EGPRS Link Adaptation

8/3/2019 EGPRS Link Adaptation

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1 © 2007 Nokia 2007-01-16 [email protected]

Optimization of EGPRS Link Adaptation

Thesis work presentation

2007-01-16

Author: Jussi Nervola

Supervisor: Professor Riku JänttiInstructor: M.Sc. Petri Grönberg




Contents

• Objectives of the thesis

• Introduction

• Basics of EDGE and EGPRS

• EGPRS link adaptation

• Starting point for the thesis - performance with original link adaptation

• Methods

• Link adaptation optimization work

• Results of the optimization

• Laboratory measurement results

• Live network measurement results

• Conclusions




Objectives of the Thesis

• Problem:

• Current EGPRS link adaptation (LA) algorithm is not behaving ideally in all radioconditions. LA is not using the most suitable Modulation and Coding Scheme (MCS)in every radio condition. That reduces the performance of the system.

• Objective:

• To adjust the operation of the EGPRS link adaptation so that its performance it at theideal level (i.e. LA chooses the best MCS in every radio condition)

• If ideal performance level can be achieved the quality of the service will be improved:

• Increased throughput

• Smaller latency

• Improved coverage for EGPRS service




EDGE and EGPRS

AuC – Authentication Centre

BSC – Base Station Controller

BTS – Base Transceiver Station

EIR – Equipment Identity Register

GGSN – Gateway GPRS Support Node

HLR – Home Location Register

MS – Mobile Station

MSC – Mobile Switching Center

PCU – Packet Control Unit

SGSN – Serving GPRS Support Node

TC – Transcoder

VLR – Visitor Location Register

• EGDE (Enhanced Data Rates for GSM Evolution) offers both packet switched andcircuit switched data services for the users of GSM network:

• Packet switched EGPRS (Enhanced General Packet Radio Service)

• Circuit switched ECSD (Enhanced Circuit Switched Data)

• EGPRS has been more popular among the manufacturers than ECSD

• Link adaptation is working on the Air-interface between MS and BTS and is controlledby the PCU in BSC

BTSMS BSC+PCUHLR

AuC

EIR

PSTN

Base Station Subsystem Network Switching Subsystem

Air A-bis A-ter

BTS

MSC/VLRTC

A

SGSN

Gb

GGSN

Internet

Gr

Gn

Gs


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EGPRS Link Adaptation

• In wireless networks the quality of the connection can changefrom very good to very poor in short time

• EGPRS has nine different Modulation and Coding Schemes(MCS-1 – MCS-9) in order to optimize the performance indifferent radio conditions. All coding schemes have differentamount of robustness and error correction.

• When user bit rate is low, robustness is high (e.g. MCS-1)

• When user bit rate is high, robustness is low (e.g. MCS-9)

• Two modulations are used:

• GMSK (Gaussian Minimum Shift Keying) for MCS-1 – MCS-4

• 8-PSK (8-Phase Shift Keying) for MCS-5 – MCS-9

• MCS that offers the best performance in current radio

environment should be selected

• Automatic selection of most suitable MCS is called linkadaptation. The selection is based on link quality measurements

MCS-7

MCS-1

22

MCS-2

28

MCS-3

37

MCS-4

44

MCS-5

56

MCS-6

74

5656

MCS-8

6868

MCS-9

74 74

redundancy fromchannel coding

RLC data block,number of bytes

RLC/MAC block(radio block)

11.2 kbps

14.8 kbps

17.6 kbps

8.8 kbps

22.4 kbps

29.6 kbps

44.8 kbps

54.4 kbps

59.6 kbps




Starting Point for the Thesis

Performance with Original Link Adaptation

• Throughput performance of link adaptation is

compared to the performance of all MCSs• Throughput is measured with FTP application in

variable RX-level environment

• Ideal LA would follow the envelope of thethroughput of different MCSs

• Problem:

• Original link adaptation was not always choosingmost suitable MCS

• Solution:

• Change to GMSK modulation has to be doneearlier (when link quality decreases)

• MCS-8 should be used more

DL FTP Throughput, va riable RX-Level, 4 TSLs

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

-110 -105 -100 -95 -90 -85 -80 -75 -70

RX-Level (dBm)

F T P

T h r o u g h p u t ( r e l a t i v e )

MCS=1

MCS=2

MCS=3

MCS=4

MCS=5

MCS=6

MCS=7

MCS=8

MCS=9

LA on

LA uses MCS-9 alt hough MCS-8would offer higher throughput

LA is unable to changeto GMSK modulation

DL FTP Throughput, va riable RX-Level, 4 TSLs

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

-110 -105 -100 -95 -90 -85 -80 -75 -70

RX-Level (dBm)

F T P


MCS=1

MCS=2

MCS=3

MCS=4

MCS=5

MCS=6

MCS=7

MCS=8

MCS=9

LA on

LA uses MCS-9 alt hough MCS-8would offer higher throughput

LA is unable to changeto GMSK modulation

UL FTP Throughput, variable RX-Level, 2 TSL

0.00

0.20

0.40

0.60

0.80

1.00

1.20

-110 -105 -100 -95 -90 -85 -80 -75 -70

RX-Level (dBm)

