01_Nokia GPRS Radio Resource Management

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NTC Version: draft © Nokia Telecommunications Oy

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Nokia GPRS Radio ResourceManagement



Contents


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The information in this document is subject to change without notice and describes only the productdefined in the introduction of this documentation. This document is intended for the use of NokiaTelecommunications' customers only for the purposes of the agreement under which the document issubmitted, and no part of it may be reproduced or transmitted in any form or means without the priorwritten permission of Nokia Telecommunications. The document has been prepared to be used byprofessional and properly trained personnel, and the customer assumes full responsibility when usingit. Nokia Telecommunications welcomes customer comments as part of the process of continuousdevelopment and improvement of the documentation.

The information or statements given in this document concerning the suitability, capacity, orperformance of the mentioned hardware or software products cannot be considered binding but shallbe defined in the agreement made between Nokia Telecommunications and the customer. However,Nokia Telecommunications has made all reasonable efforts to ensure that the instructions contained inthe document are adequate and free of material errors and omissions. Nokia Telecommunications will,if necessary, explain issues which may not be covered by the document.

Nokia Telecommunications' liability for any errors in the document is limited to the documentarycorrection of errors. Nokia Telecommunications WILL NOT BE RESPONSIBLE IN ANY EVENT FORERRORS IN THIS DOCUMENT OR FOR ANY DAMAGES, INCIDENTAL OR CONSEQUENTIAL(INCLUDING MONETARY LOSSES), that might arise from the use of this document or the informationin it.

This document and the product it describes are considered protected by copyright according to theapplicable laws.

NOKIA logo is a registered trademark of Nokia Corporation.

Other product names mentioned in this document may be trademarks of their respective companies,and they are mentioned for identification purposes only.

Copyright © Nokia Telecommunications Oy 1999. All rights reserved.

No. of

Pages

34

Edited by/Translator

Ashley Colley

Jari Malinen

Author

11.8.99

Arto Kangas

Approved by

22.9.1999

Reko Juntto

Previous issue



Contents


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Contents

1 General 41.1 Document revision history 4

2 Sharing Capacity between Circuit Switched and PacketSwitched 52.1 Territory Method 52.1.2 Parameters for Territory management 62.2 Territory Upgrade and Downgrade 72.2.1 Reasons for starting the upgrade procedure 72.2.2 Intra cell handover of CS call due to GPRS Territory

Upgrade 72.2.3 GPRS territory downgrade 82.2.4 Free TS for CS calls 82.3 Effect on existing features 9

3 PS Channel Allocation 123.2 PS Channel allocation principles 123.3 Scheduling 133.4 GPRS Territory Upgrade / Downgrade Request 143.5 GPRS MS Class 153.5.1 MS multislot class 16

4 GPRS Air Interface Channels 19

5 GPRS Uplink 225.1 Uplink TBF establishment 225.2 Medium Access (MAC) modes 245.3 Uplink data transfer (acknowledged mode) 24

6 GPRS Downlink 266.1 PS Paging 266.2 Downlink TBF establishment 266.3 Downlink Data transfer 27

7 Power Control 297.1 Uplink Power Control 297.2 Downlink power control 29

8 Coding Scheme Selection 31

9 Cell Selection and Re-selection 33



General


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1 General

This document does not belong to Nokia official customer documentation. This

document is made only to give some answers to frequently asked questionsregarding the GPRS radio resourse management principles and Nokia GPRS

BSS implementation. The GPRS development and further specification work is

ongoing both in ETSI standardisation and in Nokia R&D. This documentdescribes the current understanding of the issues as it is basis. Further changes

for subjects mentioned here are possible. The final customer documentation will

be available once the Nokia GPRS system and products implemention isfinalized. Nokia undertakes rights to make changes, corrections to subjects

described here if necessary.

Note, Items shown in italics are not supported in the 1 st

Nokia GPRS release

Responsible person: Ashley Colley / Jari Malinen

Status: 1.0

Confidentiality: Nokia Customer Confidential.

1.1 Document revision history

Version Date Author Comments

0.1 11.8.99 AKa/Aco Conversion from .ppt

0.2 31.8.99 JMa Editing

1.0 22.09.99 RJu First approval



Sharing Capacity between Circuit Switched and Packet Switched


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2 Sharing Capacity between CircuitSwitched and Packet Switched

2.1 Territory Method

In Nokia solution for each cell separate territories for circuit switched andpacket switched connections can be defined, this is shown in the figure below.

The border between the territories can move dynamically based on the load of

circuit switched and packet switched traffic.

• Circuit Switched traffic has priority

• In each cell Circuit Switched & Packet Switched territories are defined

• Territories consist of consecutive timeslots

TRX 1

TRX 2

CCCH TS TS TS TS TS TS TS

TS TS TS TS TS TS TSTS

DedicatedGPRS

Capacity

CircuitSwitched

Territory

PacketSwitchedTerritory

Territory border movesD y n a m i c a l l y based onCircuit Switched traffic load

C i r c u i t S w i t c h e d c a p a c i t y n o t a f f e c t e d

b y i n t r o d u c i n g G P R S

DefaultGPRS

Capacity

AdditionalGPRS

Capacity

Figure 1 The Territory Method

This method of defining separate territories maximises the availability of

comsecutive multislots being available in both PS and CS territories (compared

to the alternative of randomly mixing CS and PS calls together).

