1. Chih-Min Chao and Kuo-Hsiang Lu Department of Computer Science and Engineering National Taiwan Ocean University IEEE Sensor Networks, Ubiquitous and Trustworthy Computing (SUTC) 2008

2. Outline Introduction Related Work Proposed Load-awareness Multichannel MAC (LAMM) Protocol Performance Evaluation Conclusions

3. Introduction The MAC protocol of IEEE 802.11 standard is designed for accessing a single channel. It is well known that utilizing multiple channels can increase spatial reuse and hence enhance network throughput. Channel allocation problem With dedicated control channel Without dedicated control channel Multiple-transceiver[4, 5, 10, 11][3, 9] Single-transceiver[6, 12][2, 7, 8, LAMM]

4. Related work [2] P. Bahl, R. Chandra, and J. Dunagan. SSCH: Slotted Seeded Channel Hopping for Capacity Improvement in IEEE 802.11 Ad-Hoc Wireless Networks. In Proceedings of ACM MobiCom, 2004.

5. SSCH A A A A A A A A A A B B B B B B B B B B B B B B B B B B B B

6. Related work [7] J. So and N. Vaidya. Multi-Channel MAC for Ad Hoc Networks: Handling Multi-Channel Hidden Terminals Using A Single Transceiver. In Proceedings of ACM MobiHoc, 2004.

7. Related work [7] -- MMAC Beacon ATIM windowDATA window ATIM ATIM-ACK ATIM-RES Preferable Channel List (PCL) A B B

8. Related work [8] C. Son, N.-H. Lee, B. Kim, and S. Bahk. MAC Protocol using Asynchronous Multi-Channels in Ad Hoc Networks. In Proceedings of IEEE WCNC, 2007.

9. Related work [8] -- SLKB Each beacon interval is divided into three subintervals Three asynchronous channels

10. Related work All the above mentioned multi-channel protocols operate in an environment where the number of channels is fixed. They may suffer from either longer delay or higher collision probability when network load changes.

11. Proposed LAMM protocol The main idea of LAMM is to Use less number of channels When lightly loaded Use more channels When heavily loaded.

12. Proposed LAMM protocol Single transceiver No control channel The structure is similar to IEEE 802.11 PSM. In LAMM, the ATIM/ATIM-ACK include The number of pending packets

13. Proposed LAMM protocol Define a node A to be inactive if one of the following conditions holds Attempt to send ATIM  But fails to deliver Send ATIM  Not receive ATIM-ACK No ATIM to send & Not receive any ATIM

14. Proposed LAMM protocol Each node maintains a variable CU i to estimate the usage of channel i At the beginning of each beacon interval, CUi is set to zero. CU max ： indicates the maximum number of packets that can be sent during a data window. Data rate ： 2Mbps Beacon interval ： 100ms Data interval ： 80ms Packet size ： 512Bytes

15. Proposed LAMM protocol If CU i >= CU thrd The inactive node switch to next channel (i+1) mod n If CU i < CU thrd for successively k times Nodes reside on this channel should switch back to the default channel at the next beacon interval.

16. Proposed LAMM protocol

17. Performance Evaluation ParameterValue SIFS10μs DIFS50μs CWmin31 CWmax1023 ATIM Retry Limit3 Short Retry Limit7 Long Retry Limit4 Preamble Length144bits PLCP Length48bits

18. Performance Evaluation

22. Conclusions The authors propose a multi-channel MAC protocol LAMM that dynamically adjust the number of channels being utilized according to traffic load. Reduces the packet delay when the network is lightly loaded. Increases spatial reuse when heavily loaded. The simulation results verify that LAMM performs well.

23. Thank you