amr planning and optimization guidelines v2.0

AMR Planning and Optimization Guideline

S11.5, S12, S13

Version 2.0

2/73 CMO MS Network & Service Optimization Capability Management

AMR Planning & Optimization GuidelineFor Internal UseOct 2008

Copyright 2007 Nokia Siemens Networks.All rights reserved.

document description

Title and version AMR Planning and Optimization GuidelineReferenceTarget Group Radio, Transmission, CS CoreTechnology and SW release

2G, 2.5G, BSS S11.5, S12 , S13

Related Service ItemsService Item number

When applicable

AuthorDate 18 Sep 2008Approver Ville Salomaa

CHANGE RECORD

This section provides a history of changes made to this document

VERSION DATE EDITED BY SECTION/S COMMENTS

1.4 ALL First Release:1.5 18 April 2008 Sumit Sharma ALL NSN format; S13 features2.0 draft 18 Sep 2008 Sumit Sharma ALL Added Optimization sections

and updated others; Guideline renamed to include Optimization

2.0 10 Nov 2008 Sumit Sharma ALL Updates based on reviews and to Intra HO optimization

Copyright © Nokia Siemens Siemens Networks. This material, including documentation and any related computer programs, is protected by copyright controlled by Nokia Siemens Siemens Networks. All rights are reserved. Copying, including reproducing, storing, adapting or translating, any or all of this material requires the prior written consent of Nokia Siemens Siemens Networks. This material also contains confidential information which may not be disclosed to others without the prior written consent of Nokia Siemens Networks.




Table of contents

1. Purpose and Scope............................................................................9

2. Description of AMR...........................................................................10

2.1 Introduction.......................................................................................10

2.2 Channels and Codecs......................................................................10

2.3 Link Adaptation.................................................................................122.3.1 Channel Mode Adaptation...............................................................................................122.3.2 Codec Mode Adaptation (LA)..........................................................................................13

2.4 Channel Allocation............................................................................17

2.5 AMR Pools........................................................................................182.5.1 Circuit Pool Mismatch.....................................................................................................18

2.6 FER and MOS..................................................................................20

2.7 Interworking with other features........................................................222.7.1 Direct access to desired layer/band (DADL/B)................................................................222.7.2 Enhanced TRX Prioritization...........................................................................................232.7.3 Common BCCH and Multi BCF.......................................................................................232.7.4 IFH and IUO....................................................................................................................232.7.5 Satellite Abis....................................................................................................................242.7.6 Single Antenna Interference Cancellation (SAIC)...........................................................242.7.7 DFCA (Dynamic Frequency and Channel Allocation).....................................................24

3. Benefits of AMR................................................................................26

3.1 C/I v/s FER Performance for AMR FR..............................................26

3.2 C/I v/s FER Performance for AMR FR..............................................26

3.3 Speech Quality Enhancement..........................................................27

3.4 Capacity and Coverage Gains..........................................................28

3.5 Summary of Benefits........................................................................30

4. Requirements for AMR Activation.....................................................31

4.1 AMR capable MS..............................................................................31

4.2 TRX Signalling requirements............................................................31




4.3 Equipment requirements...................................................................31

4.4 BSC Capacity requirements.............................................................32

4.5 Circuit Pool Configuration.................................................................324.5.1 TCSM2 support...............................................................................................................324.5.2 TCSM3 support...............................................................................................................33

5. AMR dimensioning............................................................................34

5.1 Background......................................................................................34

5.2 Capacity increase.............................................................................34

5.3 Traffic table.......................................................................................35

6. Implementation of AMR feature to the network.................................37

6.1 Steps for AMR Implementation.........................................................37

7. AMR parameters description and Setting.........................................38

7.1 Initial codec mode selection..............................................................387.1.1 Codec sets......................................................................................................................387.1.2 Initial Codec mode..........................................................................................................38

7.2 Codec mode adaptation....................................................................407.2.1 Full Rate (FR) Channel...................................................................................................407.2.2 Half Rate (HR) Channel..................................................................................................417.2.3 Parameter Summary.......................................................................................................41

7.3 Handovers Configuration..................................................................42

7.4 HO&PC thresholds parameters for AMR..........................................46

7.5 Channel mode adaptation (Packing/Unpacking)..............................47

7.6 Unpacking and Intra-Cell Handovers................................................49

7.7 Radio link timeout.............................................................................50

7.8 Parameter grouping..........................................................................51

8. Optimizing AMR Network..................................................................53

8.1 Counters related to AMR..................................................................538.1.1 Counters in Traffic Measurement (p_nbsc_traffic)..........................................................538.1.2 Counters in Handover Measurement (p_nbsc_ho).........................................................53




8.1.3 Counters in RxQual Measurement (p_nbsc_rx_qual).....................................................538.1.4 Counters in AMR RxQual Measurement (p_nbsc_amr_rx_qual)....................................54

8.2 Network Doctor reports.....................................................................54

8.3 KPIs affected by implementation of AMR.........................................558.3.1 TCH Retainability............................................................................................................558.3.2 TCH Congestion/Blocking...............................................................................................558.3.3 Handover Reasons and Failures.....................................................................................56

8.4 AMR Penetration in the network.......................................................56

8.5 AMR Codec usage and RxQual........................................................57

8.6 AMR Codec usage and FER............................................................57

8.7 Enhanced TRX Priority in TCH Allocation.........................................58

8.8 Aggressive use of AMR HR..............................................................58

9. AMR S13 features............................................................................60

9.1 AMR Progressive Power Control (PPC)...........................................609.1.1 Introduction.....................................................................................................................609.1.2 Description......................................................................................................................609.1.3 Benefits of AMR PPC......................................................................................................629.1.4 Activation.........................................................................................................................649.1.5 Parameters......................................................................................................................649.1.6 AMR PPC Measurement.................................................................................................65

9.2 Robust AMR Signalling (FACCH/SACCH)........................................669.2.1 Introduction.....................................................................................................................669.2.2 Repeated AMR SACCH and FACCH in 3GPP Release 6..............................................679.2.3 Repeated AMR FACCH for Existing Mobiles (FR & HR).................................................679.2.4 FACCH Power Increment for Existing Mobiles................................................................68

9.3 Separate AMR UL/DL Link Threshold...............................................689.3.1 Current Implementation...................................................................................................689.3.2 New parameters..............................................................................................................68

9.4 TRAU Bicasting................................................................................699.4.1 Introduction.....................................................................................................................699.4.2 Description of the feature................................................................................................709.4.3 Activation and Monitoring................................................................................................70

9.5 AMR Signalling Measurement..........................................................71

10. Abbreviations....................................................................................72




11. References.......................................................................................73




List of Tables

Table 1: Channel and Speech codec modes for AMR........................................................................12

Table 2: Avg. MOS Vs TCH FER table...............................................................................................20

Table 3: MOS vs TCH FER Mapping - percentage of samples above MOS 3.2................................21

Table 4: MOS vs RxQual mapping - percentage of samples above MOS 3.2...................................21

Table 5: Separate MOS-FER mapping Table for DL and UL.............................................................22

Table 6: AMR parameters for IFH/IUO...............................................................................................24

Table 7: AMR codec support in base stations....................................................................................31

Table 8: Reduction of TSL required with AMR HR.............................................................................35

Table 9: Traffic table for AMR HR.......................................................................................................36

Table 10: Parameters for Initial Codec Mode selection......................................................................39

Table 11: Thresholds for Codec Mode Adaptation.............................................................................41

Table 12: Parameters for HO Configuration.......................................................................................43

Table 13: Example handover from a Talk-Family BTS.......................................................................43

Table 14: Example handover from an UltraSite BTS..........................................................................44

Table 15: Handover Control Thresholds.............................................................................................46

Table 16: Power Control Thresholds..................................................................................................47

Table 17: Parameters controlling Packing/Unpacking........................................................................48

Table 18: Radio Link Timeout parameters..........................................................................................51




List of Figures

Figure 1: AMR Codecs.......................................................................................................................11

Figure 2: Link Adaptation....................................................................................................................14

Figure 3: Codec changes during an AMR call....................................................................................15

Figure 4: In-band signalling................................................................................................................17

Figure 6: AMR FR and EFR in clean speech......................................................................................28

Figure 7: AMR HR and AMR FR in clean speech...............................................................................29

Figure 9: TCH DR timeslot implementation........................................................................................35

Figure 10: Thresholds for codec adaptation.......................................................................................40

Figure 11: Packing of FR calls to HR AMR calls due to cell load.......................................................48

Figure 12: AMR Power Control without PPC......................................................................................61

Figure 13: AMR Power Control with PPC...........................................................................................61

Figure 14: Gains in Progressive Power Control..................................................................................63

Figure 15: AMR codes and signalling (FACCH/SACCH) performance..............................................66

Figure 16: TRAU Bicasting in AMR FR/HR handover........................................................................70




1. Purpose and Scope Purpose:

This document serves as a planning and optimization guideline for the Nokia Siemens Feature, Adaptive Multi Rate Codec (AMR). This document applies to BSS software releases S11.5, S12 and S13.

This document is meant for INTERNAL USE

Scope:

The scope of the document is the following:

Explain the feature, Adaptive Multi Rate Codec (AMR) and its benefits

Implementation of AMR feature into network elements

General rules for dimensioning and planning for AMR

Optimization aspects of network with AMR

New BSS S13 feature enhancements related to AMR

This document covers AMR up to the BSS S13 software release.

If you are planning to deploy AMR in a network, read through the whole document. In case you already have AMR but are looking for information on the new enhancements, read the section on S13 features.

The document does not cover step-by-step instructions to implement and test AMR in the network. Refer the BSS S13 NED documentation “Activating and Testing BSS10004: AMR” for detailed work instructions including MML commands. The document can also be accessed from NOLS at https://www.online.nokia.com.

https://www.online.nokia.com/




2. Description of AMR

2.1 IntroductionDuring 1998-1999, the Adaptive Multi Rate (AMR) codec for GSM was standardized. The codec adapts its bit-rate allocation between speech and channel coding, thereby optimizing speech quality in various radio channel conditions. This provides the next step of speech quality improvement in GSM after the introduction of the Enhanced Full Rate (EFR) codec in 1996.

In recent years, the industry has achieved quite remarkable improvements in GSM speech coding. The Enhanced Full Rate (EFR) codec, introduced in 1996, was the first codec to provide wireline speech quality. The new AMR codec brings further quality enhancements, especially in terms of high error robustness in the full rate channel. It also provides the first codec with quality comparable to wireline for the half rate channel in good channel conditions.

All previous GSM codecs operate with fixed partitioning between speech and channel coding (error protection) bit-rates. These bit-rates have been chosen as compromises between performance in error-free and high-error channels. The AMR codec operates in either the GSM full-rate or half-rate channel and selects the optimum bit-rate trade-off between speech and channel coding, according to the channel quality, to deliver the best possible overall speech quality for the prevailing C/I conditions. To achieve overall good speech quality, the quality degradation caused by speech coding and the errors engendered by the transmission channel have to be carefully balanced.

As expected, the codecs must be supported both by the MS and the Network.

2.2 Channels and CodecsBefore the introduction of AMR, the following channel types and codecs were available on the air interface:

2 different Channel Types (Full Rate & Half Rate)

2 different codecs (coding types) – 1 at Full Rate and 1 at Half Rate

The introduction of AMR provided improvements on the speech coding schemes on the air interface. So with AMR, there are:

2 different Channel Types (Full Rate & Half Rate)

14 different codecs – 8 at Full Rate and 6 at Half Rate

The two different Channel types provide capacity by allowing 2 calls (half rate) to be severed on 1 timeslot on the TRX. The different channel codings provide different levels of tradeoffs between speech coding (voice quality) and channel coding (robustness). The idea behind having several codecs is that the optimal codec is used based on prevailing channel conditions.




Note that, with AMR, the gross bit rate of the channel types is the same (22.8 kbps for FR and 11.4 kbps for HR); what changes is the share of channel and speech coding between different codecs. This relationship is show in the figure below.

Figure 1: AMR Codecs

AMR consists of 8 different speech codec modes ( bit-rates of 12.2, 10.2, 7.95, 7.4, 6.7, 5.9, 5.15 and 4.75 kbit/s) with total of 14 channel codec modes (see table below). All the speech codecs are defined for the full rate channel, while the six lowest ones are defined for the half rate channel.

0

5

10

15

20

25

FR12.2

FR10.2

FR7.95

FR 7.4 FR 6.7 FR 5.9 FR5.15

FR4.75

HR7.95

HR 7.4 HR 6.7 HR 5.9 HR5.15

HR4.75

AMR codec mode

Ch

an

ne

l b

it-r

ate

(k

bit

/s)

Channel coding

Speech coding

SpeechSpeech QualQual

RobustnessRobustness

0

5

10

15

20

25

FR12.2

FR10.2

FR7.95

FR 7.4 FR 6.7 FR 5.9 FR5.15

FR4.75

HR7.95

HR 7.4 HR 6.7 HR 5.9 HR5.15

HR4.75

AMR codec mode

Ch

an

ne

l b

it-r

ate

(k

bit

/s)

Channel coding

Speech coding

SpeechSpeech QualQualSpeechSpeech QualQual

RobustnessRobustnessRobustnessRobustness

0

5

10

15

20

25

FR12.2

FR10.2

FR7.95

FR 7.4 FR 6.7 FR 5.9 FR5.15

FR4.75

HR7.95

HR 7.4 HR 6.7 HR 5.9 HR5.15

HR4.75

AMR codec mode

Ch

an

ne

l b

it-r

ate

(k

bit

/s)

Channel coding

Speech coding

SpeechSpeech QualQual

RobustnessRobustness

0

5

10

15

20

25

FR12.2

FR10.2

FR7.95

FR 7.4 FR 6.7 FR 5.9 FR5.15

FR4.75

HR7.95

HR 7.4 HR 6.7 HR 5.9 HR5.15

HR4.75

AMR codec mode

Ch

an

ne

l b

it-r

ate

(k

bit

/s)

Channel coding

Speech coding

SpeechSpeech QualQualSpeechSpeech QualQual

RobustnessRobustnessRobustnessRobustness




Table 1: Channel and Speech codec modes for AMR

Channel mode

Channel codecMode

Source codingbit-rate, speech

Net bit-rate, in-band channel

Channel codingbit-rate, speech

Channel coding

bit-rate, in-band

TCH/FR

CH0-FS 12.20kbit/s (GSMEFR) 0.10 kbit/s 10.20 kbit/s 0.30 kbit/s

CH1-FS 10.20 kbit/s 0.10 kbit/s 12.20 kbit/s 0.30 kbit/s


CH3-FS 7.40 kbit/s (IS-641) 0.10 kbit/s 15.00 kbit/s 0.30 kbit/s





TCH/HR

CH8-HS 7.95 kbit/s (*) 0.10 kbit/s 3.25 kbit/s 0.10 kbit/s

CH9-HS 7.40 kbit/s (IS-641) 0.10 kbit/s 3.80 kbit/s 0.10 kbit/s

CH10-HS 6.70 kbit/s 0.10 kbit/s 4.50 kbit/s 0.10 kbit/s




(*) Requires 16 kbit/s TRAU. Therefore it is not seen as a feasible codec mode and is not be supported in BSS S13.

