AMR RadioEngineering

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Radio Engineering Rules with AMR introduction inGSM networks

Document number:Document issue: 01.01 / EN

Document status: This document is for internal use only - DRAFTDate:

Copyright 2000 Nortel Networks, All Rights Reserved

Printed in France

NORTEL NETWORKS CONFIDENTIAL:

The information contained in this document is the property of Nortel Networks. Except as specifically authorized in

writing by Nortel Networks, the holder of this document shall keep the information contained herein confidential

and shall protect same in whole or in part from disclosure and dissemination to third parties and use same forevaluation, operation and maintenance purposes only.

The content of this document is provided for information purposes only and is subject to modification. It does not

constitute any representation or warranty from Nortel Networks as to the content or accuracy of the information

contained herein, including but not limited to the suitability and performances of the product or its intended

application.

The following are trademarks of Nortel Networks: *NORTEL NETWORKS, the NORTEL NETWORKS corporate

logo, the NORTEL Globemark, UNIFIED NETWORKS. The information in this document is subject to change

without notice. Nortel Networks assumes no responsibility for errors that might appear in this document.

All other brand and product names are trademarks or registered trademarks of their respective holders.


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Radio Engineering Rules with AMR introduction in GSM networks

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PUBLICATION HISTORY

DD/MMM/YYYY

Version 01.01 / EN, Provisional Creation L.Moussay


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CONTENTS

1. INTRODUCTION ............................................................................................................................ 61.1. OBJECT.................................................................................................................................... 6

1.2. SCOPE OF THIS DOCUMENT ....................................................................................................... 6

1.3. AUDIENCE FOR THIS DOCUMENT ................................................................................................ 6

2. RELATED DOCUMENTS .............................................................................................................. 7

2.1. APPLICABLE DOCUMENTS .......................................................................................................... 7

2.2. REFERENCE DOCUMENTS.......................................................................................................... 7

3. GENERALITIES ............................................................................................................................. 93.1. AMR PRINCIPLES....................................................................................................................10

3.1.1. Definition .......................................................................................................................103.1.2. AMR codecs ..................................................................................................................113.1.3. Codec adaptation principle ............................................................................................113.1.4. AMR benefits .................................................................................................................133.1.4.1. AMR Full Rate benefits ........................................................................................................ 133.1.4.2. AMR Half Rate benefits ............................................................. ........................................... 153.1.4.3. AMR Full Rate / AMR Half Rate performances ......................................................... .......... 17

3.2. NORTEL NETWORKS CHOICES .................................................................................................19

3.2.1. AMR codecs sets chosen by Nortel Networks ..............................................................193.2.2. AMR mechanisms .........................................................................................................213.2.2.1. Initial codec mode choice ........................................................... ........................................... 213.2.2.2. Codec mode adaptation parameters choice ........................................................................... 21

4. AMR COVERAGE ASPECTS .....................................................................................................25

4.1. PRINCIPLE ..............................................................................................................................25

4.2. AMR COVERAGE GAIN.............................................................................................................26

4.2.1. AMR Full Rate only .......................................................................................................264.2.2. AMR Half Rate only .......................................................................................................284.2.3. AMR Full Rate and Half Rate together .........................................................................294.2.3.1. New GSM design ............................................................. ..................................................... 304.2.3.2. Existing GSM design ............................................................................................................ 30

4.3. LIMITATIONS ...........................................................................................................................314.3.1. Simulations limitations ...................................................................................................324.3.2. Signalling channels .......................................................................................................324.3.3. AMR penetration ...........................................................................................................32

5. AMR CAPACITY ASPECTS ........................................................................................................33

5.1. PRINCIPLE ..............................................................................................................................33

5.2. AMR FREQUENCY PLANNING ...................................................................................................34

5.2.1. Non hopping frequency plan .........................................................................................345.2.1.1. AMR Full Rate only .............................................................................................................. 365.2.1.2. AMR Half Rate only ............................................................................................................. 385.2.1.3. AMR Full Rate and Half rate together ................................................................................ .. 395.2.2. Hopping frequency plan ................................................................................................425.2.2.1. AMR Full Rate only .............................................................................................................. 45


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1. INTRODUCTION

1.1. Obj ect

This document aims at giving complete and general radio engineering information related toAMR (Adaptive Multi Rate) feature that will be implemented in V14 release.

First of all, some generalities are presented:

What is AMR?

How does it work?

The AMR benefits

Then, more details are given concerning AMR introduction and implementation in GSM

networks, from:

A coverage point of view A capacity point of view

1.2. Scope of th is d ocument

This document is an internal document.

1.3. Aud ience for th is do cum ent

RF Engineering, Network Design Engineering

PLM, Account teams


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[R9] FER versus C/I for the downlink case in TU

profile

A. Gervais05/04/2002

[R10] PE/IRC/INF/0014 1/3 reuse pattern engineering information

Version 01.02, 26/03/97 R. Jacquand

[R11] PE/IRC/APP/0094 Frequency Hopping and Fractional Re-use

PatternsTechniques and Engineering rules

Version 01.02, 27/12/98 M. Laune / M. Ladki

[R12] PE/SYS/DJD/288 NMC GSM/DCS/PCS Cellular SystemsPerformances

Version 01.03, 12/01/97 Th. Billon

[R13] PE/SYS/DJD/450 Optimisation des motifs charges

fractionnaires

Version 01.03/FR, 03/07/98 Th. Billon

[R14] Data and Fractional re-use patterns

M. Laune


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3. Generalities

Any GSM operator is interested in:

Achieving a high voice quality. A better voice quality is a strong contributor to theend user perception and a competitive differentiator for operators. This importance of

voice quality is verified as long as voice represents and will represent the most

important part of the traffic for some years.

Achieving maximum coverage, capacity, spectrum efficiency and flexibility in themost cost-efficient manner. With the introduction of the data, the increasing number

of customers and the constant growth of the networks, capacity remains as one of the

major concern of operators.

To respond to these demands, Nortel Networks has evolved its equipment continuously andcreated new features.

Existing features such as -115 dBm BTS sensitivity, enhancement full rate (EFR) are perfect

examples of Nortel Networks efforts in term of network quality improvement.

Frequency hopping and cell tiering are also very good examples: it allows to maximize

network performances in term of capacity.

AMR is a new feature that will also answer to these customer objectives: AMR improves

speech services in term of capacity and quality.

Indeed, it allows to:

Increase voice quality in degraded radio conditions, due to the adaptation of the pair

{source, channel} to the radio channel quality

Increase radio capacity due to robustness of Full Rate AMR and introduction ofHalf Rate channels.


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3.1. AMR prin cip les

3.1.1. DefinitionIn GSM, speech is transmitted on a radio channel, which has a fixed raw bit rate. On this

channel, speech is transmitted using a speech coder, also called source coder. The coder

delivers speech frames every 20 ms. On the radio segment, the speech frames as elaborated by

the coder should be protected by some redundancy, which is called channel coding.

The choice is then to use a high coder rate with little redundancy, or a low coder rate with

more redundancy.

In the first case, the speech quality will be very good in excellent radio conditions, as long as

speech frames can be decoded properly. But in bad radio conditions, a high proportion of

speech frames will not be decoded, in which case some interpolation will be done by thedecoder, and speech quality actually drops.

In the second case, the speech quality will be medium or low, but will resist very well to radio

channel impairments, due to high level of redundancy.

Consequently, present techniques like FR or EFR are the result of compromises between the

source coder rate, and the channel coding.

AMR technique is Adaptive, and Multirate. It means that it allows to adapt the compromise

between source coder rate and channel coding / redundancy to actual radio conditions.

AMR may operate in Full Rate channels, or Half Rate channels. This is called the channelmode orchannel type: the channel type to use (TCH/FR or TCH/HR) is controlled by the

network.

Then, basis of AMR is that within the channel (FR or HR), there is a set of voice coders,

called codec mode. Each codec mode provides a different level of error protection through

a dedicated distribution between source coding and channel coding of the available gross bit

rate, which is 22.8 kbps in Full Rate and 11.4 kbps in Half Rate. The best combination, i.e.

the best codec mode can be selected to maximize speech quality according to conditions met

on the radio link. This is codec mode adaptation.


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3.1.2. AMR codecs

As said previously, AMR is introduced to choose in real time the repartition between rate of

the source vocoder and channel protection: When the transmission is good (in other words, good C/I), a high rate vocoder is

chosen and the number of bits dedicated to the channel protection is low,

In case of degraded radio conditions (in other words, bad C/I), the vocoder rate isdecreased, in order to provide a better channel protection and allow a better voice

quality.

