Performance of Cognitive Selective-Repeat Hybrid Automatic Repeat Request

In this paper, a novel transmission protocol is proposed based on the classical selective-repeat hybrid automatic repeat to access a primary user (PU) channel, which is referred to as the CSR-HARQ. We assume that the PU transmits information based on time-slots (TSs). During a TS, the cognitive radio transmitter first senses the PU channel. Once a free TS is found, it transmits a number of packets to the CU receiver based on the principles of the SR-HARQ. In this paper, we analyze the throughput, average packet delay, and end-to-end packets delay of the CSR-HARQ. We proposed a pair of analytical approaches. The first one is probability based, while the second one relies on the classic discrete time markov chain principles. Finally, we study the throughput, average packet delay, and the end-to-end packet delay of the CSR-HARQ both by simulations and by evaluating our formulas. The simulation-based studies agree well with the analytical results. The performance of the CSR-HARQ systems is significantly impacted by the activity of the PU channel and by the reliability of the spectrum sensing.