GPRS_RRM_B7

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FUNCTIONAL FEATURE DESCRIPTION

GPRS Radio Resource Management in Release B7

This document covers the following features:

30 10 00 Radio Resource Handling

30 10 xx and subsequent ones

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Contents

1. REFERENCES................................................................................................................................. 3

2. INTRODUCTION ............................................................................................................................. 5

3. ABSTRACT...................................................................................................................................... 6

4. CAPACITY ON DEMAND ................................................................................................................ 7

4.1 Reserved resource for GPRS................................................................................................ 7

4.2 Reserved resource for circuit-switched (CS) ......................................................................... 8

4.3 Dynamic Sharing of CS and GPRS Resources ..................................................................... 9

4.4 Pre-emption Mechanisms due to Cell Highload................................................................... 10

4.4.1 Principles of PDCH Release under High Load Conditions ..................................... 11

4.4.2 Initiating the PDCH Release: Soft Pre-emption ...................................................... 11

4.4.3 Fast PDCH Pre-emption ......................................................................................... 12

5. FAST ADJUSTMENT OF RADIO RESOURCES .......................................................................... 13

5.1 Cell Load evaluation ............................................................................................................ 13

5.2 Dynamic sharing of CS and GPRS resources enhancement .............................................. 14

6. GPRS ON SEVERAL TRX PER CELL .......................................................................................... 16

6.1 Priorities Defined by the Operator........................................................................................ 16

6.2 Allocation of Multislot Calls .................................................................................................. 17

6.2.1 Selection of the Best TRX....................................................................................... 18

6.2.2 Final Selection of the Best Solution ........................................................................ 18

7. RADIO RESOURCE RE-ALLOCATION ........................................................................................ 19

7.1 Immediate resource re-allocation ........................................................................................ 19

7.1.1 Immediate resource re-allocation upon GPRS resources decrease ...................... 19

7.1.2 Immediate resource re-allocation upon concurrent TBF establishment ................. 19

7.2 Later resource re-allocation to increase data throughput .................................................... 20

7.2.1 Evaluation of sub-optimal TBFs.............................................................................. 20

7.2.2 Evaluation of the direction of the bias ..................................................................... 20

7.2.3 Evaluation of candidate MSs .................................................................................. 20

7.2.4 Re-allocation process ............................................................................................. 20

8. FREQUENCY HOPPING MANAGEMENT .................................................................................... 21

8.1 Frequency Information......................................................................................................... 21

8.2 Selection of Hopping Resource ........................................................................................... 22

9. FLEXIBLE SHARING OF TIMESLOT BETWEEN USERS ........................................................... 23

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1. REFERENCES

3GPP 05.02 Multiplexing and Multiple Access on the Radio Path

ABBREVIATIONS

Abis Telecommunication interface between the BTS and BSC

ARFCN Absolute Radio Frequency Channel Number

BCCH Broadcast Control Channel

BSC Base Station Controller

BSS Base Station Subsystem

BTS Base Transceiver Station

CS Circuit-Switched

CS-n GPRS Channel Coding Scheme n (n = 1,… 4)

GPRS General Packet Radio Service

GSL GPRS Signalling Link

GSM Global System for Mobile communications

HSN Hopping Sequence Number

MA Mobile Allocation

MAIO Mobile Allocation Index Offset

MFS Multi-BSS Fast packet Server

MS Mobile Station

O&M Operation and Maintenance

OMC-R Operation and Maintenance Centre : Radio part

PACCH Packet Associated Control Channel

PBCCH Packet Broadcast Control Channel

PCM Pulse Code Modulation (2 Mbit/s physical line)

PDCH Packet Data Channel

TBF Temporary Block Flow (see glossary)

TRX Transceiver

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GLOSSARY

TBF A Temporary Block Flow is a temporary, unidirectional physical connection

across the Um interface, between one mobile and the BSS. The TBF is

established when data units are to be transmitted across the Um interface .

Type 1 MS Mobile Station not able to simultaneously receive and transmit. The precise

definition of type 1 is given in 3GPP Technical Specification 05.02, annex B.