Figure 1: Source and channel coding repartition

In the recommendation ([R1]), the following coding modes are defined (in kbps):

AMR FR AMR HR

12.2

10.2

7.95 7.95

7.4 7.4

6.7 6.7

5.9 5.9

5.15 5.15

4.75 4.75

Table 1: AMR Codec Modes defined by recommendations

Each one of these codecs works optimally (it means with a good quality) in a given C/I

region.

3.1.3. Codec adaptation principle

The purpose of AMR codec mode adaptation is to provide the "best" compromise between

data rate of codec mode and channel protection, according to the link quality.

This adaptation is done for uplink and downlink and there is no interdependence between the

2 links, but both sets of codec have to be identical (Half Rate or Full Rate).

Source coding

Channel coding

AMR HR AMR FR

Global Rate : 11.4 kb/s

Global Rate : 22.8 kb/sGood C/I

Bad C/I

Source coding

Channel coding

Source coding

Channel coding

AMR HR AMR FR



Bad C/IAMR HR AMR FR



Bad C/I


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The following diagram (figure 2) shows the main information flows over the key system

interfaces:

MS BTS

Uplink Speech DataCodec Mode Indication (for uplink)

Suggested Codec Mode (for downlink)

Downlink Speech Data

Codec Mode Indication (for downlink)

Codec Mode Command (for uplink)

Codec

Adaptation

Codec

Adaptation

SPD

SPD SPE

SPE CHE

CHE

CHD

CHD

CHE: Channel Encoder

CHD: Channel Decoder

SPE: Speech Encoder

SPD: Speech Decoder

TRAU

Figure 2: Codec adaptation principles

In both directions, the speech data frames are associated with a Codec ModeIndication indicating the codec mode used in the considered link

For the adaptation of the uplink codec mode , the BS must estimate the channelquality, identify the best codec for the existing propagation conditions and send this

information to the MS over the Air Interface (Codec Mode Command Data field).

For the downlink codec adaptation, the MS must estimate the downlink channelquality and send to the network aquality information, which can be mapped in the

network to a suggested codec mode(Codec Mode Request). But, the final decision

is within BTS's province: the MS just gives some indications to BTS in term of

requested codec mode.

Each 40ms, according to the requested codec mode and the applied codec mode, the BTS:

Increases by one step the rate of the codec mode, if the requested codec mode isgreater than the applied codec mode,

Decreases by one step the rate of the codec mode, if the requested codec mode islower than the applied codec mode,

Keeps the same codec mode, if the requested codec mode is equal to the appliedcodec mode.

A switch from one codec mode to another one, does not introduce any voice perturbation.

The codec choices are based on C/I estimations in uplink and downlink, which are then

compared to a set of parameters. Indeed, at each codec mode is associated a set of parameters

in each link(uplink and downlink):

one threshold,

one hysteresis (the same value is used for each codec mode, but one for FR and

another one for HR channel).

NB: for more information about codec mode adaptation, see [R6].


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3.1.4. AMR benefits

As said previously, AMR works in many codec modes, and each of them works optimally in a

given C/I range. This allows to have high quality gain.

During AMR characterization phase (ETSI standardization), many tests have been done, in

order to evaluate AMR performances. These tests have been performed under different

representative environmental conditions, in particular:

Clean Speech and Error Conditions

Background Noise and Error Conditions, which includes Street Noise, Car Noise andOffice Noise

The tests consist in evaluating the quality of AMR FR and HR codecs modes in static C/I

conditions.

These static error conditions have been provided by a simulator (developed by Ericsson and

Nortel) in the following radio channel conditions:

TU3kmph

Ideal Frequency Hopping

900 MHzThe quality is evaluated in term of:

MOS (mean opinion scores) for the clean speech condition (Absolute CategoryRating test (ACR)),

DMOS (degraded mean opinion scores) for the background noise condition(Degraded Category Rating test (DCR)).

MOS or DMOS are subjective notes given by people who compare the quality of the original

(ACR tests) or a reference signal (DCR tests) and the signal at the output of the coder.MOS and DMOS are always a value between 1 and 5: a value equal to 1 means that the

listening is unintelligible and a value equal to 5 means that the two signals are the same

(which is never the case). One estimate that a value equal to 4 corresponds to a good voice

quality.

Some of the tests results are presented in the two following paragraphs.

For more information and more results on these tests, see [R3].

3.1.4.1. AMR Full Rate benefits

The two following schemes (figure 3) provide a graphical representation in MOS / DMOS ofthe AMR FR mode according to radio conditions in C/I, in clean and car noise conditions.

The figures allow to compare the performances recorded for the best AMR Full Rate codec

mode for each C/I, with the corresponding performance of EFR(and also FR in car noise

conditions) and the related AMR performance requirement (curve Sel. Requir.).


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Figure 3: AMR FR performances in Clean and Car Noise Speech conditions

AM R FR Clean Speech Per formances

1.0

2.0

3.0

4.0

5.0

No Errors C/I=16 dB C/I=13 dB C/I=10 dB C/I= 7 dB C/I= 4 dB C/I= 1 dB

Cond i t i o n s

M OS

Sel. Requir.

AMR-FR

EFR

AMR FR Perform ances in Car Noise

1.0

2.0

3.0

4.0

5.0


Condi t ions

DMOS

Sel. Requir.

AMR-FREFR

FR

AMR FR Perform ances in Car Noise

1.0

2.0

3.0

4.0

5.0


Condi t ions

DMOS

Sel. Requir.

AMR-FREFR

FR


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These figures show that the combination of all 8 AMR FR codec modes allows to:

provide a robust quality down to 4 dB C/I in Clean Speech, which means up to 6 dBimprovement compared to EFR,

provide a robust quality down to 4 dB C/I in Background Noise, which means also

significant improvement compared to EFR and GSM FR.

So, speech quality is improved thanks to better robustness in AMR FR in comparison to EFR.

AMR FR is more robust than EFR because of the channel coding that allows to adapt and to

obtain a better protection in bad propagation conditions and then to go down to inferior C/I at

equivalent auditive quality.

And, the capacity is increased by operating a tighter frequency reuse pattern or by operating a

higher fractional load, which is equivalent in the two cases to a higher number of

Erl/km2/frequency.

3.1.4.2. AMR Half Rate benefitsThe two following schemes (figure 4) provide a graphical representation in MOS/DMOS of

the AMR HR mode according to radio conditions in C/I, in clean and car noise conditions.

The figures allow to compare the performances recorded for the best AMR Half Rate codec

mode for each C/I, with the corresponding performance ofEFR, GSM FR and HRspeech

codecs and the related AMRperformance requirement (curve Sel.Requir.).


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Figure 4: AMR HR performances in Clean and Car Noise Speech conditions

AM R HR Clean Speech Per form ances

1.0

2.0

3.0

4.0

5.0

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

Cond i t i o n s

M OS

Sel. Requir.

AMR-HR

EFR

FR

HR

AM R HR Performances in Car Noise

1.0

2.0

3.0

4.0

5.0

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

Cond i t i o n s

DMOS

Sel. Requir.

AMR-HR

EFR

FRHR


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These figures show that the combination of all 6 AMR HR codec modes allows to:

provide a good quality down to 16 dB C/I in Clean Speech, always significantlybetter than the GSM FR and GSM HR,

provide good performances in Background Noise down to 16-13 dB C/I, equivalent

to GSM FR otherwise.

It means that AMR HR offers the possibility to have in good radio conditions a capacity

increase in term of Erlang (two users can be mapped on the same TS instead of one) keeping

the quality of a FR speech.

3.1.4.3. AMR Full Rate / AMR Half Rate performances

The two previous paragraphs can be summarized in this way:

AMR is designed to provide enough flexibility to adjust speech quality and systemcapacity to all circumstances

AMR FR allows to improve quality compared to EFR, which can be translated in acapacity gain

AMR HR allows to have more capacity with a quality equivalent to FR. Now, AMRHR capacity gain is linked to radio conditions and HR penetration.

o AMR HR codec mode use requires good radio conditions. The followingfigure (figure 5) shows that the choice of C/I threshold between AMR FR and

AMR HR could favor the AMR HR mode: so, when having an important

traffic, the X threshold could be defined for a smaller C/I value.

Figure 5: AMR-FR and AMR-HR voice quality according C/I

o The capacity gain is linked to HR mobile penetration. According to simulation

results, following figures (figure 6) give the number of carried Erlang versusthe percent of half rate TCH allocation, according to the number of TRX in the

cell (on one cell equipped with n TRX):

C/Idecreasing C/IX

FRHRMOS

AMR-FR

AMR-HR

C/Idecreasing C/IX

FRHRMOS

AMR-FR

AMR-HR


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Figure 6: Traffic function of HR penetration

One can see that the offered traffic is not linear at all except for a HR penetration of 0% and

100%. It means that for a number N of TCH corresponding to a given configuration and for a

% of HR called X, the offered traffic is not the traffic offered by (N + N *X) TCH.

