1 © Nokia Siemens Networks RNO / Wind 18/01/2008 - NMI
Confidential
RNO WindPart III
Confidential
2 © Nokia Siemens Networks RNO / Wind 18/01/2008 - NMI
Part III - Content
Call Setup Time
UL Interference
PS Utilization
Cell Reselection
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Call Setup Time
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Call setup Time – Preamble PRACH
• During drive testing can be noted that there are call setup failures where the network does not seem to respond to RRC Connection Requests with RRC Connection Setup –message.These are problems due to the spiky UL noise and due to that the power ramping is not aggressive enough to provide high enough Tx power for the terminal during open loop PC
Downlink / BSDownlink / BS
Uplink / UEUplink / UEPreamble 1 Message part
…. ….
UEtxPowerMaxPRACH
Preamble n
PRACH_preamble_retrans: The maximum number of preambles allowed in one preamble ramping cycle
RACH_tx_Max: # of preamble power ramping cycles that can be done before RACH transmission failure is reported,
L1ACK/AICH
RACH
PowerOffsetLastPreamblePRACHmessage
PowerRampStepPRACHpreamble
PtxAICH
PRACHRequiredReceivedCI
Note: The power ramp-up process will continue until
1) A positive or negative AI is received from the network
2) RACH_tx_MAX value is reached
3) UE reaches UEtxPowerMaxPRACH value
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Call setup Time – Preamble PRACH
Ptx = CPICHtransmissionPower-RSCP(CPICH) +RSSI(BS) + PRACHRequiredReceivedCI (-20dB)Example:
CPICH = 33dBm (Parameter per Node-B)
RSCP = -80dBm (Measured by UE)
RSSI = -85 dBm
UL_Required_C/I = -25 dB (Parameter per Node-B)
UE PRACH First Preamble Power = 33 dBm – (-80 dBm) + (-85
dBm) + (-25 dB) = 8 dBm
Ptx = CPICHtransmissionPower-RSCP(CPICH) +RSSI(BS) + PRACHRequiredReceivedCI (-20dB)Example:
CPICH = 33dBm (Parameter per Node-B)
RSCP = -80dBm (Measured by UE)
RSSI = -85 dBm
UL_Required_C/I = -25 dB (Parameter per Node-B)
UE PRACH First Preamble Power = 33 dBm – (-80 dBm) + (-85
dBm) + (-25 dB) = 8 dBm
The parameters affecting to open loop power control are, in brackets are the recommended values:• PRACH_preamble_retrans (7)• RACH_tx_Max (16) • PowerOffsetLastPreamblePRACHmessage (2 dB)• PowerRampStepPRACHpreamble (2dB)
The PRACHRequiredReceivedCI (-20dB) allow to calculate the UEpower for the fist preambleas in thefollowing:
The parameter PRACHRequiredReceivedCI can be set to -18…-20dB instead of the default -25dB (typically -20dB is enough)
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Call setup Time – Preamble PRACH
100%
0% 0% 0%
88%
2% 5% 6%
0%
20%
40%
60%
80%
100%
1 2 3 4
# RRC Connection Request Messages per call setup
%
PRACH req. C/I = -20dB PRACH req. C/I = -25dB
Clear improvement in number of needed RRC Connection Request messages per call. For –20dB 100% of established calls are setup with only 1 RRC Connection Request message
Clear improvement number of sent preambles per RRC Connection Request for –20dB case. For –20dB 50% of cases the needed number of preambles is <=4 where as for –25dB it is ~6.5
0%
10%
20%
30%
40%
50%60%
70%
80%
90%
100%
1 2 3 4 5 6 7 8
PRACH req. C/I = -25dB PRACH req. C/I = -20dB
There should be significant improvement also for call setup delay
Typical improvement passing from -25dB to -20dB:
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Call setup Time – Preamble PRACH
The average number of acknowledged PRACH preambles during the RRI period can be calculated based on the KPI below
RACH load due to preamble can then be calculated by dividing the above further by the max number preambles can be received during RRI
• For example if RRI period is 200ms the are 10 20ms RACH frames and in each 20ms RACH frame there are 15 RACH sub slots within each it is possible to receive and decode max 4 preambles -> therefore in 200ms it is possible to receive 15*4*10=600 preambles
BLES_ACK_PREAMDENOM_RACH M1000C177
ESCK_PREAMBLSUM_RACH_A M1000C176
BLES_ACK_PREAMDENOM_RACH M1000C177
ESCK_PREAMBLSUM_RACH_A M1000C176
% 100*/600BLES_ACK_PREAMDENOM_RACH M1000C177
ESCK_PREAMBLSUM_RACH_A M1000C176 % 100*/600
BLES_ACK_PREAMDENOM_RACH M1000C177
ESCK_PREAMBLSUM_RACH_A M1000C176
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Call Setup Time – SRB Rate
Why 13.6kbit/s?