Type 2 MS Mobile Station able to simultaneously receive and transmit. The precise

definition of type 2 is given in 3GPP Technical Specification 05.02, annex B.

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2. INTRODUCTION

This document deals with the GPRS radio resource management in the BSS release B7.

The present functional feature description is a complement to the description of the features

30 10 xx related to radio resource handling up to release B7 provided within the document “GSM

900/GSM 1800 BSS Feature Description”. It includes in particular the new B7 feature 30 10 50

“GPRS Service on Several TRX per Cell”.

Moreover, it includes the features introduced in release B7.2 : "Radio resources re-allocation" (30 10

14) and "Fast adjustment of radio resources" (30 10 42).

The scope of the present document is hereafter detailed:

• In section 3, an abstract summarises the B7 resource management principles and the benefits

resulting for the operator.

• In section 4, the GPRS “Capacity on Demand” Alcatel concept is described with the pre-

emption mechanisms allowing to face load varying conditions.

• In section 5, improvements to the mechanisms of sharing of resources between CS and

GPRS depending on the cell traffic load variation are described.

• In section 6, the PDCH allocation algorithms are shown taking into account the new B7 “GPRS

on Several TRX per Cell” feature.

• In section 7, the GPRS "radio resource re-allocation" management is given.

• In section 8, the frequency hopping management of GPRS resources is presented.

• In section 9, the sharing of timeslot resource by several users is described.

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3. ABSTRACT

The basics of GPRS radio resource management have been already provided with release B6.2 for a

seamless introduction of GPRS in Alcatel GSM networks.

Radio resource management has been improved in release B7 to take into account major new

features brought by this release, in particular:

• The extension of GPRS capacity to several TRX per cell enhances the B6 principle of

“Capacity on Demand” and increases the possibility to serve the highest throughput to the

mobile user.

• The introduction of the Master Channel.

From release B7.2 onwards, radio resource management is enhanced by the introduction of two new

features which improve the already supported features "Capacity on demand" and "Basic Allocation

of Multiple Timeslots", thus leading to the following benefits:

• The maximum number of radio resources that can be granted to GPRS is dynamically

calculated depending on the instantaneous cell traffic load and smoothly follows the overall

traffic load.

• The radio resources allocated to an MS can be re-allocated when the amount of GPRS

resources has to be decreased in high-load situation, or when some TBFs are granted a sub-

optimal allocation.

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4. CAPACITY ON DEMAND

In the Alcatel BSS, both concepts of reserved resources and dynamic resources are compatible for

the operator. The operator can statically reserve a number of timeslots for GPRS or circuit-switched

(CS) services (see sections 4.1 and 4.2) whilst another number of timeslots can be dynamically

shared between GPRS and CS according to the demand (see section 4.3). This is what is called

“Capacity on Demand”.

Thanks to the “Capacity on Demand", the operator does not necessarily need to reserve any static

pool of radio and Abis resources for GPRS; GPRS can be introduced in a network by re-using

already installed transmission resources. It can avoid adding a new TRX in the cell or a new PCM

line on the Abis; thus it minimises the cost of radio and transmission resources to be installed in the

network.

Basically, the variable GPRS traffic load can be served by dynamically allocating or de-allocating

GPRS radio timeslots. A GPRS radio timeslot is called a Packet Data Traffic Channel (PDCH). This

is negotiated between the MFS equipment, which manages GPRS resources, and the BSC, which

manages the CS resources. This co-ordination is achieved through the GPRS Signalling Link (GSL)

between the MFS and BSC.

4.1 Reserved resource for GPRS

When the capacity on demand feature is applied on the full cell resources, if the circuit load in the

cell is high, there is no guarantee that a GPRS mobile can establish a call.

This is why Alcatel has given the possibility to the operator to have some GPRS resources reserved.

Even if this reservation is not mandatory, using it will make sure that some GPRS calls are possible

at any time. The parameter MIN_PDCH (formerly called MIN_PDCH_GROUP in the previous BSS

release) set at OMC-R defines the minimum number of PDCH permanently allocated to GPRS in a

cell.

