ABSTRACT
This chapter summarizes state-of-the-art cognitive radio network (CRN) technology and its research opportunities at the horizon. Since J. Mitola III proposed the concept of cognitive radio (CR), cognitive radio technology with federal communication commission endorsement has been widely considered as an emerging solution of crowded spectrum for future wireless communications. The interweave paradigm is the original idea of cognitive radio to create the opportunistic communications if the primary system is not transmitting. The overlay paradigm proceeds under the assumption that cognitive radios know the channel gains, codebooks, and messages from noncognitive radios. The networking coding concept is used to develop the principles of routing algorithm. CRN must transport packets under multiple opportunistic links, and thus spectrum sensing must be able to support networking function such as medium access control and routing for multiple CRs in the CRN, which creates a new scenario of spectrum sensing beyond traditional detection and estimation for a specific radio link.
