Robust spectrum access for hybrid interweave-underlay cognitive radio systems using probabilistic spectrum access

The hybrid cognitive radio (CR) system which combines the two classical interweave and underlay approaches has an improved spectrum efficiency compared to conventional CR systems. In this study, the authors apply the joint spectrum access and power control in a hybrid CR system in the presence of threshold estimation errors. They first formulate the performance metrics of the hybrid CR system under the optimal joint spectrum access and power control strategies by taking into account the threshold estimation errors. Then they show that the threshold estimation error decreases the probability of detecting the primary user (PU) while it increases the false-alarm probability. Next, they show that the threshold estimation error degrades the performance of the hybrid CR system in terms of outage probability, average achievable data rate and the average interference introduced to the PU. To overcome these performance degradations, they propose a modified spectrum access formulation based on the probabilistic spectrum access scheme, which reduces the impact of threshold estimation uncertainty on the performance of the hybrid CR system. Simulation results indicate that the proposed spectrum access can compensate the performance degradation of a CR system up to 65% for a detection probability of 0.7.