Cooperative relaying in interference limited cognitive radio networks

In this paper, we consider a cooperative relaying based cognitive radio (CR) networks in which the primary receivers are protected by peak interference power constraint. In such scenario, finding the transmission opportunity with a target data rate by maintaining the interference power constraint is the prime goal of the system. We show that cooperative relaying techniques can significantly reduce the outage probability equivalently, improve the transmission opportunity of the CR networks in slow-fading channels. We consider both distributed space time code (DSTC) based simultaneous transmission and single relay selection based transmission from the relays. The exact expressions of the outage probabilities of different cooperative relaying schemes are derived for arbitrary number of relays and interference power constraint in Rayleigh fading environment. Results show that the single relay selection based schemes outperform the DSTC based scheme, in terms of both outage probability and implementation complexity, in multi-relay CR network.