Use of 13.6 kbit/s SRB also in highly loaded networks
Decreased setup times (PDP context activation minimum 0.7s lower)
Improved Iub efficiency
Typical improvement passing from 3.4 to 13.6
0
1
2
3
4
5
6
7
3G-3G CS call setup PS call setup DCH allocation
Se
con
ds
Nokia RAN1.5 (3.4 kbps) + M11
Nokia RAN04 (13.6 kbps) + M12
Nokia RAN target
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Call setup Time – KPI
In RN2.2 the following counters are available to monitor the Call Setup Time
RRC Setup TimeM1001C221/M1001C222
RAB Setup TimeM1001C223 / M1001C224 for CSM1001C235 / M1001C236 for DATA BACKGR
In detail we have:
M1001C221 - SUM OF RRC SETUP TIMES Sum of RRC setup times. This counter divided by the DENOMINATOR - M1001C222 gives the averageRRC setup time. RRC setup time is defined as the time between the RRC: RRC CONNECTION REQUESTmessage and the RRC: RRC CONNECTION SETUP COMPLETE message.
M1001C223/235 - SUM OF RAB SETUP TIMES FOR CS VOICE/FOR DATA BACKGRSum of RAB setup times. This counter divided by the DENOMINATOR - M1001C224/236 gives the averageRAB setup time. RAB setup time is defined as the time between the RANAP: RAB ASSIGNMENTREQUEST and RANAP: RAB ASSIGNMENT RESPONSE messages during RAB establishment.
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Call setup Time – Annex1
MO-UE MT-UEMobile-to-mobile CS call setup on common channelsDelay CumulativeRRC connection request UE RNC 0 0RRC connection setup RNC UE 40 40RRC connection setup completeUE RNC 100 140CM service request UE CS 200 340Security mode command RNC UE 100 440Security mode complete UE RNC 200 640Setup UE CS 300 940Call proceeding CS UE 100 1040 Paging RNC UE 400 1340Radio bearer setup RNC UE 100 1140 RRC connection request UE RNC 50 1390Radio bearer setup complete UE RNC 300 1440 RRC connection setup RNC UE 40 1430
RRC connection setup completeUE RNC 100 1530Paging response UE CS 100 1630Security mode command RNC UE 100 1730Security mode complete UE RNC 200 1930Setup CS UE 300 2230Call confirmed UE CS 100 2330Radio bearer setup RNC UE 100 2430Radio bearer setup complete UE RNC 300 2730
Alerting CS UE 250 2980 CS UE 250 2980
Parallel RB setup for MO-UE and paging of MT-UE
(CS core feature)
<3.0 s mobile-to-mobile AMR call setup time
Average paging delay
of 320 ms assumed (640
ms paging cycle)
RA
CH
/FA
CH
RA
CH
/FA
CH
Typical value for CS Call Setup Time
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Call setup Time – Annex2
RRC + PDP on common channels Delay CumulativeRRC connection request UE RNC 0 0RRC connection setup RNC UE 40 40RRC connection setup complete UE RNC 100 140GPRS service request UE PC 200 340Security mode command RNC UE 100 440Security mode complete UE RNC 200 640PDP context activation request UE PC 250 890Radio bearer setup RNC UE 150 1040Radio bearer setup complete UE RNC 300 1340PDP context activation accept PC UE 200 1540
Common channels used for setup to
avoid slow synchronized
reconfigurations later
Parallel RB setup and RL/AAL2 setups (or pre-
reserved Radio links)
RA
CH
/FA
CH
<1.6 s PS call setup time
Initial bit rate DCH allocated directly together
with SRB
Typical value for PS Call Setup Time
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UL Interference
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What’s Interference?
