Optimal Analysis for Sum-Utilization and Sum-Rate in Cognitive Radio Networks with Different PU Activities

Cognitive Radio (CR) technology mitigates the spectrum scarcity problems by means of opportunistic spectrum access and spectrum sharing. The successful integration of licensed primary users (PU), and unlicensed secondary users (SUs) requires the SUs to be capable of sensing and keeping track of primary transmissions. The performance of CR networks not only depends on the sensing performance of the SUs, but also the PU activities. In general, it is assumed that PU maintains constant occupancy state throughout the SU frame. Under such an assumption, utilization of spectrum opportunity for the SU is guaranteed, and performance of the entire network can be enhanced by the optimal sensing parameters. Moreover, the more realistic approach is to be considered that the PU may arrive or depart anytime during the SU frame, and exponential holding time is assumed for each status of PU. In the paper, we investigate the sum-rate gain using the optimal sensing operation points depending on PU activity, when the constant PU occupancy state is assumed. Additionally, we extend the investigation of optimal sensing parameters for the different number of cooperative SUs. Moreover, we analyze the sum-utilization of spectrum under the constraint of successful transmission for SU when the random PU activity model is adopted. The optimal sensing parameters in terms of sensing durations and PU’s inactive times are investigated to maximize the sum-utilization of spectrum.