:
Load_Factor/Free_Factor Forced Directed Retry
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
Fast Traffic HOUseful in case of sudden traffic peaks as the process response is instantaneous (no averaging window)The principle is to force handover towards neighbour cells which have lower traffic when a request is queued in the serving cell.Interaction with Forced DR due to the use of same thresholdsOptimization method (repetitive process)
Tunes L_RXLEV_NCELL_DR(n), FREElevel_DR(n)Applies new values, checks traffic peaks, QoS indicators
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
The Pros and cons of Fast Traffic HOEfficiency depends on:
Traffic location in the loaded cellCapacity of neighbour cells
Increase of the number of HO/callIncrease of incoming HOs fail rate (risk of ping-pong effect)
In case of internal HO: use PING_PONG_HCP with T_HCPor/and enable HO CAUSE 23
Heavy to tune (has to be done for each couple of cells)
Adapted to instantaneous traffic modificationCan be used to send traffic towards a cell external to the serving BSCAdapted to hierarchical network, but also to standard ones
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
DELTA_HO_MARGIN (0,n)
CHANGE DYNAMICALLY TRAFFIC DISTRIBUTION WITH HO:Traffic HO Cause 23
Ease outgoing better condition HO on a traffic point of viewSlow down outgoing better cell HO (to be tuned for a given couple of cells)
When the better cell in radio condition is the worst cell in traffic termsOptimization method (repetitive process)
Tune DELTA_DEC_HO_MARGIN and DELTA_INC_HO_MARGINApply new values, check traffic, QoS indicators and possibly speech quality
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
The Pros and cons of DELTA_HO_MARGIN (0,n) methodEfficiency depends on:
Traffic location in the loaded cellCells overlapCapacity of neighbour cells
Increase the number of HO/callCannot be used to send traffic toward a cell external to the serving BSCThe call has to be first established on a loaded cell, before being “exported”
It can be rejected
Easy to tune (dynamic process)Adaptability to instantaneous and long-term traffic modifications
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
HO_MARGIN / LINK_FACTOR
CHANGE STATICALLY TRAFFIC DISTRIBUTION WITH HO:Ease outgoing better cell HO (to be tuned for a given couple of cells)
Decrease HO_MARGIN (can make a cell “candidate”)Increase LINK_FACTOR (used to rank candidate cells)
Optimization method (repetitive process)Look for neighbour cells able to carry extra trafficUse Abis trace to check if these cells are candidate
if yes, use LINK_FACTOR to favor themif not, use HO_MARGIN and LINK_FACTOR
Apply new values, check traffic, QoS indicators and possibly speech quality
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
The Pros and cons of LINK_FACTOR/HO_MARGINCan be efficient (up to 20% increase of capacity) in some cases
Cell overlapCapacity of neighbour cells
Increase the number of HO/callThe call has to be first established on a loaded cell, before being “exported”
It can be rejectedHeavy to tune (has to be done for each couple of cells)No adaptability to instantaneous and long-term traffic modifications
Can be used to send traffic toward a cell external to the serving BSC
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
FREE_FACTOR/LOAD_FACTOR
Taking into account the current load of cells, send the MS toward the less loaded cell with HO
Ease outgoing better cell HO, according to:Load_Factor (% of TCH occupancy) of serving and “target” cellsFree_Factor (number of free TCHs) of serving and target cells (order only)cannot make a “candidate” cell, only change ranking
Tuning method (repetitive)to be activated locally for each cell with default parameter settinglook for QoS indicators (esp. traffic intensity and blocking rate)tune tables accordingly
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
The Pros and cons of load/free factors method
Lower efficiency compared to LINK_FACTOR/HO_MARGINCalls have to be established on a loaded cell before being “exported”Tuning is performed on a cell-per-cell basisCannot be used to send traffic toward an external cell
Adapted to dynamic change of traffic and capacity (for Load_Factor)No increase of HO/call rate
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
Forced directed retry methodMechanisms
The MS is connected on an SDCCH of cell1It must switch on TCHNo TCH is free on cell1There is at least 1 neighbour cell which has:
sufficient DL level seen by the MSenough free TCHs
The MS is handed over to TCH towards this cellif there are several cells, the one with the best PBGT is selected
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
Method: trade-off between traffic and radio quality
Mainly L_RXLEV_NCELL_DR(n)parameter to tune
the lower, the better the traffic sharingthe lower, the higher the interference risks
QoS indicators and field tests (speech quality) are necessary for tuning
Cell 2: 45Cell 3: 23
Cel
l 1:
2
4
Forced Directed Retry
The following condition is checked every measurement reporting period and if at least one input pre-processed parameter AV_RXLEV_NCELL_DR(n) is available.
CAUSE = 20 (high level in neighbour cell for forced directed retry)
AV_RXLEV_NCELL_DR(n) > L_RXLEV_NCELL_DR(n) (n = 1 ... BTSnum)
and EN_FORCED_DR = ENABLE
The threshold L_RXLEV_NCELL_DR(n) is the observed level from the neighbour cell n at the border of the area where forced directed retry is enabled. This threshold fixes the size of the overlapping area where forced directed retry can be performed. It should be greater than RXLEVmin(n).
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
The Pros and cons of Forced directed retry
Highest efficiency (up to 30%)No increase of HO/call rateCan be used to send traffic toward an external cellAdapted to dynamic change of traffic Adapted to hierarchical networks, but also to standard ones
Tuning is performed on a cell-per-cell basis
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
Draw qualitatively the new serving areas on the pseudo map when enabling traffic HO with:
DELTA_DEC_HO_MARGIN=6dBDELTA_INC_HO_MARGIN=4dB
PBGT(0) = 5
05 5PBGT(0) PBGT(n)
PBGT(n) = 5
Traffic_load
Loaded cell 0 Unloaded cell n
EN_TRAFFIC_HO = 0
Cause 12Cause 12
Time allowed: 5 minutes
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
What happens when EN_FAST_TRAFFIC_HO = ENABLE and EN_TRAFFIC_HO(0,n) = DISABLE?
Time allowed: 5 minutes
QueuedAssignment
Request
PBGT(0) = 5
05 5PBGT(0) PBGT(n)
PBGT(n) = 5
Traffic_load
Loaded cell 0 Unloaded cell n
Av_Rxlev_Ncell(n) = -82 dBm Av_Rxlev_Ncell(0) = -74 dBmAv_Rxlev_PBGT_HO = -82 dBm
L_RLEV_NCELL_DR(n) = -85 dBm
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2 Examples and Exercises
2.4 Traffic Load Sharing [cont.]
What happens when EN_FAST_TRAFFIC_HO = ENABLE and EN_TRAFFIC_HO(0,n) = ENABLE?
Time allowed: 5 minutes
QueuedAssignment
Request
PBGT(0) = 9
09 -1PBGT(0) PBGT(n)
PBGT(n) = -1
Traffic_load
Loaded cell 0 Unloaded cell n
Av_Rxlev_Ncell(n) = -82 dBm Av_Rxlev_Ncell(0) = -74 dBmAv_Rxlev_PBGT_HO = -82 dBm
5 5
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Self-assessment on the Objectives
Please be reminded to fill in the formSelf-Assessment on the Objectivesfor this moduleThe form can be found in the first partof this course documentation
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Module Objectives
Upon completion of this module, you should be able to:
propose a set of parameters to solve typical radio problems
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1 Theoretical Presentation 72 Eight Case Studies 9
2.1 Tunnel Case 102.2 Radar Case 112.3 Tower Case 122.4 Resurgence Case 132.5 Forest Case 142.6 Highway Case 152.7 TCH/SDCCH Congestion Case 162.8 Indoor Cell Congestion Case 17
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1 Theoretical Presentation
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1 Theoretical Presentation
Justification
Some typical problems due to particular field configuration always occur in a GSM network
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2 Eight Case Studies
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2 Eight Case Studies
2.1 Tunnel Case
Radiating cable in a tunnelQuestion:
Risks of such a configurationTune the right parameters for the tunnel cell
Catch quickly car traffic Avoid the pedestrian traffic
Indoor BTS
Outdoor BTS
Pedestrianmobile
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2 Eight Case Studies
2.2 Radar Case
Radar situationA “radar” cell situated on top of a hill provides a wide coverage area. An industrial zone in the valley is covered by small cells but also by the “radar” cell. The serving areas in the IZ are not clearly defined.
