Performance Evaluation of the IEEE 802.16 MAC for QoS

1. Performance Evaluation of the IEEE 802.16 MAC for QoS Claudio Cicconetti, Alessandro Erta, Luciano Lenzini, and Enzo Mingozzi IEEE Transactions On Mobile Computing, VOL. 6, NO. 1, JAN. 2007. 報告者：李宗穎

2. Outline • Background • Simulation Environment • Performance Evaluation • Conclusions

3. Introduction • This paper focus following • Frame-based point-to-multipoint mode • The BS in a Time Division Multiple Access • Full-duplex Subscribe Stations

4. IEEE 802.16 • Bandwidth request mechanisms • unsolicited requests • unicast polls • broadcast/multicast polls, and • piggybacking

5. Simulation Environment • The simulator is event-driven and was developed using C++

6. Performance Metrics • gross subframe utilization • The ratio between the OFDM symbols utilized in a subframe for data transmission • Throughput • the overall amount of net user data • transfer delay • a packet arrives at the MAC connection buffer of the source node to the next protocol layer at the destination node • backlog gap • difference between the BS’s estimate of the backlog of a connection • notification delay • a new SDU is received by an SS and the time instant at which the BS receives a bandwidth request for this SDU

7. BS and SS Schedulers • Uplink • Weighted Round Robin • Downlink • Deficit Round Robin

8. Bandwidth Requests Management • When BE or nrtPS becomes busy • contention-based bandwidth request • When SS has a busy connections • piggybacking • rtPS • static allocation of periodic unicast polls ex: video 33ms VoIP 20ms • nrtPS • with unicast polls every 500ms

9. Simulation Name • N = S x C x W • W : identical basic data sources • C : connections per direction • S : overall number of stations

10. Simulation Parameters • Repeat 20 times • Run was 1200s • Warmup period of 360s • 95% confidence interval

11. Performance Evaluation • Throughput and Delay Analysis • Bandwidth Request Analysis • Evaluation of Multimedia Traffic

12. Average delay VS number of SSs Minimum traffic unit is 147Kb/s (6 Web) Offered load is N x 147Kb/s (Best Effort)

13. Throughput VS number of SSs DL : Management overhead UL : Contention Slot overhead

14. Offered Load Partitioning • The offered load N increase 10 to 90 • 6 WEB source (24.5 x 6 ~=147Kb/s)

15. Utilization VS offered load Contention Slot BWmin = 7

16. Throughput VS offered load Physical preambles

17. Bandwidth Request Analysis • Nc : a broadcast poll • Np : piggybacked on PDUs

18. Number of bandwidth requests per uplink subframe VS offered load N > 50, Nc Almost negligible Nc : contention req. Np : piggybacked req.

19. Average delay VS BWmin Capacity reserved for Contention bw-req

20. Throughput VS BWmin

21. Evaluation of Multimedia Traffic • The minimum traffic unit is 71.5Kb/s • VoIP traffic has not reported in the paper

22. CDF of the delay in the conn, source and SS cases with 30/60/90 videoconference sources the SS case incurs more overheads due to the transmission of a higher number of physical preambles compared to the conn and source cases in the conn case, the BSmight schedule an uplink grant to another connection jbefore the unicast poll to connection i is due

23. Notification delay VS offered load piggybacking/bandwidth stealing mechanisms for source and conn

24. 95% of the delay VS offered load

25. Backlog error VS time with 160 videoconference sources

26. Conclusion • There is a trade-off between average delay and throughput • SSs are able to request uplink bandwidth to the BS efficiently using piggybacked bandwidth request • Finally, paper have shown that rtPS outperforms nrtPS in terms of delay