A mobile station must implement all the codec modes. However, the network can support any combination of them.

2.3 Link AdaptationLink Adaptation is the capability of AMR feature to vary the codec used according to the prevailing link conditions. In this way both network (for uplink) and MS (for downlink) measure the radio conditions in each link and take decisions on which codec should be applied to each way.

Two different types of link adaptation algorithms are defined: Channel Mode Adaptation and Codec Mode Adaptation.

2.3.1 Channel Mode Adaptation

Channel Mode Adaptation algorithm decides on whether the speech can be handled by a Full Rate Channel or by a Half Rate Channel according to the link conditions.

The channel mode (FR or HR) is switched to achieve the optimum balance between speech quality and capacity enhancements. The channel mode is selected by the network based on measurements of the quality of the up- and down-links. The up- and down-links use the same channel mode.




This is also known by Packing (FR calls to HR calls) and Unpacking (HR calls to FR calls).

2.3.2 Codec Mode Adaptation (LA)

For the channel selected (FR or HR), the Codec Mode Adaptation algorithm decides which codec is the one that provides the best speech quality for the current radio conditions. That is, as each codec has different channel protection and speech encoding performance, the idea of the codec mode adaptation is to select the codec that provides the best speech quality for the radio conditions that the receivers are submitted to.

Codec mode information is transmitted in-band in the speech TCH, using parts of the transmission capacity dedicated to speech data transmission

Codec mode adaptation operate independently on the up- and down- links i.e. in AMR the codec used in the UL does not need to be the same as the DL, these work dynamically depending on C/I. Control depends mainly on measurements of the quality of the respective links.

For codec mode adaptation, the receiving side performs link quality measurements of the incoming link. The measurements are processed yielding a Quality Indicator. For reference purposes, the Quality Indicator is defined as an equivalent carrier to interference ratio, C/Inorm. The MS and the BSS continuously update the Quality

Indicator estimates. The Quality Indicator is derived from an estimate of the current burst bit error probability (BBEP)

The BTS commands the MS to apply a particular speech codec mode in the uplink, but MS can only request BTS to apply a particular speech codec mode in the downlink because BTS has an option to override the MS's request. This is illustrated in the figure below.




• 1.-Which DL Radio Conditions?

•2.-Request a codec for DL

•3.- Network decides which codec to use for DL

•4.-DL codec used

DL LA

•1.-Which UL radio conditions?

•2.-Command a codec for ULUL LA

•3.-MS uses the codec commanded by the

network for UL

Figure 2: Link Adaptation

The codec mode bit-rate, i.e. the bit-rate partitioning between the speech and channel coding for a given channel mode, may vary rapidly (see figure below). The codec mode can be switched one up or one down at the time so that it is not possible to switch from the mode 12.2 kbit/s to 4.75 kbit/s when for example the modes 5.9 kbit/s and 7.4 kbit/s are included to the mode set (codecs allowed to be used). Also, it should be noted that codec changes do not take place immediately after the Codec Mode Command/Request is sent: there is a delay until a frame is received with the new codec.

Codec mode adaptation for AMR is based on received channel quality estimation in both MS and BTS, followed by a decision on the most appropriate speech and channel codec mode to apply at a given time. In high-error conditions more bits are used for error correction to obtain error robust coding (at the cost of lower bits for speech coding), while in good transmission conditions a lower amount of bits is needed for sufficient error protection and more bits can therefore be allocated for source coding. The switching of codecs to protect the speech encoding eventually provides a better overall frame erasure (FER) rate and higher perceived voice quality (MOS) to the user at a certain C/I as compared to a EFR call in the same situation.

MS must support all speech codec modes, although only a set of up to 4 speech codec modes is used during a call. BSC supports all of speech codec modes, except 7.95 kbit/s on HR channel, and it has one default set for each channel mode.




Figure 3: Codec changes during an AMR call

2.3.2.1 Link Adaptation modes

There are two link adaptation (LA) modes;

Fast LA (as per ETSI standards)

Fast LA allows in-band codec mode changes on every other TCH frame (every 40ms)

Slow LA (the Nokia Siemens proprietary)

Allows in-band codec mode changes only on SACCH frame interval (every 480ms)

The choice of the LA mode is done on BSC basis with the parameter Slow AMR LA Enabled (SAL): if it is set to "N" (default) it is uses fast LA; if it is set to "Y" it uses slow LA. With slow LA, BTS allows in-band codec mode changes only on the SACCH frame interval of 480 ms and this option gives better flexibility with HO & PC algorithms (based on SACCH measurements every 480ms as well).




Parameter Level MML Name Suggested Value

Description

Slow AMR Link Adaptation enabled

BSC SAL No Enable slow link adaptation. This is a proprietary algorithm where codec mode changes happen every SACCH period (480ms) instead of as fast as 40ms.

During both LA modes BTS indicates the first and the last used codec during the last measurement interval and the average quality.

2.3.2.2 In-Band Signalling

The mobile station (MS) and the Base Transceiver Station (BTS) both perform channel quality estimation for their own receive paths. Based on the channel quality measurements, the MS sends to BTS a Codec Mode Request (Mode requested to be used in the downlink). This signalling is sent in-band, along with the speech data. The codec mode in the uplink may be different from the one used in downlink, but the channel mode (full rate or half rate) must be the same. The in-band signalling has been designed to allow fast adaptation to rapid channel variations.

An in-band signalling channel is defined for AMR that enables the MS and the BTS to exchange messages on applied or requested speech and channel codec modes. The above mentioned selected speech codec mode is then sent, by using the in-band signalling channel, to the transmitting side, where it is applied for the other link. BTS commands the MS to apply a particular speech codec mode in the uplink by Codec Mode Command. MS sends to BTS a Codec Mode Request (Mode requested to be used in the downlink), BTS has an option to override the MS's request.




CMI, CMC

DL

UL SF 1

SF 2

SF 3

SF 4 SF 6

SF 5

SF 3SF 1

SF 7

SF 7SF 5

CMR

SF 2 SF 4 SF 6 SF 8

time

8 TDMAframes

CMR

CMI CMI CMI CMI CMI CMI CMI CMI CMI

CMICMICMICMICMICMICMICMICMI

CMC CMC CMC CMC CMC CMC CMC CMC CMC

CMR CMR CMR CMR CMR CMR

SF 9DL

UL SF 1

SF 2

SF 3

SF 4 SF 6

SF 5

SF 3SF 1

SF 7

SF 7SF 5

CMRCMR

SF 2 SF 4 SF 6 SF 8

time

8 TDMAframes

CMRCMR

CMICMI CMICMI CMICMI CMICMI CMICMI CMICMI CMICMI CMICMI CMICMI

CMICMICMICMICMICMICMICMICMICMICMICMICMICMICMICMICMICMI

CMCCMC CMCCMC CMCCMC CMCCMC CMCCMC CMCCMC CMCCMC CMCCMC CMCCMC

CMRCMR CMRCMR CMRCMR CMRCMR CMRCMR CMRCMR

SF 9

CMR, CMI

SF= Speech Frame CMC = Codec Mode Command

CMI = Codec Mode Indicator CMR= Codec ModeRequest

Figure 4: In-band signalling

2.4 Channel AllocationHR and EFR principles are applied. Please see HR and EFR channel allocation for details.

The exception is that AMR call may be started in full rate channel in a new cell. How the AMR call starts in a cell depends on the parameter initAMRChannelRate (IAC). This parameter can be set to ‘Any rate’ or ‘FR’.

Parameter Level MML Name

Suggested Value

Description

Initial AMR channel rate for call setup and hand off

BSC IAC 1 ”1” = Any rate. Channel type allocation depends on further network parameters/settings. ”2” = AMR FR. AMR FR is preferred over AMR HR and allocated despite of the values of the currently used information for channel allocation. IAC=2 overrides TCHRateIntHO (HRI)

The reason behind this new parameter is that quality may not be sufficient for HR AMR call setup (radio measurement is done on SDCCH).

If AMR FR codec is not present in the Channel Type element or it cannot be allocated (e.g. AMR FR set is disabled in the target cell), then the allocation is continued with the currently used information. Parameter is valid in call setup (except FACCH call setup), internal inter cell HO and external HO. This parameter (IAC) overrides the value of




parameter TCHRateInternalHO (HRI) parameter. See section 7.3 for details of this parameter.

2.5 AMR Pools A circuit pool concept has been introduced in GSM recommendations for handling transcoders of different types. The A interface speech circuits (CIC) are divided into pools (CIP) according to the TCSM capabilities. Circuits in the same pool have the same transcoding capabilities. The main factors when dividing the circuits into pools is the channel rate and the speech codecs supported

During call setup the MS informs MSC of its transcoding capabilities. From this, the MSC will know what channel types and speech codecs are supported by the MS and the MSC will then be able to allocate a circuit. The properties of the circuit, such as codecs and channel rates supported, are described by the pool the circuit belongs to. In the Assignment Request/Handover Request message to the BSC, the MSC will request a preferred channel type which depends on the MS’s capabilities, and informs the BSC of the circuit allocated.

On receiving the Assignment Request/Handover Request message, the BSC will identify the pool each physical circuit belongs to. It then maps the allocated circuit to its pool and checks if the capabilities of that pool are compatible with the requested channel type. If it is not compatible, then the request is rejected with cause “circuit pool mismatch”. If there are no contradictions, then the BSC will check whether the requested channel type can be allocated. If not, for example because the BTS does not support AMR, then the BSC will reject the request with cause “switch circuit pool”. If possible, the MSC will then re-allocate a circuit belonging to a different pool.

Internal handovers are normally handled by the BSC. If the BSC decides to switch the circuit pool type, it must send a Handover Required to the MSC as it is the MSC that assigns the circuit. The MSC may or may not be able to change the circuit and will send the circuit to be used in a Handover Request message. Although the handover is internal to the BSC, the act of involving the MSC changes the handover type from BSC controlled to MSC controlled.

Also refer to Section 4.5 for details of the TCSM2 and TCSM3 capabilities.

2.5.1 Circuit Pool Mismatch

The selection of the TCH to be allocated during Assignment Procedure is based on the information received by the BSC from the MSC. The MSC sends an Assignment Request message to the BSC for the BSC to assign channels on the Air interface and to assign circuit on the A interface. The BSC usually responds with an Assignment Complete or an Assignment Failure message.

The Assignment request message from the MSC to BSC contains the following:

channel type: radio channel required for the call type

L3 header info

priority (optional)




circuit identification code (CIC) indicating the channel to be used on the A interface

downlink DTX flag (optional)

radio channel identity (optional)

interference band to be used (optional)

Let’s take an example of the circuit pool mismatch.

Case1: There is no AMR support.

MSC has a circuit pool X that supports FR (but not EFR)

BSC has a circuit pool Y that supports EFR and FR

The MS requests EFR (but supports FR). Since the MSC has only pool X, it allocates a circuit from Pool X (FR only). At the BSC, this is accepted since the Pool X is attached to an EFR capable transcoder, the BSC sets up an EFR call on the BSS.

Case2: With AMR

With AMR, a new circuit pool 23 is added at the MSC and BSC end. This pool only supports AMR (not EFR). So now MSC has pool X and pool 23 and BSC has pool Y and pool 23. This works fine except in one case.

Problem occurs when an AMR capable MS access a Non-AMR cell connected to the above MSC.

1. AMR capable MS access the non-AMR site

2. MSC sees that the MS supports AMR, so allocates a circuit from Pool 23 without having the knowledge of whether the BTS supports AMR or not

3. BSC however rejects the allocation since the cell does not support AMR. BSC therefore requests pool switching

4. MSC has only Pool X and Pool 23, so it re-assigns a circuit from X

This leads to the call attempt being blocked. If the BSC had pool X, then the call would be completed as a FR call.

Refer to the document KPI Impact from AMR activation 1.3 for more details on this including several examples of internal and external handover.

https://sharenet-ims.inside.nokiasiemensnetworks.com/Download/377622515





2.6 FER and MOSPerformance of radio networks has traditionally been measured using BER to quantify speech quality and dropped call rate (DCR) to quantify the rate of lost connections. As the networks and features have developed, additional quality measures such as frame erasure rate (FER) and mean opinion scoring (MOS) have become more important

Speech quality can be quantified using mean opinion score (MOS). MOS values range from 1 (bad) to 5 (perfect). These values were derived from a group of individuals listening to different speech samples, and scoring them. MOS scores are therefore opinion-based and subjective. However, there are several tools that try to measure and quantify the subjective speech quality of the link from data collected through drive tests using different algorithms.

Frame erasure rate is a very powerful performance indicator since it is highly correlated with the final voice quality the end user perceives. Different speech codecs will have however, a slightly different FER to MOS correlation since the smaller the speech codec bit rate, the more sensitive it becomes to frame erasures. The FER values in which different speech codecs will start to experience MOS degradation and the rate of such degradation is quite uniform. Therefore, FER can be efficiently used as a speech quality performance indicator.

Following tables, which were created with extensive lab testing, can be used to estimate MOS from FER samples, without costly MOS drive testing. Though MOS is a subjective measure and real user perception can vary a lot from person to person, in general, a MOS value of 3.2 and above is considered good and gives very clean speech quality. Of course MOS score varies with speech codec types, but with no error (0% FER), similar codec types for both FR and HR should perform same.