ObjectiveGive a parameter set toprevent the radar cell from catching any traffic in the industrial zone by HO assignment
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2.3 Tower Case
Tower situationThe indoor mobile selects in idle mode the outdoor cell (same LA)
ObjectiveDefine a set of parameters to avoid that effect
Outdoor cell
Indoorantenna
Indoormobile
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2 Eight Case Studies
2.4 Resurgence Case
Resurgence situationIn rural network, especially in hilly landscape, many resurgences occur from very far cells.
ObjectiveDefine a set of parameters to avoid radio link establishment to those cells and TCH traffic on those cells
Cell A
Resurgencefrom cell A
Cell B
25 Km
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2 Eight Case Studies
2.5 Forest Case
Forest situation: a highway crosses a forestHigh call drop rate (radio cause) on the cell and drive tests: strong level attenuation at the entrance of the forest
ObjectiveDefine a set of parameters to avoid radio link failure
-75 dBm
-90 dBm
Forest(ATT = 10 dB every 100 m)
Hig
hway
BTS
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2 Eight Case Studies
2.6 Highway Case
Highway situation:A highway is slightly covered (best coverage on 200m) by an ‘orthogonal’ cell (cell C on the map)
ObjectiveDefine a set of parameters to avoid traffic in the ‘orthogonal cell’
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2 Eight Case Studies
2.7 TCH/SDCCH Congestion Case
SDCCH congestion situationA railway station is located at the frontier of two LAs. Every train stopping in this station comes from LA 1 and then returns to LA 1 after the stop.
ObjectiveDefine a set of parameters to avoidSDCCH congestion on cell B (LA 2)
LA frontier
LA 1
LA 2
Cell A
Cell B
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2 Eight Case Studies
2.8 Indoor Cell Congestion Case
An indoor microcell has been introduced within a multi-layer network (macro + micro)
When the indoor microcell is congested, FDR may not be working as some the MSs can be covered only by this cell
Define parameter settings to find a good solution in case of indoor cell congestion
City center
Micro-cells
Macro-Cell
Macro-CellMacro-Cell
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Self-assessment on the Objectives
Please be reminded to fill in the formSelf-Assessment on the Objectivesfor this moduleThe form can be found in the first partof this course documentation
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End of ModuleCase Studies
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Module Objectives
Upon completion of this module, you should be able to:
…
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Table of Contents
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1 Erlang B law 72 Frequency Hopping influence on PCHO process 213 Load & Traffic evaluation 264 Handover Management 375 LCS 466 Dynamic SDCCH Allocation 637 Handover Detection for Concentric Cells 73
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1 Erlang B law
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1 Erlang B law
Erlang definition
ERLANG: unit used to quantify traffic
Example: 1 TCH is observed during 1 hourone can observe 1 call of 80 sec and 1 call of 100 secthe observed traffic is T = (80+100)/3600 = 0.05 ERLANG
Erlang definition
T = total observation durationresource usage duration
(Erlang)
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ERLANG <-> CALL MIX
CALL MIX EXAMPLE350 call/hour3 LU/callTCH duration: 85 secSDCCH duration: 4.5 sec
ERLANG COMPUTATIONTCH = (350 * 85)/3600 = 8.26 ERLANGSDCCH = [ (350 + 350*3) * 4.5 ] / 3600 = 1.75 ERLANG
1 Erlang B law
Call mix definition
350 calls * 85 sec / 1 hour(3600 sec):
TCH = (350 * 85)/3600 = 8.26 ERLANGS
350 calls means 350 SDCCH phases.
3 LU/call means 3 * 350 LUs so 1050 SDCCH phases more.
1 SDCCH phase is 4.5 sec:
SDCCH = [ (350 + 350*3) * 4.5 ] / 3600 = 1.75 ERLANG
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1 Erlang B law
Erlang B (1/5)
Erlang B lawRelationship between
offered trafficnumber of resourcesblocking rate
In a telecom system, call arrival frequency is ruled by the POISSON LAW
1 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 970
1
2
3
45
6
7
8
9
10Call
Second
The offered traffic is the traffic asked by the customers.
The graph gives the number of connection requests per second during 35 seconds.
83/30s => 83 * 2 * 60 = about 10 000 / hour
Real example in Paris on 1 BSC (LA FOURCHE).
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1 Erlang B law
Erlang B (2/5)
Call request arrival rate (and leaving) is not stableNumber of resources = average number of requests * mean durationIs sometime not sufficient => probability of blocking
=> 1 Erlang B lawPblock: blocking probabilityN: number of resourcesE: offered traffic [Erlang]Good approximation when
the blocking rate is low (< 5%) Pblock = ΣN
k=0 Ek
k !
EN
N !
Erlang B law
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There is two different ways to use this law
Using Abacus
Using SW (here Excel)Pblock = f (T, Nc)Offered = f (Nc, Pblock)Channels = f (T, Pblock)
1 Erlang B law
Erlang B (3/5)
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1 Erlang B law
Erlang B (4/5)
Example:
We have a BTS of 8 TRXs (about 60 channels (Nc))We do not want more than 2% of blocking (Pblock)=> The traffic is not to be greater than 50 Erlangs (T)
83% of resources used to reach 2% of blocking
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1 Erlang B law
Erlang B (5/5)
But be careful, the law is not linear:
In B4, we use for example a combined BCCH with a micro BTS.4 SDCCHs, Pblock = 2% => T = 1.1 E25% of resources used to reach 2% of blocking
In B5, if we decide to provide SMSCB (Cell Broadcast information)1 subchannel SDCCH is therefore used.3 SDCCHs, Pblock = 2% => T = 0.6 E25% of resources less => 50% of Traffic less !!
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CELL DIMENSIONING
Given an Offered traffic, compute the number of TRXs (and SDCCHs) needed to carry it
Default blocking rateRTCH: 2%SDCCH: 0.5%(TTCH: 0.1%)
1 Erlang B law
Cell dimensioning (1/5)
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CELL DIMENSIONING
To handle an offered traffic of 12 Erlangs (TCH), compute the number of channels, then the number of TRXs
Channels (12;2%) = 19
Example: 3 TRXs , 21 TCHs, 1 BCCH, 2 SDCCH8
1 Erlang B law
Cell dimensioning (2/5)
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CELL DIMENSIONING, based on field measurement
One is measuring a traffic of 15 Erlangs, with a blocking rate of 10%How to dimension the cell?
Offered traffic = 15 / (1-10%) = 16.7 Erlangs !!!!Channels (16.7;2%) -> 25 TCHs -> 4 TRXs needed
1 Erlang B law
Cell dimensioning (3/5)
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FORECASTING TRAFFIC/CRITICAL TRAFFIC
Traffic forecasting must be calculated according to offered trafficnot directly on measured traffic
In order to plan necessary actions soon enough, one must calculate regularly the date when the traffic of a cell will become critical
Critical traffic: when offered traffic will induce 2% of blocking
1 Erlang B law
Cell dimensioning (4/5)
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1 Erlang B law
Cell dimensioning (5/5)
WARNING: in case of too high blocking rate
First check that there is no outage on the BTS
Before starting a dimensioning/tuning action
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1 Erlang B law
Training exercise
Training exercise Complete this form in order to get less than 2% of blocking in all cases.
Erlang TCHoffered traffic
450 call/hourMean TCH call duration: 80 sec
Blocking rate TCH: 0.8%12,743 10.08 Erlang TCH 30% offered traffic
increase13.1 Erlang TCH -> 20 TCH
3 TRX
Call mix infoCell Traffic forecast Proposed configuration
12,675
12,865
330 call/hourMean TCH call duration: 129 sec
Blocking rate TCH: 4%
600 call/hourMean TCH call duration: 96 sec
Blocking rate TCH: 8%
30% offered trafficincrease
30% offered trafficincrease
cell call mix info Erlang TCH traffic forecast proposed config
12, 743 450 call/hourmean TCH call duration : 80secblocking rate TCH : 0.8%
10 Erlang TCH
(450*80)/3600=1010/.992=10.081
30 % TCH increase
10,081*1.3=13.1
13,1 Erlang TCH - > 20TCH
3 TRX
12,675 330 call/hourmean TCH call duration 129secblocking rate 4%
(330*129)/3600=11.825/0.96=12.3177
30 % TCH increase
12.3177*1.3 =16
16 Erlang TCH -> 24 TCH
4 TRX
12,865 600 call/hourmean TCH call duration 96secblocking rate 8 %
(600*96)/3600=16/.92 = 17.4
30 % TCH increase
17.4*1.3 = 22.6
22.6 Erlang TCH -> 31 TCH
5 TRX
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2 Frequency Hopping influence on PCHO process
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2 Frequency Hopping influence on PCHO process
(1/4)
Signal decoding processIn a GSM system, the number of frames that are not erased are sent as an input to the voice decoder
Inside the mobile station
Decoder
Encoder
DeinterleaveError Correction
Frame ErasureDecision
RXQUAL Frame Erasure Rate
Demod. VoiceDecoder
Air
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Quality impact of frequency hopping on the reception chain
In non-hopping networks, the RXQUAL and voice quality are correlated
In hopping networks, the voice quality is sooner correlated to the FER. This is due to interferer averaging and due to the non-linear mapping of BER to RXQUAL values.
