Outage analysis of multi-relay selection in underlay cognitive AF relay networks

We evaluate the outage probability of cognitive amplify-and-forward relay networks with cooperation between certain secondary users chosen by multi-relay selection based on the underlay approach, while adhering to the interference constraint on the primary user. A max-min strategy is employed to perform best relay or multi-relay, i.e. between two and four relays, selection. We obtain analytical expressions for the probability density function (PDF), and cumulative density function (CDF) of the received signal-to-noise ratio (SNR) and thereby provide near closed form expressions for outage probability over Rayleigh frequency flat fading channels, which are verified by numerical simulation.