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All rights reserved 2005, Alcatel
Multilayer GSM Network Radio Optimization / B9
EVOLIUM Base StationSubsystem
Multilayer GSM Network Radio
Optimization / B9
TRAINING MANUAL
3FL12033ABAAWBZZAEdition 02 - May 2006
Copyright 2005 by Alcatel - All rights reservedPassing on and copying of this document, use and communication of its
contents not permitted without written authorization from Alcatel
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Legal Notice
Switch to notes view!Safety WarningBoth lethal and dangerous voltages are present within the equipment. Do not wear conductive jewelry while
working on the equipment. Always observe all safety precautions and do not work on the equipment alone.
Caution
The equipment used during this course is electrostatic sensitive. Please observe correct anti-static precautions.
Trade Marks
Alcatel and MainStreet are trademarks of Alcatel.
All other trademarks, service marks and logos (Marks) are the property of their respective holders includingAlcatel. Users are not permitted to use these Marks without the prior consent of Alcatel or such third partyowning the Mark. The absence of a Mark identifier is not a representation that a particular product or servicename is not a Mark.
Copyright
This document contains information that is proprietary to Alcatel and may be used for training purposesonly. No other use or transmission of all or any part of this document is permitted without Alcatels writtenpermission, and must include all copyright and other proprietary notices. No other use or transmission of allor any part of its contents may be used, copied, disclosed or conveyed to any party in any mannerwhatsoever without prior written permission from Alcatel.
Use or transmission of all or any part of this document in violation of any applicable Canadian or otherlegislation is hereby expressly prohibited.
User obtains no rights in the information or in any product, process, technology or trademark which itincludes or describes, and is expressly prohibited from modifying the information or creating derivative works
without the express written consent of Alcatel.
Alcatel, The Alcatel logo, MainStreet and Newbridge are registered trademarks of Alcatel.
All other trademarks are the property of their respective owners. Alcatel assumes no responsibility for theaccuracy of the information presented, which is subject to change without notice.
2005 Alcatel. All rights reserved.
Disclaimer
In no event will Alcatel 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 has been advised of the possibility of such damages.
Mention of non-Alcatel products or services is for information purposes only and constitutes neither anendorsement nor a recommendation.
Please refer to technical practices supplied by Alcatel for current information concerning Alcatel equipmentand its operation.
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Product Line EVOLIUMBase Station Subsystem
Course Title Multilayer GSM Network Radio Optimization / B8
Course Reference 3FL 12033 ABAA - AUE
Audience
Radio Network Engineers (operator or Alcatel staff) in
charge of optimizing a hierarchical network.
Objectives
During the course, the trainee will be able todescribe the specific radio algorithms in multi-layer networks in order to enhance the offeredQoS.
By the end of the course, the participant will beable to:
- Describe the concepts and strategy of hierarchicalnetworks.
- Describe the specific type of cells implemented in
hierarchical networks.- Describe the specific radio algorithms used in the
Alcatel BSS in a hierarchical network.
- Propose default parameter values for the cells of ahierarchical network using these algorithms.
- Propose a list of specific indicators to monitor QoSand traffic in a hierarchical network.
Note: Radio Network Planning issues like micro sitedetection, site planning, frequency planning are notincluded.
Prerequisites
Training module Introduction to GSM QoS and TrafficLoad Monitoring (3FL 10491 ABAAAUE) andIntroduction to Radio Fine Tuning (3FL 10493
ABAAAUE) or equivalent level.
Training Methods
Theory / Practice.
Language
English, French
Duration
3 Days
Location
Alcatel University or Customer Premises.
Number of participants
Maximum 8
Course content
1 Multi-layer Network Architecture
1.1 Concepts and strategies 1.2 Cellular network architecture
1.3 Choosing a relevantarchitecture
1.4 Requirements
2 Algorithms and AssociatedParameters
2.1 Introduction
2.2 Idle mode selection andreselection
2.3 Call setup
2.4 Handover strategies 2.5 Main standard handover
algorithms
2.6 HO algorithms for multi-layernetworks
2.7 Candidate cells evaluation
3 Creating a Multi-layer Network
3.1 Adding a micro cellular layer inan existing network for traffic andcoverage increase
3.2 Adding hot spot microcells fortraffic
3.3 Adding indoor microcells forcoverage
3.4 Monitoring QoS in a multi-layernetwork
4 Case studies
4.1 Radar cell
4.2 Symmetric microcells at streetcorner
4.3 Asymmetric microcells at streetcorner
4.4 Indoor microcell within a
monolayer network 4.5 Trilayer network: indoor cell
within a multi-layer network
4.6 Indoor cell congestion
4.7 Transforming a microcell intoan indoor cell
4.8 Picocells in skyscrapers
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Table of Contents [cont.]
Switch to notes view!
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1 MULTI-LAYER NETWORK ARCHITECTURE
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1 MULTI-LAYER NETWORK ARCHITECTURE
Session presentation
Objective: to be able to define relevant architectures formulti-layer networks design
Program:
1.1 Concepts and strategies
1.2 Cellular network architecture
1.3 Choosing a relevant architecture
1.4 Requirements
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1 MULTI-LAYER NETWORK ARCHITECTURE
1.1 Concepts and strategies
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Multi-layer network: a powerful solution for: Network capacity enhancement
extra capacity provided by new cells / new TRXs specific radio algorithms send MSs to these new cells
Coverage increase
when introducing microcells (better indoor penetration, even for outdoormicrocells)
While keeping a good QoS
confined coverage for microcells, with less interference
less congestion
1.1 Concepts and strategies
Introduction to multi-layer networks
Since B7:
new HW capabilities with Cell split support
enhancement of QoS monitoring capabilities with counters split per TRX
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Alcatel is providing multi-layer solutions Since R3.1: mini & microcells
Improvements in B3.1 (smart speed discrimination) Improvements in B6.2 (external Directed Retry)
Improvements in B7 (indoor layer introduction)
1.1 Concepts and strategies
Support of multi-layer features
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Multi-layer networks can be introduced as continuous layer orhotspots, for:
Capacity increase Coverage increase
Indoor solution
All types of mobiles can use both layers
1.1 Concepts and strategies
Network strategy
If the speed discrimination process is activated then Phase 2 MSs will be sent more or less quickly according
to the load of the umbrella cell.