If the operator does not want to reserve resource for GPRS in the cell, he can simply set the

MIN_PDCH parameter to 0.

Upon activation of GPRS service in the cell, MIN_PDCH timeslots are allocated on the TRX(s)

having the highest priority (see chapter 5).

After this first allocation, the position of these timeslots may then evolve in time regardless of TRX

preference marks.

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4.2 Reserved resource for circuit-switched (CS)

If the operator wishes conversely to permanently reserve a certain amount of timeslots for CS

services, he can limit the number of PDCH in the cell. The parameter MAX_PDCH (formerly called

MAX_PDCH_GROUP in the previous BSS release) set at OMC-R defines the maximum number of

PDCH that can be reached in a cell. This is particularly important for small cells where the operator

can thus guarantee a minimum capacity for voice.

This parameter is an absolute maximum, which is not necessarily reached all the time. It will not be

reached in the three following cases:

• The GPRS load is low,

• The GPRS load is high but all other timeslots are used for voice and therefore not available for

GPRS at that time,

• The GPRS load is high, a few timeslots are free but the cell is defined in high load state. In this

case, another maximum applies (see below “Pre-emption Mechanisms due to Cell Overload”

section 4.4).

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4.3 Dynamic Sharing of CS and GPRS Resources

Between the MIN_PDCH and MAX_PDCH limits defined statically by the operator, the exact number

of PDCH really needed is allocated at any time. This is achieved by a permanent optimisation of the

allocation and de-allocation process:

• When GPRS load increases, new GPRS requests are served on already active PDCH first

before starting to allocate new PDCH (see below the allocation algorithms in section 5),

• When the active PDCH are not enough to serve new GPRS requests, the system tries to

allocate more PDCH,

• When GPRS load decreases, PDCH are de-allocated when no more used.

“PDCH are de-allocated” means that they are available for CS or GPRS indifferently depending on

further requests.

For de-allocating a PDCH, the following conditions must be fulfilled at the same time:

• It is “empty”: no data transfer has been on-going on the PDCH (in both directions) for a period

of time (inactivity period),

• At least MIN_PDCH other PDCH are still allocated in the cell,

When these conditions are all fulfilled the BSS releases the PDCH and the associated terrestrial 16

kbit/s transmission resources on the Abis interface.

The operator can set the PDCH inactivity period from OMC-R. For normal PDCH (i.e. not Master

Channels) this is done through the T_PDCH_Inactivity parameter, from 0 s to 100 s. The case of

dynamic Master Channels is described in the "GPRS Master Channels in Release B7" functional

feature description.

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4.4 Pre-emption Mechanisms due to Cell Highload

The operator can use a second reservation parameter for CS services: MAX_PDCH_HIGH_LOAD.

Whenever a high load situation is experienced in the cell, this parameter takes precedence over the

MAX_PDCH parameter to define a new maximum number of GPRS timeslots per cell.

Hence, by setting this MAX_PDCH_HIGH_LOAD parameter between MIN_PDCH and MAX_PDCH,

the operator can prioritise voice over data traffic and decide to have a higher number of timeslots

reserved for voice in case of high cell load, i.e. when competition occurs between CS and GPRS

services.

The load evaluation used in this process is similar to the one implemented by Alcatel for “traffic

handover”. Thresholds under operator control are used to tune this algorithm. The transition from

“normal load” to “high load” situation triggers two kinds of behaviour in the BSS depending on the

currently allocated PDCH:

• If the current number of allocated PDCHs is less than MAX_PDCH_HIGH_LOAD, the BSS will

limit subsequent allocations to keep within this limit,

• If the current number of allocated PDCHs is already greater than MAX_PDCH_HIGH_LOAD,

the BSS initiates the release of PDCH in excess, as described hereafter.

The operator can set this parameter at OMC-R.

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4.4.1 Principles of PDCH Release under High Load Conditions

The basic principle adopted by Alcatel to release a PDCH because of high load conditions is to let

the on-going data transfers complete normally before releasing this PDCH. When all transfers are

completed, the PDCH is released. This is the soft pre-emption.