The GPRS territory is a set of consecutive TS, excluding:

• TS that are not capable of full rate traffic (BCCH, SDCCH, HR)

• blocked TS

• TSL 0 when Base Band Frequency Hopping is used

• T HSCSD connection





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2.1.2 Parameters for Territory management

The following are the operator configurable parameters for territory

management:

• GPRSenabled (BTS-level)

• GPRSenabledTRX (TRX-level)

• DedicatedGPRScapacity (BTS-level)

• DefaultGPRScapacity (BTS-level)

• PreferBCCHfreqGPRS (BTS-level)

• TerritoryUpdateGuardTimeGPRS (BSC-level)

GPRS territory parameters can be changed when the cell GPRS capability is set

off by GPRSenabled parameter or when the cell is locked.

PS TCH reservation is done in two phases. First the CS RRM allocates theTCHs which the PCU may use. Abis switching through GSWB to PCU is made

to those TCHs. PCU and CCU make the frame synchronization right after the

switch. PS RRM makes the actual PS channel allocation to PS connections using

the TCHs determined by the CS RRM.

Dedicated GPRS capacity

Part of the TCHs can be reserved totally for GPRS. These TCHs are blocked for

CS.

Default GPRS capacity

The default GPRS capacity is always allocated to GPRS territory when allowedby the CS load. The CS RRM initiates upgrading and downgrading of these

TCHs. These TCHs are allocated to GPRS territory whether there is any GPRS

traffic or not.

Additional GPRS capacity

When the default GPRS capacity is allocated to GPRS territory the PS RRM can

ask for additional TCHs. The PS RRM initiates upgrade requests for theadditional resources. The CS RRM controls the reservation of the additional

TCHs based on the CS load. GPRS territory downgrade of TCHs allocated as

additional GPRS capacity can be initiated by CS or PS RRM.

Location of GPRS Territory (TRX)

The location of the GPRS territory within each cell is determined by:

• parameter PreferBCCHfreqGPRS





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• TSL Configuration

• SDCCH TSL < HR TSL < DR TSL < FR TSL

• Resource situation

• multislot HSCSD calls < busy TS < idle TSL

2.2 Territory Upgrade and Downgrade

2.2.1 Reasons for starting the upgradeprocedure

Upgrade of the GPRS territory (ie. increasing the number of TS available for

GPRS traffic) may be started for the following reasons:

• GPRS is set enabled in a BTS (BTS parameter GPRSenabled)

• GPRS-TRX is created => default GPRS capacity increases

• GPRS-TRX is deblocked, e.g. the first GPRS-TRX in a BTS

• TSL inside the GPRS territory is deblocked

• CS call is released, ie. CS load decreases

• PS RRM requests additional GPRS capacity

2.2.2 Intra cell handover of CS call due to GPRSTerritory Upgrade

GPRS territory upgrade is dependent on the CS load. If the CS load, GPRSdemand and parameter settings demand that a GPRS territory upgrade procedure

is started any CS call(s) in the TSL(s) to be included in the new GPRS territory

are handed over to other TS in the same cell. This is shown in the figure below:





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B = BCCH TSL

S = SDCCH TSL

C = CSW call

DefaultGPRScapacity = 20%

DedicatedGPRScapacity = 10%

FreeTSLsforCSW = 3

= GSM territory

= GPRS territory

B C C C C C C

S

C

C C

C

C d d D D D

C C C C

C C C

C

GPRS territory upgrade

Figure 2 Intra cell handover to CS call to GPRS TerritoryUpgrade

2.2.3 GPRS territory downgrade

A GPRS territory downgrade is initiated due to increase of CS load. PCU can

initiate GPRS resource downgrade to additional GPRS resources.

2.2.4 Free TS for CS calls

Some TS are kept free for incoming CS calls. This is to avoid:

• delays in allocating TS to CS calls

• continuous GPRS territory upgrade and downgrade, which also disturbs PStraffic (ie. To provide some hysterysis)

The amount of TS kept free depends on the cell size, this is shown in the table

below:

Free TSLs

TRXs downgrade upgrade

1 1 1

2 1 2

3 1 2

4 2 3

5 2 4

6 2 4

7 2 4

8 3 5

9 3 5

10 3 6

11 3 6

12 3 6





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Table 1 Free TS for CS calls

The numberr of free TS has been set such that:

For downgrade:

• - 95 % probability that there is no need for new downgrade procedure duringthe previous downgrade.

For upgrade:

• - 95 % probability that there will be no downgrade needed in four seconds

after the upgrade.

2.3 Effect on existing features

Introducing GPRS resources in a BTS has effect on existing features that are

based on load of circuit switched (CS) traffic. In general, resources that cannotbe used for CS calls, i.e. dedicated GPRS TS, must be totally excluded from the

available resources in various CS resources management features. However,

default GPRS resources are included in decisions since they may be allocated

for CS traffic when necessary. This gives rise to the following:

• Number of working resources for CS features = working resources in BTS -

dedicated GPRS resources

• Number of idle resources for CS features = idle CS resources + GPRS

resources - dedicated GPRS resources• Number of occupied resources for CS features = occupied CS resources.

The following lists various features and notes the impact of GPRS on each.

Interference band recommendation

TCHs in the GPRS territory are allocated to CS calls only when there are no free

TS elsewhere in the cell. Interference band recommendation is used to

allocations done in CS territory.

Frequency Hopping

TSL 0 not used for GPRS in Base Band Hopping.

Optimization Of The MS Power Level In Handovers

Power optimization is not done when reserving TCHs for CS connection from

GPRS territory.





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Intelligent Underlay Overlay

Super-reuse frequencies are not supported for GPRS.

