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Multiuser systems can benefit from multiuser diversity by assigning channels to users with better channel conditions at different time instants. In this paper, we present an opportunistic random-access scheme for orthogonal frequency-division multiple-access-based indoor power-line communication systems, based on time- and frequency-varying channel conditions, to exploit multiuser diversity. The proposed scheme dynamically adjusts the backoff time of each user according to its own channel-state variations in time and frequency domains during the contention procedure and, thus, “better” users have a higher priority to contend over their favorable subchannels. Moreover, subchannels are assigned to users with better channel conditions in order to further enhance the system throughput. In addition, an analytical throughput model for such a multiuser and multichannel system is derived to obtain the optimal parameter settings of the proposed access scheme. Simulation results show that the proposed scheme provides significant improvement in system throughput even in the case where the number of users highly exceeds that of subchannels.
Date of Publication: Oct. 2012