Example:at 50% of HR penetration and for the configuration O6 (44 TCH), the offered

traffic is not equal to the offered traffic of 66 TCH (44+44*0.5). Indeed, the traffic offered by

66 TCH is equal to 55.3 Erlang whereas the previous figure shows that the offered traffic with

an O6 at 50% of HR penetration is about 44 Erlang.

This is due to the allocator efficiency in term of HR FR interworking and the impact of

holes created by HR TS on blocking rate(there is a hole as soon as 2 HR TS are free, on 2

different radio TS in cell).


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3.2. Norte l Netwo rks cho ices

3.2.1. AMR codecs sets chosen by Nortel NetworksOnly the following coding modes are loaded in the Nortel Networks BSS:

AMR FR AMR HR

10.2

6.7 6.7

5.9 5.9

4.75 4.75

Table 2: AMR Codec Modes chosen by Nortel Networks

Due to:

Hardware capacity: all TRX types have to have the same AMR capacities (fromDCU4 up to S12000)

Recommendations (see [R1] and [R3]) limitation to 4 active codec modes at the sametime

Intrinsic quality of each codec mode in term of voice quality and functioning range.This has been taken into account from the tests (see paragraph 3.1.4 and [R3])

performed during AMR characterization phase, giving the AMR codec modes quality

according to radio conditions (C/I) (Figures 7a, 7b, 8a and 8b).

o AMR FR codec modes choice :

Figure 7a: AMR FR codecs voice quality according C/I in clean speech conditions


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Figure 7b: AMR FR codecs voice quality according C/I in noisy background conditions

These figures show that the codecs 5.15 kbps and 7.4 kbps are unuseful. They show also that

the codec 10.2 kbps is more interesting than 12.2 kbps, as it works in a larger C/I range.

So the choice for AMR FR codecs {10.2, 6.7, 5.9 and 4.75} is the optimal combination.

o AMR HR codec modes choice :

Figure 8a: AMR HR codecs voice quality according C/I in clean speech conditions


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Figure 8b: AMR HR codecs voice quality according C/I in noisy background solutions

These figures show that the codec 5.15 kbps is unuseful.

The codecs 7.95 kbps and 7.4 kbps bring a minimal quality gain over 6.7 kbps. Moreover, the

codec 7.95 kbps can not be multiplexed over a 8 kbps Abis timeslot (Nortel Networks decides

to not oversize the Abis TS to 16 kbps in AMR HR mode, providing in this way significant

savings in backhaul).

So, the choice for AMR HR codecs {6.7, 5.9 and 4.75} is the optimal combination.

It can be noticed that these choice ensure:

a good overlapping between each codec mode, an optimal voice quality, a good trade-off between stability and codec mode adaptation.

These choices concern of course the BTS. Note that the MS have to support all the codec

modes, FR and HR, defined by the standard.3.2.2. AMR mechanisms

3.2.2.1. Initial codec mode choice

At the TCH allocation, the initial codec mode (ICM) used by the MS and the BTS is the 5.9

kbps in FR AMR mode and HR AMR mode. This codec has been chosen since it is a

common codec to FR and HR and is sufficiently protected.

3.2.2.2. Codec mode adaptation parameters choice

As said previously, the codec mode adaptation is based on C/I estimations. These C/Iestimations are performed on the training sequence bit.


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Actually, the instantaneous C/I per burst are averaged and filtered to help the decision

algorithm:

Figure 9: Codec adaptation principle

Then, the C/I estimation (i.e. C/I filtered (CIF)) is compared to the sets of parameters

{threshold; hysteresis} associated to each codec mode. As there are 4 AMR FR codecs and 3codecs AMR HR codecs and as the two links (UL and DL) need to be considered, there are 8

sets of parameters in FR and 6 sets of parameters in HR.

Now, these parameters are linked to a set of factors, some of them being determined by the

BTS (frequency hopping, MS speed), others being network dependent (environment

profile).

For uplink adaptation, Nortel Networks has decided to differentiate these factors bydefining the following categories:

- Slow MS and no Frequency Hopping- Fast MS and no Frequency Hopping

- Frequency Hopping with less than 8 hopping frequencies- Frequency Hopping with 8 or more hopping frequencies

For the downlink adaptation, recommendation imposes that all the parametersprovided to the MS are in the following propagation profile, TU3-iFH_900MHz.

So, 45 parameters (((4 AMR FR codecs modes thresholds + 1 hysteresis FR) + (3 AMR HR

codecs modes thresholds + 1 hysteresis HR)) * 5) need to be defined for uplink and downlink

adaptation at OMC level.

Nortel Networks thinks that this number is to high and decides to implement the following

table (table 3) in the Nortel BSS:

C/I brut

Measurement tr eatment

Log ( )

FilteringC/I f il tered

Decision / Adaptation

Decision

Algorithm

Estimation

de la

Vitesse du

Canal

Mode or

Quality


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Uplink BSS choiceDownlink

parameters

O&Mparameters

Slow MS

no FH

Fast MSno

FH

FH with < 8

frequenciesFH with 8

frequencies

SFH 900

TU3

set 11 set 12 set 13 set 14 set 15set 21 set 22 set 23 set 24 set 25

set 31 set 32 set 33 set 34 set 35

set 41 set 42 set 43 set 44 set 45

Table 3: BSS table for codec adaptation

In this way, the operator selects the appropriate line according to network configuration (only

4 choices, instead of 45!). These 4 choices have been implemented in order to optimize the

adaptation.

Then, the BSS using the TS configuration and the MS speed applies the appropriate column

for the uplink and the appropriate cell for the downlink.

In each set, there are 7 thresholds (4 FR thresholds and 3 HR thresholds) and 2 hysteresis (1

for HR and 1 for HR). These thresholds have been set with R&D simulations, giving FER as a

function offiltered C/I (CIF).

Hereafters (table 4) are the DL thresholds deduced from the simulation of FER versus CIF in

the TU3iFH_900MHz propagation profile (in order to optimize the adaptation, three sets have

been implemented, an optimistic, a typical and a pessimistic: then, the set choice is done by

the OMC):

Optimistic set Typical set Pessimistic set

Down Up Down Up Down Up

AMR FR

12.2 kbps 12 dB 13.5 dB 13.5 dB

10.2 kbps 7 dB 14 dB 7.5 dB 15.5 dB 8.5 dB 16.5 dB

6.7 kbps 4.5 dB 9 dB 5.5 dB 9.5 dB 6 dB 11.5 dB

5.9 kbps 4 dB 6.5 dB 4 dB 7.5 dB 5 dB 9 dB

4.75 kbps 6 dB 6 dB 8 dB

AMR HR

7.4 kbps 17 dB 16.5 dB 18 dB

6.7 kbps 12 dB 19 dB 12.5 dB 19.5 dB 13 dB 21 dB

5.9 kbps 10.5 dB 14 dB 11 dB 15.5 dB 12.5 dB 16 dB4.75 kbps 12.5 dB 14 dB 15.5 dB

Table 4: DL thresholds in term of CIF (C/I filtered)

Notes:

Note that these thresholds are C/I filtered (CIF), which are different from C/I. TheCIF can be considered as a stochastic variable with a mean and a variance, which

depends on C/I and on the propagation profile. The following table (table 5) gives

the example of TU3iFH, in downlink:

C/I Mean CIF

11 10.5910 9.65

8 7.79


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6 5.99

4 4.27

2 2.68

0 1.22

-2 -0.07-4 -1.16

-6 -20.5

Table 5: C/I and CIF correspondence (TU3iFH, DL)

One can see that the higher the C/I, the lower the difference between C/I and CIF.

All the thresholds implemented in the BSS are detailed in the document [R8].

Thresholds have been set for the FR codec 12.2 kbps and the HR codec 7.4 kbps evenif they are not considered in the BSS: this is actually needed for power control and

FR->HR handover mechanisms (see [R6]).


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4. AMR coverage aspects

The paragraph 3.1.4 shows the AMR benefits in term of quality according C/I. This quality

gain can be translated in a capacity gain. This is the mean interest of AMR introduction in

GSM networks.However, AMR has other benefit, in particular in term of coverage.

4.1. Princip le

The GSM system coverage is a direct function of the minimum acceptable signal level C/N or

in other words of the sensitivities of the BTS and the MS.

