12_edge and Gprs Cs-3 Cs-4 in Release b8

EDGE and GPRS CS-3/CS-4 in Release B8

Functional Feature Description


This document covers the following features :

30 06 14: Coding Scheme CS-3

30 06 16: Coding Scheme CS-4

30 07 00: EDGE Coding Schemes

30 07 10: Support of all EDGE Modulation and Coding schemes

30 07 20: EDGE Link adaptation

30 07 30: Incremental Redundancy

30 10 55: Combined GPRS/EDGE resource management

30 14 40: Two incoming A-bis links per BTS

Alcatel File Reference Date Edition Pagedocument.doc v 2 04-KOS-1646 03/05/2004 02 1

All rights reserved. Passing on and copying of this document, use and communication of its contents not permitted without written authorization.


Contents

1. INTRODUCTION............................................................................................................4

2. HARDWARE SUPPORT................................................................................................4

2.1 Radio equipment performances.............................................................................5

2.1.1 EVOLIUM™ A9100 Base Station :............................................................5

2.1.2 EVOLIUM™ A9110 micro-BTS :...............................................................7

2.2 Support of EDGE in a first generation of EVOLIUM™ BTS....................................8

3. ARCHITECTURE PRINCIPLES :....................................................................................8

3.1 TRX classes concept............................................................................................8

3.2 2 incoming A-bis links per BTS............................................................................10

3.3 Dimensioning rules..............................................................................................11

3.3.1 EDGE/GPRS Capacity in the EVOLIUM™ BTS......................................11

3.3.2 EDGE/GPRS Capacity in the EVOLIUM™ BSC :....................................11

3.3.3 EDGE/GPRS Capacity in the EVOLIUM™ MFS/GPU.............................12

4. EDGE RADIO FEATURES...........................................................................................12

4.1 Modulation and Coding schemes.........................................................................12

4.2 Link adaptation (LA)............................................................................................13

4.3 Incremental Redundancy (IR)..............................................................................14

4.4 The EDGE Family Concept.................................................................................14

4.5 Maximum RLC window size supported by Alcatel BSS........................................15

5. CS-3 / CS-4 RADIO FEATURES.................................................................................15

5.1 Coding schemes.................................................................................................15

5.2 Coding scheme adaptation..................................................................................15

5.3 Activation of high GPRS coding schemes............................................................15

6. RESOURCE MANAGEMENT.......................................................................................17

6.1 Principles of resource management....................................................................17

6.1.1 Ranking of TRX for Circuit / packet allocation..........................................17

6.1.2 Ranking of TRX in mixed BTS configurations..........................................17

6.1.3 Support of EDGE on the BCCH TRX......................................................18

6.2 Dynamic allocation of radio resource...................................................................19

6.3 A-ter resource management................................................................................21

7. GPRS/EDGE FREQUENCY PLANNING......................................................................22

8. MAIN O&M PARAMETERS..........................................................................................22

8.1 EDGE parameters..............................................................................................23

8.2 GPRS CS-3/CS-4 parameters.............................................................................23

9. ANNEXES : QUESTIONS & ANSWERS.......................................................................25




9.1 Why is A-bis not dynamic ?.................................................................................25

9.2 Why are there limitations in multiplexing EDGE & GPRS TBF on the same

PDCH ?..............................................................................................................26

9.3 Access procedures : how does an EDGE MS perform an access ?.....................28




1. INTRODUCTION

This document deals with the support of EDGE and the highest coding schemes CS-3 and CS-4 of

GPRS in Alcatel BSS B8.

The scope of the present document is hereafter detailed:

Section 2 deals with the Hardware support of both features

In section 3, architecture principles are presented .

Section 4 describes EDGE radio features.

Section 5 focuses on GPRS CS-3 & CS-4 radio features.

In section 6, Radio Resource Management algorithms are described.

2. HARDWARE SUPPORT

The Alcatel EDGE / GPRS (all coding schemes) solution is very interesting as it minimises the initial

investment. Indeed, its introduction in a GPRS network does not require any new network element.

As a consequence, the existing GPRS network is widely prepared for EDGE/GPRS CS-3&CS-4 on

the hardware part as these features are fully compatible with:

- The A9135 MFS product (PCU function), deployed for GPRS purpose since the B6.2 release,

- The A9120 BSC.

- On the BTS side, EDGE is supported on all A9100 EVOLIUM™ BTS, shipped since 1998,

and the A9110 micro-BTS Evolution.

In addition all TRXs shipped since 2001 in the EVOLIUM™ BTS (EVOLIUM™ Evolution step 2

TRX2) are EDGE compatible. No specific TRX is needed with the Alcatel solution.

2 EVOLIUM™ Evolution step 2 TRX are usually called TRA, while first generation EVOLIUM™ TRX are called

TRE.




In networks equipped with first generation of EVOLIUM™ BTS, the support of EDGE is achieved by

simple plug & play of the EDGE TRX in the cabinet, one TRX per sector being sufficient to provide

EDGE service.

GPRS Coding Schemes CS-3 & CS-4 are supported by all A9100 EVOLIUM™ BTSs (by all

generations of TRX), by the A9110 micro BTS and by the A9110 micro-BTS Evolution.

2.1 Radio equipment performances

The GPRS/ EDGE features are supported in all GSM bands: 900, 1800, 850 and 1900 MHz.

GSM and GPRS make use of the same GMSK modulation. EDGE makes uses of both GMSK and

8-PSK modulation.