Forced Handover For O&M Reason

If there are GPRS-TS in the TRX to be blocked, the BSC moves those TS to the

CS territory and starts a downgrade procedure immediately. The BSC

downgrades all of the TS in the TRX regardless of which territory they belongto. If the TRX to be blocked does not include GPRS-TS, the BSC does not

change the territories.

Dynamic SDCCH allocation

Dynamic SDCCH is not allocated to the GPRS territory.

Preferred BCCH TRX

CS and PS can prefer either the same kind of TRXs or the opposite kind of

TRXs or prefer nothing at all.

TRX fault

When a TRX carrying TCHs becomes faulty the radio timeslots on the TRX are

blocked from use. The possible ongoing calls and also the call control resourcesin the BSC are released. TCHs belonging to a GPRS territory are downgraded

from GPRS use. The CS RRM determines the possibility of GPRS territory

upgrade to another TRX. When the number of dedicated and default GPRS

capacity TS is counted working and blocked TS are included to the total, thusthe amount that the CS RRM tries to allocate for the GPRS territory is not

changing in case of a TRX fault.

HSCSD vs GPRS

In principle CS traffic has priority over PS traffic. Multislot HSCSD is always

preferred to additional GPRS capacity TCHs.

If there has been defined default GPRS capacity in a cell (DefaultGPRScapacity

> 0) load limits for incoming HSCSD requests are calculated based on the

existing HSCSD parameters with the following changes:

-default GPRS capacity TCHs which are reserved for GPRS use are counted asoccupied TCHs

-UpperLimitCellLoadHSCSD as a criterion for interrupting multislot allocations(that is used together with MinHSCSDcapacityCell) is replaced with the new





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GPRS limit Free TSLs for CS if the latter is more restricting; thus the one is

used that limits multisot allocation earlier

In case DefaultGPRScapacity = 0 HSCSD load parameters are applied as

without GPRS.

If multislot allocation is denied transparent HSCSD requests are rejected andnon-transparent requests are served with 1 TSL as before.

If TSL amount in HSCSD allocation is not restricted T requests are servedpreferably in the CSW territory, and in the PSW territory only if necessary. If atransparent HSCSD call ends up in the GPRS territory RRMPRB does not later

try to move it elsewhere with the intra cell handover. Instead it tries to replacethe lost GPRS channels on the other side of the arrived HSCSD call. But this of

course only when the sufficient margin exists (Free TSLs for CS).

NT HSCSD requests are always served in the CS territory as long as there is at

least one TCH/F available. A normal HSCSD upgrade procedure is applied laterto fulfil the need of the NT request if the call starts with less channels thanneeded. In order for the NT call to get the needed TSL amount CS RRM

starts an intra cell handover for suitable single slot calls beside the NT

HSCSD call. At starting of the handover RRMPRB has to check that a singleslot call is able to move and that HSCSD upgrade is in general allowed.

An NT HSCSD call enters the GPRS territory only in case of congestion of theCS territory. If multislot allocation was originally defined allowed it will be

applied also within the GPRS territory to serve the NT request. If the cell load

goes later down so that GPRS upgrade becomes enabled the NT HSCSD call is

handed over to another location in the cell so that the GPRS territory can beextended.

If the HSCSD state in a cell has been defined restricted so that HSCSD

downgrade should be made as a new TCH request arrives it is made instead of

GPRS downgrade. If the cell HSCSD state does not require HSCSD downgradethen a GPRS downgrade for the possible additional TSLs is made if maintaining

of the margin Free TSLs for CS requires it. If no additionals exist actions depend

on HSCSD traffic amount: if there are HSCSD TCHs more thanMinHSCSDcapacityCell requires then an HSCSD downgrade is made rather

than a GPRS downgrade. If the minimum HSCSD capacity is not in use then a

GPRS downgrade is made to maintain the margin Free TSLs for CS.

GPRS territory upgrade can be done although minHSCSDcapacity is not in use

and there are pending HSCSD connections in the cell. Free TSLs for CS is thelimiting factor for GPRS territory upgrade.



PS Channel Allocation


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3 PS Channel Allocation

This section describes how the PS resources are allocated between different

GPRS users.

The figure below describes the uplink sheduling. Up to 7 GPRS connections canshare the resources of a single TS (this is shown on the vertical axis). The uplink

and downlink scheduling are independent, for downlink upto 9 GPRSconnections can share the resources of a single TS. In the figure below three 3

TS mobile connections are shown TFI1,TFI,2 and TFI3.

TFI1TFI1TFI1TFI2

TFI3TFI3TFI2

TFI3

DedicatedGPRS

Capacity

DefaultGPRS

Capacity

0 1 2 3 4 5 6 7

1

2

3

4

5

6

7

TSL

TFI2

Figure 3 PS Channel Allocation/Scheduling

Temporary Block Flow / Temporary Block Identifier

A Temporary Block Flow (TBF) is a physical connection used by the two RR

entities to support the unidirectional transfer of LLC PDUs on packet dataphysical channels. The TBF is allocated radio resources on one or more TCHs

and comprises a number of RLC/MAC blocks carrying one or more LLC PDUs.

A TBF is temporary and is maintained only for the duration of the data transfer.

TBF is identified by Temporary Flow Identity (TFI).

3.2 PS Channel allocation principles

Packet Switched channels are allocated acording to the following:

1. Downlink and uplink are separate resources





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2. Multiple phones can share one TCH, but the TCH is dedicated to one MS

(TBF) at a time. That means that the TCH is reserved for multiple MSs, but oneMS is transmitting or receiving at a time. It is possible to allocate 7

simultaneous uplink MSs and 9 simultaneous downlink MSs on the same TCH.

