amr half rate feature engineering notes

GSM HR, AMR Feature Engineering Notes

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GSM Half Rate and AMR

Feature Engineering Notes

Abstract: This document contains all information regarding GSM HR and AMR (Full and Half Rate) necessary to understand the benefits of the feature, including real world results as well as information of which parameters to tune to make it work effectively in the field. If the reader has any questions or suggestions to improve the document, please feel free to email to above address.

GSM HR, AMR Feature Engineering Notes __________________________________________________________________________________

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Motorola Internal Use Only

SIGN-OFF FORM

Author signature Date

Revised signature Date

Revised signature Date

HISTORY OF REVISIONS

Revision Date Author Revised by Changes Description

0.1 draft

0.2 internal review

1.0 released

GSM HR, AMR Feature Engineering Notes

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___________________________________________________________________________________ Page 1 Motorola Internal Use Only

1 Table of Contents

1 Table of Contents ................................................................................................ ............................... 1

2 Table of Figures ................................................................................................................................ . 4

3 Tables................................................................................................................................ .................. 5

4 Introduction................................................................................................................................ ........ 6

5 Feature Summary............................................................................................................................... 6 5.1 Fundamentals of AMR......................................................................................................................... 6 5.2 Fundamentals of GSM Half Rate................................................................................................ ........ 7

6 AMR in more detail................................................................................................ ............................ 8 6.1 AMR Codec Modes ................................................................................................ .............................. 8 6.2 AMR Link Adaptation ....................................................................................................................... 11

6.2.1 Link Adaptation In-Band control loop ........................................................................................................... 126.2.2 Active Codec Set, Initial Codec Mode and Threshold & Hysterisis table ....................................................... 13

6.3 MS Monitor ........................................................................................................................................ 15

6.4 8 Kbps Backhaul – DSW2 .................................................................................................................. 16

6.5 Impact of the 7.95 Kbps codec ........................................................................................................... 16

6.6 AMR transcoder requirements, GDP2 and RXU3 .......................................................................... 16

7 GSM Half Rate transcoder requirements ........................................................................................ 178 Enhanced auto-connect (EAC) mode/ cic validation ..................................................................... 189 New database parameters ................................................................................................................ 19

9.1 AMR Parameters ............................................................................................................................... 199.1.1 Enabling and Disabling of AMR Full and Half Rate ...................................................................................... 199.1.2 Configuration of AMR capable cell for link adaptation. ................................................................................. 209.1.3 Configuration of AMR parameters from the OMC ......................................................................................... 22

9.2 Enabling and Disabling of GSM Half Rate ...................................................................................... 25

9.3 Enable Half Rate on a carrier basis (RTF) ....................................................................................... 26

9.4 Feature Control - AMR Full Rate ..................................................................................................... 26

9.5 Feature Control - AMR Half Rate and GSM Half Rate .................................................................. 27

9.6 force_hr_usage ................................................................................................................................... 27

9.7 new_calls_hr, inner_hr_usage_thres, hr_res_ts and reconfig_fr_to_hr ......................................... 27

9.8 new_calls_hr ....................................................................................................................................... 27

9.9 inner_hr_usage_thres ......................................................................................................................... 27


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9.10 hr_res_ts ............................................................................................................................................. 28

9.11 reconfig_fr_hr ..................................................................................................................................... 28

9.12 reconfig_fr_to_hr ............................................................................................................................... 32

9.13 Handover and Power Control ........................................................................................................... 34

9.14 Half Rate to Full Rate intra-cell handovers. .................................................................................... 37

10 Parameter Optimisation ............................................................................................................... 3810.1 Thresholds for Half Rate Usage ........................................................................................................ 38

10.2 HDPC Settings for Half Rate Channels ............................................................................................ 41

10.3 AMR link adaptation thresholds, hysterisis and codecs .................................................................. 41

11 BSS planning – Half Rate dimensioning .................................................................................... 4312 Statistics ........................................................................................................................................ 44

12.1 MA_REQ_FROM_MSC ................................................................................................................... 44

12.2 MA_COMPLETE_TO_MSC ............................................................................................................ 44

12.3 HO_REQ_FROM_MSC .................................................................................................................... 45

12.4 HO_REQ_ACK_TO_MSC ................................................................................................................ 45

12.5 FER, FER_AMR_FR, FER_AMR_HR, FER_GSM_HR, FER_GSM_FR_EFR .......................... 45

12.6 INTRA_CELL_HO ............................................................................................................................ 46

12.7 INTRA_BSS_HO_CAUSE_SUC ...................................................................................................... 46

12.8 TCH_CONGESTION_HR ................................................................................................................ 46

12.9 TCH_CONG_INNER_ZONE_HR ................................................................................................... 47

12.10 BUSY_TCH_HR ............................................................................................................................ 47

12.11 BUSY_TCH_CARR_HR ............................................................................................................... 47

12.12 AVAILABLE_TCH_HR ............................................................................................................... 47

12.13 ALLOC_TCH_HR ......................................................................................................................... 47

12.14 ALLOC_TCH_FAIL_HR ............................................................................................................. 47

12.15 RF_LOSSES_TCH_HR ................................................................................................................. 47

12.16 CALL_SP_VERS_DOWNGRADE_MONITOR ......................................................................... 47

12.17 AMR_DECREASE_THRESH_ADJUST ..................................................................................... 48

12.18 AMR_INCREASE_THRESH_ADJUST ...................................................................................... 48

12.19 AMR_FR_DL_CODEC_MODE_USAGE ................................................................................... 48

12.20 AMR_FR_UL_CODEC_MODE_USAGE ................................................................................... 48

12.21 AMR_HR_DL_CODEC_MODE_USAGE .................................................................................. 49


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12.22 AMR_HR_UL_CODEC_MODE_USAGE .................................................................................. 49

12.23 AMR_FR_DL_ADAPTATION ..................................................................................................... 49

13 Benchmarking .............................................................................................................................. 5013.1 Speech Quality .................................................................................................................................... 50

14 Tools .............................................................................................................................................. 5414.1 Motorola Drive Test Tool (CTP Windows MDTT GSR7v1.0) ....................................................... 54

14.2 CTP-NT ............................................................................................................................................... 56

14.3 Measurement Reports. ....................................................................................................................... 60

Appendix A - Full Rate/Half Rate Channel Selection ............................................................................ 62


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2 Table of Figures

Figure 1 Downlink Qvoice Pace vs C/I for FR, EFR and AMR Codecs. ................................ ............ 9 Figure 2 Uplink Qvoice Pace vs C/I for FR, EFR and AMR Codecs, None Hopping. ...................... 10Figure 3 AMR Link Adaptation. ......................................................................................................... 11Figure 4 LA In-Band control loop. ..................................................................................................... 12Figure 5 Graphical representation of Link Adaptation. ...................................................................... 14Figure 6 OMC, BSS detailed view ...................................................................................................... 23Figure 7 OMC, Cell detailed view for AMR FR. ................................................................................ 24Figure 8 OMC, Cell detailed view for AMR HR. ............................................................................... 25Figure 9 Two carrier cell which has a total resource count of 14. .................................................... 30Figure 10 Cell at 36 % Full Rate occupancy. .................................................................................... 30Figure 11 Cell at 50 % occupancy. .................................................................................................... 31Figure 12 Next call handed in or set up in the cell is allocated a Half Rate Channel (TCH/H). .......... 31Figure 13 Flow chart of Full Rate to Half Rate reconfiguration. .......................................................... 33Figure 14 Full Rate SACCH Frame. ..................................................................................................... 34Figure 15 Half Rate SACCH Frame. ..................................................................................................... 34Figure 16 Recommanded RxQual bands for GSM/AMR Half Rate. .................................................... 36Figure 17 Qvoice Pace for different RxQual collected in Laboratory. ................................................. 37Figure 18 1 Carrier probability of HR usage. ........................................................................................ 39Figure 19 2Carrier probability of HR usage. ......................................................................................... 39Figure 20 3 Carrier probability of HR usage. ........................................................................................ 40Figure 21 GSM HR and FR QVoice Pace scores, collected under laboratory static conditions. .......... 50Figure 22 GSM HR and FR QVoice Pace scores collected on a BSC wide basis. ............................... 51Figure 23 Comparison of AMR FR/HR to EFR/GSM HR downlink speech quality. .......................... 52Figure 24 Comparison of AMR FR/HR to EFR/GSM HR uplink speech quality. ............................... 53Figure 25 MDTT AMR Configuration. ................................................................................................. 55Figure 26 MDTT AMR Codec Log ....................................................................................................... 55Figure 27 MDTT AMR Graphical Parameters Display. ....................................................................... 56Figure 28 AMR parameter distributions from CTP-NT ........................................................................ 57Figure 29 Example of Uplink adaptation for ACS 12.2, 10.2,7.4 and 5.15 .......................................... 58Figure 30 CTP_NT C/I distribution for individual carriers. .................................................................. 59


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3 Tables Table 1 List of all possible AMR codec modes. ................................................................ .................. 8 Table 2 Motorola implemented Full rate codecs................................................................. ................. 8 Table 3 Motorola implemented Half Rate codecs................................................................. ............... 8 Table 4 Parameters to enable AMR FR and AMR HR on a BSC and on a per cell basis. ................ 19Table 5 BTS Platforms that support AMR FR/HR and GSM HR. .................................................... 19Table 6 AMR LA parameters. ............................................................................................................ 21Table 7 Parameters to enable GSM HR on a BSC and on a per cell basis. ....................................... 26Table 8 New HDPC parameters introduced for half rate channels. ................................................... 37Table 9 Summary of Peak Pace for all codec modes. ........................................................................ 53


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4 Introduction In the first days of GSM the Motorola BSS offered GSM Full Rate (FR) as the speech codec (coder-decoder). As GSM evolved and a higher level of Quality of service, particularly speech quality was demanded by subscribers, the Enhanced Full Rate (EFR) codec was added to the BSS. The EFR codec produces higher quality speech than the original FR. From GSR 7 onwards Motorola has introduced support for AMR (Adaptive Multi Rate) and GSM Half Rate. These new features provide an opportunity to improve Quality of service even further and offer large capacity gains through the use of Half Rate channels.

5 Feature Summary

5.1 Fundamentals of AMR When a GSM call is established a channel mode and speech version is allocated which is used throughout the BSS system and across the air interface. The channel mode and speech version is allocated based on the capabilities of the BSS and the MS. Although changes are possible, it is normally the case that the channel mode and speech version allocated at the start of the call will be used throughout the life of the entire call i.e. if GSM Speech version 2 (EFR) was allocated at the start of the call then it is highly likely that EFR would be used throughout, even taking Inter-BSC handovers and Inter-MSC handovers into account. The FR and EFR codecs are designed to overcome interference on the air interface using channel encoding techniques i.e. forward error coding. Up until a certain point the encoding scheme will be able to correct errors that occur due to interference, beyond this errors will occur in the data stream. The amount of error correction depends on the available bandwidth within the channel, if the speech codec uses less bandwidth, then there is more available for error protection. AMR has several different codecs available which give a spread of choices from high bit rate codecs with lower immunity to interference to low bit rate codecs with higher immunity to interference. The Carrier to Interference ratio “C/I” is used as a measure of the radio environment and indicates the level of interference compared to the wanted signal. In a high C/I environment i.e. >15dB, higher bit rate codecs offer superior speech quality. In a lower C/I environment the lower bit rate codecs that have higher error protection will offer better speech quality. AMR takes advantage of the different properties of the codecs and uses Link Adaptation to switch between the codecs depending on the C/I conditions. Link Adaptation functions independently on the Uplink and the Downlink which ensures that the lower bit rate codecs are only used when necessary on each link. Unlike a handover, switching between codecs is relatively transparent to the subscriber and a relatively quick operation ~ 160mS. In summary the AMR feature enables a theoretically higher QOS for Full Rate Channels and enhanced capacity with theoretically higher QOS for Half Rate channels when compared to the conventional GSM Half Rate Speech Version 1 codec.


