WLC32-3: A Distributed Opportunistic Access Scheme for OFDMA Systems

In this paper, we propose a distributed opportunistic access scheme for uplink OFDMA systems. The sub-carriers are grouped into several sub-channels and users access those sub-channels through a distributed access scheme without requiring extensive information exchange with the access point. Our proposed scheme allows several parallel contention subchannels to exploit multiuser diversity. Using knowledge of all the sub-channels, obtained through a periodically-transmitted beacon signal from the access point, all users contend on their strongest sub-channel(s). The proposed scheme applies a novel backoff mechanism utilizing this sub-channel knowledge to yield further throughput improvement in addition to the throughput gain obtained by the collision reduction design. To a user, the better the sub-channel gain is, the smaller the backoff time on that sub-channel, and hence, the higher the access priority of the user on that sub-channel. Compared with the traditional centralized OFDMA systems, our proposed scheme reduces overhead significantly and achieves a better spectral efficiency as corroborated by the simulation results.