Multiple Access in Wireless Networks
Dr. J. Rockey Luo - CS Faculty Candidate
Thursday, February 2, 2006
1:30PM - CSB-232
Abstract
Due to the broadcast nature of wireless transmissions, wireless channel is usually shared by multiple terminals. Multiple access schemes in wireless systems can be divided into two major categories: the random multiple access, and the coordinated multiple access. In the first part of this talk, we consider a finite-terminal random multiple access system over a general wireless channel. We assume terminals transmit short packets to the common receiver in an opportunistic fashion. We look at the system from three different angles and characterize the supported traffics of the system in terms of the stability, the throughput and the capacity regions. Fundamental relations among these regions and the key reasons of their similarity are explained. In the second part of the talk, we consider the coordinated multiple access scheme. We assume terminals share the channel in a fully coordinated manner. It is shown that, in a multiple access environment, most of the existing network systems use Time-Division Multiple Access (TDMA) scheme to share the communication channel. The dominance of TMDA channel sharing is due to its simplicity and due to the belief on the marginality of its suboptimality. However, when the receiver has multiple antennas and energy efficiency is of primary concern, we show that TDMA is significantly suboptimal in terms of spectral efficiency. The inefficiency of TDMA is due to the fact that it does not exploit the multiuser multiplex gain. We also show that there is another channel sharing scheme that is on one hand simpler than TDMA and on the other hand achieves much higher spectral efficiency than TDMA.
Short Bio
J. Rockey Luo received the B.S. and M.S. degrees in Electrical Engineering from Fudan University, Shanghai, P.R.China, in 1995 and 1998, respectively. He received the Ph.D. degree in Electrical and Computer Engineering from University of Connecticut in 2002. Since September 2002, he has been a Research Associate with the Institute for Systems Research (ISR), University of Maryland, College Park. His current research focuses on cross-layer issues, particularly the interactions among the bottom layers, in wireless communication networks. His general areas of research interests include wireless communications, wireless networking, information theory and signal processing.
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