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5.2 Fundamentals of GSM Half Rate The GSM Half Rate codec has been specified since the beginning of GSM. Motorola has not previously offered this mode mainly due to potentially worse quality of service when compared to the GSM Full Rate and EFR modes. Demand for GSM Half Rate has increased in recent years and in response, from GSR 7, GSM Half Rate speech version 1 has been introduced into the BSS product. In theory the addition of GSM Half Rate can provide a 100% capacity increase on the radio layer. The extra capacity is achieved because the air interface bandwidth required is half the amount i.e. a GSM Full Rate, EFR or AMR Full Rate call require a 16kbps air interface timeslot. For GSM Half rate (and AMR Half Rate) the air interface bandwidth requirement is reduced to 8Kbps – half of one air interface timeslot. When half rate modes are used, each air interface timeslot can carry two half rate calls simultaneously. To take advantage of the additional capacity offered on the air interface, the links carrying voice traffic between the BTS, BSC and RXDCR (backhaul) can be modified to use an 8Kbps structure instead of the current 16Kbps. The BSS infrastructure will support the transportation of 8Kbps voice in a 16Kbps structure, however to realise any capacity increase the number of backhaul links between the BSS entities will have to be increased. The modification of backhaul for 8Kbps switching requires the addition of new hardware devices (replacement of KSW boards) at the BSC and RXCDR. In order to carry more traffic in the BSS it may also be necessary to increase the number of trunks between the MSC and BSS, meaning additional hardware requirements at the RXCDR and MSC. In summary, the GSM Half Rate feature is focussed on system capacity expansion which depending on the amount of additional capacity may lead to additional hardware requirements. Provided that a good C/I environment exists, the GSM Half Rate mode can provide substantial system capacity gains with satisfactory Quality of Service for the subscriber. The AMR Half Rate feature offers the same capacity gains but with enhanced Quality of Service through the use of Link Adaptation. At the time of writing, the GSM Half Rate capable mobile penetration throughout the world is quite high, >90%. In contrast the current AMR capable mobile penetration is relatively low <5%. It is anticipated that the AMR capable mobile penetration will increase which will provide a migration path from GSM Half Rate to AMR Half rate in the future. The additional hardware to provide 8Kbps switching at the BSC and RXCDR is identical for both GSM Half Rate and AMR Half Rate. Assuming GSM Half Rate was deployed with 8Kbits switching, a future deployment of AMR Half Rate when mobile penetration levels increase would require less investment and effort.


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6 AMR in more detail

6.1 AMR Codec Modes As previously mentioned there are several different bit rate codecs defined by ETSI for use by AMR, refer to Table 1. The higher bit rate codecs provide high speech quality in good C/I conditions and the lower bit rate codecs provide better speech quality than EFR or GSM Full Rate speech in low C/I conditions. To give some idea, the AMR Full Rate codec is very close in performance to the EFR codec (same bit rate 12.2Kbps).

Codec mode Source codec bit-rate AMR_12.20 12,20 kbit/s (GSM EFR) AMR_10.20 10,20 kbit/s AMR_7.95 7,95 kbit/s AMR_7.40 7,40 kbit/s (IS-641) AMR_6.70 6,70 kbit/s (PDC-EFR) AMR_5.90 5,90 kbit/s AMR_5.15 5,15 kbit/s AMR_4.75 4,75 kbit/s

Table 1 List of all possible AMR codec modes. Due to limitations in some of the BTS platforms, Motorola offer a sub-set of the ETSI defined codecs. The AMR codecs supported by Motorola are shown in Tables 2 and 3.

AMR Full Rate Codecs 12.2 kbps 10.2 kbps 7.4 kbps 6.7 kbps 5.15 kbps

Table 2 Motorola implemented Full rate codecs.

AMR Half Rate Codecs 7.95 kbps 7.4kbps 6.7 kbps 5.9 kbps 5.15kbps

Table 3 Motorola implemented Half Rate codecs.

The sub-set of codecs offered by Motorola is in no way seen to cause any problems with respect to the operation of AMR or the Quality of Service offered. The unsupported 4.75Kbps codec has been shown by ETSI in performance modelling to produce marginally better performance than 5.15Kbps at very low


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C/I values, however from a speech quality point of view it is perceived that the difference will be negligible. The other two unsupported Full Rate AMR codecs 5.9Kbps and 7.95Kbps are more than adequately covered by the 6.7Kbps and 7.4Kbps codecs. The following charts Figures 1 and 2, show examples of tests performed in a lab environment using a fader to generate a dynamic RF path (6 tap TU50 profile). The tests were performed using QVoice, an end to end speech quality test tool. The C/I environment was generated artificially using a signal generator with a GMSK modulator. Approximately 40, five second duration speech samples were captured at C/I levels of 20, 15, 13, 11, 9 and 7dB. How to read figures 1 and 2. The X axis shows C/I, towards the left hand side there are lower values of C/I meaning higher interference, towards the right hand side there are higher levels of C/I (less interference). The Y axis shows “PACE”, this is the unit of speech quality measurement provided by QVoice. A PACE value of up to 5 represents perfect CD quality speech, a PACE value of 1 indicates virtually no speech or silence. To interpret the charts, there is better speech quality given by the higher bit rate codecs on the right hand side – good C/I. The speech quality of the 5.15Kbps codec is the best on the extreme left hand side of the chart – poor C/I.

Horizon CTU TU50 Full Rate Downlink - No Hopping

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6

3.8

4

7 9 11 13 15 17 19

dB C/I

PAC

E

GSM FRGSM EFRAFS 12.2AFS 10.2AFS 7.4AFS 6.7AFS 5.15

Figure 1 Downlink Qvoice Pace vs C/I for FR, EFR and AMR Codecs.


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Horizon CTU TU50 Full Rate Uplink - No Hopping

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6

3.8

4

5 7 9 11 13 15 17 19

dB C/I

PAC

E

GSM FRGSM EFRAFS 12.2AFS 10.2AFS 7.4AFS 6.7AFS 5.15

Figure 2 Uplink Qvoice Pace vs C/I for FR, EFR and AMR Codecs, None Hopping.

Note: At this point in the document it should be noted that the encoding and error protection applied to the SACCH channel does not change for AMR or GSM Half Rate. The extra protection offered by lower bit rate codecs applies only to speech and not link control data. With this information in mind there are predicted to be no changes in drop call rate or RF loss statistics. The choice of “which codecs and when” is operator definable and will be covered in more detail later in this document.


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6.2 AMR Link Adaptation AMR provides better overall quality of service compared to the GSM Full Rate or EFR because of it’s ability to dynamically switch to more robust codec modes when poor C/I conditions prevail. There are three components linked together in the system that perform speech encoding / decoding functions.

• Mobile Station codec • BTS Channel coder • XCDR DSP

Codec

Mobile

Channel Coder

BTS

KSW / DSW 2

BSC

DSP

XCDR

64KbpsPCM

MSC

Encodes and decodes air interface to and from Microphone and ear piece

Encodes and decodes 8Kbps or 16Kbps TRAU to and from air interface

Performs cross point switch operation

Encodes and decodes 8Kbps or 16Kbps TRAU to and from 64Kbps PCM

Figure 3 AMR Link Adaptation.

The block diagram in Figure 3 shows the system components that perform encoding and decoding functions in the system as far as the speech path is concerned. Each of the three components needs to encode and decode using the same coding scheme and transport frames (TRAU) at the same time i.e. if the channel mode is EFR, then the codec in the mobile and the channel coder in the BTS have to use EFR encoding; similarly the DSP device in the XCDR has to encode / decode EFR TRAU frames. Every time that Link Adaptation is performed i.e. a change from one codec to another, each of the three system components has to change in unison to ensure that end to end speech is preserved.


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6.2.1 Link Adaptation In-Band control loop

MS BTS RXCDR

CMR-CMI-CMR-CMI CMR-CMI-CMR-CMI

CMC-CMI-CMC-CMI CMC-CMI-CMC-CMI

Downlink

C/I Estimate

Uplink

C/I Estimate

CODECChannel Coder

XCDR DSP

Figure 4 LA In-Band control loop.

The diagram in Figure 4 shows the control loop used to perform Link Adaptation in AMR. The control loop is implemented within the channel itself i.e. there is no extra signalling channel associated. This is known as In-Band signalling. There are three types of control message used:

• CMI – Codec Mode Indicated • CMC – Codec Mode Command • CMR – Codec Mode Request

A CMI message indicates the current codec being used on a particular link. In AMR Link Adaptation, the uplink and downlink are treated separately since the radio conditions may well be different on each link. As an example the uplink radio conditions may be good so an uplink CMI may indicate 12.2 Kbps, while at the same time there maybe heavy interference on the downlink and the downlink CMI may be indicating 5.15 Kbps. A CMC message is a command message that originates from the BSS. The CMC message is only found on the Downlink and is used to “command” the mobile to use a certain codec in the uplink direction.


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A CMR message is a request message sent from the mobile. The mobile sends this message to request that a certain codec is used in the downlink direction. Each control message (CMI, CMC or CMR) takes 20mS to transmit. When in an AMR call, the In-Band signalling link for the uplink (MS to BSS) contains a continuous stream of alternate CMI and CMR messages. The downlink In-Band signalling link of the same call contains a continuous stream of CMI and CMC messages. There will be a new CMI and CMC command sent to the mobile every 40mS and a new CMI and CMR request sent to the BSS every 40mS. To enable Link Adaptation to function, both the BTS and MS have a C/I estimator implemented. The purpose of the C/I estimator is to estimate the Carrier to Interference ratio on a particular link. The C/I ratio determines the behaviour of AMR link adaptation. Downlink C/I is estimated by the mobile every 20mS. Uplink C/I is estimated by the BTS every 20mS.

6.2.2 Active Codec Set, Initial Codec Mode and Threshold & Hysterisis table To understand the system operation of AMR Link Adaptation, the following terms have to be explained.

• Active Codec Set (ACS) • Initial Codec Mode (ICM) • Threshold and Hysterisis tables.

The Active Codec Set (ACS) defines the codecs that will be used during Link Adaptation. There may be a maximum of four codecs defined per channel mode i.e. up to four codecs for Half Rate AMR and up to four codecs for Full Rate AMR. For link adaptation there must be at least two codecs defined. The ACS is common between the uplink and downlink, even though the codec used on the uplink and downlink may be different at any one time, the codecs used on each link will be chosen from the same ACS. The Initial Codec Mode (ICM) is set to define the codec in which the call will start. The ICM has to be one of the codecs within the ACS and again is common for both the uplink and downlink. After the call is established Link Adaptation will dictate any changes necessary for the codec mode used independently for the uplink and downlink. The Threshold and Hysterisis table contains a set of C/I thresholds which dictate at which C/I estimate a change in codec will be made. There are separate tables for uplink and downlink for both Full Rate AMR and Half Rate AMR. Additionally there are individual settings for cells that employ frequency hopping and for those that don’t. When a C/I estimate falls below a threshold, a codec change to the next lowest codec is instigated (if possible – there will be no affect if the lowest codec mode is already in use). The C/I estimate has to rise


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above a threshold by an additional hysterisis amount before a move to the next highest codec in the ACS is started. It is only possible to move up or down one codec in the table at one time. . Initial field trial results showed that the uplink C/I environment led to excessive link adaptation and often the mobile was instructed to spend too much time in the lower codec modes. This led to slightly worse speech quality than expected. To resolve this problem, there is now a dependency on Uplink Bit Error Rate i.e. the uplink C/I estimate is used in conjunction with the Uplink Residual Bit Error Rate to determine uplink link adaptation behaviour. In simple terms this means that to link adapt to a lower codec mode, both the conditions of poor Bit Error Rate and C/I threshold have to be met. This may lead to confusion when performing lab demonstrations of uplink link adaptation. It is recommended that an uplink interfering signal is used to generate a poor BER environment in addition to variations in C/I to demonstrate uplink adaptation. The high BER environment has not been found necessary in the downlink direction. The ACS, ICM and Threshold & Hysterisis tables are set at a per cell level in the Motorola implementation. As part of the AMR call setup and inter cell handover process, the AMR mobile will be sent the threshold and hysterisis table to be used for the duration of the call, while the mobile is in a particular cell. The transfer of the table is achieved through use of the multi rate configuration element which is contained in the Layer3 Assignment Command and Handover Command messages.

12.2 Kbps

10.2 Kbps

7.4 Kbps

5.15 Kbps

C/I

15dB

12dB

7dB

+2

+2

+2

0dB

31.5dB

Figure 5 Graphical representation of Link Adaptation.