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1 MULTI-LAYER NETWORK ARCHITECTURE
1.2 Cellular network architecture
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Conventional Single cell
Concentric cell Extended cell
Multi-band cell
Hierarchical: introducing Upper and Lower cell layers Indoor cell
Micro cell
Mini cell
Umbrella cell
1.2 Cellular network architecture
Cell environment
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One unique combination of the five parameters
CELL_DIMENSION_TYPE: macro, micro
CELL _LAYER_ TYPE : single, upper, lower, indoor
CELL _PARTITION_ TYPE : normal, concentric
CELL _RANGE: normal, extended inner, extended outer
FREQUENCY_RANGE : PGSM(GSM900); DCS1800; EGSM;
DCS1900; PGSM-DCS1800; EGSM-DCS1800 and GSM 850 based on BCCH frequency
1.2 Cellular network architecture
Cell profile
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1.2 Cellular network architecture
Mono-band Cell profiles
DCS1800 or DCS1900DCSNormalNormalIndoorMicroDCS indoor micro cell
PGSM or EGSMGSMNormalNormalIndoorMicroGSM indoor micro cell
DCS1800 or DCS1900DCSNormalConcentricUpperMacroDCS concentric umbrella
PGSM or EGSMGSMNormalConcentricUpperMacroGSM concentric umbrella
DCS1800 or DCS1900DCSNormalConcentricSingleMacroDCS concentric cell
PGSM or EGSMGSMNormalConcentricSingleMacroGSM concentric cell
DCS1800 or DCS1900DCSExtended-outerNormalSingleMacroDCS extended outer cell
PGSM or EGSMGSMExtended-outerNormalSingleMacroGSM extended outer cell
DCS1800 or DCS1900DCSExtended-innerNormalSingleMacroDCS extended inner cell
PGSM or EGSMGSMExtended-innerNormalSingleMacroGSM extended inner cell
DCS1800 or DCS1900DCSNormalNormalUpperMacroDCS umbrella cell
PGSM or EGSMGSMNormalNormalUpperMacroGSM umbrella cell
DCS1800 or DCS1900DCSNormalNormalLowerMacroDCS mini cell
PGSM or EGSMGSMNormalNormalLowerMacroGSM mini cell
DCS1800 or DCS1900DCSNormalNormalLowerMicroDCS micro cell
PGSM or EGSMGSMNormalNormalLowerMicroGSM micro cell
DCS1800 or DCS1900DCSNormalNormalSingleMacroDCS single cell
PGSM or EGSMGSMNormalNormalSingleMacroGSM single cell
Frequency rangeCell band
type
Cell
range
Cell partition
type
Cell layer
type
Cell dimension
type
Parameters
Cell Profile
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1.2 Cellular network architecture
Multi-band Cell profiles
PGSM-DCS1800 orEGSM-DCS1800
DCSNormalConcentricIndoorMicroDCS multiband indoor micro cell
PGSM-DCS1800 orEGSM-DCS1800
GSMNormalConcentricIndoorMicroGSM multiband indoor micro cell
PGSM-DCS1800 orEGSM-DCS1800
DCSNormalConcentricUpperMacroDCS multiband umbrella cell
PGSM-DCS1800 orEGSM-DCS1800
GSMNormalConcentricUpperMacroGSM multiband umbrella cell
PGSM-DCS1800 orEGSM-DCS1800
DCSNormalConcentricLowerMacroDCS multiband mini cell
PGSM-DCS1800 orEGSM-DCS1800
GSMNormalConcentricLowerMacroGSM multiband mini cell
PGSM-DCS1800 orEGSM-DCS1800
DCSNormalConcentricLowerMicroDCS multiband micro cell
PGSM-DCS1800 orEGSM-DCS1800
GSMNormalConcentricLowerMicroGSM multiband micro cell
PGSM-DCS1800 orEGSM-DCS1800
DCSNormalConcentricSingleMacroDCS multiband single cell
PGSM-DCS1800 orEGSM-DCS1800GSMNormalConcentricSingleMacroGSM multiband single cell
Frequency rangeCell band
typeCell
rangeCell partition
typeCell layer
typeCell dimension
type
Parameters
Cell Profile
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1.2 Cellular network architecture
Cell profiles: example
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1 MULTI-LAYER NETWORK ARCHITECTURE
1.3 Choosing a relevant architecture
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Multi-layer concept: 3 available layer types
All these cells can be or not operating in the same band and defined asconcentric cells
1.3 Choosing a relevant architecture
Concept
mini
umbrella
micro
indoor
micro micro
umbrella
micro
indoor
single
mini
umbrellaUPPER
SINGLE
LOWER
INDOOR
3 layers are defined in the system, but more layers can be created by parameter tuning. For example,
skyscrapers specific configuration is made up of several consecutive layers designed with cells of the samesystem layer.
Indoor layer has been introduced in B7.
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Microcells configuration will depend on their position in the lower layer
Microcell classes are introduced to deal with typical parameters settings
in each of these cases
1.3 Choosing a relevant architecture
Microcell classes
Indoor Microcell
Border Microcell
Inner MicrocellHotspot Microcell
Defining microcell classes is a very efficient way to set network parameters. It avoids defining a specific
configuration for each cell.
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1 MULTI-LAYER NETWORK ARCHITECTURE
1.4 Requirements
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A multi-layer architecture can be built over all types of Hardware
Since R3.1
Microcell feature is NOT reserved to micro BTS!
Improvement in B6.2 with external Directed Retry
From R3.1 to B4.1, since Directed Retry was only Internal:
microcells had to be introduced within umbrella BSC
OR microcells were barred (traffic allocation was done by handover fromumbrella cells)
Since B6.2, External Directed Retry is available
Microcells and Umbrella cells can belong to different BSCs
1.4 Requirements
Software & Hardware requirements
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2 ALGORITHMS AND ASSOCIATEDPARAMETERS
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2 ALGORITHMS AND ASSOCIATED PARAMETERS
Session presentation
Objective: to be able to describe algorithms dedicated tomulti-layer networks management
Program:
2.1 Introduction
2.2 Idle mode selection and reselection
2.3 Call setup
2.4 Handover strategies
2.5 Main standard handover algorithms
2.6 Handover algorithms for multi-layer networks
2.7 Candidate cell evaluation
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2 ALGORITHMS AND ASSOCIATEDPARAMETERS
2.1 Introduction
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With the introduction of new feature and algorithms:
Multi-layer
Designing, managing and monitoring complex networks is more difficult,
as all these features will interact
An in-depth knowledge of all available algorithms is necessary to understand
all possibilities and difficulties. A relevant choice of architecture and parameters
settings will precede the introduction of a new layer in the existing network
2.1 Introduction
Justification
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In all this document
System parameters (can be set at the OMC-R level) will always be written inBLUE BOLD FONT
Variables (averages, internal system variables, etc.) will be typed in NORMAL
FONT
Light blue font highlights important points
2.1 Introduction
Typing conventions
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2 ALGORITHMS AND ASSOCIATEDPARAMETERS
2.2 Idle mode selection and reselection
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Adding a new layer is a powerful way of increasing network capacity ifthe MS can be sent to the preferred cell
In dedicated mode: see next sections
But also in idle mode, so that the call is established directly in the preferredcell
Really increase capacity
Maintain high QoS level, without creating extra HO
2.2 Idle mode selection and reselection
Strategy
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At startup (IMSI Attach), the MS is selecting cell with
Defined priorities with CELL_BAR_QUALIFY
Best C1 amongst highest priority cells (using CBQ)
Once camped on one cell (in idle mode)
The MS can decide to reselect another one if:
C1 criterion is too low
The MS cannot decode downlink messages
The current cell is becoming forbidden (e.g. barred)
The MS cannot access the cell
there is a better cell, regarding C2 criterion
2.2 Idle mode selection and reselection
Selection and reselection principles
Note:
Cell selection (first selection) is performed using C1 criterion only (the chosen cell is the one with the best C1)
Reselection is done using the mechanisms referenced above.
e.g., the MS cannot access the cell.
It can be linked to SDCCH congestion, filtering of CHARQD due to TA greater than RACH_TA_FILTER, radioaccess problem during the Radio Link Establishment phase.
If SDCCH is to be seized for LU purpose, the MS will reselect on another cell.
If SDCCH is seized for something else (e.g., MOC), the MS may reselect (this is up to the MSvendor choice!!!). Some MSs do nothing. Call will never be possible. Some others do reselect. In thatcase, the user has to reattempt his call (after the reselection, but before the MS is back to the original
cell due to better C2, etc. (done after 5 s, etc.)).
