1. Performance Enhancement of Multirate IEEE 802.11 WLANs with Geographically Scattered Stations 1 Duck-Yong Yang, 2 Tae-Jin Lee, 3 Kyunghun Jang, 3 Jin-Bong Chang, and 4 Sunghyun Choi 1 Information Technology lab, LG Enectronics 2 School of Information and Communication Engineering, Sungkyunkwan University 3 Communications and Networking Lab, Samsung 4 School of Electrical Engineering, Seoul National University IEEE Tran. on Mobile Computing, Vol. 5, No. 7, July 2006

2. Outline Introduction Introduction Modeling of scattered stations in WLANs Modeling of scattered stations in WLANs Proposed protocol Proposed protocol Performance evaluation Performance evaluation Simulation results Simulation results Conclusion Conclusion

3. 3 Introduction The performance of a WLAN is degraded by stations using low rate transmission The performance of a WLAN is degraded by stations using low rate transmission Performance of stations with high rate transmission is heavily degraded Performance of stations with high rate transmission is heavily degraded –Performance anomaly

4. Goal of this paper This paper interests in This paper interests in –Modeling the WLAN incorporating stations with multiple transmission rate –Analyzing performance anomaly

5. Mathematical model

6. A WLAN with geographically scattered stations

7. Retry count vs. backoff stages i : group k : backoff stage w i : backoff window u i : max backoff stage

9. State transmission probabilities of the Markov chain Decrease backoff counter by 1 (idle) Sense busy Transmission Collision Successful transmission Drop a frame

10. Steady state distribution ( 穩 態分佈 ) of a Markov chain Collision probability in group i

11. Probability of a station in i transmits or senses busy during a slot

12. Probability of a station in i has transmission collision

13. Probability that the channel is busy in a slot All stations in each group do not transmit

14. Probability of a successful transmission

15. Collisions among different groups

16. Upper i-heterogeneous collisions

17. Lower i-heterogeneous collisions

18. Probability of i- homogeneous collisions

19. Probability of i- heterogeneous collisions

20. Other equations involve in mathematical model

21. Proposed protocol

22. 1. Different initial backoff window size for different group 2. Different frame size for different group 3. Different max backoff stage 4. Combination of 1. and 2.

23. Performance evaluation

24. A network topology for performance evaluation

25. Parameters used in performance evaluation

26. Saturation throughput of each group with different backoff window

27. Total throughput with different backoff window

28. Throughput of each group with different frame size

29. Total throughput with different frame size

30. Throughput with different max backoff stage

31. Total throughput with different max backoff stage

32. Throughput with different initial backoff window and frame size

33. Total throughput with different initial backoff window and frame size

34. Summary Throughput gain is not significant when reducing the size of the frames for low-rate stations Throughput gain is not significant when reducing the size of the frames for low-rate stations Different max backoff stages for different groups have very little impact Different max backoff stages for different groups have very little impact

35. Simulation results

36. environments OPNET 10.0A OPNET 10.0A RTS threshold=3000 B RTS threshold=3000 B –RTS/CTS are disable Retry limit is 7 Retry limit is 7

37. Throughput: analysis and simulation results

38. BSS with one station moving away from AP

39. Throughput when there is one moving station

40. Total throughput when there is one moving station

41. Throughput as the traffic load increases from 0.5 to 4 Mbps

42. Total throughput as the traffic load increases from 0.5 to 4 Mbps

43. Throughput vs. IEEE 802.11e with TXOP

44. Conclusions This paper This paper –investigates the phenomenon analytically using a Markov chain –Derives the saturation throurghput –Proposes remedies to mitigate the performance anomaly

45. Thank you!!