Nevertheless, the operator may want to guarantee that the PDCH release be completed within a

given maximum time. The operator can define this maximum time at OMC-R, through the

T_PDCH_PREEMPTION parameter, ranging from 0 s to 240 s.

After this period of time, the concerned PDCH is released even if there are remaining data transfers

on-going. This is the fast PDCH pre-emption.

This 2-step process (soft pre-emption + fast pre-emption) is described in the rest of this chapter.

4.4.2 Initiating the PDCH Release: Soft Pre-emption

The “soft pre-emption” process first consists of selecting the extra PDCH (above

MAX_PDCH_HIGH_LOAD) to be released, according to the following principles:

• The TRX are sorted according to their priorities, determined by their preference mark (see

next chapters in this document).

• Then for each TRX (starting from the lowest priority) each PDCH (starting from the highest

timeslot number on the TRX) is marked as unusable for new data transfer, until the number of

PDCH to release is reached.

• The same process applies to Master PDCH and normal PDCH separately. Normal PDCH are

considered first, Master Channels are considered only if not enough normal PDCH have been

found.

Once a PDCH has been selected for release, the system waits for the completion of all on-going data

transfers on that PDCH, then releases the PDCH. However, if after T_PDCH_PREEMPTION

seconds, there are still remaining data transfers then the fast PDCH pre-emption is initiated.

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4.4.3 Fast PDCH Pre-emption

After T_PDCH_PREEMPTION seconds, each mobile still using the selected PDCH is informed that

the PDCH is being released and the on-going data transfer continues on other PDCH still assigned to

that mobile, if any. It results in a reduction of data throughput as seen from the end-user.

However, if the mobile is using this PDCH for signalling purpose i.e. if the Packet Associated Control

Channel (PACCH) is carried by this PDCH, then the data transfer is interrupted. This may only

happen to long-lasting transfers. The data transfer will be re-established on other PDCH, either by

the mobile in case of uplink transfer, or by the BSS in case of downlink transfer, as recommended by

the GSM standards.

The following figure illustrates the various mechanisms of the capacity on demand:

normal loadhigh loadnormal load

time

MAX_PDCH

MAX_PDCH_HIGH_LOAD

MIN_PDCH

Allocated PDCH

(1)

(2)

(3) (4)(5)

Figure 1: Illustration of the Capacity on Demand Process

(1): GPRS is enabled in the cell. MIN_PDCH timeslots are established.

(2): As the packet traffic is increasing, more and more PDCH are established, until the maximum

number of PDCH (MAX_PDCH) is reached.

(3): The cell then enters into high load conditions. Soft pre-emption is initiated.

(4): T_PDCH_PREEMPTION seconds later, the fast pre-emption process is initiated for the

exceeded PDCH.

(5): Later on, the cell goes back into normal load conditions.

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5. FAST ADJUSTMENT OF RADIO RESOURCES

In case the operator activates the feature through the O&M parameter

EN_DYN_PDCH_ADAPTATION, the mechanisms of "Capacity on demand" presented in the

previous section are enhanced, thus improving the performances of a mature GPRS network, where

a high number of GPRS users is foreseen.

Some parameters are used for both "Capacity on Demand" or "Fast adjustment of radio resources"

features. However, when "Fast adjustment of radio resources" is enabled, new definitions should be

taken into account.

As already supported with "Capacity on demand" concept, the operator is allowed to:

- Reserve some GPRS resources thanks to the parameter MIN_PDCH;

- Limit the maximum number of PDCHs that can be allocated among the total number of

available TS in the cell. This limit is set by MAX_PDCH parameter value.

When "Fast adjustment of radio resources" is enabled, the parameter High_Traffic_Load_GPRS is

tuned in order to keep free a certain percentage of the overall radio resources for incoming CS

requests. The way the Alcatel BSS handles the dynamic sharing of CS and GPRS resources with

the enhanced GPRS radio resource allocation algorithm is described in the following part:

5.1 Cell Load evaluation

In previous releases, the Alcatel BSS supports a long-term cell traffic load evaluation similar to the

one implemented for “traffic handover”.

