Outage Performance Comparison of Dual-Hop Full Duplex Underlay Cognitive Relay Networks

This paper investigates the outage probability performance of the secondary user (SU) in an underlay dual-hop, decode and forward (DF), full duplex cognitive relay network (FDCRN). First, we develop analytical closed form expression for outage probability and throughput for a dual-hop DF FDCRN by making use of the direct link signal as a useful signal to improve the signal-to-noise ratio at the secondary destination. Next, we compare the outage and throughput performance of various FDCRN and half duplex cognitive relay network (HDCRN) protocols, namely, (1) dual-hop DF FDCRN with direct link treated as interference, (2) dual-hop DF FDCRN with direct link signal cancelled by employing recursive backward interference cancellation technique, and (3) dual-hop DF HDCRN that employs maximal ratio combining at SD. Closed form expressions for the outage probabilities experienced in the secondary network are derived by taking into account the residual self-interference at the full duplex relay node, in independent non-identical Rayleigh fading channels. The analysis considers the maximum transmit power constraint of the individual secondary nodes and the tolerable interference threshold power constraint of the primary destination as well. The results demonstrate that the outage performance of the SU gets improved significantly when the direct link is exploited at the secondary destination. Further, we evaluate the impact of relay location and the power allocation ratio among secondary source and relay on the outage probability. The analytical results are validated by extensive Monte-Carlo simulations.