High-Performance MAC for High-Capacity Wireless LANs

1. High-Performance MAC for High-Capacity Wireless LANs Yuan Yuan, Daqing Gu, William Arbaugh, and Jinyun ZhangComputer Science Department, University of Maryland13th International Conference on Computer Communications and Networks (ICCCN), 2004

2. Outline • Introduction • Limited of current IEEE CSMA/CA MAC • Adaptive Distributed Channel Access (ADCA) MAC protocol • Simulations • Conclusions

3. Introduction • Recent advances provide very high-capability wireless links at the PHY layer • 802.11n • 802.15.3a

4. Introduction • MAC layer throughput achieved by DCF when PHY layer is 216 Mb/s

5. Two Challenges for High-performance MAC Design (1) • How to minimize the protocol overhead • Control messages, contention backoff, and inter-frame spacing parameters incur high overhead • When PHY rate increases, the data-carrying time shrinks as the overhead time remains fixed

6. Two Challenges for High-performance MAC Design (2) • How to improve the overall channel throughput by leveraging the good channel quality of hosts • Wireless channel condition of a host is location dependent and time varying

7. Summary • Current MAC solutions are not designed for the high-capacity PHY layer • 802.11: incurs considerable overhead • 802.11e: focuses on MAC QoS but does little to improve channel efficiency • 802.15.3: works well for constant-bit-rate multimedia apps., but is not efficient for bursted data apps.

8. Goal • This paper proposes Adaptive Distributed Channel Access (ADCA) MAC for high-capability PHY in infrastructure mode by • Adaptive batch transmission • Opportunistic selection of high rate hosts

9. Overview of ADCA • Each station initiates its parameter according to received Beacon frame • When a station wins channel contention, it will independently determine whether it is eligible for accessing channel

10. ADCA Parameters (1) • Each station initiates values for Sf, Rf, Bf and Af according to received Beacon frame • Sf: reference packet size • Rf: reference rate • Bf: reference batch size • Af: number of back-to-back transmitted frame

11. ADCA Parameters (2) • Each station maintains two credit count • Credith: an accumulated credit for channel accessing time • Creditl: an accumulated credit for stations when stations win the contention, but not access channel

12. ADCA Transmit Bpackets Yes Number of packets Ballowing for transmittingis greater than Bf Yes Rate of the stationR isgreater than Rf Backoff and increase credit A station winschannel contention No Transmit Bpackets Yes Creditl is greater thanthe present threshold No Backoff and increase credit No

13. R >= Rf Number of packets allowing for transmitting in this transmission

14. R < Rf

15. PHY/MAC Parameters • Ns-2 simulator is used Service differentiation mechanism is similar to 802.11e

16. (Sf/Rf)*Bf = 3ms Rf = 216Mb/s Sf = 1280B Af = 3 Throughput vs. Transmission Rate

17. 10 hosts with UDP flows 5 hosts transmit at 216Mb/s and source rate is 20Mb/s 5 hosts transmit at 54Mb/s and source rate is 5Mb/s Packet size = 1280B (Sf/Rf)*Bf = 3ms Af = 1 Throughput vs. Rf

18. Throughput Gain vs. Background Traffic • Packet size = 1280B • (Sf/Rf)*Bf = 3ms • Af = 1

19. Mean Delay vs. Background Flows

20. Throughput

21. Mean Delay

22. Throughput

23. Mean Delay

24. Conclusions • ADCA minimizes the MAC overhead via adaptive batch transmission and block ACK • ADCA ensures the same access time among high-rate hosts

25. Thank you!!