From release B7.2, the load evaluation period used for GPRS traffic adaptation is shortened,

enabling the BSS to react more efficiently to sudden traffic situation changes. The operator can

define the load evaluation period for load averaging supported with the enhanced GPRS traffic

adaptation algorithm, thanks to the new parameter: Load_EV_Period_GPRS.

Moreover, the normal/high load states transition concept, presented in section (4.4.3), is no longer

used. The only reference being the parameter High_Traffic_Load_GPRS. With every new load

evaluation, the BSC re-calculates the maximum number of PDCHs that could be allocated without

crossing the High_Traffic_Load_GPRS threshold.

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5.2 Dynamic sharing of CS and GPRS resources enhancement

The BSC will evaluate the maximum number of TS, which can be granted dynamically to GPRS. This

variable computed number of TS, MAX_PDCH_DYN, will always be in the range of

[MAX_PDCH_HIGH_LOAD;MAX_PDCH].

The number of PDCHs that can be allocated to GPRS ( MAX_PDCH_DYN) is calculated depending

on the total number of available TS, the number of already allocated PDCHs and the current CS

traffic load in the cell. Thus the number of PDCHs is dynamically adapted to cell load variation.

In normal load situation, the upper limit of GPRS resources will be set to MAX_PDCH.

In high load situation, if the current number of allocated PDCHs exceeds the computed value of

MAX_PDCH_DYN, the Alcatel BSS will decrease the upper limit of GPRS resources to

MAX_PDCH_DYN, and soft and then fast pre-emption of the needed amount of PDCHs will be

applied (as described in previous sections).

It has to be highlighted that only the needed amount of GPRS resources is pre-empted. Depending

on the operator settings, the number of PDCHs will not inevitably be decreased down to

MAX_PDCH_HIGH_LOAD. A high gain in terms of GPRS resources is foreseen especially since

"GPRS service on several TRXs per cell" feature introduction (see section 6).

The following figure illustrates the mechanisms of fast adjustment of radio resources:

time

MAX_PDCH

MAX_PDCH_HIGH_LOAD

MIN_PDCH

Allocated PDCH

(4)High_Traffic_Load_GPRS

CS traffic

PS traffic

(A) (B) (C)

(1)

(2)

(3)

(5)

(4)

MAX_PDCH_DYN variations

(6)

Figure 2: Illustration of the fast adjustment of radio resources Process

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Situation A: Low CS traffic and Total traffic in the cell < High_Traffic_Load_GPRS

(1):GPRS is enabled in the cell. Min_PDCH timeslots are established.

(2): The packet traffic is increasing and as the CS traffic is low, up to MAX_PDCH PDCHs can be

allocated in this specific case.

Situation B: Total traffic in the cell > High_Traffic_Load_GPRS

(3): The circuit traffic is increasing and the total traffic in the cell exceeds High_Traffic_Load_GPRS

threshold.

The enhanced radio resource management algorithm aims at maintaining the total traffic under the

limit:

- MAX_PDCH_DYN value is reduced

- Soft and then fast pre-emption of one PDCH is performed, so that the number of PDCHs

allocated does not exceed MAX_PDCH_DYN.

(4): The circuit traffic is still increasing and the total traffic in the cell still exceeds

High_Traffic_Load_GPRS threshold.

As in the previous case, the enhanced radio resource management algorithm aims at maintaining

the total traffic under the limit:

- MAX_PDCH_DYN value is reduced

- Soft and then fast pre-emption of one PDCH is performed, so that the number of PDCHs

allocated does not exceed MAX_PDCH_DYN.

Remark: If the circuit traffic keeps on increasing, the value of MAX_PDCH_DYN could be smoothly

decreased down to MAX_PDCH_HIGH_LOAD value.

Situation C: High CS traffic and Total traffic in the cell < High_Traffic_Load_GPRS

(5): The amount of CS traffic has decreased so that the total traffic in the cell is now below the

threshold High_Traffic_Load_GPRS. However, if an additional PDCH was allocated, the current

traffic load would exceed the High_Traffic_Load_GPRS limit. MAX_PDCH_DYN value is not

changed.