3. Channels allocated to a TBF must be allocated from the same TRX

4. Those TCHs which give the maximum possible capacity for the TBF are

allocated for the TBF within the limits of the multislot class of the mobile. An

exception for the above are short closed ended TBFs. In these cases only one

channel is allocated.

TCH selection to TBF

The channel allocator determines the number of TCHs that are needed and

counts the best throughput for that amount of TCHs. Eg. (see above figure) TFI3

will have TS 3, 4 and 5 since it will have 1/1 + 1/1 + 1/2 (=2½) service as TS 4,5 and 6 would offer 1/1 + 1/2 + 1/2 (=2) service and TS 5, 6 and 7 would offer

1/2 + 1/2 + 1/2 (=1½) service.

When the load of TCH combinations is equal they are first compared first by the

capacity type (additional < default < dedicated) and then by the PACCH load.

PACCH load is the amount of TBFs using a certain TCH as PACCH.

PACCH

Packet Associated Control Channel (PACCH) conveys signaling informationrelated to a given MS. The signaling information includes e.g.

acknowledgements and power control information. The PACCH also carries

resource assignment and reassignment messages, comprising the assignment of

a capacity for TCH(s) and for further occurrences of PACCH. One PACCH isassociated to one or several TCHs that are concurrently assigned to one MS.

PACCH is bi-directional channel. It can be allocated both on the uplink and on

the downlink regardless on whether the corresponding TCH assignment is foruplink or downlink. Assigned TCHs are used for PACCH for the direction the

data is sent. For the opposite direction the MS multislot capability has to be

taken into account when allocating the PACCH.

3.3 Scheduling

In this scheme each TBF has the following parameters:

• A time when it should be served.





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• A time interval by which its serving time is increased each time the TBF

gets a turn.

In addition a virtual time is kept. In each TCH, the first TBF is selected which

has the lowest serving time. When it has been served, its serving time isincremented by its time interval. Virtual time is incremented by the same time

interval.

In release 1 this works as Round Robin (ie. equal level of service to all), but this

can be easily updated to provide QoS and priorities in future releases.

The scheduler is responsible for scheduling the following:

Downlink:

• scheduling of RLC/MAC control blocks (prioritized over data blocks)

• scheduling of RLC data blocks

• Relative Reserved Block Period (RRBP) for polling requests

• Dummy control blocks

• Idle PCU frames to BTS, when nothing else to send

Uplink:

• single block reservations (for Packet Resource Request messages in two

phase uplink access)

• Dynamic MAC mode with USF (Uplink State Flag)

• reservations for Packet Uplink Ack/Nack messages (ordered by RRBP)

• CCU Uplink decoding mode (normal / access / idle)

3.4 GPRS Territory Upgrade, DowngradeRequest

PS RRM may request more TCHs to GPRS territory when the Default GPRS

capacity is already allocated to GPRS territory. The PS RRM is also responsiblefor requesting downgrade of the additional GPRS capacity TCHs when there is

not need for them.The algorithm uses internal parameters X1, X2 and X3, these are not directly

user definable but are set by the user definable radio NW parameters described

previously.





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PS RRM requests new TCH(s) to the GPRS territory when the average number

of TBFs in TCHs in the GPRS territory is greater than X1. The target averagenumber of TBFs in TCHs (X2) in the GPRS territory determines the number of

TCHs that the PS RRM is requesting from CS RRM.

When the average number of TBFs in TCHs in the GPRS territory is less than

X3, the PS RRM will request GPRS territory downgrade. The target averagenumber of TBFs in TCHs (X2) in the GPRS territory determines the number of

TCHs that the PS RRM is requesting the CS RRM to downgrade.

3.5 GPRS MS Class

Different classes and types of GPRS terminal are specified, this is shown in the

figure below:

• Classes

• A simultaneous CS and PS

• B ready for both, one active at a t ime

• C either CS MS or PS MS

• TypesType 1, multislot classes 1-12, like HSCSD- max 4 downlink and 2 uplink

Type 2, multislot classes 13-18, simultaneous receive&transfer- max 8 downlink and 8 uplink

Type 1, multislot classes 19-29, enhancements for GPRS- max 6 downlink but only 2 uplink due to USF scheduling

Figure 4 GPRS Terminals

The purpose of the definition of the GPRS MS Classes is to enable the differentneeds of the various market segments to be satisfied by a number of MS types

with distinct capabilities.

CLASS A: Supports simultaneous attach, simultaneous activation, simultaneous

monitor, simultaneous invocation and simultaneous traffic.CLASS B: Simultaneous traffic shall is not supported. The mobile user canmake and/or receive calls on either of the two services sequentially but not

simultaneously. The selection of the appropriate service is performed

automatically, i.e. an active GPRS virtual connection is put on hold, if the user





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accepts an incoming circuit switched call or establishes an outgoing circuit

switched call.

CLASS C: Supports only non-simultaneous attach. Alternate use only. If bothservices (GPRS and Circuit Switched) are supported then a Class C MS can

make and/or receive calls only from the manually or default selected service,

i.e., either GPRS or Circuit Switched service. The status of the service whichhas not been selected is detached i.e., not reachable.

3.5.1 MS multislot class

The MS multislot class determines the number of simultaneous downlink and

uplink TS. For details, see GSM05.02.

