Dynamic selection of CWmin in cognitive radio networks for protecting IEEE 802.11 primary users

Time domain spectrum sharing between primary user (PU) and cognitive radio (CR) networks is considered. The Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol is suitable for this type of spectrum sharing with unslotted access in which PUs and secondary users (SUs) are asynchronous. The goal is to maximize the average throughput of the SUs while guaranteeing the average throughput of the PUs. To achieve this, in our proposal the CR network adaptively changes its minimum contention window size (CWmin), depending on the channel occupancy rate (COR) from the PU network. The COR is approximately proportional to the average throughput and is estimated based on the observed traffic. In this paper, we analytically derive the optimum CWmin to maximize the COR of the CR network, while guaranteeing the COR of the PU network. In addition, to further protect saturated (high load) PUs, we also propose using a margin in the CWmin selection process. The simulation results show that the proposed approach does maximize the COR of the CR network and that it does converge faster in dynamic situations than the previous proposals. Also, the simulation results show the effectiveness of the proposed approach with margin.