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Cell selection, use of CELL_BAR_QUALIFY:
set on a per cell basis broadcast on the BCCH
2 possible values:
0 = normal priority (default value)
1 = lower priority
The MS selects the suitable (C1 > 0) cell with the highest C1 belonging to thelist of highest priority
2.2 Idle mode selection and reselection
Cell Selection with CBQ (1/3)
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Example: highest priority set on microcell
The MS will select the microcell (if available, C1>0), whatever the level of themacrocell
2.2 Idle mode selection and reselection
Cell Selection with CBQ (2/3)
2525microcellCELL_BAR_QUALIFY = 0
2020
macrocell
CELL_BAR_QUALIFY = 1
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WARNING: usage of CELL_BAR_QUALIFY:
interacts with CELL_BAR_ACCESSA cell with low priority (CELL_BAR_QUALIFY= 1) cannot be barred
Some MSs will be able to access it, whatever the value of CELL_BAR_ACCESS
2.2 Idle mode selection and reselection
Cell Selection with CBQ (3/3)
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C1
ensures that, if a call was attempted, it would be done with a sufficient
downlink and uplink received level
based on 2 parameters, broadcast on the BCCH
RXLEV_ACCESS_MIN [dBm]
- Minimum level to access the cell- Default value (for Evolium): -103 dBm
MS_TXPWR_MAX_CCH [dBm]
- Maximum level for MS emitting- Default value: 33 dBm
2.2 Idle mode selection and reselection
C1 criterion (1/2)
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C1
evaluated every 5 s (minimum)
C1 = A - MAX(0,B) > 0
A = RxLev -RXLEV_ACCESS_MIN
assess that the MS received level is sufficient
B = MS_TXPWR_MAX_CCH - P
P maximum power of MS
assess that the BTS received level will be sufficient
if MS_TXPWR_MAX_CCH < P
2.2 Idle mode selection and reselection
C1 criteria (2/2)
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C2 IfCELL_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) = 0
- used to avoid locating on transient cell
- CELL_RESELECT_OFFSET used to favor a 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 comparison with C2 C2neighboring > C2current if cells belong to the same LA
C2neighboring > C2current+CELL_RESELECT_HYSTERESIS if cells fromdifferent LA
2.2 Idle mode selection and reselection
C2 criterion
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 neighboringcells. To penalize a cell compared to one neighboring cell, one should better boost the neighboring cell(using first formula).
The first formula is very useful to favor an indoor cell or a microcell.
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CELL_RESELECT_PARAM_IND C2 parameters are broadcast if = 1 (default)
otherwise C2 = C1
PENALTY_TIME 0 to 31, =20s + 20s step, default value = 0
From 0=20s to 30=620 s, plus 31: infinite penalty
CELL_RESELECT_OFFSET 0 to 63, 2 dB step, default value = 0
From 0 dB to 126 dB
TEMPORARY_OFFSET 0 to 7, 10 dB step, default value = 0
From 0 dB to 60 dB, plus 7: infinite dB
2.2 Idle mode selection and reselection
C2 parameters
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2.2 Idle mode selection and reselection
Application
MINIMINI
MINI 900
CELL_RESELECT_OFFSET = 20
dBTEMPORARY_OFFSET = 0 dB
PENALTY_TIME = 0 (20 s)UMBUMB
UMBRELLA 900
CELL_RESELECT_OFFSET = 0 dB
TEMPORARY_OFFSET = 0 dB
PENALTY_TIME = 0 (20 s)
C2(MINI) = C1(MINI) + 20
C2(900) = C1(900)
=> the reselection of the mini cell is favored
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2 ALGORITHMS AND ASSOCIATEDPARAMETERS
2.3 Call setup
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Call setup is to be made on the cell selected in idle mode
Priorities have been defined with idle mode parameters
MSs are sent to the preferred cell
Lower layers
What is the risk??
2.3 Call setup
Principles
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The risk is to have congestion in the preferred cell!
Old cells (old layer capacity) are unloaded
as all MSs are sent to new cells
This phenomenon is amplified by handovers behavior
Dual layer algorithms are based on CAPTURE mechanisms
Send the MS in the preferred cell as soon as it is OK
Without comparing serving and preferred cells
to reach the maximum capacity increase
See handover parts for details
2.3 Call setup
Congestion in the preferred cell
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2.3 Call setup
Algorithms principles (1/3)
new
capacity
Trafficincrease
old
capacity
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2.3 Call setup
Algorithms principles (2/3)
new
capacity
Water Valve with filter:
Dual layer algorithms
Trafficincrease
old
capacity
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2.3 Call setup
Algorithms principles (3/3)
new
capacity
Water Pump:Forced
Directed Retry
Trafficincrease
old
capacity
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A Directed Retry:
Is an SDCCH to TCH intercell handover
Is triggered during a call setup procedure
If the serving cell is completely congested, the MS is allocated an SDCCH
If no TCH is available, the MS is queued
Under certain conditions, the MS obtains a TCH in another cell
SDCCH-TCH handover on:
better condition or emergency causes = Directed Retry
cause 20 = Forced Directed Retry
Internal and External Directed Retries are possible (since B6.2)
2.3 Call setup
Directed Retry principles
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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 and13 (concentric cells) and causes 15 and 16 (intracell HO))
candidate cell evaluation process: same as for TCH HO
2.3 Call setup
Directed Retry
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CAUSE 20: Forced Directed Retry
AV_RXLEV_NCELL_DR(n) > L_RXLEV_NCELL_DR(n)
AndEN_FORCED_DR = ENABLED
EN_FORCED_DR value is only relevant if EN_DR = true
AV_RXLEV_NCELL_DR(n) is calculated with theA_PBGT_DR window
if less than A_PBGT_DR samples are available, the average value iscalculated with the available samples and the averaging window is filled inwith -110 dBm
2.3 Call setup
Forced Directed Retry: cause 20
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Pre-ranking using PREF_LAYER, PRIORITY(0,n), frequency band
Filtering process AV_RXLEV_NCELL_DR(n) > RXLEVmin(n) + max(0,MS_TXPWR_MAX(n) - P)
Number of free TCHs t(n) > FREElevel_DR(n)
The remaining cells are sorted according to their PBGT_DR(n)(averaging windowA_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)
2.3 Call setup
FDR: Candidate cell evaluation
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L_RXLEV_NCELL_DR(n): level required in the neighboring cell n
The parameter considered is the one set in the neighboring cell
The default value depends on the network architecture
See the next slide
Freelevel_DR(n): number of free TCH channels required in theneighboring cell n
The parameter considered is the one set in the neighboring cell
Default value = 0 to 4 TCHs (linked to the nb of TRXs)
A_PBGT_DR: average window
Default value = 4 SACCHs
2.3 Call setup
FDR: parameters
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Thanks to idle mode parameters, Access to one preferred cell
Micro / Indoor layer: layer with very good QoS
For a better capacity increase and to avoid QoS degradation that may beinduced by an increase in HO attempts
Prevention of congestion in the preferred cell Forced Directed Retry to the old cells
Prevention of congestion in the old cells MSs are sent in idle mode to the preferred cell HO strategy favoring the preferred cell in dedicated mode
2.3 Call setup
Access strategy
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2.3 Call Setup
Exercise
Timeallowed:
10 minutes
A dual layer network is considered
Umbrella cells 900
Micro cells 900
Set FDR parameters to avoid interference and allow apowerful TCH resource usage
Umbrella cells
microcells
FDRcapture
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2 ALGORITHMS AND ASSOCIATEDPARAMETERS
2.4 Handover strategies
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Maximizing capacity
Intelligent MS sharing between available resources
Avoid congestion of historical band (for old MS)
Consider traffic conditions of all layers
Consider MS speed for layer discrimination
Keep mobiles in the same layer as long as possible
2.4 Handover strategies
Objectives (1/2)
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Assuring good quality communications and avoiding call drops
Send MS towards the layer that will provide the best QoS
Minimize the number of HO between cells for good speech Quality
Fast moving mobiles are handled by the macrocell layer
Identify a best target for emergency handovers cases
The tuning of the parameters will result in trade-offs