Multislotclass

Maximum number of slots Minimum number of slots Type

Rx Tx Sum Tta Ttb Tra Trb

1 1 1 2 3 2 4 2 1

2 2 1 3 3 2 3 1 13 2 2 3 3 2 3 1 1

4 3 1 4 3 1 3 1 1

5 2 2 4 3 1 3 1 1

6 3 2 4 3 1 3 1 17 3 3 4 3 1 3 1 1

8 4 1 5 3 1 2 1 19 3 2 5 3 1 2 1 1

10 4 2 5 3 1 2 1 1

11 4 3 5 3 1 2 1 1

12 4 4 5 2 1 2 1 1

13 3 3 NA NA a) 3 a) 2

14 4 4 NA NA a) 3 a) 2

15 5 5 NA NA a) 3 a) 2

16 6 6 NA NA a) 2 a) 2

17 7 7 NA NA a) 1 0 2

18 8 8 NA NA 0 0 0 2

19 6 2 NA 3 b) 2 c) 1

20 6 3 NA 3 b) 2 c) 1

21 6 4 NA 3 b) 2 c) 122 6 4 NA 2 b) 2 c) 1

23 6 6 NA 2 b) 2 c) 1

24 8 2 NA 3 b) 2 c) 1

25 8 3 NA 3 b) 2 c) 1

26 8 4 NA 3 b) 2 c) 1

27 8 4 NA 2 b) 2 c) 1

28 8 6 NA 2 b) 2 c) 1

29 8 8 NA 2 b) 2 c) 1

Table 2 MS multislot class

Type 1 MS are not required to transmit and receive at the same time. Type 2 MSare required to be able to transmit and receive at the same time.

Rx describes the maximum number of receive timeslots that the MS can use per

TDMA frame. The receive TS need not be contiguous.





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Tx describes the maximum number of transmit timeslots that the MS can use per

TDMA frame. The transmit TS need not be contiguous.

Sum is the total number of uplink and downlink TS that can actually be used bythe MS per TDMA frame.

Tta relates to the time needed for the MS to perform adjacent cell signal levelmeasurement and get ready to transmit. For type 2 MS it is not applicable.

Ttb relates to the time needed for the MS to get ready to transmit. This minimum

requirement will only be used when adjacent cell power measurements are notrequired by the service selected.

Tra relates to the time needed for the MS to perform adjacent cell signal levelmeasurement and get ready to receive.

Trb relates to the time needed for the MS to get ready to receive. This minimum

requirement will only be used when adjacent cell power measurements are not

required by the service selected.Example: Multislot class 12

Maximum number of DL channels = 4, UL channels = 4, time needed toswitch from receiving to sending Ttb = 1, time needed to switch from

sending to receiving and to perform measurements Tra = 2.

There can be several channel configurations which conform with the above

restrictions. One example, where four downlink TCHs (x) are allocated fordata transfer and the place of the uplink PACCH (p) is determined:

DL x x x xtb ra ra

UL

Figure 6 Multislot class 12

Type 1, MS multislot classes 1 - 12

Multislot classes 1 - 18 were defined at the time when HSCSD was specified.

There the type 1 classes 1 - 12 enables maximum of four downlink or uplink TSand five as a sum of donwlink and uplink TS (see example). For HSCSD only

downlink biased asymmetry is possible, so 3+2 (downlink+uplink) and 4+1 arethe maximum configurations. In GPRS the asymmetry can be also uplink biased.

There the maximum number of uplink TS is dependent on the allocation method

(see uplink data transfer):





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• 2 with dynamic allocation

• 3 with extended dynamic allocation

• 4 with fixed allocation

Only dynamic allocation is supported in Nokia GPRS release 1. Data traffic is

very downlink biased and MS hardware implementation is more complex themore there are uplink channels.


These types include separate radio parts for receiving and transmitting, so there

are no restrictions to have time to change frequencies during the datatransmission. From the network point of view up to eigth TS can be supported

for both downlink and uplink (regardless of the uplink allocation method) in

GPRS. These kind of MSs would be very high priced and may not be available

in the near future.


These types were introduced with GPRS knowing the fact that there doesn'tneed to be transmission to both dowlink and uplink direction in every TDMA-

frame. Example in the figure (where is it) shows a six TSL downlink data

transmission. TDMA-frames where the MS sends an acknowledgement canhave only four DL TCH TS, but TDMA-frames where there is no uplink

signalling six TS can be used.

Nokia GPRS release one supports maximum of six downlink TS to these

multislot classes. In theory it could be eight, but there needs to be time for theMS to make neighbour cell measurements and if the eight TS were assigned to

an MS, the network should schedule also gaps for MSs neighbour cell

measurements and that would complicate the PCU implementation. Seven or

eigth TS MSs are not expected to be on market in the near future.

In the uplink direction same restrictions apply as for multislot classes 1 - 12.



GPRS Air Interface Channels


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4 GPRS Air Interface Channels

The figure below shows the GPRS air interface data flow.

BH

FH

LLC layer

RLC/MAC layer

Physical layer

Information field FCS

Normal burst Normal burst Normal burst Normal burst

Info fieldBH BCSRLCblocks

LLC frame

Primaryblock

Followingblock

Info field BCS Info fieldBH BCS

FH = Frame HeaderFCS= Frame Check SequenceBH = Block HeaderBCS= Block Check Sequence

(When SDCCH coding is used, BCS corresponds to the Fire code)

Figure 7 Transmission and Reception Data Flow

LLC

Logical Link Control (LLC): This layer provides a highly reliable cipheredlogical link. LLC shall be independent of the underlying radio interface

protocols in order to allow introduction of alternative GPRS radio solutions withminimum changes to the NSS.

