Hybrid cooperative MAC protocol for wireless ad hoc networks

In this paper, we propose hybrid cooperative medium access control (MAC) protocol that adaptively uses single relay path or two relay paths for enhanced throughput and delay performance under fast Rayleigh fading conditions. The proposed protocol, termed as 2rcMAC, invokes two best relay (cooperating) paths for improved spatial diversity that offer higher transmission rate compared to the direct transmission path. It transmits through primary relay path for higher throughput performance and uses secondary relay path for reliable backup transmission. In case, only one best relay path (with higher rate than the direct transmission path) is available, the 2rcMAC protocol transmits directly to the destination node and invokes the secondary relay path for backup transmission only. Furthermore, handshaking and single bit feedback in 2rcMAC protocol resolve contentions among relay nodes in close proximity at the time, and further provide source node with rate information on source-to-destination, source-to-relay and relay-to-destination links. Simulation results clearly show average throughput improvement of 7% and 25% and average delay improvement of 94.8% and 98.9% compared to UtdMAC and CoopMAC I, respectively [4], [5], [7].