Throughput maximization for cognitive radio networks using active cooperation and superposition coding

We propose a three-message superposition coding scheme in a cognitive radio relay network exploiting active cooperation between primary and secondary networks. The time resource is split into three transmission phases. The first two phases are dedicated to primary communication, while the third phase is for the secondary's transmission. We formulate a throughput maximization problem for the secondary network subject to primary user rate constraints and per-node power constraints with respect to the time durations of primary transmission and the power allocation at the primary and the secondary users. We provide an analytical solution to our problem and validate it by numerical optimization. We demonstrate significant throughput gains for both the primary and the secondary users through this active cooperation scheme. We find that most of the throughput gains come from minimizing the second phase transmission time. Finally, we demonstrate the superiority of our proposed scheme compared to best relay selection.