LLC frames are sent between MS and SGSN. LLC has its own ARQ

(retransmissions).

RLC

The Radio Link Control function provides a radio-solution-dependent reliable

link. RLC blocks are sent between MS and BSS (PCU). There are two RLC

modes: acknowledge and unacknowledge mode. The latter doesn't have

retransmission.

Downlink data transmission

PCU receives LLC frames from SGSN, segments them to RLC blocks and sendsRLC blocks to MS. In normal case LLC frame is buffered in PCU as long as it

has been sent to MS including retransmission.





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Uplink data transmission

The PCU receives RLC data blocks from MS, reassembles them to LLC frames.

When the LLC frame is ready it is sent to SGSN and released from PCU buffer.However, the LLC frames have to be sent to SGSN in the order they are

received from the MS.

MS BSS SGSN

CHANNEL REQUEST

IMMEDIATE ASSIGNMENT

PACKET RESOURCE REQUEST

PACKET UPLINK ASSIGNMENT

(OPTIONAL)

(OPTIONAL)

RACH

AGCH

PACCH

PACCH

Figure 8 Packet Data Transfer:Uplink

Common Control Channel signalling

Common control channel signalling is used for the following:

Paging

• SGSN initiates, paging area is BSS, Location Area, Routing Area or Cell

• Special case is a CS page on PACCH when MS is in GPRS transfer state

Uplink TBF setup

• single block access on two phase uplink access

• one phase access, where only 1 TCH is reserved

Downlink TBF setup

PACCH usage

The PACCH is used for the following functions:

• Uplink two phase access

• Establishment of other side (uplink or downlink) TBF when other side exists

• Packet Uplink ACK/NACK





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• Packet Downlink ACK/NACK

• Packet Polling procedure to obtain initial Timing Advance value during

downlink TBF establishment

• Radio resource re-assignment



GPRS Uplink


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5 GPRS Uplink

5.1 Uplink TBF establishment

When the MS wants to send data or upper layer signaling messages to the

network, it requests establishment of an uplink TBF. If the MS is initially in the

packet idle mode, the request is sent via the CCCH channel. The establishment

is carried out either as one phase access, or two phase access depending on theneeds for the data transfer. If the MS is already in the packet transfer mode i.e. it

has a downlink TBF, the request can be sent using the PACCH channel assigned

to the downlink TBF. This may be needed eg. for upper layer

acknowledgements.

One phase access

In one phase access the MS sends the network CHANNEL REQUEST message

with establishment cause 'one phase access'. PCU can allocate one TCH for such

request, which is told to MS in IMMEDIATE ASSIGNMENT message. TFI and

USF values are told in the message. MS sends its TLLI in the first data blocksand the one phase access is finalized when the PCU sends PACKET UPLINK

ACK/NACK message to the MS containing the TLLI (contention resolution).

Note that contention resolution in one phase access is not included to signaling

figures.

If there are no TCHs to give for the MS, IMMEDIATE ASSIGMENT REJECT

message is sent to MS. One phase access is guarded by a timer in PCU.

Two phase access

In two phase access the MS sends the PCU CHANNEL REQUEST message

with establishment cause 'single block access'. PCU allocates one TCH for that

request and also schedules a certain frame number for that block. The TCH andthe frame number are told to MS in IMMEDIATE ASSIGNMENT message.

MS uses the allocated block to send the PCU more accurate request with

message PACKET RESOURCE REQUEST.

If there are no TCHs to give for the MS, IMMEDIATE ASSIGMENT REJECT

message is sent to MS.

The actual configuration for uplink TBF is made by the information received in

PACKET RESOURCE REQUEST message. The TCH configuration, USF

value for each TCH and TFI are told to MS in PACKET UPLINKASSIGNMENT message sent in PACCH. The PACCH is sent in the same TSL



GPRS Uplink


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as was used in first phase, but assigned TCHs may be elsewhere. The two phase

access is finalized when the first block on the assigned TCHs is received.

In two phase access the contention resolution procedure is done in a way thatMS sends its TLLI in the PACKET RESOURCE REQUEST message and the

PCU includes that in the PACKET UPLINK ASSIGNMENT message.

The channel allocation in the second phase of the two phase access is

independent of the first phase and if there are no TCHs to give for the MS,

PACKET ACCESS REJECT message is sent to MS. Second part of the two

phase access is also quarded with a timer.

Uplink TBF establishment when downlink TBF exists

During a downlink TBF the MS can request resources for an uplink TBF by

including Channel Request Description IE in the PACKET DOWNLINK

ACK/NACK message. If there is no need to change the downlink TCHconfiguration PACKET UPLINK ASSIGNMENT message is used to tell the

uplink TCH configuration, USF values for each TCH and TFI to the MS. If thedownlink TCH configuration is changed PACKET TIMESLOT

RECONFIGURE message is used to tell the MS both the uplink and downlink TCH configurations, USF values for the uplink TCHs and uplink and downlink

TFIs. The procedure is ready when first block on the assigned uplink TCHs is

received.

This procedure is guarded by a timer. If PACKET UPLINK ASSIGNMENTfails, the uplink TBF is released. If the PACKET TIMESLOT RECONFIGURE

fails, both downlink and uplink TBFs are released.

