48400260 amr half rate feature enhancements overview

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AMR Half Rate featureenhancement trial guideline


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Internal AMR Half Rate feature enhancement trial guideline 3(17)

Document HistoryDocument type: Trial GuidelineCreator: Pradeep ChattikalReviewer: Harry Kuosa

Approver: Prashant Agnihotri

Version Date Version history1.0 30.10.2009 Approved

Sales Item Feature Feature ID ReleaseBSC00136 AMR Robust signalling

(FACCH/SACCH) BSS20872 BSS13

BSC00112 Progressive AMR power control BSS20776 BSS13

2003497 AMR Unpacking Optimization BSS21120 RG10


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Table of Contents

TUDocument History UT ..................................................................................................................3 TU1 UT TUPurpose of the Trial Guideline document UT .....................................................................5

TU2 UT TUWhy Successful Customer Trials are needed? UT ............................................................5

TU3 UT TUExecutive Summary UT ........................................................................................................5

TU4 UT TUSimulation, Field results & Typical achievable gains UT ..................................................6

TU4.1 UT TU AMR Robust signall ing (FACCH/SACCH) UT........................................................................................... 6 TU4.2 UT TUProgressive AMR Power Control UT......................................................................................................... 7

TU4.3 UT TU AMR Unpacking Optimizat ion UT.............................................................................................................. 8

TU5 UT TUQuick Trial Startup Guide UT...............................................................................................9

TU5.1 UT TURecommended AMR sub features deployment steps UT....................................................................... 9 TU5.2 UT TUCriterias t o select the Right Trial Cluster UT ......................................................................................... 10

TU5.2.1 UT TUCluster selection to demonstrate AMR Unpacking Optimisation: UT.......................................................... 10 TU5.2.2 UT TUCluster selection to demonstrate AMR Robust signalling: UT......................................................... ............ 11 TU5.2.3 UT TUCluster selection to demonstrate Progressive AMR Power Control: UT ..................................................... 12

TU5.3 UT TUDefault parameters need Network specific optimization UT................................................................ 13 TU5.4 UT TURecommended KPIs: UT ......................................................................................................................... 14 TU5.5 UT TUSteps to Demonstrate Gains UT.............................................................................................................. 15 TU5.6 UT TUPre-requisites & Interworking for these features/functionality UT...................................................... 16

TU6 UT TUReferences UT.....................................................................................................................17

TU6.1 UT TUWhy NSN solution and mobile device support UT ................................................................................ 17 TU6.2 UT TU Abbreviations: UT ..................................................................................................................................... 17


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1 Purpose of the Trial Guideline document

This document is an internal trial guideline. Objective is to provide customer teamsguidance on how to prove our messages on feature gains with successful customertrials.

2 Why Successful Customer Trials are needed?

The primary objectives of a successful trial is to get

1) Public Press Release2) Public Customer References3) Customer Testimonials

4) Commercial contract for sales, market share and profitability

3 Execut ive Summary

Traditionally AMR has been proposed as one of the major steps towards improvingSpectral Efficiency due to increased robustness of AMR codecs.However operator feedbacks have been somewhat negative with increased droppedcall rate, especially post implementation of AMR Half rate.

With the introduction of AMR codecs, AMR users perceive improved voice quality

thereby transmitting lesser power. However introducing AMR Half rate also increasessignalling due to large number of Intracell handovers in the network.

The associated SACCH & FACCH channels used for signalling are not as robust as the AMR voice codecs. This weak link leads to the increased dropped calls rate seen with AMR deployment.

However starting BSS13 many improvements have been introduced that help improvesthe retainability of AMR calls and thereby fully utilize the benefits of robust codecs,leading to Improved Spectral efficiency.

The benefits of these features are seen primarily in interfered or low coverage patches

in networks. Hence this document tries to narrow down the scenarios under which thesefeatures can be successfully demonstrated to customer. The objective is also to clarifythat some of these benefits will be visible network wide only with increase in traffic.

This document covers the benefits of these AMR enhancement features1) AMR Robust signalling2) Progressive AMR power control3) AMR Unpacking Optimization


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FACCH REPETITION & POWER OFFSET - DCR BEST CASE

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REDUCTION OF 20% ON DCR @ 12 % EFL

INCREASE OF 18% ON CAPACITY @ 1% DCR

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INCREASE OF 18% ON CAPACITY @ 1% DCR

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4 Simulation, Field result s & Typical achievable gains 4.1 AMR Robus t signall ing (FACCH/SACCH)

USimulation results U:

Fig.1: Simulations resultsindicate Dropped Call rateImprovement of around20% by implementingRobust AMR signalling.

UField Results:

Fig.2: Field results indicatedropped call rateimprovements in 10% to20%.

