Multi-User Diversity in Single-Radio OFDMA Ad Hoc Networks Based on Gibbs Sampling

Multiuser Diversity Medium Access or MDMA is a new cross-layer channel allocation scheme that exploits channel fading diversity and attains concurrency utilizing OFDMA in single-radio ad hoc networks. Channel throughput is enhanced by enabling concurrent transmissions from multiple nodes to the same receiver or from a single transmitter to multiple receivers over orthogonal Subchannels. Also, concurrency is attained when two hop away neighbors can utilize the same subchannel to transmit data to nodes not neighboring the other two hop neighbor. Each subchannel uses a portion of the available bandwidth and contains a grouping of subcarriers or tones which are orthogonal carriers of lower-rate input data streams. A new subchannel assignment algorithm based on Gibbs sampling is presented. This algorithm operates alongside the proposed MAC signaling to distribute subchannels among nodes to exploit channel fading condition on each communication link and to minimize hidden terminal interference. The new MAC addresses the synchronization requirements of OFDMA and the needs of the subchannel assignment algorithm. We present simulation results on the throughput gains obtained with our design compared to traditional channel assignment techniques for multi-channel networks.