Pursuing multiuser diversity in an OFDM system with decentralized channel state information

Usually, centralized channel state information (CSI) is assumed to pursue the multiuser diversity with a smart transmission scheduler. However, such centralized CSI will be impractical for a broadband system with a huge number of mobile users. In this paper, by concentrating on an orthogonal frequency division multiplex (OFDM) based broadband wireless communication system, a decentralized method to pursue multiuser diversity is proposed. The key in our proposal is the channel-aware ALOHA based subcarrier assignment: Each mobile user measures the channel on all subcarriers and tries to capture particular ones, by transmitting a request packet with probability p on these subcarriers, when it believes that its channels are good enough (e.g., when the measured channel fading level exceeds a predetermined threshold γ). Several implementation schemes are developed, by attacking the optimization of p and γ with objective functions based on the downlink sum throughput. Computer simulations show that in comparison with the round-robin scheme, the developed schemes offer quite distinct throughput benefit and some further throughput improvement can be obtained when the correlation among the subcarrier channel gains is exploited with a subcarrier merging technique.