Optimal power allocation for cognitive radio networks with primary user secrecy rate loss constraint

This paper considers a cognitive radio (CR) network in the presence of a malicious eavesdropper who attempts to receive confidential messages from a pair of primary users (PUs). Under the PU secrecy rate loss constraint and the SU maximum transmit power constraint, a pair of secondary users (SUs) is proposed to interfere with the eavesdropper to improve the PU secrecy level and thus gain its own transmission opportunities. Then, the closed-form optimal power allocation strategy for the SU to maximize its transmission rate subject to the aforementioned constraints is derived. Extensions of the results to the scenarios with multiple eavesdroppers and multiple SUs are also presented, respectively. Numerous simulation results are illustrated to investigate the impacts of various system parameters on the SU transmission rate and the PU secrecy rate. Our results indicate that the PU secrecy rate improves significantly with the help of the SU transmission.