The previous section shows that AMR in Full Rate mode allows to reduce this C/N threshold

keeping a speech quality level equivalent to the one obtained with current speech coders (FR,

HR and EFR): this translates to an improvement in MS or BTS sensitivity. This sensitivity

improvement may be exploited for improved coverage in marginal conditions such as in

buildings or potentially forrange extension.

On the other hand, AMR in Half Rate mode requires high C/N compared to EFR, FR or HR.

It means that the coverage is reduced compared to the one obtained with EFR, assuming an

equal quality.

Thats why the coverage improvement is applicable only with applications where AMR i s

used in Full Rate mode only or in both Half and Full rate modes.

The following paragraph aims at quantify more precisely this sensitivity improvement.

Figure 10: AMR-FR and AMR-HR voice quality according C/N

C/Ndecreasing C/N

Quality

AMR

-FR

EFR

Cell Edge

?dB improvment

C/Ndecreasing C/N

Quality

AMR

-FR

EFR

Cell Edge

?dB improvment


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4.2. AMR co verag e gain

Many simulations have been done by Nortel Networks signal processing team (see [R7]).

These simulations consist in determining the expected sensitivity achieved by Nortel

Networks BTS for the different AMR modes. The sensitivity for GSM EFR has been

evaluated together with those of the different modes of the GSM AMR, in order to make acomparison.

This provides a reference on a service that is widely used with Nortel Networks BSS solution.

The performances are reported in term of delta with respect to the EFR at different FER

values. This delta is defined in the following way:

Sensitivity = EFR_SensitivityAMR_Sensitivity (1)The EFR sensitivity is defined at FER specified by the standard (GSM 45.005): it depends on

the propagation profile, the frequency (most of time, it is 4%)

As AMR performances in term of FER value have been evaluated at EFR sensitivity point but

also at other FER values, there are two ways of reading the simulations:

At Sensitivity = 0, compare the quality (in term of FER) achieved with AMR to thequality achieved in EFR.

At quality of EFR (given by the standard), compare the sensitivity achieved with

AMR to the one achieved in EFR. So, a positive Sensitivity means AMR is better

than EFR in term of sensitivity. Inversely, a negative Sensitivity means AMR is

worse than EFR in term of sensitivity.

Results are summarised in the two following sections.

4.2.1. AMR Full Rate only

The two following tables (table 6) give a summary of all the simulations (available at this

date) concerning AMR FR.

The first table (table 6a) gives the FER achieved in EFR (first value) and the one

achieved in AMR FR (second value) for the same sensitivity (Sensitivity = 0):

AMR FR 10.2

4 0.01% 4% -> 0.01%

TU 50, no FH 4% -> 1.3% 4% -> 0.01% 4% -> 0.01% 4% -> 0.01%

RA 130, no FH 3% -> 1.1% 3% -> 0.01% 3% -> 0.01% 3% -> 0.01%

HT 100, no FH 7% -> 2.6% 7% -> 0.01% 7% -> 0.01% 7% -> 0.01%

With Diversity (UL)

TU 50, no FH 4% -> 0.1%

850 / 900 MHz

Without Diversity (DL)

Static case 0.1% - > 0.01% 0.1% - > 0.01% 0.1% - > 0.01% 0.1% - > 0.01%TU 50, iFH 3% -> 1% 3% -> 0.01% 3% -> 0.01% 3% -> 0.01%

TU 50, no FH 8% -> 3.6% 8% -> 0.3% 8% -> 0.2% 8% -> 0.01%


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RA 250, no FH 3% -> 1.1% 3% -> 0.01% 3% -> 0.01% 3% -> 0.01%

HT 100, no FH 7% -> 2.6% 7% -> 0.01% 7% -> 0.01% 7% -> 0.01%

Table 6a:Quality (FER) for EFR and AMR FR codecs at Sensitivity = 0

One can see that the FER achieved in AMR is always better than the FER achieved in EFR.So, compared to EFR, a significant gain exists for all codecs of AMR FR mode in term of

quality.

The second table (table 6b) gives for all AMR FR codecs the Sensitivity (in dB)defined as EFR_SensitivityAMR_Sensitivity, at FER of EFR sensitivity:

AMR FR 10.2

4


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So, simulations results can be summarized on this way (not taking into account static case, as

it is non realistic):

AMR Full Rate allows to provide a quality improvement or a sensitivity improvement* of

about 4 dB (up to 5 dB with the 4.75 kbps codec)compared to EFR.

Note*: this improvement may be reviewed due to signalling limitation (see section 4.3).

4.2.2. AMR Half Rate only

The two following tables (table 7) give a summary of all the simulations (available at this

date) concerning AMR HR.

The first table (table 7a) gives the FER achieved in EFR (first value) and the one

achieved in AMR HR (second value) for the same sensitivity (Sensitivity = 0):

AMR HR 6.7

3.9 8% 4% -> 2%

TU 50, no FH 4% -> 13.3% 4% -> 9% 4% -> 2.2%

RA 130, no FH 3% -> 10.3% 3% -> 6.8% 3% -> 2%

HT 100, no FH 7% -> 18% 7% -> 12% 7% -> 3%850 / 900 MHz

Without Diversity

Static case 0.1% -> 0.2% 0.1% -> 0.1% 0.1% -> 0.1%

TU 50, iFH 3% -> 10.5% 3% -> 7% 3% -> 1.5%

TU 50, no FH 8% -> 12.5% 8% -> 8.2% 8% -> 2%

RA 250, no FH 3% -> 10.4% 3% -> 6.8% 3% -> 2%

HT 100, no FH 7% -> 17.2% 7% -> 11.5% 7% -> 2.7%

Table 7a: Quality (FER) for EFR and AMR HR codecs at Sensitivity = 0One can see that the FER achieved in AMR is only better than the FER achieved in EFR

for the 4.75 kbps codec. The other codecs are not enough protected.

The second table (table 7b) gives for all AMR HR codecs the Sensitivity (in dB)defined as EFR_SensitivityAMR_Sensitivity, at FER of EFR sensitivity:

AMR HR 6.7

3.9


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RA 130, no FH -3.1 -1.7 0.7

HT 100, no FH -1.8 -1 1.3

850 / 900 MHz

Without Diversity

Static case -0.2 0 0.5TU 50, iFH -2.1 -1.3 0.8

TU 50, no FH -0.8 0 1.9

RA 250, no FH -3.1 -1.7 0.7

HT 100, no FH -1.7 -0.9 1.3

Table 7b: Sensitivity (dB) for AMR HR codecs at FER of EFR sensitivitySo, only 4.75 kbps HR codec provides a sensitivity gain compared to EFR, but this gain

is not very significant (about 1 dB) compared to the gain provided by AMR FR mode.

Moreover, like in the FR case, this codec use induces a quality degradation (in term of MOS).

So, for a radio design, its better to consider the two other codecs: but, they dont improve the

sensitivity.Actually, since the gross bit rate is divided by two in half rate mode, the level of protection is

very low: the consequence is that half rate modes can not work in bad radio conditions. On

the other hand, these two codecs need high C/N compared to EFR, to ensure the same quality.

The previous tables show also the impact of frequency hopping and environments on the

results. Now, differences are not enough significant to give any conclusions.

So, simulations results can be summarized on this way (not taking into account static case, as

it is non realistic):

AMR Half Rate does not provide a quality improvement orasensitivity improvement.

Actually, only the codec 4.75 kbps provides improvements, but this should not be considered

for a radio design.

4.2.3. AMR Full Rate and Half Rate together

The two previous sections shows that AMR in Full Rate mode allows to improve BTS

sensitivity of 4 dB keeping a speech quality level equivalent to the one obtained with current

speech coder, i.e. EFR.

Assuming the same improvement for MS*, this sensitivity improvement can betranslated in a coverage improvement.

Note: *indeed, the previous simulations are based on Nortel Networks BSS and not on MS, so

it is maybe optimistic to use these simulations to deduce AMR performances of MS.

On the other hand, AMR in Half Rate mode needs high C/N compared to EFR. It means that

the coverage is reduced compared to the one obtained with EFR. Thats why one can speak of

coverage improvement with AMR, only if Half Rate mode is used with Full Rate mode.

Then, Half Rate mode will be used in good radio (C/N) conditions.


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Then, the benefits of coverage improvement provided by AMR wont be the same according

to the operator position. Two cases can be considered:

Case of a new GSM design

Case of an existing GSM design (speech coder used is EFR)

4.2.3.1. New GSM design

As AMR sensitivities (MS and BS) are increased by 4 dB, the available pathloss with AMR

will be increased by 4 dB (compared to the one in EFR), which allows a higher coverage.

