optimizing uplink noise

For internal use only1 © Nokia Siemens Networks Presentation / Author / Date

Simon Browne

April 2011

Optimizing Uplink Noise


Problem description

• Many networks are currently suffering from performance issues resulting from high uplink loading/power spiking

• This leads to uplink AC failures (RRC, RAB, PS user plane..) and call drops

• WCDMA UL is not orthogonal i.e. the UE transmission interferes the other UEs causing a snowball effect and high uplink rise

• PrxTargets were generally increased but tighter control is now needed to prevent excessive cell shrinkage

For internal use only3 © Nokia Siemens Networks

Example Noise Profiles

• Short duration spikes can be seen in addition to more general, longer-term, noise rises.

6 sec

5 sec

6 sec

NR = 5-6 dBNR = 1-2 dB

14 sec

1-2 sec

Spikes on high loaded cellSpikes on low/medium loaded cell

1-2 sec


Power spiking source categorization

• Network allocates too much traffic in the cell– Non-optimal network parameterization– SW bugs

• Network configuration– Missing neighbors cause high interference as the UE is not power controlled by

the best cell– Antenna/feeder issues can cause interference and coverage holes in the

network affecting traffic distribution

• Network signaling load– Delayed handover has a similar effect as a missing neighbour

• UE behaviour– UE using only partially the capacity allocated to it and suddenly starts

transmitting with full rate– UE continues power ramp-up on RACH w/o noticing AICH– UE acknowledging RRC Connection Setup erroneously

Fast dormancy highlights this as RRC Connection Setup happens more often


RNC SW enhancements for UL admission control (1/2)

• The following are covered in Technical Note TN159 available from NOLS.

• Power estimation improvements– Better power estimator adaption to the reported RTWP

– Power estimator scaling fixes

– Inter cell interference accommodation within one BTS

– System noise update improvements

– Power based Admission Control for the HSUPA call setups

• Overload control improvements for faster spiking elimination– Candidate prioritization and bit rate selection in PBS

– Prioritization of high R99 bit rate users for overload control

– Preferring TFC method for limiting bit rate during high noise


RNC SW enhancements for UL admission control (2/2)• Radio link handling improvements

– HSUPA maximum SIR target decrease – Limited value of UL DPCCH power offset for the first RL setup during high noise

– Faulty RRC Connection Setup Request filtering– Additional state transfer command before RL release in case of RLC error

• Mobility handling improvements– Downgrading the PS NRT DCH for the soft handover branch addition

congestion handling– PRFILE parameter control for triggering the channel type switching from the

SIR error

• Counter corrections– Cell resource counter fixes


Parameter Recommendations

TN159 provides many parameter recommendations to better control uplink load.

L

ΔL

ΔPrx_nc

Prx_nc

Load factorL

ΔL

ΔPrx_nc

Prx_nc

Load factorCurrent load L and current received Non-Controllable power Prx_nc are measured

Parameter recommendations are focused on the key areas:

•Load reduction (RACH, Initial SIRs, retransmission timers…)

•Control over the load curve, right. Optimum AC operation requires the system to have a clear view of the location of the load on the curve, i.e. accurate estimation of Prx_nc –> the non-controllable load.

•Load control – PrxTargets..


Decrease of the UL load by decrease of the RACH power

• Lower RACH message power

• Faster preamble power ramp-up Less preambles

• Higher minimum waiting time for RACH transmission

• Higher AICH power

Example of frequency analysis of spikes caused by P-RACH preamble caught by a spectrum analyzer. The narrow spikes caused by the preamble are clearly visible.