2 Frequency Hopping influence on PCHO process
(2/4)
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Quality impact of frequency hopping on the reception chainFER is improved when frequency hopping is activated (cyclic or random)RxQual is not impacted whereas the speech quality is better
2 Frequency Hopping influence on PCHO process
(3/4)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
RxQ Average
0.00%
0.50%
1.00%
1.50%
2.00%
2.50%
FER Average
Ref Cyclic RandomRxQ AverageFER Average
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Conclusion
When frequency hopping is activatedWe can accept in Power Control and Handover processes, a threshold increase:
OFFSET_HOPPING_PC andOFFSET_HOPPING_HO
2 Frequency Hopping influence on PCHO process
Conclusion (4/4)
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3 Load & Traffic evaluation
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3 Load & Traffic evaluation
Cell TCH radio resource evaluation usage
FREEfactorLOADfactor
Loadevaluation
Speed discrimination for hierarchical networkFull Rate/Half Rate channel allocation
Power budget HandoverTraffic Handover
Multiband capture HandoverGeneral capture Handover
N_TRAFFIC_LOAD x A_TRAFFIC_LOAD x TCH_INFO_PERIOD
Shortterm
Mediumterm
Longterm
LOAD_EV_PERIOD x TCH_INFO_PERIOD
TCH_INFO_PERIOD
Period Usage
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3 Load & Traffic evaluation
Load evaluation (1/5)
Nb of free TCHsLOADfactorsFREEfactors
Load evaluation
TCH_INFO_PERIOD sec
LOAD_EV_PERIOD
Non-sliding average
Medium term measurement of the load of a cellCorresponds to function AV_LOAD(cell)A new sample of the “Nb free TCH” in the cell is available everyTCH_INFO_PERIOD secondsAV_LOAD() is a non-sliding window load average from Nb free TCH samples updated every LOAD_EV_PERIOD x TCH_INFO_PERIOD sec
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3 Load & Traffic evaluation
Load evaluation (2/5)
AV_LOAD(cell n) calculated from N Nb free TCH samples available during LOAD_EV_PERIOD x TCH_INFO_PERIOD sec
LOADfactors and FREEfactors also determined from Nb free TCH samples every TCH_INFO_PERIOD seconds (short term evaluation)LOADlevels are boundaries of load intervals associating a LOADfactor (db) to a Nb of free TCH samplesFREElevels are boundaries of Nb of free TCH intervals associating a FREEfactor (db) to a Nb of free TCH samples
AV_LOADdefinition
AV_LOAD = Nsamples1 Σ
Nsamples
i = 1
(1 - Nb total TCH (n)Nb free TCH (n)
) x 100
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3 Load & Traffic evaluation
Load evaluation (3/5)
LOADfactor determination:
LOADlevel in %LOADfactor in dB
LOADfactor
LOADfactor_1
LOADfactor_2
LOADfactor_3
LOADfactor_4
LOADfactor_5
t = (1 - Nb free TCH/Total Nb TCH) x 100
t <= LOADlevel_1
LOADlevel_1 < t <= LOADlevel_2
LOADlevel_2 < t <= LOADlevel_3
LOADlevel_3 < t <= LOADlevel_4
LOADlevel_4 < t
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3 Load & Traffic evaluation
Load evaluation (4/5)
FREEfactor determination:
FREElevel in absolute number of TCHFREEfactor in dB
FREEfactor
FREEfactor_1
FREEfactor_2
FREEfactor_3
FREEfactor_4
FREEfactor_5
Nb free TCH
t <= FREElevel_1
FREElevel_1 < t <= FREElevel_2
FREElevel_2 < t <= FREElevel_3
FREElevel_3 < t <= FREElevel_4
FREElevel_4 < t
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3 Load & Traffic evaluation
Load evaluation (5/5)
Example: cells with 4 TRXs (28 TCHs)
In cell evaluation of cell n for outgoing HO from cell 0:In GRADE(n): + LOADfactor(n) = +0 = 0 dBIn ORDER(n): + FREEfactor(n) – FREEfacfor(0) = +7 – (-8) = +15 dB
LOADfactor+10 dB+5 dB0 dB
-10 dB-15 dB
Load = (1 - Nb free TCH/Total Nb TCH) x 100t <= 10%10% < t <= 25%25% < t <= 50%50% < t <= 80%80% < t
FREEfactor-16 dB-8 dB0 dB
+7 dB+10 dB
Nb free TCHt <= 33 < t <= 88 < t <= 1515 < t <= 2121 < t
Cell nCell 0
HO ?Nb free TCHs = 4Load = 85.7%
LOADfactor(0) = -15 dBmFREEfactor(0) = -8 dBm
Nb free TCHs = 20Load = 28.6%
LOADfactor(n) = 0 dBmFREEfactor(n) = +7 dBm
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3 Load & Traffic evaluation
Traffic evaluation (1/4)
Long term measurement of the load of a cellCorresponds to function Traffic_load(cell)Traffic_load() value is determined from a number N_TRAFFIC_LOAD of consecutive non-sliding window load averages AV_TRAFFIC_LOAD calculated from Nb of free TCH samples updated every A_TRAFFIC_LOAD x TCH_INFO_PERIOD sec
Nb of free TCHsLOADfactorsFREEfactors
Traffic evaluation
TCH_INFO_PERIOD sec
A_TRAFFIC_LOAD(N_TRAFFIC_LOAD non-sliding average)
TRAFFIC_EV_PERIOD
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3 Load & Traffic evaluation
Traffic evaluation (2/4)
3 possible values for Traffic_load(): high, low, indefiniteInitialization: Traffic_load() = indefiniteTraffic_load() becomes:
High if the last N_TRAFFIC_LOAD consecutiveAV_TRAFFIC_LOAD load averages are all greater than HIGH_TRAFFIC_LOAD thresholdLow if the last N_TRAFFIC_LOAD consecutiveAV_TRAFFIC_LOAD load averages are all lower than LOW_TRAFFIC_LOAD threshold
Traffic loadThresolds comparisonwith N_TRAFFIC_LOAD
averages
AV_TRAFFIC_LOADAveraging onA_TRAFFIC_LOAD
load samples
Load samples
HIGH_TRAFFIC_LOAD
LOW_TRAFFIC_LOAD
IND_TRAFFIC_LOAD
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Traffic_load() becomes indefinite if:Traffic_load() was high and the last AV_TRAFFIC_LOAD load average is lower than LOW_TRAFFIC_LOAD (or IND_TRAFFIC_LOAD if not 0%)Traffic_load() was low and the last AV_TRAFFIC_LOAD load average is greater than HIGH_TRAFFIC_LOAD (or IND_TRAFFIC_LOAD if not 0%)
Traffic_load(n) is always equal to indefinite if cell n is external to BSC
HIGH_TRAFFIC_LOAD ≥ IND_TRAFFIC_LOAD ≥ LOW_TRAFFIC_LOAD
3 Load & Traffic evaluation
Traffic evaluation (3/4)
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3 Load & Traffic evaluation
Traffic evaluation (4/4)
HIGH_TRAFFIC_LOAD
Variation ofAV_TRAFFIC_LOAD
IND_TRAFFIC_LOAD
LOW_TRAFFIC_LOAD
Traffic_load = high
Traffic_load =indefinite
Traffic_load =indefinite
Traffic_load = low Traffic_load = lowTraffic_load =
indefinite
Traffic_load =indefinite
Traffic_load = high
IND_TRAFFIC_LOAD = 0IND_TRAFFIC_LOAD <> 0
Example with N_TRAFFIC_LOAD = 3
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4 Handover Management
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Handover Management made up of: Cell Filtering Process (according to call history)Handover Decision (according to the best cell in the list)
Handover Management followed by: Handover Protocol
4 Handover Management
Principles
RadioLink Measurements
ActiveChannelPre-processing
BTS BSC
HO Detection HO CandidateCell Evaluation
HO management
MSC
HO protocol
HO Preparation
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4 Handover Management
Global Handover Process
Handover preparation
Handoverdetection
Handover management
Cellfilteringprocess
Handoverprotocol
Externalor internalchannelchange
Candidate cell
evaluationHandoverdecision
Rawcell list
Orderedtarget
cell list
Filteredtargetcell list
Executiontarget
cell list
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Three cell lists:
Ordered target Cell list
target cells provided by Candidate Cell Evaluation
REJ_CELL_LIST
cells internally rejected by the MSC or BSC
MS_CELL_REJ_LIST
cells to which the MS failed to hand over
4 Handover Management
Cell Lists usage
Since B6 release, some changes have been provided to the HO management process which is in charge of the HO execution triggering, when the need of handover is detected by the HO preparation process.
