Study of a multi-relay scheme and co-channel interference within an underlay cognitive radio network

This work studies the impact of a multi-relay scheme and co-channel interference (CCI) on the performance of a dual-hop underlay cognitive radio (CR) network. An amplify-and-forward (AF) relay protocol is considered at the relay nodes. Besides the effect of CCI on the secondary network, the interference from the primary transmit node is also considered. Based on opportunistic selection, the best relay is selected to establish the transmission between source and destination node. First, the equivalent per hop signal-to-interference-plus-noise ratio (SINR) is obtained. Then, an exact per hop cumulative distribution function (CDF) for the equivalent SINR is derived. From this, the outage probability performance is investigated. The results show that considering a multi-relay scheme is an efficient way to combat the impact of the interference power constraint and CCI. In addition, they show that CCI could severely degrade the system performance, especially when its power linearly increases with the secondary transmit powers. To validate the theoretical results, Monte Carlo simulations are also provided.