1. Improving IEEE 802.11 WLAN: QoS and Throughput Perspective Sunghyun Choi, Ph.D. Assistant Professor School of Electrical Engineering Seoul National University E-mail: schoi@snu.ac.krschoi@snu.ac.kr URL: http://ee.snu.ac.kr/~schoihttp://ee.snu.ac.kr/~schoi

2. 2 Introduction to My Group in SNU Multimedia & Wireless Networking Lab. (MWNL)  Within School of Electrical Engineering, Seoul National University Started September 2003  One of the youngest groups in SoEE, SNU 1 (+2) Ph.D. & 3 masters students

3. 3 Introduction to My Group in SNU (Cont’d) Working on WLAN MAC and around  Resource management – power, rate, …  QoS & mobility  TCP/UDP over WLAN 4G wireless network Cross-layer design (Sensor networks)

4. 4 Contents Introduction QoS provisioning Throughput enhancement Conclusion

5. 5 Introduction to IEEE 802.11 WLAN Wireless Ethernet with comparable speed  Supports up to 11 and/or 54 Mbps within >100 m range Enable (indoor) wireless and mobile high- speed networking  Runs at unlicensed bands at 2.4GHz and 5GHz  Connectionless MAC and multiple PHYs

6. 6 Limitations of Current 802.11 Lack of QoS support  Best-effort service with contention-based MAC Low throughput due to large overhead  < 5 Mbps throughput at 11 Mbps 802.11b link My group is currently working on improving both aspects  Will show only preliminary results here

7. 7 QoS Improvement

8. 8 Emerging IEEE 802.11e MAC New draft standard for QoS provisioning  Expected to be finalized by early next year Defining a new MAC backward compatible with the legacy MAC  Legacy 802.11 MAC – DCF (+ PCF)  802.11e MAC – HCF with two access mechanisms Controlled channel access Contention-based channel access (EDCA)

9. 9 802.11 Distributed Coordination Function (DCF) Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)

10. 10 802.11e Access Category (AC) Access category (AC) as a virtual DCF 4 ACs implemented within a QSTA to support 8 priorities Multiple ACs contend independently The winning AC transmits a frame

11. 11 Differentiated Channel Access of 802.11e EDCA Each AC contentds with  AIFS[AC] (instead of DIFS) and CWmin[AC] / CWmax[AC] (instead of CWmin / CWmax)

12. 12 Simulation Results - DCF vs. EDCA Delay comparison  2 video (1.5 Mbps CBR), 4 voice (36.8 kbps CBR), 4 data (1 Mbps Poisson)

13. 13 Our Software-Based Approach for RT Traffic Support IEEE 802.11e is not available yet Even if it becomes available, many existing legacy 802.11 APs will be there  Especially, for WISP with many deployed APs, replacing existing APs costs a lot of money Software (or firmware) upgrade-based approach is very desirable at least in the short term

14. 14 System Architecture Device Driver TCP/UDP IP PHY MAC RT+NRT frame processing TCP/UDP IP PHY MAC RT+NRT RTNRT frame processing (a) Original Host AP driver (b) Modified Host AP driver

15. 15 Measurement Configuration Linux + HostAP driver for Intersil chipsets  one RTP (1.448 Mbps CBR) + one FTP Console Server Host AP Client switch Implement dual queue

16. 16 One-Way Delay of RTP Traffic Original Modified

17. 17 Percentage Gain in Performance Parameters Test 1 Comparison Percentage gain Original Two Queue Throughp ut TCP3.8513.703-3.84% RTP1.448 0.00% Jitter of RTP Avg.2.92.6-10.34% Max.4.03.0-25.00% min.2.0 0.00% One-way delay of RTP Avg.30.720.2-34.20% Max.32.023.0-28.13% min.32.018.0-40.00% Max delay variation of RTP 27.018.0-33.33%

18. 18 Limitations and Future Work Limitations of the current approach  Running on top of legacy MAC with a single FIFO queue  AP cannot prevent/control contention from stations  Downlink RT transmission could be severely delayed due to the uplink contentions How to handle this situation is an on-going effort

19. 19 Throughput Improvement

20. 20 IEEE 802.11n Initiative A new standardization effort to achieve over 100 Mbps throughput over WLAN Via both PHY and MAC enhancement We are considering the MAC improvement for throughput enhancement

21. 21 Frame Size Affects Throughput 802.11 MAC/PHY have big fixed overheads  MAC header, IFSs, ACK, and Backoff  PLCP preamble & header

22. 22 Theoretical Throughput for 54 Mbps Preferred Operation Range

23. 23 Packet Size Statistics This statistics is from the measurement taken in the 802.11 standard meeting room in the morning of July 22 nd 2003

24. 24 Frame Aggregation Aggregation of multiple frames in order to reduce the fixed overheads relatively! Multiple frames are aggregated above the MAC SAP  The aggregated frame is transmitted via a data frame

25. 25 Frame Formats Original With aggregation

26. 26 Theoretical Throughput w/ Aggregation (w/o channel error)

27. 27 Theoretical Throughput w/ Aggregation (w/ channel error)

28. 28 Performance Measurement Implement frame aggregation in real platform Linux & Intersil-based platform (.11b) Measure the throughput performance of UDP and TCP traffic Note: Frame aggregation is only applied when there are multiple frames in the queue Traffic generator AP STA

29. 29 Measurement Results - UDP Throughput performance of packet aggregation with fixed rate UDP

30. 30 Measurement Results - TCP Throughput performance of packet aggregation with TCP

31. 31 Summary and Future Work Shown that frame aggregation is a good way to improve 802.11 MAC throughput  Via both analysis and measurements Frame aggregation can be done above the MAC SAP very easily Needs further measurements/simulations for more realistic scenarios

32. 32 Concluding Remarks IEEE 802.11 WLAN is becoming real popular these days There is still a big room to improve the current 802.11 systems Important to consider how any improved system co-exists with legacy systems