Any working point turned off from the expected load curve can be considered as interference.
Interference can be internal or external.
Internal interference can be caused by not appropriate dimensioning, planning or commissioning
External is usually referred to mobile or other RF sources
Prx Target [dB]
PrxTarget [dB] + PrxOffset [dB]Overload Area
Marginal Load Area
Feasible Load Area
Own cell load factor
Wi d
eb
an
d p
ow
er
l ev
el
I tot a
l
LRT UnloadedRT and LNRT UnloadedNRT
Unloaded Area
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Load vs. Power
Typical mismatch among load and Power can be easily found in a live network.
Above is reported a qualitative behaviour in class_1 power for some Wind WBTSs that are experiencing a 1<rt_load<2 (rt_load relative value from 0 to 4) and the related nrt_load and Prx_power.
The nrt load added to rt can not give sense of the Prx spike
Class1_Prx/Load
-5000
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 50 100 150 200 250
WBTS
Rel
. Am
plit
ud
e
ave_lrt_class_1 ave_lnrt_class_1 ave_prxtot_class_1
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NSN Load Areas & Class of Power
CLASS AREA INCREMENTED IF
CLASS 0 Unloaded (Lrt=<UnloadedRT) AND (Lnrt=<UnloadedNRT)
CLASS 1 Feasible_Load_Area_1 (PrxTarget -PrxOffset >= PrxTotal ) AND ((Lrt>UnloadedRT) OR (Lnrt>UnloadedNRT))
CLASS 2 Feasible_Load_Area_2 (PrxTarget > PrxTotal > PrxTarget -PrxOffset) AND ((Lrt>=UnloadedRT) OR (Lnrt>= UnloadedNRT))
CLASS 3 Marginal_Load_Area (PrxTarget + PrxOffset > PrxTotal >=PrxTarget) AND ((Lrt>UnloadedRT) OR(Lnrt> UnloadedNRT))
CLASS 4 Overload_Area (PrxTotal >= PrxTarget + PrxOffset) AND ((Lrt>UnloadedRT) OR (Lnrt>UnloadedNRT))
Prx Target [dB]
PrxTarget [dB] + PrxOffset [dB]
Overload Area
Marginal Load Area
Feasible Load Area_1
Own cell load factor
Wid
eb
an
d p
ow
er
l ev
el
I tot a
l
LRT UnloadedRT and LNRT UnloadedNRT
Unloaded Area
Feasible Load Area_2
Class4
Class3
Class2
Class1
Class0
PrxTarget [dB] - PrxOffset [dB]
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UL Interferece Detection Method
Different approach can be applied to detect UL interference.
Mainly we have:
- Field measurement
- Counters Analysis
Using the Counters Analysis approach dedicate counters are available for UL Interfernce detection as MAXPrxNoise and MINPrxNoise (M1000C12 and M1000C13)
The UL interference severity can be estimated by analysing: MAXPrxNoise – MINPrxNoise, but these counters are incremented only when cell is unloaded.
Here we propose a line for a method that approximately return the WBTS interfered.
The method takes the basis from the autotuning algorithm and use the value of Prx returned to detect the interfered cell.
The first step is the localization of reference point for each class
Then different kind of statistical model can be applied for evaluating the drawn from them
Finally a w.w.w concept is used to derive information from space and time recurrence
Some help could come from counters that trigger downgrade or release bocause of interference (e.g. M1000C147RB_DOWNGR_DUE_PBS_INTERF M1000C159RB_RELEASE_DUE_PBS_INTERF if PBS is enabled)
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Prx Autotuning
Prx Target_t0 [dB]
Overload Area
Marginal Load Area
Feasible Load Area 1
Time
Wid
eb
an
d p
ow
er
l ev
el
I tot a
l
Unloaded Area
t0 t1
Prx Target_t1 [dB]
The auto-tuning algorithm moves the reference point of the load curve and this means that all the areas can be shifted up and down during the day this means that a certain value of PrxTotal (which is measured by the bts) may trigger different areas during the day. For example the sample 4 triggers in the first case the class 2 while in the second case the class 1, but it’s the same value of power!