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There are four codecs shown in the ACS i.e. 12.2, 10.2, 7.4 and 5.15 Kbps. The 15, 12 and 7 dB thresholds have been set as the switching thresholds and there is a +2dB hysterisis value. The blue arrow indicates the current C/I estimation at approximately 10dB and the current codec mode is 7.4 Kbps. If the C/I estimate were to fall below 7dB then a codec change to 5.15 Kbps would result. If the C/I estimate rises to at least 12dB + 2dB (hysterisis) = 14dB then a code change from 7.4 Kbps to 10.2 Kbps would occur. Note that the hysterisis value is included to reduce “oscillation” between codec modes and is only employed in the “up” direction.

6.3 MS Monitor The accuracy of the C/I estimator in the BTS and the mobile is important for correct operation of Link Adaptation. The accuracy of the BTS C/I estimator is set by the Motorola design and therefore can be controlled. The accuracy of the mobile C/I estimator is however not necessarily controllable by Motorola i.e. Motorola has no control over the accuracy of a Nokia mobile C/I estimator. To overcome this potential problem an MS Monitor is provided. The purpose of the MS monitor is to track the Codec Mode Requests (CMR) being sent from an AMR mobile and compare them to the downlink interference (RxQual) being reported. If the mobile CMR is continually requesting that the BSS uses a low codec mode on the downlink, but the downlink RxQual (reported via measurement reports) is good it is likely that the mobile is estimating lower than actual C/I values. Conversely, if the mobile is continually requesting high codec modes and the downlink RxQual indicates poor quality, it is likely that the mobile C/I estimator is providing higher than actual C/I estimates. The MS Monitor detects over or under estimating conditions and then applies a fixed C/I offset to the codec switching thresholds. The period over which the MS is monitored is user definable via the db parameter AMR_MS_MONITOR_PERIOD and is entered as a number of SACH periods. If the number of CMRs being request over this period exceeds either AMR_MS_HIGH_CMR or AMR_MS_LOW_CMR then providing the criteria below for RxQual is also met the MS will be instructed to adjust its thresholds and hysteresis by an amount specified by AMR_DL_THRESH_ADJUST. i.e. IF total CMRs requesting the highest codes rate (i.e. 12.2) during AMR_MS_MONITOR_PERIOD > AMR_MS_HIGH_CMR And average RxQual during AMR_MS_MONITOR_PERIOD > AMR_MS_HIGH_RXQUAL THEN adjust thresholds and hysteresis by AMR_DL_THRESH_ADJUST. The frequency of the AMR codec changes in the downlink can be restricted by the data base parameter AMR_DL_LA_MODE_CHANGE_MIN, see section 9.


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6.4 8 Kbps Backhaul – DSW2 GSM Half Rate and AMR Half Rate provide the opportunity to carry twice as many calls on the air interface when compared to Full Rate channel modes. The large increase in capacity is made possible through the air interface timeslot being split into two sub channels. A Full Rate air interface call (which occupies one whole air interface timeslot) requires 16 Kbps of “backhaul” – the voice circuit path between the BTS and RXCDR. Currently in a Full Rate channel mode BSS, the Kilo Port Switch (KSW) fitted at the BSC and RXCDR is used to switch complete 16 Kbps voice channels. When GSM Half Rate or AMR Half Rate calls are considered, the backhaul requirement is reduced to 8 Kbps due to the reduction in bandwidth required by the Half Rate codecs. The Full Rate BSS system using a KSW is still capable of switching of 8Kbps speech, however system capacity gains will not be realised unless additional voice circuits are added from the BTS to RXCDR path. To explain further, the minimum amount of bandwidth that the KSW can switch is 16Kbps i.e. one Full Rate speech circuit. When Half Rate channels are used, half of the 16 Kbps backhaul will be used to carry the 8 Kbps speech and the other half will be redundant. To carry more traffic, additional 16 Kbps voice circuits will have to be added between the BTS and RXCDR. This is one possible solution but does carry additional cost in terms of implementation of transport links (MMS) and potentially more hardware (MSI, NIU etc). As an alternative solution a new version of the KSW has be introduced intended for deployment at the BSC and RXCDR. The DSW2 switch performs the same system functions as a KSW but has the capability of switching either at 16 Kbps or 8 Kbps. The DSW2 extends the capacity gain achieved on the air interface to the backhaul i.e. additional links and associated hardware are not required to increase the backhaul requirements for Half Rate speech circuits.

6.5 Impact of the 7.95 Kbps codec All of the AMR Half Rate codecs fit inside the bandwidth of one sub timeslot on the air interface. When the backhaul from the BTS to the XCDR function is considered all of the codecs, except 7.95 Kbps, will fit inside the 8 Kbps transport (TRAU) link. The 7.95 Kbps codec does not allow enough bandwidth within an 8 Kbps TRAU link (8 – 7.95 = 0.05 Kbps) to perform all of the necessary control operations. If 7.95 Kbps is included in the Active Codec Set (ACS) then 8Kbps backhaul is prohibited. At first this may seem a disadvantage, however given that the speech quality performance of the 7.4 Kbps codec is very similar to that of 7.95 Kbps, to use 7.4 Kbps with 8 Kbps TRAU instead of 7.95 Kbps with 16 Kbps TRAU would be a sensible trade off.

6.6 AMR transcoder requirements, GDP2 and RXU3 Link Adaptation requires the DSP located at the transcoder function to be capable of supporting all of the AMR codec modes i.e. an additional 10 codecs have to be catered for. The original GDP card was designed to transcode a combination of, 30 channels of Full Rate speech, Enhanced Full Rate speech or Phase 2 data services. Due to the new codecs and complexity of AMR, the DSP devices fitted to the GDP no longer have enough “horse power” to process 30 channels.


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Original GDP cards may still be used for transcoding AMR channels however there maximum number of channels supported is 15. Two original GDP cards may be used as a “pair” to provide 30 channels of all channel modes, however this leaves an overall system capacity reduction. To address this situation a new GDP card has been developed (GDP2). The GDP 2 card performs the same system functions as the GDP but provides the capability for transcoding 60 channels of GSM Full Rate speech, Enhanced Full Rate speech, AMR Half Rate speech, AMR Full Rate speech and Phase 2 data services. The original GDP card has one E1 connection provided, this is sufficient for 30 channels of transcoding plus a 64 Kbps timeslot for routing a control channel (MTL, OML etc). To provide 60 channels of transcoding, the GDP2 card has been designed with two E1 connections. To take advantage of the additional capacity offered by the GDP2, it is necessary to deploy an accompanying new cabinet – the RXU3. The RXU3 cabinet supports the dual E1 connection GDP2 and makes provision for additional E1 termination points on the top of the cabinet. The GDP2 card can still be fitted to existing RXU cabinets but with only one E1 connection available. The advantage of the new GDP2 card fitted in an existing RXCDR cabinet (not RXU3) is that the GDP2 will support 30 channels of GSM Full Rate, EFR, AMR Half Rate, AMR Full Rate and Phase 2 Data Services as opposed the 15 channels offered by the original GDP. Note: The original XCDR card does not support any AMR Channels or GSM HR.

7 GSM Half Rate transcoder requirements The GSM Half Rate feature is not as complex as AMR since there is only one new codec required to support and no Link Adaptation. The original GDP has been adapted to add GSM Half Rate as a new mode meaning that the GDP can support a mixture of 30 channels Full Rate, Enhanced Full Rate, GSM Half Rate and Phase 2 Data Services. Support for GSM Half Rate using GDP cards can mean less initial hardware investment. Currently the GDP2 card does not support GSM Half Rate; this functionality is scheduled for a future release. Note: The original XCDR card does not support any GSM Half Rate channels. FR EFR GSM HR AMR HR AMR FR RXCDR 30 N/A N/A N/A N/A GDP 30 30 30 N/A N/A GDP Enhanced Mode 15 15 N/A 15 15 GDP Enhanced Mode equipped as GDP pair.

30 30 N/A 30 30

GDP2 (1 E1 per MSI) 30 30 30* 30 30 GDP2 (2 E1 per MSI) ngRXCDR

60 60 60* 60 60


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Table 4. Speech version capability and channel capacity for transcoder board type. (* GSR8 only)

8 Enhanced auto-connect (EAC) mode/ cic validation Motorola now allows three methods of backhaul provisioning:-

• Backward compatible Mode where cics and Aters are statically mapped between BSC and RXCDR.

• Auto-connect mode allows for the dynamic provisioning on a per call basis of channels between the RXCDR and BSC (Aters).

• EAC is an extension of the Auto-connect feature and allows the dynamic allocation of 8K Aters. EAC is only relevant when both the remote RXCDR and BSS are fully populated with DSW2 boards (i.e. 8Kbps back haul is applicable) and there is at least one half rate capable (AMR HR or GSM HR) transcoder board at the RXCDR (EGDP or GDP2).

Since it is possible to have a mixture of transcoding capabilities at a remote RXCDR i.e. AMR FR/HR and GSM HR etc, cic_validation must be enabled along with at least one XBL link. This is so that the BSC can determine a CICs transcoding capability and down grade accordingly, if necessary. Note: AMR/GSM HR can be enabled for a BSS when CIC Validation is disabled, but no AMR/GSM HR calls will be possible, i.e. the BSC will default to FR\EFR in order to avoid being allocating a CIC through an incompatible transcoder board. Note: EAC mode does not need to be equipped in order to make AMR or GSM HR calls, only if 8Kbps back haul across the Ater interface is required. Since there is no fixed mapping of CICs on the Ater interface the CICs can now be considered as a separate pooled resource between RXCDRs and BSCs. This pooling means that it is no longer necessary to have the same number of CICs going through an RXCDR as Aters from the BSC to the RXCDR. If the CIC - Ater provisioning is equal then EAC mode is not needed and the system will revert back to auto connect mode. Note: Since a BSC may interconnect with several RXCDRs, and vice-versa, it is possible for Static Mode, Auto Connect Mode, and Enhanced Auto Connect Mode to all be in use at one time (one mode per BSC-RXCDR combination), this is seamless to the user. Having less Aters than CICs through the RXCDR assumes that a percentage of calls will utilise 8Kbps back haul, if this proves not to be true, capacity will be lost due to lack of Ater resources. To avoid this


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scenario the BSC provides a means of blocking CICs at the MSC when the number of Aters available to a RXCDR reaches a define threshold. These thresholds are set by cic_block_thresh and cic_unblock_thresh parameters and by default are disabled. The user is prompted for the block thresholds when EAC mode is enabled.

9 New database parameters In order to control AMR and GSM Half Rate there are several new parameters added to the GSR 7 database. Because of similarities between AMR Half Rate and GSM Half Rate, some of the parameters apply to both features simultaneously.

9.1 AMR Parameters

9.1.1 Enabling and Disabling of AMR Full and Half Rate The AMR feature must be unrestricted through the options object (object 13). The list of features contained in the options object is controlled by the Software Licensing Distribution Centre in Swindon. Contact SDLC if there are any problems with the options object. Parameter Range Setting Default Description amr_bss_full_rate_enabled 0 or 1 0 = Disabled

1 = Enabled 0 Enables / Disables AMR Full Rate

on a BSC basis amr_bss_half_rate_enabled 0 or 1 0 = Disabled

1 = Enabled 0 Enables / Disables AMR Half Rate

on a BSC basis amr_full _rate _enabled 0 or 1 0 = Disabled

1 = Enabled 0 Enables / Disables AMR Full Rate

on a cell basis amr_half _rate _enabled 0 or 1 0 = Disabled

1 = Enabled 0 Enables / Disables AMR Half Rate

on a cell basis Table 4 Parameters to enable AMR FR and AMR HR on a BSC and on a per cell basis.

AMR Half Rate and GSM HR can only be enabled on BTS platforms that support those speech versions. Table 5 indicates the platforms that currently support AMR Half Rate. BTS Platform Radio Type MCell 2 TCU A, TCU B MCell 6 TCU A, TCU B Horizon Macro I CTU, CTU2 Horizon Macro II CTU, CTU 2 Table 5 BTS Platforms that support AMR FR/HR and GSM HR.


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9.1.2 Configuration of AMR capable cell for link adaptation. The operator has the ability to enable and disable AMR link adaptation on a per cells basis both in the uplink and downlink direction and for full rate and half rate calls. This is controlled by the following parameters: Parameter Range Setting Default Description amr_dl_la_mode_chg_min 0 - 63 Number of

20ms periods.

5 This BSC parameter specifies the minimum delay between downlink adaptations. i.e. The delay between the MS requesting a new codec and the downlink using the requested rate. Note: There is a minimum round trip delay of between 7 to 12 frames, giving an effective delay range of 240ms to 1.26s

amr_ms_monitor_period 10 to 1200

SACH periods.