These changes are :
use of the T_FILTER parameter in a different way than for B5,
the parameter NBR_HO_ATTEMPTS which was used for internal HO in B5 is removed,
use of the T7 parameter and of the REJ_CELL_LIST list also for internal HO in B7,
same behavior in case of internal and external HO in B7,
immediate attempt after rejection or failure without waiting for a new alarm in case of internal and external HO in B7,
implicit rejection of cells in B7 with the help of the target cell identity in the HO command received from the MSC.
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T_FILTER: controls the global handover procedurestarted: when a cell list is to be sent by Candidate Cell Evaluationexpiry ⇒ empty target cell list sent to the Handover Management
T7: controls the clean-up of REJ_CELL_LISTstarted: when a target cell list is to be sent to Handover Protocolexpiry ⇒ empty REJ_CELL_LIST
T_MS_CELL_REJ: clean-up of MS_CELL_REJ_LISTstarted: when an MS reports a failure to seize the target channelexpiry ⇒ empty MS_CELL_REJ_LIST
T_HO_REQ_LOST: to supervise answer of MSC (no HANDOVER REQUIRED REJECT message sent)
Started: HO REQUIRED sentStopped: HO COMMAND received Expiry ⇒ external channel change procedure is terminated.
4 Handover Management
Timers usage
If the candidate cell list provided by the candidate cell evaluation process is different from the previous one (the number of cells is different or same number of cells but new cells in the list), an alarm is sent to the HOM process. In B7, if T_FILTER expires, it means that the HO is no more necessary.
For both internal and external HOs in case of HO failure from the MS, the cell is filtered until the expiry of the T_MS_CELL_REJ timer. When the T_MS_CELL_REJ timer expires, the rejected cell may be a candidate.
In B7 release, T7 timer is used to manage the REJ_CELL_LIST list and a subsequent HO REQUIRED can be sent to the MSC before T7 expiry if the target cell list has changed (new cell or removed cell).
The REJ_CELL_LIST list is used for both internal and external Hos.
T_HO_REQD_LOST Expiry
This timer is used to supervise response from the MSC. It is started when sending the first HANDOVER REQUIRED to the MSC and it is stopped in the following cases:
• when HANDOVER COMMAND is received from the MSC or
when HANDOVER REQUIRED REJECT is received from the MSC only if the same number of HANDOVER REQUIRED REJECT messages have been received from the MSC than the number of HANDOVER REQUIRED messages sent to the MSC for this channel change procedure) (i.e. no message crossing over A interface).
In case where more HANDOVER REQUIRED messages have been sent to the MSC, the timer T_HO_REQD_LOST is not stopped upon HANDOVER REQUIRED REJECT receipt, as there is no way for the BSC to know if the received HANDOVER REQUIRED REJECT is a response to the last HANDOVER REQUIRED message or a response to a previous one (message crossing over A interface).
On expiry, an O&M error report is raised only when no message has been received from the MSC since the last HANDOVER REQUIRED message, and the external channel change procedure is terminated.
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4 Handover Management
Handover Execution Process
Handover preparation
Cell filtering process
remove cells previously rejectedfrom MSC or BSCremove cells previously rejectedfor MS failure reasonremove cells not suitable due toO&M reason
Filteredtarget
cell list
Cell 4Cell 2Cell 8
Filteredtarget
cell list
Cell 2
InternalHandover
InternalHandover
Handoverprotocol
Handover decision
Relevant handover protocol ischosen according to the type ofGSM procedure ongoing and thefirst target cell of the list
T7 is started
List of cellspreviously rejected
for MS failure
Cell 8MS_CELL_REJ_LIST listcleared atT_MS_CELL_REJ expiry
List of cellspreviously rejectedfrom MSC or BSC
Cell 4REJ_CELL_LIST listcleared at T7 expiry
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4 Handover Management
HO execution example
Handover management
Orderedtarget cell list
Cell 1Cell 2Cell 3
Rejected lists
MS emptyBSC/MSC empty
Orderedtarget cell list
Cell 1Cell 2Cell 3
Update
Cell 1 -> MSrejected list
Handover management
Orderedtarget cell list
Cell 1Cell 2Cell 3
Rejected lists
MS cell 1BSC/MSC empty
Orderedtarget cell list
Cell 1Cell 2Cell 3
Handoverprotocol
HO failson cell 2
ROC
Update
T_MS_CELL_REJexpires
MS rejected listempty
Update
Cell 2 -> MSrejected list
Cell 1 -> BSCrejected list
Handover management
Orderedtarget cell list
Cell 1Cell 2Cell 3
Rejected lists
MS cell 2BSC/MSC cell 1
Orderedtarget cell list
Cell 1Cell 2Cell 3
Handoverprotocol
HO tocell 3
Handoverprotocol
HO failson cell 1
ROC
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End of Handover procedure = T_FILTER timer expiry
T_FILTER restarted each time a target cell list is to be sent by Candidate Cell
Evaluation to the Handover Management (same list than the one previously
sent or not)
The target cell list is sent to the Handover Management if different from the
last target cell list previously sent
T_FILTER expiry means no handover is needed anymore
4 Handover Management
T_FILTER controls HO procedure (1/2)
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4 Handover Management
T_FILTER controls HO procedure (2/2)
Is T_FILTER running?
YesNo
Restart T_FILTER
New candidate cell list from thecandidate cell evaluation function
Start T_FILTER:an HO alarm containing thecandidate cell is sent to the
HO management entity
YesNo
Is the candidate cell listdifferent from the previous one?
Restart T_FILTER:an HO alarm containing thecandidate cell is sent to the
HO management entity
No Handover is on-going A Handover is on-going
A Handover is now on-going
T_FILTER is restartedeach time the alarm is still on
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5 LCS
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5 LCS
Definitions
New end-user services which provide the geographical location of an MS:
On MS request to know its own location On network request (especially during Emergency calls)On external request (LCS Client)
Several positioning methods:Cell-ID or Cell-ID + TA (Timing Advance)Conventional (standalone) GPSAssisted GPS (with A-GPS server help to compute location)
MS-based (MB): the MS is able to perform a pre-computationMS-assisted (MA): the MS sends info, Network computes
Assisted GPS Method:
Mobile-based: The MS performs OTD signal measurements and computes its own location estimate. In this case, the network provides the MS with the additional information such as BTS coordinates and the RTD values. These assistance data can be either broadcast on the CBCH (using SMSCB function) or provided by the BSS in a point-to-point connection (either spontaneously or on request from the MS).
Mobile-assisted: The MS performs and reports OTD signal measurements to the network and the network computes the MS’s location estimate.
WithOTD: Observed Time Difference: the time interval that is observed by an MS between the receptions of signals (bursts) from two different BTSs.
RTD: Real Time Difference: This means the relative synchronization difference in the network between two BTSs.
Finally, 4 methods are possible for positioning:
Cell ID+ TA.
This is the simplest method for determining the location of a mobile. It relies on the hypothesis that the geographical coverage of a cell corresponds to that predicted by radio coverage studies. When an active mobile is connected to a base station, the mobile is assumed to be located geographically within the area predicted to be best served by this base station
Conventional (MS equipped with GPS System).
MS-based Assisted GPS.
MS-Assisted GPS.
