Cognitive Access Policies under a Primary ARQ process via Forward-Backward Interference Cancellation

TL;DR

This paper proposes a new cognitive radio access method that exploits primary ARQ protocols for interference cancellation, significantly improving secondary user throughput while respecting primary user performance constraints.

Contribution

It introduces forward and backward interference cancellation techniques leveraging primary ARQ, and designs optimal access policies for secondary users in such environments.

Findings

Enhanced secondary throughput through interference cancellation

Optimal access policies prioritize states with known primary messages

Numerical results demonstrate significant throughput gains

Abstract

This paper introduces a novel technique for access by a cognitive Secondary User (SU) using best-effort transmission to a spectrum with an incumbent Primary User (PU), which uses Type-I Hybrid ARQ. The technique leverages the primary ARQ protocol to perform Interference Cancellation (IC) at the SU receiver (SUrx). Two IC mechanisms that work in concert are introduced: Forward IC, where SUrx, after decoding the PU message, cancels its interference in the (possible) following PU retransmissions of the same message, to improve the SU throughput; Backward IC, where SUrx performs IC on previous SU transmissions, whose decoding failed due to severe PU interference. Secondary access policies are designed that determine the secondary access probability in each state of the network so as to maximize the average long-term SU throughput by opportunistically leveraging IC, while causing bounded average long-term PU throughput degradation and SU power expenditure. It is proved that the optimal policy prescribes that the SU prioritizes its access in the states where SUrx knows the PU message, thus enabling IC. An algorithm is provided to optimally allocate additional secondary access opportunities in the states where the PU message is unknown. Numerical results are shown to assess the throughput gain provided by the proposed techniques.