1 © 2007 Nokia Optimization of EGPRS Link Adaptation Thesis work presentation Author: Jussi Nervola Supervisor:Professor Riku Jäntti Instructor:M.Sc. Petri Grönberg

2 © 2007 Nokia 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 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 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 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 BTS MS BSC+PCU HLR AuC EIR PSTN Base Station Subsystem Network Switching Subsystem Air A-bis A-ter BTS MSC/VLR TC A SGSN Gb GGSN Internet Gr Gn Gs

5 © 2007 Nokia 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-1 22 MCS-2 28 MCS-3 37 MCS-4 44 MCS-5 56 MCS MCS-8 68 MCS-9 74 redundancy from channel 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 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 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

7 © 2007 Nokia 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)

8 © 2007 Nokia 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 BTSBSCSGSNGGSNServer

9 © 2007 Nokia 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-levelDL+7%+4 dBUL+17%+5 dB C/IDL+15%+1 dBUL+3%+6 dB Live Measurements Throughput improvement Coverage improvement Throughput improvement Coverage improvement drive routeDL+11% UL+31%

10 © 2007 Nokia 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 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.

11 © 2007 Nokia 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 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

13 © 2007 Nokia 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 Thank You! Questions / Comments ?