amr half raamr-half-rate-feature-enhancementste feature enhancements overview

AMR Half Rate feature enhancement trial guideline

Internal AMR Half Rate feature enhancement trial guideline 2(17)

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Document History Document type: Trial Guideline Creator: Pradeep Chattikal Reviewer: Harry Kuosa Approver: Prashant Agnihotri Version Date Version history 1.0 30.10.2009 Approved

Sales Item Feature Feature ID Release BSC00136 AMR Robust signalling

(FACCH/SACCH) BSS20872 BSS13

BSC00112 Progressive AMR power control BSS20776 BSS13 2003497 AMR Unpacking Optimization BSS21120 RG10


Table of Contents

TUDocument HistoryUT ..................................................................................................................3

TU1UT TUPurpose of the Trial Guideline documentUT .....................................................................5

TU2UT TUWhy Successful Customer Trials are needed?UT ............................................................5

TU3UT TUExecutive SummaryUT ........................................................................................................5

TU4UT TUSimulation, Field results & Typical achievable gainsUT ..................................................6 TU4.1 UT TUAMR Robust signalling (FACCH/SACCH)UT........................................................................................... 6 TU4.2 UT TUProgressive AMR Power ControlUT......................................................................................................... 7 TU4.3 UT TUAMR Unpacking OptimizationUT.............................................................................................................. 8

TU5UT TUQuick Trial Startup GuideUT ...............................................................................................9 TU5.1 UT TURecommended AMR sub features deployment steps UT....................................................................... 9 TU5.2 UT TUCriterias to select the Right Trial Cluster UT ......................................................................................... 10

TU5.2.1UT TUCluster selection to demonstrate AMR Unpacking Optimisation:UT .......................................................... 10 TU5.2.2UT TUCluster selection to demonstrate AMR Robust signalling:UT ..................................................................... 11 TU5.2.3UT 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 KPI’s: UT ......................................................................................................................... 14 TU5.5 UT TUSteps to Demonstrate Gains UT .............................................................................................................. 15 TU5.6 UT TUPre-requisites & Interworking for these features/functionalityUT...................................................... 16

TU6UT TUReferences UT.....................................................................................................................17 TU6.1 UT TUWhy NSN solution and mobile device supportUT ................................................................................ 17 TU6.2 UT TUAbbreviations: UT ..................................................................................................................................... 17


1 Purpose of the Trial Guideline document

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

2 Why Successful Customer Trials are needed?

The primary objectives of a successful trial is to get 1) Public Press Release 2) Public Customer References 3) Customer Testimonials 4) Commercial contract for sales, market share and profitability

3 Executive Summary

Traditionally AMR has been proposed as one of the major steps towards improving Spectral Efficiency due to increased robustness of AMR codec’s. However operator feedbacks have been somewhat negative with increased dropped call rate, especially post implementation of AMR Half rate. With the introduction of AMR codec’s, AMR users perceive improved voice quality thereby transmitting lesser power. However introducing AMR Half rate also increases signalling 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 codec’s. This weak link leads to the increased dropped calls rate seen with AMR deployment. However starting BSS13 many improvements have been introduced that help improves the retainability of AMR calls and thereby fully utilize the benefits of robust codec’s, 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 these features can be successfully demonstrated to customer. The objective is also to clarify that some of these benefits will be visible network wide only with increase in traffic. This document covers the benefits of these AMR enhancement features 1) AMR Robust signalling 2) Progressive AMR power control 3) AMR Unpacking Optimization


FACCH REPETITION & POWER OFFSET - DCR BEST CASE

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4 Simulation, Field results & Typical achievable gains 4.1 AMR Robust signalling (FACCH/SACCH)

USimulation results U:

Fig.1: Simulations results indicate Dropped Call rate Improvement of around 20% by implementing Robust AMR signalling.

UField Results:

Fig.2: Field results indicate dropped call rate improvements in 10% to 20%.

The results in this field trial indicates a dropped call rate 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 in interfered clusters. Please note the improvements in dropped call rate are generally influenced by the contribution of handover related drops in the overall dropped call rate.

