Decentralized heuristic access policy design for two cognitive secondary users under a primary Type-I HARQ process

In this paper, decentralized heuristic access policies are designed for two secondary users (SUs) in an underlay cognitive radio network in which the PU employs Type-I Hybrid ARQ. Exploiting the redundancy in PU retransmissions, each SU receiver applies interference cancellation (IC) to remove a successfully decoded PU message in the subsequent PU retransmissions. There is no central control unit and we consider two different scenarios. In the first scenario, each SU transmitter only knows the PU message knowledge state of its corresponding SU receiver. In the second scenario, the SU transmitters are unaware of any PU message knowledge states at the SU receivers. We design access policies in both offline and online modes, where in an online mode each SU can learn from its own local information. Using heuristic approaches for the considered scenarios, decentralized access policies are proposed to maximize the average sum throughput of SUs under a PU throughput degradation constraint. The results also show that heuristic access policies using the online mode have a performance gain close to that obtained using the offline mode, while providing increased robustness and flexibility.