2.4 Handover strategies
Objectives (2/2)
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2.4 Handover strategies
Functional Entities
Radio
Link
Measurements
Active
Channel
Pre-processing
Assignment of HO functions in the ALCATEL BSSAssignment of HO functions in the ALCATEL BSSAssignment of HO functions in the ALCATEL BSSAssignment of HO functions in the ALCATEL BSS
BTS BSC
HO Detection HO Candidate
Cell Evaluation
HO
management
MSC
HO
protocol
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HO causes for standard networks
cause 2 : too low quality on the uplink
cause 3 : too low level on the uplink cause 4 : too low quality on the downlink
cause 5 : too low level on the downlink
cause 6 : too large distance between the MS and the BTS
cause 15 : high interference on the uplink (intra-cell HO)
cause 16 : high interference on the downlink (intra-cell HO)
cause 26 : AMR channel adaptation HO (HR to FR)
cause 12 : power budget evaluation
cause 23 : traffic
cause 27 : AMR channel adaptation HO (FR to HR) cause 28 : Fast traffic HO
cause 29 : TFO HO
cause 20 : FDR
2.4 Handover strategies
Handover causes (1/2)
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HO causes for multi-layer networks
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 highthreshold
cause 14 : high level in the neighboring cell of a lower or indoor layer forslow mobile
cause 24 : general capture
2.4 Handover strategies
Handover causes (2/2)
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cause 7 : consecutive bad SACCH frames received in a microcell cause 17 : too low level on the uplink in a cell compared to a high threshold cause 18 : too low level on the downlink in a cell compared to a high threshold
cause 2 : too low quality on the uplink cause 3 : too low level on the uplink cause 4 : too low quality on the downlink cause 5 : too low level on the downlink cause 6 : too large distance between the MS and the BTS cause 10 : too low level on the uplink in the inner zone cause 11 : too low level on the downlink the in inner zone cause 26 : AMR channel adaptation HO (HR to FR) cause 15 : high interference on the uplink (intra-cell HO) cause 16 : high interference on the downlink (intra-cell HO) cause 21 : high level in the neighboring cell in the preferred band
cause 14 : high level in neighboring cell of a lower or an indoor layer cell for slowmobile
cause 24 : general capturecause 12 : power budget evaluationcause 23 : traffic
cause 13 : too high level on the uplink and downlink in the outer zone cause 27 : AMR channel adaptation HO (FR to HR) cause 20 : Forced Directed Retry DR cause 28 : Fast traffic HO
2.4 Handover strategies
Handover causes priority
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2 ALGORITHMS AND ASSOCIATEDPARAMETERS
2.5 Main standard handover algorithms
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Emergency intercell handovers
cause 2 : too low quality on the uplink
cause 3 : too low level on the uplink
cause 4 : too low quality on the downlink
cause 5 : too low level on the downlink
cause 6 : too large distance between the MS and the BTS
May be triggered
From any cell type / band / layer / zone
Towards any cell except the serving one
2.5 Main standard handover algorithms
Emergency Intercell Handovers
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CAUSE 2: too low quality on the uplink
AV_RXQUAL_UL_HO >L_RXQUAL_UL_H + OFFSET_RXQUAL_FH
and AV_RXLEV_UL_HO
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CAUSE 3: too low level on the uplink
AV_RXQUAL_UL_HO
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2.5 Main standard handover algorithms
Handover Cause 4: DL Quality
CAUSE 4: too low quality on the downlink
AV_RXQUAL_DL_HO > L_RXQUAL_DL_H + OFFSET_RXQUAL_FH
and AV_RXLEV_DL_HO
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2.5 Main standard handover algorithms
Handover Cause 5: DL Level
QUAL
LEV
CAUSE 5: too low level on the downlink
AV_RXQUAL_UL_HO
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2.5 Main standard handover algorithms
Handover Cause 6: Distance
CAUSE 6 : Too long distance
AV_RANGE_HO >U_TIME_ADVANCE
and EN_DIST_HO = ENABLED
Size of window for distance average:A_RANGE_HO
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. These spurious coverages is the probable production of ahigh level of co-channel interference.
This cause is different from the others as it is more preventive. It does not make use of the propagationconditions 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 provideexceptional quality and level although the serving BTS is far and another is closer and should be the one themobile 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 nothave happened if the mobile had been connected to the closest cell. For these reasons also, this cause doesnot wait for the power control to react.
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Emergency intracell handovers
cause 15 : high interference on the uplink (intra-cell HO)
cause 16 : high interference on the downlink (intra-cell HO)
May be triggered
From any cell type / band / layer / zone
Towards the same cell
2.5 Main standard handover algorithms
Emergency Intracell Handovers
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CAUSE 15: High interference on the uplink
Intra-cell HO
AV_RXQUAL_UL_HO > THR_RXQUAL_CAUSE_15 +OFFSET_RXQUAL_FH
and AV_RXLEV_UL_HO >RXLEV_UL_IH
and EN_CAUSE_15 = ENABLED
and [ no previous intracell handover for this connectionfailed
or EN_INTRACELL_REPEATED = ENABLED ]
Size of window for averaging quality:A_QUAL_HO
Size of window for averaging level:A_LEV_HO
2.5 Main standard handover algorithms
Handover Cause 15: UL Interference
THR_RXQUAL_CAUSE_15 and EN_CAUSE_15 are not parameters but variables defined just after.
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CAUSE 16: High interference on the downlink
Intra-cell HO
AV_RXQUAL_DL_HO > THR_RXQUAL_CAUSE_16 +OFFSET_RXQUAL_FH
and AV_RXLEV_DL_HO >RXLEV_DL_IH
and EN_CAUSE_16 = ENABLED
and [ no previous intracell handover for this connectionfailed
or EN_INTRACELL_REPEATED = ENABLED ]
Size of window for averaging quality:A_QUAL_HO
Size of window for averaging level:A_LEV_HO
2.5 Main standard handover algorithms
Handover Cause 16: DL Interference
THR_RXQUAL_CAUSE_16 and EN_CAUSE_16 are not parameters but variables defined after.
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2.5 Main standard handover algorithms
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
HOP
THR_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_XXfor a non-AMR call
EN_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 = DISABLED, when a HO CAUSE 15 (or 16) fails, it can bemodified as UPLINK (or DOWLINK) QUALITY, HO CAUSE 2 (respectively HO CAUSE 4).
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CAUSE 12: Power budget
Normal handover type, no matter of emergency
Checked between
Cells of the same layer only
Specific case of Fast MSs: after detection of cause 12 in the lower or indoor layer,they can execute cause 12 HO towards the upper layer
Cells may be of different cell_band_type, depending on parameterEN_MULTIBAND_PBGT_HO
if EN_MULTIBAND_PBGT_HO = DISABLED and if the MS is located in the innerzone of a multi-band cell, it can only go to another multi-band cell
2.5 Main standard handover algorithms
Handover Cause 12: Power Budget (1/5)
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CAUSE 12:
Based on 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)
Size of window for level averaging:A_PBGT_HO
2.5 Main standard handover algorithms
Handover Cause 12: Power Budget (2/5)
The value of PBGT(n) is calculated every SACCH period for each neighboring cell n whose measures are kept
in the book-keeping list
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CAUSE 12: Power budget
if EN_TRAFFIC_HO(0,n)=ENABLED
then PBGT(n) >HO_MARGIN(0,n) +OFFSET_HO_MARGIN_INNER
+ max(0, DELTA_HO_MARGIN(0,n))
else PBGT(n) >HO _MARGIN(0,n) + OFFSET_HO_MARGIN_INNER
and AV_RXLEV_PBGT_HO RXLEV_LIMIT_PBGT_HO
and EN_PBGT_HO = ENABLED
Size of window for level averaging:A_PBGT_HO
2.5 Main standard handover algorithms
Handover Cause 12: Power Budget (3/5)
Cause 12 HO is correlated with cause 23 HO. This is why there are two equations according to the
activation of cause 23 HO (EN_TRAFFIC_HO).
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CAUSE 12: Power budget
DELTA_HO_MARGIN(0,n): evaluated according to the traffic situation of theserving cell and the neighboring 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
ElseDELTA_HO_MARGIN(0,n) = 0
Philosophy
This mechanism aims at penalizing cause 12 detection when the traffic in theserving cell is low and is high in the cell n.
