(E)gprs coding schemes

1 © Nokia Siemens Networks

BSSPAR1: Chapter 12(E)GPRS


Course Objectives

• Give an overview of CS and MCS coding schemes

• Explain parameters required for enabling GPRS/EDGE

• Explain how cell reselection is done in EGPRS

• Explain the parameter for EGPRS resource allocation and the setting of CS and PS territory parameters

• Describe parameters controlling link adaptation in GPRS and EDGE

• Explain how power control is done in EGPRS and the parameters controlling it

• Describe parameters for TBF release delay


System PrinciplesNetwork elements and interfaces

Protocols

Air interface and logical channels


(E)GPRS Network Infrastructure

GPRS IPBackboneNetwork

DNS

CG

GGSN

Internet

Corporate 1Intranet

LIG

Corporate 2Intranet

SS7Network

PSTNMSCBSCBTS

MS

EIR

HLR/AuC

SMS-GMSC

SGSN

SGSN

SGSN

MODEMPOOL FOR DIALUP

Nokia IP650 sec GW

Router

Router

RouterSTM-1

STM-1

SGSN

GGSN

Router

Router

Nokia Security GW

LAN SWITCH

MODEMPOOL FOR DIALUP

Nokia Security GW

Nokia Security GW

Nokia IP650 sec GW

Nokia IP650 sec GW

Nokia Security GW


(E)GPRS Network Elements and Primary Functions

SGSN• Mobility Management• MS Authentication• Ciphering• Interaction with

VLR/HLR• Charging and statistics• GTP tunnelling to

other GSNs

GGSNGTP tunnelling to other GSNsSecure interfaces to external networksCharging & statisticsIP address management

Charging Gateway

CDR consolidation

Forwarding CDR information to billing center

Border Gateway• Interconnects

different GPRS operators' backbones

• Enables GPRS roaming• Standard Nokia IP

router family

Domain Name Server• Translates IP host names to IP

addresses• Makes IP network configuration

easier• In GPRS backbone SGSN uses DNS

to get GGSN and SGSN IP addresses

• Two DNS servers in the backbone to provide redundancy

Legal Interception Gateway• Enables authorities to intercept

subscriber data and signaling• Chasing criminal activity• Operator personnel has very

limited access to LI functionality• LI is required when launching the

GPRS service


NSN - Fully ETSI Compliant Interfaces

Gf

D

Gi

Gn

GbGc

CE

Gp

Gs

Signaling and Data Transfer InterfaceSignaling Interface

MSC/VLR

TE MT BSS TEPDN

R Um

GrA

HLR

Other PLMN

SGSN

GGSN

Gd

SM-SCSMS-GMSCSMS-IWMSC

GGSN

EIR

SGSN

Gn


Bursts on the Air Interface – Mapping RLC blocks

1 TDMA frame = 4.615 ms= BURST PERIOD

RLC/MAC Blocks

TDMA Bursts

RLC Blocks

4 x TDMA Frames = 4 Bursts = 1 Radio block = 1-2 RLC block(s)

Note: Amount of RLC blocks per radio block

depends on used (modulation) coding

scheme (M)CS0 70 70 70 7

12 x RLC/MAC Blocks = 1 x 52 PDCH MultiFrame = 240 ms12 radio Blocks / 0.240 s = 50 RLC/MAC Blocks / s

0 1 2 3 4 5 6 7 8 9 10

11

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51

B0(0..3)

B1(4..7)

B2 (8..11)

PTCCH

B3(13..16)

B4(17..20)

B5(21..24)

IDLE

B6(26..29)

B7(30..33)

B8(34..37)

PTCCH

B9(39..42)

B10(43..46)

B11(47..50)

IDLE

52 TDMA Frames (240 ms)


(E)GPRS Logical Channels

GPRS Air Interface Logical Channels

CCCHCommon Control Channels

DCHDedicated Channels

PCHPaging CH

AGCHAccess Grant CH

RACHRandom Access CH

Existing GSM Channels

PACCHPacket Associated

Control CHPDTCH

Packet Data TCH

NEW GPRS Channels

No new EGPRS parameters related to logical channels! AGCH PCH setting affect both GSM voice and data.


State and Mobility Management and TBF establishmentGPRS Attach / DetachRA / LA UpdatePDP Context ActivationTBF establishment


(E)GPRS Mobile StatesNSN SGSN parameters

Idle

Standby

Ready

PacketTX/RX

STANDBYTimer Expiry

STBY

GPRSAttach/ Detach

MSRT, DET

READYTimer Expiry

RDY

MS location known to SGSN level.MS is capable of receiving Point-to-Multipoint data and being paged for Point-to-Point data

MS location not known. Subscriber is notreachable by the GPRS NW.

MS location known to cell level.MS is transmitting or has just been transmitting. MS is capable of receiving Point-to-Point data and Point-to-Multipoint data.