Number of lost frames 0 - 0 1 - 1 2 - 2 3 - 3 4 - 4 5 - 5 6 - 6 7 - 96FER Range (%) 0 to 1% 1 to 2% 2 to 3% 3 to 4% 4 to 5% 5 to 6% 6 to 7% 7 to 100%Average FER (%) per FER class 0.00 1.04 2.08 3.13 4.17 5.21 6.25 10Codec / FER Class 0 1 2 3 4 5 6 7EFR 4.27 3.88 3.58 3.34 3.20 3.02 2.90 2.51FR 12.2 4.27 3.88 3.58 3.34 3.20 3.02 2.90 2.51FR 7.4 4.04 3.74 3.48 3.24 3.03 2.85 2.70 2.28FR 5.9 3.78 3.51 3.28 3.07 2.89 2.73 2.59 2.17FR 4.75 3.52 3.30 3.10 2.92 2.75 2.60 2.46 2.04HR 7.4 4.02 3.72 3.46 3.24 3.05 2.89 2.75 2.37HR 5.9 3.60 3.36 3.20 2.99 2.87 2.76 2.68 2.40HR 4.75 3.45 3.23 3.04 2.89 2.75 2.64 2.54 2.23

Red = MOS < 3.2

Table 2: Avg. MOS Vs TCH FER table




Percentage of samples over 3.2Number of lost frames0 - 0 1 - 1 2 - 2 3 - 3 4 - 4 5 - 5 6 - 6 7 - 96FER Range (%) 0 to 1% 1 to 2% 2 to 3% 3 to 4% 4 to 5% 5 to 6% 6 to 7% 7 to 100%Average FER (%) per FER class0.00 1.04 2.08 3.13 4.17 5.21 6.25 10Codec / FER Class 0 1 2 3 4 5 6 7EFR 100.0% 100.0% 92.1% 74.1% 51.7% 48.7% 21.7% 1.8%HR7.95 100.0% 100.0% 92.0% 65.0% 45.0% 30.0% 15.0% 0.0%HR 7.4 100.0% 100.0% 92.0% 61.3% 43.5% 18.9% 9.0% 0.0%HR 6.8 100.0% 100.0% 80.0% 50.0% 25.0% 12.0% 5.0% 0.0%HR 5.9 100.0% 100.0% 65.0% 41.4% 16.4% 6.4% 0.0% 0.0%HR 5.15 100.0% 94.0% 54.0% 31.0% 5.0% 1.0% 0.0% 0.0%HR 4.75 100.0% 89.0% 41.9% 21.7% 1.3% 0.0% 0.0% 0.0%FR 12.2 100.0% 100.0% 92.1% 74.1% 51.7% 48.7% 21.7% 1.8%FR 10.2 100.0% 100.0% 92.0% 70.0% 47.0% 40.0% 18.0% 0.5%FR 7.95 100.0% 100.0% 92.0% 65.0% 43.0% 33.0% 16.0% 0.0%FR 7.4 100.0% 100.0% 83.3% 61.8% 40.5% 25.8% 14.6% 0.0%FR 6.8 100.0% 100.0% 76.0% 49.0% 22.0% 10.0% 5.0% 0.0%FR 5.9 100.0% 100.0% 69.4% 35.8% 17.9% 4.6% 0.0% 0.0%FR5.15 100.0% 95.0% 58.0% 25.0% 5.0% 1.0% 0.0% 0.0%FR 4.75 100.0% 91.3% 48.3% 20.3% 3.8% 0.0% 0.0% 0.0%

Table 3: MOS vs TCH FER Mapping - percentage of samples above MOS 3.2

Percentage of samples over 3.2BER Range (%) 0-0.2 0.2-0.4 0.4-0.8 0.8-1.6 1.6-3.2 3.2-6.4 6.4-12.8 12.8-100Typical BER (%) 0.14 0.28 0.57 1.13 2.26 4.53 9.05 18.1

Codec / RxQual Class 0 1 2 3 4 5 6 7EFR 100.0% 100.0% 100.0% 91.6% 80.0% 45.0% 9.1% 0.0%FR 12.2 100.0% 100.0% 100.0% 91.6% 80.0% 45.0% 9.1% 0.0%FR 10.2 100.0% 100.0% 100.0% 95.0% 86.2% 55.4% 15.7% 3.4%FR7.95 100.0% 100.0% 100.0% 100.0% 93.3% 66.6% 23.2% 7.3%FR 7.4 100.0% 100.0% 100.0% 100.0% 95.0% 70.0% 25.0% 8.3%FR 6.8 100.0% 100.0% 100.0% 100.0% 95.0% 74.0% 27.0% 7.8%FR 5.9 100.0% 100.0% 100.0% 100.0% 100.0% 80.0% 30.0% 7.0%FR 5.15 100.0% 100.0% 100.0% 100.0% 95.0% 80.0% 40.0% 6.8%FR 4.75 100.0% 100.0% 100.0% 100.0% 95.0% 80.0% 45.0% 6.6%HR 7.95 100.0% 100.0% 90.0% 62.0% 20.0% 0.0% 0.0% 0.0%HR 7.4 100.0% 100.0% 90.0% 65.0% 25.0% 3.9% 0.0% 0.0%HR 6.8 100.0% 100.0% 91.0% 71.0% 33.0% 5.3% 0.0% 0.0%HR 5.9 100.0% 100.0% 92.5% 80.0% 45.0% 7.5% 1.5% 0.0%HR 5.15 100.0% 100.0% 92.5% 83.3% 51.5% 12.4% 3.2% 0.0%HR 4.75 100.0% 100.0% 92.5% 85.0% 55.0% 15.0% 4.1% 0.0%

Table 4: MOS vs RxQual mapping - percentage of samples above MOS 3.2




MOS – FER mapping for DL and UL separately

Table 5: Separate MOS-FER mapping Table for DL and UL

2.7 Interworking with other features

2.7.1 Direct access to desired layer/band (DADL/B)

In case a network with AMR has 2nd generation BTSs (which do not support AMR), the feature DADL/B can be used to handover AMR calls during call setup to co-located BTSs that support AMR. Both intra and inter BSC DADL/B handovers are possible and preferably inside one frequency band as the failure probability is higher with DADL/B handovers between bands.

In order to support AMR call continuation even after internal or external HO, the handover target cell list is manipulated so, that AMR capable cells where load is low, are on the top. The candidate cells on the target list are already pruned by the adjacent cell parameter hoMarginPbgt (PBGT). AMR capable cells are verified by the adjacent cell parameter amrDadlbTargetCell (DADLA) and those AMR capable adjacent cells are prioritised that are below the threshold of BTS parameter btsLoadThreshold (BLT) (see figure below).




Whether DADL/B handover is applied during TCH assignment is based on the following:

If there are no TCHs available in the accessed cell when an AMR call is attempted, Directed Retry due to congestion, with or without queuing, is made

If there are TCHs available in the accessed cell, and there are adjacent cells defined as DADL/B handover target cells, (with the parameter amrDadlbTargetCell (DALDA)) then the DADL/B handover is applied.

Adjacent cells are not verified according to the MS capabilities (single band, dual band or tri-band), but they have to fulfil the current signal level requirements in order to be considered as a target cell for DADL/B handover. Current method for sorting the target adjacent cells is used

If there are no DADL/B handover target cells defined, the TCH is allocated from the accessed cell and another speech codec than AMR is chosen.

2.7.2 Enhanced TRX Prioritization

With the trxPriorityInTCHAlloc (TRP) parameter, you can direct AMR calls primarily to non-BCCH TRX and non-AMR calls primarily to BCCH TRX. This is set by the parameter TRP = 3.

2.7.3 Common BCCH and Multi BCF

In segment environment, if the AMR codec set of the BCCH BTS of the cell is disabled, it must also be disabled in the other BTSs of that segment. Similarly, if it is enabled, it must also be enabled in the other BTSs of that segment.

AMR FR and AMR HR codec sets can be disabled or enabled separately.

2.7.4 IFH and IUO

AMR specific good and bad C/I thresholds are specified for HR and FR AMR:

super reuse good C/I threshold for AMR HR – amrHoHrSupReuGoodCiThr (GCIH)

super reuse bad C/I threshold for AMR HR – amrHoHrSupReuBadCiThr (BCIH)

UltraSite (co-located)

2nd gen BTS

TCH

SDCCH

1) DADL/B used to direct AMR mobiles to AMR capable cells

2) Prioritisation of AMR capable cells in handovers

Figure 5: DADL/B with AMR




super reuse good C/I threshold for AMR FR – amrHoFrSupReuGoodCiThr (GCIF) super reuse bad C/I threshold for AMR FR – amrHoFrSupReuBadCiThr (BCIF)

Table 6: AMR parameters for IFH/IUO


Suggested Value

Description

AMR Handover FR Bad CI Ratio

BTS BCIG 10 With this parameter you define the downlink C/I ratio on a super-reuse TRX for triggering the HO from the super-reuse TRX. Defined for AMR FR calls.

AMR Handover FR Good CI Ratio

BTS BGIF 17 With this parameter you define the downlink C/I ratio on a super-reuse TRX for triggering the HO to the super-reuse TRX. Defined for AMR FR calls.

AMR Handover HR Bad CI Ratio

BTS BCIH 10 With this parameter you define the downlink C/I ratio on a super-reuse TRX for triggering the HO from the super-reuse TRX. Defined for AMR HR calls.

AMR Handover HR Good CI Ratio

BTS GCIH 17 With this parameter you define the downlink C/I ratio on a super-reuse TRX for triggering the HO to the super-reuse TRX. Defined for AMR HR calls

Current Nx and Px values of C/I thresholds are used.

The new threshold values for HR AMR serve also the basic HR. The current good and bad threshold pair (super reuse good C/I threshold and super reuse bad C/I threshold) is going to serve the basic FR.

With these thresholds operator can control, which type of speech calls are preferred to enter the super layers cells, e.g. HR AMR calls could be packed to the super layer in order to increase the capacity of regular layer cells (good value for HR AMR e.g. - 5 dB (compared to the current value) and good value for FR AMR e.g. + 5 dB).

2.7.5 Satellite Abis

Only AMR FR is supported with Satellite Abis.

2.7.6 Single Antenna Interference Cancellation (SAIC)

When Single Antenna Interference Cancellation (SAIC) is used in the network together with AMR, the SAIC-specific counters are updated in AMR RX Quality Measurement

2.7.7 DFCA (Dynamic Frequency and Channel Allocation)

AMR codecs are supported when DFCA is in use. The initial AMR channel rate (IAC) parameter allows you to specify the initial channel rate for adaptive multi-rate (AMR). When forced HR mode is triggered for DFCA, it overrides the IAC parameter. This means that forced HR is used for AMR MSs despite of the value of the IAC parameter.




Channel allocation decisions in DFCA algorithm are based on C/I criteria. In the channel selection process, different degrees of interference tolerance of different connection types (EFR, AMR FR, AMR HR) are taken into account. Networks with higher penetration of AMR capable MS will see greater benefits on spectral efficiency from the introduction of DFCA.




3. Benefits of AMRLet’s first look at the link level performance of AMR FR and HR codecs. The effect of the codecs on FER performance is where the benefits lie.

3.1 C/I v/s FER Performance for AMR FRThe figure below shows the comparison of AMR FR codecs with GSM FR, HR and EFR in different C/I conditions.

Note that with poor C/I conditions, the use of a lower speech codec for FR maintains the FER performance, providing a gain of upto 5.5dB in C/I at 1% FER.

3.2 C/I v/s FER Performance for AMR FRThe figure below shows the comparison of AMR HR codecs with GSM HR in different C/I conditions.

Compare this figure with the previous one, with the reference as the performance of GSM HR (seen on both figures).

Frame Error Rates (FER) for ARM, EFR and FR Codecson Different C/I conditions (FR -Channel)

0.00%

2.00%

4.00%

6.00%

8.00%

10.00%

12.00%

14.00%

12345678910111213141516

C/I [dB]

FER

[%]

GSM EFR

GSM FR

AMR 12.2 kbit/s

AMR 10.2 kbit/s

AMR 7.95 kbit/s

AMR 7.4 kbit/s

AMR 6.7 kbit/s

AMR 5.9 kbit/s

AMR 5.15 kbit/s

AMR 4.75 kbit/s

GSM HRTU3-iFHTU3-iFH

5-6 dB




Note that in case of better C/I conditions, HR codecs can be used without degrading the FER. This provides capacity by being able to serve 2 HR calls on one timeslot without compromising on FER.

Note the difference from FR case – HR codes are not providing better speech quality in poor radio conditions. They allow maintaining the FER in better C/I conditions even if call shifts from FR to HR.

3.3 Speech Quality EnhancementWith AMR, it is possible to achieve very good speech quality in FR mode even in low C/I conditions, or increase the speech capacity by using the HR mode and still maintain the quality level of current FR calls.

The AMR system exploits the implied performance compromises by adapting the speech and channel coding rates according to the quality of the radio channel. This gives better clear channel quality and better robustness to errors (FER), thus increasing the probability for maintaining the call. These benefits are realised whether operating in full rate or half rate channels. An example to explain this concept in a more intuitive way can be this: consider the situation where the mobile is in a zone of the cell border where you have a bad C/I (for example 7dB). With EFR you have a degradation of the quality of the speech due to interference. But with AMR similar quality can be achieved with a reduced number of speech coded bits, which allows more bits to be

Frame Error Rates (FER) for ARM HR Codecson Different C/I conditions (HR -Channel)

0.00%

2.00%

4.00%

6.00%

8.00%

10.00%

12.00%

14.00%

12345678910111213141516

C/I [dB]

FER

[%]

GSM HR

AMR 7.95 kbit/s

AMR 7.4 kbit/s

AMR 6.7 kbit/s

AMR 5.9 kbit/s

AMR 5.15 kbit/s

AMR 4.75 kbit/s

TU3-iFH




used for error protection and correction. See below figure for ETSI Mean Opinion Score test results for current EFR and AMR FR.

Figure 6: AMR FR and EFR in clean speech

3.4 Capacity and Coverage GainsTogether with quality improvements, the need to enhance capacity by allocating half rate channels to some or all mobiles in the network is also recognised. The radio resource algorithm, enhanced to support AMR operation, allocates a half rate or full rate channel according to channel quality and the traffic load on the cell in order to obtain the best balance between quality and capacity.

An example of the increase in capacity can be this: in normal C/I condition two voice channels can use a single timeslot in the case of Half rate coding (HR) with little or no compromise in voice quality compared to EFR. The channel selection is done on the basis of BTS load conditions. In case of an AMR HR capable cell, the calls that meet the quality criteria to switch to HR increase with the use of more robust codecs, increasing the number of total calls that the cell can take. Hence it provides the capacity gain in that cell. Moreover, AMR HR provides more control with packing and unpacking procedures, with Quality control parameters. See figure below for ETSI Mean Opinion Score test results for current FR and AMR HR.




1.0

2.0

3.0

4.0

5.0

No Errors 19 dB C/I 16 dB C/I 13 dB C/I 10 dB C/I 7 dB C/I 4 dB C/I

AMR HRAMR FR

MOS (Mean Opinion Score)

AMR Half Rate performance compared to Full Rate in Clean Speech

Figure 7: AMR HR and AMR FR in clean speech

In addition, increased robustness to channel errors can be utilized in the cell coverage, i.e. lower C/I can be allowed at the cell edge. However, in the mixed traffic case the cell coverage has to be planned according to EFR mobiles.

The figure below shows the comparison of FR, AMR HR and AMR FR in a drive test (European operator, 2004) to clearly show the gain in coverage distance from a base station.

AMR_FR Route

AMR_HR Route

FR Route

Distance from BTS about 7.7 Km.


