On the performance of underlay cooperative cognitive networks with relay selection under imperfect channel information

This paper studies the outage performance of the reactive relay selection scheme in underlay cooperative cognitive networks, taking into account primary outage constraint, maximum transmit power constraint, and channel estimation error. To eliminate time-consuming simulations, we propose an exact closed-form outage probability expression for unlicensed users. Several results verify its validity and illustrate considerable performance enhancement with respect to the increase in the number of relays, significant performance degradation due to imperfect channel information, as well as system performance saturation.