40 This defines the period over which the number of CMRs sent from the mobile will be counted. See section 6.5.

amr_ms_high_cmr 50 to 100

Percentage 95 Threshold of requested codec changes to highest codec mode to trigger MS Monitor.

amr_ms_low_cmr 50 to 100

Percentage 99 Threshold of requested codec changes to lowest codec mode to trigger MS Monitor.

amr_ms_high_rxqual 0 to 7 BER Qbands 4 If MS monitor has detected a high percentage of CMR’s requesting the highest codec, then if the average rxqual over the period “amr_ms_monitor_period” > “this threshold value” the MS is requesting the highest codec but RxQual is poor. This indicates the MS C/I estimator is incorrect. The MS Monitor function will instruct the mobile to increase its LA thresholds by the value set in amr_ms_low_rxqual. This will reduce the probability of being in


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the highest codec mode with poor RxQual.

amr_ms_low_rxqual 0 to 7 BER Qbands 3 If MS monitor has detected a high percentage of CMR’s requesting the lowest codec, then if the average rxqual over the period “amr_ms_monitor_period” < “this threshold value” the MS is requesting the lowest codec but RxQual is good. This indicates the MS C/I estimator is incorrect. The MS Monitor function will instruct the mobile to decrease its LA thresholds by the value set in amr_ms_low_rxqual. This will reduce the probability of being in the lowest codec mode with good RxQual.

amr_dl_thresh_adjust 1 to 7 db’s 3 This represents the number of dbs the downlink LA threshold can be adjusted if the MS monitor function detects the MS C/I estimator is incorrected.

amr_fr_dl_la_enabled 0 or 1 Dis/Enabled 1 Enables Link adaptation. amr_fr_ul_la_enabled 0 or 1 Dis/Enabled 1 Enables Link adaptation. amr_hr_dl_la_enabled 0 or 1 Dis/Enabled 1 Enables Link adaptation. amr_hr_ul_la_enabled 0 or 1 Dis/Enabled 1 Enables Link adaptation. Table 6 AMR LA parameters.

As well as enabling and disabling link adaptation (LA) on a cell by cell basis it might also be necessary to have different cells configured to perform LA with different codec choices, adaptation thresholds or hystersis. This is made possible by the inclusion of the “chg_acs_params” command. This command allows for discrimination between uplink and downlink LA thresholds as well as frequency hopping and non-frequency hopping thresholds. It allows the specification of the following codec settings and thresholds for all combination of uplink, downlink, FR/HR, hopping and non-hopping. ACS: Active Codec Set, up to 4 codec to be used ICS: Initial Codec Set, the initial codec mode used when the call is first established. Threshold: The levels of C/I at which the codec mode should switch to a lower/higher rate.


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Hysteresis: The offset level that should be added to a Threshold when moving up codec modes to avoid unnecessary bouncing between to codec modes. Note: The values of Thresholds and hysteresis entered using this command are in ½ dBs steps. AMR Half Rate active codec set 2 3 4 5 . . . AMR Half Rate link adaptation thresholds 40 30 20 [actual 20dB 15dB 10dB] AMR Full Rate uplink adaptation hysteresis: 5 8 10 [actual 2.5dB 4dB 5db] When the C/I estimate reaches < 20dB the codec mode would switch from 2 ( 7.95Kbps) to 3 (7.4Kbps), but only when the C/I > 22.5dB would a switch from 3 (7.4Kbps) to 2 (7.95Kbp) occur. Note: disp_acs_params allows the current AMR configuration to be displayed for a given cell. disp_acs <cell id> AMR Full Rate active codec set: 0 1 3 6 AMR Full Rate initial codec mode: 1 AMR Full Rate uplink adaptation thresholds: 32 24 16 The acs displayed via the disp_cell <cell-id> full command is displayed in a bit map format:- amr_fr_acs = 210 = 0xD2 = 11010010 (binary) i.e. codec 0 – bit 7(msb)…. Code 6 = bit 1 (lsb+1) Hence codecs 0,1,3,6 have been selected.

9.1.3 Configuration of AMR parameters from the OMC The GSR 7 version of OMC supports the configuration and control of AMR and GSM Half Rate features. There are two detailed view forms that have been updated to support this functionality. Figure 6 shows the BSS detailed view and Figures 7 and 8 show the CELL detailed view for Full Rate and Half Rate AMR.


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Figure 6 OMC, BSS detailed view


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Figure 7 OMC, Cell detailed view for AMR FR.


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Figure 8 OMC, Cell detailed view for AMR HR.

As shown in Figures 7 and 8, the codecs for the ACS are selected form the “pop-up” box and then applied.

9.2 Enabling and Disabling of GSM Half Rate Similar to AMR the GSM Half Rate feature must be unrestricted through the options object (object 13). Parameter Range Setting Default Description gsm_bss_half_rate_enabled 0 or 1 0 = Disabled

1 = Enabled 0 Enables / Disables GSM Half Rate

on a BSC basis gsm_half_rate_enabled 0 or 1 0 = Disabled

1 = Enabled 0 Enables / Disables GSM Half Rate

on a cell basis


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Table 7 Parameters to enable GSM HR on a BSC and on a per cell basis.

9.3 Enable Half Rate on a carrier basis (RTF) To make AMR Half Rate or GSM Half Rate possible it is necessary to enable half rate on a carrier basis (RTF). The RTF device has been updated to control the use of Half Rate. When equipping an RTF, a new prompt has been added:- “Enter the value for Half Rate enabled:” If the RTF being equipped is not to be Half Rate capable then enter ‘0’. If the RTF being equipped is to be Half Rate capable then a ‘1’ is entered. It is not possible to use the “modify_value” command to change the value of “Half Rate Enabled” on an RTF basis. The RTF must be either, un-equipped and re-equipped with the desired value, or changes are made to the 02 database object before a download. Note: If 8k back haul is required i.e. DSWs have been installed at the BSC/RXCDR then “allow_8k_trau” must also be set when equipping the RTF. Note: If KSW’s are equipped at the BSC and “allow_8k_trau = 1” then half rate calls will not be possible, all calls will be downgraded to full rate.

9.4 Feature Control - AMR Full Rate When enabled, the deciding factors of whether an AMR full rate channel is used or not depends on the mobiles capability and the speech version and rate specified by the MSC. In a mobile originated call, during the call setup signalling sequence, the mobile will pass its speech version capability and preference to the MSC in the Layer 3 Setup message. Using this information the MSC will match the capabilities and preferences of the mobile with the most preferred MSC speech version. Channel Modes and Speech versions are held in a list used to build the Assignment Request message, the first Channel mode and Speech version in the list is the most preferred by the MSC (Network operator’s choice). The MSC generates an Assignment Request message and assuming the BSS has suitable resources available the channel will be allocated via an Assignment Command message. In a mobile terminated call (page response) the mobiles capability is transferred using the “Call confirmed” Layer 3 signalling message and a similar matching exercise is performed by the MSC. Note: Half rate calls (AMR HR or GSM HR) will not be possible if the MSC sends changes not allowed in its assignment command, see appendix A.


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9.5 Feature Control - AMR Half Rate and GSM Half Rate The BSS implementation of Half Rate channel allocation is the same for AMR Half and GSM Half Rate. This section of the document will treat AMR Half Rate and GSM Half Rate the same and use the general term “Half Rate”. There are a number of methods available to provide a Half Rate Channel.

• “force_hr_usage” • “new_calls_hr” • “reconfig_fr_to_hr”

9.6 force_hr_usage This is a BSC wide parameter which when enabled will result in the BSS forcing a Half Rate resource (assuming a resource is available) in response to an assignment request from the MSC which contains either AMR Half Rate or GSM Half Rate in the speech version. In cases where a mobile supports both AMR Half Rate and GSM Half Rate the MSC preference list will be used to determine the speech version allocated.

9.7 new_calls_hr, inner_hr_usage_thres, hr_res_ts and reconfig_fr_to_hr These parameters are per cell and designed to be used in situations where under “normal” circumstances Full Rate channels and speech versions are used. The parameters control the allocation of Half Rate channels provoked by the volume of traffic in the cell.

9.8 new_calls_hr Parameter Range Setting Default Description new_calls_hr 0 to 101 Steps of 1%

per Cell 101 Sets a percentage threshold as to

the amount of resources being used in a cell before any new calls entering the cell would be allocated a Half Rate resource. A value of 101 disables the functionality.

9.9 inner_hr_usage_thres Parameter Range Setting Default Description inner_hr_usage_thres 0 to 101 Steps of 1%


the amount of resources being used on the inner zone of a multi zone cell before any new calls entering the cell would be allocated a Half Rate resource. A value of 101 disables the functionality.


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9.10 hr_res_ts Parameter Range Setting Default Description hr_res_ts 0 to 255 Integer steps 2 Sets the number of Half Rate

capable timeslots to reserve within each zone of the cell.

9.11 reconfig_fr_hr Parameter Range Setting Default Description Reconfig_fr_to_hr 0 to 101 Steps of 1%


the amount of Full rate resources being used in a cell before existing Half Rate capable calls are reconfigured from Full Rate to Half Rate. A value of 101 disables the parameter.

“new_calls_hr” is used to set a threshold, using an implementation similar to congestion relief, where when the threshold is exceeded any call setups or calls handing in (from mobiles that are GSM and/or AMR Half Rate capable) will be allocated a Half Rate resource. The threshold is a percentage of the total resource being used in the cell and if in a multi-zone cell (i.e. Single BCCH) is measured on the outer zone only. For multi zone cells i.e. Single BCCH, before the “new_calls_hr” or the “reconfig_fr_hr” thresholds can be active the “inner_hr_usage_thres” threshold must be exceeded. The calculations for Total Resource and Busy Resource to determine whether the inner_hr_usage_thres has been exceeded for the inner zone are the same as described for the outer zone. To disable this functionality in a multi zone cell, set inner_hr_usage_thres to a value of 101. hr_res_ts This parameter sets a “soft” reserve for the number of Half Rate capable timeslots on the inner and outer zone (if applicable). The default value is 2, meaning that 2 timeslots will be kept free in each zone until such time as they are needed by either Full Rate or Half Rate calls. The term “soft” reserve means that the timeslots are not reserved solely for the use of half rate calls. The timeslots will be the last to be allocated. The intent of this parameter is for cells which have a small amount of AMR / GSM Half Rate capable resources assigned i.e. one carrier, the likelihood is that the reserved timeslots will still be available for use. If the reserve was not in place then all Half Rate capable timeslots may have been allocated to full rate calls meaning no half rate calls would be possible. In addition the parameter could be used to keep Half Rate resources available in the inner zone. To disable this functionality set hr_res_ts to a value of 0.


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Carriers that do not have the half rate capable flag set on the RTF (carriers which are not half rate capable), will show in use timeslots marked as TCH/F. Carriers that have the half rate capable flag set and the system has been configured for GSM / AMR Half Rate will show in use timeslots marked as TCH/H Active. TCH/G is the classification used to describe generic timeslots (timeslots that are idle but may be configured for multiple purposes) i.e. TCH/F, TCH/H and GPRS. To calculate the Total resource in the cell the following formula is used. Total Resource = (TCH/G + (Busy TCH/H) / 2 + Idle TCH/F + Busy TCH/F). The busy (in use) resource is calculated using the following formula. Busy Resource = ((Number of Busy TCH/H) / 2 + Number of Busy TCH/F). To determine whether the new_calls_hr threshold has been exceeded the following calculation is performed. (Busy Resource / Total Resource) X 100 % > “new_calls_hr” Figures 9, 10, 11 and 12 demonstrate the concept of the “new_calls_hr” parameter. For the example shown assume that the “new_calls_hr” threshold has a value of 50 i.e. when over 50% of the cells resources are used, any half rate capable new call setups or hand-ins to the cell will be allocated a half rate resource.


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BCCHSDCCHTCH/FTCH/FTCH/FTCH/FTCH/GTCH/G

Carrier 1

TCH/GTCH/GTCH/GTCH/GTCH/GTCH/GTCH/GTCH/G

Carrier 2

Total Resource = (TCH/G + (Busy TCH/H) / 2 + Idle TCH/F + Busy TCH/F)

= ( 10 + ( 0 / 2 ) + 4 + 0 )

Total Resource = 14

Figure 9 Two carrier cell which has a total resource count of 14.

