On the outage behavior of cognitive relay assisted MIMO multiple access channel

We consider a cognitive relay assisted multiple-input multiple-output (MIMO) communication scenario where multiple secondary users wish to communicate with the secondary receiver through Rayleigh fading channels in the presence of a primary user. We assume that secondary users transmits simultaneously with the primary user over the same channel instead of waiting for an idle channel which is traditional for a cognitive radio. We 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 also present the closed form expressions for the outage probabilities and complementary cumulative distribution functions (CCDFs) of mutual information received at the primary and secondary receivers in the absence of cognitive relay. Our results show that in the presence of cognitive relay, not only both the primary and multiple secondary users are able to communicate with intended 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 cognitive relaying.