Abstract: Cognitive radio is a communication technology which is designed to serve users to make use of the available bandwidth in a greatest possible amount. Though more research has been done on spectrum sensing and allocation problems, cognitive radio has recently attracted a lot of research interest. This paper shows the concept of cognitive radio networks (CRNs). Cognitive radio is an intelligent form of wireless communication. It consists of a transceiver which detects the channels which are in use for communication or which are not in use. It can automatically search vacant channels in a wireless spectrum. The cognitive radio depends on spectrum allocation and channel selection. This paper gives the survey on various methods for cognitive radio.

Keywords: Cognitive Radio Networks (CRNs), Spectrum allocation, Primary Users(PU), Secondary Users(SU).