Therefore the output power of EDGE TRX is expressed for both modulations.

2.1.1 EVOLIUM™ A9100 Base Station :

The radio performances of the EVOLIUM™ A9100 Base Station are detailed in 3DC 21083 0001

TQZZA EVOLIUM™ A9100 Base Station Product Description and are recalled hereafter :

TX power of EVOLIUM™ Evolution step 2 TRX :

Frequency band TX output power, GMSK TX output power, 8-PSK (EDGE)

GSM 850 45 W = 46.5 dBm 15 W = 41.8 dBm

GSM 900 MP 45 W = 46.5 dBm 15 W = 41.8 dBm

GSM 900 HP 60 W = 47.8 dBm 25 W = 44.0 dBm

GSM 1800 MP 35 W = 45.4 dBm 12 W = 40.8 dBm

GSM 1800 HP 60 W = 47.8 dBm 25 W = 44.0 dBm

GSM 1900 45 W = 46.5 dBm 25 W = 44.0 dBm

TX power of EVOLIUM™ Evolution TRX (first generation):

Frequency band TX output power, GMSK

GSM 900 35 W = 45.4 dBm

GSM 1800 35 W = 45.4 dBm

In GSM 900 and 1800, two types of TRX support EDGE and GPRS: the Medium Power (MP) TRX

and High Power (HP) TRX. It is up to the Operator to select the TRX type, depending on the

environment and required radio data throughputs.




Why is there a difference between GMSK and 8-PSK output power ?

8-PSK modulation brings severe constraints on linearity because of its non-constant modulation

envelope: Power amplifiers can not be used at their maximum power, unlike with GMSK modulation.

This results in a difference between maximum output power for GMSK and 8-PSK modulations,

called back-off or sometimes APD (Average Power Decrease). The impact of the back-off is

relatively small, and only determines the extent of the 8-PSK coverage ,which depends on the radio

environment as well . In urban areas the impact is smaller than in rural environment.

RX sensitivity of TRX :

The RX sensitivity of the TRX allows the delivery at antenna connector of the following values

independently from the frequency band.

Reference sensitivity, GMSK : - 111 dBm (static and dynamic)

Reference sensitivity, 8-PSK (EDGE):< -111 dBm, (static, MCS-1)-108 dBm, (static, MCS-5)-99 dBm, (static, MCS-9)

Why is there a difference in sensitivity between various MCS ?

3GPP standard (Rec. 05.05) defines various sensitivity levels for various MCS. These different

sensitivities simply mean that high throughputs (high MCS) require better radio conditions (higher

signal to noise ratio) than lower data throughputs. The noise factor in the BTS is kept unchanged,

whatever the coding scheme.




2.1.2 EVOLIUM™ A9110 micro-BTS :

A9110 micro-BTS Evolution :

The radio performances of the EVOLIUM™ A9110-E Micro-BTS are detailed in 3DC 21083 0003

TQZZA Ed. 07 EVOLIUM™ A9110 Micro-BTS Product Description and are recalled hereafter :

Frequency bandNb of antennas

TX output power, GMSK TX output power, 8-PSK (EDGE)

GSM 850 & 900

1 antenna

3.2 W = 35.1 dBm 2.3 W = 33.6 dBm

GSM 1800 & 1900

1 antenna

3.2 W = 35.1 dBm 1.8 W = 32.6 dBm

GSM 850 & 900

2 antennas

7.0 W = 38.5 dBm 5.0 W = 37.0 dBm

GSM 1800 & 1900

2 antennas

7.0 W = 38.5 dBm 4.0 W = 36.0 dBm

Reference sensitivity, GMSK : - 110 dBm (static and dynamic)

Reference sensitivity, 8-PSK (EDGE):< -110 dBm, (static, MCS-1)-1068 dBm, (static, MCS-5)-96 dBm, (static, MCS-9)

A9110 micro-BTS :

TX output power : GMSK : 2 W or 33 dBm

In low Loss configuration, GMSK : 4.5 W or 36.5 dBm

The sensitivity of A9110 BTSs (at the BTS antenna connector) is -107 dBm.




2.2 Support of EDGE in a first generation of EVOLIUM™ BTS

The Operator simply has to plug as many EDGE TRX (TRA) as EDGE traffic requires.

EDGE TRX (TRA) may provide with a higher GMSK output power than TRE (indeed, a TRE 900

offers 35W while a Medium Power TRA offers 45W)

In case of mixed TRA / TRE configuration, GMSK output power of the EDGE TRX is

automatically aligned to the power of the TRE of the cell, while the 8-PSK output power is

kept untouched.

As a consequence, in a GSM 900 BTS made of a mix of TRE and TRA, the power per TRX will be:

GMSK 8-PSK

High Power TRA : 60 W 35 W 25W

Medium Power TRA : 45 W 35 W 15 W

3. ARCHITECTURE PRINCIPLES :

With the introduction of EDGE or GPRS CS-3/CS-4, a new technical issue appears: the throughput

on the air interface becomes too big and the data traffic corresponding to one radio timeslot cannot

anymore be transported over one single 16kb/s nibble on the terrestrial (A-bis or A-ter) interface, as

it was the case with voice or low data rates; it thus becomes mandatory to use higher bandwidth on

A-bis and A-ter.

The Alcatel solution consists in using several 16kb/s nibbles on A-bis and A-ter interfaces for the

transport of one radio timeslot supporting EDGE or GPRS CS-3 / CS-4.

