Maximization of Long-Term Average Throughput for Cooperative Secondary System With HARQ-Based Primary System in Cognitive Radio Network

Abstract

We consider a cognitive radio network in which a secondary system (SS) coexists with a hybrid-automatic-repeat-request (HARQ)-based primary system (PS) over block-fading channels. We propose a coexistence scheme in which the SS acts as a relay for the PS and gains spectrum access opportunities as a reward for the cooperation. The proposed scheme aims at achieving nontrivial throughput gain for the SS without affecting the performance of the PS. To this end, we first analyze the long-term average throughputs (LATs) of the PS and SS by applying total probability theorem and a mixture-of-Gamma approximation. Then, we optimize the transmit power ratio and the target rate of the SS to maximize its LAT. In simulations, the proposed scheme provides significant LAT gain for the SS while maintaining the LAT of the PS.