Object Parameter Default Recommended

WCEL PowerOffsetLastPreamblePRACHMessage 2 dB -3 dB

WCEL PowerRampStepPRACHPreamble 2 dB 3 dB

WCEL RACH_Tx_Max 8 4

WCEL RACH_Tx_NB01min 0 20 - 30

WCEL PtxAICH -8 dB -3 dB


Minimum and initial bit rate parameterization

RNC-HSDPAinitialBitrateUL; Default value: 64 kbps

RNC- HSDPAminAllowedBitrateUL; Default value: 64 kbps

• Initial and minimum bit rate values are subjects for radio network planning. Lower values allow naturally more capacity but throughput of certain user is then more limited. Lower parameter values improve call setup success rate.

• Enhanced Priority Based Scheduling RN40_MAINT_028 (allocated bit rate is lowered in case of congestion) shall be enabled by setting the Bit1 (BTS and TRS congestion) and Bit2 (power congestion).

• These two parameters will be cell-based objects in RU30.

Presentation / Author / Date

1-antenna cells 2- or 4-antenna cells Mass eventsNSN recommended parameter value

64 kbps 64 kbps 16 kbps


16 kbps 16 kbps 16 kbps


Initial SIR target parameterization – O2 UK Trial

The WRAB changes are highlighted below. Reduced SIR targets are implemented for DPCCH for HS return channels together with the general setting for DPDCH.

The Phase 5 configuration was that selected as the most appropriate for rollout and included the Phase 3 SIR settings with RRMULDCHActivityFactor setting of 50% for PS NRT bearers, increased from 35%.

Parameter Default Phase 1 Phase 2 Phase 3 Phase 4 Phase 5UL SIR target with HS-DPCCH - DPDCH SF 4 12.0 9.0 9.5 10.0 11.0 10.0UL SIR target with HS-DPCCH - DPDCH SF 8 11.0 8.0 8.5 9.0 10.0 9.0UL SIR target with HS-DPCCH - DPDCH SF 16 10.5 7.5 8.0 8.5 9.5 8.5UL SIR target with HS-DPCCH - DPDCH SF 32 9.0 6.0 6.5 7.0 8.0 7.0UL SIR target with HS-DPCCH - DPDCH SF 64 7.5 4.5 5.0 5.5 6.5 5.5UL SIR target with HS-DPCCH - DPDCH SF 128 7.5 4.5 5.0 5.5 6.5 5.5UL SIR target with HS-DPCCH - DPDCH SF 256 7.5 4.5 5.0 5.5 6.5 5.5SIR target for UL outerloop power control with DPDCH 0.0 -2.0 -2.0 -2.0 -2.0 -2.0

TN159


Initial SIR Setting: HSDPA Return Channel

The SIR target for the DPCCH influences HS-DPCCH and DPDCH power by means of the relative power setting of these to the DPCCH. The Initial SIR target for DPCCH is calculated as follows.

The uplink outer loop controller of the RNC is configured by the initial uplink SIR target value in [dB]:

targetSIRDPCCH = targetSIRRx + offsetSIRNRx + offsetDCH

targetSIRRx = SIRDPCCHInitialDCHHSsf + SIRDPCCHInitialDCHRxDiv2 (assuming 2-way diversity, default value = -3dB)

SIRDPCCHInitialDCHHSsf is given by the parameter associated with the return channel minimum spreading factor, e.g. SIRDPCCHInitialDCHHS16.

offsetSIRNRx is given by: 0 dB if RxDivIndicator = 1 antenna3 dB if RxDivIndicator = 2 antennas6 dB if RxDivIndicator = 4 antennas

offsetDCH = SIRDPCCHInitialDCHOffset if E-DCH is not configured. Note that this parameter is also used in an equivalent calculation of initial SIR for all non-E-DCH DPDCH links, including AMR and SRB setup. E-DCH initial SIR targets are hard-coded.


Average RTWP Class

0

1

2

3

4

5

6

7

2011

0124

00

2011

0125

14

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0128

00

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0129

14

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0131

04

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0201

18

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0203

08

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0204

22

2011

0206

12

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0208

03

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0209

17

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0211

07

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0212

21

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0214

11

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0216

01

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0217

15

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0219

05

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0220

20

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0222

10

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0224

00

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0225

14

2011

0227

04

RTWP Results

The below shows the hourly average RTWP class across the RNC. A reduction of ~1.3 in class is seen comparing the first two trial phase results with the pre-trial values and ~1 in phase 3.

