Secrecy performance of threshold-based decode-and-forward cooperative cognitive radio network

This paper evaluates the intercept and outage probability of a decode-and-forward (DF) underlay cognitive radio network. The secondary users are subject to interference limitations from the primary network, with an eavesdropper tapping the second hop of cognitive network, when all the links undergo Rayleigh fading. For this threshold-based system, without assuming that the DF relays can always decode the message correctly, here we consider that only a set of relays whose SNR satisfies a predetermined threshold can decode the message successfully. We have obtained asymptotic analysis for both cases, when average SNRs of secondary source-relay and relay-destination links are balanced or unbalanced. We have shown that the desired secrecy rate, predetermined threshold, eavesdropper channel quality and interference power limitations significantly affects the secrecy performance of the cognitive radio system. We have investigated the outage and intercept probability of relay selection scheme, when either full instantaneous channel state information (ICSI) or statistical channel state information (SCSI) of all the links is available. We have shown that the optimal relay selection improves the performance of the multi-relay cognitive system, when the number of relays is increased.