3.1 TRX classes concept

To support these high data throughputs, Alcatel has developed a solution, which aims at providing

the best trade-off between offered radio throughput and impact on the telecom resource

consumption.

This solution is based on the concept of multiple classes of TRX, which support more or less data

throughput. The higher the packet class, the higher the maximum data throughput, the higher the

impact on BSS Telecom resources.




Five TRX classes have been defined :

TRX class Supported packet coding scheme

Class 1“Simple” TRX

CS 1,2MCS 1,2

Class 2“Double” TRX

CS 1,2,3,4MCS 1,2,3,4,5,

Class 3“Triple” TRX

CS 1,2,3,4MCS 1,2,3,4,5,6,

Class 4“Quad” TRX

CS 1,2,3,4MCS 1,2,3,4,5,6,7,8

Class 5“Quintuple” TRX

CS 1,2,3,4MCS 1,2,3,4,5,6,7,8,9

All TRX, whatever their class, support also voice traffic.

The Operator defines per cell the number of TRXs of each class. A class 3 TRX offers up to 30 kb/s

per radio timeslot, while a class 1 offers up to 11 kb/s. As a consequence, a class 3 TRX consumes

on the A-bis interface three times more than a class 1 TRX.

The following figures illustrate the example of a cell with one Class 3 TRX and two Simple TRX - the

triple TRX is transported over 6 64 kbps timeslots on A-bis.

1 PDCH = 3 terrestrial nibbles = 1 “main nibble”, also used for voice

+ 2 additional nibbles, only used for packet

Radio

TRX1

TRX2

TRX3

B S

Cell

RSL

TRX1

TRX2

TRX3

Abis

3 nibbles

EDGE TRX (triple)

Main nibbles:voice &packet

additional nibbles:packetonly

The distribution of the TRX classes is a choice let to the Operator according to the expected data

traffic, the radio conditions and the requested data throughput:




For example in a rural environment with large cells, the proportion of mobiles which could get benefit

from the highest Modulation & Coding Schemes is quite low, and the mean data throughput with a

class 3 TRX is almost as high as the one obtained with a class 5 TRX.

3.2 2 incoming A-bis links per BTS

The EVOLIUM™ BTS can support up to 12 TRX. For such large configuration, and when filled with

simple TRXs, a single PCM (2Mb/s E1 link) is already almost full. To support EDGE in such large

BTS, The EVOLIUM™ BTS is able to transport data on a second E1 link.

The following table provides non exhaustive examples of the supported configurations, with one or

two E1 links:

BTS configuration One A-bis link per BTS

Possible distribution of TRX

per cell

Two A-bis links per BTS

Possible distribution of TRX

per cell

BTS 12 TRX

3 cells @ 4 TRX

4 simple TRX 1 class 5 + 1 double TRX + 2 simple TRX

or

1 triple + 3 double TRX

or

1 triple TRX+ 1 quad TRX +2 simple TRX

BTS 9TRX

3 cells @ 3 TRX

1 double + 2 simple TRX

2 quad TRX + 1 simple TRX

or

3 triple TRX

BTS 6TRX

3 cells @ 2 TRX

1 triple + 1 simple TRX

2 quad TRX

BTS 3 TRX

3 cells @ 1 TRX

1 class 5 TRX

The second incoming A-bis link of a BTS is used for packet traffic only. The first link is used for both

packet and circuit.

A parameter MAX_EXTRA_TS_PRIMARY defines the number of additional A-bis timeslots

dedicated to packet on the primary link. This allows the Operator keeping some free timeslots on the

primary link, for example in anticipation of a further TRX extension of the BTS.




The following figure depicts examples of A-bis topology. Primary link is directly connected from BSC

to BTS. Secondary link may terminate a daisy chain.

BSC

BTS

EVOLIUMBTS

Primary Abis

Secondary Abis

Primary Abis

Secondary Abis

EVOLIUMBTS

BTS

Examples of A-bis topology –

Note: There is no constraint about the position of the primary and secondary links in the BSC. They

may be connected to different A-Bis TSUs, and even different BSC racks.

The support of a second incoming A-bis link requires a SUMA (EVOLIUM™ Evolution step 1 board).

For the older Alcatel BTS generations, the replacement of SUMP by SUMA is necessary.

In case of very high packet traffic, the Operator can use the “cell split over two BTS” feature.

Thanks to this feature a cell can be splitted between 2 BTS which can be equipped with two A-bis

links each, delivering in total 4 A-bis links.

3.3 Dimensioning rules

3.3.1 EDGE/GPRS Capacity in the EVOLIUM™ BTS

All TRXs of a BTS may support GPRS/EDGE.

3.3.2 EDGE/GPRS Capacity in the EVOLIUM™ BSC :

The global BSC capacity remains unchanged with the introduction of EDGE or GPRS CS-3/CS-4.

As an example, a BSC configuration 6, is able to handle 3584 (448 * 8) channels @ 16 kb/s,

whatever the type of traffic conveyed: voice, GPRS or EDGE.

In terms of number of TRX, the support of “one class N” TRX consumes in the BSC the equivalent

of the connectivity consumed by N simple Full Rate TRXs.




This is similar to the management of Dual Rate TRXs, where one DR TRX is equivalent to 2 FR

TRX.

In the same way, for high data traffic, we will have :

1 class 2 TRX ~ 2 FR TRX,

1 class 3 TRX ~ 3 FR TRX

1 class 4 TRX ~ 4 FR TRX

1 class 5 TRX ~ 5 FR TRX.

