Switch-and-Examine Relaying Scheme for Cognitive AF Relay Networks in Rayleigh Fading Channels

This paper introduces cognitive amplify-and-forward (AF) relay networks employing the low complexity switch-and-examine diversity combining (SEC) relaying scheme. This scheme requires low amount of channel estimations compared to the opportunistic relaying and it is based on the SEC diversity combining technique in which a relay out of multiple relays is selected to forward the source message to destination. The selection process is performed such that the end-to-end (e2e) signal-to-noise ratio (SNR) of the selected relay satisfies a predetermined switching threshold. In addition, the paper derives approximate expressions for the outage probability and symbol error probability (SEP) of the proposed system. The channel capacity is also numerically calculated. Furthermore, the system is studied at high SNR values where the diversity order and coding gain are derived. Results show that the diversity order of the studied cognitive AF relaying with SEC selection is the same as its non-cognitive counterpart.