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5 LCS
Architecture
MS Request1Network Request2External Request3
A-GPSGMLCLCSSMLC
: Assisted GPS: Gateway Mobile Location Center: Location Services: Serving Mobile Location Center
BTS
Abis
MFS
BTS
OSP
SMLC
A-GPSserver
GPS receiversreference network
GMLC ExternalLCS client
MSCBSC
HLR
Abis
A Lg Le
Lh
Lb
Emergency call
2 3
SAGI
Where isthe accident?
Where ismy son?
Where am I?
1
SMLC function integrated in MFS:- receives the location request from the GMLC through the MSC/BSC- schedules all the necessary actions to get MS location- computes MS location- provides the result back to the GMLC
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5 LCS
LCS Positioning Procedure
BTS
MFS
BTS
OSP
SMLC
GMLCMSC
BSC
HLR
Locationrequest
1
Routinginformation
2
Providesubscriber
location3
Paging,authentication,
ciphering,notification
4
Providesubscriber location
5
Individualpositioning
6 Location report7 7Locationresponse
8
If the MS is in idle mode, the MSC first performs a CS paging, authentication and ciphering in order to establish an SDCCH with the MS. The MS subscriber is not aware of it, i.e. no ringing tone, except towards GPRS MS in Packet Transfer Mode which may suspend its GPRS traffic in order to answer to the CS Paging (i.e. not fully transparent for the subscriber).
When the MS is in dedicated mode (after a specific SDCCH establishment for location, or during an on-going call), the MSC sends the location request to the BSC in the existing SCCP connection for the current call, which forwards it to the SMLC.
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5 LCS
LCS Protocols
BSC SMLC(MFS)
Um Lb
L1-GSL
L2-GSL
BSSLAP
L2-GSL
BSSAP-LE
L1-GSLL1
L2(LAPDm)
RR
Relay
RRLP(04.31)
BSSLAP(08.71)
BSSAP-LE(09.31)
Target MS
L1
RR(04.18)
L2(LAPDm)
RRLP(04.31)
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5 LCS
LCS Protocols [cont.]
Example: Mobile terminated location request success (External request)MS BTS BSC SMLC MSC GMLC HLR
Adequate positioning methodchosen by SMLC with
optional additional scenario
StartsT_Location
StopT_Location
LCS Service Request
Send_Routing_Info request
Send_Routing_Info response
Provide_Subscriber_Location
Authentication + Ciphering
BSSMAP Perform_Location_Request
BSSAP-LE Perform_Location_Request
BSSAP-LE Perform_Location_Response
BSSMAP Perform_Location_Response
Provide_Subscriber_Location Result
LCS Service Response
MSSMAP Clear Command and Release
LCS client
Paging
T_location_Longer used in case of optional additional scenario (see graph):
Upon receipt of the MS POSITION COMMAND message from the SMLC (optional additional scenario), the BSC stops the T_Location timer, and starts instead the T_Location_Longer timer. This timer is stopped only at the end of the location procedure in the BSC, i.e. when an 08.08 PERFORM LOCATION RESPONSE message is sent back to the MSC.
Aborts:
Abort by MSC
Depending on the location procedure and its current state of execution, upon PERFORM LOCATION ABORT message receipt, the BSC sends immediately to the MSC a PERFORM LOCATION RESPONSE message (when no exchange on the Lb interface is on-going), or to the SMLC either a PERFORM LOCATION ABORT or an ABORT message. The BSC starts the timer T_Loc_abort to supervise the SMLC response.
Abort by BSS
The BSC must send either a PERFORM LOCATION ABORT message or a ABORT message to the SMLC and starts the timer T_Loc_abort, if an ongoing location request is interrupted at the BSC level for the following reasons:
by an inter-BSC handover, or
if the main signaling link to the target MS is lost or released, or
the SCCP connection on the A interface is released, or
if the timer T_Location expires,
The useful B8 content of the received PERFORM LOCATION REQUEST message is:
Location type,
Classmark information 3,
Requested QoS: provides service requirement concerning geographic positioning and response time
accuracy, the response time category (Low Delay or Delay Tolerant),
Current Cell Id + TA information are always provided to the SMLC.
The time of transfer of the assitance data on the SDCCH is estimated about 14s for a 1000 octets information.
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5 LCS
Positioning Methods: CI+TA Positioning
Principles of CI + TA Positioning Method
LCS_LONGITUDE
LCS_LATITUDE
LCS_AZIMUTH(Main Beam Directiongiven by the azimuth)
HALFPWR_BEAM_WIDTH
Serving cell (CI)
TA
3dB pointgiven by the azimuth
and the HPBW
3dB pointgiven by the azimuth
and the HPBW
553 m
MSestimated location
With the TA positioning method, no signaling exchange is required between the SMLC and the MS (i.e. RRLP protocol is not required). The TA positioning method is applicable to all the MSs (supporting LCS or not).
Based on:
Cell Identity (CI) of the serving cell and
Timing Advance (TA) value reported by MS
intersection point of a line from the BTS antenna in its main direction with a circle which radius is corresponding with the propagation delay (timing advance) is the MS estimated position
Omni-directional cells: MS position = site position
Parameters:
EN_LCS – flag to enable/disable the Location Services per BSS
0 = Enabled; 1= Disabled; Default = 0
IF EN_LCS=1, CI+TA method is enabled in all the BSS cells
LCS_LATITUDE: Latitude of the BTS supporting the cell
LCS_LONGITUDE: Longitude of the BTS supporting the cell
LCS_AZIMUTH: Antenna direction orientation for the sector supporting the cell
HALFPWR_BEAM_WIDTH: Antenna half power beamwidth for the sector supporting the cell
Optimization parameters:ARC_SIZE_FACTOR: Factor used in the computation of the width in degree of the ellipsoid arc returned by the MFS
when computing location estimate based on TA positioning method.MIN_RADIUS_FACTOR: Factor used in the computation of the minimum radius of the ellipsoid arc returned by the
MFS when computing location estimate based on TA positioning method.MAX_RADIUS_FACTOR: Factor used in the computation of the maximum radius of the ellipsoid arc returned by the
MFS when computing location estimate based on TA positioning method.
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5 LCS
Positioning Methods: Conventional Positioning
Conventional GPS location procedureThis optional location procedure is chosen by the SMLC (if the MS supports it) upon reception of a Perform Location Request message from the BSC
PerformLocationRequest
MS BTS BSC SMLC
Measurement Position Request
Measurement Position Response (X,Y)
PerformLocation
Response (X,Y)(X,Y):
computed position
(X,Y)
LocationRequest
LocationResponse
The MS continuously computes its position.
The terminal searches for satellites, acquires all the GPS data, computes its own position and finally provides the location estimation to the SMLC.
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5 LCS
Positioning Methods: Assisted GPS Positioning
Assisted GPS Positioning Method (A-GPS)Assisted GPS Positioning Method is split into:
MS Based A-GPS methodMS Assisted A-GPS method
- GPS acquisition assistance- Navigation model (almanac, ephemeris)- Ionospheric model- Time integrity
GPS MS A-GPSserver
GPS receiversreference network
Assistance data on request
Assistance data gathered from a GPS reference network receiver is broadcast to the GPS MS.
Flags/Parameters
EN_LCS = 1
EN_MS_BASED_AGPS – enables/disables the positioning method MS Based A-GPS per CELL
0 = disabled; 1 = enabled; default = 0
EN_MS_ASSISTED_AGPS – enables/disables the positioning method MS Assisted A-GPS per CELL
0 = disabled; 1 = enabled; default = 0
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5 LCS
Positioning Methods: Assisted GPS Positioning [cont.]
A-GPS location procedure / MS Based A-GPS
PerformLocationRequest
MS BTS BSC SMLC
LocationRequest
A-GPSServer
GPS infoRequest
GPS infoResponse
Measurement Position Request
Assistance Data
Assistance Data Acknowledge
Measurement Position Response (X,Y)
PerformLocation
Response (X,Y)
LocationResponse
PositionRequest
PositionResponse
AssistanceData
(X,Y)
(X,Y):computed position
Positioning calculation:latitude, longitude
and altitude
Using assistance data, the MS computes by itself the position and sends it back to the SMLC.
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5 LCS
Positioning Methods: Assisted GPS Positioning [cont.]