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


4.2 Progressive AMR Power Control USimulation Results:

Fig.3: Simulations results have shown Dropped Call Rate Improvement of up to 50% with AMR PPC

UField Results:

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

UTypical Gains achieved with this feature:

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


4.3 AMR Unpacking Optimization USimulation Results:

Fig.5: Simulation results indicate an improvement of around 25% at high traffic load (@ 12% EFL)

UField Results:

Fig.6: Field results indicate 30-40% in improvement in Intracell handover related 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 of 15% can be committed in networks with large % of AMR-HR traffic and a significant % of bad quality.


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 additional intracell handovers introduce possibilities of increased drop calls especially under bad radio conditions. To minimize these drops it’s highly recommended to deploy AMR Unpacking Optimisation along with AMR HR.

Also while deploying AMR, it’s advisable to deploy AMR Full Rate across entire BSC, instead of AMR deployment at cluster level. AMR deployment at site or cluster level can improve link level performance for users, however system level improvements are only achieved with larger deployments of AMR where improved quality, reduced power and impacts overall Network level quality and retainability KPI’s .

Cluster level AMR deployment also leads to unnecessary A interface pool switchovers especially in cases where transcoders need separate pools to be defined for AMR & EFR

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5.2 Criterias to select the Right Trial Cluster

5.2.1 Cluster selection to demonstrate UAMR Unpacking Optimisation: U

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

With the introduction of AMR, packing & unpacking handovers( i.e. intracell handovers) normally outnumber the number of normal intercell handovers triggered in cells. Unpacking attempts due to low quality on AMR-HR calls happen more often than packing attempts (AMR-FR to AMR-HR). Packing is triggered based on 1) Cell load, 2) Quality of ongoing calls meeting a predefined threshold and 3) An even more stringent criteria for calls to be on the 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 handover related drops exceed even intercell handover related drops. A majority of these tend to be due to unpacking attempts that lead to dropped calls because of either low signal strength or quality.

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

Fig.8: High Intracell drops

Fig.9: High AMR Half Rate traffic

High Half Rate Traffic

High Intracell drops in busy hours


5.2.2 Cluster selection to demonstrate UAMR Robust signalling: U

For Robust AMR to be demonstrated successfully identify a cluster with high interference 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 and repeated messages to improve the decoding capability of signalling messages sent on the FACCH channel.

For Rel-5 or earlier handsets the transmit power used on the FACCH signalling channel is increased by a few dB’s vs. the power levels used by the associated traffic channel.

It’s recommended to demonstrate the benefits in an interfered cluster. However if the feature needs to be demonstrated to an operator with large bandwidth then a suitable weak coverage patch should be identified (see snapshot of measurement samples below)

Radio interface drops occur primarily due to 2 reasons:

1) Radio Link timeouts (drops due to severe degradation of ongoing call quality 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 drops improvements.

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

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

Fig.10: Rxlevel Vs RxQuality profile


5.2.3 Cluster selection to demonstrate UProgressive AMR Power Control U:

The maximum performance gains from AMR PPC can be seen in highly interfered clusters. The feature can help reduce the % of users radiating almost at 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 cannot help 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 demonstrate improvements/gains with this feature.


5.3 Default parameters need Network specific optimization The right cluster selection is very important for the successful demonstration of the 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 have many parameters. It’s important to analyze the existing power control and handover parameters to decide on the optimal parameter set for the new feature

U1)AMR Unpacking optimization (RxQual Vs Unpacking & Intercell handover threshold)

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

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

All AMR-HR calls that experience call quality of <4 will attempt unpacking to AMR-FR in the same cell, However if the quality degrades to <6 an intercell handover is attempted.

AMR Unpacking optimization should be set > Existing AMR unpacking threshold but < Quality threshold for Intercell handover

E.g. AMR Unpacking optimization threshold of 5 will allow unpacking for all AMR-HR calls which experience Rx Quality of 4 or 5.However for all calls with RxQuality <5 no unpacking attempts are allowed

In the above example Intracell unpacking handover attempts can be triggered between RxQual 4 and 7.If Rx Quality based inter-cell handover threshold is 6 set the Unpacking limit to 5.