Distance from BTS about 6.6 Km.AMR_FR Route

AMR_HR Route

FR Route




ColorLegend

0 to <= 4

4 to <= 7

ColorLegend

0 to <= 4

4 to <= 7

Effective Coverage gain ~ 35% (5dB)Compared between normal Fullrate (FR) and AMR Fullrate (AMR_FR)

Effective Coverage gain ~ 35% (5dB)Compared between normal Fullrate (FR) and AMR Fullrate (AMR_FR)

Quality Range :

Figure 8: AMR Covreage Gain Comparison




3.5 Summary of BenefitsTherefore the key benefits of the AMR feature are:

1. Speech quality enhancement: AMR maintains good speech quality in the situation where the connection faces low C/I or low signal level

2. Coverage gain: Link level simulation results illustrated improvement in terms of TCH FER (up to 5.5dB at 1% FER in C/I)

3. Capacity gain: Compared to GSM HR codec, AMR HR codec obtains remarkable better speech quality through link adaptation. The increased half rate utilization increases the amount of calls served by a cell, especially during busy hours

4. Interference reduction: In case of high penetration of AMR mobiles, the reduced interference (due to aggressive power control for AMR mobiles) benefits the EFR mobiles and may allow tightening of the frequency reuse




4. Requirements for AMR Activation AMR is a technology that enables operators smoothly and cost-efficiently to add voice capacity in their networks. This only requires a software upgrade (BSC: S10 onwards; MSC: M10 onwards; BTS: see 4.3). However, depending on the current Core and Radio configuration additional capacity may be required including transcoders, Ater interface (16kbit/s) and TRXSIG addition (32k). Furthermore, if there is non-NSN (North) MSC core network, the interworking of circuit pool switching needs to be checked.

4.1 AMR capable MSAMR codec support is required by the mobile stations. It is not possible to assess potential AMR traffic levels on a network before AMR is activated. The AMR statistics for AMR call requests are only updated if AMR is activated.

It is difficult to correctly estimate the penetration of AMR capable MS in the network if AMR is not active. The only estimate can be drawn from the IMEI snapshot (difficult and lot of missing information) or thru the operator’s handset sales information (if available). In either case, one has to know which MS from different vendors have the AMR capability.

4.2 TRX Signalling requirementsIntroduction of AMR HR causes increased load in measurement reporting due to an increase in the number of voice channels on the TRX; therefore it can happen that a capacity of 16 kbit/s LAP-D signalling link is not sufficient in all cases. This is certainly the case if the TRX is filled with HR and also has an SDCCH/8 TSL. The TRX could have 22 telecom channels. 16 kbps can only support 18. When the TRX contains merely HR or DR TCH resources, the situation becomes even worse if the SDCCHs have also been configured on the TRX. Therefore a 32 kbit/s LAP-D link should be introduced to support the telecom signalling.

4.3 Equipment requirementsAMR codecs are supported by different Network Elements as follows:

AMR codec support in Base Stations:

Table 7: AMR codec support in base stations

BTS AMR FR AMR HR SW Ver2nd Gen Base Station No support for AMR No support for AMR N/A

Talk Family Base Station

4.75, 5.90, 7.40, 12.2 kbps

4.75, 5.90, 7.40 kbps DF7 or later

Prime Site Base Station

4.75, 5.90, 7.40, 12.2 kbps

4.75, 5.90, 7.40 kbps DF5.0 (last Rel supporting AMR)

Insite Base Station No support for AMR No support for AMR N/A

Ultrasite Base Station All All except 7.90 kbps CX 3.0 or later

Metrosite Base Station All All except 7.90 kbps CXM 3.0 or later




Flexi EDGE Base Station

All All except 7.90 kbps EP1.0 or later

Note : PrimeSite BTS AMR support is similar to that of Talk-family BTS. Due to limited DSP processor/memory capacity the frequency hopping functionality will be removed from PrimeSite BTSs to enable this SW modification. This means that the last PrimeSite SW release supporting frequency hopping will be DF5.0.

AMR codecs support in BSC and TCSM:All the BSCs and TCSM2 with software version S10 onwards have full AMR support except 7.95 kbit/s on HR channel.

AMR Code Support in MSC:MSC has AMR support from M10 onwards.

4.4 BSC Capacity requirements BSC capacity is dependant upon the BSC type. E.g. BSC3i2000 can support upto 2000 TRXs full rate or 1000 TRXs dual rate. This is because dual rate use twice the group switch capacity. In reality the capacity will fall somewhere between the two extremes since not all TRXs will be dual rate enabled. This actual capacity limit therefore needs to be calculated by checking the amount of full rate and dual rate TRXs configured in the BSC.

4.5 Circuit Pool ConfigurationThe A interface speech circuits (CIC) are divided into pools (CIP) according to the TCSM capabilities. Circuits in the same pool have the same transcoding capabilities. The main factors when dividing the circuits into pools is the channel rate and the speech codecs supported

4.5.1 TCSM2 support

Circuit pool 23 is the only AMR pool that is supported by S11/S11.5 BSC and TCSM2. This particular pool does not support any other speech coding than AMR and therefore pool switching is needed during call setups and handovers when MSC has allocated AMR circuit but BSC selects non-AMR speech coding, and vice versa, when MSC has allocated non-AMR circuit but BSC selects AMR coding. Circuit pool switching affects TCH request, reject and success statistics. Changes in statistics (can) have an impact on KPIs including counters that are affected by pool switching.

The counter c1208 (A_IF_CRC_MISMATCH_CALL_SETUP) counts the number of the TCH requests rejected because of the mismatch between the types of the requested channel and the A interface circuit (updated in call setup phase only).

This means that when AMR is introduced to the network, either a current pool is modified to support AMR or a new one is introduced for AMR use only. The new circuit pool (pool 23) is needed in A interface configuration. AMR feature need to be activated first and Abis parameters need to be set on Abis interface.




There are two alternative ways to modify existing circuit pool (refer to BSS S13 NED Documentation: Modifying Speech Circuits):

speech circuits are removed and added during modification

speech circuits are transferred automatically during modification

4.5.2 TCSM3 support

TCSM3i supports all speech codecs simultaneously on pools 28 and 32. TCSM3 requires BSS S12 or higher release.

Pool 28 supports both FR and HR speech, EFR speech, AMR full and half rate speech, and a maximum of 14.5 kbit/s radio interface data rate in one full rate channel.

Pool 32 supports, in addition to the codecs supported by pool 28, also High Speed Circuit Switched Data (HSCSD) with a maximum of 4 full rate channels on a multislot configuration.

The benefit of having all speech codecs in the same circuit pool is that after the TCSM is taken into use, there is no need to change the configuration even if the traffic pattern in the network changes. This may happen, for example, when AMR capable mobile terminal penetration will gradually increase over time and the higher speech quality and end-to-end network efficiency of AMR is needed.

In addition, the pool switching will not be required when handing over of calls from AMR capable cell to a non-AMR capable cell and vice-versa. This reduces the potential of drops calls during such handovers.




5. AMR dimensioning

5.1 BackgroundThe dimensioning of the network will be different when AMR half rate (HR) is used because the Erlang-B table is not applicable any more. This means that when assuming all the timeslots configured as dual rate (DR) the maximum traffic that can be served with less than 2% GoS does not equal with the result received when doubling the number of channels in Erlang-B table. This is because the AMR HR is used only in good radio conditions.

For AMR HR dimensioning new tables has been developed using mathematical model based on Markov process. These tables consider the HR traffic share. In case there is no suitable Markov table available for a given blocking probability, the Erlang table will be applied.

A case of 2 TRX per cell, where AMR HR is introduced is presented below. The voice capacity theoretically increases more than double. In practice all the AMR HR time slots could not be necessarily used due to bad radio conditions.

5.2 Capacity increaseThe capacity increase brought by AMR HR compared to AMR FR is described below. The DR time slot implementation of 2 TRX cell is shown in three phases.

Introducing AMR HR in 2 TRX Cell

Phase 0: Existing EFR FR: 16 ch/cell, 13 voice ch, max. 7 Erl/cell *)

Time slot 0 1 2 3 4 5 6 7TRX1 S S F F F F F G

TRX2 F F F F F F F F

Phase 1: Adding 1 DR TSL/TRX: 18 ch/cell, 15 voice ch, max. 9 Erl/cell *)

Time slot 0 1 2 3 4 5 6 7TRX1 S S D F F F F G

TRX2 D F F F F F F F




Phase 2: All voice TSL are DR: 29 ch/cell, 26 voice ch, max. 18 Erl/cell *)

Time slot 0 1 2 3 4 5 6 7TRX1 S S D D D D D G

TRX2 D D D D D D D D

S= Signalling channel, F = Full Rate channel, G= GPRS channel, D= Dual Rate channel

*) At 2% Blocking rate, using Erlang B considering HR is used without Radio Link Constraints

Figure 9: TCH DR timeslot implementation

It is seen that the Phase 2 doubles the voice capacity compared to phase 0. Signalling load between BSC and MSC has to be considered as well. The next table shows the percentage of saved capacity after the AMR HR implementation. The share of AMR HR users based on good C/I is considered in the table. The figure below shows the Reduction of TSL required with AMR HR

Table 8: Reduction of TSL required with AMR HR

5.3 Traffic tableThe table below displays the traffic that can be served with different number of Time Slots (TS) available and different penetration of AMR HR. For example, 70% HR

Savi

ng in

res

ourc

es

2% GoS

# Time Slots 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

1 0.0% 0.2% 0.5% 1.2% 2.3% 3.7% 6.5% 7.5% 17.2% 34.0% 50.0%2 0.0% 0.8% 2.5% 5.2% 9.2% 13.9% 19.7% 25.7% 32.5% 41.4% 50.0%3 0.0% 1.0% 3.2% 6.6% 11.1% 16.2% 22.1% 28.3% 35.3% 42.6% 50.0%4 0.0% 1.3% 4.1% 8.1% 12.9% 18.3% 24.1% 30.0% 36.5% 43.2% 50.0%5 0.0% 1.6% 4.8% 9.2% 14.3% 19.6% 25.3% 31.0% 37.2% 43.6% 50.0%6 0.0% 2.0% 5.4% 10.0% 15.2% 20.5% 26.1% 31.7% 37.6% 43.8% 50.0%7 0.0% 2.2% 5.9% 10.6% 15.9% 21.1% 26.6% 32.1% 38.0% 44.0% 50.0%8 0.0% 2.5% 6.4% 11.1% 16.4% 21.6% 27.0% 32.5% 38.2% 44.1% 50.0%9 0.0% 2.8% 6.7% 11.5% 16.7% 21.9% 27.3% 32.7% 38.4% 44.2% 50.0%

10 0.0% 3.0% 7.0% 11.8% 17.1% 22.2% 27.6% 33.0% 38.5% 44.3% 50.0%11 0.0% 3.1% 7.3% 12.1% 17.3% 22.5% 27.8% 33.1% 38.7% 44.3% 50.0%12 0.0% 3.2% 7.4% 12.3% 17.5% 22.7% 28.0% 33.3% 38.8% 44.4% 50.0%13 0.0% 3.3% 7.6% 12.5% 17.7% 22.9% 28.1% 33.4% 38.9% 44.4% 50.0%14 0.0% 3.4% 7.7% 12.6% 17.9% 23.0% 28.2% 33.5% 38.9% 44.5% 50.0%15 0.0% 3.5% 7.9% 12.8% 18.0% 23.1% 28.4% 33.6% 39.0% 44.5% 50.0%16 0.0% 3.6% 8.0% 12.9% 18.1% 23.2% 28.4% 33.7% 39.1% 44.5% 50.0%24 0.0% 4.0% 8.6% 13.6% 18.7% 23.8% 28.9% 34.1% 39.4% 44.7% 50.0%32 0.0% 4.2% 8.8% 13.8% 18.9% 24.0% 29.1% 34.3% 39.5% 44.8% 50.0%40 0.0% 4.2% 8.9% 13.9% 19.1% 24.2% 29.3% 34.4% 39.6% 44.9% 50.0%48 0.0% 4.2% 9.0% 14.0% 19.2% 24.3% 29.4% 34.5% 39.7% 44.9% 50.0%56 0.0% 4.2% 8.9% 14.0% 19.3% 24.3% 29.5% 34.6% 39.8% 44.9% 50.0%

% of users with good conditions to use AMR-HR (for example C/I > 12dB)

Saving Factor = % of resources (TS) saved by using AMR-HR

By using AMR HR, when 70% of network has conditions for

AMR HR, we can save 34% if 24

AMR HR capable TSLs are available (we would need 36 TSLs with only FR to serve the same

traffic)

Savi

ng in

res

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es

2% GoS

# Time Slots 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

1 0.0% 0.2% 0.5% 1.2% 2.3% 3.7% 6.5% 7.5% 17.2% 34.0% 50.0%2 0.0% 0.8% 2.5% 5.2% 9.2% 13.9% 19.7% 25.7% 32.5% 41.4% 50.0%3 0.0% 1.0% 3.2% 6.6% 11.1% 16.2% 22.1% 28.3% 35.3% 42.6% 50.0%4 0.0% 1.3% 4.1% 8.1% 12.9% 18.3% 24.1% 30.0% 36.5% 43.2% 50.0%5 0.0% 1.6% 4.8% 9.2% 14.3% 19.6% 25.3% 31.0% 37.2% 43.6% 50.0%6 0.0% 2.0% 5.4% 10.0% 15.2% 20.5% 26.1% 31.7% 37.6% 43.8% 50.0%7 0.0% 2.2% 5.9% 10.6% 15.9% 21.1% 26.6% 32.1% 38.0% 44.0% 50.0%8 0.0% 2.5% 6.4% 11.1% 16.4% 21.6% 27.0% 32.5% 38.2% 44.1% 50.0%9 0.0% 2.8% 6.7% 11.5% 16.7% 21.9% 27.3% 32.7% 38.4% 44.2% 50.0%

10 0.0% 3.0% 7.0% 11.8% 17.1% 22.2% 27.6% 33.0% 38.5% 44.3% 50.0%11 0.0% 3.1% 7.3% 12.1% 17.3% 22.5% 27.8% 33.1% 38.7% 44.3% 50.0%12 0.0% 3.2% 7.4% 12.3% 17.5% 22.7% 28.0% 33.3% 38.8% 44.4% 50.0%13 0.0% 3.3% 7.6% 12.5% 17.7% 22.9% 28.1% 33.4% 38.9% 44.4% 50.0%14 0.0% 3.4% 7.7% 12.6% 17.9% 23.0% 28.2% 33.5% 38.9% 44.5% 50.0%15 0.0% 3.5% 7.9% 12.8% 18.0% 23.1% 28.4% 33.6% 39.0% 44.5% 50.0%16 0.0% 3.6% 8.0% 12.9% 18.1% 23.2% 28.4% 33.7% 39.1% 44.5% 50.0%24 0.0% 4.0% 8.6% 13.6% 18.7% 23.8% 28.9% 34.1% 39.4% 44.7% 50.0%32 0.0% 4.2% 8.8% 13.8% 18.9% 24.0% 29.1% 34.3% 39.5% 44.8% 50.0%40 0.0% 4.2% 8.9% 13.9% 19.1% 24.2% 29.3% 34.4% 39.6% 44.9% 50.0%48 0.0% 4.2% 9.0% 14.0% 19.2% 24.3% 29.4% 34.5% 39.7% 44.9% 50.0%56 0.0% 4.2% 8.9% 14.0% 19.3% 24.3% 29.5% 34.6% 39.8% 44.9% 50.0%