The following table (table 8) gives some examples of cell range and coverage achieved in

EFR and AMR at 1800 MHz:

EFR cell

range (km)

EFR

coverage

(km2)

AMR cell

range (km)

AMR

coverage

(km2)

% of site

savings

DenseUrban

(H4D) 0.294 km 0.169 km2

0.382 km 0.285 km2

40%Urban

(H2D)0.534 km 0.555 km2 0.693 km 0.937 km2

Rural (Dp) 7.395 km 106.557 km 9.664 km 182 km

Table 8: Cell range and coverage achieved with EFR and AMR in dense urban, urban and rural

environments

This table shows that 4 dB of improvement in pathloss induces a cell range increase of 30%

and a coverage increase of 70%, which means a site saving ofabout 40% compared to EFR.

So, design a GSM network with AMR means for a greenfield operator an important costsaving.

4.2.3.2. Existing GSM design

All the existing GSM designs have been made assuming the use of current speech coders,

EFR or FR. So, introduce AMR in these existing networks will allow to improve coverage

quality in marginal conditions such as in buildings.

Lets take an example of a design made with EFR in Geneva. Hereafter (figure 11) is the

corresponding coverage map with the different achieved field strength values:


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Figure 11: Geneva coverage mapEFR design

As with AMR, the pathloss is improved of about 4 dB, the field strength levels will be

increased by 4 dB:

Achieved level in EFR Achieved level in AMR

-65 dBm - 61 dBm

-70 dBm -66 dBm

-75 dBm -71 dBm

-81 dBm -77 dBm

-90 dBm -86 dBm

Table 9: Achieved levels in EFR and AMR

This table means that:

Where indoor window coverage is achieved with EFR, indoor coverage will beachieved in AMR

Where indoor coverage is achieved with EFR, deep indoor coverage will beachieved in AMR

Where deep indoor coverage is achieved with EFR, coverage will be even betterSo, coverage quality will be improvedall over the networks, in particular in critical areaslike in buildings or where there are coverage holes (see purple circles on figure 11).

4.3. Lim itat ion s

As said previously, AMR allows to improve coverage compared to EFR. Benefits are

different according to the operator position:

A greenfield operator who wants to open a new GSM network will save a lot of sitescompared to EFR.

An existing operator who has already deployed its GSM network will offer a best

quality to its subscribers.Now, there can be some limitations to these benefits.


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4.3.1. Simulations limitations

Most of simulations presented in section 4 are performed in DL, using the LS algorithm. Only

one simulation has been made in UL, so only this one is really representative on the BS

sensitivity performances. It would be good to perform other simulations in UL just to check

that there is no big difference with the DL and reinforce our conclusion.

All the simulations are based on Nortel Networks BSS. Of course, MS performances are not

simulated. But, our conclusion is based on the fact that AMR MS sensitivity is improved as

much as BS sensitivity.

4.3.2. Signalling channels

The coverage improvement brought by AMR is subject to the limit of robustness of the

signalling channels.

Indeed, it is important to note that the limiting factor may be for the lowest rate of the AMR

no more the performances of the traffic channel but those of the signalling channels.

Thats why before speaking about a real coverage gain with AMR, we need to verify that

signalling channels are not limiting.

In order to solve this point, first simulations have been performed by Signal Processing

Team and: they are presented in section 5.3.

4.3.3. AMR penetration

The AMR penetration will also have a big influence on the AMR coverage benefits, in

particular in case of a new design.Indeed, designing a new network with AMR assumes a great majority of AMR terminals,

otherwise there will be performance problems with terminals without AMR such as roamers

and EFR or FR or data terminals. Indeed, voice (EFR, FR) and data quality will be degraded

and offered throughput will be reduced, in particular at cell edge.

So, one should take care of networks with a mix of services, where the penetration of

AMR is not 100%.

In case of an existing design (designed with EFR at the beginning), there is no real

problem: only subscribers with AMR terminals will see a quality improvement.


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5. AMR capacity aspects

As said previously (paragraph 3.1.4), AMR allows to increase capacity.

This capacity benefit has two origins: Improved robustness in Full Rate allows reduction in frequency reuse pattern

Half Rate channels will free available capacity for more traffic

5.1. Princip le

The GSM system capacity is a direct function of the minimum acceptable C/I ratio for an

expected Grade of Service (for example 90 % of the cell area).

As seen before, with AMR in Full Rate mode, the C/I threshold for an acceptable speech

quality level may be reduced compared to the system operation with the current speech coders(FR, HR or EFR). In other words, robust AMR codecs tolerates higher interference (low C/I):

it allows for tighter frequency reuse patterns or higher loading levels using fractional

frequency reuse.

On the other hand, AMR in Half Rate mode needs high C/I compared to EFR, FR or HR. It

means that if AMR is used in Half Rate mode only, the above improvement is not true: on

the other hand, a higher frequency reuse pattern or a lower fractional load are required to

ensure the same quality than in EFR or FR.

However, as a half rate TCH carries information at half of the full rate channel, AMR half rate

allows to increase capacity per radio without adding new equipment or sites (roughly, 2

mobiles can be multiplexed on a given TS instead of 1).

So, it means that the capacity gain provided by AMR will be maximized when both Full Rate

and Half Rate will be used:

Full Rate will allow to increase capacity by reducing the frequency reuse pattern or byusing higher fractional load on hopping layer,

Half Rate will allow to increase capacity where quality will be acceptable (good C/I).

The following paragraphs aim at detailing these capacity gains and the engineering rules in

term of frequency plan when AMR is implemented on the networks.


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5.2. AMR frequency plannin g

Some simulations have been done by Nortel Networks signal processing team (see [R9]).

These simulations consist in determining the performances in term of FER versus C/I for thedifferent AMR modes in different kinds of propagation profiles. The idea is then to compare

these performances to those achieved in EFR, in order to quantify the gain or the loss brought

by AMR and deduce engineering rules in term of frequency planning, non hopping and

hopping, when AMR is implemented on the networks.

5.2.1. Non hopping frequency plan

Cellular networks are generally planned with a fixed frequency group pattern. The idea is to

split the available spectrum into different sets of N frequencies and allocate these sets to

different cells. According to the number of sets, different patterns are possible:

9 sets, which gives a 3*9 pattern. It means that 3 tri-sectorised sites share 9 sets of Nfrequencies.

12 sets, which gives a 4*12 pattern. It means that 4 tri-sectorised sites share 12 setsof N frequencies.

21 sets, which gives a 7*21 pattern. It means that 7 tri-sectorised sites share 21 setsof N frequencies.

The set of adjacent cells using the whole available spectrum is called a cell cluster.

The figure 12 represents the case of a 4*12 pattern (N = 12):

Spectrum split into 12 sets of N frequencies

Figure 12: Reuse pattern 4*12 (N = 12)

The greater the pattern, the less the interference and the better the quality.

This is demonstrated by the following formula, which gives the C/I value according to the

pattern N:

)

*6

1log(*10

)13(

NIC

(2)

Note: is the propagation coefficient (it is assumed equal to 3.522 in the following).


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Note that this C/I value is independent of the technology used, EFR, FR, HR or AMR: it only

depends on the reuse distance D, i.e. the frequency pattern N (see figure 13):

A3 A1

B1

B2

C2

C1C3

D3

D2

D1

A1

A2

A3

R

D 3

DA3

A2

A1

B1

B2

B3

C2

C1C3

D3

D2

D1

A1

A2

A3

R

D 3

D

Figure 13: Reuse distance definition in a reuse pattern N (N=12 in this example)

Now, the greater the pattern, the lower the capacity for a given spectrum. It means that there

is a trade-off quality-capacity that we need to optimise.

Nortel Networks experiments and simulations had proven that a 4*12 pattern is the most

suitable solution from capacity and quality points of view:

From a capacity point of view, the number of TRX per cell is the entire part of theratio B/12, where B is the available spectrum and 12 the reuse pattern.

From a quality point of view, the above formula (2) shows that a 4*12 allows toensure a C/I of 17 dB. Simulations had also proven that it corresponds to a very

acceptable FER, lower than 1% (see [R10]).

Note that the relation between C/I and FER depends on the considered technology, i.e. EFR or

AMR. It depends also on the propagation profile, the frequency and the activated features.

Hereafter (figure 14) is the FER versus C/I for EFR in the following conditions:

Frequency 1800 / 1900 MHz

No diversity

TU3 propagation profile

No frequency hoppingThis simulation has been performed with the LS training algorithm, i.e. in DL.


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Figure 14: FER versus C/I achieved with EFR in DL, TU3, noFH, without Diversity, 1800 / 1900 MHz

conditions

One can see that to achieve a FER of 1%, the required C/I is 17 dB, so a 4*12 (N = 12) is

needed (it coincides with the previous notes).

