On avoiding collisions and promoting cooperation: Catching two birds with one stone

A cross-layer approach, called CoopMAC, has been proposed recently to integrate cooperation at the physical layer with the medium access control sublayer, thereby achieving substantial throughput and delay performance improvements. CoopMAC capitalizes on the broadcast nature of wireless channels, recruiting a relay opportunistically and on the fly to support the communication of a particular source-destination pair. Herein, we study a cross-layer framework that uses randomized cooperative coding, and allows the simultaneous recruitment of multiple relays which collectively act as the antennas of a distributed transmission array, by simply randomizing the antenna code selection rule. We show that randomized cooperation not only alleviates the burden associated with the relay selection process, but also fully exploits the available spatial diversity.