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GPRS/EGPRS

Radio Link Adaptation

• This documents aims to describe the CS and MCS Adaptation

Algorithm

• It includes 2 parts:

– CS Adaptation

– MCS Adaptation

• Changeable (tunable) Parameters within this presentation are in

BLUE

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Objective

• GPRS/EGPRS link Adaptation is implemented to adjust GPRS/EGPRS coding schemes

dynamically according to the radio link quality during packet data transmission.

• It enables coding schemes to adapt to the variation of the radio environment,

• maximizes the data throughput, and increases the data rate and system capacity.

• CS and MCS and maximum throughputs of GPRS and EGPRS:

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Introduction

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CS Adaptation

• The coding schemes initially used for a GPRS service are specified

by UPDEFAULTCS and DNDEFAULTCS:

– UPDEFAULTCS = CS1

– DNDEFAULTCS= CS2

• Whether the coding schemes can be dynamically adjusted on the basis of signal qualities during the GPRS service processing is

specified by UPFIXCS and DNFIXCS:

– UPFIXCS= UNFIXED

– DNFIXCS= UNFIXED

• The retransmission rate of TBF is used as the adjustment trigger.

• With the current setting CS3 and CS4 are not used

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CS Adaption

• For uplink GPRS TBF,

• if the signal quality is good and the TBF retransmission rate is

lower than the predefined threshold, the GPRS coding schemes are

adjusted to high-rate coding schemes

– The involved parameters are as follows:

• if the signal quality is poor and the TBF retransmission rate is

higher than the predefined threshold, the GPRS coding schemes

are adjusted to low-speed coding schemes. – The involved parameters are as follows:

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UL CS Adaption

Huawei Parameter ID Huawei Parameter name Current Value UPTHDCSUPGRADE1 Uplink TBF Threshold from CS1 to CS2 5

UPTHDCSUPGRADE2 Uplink TBF Threshold from CS2 to CS3 0

UPTHDCSUPGRADE3 Uplink TBF Threshold from CS3 to CS4 0

Huawei Parameter ID Huawei Parameter name Current Value UPTHDCSDEGRADE1 Uplink TBF Threshold from CS2 to CS1 5

UPTHDCSDEGRADE2 Uplink TBF Threshold from CS3 to CS2 0

UPTHDCSDEGRADE3 Uplink TBF Threshold from CS4 to CS3 0

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UL CS Adaption

CS2

CS1 or CS2 UPTHDCSUPGRADE1 = 5%

UPTHDCSDEGRADE1 =10%

Uplink Retransmission Rate%

CS1

• For Downlink GPRS TBF,

• if the signal quality is good and the TBF retransmission rate is

lower than the predefined threshold, the GPRS coding schemes are adjusted to high-rate coding schemes

– The involved parameters are as follows:

• if the signal quality is poor and the TBF retransmission rate is

higher than the predefined threshold, the GPRS coding schemes

are adjusted to low-speed coding schemes.

– The involved parameters are as follows:

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DL CS Adaption

Huawei Parameter ID Huawei Parameter name Current Value DNTHDCSUPGRADE1 Downlink TBF Threshold from CS1 to CS2 5

DNTHDCSUPGRADE2 Downlink TBF Threshold from CS2 to CS3 0

DNTHDCSUPGRADE3 Downlink TBF Threshold from CS3 to CS4 0

Huawei Parameter ID Huawei Parameter name Current Value DNTHDCSDEGRADE1 Downlink TBF Threshold from CS2 to CS1 5

DNTHDCSDEGRADE2 Downlink TBF Threshold from CS3 to CS2 0

DNTHDCSDEGRADE3 Downlink TBF Threshold from CS4 to CS3 0

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DL CS Adaption

CS2

CS1 or CS2 DNTHDCSUPGRADE1 =5%

DNTHDCSDEGRADE1 =10%

Downlink Retransmission Rate

CS1

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MCS Adaptation

• EGPRS adopts a set of high-efficiency link quality control algorithms.

• It defines two link quality control modes: link adaptation (LA) and

incremental redundancy (IR).

• The link quality control mode is set by the parameter LQCMODE – LQCMODE= IR

• In LA mode, the sender selects the best modulation and coding

schemes based on the actual radio environment, and the receiver

need not buffer the erroneous data blocks received.

• In IR mode, the sender uses a coding scheme with high rates but weak

data protection for initial data transmission. If the data is received

erroneously, the sender retransmits the data by using a different

puncturing scheme.

– The receiver combines the new data with the previously received data and then

performs decoding.

– This process is repeated until the decoding succeeds.

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MCS Adaption

• For UL EGPRS TBF:

• The BSC determines whether to use the fixed MCS coding

scheme in the uplink based on the setting of UPFIXMCS.

– UPFIXMCS= UNFIXED

• The uplink initial coding scheme is specified by

UPDEFAULTMCS

– UPDEFAULTMCS = MCS5

• The BSC adjusts the uplink coding scheme according to the

uplink BEP measurement report sent from the BTS

– ADJUSTULMCSTYPE (Support EGPRS Uplink MCS Dynamic Adjust) = 2

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UL MCS Adaption

• The BSC adjusts the UL coding scheme according to the UL BEP

• BTS sends the BEP measurement report to the BSC through an

uplink data frame.