It has to be noted that Dual Rate can be also supported on a class N TRX ; the support of “one dual

rate class N” TRX consumes in the BSC the equivalent of the connectivity consumed by (N+1)

simple Full Rate TRXs.

3.3.3 EDGE/GPRS Capacity in the EVOLIUM™ MFS/GPU

The GPU is able to handle both GPRS and EDGE traffic.

The maximum number of simultaneously active PDCH obviously depends on the type of the PDCH,

as an EDGE MCS-9 PDCH transports much more data than a GPRS CS-2 PDCH.

The number of GPU to address the packet traffic can be increased up to 6 GPU per BSS.

More information about Dimensioning Rules can be obtained in “Dimensioning Rules for CS and PS

traffic with BSS Software Release B8” .

4. EDGE RADIO FEATURES

4.1 Modulation and Coding schemes

Nine Modulation and Coding Schemes have been defined by the Standard for E-GPRS.

Their modulation (either GMSK or 8-PSK) as well as their data throughput, per radio timeslot, are

depicted in the table below.




System Scheme Modulation

schemes

Maximum data rate

per time slot (RLC payload)

[kbps]

EGPRS MCS-9 8PSK 59.2

MCS-8 8PSK 54.4

MCS-7 8PSK 44.8

MCS-6 8PSK 29.6

MCS-5 8PSK 22.4

MCS-4 GMSK 17.6

MCS-3 GMSK 14.8

MCS-2 GMSK 11.2

MCS-1 GMSK 8.8

All EDGE Modulation and Coding schemes (MCS) from MCS1 up to MCS 9 are supported by the

EVOLIUM™ BSS in the downlink.

Standardisation bodies have defined two classes of EDGE MS: a class 1 MS supports 8-PSK MCSs

in downlink only, while a class 2 MS supports 8-PSK MCSs in both directions. Alcatel BSS supports

both classes of MS, and provides them with MCS1 up to MCS-4 in uplink.

4.2 Link adaptation (LA)

The selection of the most suitable MCS (Link Adaptation) is based on measurements reported by

the MS for the downlink path and performed by the BTS for the uplink path. New metrics have been

introduced with EDGE : «MEAN_BEP » and « CV_BEP » variables, which represent respectively

the mean quality of the channel (BEP stands for Bit Error Probability) and its variance. These

variables are defined in 3GPP Recommendation 05.08.

The choice of the MCS is based on these two variables. Simulations have been run in order to fill

look-up tables which define the optimal MCS as a function of (MEAN_BEP; CV_BEP). Several

tables have been defined, as this function depends on the activation of the feature “incremental

redundancy”, on the current modulation, and on the APD (average power decrease, difference

between 8-PSK and GMSK output power).




4.3 Incremental Redundancy (IR)

In addition to Link Adaptation, the feature Incremental Redundancy3 is introduced for EGPRS. This

function was specified by ETSI as optional for base stations and mandatory for mobiles. The Alcatel

BSS implementation makes use of this feature.

If a block transmitted by the BTS is not properly decoded in the first instance, the bits are stored in

the mobile, as “soft bits”. The same block is repeated with a different puncturing scheme. The

resulting soft bits of the second (and, if necessary, third) transmission are then combined with the

previously transmitted block(s). The decoding is then based on several transmissions and not only

one: this is called joint decoding. This improves the likelihood of ending up with the correct data.

Even if one block of data is found to be not good, it still can be used to improve the total bit error

rate of the system.

In B8 Release, Incremental Redundancy is supported in downlink.

Thanks to Incremental Redundancy, the link adaptation procedure can be more aggressive : if the

chosen MCS is a bit too optimistic, the general quality will not be affected, as Incremental

Redundancy will correct it thanks to joint decoding. However it would be quite dangerous to rely on

Incremental redundancy only since there may be memory shortage in the MS, and the TBF would

then be lost. If the MS indicates that IR operation shall be stopped, the Alcatel BSS will switch to a

mode where IR is not used, which is referred to as type 1 ARQ.

For optimal radio performances, the Alcatel BSS combines both Incremental Redundancy and Link

Adaptation.

4.4 The EDGE Family Concept

In EDGE the family concept allows to change the modulation and coding scheme within a given

family during re-transmission. The re-transmission of a block may be done with the same MCS as

used for the first transmission or with a different more robust MCS.

The Alcatel equipment is fully compliant with this feature.

There are 3 families of modulation and coding schemes:

- family A: MCS-3, MCS-6, MCS-8 and MCS-9

- family B: MCS-2, MCS-5 and MCS-7

- family C: MCS-1 and MCS-4

3 Incremental Redundancy is also referred to as type 2 ARQ (Automatic Repeat Request) mechanism.




4.5 Maximum RLC window size supported by Alcatel BSS

Contrary to GPRS, where the maximum RLC window size has a fixed value equal to 64, the EDGE

maximum window size depends on the multislot characteristic of the TBF. The maximum window

size implemented in Alcatel BSS is 512, which is the maximum supported by a 4 timeslots capable

MS, as defined in 3GPP 04.60.

5. CS-3 / CS-4 RADIO FEATURES

5.1 Coding schemes

Four Modulation and Coding Schemes have been defined by the Standard for GPRS.

Their data throughput, per radio timeslot, is depicted in the table below.

System Scheme Maximum data rate

per time slot (RLC payload)

[kbps]

GPRS CS-4 20

CS-3 14.4

CS-2 12

CS-1 8

5.2 Coding scheme adaptation

A new mechanism is introduced for coding scheme adaptation between CS-3 and CS-4 on the

downlink path.