The relation of Mobile states:

• Ready State Timer (RDY) – Default: 44 seconds• STANDBY state timer (STBY) – Default: 44 seconds• Periodic update timer (PER) = default 54 minutes• Force to Standby (FTS) – Default: N• Detach timer (DET) – Default: 00 hours – 00 minutes• MS Reachable Timer (MSRT) – Default: 120 minutes


Routing Area

• Routing Areas are used for GPRS Mobility Management– A RA is a subset of one, and only one,

Location Area– A RA is served by only one SGSN– For simplicity, the LA and RA can be the same

• Routing area identification – (RAI) = MCC+MNC+LAC+RAC Routing Areas are created in the BSS Radio

Network Configuration Database (BSDATA)

• NSN SGSN parameters related to RA:– Periodic RA Update Timer (PRAU) – Default:

54 minutes– RA Paging Area (RPA) – Default: 2– RA Paging Repetition (RPR) – Default: 3.5

seconds

Location Area (LA)

Routing Area (RA)

SGSN

MSC/VLR

Gs Interface


Attach Procedure

• GPRS Attach procedure is used for the following two purposes:– a normal GPRS Attach - attach the IMSI for GPRS services only

– a combined GPRS Attach - attach the IMSI for GPRS and non-GPRS services (needs Gs interface)

• Attach procedure description– MS initiates by sending Attach Request

– If network accepts, it sends Attach Accept

– If network does not accept it sends Attach Rejected

– MS can respond for Attach Accept message with Attach Complete (if P-TMSI changes)

Attach Request

Attach Accept


• PDP Context (Packet Data Protocol): • Network level information which is used to bind a mobile station

(MS) to various PDP addresses and to unbind the mobile station from these addresses after use

• PDP Context Activation• Gets an IP address from the network• Initiated by the MS• Contains QoS and routing information enabling data transfer

between MS and GGSN• PDP Context Activation and Deactivation should occur within 2

seconds

Session Management - Establishing a PDP Context

PDP Context Request

155.131.33.55


Temporary Block Flow

Temporary Block Flow (TBF):• Physical connection where multiple mobile stations can share one or more traffic

channels – each MS has own TFI (Temporary Flow Indicator)• The traffic channel is dedicated to one mobile station at a time (one mobile station

is transmitting or receiving at a time)• Is a one-way session for packet data transfer between MS and BSC (PCU)• Uses either uplink or downlink but not both (except for associated signaling)• Can use one or more TSLs

Comparison with circuit-switched:normally one connection uses both the uplink and the downlink timeslot(s) for traffic

In two-way data transfer:uplink and downlink data are sent in separate TBFs - as below

BSCBSC

Uplink TBF (+ PACCH for downlink TBF)

Downlink TBF (+ PACCH for uplink TBF)

PACCH (Packet Associated Control Channel): Similar to GSM CS SACCH


PSW territory and multislot usage(E)GPRS Territory

PSW Activation, Territory and Allocation

Free TSL Size

Configuration parameters


(E)GPRS TerritoryIntroduction

• Territories consists of consecutive timeslots (starting from RTSL7)

• GPRS dedicated time slots (CDED) can be defined. Only (E)GPRS can use them.

• PS territory TRX has to be defined by enabling the GTRX parameter

• Dedicated territory (CDEF) is subset of Default territory

• The Maximum GPRS capacity (CMAX) defined the total maximum size for the (E)GPRS territory

Dedicated GPRS Capacity (%)

TS TS TS TS TS TS TSTS

Default GPRS Capacity CDEF (%)

Additional GPRS capacity

Maximum GPRS

Capacity (%)Free time slots in Circuit Switched territory

GTRX=Y



• Territory movement (upgrade and downgrade) are affected by– PS traffic Nr of TBFs per Radio timeslot can get above the allowed threshold () and the

territory will be upgraded (if possible)

– CS traffic CS has priority over PS outside the dedicated territory and can downgrade

the territory

• The amount of timeslots for data will depend also on the parameters– CSU - Free TSL for CS Upgrade

– CSD - Free TSL for CS Downgrade

– Territory upgrade in interval of Territory Upgrade Guard Time (both for upgrade and downgrade)



BCCHTRX 1, GTRX=N

TRX 2, GTRX=Y

TSCircuit Switched Territory

Circuit / Packet Switched TerritoryDedicated GPRS

Capacity (%)

TS TS TS TS TS TS

TS TS TS TS TS TS TSTS

Territory downgrade forced by the Circuit Switched traffic

Territory upgrade in interval of Territory Upgrade Guard Time. Valid for upgrades / downgrades due to (E)GPRS traffic.

Default GPRS capacity thresholdAdditional GPRS capacity

Free time slots in Circuit Switched territory

Default GPRS Capacity (%)

Maximum GPRS

Capacity (%)


PSW Activation, Territory and Allocation ParametersPSW Activation BTSGPRS Enabled (GENA)EGPRS Enabled (EGENA)GPRS Cell Barred (GBAR)Not Allowed Access Classes (ACC) TRXGPRS Enabled TRX (GTRX)NeighbourAdjacent GPRS Enabled (AGENA)

Territory SettingsBTSDefault GPRS Capacity (CDEF)Dedicated GPRS Capacity (CDED)MAX GPRS Capacity (CMAX)BSCGPRS territory update guard time (GTUGT)

Channel Allocation Parameters SEGPrefer BCCH frequency GPRS (BFG)TRX priority in TCH allocation (TRP)

Free TSLsBSCFree TSL for CS Upgrade (CSU) Free TSL for CS Downgrade (CSD)


Territory Setting Parameters – calculation method

• Dedicated GPRS Capacity (CDED) – timeslots only for PS (no CS)

• Default GPRS Capacity (CDEF) - timeslots primarily for PS (CS can overtake)

• MAX GPRS Capacity (CMAX) –maximum territory size

• CDED/CDEF/CMAX percentage is converted to TSL by multiplying it with all FR traffic capable TSLs (FR/DR) of the cell where GTRX=Y.

• Signaling and HR TSLs of TRXs (where GTRX=Y) are not taken into account in the calculation.

• The product of CDED/CDEF/CMAX and FR capable TSLs (GTRX=Y) is rounded down to a whole number

• Rounding up will take place only when CDED/CDEF/CMAX value > 0% and rounding would result to 0.

