Improvement of spectrum utilization with retransmission in cognitive radio networks: Analytical approach

Cognitive radio (CR) is an efficient technique to increase the spectrum utilization through opportunistic spectrum access (OSA) strategies. The under-utilization of spectrum creates an opportunity for secondary users (SUs) to achieve desired performance through CR techniques. The spatial and temporal variations of the primary user (PU) activity under different PU and SU co-existing network topologies characterize the spectrum utilization in a dynamic radio environment of CR networks. The successful utilization of spectrum depends on the channel conditions, sensing results, detection of spectrum opportunity, and successful transmission of packet in a given time slot. In the paper, we formulate and analyze the sum utilization of spectrum, with retransmissions for the SU, to ensure the reliable packet delivery under different network topologies. First, we investigate the inherent tradeoff of sum utilization of spectrum without considering any retransmission for the SU. The optimal sensing durations subject to maximum sum utilization of spectrum are identified. Next, we analyze the sum utilization of spectrum when SU needs to retransmit its packet, considering the same PU mean inactive duration, and SU packet length, in order to improve the link reliability. The simulation results demonstrate the performance of the sum utilization of spectrum under different network parameters for both cases of transmission, i.e., with and without retransmissions.