Access policy design for a cognitive secondary user under a primary type-II HARQ process

This paper proposes access policies for the secondary user (SU) of a cognitive radio network (CRN). The SU transmits in the same band as the primary user (PU) where the latter employs Type-II Hybrid-ARQ with incremental redundancy (IR-HARQ). The SU receiver applies interference cancelation to remove a successfully decoded PU message in the subsequent PU transmissions in each HARQ round. The SU transmitter exploits this PU message knowledge state at its receiver as well as the accumulated mutual information (ACMI) and ACK/NACK feedback transmitted by the PU receiver. The ACK/NACK message demonstrates the successful/unsuccessful decoding of the PU message at the PU receiver. With this approach and using a Constrained Markov Decision Process (CMDP) model, access policies for the SU are proposed to maximize its average throughput under a constraint on the PU throughput.