Territory size (TSL) =

Rounddown (CDED/CDEF/CMAX(%) x FR capable TSLs, where GTRX=Y)


Territory setting parameters - example

Table below provides example how same parameter setting can result different territory sizes with different GRTX/TRX configurations

23 RTSL17 RTSL11 RTSL5 RTSLCMAX = 80%

8 RTSL6 RTSL4 RTSL2 RTSLCDEF = 30%

1 RTSL1 RTSL1 RTSL1 RTSLCDED = 1%

3221# of signaling RTSL (GTRX =Y)

4321# of TRXs (GTRX=Y)

Any setting 1…20% of CDEF with 1 TRX configuration (GTRX=1) will result 1 TSL territory.


Resource Allocation PSW Activation and Territory - SEGTRX priority in TCH allocation (TRP) - voice

– TRP defines whether the BCCH TRX or other TRXs are preferred in traffic channel allocation.

• Values– 0 (No prioritization between TRXs, all TRXs are

treated equally in TCH allocation)

– 1 (Traffic channel is allocated primarily from the BCCH TRX.)

– 2 (Traffic channel is allocated primarily from another TRX than the BCCH TRX)

– 3 (Traffic channel is allocated primarily from the BCCH TRX for the non-AMR users and for the AMR users primarily beyond the BCCH TRX)

• Default– No Priority (0)

Prefer BCCH frequency GPRS (BFG) - data– BFG defines whether the BCCH TRX or other TRXs

are preferred in GPRS channel allocation.

• Values– 0 (no prioritization is determined between TRXs),

– 1 (GPRS channels are allocated primarily from the BCCH TRX),

– 2 (GPRS channels are allocated primarily beyond the BCCH TRX)

• Default– No (0)

GPRSTRX3

GPRSTRX2 12

EGPRSTRX1 (BCCH)

BTS1

BFGTRPTRX capabilityTRX IDBTS ID

An example how to allocate voice primarily to nonBCCH and

data to BCCH (because of EGPRS capability of BCCH TRX):


Free TSL Size (after CS Upgrade and Downgrade)

When a downgrade or upgrade procedure is requested, then the CSD and CSU parameters can reduce or increase the border between CSW andPSW territories.

TSL number after CS downgrade

TRX number 1 2 3 4 5

70 0 0 0 1 1

95 1 1 1 2 2

99 1 1 2 2 3

TSL number after CS upgradeTRX number 1 2 3 4 5

1 0 1 1 1 2

4 1 2 2 3 4

7 1 2 3 4 5

10 2 3 4 5 6

free TSL for CS downgrade (%) (CSD)

free TSL for CS upgrade (sec) (CSU)


Abis Basic ConceptsPCM frame (E1)

One 64 kbit/s (8 bits) channel in PCM frame is called timeslot (TSL)One 16 kbit/s (2bits) channel timeslot is Sub-TSLPCM frame has 32 (E1) or 26 (E1) TSLs

One Radio timeslot corresponds one 16 kbit/sSub-TSL (BCCH, TCH/F etc.) and one TRX takes two TSLs from Abis

0 MCB LCB123456789101112131415161718 TCH 0 TCH 1 TCH 2 TCH 319 TCH 4 TCH 5 TCH 6 TCH 7202122232425 TRXsig2627 BCFsig28293031 Q1-management

One TRX has dedicated TRXsig of 16, 32 or 64 kbit/s

One BCF has dedicated BCFsig (16 or 64 kbit/s) for O&M

TRX1

Q1-management needed if TRS management under BSC

MCB/LCB required if loop topology is used


(E)GPRS Dynamic Abis Pool DAP Introduction• Fixed resources for signaling and voice

• Dynamic Abis pool (DAP) for data– Also named EDAP

– Predefined size 1-24 PCM TSL per DAP(Typically used range from 4 to 8 TSL)

– DAP can be shared by several TRXs in the same BCF (and same E1/T1)

– Max 20 TRXs per DAP

– Max 1600 DAPs per BSC3i 2000

– DAP + TRXsig + TCHs have to be in same PCM

– UL and DL DAP use is independent

– DAP schedule rounds for each active Radio Block

– Different users/RTSLs can use same DAP Sub-TSL

0 MCB LCB1234 TCH 0 TCH 1 TCH 2 TCH 35 TCH 4 TCH 5 TCH 6 TCH 76 TCH 0 TCH 1 TCH 2 TCH 37 TCH 4 TCH 5 TCH 6 TCH 78 TCH 0 TCH 1 TCH 2 TCH 39 TCH 4 TCH 5 TCH 6 TCH 7101112131415 EDAP EDAP EDAP EDAP16 EDAP EDAP EDAP EDAP17 EDAP EDAP EDAP EDAP18 EDAP EDAP EDAP EDAP19 EDAP EDAP EDAP EDAP20 EDAP EDAP EDAP EDAP21 EDAP EDAP EDAP EDAP22 EDAP EDAP EDAP EDAP232425 TRXsig1 TRXsig226 TRXsig327 BCFsig28293031 Q1-management

TRX1TRX2TRX3

EGPRS

pool


Configuration setupDAP configuration parameters Transceiver (TRX) radio network object parameters• dynamic abis pool ID (DAP)

– Used for indicating the dynamic Abis pool ID. This can be given only if the site type is Nokia MetroSite, Nokia UltraSite or Nokia FlexiEDGE.