BCCHSDCCHTCH/FTCH/FTCH/FTCH/FTCH/FTCH/G

Carrier 1

TCH/GTCH/FTCH/GTCH/GTCH/FTCH/GTCH/GTCH/G

Carrier 2

Busy Resource = ((Number of Busy TCH/H) / 2 + Number of Busy TCH/F)

= ((0 / 2) + 5) = 5

new_calls_hr exceeded ( 50 %)?

(Busy Resource / Total Resource) X 100 %

= ( 5 / 14) X 100%

= 36 % (Threshold Not Exceeded)

Figure 10 Cell at 36 % Full Rate occupancy.


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Carrier 1

TCH/GTCH/FTCH/GTCH/GTCH/FTCH/GTCH/GTCH/G

Carrier 2


= ((0 / 2) + 7) = 7



= ( 7 / 14) X 100%

= 50 % (Threshold met but not Exceeded)

Figure 11 Cell at 50 % occupancy.

This is exactly on the limit of the 50% new_calls_hr threshold. Assuming the existing seven calls remain, when the next call arrives from a setup or hand in, and the call is GSM or AMR Half Rate capable, it will be assigned a Half Rate channel.


Carrier 1

TCH/GTCH/FTCH/GTCH/GTCH/FTCH/GTCH/G

TCH/H TCH/H

Carrier 2


= ((1 / 2) + 7) = 7.5



= ( 7.5 / 14) X 100%

= 54 % (Threshold Exceeded)

Figure 12 Next call handed in or set up in the cell is allocated a Half Rate Channel (TCH/H).


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Half Rate resources will continue to be allocated to capable calls until either the cell runs out of resource (blocking) or the level of traffic drops below the 50% new_calls_hr threshold.

9.12 reconfig_fr_to_hr This parameter works in a similar fashion to “new_calls_hr” and the method for determining if the threshold has been exceeded uses the same calculations previously shown. The purpose of the reconfig_fr_hr parameter is to set a threshold that when exceeded will reconfigure existing Full Rate calls (that are Half Rate capable) from Full Rate to Half Rate timeslots in the same cell. When the reconfig_fr_hr threshold is exceeded, all of the calls that are Half Rate capable will be evaluated using the congestion relief criteria (assuming that the conventional congestion relief threshold has not been reached). Any calls that qualify for conventional congestion relief will be excluded from the reconfiguration operation. Up to a maximum of 16 remaining mobiles will be reconfigured from Full Rate to Half Rate channels using intra-cell assignment commands. The flow chart in Figure 13 shows the system operation for reconfig_fr_hr.


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Calculate Total Resource

Calculate Busy Resource

Busy Resource / Total Resource X 100% > reconfig_fr_hr

?

Identify Half Rate capable calls

Build a list of the calls that do notmeet congestion relief criteria

PBGT > Congestion margin

Reconfigure from Full Rate to Half Rate the first 16 calls from the list while idle

Half Rate resources remain.

valid_candidate_periodexpired ?

Yes

No

Yes

No

Figure 13 Flow chart of Full Rate to Half Rate reconfiguration.


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9.13 Handover and Power Control The half rate channel mode introduces a new challenge on the air interface. There are half the number of bits transferred in the same time. For a Full Rate channel, in one Sacch period (480mS) there will be 24 speech frames, one Sacch and one idle frame per call. For Half Rate in the same period (480mS) there will be 12 speech frames and one Sacch frame per call. The remaining 12 speech frames and Sacch frame will be used for a second call on the same timeslot. Hence Half Rate provides double the capacity on the air interface. Figures 14 and 15 show the differences in frame structure between Full Rate and Half Rate channels.

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

SACC

H

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

Speech A

IDLE

480 mS

Full Rate

Figure 14 Full Rate SACCH Frame.

Speech A

Speech B

Speech A

Speech B

Speech A

Speech B

Speech A

Speech B

Speech A

Speech B

Speech A

Speech B

SACC

H A

Speech A

Speech B

Speech A

Speech B

Speech A

Speech B

Speech A

Speech B

Speech A

Speech B

Speech A

Speech B

SACC

H B

480 mS

Half Rate

Figure 15 Half Rate SACCH Frame.

Since the Half Rate channel mode uses half the number of bits when compared to full rate, the impact of losing bits from disturbance on the air interface (bit errors caused by interference) is higher for Half


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Rate. In other words, given the same interference levels a half rate call is likely to suffer worse quality of service (speech quality) than a full rate call. This does not mean that there will be more dropped calls with half rate – in fact the drop call rate should be identical between full and half rate as the encoding used for the uplink and downlink Sacch are identical for Full Rate and Half Rate channel modes. To counteract the difference in speech quality caused by bit errors in Half Rate channel modes, new receive quality based (rxqual) handover and power control thresholds have been introduced. The principle behind the new parameters is to provide a method of protecting half rate channels more than full rate channels (if required) so that power control and quality based handovers take place in lower BER environments compared to full rate. There have been no changes made to any of the Rxlevel based parameters since there are no differences in RF levels between full rate and half rate channel modes. Figure 16 shows how the half rate power control and quality handover thresholds can be set differently to the full rate parameters in the same cell.


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7

6

5

4

3

2

1

0

Quality Power Box

Quality Handover

7

6

5

4

3

2

1

0

Quality Power Box

Quality Handover

Full Rate Half Rate

u_rxqual(ul/dl)_p

l_rxqual(ul/dl)_p

l_rxqual(ul/dl)_h

RxQual (QBand units)

u_rxqual(ul/dl)_p_hr

l_rxqual(ul/dl)_p_hr

l_rxqual(ul/dl)_h_hr

Figure 16 Recommanded RxQual bands for GSM/AMR Half Rate.

Note – the parameters affect both GSM and AMR Half Rate and either QBand units or BER may be specified dependant on the setting of alt_qual_proc. From experiments conducted in the laboratory it was observed that speech quality (measured using Qvoice; Pace) was not affected for GSM HR calls until RxQual was greater than 5 (453 BER), the default value for l_rxqual(ul/dl)_h. Hence to avoid unnecessary handovers it is suggested that l_rxqual(ul/dl)_h_hr be set to the current settings of l_rxqual(ul/dl)_h used within the network, providing this value is not greater than 5, (453 BER).


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UL HR Pace Vs RXQUAL

-505

10152025303540

1 1.3 1.6 1.9 2.2 2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9

Pace

Num

Sam

ples

TU50 RXQUAL 6/7RXQUAL7RXQUAL 6RXQUAL 5RXQUAL 3

Figure 17 Qvoice Pace for different RxQual collected in Laboratory.

l_rxqual_dl_h_hopping_hr l_rxqual_dl_h_hr l_rxqual_dl_p_hopping_hr l_rxqual_dl_p_hr l_rxqual_ul_h_hopping_hr l_rxqual_ul_h_hr l_rxqual_ul_p_hopping_hr l_rxqual_ul_p_hr u_rxqual_dl_p_hr u_rxqual_ul_p_hr

Table 8 New HDPC parameters introduced for half rate channels.

9.14 Half Rate to Full Rate intra-cell handovers. During call setup in a cell, if the new_calls threshold has been exceeded or Half Rate usage is being forced then a mobile that is capable of half rate will be assigned to a half rate channel. This procedure is achieved using the assignment command sent to the mobile. If the reconfigure threshold is exceeded and a mobile is currently on a full rate channel and does not qualify for congestion relief then the mobile will be sent an assignment command assigning it to a half rate channel in the same cell. This procedure


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is the same as the existing intracell handover process except a half rate instead of full rate channel is specified. The parameter hr_intracell_ho_allowed has been introduced to control the behaviour of half rate intracell handovers. There are effectively two circumstances where intracell handovers will take place to or from Half Rate channels.

• Reconfigure threshold exceeded – intracell from Full Rate to Half Rate • Quality reasons – intracell from Half Rate to Full Rate and if configured

(hr_intracell_ho_allowed = 3) Intracell from Half Rate to Half Rate.

There are 4 settings of the parameter:- 0 – The BSS does not perform intracell handovers, a handover required message is sent to the MSC. 1 – Half Rate intracell handovers are disabled, no handover required message is generated. 2 – Half Rate intracell handovers are enabled but only handovers from Half Rate channels to Full Rate channels are permitted. 3 – Half Rate intracell handovers are enabled; handovers from Half Rate to Half Rate and Half Rate to Full Rate are permitted. In addition to the control of Half Rate intracell handovers another new parameter has been added to control the number of Half Rate intracell handovers allowed before escalation to an inter-cell quality handover. There is an existing parameter:- hop_count which is used in conjunction with hop_count_timer to provide this functionality for Full Rate channels. The parameter hop_count_hr has been added and is used with the existing hop_count_timer to control the number of Half Rate intracell handovers allowed.

10 Parameter Optimisation Parameter optimisation can be split into 3 categories.

• Thresholds for half rate channel usage – for both GSM Half Rate and AMR Half Rate. • HDPC settings - GSM Half Rate and AMR Half Rate. • AMR link adaptation thresholds, hysterisis and codecs.

10.1 Thresholds for Half Rate Usage As previously mentioned the new calls and reconfigure settings determine the “trade off” between capacity and Quality of Service. There are several scenarios that could be imagined where half rate channels could be deployed to give maximum benefit. Some examples may be:-

• Offer extra capacity during busy traffic periods i.e. at busy hour • Provide additional capacity at an event such as sport, exhibition, music concert etc. • Force the use of half rate for a lower tariff subscriber scheme.


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The choice of where, when and how Half Rate channels are used is really a decision for the Network operator and their network strategy. Unnecessary use of Half Rate could lead to degradation in Quality of Service and in contrast, if Half Rate channels are not allocated until there are few resources left in a cell then the full capacity gain will not be realised.

Thresh 24 57%

3 8 14 20 3 8 14 20 3 8 14 20 H F H F H F H F0 0% 100% 100% 100% 100% 2% 88% 100% 100% 100% 100% 100% 100% 100% 0% 100% 0% 100% 0% 100% 0%1 14% 75% 89% 93% 95% 6% 95% 100% 100% 77% 99% 100% 100% 76% 24% 94% 6% 97% 3% 98% 2%2 28% 53% 78% 87% 90% 15% 98% 100% 100% 60% 100% 100% 100% 56% 44% 89% 11% 93% 7% 95% 5%3 42% 35% 68% 80% 86% 30% 99% 100% 100% 54% 100% 100% 100% 44% 56% 84% 16% 90% 10% 93% 7%4 57% 21% 57% 74% 81% 50% 100% 100% 100% 60% 100% 100% 100% 40% 60% 79% 21% 87% 13% 91% 9%5 71% 11% 48% 67% 76% 72% 100% 100% 100% 75% 100% 100% 100% 43% 57% 74% 26% 84% 16% 88% 12%6 85% 5% 39% 61% 72% 90% 100% 100% 100% 90% 100% 100% 100% 48% 52% 69% 31% 81% 19% 86% 14%

Prob of HR access Prob of in call change to HR Overall prob of HR 31 CarrierTraffic Dist

8 14 20Thresh 1

Figure 18 1 Carrier probability of HR usage.

Thresh 27 50%

4 8 14 20 4 8 14 20 4 8 14 20 H F H F H F H F0 0% 1 100% 100% 100% 0% 13% 94% 100% 100% 100% 100% 100% 100% 0% 100% 0% 100% 0% 100% 0%1 7% 80% 89% 93% 95% 0% 22% 97% 100% 80% 91% 100% 100% 80% 20% 90% 10% 97% 3% 98% 2%2 14% 62% 78% 87% 90% 0% 34% 99% 100% 62% 86% 100% 100% 62% 38% 82% 18% 93% 7% 95% 5%3 21% 45% 68% 80% 86% 1% 49% 100% 100% 45% 84% 100% 100% 45% 55% 76% 24% 90% 10% 93% 7%4 28% 31% 57% 74% 81% 2% 65% 100% 100% 33% 85% 100% 100% 32% 68% 71% 29% 87% 13% 91% 9%5 35% 20% 48% 67% 76% 5% 78% 100% 100% 24% 89% 100% 100% 22% 78% 68% 32% 84% 16% 88% 12%6 42% 12% 39% 61% 72% 12% 88% 100% 100% 22% 93% 100% 100% 17% 83% 66% 34% 81% 19% 86% 14%7 50% 6% 31% 55% 67% 23% 95% 100% 100% 28% 96% 100% 100% 17% 83% 64% 36% 78% 22% 84% 16%8 57% 3% 24% 49% 63% 39% 98% 100% 100% 41% 99% 100% 100% 22% 78% 61% 39% 75% 25% 81% 19%9 64% 1% 17% 43% 58% 59% 99% 100% 100% 59% 100% 100% 100% 30% 70% 58% 42% 72% 28% 79% 21%10 71% 1% 12% 38% 54% 77% 100% 100% 100% 78% 100% 100% 100% 39% 61% 56% 44% 69% 31% 77% 23%11 78% 0% 8% 32% 49% 91% 100% 100% 100% 91% 100% 100% 100% 46% 54% 54% 46% 66% 34% 75% 25%12 85% 0% 5% 27% 45% 98% 100% 100% 100% 98% 100% 100% 100% 49% 51% 53% 47% 64% 36% 73% 27%13 92% 0% 3% 23% 41% 100% 100% 100% 100% 100% 100% 100% 100% 50% 50% 52% 48% 61% 39% 71% 29%

Overall prob of HRProb of in call change to HRProb of HR accessTraffic Dist

4 8 14 20Thresh 1

2 Carriers

Figure 19 2Carrier probability of HR usage.