• BSC filters the BLER and BEP measurement reports

• After filtering the measured BEP values of the radio blocks, the

BSC obtains the MEAN_BEP and CV_BEP values on each timeslot.

• Then, the BSC sums up the MEAN_BEP and CV_BEP values on the

timeslots occupied by the TBF to obtain the MEAN_BEP and CV_BEP

values of the TBF.

• Based on the MEAN_BEP and CV_BEP values of the UL TBF, the BSC

chooses the required coding scheme against the UL BEP to coding

scheme mapping table.

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UL MCS Adaption

• To enhance the stability of coding scheme adjustment the leaky

bucket algorithm is used when the coding scheme in GMSK is

changed to the one in 8PSK.

• The basic principles of the leaky bucket algorithm are as follows:

– Each time the BSC adjusts the coding scheme in GMSK to the one in 8PSK, the

bucket size increases;

– each time the BSC adjusts the coding schemes within GMSK, the bucket size

decreases.

– The adjustment from GMSK to 8PSK is allowed only when the bucket size

reaches a specific value.

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UL MCS Adaption

CV_BEP

0 1 2 3 4 5 6 7

ME

AN

_B

EP

0 5 5 5 5 1 1 1 1

1 5 5 5 5 1 1 2 2

2 5 5 5 5 1 2 2 2

3 5 5 5 5 2 2 3 3

4 5 5 5 5 2 2 3 3

5 5 5 5 5 5 3 3 3

6 5 5 6 5 5 3 3 3

7 5 5 6 5 5 5 3 3

8 5 5 6 5 5 3 3 4

9 7 6 6 6 5 5 5 4

10 7 6 6 6 5 5 5 5

11 7 6 6 6 6 5 5 5

12 7 6 6 6 6 6 5 5

13 7 6 6 6 6 6 5 5

14 7 6 6 6 6 6 5 6

15 7 7 6 6 6 6 6 6

16 7 7 7 7 6 6 6 6

17 7 7 7 7 7 7 7 6

18 7 7 7 7 7 7 7 7

19 7 7 7 7 7 7 7 7

20 7 7 8 7 7 7 7 7

21 7 8 8 8 8 7 7 7

22 8 8 8 8 8 8 8 8

23 8 8 8 8 8 8 8 8

24 8 8 8 8 8 8 8 8

25 8 8 8 8 8 8 8 8

26 8 8 8 8 9 9 9 9

27 8 8 8 9 9 9 9 9

28 9 9 8 9 9 9 9 9

29 9 9 8 9 9 9 9 9

30 9 9 8 9 9 9 9 9

31 9 9 9 9 9 9 9 9

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UL MCS Adaption

• Example of Link Adaptation Table

• For DL EGPRS TBF:

• The BSC determines whether to use the fixed MCS coding

scheme in the DL based on the setting of DNFIXMCS.

– DNFIXMCS = UNFIXED

• The DL initial coding scheme is specified by DNDEFAULTMCS

– DNDEFAULTMCS = UNFIXED

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DL MCS Adaption

• The MS measures the DL quality periodically and filters

the measured values to generate a DL EGPRS channel

quality report.

• The DL EGPRS channel quality report is carried by the

EPDAN message sent from the MS to the BSC.

• The filtering period of downlink quality measured

values is specified by BEPPERIOD =5.

• The MEAN_BEP and CV_BEP values of the TBF are used

for the DL Link adaptation

• Based on the value of the MS OUT OF MEMORY field in

the EPDAN message, the DL MCS can be adjusted in the

following ways: next slide

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DL MCS Adaption

• If the value of the MS OUT OF MEMORY field is 0, – the MS has sufficient memory to perform the IR function

– The BSC adjusts the MEAN_BEP value of the TBF based on the BLER.

– Then, based on the MEAN_BEP and CV_BEP values of the TBF, the BSC chooses the required MCS in mapping table in IR mode.

• If the value of the MS OUT OF MEMORY field is 1, – the MS has no sufficient memory to perform the IR function.

– Then, based on the MEAN_BEP and CV_BEP values of the TBF

– The BSC chooses the required MCS in mapping table in LA mode

– To prevent ping-pong between MCS, the leaky bucket algorithm is triggered when the coding scheme is changed from GMSK to 8PSK.

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DL MCS Adaption

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CS/MCS Usage within LLV

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

CS/MCS Usage within LLV Cluster

CS1 Codec Scheme Radio CS2 Codec Scheme Radio CS3 Codec Scheme Radio CS4 Codec Scheme Radio MCS1 Codec Scheme Radio

MCS2 Codec Scheme Radio MCS3 Codec Scheme Radio MCS4 Codec Scheme Radio MCS5 Codec Scheme Radio MCS6 Codec Scheme Radio

MCS7 Codec Scheme Radio MCS8 Codec Scheme Radio MCS9 Codec Scheme Radio

• MCS9 is used at 35% of time, this can be improved

• This linked to the high usage of MCS2 (up to 80%) on the cells

below, this high usage is due to Transmission problem (Abis) and/or

Lack of Abis resources

• Impacted Cells:

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CS/MCS Usage within LLV

0 10 20 30 40 50 60 70 80 90

100

MCS2 Codec Scheme Radio

MCS2 Codec Scheme Radio

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END