Dynamic Abis Pool (DAP) radio network object parameters• BCSU ID (BCSU)

– This parameter identifies the base station signaling unit where the physical PCU card is installed and which should be attached to the logical PCU object

• PCU index (PCU)– This parameter identifies the packet control unit logical index of the physical

card.

• circuit (CRCT)– The parameter defines the Abis interface ET-PCM number and the time slots

reserved from the ET-PCM for the dynamic Abis pool. The pool size is from 1 to 24 ET-PCM TSLs.


Configuration setupDAP configuration parametersDynamic Abis Pool (DAP) radio network object parameters (cont.)• new first time slot (NFT)

– This parameter defines the new first time slot.

• new last time slot (NLT)– This parameter defines the new last time slot.

• Network Service Entity Identifier (NSEI)

• packet service entity identifier (PSEI)– This parameter identifies the Packet Service Entity object in the BSC (PSE). The Packet

Service Entity Identifier (PSEI) is used in the BSS to determine Packet Control Pool (PCP).

• pool identification (ID)– This parameter identifies the Pool id of the ACP object.

• pool size (SIZE)– This parameter defines the Pool size.


TSL utilizationAcknowledgement Request

Pre-emptive transmission

BS_CV_MAX


Acknowledgement Request

Acknowledgement Request• GPRS Uplink Penalty (default: 3)• GPRS Uplink Threshold (default: 22)• GPRS Downlink Penalty (default: 2)• GPRS Downlink Threshold (default: 16)• EGPRS Uplink Penalty (default: 1)• EGPRS Uplink Threshold (default: 25)• EGPRS Downlink Penalty (default: 1)• EGPRS Downlink Threshold (default: 25)

PRFILE PCU Telecom ParametersParameter 046: 0047 - 0054

• Functionality of EGPRS DL requests:– These parameters are used by the RLC

ACK algorithm to determine how frequently the PCU polls the mobile station having a TBF in EGPRS mode.

– The PCU has a counter, which is incremented by one whenever an RLC data block is transmitted for the first time

– The counter is incremented by (1 + EGPRS_DOWNLINK_PENALTY) whenever a negatively acknowledged RLC data block is retransmitted.

– The mobile station is polled when the counter exceeds the threshold value of EGPRS_DOWNLINK_THRESHOLD.


3

3

1

3

1

1

1

1

1

1

1

1

PenaltyIncrement

CounterTotal

3

6

9

10

11

12

13

14

15

16

17

18

RLC data block retransmission

New RLC data Block

RLC data block with poll

PCU

Packet Downlink ACK/NACK

Tim

e

Bitmap (64 Blocks)

MS

Acknowledgement Request - retransmission

GPRS Uplink Penalty = 3

GPRS Uplink Threshold = 18


Acknowledgement Request – no response

3

1

3

1

1

1

1

1

1

4

5

6

9

21

22

23

RLC data transmission

Packet Uplink ACK/NACK

USF

Time

PCU

MS

Packet Control ACK/NACK

PenaltyIncrement

CounterTotal


BS_CV_MAX

• The BS_CV_MAX functionality contains the following items:

– Transmission and acknowledgement MS is not expecting to receive NACK for the transmitted block until

(max(BS_CV_MAX,1) – 1) in RLC/MAC block period (20ms).

So the NACK in the PACKET UPLINK ACK/NACK message will be ignored, if the round trip time is less than (max(BS_CV_MAX,1) – 1).

If the BS_CV_MAX is e.g. 9, than the RTT will be (9-1)*20ms ->160ms

– BS_CV_MAX is also impacting T3200 (MS timer), N3104 (MS timer) and Countdown procedure


BS_CV_MAX

Nack message transmitted

MS BSS

Tim

e

BS_C

V_M

ax


TBF release and RTTTBF Release Delay

TBF Release Delay Extended


TBF Release Delay

• If there is not any RLC/MAC block received, the TBF will not be released immediately, but it can be kept alive for a given time period.

• There are two modifiable parameters related to Delayed TBF feature among PRFILE parameters:

– DL_TBF_RELEASE_DELAY (0,1-5sec, def 1s) Parameter 46:0067 Adjust the delay in downlink TBF release.

During DL delay period the possibly following uplink TBF can be established faster and frequent releases and re-establishments of downlink TBF can be avoided

– UL_TBF_RELEASE_DELAY (0,1-3sec, def 0,5s) Parameter 46:0068 This parameter is used to adjust the delay in uplink TBF release.

During UL delay period following downlink TBF can be established faster.


UL TBF Release with Extended UL TBF Mode (EUTM)• EUTM is Rel4 feature - MS support required. • If EUTM is activated (MML: ZWOA,PRFILE) and MS supports it the UL

TBF Release parameter is ignored.

• UL_TBF_REL_DELAY_EXT– This parameter defines the uplink TBF release delay time for mobile stations supporting

the Extended UL TBF Mode. – Default value: 1000D– Allowed values: 300D - 3000D, Increments: 100

• UL_TBF_SCHED_RATE_EXT– This parameter defines how often a USF is scheduled for the MS during the inactivity

period in Extended UL TBF Mode. Parameter value unit is 20 ms (block period). Eg. value 5 means 100 ms (5 block periods).

– Default value: 5D– Allowed values: 2D - 50D, Increments: 1


UL TBF Release with Extended UL TBF mode

MS BSC / PCU

Data block with CV = 0

EUTM delay timer starts

Schedule USF turn for MSUL dummy control block


EUTM delay timer expiresPACKET UL ACK/NACK (FAI=1, Polling=YES)

PACKET UL ACK/NACK (FAI=0, Polling=NO)

PACKET CONTROL ACKUL TBF terminated

Data block with CV = 1U

L TB

F ex

tend

ed s

tate

Short description:

• Countdown procedure is ongoing. EUTM supporting mobile is allowed to recalculate CV during procedure, if it gets more data to send. PCU notices this by monitoring Block Sequence Number (BSN) and Countdown value (CV) sent by MS.