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Thresh 211 52%

8 14 20 30 8 14 20 30 8 14 20 30 H F H F H F H F0 0% 1 100% 100% 100% 0% 16% 90% 100% 100% 100% 100% 100% 100% 0% 100% 0% 100% 0% 100% 0%1 4% 89% 93% 95% 97% 0% 24% 94% 100% 89% 95% 100% 100% 89% 11% 94% 6% 97% 3% 98% 2%2 9% 78% 87% 90% 94% 0% 35% 97% 100% 78% 91% 100% 100% 78% 22% 89% 11% 95% 5% 97% 3%3 14% 68% 80% 86% 90% 0% 47% 98% 100% 68% 89% 100% 100% 68% 32% 85% 15% 93% 7% 95% 5%4 19% 57% 74% 81% 87% 1% 60% 99% 100% 58% 89% 100% 100% 58% 42% 82% 18% 90% 10% 94% 6%5 23% 48% 67% 76% 84% 2% 72% 100% 100% 49% 91% 100% 100% 48% 52% 79% 21% 88% 12% 92% 8%6 28% 39% 61% 72% 81% 4% 82% 100% 100% 41% 93% 100% 100% 40% 60% 77% 23% 86% 14% 90% 10%7 33% 31% 55% 67% 78% 7% 89% 100% 100% 36% 95% 100% 100% 33% 67% 75% 25% 84% 16% 89% 11%8 38% 24% 49% 63% 74% 13% 94% 100% 100% 33% 97% 100% 100% 29% 71% 73% 27% 81% 19% 87% 13%9 42% 17% 43% 58% 71% 22% 97% 100% 100% 36% 98% 100% 100% 26% 74% 71% 29% 79% 21% 86% 14%10 47% 12% 38% 54% 68% 34% 99% 100% 100% 42% 99% 100% 100% 27% 73% 69% 31% 77% 23% 84% 16%11 52% 8% 32% 49% 65% 49% 100% 100% 100% 53% 100% 100% 100% 31% 69% 66% 34% 75% 25% 83% 17%12 57% 5% 27% 45% 62% 65% 100% 100% 100% 66% 100% 100% 100% 36% 64% 64% 36% 73% 27% 81% 19%13 61% 3% 23% 41% 59% 78% 100% 100% 100% 79% 100% 100% 100% 41% 59% 61% 39% 71% 29% 79% 21%14 66% 2% 19% 37% 56% 88% 100% 100% 100% 89% 100% 100% 100% 45% 55% 59% 41% 68% 32% 78% 22%15 71% 1% 15% 33% 53% 95% 100% 100% 100% 95% 100% 100% 100% 48% 52% 57% 43% 66% 34% 76% 24%16 76% 0% 11% 29% 50% 98% 100% 100% 100% 98% 100% 100% 100% 49% 51% 56% 44% 65% 35% 75% 25%17 80% 0% 9% 26% 47% 99% 100% 100% 100% 99% 100% 100% 100% 50% 50% 54% 46% 63% 37% 73% 27%18 85% 0% 6% 22% 44% 100% 100% 100% 100% 100% 100% 100% 100% 50% 50% 53% 47% 61% 39% 72% 28%19 90% 0% 4% 19% 41% 100% 100% 100% 100% 100% 100% 100% 100% 50% 50% 52% 48% 59% 41% 70% 30%20 95% 0% 3% 16% 38% 100% 100% 100% 100% 100% 100% 100% 100% 50% 50% 52% 48% 58% 42% 69% 31%

Traffic Distribution3 Carriers Prob of HR access Prob of in call change to HR Overall prob of HR 8 14 20 30Thresh 1

Figure 20 3 Carrier probability of HR usage.

The tables shown in Figures 18, 19 and 20 show the probabilities of a subscriber being allocated a Half Rate channel depending on the settings of the new calls and reconfigure threshold versus traffic loading in the cell. Figure 14 represents a 1 carrier cell, Figure 15 a 2 carrier cell and Figure 16 a 3 carrier cell. To interpret the tables, “Thresh 1” represents the new calls threshold as a percentage and “Thresh 2” represents the reconfigure threshold as a percentage. The row of numbers highlighted in yellow show the traffic level in Erlangs. The row highlighted in green shows the probability figures for the recommended “typical” settings for the thresholds. Example: From Figure 18:- New calls threshold = 33% - i.e. half rate channels are allocated when more than 33% of the cells resource is used. Reconfigure threshold = 52% - i.e. mobiles are reconfigured to half rate when over 52% of resources are in use. The probability of a subscriber being allocated a half rate channel when there are 8 Erlangs of traffic in the cell is 31%, 55% at 14 Erlangs, 67% at 20 Erlangs and 78% at 30 Erlangs. The probability of a subscriber being handed over from a full rate channel to a half rate channel while in call in the cell is 7% at 8 Erlangs, 89% at 14 Erlangs, 100% at 20 Erlangs and 100% at 30 Erlangs. The other two columns in the table show the overall probability of a subscriber being allocated a half rate channel at any time while in the cell and the split between Half Rate and Full Rate usage in the cell – all dependant of traffic level. The tables in Figures 18, 19 and 20 may be useful in estimating the effects of changing the thresholds dependant on traffic load.


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The settings of 33% new calls and 52% reconfigure in a 3 carrier cell offer a compromise and ensure that half rate channels are allocated early enough before resources are exhausted. As previously mentioned the network operator will have to decide on the exact settings of the thresholds.

10.2 HDPC Settings for Half Rate Channels At the time of writing this document there has not been sufficient work carried out to provide a recommendation for the setting of the power control and handover thresholds for half rate channels to provide optimum Quality of Service. What can be said is during the initial field trial, the half rate settings for the parameters were made to be the same value as the full rate settings. This did not lead to any reported degradation in performance or a shift in handover distribution due to uplink or downlink quality. There were no recorded cases of bad speech quality in the areas where half rate was deployed. A more detailed study would be required using handover cause statistics and speech quality measuring equipment i.e. QVoice before a recommendation could be made. The initial findings in a fairly well optimised network suggest that the handover and quality thresholds do not necessarily have to be different however some advantage could be gained through the optimisation of the parameters depending on existing full rate performance.

10.3 AMR link adaptation thresholds, hysterisis and codecs Extensive lab testing was performed to assess each of the Full Rate and Half Rate codec performances offered in the AMR solution. Tests were conducted in static and dynamic channel modes in a variable C/I environment so that a chart of speech quality versus C/I could be generated. Using the lab results a codec set was decided upon along with threshold and hysterisis values. The results from the initial field trial showed that the Full Rate AMR downlink settings offer at least as good performance as the EFR channel mode. The Full Rate AMR uplink results however showed degradation in speech quality when compared with EFR. The reason for this was a high amount of link adaptation. Since the initial trial, the internal algorithms for uplink link adaptation have been modified and now take into account the channel coder bit error rate in addition to the uplink C/I estimate. The default values were derived empirically using the results of several weeks drive testing. It was discovered that a small change to the default C/I thresholds could cause unnecessary link adapation resulting in poorer over all speech quality. Changes to AMR thresholds and codecs should only be made if the necessary speech quality test equipment is available to validate the result, (i.e. Qvoice). Derived AMR default settings: AMR Full Rate Full Rate Active Codec Set: 0(=12.2kbps), 1(=10.2kbps), 3(=7.4kbps), 6=(5.15kbps) Full Rate Initial Codec Mode: 1(=10.2kbps) Full Rate Uplink adaptation thresholds with no hopping: 26(=13db), 20(=10db), 14(=7db) Full Rate Uplink adaptation hysteresis with no hopping: 1 (=.5db), 1 (=.5db), 1 (=.5db) Full Rate Uplink adaptation thresholds with hopping: 26(=13db), 20(=10db), 14(=7db) Full Rate Uplink adaptation hysteresis with hopping: 1 (=.5db), 1 (=.5db), 1 (=.5db)


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AMR Half Rate Half Rate Active Codec Set: 3(=7.4kbps), 5(=5.9kbps), 6=(5.15kbps) Half Rate Initial Codec Mode: 5(=5.9kbps) Half Rate Uplink adaptation thresholds with no hopping: 28(=14db), 22(=11db) Half Rate Uplink adaptation hysteresis with no hopping: 1 (=.5db), 1 (=.5db) Half Rate Uplink adaptation thresholds with hopping: 28(=14db), 22(=11db) Half Rate Uplink adaptation hysteresis with hopping: 1 (=.5db), 1 (=.5db)


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11 BSS planning – Half Rate dimensioning When dimensioning a Half Rate system, the start point must be to set a clear objective with the network operator in terms of how much additional traffic the solution must carry. The successful use of either GSM Half Rate or AMR Half Rate relies on the entire system being dimensioned correctly to carry an increased amount of traffic. To deploy Half Rate at the radio layer i.e. on the air interface is probably the simplest part. Both GSM Half Rate and AMR Half Rate are software features which require only a few criteria to bet met before they can be used.

• Capable BTS platform • Enabled at the RTF (Carrier level) • Enabled at the cell level • Enabled at the BSC level • Unrestricted feature in the Options object.

Assuming the above list has been satisfied then the radio layer is ready for Half Rate. Other parts of the system need to be checked and / or expanded to provide the additional capacity. In particular, the system can only carry as much traffic as there are CIC’s available. Once all of the terrestrial circuits have been used then no matter how many more radio resources are available, no more traffic can be carried If Half Rate is to be used to offer additional capacity in the network at peak times carrying a regular amount of traffic, then there may well be enough CIC capacity already provisioned. If however Half Rate is going to be used to carry a large amount more traffic than is normal i.e. a large sporting event, then it is likely that additional CIC resources will have to be provisioned. The point being made is that the operator will have to decide first of all how much additional traffic is to be carried and then provision additional CIC resource at the MSC and MSC to RXCDR links to carry this traffic. Once this decision has been made the rest of the system will need to be checked and expanded where necessary. The planning guide has been updated to take into account GSM Half Rate and / or AMR Half Rate. The guide was used successfully on the GSM Half Rate initial field trial without any problems. The planning guide should be used as the official recommendation when checking the dimensions of the system. The following actions were taken prior to the initial field trial of GSM Half Rate.

• Additional CIC resources added (trunks) • Additional RXCDR cages and GDP cards fitted • Additional ATER (RXCDR to BSC) links added • Additional MTL timeslots equipped where necessary • New XBL links equipped • Sites per LCF checked • DSW cards fitted at BSC


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• 8K backhaul between BSC and BTS equipped • Additional MMS links between BSC and BTS fitted where required. • Additional RSL timeslots equipped where required. The amount of traffic carrying resource was expanded. Additional traffic will naturally lead to an increase in the amount of signalling and therefore the MTL, RSL and LCF capabilities need to be recalculated and increased if necessary. Some of the BTS sites had no timeslots left to add additional RSL links; this mandated a need for additional transmission.

12 Statistics As with most other new features, GSM Half Rate and AMR have lead to the introduction of new statistics and have changed the implementation of some of the existing statistics. Further information may be found in the Statistics manual. The new and modified existing statistics are described below.