This translates to an average noise rise reduction of at least the same amount in dB (the low RTWP classes spanning a 1dB range, but the higher classes spanning wider ranges).

Some increases in RTWP occurred in late Phase 3 and early Phase 4, however the levels have settled down since, indicating local site issues were likely to have been the cause.

Phase 1 Phase 2 Phase 3 Phase 4 Phase 5


RTWP Hourly Distribution

The RNC-level distribution across the different RTWP classes in PDF format is below.

The curves represent the distribution for the busy hours of 1200 and 1300 on Jan 25 th (Pre), 27th (P1) , Feb 1st (P2), Feb 8th (P3), Feb 16th (P4) and Feb 23rd (P5). The shift in classes is very clear with an increase in classes 0-7 ( <=-101dBm) and a reduction in classes 8 and above (> -101dBm). Results from P1 and P2 are indistinguishable,P3 shows a very small increase and with P4 the results are seen to increase more strongly in the direction of the pre-trial results. P5 shows very low values which is in part influenced by the school holiday traffic reduction.

The ‘knee’ at class 11 is a result of this range spanning 3dB rather than 1dB with all the lower classes.

RTWP PDF - Hourly

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

RT

WP

_C

LA

SS

_0

RT

WP

_C

LA

SS

_1

RT

WP

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LA

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_2

RT

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LA

SS

_3

RT

WP

_C

LA

SS

_4

RT

WP

_C

LA

SS

_5

RT

WP

_C

LA

SS

_6

RT

WP

_C

LA

SS

_7

RT

WP

_C

LA

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_8

RT

WP

_C

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_9

RT

WP

_C

LA

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_1

0

RT

WP

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_1

1

RT

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_1

2

RT

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3

RT

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RT

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_1

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RT

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6

RT

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7

RT

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8

RT

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_1

9

RT

WP

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LA

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_2

0

RT

WP

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LA

SS

_2

1

2011012512

2011012513

2011012712

2011012713

2011020112

2011020113

2011020812

2011020813

2011020912

2011020913

2011021612

2011021613

2011022312

2011022313


HSDPA Active Throughput (kb/s)

1,200

1,300

1,400

1,500

1,600

1,700

1,800

1,900

17/0

1/20

1118

/01/

2011

19/0

1/20

1120

/01/

2011

21/0

1/20

1122

/01/

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23/0

1/20

1124

/01/

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25/0

1/20

1126

/01/

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27/0

1/20

1128

/01/

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29/0

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1130

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31/0

1/20

1101

/02/

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02/0

2/20

1103

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04/0

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1105

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06/0

2/20

1107

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2011

08/0

2/20

1109

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10/0

2/20

1111

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2/20

1113

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2011

14/0

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1115

/02/

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16/0

2/20

1117

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18/0

2/20

1119

/02/

2011

20/0

2/20

1121

/02/

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22/0

2/20

1123

/02/

2011

24/0

2/20

1125

/02/

2011

26/0

2/20

1127

/02/

2011

CQI Decoding Failure Rate

8.0%

8.5%

9.0%

9.5%

10.0%

10.5%

17/0

1/20

1118

/01/

2011

19/0

1/20

1120

/01/

2011

21/0

1/20

1122

/01/

2011

23/0

1/20

1124

/01/

2011

25/0

1/20

1126

/01/

2011

27/0

1/20

1128

/01/

2011

29/0

1/20

1130

/01/

2011

31/0

1/20

1101

/02/

2011

02/0

2/20

1103

/02/

2011

04/0

2/20

1105

/02/

2011

06/0

2/20

1107

/02/

2011

08/0

2/20

1109

/02/

2011

10/0

2/20

1111

/02/

2011

12/0

2/20

1113

/02/

2011

14/0

2/20

1115

/02/

2011

16/0

2/20

1117

/02/

2011

18/0

2/20

1119

/02/

2011

20/0

2/20

1121

/02/

2011

22/0

2/20

1123

/02/

2011

24/0

2/20

1125

/02/

2011

26/0

2/20

1127

/02/

2011

HSDPA Performance

The CQI decoding failure rate has apparently increased by ~0.4% (absolute) with phases 1 and 2, however the increase is reduced with phase 3. With phase 4 the level has returned to pre-trial values.