2% GoS

# Time Slots 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

1 0.0% 0.2% 0.5% 1.2% 2.3% 3.7% 6.5% 7.5% 17.2% 34.0% 50.0%2 0.0% 0.8% 2.5% 5.2% 9.2% 13.9% 19.7% 25.7% 32.5% 41.4% 50.0%3 0.0% 1.0% 3.2% 6.6% 11.1% 16.2% 22.1% 28.3% 35.3% 42.6% 50.0%4 0.0% 1.3% 4.1% 8.1% 12.9% 18.3% 24.1% 30.0% 36.5% 43.2% 50.0%5 0.0% 1.6% 4.8% 9.2% 14.3% 19.6% 25.3% 31.0% 37.2% 43.6% 50.0%6 0.0% 2.0% 5.4% 10.0% 15.2% 20.5% 26.1% 31.7% 37.6% 43.8% 50.0%7 0.0% 2.2% 5.9% 10.6% 15.9% 21.1% 26.6% 32.1% 38.0% 44.0% 50.0%8 0.0% 2.5% 6.4% 11.1% 16.4% 21.6% 27.0% 32.5% 38.2% 44.1% 50.0%9 0.0% 2.8% 6.7% 11.5% 16.7% 21.9% 27.3% 32.7% 38.4% 44.2% 50.0%

10 0.0% 3.0% 7.0% 11.8% 17.1% 22.2% 27.6% 33.0% 38.5% 44.3% 50.0%11 0.0% 3.1% 7.3% 12.1% 17.3% 22.5% 27.8% 33.1% 38.7% 44.3% 50.0%12 0.0% 3.2% 7.4% 12.3% 17.5% 22.7% 28.0% 33.3% 38.8% 44.4% 50.0%13 0.0% 3.3% 7.6% 12.5% 17.7% 22.9% 28.1% 33.4% 38.9% 44.4% 50.0%14 0.0% 3.4% 7.7% 12.6% 17.9% 23.0% 28.2% 33.5% 38.9% 44.5% 50.0%15 0.0% 3.5% 7.9% 12.8% 18.0% 23.1% 28.4% 33.6% 39.0% 44.5% 50.0%16 0.0% 3.6%

2% GoS

# Time Slots 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

1 0.0% 0.2% 0.5% 1.2% 2.3% 3.7% 6.5% 7.5% 17.2% 34.0% 50.0%2 0.0% 0.8% 2.5% 5.2% 9.2% 13.9% 19.7% 25.7% 32.5% 41.4% 50.0%3 0.0% 1.0% 3.2% 6.6% 11.1% 16.2% 22.1% 28.3% 35.3% 42.6% 50.0%4 0.0% 1.3% 4.1% 8.1% 12.9% 18.3% 24.1% 30.0% 36.5% 43.2% 50.0%5 0.0% 1.6% 4.8% 9.2% 14.3% 19.6% 25.3% 31.0% 37.2% 43.6% 50.0%6 0.0% 2.0% 5.4% 10.0% 15.2% 20.5% 26.1% 31.7% 37.6% 43.8% 50.0%7 0.0% 2.2% 5.9% 10.6% 15.9% 21.1% 26.6% 32.1% 38.0% 44.0% 50.0%8 0.0% 2.5% 6.4% 11.1% 16.4% 21.6% 27.0% 32.5% 38.2% 44.1% 50.0%9 0.0% 2.8% 6.7% 11.5% 16.7% 21.9% 27.3% 32.7% 38.4% 44.2% 50.0%

10 0.0% 3.0% 7.0% 11.8% 17.1% 22.2% 27.6% 33.0% 38.5% 44.3% 50.0%11 0.0% 3.1% 7.3% 12.1% 17.3% 22.5% 27.8% 33.1% 38.7% 44.3% 50.0%12 0.0% 3.2% 7.4% 12.3% 17.5% 22.7% 28.0% 33.3% 38.8% 44.4% 50.0%13 0.0% 3.3% 7.6% 12.5% 17.7% 22.9% 28.1% 33.4% 38.9% 44.4% 50.0%14 0.0% 3.4% 7.7% 12.6% 17.9% 23.0% 28.2% 33.5% 38.9% 44.5% 50.0%15 0.0% 3.5% 7.9% 12.8% 18.0% 23.1% 28.4% 33.6% 39.0% 44.5% 50.0%16 0.0% 3.6% 8.0% 12.9% 18.1% 23.2% 28.4% 33.7% 39.1% 44.5% 50.0%24 0.0% 4.0% 8.6% 13.6% 18.7% 23.8% 28.9% 34.1% 39.4% 44.7% 50.0%32 0.0% 4.2% 8.8% 13.8% 18.9% 24.0% 29.1% 34.3% 39.5% 44.8% 50.0%40 0.0% 4.2% 8.9% 13.9% 19.1% 24.2% 29.3% 34.4% 39.6% 44.9% 50.0%48 0.0% 4.2% 9.0% 14.0% 19.2% 24.3% 29.4% 34.5% 39.7% 44.9% 50.0%56 0.0% 4.2% 8.9% 14.0% 19.3% 24.3% 29.5% 34.6% 39.8% 44.9% 50.0%



By using AMR HR, when 70% of network has conditions for

AMR HR, we can save 34% if 24

AMR HR capable TSLs are available (we would need 36 TSLs with only FR to serve the same

traffic)




penetration the number of TS required to serve 16.7 Erlangs is 16, while for pure AMR-FR it would require around 24 time slots to serve the same traffic (around 33% saving in resources). Figure below shows the Traffic table for AMR HR

Table 9: Traffic table for AMR HR

2% GoS# Time Slots 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

1 0.0204 0.02 0.02 0.02 0.02 0.03 0.03 0.03 0.06 0.11 0.222 0.2236 0.23 0.24 0.25 0.28 0.32 0.37 0.45 0.58 0.79 1.093 0.6024 0.62 0.65 0.70 0.77 0.87 1.01 1.19 1.44 1.80 2.284 1.0927 1.12 1.18 1.28 1.42 1.59 1.82 2.10 2.47 2.97 3.635 1.6578 1.71 1.81 1.96 2.17 2.42 2.73 3.11 3.60 4.25 5.086 2.2769 2.35 2.50 2.71 2.99 3.31 3.71 4.19 4.80 5.60 6.617 2.9367 3.04 3.24 3.51 3.85 4.25 4.74 5.32 6.06 7.00 8.208 3.6287 3.77 4.01 4.35 4.76 5.24 5.81 6.50 7.36 8.45 9.839 4.3468 4.53 4.82 5.21 5.70 6.25 6.92 7.71 8.69 9.93 11.49

10 5.0864 5.31 5.65 6.11 6.66 7.29 8.05 8.94 10.05 11.45 13.1811 5.8443 6.11 6.51 7.02 7.64 8.35 9.20 10.20 11.44 12.98 14.9012 6.6178 6.92 7.37 7.94 8.65 9.43 10.37 11.48 12.84 14.53 16.6313 7.405 7.75 8.25 8.89 9.66 10.53 11.56 12.77 14.26 16.11 18.3814 8.204 8.60 9.15 9.85 10.69 11.64 12.76 14.08 15.70 17.69 20.1515 9.0137 9.45 10.06 10.82 11.74 12.77 13.98 15.41 17.15 19.29 21.9316 9.8328 10.32 10.98 11.81 12.79 13.90 15.21 16.74 18.61 20.91 23.7324 16.636 17.50 18.60 19.94 21.52 23.27 25.33 27.72 30.62 34.13 38.3932 23.729 24.98 26.52 28.37 30.52 32.93 35.75 39.04 42.99 47.73 53.4340 30.998 32.62 34.61 36.98 39.74 42.82 46.41 50.59 55.58 61.55 68.6948 38.387 40.36 42.80 45.71 49.08 52.84 57.20 62.28 68.32 75.52 84.1056 45.863 48.16 51.05 54.51 58.52 62.96 68.09 74.07 81.16 89.60 99.62

% of users with good conditions to use AMR-HR

The use of the above table is demonstrated with an example below.

Example: Traffic per user is assumed to be 25mErl. There are 800 people under the cell with a penetration of 50%.

Traffic offered: 800 x 0.5 x 25mErl = 10 Erl

Case1: Based on Erlang B table, with 2% GoS ==> 17 Ch needed. With the signalling channels included, 3 TRXs would be required

Case2: Based on Traffic table for AMR HR, if the % of users with good conditions for AMR HR is 70% ==> 11 Ch needed. With the signalling channels included, only 2 TRXs are required.




6. Implementation of AMR feature to the network AMR Full Rate (FR) and AMR Half Rate (HR) are both licence-based software products. The usage of AMR FR is controlled by an ON/OFF licence and the usage of AMR HR by a capacity licence based on TRX count.

You can activate AMR FR, AMR HR, or both.

For details and MML commands, see the BSS S13 BSC/TCSM NED documentation:

Activating and Testing BSS6115: Half Rate

Activating and Testing BSS10004: AMR

6.1 Steps for AMR ImplementationBasic steps for implementation of AMR are listed below. Detailed steps of implementation are not in the scope of this document and should be referred to in the BSS S13 NED Documentation.

1. Implement PRFILE parameter 619 in BSC for AMR FR and ensure licences for AMR HR are installed and activated (check with ZW7I:FEA,FULL:FEA=1;)

2. Create AMR pool (23) on Transcoder for AMR calls and pool (20) for non-AMR calls (EFR)

3. Create Speech circuit on MSC and BSC

4. Download AMR related parameters for BTS/BSC level

5. In case of AMR HR, ensure that the timeslots are configured as TCHD (dual rate) or TCHH (half rate). TCHD is preferred over TCHH since those timeslots can be used for HR, FR as well as EGPRS use. TCHH timeslots can’t be used for EGPRS or FR.

6. Unlock speech circuits on MSC - For Live AMR calls. If not carried out then AMR will not work and normal calls will proceed. AMR must be activated before MSC Speech circuits are unlocked as drops may occur. The MSC/NSS has no knowledge if the BSC has AMR activated or not.

Basic call and handover tests must be done immediately after the feature activation. Testing should cover at least the following aspects

Call origination/termination – MOC/MTC

Non-AMR MS in AMR capable cell

Handover tests – across BSC, MSC boundary for AMR and non-AMR MS

Handover from AMR to non-AMR cells and back

Packing/Unpacking intra-cell HO




7. AMR parameters description and SettingThis chapter describes the AMR related parameters, proper settings and best practices. Some aspects of the AMR functionality will be explained with the related parameters. All the parameters are on cell basis.

7.1 Initial codec mode selection

7.1.1 Codec sets

It has to be remembered that MS supports all speech codec modes, although only a set of up to 4 speech codec modes is used during a call (codec set for FR or HR can be updated during the call in case of a handover to another BTS) and BSC supports all of speech codec modes, except 7.95 kbit/s on HR channel.

The two parameters amrConfFrCodecModeSet (FRC) and amrConfHrCodecModeSet (HRC) specify which of the possible speech coding bit-rate are implemented in the serving cell.

The value for these parameters is specified as a bit mask. In the figure below, the default codec sets for FR are 12.2, 7.9, 5.9 and 4.75kbps. This can be specified as value 149 in decimal (from 10010101 in binary).

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0FR 12.2 10.2 7.95 7.4 6.7 5.9 5.15 4.75HR 7.4 6.7 5.9 5.15 4.75

FR 1 0 0 1 0 1 0 1 = 149 (decimal)HR 0 0 0 1 0 1 0 1 = 21 (decimal)

Similarly, the default set for HR is 7.4, 5.9 and 4.75kbps (value 21 in decimal)

The default sets are good to start with and usually do not need to be modified. Both have the least and most robust codecs in the set and additional codec(s) in between those two.

7.1.2 Initial Codec mode

The Initial Codec mode to start the speech coding operation at call set-up and after handover may be signalled by layer 3 signalling, in which case it shall be used by BTS and MS.

You can either allow the initial codec to be decided by a rule (based on amount of codecs in the codec set) or you can specify the exact codec to start with.

amrConfFrInitCodecMode (ICMI and FRI)

Value 0: Initial codec mode is defined by the implicit rule provided in GSM (3GPP) 45.009.

Value 1: Initial codec mode is defined by the Start Mode field (parameter amrConfFrStartMode (FRS))




Implicit rule provided in 3GPP 45.009:

If the codec mode set contains 1 mode, it is the Initial Codec mode

If the codec mode set contains 2 or 3 modes, the Initial Codec mode is the most robust mode of the set (lowest bit rate).

If the codec mode set contains 4 modes, the Initial Codec mode is the second most robust mode of the set (the second lowest bit rate).

amrConfFrStartMode (FRS) range is 00, 01, 10, 11 ==> codec mode 1,2,3, 4.

Of course the choice of the most robust codec available (less bit rate for speech) is recommended for higher success rate during call setup and after handover.

Similar to the above parameters for FR, there are parameters for HR. See table below for a summary of the parameters.

Table 10: Parameters for Initial Codec Mode selection


Description

AMR Configuration FR Codec Mode Set

BTS FRC 149 With this parameter you define the codec mode set for a full rate channel. If the parameter is defined as disabled, then the whole codec mode set is disabled. Codec set used is 12.2, 7.40, 5.9, 4.75 kbit/s

AMR Configuration FR Init Codec Mode

BTS FRI 0 With this parameter you define whether the initial codec mode used by the mobile station is defined explicitly in the AMR codec mode set or is it implicitly derived by the mobile station from the amount of codec modes in the AMR codec mode set.

AMR Configuration FR Start Mode

BTS FRS 0 With this parameter you define explicitly the initial codec mode used by the mobile station.

AMR Configuration HR Codec Mode Set

BTS HRC 21 With this parameter you define the codec mode set for a full rate channel. If the parameter is defined as disabled, then the whole codec mode set is disabled. Codec set used is 7.40, 5.9, 4.75 kbit/s

AMR Configuration HR Init Codec Mode

BTS HRI 1 With this parameter you define whether the initial codec mode used by the mobile station is defined explicitly in the AMR codec mode set or is it implicitly derived by the mobile station from the amount of codec modes in the AMR codec mode set.

AMR Configuration HR Start Mode

BTS HRS 1 With this parameter you explicitly define the initial codec mode used by the mobile station.

With HR, it is recommended to start with the codec 5.9kbps, which is the second most robust. This is to have better voice quality than starting with codec 4.75 (default). LA can change the codec to 4.75 during the call if necessary.




With initAmrChannelRate (IAC) parameter you define the initial channel in call set-up (except FACCH call set-up), internal inter cell handover (HO) and external HO for an AMR call. This parameter was discussed in Section 2.4.

The parameter IAC defines the preference for channel mode (FR/HR) whereas the parameters FRI/HRI define the initial codec to be used.

7.2 Codec mode adaptation

7.2.1 Full Rate (FR) Channel

As upto 4 codecs can be used in a call in a cell, a codec set has 4 codecs defined. The switching of codecs within this set is controlled by three thresholds.

For FR, these thresholds are

amrConfigurationFr: threshold1 – for changing form codec 2 (second lowest bit rate) to codec 1 (lowest bit rate, most robust)

amrConfigurationFr: threshold2 – for changing form codec3 to codec2

amrConfigurationFr: threshold3 – for changing from codec 4 to codec3

Corresponding to each threshold, there is a hysteresis value defined for switching codecs from more robust to less robust ones. See figure below for explanation.