12.1 MA_REQ_FROM_MSC Existing statistic:- modified to include a count of the number of assignment requests from the MSC for AMR HR, AMR FR and GSM HR channel types. BIN Name Description 0 FR Counts the number of full rate assignment requests from the MSC 1 EFR Counts the number of enhanced full rate assignment requests from the MSC 2 AMR_FR Counts the number of Adaptive Multi-rate full rate assignment requests from the MSC 3 AMR_HR Counts the number of Adaptive Multi-rate half rate assignment requests from the MSC 4 SISNALLING Counts the number of SDCCH channel assignment requests from the MSC. 5 DATA Counts the number of data assignment requests from the MSC. 6 GSM_HR Counts the number of GSM half rate assignment requests from the MSC.

12.2 MA_COMPLETE_TO_MSC Existing statistic:- modified to include a count of the number of successful assignment complete messages to the MSC for AMR HR, AMR FR and GSM HR channel types. BIN Name Description 0 FR Counts the number of full rate assignment requests forwarded 1 EFR Counts the number of enhanced full rate assignment requests forwarded from the MS to the MSC. 2 AMR_FR Counts the number of Adaptive Multi-rate full rate assignment requests forwarded from 3 AMR_HR Counts the number of Adaptive Multi-rate half rate assignment requests forwarded from the MS to

the MSC. 4 SISNALLING Counts the number of SDCCH channel assignment requests forwarded from the MS 5 DATA Counts the number of data assignment requests forwarded from the MS to the MSC. 6 GSM_HR Counts the number of GSM half rate assignment requests forwarded from the MS to the MSC.


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12.3 HO_REQ_FROM_MSC Existing statistic:- modified to include a count of the number of handover requests from the MSC for AMR HR, AMR FR and GSM HR channel types. BIN Name Description 0 FR Counts the number of full rate handover requests from the MSC 1 EFR Counts the number of enhanced full rate handover requests from the MSC 2 AMR_FR Counts the number of Adaptive Multi-rate full rate handover requests from the MSC 3 AMR_HR Counts the number of Adaptive Multi-rate half rate handover requests from the MSC 4 SISNALLING Counts the number of SDCCH channel handover requests from the MSC. 5 DATA Counts the number of data assignment handover from the MSC. 6 GSM_HR Counts the number of GSM half rate handover requests from the MSC.

12.4 HO_REQ_ACK_TO_MSC Existing statistic: - modified to include a count of the number of successful ho_req_ack messages to the MSC for AMR HR, AMR FR and GSM HR channel types. Formerly known as HO_REQ_MSC_OK. BIN Name Description 0 FR Counts the number of full rate handover request acknowledgements sent to the MSC. 1 EFR Counts the number of enhanced full rate handover request acknowledgements sent to the MSC. 2 AMR_FR Counts the number of Adaptive Multi-rate full rate handover request acknowledgments sent to the

MSC. 3 AMR_HR Counts the number of Adaptive Multi-rate half rate handover request acknowledgments sent to the

MSC. 4 SISNALLING Counts the number of SDCCH channel handover request acknowledgments sent to the MSC. 5 DATA Counts the number of data handover request acknowledgments sent to the MSC. 6 GSM_HR Counts the number of GSM half rate handover request acknowledgments sent to the MSC.

12.5 FER, FER_AMR_FR, FER_AMR_HR, FER_GSM_HR, FER_GSM_FR_EFR

FER is the ratio of successfully decoded good speech frames to unsuccessfully decoded bad speech frames, averaged over a 480ms period. Name Description Granularity FER Pegged every 480ms regardless of speech version used. Per Timeslot FER_GSM_FR_EFR Pegged every 480ms for speech version 1,2 full rate only. Per Carrier FER_GSM_HR Pegged every 480ms for speech version 1 Half rate only. Per Carrier FER_AMR_FR Pegged every 480ms for speech version 3 Full rate only. Per Carrier FER_AMR_FR Pegged every 480ms for speech version 3 Half rate only. Per Carrier Note: FER_GSM_FR_EFR replaced FER_NON_AMR from 1760 onwards.


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12.6 INTRA_CELL_HO Existing statistic:- modified to take into account Half Rate to Half Rate, Full Rate to Half Rate and Half Rate to Full Rate Intra cell handovers. BIN Name Description 0 INTRA_CELL_HO_REQ Number of assignment commands sent to MS during a full-rate to full-rate

intra-cell handover. 1 INTRA_CELL_HO_ATMPT_FR_FR Number of assignment commands sent to MS during a half-rate to half-

rate intra-cell handover. 2 INTRA_CELL_HO_ATMPT_HR_HR Number of assignment commands sent to MS during a half-rate to full-rate

intra-cell handover. 3 INTRA_CELL_HO_ATMPT_HR_FR Number of assignment commands sent to MS during a half-rate to full-rate

intra-cell handover. 4 INTRA_CELL_HO_ATMPT_FR_HR Number of assignment commands sent to MS during a full-rate to half-rate

intra-cell handover. 5 INTRA_CELL_HO_SUC Number of successful intra-cell handovers. 6 INTRA_CELL_HO_LOSTMS Number of failed intra-cell handovers that also failed to recover to the

original cell. 7 INTRA_CELL_HO_RETURN Number of failed intra-cell handovers that recovered to the original

cell/channel. 8 INTRA_CELL_EQUIP_FAIL Number of attempted intra-cell handover failures due to equipment failure. 9 INTRA_CELL_HO_CLEARED Number of incoming intra-cell handovers aborted due to call clearing. This

scenario corresponds to the receipt of a Clear Command, SCCP Released, or Release Done (internal message) during the handover procedure.

12.7 INTRA_BSS_HO_CAUSE_SUC Existing statistic:- modified pegging of the Congestion bin to include Full Rate to Half Rate handovers. Also the Uplink / Downlink Interference bins will peg for Half Rate to Full Rate quality based handovers. BIN Cause Description 0 UPLINK_QUALITY Handovers due to uplink quality. 1 UPLINK_LEVEL Handovers due to uplink level. 2 DOWNLINK_QUALITY Handovers due to downlink quality. 3 DOWNLINK_LEVEL Handovers due to downlink level. 4 DISTANCE Handovers due to distance. 5 UPLINK_INTERFERENCE Handovers due to uplink interference. 6 DOWNLINK_INTERFERENCE Handovers due to downlink interference. 7 POWER_BUDGET Handovers due to power budget. 8 CONGESTION Handovers due to congestion.

12.8 TCH_CONGESTION_HR New Statistic:- Same implementation as existing Full Rate TCH_CONGESTION. The statistic tracks the duration of time when there are no half rate AMR and/or GSM Half Rate TCHs available. For multi


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zone cells, this measurement indicates AMR Half Rate and/or GSM Half Rate TCH congestion for the outer zone.

12.9 TCH_CONG_INNER_ZONE_HR New Statistic:- Same implementation as existing Full Rate TCH_CONG_INNER_ZONE. The statistic tracks the duration of time when there are no AMR Half Rate and/or GSM Half Rate TCHs available in the inner zone of a multi zone cell.

12.10 BUSY_TCH_HR New Statistic:- Same implementation as existing Full Rate BUSY_TCH. The statistic tracks the number of GSM Half Rate and / or AMR Half Rate TCHs allocated during the statistics interval.

12.11 BUSY_TCH_CARR_HR New Statistic:- Same implementation as existing Full Rate BUSY_TCH_CARR. The statistic reports a maximum and average value for the amount of AMR Half Rate and/or GSM Half Rate TCHs in use on a per carrier basis.

12.12 AVAILABLE_TCH_HR New Statistic:- Same implementation as existing Full Rate AVAILABLE_TCH. The statistic reports a maximum and average value for the amount of AMR Half Rate and/or GSM Half Rate TCHs that are in use or available to be used within the cell.

12.13 ALLOC_TCH_HR New Statistic:- Same implementation as existing Full Rate ALLOC_TCH. The statistic tracks the number of successful AMR Half Rate and/or GSM Half Rate TCH allocations within a cell for both call originations and hand-ins.

12.14 ALLOC_TCH_FAIL_HR New Statistic:- Same implementation as existing Full Rate ALLOC_TCH_FAIL. The statistic tracks the number of unsuccessful allocations of an AMR Half Rate and/or GSM Half Rate TCH within a cell for both call origination and hand in. Cases involving Immediate Assignment Reject are also included in the peg count.

12.15 RF_LOSSES_TCH_HR The statistic tracks the number of calls lost while using a half rate AMR and/or GSM TCH. This statistic pegs the number of calls that were terminated because of RF problems. It is composed of calls lost while using a half rate AMR and/or GSM TCH.

12.16 CALL_SP_VERS_DOWNGRADE_MONITOR This statistic tracks the number of call rejects and call downgrades due to not supporting requested speech versions. The statistic keeps a count of the number of times that the codec mode was downgraded for EFR, HR AMR FR AMR and GSM HR calls on a per BSS basis.


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Bin Cause Description 0 EFR_REQUEST_DOWNGRADE Pegged when the call is downgraded due to CIC capabilities Assignment

request for or including EFR Handover request for or including EFR In call modification request for or including EFR.

1 AMR_FR_CALL_DOWNGRADE Pegged when the full-rate AMR call is downgraded. 2 AMR_HR_CALL_DOWNGRADE Pegged when the half-rate AMR call is downgraded. 3 GSM_HR_CALL_DOWNGRADE Pegged when the half-rate GSM call is downgraded.

12.17 AMR_DECREASE_THRESH_ADJUST This statistic keeps a count of the number of times that the BSS MS monitor decreases the C/I codec mode adaptation thresholds for AMR calls on a per-cell basis. The statistic pegs each time that the BSS MS monitor decreases the downlink codec mode adaptation thresholds due to inaccurate C/I estimation by the MS.

12.18 AMR_INCREASE_THRESH_ADJUST This statistic keeps a count of the number of times that the BSS MS monitor increases the C/I codec mode adaptation thresholds for AMR calls on a per-cell basis. The statistic pegs each time that the BSS MS monitor increases the downlink codec mode adaptation thresholds due to inaccurate C/I estimation by the MS.

12.19 AMR_FR_DL_CODEC_MODE_USAGE This statistic keeps a count of each AMR full-rate codec mode used on the downlink of AMR full-rate calls on a per-cell basis. Bin Description 0 AMR full-rate DL codec mode usage of AFS 12.2kbps 1 AMR full-rate DL codec mode usage of AFS 10.2kbps 2 AMR full-rate DL codec mode usage of AFS 7.4kbps 3 AMR full-rate DL codec mode usage of AFS 6.7kbps 4 AMR full-rate DL codec mode usage of AFS 5.15kbps

12.20 AMR_FR_UL_CODEC_MODE_USAGE This statistic keeps a count of each AMR full-rate codec mode used on the uplink of AMR full-rate calls on a per-cell basis. Bin Description 0 AMR full-rate UL codec mode usage of AFS 12.2kbps 1 AMR full-rate UL codec mode usage of AFS 10.2kbps 2 AMR full-rate UL codec mode usage of AFS 7.4kbps 3 AMR full-rate UL codec mode usage of AFS 6.7kbps 4 AMR full-rate UL codec mode usage of AFS 5.15kbps


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12.21 This statistic keeps a count of each AMR half-rate codec mode used on the downlink of AMR half-rate calls on a per cell basis.

AMR_HR_DL_CODEC_MODE_USAGE

Bin Description 0 AMR half-rate DL codec mode usage of AFS 7.95kbps 1 AMR half-rate DL codec mode usage of AFS 7.4kbps 2 AMR half-rate DL codec mode usage of AFS 6.7kbps 3 AMR half-rate DL codec mode usage of AFS 5.9kbps 4 AMR half-rate DL codec mode usage of AFS 5.15kbps

12.22 AMR_HR_UL_CODEC_MODE_USAGE

This statistic keeps a count of each AMR half-rate codec mode used on the uplink of AMR half-rate calls on a per cell basis. Bin Description 0 AMR half-rate UL codec mode usage of AFS 7.95kbps 1 AMR half-rate UL codec mode usage of AFS 7.4kbps 2 AMR half-rate UL codec mode usage of AFS 6.7kbps 3 AMR half-rate UL codec mode usage of AFS 5.9kbps 4 AMR half-rate UL codec mode usage of AFS 5.15kbps

12.23 This statistic keeps a count of the number of times the codec mode is adapted on the downlink of full-rate AMR calls on a per-cell basis. There are up to four codecs in the Active Codec Set (ACS) and the format of this statistic allows for this. The codecs are referenced sequentially from the lowest speech coding rate to the highest. The lowest speech coding rate is called the 1st codec. If there are less than four codecs in the ACS, the higher bit rates are not valid and contain the value zero.

