Opportunistic Spectrum Sharing Based on Exploiting ARQ Retransmission in Cognitive Radio Networks

In this paper, we consider a pair of cognitive radio (CR) users co-existing with a pair of ARQ- based primary users (PU). The secondary user (SU) overhears the ACK/NACK feedback sent from the receiver of the primary system, and then decides to access the spectrum or not. An opportunistic sharing scheme, referred to as Spectrum sHaring with ARQ Retransmission and Probing timeslots (SHARP), is proposed to exploit spectrum opportunities based on the ACK/NACK of PU only. Numerical results show that the analytical outcomes perfectly match those from the Monte Carlo simulation. Moreover, the goodput of SU increases dramatically while the outage probability of the primary remains small.