AA--GPS location procedure / MS Assisted AGPS location procedure / MS Assisted A--GPSGPS
(X,Y):computed position
Pseudo-rangemeasurements (M)
PositionResponse
PerformLocationRequest
MS BTS BSC SMLC
LocationRequest
A-GPSServer
GPS infoRequest
GPS infoResponse
Measurement Position Request
Assistance Data
Assistance Data Acknowledge
PerformLocation
Response (X,Y)
LocationResponse
PositionRequest
AssistanceData
(X,Y)
Measurement Position Response (M)
GPS LocationRequest (M)
GPS LocationResponse (X,Y)
Using a reduced set of assistance data, the MS makes pseudo–range measurements and sends the result to the A-GPS server, which fixes the position in the end.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Annexes1 · 6 · 57
5 LCS
LCS Impact on HO
HO preparationInhibition of “better cell handovers”Other HO
MS BTS BSC SMLC MSC GMLC HLR
StartsT_Location
EmergencyHO
detection
LCS Service Request
Send_Routing_Info request
Send_Routing_Info response
Provide_Subscriber_Location
Authentication + Ciphering
BSSMAP Perform_Location_Request
BSSAP-LE Perform_Location_Request
LCS client
Paging
BSSLAP - Reset
HO needed during LCS procedure
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5 LCS
LCS Impact on HO [cont.]
HO managementInternal HO
MS BTS BSC SMLC MSC GMLC HLR
HOcomplete
BSSMAP Perform_Location_Request
BSSAP-LE Perform_Location_Response
LCS client
BSSLAP - Reset
Intra BSCHO
on going
BSSMAP perform location response (cause = "Intra-BSC Handover Complete)
Mobile in communication
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5 LCS
LCS Impact on HO [cont.]
HO managementExternal HO
MS BTS Serving BSC SMLC MSC GMLC HLR
ExternalBSC HO
BSSAP-LE Perform_Location_Abort
LCS client
BSSAP-LE Perform_Location_Response
BSSMAP HO required
BSSAP-LE Perform_Location_Response
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5 LCS
BSS Parameters
Timers
T_LocationT_Location_longerT_Loc_AbortT_LCS_delay_tolerantT_LCS_LowDelayT_RRLP_low_delayT_RRLP_delay_tolerant
FLAGS
EN_LCSEN_SAGI
OPTIMIZATION DATA
ARC_SIZE_FACTORMIN_RADIUS_FACTORMAX_RADIUS_FACTOR
BSS PARAMETERSEN_LCS (BSC)
Flag which enables or disables the LCS feature in the BSS.EN_SAGI
Flag indicating whether SAGI is configured or not for this BSS.T_Location:
BSC timer on a per call basis to guard the response from the SMLC in case of Location Request, when no RRLP exchange is triggered with the MS.
T_Location_longer:BSC timer on a per call basis to guard the response from the SMLC in case of Location Request, when an RRLP exchange is triggered with the MS. Replace T_Location timer in case of Conventional GPS, MS-Assisted A-GPS, MS-Based A-GPS.
T_Loc_AbortBSC timer to guard the response from the SMLC in case of Location Abort.
T_LCS_LowDelaySMLC timer to guard the calculation of the MS position (including the RRLP message exchange with the target MS) in case of a LowDelay Location Request.
T_LCS_DelayTolerantSMLC timer to guard the calculation of the MS position (including the RRLP message exchange with the target MS) in case of a Delay Tolerant Location Request.
T_LCS_LowDelaySMLC timer to guard the calculation of the MS position (including the RRLP message exchange with the target MS) in case of a LowDelay Location Request.
T_RRLP_Low_delayTimer to guard the RRLP exchange between the SMLC and the MS.
T_RRLP_delay_tolerantTimer to guard the RRLP exchange between the SMLC and the MS.
Optimization data:ARC_SIZE_FACTOR
Factor used in the computation of the width in degree of the ellipsoid arc returned by the MFS when computing location estimate based on TA positioning method.
MIN_RADIUS_FACTORFactor used in the computation of the minimum radius of the ellipsoid arc returned by the MFS when computing location estimate based on TA positioning method.
MAX_RADIUS_FACTOR Factor used in the computation of the maximum radius of the ellipsoid arc returned by the MFS when computing location estimate based on TA positioning method.
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5 LCS
Cell Parameters
SITE DATA
LCS_LATITUDELCS_LONGITUDELCS_SIGNIFICANT_GCLCS_AZIMUTHHALF_POWER_BANDWIDTH
EN_CONV_GPSEN_MS_ASSISTED_AGPSEN_MS_BASED_AGPS
FLAGS
CELL PARAMETERSEN_CONV_GPS
Flag to enable/disable the Conventional GPS positioning method.EN_MS_ASSISTED_AGPS
Flag to enable/disable the MS Assisted A-GPS positioning method.EN_MS_BASED_AGPS
Flag to enable/disable the MS Based A-GPS positioning method. LCS_LATITUDE
Latitude of the BTS supporting the cell (used by the MFS to compute location estimate based on TA positioning method).
LCS_LONGITUDE Longitude of the BTS supporting the cell (used by the MFS to compute location estimate based on TA positioning method).
LCS_SIGNIFICANT_GCIndicates whether latitude and longitude are significant or not.
LCS_AZIMUTHAntenna direction orientation for the sector supporting the cell (used by the MFS to compute location estimate based on TA positioning method).
HALF_POWER_BANDWIDTH Half power beam width of the antenna for the sector supporting the cell (used by the MFS to compute location estimate based on TA positioning method).
Remark: To have LCS supported for a cell, the operator must activate LCS on the BSS handling this cell but he must also activate GPRS for this cell (i.e. setting of MAX_PDCH to a value > 0, the cell being kept locked for GPRS if the operator does not want to have GPRS running on this cell) and configure all the required transmission resources (Ater and Gb resources) on the GPU(s) connected to this BSC.
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5 LCS
Positioning Methods: CI+TA Positioning
Ellipsoid arc definition:
Point (O)= serving BTS site coordinateθ= serving cell antenna azimuth - β /2β =A*width of serving cell sector in [°],calculated from bisector anglesof co-sited antenna azimuthsr1= inner radius ofTA ring-(B-0.5)*554 in [m]R2=(B+C)*554 in [m]
A: ARC_SIZE_FACTORB: MIN_RADIUS_FACTORC: MAX_RADIUS_FACTOR
Serving cell (CI)
E
North
S
W β
θ
r1
r2
Point (O)
An ellipsoid arc is a shape characterized by the co-ordinates of an ellipsoid point o (the origin), inner radius r1, uncertainty radius r2, both radii being geodesic distances over the surface of the ellipsoid, the offset angle (θ) between the first defining radius of the ellipsoid arc and North, and the included angle (β) being the angle between the first and second defining radii. The offset angle is within the range of 0° to 359,999…° while the included angle is within the range from 0,000…1° to 360°. This is to be able to describe a full circle, 0° to 360°
For CI+TA method which is default one, the answer is given by description of "ellipsoid arc".
Optimization parameters:ARC_SIZE_FACTOR
Factor used in the computation of the width in degree of the ellipsoid arc returned by the MFS when computing location estimate based on TA positioning method.
MIN_RADIUS_FACTORFactor used in the computation of the minimum radius of the ellipsoid arc returned by the MFS when computing location estimate based on TA positioning method.
MAX_RADIUS_FACTOR Factor used in the computation of the maximum radius of the ellipsoid arc returned by the MFS when computing location estimate based on TA positioning method.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Annexes1 · 6 · 63
6 Dynamic SDCCH Allocation
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6 Dynamic SDCCH Allocation
Purpose
SDCCH/8 time slots can be dynamically allocated on demand on a cell-per-cell basis.
“Dynamic SDCCH/8 time slots”“Static SDCCH time slots”
Min
Max
Static SDCCHtimeslots
AllocatedDynamic SDCCH/8
timeslots
0
TCH Capacity
A Static SDCCH timeslot is a physical timeslot fixed allocated on the air interface. It contains 3, 4, 7 or 8 SDCCH sub-channels depending on whether the timeslot is an SDCCH/3, SDCCH/4, SDCCH/7, or SDCCH/8 timeslot.
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6 Dynamic SDCCH Allocation
Principles
PrinciplesToo few SDCCH time slots could result in high blocking rate on SDCCH (Configuration 1)Too many SDCCH time slots could lead to a lack of TCH resources (Configuration 2)
SDCCHtime slots
TCH CAPACITY
SDCCHtime slots
TCH CapacityTCH Capacity
Configuration 1 Configuration 2
Low signaling capacity
More TCH capacity
High signaling capacity
Less TCH capacity
Definition
An SDCCH is a logical SDCCH sub-channel mapped on a Static SDCCH timeslot or a Dynamic SDCCH/8 timeslot.