AMR_FR_DL_ADAPTATION

Bin Description 0 AMR full-rate DL codec mode usage adaptation from 1st to 2nd codec mode. 1 AMR full-rate DL codec mode usage adaptation from 2nd to 3rd codec mode. 2 AMR full-rate DL codec mode usage adaptation from 3rd to 4th codec mode. 3 AMR full-rate DL codec mode usage adaptation from 2nd to 1st codec mode. 4 AMR full-rate DL codec mode usage adaptation from 3rd to 2nd codec mode. 5 AMR full-rate DL codec mode usage adaptation from 4th to 3rd codec mode.


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13 Benchmarking

13.1 Speech Quality Ascom Qvoice was used to collect speech samples for all speech versions supported in GSR 7, EFR, FR, AMR FR, AMR HR and GSM HR.

GSM HR and FR Speech Samples under static channel conditions.

0.0%10.0%20.0%30.0%40.0%50.0%60.0%70.0%80.0%

1

1.3

1.6

1.9

2.2

2.5

2.8

3.1

3.4

3.7 4

4.3

4.6

4.9

Pace

UL HR Pace 3.2

DL HR Pace 3.3

UL FR Pace 3.3

DL FR Pace 3.4

Figure 21 GSM HR and FR QVoice Pace scores, collected under laboratory static conditions.


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Speech Samples vs Pace with Handovers Removed, (Force GSM HR Enabled).

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%1

1.2

1.4

1.6

1.8 2

2.2

2.4

2.6

2.8 3

3.2

3.4

3.6

3.8 4

4.2

4.4

4.6

4.8 5

Pace

% V

oice

Sam

ples

DL FR Pace 3.5

UL FR Pace 3.6

UL HR Pace 3.2

DL HR Pace 3.3

Figure 22 GSM HR and FR QVoice Pace scores collected on a BSC wide basis.


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DownLink speech, No Handovers

0.0%10.0%20.0%30.0%40.0%50.0%60.0%70.0%

1

1.4

1.8

2.2

2.6 3

3.4

3.8

4.2

4.6 5

Pace

% S

ampl

es

AMR FR and EFR Peak @ 3.8

AMR HR Peak @ 3.6

GSM HR Peak @ 3.3, (Static Channel Reference).

Figure 23 Comparison of AMR FR/HR to EFR/GSM HR downlink speech quality.


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Uplink Speech, No Handovers

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%1

1.3

1.6

1.9

2.2

2.5

2.8

3.1

3.4

3.7 4

4.3

4.6

4.9

Pace

% S

ampl

es

AMR HR Peak @ 3.5

EFR Peak @ 3.6AMR FR Peak @ 3.7

GSM HR Peak @ 3.2, (static Channel referene).

Figure 24 Comparison of AMR FR/HR to EFR/GSM HR uplink speech quality.

Speech Codec Peak. UL Pace. Peak.DL Pace

FR 3.6 3.5 GSM HR 3.2 3.3 AMR HR 3.5 3.6

EFR 3.6 3.8 AMR FR 3.7 3.8

Table 9 Summary of Peak Pace for all codec modes.

All samples were collected during a BSC wide drive test, the selected route was considered urban and was well optimized. The results show that AMR FR performs as good as EFR in the downlink direction and better in the uplink. This is as expected for a well optimized dive test route, since the AMR codec rate 12.2kbps has


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the same voice quality as EFR. Only in poor RF environments will the benefits of AMR FR become apparent. To demonstrate the true advantage of AMR FR over EFR care should be taken to select a drive test route that includes a significant percentage of poor quality audio calls. AMR HR speech quality is as good as GSM FR and significantly better the GSM HR which has the poorest speech quality of all the speech codec’s. However, the peak pace for all speech versions is greater that 3.1 which can be classified as excellent using the Motorola specified grading of pace scores shown below. BAD PACE <1.9 GOOD PACE 1.9 < 3.2 EXCELLECNT PAVE >= 3.2

14 Tools

14.1 Motorola Drive Test Tool (CTP Windows MDTT GSR7v1.0) Three new monitoring functions have been added to MDTT for AMR, they can be selected from the “Monitor” options on the MDTT user interface. From these data windows information on link adaptation, codec mode usage and the AMR call configuration can be determined. The AMR config window shows the AMR call type, Full Rate or Half Rate and the uplink and downlink active codec sets, i.e. those specified using chg_acs_params command. The current active codec mode is shown in parenthesis, also displayed is the adaptation thresholds, the hysteresis values and the downlink FER values.


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Figure 25 MDTT AMR Configuration.

The AMR Codec Log window shows the in band signalling taking place between the mobile and the BSS to select the required codec mode. The CMI UL/DL indicates the current codec mode, whilst CMC is what the BSS is requesting the mobile uses on the uplink and the CMR is the mobile requesting what the BSS should use on the downlink. In the example shown below the BSS is requesting the mobile use codec mode 7.4 (CMC = 7.4), the following period the CMI UL has changed to 7.4 indicating that the mobile is now using the requested mode in the uplink. The table also shows the downlink C/I in dB’s averaged over the last 480ms SACH period.

Figure 26 MDTT AMR Codec Log

The AMR Params Graph window displays the long term codec mode usage in a graphical format. This is useful when a lot of link adaptation is occurring.


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Figure 27 MDTT AMR Graphical Parameters Display.

14.2 CTP-NT Call trace allows the distribution of AMR parameters to be displayed for selected cells on selected network elements, determined by the user filter criteria. Figure 28 below shows the output of AMR distribution application, each parameter can be viewed separately either in graphical or tabular format and the average or individually distribution of each carrier or cell displayed, as shown in figure 29/30. FER: This shows the ratio of correctly decoded uplink AMR speech frames to incorrectly decoded speech frames over a 480ms period (average of 24 frames). The distribution is split into bins 0 to 9 ranging from 0% errors to 100% errors. No distinction is made between AMR FR and AMR HR speech frames. RBER: Is a ratio of the number of bits received as errors to the total number of bits received for frames classified as good frames. The distribution is over bins 0 to 7 with bin 0 = 0 to 0.2 BER and bin 7 > 12.8 BER. C/I (sub/full): The is a distribution of the uplink C/I estimate expressed in dBs the C/I is estimated every 20ms and averaged over a 480ms SACH period. For the sub values only SID and SACH frames are averaged over the 480ms period, i.e. during periods when uplink dtx is evoked. The full takes into account all frames.


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CMI (up/down): Codec mode Indicate, in band signalling used to indicate the current codec mode used by the mobile and BSS. The four bins represent the four codec modes specified using chg_acs_params, with bin 0 being the lowest (most protected) and bin 3 being the highest codec rate (least protected). CMR/CMC: This is a distribution of the Codec Mode Requests, i.e. the uplink/downlink requesting a codec mode changes. The bins are similar to CMI. Up/Down link Adaptation: This is a distribution of adaptations between two consecutive codec rates. Assume an ACS with 12.2, 10.2, 7.4 and 5.15 then the Up/Down link adaptation distribution can be interpreted as shown below in figure 29.

Figure 28 AMR parameter distributions from CTP-NT

Note: Different cells and call configurations (AMR-FR/AMR-HR) will have different codec modes defined in there active codec set (ACS). Therefore prior knowledge of the ACS and the selected cells is needed to determine the bins classification. Therefore care should be taken to limit the scope of the data


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used for CMI/CMC/CMR and LA distributions to a known ACS and speech version to provide meaningful debug data.

0

20

40

60

80

100

120

5.15 to 7.4 7.4 to 5.15 7.4 to 10.2 10.2 to 7.4 10.2 to 12.2 12.2 to 10.2

Figure 29 Example of Uplink adaptation for ACS 12.2, 10.2,7.4 and 5.15


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All Data (StdDev=7.5)Hopping Carrier (StdDev=5.01)Carrier 806 (StdDev=5.68)Carrier 808 (StdDev=8.47)

C/I (Sub)

Server: zuk28-2019 Database: CTtestContext: Cell 00139-55883

C/I w ithout DTX / dBm32302826242220181614121086420-2

Perc

enta

ge o

f Mea

sure

men

t Rep

orts

11

10

9

8

7

6

5

4

3

2

1

0

Figure 30 CTP_NT C/I distribution for individual carriers.


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14.3 Measurement Reports. The following iir_mod can be run on a dri to capture the average uplink C/I and the number of CMI/CMR per SACCH period, 480ms. Care should be taken when running on high capacity carriers. iir_mod 49 03FFF09h ------------------------------- ------------------------------- DRI Filter-> DRI: 0 Segment: TS 1 Direction: DRI->RSS More: No data: MS Monitor: T:33 CMR:0/0/0/12 Rxqual:14 SUMS CMR:0/0/0/48 Rxqual:23 MS Monitor: UCMI:3/0/4/5 DCMI:0/0/12/0 RSS HO: ULA:0/1/1/2/1/2 DLA:0/0/0/0/0/0 CI:17/14 MEASUREMENT REPORT #6 DRI 0 TS 1 TCH(full) EQ MODE: Rel BSS: DTX 0 RXL 1/0 RXQ 5/5 FER 0 RBER 0 TA 0 BS PWR 6 MS PWR 19 MS: BA 1 DTX 0 MV y RXL 50/52 RXQ 0/0 REL TA 0/0 NCELLS 0 freq/bsic/rxl: 65535/00h/00 65535/00h/00 65535/00h/00 65535/00h/00 65535/00h/00 65535/00h/00 What fields mean what?? ------------------------ CMR = CMRs received from MS requesting codec in DL SUMS CMR = Running sum of CMR data for MS Monitor purposes (resets every MS Monitor period) UCMI = CMIs received from MS in UL indicating UL codec being used by MS DCMI = CMIs sent to MS in DL indicating DL codec being used by BTS Assuming ACS uses 4 codecs: Codec 0 = most protected codec Codec 3 = least protected codec CMR: Codec 0 / Codec 1 / Codec 2 / Codec 3 UCMI: Codec 1 / Codec 0 / Codec 3 / Codec 2 DCMI: Codec 1 / Codec 0 / Codec 3 / Codec 2 ULA: Codec 1->0 / Codec 0->1 / Codec 2->1 / Codec 1->2 / Codec 3->2 / Codec 2->3 DLA: Codec 1->0 / Codec 0->1 / Codec 2->1 / Codec 1->2 / Codec 3->2 / Codec 2->3


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SUMS CMR: Codec 0 / Codec 1 / Codec 2 / Codec 3 C/I: an unsigned 8 bit number (need to convert to signed and divide by 2 to get value) MR data alignment (see example log below): - The data in a MR log is grouped as follows: - the 4 lines starting with MEASUREMENT REPORT #... - the 2 MS Monitor lines immediately above MEASUREMENT REPORT #... - the RSS HO line immediately above MEASUREMENT REPORT #... - All of these data sets correspond to the same MR period The RxQual values contained within the first MS Monitor line correspond to the RxQual of the current MR report and the average RxQual over the MS monitoring period respectively. The default presentation is BER as determined by alt_qual _proc. -------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------


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Appendix A - Full Rate/Half Rate Channel Selection

Start Allocation Process

HR Preferred?

Changes allowed after initial assignment

new_calls_hrexceeded?

GSM HR enabled@ Cell?

AMR HR enabled@ BSS?

GSM HR enabled @ BSS?

GSM HRCIC?

AMR HRCIC?

AMR HR enabled@ Cell?

force_hr_useage?

FR resourceAvail?

Allocate FullRate Resource

no

yes

FR resourceAvail?

yes

yes


AMR HR enabled@ BSS?

AMR HRCIC?

AMR HR enabled@ Cell?

Go to AMR HRChan Selection

FR resourceAvail?

yes

yes

yes

yes

yes

yes

yes

yes

yes

no

no

no

no

Full Rate Chan Allocation FAILS

Go to AMR/GSM HRChan Selection

Go to GSM HRChan Selection

no

no

no

no

no

HR Allowed?


yes

yes

no

yes

Full Rate Chan Allocation FAILS

no

This flowchart indicates the resultant channel type chosenwhen presented with the given information. The order of the decision processes may be different in implementation.

no

yes

yes

no

no

no

amr half rate feature engineering notes

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