2.5 Main standard handover algorithms
Handover Cause 12: Power Budget (4/5)
HIGH LOW
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CAUSE 12: Power budget Traffic_load() is managed for every cell of a BSC
Traffic_load() can have three values: HIGH: cell is loaded
LOW: cell is unloaded
INDEFINITE: cell load is neither loaded nor unloaded, or unknown
The traffic_load() value is modified according to the long term traffic evaluationalgorithm using the following parameters:
A_TRAFFIC_LOAD, N_TRAFFIC_LOAD, HIGH_TRAFFIC_LOAD,IND_TRAFFIC_LOAD, LOW_TRAFFIC_LOAD: can be modified per cell
TCH_INFO_PERIOD: cannot be modified (5 s)
2.5 Main standard handover algorithms
Handover Cause 12: Power Budget (5/5)
Annex 1
TCH_INFO_PERIOD = 5 s period used by the BSC to count the number of free TCH.
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HO_MARGIN(0,n)
A high value is usually used to avoid ping-pong HO in urban environment
where signal strength varies rapidly due to fading Default value: site dependent (but 10 dB observed for dense urban microcellular
area)
To be optimized: can be reduced to 5dB and even 0 dB when applying an anti ping-pong mechanism
A_PBGT_HO
To find a compromise with HO_MARGIN(0,n)
Default value: 8 SACCHs for urban microcells, 6 for dense urban
2.5 Main standard handover algorithms
Cause 12: tuning of microcells parameters
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HO_MARGIN(0,n) optimization
Not triggering too many HOs
(ping-pong)
Not triggering HO to a bad target cell (for example, theperpendicular cell at a crossroads)
Not favoring emergency HO (towards theumbrella cell) with respect to power budget HObetween 2 micro cells (for example when turning
at a street corner)
2.5 Main standard handover algorithms
Cause 12: tuning of microcells parameters
Micro 1Micro 2
Micro 3
PBGT HO between micro cells 1,2
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Speed discrimination process in micro cells:
speed estimation based on the connection time in the cell
speed is estimated from the last handover from another microcell
if this connect time is below MIN_CONNECT_TIME, MS_SPEED is set to FAST.Consequently the MS will be sent to an unloaded umbrella cell.
C_DWELL is a counter measuring the number of SACCH periods of monitoringserving micro cell
if the call has been established after an intra-BSC handover from another micro cellthen C_DWELL is compared to the threshold 2*MIN_CONNECT_TIME in order todetermine MS speed
if C_DWELL < 2*MIN_CONNECT_TIME then MS_SPEED is set to FAST
MIN_CONNECT_TIME is not modified according to the load of the micro orumbrella cells
2.5 Main standard handover algorithms
Cause 12: speed discrimination in microcells (2/2)
Initialization of C_DWELL in serving micro cells
after call setup or incoming inter-cell handover
C_DWELL = 0
after intra-cell handover
C_DWELL is unchanged
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2.5 Main standard handover algorithms
Handover Cause 23: Traffic (1/2)
CAUSE 23: Traffic Handover
The aim of this cause is to speed HO detection when
The serving cell is loaded
The target cell is unloaded
When traffic distribution is taken into account for handover detection, this
cause reacts in the opposite way of cause 12, to maintain an equivalent
ping-pong static hysteresis
Checked between
Cells of the same layer only
If EN_MULTIBAND_PBGT_HO = disabled
Cells of the same cell_band_type only if the MS is located in the inner zone of a multi-band cell, it can only go to
another multi-band cell
Else any other cells whatever their cell_band_type
HIGH LOW
In some multi-band networks, the radio coverage is ensured by DCS cells in one geographical area and by
GSM cells in another geographical area. As these cells form a multi-band and mono-layer network, thecapture handovers between cells of different bands will be inefficient to regulate the CS traffic load in theserving cell neighboringhood.
The solution consists in allowing intra-layer traffic handovers (Cause 23) based on a power budgetevaluation between cells of different bands.
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2.5 Main standard handover algorithms
Handover Cause 23: Traffic (2/2)
CAUSE 23: Traffic Handover
DELTA_HO_MARGIN(0,n) < 0 dB
and PBGT(n)>HO_MARGIN(0,n)+OFFSET_HO_MARGIN_INNER
+ DELTA_HO_MARGIN(0,n)
and EN_TRAFFIC_HO(0,n) = ENABLED
Size of window for level average: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 willbe triggered earlier.
It is recommended to inhibit Traffic handover towards 1 TRX cells. These cells do not have enough resourcesto receive incoming handovers due to congestion of neighboring cells. Moreover because of the greatvariation 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 checkedbetween 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 isas 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 checkedbetween 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 theneighboring 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 theneighboring 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 theneighboring cells without any cell frequency band restriction.
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2.5 Main standard handover algorithms
Handover Cause 28: Fast Traffic HO (1/3)
CAUSE 28: Fast Traffic Handover Push out of a cell a mobile in dedicated mode to allow a queued request
to be served in the serving cell
May be triggered From any non concentric cell OR concentric outer zone
Towards any cell except the serving one
HO
New call attempt Most appropriate MSto be pushed out
Congested cell
New call attempt
HO
Most appropriate MSto be pushed out
Upper Layer Cell
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2.5 Main standard handover algorithms
Handover Cause 28: Fast Traffic HO (2/3)
CAUSE 28: Fast Traffic Handover
Cause 28 is only checked if the channel of the candidate MS can support thechannel rate (HR or FR) required by the queued request:
HO is triggered when a request is queued at the top of the queue
FR (whatever the TRX type)FR
HR
or
FR on dual rate TRX
HR
Candidate MSQueued Request
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2.5 Main standard handover algorithms
Handover Cause 28: Fast Traffic HO (3/3)
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 = ENABLED
and EN_FAST_TRAFFIC_HO = ENABLED
Size of window for averaging level:A_PBGT_DR
Same thresholds and window as Cause 20 (FDR)EN_CAUSE_28 is an internal HOP process variable, ENABLED when a request
is queued
HO cause 28 process:
If EN_FAST_TRAFFIC_HO = enabled, when an assignment request (or external emergency HOrequest) is queued, the RAM process sends to the HOP process a Fast Traffic HO request whichcontains the queued request reference and its channel rate.
Then, HO cause 28 becomes checkable (EN_CAUSE_28=enabled).
Once an HO alarm for cause 28 is triggered, the flag EN_CAUSE_28 is set to disabled so as not toperform more than one handover. In the same time, the HOP process gets back to the RAM process aFast Traffic HO Acknowledge which contains the queued request reference and the reference of theMS that can perform HO.
If several answers are sent to the RAM process, only the first one corresponding to the queued requestis taken into account.
The RAM process checks if the request is still queued. If it is so, RAM asks HOP to start HO for thismobile; otherwise the process is stopped.
Once the HOP process receives this message, the first two conditions of Cause 28 (good enoughlevel, enough free resources in the target cell) are checked one more time. If the conditions arefulfilled, 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 stillvalid when the cause 28 start HO message is received from the RAM process.
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Is cause 12 triggered?
2.5 Main standard handover algorithms
Exercise (2/2)
9009001800900Band
FastFastSlowIndMS speed
Cause 12 ?
PBGT ?