• After receiving CV=0 block PCU starts UL extended state. It sends Packet Uplink Ack/Nack message to MS with no Final Ack Indicator (FAI) on, but acknowledging all received blocks.

• During UL extended state PCU schedules USFs for MS according adjustable scheduling rate parameter. If MS has no new data to send it sends UL dummy control blocks on its sending turn.

• When UL extended state ends, according adjustable release delay parameter, PCU sends Packet Uplink Ack/Nack message to MS with Final Ack Indicator (FAI) on.

UL TBF Schedule Rate Ext


MS does not continue TBF


UL TBF Release with Extended UL TBF mode

Short description:

• Countdown procedure is ongoing. After receiving CV=0 block PCU starts UL extended state. It sends Packet Uplink Ack/Nack message to MS with no Final Ack Indicator (FAI) on, but acknowledging all received blocks.

• During UL extended state PCU schedules USFs for MS according adjustable scheduling rate parameter. If MS has no new data to send it sends UL dummy control blocks on its sending turn.

• When MS gets new data to send during extended state, it sends UL data block with new BSN, and also new CV value when needed. Due BSN PCU knows that new UL LLC is to be sent by MS, and UL TBF continues as normally.

UL

TBF

exte

nded

sta

teMS BSC / PCU

Data block with CV = 0

EUTM delay timer starts

Schedule USF turn for MS

Data block with new BSN and CV

Schedule USF turn for MS

UL dummy control block

EUTM delay timer stopped, TBF continues

PACKET UL ACK/NACK (FAI=0, Polling=NO)

Data block

UL TBF Schedule Rate Ext

MS continues data transfer on TBF


Link AdaptationsGPRS Link Adaptation (CS1-2)

EGPRS Link Adaptation


Coding Scheme

Payload (bits)per RLC block

Data Rate (kbit/s)

CS1 181 9.05

CS2 268 13.4

CS3 312 15.6

CS4 428 21.4

More Data =

Less Error Correction

NSN GPRSPCU

• CS1 & CS2 – Implemented in all NSN BTS without HW change

• CS1 & CS4 – S11.5 (with PCU2) and UltraSite BTS SW CX4.1 CD1 (Talk does not support CS3 and CS4)

Da

ta

Err

or

Co

rre

ctio

n

GPRS Link Adaptation Algorithm (CS1-2)GPRS Coding Schemes

NSN GPRSPCU2


GPRS Link Adaptation Algorithm (CS1-2)Introduction with PCU1• The coding scheme will change based on BLER Thresholds.

• The BLER thresholds are defined by simulations and change from hopping to non hopping

networks

X

CS1 & CS2 Crosspoint

The crosspoint is defined by the following formula:

8.0 kbps * (1 - BLER_CP_CS1) = 12 kbps * (1 - BLER_CP_CS2) ,

where:– 8.0 kbps is the theoretical maximum bit rate for CS-1

– 12.0 kbps is the theoretical maximum bit rate for CS-2

– BLER_CP_CS1 is the block error rate at the crosspoint when CS-1 is used

– BLER_CP_CS2 is the block error rate at the crosspoint when CS-2 is used

– Averaging is based on 10 RLC/MAC blocks

The parameters on the following slides correspond to the BLER_CP_CS1. C/I (dB)

RLC/MAC throughput

(kbps)


GPRS Link Adaptation Algorithm (CS1-2) Parameters with PCU1• GPRS Coding Scheme No Hopping (COD)

– The selection of Coding Scheme in RLC Acknowledged mode is indicated (frequency hopping is not used). Range: Link Adaptation used (0),

CS-1 used (1), CS-2 used (2).

Default: CS-2 used (2)

• DL BLER Crosspoint for CS Selection Non Hopping (DLB)– The RLC BLER (block error rate percentage) for CS-1 channel coding is indicated. – At this point CS-1 and CS-2 give the same effective bit rate and Coding Scheme selection

criteria in RLC Acknowledged mode for downlink TBFs changes. – The parameter is meaningful only if link adaptation is used in case of no frequency

hopping. Range: 0...100 %, step 1 % . Default: 90%

• UL BLER Crosspoint for CS Selection Non Hopping (ULB)– Same as above but for UL Range: 0...100 %, step 1 % . Default: 90%


GPRS Link Adaptation Algorithm (CS1-2) Parameters with PCU1• GPRS Coding Scheme Hopping (CODH)

– The selection of Coding Scheme in RLC Acknowledged mode is indicated (frequency hopping is used). Range: Link Adaptation used (0), CS-1 used (1), CS-2 used (2). Default: Link Adaptation used (0)

• DL BLER Crosspoint for CS Selection Hopping (DLBH)– The RLC BLER (block error rate percentage) for CS-1 channel coding is

indicated. – At this point CS-1 and CS-2 give the same effective bit rate and Coding

Scheme selection criteria in RLC Acknowledged mode for downlink TBFs changes.

