Network-level cooperation with enhancements based on the physical layer

Recently, cognitive cooperation has received a great deal of attention, where the cognitive relay utilizes the periods of source silence to enable cooperation without consuming extra network resources. In this paper, we investigate more enhanced cooperative techniques on top of the existing network-layer conventional cognitive cooperation by exploiting more degrees of freedom at the physical layer. In a wireless multiple-access relay channel with two primary users and a cognitive relay, we first study a dynamic decode-and-forward scheme in which the relay can also be activated during the primary user's transmission, to provide more assistance for successful reception at the destination. Then, an adaptive superposition scheme is proposed by allowing the relay node to simultaneously serve packets relayed from the two users, according to the instantaneous channel feedback. The enhanced cooperation schemes are evaluated in the performance measure of the stable throughput region.