Figure 10: Thresholds for codec adaptation

In the figure above, FRT1 = 4dB, FRT2 = 7dB and FRT3 = 11dB.

To understand the figure, start from the top right with the orange line where the call is at FR12.2 codec. As the C/I ratio degrades, the LA allocates more robust codecs FR 7.4, FR 5.9 and eventually FR 4.75 to try to keep the FER from degrading. The codec is switched at the threshold value (without hysteresis).

Now as the C/I starts to improve, the LA allocates codecs that are less robust but provide higher speech quality (follow the pink line). To avoid ping-pong codec changes, the Hysteresis value must be fulfilled before the change of codec as C/I improves.




The default values are 4dB, 7dB, and 11dB (in ideal conditions simulations show that also the values 6dB, 9dB and 13dB give good results in terms of FER (Frame Error Rate) and mean opinion score (MOS). Setting the thresholds higher is a more conservative setting (playing it safe) that allows higher use of more robust codecs. As an example, if FRT1 is set to 13dB, the change from FR12.2 to FR7.4 would happen when the C/I reaches 13 dB (as compared to waiting till 11dB, the default value).

From the BSS counters, it is possible to get the distribution of call samples by codecs and RxQual classes UL and DL. This information can be used to check the performance of the codecs when optimizing the thresholds.

Aggressive (low C/I) thresholds increases the number of TCH frame errors since the high modes are used even with low C/I values. Conversely, thresholds that are set too high decrease the usage of higher modes thus some speech quality is lost due to lower number of speech bits.

7.2.2 Half Rate (HR) Channel

Similarly, for HR, these thresholds are

amrConfigurationHr: threshold1



Corresponding to each threshold, there is a hysteresis value defined for switching codecs from more robust to less robust ones.

In case of only three codec modes (default HR codecModeSet) threshold 3 and hysteresis 3 are set to "0" in order not to use them

7.2.3 Parameter Summary

Table 11: Thresholds for Codec Mode Adaptation


Description

AMR Configuration FR Hysteresis 1 (dB)

BTS FRH1 1 With this parameter, together with AMR FR threshold 1, you define the threshold for switching from codec mode 0 (lowest bit-rate) to codec mode 1 (second lowest bit-rate). Unused hysteresis is set as 0.


BTS FRH2 1 With this parameter, together with AMR FR threshold 2, you define the threshold for switching from codec mode 1 (second lowest bit-rate) to codec mode 2 (third lowest bit-rate). Unused hysteresis is set as 0.





BTS FRH3 1 With this parameter, together with AMR FR threshold 3, you define the threshold for switching from codec mode 2 (third lowest bit-rate) to codec mode 3 (highest bit-rate). Unused hysteresis is set as 0.

AMR Configuration FR Threshold 1 (dB)

BTS FRT1 9 With this parameter you define the threshold for switching from codec mode 1 to codec mode 0. Unused threshold is set as 0.





AMR Configuration HR Hysteresis 1 (dB)

BTS HRH1 1 With this parameter you define the threshold for switching from codec mode 0 to codec mode 1. Unused threshold is set as 0.





AMR Configuration HR Threshold 1 (dB)

BTS HRT1 14 With this parameter you define the threshold for switching from codec mode 1 to codec mode 0. Unused threshold is set as 0.





Note that the thresholds have a step of 0.5dB. So a value of 18 in the OSS database would mean 9dB on MML. The thresholds suggested above are on the safer side, i.e., more robust codecs are used as compared to setting the thresholds lower.

7.3 Handovers ConfigurationTwo BSC related parameter refers to the behaviour during internal and external handovers: amrConfInHandovers (ACH) and amrSetGradesEnabl (ASG).

With amrConfInHandovers (ACH) it is possible to define the preference between the currently used multirate configuration (if it is suitable for target channel rate) or the one defined for the target BTS during internal and external handovers.




With amrSetGradesEnabl (ASG) it is possible to define whether codec mode set downgrades during internal HOs and upgrades after internal HOs are applied or not.

Table 12: Parameters for HO Configuration

Parameter Level MML Name Suggested

Value

Comments

AMR configuration in handover

BSC ACH 1 ”1” = the currently used multirate configuration is preferred. ”2” = the multirate configuration of target BTS is preferred If multirate configuration of source and target BTS are the same then ACH and ASG have no impact

AMR set grades enabled BSC ASG No Y = downgrades and upgrades are applied N = downgrades and upgrades are not applied. If multirate configuration of source and target BTS are the same then ACH and ASG have no impact

In order to make it possible to connect unidirectional speech path on target side, the multirate configuration on both sides should be the same (reduce muting period during HO).

If multirate configuration of source and target BTS are difference (e.g. Talk family BTS supports less codecs than UltraSite), the multirate configuration can be aligned before or after HO.

1. The codec set defined on the target side differs from the current codec set, but it can be aligned with the source side by selecting the current codec set. The target side alignment depends on the codec mode support of the target BTS. If the AMR configuration in handovers parameter prefers the codec set of the target BTS, the target side is upgraded back to its original AMR codec set after the handover if the parameter AMR set grades enabled allows it.

Table 13: Example handover from a Talk-Family BTS

Source: Talk-Family

Target: Nokia UltraSite

Set selectedfor target

Set upgradedafter handover

12.2 12.2 12.2 12.2

7.4 10.2 7.4 10.2

5.9 6.7 5.9 6.7

4.75 5.15 4.75 5.15

The table shows the codec set selected for the target side during a handover and also the result of a possible upgrade after the handover. Mode modify is




triggered for BTS and MS on target side after HO if target BTS support more codec (upgrade, Talk family → UltraSite)

2. The codec set defined on the target side differs from the current codec set, but it cannot be aligned with the source side because of the target side codec mode support. That is why the source side is aligned with the target side by triggering a downgrade procedure on the source side, if the parameter AMR set grades enabled allows it. If the downgrade is not allowed, use of the unidirectional downlink speech path connection on the target BTS side is not possible. Downgrades take place if the parameter AMR configuration in handovers prefers the currently used codec set.

Table 14: Example handover from an UltraSite BTS

Source: Nokia UltraSite (before downgrade)

Source: Nokia UltraSite (after downgrade)

Target:Talk-Family

12.2 12.2 12.2

10.2 7.4 7.4

6.7 5.9 5.9

5.15 4.75 4.75

The table shows the codec set situation on the source side both before and after the downgrade and it also shows that the target side is kept as it is during the handover. Mode modify is triggered for BTS and MS on source side before HO if target BTS supports less codecs (downgraded, UltraSite → Talk family)

There are two types of destination properties that need to be taken care of in handover: Traffic channel type (AMR FR, AMR HR, EFR) and the codec used in the destination cell. To handle the traffic channel type, two parameters are used: Initial AMR configuration and HRI. With Initial AMR conf set to AMR FR, HRI is not used; however we can have five different parameter setting for TCH in handover (HRI), when initial AMR conf is set to ‘Any’ rate. The codec selection within a channel type (FR or HR) is done with AMR conf in handover and AMR set grades Enabled, as described above.

Also amrConfigurationHr is used when initial AMR channel rate is set to 0 (= any rate).

In channel allocation for Intra and Internal handovers, the channel type selection is governed by two BTS level parameters: tchRateInternalHo (HRI) and tchRateIntraCellHo (TRIH)

Parameter tchRateInternalHo (HRI):

tchRateInternalHo (HRI) is used to control the speech and channel type changes in handover when IAC=1

If set HRI=1, channel type and speech codec used in source BTS are primarily allocated in the target BTS





Suggested Value

Description

TCH in handover

BSC HRI 1 With this parameter you define the traffic channel allocation during BSS internal or external handovers. The parameter controls the target cell selection and the TCH channel rate and speech codec determination in traffic channel allocation. The parameter can have the following values:

1 ... The call serving type of TCH has to be primarily allocated. The call serving type of speech codec inside the call serving type of TCH can change.2 ... The call serving type of TCH and the call serving type of speech codec are preferred to be primarily allocated during the speech connection. The channel rate change is possible during data connection, if necessary, and if the radio interface data rate allows it.3 ... The channel rate and speech codec changes are totally denied.4 ... The preferred channel rate of TCH and preferred speech codec have to be primarily allocated.5 ... TCH has to be primarily allocated from the best BTS of the handover candidate list.

Parameter tchRateIntraCellHo (TRIH):

With this parameter you control the TCH channel rate determination in TCH allocation and the TCH speech codec to be allocated during internal intra-cell handover


Suggested Value

Description

TCH Rate Intra-Cell Handover

BTS TRIH 0 With this parameter you control the TCH channel rate determination in TCH allocation and the TCH speech codec to be allocated during internal intra-cell handover.

0 (No constraints - follow HRI settings) 1 (the call serving type of TCH and the call serving type of speech codec are preferred to be primarily allocated) 2 (the call serving type of TCH and the call serving type of speech codec are preferred to be primarily allocated during the speech connection. The channel rate change is possible during data connection when needed if the radio interface data rate allows it)3 (the channel rate and speech codec changes are totally denied. The call serving type of channel is the only alternative in TCH allocation)4 (the preferred channel rate of TCH and preferred speech codec have to be primarily allocated)




For the best possible setting, the value for TRIH should be set to 0 and HRI set to 1, so that there will be no constraints for the any of the handover cases.

7.4 HO&PC thresholds parameters for AMR

Handover and Power control for AMR calls is done based on Rx Quality. Separate RxQual thresholds (for PC and HO) are specified for FR and HR AMR sets. RXLEV and Power Budget HO parameters are identical for AMR and EFR.

The following 4 parameters are for defining thresholds for HO due to Quality.

Table 15: Handover Control Thresholds


Description

AMR Handover FR Threshold Dl Rx Qual

BTS QDRF 5 With this parameter you define the threshold level of the downlink signal quality measurements for the BTS power decrease. Defined for the default FR AMR set.

AMR Handover FR Threshold Ul Rx Qual

BTS QURF 5 With this parameter you define the threshold level of the uplink signal quality measurements for the BTS power decrease. Defined for the default FR AMR set.

AMR Handover HR Threshold Dl Rx Qual

BTS QDRH 5 With this parameter you define the threshold level of the signal quality downlink measurements for triggering the handover. Defined for the default AMR HR set.

AMR Handover HR Threshold Ul Rx Qual

BTS QURH 5 With this parameter you define the threshold level of the signal quality uplink measurements for triggering the handover. Defined for the default AMR HR set.

With these parameters it is possible to define the threshold level of the signal quality downlink/uplink measurements for triggering the handover. Values for these thresholds should be set according to the default AMR codec sets. Current Nx and Px values of RxQual thresholds are used.

If operator wants to replace or remove the most robust mode on AMR set, the corresponding PC and HO RxQual thresholds has to be edited manually. This also applies to the least robust mode. Replacement or removal of a middle mode on AMR set does not effect on the new PC and HO thresholds.

One solution to benefit from AMR penetration is to use more aggressive (higher values) power control for AMR mobiles and thus decrease the average interference. This can be done by having different power control thresholds for AMR mobiles. By using higher thresholds for AMR mobiles (1-2 classes more), lower transmission powers are used and therefore less interference is caused.

The following 8 parameters are for defining thresholds for PC due to Quality. In general, PC can be more aggressive in AMR as compared to EFR due to better FER performance of AMR.




Table 16: Power Control Thresholds


Description

AMR Power Control FR PC Lower Threshold DL Rx Qual

BTS LDRF 3 With this parameter you define the threshold level of the downlink signal quality measurements for the BTS power increase. Defined for the default FR AMR set.

AMR Power Control FR PC Lower Threshold UL Rx Qual

BTS LURF 3 With this parameter you define the threshold level of the downlink signal quality measurements for the MS power increase. Defined for the default FR AMR set.

AMR Power Control FR PC Upper Threshold DL Rx Qual

BTS UDRF 1 With this parameter you define the threshold level of the downlink signal quality measurements for the BTS power decrease. Defined for the default FR AMR set.

AMR Power Control FR PC Upper Threshold UL Rx Qual

BTS UURF 1 With this parameter you define the threshold level of the downlink signal quality measurements for the MS power decrease. Defined for the default FR AMR set.

AMR Power Control HR PC Lower Threshold DL Rx Qual

BTS LDRH 2 With this parameter you define the threshold level of the downlink signal quality measurements for the BTS power increase. Defined for the default HR AMR set.

AMR Power Control HR PC Lower Threshold UL Rx Qual

BTS LURH 2 With this parameter you define the threshold level of the downlink signal quality measurements for the BTS power increase. Defined for the default HR AMR set.

AMR Power Control HR PC Upper Threshold DL Rx Qual

BTS UDRH 0 With this parameter you define the threshold level of the downlink signal quality measurements for the BTS power decrease. Defined for the default HR AMR set.

AMR Power Control HR PC Upper Threshold UL Rx Qual

BTS UURH 0 With this parameter you define the threshold level of the downlink signal quality measurements for the MS power decrease. Defined for the default HR AMR set.

7.5 Channel mode adaptation (Packing/Unpacking)Channel mode adaptation considers the traffic in the cell and the set quality thresholds to make decisions on Packing and Unpacking. RxQual HO thresholds are specified for FR and HR AMR and they are taken into account when making intra-cell handovers between FR AMR and HR AMR. Current Nx and Px values of RxQual thresholds are used. In addition, thresholds are set on BSC and BTS level for defining cell load.

Packing is triggered due to cell load while unpacking is triggered due to call quality.

Refer to Figure 11 for an example of packing of AMR FR calls to AMR HR. Spontaneous packing of FR AMR calls to HR AMR calls is triggered when




The cell load is high enough, i.e. the number of free full rate resources reduces below the value of the parameter lower limit for FR TCH resources (FRL)

AND at least 2 calls in which quality is above the amrHandoverFr(IHRF)

Packing continues until the cell load is low enough, i.e. the number of free full rate resources increases above the value of the parameter upper limit for FR TCH resources (FRU). Spontaneous packing is triggered by any new channel allocation.

Figure 11: Packing of FR calls to HR AMR calls due to cell load

The packing algorithm tries to fill the timeslots in HR channel pairs or tries to find an empty half for one HR channel allocation. Before FR – HR handover decision the number of timeslots having only one HR connection are measured. For example, if there is only one half timeslot available, that is allocated first. Then, if more FR – HR handovers are required, those will be made in pairs so that two FR connections are selected and allocated to same timeslot.

Spontaneous unpacking of AMR HR calls to AMR FR calls is triggered when the quality of an AMR HR call degrades below the amrHandoverHr (IHRH) for UL or DL. Cell load does not have an effect.

Table 17: Parameters controlling Packing/Unpacking


Suggested Value

Description

AMR Handover FR Intra Threshold DI Rx Qual

BTS IHRF 0 With this parameter you define the threshold level of the signal quality downlink and uplink measurements for triggering the intra-cell handover process for an AMR FR call in order to switch it to an AMR HR call.