Feasible Load Area 2 4 4
Main idea is to use this gap to detect interference
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Permanence in Class1>45min
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53
WBTS
Prx
Rel
. A
mp
litu
de
Class Power Reference Point
It is not an easy task to find the expected value of Prx in each class.
Different masking effect are present either for the granularity of the measurement available that are not appropriate for this kind of analysis or for the inherent difficulty in evaluating the real load experienced.
Here a shot for class1 considering the stay time in the class is attempted
Permanence in Class1<15min
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1 74 147 220 293 366 439 512 585 658 731 804 877 950 1023 1096 1169 1242 1315
WBTS
Prx
Rel
. A
mp
litu
de
The spike are more accentuated for low permanence and diluited for the high one
An average can be attempted filtering off the spike and the default value
Prx Displacement
Prx Displacement
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Power Class Distribution Function
Here a Prx Distribution over the all WCELs is presented. Typical value of the reference point are represented individuating areas where interference can be detected.The different shape of the curve of the Feasible_Load_Area_2 and the Marginal_Load_Area_2 respect to the Class_0, Class_1 and Class_4 seems due to the different behaviour of the algorithm.The step visible in C2 and C3 could be due to the strict margin in term of Power Budget to react to the load increase. The overshoot of the C0 curve over the C1 is due to to the different triggering condition that for C0 is load based instead of Power Level driven. Finally C1 having a greater budget maintain a smoother shape.
Prx_Dist. function
0
0.2
0.4
0.6
0.8
1
0 200 400 600 800 1000 1200 1400 1600 1800
WBTS
Rel
. A
mp
litu
de c2
c1
c0
c3
c4
Probable Interfered
WCEL
Probable Interfered
WCEL
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W.W.W. Approach
A single interfernce event can not raise any relevant bother. A statistical analysis is needed. The Who? When? Where? approach is used to derive information and troubleshoot the probable interferer source. The space-time diagram has to be intended as a recurrence indicator for the interference event. In the left side of the F_space axis are reported occurences not adjoined in space. Same concept for F_time.
F_space
F_
tim
e
+
+
-
-
stable interference for a adjacent cluster of cell
periodical spot interference
Fixed Ext. SourceCommissioning /
Dimensioning
Mobile Ext. Source
Adj missing
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Class 0
Class0 can act as the third dimension of the WWW Approach diagram.Considering Class0 as the unlaoded class in the sense that the unloaded limit for RT and NRT (1% and2% respectively) is not exceeded the interference detection in this class can have two advantages:
a) More interference sentivity because of low loadb) Easier discrimination between internal and external interference
The first point is assured by the triggering condition and can be strenghtened superimposing a secondcondition over the load. Imposing the LoadRT = 0 and LoadNRT = 0 we have more reliable result for interference This condition triggered mainly during the nigh-time returns the possibility to have an easiertroubleshooting
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PS Utilization
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Traffic Mix KPI
The KPI provides an indication of the percentage of CS voice, CS data, PS data RAB establishment attempts relative to the total number of RAB establishment attempts
The KPI is meaningful for cluster/cell level and on day/hour basis. Same KPI can be obtained using RAB ACC COMP
These KPI are intended to provide a high level indication of the traffic profile loading the network:
• CS_VOICE
• CS_CONV
• CS_STREA
• PS_CONV
• PS_STREA
• PS_INTER
• PS_BACKG
Example for CS_VOICE:
T_PS_BACKGRAB_STP_AT T_PS_INTERRAB_STP_AT T_PS_STREARAB_STP_AT T_PS_CONVRAB_STP_AT T_CS_STREARAB_STP_AT T_CS_CONVRAB_STP_AT T_CS_VOICERAB_STP_AT
T_CS_VOICERAB_STP_AT
BACKGPSSTPRABINTERPSSTPRABSTREACSSTPRABCONVCSSTPRABVOICECSSTPRAB
VOICECSSTPRAB
_______________
___
BACKGPSSTPRABINTERPSSTPRABSTREACSSTPRABCONVCSSTPRABVOICECSSTPRAB
VOICECSSTPRAB
_______________
___
Traffic Mix
51%
1%
32%
16%
Voice
Data Conv
PS Inter
PS Backg
To take into consideration that PS might cause many attempts in each call another option is to consider the
duration counters!
