Coexistence solution using time schedule and user position in cognitive radio networks

In cognitive radio network, a secondary user opportunistically accesses an empty channel based on periodic sensing results for avoiding possible interference to the primary users. However local sensing does not guarantee the full protection of the primary users because hidden primary receivers may exist within the interference range of the secondary transmitter. To protect primary systems and simultaneously to maximize utilization of the secondary users, we need to derive carefully designed coexistence solutions for various network scenarios. In this paper, we propose coexistence conditions without any harmful interference in accordance with the uplink/downlink schedule and user position. We have classified the coexistence conditions into four different scenario cases depending on the provided information to the secondary network base stations. For each case, we have shown that which secondary devices can access the channel at which time period and the possible maximum throughput of the secondary system is also derived. Computer simulation results demonstrated that the proposed method can be applied to the real cognitive radio system to improve the communication probability of CR devices.