– The parameter is meaningful only if Link Adaptation and Frequency Hopping are used. Range: 0...100 %, step 1 % . Default: 20%

• UL BLER Crosspoint for CS Selection Hopping (ULBH)– Same as above but for UL. Range: 0...100 %, step 1 % . Default: 24%


GPRS Link Adaptation Algorithm (CS1-2) Parameters with PCU1

Calculation of the cross point of CS1 and CS2 is based on the following formula: 8.0 kbps * (1 - BLER_CP_CS1) = 12 kbps * (1 - BLER_CP_CS2)

The below examples shows the relation CS1 and CS2 from BLER point of view:

• COD (set to 2) with default DLB (set to 90%)– 8.0 kbps * (1 - BLER_CP_CS1(DLB: 90%)) = 12 kbps * (1 - BLER_CP_CS2(calculated: 94,4%))

CS1 will be selected instead of CS2 if CS2 has worse BLER than 94.4 %

• CODH (set to 2) with default DLBH (set to 20%)– 8.0 kbps * (1 - BLER_CP_CS1(DLB: 20%)) = 12 kbps * (1 - BLER_CP_CS2(calculated: 46,6%))

CS1 will be selected instead of CS2 if CS2 has worse BLER than 46.6 %

Remark: When the LA algorithm is used, the initial CS value at the beginning of a TBF is CS-2.


GPRS Link Adaptation Algorithm (CS1-2) Parameters with PCU1

• DL adaptation probability threshold (DLA)– The allowed probability (%) is defined for the system to make a wrong decision

in downlink adaptation. Range: 0...50 %, step 1 %

Default: 20%

• UL adaptation probability threshold (ULA)– The allowed probability (%) is defined for the system to make a wrong decision

in uplink adaptation. Range: 0...50 %, step 1 %

Default: 10%


GPRS Link Adaptation Algorithm (CS1-2) Introduction with PCU2

• A new Link Adaptation algorithm is introduced with PCU2, which replaces the previous GPRS LA algorithm implemented on PCU1 and covers the following coding schemes:– CS-1 and CS-2 if CS-3 and CS-4 support is disabled in the territory in question

– CS-1, CS-2, CS-3, and CS-4 if CS-3 and CS-4 support is enabled (BSSPAR2)

• PCU2 uses two 2-dim tables for the LA operation (Acks/Nacks and DL/UL separately)– The values in the tables are initially based on the simulations

– Fixed values used if adaptive LA algorithm (ALA)= ‘N’

– If ALA = ‘Y’, the table is updated based on RXQual measurements

– LA algorithm defines the optimal CS based on the updated values

Coding Scheme

RXQ

Updated based on RXQuality

measurements


GPRS Link Adaptation Algorithm (CS1-2) Parameters

• coding schemes CS3 and CS4 enabled (CS34)– With this parameter the operator can define whether the Coding

Schemes CS-3 and CS-4 capability is enabled in the BTS. Range: Coding schemes CS3 and CS4 are disabled (N) (0), Coding schemes

CS3 and CS4 are enabled (Y) (1). Default: Adaptive LA algorithm is enabled (Y) (0)

More information is available in BSSPAR2

• adaptive LA algorithm (ALA)– With this parameter the operator can define if the used GPRS Link

Adaptation algorithm is adaptive or not. Range: Adaptive LA algorithm is enabled (Y) (0), Adaptive LA algorithm is

disabled (N) (1). Default: Adaptive LA algorithm is enabled (Y) (0)


GPRS Link Adaptation Algorithm (CS1-2)Parameters

• DL Coding Scheme in Acknowledged Mode (DCSA)

• UL Coding Scheme in Acknowledged Mode (UCSA)– Defines the initial CS in acknowledge mode in downlink/uplink direction. Range: CS1 (0), CS2 (1), CS3 (2), CS4 (3), LA with initial CS1 (4), LA with

initial CS2 (5), LA with initial CS3 (6), LA with initial CS4 (7).

Default: CS2 (1)


Remark: The parameter values 2,3,6 and 7 are valid only for Nokia MetroSite, Nokia UltraSite and Nokia Flexi EDGE


GPRS Link Adaptation Algorithm (CS1-2)Parameters

• DL Coding Scheme in Unacknowledged Mode (DCSU)

• UL Coding Scheme in Unacknowledged Mode (UCSU)– Define the initial CS in unacknowledged mode downlink/uplink

direction. Range: CS1 (0), CS2 (1), CS3 (2), CS4 (3), LA with initial CS1 (4), LA with

initial CS2 (5), LA with initial CS3 (6), LA with initial CS4 (7).

Default: CS2 (1)


Remark: The parameter values 2,3,6 and 7 are valid only for Nokia MetroSite, Nokia UltraSite and Nokia Flexi EDGE


EGPRS Link Adaptation Introduction

• Link Adaptation– The task of the LA algorithm is to

select the optimal MCS for each radio condition to maximize RLC/MAC data rate, so the LA algorithm is used to adapt to situations where signal strength and/ or C/I level is pure and changing within time

– Normally, LA adapts to path loss and shadowing but not fast fading. IR is better suited to compensate fast fading

• Incremental Redundancy– The retransmission process is

based on Incremental Redundancy

– LA must take into account if IR combining is performed at the receiver.

– LA must take into account the effect of finite IR memory.


Coding Schemes in EGPRS

Scheme Code rate Header Code rate

Modulation RLC blocks per Radio

Block (20ms)

Raw Data within one

Radio Block

Family BCS Tail payload

HCS Data rate kb/s

MCS-9 1.0 0.36 2 2x592 A 59.2

MCS-8 0.92 0.36 2 2x544 A 54.4

MCS-7 0.76 0.36 2 2x448 B

2x12 2x6

44.8

MCS-6 0.49 1/3 1 592 544+48

A 29.6 27.2

MCS-5 0.37 1/3

8PSK

1 448 B 22.4

MCS-4 1.0 0.53 1 352 C 17.6

MCS-3 0.80 0.53 1 296 272+24

A 14.8 13.6

MCS-2 0.66 0.53 1 224 B 11.2

MCS-1 0.53 0.53

GMSK

1 176 C

12

6

8

8.8

NOTE: the italic captions indicate the padding.