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Traffic Mix KPI
For each traffic class there are counters for RAB Holding time (incremented when the RAB is released only on the cell that was the reference when the RAB is released)
If a distribution on cell level is required the RAB_HOLD_TIME_IN_REF_CELL can be used
For NRT traffic classes (inter and backg) there are also counters for DCH Holding time (incremented when the RAB is released only on the cell that was the reference when the RAB is released)
)(100/_____
_____s
INTERPSTMHLDRABDENOM
INTERPSTMHLDRABAVG)(100/
_____
_____s
INTERPSTMHLDRABDENOM
INTERPSTMHLDRABAVG
)(100/_____
_____s
INTERPSTMHLDDCHDENOM
INTERPSTMHLDDCHAVG)(100/
_____
_____s
INTERPSTMHLDDCHDENOM
INTERPSTMHLDDCHAVG
For each Traffic Class
For each Traffic Class
Only for NRT Traffic Class
Only for NRT Traffic Class
RAB Holding Time [s]
20
40
60
80
100
120
140
160
180
200
More
DCH Holding Time [s]20
40
60
80
100
120
140
160
180
200
More
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From Cell_DCH to Cell_FACH
CELL_
FACH
CELL_
DCH
UE
RLC
bu
ffer
paylo
ad
RLC
bu
ffer
paylo
ad
(tra
nsp
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ch
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nel tr
affi
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olu
me)
(tra
nsp
ort
ch
an
nel tr
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c v
olu
me)
CELL_FACH state
CELL_DCH state
InactivityTimerUL(DL)DCH
After the inactivity timer expires the RRC radio bearer reconfiguration–procedure is performed.
RRC sends an RRC: RADIO BEARER RECONFIGURATION message to the UE.
UE acknowledges by sending the RRC: RADIO BEARER RECONFIGURATION COMPLETE –message to the
RRC signaling entity of the RNC which starts L2 reconfiguration (as well as PS is informed about the
cell state change).
Radio link and AAL2 resources are then released and UE is changed to CELL_FACH state.
In case the UE is having RT RB which has become inactive and at the same time it is having inactive
NRT RB then RADIO BEARER RELEASE procedure is used (instead of RADIO BEARER RECONFIGURATION).
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From Cell_FACH to Cell_DCH
In uplink direction the need for the capacity is detected by the MAC of UE.
UE requests dedicated capacity by sending an RRC: MEASUREMENT REPORT message on RACH to the
RRC signaling entity of RNC
After the procedure, data transmission on DCH can begin and UE is in CELL_DCH state.
In downlink direction the capacity need is detected by the UE MAC entity of RNC.
PS requests the RRC signaling entity of RNC to start transport channel reconfiguration –procedure
The RRC signaling entity sends an RRC: TRANSPORT CHANNEL RECONFIGURATION message to the UE
on FACH, which is acknowledged with an RRC: TRANSPORT CHANNEL RECONFIGURATION COMPLETE
After the procedure, data transmission on DCH can begin and UE is in CELL_DCH state.