(6): The amount of CS traffic is decreased. MAX_PDCH_DYN value is updated in order to keep the

cell traffic load under the limit set by High_Traffic_Load_GPRS parameter.

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6. GPRS ON SEVERAL TRX PER CELL

In release B7, GPRS is supported on several TRX in the cell. In case of a concentric or multi-band

cell, the GPRS TRX can be defined only in the outer zone.

In B7 release, the resource allocation process is enlarged with the choice of the most suited TRX

among possible ones. Moreover, in the Alcatel BSS, the flexibility is left to the operator to influence

this choice by priorities (see section 6.1).

6.1 Priorities Defined by the Operator

The Alcatel BSS let all the flexibility to the operator to indicate preferences in the allocation of GPRS

resources on particular TRX. This can prove very useful for example to deal with frequency planning

considerations.

For each TRX, one parameter can be configurable at the OMC-R: the GPRS_PREF_MARK (GPRS

preference mark) on a per TRX basis. Each parameter can be set to 0 (lowest priority), 1, 2 or 3

(highest priority). With the “0” value, the operator can also indicate that the TRX does not support

GPRS.

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6.2 Allocation of Multislot Calls

The Alcatel BSS handles all mobile stations whatever multislot class they have (feature 30 10 10). It

tries to allocate as much as possible the number of consecutive timeslots corresponding to the

multislot class of the mobile.

The maximum number of consecutive timeslots that can be allocated to a mobile by the Alcatel BSS

depends on whether the MS is of type 1 (half-duplex) or type 2 (full-duplex), see glossary:

• Type 1 MS is allocated up to 4 timeslots in the downlink and 2 timeslots in the uplink path.

• Type 2 MS is allocated up to 5 timeslots in the downlink and 5 timeslots in the uplink path,

However, the Alcatel BSS offers to the operator the possibility to limit this number to a lower value,

through the MAX_PDCH_PER_TBF parameter set at OMC-R, between 1 and 5. This may be used to

prevent one multislot MS to use too many PDCH each time it wants to transmit data, to the detriment

of others. Therefore, this parameter can be seen as a leverage to control the overall number of

GPRS MS transferring in a cell versus the quality of service offered.

The BSS resource allocation process is then performed in two steps:

• Selection of the best TRX(s),

• Selection of the best solution on this (these) TRX(s).

This process is carried out taking into account the following constraints:

• The maximum number of PDCH allowed per data transfer (MAX_PDCH_PER_TBF).

• The maximum number of users per PDCH. Full PDCH cannot be allocated to the new mobiles

(see section 7).

• The number of available PDCH in the cell (according to the Capacity on Demand process).

• Possible constraints on PDCH location due to a concurrent data transfer in the opposite

direction.

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6.2.1 Selection of the Best TRX

The TRX are selected according to the following criteria:

• Their priority, as defined by the operator: the TRX(s) are ranked according to their

GPRS_PREF_MARK.

• The number of PDCH they can offer to serve the request.

A set of one or several TRX might actually come out this selection process and fulfil the same level

of requirement. Also several PDCH combinations per TRX might be possible.

The optimum solution is then sought among all the possible combinations pertaining to these

candidates TRX by performing a second step of selection, as described in next section.

6.2.2 Final Selection of the Best Solution

The PDCH combinations resulting from the “best” TRX selection process are finally sorted out by a

scoring evaluation function based on such criteria:

• The number of additional PDCH to establish should be minimised,

• The combinations minimising the number of busy PDCH are favoured,

• Traffic score: lowest number of established connections per PDCH.

The optimum combination resulting from these criteria is defined as the best solution for the

allocation.

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7. RADIO RESOURCE RE-ALLOCATION

In release B7.2, radio resource re-allocation may happen in different situations.

Immediate resource re-allocation will be triggered either for an already established TBF whose

PACCH is carried by a PDCH marked by the soft PDCH pre-emption process or at concurrent TBF

establishment and the best candidate timeslot allocation requires re-allocating the resources granted

to the existing TBF.

Also resource re-allocation will be triggered periodically for TBFs candidate for non-immediate

resource re-allocation. Several events are defined that can lead to marking a MS as candidate for

resource re-allocation at a later stage.