The results in this field trialindicates a dropped callrate improvement of 19%at BSC level

UTypical Gains achieved with this feature U:

Based on field results typically achieved gain of 10%-15% can be committed ininterfered clusters. Please note the improvements in dropped call rate aregenerally influenced by the contribution of handover related drops in the overalldropped call rate.

Higher the % of Handover related drops higher the possibility of improvementswith AMR Robust signalling


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4.2 Progressive AMR Power ControlU

Simulation Results:Fig.3: Simulationsresults have shownDropped Call RateImprovement of up to50% with AMR PPC

UField Results:

Fig.4: The above field result indicates the improvement in % of cells that meetthe 2% Dropped Call Rate threshold. Significant improvement of 20% seen atBSC level

UTypical Gains achieved with this feature:

Based on field results typically achieved gain of 15%-20% can be committed inhighly interfered clusters. Please note the improvements in dropped call rateare heavily by influenced by the current power control settings. An aggressivepower control setting before AMR PPC implementation can lead to minimized

gains


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4.3 AMR Unpacking OptimizationUSimulation Results:

Fig.5: Simulationresults indicatean improvementof around 25%at high trafficload (@ 12%EFL)

UField Results:

Fig.6: Field results indicate 30-40% in improvement in Intracell handoverrelated drops, thereby contributing to 15% to 20% of overall Drop Call Rate %.

UTypical Gains achieved with this feature:

Based on field results typically achieved Dropped Call Rate improvement of15% can be committed in networks with large % of AMR-HR traffic and asignificant % of bad quality.


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5 Quick Trial Startup Guide

5.1 Recommended AMR sub features deployment steps

Fig.7:AMR deployment steps

AMR Half Rate introduces additional intracell handovers due to packing &unpacking of AMR-FR and AMR-HR calls respectively. These additionalintracell handovers introduce possibilities of increased drop calls especiallyunder bad radio conditions. To minimize these drops its highly recommendedto deploy AMR Unpacking Optimisation along with AMR HR.

Also while deploying AMR, its advisable to deploy AMR Full Rate across entireBSC, instead of AMR deployment at cluster level. AMR deployment at site orcluster level can improve link level performance for users, however systemlevel improvements are only achieved with larger deployments of AMR whereimproved quality, reduced power and impacts overall Network level quality andretainability KPIs .

Cluster level AMR deployment also leads to unnecessary A interface poolswitchovers especially in cases where transcoders need separate pools to bedefined for AMR & EFR

FR, HR, EFR

AMR Full Rate

AMR Unpacking Optimisation

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d e p l o

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AMR Robust Signalling

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AMR Robust Signalling

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5.2 Criterias to select the Right Trial Cluster

5.2.1 Cluster selection to demonstrateU AMR Unpacking Optimisation: U

A cluster with 1) High % of Half Rate traffic 2) Intracell Handover drop countsmore than Intercell drops.

With the introduction of AMR, packing & unpacking handovers( i.e. intracellhandovers) normally outnumber the number of normal intercell handoverstriggered in cells. Unpacking attempts due to low quality on AMR-HR callshappen more often than packing attempts (AMR-FR to AMR-HR). Packing istriggered based on 1) Cell load, 2) Quality of ongoing calls meeting apredefined threshold and 3) An even more stringent criteria for calls to be onthe Least Robust codec.

There are multiple thresholds to be met for AMR packing. However Uunpacking U can be triggered much easily due to low Quality or Rxlevel triggers

Example below indicates a case where the numbers of Intracell handoverrelated drops exceed even intercell handover related drops. A majority of thesetend to be due to unpacking attempts that lead to dropped calls because ofeither low signal strength or quality.

AMR unpacking optimization feature introduces new thresholds to preventunpacking attempts that can lead tog potential call drops.

Fig.8: HighIntracell drops

Fig.9: High AMRHalf Rate traffic

High Half RateTraffic

High Intracelldrops in busyhours


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5.2.2 Cluster selection to demonstrate U AMR Robust signalling: U

For Robust AMR to be demonstrated successfully identify a cluster with highinterference or low coverage.

If a large % of the RxQuality samples are of good (RxQual0-5) e.g. 97 to 98%in busy hour avoid demonstrating this feature in such clusters.

Rel 6 , repeated ACCH capable handsets can soft combine corrupted andrepeated messages to improve the decoding capability of signalling messagessent on the FACCH channel.

For Rel-5 or earlier handsets the transmit power used on the FACCH signallingchannel is increased by a few dBs vs. the power levels used by the associated

traffic channel.Its recommended to demonstrate the benefits in an interfered cluster.However if the feature needs to be demonstrated to an operator with largebandwidth then a suitable weak coverage patch should be identified (seesnapshot of measurement samples below)

Radio interface drops occur primarily due to 2 reasons:

1) Radio Link timeouts (drops due to severe degradation of ongoing callquality enough to force either MS or BTS to release the affected channel)

2) Handover Related drops associated to timeouts of related BSS timers

For Rel-5 or earlier handsets (which forms majority of the existing handsets)improvements can be seen primarily due to Handover related dropsimprovements.