CELL_
FACH
CELL_
DCH
UE
RLC
bu
ffer
paylo
ad
RLC
bu
ffer
paylo
ad
(tra
nsp
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nel tr
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c v
olu
me)
(tra
nsp
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ch
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nel tr
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c v
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me)
TrafVolThresholdDL(UL)Low
(WCEL)
CELL_FACH state
CELL_DCH
state TrafVolThresholdDL(UL)High
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Cell-DCH/Cell-FACH KPIs
Percentage of time in cell dch:
NRT RB data transfer activeNRT RB inactivity timer running
Downlink DCH
Uplink DCH
CELL_FACH CELL_DCH CELL_FACH
%100_____
_____
INTERPSTMHLDRABAVG
INTERPSTMHLDDCHAVG%100
_____
_____
INTERPSTMHLDRABAVG
INTERPSTMHLDDCHAVG
DCH Time %10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
More
Similar KPI giving the ratio between FACH and DCH can be constructed starting from
M1006C90 SUM OF UE OPERATING TIME IN CELL_FACH
M1006C87 SUM OF UE OPERATING TIME IN CELL_DCH
Dividing per the number of UE is possible to have average time for user:
M1006C90 SUM OF UE OPERATING TIME IN CELL_FACH/M1006C92 NUM OF UE MEASURED IN CELL_FACH
M1006C87 SUM OF UE OPERATING TIME IN CELL_DCH / M1006C89 NUM OF UE MEASURED IN CELL_DCH
The number of transition can be monitored as well:
M1006C45 CELL DCH STATE TO CELL FACH
M1006C46 CELL FACH STATE TO CELL DCH
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Measuring the RACH/FACH Channel
The RACH channel average throughput for both data and signaling can be measured by the following KPI
kbps /1000_3RACH_DENOM M1000C61
THROUGHPUTAVE_RACH_ M1000C60 kbps /1000
_3RACH_DENOM M1000C61
THROUGHPUTAVE_RACH_ M1000C60
The FACH Total throughput means all the user related data (FACH-u) and signalling (FACH-c) for a SCCPCH
including PCH can be measured by the follwing KPI
Load KPI are available as well using the following countersM1000C64 AVE SCCPCH INC PCH LOADM1000C65 SCCPCH LOAD DENOM 0When the throughput approach the maximum allowed or the load the 100% for the actual configuration aparameter tuning to avoid the starvation in CCH or an expansion of RACH and FACH channel is required. Thedecision outcomes from different input:
DCH resources availableMarketing Strategy
bit/s ENOM_0TOT_TPUT_DFACH_USER_ M1000C67
SCCP_PCH_TOT_TPUT_AVE_FACH_U M1000C66
bit/s ENOM_0TOT_TPUT_DFACH_USER_ M1000C67
SCCP_PCH_TOT_TPUT_AVE_FACH_U M1000C66
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Cell Reselection
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Cell Reselection List
GSM MS starts WCDMA measurements if :RLA_C< F(Qsearch_I) for 0<Qsearch_I<=7
orRLA_C> F(Qsearch_I) for 7<Qsearch_I<=15
If, for suitable UMTS cell & for a period of 5 s:
CPICH RSCP > RLA_C + FDD_Qoffset
CPICH Ec/No FDD_Qmin
and
WCDMA cellreselection
BCCH: FDD_Qmin, FDD_Qoffset
Cell Reselection 2G -> 3G
Startmeasurement
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Depending on operator´s 2G – 3G interworking strategy parameter Q_search_I should planned accordingly.
Configuration 1RLA_C<
F(Qsearch_I) ( 0<Qsearch_I<=6 )
GSM 3G
Configuration 2RLA_C> F(Qsearch_I) ( 7<Qsearch_I<=15 )
In the best case, 3G cell measurements are restricted to the condition: RLA_C level > –78 dBm
GSM
3G
In the best case, 3G cell measurements are possible when RLA_C level < –74 dBm
GSM
3G
Configuration 3RLA_C< (always).
(Qsearch_I=7)
2G -> 3G Measurement
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2G -> 3G Cell Re-selection Parameters
Qsearch_I and Qsearch_P define the threshold for non-GPRS/GPRS (respectively) capable UEs to measure 3G
neighbour cells when a running average of the received downlink signal level (RLA_C) of the serving cell
below (0-7) or above (8-15) the threshold
Value 0 1 … 6 7 8 9 10 … 14 15
dBm -98 -94 … -74 Always -78 -74 -70 … -54 Never
FDD_Qoffset and FDD_GPRS_Offset the non-GPRS/GPRS (respectively) capable UEs add this offset to the
RLA_C of the GSM cells. After that the UE compares the measured RSCP values of 3G cells with signal levels
of the GSM cells
Value 0 1 2 3 … 8 … 14 15
dBm Always -28 -24 -20 … 0 … 24 28
Always select irrespective of RSCP value Reselect in case RSCP >
GSM RXLev (RLA_C) +28dB
If RLA_C < -94 UE starts 3G measurements
UE always measures 3G cells
If RLA_C > -70 UE starts 3G measurements
FDD_Qmin, defines minimum Ec/No threshold that a 3G cell must exceed, in order the UE makes a cell reselection from 2G to 3G.
