On the mutual information of cognitive relay assisted Rayleigh fading MIMO channel

In this paper, we study a Multiple-Input Multiple-Output (MIMO) communication scenario through Rayleigh fading cognitive radio channel in which two users, called the primary and the secondary users wish to communicate with two different receivers, in the presence of a cognitive relay. We assume that the secondary user transmits simultaneously with the primary user over the same channel instead of waiting for an idle channel which is traditional for a cognitive radio. The cognitive relay has access to the messages transmitted by both the users and assists them in communicating the messages successfully to their respective destinations. We address the problem of analyzing fading MIMO cognitive relay channels and derive the expressions for mutual information received at the primary and secondary receivers in both the cases when cognitive relay is present or not. We focus on the investigation of outage behavior of proposed model. Our results show that in the presence of cognitive relay, not only both the primary and secondary users are able to communicate with corresponding receivers compensating interferences created at their receivers, but also the outage performance of primary and secondary users are improved due to the additional diversity obtained via relaying.