Assuming that a FER of 1% is the quality target, the idea of the two following sections is

to compare (in the same conditions) the C/I achieved with the different AMR codecs* to the

one achieved with EFR, and deduce the required pattern to ensure a such C/I and so the

capacity gain or loss brought by AMR.

Note: *like in the coverage case, its the codec 4.75 kbps which will allow the highest

improvement in term of capacity, since it is able to work at the lowest C/I. Meanwhile, since

this codec use induces a quality degradation (in term of MOS), its better to consider the

nextcodec, i.e. 5.9 kbps. So, only the codec 5.9 kbps is considered in the two next sections.

5.2.1.1. AMR Full Rate onlyHereafter (figure 15) is presented the simulation for the codec AMR FR 5.9 kbps in the

following conditions:


No diversity


No frequency hoppingLike for the EFR case, this simulation has been performed with the LS training algorithm, i.e.

in DL.


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Figure 15: FER versus C/I achieved with AMR FR 5.9 kbps codec in DL, TU3, noFH, without Diversity,

1800 / 1900 MHz conditions

The conclusion resulting from the comparison between figures 14 and 15 is that the codec

AMR FR 5.9 kbps allows to work at lower C/I compared to EFR keeping an equivalent

quality, in term of FER.

Indeed, for a same FER of 1 %, the required C/I with AMR FR 5.9 kbps is 13 dB whereas

the required C/I with EFR is 17 dB, let a C/I gain of4 dB.

Using the formula (2), we can deduce the required reuse pattern to ensure these C/I at 90% of

probability:

EFR AMR FR

Required C/I for a FER of 1% 17 dB 13 dB

Required reuse pattern N 12 8

Table 10: Required C/I and reuse pattern in EFR and AMR FR

So, a pattern at 8 cells should be applied to achieve the same EFR quality, which means atleast 4 frequencies saving compared to EFR or in other words a capacity gain.

Lets consider the following example in order to quantify and compare the capacity achieved

with EFR and AMR FR on frequency reuse TCH plan.

Example:let be a spectrum of 4.8 MHz, i.e. 24 TCH frequencies (SDCCH TS are removed for

the capacity calculation).

With pattern at N = 12 (pattern in EFR), it allows to have S222 BTS configuration,which gives a capacity of 27 Erlangs at 2% of blocking.

With apattern at N = 8 (pattern in AMR FR), this gives aS333 BTS configuration,which allows a capacity of 44.7Erlangs at 2% of blocking.

So, in this example, an upgrade from 12-cell reuse cluster to a 8-cell reuse cluster allows toprovide a direct 65% capacity increase in term of Erlangs.


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So, the conclusion is the following:

In case of non-hopping frequency plan, AMR Full Rate allows to increase capacitycompared to EFR, by reducing reuse pattern.

5.2.1.2. AMR Half Rate only

Hereafter (figure 16) is presented the simulation for the codec AMR HR 5.9 kbps in the

following conditions:


No diversity

TU3 propagation profile No frequency hopping

Like for the EFR case, this simulation has been performed with the LS training algorithm, i.e.

in DL.

Figure 16: FER versus C/I achieved with AMR HR 5.9 kbps codec in DL, TU3, noFH, without Diversity,

1800 / 1900 MHz conditions

The conclusion resulting from the comparison between figures 14 and 16 is that the codec

AMR HR 5.9 kbps does not allow to work at lower C/I compared to EFR keeping an

equivalent quality, in term of FER.

Indeed, the required C/I with AMR HR 5.9 kbps is exactly the same (i.e. 17 dB) than in the

EFR case, for a same FER of 1 %.

The consequence is that the required reuse pattern with AMR HR is also the same than inEFR, i.e. a 4*12.


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Meanwhile, the capacity with AMR HR will be higher than in the EFR, thanks to the Half

Rate usage (2 users on the same TS instead of 1).

Lets consider the following example in order to quantify and compare the capacity achieved

with EFR and AMR HR on frequency reuse TCH plan.Example:let be the spectrum of 4.8 MHz, i.e. 24 TCH frequencies (SDCCH TS are removed

for the capacity calculation).

With a pattern at N = 12 (pattern in EFR), it allows to have S222 BTS configuration,which gives a capacity of 27 Erlangs at 2% of blocking.

With a pattern at N = 12 (pattern in AMR HR), this gives also S222 BTSconfiguration, but the capacity is 58.5 Erlangs at 2% of blocking ((19.5*3) Erlangs,

from figure 6 and [R6], considering 100% of HR).

So, in this example, even if the cell reuse cluster is the same, AMR HR allows to increase the

capacity in term of Erlangs of 116%.


In case of non-hopping frequency plan, AMR Half Rate does not allow to reduce the reuse

pattern compared to EFR. However, the capacity is increased thanks to the Half Rate

transmission.

5.2.1.3. AMR Full Rate and Half rate together

The two previous sections show that only AMR in Full Rate mode allows to reduce the reuse

pattern, keeping a speech quality level equivalent to the one obtained with current speechcoder, i.e. EFR. Indeed, AMR Half Rate use requires the same reuse pattern than EFR.

It means that frequencies are saved thanks to AMR Full Rate only.

So, one can speak ofcapacity improvement due to reuse pattern reduction in AMR, only

if Half Rate mode is used with Full Rate mode (or if Full Rate is used without Half Rate).

Then, Half Rate mode will be used in good radio conditions (good C/I), allowing also a

capacity improvement in this zone as Half Rate allows to have 2 subscribers instead of 1 on a

single TS.

But, if the pattern is reduced, the C/I distribution will be degraded and the percentage of

Half Rate used in the network will be reduced (figure 17)


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Reuse pattern N = 12 : Reuse pattern N = 8 :

Figure 17: HR usage in a 12 and 7 reuse patterns

Lets try to quantify the percentage of Half Rate usage in DL, when reuse pattern is reduced

from 12 to 8 (thanks to AMR Full Rate).

The table 4 shows that AMR Half Rate (when both Full Rate and Half Rate are implemented)

will be used in DL since CIF is equal to 15.5 dB (typical case), which is almost the same

thing in term of C/I.

Then, using the following formula giving C/I as a function of r (in order to have the C/I

distribution on the cell (Cste is so that at cell edge, the C/I is the one given by the formula

(2)):

CsteIC

N

r

)

*6

log(*10

)13(

(3)

one can see that:

A pattern N = 12 allows to have a C/I higher than 15-16 dB on 100% of cell surface

A pattern N = 8 allows to have a C/I higher than 15-16 dB on 70% of cell surfaceAs assumed before, half rate usage is reduced, in particular of30%.

Now, lets see the impact in term of capacity, taking the same example, i.e. 4.8 MHz of

spectrum, equivalent to 24 TCH frequencies (SDCCH TS are removed for the capacity

calculation):

With pattern at N = 12, it allows to have S222 BTS configurations. With suchconfiguration and 100% of HR penetration, the achieved capacity on one site is 58.5

Erlangs at 2% of blocking rate (19.5 Erlangs*3, from figure 6 and [R6]).

With a pattern at N = 8, this gives a S333 BTS configuration. With suchconfiguration and 70% of HR penetration, the achieved capacity on one site is 66

Erlangs at 2% of blocking rate (3*22 Erlangs, from figure 6 and [R6]).

So, this example shows that even if the percentage of Half Rate usage is lower when the reuse

pattern is reduced (which is possible with AMR Full Rate), the capacity is greater than in the

case of keeping the initial reuse pattern: the improvement is about 13% (in term of Erlangs).


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In case of non-frequency hopping plan, AMR allows to increase capacity compared to

EFR, by reducing reuse pattern. The capacity is then maximised with the Half Rate use inthe good C/I conditions.


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5.2.2. Hopping frequency plan

The frequency plan presented in the previous section (7*21, 4*12, 3*9) are non-hopping, it

means that only one frequency is allocated to each TRX.

It is possible to tighten even more the reuse pattern of the traffic channels to increase the

capacity in the system. But, to counteract the possible increase in interference, features like

power control, DTX and frequency hopping need to be utilized (note that these features

cannot be applied to control channels (see [R11])).

Frequency hopping means that TRXs are hopping on a frequency group. In this case, the

quality is ensured with the frequency load control. The frequency load represents the time

fraction for a given frequency being used in the network. It is also the ratio between the

number of hopping TRX in a cell and the number of hopping frequencies.

