Optimal and suboptimal resource allocation for two-hop OFDM-based multi-relay cognitive networks

We consider a cognitive relay network with multi-relay nodes where the cognitive network transmits over the unused spectrum bands originally allocated to the primary system. This paper presents an optimal and suboptimal schemes that optimize the subcarrier pairs, relay selection and power allocation so that the total system capacity is maximized while guaranteeing that the interference introduced to the primary system is not harmful. The optimal scheme adopts the dual decomposition technique to allocate the different resources. In order to reduce the computational complexity of the optimal scheme, a greedy suboptimal algorithm is proposed. The suboptimal algorithm jointly allocates the different resources by considering channels quality, interference to the primary system and relaying strategy. The performance of the different scheme is discussed through the numerical simulations.