Cognitive Amplify-and-Forward Relay Networks with Switch-and-Examine Relaying in Rayleigh Fading Channels

This letter introduces cognitive channel-state-information (CSI)-assisted amplify-and-forward (AF) relay networks employing the low-complexity switch-and-examine diversity combining (SEC) relaying scheme. The scheme 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 letter derives closed-form expressions for the outage probability and symbol error probability (SEP) of the proposed system. The system is also studied at high SNR values where approximate expressions for the outage probability, 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.