ABSTRACT
A cognitive radio is a flexible transceiver based on a software-defined radio that is able to sense the radio frequency spectrum (RFS) and dynamically determine what spectrum bands are unoccupied and can be used for opportunistic transmission. This chapter starts by introducing the topics of software-defined radio and the consequent cognitive radio with an overall of these architectures. The key element for cognitive radio is its ability to detect unused RFS; this technique is called spectrum sensing. In this chapter, spectrum sensing is divided in three areas; first, spectrum analysis, followed by signal detection, and then noise model. Different spectrum analysis techniques are explored and explained. In signal detection, the binary decision of determining a channel occupation is explained. The noise model analyses the determination of the threshold for that decision. The chapter ends by exploring the application of spectrum sensing in the recent trend of multiple-input, multiple-output (MIMO) communications with highly directional transmissions, using spatial spectrum sensing to allow an even more efficient reuse of spectrum resources.