In phases 1 and 2, the HSDPA active user throughput has shown a very small reduction (~2%), probably resulting from the smaller power in the ACK/NACK messaging. In phases 3, 4 and 5 the results show values similar to the pre-trial levels.

P1 P2 P1 P2P3 P3P4 P4P5 P5


Parameterization for wait time in RRC Connection Reject RNC- WaitTimeRRCconversational; Default value: 3 s

RNC- WaitTimeRRCstreaming; Default value: 3 s

RNC- WaitTimeRRCinteractive; Default value: 5 s

RNC- WaitTimeRRCbackground; Default value: 5 s

RNC- WaitTimeRRCsubscribed; Default value: 3 s

RNC- WaitTimeRRCemergency; Default value: 1 s

RNC- WaitTimeRRCinterRATreselection; Default value: 3 s



4 s 4 s 4 s


4 s 4 s 4 s


8 s 8 s 8 s


8 s 8 s 8 s


4 s 4 s 8 s


1 s 1 s 1 s


4 s 4 s 8 s


Parameterization for wait time in RRC Connection Reject RNC- WaitTimeRRCregistration; Default value: 1 s

RNC- WaitTimeRRChighPrioritySignalling; Default value: 1 s

RNC- WaitTimeRRClowPrioritySignalling; Default value: 5 s

RNC- WaitTimeRRCunknown; Default value: 1 s

RNC- WaitTimeRRCother; Default value: 0 s

• Above mentioned parameter value changes increase call setup success rate. Longer wait time in RRC connections setup for various types of RRC connection requests decreases rush in the RACH.

• Defines the value of the Wait Time included in the RRC: RRC Connection Reject message, when the Establishment Cause value received originally in the RRC is one of the following: Originating Conversational Call, Terminating Conversational Call, Originating Streaming Call, Terminating Streaming Call, Originating Interactive Call, Terminating Interactive Call, Originating Background Call, Terminating Background Call, Originating Subscribed Traffic Call, Emergency Call, Inter-RAT cell re-selection, Inter-RAT cell change order, Registration, Detach, Originating high priority signalling, Terminating high priority signalling, Originating low priority signalling, Terminating low priority signalling, Terminating - cause unknown, Call re-establishment



4 s 4 s 8 s


4 s 4 s 8 s


8 s 8 s 8 s


4 s 4 s 8 s


4 s 4 s 8 s


PRX Noise autotuning parameterization

RNC-PrxNoiseMaxTuneAbsolute; Default value: 255

• Wrong Prx Noise level causes error to estimated power in PIE (Power Increase Estimation) and PDE (Power Decrease Estimation) algorithms. Erroneous estimation results in turn causes power spiking in the uplink spectrum.

• Recommended parameter value is 2 dB. Value 2 dB allows 4 dB range in Prx Noise autotuning functionality. In this case PrxNoise should have default value -105 dBm. It is important to verify that prxnoise in the unloaded cell is close to -105 dBm. If that is not the case the cell needs further investigation.

• Value 0 switches Prx Noise autotuning functionality off. Parameter PrxNoise defines then directly Prx Noise level.



