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In Confidence O2 UK Radio Engineering UTRAN CPICH to RAB Power Offset Ref : UKRE/08/076 Trial Report Page : 1 of 9 UTRAN CPICH to RAB Power Offset Trial Report Summary It was recommended that increasing the power available in the Downlink (DL) at the cell edge may potentially increase the 3G MPD, as links are typically DL limited. The parameter responsible for the maximum power allocated in DL is called CPICHToRefRABOffset and it actually sets the offset (currently 0dB) between the CPICH power and the maximum power allocated per radio link. This trial, on the O2 UK network, has proved that by decreasing the offset between the CPICH and the maximum power per radio link, more power is allocated per UE in poor radio conditions. The parameter change did not cause any rise in the background interference levels, as the change did not affect the Ec/Io distribution. The statistics did not show any capacity impact (as additional 2dB allocated for a relatively small number of UEs is negligible at the RNC level) and higher values of the MPD were recorded during the course of the trial (maximum values of MPD in pre- and post-benchmarking weeks were 208 and 200. The maximum value of MPD during the course of the trial was 233). The CCSR was not evaluated due to an insufficient number of samples obtained from the drive tests). The modifications in PCrangeDL parameter was required to compensate change in dynamic range due to CPICHToRefRABOffset parameter change. Based on the above results a rollout of changes across the network is recommended. Author(s): Alexey Sutyagin Date: 7 October 2008 Version: Draft B Reference: UKRE/08/076 Approved by: Date: Version : Draft B Date : 07/10/08

CPICHToRefRABOffset

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Page 1: CPICHToRefRABOffset

In Confidence

O2 UK Radio EngineeringUTRAN CPICH to RAB Power Offset Ref : UKRE/08/076Trial Report Page : 1 of 9

UTRAN CPICH to RAB Power OffsetTrial Report

SummaryIt was recommended that increasing the power available in the Downlink (DL) at the cell edge may potentially increase the 3G MPD, as links are typically DL limited. The parameter responsible for the maximum power allocated in DL is called CPICHToRefRABOffset and it actually sets the offset (currently 0dB) between the CPICH power and the maximum power allocated per radio link. This trial, on the O2 UK network, has proved that by decreasing the offset between the CPICH and the maximum power per radio link, more power is allocated per UE in poor radio conditions. The parameter change did not cause any rise in the background interference levels, as the change did not affect the Ec/Io distribution. The statistics did not show any capacity impact (as additional 2dB allocated for a relatively small number of UEs is negligible at the RNC level) and higher values of the MPD were recorded during the course of the trial (maximum values of MPD in pre- and post-benchmarking weeks were 208 and 200. The maximum value of MPD during the course of the trial was 233). The CCSR was not evaluated due to an insufficient number of samples obtained from the drive tests).The modifications in PCrangeDL parameter was required to compensate change in dynamic range due to CPICHToRefRABOffset parameter change.Based on the above results a rollout of changes across the network is recommended.

Author(s): Alexey SutyaginDate: 7 October 2008Version: Draft BReference: UKRE/08/076Approved by:Date:

Version : Draft B Date : 07/10/08

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DISTRIBUTION LISTALALASUNDARAM Chelian (UK)Allen PaulAziz MohamedBenson DavidBocanu MirceaBremner Kevin (NSN)Brown Steve Button JohnChristopher Johnson (NSN) Clarkson Paul Conlan TonyCordingley Mark Coy Geoff Crisp PaulDenley ChrisDiaconu CatalinFormica GianlucaFraley DaveFreeman AlanGarelli MicheleGilbert MartinGilbert Martin Graham Danny Greaves Garry Hamendra Chand TikkaInglis MalcolmJames Will Kenni Rasmussen (NSN)

Larkin CliveMark Smith (NSN)Martin NuriaMcCrea BarryMcfarland Colin Miller IanMorris DavidMuthiah BalanNagarajan NarayanaO’Reilly BrendanOwens DavidOwens RichardPowney JimPrice CoreyRadhakrishna KrishnaswarmyRay ConradRoychowdhury PinakiSargeant Tony Sharples Adrian Smith TerryStephens WayneSuttie IanTaylor Peter TCQFThornton TerryTSG Radio Access-Dist (UK)White Bob

CHANGE HISTORY

Tool used Microsoft Word 97File locationCreate, save & print dates 07/10/2008 10:16:00 13/10/2008 08:08:00 AM 23/04/2002

10:45:00 AMVersion Date Changed by ChangesDraft A 05/10/08 Alexey Sutiagin Initial draftDraft B 07/10/08 Patryk Debicki After modifications from Patryk Debicki

Version : Draft B Date : 07/10/08

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TABLE OF CONTENTS

1. Scope and Objectives......................................................................................................................4

2. Introduction....................................................................................................................................4

3. Trial Description.............................................................................................................................4

4. Results..............................................................................................................................................4

4.1. Drive Test Results..................................................................................................................................44.2. Statistical Counters................................................................................................................................6

5. Conclusions and Recommendations.............................................................................................9

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1. Scope and Objectives

The objective of this document is to describe fully the results of a trial of RAB power offset settings in NSNa UTRAN. The scope of this document covers trial description, parameter and network changes, results and recommendations.

