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Dola's First Colloquium

On Channel Access in Wireless Networks

Prof. J. Rockey Luo
ECE, Colorado State University
ECE Department Seminar, Tues, Oct 9

Due to the broadcast nature of wireless transmissions, wireless channel is usually shared by multiple terminals. Channel access schemes in wireless systems can be divided into two major categories: random access and coordinated access. Initially, he considers a random access system where a transmitter transmits information in the form of packets to a receiver over an ergodic block fading channel. A packet is successfully received only if the information reliability exceeds a predetermined threshold. Such reliability requirement is posed by a tradeoff between the packet internal data rate and a minimum signal to noise ratio (SNR) requirement, assuming the transmitter only knows about channel distribution. The results show that in the low power regime, the optimal SNR threshold that maximizes the throughput is proportional to the transmit power; the ratio between the two parameters does not depend on the packet internal coding scheme.

Then, he considered a multiple access system, where terminals share the channel in a fully coordinated manner. Most of the existing multiple access network systems use Time-Division Multiple Access (TDMA) scheme to share the communication channel even though the suboptimality of TDMA is well known. The dominance of TMDA channel sharing is due to the conjecture that its suboptimality is not significant enough to offset its simplicity. However, when the receiver has multiple antennas and energy efficiency is of primary concern, then 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 multiplexing gain. Results 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.

Last modified 14 November 2007 at 8:19 am by sahad