-80 dBm-65 dBm- 65 dBm-80 dBmRx_Lev(n)
HIGHLOWLOWINDTraffic(n)
MicroUmbrellaUmbrellaSingleType
Target
-90 dBm-90 dBm- 90 dBm-85 dBmRx_Lev(0)
NoYesYesNoEN_SPEED_DISC
900900900900Band
MiniMicroMicroSingleType
Source
Case 4Case 3Case 2Case 1Inputs
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2 ALGORITHMS AND ASSOCIATEDPARAMETERS
2.6 Handover algorithms for multi-layer networks
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An MS is located in a lower or an indoor layer of a hierarchical network
A problem is detected on the radio link between the MS and the BTS, thisproblem is reported with an alarm cause:
Identical to standard networks
cause UL or DL quality (cause 2 and 4)
cause UL or DL Level - Low threshold (cause 3 and 5)
cause Distance (cause 6)
Specific to microcells or indoor cells
cause UL or DL for Microcell - High threshold (cause 17 and 18)
cause consecutive bad SACCH frames (cause 7)
2.6 Handover algorithms for multi-layer networks
Emergency handovers: introduction (1/2)
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An MS is located in a micro or an indoor cell
During an emergency HO, the MS is directed preferably towards an upper or
a single cell
An MS is located in a mini cell
During an emergency HO, the MS is directed preferably towards neighboringmini cells
2.6 Handover algorithms for multi-layer networks
Emergency handovers: introduction (2/2)
in
umbrella
mini
umbrella
mini
single
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Emergency handovers specific to microcells
cause 7 : consecutive bad SACCH frames received in a microcell
cause 17 : too low level on the uplink in a microcell compared to a highthreshold
cause 18 : too low level on the downlink in a microcell compared to a highthreshold
May be triggered
From microcells only (cell_dimension_type = micro)
Outdoor microcell (micro layer)
Indoor microcell (indoor layer)
Towards any cell except the serving one
If the MS is connected to the inner zone of a multi-band cell, the serving cell isa candidate
2.6 Handover algorithms for multi-layer networks
Emergency Handovers specific to microcells
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CAUSE 7: consecutive bad SACCH frames received in a microcell
Last N_BAD_SACCH frames received are not correct
and EN_MCHO_RESCUE = ENABLED
N_BAD_SACCH
Default value: 4 SACCHs
Rule:N_BAD_SACCH >RADIOLINK_TIMEOUT_BS -N_BSTXPWR_M
to be sure that Radio Link Recovery in the microcell will be triggered before trying tomake a handover towards the umbrella
RADIOLINK_TIMEOUT_BS = 18 SACCH
N_BSTPWR_M = 15 SACCH
2.6 Handover algorithms for multi-layer networks
Cause 7: consecutive bad SACCH frames received in a microcell
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CAUSE 17: too low level on the UL in a microcell compared to a highthreshold
AV_RXLEV_UL_MCHO(i) U_RXLEV_UL_MCHO
and EN_MCHO_H_UL = ENABLED
Averaging window:A_LEV_MCHO
2.6 Handover algorithms for multi-layer networks
Cause 17: too low level on the UL in a cell compared to high thr.
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CAUSE 18: too low level on the DL in a microcell compared to a highthreshold
AV_RXLEV_DL_MCHO(i) U_RXLEV_DL_MCHO
and EN_MCHO_H_DL = ENABLED
Averaging window:A_LEV_MCHO
2.6 Handover algorithms for multi-layer networks
Cause 18: too low level on the DL in a cell compared to high thr.
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High threshold (U_RXLEV_XX_MCHO)
the HO is triggered when the signal drops under the threshold
the corresponding HO causes consist in comparing, at 2 successive SACCH periods, the DL
and UL levels in the serving microcell with a high threshold
Beginning a call under the threshold does not trigger an HO
2.6 Handover algorithms for multi-layer networks
Cause 17 & 18: comparison to high threshold (1/4)
ii-1
t
AV_RXLEV_XX_MCHO
High
Threshold
HO alarm
ii-1
t
AV_RXLEV_XX_MCHO
High
Threshold
no HO alarm
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High threshold (U_RXLEV_XX_MCHO)
With high value, mobiles will be sent too early to the macro layer
With low value, mobiles turning at a street corner will be maintained in the
microcell layer during a longer period
In theory, there is risk of call drop
In practice, with appropriate parameters,
-A PBGT HO should be triggered before (speed < 40 km/h)
- Low Threshold for safety
Problems of indoor mobiles with a signal strength level close to the high threshold
that should be kept as long as possible in the micro-layer
2.6 Handover algorithms for multi-layer networks
Cause 17 & 18: comparison to high threshold (2/4)
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U_RXLEV_XX_MCHO compared to L_RXLEV_XX_H
typical gap taken: 2dB
for DL:
L_RXLEV_DL_H = -93 dBm
U_RXLEV_DL_MCHO = -91 dBm
for UL:
L_RXLEV_UL_H = -95 (M2M), -98 (M4M), -102 (Evolium) dBm
U_RXLEV_UL_MCHO = -93 (M2M), -96 (M4M), -100 (Evolium) dBm
2.6 Handover algorithms for multi-layer networks
Cause 17 & 18: comparison to high threshold (3/4)
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A_LEV_MCHO
The averaging window size shouldnt be too small in order to:
avoid triggering too easily an HO on fading and overloading needlessly the macrocell
favor as much as possible between 2 micro cells PBGT HO
Typical value: 10 SACCHs
The high threshold is used to modelize a slow decrease of the signal level at microcellborder
Really urgent handovers will be triggered using the Low Threshold (cause 3 & 5) with ashort averaging window size
A_LEV_HO
Default value: 6 SACCHs for urban micro cells, 4 for dense urban ones
2.6 Handover algorithms for multi-layer networks
Cause 17 & 18: comparison to high threshold (4/4)
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CAUSE 14: high level in a neighboring cell of a lower or an indoor layer for slowmobiles
in order to keep dual band MSs in the preferred band, cause 14 is not checked in thefollowing cases, when EN_BI-BAND_MS(n) = DISABLED
The same scheme can be drawn between lower and indoor layers
2.6 Handover algorithms for multi-layer networks
Cause 14: high level in a lower or an indoor layer for slow MSs (2/4)
CELL_BAND_TYPE = Preferred_band
CELL_LAYER_TYPE =
upper
CELL_LAYER_TYPE =
lower or indoor
EN_BI-BAND_MS = DISABLED
CELL_BAND_TYPE = CELL_BAND_TYPE(0)
EN_BI-BAND_MS = DISABLED
CELL_BAND_TYPE Preferred_band
CELL_BAND_TYPE = Preferred_bandCELL_BAND_TYPE Preferred_band
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CAUSE 14: high level in a neighboring cell of a lower or an indoor layer forslow mobiles
If cell_layer_type (0) = upper
AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n)
and MS_SPEED = SLOW
and EN_MCHO_NCELL = ENABLED
Averaging window:A_PBGT_HO
Anti ping-pong: not checked if T_INHIBIT_CPT is running
2.6 Handover algorithms for multi-layer networks
Cause 14: high level in a lower or an indoor layer for slow MSs (3/4)
mini
umbrella
micro indoor
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CAUSE 14: high level in a neighboring cell of a lower or an indoor layer forslow mobiles
If cell_layer_type (0) = lower
AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n)
and MS_SPEED FAST
and EN_MCHO_NCELL = ENABLED
Averaging window:A_PBGT_HO
Anti ping-pong: not checked if T_INHIBIT_CPT is running
2.6 Handover algorithms for multi-layer networks
Cause 14: high level in a lower or an indoor layer for slow MSs (4/4)
mini micro
indoor
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Speed discrimination objectives
maximize capacity (maximum traffic in microcells)
while optimizing quality (minimize the number of handovers)
Smart speed discrimination:
The higher the load in the umbrella cell, the higher the speed of MSs can be beforebeing directed to microcells
- to maximize capacity
- to maximize quality (avoid multiple handovers) when the load is low
Fast moving mobiles are directed to umbrella cells
a fast moving MS connected to a microcell or an indoor cell is directed to anunloaded umbrella cell (see previous part)
2.6 Handover algorithms for multi-layer networks
Cause 14: speed discrimination (1/6)
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Interlayer HO based on speed discrimination
2.6 Handover algorithms for multi-layer networks
Cause 14: speed discrimination (2/6)
Lower layer
Upper layer
Indoor layer
Cause12MS_speed = FAST
Cause12MS_speed = FAST
Cause14MS_speed = SLOW
Or INDEFINITE
Cause14MS_speed = SLOW
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Speed discrimination process in umbrella cells speed estimation based on the dwell time in the neighboring micro cells
if this dwell time exceeds MIN_DWELL_TIME, the MS is slow and is sent to themicrocell
C_DWELL(n) is a counter measuring the number of SACCH periods of monitoringneighboring cell n over the threshold L_RXLEV_CPT_HO(0,n)
C_DWELL(n) is compared to the threshold 2*MIN_DWELL_TIME in order todetermine MS speed
- MIN_DWELL_TIME is a variable linked to the load of the serving umbrella cell)
if for one neighboring cell n, C_DWELL(n) >= 2*MIN_DWELL_TIME then MS_SPEEDis set to SLOW
2.6 Handover algorithms for multi-layer networks
Cause 14: speed discrimination (3/6)
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Initialization of C_DWELL(n) in serving umbrella cells:
for all neighboring cells n of a lower layer
if EN_SPEED_DISC = ENABLED
- C_DWELL(n) = 0
else if EN_SPEED_DISC = DISABLED
- C_DWELL(n) = (MIN_DWELL_TIME -L_MIN_DWELL_TIME)*2
Consequences
if EN_SPEED_DISC = DISABLED
MSs will handover to the lower layer after L_MIN_DWELL_TIME seconds
if EN_SPEED_DISC = ENABLED
MSs will have to receive sufficient level from a lower layer cell duringMIN_DWELL_TIME seconds before leaving the upper layer
2.6 Handover algorithms for multi-layer networks
Cause 14: speed discrimination (4/6)
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Example with default values
Initial values
MIN_DWELL_TIME = H_MIN_DWELL_TIME = 20s
L_MIN_DWELL_TIME = 8s
C_DWELL(n) = (MIN_DWELL_TIME -L_MIN_DWELL_TIME)*2
C_DWELL(n) = ( 2 - 8 )*2
C_DWELL(n) = 12*2s
Algorithm
MS is deemed as slow if C_DWELL(n) > MIN_DWELL_TIME
2.6 Handover algorithms for multi-layer networks
Cause 14: speed discrimination (5/6)
0 2 4 6 8 10 12 14 16 18 20 22
: EN_SPEED_DISC = Disable
: EN_SPEED_DISC = Enable
INDEFINITE or FAST SLOW
Maximum time to reach
MIN_DWELL_TIME
=
L_MIN_DWELL_TIME
C_DWELL MIN_DWELL_TIMEC_DWELL
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Traffic regulation through the variation of MIN_DWELL_TIME
Parameters: L_MIN_DWELL_TIME, DWELL_TIME_STEP,
H_MIN_DWELL_TIME, H_LOAD_OBJ, L_LOAD_OBJ
2.6 Handover algorithms for multi-layer networks
Cause 14: speed discrimination (6/6)
100%
Load in theumbrella Cell
H_LOAD_OBJ
L_LOAD_OBJ
L_MIN_DWELL_TIME10 seconds
DWELL_TIME_STEP5 seconds
H_MIN_DWELL_TIME40 seconds
end: low traffic
start: low traffi
Regulation of
traffic peak
Default values
dependent on
the number of
TRXs
Default values: 8 seconds 2 seconds 20 seconds
MIN_DWELL_TIME
The initial value of MIN_DWELL_TIME is the H_MIN_DWELL_TIME parameter value.
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CAUSE 24: general capture
new capture handover
Introduced in B6.2
Improved in B7 (anti ping-pong)
May be triggered
From all cells
Towards any cell except the serving one
Can be used to capture traffic by any cell, whatever its type, band, etc.
2.6 Handover algorithms for multi-layer networks
Cause 24: general capture (1/3)
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CAUSE 24: general capture
in order to keep dual band MS in the preferred band, cause 24 is not checked
in the following cases, when EN_BI-BAND_MS(n) = DISABLED
2.6 Handover algorithms for multi-layer networks
Cause 24: general capture (2/3)
CELL_BAND_TYPE = Preferred_band
EN_BI-BAND_MS = DISABLED
CELL_BAND_TYPE = CELL_BAND_TYPE(0)
EN_BI-BAND_MS = DISABLED
CELL_BAND_TYPE Preferred_band
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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_CONDITION
and Traffic_load(n) HIGH
and EN_GENERAL_CAPTURE_HO = ENABLED
Size of window for averaging level:A_PBGT_HO
CAPTURE_TRAFFIC_CONDITION can take 3 values: ANY_LOAD (default),
HIGH, NOT_LOW Anti ping-pong: not checked if T_INHIBIT_CPT is running
2.6 Handover algorithms for multi-layer networks
Cause 24: general capture (3/3)
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Use of cause 21 or 14?
Considering the following network
Which cause has to be used for capture? 14 or 21?
Highlight one complexity linked to causes 14 and
21 interworking when using traffic discrimination
2.6 Handover algorithms for multi-layer networks
Exercises (1/3)
900
mini1800
Timeallowed:
5 minutes
CAUSE 21: high level in the neighboring cell in the preferred band
AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n) +max (0, [MS_TXPWR_MAX(n) - P])
and Traffic_load(0) =MULTI-BAND_TRAFFIC_CONDITION
and Traffic_load(n) HIGH
and EN_PREFERRED_BAND_HO = ENABLED
Size of window for average level:A_PBGT_HO
MULTI-BAND_TRAFFIC_CONDITION can take 3 values: ANY_LOAD (default), HIGH, NOT_LOW
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2.6 Handover algorithms for multi-layer networks
Exercises (3/3)
Timeallowed:
5 minutes
Speed discrimination
What is the role of parameter EN_SPEED_DISC?
If EN_SPEED_DISC is disabled, can fast MSs bedirected toward microcells?
What is the difference between EN_SPEED_DISC =DISABLED and EN_SPEED_DISC = ENABLED whenL_LOAD_OBJ = 0% and H_LOAD_OBJ = 100%?
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2 ALGORITHMS AND ASSOCIATEDPARAMETERS
2.7 Candidate cell evaluation
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As soon as an intercell HO alarm has been detected
HO Detection sends to Candidate Cell Evaluation
the HO cause value
the preferred layer for the target cell indicated by the variable PREF_LAYER (it
depends on the cell network architecture and on the operator strategy)
the list of potential candidates (it depends on type of handover cause)
2.7 Candidate cell evaluation
From HO Detection to Candidate Cell Evaluation
CandidateCell
Evaluation
Handover
Detection
Raw cell list
cell 1: cause C1cell 2: cause C2
cell 3: cause C3
Max 32 cells
PREF_LAYER
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Standard cell environment
CELL_LAYER_TYPE = SINGLE
Better condition HO cause
Emergency HO cause
* if the MS is in the DCS 1800 inner zone of a multi-band cell then it includes the serving
cell
2.7 Candidate cell evaluation
Raw Cell List and PREF_LAYER (2/4)
upper + singlePREF_LAYER
subset of cells verifying the HO causesRaw cell list
upper + singlePREF_LAYER
all neighboring cells*Raw cell list
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Hierarchical cell environment
CELL_LAYER_TYPE = UPPER
Better condition HO cause
Emergency HO cause
* if the MS is in the DCS 1800 inner zone of a multi-band cell then it includes the serving
cell
2.7 Candidate cell evaluation
Raw Cell List and PREF_LAYER (2/4)
nonePREF_LAYER
subset of cells verifying the HO causesRaw cell list
upper + singlePREF_LAYER
all neighboring cells*Raw cell list
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CELL_LAYER_TYPE = LOWER or INDOOR
Better condition HO cause
Emergency HO cause
* if the MS is in the DCS 1800 inner zone of a multi-band cell then it includes the serving cell