2 dB 2 dB 2 dB


PRX Noise autotuning parameterization

• Values 0-2 dB may require adjustment of parameters PrxTarget, PrxTargetPSMin, PrxTargetPSMax. Furthermore it is very important that PrxLoadmarginDCH>0, see chapter 5.5. When recommended parameter value is used autotuning of PrxNoise does not provide capacity increase in the cell anymore. Capacity increase occurred when PrxNoise autotuning tuned PrxNoise to higher value and because PrxTarget is relational to PrxNoise also absolute target load threshold increased.

• If capacity increase is wanted, then values of the above mentioned parameters must be increased. That can however cause power spiking and shrinking of cell coverage.

• If call setup success rate decreases when parameter values 0…2 dB is used, then values of the above mentioned parameters may need to be increased.


For internal use only19 © Nokia Siemens Networks /

UL Accessibility: Reduction of the activity factor for HSDPA return channel and efficient UL PS

UL activity factor on the HSDPA return channel is typically far below the 95% used in NSN default configuration. They were reduced to 50%, following PL recommendation, in order allow for the DPCCH overhead.

Allocated channel usage

49.3 %

4.6 %6.4 %

0.0 %

10.0 %

20.0 %

30.0 %

40.0 %

50.0 %

60.0 %

Activity - Speech Activity - NRT_PS Activity - NRT_PS_HS

Act

ivit

y %

Series1

The lower activity factor values are used by AC and PS and reduce rejection rates in cells where the actual traffic is low but Prx is high. Therefore an improvement of HSPA accessibility is expected.

Object Parameter Default Recommended

WBTS RRMULDCHActivityFactorCSAMR 50 % 50 %

WBTS RRMULDCHActivityFactorPSBackgr 95 % 50 %

WBTS RRMULDCHActivityFactorPSStream 95 % 50 %

WBTS RRMULDCHActivityFactorPSTHP1 95 % 50 %



WCEL PrxLoadMarginDCH 2 dB 2 dB … 5.8 dB

WCEL DeltaPrxMaxdown 0.8 dB 2 dB

WBTS RRIndPeriod 400 ms 200ms

WBTS PrxMeasAveWindow 10 Frames 20 Frames


Activity factor parametrization

WBTS- RRMULDCHActivityFactorCSAMR; Default value: 95 %WBTS- RRMULDCHActivityFactorPSBackgr; Default value: 95 %WBTS- RRMULDCHActivityFactorPSStream; Default value: 95 %WBTS- RRMULDCHActivityFactorPSTHP1; Default value: 95 %WBTS- RRMULDCHActivityFactorPSTHP2; Default value: 95 %WBTS- RRMULDCHActivityFactorPSTHP3; Default value: 95 %

• Activity factor is used in load evaluation of a certain service when AC decision is made. Parameter values are used in both power and throughput based load evaluation. Lower value provides lower estimated load value and thus allows more allocations. Activity factor 50% describes better the actual utilisation of the UL DCH as the return channel for HSDPA.

• The accuracy of the value used is dependent on the bit-rate influencing features deployed, such as TBO (Throughput based optimization), TBT (Transport bearer tuning) and FU (Flexible upgrade). Without these features, lower activity factors will be found than in networks with these enabled. 50% has been found appropriate in some networks but that it should be adapted locally to the network configuration.

• Recommended value may improve call setup success rate.



50 % 50 % 50 %


Admission Control and Packet Scheduling control parameterizationWCEL- DeltaPrxMaxUp

Default value: 1.2 dB

• This parameter defines the maximum received uplink power increase in a cell, used when bit rates are allocated or increased by the packet scheduler. PrxTotal shall be used as reference (007:0283 RN40_MAINT_013, Bit13=0). Lower values may limit the DCH bit rates so that the share of the utilized DCH bit rates shift to the lower bit rates.



1.2 dB 1.2 dB 1.2 dB


Admission Control and Packet Scheduling control parameterizationWCEL- DeltaPrxMaxdown

Default value: 0.8 dB

• This parameter defines the maximum received uplink power decrease in a cell, used when bit rates are decreased by the packet scheduler. Parameter value 2 dB correlates better with fast decrease of the interference.