Also ensure that power control settings are triggered earlier than any handover decisions by using shorter averaging windows /thresholds than the corresponding handover related parameter settings.

With DTX enabled please ensure that Weighting parameters for Rxlevel and RxQual samples are set to either 2 or max 3 to ensure right processing of measurements.


2)AMR PPC: The existing AMR Power Control settings along with the AMR PPC parameters decides the most or least aggressive power control threshold that will be used along with link adaptations.

A existing aggressive AMR power control setting can push the dynamic AMR power control threshold to aggressive thresholds. Such an aggressive threshold can delay the power control to such an extent that quality improvement might not be possible leading to increased drop call.

In such cases the current AMR power control thresholds might need to be modified.

5.4 Recommended KPI’s: Please contact your local network planning team for details about the KPI’s that can be used to demonstrating the feature gains. UAMR Robust Signalling: This feature delivers gains primarily by reducing the number of handover related drops.Therefore Dropped Call Rate (DCR) and also Handover related drop counts which is a subset of DCR needs to be benchmarked UProgressive AMR power control: AMR PPC help’s reduce the peak power transmitted by both MS & BTS, thereby reducing Interference at network level. Reduced network level interference leads to lesser RF failures due to Radio Link Timeouts. RF Failures, DCR, MS & BTS transmitted power/attenuation profiles. UAMR Unpacking Optimization: This feature primarily focuses on reducing the risk of dropped calls while unpacking an AMR half rate call to AMR full rate. Hence Intracell Handover performance is the most critical KPI to benchmark in addition to overall DCR.


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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 layer tend to be better Vs the non-BCCH TRX’s which are often planned with reuse of 6 or lesser. Also BCCH TRX’s radiate at full power on all TS’s irrespective of whether a call occupies a TS or not.

Irrespective of the number of calls carried by the BCCH the level of interference generated is the same, be it 1 call or be it 8 calls (e.g. with Dual rate enabled & 4TS occupied for signalling & data, remaining 8 TS’s can carry up to 8Erlangs). Result, performance on BCCH is usually flat with increasing load/ EFL.

Fig12: Performance on BCCH layer

If calls are already prioritized to BCCH TRX in trial cluster ~8 Erl can be carried by BCCH TRX after which traffic spills over to the non-BCCH TRX’s

Fig13: Performance on Hopping layer

However unlike the BCCH TRX’s the interference on the non-BCCH/hopping layer increases linearly with traffic on this layer and so does the performance.

Hence it’s highly recommended to change prioritization of calls to non-BCCH layer (by setting TRP=2) to 1) simulate increased interference 2) Recreate a future scenario with increased traffic.


5.6 Pre-requisites & Interworking for these features/functionality 1) AMR Robust signalling (FACCH/SACCH)

Required Software

3GPP Release 6 compliant MS is required for SACCH repetition.

2) Progressive AMR power control

Required software shows the earliest version (BSS10) that supports AMR Progressive Power Control (PPC).

Either AMR FR or AMR HR or both must be activated before it is possible to define the AMR Progressive Power Control parameters for AMR FR or AMR HR calls.

3) AMR Unpacking Optimization

BSS14 is required in addition to AMR FR & HR deployment.Pre-BSS14 the Unpacking optimization parameters are available as a patch in BSC


6 References

6.1 Why NSN solution and mobile device support 1) AMR Robust signalling (FACCH/SACCH) is a 3GPP Rel-6 specification to improve AMR signalling performance, specifically retainability that helps deliver the Spectral Efficiency benefits of AMR. All vendors support these features.

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

To improve the retainability for legacy handsets NSN has implemented a proprietary enhancement called FACCH Power Boost to boost power of FACCH signalling bursts only by a few dB’s vs. the corresponding voice codec requirements.

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

Progressive power control provokes AMR adaptation to use codec rates progressively along power control range

Better interaction between AMR adaptation and power control by favouring increase of power over AMR adaptation with low power levels and avoid increase of power and favouring AMR adaptation with higher power levels and thus 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

amr half raamr-half-rate-feature-enhancementste feature enhancements overview

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