An ARQ-based protocol for cooperative spectrum sharing in underlay cognitive radio

In this paper, a cooperative spectrum sharing protocol is proposed for cognitive radio networks (CRNs) which operates in underlay mode with an automatic repeat-request (ARQ)- based primary user (PU) including primary transmitter (PT) and primary receiver (PR) nodes and a bidirectionally communicating secondary user (SU) which consists of the nodes S1 and S2. In ARQ-based PU, ACKnowledgement/Negative-ACKnowledgement (ACK/NACK) messages are send from PR to PT and listened by S1 and S2 to control the PU's package achievement. PU transmits its package by accessing the spectrum alone or by cooperating with SU or under interference caused by SU. It is shown by analytical and simulation results for the throughputs of PU and SU that the proposed protocol significantly improves the PU's throughput compared to conventional non-CR model while stabilizing the secondary user throughput.