In both cases, the MS can be re-allocated on the same TRX or on another TRX, provided that it

belongs to the pool of TRXs available for resource re-allocation

7.1 Immediate resource re-allocation

An already established TBF candidate for an immediate resource re-allocation, will be served before

any new request of TBF establishment from a new Mobile Station.

7.1.1 Immediate resource re-allocation upon GPRS resources decrease

In cell high-load situation, some PDCHs might be pre-empted for new CS requests (see sections 4

and 5). A PDCH carrying the PACCH of an already established TBF can be fast pre-empted, thus

leading to an abnormal release of the corresponding TBF.

In this situation, in order to avoid such an abnormal release, the Alcatel BSS radio resource

allocation entity will find the best PDCH allocation among the available resources to re-allocate the

TBF. The TBF resources will be reconfigured even if the number of allocated PDCHs does not reach

the maximum allowed by the MS multislot class. Indeed, the aim of this procedure is to maintain the

TBF alive.

7.1.2 Immediate resource re-allocation upon concurrent TBF establishment

When concurrent TBF establishment is requested in the opposite direction of an on-going TBF, the

BSS evaluates possible PDCH allocations for both the on-going and the new TBFs. Though upon the

initial on-going TBF establishment, the BSS had anticipated the concurrent direction, it may happen

that the best candidate allocation requires re-allocating the existing TBF. In this case, the already

established TBF is re-allocated, and the concurrent TBF is established.

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7.2 Later resource re-allocation to increase data throughput

After the incoming queued UL TBF and DL TBF establishment requests have been served, resource

re-allocation is triggered periodically (every T_CANDIDATE_TBF_REALLOC) for MSs that are

candidate for resource reallocation.

7.2.1 Evaluation of sub-optimal TBFs

Different events can result in marking a TBF with "sub-optimal allocation":

- The TBF was not initially allocated the maximum number of PDCHs supported by the MS

multislot class, due to temporary GPRS resource shortage,

- The data throughput of the TBF has been decreased because of fast pre-emption of one or

several PDCHs (not carrying the PACCH of the TBF).

7.2.2 Evaluation of the direction of the bias

The Alcatel BSS periodically evaluates for each mobile station the direction of the bias. It

corresponds to the direction in which most of the data packets are exchanged. It is assumed that it is

the direction of the on-going end-user application. The Alcatel BSS therefore attempts offering the

best available throughput in that direction. The past activity is taken into account in order to mitigate

the number of bias changes, especially in case of balanced activity.

7.2.3 Evaluation of candidate MSs

Several conditions have to be met by a Mobile Station so that it becomes candidate for resource

reallocation at a later stage:

- The TBF serving the MS in the direction of the bias has a sub-optimal allocation,

- A sufficient number of octets has been sent or received for that mobile station,

- There is no possibility of fast downlink TBF re-establishment.

7.2.4 Re-allocation process

Upon each expiry of T_CANDIDATE_TBF_REALLOC, the Alcatel BSS attempts reallocating the

resources of all candidate MSs. Resource reallocation is only performed if it can increase the

throughput currently served to a given Mobile Station in the direction of the bias.

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8. FREQUENCY HOPPING MANAGEMENT

In release B7, several TRX within a cell can support GPRS. Among these TRX, some ones may be

hopping and some others may not. In a given cell, one frequency hopping law can be defined for all

hopping TRX used for GPRS.

A frequency hopping law is determined by a list of radio frequency channels and a Hopping

Sequence Number (HSN). This is also known as the GPRS Mobile Allocation (MA). One or several

TRX can use the same GPRS MA. This is under operator’s control, from OMC-R.

Note: Setting these hopping laws at OMC-R is not specific to GPRS and is outside the scope of this

document.

8.1 Frequency Information

Several frequency hopping laws (i.e. MA and HSN) can be defined per cell. Only one of them can be

used for GPRS. This law can be mapped onto one or several TRX.

According to the standard, the GPRS frequency hopping law has to be broadcast to the mobile

stations, as system information.

