Enhancing Security of Primary User in Underlay Cognitive Radio Networks With Secondary User Selection

This paper investigates the effect of multiuser gain provided by the secondary user selection on the secrecy performance of the primary users. We first propose a simple scheme where the user with the minimal interference channel is selected, and derive a closed-form lower bound of the achievable ergodic secrecy rate (ESR) of the primary users. In the high signal-to-noise ratio (SNR) regime, asymptotic result shows that the multiuser gain scales logarithmically with the number of the secondary users for a fixed interference temperature. Inspired by non-orthogonal multiple access strategy, we then propose a maximal jamming rate-based scheme, where the secondary with maximal interference channel is selected and it will transmit with an elaborately designed rate so that the primary receiver can cancel out the interference completely with successive interference cancellation. A closed-form expression of achievable ESR is also presented. Theoretical and simulation results show that the both proposed schemes can achieve multiuser gain and improve the security of the primary users significantly.