AMR Handover HR Intra Threshold Dl Rx Qual

BTS IHRH 4 With this parameter you define the threshold level of the signal quality downlink and uplink measurements for triggering the intra-cell handover process for an AMR FR call in order to switch it to an AMR HR call.




Limit For FR TCH Resources Lower (%) FRL

BTS FRL 40 (variable)

With this parameter you define the percentage of full rate TCH resources that must be available for traffic channel allocation. Full rate TCHs are allocated until the number of free full rate resources is reduced below the threshold given in the parameter. The half rate resources are then allocated.

Limit For FR TCH Resources Upper (%) FRU

BTS FRU 60 (variable)

With this parameter you define the percentage of full rate TCH resources that must be available for traffic channel allocation. Full rate TCHs are again allocated when the number of the free full rate resources increases above the threshold given by the parameter.

Lower limit for FR TCH resources

BSC HRL 20 btsLoadDepTCHRate (HRL) and btsLoadDepTCHRate (HRU) are considered in call set-up and handovers only when IAC=1. HR is to be assigned if free resources go below HRL.

Upper limit for FR TCH resources

BSC HRU 40 FR is to be assigned if free resources go above HRU

Note that FRL and FRU are BTS level parameters and have priority over the corresponding BSC level parameters HRL and HRU. The packing/unpacking mechanism based on cell load is disabled if the lower limit is set higher than the upper limit i.e. HRL > HRU or FRL > FRU. In practice, it has been seen that it’s better to set HRL > HRU and FRL > FRU to be sure that the feature is disabled.

The default value of IHRF is 0 which means that only FR calls with excellent Rx Quality will be candidates for packing to HR. In case more HR is required due to congestion, the value can be adjusted (IHRF = 1) to allow more calls to be packed.

7.6 Unpacking and Intra-Cell HandoversAMR HR is not robust enough to cope with bad RF conditions compared to AMR FR. It has been observed in live networks that when a AMR HR call unpacks to AMR FR in bad RF conditions, the chances of the call getting dropped is very high. Due to this, some networks have disabled unpacking altogether to reduce the drops during intra-cell handovers. In case unpacking does not happen, the call would continue on HR and may get handed over to another cell (inter-cell handover).

The solution to the problem is available from S11.5 as a patch to UTPFIL parameters that govern the quality and level based thresholds to AMR unpacking.

RCS_INTF_LEV_DFCA_THR_PRM_C (parameter ID: 80)

This parameter is used to control handovers caused by AMR unpacking and interference based on RxLevel. If the average RxLevel is lower than the value of this parameter, handovers caused by AMR packing/unpacking or interference are not allowed. A suitable value for this parameter would be between -90 to -100 dBm

The value of this parameter can be between 1 and 63. If no value is given, the parameter is not in use.




RCS_QUAL_LIMIT_DFCA_PRM_C (parameter ID: 81)

This parameter is used to control handovers caused by AMR unpacking and interference based on RxQuality. If the average RxQuality is worse than or equal to the value of this parameter, handovers caused by AMR packing/unpacking or interference are not allowed. A suitable value for this parameter would be 5 (HR calls with quality worse than 5 would not unpack)

The value of this parameter can be between 1 and 7. If no value is given, the parameter is not in use.

These parameters would be available as regular BTS parameters in S14.

You can check the UTPFIL parameter values with the command: ZDFD: MCMU, 0:5AC006B,, N,W,: ;

Here is an example of how it will look like when checking by MML:

MCMU-0 FILE N:O 05AC006B RECORD N:O 00000000

01B3 007F 0000 0000


01B3 0080 000B 0000


01B3 0081 0007 0000

7.7 Radio link timeoutThe parameter Radio Link Timeout (RLT) is used in radio link failure (dropped call) situations to control whether the radio resources have been released or not. This is based on a counter which is increased by 2 when the mobile measurement has been successfully received during the SACCH frame. If the measurement report is not received, the counter is decreased by 1. In case the counter reaches 0, the radio connection between BTS and MS will been released. With this method it is ensured that the release will not normally occur until the call has degraded to a quality below which the majority of subscribers would have manually released it.

RLT is based on SACCH deletion. However, SACCH is not using a dynamic codec like voice in AMR, which means:

Using the EFR RLT value an AMR customer can have the call dropped because RLT reaches 0 when the FER is still good

RLT is not anymore reliable with the same value in AMR than in EFR

Due to the fact that the FER performance is different when comparing AMR calls to EFR calls, the Radio Link Timeout needs to be defined separately for AMR.

Changing the radio link timeout has a direct impact on the TCH Retainability (1 - Drop call ratio). Increasing the RLT reduces the drop call ratio, so its important to be aware of the RLT setting when looking at the DCR performance.




The Radio Link Timeout parameter for AMR is radioLinkTimeoutAmr (ARLT), available from S11.5. The principle of ARLT is the same as in the RLT but it is used only for the AMR capable mobile stations.

With S13, there is a separate parameter available to define Radio Link Timeout for HR calls – this is called radioLinkTimeoutAmrHr (AHRLT).

Table 18: Radio Link Timeout parameters


Description

AMR HR Radio Link Timeout

BTS AHRLT 20 With this parameter you define the maximum value of the radio link counter expressed in SACCH blocks for AMR HR connections

AMR Radio Link Timeout BTS ARLT 32 With this parameter you define the maximum value of the radio link counter expressed in SACCH blocks for AMR connections

Note that the Talk Family base stations do not support the parameter ARLT.

7.8 Parameter groupingThe figure below shows the parameters discussed in the previous section as a quick reference.




8. Optimizing AMR NetworkThis section discusses the counters and measurements specific to AMR monitoring and performance. The parameters for AMR have been covered in the previous section.

This section also discusses the impact of AMR on KPIs and some of the strategies for AMR optimization.

8.1 Counters related to AMR

8.1.1 Counters in Traffic Measurement (p_nbsc_traffic)

The following counters were added in S10

Counter ID Measurement Counter name

001182 TRAFFIC FULL_TCH_SEIZ_INTRA_AMR_HO001183 TRAFFIC HALF_TCH_SEIZ_INTRA_AMR_HO001184 TRAFFIC TCH_CALL_REQ_FOR_AMR001185 TRAFFIC SUCC_AMR_CODEC_SET_DOWNGR001186 TRAFFIC UNSUCC_AMR_CODEC_SET_DOWNGR001187 TRAFFIC SUCC_AMR_CODEC_SET_UPGR001188 TRAFFIC UNSUCC_AMR_CODEC_SET_UPGR

8.1.2 Counters in Handover Measurement (p_nbsc_ho)


004142 HO HO_ATT_FOR_AMR_TO_HR004143 HO HO_ATT_FOR_AMR_TO_FR

These counters are updated in case of packing (counter 004142) and unpacking (004143) which are type of Intra cell handovers.

8.1.3 Counters in RxQual Measurement (p_nbsc_rx_qual)

The counters added to this measurement provide the RxQual samples (from 0 to 7) for FR/HR and for UL/DL direction. In addition, the counters are separated by the codec used (of the possible 4 codecs used during a call)

As an example, the list of counters for AMR FR, Codec mode 1 for UL are listed below.


014021 RXQUAL AMR_FR_MODE_1_UL_RXQUAL_0014023 RXQUAL AMR_FR_MODE_1_UL_RXQUAL_1014025 RXQUAL AMR_FR_MODE_1_UL_RXQUAL_2014027 RXQUAL AMR_FR_MODE_1_UL_RXQUAL_3014029 RXQUAL AMR_FR_MODE_1_UL_RXQUAL_4014031 RXQUAL AMR_FR_MODE_1_UL_RXQUAL_5014033 RXQUAL AMR_FR_MODE_1_UL_RXQUAL_6014035 RXQUAL AMR_FR_MODE_1_UL_RXQUAL_7




There are a total of 128 such counters added

In addition, the following two counters are added to this measurement

Counter ID Measurement Counter name014149_1 RXQUAL AMR_FR_CODEC_MODE_SET014149_2 RXQUAL AMR_HR_CODEC_MODE_SET

Since the codec type in the above counters is not specifically identified, problems occur when different BSCs have a different codec set in use. The reporting in such cases becomes unreliable.

8.1.4 Counters in AMR RxQual Measurement (p_nbsc_amr_rx_qual)

This measurement was added in S12 and is an optional measurement. The measurement is similar to the previous measurement but there are separate counters for each of the AMR codecs available in FR and HR. The measurement is on TRX Level.

As an exampled, the list of counters for AMR FR, for UL and RxQUal 0 are listed below. Samples for each codec are counted in separate counter.


107005 AMR_RXQUAL FR_475_UL_RXQ_0107021 AMR_RXQUAL FR_515_UL_RXQ_0107037 AMR_RXQUAL FR_590_UL_RXQ_0107053 AMR_RXQUAL FR_670_UL_RXQ_0107069 AMR_RXQUAL FR_740_UL_RXQ_0107085 AMR_RXQUAL FR_795_UL_RXQ_0107101 AMR_RXQUAL FR_102_UL_RXQ_0107117 AMR_RXQUAL FR_122_UL_RXQ_0

A total of 208 such counters are added:

8 FR codecs for UL and DL for RxQual 0 to 7 = 128 counters 5 HR codecs for UL and DL for RxQual 0 to 7 = 80 counters

8.2 Network Doctor reportsThe following Network Doctor reports provide AMR related counters and KPIs. Some of these reports are discussed in the following sections.

– 204 – some AMR counters included– 244 - Distribution of call samples by codecs and quality classes (BER)– 245 - Distribution of call samples by codecs and quality classes (FER)– 246 - AMR call time and quality, dynamic time and object aggregation– 247 - Transcoder failure ratio– 248 - Codec set modification failure ratio– 249 - AMR counters summary




– 053 - AMR Parameters

8.3 KPIs affected by implementation of AMRWhen AMR is used in the network there may occur a need to change the used speech codec between AMR and (E)FR/HR in a call setup or in a handover. Changing the used speech codec i.e. circuit pool switching affects the TCH request and TCH request reject statistics. The corresponding KPis may therefore be affected. Refer to 2.5.1 for details.

8.3.1 TCH Retainability

Introduction of AMR itself does not affect the DCR of individual connections as much as the overall system impact of it. AMR calls can be subjected to aggressive power control settings, thus driving the overall interference low.

Radio Link Timeout must be adapted to AMR in order for dropped calls to maintain the same correlation with voice quality degradation as with EFR (RLT value could be moved from 20 to 36, for instance). When ARLT parameter is available, then RLT and ARLT can be set separately. See the impact of changing ARLT from 20 to 32 in the chart below on drop calls.

8.3.2 TCH Congestion/Blocking




When AMR HR is used, it provides extra capacity by serving two calls on one physical timeslot. This will reduce the TCH raw blocking and TCH congestion in busy hour. Percentage of call time used by non-AMR, AMR FR and AMR HR calls can be obtained from BSC counters.

8.3.3 Handover Reasons and Failures

RxLev and Power Budget HO parameters are identical for AMR and EFR. An AMR call would handover at the same point as an EFR call. Therefore, the thresholds for RxLev and PBGT handovers should be set the same for AMR and EFR.

However, there are separate RxQual threshold settings for AMR, and these are usually set to trigger later than EFR (e.g. EFR =5, AMR = 6). With these settings AMR calls would be expected to have fewer HO due to quality.

Packing/Unpacking within a cell is an intra-cell handover. Packing and unpacking attempts are measured in a counter but the success rate of the same is not measured.

If AMR handover thresholds parameters are set too aggressive, it could have a negative impact on handover failures.

8.4 AMR Penetration in the networkOne of the first things to know is the share of AMR capable MS in the network to the total. This varies a lot with the values from 40% to over 90% in different networks.

From the radio network, comparing the AMR traffic to the total traffic gives an idea of the penetration of AMR mobile in the networks. However this value will be more accurate if AMR is implemented across the network and there is circuit pool congestion.

Apart from looking at the codec distribution, there is no straightforward way to get an estimate of the AMR capable mobile in the network.

The following pie chart shows the distribution of AMR FR, AMR HR, EFR and FR based on TCH seizures. Note that the packing and unpacking also cause the TCH seizures to be pegged, so this is not an indication of actual FR and HR traffic.




The following charts shows the share of codec usage and will be a better indicator.

8.5 AMR Codec usage and RxQualWith the availability of counters for each codec and each quality class (BER based), it is possible to check the share of the codec usage as well as the reported RxQUal. This can be obtained from Network Doctor report 244 a sample of which is shown below.

This gives you the quality (BER) distribution for each codec but doesn’t tell the share of each codec. This report provides a measure of the quality of the network (radio link) since it is based on BER. Poor quality (worse BER) will impact the correct decoding of SACCH blocks, thus affecting the DCR.

The report identifies the codecs in the codec set as M1…M4 (with M1 being the codec with lowest bit rate) without specifically identifying the codec. So the report will contain correct information only when the codec set is the same across all the BTSs.

8.6 AMR Codec usage and FER

Codec usage based on ND245 period 9.-17.10.2006 AMR Trial BSC_B

EFR61.9%

AMR FR 12.233.5%

AMR FR 7.51.2%

AMR FR 5.92.1%

AMR FR 4.751.3%

EFR

AMR FR 12.2

AMR FR 7.5

AMR FR 5.9

AMR FR 4.75




The report 245 provdies FER per quality class for each codec. Unlike report 244, the codecs in this report are identified specifically, so the report output is correct even if you have a mix of BTSs using different codec sets.

This report provides a measure of the quality of speech since it is based on FER. A poor FER directly impacts the MOS experienced by the subscribers.

8.7 Enhanced TRX Priority in TCH AllocationA network will have a mix of AMR and non-AMR capable terminals. The AMR terminals are able to tolerate lower C/I radio conditions than the other terminals. Non-AMR terminals can have better signal quality on a BCCH TRX which is usually planned to have minimum interference.

A new value of the parameter TRP (TRX Priority in TCH Allocation) allows the non-AMR traffic to be preferred on the BCCH TRX.

TRP Effect

0(default)

All TRXs are treated equally in TCH allocation

1 A traffic channel is allocated primarily from the BCCH TRX

2 A traffic channel is allocated primarily beyond BCCH TRX

3(new value)

A traffic channel is allocated primarily from the BCCH TRX for the non-AMR users and for the AMR users beyond the BCCH TRX

8.8 Aggressive use of AMR HRAMR HR is mainly utilized to reduce congestion or blocking in the cells without the need for adding additional hardware. However strategies have been tried to increase the use of AMR HR to reduce the overall interference in the area.

When the use of AMR HR is high, fewer physical timeslots are in use in the network as compared to having all those calls on AMR FR. This also reduces the overall interference in the network if the area is interference limited. The downside of having more calls on AMR HR is the lower MOS as compared to AMR FR.




The two charts below compares the HR penetration of 25% with HR penetration of 85% on one BSC in a city area. The DL FER distribution was obtained from TEMS.

There is a slight improvement in FER and RxQual distribution as a result of interference reduction. Good DL FER samples improved 89% to 91%.