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Cell Re-selection Example-Weaker WCDMANon GPRS case
t
Serving GSM Cell
Neighbour WCDMA Cell
Ec/NoRSCP/RLA_C
5 sec.
Cell re-selection to WCDMA
FDD_Qmin=0(-20 dB)
FDD_Qoffset =6 (-8 dB)
Qsearch_I=0 (-98 dBm)
RLA_C
Measurements starts (serving cell)
Minimum Quality Requirement for WCDMA
Ec/N0
RSCP
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Cell Re-selection Example-Weaker WCDMAGPRS case
t
Serving GSM Cell (Best)
Neighbour WCDMA Cell
Ec/NoRSCP/RLA_C
5 sec.
Cell re-selection to WCDMA
FDD_Qmin=-20 dB
FDD_GPRS_Qoffset =10 (8 dB)
Qsearch_P=0(-98 dBm)
RLA_P
Measurements starts (serving cell)
Minimum Quality Requirement for WCDMA
Ec/N0
RSCP
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Cell Reselection 3G -> 2G
Whilst camping in a 3G cell the UE performs intra-frequency, inter-frequency, and inter-system
measurements based on the measured CPICH EcNo.
Serving cell parameters Sintrasearch, Sintersearch and SsearchRAT are compared with Squal (CPICH Ec/No – Qqualmin) in S-criteria for cell re-selection
1 - None (Squal > Sintrasearch )
2 - WCDMA intra-frequency (Sintersearch < Squal Sintrasearch)
3 - WCDMA intra- and inter- frequency, no inter-RAT cells (SsearchRAT < Squal Sintersearch)
4 - WCDMA intra- and inter-frequency and inter-RAT cells (Squal SsearchRAT )
Sintrasearch Sintersearch SsearchRAT
WCDMA
CELL
1234
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Cell Reselection 3G -> 2G
First ranking of all the cells based on CPICH RSCP (WCDMA) and RSSI (GSM)
Rs = CPICH RSCP + Qhyst1Rn= Rxlev(n) - Qoffset1
First ranking of all the cells based on CPICH RSCP (WCDMA) and RSSI (GSM)
Rs = CPICH RSCP + Qhyst1Rn= Rxlev(n) - Qoffset1
Rn (GSM) > Rs (WCDMA)And
Rxlev (GSM) >QrxlevMin
Rn (GSM) > Rs (WCDMA)And
Rxlev (GSM) >QrxlevMin
YesNo
Cell re-selection to GSM
Cell re-selection to GSM
Neighbour WCDMA or GSM cell calculation with offset
parameter
Serving WCDMA cell calculation, with
hysteresis parameter
UE starts GSM measurements if CPICH Ec/No =< qQualMin + sSearchRAT
UE starts GSM measurements if CPICH Ec/No =< qQualMin + sSearchRAT
SintraSearch
SinterSearch
SsearchRAT
CPICH EcNo
qQualMin
Second ranking only for WCDMA cells based on CPICH Ec/No
Rs = CPICH Ec/No + Qhyst2Rn=CPICH_Ec/No(n)-Qoffset2
Second ranking only for WCDMA cells based on CPICH Ec/No
Rs = CPICH Ec/No + Qhyst2Rn=CPICH_Ec/No(n)-Qoffset2 Cell re-selection to
WCDMA cell of highest R value
Cell re-selection to WCDMA cell of highest
R value
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Cell Reselection 3G -> 2G
UE ranks the serving cell and the measured neighboring cells to find out if reselection should be made• All the measured suitable cells (S-criteria) are included in the ranking. • Criteria for a suitable cell (S-criteria) is defined as
– WCDMA intra-frequency neighbour cell: CPICH Ec/No > AdjsQqualmin and CPICH RSCP > AdjsQrexlevmin
– WCDMA inter-frequency cell: CPICH Ec/No > AdjiQqualmin and CPICH RSCP > AdjiQrexlevmin
– GSM cell:Rxlev > Qrxlevmin
Ranking is done using Criteria R, and the UE reselects to the cell with highest R-criteria. R-criteria is definedas:• For serving cell: Rs = Qmeas,s + Qhysts • For neighboring cell Rn = Qmeas,n – Qoffsetts,n
Qmeas is CPICH Ec/No for WCDMA cell and RxLev for GSM cell
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How to avoid ping pong ?
