5. Spectrum Sensing

Cognitive radio has emerged as an efficient approach to implement reuse of the licensed spectrums. Among the cognitive radio technologies, cooperative spectrum sensing has been corroborated to be an effective approach to counter channel fading. In this chapter, we consider the terrestrial system as secondary user (SU) and the satellite system as primary user (PU), where secondary terrestrial users attempt to sense and access the primary satellite systems’ licensed spectrum. We first advance a strategy for SUs to search available spectrums with asynchronous MAC-layer sensing. With this method, the SUs do not need to know the communication mechanisms in satellite network when dynamically accessing. Then, we discuss the asynchronous cooperative sensing situation, and derive the optimal sensing parameters under such asynchronous scenario. Finally, we propose a density control mechanism for managing number of terrestrial secondary transmitters around one satellite ground station in order to guarantee that the primary communications are not interfered. Note that in the remaining of this section, all the “SUs” refer to the terrestrial unlicensed users and all the “PUs” refer to the licensed satellite systems.