Signaling Load Cases
Timeslot split between signaling and traffic channels depends on the network signaling load. The main cases are:
Normal signaling load cells:
Rural area cells in center of Location Areas
(e.g. 1 SDCCH timeslot for a 3-TRX cell)
High signaling load cells:
Urban or suburban area cells in the center of a Location Area
Rural area cells at the border of Location Areas
(e.g. 2 SDCCH time slots for a 3-TRX cell)
Very high signaling load cells:
Urban or suburban area cells at the border of a Location Area
Cells with high SMS load (more than one SMS per call)
(e.g. 3 SDCCH time slots for a 3-TRX cell)
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6 Dynamic SDCCH Allocation
Principles [cont.]
Allocation and de-allocation of Dynamic SDCCH/8 time slotsAn additional dynamic SDCCH/8 timeslot is allocated by the BSC if there is no SDCCH sub-channel free in the cell.A dynamic SDCCH/8 timeslot is de-allocated by the BSC after T_DYN_SDCCH_HOLD (10s) delay if all of its SDCCH sub-channels become free
BCC SDC TCH TCH
TCH TCH TCH TCH
TCH TCH TCH TCH
TCH TCH TCH TCH
TCH TCH TCH TCH TCH TCH TCH TCHCell
Allocation ofDynamic SDCCH/8
times slots
BCC SDC
SDD TCH
TCH TCH
BCC SDC
SDD TCH
SDD TCH
BCCSDCSDD
: BCCH: Static SDCCH: Dynamic SDCCH
The location of the Dynamic SDCCH/8 time slots are fixed by O&M configuration.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Annexes1 · 6 · 67
6 Dynamic SDCCH Allocation
Timeslot Types
NEW TIMESLOT TYPES:SDCCH Pure SDCCH or “ static SDCCH “TCH Pure TCHTCH/SDCCH “ dynamic SDCCH”TCH/SPDCH
MPDCH
The OMC-R provides the BSC with the following O&M type of radio timeslots:
Main BCCH timeslot (BCC): It is a timeslot carrying FCCH + SCH + BCCH + CCCH.
Main combined BCCH timeslot (CBC): It is a timeslot carrying FCCH + SCH + BCCH + CCCH + SDCCH/4 + SACCH/4.
Static SDCCH timeslot (SDC): It is a timeslot carrying SDCCH/8 + SACCH/8.
Dynamic SDCCH/8 timeslot (SDD): It is a timeslot carrying TCH + SACCH or SDCCH/8 + SACCH/8.
TCH timeslot (TCH): It is a timeslot carrying TCH + SACCH or PDCH.
From RAM point of view, a radio timeslot can be defined as:
Pure BCCH timeslot: The BCCH timeslot is the radio timeslot configured as BCC by O&M. Such a timeslot only carries common CS signaling.
Pure SDCCH timeslot: A pure SDCCH timeslot is a timeslot configured as a CBC or SDC by O&M. Such a timeslot can carry SDCCH traffic.
Pure TCH timeslot: A pure TCH timeslot is a timeslot configured as TCH by O&M. Such a timeslot only carries TCH traffic.
TCH/SDCCH timeslot: A TCH/SDCCH timeslot is a timeslot configured as SDD by O&M. Such a timeslot is dynamically allocated as TCH or as SDCCH depending on the usage of the timeslot. It can carry TCH traffic or SDCCH traffic.
TCH/SPDCH timeslot: A TCH/SPDCH timeslot is a timeslot configured as TCH by O&M. Such a timeslot is dynamically allocated as TCH or as SPDCH depending on the usage of the timeslot. It can carry TCH traffic or PS traffic.
MPDCH timeslot: A MPDCH timeslot is a timeslot configured as TCH by O&M. Such a timeslot can only carry common PS signaling.
A pure SDCCH timeslot can carry x SDCCH sub-channels where x equal to:
4 in case of combined CCCH and when CBCH is not configured on the timeslot,
7 in case of non-combined CCCH and when CBCH is configured on the timeslot,
3 in case of combined CCCH and when CBCH is configured on the timeslot,
8 for a normal SDCCH timeslot.
When allocated as SDCCH, a TCH/SDCCH timeslot can carry up to 8 SDCCH sub-channels.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Annexes1 · 6 · 68
6 Dynamic SDCCH Allocation
Allocation Algorithms
SDCCH Request
SDCCH mapped on "TCU very high load state" removal
Are they any free SDCCH sub-channelamong Static SDCCH timeslots?
Selection of oneSDCCH sub-channel
Yes No
Are they any free SDCCH sub-channelamong Dynamic SDCCH/8 already allocated?
Selection oneSDCCH sub-channel
Yes
Are they any Dynamic SDCCH/8 timeslotsavailable and free in the cell?
No
Allocate one DynamicSDCCH/8 timeslot
Yes No
SDCCH Requestrejected!!!
Principle 1: Preference is given to pure SDCCH timeslots
Principle 2: Balance TCU processor load between different TCUs
In fact before entering in this algorithm (see slide) the first step is: Removal of all the SDCCH subchannels mapped on TCU in « Very High Overload » state.
Principle 3: FR TRX preference
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6 Dynamic SDCCH Allocation
SDCCH Sub-Channel Selection
Pure SDCCH TimeslotTS with LOWEST TCU LOADTS with MAXIMUM FREE SDCCH Sub channelsTS with lowest index on TRX with lowest TRX_ID
TCH/SDCCH TS allocated as SDCCHTS on FR TRXTS with lowest index on TRX with lowest TRX_ID
TCH/SDCCH TS allocated as TCHTS with LOWEST TCU LOADTS on FR TRXTS with lowest index on TRX with lowest TRX_ID
Note that a SDCCH request cannot access the timeslots reserved by NUM_TCH_EGNCY_HO. If all remaining TCH/SDCCH timeslots are reserved by NUM_TCH_EGNCY_HO, then the SDCCH request shall be rejected.
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6 Dynamic SDCCH Allocation
De-Allocation Algorithm
GENERAL CASE:all SDCCH sub-channels of a TCH/SDCCH timeslot become back free.the T_DYN_SDCCH_HOLD timer (10s, not tunable) is started.If the timeslot is still free of SDCCH sub-channel when the timer expires, it is de-allocated (it becomes back TCH).
SPECIAL CASE:Several TCH/SDCCH timeslots are allocated as SDCCHOne of them becomes free of SDCCH sub-channels. Its timer starts.A subsequent one becomes free of SDCCH sub-channels too before expiration of the first one’s timer (10s).One of them is immediately de-allocated (the one with “lowest priority”: see previous slide in reverse order) and becomes back TCH.For the last one, its timer is restarted (it will be de-allocated in 10s).
The de-allocation algorithm ensures that:
TCH/SDCCH timeslots are not allocated too fast to TCH after de-allocating them
TCH/SDCCH timeslots are not re-allocated too frequently to SDCCH
Note: while T_DYN_SDCCH_HOLD is running:
the dynamic SDCCH/8 timeslot marked as “HOLD” is still considered as allocated to SDCCH (and cannot be allocated to TCH).
If a subsequent dynamic SDCCH/8 timeslot (used as SDCCH and in the same cell) becomes free:
If this just freed dynamic SDCCH/8 timeslot has a higher priority, T_DYN_SDCCH_HOLD is re-started and precedent dynamic SDCCH/8 timeslot in “HOLD” state is de-allocated immediately.
If this just freed dynamic SDCCH/8 timeslot has lower priority, and T_DYN_SDCCH_HOLD is re-startedand the just freed dynamic SDCCH/8 timeslot is de-allocated immediately.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Annexes1 · 6 · 71
6 Dynamic SDCCH Allocation
O&M Configuration
Selection of static or dynamic SDCCH
Timeslot configuration menu
BTS
BTS
BTS
BTS
2
4
7
3
1
10
9
6
12
8
5
11
Massive modification by script10 templates Template customizationTemplate launched through PRC
Dynamic SDCCH Rules
The CBCH must be configured on a static SDCCH/8 or SDCCH/4 timeslot.
Combined SDCCHs (SDCCH/4 + BCCH) are always static.
To avoid incoherent allocation strategy between SDCCH and PDCH, a dynamic SDCCH/8 timeslot cannothave the characteristic of being a PDCH (it cannot carry GPRS traffic).
