+ All Categories
Home > Documents > Optimization of EGPRS link adaptation

Optimization of EGPRS link adaptation

Date post: 31-Dec-2016
Category:
Upload: lehanh
View: 222 times
Download: 0 times
Share this document with a friend
14
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 Jäntti Instructor: M.Sc. Petri Grönberg
Transcript

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

Optimization of EGPRS Link Adaptation

Thesis work presentation2007-01-16

Author: Jussi NervolaSupervisor: Professor Riku JänttiInstructor: M.Sc. Petri Grönberg

2 © 2007 Nokia 2007-01-16 [email protected]

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

3 © 2007 Nokia 2007-01-16 [email protected]

Objectives of the Thesis

• Problem:• Current EGPRS link adaptation (LA) algorithm is not behaving ideally in all radio

conditions. 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 the

ideal 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

4 © 2007 Nokia 2007-01-16 [email protected]

EDGE and EGPRS

AuC – Authentication CentreBSC – Base Station ControllerBTS – Base Transceiver StationEIR – Equipment Identity RegisterGGSN – Gateway GPRS Support NodeHLR – Home Location Register MS – Mobile StationMSC – Mobile Switching CenterPCU – Packet Control UnitSGSN – Serving GPRS Support NodeTC – TranscoderVLR – Visitor Location Register

• EGDE (Enhanced Data Rates for GSM Evolution) offers both packet switched and circuit 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 controlled by the PCU in BSC

BTSMS BSC+PCUHLRAuCEIR

PSTN

Base Station Subsystem Network Switching Subsystem

Air A-bis A-ter

BTS

MSC/VLRTC

A

SGSN

Gb

GGSNInternet

Gr

Gn

Gs

5 © 2007 Nokia 2007-01-16 [email protected]

EGPRS Link Adaptation

• In wireless networks the quality of the connection can change from 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 in different radio conditions. All coding schemes have different amount 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 link adaptation. The selection is based on link quality measurements

MCS-7

MCS-122

MCS-228

MCS-337

MCS-444

MCS-556

MCS-674

5656

MCS-86868

MCS-974 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

6 © 2007 Nokia 2007-01-16 [email protected]

Starting Point for the ThesisPerformance 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 the throughput of different MCSs

• Problem:• Original link adaptation was not always choosing

most suitable MCS

• Solution:• Change to GMSK modulation has to be done

earlier (when link quality decreases)• MCS-8 should be used more

DL FTP Throughput, variable 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 -70RX-Level (dBm)

FTP

Thro

ughp

ut (

rela

tive

)

MCS=1MCS=2MCS=3MCS=4MCS=5MCS=6MCS=7MCS=8MCS=9LA on

LA uses MCS-9 although MCS-8 would offer higher throughput

LA is unable to change to GMSK modulation

DL FTP Throughput, variable 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 -70RX-Level (dBm)

FTP

Thro

ughp

ut (

rela

tive

)

MCS=1MCS=2MCS=3MCS=4MCS=5MCS=6MCS=7MCS=8MCS=9LA on

LA uses MCS-9 although MCS-8 would offer higher throughput

LA is unable to change to 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 -70RX-Level (dBm)

FTP

Thro

ughp

ut (r

elat

ive)

MCS=1MCS=2MCS=3MCS=4MCS=5MCS=6MCS=7MCS=8MCS=9LA on

LA is unable to change to 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 -70RX-Level (dBm)

FTP

Thro

ughp

ut (r

elat

ive)

MCS=1MCS=2MCS=3MCS=4MCS=5MCS=6MCS=7MCS=8MCS=9LA on

LA is unable to change to GMSK modulation

7 © 2007 Nokia 2007-01-16 [email protected]

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 tables1. Selection of modulation2. Selection of MCS

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

8 © 2007 Nokia 2007-01-16 [email protected]

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

9 © 2007 Nokia 2007-01-16 [email protected]

Results of the Optimization – Summary

• After the best version of optimized link adaptation was chosen, the performance improvement 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

Laboratory measurements  

Throughput improvement

Coverage improvement    

Throughput improvement

Coverage improvement

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

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

 

Live Measurements  

Throughput improvement

Coverage improvement    

Throughput improvement

Coverage improvement

 drive route DL +11%

<not measured>   UL +31%

<not measured>

10 © 2007 Nokia 2007-01-16 [email protected]

Results of the Optimization – Laboratory MeasurementsVariable 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 all MSs

• Downlink throughput performance of optimized LA is at the ideal level with new MSs

• With some older MSs there is 1 – 2 dB wide area where throughput is not optimal. This is not a problem in fading environment.

DL Throughput, variable RX-Level, 4 TSLs

0%

20%

40%

60%

80%

100%

-110 -105 -100 -95 -90 -85 -80 -75 -70RX-Level (dBm)

Thro

ughp

ut (r

elat

ive)

Original LAOptimized LA11 6280Optimized LA11 7270Optimal LA

UL Throughput, variable RX-Level, 2 TSL

0%

20%

40%

60%

80%

100%

-110 -105 -100 -95 -90 -85 -80 -75 -70RX-Level (dBm)

Thro

ughp

ut (r

elat

ive)

Original LAOptimized LA11Optimal LA

11 © 2007 Nokia 2007-01-16 [email protected]

Results of the Optimization – Live Network Measurements

• Drive tests executed in Ruoholahti with Nokia UltraSite

• FTP throughput was measured on uplink and downlink separately

• Improvement in average Downlink FTP throughput +11%

• Improvement in average Uplink FTP throughput +31%

12 © 2007 Nokia 2007-01-16 [email protected]

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 along different parts of the route:

RX-level

RX-level

RX-level

RX-level

13 © 2007 Nokia 2007-01-16 [email protected]

Conclusions• The results achieved in the thesis are well in accordance with the original

objectives• Performance improvement of optimized link adaptation was clearly seen in

laboratory and live network• The optimized link adaptation version created in this thesis is available for the

customers 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

14 © 2007 Nokia 2007-01-16 [email protected]

Thank You!

Questions / Comments ?


Recommended