2. Introduction

Implementation of HSDPA and recent change in mobile data usage have impacted the DL power levels and increased DL interference. This has affected mobiles at the edge of the coverage as they become downlink limited due to lack of power in DL direction to compensate increase in noise level. It was demonstrated in 2006 trial that increasing the power available in DL at the cell edge may increase the call completion success rate.

The parameter responsible for the maximum power allocated in DL is called CPICHToRefRABOffset and it sets the offset between the CPICH power and the maximum power allocated per radio link. Following recommendations from trial conducted in 2006 was set to 0dB. It means that having the CPICH power set to 33dBm, the maximum power allocated per reference service (12.2 AMR) radio link is equal to 33dBm.

Another parameter, associated with the CPICHToRefRABOffset is PCrangeDL which set the span of the dynamic power range. The current network setting is 17dB, which sets the minimum power allowed per reference service to be 16dBm.

During the period of the trial the CPICHToRefRABOffset was modified from 0 to -2dB, PCrangeDL from 17dB to 19dB.

3. Trial Description

The trial took place in RNC78 and covered all cells within the RNC. The trial lasted for 3 weeks, commencing on the 8th September 2008. The trial covered the Glasgow area. A full breakdown of the trial dates and parameter settings are given in Table 1 below.

Table 1. Trialed parameters and dates details.

Phase Start /End Dates CPICHToRefRABOffset PCrangeDLBenchmark 8/09 - 14/09 2008 0dB 17dBTrial setting 1 15/09 - 21/09 2008 -2dB 19dBPost trial benchmark 22/09 - 28/09 2008 0dB 17dB

4. ResultsThe results of this trial are based on the drive tests (SIR Target and EcIo distributions) and network statistics (MPD, Average power per RL, Maximum transmitted power and relative duration of the 384kbps bearer). Call completion success rate was not evaluated as it would require a huge number of samples to generate statistically significant results.

4.1.Drive Test Results

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The SIR Target set by the outer loop power control (about every 200ms) has been used as an indication of the relative power assigned per radio link. Direct information of the actual transmitted power is not available as this is transmitted 1500 times a second and it would simply overflow the log file.

A UE sets the SIR Target, based on the target BLER, obtained from the RNC. If the calculated BLER is below the BLER target then SIR Target is increased. The SIR Target, in turn, feeds the inner loop power control. Whenever the actual SIR is below the SIR Target, the UE sends the power-up command; otherwise the power-down command is transmitted.

The charts in Figure 1 represent the SIR Target comparison between the benchmark and trial weeks. The change in the distribution is not very significant, but visible, especially at the high end of the SIR Target values where quality is poorer. It can be interpreted that the samples, collected during the calls, were reaching lower values of SIR Target. RNC monitors BLER, and if quality of transmission is too low, higher SIR target is sent to Node B. In case of too good transmission quality, lower SIR target is sent to Node B. Having more samples with lower SIR Target actually means that BLER target is achieved and overall link quality is increased.

Figure 1. Comparison of SIR Target CDFs; Comparison between the benchmark and the trial week;

Figure 2 illustrates the Ec/Io distribution measured during the drive tests in dedicated mode. It can be seen that the Ec/Io distribution is within the drive test accuracy for a two subsequent drive testing.

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Figure 2. Ec/Io distribution.

4.2.Statistical Counters

Figure 3 shows the MPD trend during the trial. The maximum values were achieved during trial week were the values ranged from 210MPD to 234MPD. The values in a pre-benchmarking week ranged from 181MPD to 226MPD and in post-benchmarking week from 177MPD to 200MPD. Thus the MPD gain during the trial is between 10 and 34 and about 20 on average.

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Figure 3. MPD during the trial period.

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Figure 4 represents drop call rate (DCR). There is noticeable improvement in DCR during trial week.

DCR

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Figure 4. DCR.

The parameter changes have very little impact on HSDPA availability and HSDPA downgrades. RNC doesn’t have many data hotspot sites, but HSDPA data volume is at average level, comparing to other RNCs.

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Figure 5. HSPDA accessibility remains constant during a trial and HSDPA released due to Power are slightly up.

The parameter changes have little impact on the capacity. This is due to the fact that the parameter change actually does not raise the power to all active connections but only to these that experience a poor radio quality and could benefit from the increased power.The percentage of such calls is relatively small and thus the averaged total transmitted power remains at the same level. Figure 6 illustrates the absolute DL transmitted power averaged over the trialled RNC.

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Figure 6. Absolute DL transmitted power per RL slightly increased during the trial.

The increase in InterRAT HHO per call rate is within the trend associated with the traffic growth. The traffic level during the trial week increases accordingly to the general traffic growth within the network (Figure 8).

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Figure 7. HHO per call rate. There is an increase in HHO per call during trial week.

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Figure 8. CS Traffic remains the same to pre-trial week, but increases in post trial week.

5. Conclusions and Recommendations

The trial showed a significant improvement in voice MPD without noticeable impact on capacity. The trial proved that by decreasing the offset between the CPICH and the maximum power per RL, more power is allocated per UE in poor radio conditions, thus improving the calls probability of success (the quantification of improvement was not possible due to insufficient number test calls to provide the statistically valid CCSR). This fact was reflected in the improved MPD.Based on the above results it is recommended to run an extended FOA on busy London RNCs before the rollout across the whole network.

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Version : Draft B Date : 07/10/08