When phone is camped on 3G, GSM measurements can start when CPICH Ec/Io of serving cell is below Ssearch_RAT + QqualMin.
When phone is camped on GSM, cell reselection to 3G is possible if CPICH Ec/Io of the candidate is above FDD_Qmin.
Therefore, to avoid ping pongs between 3G and GSM the following condition should be met:
FDD_Qmin >= QqualMin + Ssearch_RAT
QqualMin=-18 dB
Ssearch_RAT=4 dB
CPICH Ec/Io
FDD_Qmin >= -12 dB
QqualMin +Ssearch_RAT
t
Camping on 3G Measure GSM Camping on 3G
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How to avoid ping pong ?
Parameters for cell reselections
• Qqualmin = -18dB Ssearch_RAT =2dB -> the 3G->2G cell reselection starts when Ec/No hits -16dB
• FDDQmin(GPRSFDDQmin) = -14dB (6) and QsearchP/QsearchI = always
The cell reselection paramters 3G -> 2G and 2G -> 3G provide only 2dB hysteresis which is not enough and should be noticed from the RNC statistics as high amount of INTR_RAT_CELL_RE_SEL_ATTS from all the RRC Connection Setup Attempts
• Recommendation is to adjust the FDDQmin from -14dB to -10dB (or even up to -8dB) to provide 6 to 8 dB hysteresis between 3G to 2G cell reselection and 2G to 3G cell reselection
• Another parameter to tune is Qrxlevmin
On top of Treselection the above parameters will slow down further the 2G to 3G and 3G to 2G cell reselections
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Treselection
How long the reselection conditions must be fulfilled before reselection is triggered?Treselection
Impacts all cell reselections : Inter RAT, intra frequency and inter frequencyThe UE reselects the new cell, if the cell reselection criteria (R-criteria, see next slide) are fulfilled during a time
intervalTreselectionAs this parameter impacts on all the cell reselections too long Treselection timer might cause problems in high mobility areas but too short timer causes too fast cell reselections and eventually causes also cell reselection ping pongRecommended value 1s should work in every conditions i.e. enough averaging to make sure that correct cell is selectedHowever careful testing is needed to check the performance of different areas• (Dense) Urban area, slow moving UEs with occasional need for fast and accurate (to correct cell) reselections e.g.
outdoor to indoor scenarios or city highways – in some cases cell by cell parameter tuning is performed to find most optimal value between 0s and 2s but typically 1s is optimal value when workload is considered as well
• Highways, fast moving UEs must reselect correct cell – typically 1s works the best (however occasionally also 0s might be needed in fast speed outdoor to indoor cell reselections e.g. tunnels)
• Rural areas, slow or fast moving UEs need very often reselect between different RATs and make proper cell reselections even when the coverage is poor – typically 1s works the best
• Location Area Borders, usually the coverage is fairly poor – typically 1s works the best but sometimes to reduce location area reselection ping pong 1s is used when going from LA1 to LA2 and 2s from LA2 to LA1
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Cell Reselection KPIs
RRC connection request amount for inter RAT cell reselection ratio to all RRC Connection request causes
• When hysteresis is increased this KPI should decrease
RRC connection request amount for registrations ratio to all RRC Connection request causes
• When hysteresis is increased this KPI should decrease
TP_ATTRRC_CONN_SM1001C0
_ATTSELL_RE_SELINTR_RAT_C M1001C42
TP_ATTRRC_CONN_SM1001C0
ON_ATTSREGISTRATI M1001C46