2 reuse patterns are commonly used with frequency hopping (one speaks about fractionalreuse pattern):

1*3 fractional reuse pattern:The TCH frequencies are divided in three groups T1, T2 and T3 and allocated as following:

T1

T2

T3

T1

T2T3

reuse distance

T1

T1

T2

T2

no co-channel adjacent cells

Figure 18: 1*3 fractional reuse pattern

1*1 fractional reuse pattern:All the TCH frequencies are gathered in one unique group T that is allocated to every cell as

following:

T

T

T

T

T

T re use distance

T

T

T

T

all adjacent cells are co-channel

Figure 19: 1*1 fractional reuse pattern


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Based on Nortel Network simulations and experiments (see [R10] and [R11]), the following

figures for maximum frequency load are recommended:

Reuse pattern Maximum frequency load

1*1 16%1*3 50%

Table 11: Maximum fractional loads values according to the fractional reuse pattern

The achieved fractional load in frequency hopping depends on the signal processing (de-

interleaving, decoding, errors correcting): so, it depends on speech coder used (EFR, FR,

HR, AMR).

Note: the above fractional loads concern EFR speech coder.

The gain of frequency hopping can be measured, comparing the curves of FER = f(C/I), with

and without frequency hopping, in function of the environment, the frequency band and the

activated features.As frequency hopping brings greater gains as soon as the user is slow, its better to take a

TU3 propagation profile.

The frequency hopping gain depends also on the frequency band and the activated features.

Hereafter (figures 20 and 21) are the FER versus C/I for EFR in the following conditions:



No diversity

With and without frequency hoppingThese simulations have been performed with the LS training algorithm, i.e. in DL.

Figure 20: FER versus C/I with EFR in DL, TU3, no FH, without Diversity, 1800 / 1900 MHz conditions


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Figure 21: FER versus C/I with EFR in DL, TU3, with FH, without Diversity, 1800 / 1900 MHz conditions

These simulations show that frequency hopping brings a gain of 6.5 dB in EFR, at 1% of

FER. Like in the previous section (non hopping plan), 1% of FER is assumed to be the

quality target. Besides, simulations have shown that quality achieved with 4*12 and 1*3

with a fractional load of 50% is almost the same (see [R10] and [R11]).

The idea of the two following paragraphs is to evaluate the frequency hopping gain

achievable with the different AMR codecs at 1% of FER and compare it to the one of EFR.

The results of this comparison would be according to the AMR codecs:

Either, the frequency hopping gain is higher in AMR than in EFR

Or, the frequency hopping gain is lower in AMR than in EFRwhich means a quality gain or a quality loss, which can be translated into a capacity gain or a

capacity loss.

Indeed, in [R12], it is demonstrated that capacity is directly proportional to the available

bandwidth and the C/I ratio.

So, if

SFH is the frequency hopping gain increase or reduction achieved in AMR comparedto EFR, the new fractional load achievable in AMR would be:

SFHFLFL EFRAMR * (4)


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5.2.2.1. AMR Full Rate only

Hereafter (figures 22 to 27) are presented the simulations giving FER = f(C/I) for the codecs

AMR FR 10.2, 5.9 and 4.75 kbps* in the following conditions: Frequency 1800 / 1900 MHz

No diversity


With and without frequency hoppingLike for the EFR case, these simulations have been performed with the LS training algorithm,

i.e. in DL.

Note: *simulations for 6.7 kbps codec are not available at this time.

Figure 22: FER versus C/I with AMR FR 10.2 kbps, in DL, TU3, no FH, without Diversity, 1800 / 1900

MHz conditions


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Figure 23: FER versus C/I with AMR FR 10.2 kbps, in DL, TU3, with FH, without Diversity, 1800 / 1900

MHz conditions


MHz conditions


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MHz conditions


MHz conditions


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MHz conditions

The following frequency hopping gains result from the analysis of these curves:

Frequency hopping

gain

Difference / EFR

SFHAMR FR 10.2 kbps 6.5 100%

AMR FR 5.9 kbps 7.5 126%

AMR FR 4.75 kbps 7 112%

EFR 6.5 NA

Table 12: Frequency hopping gains and SFH in AMR FR and EFR

Applying the equation (4) (and taking into account the maximum frequency loads for EFR

given in table 11), the maximal fractional load achieved with AMR FR (with 10.2, 5.9 and

4.75 kbps codecs) will be:

Reuse pattern Maximal frequency load

AMR FR 10.2 AMR FR 5.9 AMR FR 4.75

1*1 16% 20% 18%

1*3 45% 63% 56%

Table 13: Maximal fractional loads values in AMR FR according to the fractional reuse pattern

So, the fractional load can be increased up to 20% in a 1*1 and up to 63% in a 1*3 when

AMR Full Rate is implemented on the network.

Note: fractional load for AMR FR 6.7 kbps has not been calculated. It should be interesting to

calculate this fractional load (when simulations are available), in order to see if frequencyload could be even more increased.


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Higher fractional load means higher capacity.Lets consider the following example in order to quantify and compare the capacity achieved

with EFR and AMR FR on fractional reuse TCH plan (1*1 is considered).

Example:let be the spectrum of 4.8 MHz, i.e. 24 TCH frequencies. That gives the following

BS configuration (SDCCH TS are removed for the capacity calculation): S344 in EFR (1*1 with a FL of 16%), which gives a capacity of 58.7 Erlangs at 2%

of blocking.

S455 in AMR FR (1*1 with a FL of 20%), which gives a capacity of 78.4 Erlangs at2% of blocking.

So, AMR Full Rate allows to have 33% of capacity increase in term of Erlangs, compared to

EFR.


In case of frequency hopping plan, AMR Full Rate allows to increase capacity comparedto EFR, by increasing fractional load.

5.2.2.2. AMR Half Rate only

Hereafter (figures 28 to 31) are presented the simulations giving FER = f(C/I) for the codecs

AMR HR 5.9 and 4.75 kbps* in the following conditions:


No diversity


With and without frequency hoppingLike for the EFR case, these simulations have been performed with the LS training algorithm,

i.e. in DL.

Note: *simulations for 6.7 kbps codec are not available at this time.


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Figure 28: FER versus C/I with AMR HR 5.9 kbps, in DL, TU3, no FH, without Diversity, 1800 / 1900

MHz conditions

Figure 29: FER versus C/I with AMR HR 5.9 kbps, in DL, TU3, with FH, without Diversity, 1800 / 1900

MHz conditions


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Figure 30: FER versus C/I with AMR HR 4.75 kbps, in DL, TU3, no FH, without Diversity, 1800 / 1900

MHz conditions

Figure 31: FER versus C/I with AMR HR 4.75 kbps, in DL, TU3, with FH, without Diversity, 1800 / 1900

MHz conditions


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The following frequency hopping gains result from the analysis of these curves:

Frequency hopping

gain

Difference / EFR

SFHAMR HR 5.9 kbps 4 dB 56.2%

AMR HR 4.75 kbps 4 dB 56.2%

EFR 6.5 dB NA

Table 14: Frequency hopping gains and SFH in AMR HR and EFR

AMR Half Rate codecs provide lower frequency hopping gain compared to EFR, which

results in a lower maximal fractional load.

Applying the equation (4) (and taking into account the maximum frequency loads for EFR

given in table 11), the maximal fractional load achieved with AMR HR (with 5.9 and 4.75

kbps codecs) will be:

Reuse pattern Maximal frequency load

AMR HR 5.9 AMR HR 4.75

1*1 9% 9%

1*3 28% 28%

Table 15: Maximal fractional loads values in AMR HR according to the fractional reuse pattern

So, the fractional load is decreased down to 9% in a 1*1 and down to 28%in a 1*3 when

AMR Half Rate is implemented on the network.Note: fractional load for AMR HR 6.7 kbps has not been calculated. It should be interesting

to calculate this fractional load (when simulations are available), in order to see if frequency

load could be higher.

The fractional load reduction implies more frequencies. The following table (table 16) gives

the minimum number of needed frequencies for having at least one hopping TRX per cell:

Reuse pattern Minimum number of frequencies

1*1 11

1*3 11

Table 16: Minimum number of needed frequencies for AMR HR

AMR Half Rate use in fractional reuse pattern requires roughly the same number frequencies

than in non-hopping case (4*12 pattern). So, AMR Half Rate use in hopping plan can be

contested from a spectral efficiency point of view.

Moreover, lower fractional load means capacity loss. However, this capacity loss is

compensated by the use of Half Rate, i.e. 2 users on the same TS instead of 1.

Lets consider the following example in order to quantify and compare the capacity achievedwith EFR and AMR HR on fractional reuse TCH plan (1*1 is considered).


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Example:let be the spectrum of 4.8 MHz, i.e. 24 TCH frequencies. That gives the following

BS configuration (SDCCH TS are removed for the capacity calculation):

S344 in EFR (1*1 with a FL of 16%), which gives a capacity of 58.7 Erlangs at 2%of blocking.