EGPRS MCS Families

37 octets 37 octets 37 octets37 octets

MCS-3

MCS-6

Family A

MCS-9


MCS-2

MCS-5

MCS-7

Family B

22 octets22 octets

MCS-1

MCS-4

Family C

34+3octets34+3octets

MCS-3

MCS-6Family Apadding

MCS-8


• The MCSs are divided into different families A, B and C

• Each family has a different basic unit of payload: 37 (and 34), 28 and 22 octets respectively.

• Different code rates within a family are achieved by transmitting a different number of payload units within one Radio Block.

• For families A and B, 1 or 2 or 4 payload units are transmitted, for family C, only 1 or 2 payload units are transmitted

• When 4 payload units are transmitted (MCS 7, MSC-8 and MCS-9), these are splitted into two separate RLC blocks (with separate sequence BSN numbers and BCS, Block Check Sequences)

• The blocks are interleaved over two bursts only, for MCS-8 and MCS-9.

• For MCS-7 the blocks are interleaved over four bursts


EGPRS Link Adaptation Parameters

• EGPRS Link Adaptation Enabled (ELA)– The EGPRS link adaptation can be enabled /

disabled on cell level.

– If disabled the system uses the MCS value defined by initial MCS for acknowledged mode or initial MCS for unacknowledged mode parameters or a lower MCS. Range: EGPRS link adaptation is disabled (0),

enabled for RLC acknowledged mode (1), enabled for RLC acknowledged and unacknowledged (2) .

Default: enabled for RLC acknowledged and unacknowledged (2)

0

10

20

30

40

50

60

0 5 10 15 20 25 30

MCS-1MCS-2MCS-3MCS-4MCS-5MCS-6MCS-7MCS-8MCS-9LA

C/I (dB)

RLC/MAC throughput

(kbps)


EGPRS Link Adaptation Parameters

• Initial MCS for Acknowledged Mode (MCA)– Modulation and Coding Scheme (MCS) used at the beginning of a TBF for

acknowledged mode. The parameter is used in EGPRS link adaptation. Range: 1...9, step 1. Default: 6

• Initial MCS for Unacknowledged Mode (MCU)– MCS used at the beginning of a TBF for unacknowledged mode. The parameter

is used in EGPRS link adaptation Range: 1...9, step 1. Default: 5

• Remark– PCU1 uses always initial MCS value read from user parameter for new

established TBF.

– PCU2 uses last used MCS of previous TBF as initial MCS for new TBF in situation when opposite direction of TBF has been active from last TBF release to new TBF establishment (so the MS context has stayed stored in PCU2 memory), and if no BTS re-selection was done for opposite direction of TBF.


EGPRS Link Adaptation Parameters - SEG• Maximum BLER in Acknowledged Mode (BLA)

– This parameter indicates the maximum block error rate of first transmission in acknowledged mode. The parameter is used in EGPRS link adaptation. Range: 10...100 %, step 1 %. Default: 90%

• Maximum BLER in Unacknowledged Mode (BLU)– With this parameter you indicate the maximum block error rate in

unacknowledged mode. The parameter is used in EGPRS link adaptation. Range: 10...100 %, step 1 %. Default: 10%

• Remark:– The BLA 90% means that the coding scheme selection is done by LA algorithm,

if the BLER is less than 90%. – If the BLER is higher than 90%, then the decision of LA will be ignored and

MCS will be downgraded


EGPRS Link Adaptation Parameters - SEG

• MBG and MBP parameters adjusts the MCS and modulation preferences.

• Mean BEP Offset GMSK (MBG)– This is the offset added to reported GMSK mean BEP values before BEP table

lookups.

– The value applies to both uplink and downlink directions. Range: -31...31, step 1. Default: 0

• Mean BEP Offset 8PSK (MBP)– This is the offset added to reported 8PSK mean BEP values before BEP table

lookups.

– The value applies to both uplink and downlink directions. Range: -31...31, step 1. Default: 0


EGPRS Link Adaptation Parameters• The matrix shows an example how the MCSs are selected based on

GMSK_CV_BEP and GMSK_MEAN_BEP figures.– More tables are available from NED/NOLS

• MBG can be used to move the selection decision information to both directions to have more robust or less robust CS decision for the same GMSK_CV_BEP and GMSK_MEAN_BEP figures.

4

3

2

2

1

1

1

5

444444420-31

233333310-19

22233337-9

11222226

11112225

11111114

11111110-3

7643210GMSK_CV_BEP

GMSK_MEAN_BEP

MBG with positive values

MBG with negative values

Remark: the values in the matrix are an example.


