Friday March 9 11:00 - 11:50 AM Kelley 1005
Ben Liang Assistant Professor Department of Electrical and Computer Engineering University of Toronto Rank-based Medium Access in Multihop Wireless Networks A main challenge in multihop wireless networking is to ensure the reliable and efficient transmission of mission-critical data across multiple hops of unstable wireless links. Medium access control schemes based on random contention (such as IEEE 802.11 DCF) improve the channel-usage efficiency over deterministic scheduling schemes (such as TDMA and OFDMA), but they lack stability in quality-of-service provisioning. In this talk, we argue that the rank-based approach to medium access provides the middle-ground and a proper balance between stability and efficiency for multihop wireless networks. We first discuss random rank-based packet scheduling, to maintain both fairness and efficiency in data transmission over multihop wireless contention. We study a medium access control protocol that makes use of granule time slots and sequences of pseudo-random numbers to promote spatial reuse and to distribute the throughput fairly among nodes. The protocol has two versions: Randomly Ranked Mini Slots (RRMS) utilizes control-message handshakes similar to IEEE 802.11; Randomly Ranked Mini Slots with Busy Tone (RRMS-BT) provides higher throughput but requires a receiver busy tone. Using computer simulation, we demonstrate the performance of this protocol based on appropriate metrics of long-term and short-term fairness. With both fixed and random topologies, we show that these results are robust to difficult network configurations and unsynchronized clocks. We then discuss deterministic rank-based packet scheduling in a multihop wireless network with end-to-end delay constraints. The emphasis is to determine the proper relative weights assigned to the remaining distance and the remaining lifetime in order to rank the urgency of a packet. We consider a general class of transmission schemes that represents such relative weights using a single lifetime-distance factor. We present an analytical framework to study the effect of the lifetime-distance factor on packet loss probability in a general multihop environment, with different configurations of peer-node channel contention. We demonstrate quantitatively how the proper balance between distance and lifetime in a transmission schedule can significantly improve the network performance, even under imperfect schedule implementation. Biography: Ben Liang received honors simultaneous B.Sc. (valedictorian) and M.Sc. degrees in electrical engineering from Polytechnic University in Brooklyn, New York, in 1997 and the Ph.D. degree in electrical engineering with computer science minor from Cornell University in Ithaca, New York, in 2001. In the 2001 - 2002 academic year, he was a visiting lecturer and post-doctoral research associate at Cornell University. He joined the Department of Electrical and Computer Engineering at the University of Toronto as an Assistant Professor in 2002. His current research interests are in mobile networking and multimedia systems. He received an Intel Foundation Graduate Fellowship in 2000 toward the completion of his Ph.D. dissertation, the Best Paper Award at the IFIP Networking conference in 2005, and the Runner-up Best Paper Award at the International Conference on Quality of Service in Heterogeneous Wired/Wireless Networks in 2006. He is a senior member of IEEE and a member of ACM and Tau Beta Pi.
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