For Rel-6 handsets even drops due to Radio Link Timeout can be improved (inaddition to handover related drops). However please ensure that the existingRLT & ARLT values are not set to unrealistic values e.g. >40. In such casesalmost no features can help reduce instances of Radio Link timeout relateddrops.

Identify areas with high handover related drops or alternatively use signalstrength profile reports from Celldoctor reports 204 to identify highly interferedor low coverage areas.

Fig.10: Rxlevel VsRxQuality profile


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5.2.3 Cluster selection to demonstrate UProgressive AMR Power Control U:

The maximum performance gains from AMR PPC can be seen in highlyinterfered clusters. The feature can help reduce the % of users radiating almostat peak power levels thereby minimizing overall interference levels

.E.g.: MS transmitting at 30 or 33dBm.

Please note that the cluster should not be coverage limited. AMR PPC cannothelp users radiate at lesser power if degrading coverage is the main reason.

Fig.11: MS/BTS transmitted power levels

More the samples in the maximum power range (or 0dB attenuation from

Maximum power) in a bad quality patch better the possibility to demonstrateimprovements/gains with this feature.


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5.3 Default parameters need Network specif ic opt imization

The right cluster selection is very important for the successful demonstration ofthe feature gains. Equally important is the optimal setting of the parameters of

the feature being trialled.

Some of these features have only few parameters whereas some others havemany parameters. Its important to analyze the existing power control andhandover parameters to decide on the optimal parameter set for the newfeature

U1)AMR Unpacking optimization (RxQual Vs Unpacking & Intercell handoverthreshold)

Without AMR unpacking optimization all AMR HR calls that experience bad callquality can unpack below the Unpacking Quality threshold.

E.g. If Unpacking (Intracell HO) threshold is 4 and Quality threshold for Intercellhandover is 6

All AMR-HR calls that experience call quality of


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5.5 Steps to Demonstrate Gains

The way calls are prioritized/ allocated to either BCCH (TRP=1) or non-BCCH(TRP=2) also impacts the level of interference seen in the network.

BCCH layer is planned with a reuse of atleast 12, hence quality on this layertend to be better Vs the non-BCCH TRXs which are often planned with reuseof 6 or lesser. Also BCCH TRXs radiate at full power on all TSs irrespective ofwhether a call occupies a TS or not.

Irrespective of the number of calls carried by the BCCH the level ofinterference generated is the same, be it 1 call or be it 8 calls (e.g. with Dualrate enabled & 4TS occupied for signalling & data, remaining 8 TSs can carryup to 8Erlangs). Result, performance on BCCH is usually flat with increasingload/ EFL.

Fig12:Performance onBCCH layer

If calls are alreadyprioritized toBCCH TRX in trialcluster ~8 Erl canbe carried byBCCH TRX afterwhich traffic spillsover to the non-

BCCH TRXs

Fig13:Performance onHopping layer

However unlikethe BCCH TRXsthe interference onthe non-BCCH/hoppinglayer increaseslinearly with trafficon this layer andso does theperformance.

Hence its highly recommended to change prioritization of calls to non-BCCHlayer (by setting TRP=2) to 1) simulate increased interference 2) Recreate afuture scenario with increased traffic.


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6 References

6.1 Why NSN solu tion and mobi le device support1) AMR Robust signalling (FACCH/SACCH) is a 3GPP Rel-6 specification toimprove AMR signalling performance, specifically retainability that helps deliverthe Spectral Efficiency benefits of AMR. All vendors support these features.

However legacy handsets,ie Rel5 or earlier handsets do not benefit much fromthese enhancements.

To improve the retainability for legacy handsets NSN has implemented aproprietary enhancement called FACCH Power Boost to boost power ofFACCH signalling bursts only by a few dBs vs. the corresponding voice codecrequirements.

2) AMR Progressive Power Control is another NSN unique feature.

Progressive power control provokes AMR adaptation to use codec ratesprogressively along power control range

Better interaction between AMR adaptation and power control by favouringincrease of power over AMR adaptation with low power levels and avoidincrease of power and favouring AMR adaptation with higher power levels andthus reduce overall interference

6.2 Abbreviations:

AMR Adaptive Multi Rate

FACCH Fast Associated Control Channel

SACCH Slow Associated Control Channel

EFL Effective Frequency Load

HR Half Rate

FR Full Rate

EFR Enhanced Full Rate

ACCH Associated Control Channel

DTX Discontinuous Transmission

TRP Transreceiver Priority

48400260 amr half rate feature enhancements overview

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