2 dB 2 dB 2 dB


Admission Control and Packet Scheduling control parameterizationWBTS- SchedulingPeriod

Default value: 100 ms

• This parameter defines the period of the resource allocation for the resource requests of the PS interactive and background services. Default value 100ms improves the accuracy of packet scheduling and admission control decisions compared to 200ms setting.



100 ms 100 ms 100 ms


Admission Control and Packet Scheduling control parameterizationWCEL- OCULNRTDCHGrantedMinAllocT

Default value: 10 s

• This parameter defines the limit time for the NRT DCH allocation after which the DCH is allowed to be downgraded by reconfiguring it in the overload of the UL NRT DCH resources when an E-DCH MAC-d flow is established in the cell. Higher value increases probability that transport format combination control (TFCC) procedure is used first instead of RL reconfiguration. TFCC is faster and more reliable in high load conditions.



20 s 20 s 20 s


Traffic volume measurement parameterization

RNC- TrafVolPendingTimeUL

Default value: 2 s

• This parameter indicates the time (in seconds) during which UE is forbidden to send any new traffic volume measurement reports with the same traffic volume event identity, even if the triggering condition is fulfilled again. Recommended parameter value decreases amount of uplink capacity requests.



4 s 4 s 8 s


Admission Control and Packet Scheduling control parameterizationWCEL- PrxLoadMarginDCH

Default value: 2 dB

• This parameter defines guaranteed load level in the cell. Below this load threshold no power based admission decision is done. 2 dB corresponds to load factor 0.369. Higher value like 5.8 dB corresponds to load factor 0.737 and can be used in mass events to guarantee higher load without power based AC/PS evaluation. Higher parameter values increase RTWP spiking and may increase the call drops and setup failures due to radio reasons.

• With a value of 0 very high AC blocking can result in periods of high load leading to extended service degradation



2 dB 2 dB 2…5.8 dB


Uplink interference target parameterization

WCEL- PrxMaxTargetBTS; Default value: 6 dB

WCEL- PrxTarget; Default value: 4 dB WCEL- PrxTargetPSMin; Default value: 4 dB WCEL- PrxTargetPSMax; Default value: 4 dB

• Higher values than default 6 dB and 4 dB can be used. However, too high interference level in the cell shrinks its coverage. It is recommended to use equal values in PrxTarget, PrxTargetPSMin and PrxTargetPSMax (dynamic resource allocation should be based on downlink functionality only).

• The mass events should be run using throughput based RRM as RACH may cause heavy noise rise. See parameter PrxLoadMarginDCH.



8 dB 8 dB 8 dB


6 dB 6 dB 12 dB


HSUPA Considerations (1)

The HSUPA layer-1 (E-DPCCH) can contribute significant uplink load. On cells with high numbers of HSUPA users we can see very high noise rises.

By changing MaxTotalUplinkSymbolRate (3840/1920/960) we can influence the uplink rise.

The graph shows a current example from a cell with over 40 HSUPA users with noise rise plotted against the number of active users for the settings of 1920 and 3840 ksps. A reduction to 960ksps can be considered for special-event or hotspot situations.


HSUPA Considerations (2)

Forthcoming changes in RNC sw will help with the HSUPA high load case.

In RU20 MP3 -> Dynamic HSUPA Power Offset feature (basic sw, enabled with PRFILE)

This reduces the bit rate via the power offset when high load conditions are experienced.

In RU40 EP, Dynamic HSUPA BLER is introduced.


Summary

The recommendations in TN159 should be considered as a means of helping with uplink load problems.

The vast majority of the changes have been proven in the field, including the UL AC Task Force project at SFR.

The main focus so far has been R99 uplink, however the focus is likely to change to HSUPA as penetration of HSUPA-capable devices increases. The HSUPA L1 overhead is greater than the R99 overhead (16k bit rate) and so higher noise rises can be anticipated for the same number of active users.

optimizing uplink noise

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