F T P T

h r o

u g h p u t ( r e l a t i v e )

MCS=1

MCS=2

MCS=3

MCS=4

MCS=5

MCS=6

MCS=7

MCS=8

MCS=9

LA on

LA is unable t o change

to GMSK modulat ion

UL FTP Throughput, variable RX-Level, 2 TSL

0.00

0.20

0.40

0.60

0.80

1.00

1.20

-110 -105 -100 -95 -90 -85 -80 -75 -70

RX-Level (dBm)

F T P T

h r o

u g h p u t ( r e l a t i v e )

MCS=1

MCS=2

MCS=3

MCS=4

MCS=5

MCS=6

MCS=7

MCS=8

MCS=9

LA on

LA is unable t o change

to GMSK modulat ion




Operation of EGPRS Link Adaptation

• In EGPRS link quality is measured in terms of Bit Error Probability (BEP).BEP values are received in measurement reports from MS and BTS

• Mean 8-PSK BEP and coefficient of variation of 8-PSK BEP

• Mean GMSK BEP and coefficient of variation of GMSK BEP

• MCS is selected according to BEP values by using look-up tables

1. Selection of modulation

2. Selection of MCS

• from GMSK MCS-selection table or

• from 8-PSK MCS-selection table (below, from 3GPP specification)




Optimization Work

• Methods:

• Measure the performance of the current link adaptation (LA)

• Specify new parameter / table values for LA

• Measure the performance of the optimized LA and adjust values further

• The measurements were executed in laboratory using real network elements:

• Three different laboratory scenarios:

• Variable RX-level, Variable C/I and Fading with variable RX-level

• Measured quantities:

• Downlink and Uplink throughput (with FTP and HTTP)

• RTT (with ping)

MS BTS BSC SGSN GGSN Server




Results of the Optimization – Summary

• After the best version of optimized link adaptation was chosen, the performanceimprovement was verified with several MSs in laboratory and live network

• Good results achieved through the optimization work:

• System performance was improved in all cases

• Throughput performance was improved in whole cell area in average by +11%

• Coverage of EGPRS service was improved by 1 – 6 dB depending on the conditions

• On the following slides some of the measurement results are explained briefly

Laboratorymeasurements

Throughputimprovement

Coverageimprovement


Coverageimprovement

RX-level DL +7% +4 dB UL +17% +5 dB

C/I DL +15% +1 dB UL +3% +6 dB

LiveMeasurements


Coverageimprovement


Coverageimprovement

driveroute DL +11%

<notmeasured> UL +31%

<notmeasured>




Results of the Optimization – Laboratory Measurements

Variable RX-level Scenario

• Throughput performance was compared:

• Original LA

• Optimized LA

• Optimal LA

• Uplink throughput performance of

optimized LA is at the ideal level with allMSs

• Downlink throughput performance ofoptimized LA is at the ideal level with newMSs

• With some older MSs there is 1 – 2 dBwide area where throughput is notoptimal. This is not a problem in fadingenvironment.

DL Throughput, variable RX-Level, 4 TSLs

0%

20%

40%

60%

80%

100%

-110 -105 -100 -95 -90 -85 -80 -75 -70

RX-Level (dBm)

T

h r o u g h p u t ( r e l a t i v e )

Original LA

Optimized LA11 6280

Optimized LA11 7270

Optimal LA

UL Throughput, variable RX-Level, 2 TSL

0%

20%

40%

60%

80%

100%

-110 -105 -100 -95 -90 -85 -80 -75 -70

RX-Level (dBm )


Original LA

Optimized LA11

Optimal LA




Results of the Optimization – Live Network Measurements

• Drive tests executed in

Ruoholahti with Nokia UltraSite• FTP throughput was measured

on uplink and downlinkseparately

• Improvement in averageDownlink FTP throughput+11%

• Improvement in average Uplink

FTP throughput +31%




Uplink Throughput Performance

RX-level during this part of the route: -85 – -105 dBm RX-level during this part of the route: -70 – -88 dBm

Original link adaptation

Optimized link adaptation

Original link adaptation

Optimized link adaptation

-> Reason for improvement:

•Earlier change to GMSK modulation

-> Reason for improvement:

•Using more MCS-8 instead of MCS-9

• RLC uplink throughput figures alongdifferent parts of the route:

RX-level

RX-level

RX-level

RX-level




Conclusions

• The results achieved in the thesis are well in accordance with the originalobjectives

• Performance improvement of optimized link adaptation was clearly seen inlaboratory and live network

• The optimized link adaptation version created in this thesis is available for thecustomers in newest BSC software update in 1/2007

• Further Study Items

• Measurements with various MSs from different vendors

• Effect of certain GSM features (such as frequency hopping) on Link Adaptation

• Analysis in commercial operators’ networks by using BSC KPI (Key Performance

Indicator) data

• Link adaptation algorithm enhancement by introducing new algorithm inputs

• This would optimize modulation change with all MSs also on static conditions




Thank You!

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EGPRS Link Adaptation

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