What is Secondary User

Cognitive radio emerged as one of the key enabling technologies of dynamic spectrum access, addressing the problem of inefficient usage of the available radio spectrum. It aims at providing more effective and convenient communication capabilities. Cognitive radio which is considered as the key technology for future mobile computing and wireless communications can form cognitive radio networks (CRN) by extending the features of radio link to network layer functions and above. The cognitive radio systems have the ability to exploit the spectrum holes by detecting and using them in an opportunistic manner through spectrum sensing. This chapter will brief the various architectures of cognitive radio networks, terminal capabilities of cognitive radio as nodes of CRN highlighting the spectrum sensing ability and different methods of it, and some applications of CRN.