Actually this new mechanism is mandatory, as RXQUAL may be not relevant in CS-4 (3GPP

recommendations allow the MS to report systematically a value of 7).

A new metric is therefore used : it is an estimation of SIR (Signal to Interference Ratio), based on

measurements reported by the Mobiles . These measurements, called I_level (level of interference),

are defined in Rec. 05.08. It may happen that I_level is not transmitted by the MS to the BSS ( in

case of usage of BCCH frequency). In this case, the BSS performs an estimation of the Block Error

Rate (BLER).

This metric (SIR or possibly BLER) is used for CS-4 to CS-3 adaptation.




The adaptation from CS-3 to CS-4 makes usage of both RXQUAL and I_level (resp. BLER).

RXQUAL is used for coding scheme adaptation between CS-2 and CS-3.

In the uplink path, RXQUAL is always used for coding scheme adaptation.

5.3 Activation of high GPRS coding schemes

The Operator may define, for each cell, the maximum GPRS coding scheme allowed in this cell,

through an O&M parameter MAX_GPRS_CS. This parameter can take the values CS-2, CS-3 or

CS-4.

Indeed, the choice of the Operator will be determined by the radio conditions in the cell and the

maximum expected throughput.

As CS-4 is not recommended in case of frequency hopping, the choice of CS-3 in a cell where

EDGE and frequency hopping are activated bring high GPRS data throughput at no additional cost.




6. RESOURCE MANAGEMENT

6.1 Principles of resource management

6.1.1 Ranking of TRX for Circuit / packet allocation

In Radio Resource Management, the first principle is to avoid conflicts between Circuit and Packet :

TRX with the highest priority for circuit have the lowest priority for packet, and reciprocally. This

maximizes the chance of having a contiguous set of timeslots available for packet-switched traffic

while ensuring also that PS traffic is taking the most benefit from the high TRX classes.

The Operator may use the parameter TPM (TRX Preference Mark) to define his preference about

Circuit allocation.

A TRX with a non null TPM is reserved for circuit. The higher the value of TPM, the higher the

priority for circuit.

TRXs with TPM equal to 0 may be used for both packet and circuit. They have the lowest priority for

circuit.

A specific flag concerning the BCCH TRX has been added “PS_PREF_BCCH_TRX” which allows to

direct packet preferably on the BCCH TRX.

On TRXs where packet is allowed, TRXs are ranked depending on their class : packet is preferably

allocated on a high class TRX.

For equivalent TPM and classes, Circuit is allocated first on TRX with high identity, while packet is

allocated first on TRX with low identity.

Example :

TRX identity TPM

O&M parameter

TRX class Voice allocation ranking

Packet allocation ranking

1 3 1 1 X

2 2 1 3 X

3 2 1 2 X

4 0 4 6 1

5 0 1 5 2

6 0 1 4 3




6.1.2 Ranking of TRX in mixed BTS configurations

It may happen that a cell is made of several TRX equipment with different 8-PSK capabilities.

For example, in a BTS EVOLIUM™, there may be a mix of :

- EVOLIUM™ TRX (usually called TRE), supporting all GPRS coding schemes but no EDGE,

- EVOLIUM™ Evolution step 2 TRX (TRA) with Medium Power

- EVOLIUM™ Evolution step 2 TRX (TRA) with High Power.

There is an automatic mapping of logical TRX on TRX equipment. The highest class TRX are

mapped on the highest EDGE capability TRX equipment.

On the opposite, dual rate is mapped on TRX equipment with lower packet capability.

The following figure depicts in an example the mapping between hardware and software, leading to

the best EDGE/GPRS throughput:

TRE

TRE

TRA

MP

TRA

HP

Hardware configuration

Logical cell

TRX1 (BCCH)

TRX2 (1 SDCCH)

TRX3

TRX4

Packet VoiceAllocation

Example : One 4TRX cell, made of 2 TRE, one TRA Medium Power and one TRA High Power




6.1.3 Support of EDGE on the BCCH TRX

Support of EDGE on the BCCH TRX is possible. However the activation of EDGE on the BCCH

TRX should be performed cautiously. 3GPP Rec. 05.08 has defined a constraint on the transmitted

power of BCCH frequency. This frequency shall usually be transmitted at a constant level. A

tolerance has been introduced with 8-PSK modulation : a fluctuation of up to 2 dB is allowed.

Depending on the configuration in the BTS, it may happen that the difference between GMSK and 8-

PSK power on the BCCH TRX is greater than 2dB. In this case, the Operator is informed that the

back-off is high, and that EDGE should not be activated on the BCCH TRX.

6.2 Dynamic allocation of radio resource

The principles which are applied since the introduction of GPRS in Release B6 are kept for EDGE

(“capacity on demand”). They use the allocation of dynamic pools for circuit and for packet,

depending on the traffic conditions in the cell.

Inside the packet pool, new mechanisms are introduced for the management of GPRS/EDGE traffic.

The main principles are the following :

There are no dedicated (reserved) resource for EDGE traffic: this would be difficult to be tuned by

the Operator, as the penetration of EDGE handsets will increase progressively.

Both GPRS and EDGE traffic are directed to the highest class TRX,

When GPRS and EDGE MS are mixed on the same timeslots, the GPRS traffic is “pushed” towards

timeslots without EDGE, to allow a maximum EDGE traffic availability.