0

1

2

3

4

5

6

7

8

9

0 50 100 150

Time (s)

Co

din

gS

che

me

(MC

S)

0

2

4

6

8

10

12

14

16

18

20Used MCSC/IAveraged C/I

•Example of coding schemes modification by the LA algorithm in various radio

environment during drive tests in Helsinki

EGPRS Link Adaptation Functionality

CI (dB)


Multiplexing


MultiplexingTSL sharing

The max amount of TBFs per TSL can be limited by the following parameters:

• Maximum Number of DL TBF (MNDL)– This parameter defines the maximum number of TBFs that a radio time

slot can have in a GPRS territory, in the downlink direction. Range: 1...9, step 1. Default: 9

• Maximum Number of UL TBF (MNUL)– This parameter defines the maximum number of TBFs that a radio time

slot can have in a GPRS territory, in the uplink direction. Range: 1...7, step 1. Default: 7


MultiplexingDL TSLs in (E)GPRS/GPRS multiplexing

• In PCU2 USF Granularity 4 is used, meaning that 1 block carrying USF signaling to GPRS TBF assigns transmission turn to GPRS TBF for 4 consecutive UL radio blocks. • Originally 4 DL 8-PSK TSLs (TSL 4-7) were used, but now TSL 6 and 7 are GMSK modulated,

because of USF is pointed to GPRS MS

USFUSF……

USFUSFRadio Block 4

USFUSFRadio Block 3

USFUSFRadio Block 2

USFUSFRadio Block 1

76543210

USFUSF……

Radio Block 4

Radio Block 3

Radio Block 2

USFUSFRadio Block 1

76543210

• Originally 4 DL 8-PSK TSLs (TSL 4-7) were used, but now TSL6 and 7 are GMSK modulated, because of USF is pointed to GPRS MS

USF 4 not in

useUSF 4 not in

use

USF 4 in

useUSF 4 in

use

GMSK

GMSK

GMSK


MultiplexingTerritory upgrade/downgrade• The algorithm checks the need for re-allocation in given period defined by

TBF_LOAD_GUARD_THRSHLD, in order to separate TBFs.– The Territory Upgrade/Downgrade procedure is performed with three parameters:

– X1: 1.5, X2: 1, X3: 0.5– The PS RRM request an upgrade when the average number of TBF's per TSL in the PS territory is

greater than X1 (and Default territory is already allocated)– The target average number of TBFs in the PS territory is defined by X2– When the average number of TBF per TSL in the PS territory is less than X3, the PS RRM will request

a GPRS downgrade. (but only as far as the default boundary)– PRFILE modifiable parameter (default=50; values 0-255)

• GPRS Territory Update Guard Timer (GTUGT, default: 5s)– This parameter defines the time which must elapse between two subsequent territory updates.

• Example:– The average number of TBF / TSL is 1.75 on the TRX below, so there will be a territory

upgrade request to achieve 1 TBF / TSL ratio

TBF1

TBF2

TBF1

TBF2

TBF1

TBF2

TBF1signaling

TSL7TSL6TSL5TSL4TSL3TSL2TSL1TSL0


(E)GPRS Power Control


Uplink Power Control

• UL Power control – Reduces Interference in the NW

– Saves battery power

– Open loop power control – UL TX powers based on MS received signal level (DL).

• No DL PC available yet

• UL PC Parameters– Alpha: determines the slope by which the downlink RX_Level affects the MS

power

– Gamma : determines the minimum MS output power

– IFP : changes the averaging for the field strength values in idle mode

– TFP: changes the averaging for the field strength values in transfer mode



PC parameters for MS are transmitted on BCCH

PCH = min( CH - C + 48),PMAX)

CH, sets the minimum power level• Range 0…62

• Default 34 (GSM900) , 36 (GSM1800)

, sets the slope for the uplink power level

• Range 0…10 equivalent 0.0….1.0

• Default 7 (GSM900) , 8 (GSM1800)

C, received signal level 0, 39(GSM900), 36 (GSM1800)

PMAX, max MS power allowed in the cell


0

5

10

15

20

25

30

35

-48

-50

-52

-54

-56

-58

-60

-62

-64

-66

-68

-70

-72

-74

-76

-78

-80

-82

-84

-86

-88

-90

-92

-94

-96

-98

-10

0

-10

2

-10

4

-10

6

-10

8

-11

0

Signal Strength (dBm)M

s O

utp

ut

Po

we

r (d

Bm

)

0,3

1


Uplink Power Control Averaging Parameters

Parameter Range DefaultPacket Idle Mode Signal Strength Filter Period 0…25 9

Packet Transfer Mode Signal Strength Filter Period 0…25 13

Packet Transfer Mode Packet Idle Mode

Ready Standby

MeasurementMode

Mobile State


Uplink Power Control Averaging Parameters

Mobile Output Power

-80

-60

-40

-20

0

20

40

1 19 37 55 73 91 109 127 145 163 181 199 217 235 253 271 289 307 325 343 361 379 397 415 433 451

Po

we

r SS

P_IDLE

P_TRANSFER

Mobile Output Power

-80

-60

-40

-20

0

20

40

1 16 31 46 61 76 91 106 121 136 151 166 181 196 211 226 241 256 271 286 301 316 331 346 361 376 391 406 421 436 451

Po

wer

Packet Transfer / Idle Mode Signal Strength Filter Period = 25

Packet Transfer / Idle Mode Signal Strength Filter Period = 1


(E)GPRS MobilityC1/C2

HYS


(E)GPRS mobility

• Network Control Mode (NCM) defines how cell re-selection is performed:– Network Control Mode = 0 (NC0): the MS will perform an autonomous cell reselection.– Network Control Mode = 2 (NC2): the MS sends neighbors cell measurements to the

network and the network commands the MS to perform cell re-selection (Network Controlled Cell Re-selection). NCM is modified with MML command ZEEM.

• The GSM idle mode functionality is used for (E)GPRS cell (re)-selection, if NC0 is implemented.– C1 and C2 parameter setup is taken into account in (E)GPRS cell selection and re-

selection process

• HYS parameter– the HYS parameter is used for all the cell changes, if a TBF is ongoing– In case of standby mode (TBF is not established), the HYS parameters is used on RA

border only