MS BSS SGSN

DATA BLOCK

DATA BLOCK

PACKET UPLINK ACK/NACK

DATA BLOCK

DATA BLOCK (last)

PACKET UPLINK ASSIGNMENT


PACKET CONTROL ACK

LLC PDU

PDTCH

PDTCH

PDTCH

PDTCH

PACCH

PACCH

PACCH

PACCH

Figure 9 Packet Data Transfer:Uplink



GPRS Uplink


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5.2 Medium Access (MAC) modes

The PCU can assign multiple MSs to the same uplink TCHs. ETSIspecifications allow the scheduling of uplink transmission turns to be done by

three different MAC modes: dynamic allocation, extended dynamic allocation

and fixed allocation. Nokia GPRS release 1 will support only dynamicallocation.

Dynamic allocation

In the assignment message the MS is given an USF value for each assignedTCH. the MS monitors the downlink RLC blocks on the TCHs it has been

assigned. Whenever the MS finds the USF value in the downlink RLC block, it

may send an uplink RLC block in the corresponding uplink frame. The

scheduling of RLC data block in each TSL is independent of other TS.

5.3 Uplink data transfer (acknowledgedmode)

RLC data blocks are collected to PCUs buffer. PCU has a receive window for 64

RLC blocks. That is the maximum number of unacknowledged RLC blocks. To

make the RLC data flow fluent the acknowledgements should be sent morefrequently. PCU can schedule the MS to send further RLC data blocks along

with the acknowledgement procedure.

PCU can sent PACKET UPLINK ACK/NACK message to MS whenever itwants. This however requires usage of downlink PACCH and is not reasonableto sent them too often. PACKET UPLINK ACK/NACK message includes a

bitmap which tells the correctly received blocks relative to the last correctly

received block (details can be found from GSM04.60). PACKET UPLINKACK/NACK message can be used for other purposes too, eg. to change coding

scheme and that also effects to the frequency of the acknowledgements.

PCU has a counter to control the MSs ability to sent RLC blocks in the frames it

has been assigned by USF values. Counter is reset always when the MS uses theframe it has been scheduled. If the counter reaches its maximum value the

uplink TBF is released.

PCU can change the uplink TCH configuration whenever it wants by sending

the MS PACKET UPLINK ASSIGNMENT or PACKET TIMESLOT

RECONFIGURE message. Reasons for reallocation are:

• GPRS territory downgrade



GPRS Uplink


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• downlink TBF establishment

• MSs change of requirements

If the reallocation is impossible for example in the case of GPRS territory

downgrade the PCU may release a TBF by PDCH RELEASE message.

Normal uplink TBF release is done by a countdown procedure. There the MScounts down the last RLC data blocks (15 or less) with the last last block numbered 0. There may be still some retransmission. When all the RLC data

blocks have been received correctly the PCU sends the LLC frame to SGSN and

a PACKET UPLINK ACK/NACK message with final ack indicator to MS. MSresponds to that with PACKET CONTROL ACK message and the TBF can be

released.



GPRS Downlink


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6 GPRS Downlink

6.1 PS Paging

The PCU forwards the paging to the correct CCCH(s). The MS's paging

response is as any other uplink data transmission. MS sends some LLC frame to

SGSN and cell id is included in the message towards the SGSN. This is shown

in the figure below.

MS BSS SGSN

Packet Paging Request

Packet Paging Request

CHANNEL REQUEST


DATA BLOCK (last)


PACKET CONTROL ACK

LLC PDU

PDTCH

PACCH

PACCH

PCH

RACH

AGCH

Figure 10 GPRS Paging

6.2 Downlink TBF establishment

Once the SGSN knows the MS location it can send LLC frames to correct PCU.SGSN tells the cell id in every message where it sends the LLC frame. PCU

allocates TCHs for the TBF. Assigned TCH and TFI are told to MS in

IMMEDIATE ASSIGNMENT message. Only one TCH can be assigned in theIMMEDIATE ASSIGNMENT. The actual allocation for multislot is done in the

beginning but it is told to MS by reallocation message.

When the MS is ready, the PCU sends a control message to the MS and requests

acknowledgement from the MS. This is done in order to determine the initialTiming Advance for the MS. If the channel configuration reserved for the DL

TBF consists only of one channel already assigned to the MS, the control



GPRS Downlink


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message sent is PACKET POLLING REQUEST. If the resources allocated form

a multislot configuration a PACKET DOWNLINK ASSIGNMENT message issent, and the whole configuration is given to the MS. The Timing Advance

value measured by BTS is included in PACKET POWER CONTROL/TIMING

ADVANCE message sent to MS.

In the case the are no radio resources for new TBF, the LLC frame is discardedand DISCARD message is sent to SGSN. Assignment procedure is guarded withtwo timers, one for resending the IMMEDIATE ASSIGNMENT message and

one for aborting the establishment.

Downlink TBF establishment when Uplink TBF exists

This follows the same principles as uplink TBF establishment when downlink

TBF exists.

6.3 Downlink Data transfer

MS BSS SGSN

PACKET DOWNLINK ASSIGNMENT

LLC PDU


Four access bursts

DATA BLOCK

PACKET DOWNLINK ASSIGNMENT

DATA BLOCK (polling, final)

PACKET DOWNLINK ACK/NACK

PDTCH

PDTCH

PDTCH

PDTCH

PACCH

PACCH

PACCH

AGCH

PACKET POWER CONTROL/TIMING ADVANCE

Figure 11 Packet Data Transfer:Downlink

The MS recognizes the RLC blocks sent to it by the TFI, which is included in

every RLC block header.

The PCU has 64 block transmit window, that is the maximum number of

unacknowledged RLC blocks. The PCU can ask whenever the MS to send an

DOWNLINK ACK/NACK message by setting polling flag to RLC data block header. PCU can sent further RLC data blocks along with the acknowledgement



GPRS Downlink


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procedure. Due to Abis transmission delays the fluent polling mechanism is

important especially in downlink data transfer.