More details on GPRS and EDGE Resource management :

The packet resource management algorithm aims at maximising data throughputs, both for EDGE

and GPRS. Therefore the allocation is performed first on the highest class TRX.

Hereafter are detailed mechanisms which are triggered, when the most suitable timeslots (on the

highest class TRX) are already busy. They depend on the type of the new TBF (EDGE or GPRS)

and on the type of the already allocated TBF :

Already allocated : GPRS or EDGE TBF; new demand : GPRS TBF

As in previous BSS Releases, this GPRS TBF is allocated on other PDCH, as long as packet

resources are available. Otherwise the new GPRS TBF shares PDCH with previously allocated

TBF, until the maximum number of piled TBF is reached.




Already allocated : GPRS TBF, new demand : EDGE TBF

The EDGE TBF is allocated in the same way as if the GPRS TBF was not present. The GPRS TBF

becomes a candidate for reallocation, and is pushed through this reallocation towards other radio

timeslots. This is performed through a new reallocation process, which is triggered for a GPRS UL

when it shares at least one PDCH with a downlink EDGE TBF. Before the re-allocation is

performed, the EDGE TBF is limited to GMSK modulation (see the annex for more details about the

limitations in multiplexing EDGE and GPRS on the same timeslot).

Already allocated : EDGE TBF, new demand : EDGE TBF

In order to take into account the various throughputs offered by the different EDGE capable TRXs,

specific conditions are defined for TRX selection in case of a new EDGE TBF establishment.

Consequently, as long as the TRXs with the highest throughput do not support a maximum number

of EDGE TBF, the other EDGE capable TRXs (of lower class) are not chosen for EDGE allocation.

As a summary, it is preferred to pile several EDGE TBF on the same high class TRX, rather than

spreading them over TRX of lower class.

Parameters have been defined which indicate for each TRX class the number of TBFs beyond

which it becomes more interesting to serve new EDGE MS on TRX with a lower EGPRS capability.

As an example, in a cell with a class 5 TRX and a class 2 TRX, two EDGE TBF will be piled upon

the class 5 TRX before allocating an EDGE TBF on the class 2 TRX.

TBF Re-allocation

The mechanisms for re-allocation defined in Alcatel B7 Release for GPRS MS apply also for EDGE

and GPRS TBF in B8.

There were three types of re-allocation :

The immediate resource re-allocation upon packet resources decrease (due to load increase in the

cell),

The immediate resource re-allocation upon concurrent TBF establishment,

The re-allocation of the TBF which is allocated less timeslots than its multislot capability.

In addition, an EDGE TBF may be re-allocated if it is not established on the highest class TRX .

This criteria applies for EDGE MS only.




A GPRS TBF will be re-allocated if it shares timeslots with EDGE, as mentioned in the previous

paragraph.

It has to be noted that a re-allocation can not change the type of the TBF, as this has not been

standardised : an EDGE TBF can only be re-allocated as an EDGE TBF, while a GPRS TBF is re-

allocated as a GPRS TBF.

Maximum number of timeslots allocated to an EDGE or GPRS MS :

A mobile may have different multislot classes for EDGE and for GPRS. The Alcatel BSS makes use

of the EDGE multislot class, for allocating an EDGE TBF.

There is no difference between GPRS and EDGE in the maximum number of timeslots which can

be allocated.

The Alcatel BSS supports the dynamic allocation MAC mode.

The BSS always tries to allocate the maximum number of timeslots to one MS. The theoretical

maximum number of consecutive timeslots that can be allocated to a MS by the BSS depends on

whether the MS is half-duplex or full-duplex :

full-duplex MS will be allocated up to 5 timeslots for uplink and 5 timeslots for downlink,

half-duplex MS will be allocated up to 4 timeslots in the downlink path and 2 timeslots in the uplink

path for TX.

Maximum number of MS which can share a radio timeslot :

There is no difference between GPRS and EDGE in number of MS which can share a PDCH.

Up to 6 TBF on the uplink and 10 TBF on the downlink can be allocated.

The Operator may reduce the maximum number of TBF in each direction through O&M parameters

(MAX_UL_TBF_SPDCH & MAX_DL_TBF_SPDCH).

6.3 A-ter resource management

As in B7 Release, GCH are allocated dynamically on the A-ter interface. A PDCH allocated on a

class N TRX uses N GCH on the A-ter interface. This is valid whatever the TBF allocated on this

PDCH (EDGE or GPRS).

It may happen that the system encounters A-ter congestion. These situations are managed through

a new A-ter Congestion Control mechanism.




The system enters A-ter congestion state when the number of free GCH on the A-ter interface

becomes lower than a pre-defined threshold.

In this situation, the number of GCH allocated to PDCH carrying only GPRS is reduced. This is valid

for new GPRS establishment and also for on-going GPRS TBF.




7. GPRS/EDGE FREQUENCY PLANNING

A full flexibility is offered to the Operator for frequency planning, and packet may be activated on:

- Non hopping TRX,

- Baseband hopping TRX,

- Synthesised radio hopping TRX.

Whatever the type of frequency hopping, the support of EDGE can be effective by just plugging one

EDGE capable TRX in the cell.

Therefore it will be possible for the Operator to introduce EDGE without changing its current

frequency planning.

There is a specific issue regarding the support of CS-4, which is not recommended on TRX with

frequency hopping.

