Outage Probability Analysis and Optimization of Cognitive Full-Duplex Relay Networks

This paper investigates the outage probability performance of the secondary user in a two-hop underlay cognitive full-duplex relay network. To improve the outage performance of the secondary user, we investigate optimal power allocation (OPA) for the secondary network, i.e., finding the optimal transmit power at the source and relay nodes in the secondary network that minimizes the outage probability. We derive analytical expressions for the optimal transmission power for the source and relay nodes by considering multiple power constraints, viz., constraint on total available transmission power for the secondary network and the constraint on maximum tolerable interference power at the primary receiver. Further, we investigate joint optimization of transmit power and relay location, i.e., jointly finding the optimal transmit power vector and the relay location in the secondary network, that minimizes the outage probability experienced by the secondary user. Extensive analytical and simulation studies show that OPA outperforms equal power allocation in terms of outage probability. Further, the results show that joint transmit power-relay location optimization can provide significant improvement in outage probability as compared to transmit power optimization.