Three Regions for Space–Time Spectrum Sensing and Access in Cognitive Radio Networks

In this paper, spectrum holes in space-time dimensions are exploited to improve the spectrum utilization of cognitive radio networks (CRNs). To achieve this goal, we design the architecture of three regions, which are separately known as the black region, the gray region, and the white region. Temporal spectrum holes exist in the gray region, where secondary users (SUs) can opportunistically access the licensed spectrum with interweave spectrum sharing. In the white region, SUs can exploit spatial spectrum opportunities and transmit at any time by taking advantage of their long distances from the primary users (PUs), without causing severe interference to PUs. Moreover, the existence condition of the transition zone between the gray region and the white region is theoretically analyzed, where power control should be implemented in SUs. Closed-form bounds of three regions are obtained, which can be used in space-time spectrum sensing and access in CRNs. Finally, we provide numerical results to evaluate the relations among the key parameters in the three regions.