9. AMR S13 features

9.1 AMR Progressive Power Control (PPC)

9.1.1 Introduction

AMR Progressive Power control (AMR PPC) is enhancement to the existing Power Control (PC) algorithm running in the BSC and controlling the transmitting power of the MS and BTS.

AMR PPC provides mechanism to change quality thresholds depending on used power level so that AMR PPC favours increase of power with low power levels and avoid increase of power with higher power levels. Following results are striven by this:

Better power distribution - introducing less interference to the network

Better quality distribution - yielding to better speech codec distribution

The aim of this feature is get additional capacity gain and decrease Dropped Call Rate (DCR).

AMR PPC is applied to both UL and DL and allows control of the transmitted power of MS and BTS separately. AMR PPC is used only for AMR calls. When the AMR PPC algorithm is disabled, the normal PC algorithm is used also for AMR calls.

9.1.2 Description

In the current power control algorithm, the quality thresholds set for power control do not change with a change in the transmitted power of the MS or BTS. The decision to increase or decrease power is based on comparison of the measured RXQUAL with the set quality thresholds.

With the current power control, voice quality (based on TCH FER) and drop call rate (based on SACCH RLT) cannot be optimised at the same time. For example RXQUAL low thresholds 5 and high thresholds 6 provides low drop call rate, but poor voice quality. This means that used power control algorithm AMR RXQUAL thresholds have to be selected so that trade-off between voice quality and system capacity is made.

The figure below shows the power control without the PPC feature. The Increase or decrease in MS/BTS power is based on RxQual thresholds alone, irrespective of the transmitted power level.




Figure 12: AMR Power Control without PPC

To further improve AMR quality and capacity with AMR and also with new SAIC phones “Progressive AMR Power Control” is introduced. Instead of using constant RX_QUAL threshold values, progressive power control uses higher RX_QUAL threshold values for higher TX power levels. This is achieved by applying offsets to the existing RxQual threshold values. These offsets are fixed to be -2, -1, 0, +1, +2 and are applied at a certain transmit power level as defined by the parameters.

Figure 13: AMR Power Control with PPC




In the above figure, the thresholds for transmitted power level are identified as X1, X2, X3 and X4. Offsets are applied as per the table below.

Threshold for power level Offset to RxQual thresholdBetween Min power and X1 Offset of -2Between X1 and X2 Offset of -1Between X2 and X3 No offset appliedBetween X3 and X4 Offset of +1Between X4 and Max power Offset of +2

Taking an example, if the MS power level is at 15 (lowest power level), the algorithm will trigger an increase in MS power if the RxQual (UL) degrades beyond RxQual = 3. Compared to the algorithm without PPC, the MS power would have been increased if the RxQual degraded beyond RxQual = 5. Since the MS is at its lowest power level, the PPC algorithm is playing safe by increasing the power much before the RxQual degrades to a level where spikes in interference could degrade the quality significantly.

On the other hand, if the MS is at power level 2, the algorithm will further increase the power only if the RxQual degrades beyond RxQual = 6 (as compared to RxQual = 5 without PPC).

The AMR link adaptation algorithm is also capable of changing codecs to counter degrading C/I conditions. In conjunction with the AMR codec adaptation, the PPC algorithm

favours increase of power over AMR codec adaptation with low power levels and avoids increase of power, and

favours AMR codec adaptation with higher power levels and thus reduces overall interference.

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

9.1.3 Benefits of AMR PPC

Progressive power control reduces the usage of highest transmitted power levels and thus reduces overall interference. The figure below shows simulated power distribution changes with current power control and progressive power control.




A positive offset (of +1 or +2) at higher transmit power levels mean that compared to the current PC, the PPC algorithm starts to reduce the transmit power at higher levels at earlier RxQual values (e.g., at RxQual 5 instead of RxQual 3). This reduces the share of the highest power levels, as seen in the figure above.

Benefits derived from this feature are:

Reduced interference in the network because of better power distribution

Better speech codec distribution because of better quality distribution

Reduced dropped call rate

Simulations show 50% reduction in dropped call rate (DCR) or, with the same DCR, traffic increase of 15%. Gives better balance between AMR codec modes and power control.

Figure 14: Gains in Progressive Power Control




Network level gains are expected to be at a similar level for both AMR/FR and AMR/HR.

9.1.4 Activation

AMR PPC is application software in S13 and it contains two separate functionalities which can be separately controlled with Licence and Feature Handling MML (LFHMML).

AMR PPC for MS power controlling

AMR PPC for BTS power controlling

9.1.5 Parameters

AMR PPC enables you to define four different power level points in which the quality thresholds are changed compared to the ones used in the existing power control algorithm for AMR calls.

You can define these points separately for AMR FR and AMR HR, and in the downlink and uplink direction. This introduces 32 new BSC level parameters.




The range for all the above parameters is from 0 to 30dB and it covers power levels from the maximum power level to the minimum power level. It will be wise to start with less aggressive settings and then change them based on the DCR performance. The default values for the thresholds (in order X1, X2, X3, X4) are 30dB, 16dB, 6dB and 0dB, which are less aggressive than the values in Figure 13.

Note that the power control quality threshold values are only changed within the algorithm during an AMR call. The values of the actual parameters, such as LDRF are not changed.

With AMR PPC, the BSC uses the same Px and Nx values and averaging windows as with the normal power control algorithm.

9.1.6 AMR PPC Measurement

AMR PPC introduces one new measurement type - AMR PPC Measurement. This new measurement is for measuring the average signal quality vs. power level distribution in TRX level

• BSC HW: no special requirements

• BSC SW: S13

• BSC Application SW: licence for AMR PPC and licence for AMR FR or/and AMR HR required.




• Other NW elements: NetAct OSS4.2

• MS requirements: AMR capability

9.2 Robust AMR Signalling (FACCH/SACCH)

9.2.1 Introduction

Low-rate AMR FR codecs (e.g. AMR 4.75) provide satisfactory speech quality in radio channels whose carrier-to-interference ratio (C/I) is up to 4 dB worse than that needed to give reliable operation of the FACCH and SACCH control channels. This results in calls being dropped even though their speech quality is still acceptable. Main problem is downlink FACCH/SACCH performance which can cause dropped calls and HO failures.

The effective C/I for downlink FACCH and uplink/downlink SACCH can be improved by increasing the base station (BTS) Tx power for FACCH, or by repeating the FACCH/SACCH block (introduced in 3GPP Rel6).

Refer also to S13 NED Documentation for Robust AMR Signalling.

Figure 15: AMR codes and signalling (FACCH/SACCH) performance

Robust AMR Signalling feature consists of four separate features:

1. FACCH and SACCH repetition for “repeated ACCH” capable mobiles on AMR TCH

2. FACCH repetition for legacy mobiles on AMR FR

3. FACCH repetition for legacy mobiles on AMR HR




4. FACCH Power Increment (for existing mobiles)

FACCH/SACCH repetition and FACCH Power Increment proposals are specified together as single repeat/power increment functionality so that BTS can optimise use of the power increment and repetition according to BTS Tx power level, mobile capability and channel (AMR FR, AMR HR) used.

Role of BSC is to provide parameters related to this feature to BTS. BSC checks mobile’s capability and sends parameters related to this feature to the BTS at the beginning of a call (Channel Activation message) and it is up to BTS how it uses these features.

BTS indicates usage of FACCH/SACCH repetition and soft combining of repeated blocks in Measurement Result message to the BSC. This information is used for monitoring of Robust AMR signalling.

With FACCH repetition the time taken to get a command to mobile increases, so repetition should only be applied when needed. Uplink SACCH repetition reduces frequency of measurements from the mobile, so it should also be used only when needed. Repetition of the same measurement reports affects also averaging of measurements and reaction speed of handover and power control algorithm.

9.2.2 Repeated AMR SACCH and FACCH in 3GPP Release 6

From 3GPP Release 6 onwards, the mobile stations (MSs) and BTSs can ask for SACCH frames to be repeated exactly on transmit, so that the original frame and its repeat can be decoded together using incremental redundancy (soft combining) type decode, similar to the incremental redundancy defined for EGPRS data. The transmit repeat and incremental redundancy on decode can also be used with downlink FACCH frames.

This gives about a 4 dB improvement in the C/I needed to decode the SACCH and FACCH, so that these channels are as robust as the lowest rate AMR codecs.

BSS13 supports the 3GPP protocol for repeated SACCH and FACCH, and will use the Incremental Redundancy on the uplink SACCH when needed for good normal operation of the control channels.

9.2.3 Repeated AMR FACCH for Existing Mobiles (FR & HR)

For mobiles designed according to ‘old’ 3GPP releases (i.e. releases up to and including release 5), 3GPP have enhanced the radio interface protocol so that the downlink FACCH can be repeated, to give the mobile two chance to decode the FACCH before each link timeout and retry of the protocol.

This gives about a 2 dB improvement in the C/I needed to decode the FACCH, so that this channel is more robust and the dropped call rate in handovers is reduced.

BSS13 will use the repeated downlink FACCH, when the Mobile is indicating poor downlink quality by requesting a low-rate AMR codec.

The 2 dB improvement in C/I is not enough for reliable operation with the very lowest rate AMR/FR codecs, so there is also FACCH Power Increment feature for existing mobiles.




9.2.4 FACCH Power Increment for Existing Mobiles

For legacy MSs (Release 5 or older), the BTS Tx power for downlink AMR FACCH bursts can be increased by 2 dB up to the maximum transmission power of the BTS (Pmax). FACCH repetition and power increment together provide an improvement of up to 4 dB in C/I for FACCH decode.

9.3 Separate AMR UL/DL Link Threshold S13 allows separate AMR Uplink and Downlink Link Adaptation thresholds for better optimisation of link balance with AMR.

9.3.1 Current Implementation

Current AMR feature implementation utilises a common set of codec change thresholds for both Uplink and Downlink directions (though separate for FR and HR). The current implementation tends to prefer to assign codecs more pessimistically (choosing the more robust codec) than the actual RF conditions would dictate for a given link. Specifically, the most robust UL codec is assigned more liberally across all UL RxQuality bands than is the most robust DL codec with respect to DL RxQuality bands.

9.3.2 New parameters

This feature allows effective optimisation techniques to determine the appropriate codec to serve the call. A separate set of UL and DL LA thresholds is introduced in order to better optimise AMR LA, and to effectively and independently respond to RF conditions on either link.

Both AMR FR and HR have their own separate threshold and hysteresis value.

The following figure illustrates the new usage of thresholds and hysteresis in choosing the appropriate codec mode. In this example the DL threshold values (xTD1 to xTD3, x = FR or HR) define boundaries between DL codec modes 1 to 4, and UL thresholds (xTU1 to xTU3) define boundaries between UL codec modes 1 to 4 respectively. The hysteresis value set xH1 to xH3 is common for both directions, as before. There can be up to 4 codecs in the active codec mode set, as before.




This introduces 6 thresholds for FR and 6 thresholds for HR. These are shown below.

9.4 TRAU Bicasting

9.4.1 Introduction

AMR packing/unpacking uses intra-BSC handovers in order to change speech coding between AMR HR and AMR FR. In these handovers, there is a break in the downlink speech path, and this break can be reduced if the BSC uses unidirectional connection.

Unidirectional connection means that the BSC transmits TRAU speech frames received from the TC simultaneously to both source and target BTS




Unidirectional connection can be used only when the same TRAU speech frame format is used on both sides of the intra-BSC HO. Currently AMR FR<=>AMR HR Handover is a scenario where it is not possible to establish unidirectional DL connection.

TRAU Bicasting in AMR FR/HR handover feature makes it possible to prepare connection to target resource also in AMR FR/HR intra-BSC handovers meaning better speech quality for the end-user by reduced break in DL speech path.

9.4.2 Description of the feature

The feature makes it possible to establish unidirectional connection also in AMR FR/HR intra-BSC handovers. This method, show in the figure below, tries to ensure that valid speech frames are being transmitted in DL over the air interface before the MS retunes from the source to the target channel.

Figure 16: TRAU Bicasting in AMR FR/HR handover

In order to reduce Audio breaks during HO, BSC tries to establish unidirectional connection in downlink towards the target channel.

When this feature is used source and target BTSs and TC are all using 8 kbit/s TRAU frame format for the Abis and Ater transmissions during the AMR packing/unpacking handover. In practice this means that 8 kbit/s TRAU frames are submultiplexed onto 16 kbit/s Abis channel of BTS that is sending/receiving TCH/AFS radio frames.

As explained above, unidirectional connection is currently not possible during AMR packing or unpacking handovers (different TRAU frame format on source and target BTS), two-way hard switching needs to be performed instead leading to an audible break (100-400 ms) in downlink speech (Step 2 in the above figure is skipped).

9.4.3 Activation and Monitoring

Step 1 Step 2 Step 3




The feature is non-optional. It is an enhancement to AMR and it is activated when both AMR FR and AMR HR are activated. If required, the feature can be disabled by patching of UTPFIL parameters in the BSC.

There are 7 new counters introduced in Traffic Measurement due to this feature. Refer to BSS S13 NED Documentation for the details on these counters.

9.5 AMR Signalling MeasurementThe AMR Signalling Measurement (AMR_SIG) measures a proportion of Repeated ACCH Capable mobiles in network and usage of repeated SACCH and FACCH features.

This optional measurement is a part of Robust AMR signalling (FACCH / SACCH). There are 6 new counters introduced by this measurement. Refer to BSS S13 NED Documentation Counters of AMR Signalling Measurement for details of each counter.

The measurement can be started when at least one state of the features has been set to value ON.

• FACCH and SACCH repetition for repeated ACCH capable mobiles on AMR

• FACCH repetition for legacy mobiles on AMR FR

• FACCH repetition for legacy mobiles on AMR HR




10. AbbreviationsAMR Adaptive Multi Rate Codec

BSC Base Station Controller

BSS Base Station Subsystem

BTS Base Transceiver Station

C/I Carrier To Interference Ratio

DL Down Link (connection from BTS to MS)

DTX Discontinuous transmission

EFR Enhanced Full Rate

EFL Effective Frequency Load

FER Frame Error Rate

FH Frequency Hopping

FR Full Rate

HO Handover

HR Half Rate

DR Dual Rate

IFH Intelligent Frequency Hopping

IUO Intelligent Underlay Overlay

LA Link Adaptation

MOS Mean Opinion Score

MS Mobile Station

MSC Mobile Switching Centre

PC Power Control

RX Receiving

TCH Traffic Channel

TRX Transceiver

TX Transmitting

UL Up Link (connection from MS to BTS)




11. References

[1] Nokia Siemens GSM/EDGE BSS S13 Product Documentation (NED)

[2] BSS S13 features under development

[3] Advanced RANOP Course – Chapter AMR

[4] GSM, GPRS and EDGE Performance, Appendix B: Hardware dimensioning studies

[5] KPI Impact from AMR activationhttps://sharenet-ims.inside.nokiasiemensnetworks.com/Download/377622515

[6] AMR Info Session – 3 partshttps://sharenet-ims.inside.nokiasiemensnetworks.com/Download/371670835







amr planning and optimization guidelines v2.0

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