Centralized Access Policy Design for Two Cognitive Secondary Users under a Primary ARQ Process

In this paper, an underlay cognitive radio network that consists of two secondary users (SU) and one primary user (PU) is considered, in which the PU employs Type-I Hybrid ARQ. Exploiting the redundancy in PU retransmissions, each SU receiver applies interference cancelation to remove a successfully decoded PU message in the subsequent PU retransmissions. With this approach and using a Constrained Markov Decision Process (CMDP) model, centralized optimum access policies for two SUs are proposed to maximize their average sum throughput under a PU throughput constraint. To obtain the optimal solution, a linear program (LP) corresponding to the CMDP is applied. Numerical results demonstrate the benefits of the proposed optimal policies.