If the PCU doesn't receive PACKET DOWNLINK ACK/NACK message whenit has polled, it increments a counter. After N consecutive unanswered pollings

the MS is considered lost and the downlink TBF is released, the LLC frame is

discarded from the PCU buffer and discard message is sent to SGSN.

PCU can change the downlink TCH configuration whenever it wants by sending

the MS PACKET DOWNLINK ASSIGNMENT or PACKET TIMESLOT

RECONFIGURE message. Reasons for reallocation are:

• GPRS territory downgrade

• uplink TBF establishment

• SGSN change of requirements

If the reallocation is impossible for example in the case of GPRS territory

downgrade the PCU may release a TBF by PDCH RELEASE message.The normal downlink TBF release is initiated by the PCU by setting a Final

Block Indicator FBI bit in the last RLC block header. There may be still some

retransmission. TBF can be released and the LLC frame removed from the PCUbuffer when the MS sends PACKET DOWNLINK ACK/NACK message with

Final Ack Indicator bit on.



Power Control


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7 Power Control

7.1 Uplink Power Control

Nokia GPRS Release 1 supports uplink power control. It is used for optimising

the signal strength from MS to BTS.

• Uplink power control

PCH = min(Γ 0

− Γ CH - α∗(C + 48),PMAX)

0

5

1015

20

2530

35

- 4 5

- 5 0

- 5 5

- 6 0

- 6 5

- 7 0

- 7 5

- 8 0

- 8 5

- 9 0

- 9 5

- 1 0 0

- 1 0 5

- 1 1 0

Signal Strength (dBm)

M S O u t p

u t P o w e r

( d

B m )

gamma_ch = 30 alfa = 0.8

gamma_ch = 20, alfa = 0.3

Figure 12 Power control

Power Control parameters

Operator is given cell specific parameters α and Γ CH used in formula

• Γ CH, sets the minimum power level

• α, sets the slope for field streng effect to uplink power level

7.2 Downlink power control

The standardization of downlink power control is still ongoing.



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The downlink power control is a feature candidate for future releases (BSS10)

Power of each block needs to be sufficient for two MSs

• MS receiving the data

• MS receiving the USF flag

By the current ETSI specs the uplink MSs receiving the USFs in downlink direction are not reporting any measurements. Each new TBF is started with

maximum power. MSs Adaptive Gain Control:

• Dynamic downlink power control range 10 dB

• B0 of each multiframe must be sent with max power



Coding Scheme Selection


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8 Coding Scheme Selection

Nokia Simulations - polling interval = 18 blocks, non-frequency hopping)

• All Nokia BTS support GPRS without any modification (CS1 & CS2)

•8 Timeslot parallel connections supported

0

5

10

15

20

25

30

35

40

45

4 6 8 10 12 14 16 18 20 22 24

0

5

10

15

20

25

4 6 8 10 12 14 16 18 20 22 24

K b i t / s

C/I

CS-4

CS-3CS-2

CS-1

Network throughput - 1 Timeslot

Typical NW C/I

Minimum Average

C/I

Network throughput - 3 Timeslots

Typical NW C/I

Minimum AverageCS-2

CS-1

K b i t / s

Figure 13 GPRS Coding Schemes

Coding schemes

Stealing bits in the channel coding (for more information see GSM05.03) are

used to indicate the actual coding scheme (CS) which is used for each block

sent.

In downlink packet transfer the PCU selects the CS and the code word for the

selected CS is included in each sent RLC data block. If the CS is changed duringone TBF reservation, the new CS code word is included to the blocks.

In uplink data transfer the initial CS to be used is told to the MS in either theIMMEDIATE ASSIGNMENT or PACKET UPLINK ASSIGNMENT message.

The PCU can command the MS to change the CS by sending PACKET

UPLINK ACK/NACK message, which includes the Channel Coding Command

field.

In retransmission the same CS has to be used as in the initial block transmission.

Coding schemes CS-1 and CS-2 are supported in Nokia GPRS release 1.

GPRS radio link measurements

• Uplink RX_LEV and RX_QUAL in uplink transfer



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• Downlink RX_LEV, RX_QUAL, SIGN_VAR and interference level in

downlink transfer

Uplink CS selection

CS change will be based on the BLER.

Downlink CS selection

CS change will be based on the BLER.



Cell Selection and Re-selection

9 Cell Selection and Re-selection

• MS selects the cell in standby state

• C1/C2

• MS reselects the cell in ready state (handover)

• C1/C2

• MS stops the transmission in the old cell

• MS reads system information messages in the new cell

• MS reports to the SGSN

• initiates uplink TBF (data, signalling or dummy) or

• makes routing area update

• If the target cell is in the same RA and handled by the same PCU the data isrerouted

• If the target cell is in different RA or PCU, the data is discarded

Figure 14 GPRS Cell Selection and Re-selection

Network Control Order

The network may request measurement reports from the MS and control its cell

re-selection. This is indicated by the parameter

NETWORK_CONTROL_ORDER:

• NC0, the MS performs autonomous cell re-selection.

• NC1, the MS sends measurement reports to the network, but performs still

autonomous cell re-selection.

• NC2, the MS sends measurement reports to the network and the network performs the cell re-selection.

The parameter values NC1 and NC2 only apply in Ready state. In Standby state,

the MS shall always use normal MS control independent of the ordered NC

mode.

NC0 method is supported in Nokia GPRS release 1

01_Nokia GPRS Radio Resource Management

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