S222in AMR HR (1*1 with a FL of 9%), which gives a capacity of 58.5Erlangs at2% of blocking(19.5*3 Erlangs,from figure 6 and [R6], considering 100% of HR).

So, AMR Half Rate induces a high capacity decrease in term of TCH (about 45%). Now, this

capacity in term of Erlangs is not so impacted thanks to Half Rate usage: globally, it is the

same than in EFR.


In case of frequency hopping plan, AMR Half Rate requires lower fractional loads,

compared to EFR. However, the capacity is globally the same than in EFR, thanks to the

Half Rate usage.

5.2.2.3. AMR Full Rate and Half Rate together

The two previous sections show that AMR in Full Rate mode allows to increase the maximum

fractional load whereas AMR Half Rate requires lower fractional load, keeping a speech

quality level equivalent to the one obtained with the current speech coder, i.e. EFR.

So, one can speak ofcapacity improvement due to higher fractional load in AMR, only if

Half Rate mode is used with Full Rate mode (or if Full Rate is used without Half Rate). Then,Half Rate mode will be used in good radio conditions (good C/I), allowing also a capacity

improvement in this zone as Half Rate allows to have 2 subscribers instead of 1 on a single

TS.

It would be interesting to quantify the percentage of Half Rate usage, in case of frequency

hopping with high fractional load, up to 20% (thanks to AMR Full Rate).

This will depend on the C/I distribution over the network, as Half Rate is used since C/I is

higher than a given value (for instance, 15 dB in DL in the typical case (see table 4)). But, in

case of frequency hopping, the C/I distribution is not deterministic at all (like in non hopping

pattern): on the other hand, it is statistical. Moreover, it depends a lot on:

The traffic load on the network,

The traffic distribution over the network (some cells are much load than others) So, simulations are required in order to have C/I distribution over the frequency-hopping

network.

It would be interesting to perform these simulations, considering different fractional load and

traffic load, in order to evaluate exactly the percentage of Half Rate use.

As these simulations are not available at this time, lets take the following assumption, 60%

of half rate penetration, in order to calculate and compare the carried capacity in EFR and in

AMR in our example (1*1 is considered).

Example:let be the spectrum of 4.8 MHz, i.e. 24 TCH frequencies. That gives the followingBS configuration (SDCCH TS are removed for the capacity calculation):


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S344 in EFR (1*1 with a FL of 16%), which gives a capacity of 58.7 Erlangs at 2%of blocking.

S455 in AMR (1*1 with a FL of 20%). With such configuration and 60% of HRusage, the achieved capacity is 105 Erlangs at 2% of blocking (29 + 2*38 Erlangs ,

from figure 6 and [R6], considering 60% of HR).

Note: 60% of HR penetration is maybe a too high value. Meanwhile, some systems

simulations have already been done to test different features, like cell tiering for instance and

they show that:

in DL, C/I higher than 15 dB is achieved with a probability of 60% (see [R13])

in UL, C/I higher than 15 dB is achieved with a probability of 70% (see [R13])of course, these simulations have been performed to test the cell tiering efficiency, and not the

AMR efficiency. Now, one can assume that AMR used in its optimal performances gives

the same results than cell tiering used in optimal way. But, its just an assumption and it needs

to be checked by appropriate and accurate simulations.


In case of hopping frequency plan, AMR allows to increase capacity compared to EFR, by

increasing fractional loads (it is possible with Full Rate usage). The capacity is then

maximised with the Half Rate use in the good C/I conditions.

5.2.3. Frequency plan conclusion

The following table (table 17) summarizes the capacity results obtained in the two previoussections with the example of 4.8 MHz of available spectrum, i.e. 24 frequencies available for

TCH plan:

Non Hopping TCH plan Hopping TCH plan 1*1

EFR

S222

27 Erlangs

(Reuse pattern N = 12)

S344

58.7 Erlangs

(FL = 16%)

AMR Full Rate only

S333

44.7 Erlangs


S455

78.4 Erlangs

(FL = 20%)

AMR Half Rate only

S222

58.5 Erlangs


S222

58.5 Erlangs

(FL = 9%)

AMR Full and Half Rate

S333

66 Erlangs

(Reuse pattern N = 8 and 70%

of HR)

S455

105 Erlangs

(FL = 20%, 60% of HR*)

Table 17: Capacity comparison EFRAMR

Note*: this assumption needs to be checked by simulations.


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It emerges from this analysis the following conclusions:

AMR implies a capacity gain compared to EFR, in non-hopping as well ashopping frequency plan.

Meanwhile, the capacity gain is the highest in the hopping case.

The capacity gain is the highest when AMR is used in both modes, Full Rate andHalf Rate

On the other hand, when only one mode is used:o The highest gain is achieved with Full Rate mode in the hopping case.o Whereas, the highest gain is achieved with Half Rate mode in the non hopping

case. Indeed, although the pattern needs to be higher in Half Rate mode than in

Full Rate mode, the global capacity is higher thanks to the Half Rate usage.

In case of AMR use in both modes (FR and HR), it is very difficult to estimate the half rate

penetration, since it is linked to the C/I distribution on the network and since this one

depends a lot on the network configuration.

Indeed, the C/I distribution is a function of the frequency re-use pattern, and directly related

to the activation and performances of the radio features of the system, such as Frequency

Hopping, Power Control, DTX, etc. It depends also on the propagation conditions in the area

of concern, such as shadowing characteristics, applicable propagation losses, antenna heights

and apertures. Finally, it depends on the traffic load on the network.

For all these reasons, it is very difficult to make accurate estimates of capacity achieved when

both Half Rate and Full Rate are activated.

So, the capacity result given in table 17 when AMR Full Rate and Half Rate are used both in

hopping case should be considered with care, as the percentage of Half Rate is only an

assumption.

Simulations at system level are necessary to refine this value.This type of simulations could be very useful to define the best strategy in term of frequency

plan, when AMR FR and HR are implemented. For instance, simulations could show that the

percentage of Half Rate is not so high, when hopping pattern is loaded at 20%. In this case, it

would be more interesting:

to put Half Rate in a separated non hopping frequency plan and have globally a highercapacity

or

to reduce the frequency load, in order to increase the percentage of Half Rate andhave globally a higher capacity.


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5.3. Lim itat ion s and dif f icu l t ies

AMR seems to be a revolutionary solution in term of GSM capacity. Unfortunately, there are

some limitations to these benefits, described hereafter.

5.3.1. Simulations limitations

All the conclusions of section 5 are based on simulations performed in DL, since they are the

only available at this time, in particular for the EFR.

No simulations are presented in UL. It would be good to perform these simulations just to

check that there is no big difference with the DL and reinforce our conclusions.

In the same way, these conclusions are based on AMR simulations performed with 10.2, 5.9

and 4.75 kbps codecs: simulations for 6.7 kbps codec are not available at this time. As soon as

these simulations are available, it would be good to analyse the achieved performances in

order to see if our conclusion are the same or need to be changed.

Finally, all the simulations are based on Nortel Networks BSS. Of course, MS performances

are not simulated. It means that our conclusions are based on the fact that AMR MS

performances are the same than AMR BS performances.

5.3.2. Signalling channels

The capacity improvement brought by AMR is subject to the limit of robustness of the

signalling channels.

Indeed, it is important to note that the limiting factor may be no more the performances of the

traffic channel but those of the signalling channels, i.e. SACCH, FACCH and also SDCCH.

SACCH and FACCH performances:There are some constraints concerning SACCH and FACCH performances in term of BLER:

SACCH BLERneeds to be lower than 20%*, so that there are no problems at L1Mlevel

FACCH BLERneeds to be lower than 30%, so that a Lapdm message is received inless than 5 repetitions (which corresponds to a good working of the system).

Note: *this value is a first approximation that needs to be checked on field.

First simulations have been performed by Signal Processing Team in order to know the

relationship between these BLER and the C/I

The two following figures (figures 32 and 33) gives:

The SACCH performances in term of BLER versus C/I

The FACCH performances in term of failure versus C/I with a maximum of 5repetitions. FACCH failure is actually representative of the BLER.

in the following conditions:

TU3 iFH

No diversity

ULFull Rate channel has been considered.


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BLER SACCH

0102030405060708090

100

0 1 2 3 4 5 6 7 8 9 10C/I

%

Figure 32: BLER SACCH versus C/I in DL, TU3, with FH, with diversity

FACCH Failure (5 Times)

0

10

20

30

40

50

60

70

80

90

0 2 4 6 8 10

Figure 33: BLER FACCH versus C/I in DL, TU3, with FH, with diversity

One can see that:

C/I needs to be higher tha

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