The operator must configure at least one static SDCCH/8 or SDCCH/4 timeslot on BCCH TRX in a cell.
In cells with E-GSM, only the TRX, which do not belong to the G1 band, can support dynamic and static SDCCHs.
In multiband and concentric cells, only the TRX, which belongs to the outer zone, can support dynamic and static SDCCHs.
Up to 24 static/dynamic SDCCH sub-channels can be configured per TRX.
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Annexes1 · 6 · 72
6 Dynamic SDCCH Allocation
O&M Configuration [cont.]
Default configuration for a cell which has only Full rate TRX
Number of TRXin the cell
Number ofStatic SDCCH
Number ofDynamic SDCCH
Total numberof SDCCH
MaximumSDCCH/TRX
ratio
Is BCCH/CCCHcombined with
SDCCH?
1223456789
10111213141516
4488888
16161616161616242424
88161624242424243232324040404848
1212242432323240404848485656647272
12.0 (note 1)6.0
12.08.08.06.45.35.75.05.34.84.44.74.34.64.84.5
YesYesNoNoNoNoNoNoNoNoNoNoNoNoNoNoNo
Note1: For one TRX, dynamic SDCCHs are over-dimensioned because of the granularity of 8. According to the Alcatel-Lucent traffic model, all dynamic SDCCHs will not be used.
Note2: An additional dynamic SDCCH/8 must be provided for each DR TRX (these are expected mainly on small cells).
Rules:
At least one static SDCCH/4 or SDCCH/8 on BCCH TRX.
Up to 24 static/dynamic SDCCH sub-channels per TRX.
Up to 32 static/dynamic SDCCH sub-channels per TCU.
Up to 88 static/dynamic SDCCH sub-channels per CELL.
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7 Handover Detection for Concentric Cells
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7 Handover Detection for Concentric Cells
Algorithms
Emergency handovers specific to concentric cellsIntracell handovers from inner to outer zonecause 10: too low level on the uplink in inner zonecause 11: too low level on the downlink in inner zone
May be triggeredFrom inner zone of a concentric cellTowards outer zone, same cell
Concentric cell
I n n e r z o n e
Outer zone
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7 Handover Detection for Concentric Cells
Handover Algorithm Cause 10
CAUSE 10: too low level on the uplink in the inner zone
AV_RXLEV_UL_HO < RXLEV_UL_ZONEand MS_TXPWR = min (P, MS_TXPWR_MAX_INNER)
Averaging window: A_LEV_HO
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7 Handover Detection for Concentric Cells
Handover Algorithm Cause 11
CAUSE 11: too low level on the downlink in the inner zone
AV_RXLEV_DL_HO < RXLEV_DL_ZONEand BS_TXPWR = BS_TXPWR_MAX_INNER
Averaging window: A_LEV_HO
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7 Handover Detection for Concentric Cells
Handover Algorithm Cause 13
CAUSE 13: too high level on UL and DL in the outer zoneBetter condition intracell handoverIf the cell is a multi-band cell, cause 13 is checked only for multi-band MSs
May be triggeredFrom outer zone of a concentric cellTowards inner zone, same cell
Concentric cellI n n e r z o n e
Outer zone
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7 Handover Detection for Concentric Cells
Handover Algorithm Cause 13 [cont.]
CAUSE 13: too high level on UL and DL in the outer zone
AV_RXLEV_UL_HO > RXLEV_UL_ZONE +
+ ZONE_HO_HYST_UL +
+ (MS_TXPWR -
MS_TXPWR_MAX_INNER) +
+ PING_PONG_MARGIN(0,call_ref)and AV_RXLEV_DL_HO > RXLEV_DL_ZONE +
+ ZONE_HO_HYST_DL ++ (BS_TXPWR -
BS_TXPWR_MAX_INNER) ++ PING_PONG_MARGIN(0,call_ref)
and AV_RXLEV_NCELL_BIS(n) <= neighbour_RXLEV(0,n)and EN_CAUSE_13 = ENABLE (B7)and EN_BETTER_ZONE_HO = ENABLE
Averaging windows: A_LEV_HO and A_PBGT_HO (for n)
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7 Handover Detection for Concentric Cells
Handover Algorithm Cause 13 [cont.]
ZONE_HO_HYST_ULUL static hysteresis for interzone HO from outer to inner
In case of multi-band cell, should take into account the difference of propagation between GSM and DCS
Added to cause 10 threshold RXLEV_UL_ZONE
ZONE_HO_HYST_DLDL static hysteresis for interzone HO from outer to inner
In case of multi-band cell, should take into account the difference of propagation between GSM and DCS and the difference of BTS transmission power in the two bands
Added to cause 11 threshold RXLEV_DL_ZONE
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7 Handover Detection for Concentric Cells
Handover Algorithm Cause 13 [cont.]
PING_PONG_MARGIN(0,call_ref)Penalty PING_PONG_HCP put on cause 13 if
The immediately preceding zone in which the call has been is the inner zone of the serving cellAnd The last handover was not external intracellAnd T_HCP is still running
PING_PONG_MARGIN(0,call_ref) = 0If the call was not previouslyin serving’s inner zoneOr T_HCP has expired
Concentric cell
I n n e r z o n e
Outer zone
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7 Handover Detection for Concentric Cells
Handover Algorithm Cause 13 [cont.]
neighbour_RXLEV(0,n)
Concentric cells are designed to create an INNER zone
protected from external interferersand creating no interferences on other cells… to be able to face more aggressive frequency reuse in INNER zone TRXs
neighbour_RXLEV(0,n) tuning enables to avoid handovers if the MS position will lead to interferencesthe condition is checked towards all neighbor cells belonging to the same layer and band as the serving cell
Concentric cellOuter zone
?
Inner zoneinterferer 1
Inner zoneinterferer 2Inner zone
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EVOLIUM Base Station Subsystem · Introduction to Radio Fine Tuning B10Radio Fine Tuning · Annexes1 · 6 · 82
7 Handover Detection for Concentric Cells
Handover Algorithm Cause 13 [cont.]
EN_CAUSE_13Load balance between inner and outer zones may be allowed by setting EN_LOAD_BALANCE = ENABLE
If EN_LOAD_BALANCE = ENABLEIf INNER zone is less loaded than OUTER,EN_CAUSE_13 = ENABLEIf INNER zone is more loaded than OUTER,EN_CAUSE_13 = DISABLE
If EN_LOAD_BALANCE = DISABLEEN_CAUSE_13 = ENABLE
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7 Handover Detection for Concentric Cells
Outgoing Intercell Handovers from Concentric Cell
Outgoing intercell handovers from concentric cellsAs explained here before, the MS located in a concentric cell can make intercell, emergency or better condition HO regardless their current zone
For example, an MS locatedin the INNER zone of aconcentric cell can makedirectly an HO cause 12towards another cell,WITHOUT having totrigger any cause 10 or 11to the OUTER zone before.
Concentric cellOuter zone
Inner zone
Concentric cellOuter zone
Inner zone
Concentric cellOuter zone
Inner zone
The only restrictions are linked to EN_MULTI-BAND_PBGT_HO and EN_BI-BAND_MS parameters.
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7 Handover Detection for Concentric Cells
Incoming Intercell Handovers from Concentric Cell
Incoming intercell handovers towards a concentric cellIn case an MS makes an incoming handover towards a concentric cell (due to outer PBGT measurements,etc.), a TCH may be allocated
either in the INNER or in the OUTER zone, as for call setupdepending on radio conditions
In case of a multi-band cell, if the MS is not multi-band, it will always be sent to the OUTER zone
Concentric cellOuter zone
Inner zone
Cell
??
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7 Handover Detection for Concentric Cells
Incoming Intercell Handovers from Concentric Cell [cont.]
Use part of Handover cause 13 algorithm on each potential targetIF Cell(n) is external
The MS is directed to the OUTER zone of (n)ELSE (cell(n) is internal)
IFAV_RXLEV_NCELL(n) > RXLEV_DL_ZONE + ZONE_HO_HYST_DL +
+ (BS_TXPWR - BS_TXPWR_MAX_INNER)and EN_BETTER_ZONE_HO = ENABLE
The MS is directed towards the INNER zoneELSE
The MS is directed towards the OUTER zone
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Self-assessment on the Objectives
Please be reminded to fill in the formSelf-Assessment on the Objectivesfor this moduleThe form can be found in the first partof this course documentation
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