CSI Knowledge Effect on Secrecy of Threshold-Based Underlay Cognitive Decode-and-Forward Relaying

Abstract

This paper evaluates the outage probability of underlay cognitive DF relaying system, under two scenarios of with and without the availability of channel knowledge at the transmitter for all the links. In this underlay mode, there are interference constraints on the secondary user from the primary network, such that the QoS of the primary transmission is not disturbed. Threshold-based relaying is considered where, the DF relay can decode the source message correctly, only if the predetermined threshold is met. Asymptotic analysis is obtained for each instances, while for secondary source to relay and secondary relay to destination average link SNRs are kept balanced or unbalanced. We have also shown that CSI knowledge can improve secrecy, and the amount of improvement for the outage probability is more when the required rate is low and for low operating SNR. It is proven that the required secrecy rate, the predefined threshold, the channel knowledge at transmitter and the interference power constraints appreciably affects the cognitive DF threshold-based relaying system secrecy.