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Department of Computer Science Seminar
2009 Series

Capacity of Large-scale CSMA Wireless Networks

Dr. Chi-Kin Chau
University College London & University of Cambridge

Date: October 5, 2009 (Monday)
Time: 2:30 - 3:30 pm
Venue: SCT909, Cha Chi Ming Science Tower, Ho Sin Hang Campus

In the literature, asymptotic studies of multi-hop wireless network capacity often consider only centralized and deterministic TDMA (time-division multi-access) coordination schemes. There have been fewer studies of the asymptotic capacity of large-scale wireless networks based on CSMA (carrier-sensing multi-access), which schedules transmissions in a distributed and random manner. With the rapid and widespread adoption of CSMA technology, a critical question is that whether CSMA networks can be as scalable as TDMA networks. To answer this question and explore the capacity of CSMA networks, we first formulate the models of CSMA protocols to take into account the unique CSMA characteristics, not captured by existing interference models in the literature. These CSMA models determine the feasible states, and consequently the capacity of CSMA networks. We then study the throughput efficiency of CSMA scheduling as compared to TDMA. Finally, we tune the CSMA parameters so as to maximize the throughput to the optimal order. As a result, we show that CSMA can achieve throughput as Omega(1/sqrt{n}), the same order as optimal centralized TDMA, on uniform random networks. Our CSMA scheme makes use of an efficient backbone-peripheral routing scheme and a careful design of dual carrier-sensing and dual channel scheme. We also address practical implementation issues of our capacity-optimal CSMA scheme.

This talk is based on a joint paper with Minghua Chen & Soung Chang Liew (The Chinese University of Hong Kong), to appear in ACM MobiCom 2009.

Chi-Kin Chau is a Croucher Foundation research fellow at Department of Electronic and Electrical Engineering, University College London, awarded a Croucher Foundation fellowship. Meanwhile, he is also affiliated with University of Cambridge as a primary researcher for the International Technology Alliance in Network and Information Science (ITA) consortium (, which is a joint research consortium of 24 leading academic and industrial institutes in the US and the UK.

He has been a visiting scholar, frequently invited to various overseas institutes, such as IBM Watson Research Center (Hawthorne, US), BBN Technologies (Boston, US), and the Institute of Theoretical Computer Science and Communications (at The Chinese University of Hong Kong). He has recent publications in top-tier IEEE journals and highly-competitive flagship conferences, such as ACM MobiCom, ACM SIGCOMM, IEEE INFOCOM. He received the Ph.D. from University of Cambridge (supported by a Croucher Foundation scholarship), and the B.Eng. (First Class Honours) in Information Engineering from The Chinese University of Hong Kong.

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