Therefore Alcatel has introduced in BSS Release B8 the support of several non-hopping TRX in a

hopping cell. These TRX may be allocated the highest priority for packet allocation, and provide with

up to 8 timeslots at the same radio frequency.

These non-hopping TRX may benefit from a specific radio planning, in order to ensure higher C/I

conditions and offer better throughputs, both for GPRS and EDGE.

If all TRX of the cell are hopping, it is recommended to set MAX_GPRS_CS = CS-2 or CS-3.

8. MAIN O&M PARAMETERS

TRX_Pref_Mark this parameter relates to a TRX. A null value indicates that packet is

allowed on the TRX. A value between 1 and 7 indicates that packet is not allowed and provides with

the priority of circuit allocation (highest value means highest priority)

PS_PREF_BCCH_TRX this flag at cell level indicates whether the Operator wishes to allocate

packet on the BCCH TRX with highest priority

MAX_EXTRA_TS_PRIMARY This is the maximum number of extra A-bis timeslots the system

is allowed to allocate on the primary A-bis of a BTS (makes sense if a second A-bis link is used for

the transport of packet timeslots).




8.1 EDGE parameters

En_EGPRS this flag enables/disables EDGE on a per cell basis

En_IR this flag, at BSS level, enables/disables the activation of Incremental

redundancy feature

Max_EGPRS_MCS this parameter indicates the highest usable MCS (from MCS-1 up to MCS-

9), which is allowed in a cell

TBF_DL_Init_MCS this parameter indicates the initial MCS to be used at the establishment of

a Downlink EDGE TBF in the cell

TBF_UL_Init_MCS this parameter indicates the initial MCS to be used at the establishment of

an Uplink EDGE TBF in the cell

8.2 GPRS CS-3/CS-4 parameters

MAX_GPRS_CS this parameter, at cell level, indicates the maximum coding scheme

to be used in the cell . it can take the values CS-2, CS-3 or CS-4.

CS_QUAL_DL_2_3_FH_ACK this parameter, at BSS level, indicates the threshold on RXQUAL

used in the radio link supervision to change the TBF coding scheme from CS-2 to CS-3 in downlink

in RLC acknowledged mode, on a TRX where Frequency hopping is activated.

CS_QUAL_DL_3_4_FH_ACK threshold used in the radio link supervision to change the TBF

coding scheme from CS-3 to CS-4 in downlink in RLC acknowledged mode, on a TRX where

Frequency hopping is activated.

CS_SIR_DL_3_4_FH_ACK threshold used in the radio link supervision to change the TBF

coding scheme from CS-3 to CS-4 in downlink in RLC acknowledged mode, on a TRX where

Frequency hopping is activated.

CS_SIR_HST_DL Signal to Interference Ratio hysteresis used in the link adaptation

algorithms to change the Coding Scheme from CS-4 to CS-3 in the downlink direction.

In the same way, there are all parameters for coding scheme adaptation, based on RXQUAL or SIR,

for frequency hopping and non hopping cases, for acknowledged and non acknowledged RLC

mode, in uplink and downlink, between CS-2 and CS-3, and CS-3 and CS-4.Hereafter is the list

related to downlink:

CS_QUAL_DL_2_3_FH_NACK

CS_QUAL_DL_3_4_FH_NACK




CS_SIR_DL_3_4_FH_NACK

CS_QUAL_DL_2_3_NFH_ACK

CS_QUAL_DL_3_4_NFH_ACK

CS_SIR_DL_3_4__NFH_ACK

CS_QUAL_DL_2_3_NFH_NACK

CS_QUAL_DL_3_4_NFH_NACK

CS_SIR_DL_3_4__NFH_NACK




9. ANNEXES : QUESTIONS & ANSWERS

9.1 Why is A-bis not dynamic ?

The principle of Dynamic Resource allocation of a terrestrial interface is to under-dimension this

interface, in order to take benefit of the fact that not all radio resources are busy at the same time.

As an example, there is usually dynamic allocation of voice traffic on the A-ter interface, as the

probability to have all radio channels of all cells of a BSS busy at the same time is quite low . The

benefit of this dynamic allocation is the ability to gain a ratio of circa 0.8 between radio interface and

A-ter links, the probability of blocking due to the A-ter interface is then 0.1%.

On the A-bis interface, it is more difficult to expect a significant gain of dynamic implementation, as

the number of resources which can be shared is quite small (31 channels on an E1 link). Dynamic

implementation requires quite a “large number” of common resources to become efficient, and take

benefit from a “statistical effect”. This is not the case with A-bis interface.

If the A-bis interface is under-dimensioned, there will be too many conflicts to be solved between

various packet demands : either only first demands are served, and the following demands are

rejected, or a low grade of service is granted to all demands.

To increase even more the number of resources to be shared, dynamic A-bis could also be

imagined for voice demands, but it is quite unlikely that Operators would appreciate a degradation of

grade of service for voice calls, due to A-bis blocking.

Moreover, dynamic A-bis can hardly reduce the number of required A-bis links :

Let’s consider the case of an EVOLIUM™ BTS, with 12 TRX ( 3 cells @4TRX each).

Each TRX requires 2 64 kbps timeslots for normal voice support. This BTS requires 2*12 =24

channels for voice support. 3 channels for signaling have to be added.

As a consequence, on the E1 link, only 31 – (24 +3) = 4 timeslots are left free.

If these 4 timeslots are considered as a global pool for packet, they may be used for supporting any

EDGE TBF. A mobile using MCS-9 and having a multislot capability of 4 requires will occupy all the

timeslots of the pool. As a consequence, there is no EDGE service available in the other cells.