2.7 Candidate cell evaluation
Raw Cell List and PREF_LAYER (3/4)
noneLower + indoorUpper + SinglePREF_LAYER
All neighboring cells* exceptumbrella cells which do notverify AV_Rxlev_Ncell(n) >
OUTDOOR_UMB_LEV(0,n)
All neighboring cells* exceptumbrella cells which do notverify AV_Rxlev_Ncell(n) >
OUTDOOR_UMB_LEV(0,n)
All neighboring cells* exceptumbrella cells which do notverify AV_Rxlev_Ncell(n) >
OUTDOOR_UMB_LEV(0,n)
Raw cell list
EN_RESCUE_UM = indefiniteEN_RESCUE_UM = DISABLEDEN_RESCUE_UM = ENABLED
noneUpperPREF_LAYER
Subset of cells verifying the HOcauses
Subset of cells verifying the HOcauses plus all neighboring
umbrella cells withTraffic_Load(n) = LOW
Raw cell list
MS_SPEED FAST or
HO Cause 12
MS_SPEED = FAST and
There is a cell in the listbecause of cause 12
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Emergency handovers from lower or indoor layers
behavior depends on EN_RESCUE_UM
Normal parameter settings for minicells
EN_RESCUE_UM = DISABLED
thus PREF_LAYER = lower
Emergency handovers are preferably sent to neighboring minicells
Normal parameter settings for microcells
EN_RESCUE_UM = ENABLED
thus PREF_LAYER = upper + single
Emergency handovers are preferably sent to umbrella cells or neighboring
macrocells
2.7 Candidate cell evaluation
Raw Cell List and PREF_LAYER (4/4)
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2.7 Candidate cell evaluation
Evaluation process
Measurement
Preprocessing
A_LEV_HO
A_QUAL_HO
A_PBGT_HO
A_RANGE_HO
HO Detection
Cause 2: uplink quality
Cause 3: uplink level
Cause 4: downlink quality
Cause 5: downlink level
Cause 6: distanceCause 12: power budget
Performed every SACCHPerformed every SACCH
Pre-ranking
Priority (0, n) = 0
Cell 2: cause C2
Cell 3: cause C2
Cell 4: cause C2
Priority (0, n) = 1
Cell 1: cause C2
Priority (0, n) = 2Priority (0, n) = 3
Cell 5: cause C2
Cell 6: cause C2
Cell 7: cause C2
Cell 8: cause C2
Priority (0, n) = 4
Priority (0, n) = 5
Priority (0, n) = 0
Cell 2: cause C2
Cell 3: cause C2
Cell 4: cause C2
Priority (0, n) = 1
Priority (0, n) = 2
Priority (0, n) = 3
Cell 6: cause C2
Cell 8: cause C2
Priority (0, n) = 4
Priority (0, n) = 5
PBGT filteringHO_MARGIN_XX(0,n)
Grade
Priority (0, n) = 0
Cell 4: cause C2
Cell 2: cause C2
Cell 3: cause C2
Priority (0, n) = 1Priority (0, n) = 2
Priority (0, n) = 3
Cell 6: cause C2
Cell 8: cause C2
Priority (0, n) = 4
Priority (0, n) = 5
Order
Priority (0, n) = 0
Cell 4: cause C2
Cell 3: cause C2
Cell 2: cause C2
Priority (0, n) = 1Priority (0, n) = 2
Priority (0, n) = 3
Cell 6: cause C2
Cell 8: cause C2
Priority (0, n) = 4
Priority (0, n) = 5
Cell evaluation process (Order or Grade)
HO Candidate Cells Evaluation
Max
every SACCH
Preprocessmeasurement
Measurementresult
Raw cell list
Cell 1: cause C2
Cell 2: cause C2
Cell 3: cause C2
Cell 4: cause C2Cell 5: cause C2
Cell 6: cause C2
Cell 7: cause C2
Cell 8: cause C2
... max 32 cells
The HO candidate evaluation process is run after all intercell handover alarms.
In case of intra-cell handover alarm (HO causes 10, 11, 13, 15, 16), the candidate cell evaluation process isskipped: the target cell is the serving cell.
The handover detection gives as indication the raw cell list (built from the book-keeping list) and thepreferred layer for the handover.In case of emergency handover alarms or cause 20 alarm, the cellevaluation will order the cells given in the raw list, putting in the first position the cells belonging to thepreferred layer, having the highest priority (if EN_PRIORITY_ORDERING=ENABLED) and/or having the samefrequency band type as the serving cell. In case of an intercell handover alarm, if the serving cell belongs tothe raw cell list (emergency handover from the DCS 1800 inner zone of a multi-band cell), this cell is put atthe 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 inthe raw list, putting in the first position the cells belonging to the preferred layer and having the highest
priority (if EN_PRIORITY_ORDERING=ENABLED).
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2.7 Candidate cell evaluation
Pre-ranking in standard networks
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 a 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 and PBGT
nevertheless it can be skipped over by filtering processes
low interest for standard networks
Serving cell
Candidate cell 1: RxLev: - 70 dBm, pbgt: + 10 dB
Candidate cell 2: Rxlev: - 90 dBm, PBGT: + 5dB
P0
P1
PRIORITY(0,n) can take 6 different values since B7, to take into account new indoor layers.
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In hierarchical or multi-band networks, pre-ranking is used
For emergency handovers + Forced Directed Retry
Cell_layer_type: single, upper, lower, indoor
PRIORITY(0,n): 0 to 5
Cell_band_type: GSM or DCS
For better condition handovers
Cell_layer_type: single, upper, lower, indoor
PRIORITY(0,n): 0 to 5
PRIORITY(0,n) are taken into account only ifEN_PRIORITY_ORDERING isset to enabled on the serving cell
2.7 Candidate cell evaluation
Pre-ranking in complex networks (1/3)
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Pre-ranking in case of emergency HO, plus cause 20 and 28 :
2.7 Candidate cell evaluation
Pre-ranking in complex networks (2/3)
Cell_layer_type = Pref_layer
Cell_layer_type Pref_layer
List of candidate cells n
Cell_band_type = serving cell
Cell_band_type serving cell
Priority(0,n) = 0
Priority(0,n) = 1
Priority(0,n) = 5
Priority(0,n) = 0
Priority(0,n) = 1
Priority(0,n) = 5
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Pre-ranking in case of better condition HO:
2.7 Candidate cell evaluation
Pre-ranking in complex networks (3/3)
Cell_layer_type = Pref_layer
Cell_layer_type Pref_layer
List of candidate cells n
Priority(0,n) = 0
Priority(0,n) = 1
Priority(0,n) = 5
Priority(0,n) = 0
Priority(0,n) = 1
Priority(0,n) = 5
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2.7 Candidate cell evaluation
PBGT Filtering
PBGT filtering: process introduced since B5 optional, activated through the flag EN_PBGT_FILTERING
filter out cells from the target list inhibited for better conditions handovers
based on power budget
Mandatory for multi-band networks
PBGT(n) > HO_MARGIN_XX (0,n) + OFFSET_HO_MARGIN_INNER
HO_MARGIN_XX (0,n) = HO_MARGIN_QUAL (0,n) for causes 2, 4, 7
HO_MARGIN_XX (0,n) = HO_MARGIN_LEV (0,n) for causes 3, 5, 17, 18, 28
HO_MARGIN_XX (0,n) = HO_MARGIN_DIST (0,n) for cause 6
OFFSET_HO_MARGIN_INNER is only applied when the MS is in the inner zone of aconcentric or multi band cell
The average 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 onthe handover cause.
Note: the average window used for this process is A_PBGT_HO (even for emergency handovers, wherehandover alarm could have been raised through A_LEV_HO or A_QUAL_HO samples).
Warning: HO_MARGIN_xx (LEV, DIST or QUAL) has nothing to do with a handover margin value, specific forcertain handover causes (anyway, these handovers cause only tackle source cell and are not looking at levelof targets for handover detection).
HO_MARGIN is used for handover detection (cause 12 or 23).
HO_MARGIN_xx are used for candidate cell evaluation.
Thus, there is no having HO_MARGIN = HO_MARGIN_xx! Let us see three examples:1) If HO_MARGIN_xx = HO_MARGIN = 5 dB
In that case, when an emergency handover is triggered (level, quality, distance, etc.), all neighboring cellsare filtered regarding their PBGT compared to 5 dB! By the way, if a cell that is not greater than theserving one + 5 dB will be filtered out: this handover, detected as an emergency case, is in fact abetter cell one.
2) If HO_MARGIN_xx is very small (for example, -30 dB),
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