When a Master Channel is present in the cell, the complete description of the frequency law used for

packet services is broadcast to the mobiles through the Packet System Information Type 2 message

over the PBCCH.

If the Master Channel itself is hopping, its hopping law is broadcast in System Information Type 13

message over BCCH.

Note: If the Master Channel is not hopping, the System Information Type 13 message over BCCH

broadcasts the Absolute Radio Frequency Channel Number (ARFCN) of the Master Channel

(i.e. its fixed frequency), and the frequency hopping law of the hopping GPRS TRX, if any.

When there is no Master Channel in the cell, the Alcatel BSS broadcasts the frequency hopping law

of the hopping GPRS TRX, if any, via the System Information Type 13 message on BCCH.

The hopping law used for GPRS may correspond to one or several TRX.

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8.2 Selection of Hopping Resource

The data transfer may be performed either on a non-hopping TRX or on a TRX hopping with the law

broadcast in System Information Type 13 message and/or Packet System Information Type 2

message, as explained in section 6.1. Consequently, it is up to the operator to map the same law

onto as many hopping TRX as possible in the cell, to have all of them usable for GPRS and get the

highest GPRS traffic capacity in this cell.

To establish the packet radio communication pipe between the mobile and BSS, i.e. the Temporary

Block Flow (TBF, see glossary), the BSS gives the mobile the reference of the frequency law it shall

use, together with the Mobile Allocation Index Offset (MAIO) to apply along the TBF.

Note: Using an indirect reference to the broadcast frequency law when establishing a TBF reduces

the signalling and therefore the TBF establishment time.

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9. FLEXIBLE SHARING OF TIMESLOT BETWEEN USERS

GPRS is a packet service that enables to share the bandwidth dynamically between several mobiles

(feature 30 10 30). This is possible on a per radio timeslot basis.

The sharing enables to serve up to 16 GPRS requests with a unique timeslot: up to 6 in uplink, and

up to 10 in downlink. This makes GPRS differentiate from circuit-switched data services that require

at least one timeslot per user. This increased efficiency is all the more noticeable when a lot of users

can be served with low data rate applications.

In the considered release, the bandwidth per timeslot is equally shared between all users

simultaneously assigned on this channel. To give full flexibility to the operator, Alcatel has also

introduced the parameter N_TBF_PER_SPDCH (was formerly called N_TBF_PER_PDCH in the

previous BSS release). This parameter defines for each PDCH the “suitable” number of users

sharing a timeslot, that should not be exceeded under normal load conditions. This number,

comprised between 1 and the above-defined maximum, enables to ensure a good bit rate as long as

GPRS load is normal. The system tries to maintain the number of TBF per PDCH below, or equal to

this value. When this value is exceeded on a PDCH, the system tries to establish one more PDCH in

the cell.

The N_TBF_PER_SPDCH parameter does not apply to the Master Channels. Instead of it, a default

value of "0" is used. This is to preserve the signalling capacity of the Master Channels. The system

first tries to fill the normal PDCH until the N_TBF_PER_SPDCH value is reached on all normal

PDCH and the maximum number of PDCH is reached in the cell (MAX_PDCH or

MAX_PDCH_HIGH_LOAD depending on the current load).

If the maximum number of PDCH is reached in the cell, the system serves the new GPRS requests

with the available PDCH until the maximum number of TBF per PDCH is reached i.e. the PDCH are

considered as full by the system.

The setting of these parameters is therefore a compromise between the resource efficiency provided

by the sharing and the quality of service.

For example, if the N_TBF_PER_SPDCH=2, the preferred bandwidth per user on the PDCH is 1/2 of

the total bandwidth. When the number of users on the PDCH reaches N_TBF_PER_SPDCH, the

PDCH is declared as “busy” and will preferably not accept a third user (see also section 6.2 allocation

of multislot calls). Of course, as long as there is only one user on the timeslot (no sharing), this user

benefits from the total bandwidth.

End of Document

GPRS_RRM_B7

Documents

temporary block flow

remaining data transfers

frequency hopping management

alcatel bss handles

ms multislot class

frequency hopping law

normal load conditions

high load conditions