Whatever the chosen solution, a second E1 link to this BTS is mandatory for supporting EDGE.

On the contrary, in a small BTS, a single E1 link is sufficient for supporting EDGE data traffic,

whatever A-bis mapping, static or dynamic.




As a conclusion, Dynamic A-bis in most cases does not reduce the number of E1links to be

connected to the BTS ; it brings conflicts between various demands and degrades quality of service.

Therefore Alcatel decided not to implement dynamic A-bis in the support of EDGE, in order to have

data rate determined by radio conditions, and not by the actual traffic load in the BTS.

9.2 Why are there limitations in multiplexing EDGE & GPRS TBF on the same PDCH ?

The issue :

There are technical issues, identified by the 3GPP Standard, for mixing EDGE and GPRS Mobiles

on the same timeslots, as soon as there is EDGE traffic on the Downlink and GPRS traffic on the

Uplink path.

In packet mode, a mobile permanently listens to downlink blocks in order to know whether it is

allowed to transmit on the uplink path : the BSS transmits in each block an USF (Uplink State Flag),

which indicates which mobile will transmit on the uplink path. A GPRS mobile can not decode 8-PSK

modulation, therefore its USF has to be transmitted over the GMSK modulation, even if it is part of

an EDGE block : this potentially reduces the throughput of an EDGE MS, on the downlink path.

Potential solutions :

3GPP standards have proposed a solution for mitigating the throughput loss that might be

experienced by EGPRS users. This is known as “USF granularity 4”. See the explanations in section

“Technical details”.

However this solution does not allow an EDGE MS multiplexed with a GPRS MS to experience

100% of 8-PSK modulation. The EDGE TBF is still limited to GMSK modulation for ~25% of its

transmission.

Moreover this feature “USF granularity4” has not been tested extensively on all GPRS MS, as it was

not implemented in BSS. There is therefore a risk with some GPRS mobiles, that they do not

support properly this feature.

Alcatel choice :

Alcatel has decided to keep the well proven “USF granularity 1”, and has implemented a mechanism

for separating EDGE and GPRS MS, in order to allow 8-PSK modulation for EDGE MS 100% of

their time. When GPRS and EDGE MS are multiplexed, a re-allocation for GPRS MS is triggered

which “pushes” GPRS TBF out of the PDCH allocated to EDGE MS. This solution brings the best

possible throughput to EDGE MS.




Technical details :

In dynamic USF MAC mode, an uplink state flag (USF) is appended to each downlink radio block to

identify the active TBF that will be allowed to send data in uplink during the next radio block period.

Consequently, a MS performing an uplink packet communication monitors the USF on every

downlink radio block on all the PDCHs it has been assigned at call set-up. When it recognises its

previously assigned USF during radio block period DBN=N (Downlink Block Number), it can transmit

during radio block period UBN=N+1 (Uplink Block Number).

Radio blocks which carry an USF for an uplink GPRS TBF have to be GMSK modulated, while radio

blocks with an USF addressed to an uplink EDGE TBF may be either GMSK or 8-PSK modulated.

Consequently, a throughput loss may occur when GPRS TBFs in uplink and EGPRS TBFs in

downlink are simultaneously active on the same PDCH: some EDGE downlink radio blocks are

forced to be GMSK modulated because they carry an USF intended for an uplink GPRS TBF,

although they could have been 8-PSK modulated.

3GPP standards proposed an alternate solution for mitigating the throughput loss that might be

experienced by EGPRS users. This is known as “USF granularity 4”.

Using this method, once addressed on the DBN=N by its USF, an uplink (GPRS) TBF is allowed to

transmit 4 radio blocks in 4 consecutive uplink radio blocks UBN=N+1, N+2, N+3 and N+4. As a

result, DBN N+1, N+2 and N+3 are no more constrained to be GMSK modulated, as illustrated in

following figure :

G G G

G G G G G G G

DL

UL

DL

UL

GMSK

8-PSK

USF Granularity 1

USF Granularity 4 G GPRS

G G G G

On the first part of the figure, USF granularity 1 is implemented. The blocks of EDGE data in

downlink are GMSK modulated because they carry an USF that is designated to a GPRS mobile.

On the second part of the figure, USF granularity 4 is implemented. Only one block among 4 has to

be GMSK modulated in order that the GPRS MS can transmit four consecutive uplink blocks.




9.3 Access procedures : how does an EDGE MS perform an access ?

The BSS indicates in System Information on the (P)BCCH whether EDGE is supported in the cell

where the MS camps and if yes, whether the EGPRS PACKET CHANNEL REQUEST message is

supported. If the latter is not supported, an EDGE MS in an EDGE-capable cell has to perform a

two-phase access which lengthens the TBF establishment time. The Alcatel BSS always supports

the EGPRS PACKET CHANNEL REQUEST, both on CCCH and PCCCH.

If EDGE is enabled in the cell, the mobile indicates its EDGE capability by using a new training

sequence.

Two new training sequences are defined for indicating EDGE support in the handset :

One training sequence (TS1) is used to indicate 8-PSK capability both in uplink and downlink and

another one (TS2) to indicate 8-PSK capability only in downlink.

The Alcatel BSS supports both training sequences.

This mechanism allows for one phase access EGPRS TBF establishment for mobiles on PCCCH or

on CCCH.

End of Document



Documents

12_edge and Gprs Cs-3 Cs-4 in Release b8