Sensing-based spectrum awareness in Cognitive Radio: Challenges and open research problems

Owing to the opportunistic nature of its operation principle, the performance of Dynamic Spectrum Access/Cognitive Radio (DSA/CR) systems depends on the spectrum occupancy pattern of primary systems. DSA/CR systems can monitor periodically the occupancy state of licensed channels in order to gain statistical information on their occupancy patterns, and exploit this information in decision-making processes. This paper provides an overview of relevant research topics related with the problem of providing DSA/CR systems with the ability to gain accurate, reliable and exploitable information on realtime spectrum occupancy. In particular, this paper reviews the following problems: i) spectrum sensing algorithms for spectrum occupancy estimation; ii) estimation of spectrum occupancy statistics based on spectrum sensing; and iii) statistical models for spectrum occupancy. Existing solutions are reviewed and open research problems are discussed as well.