Spectrum is a life blood of radio frequency wireless communication. The population nowadays is accessing the wireless devices like cellular phone, laptop etc., due to its portability and connection to network at anytime, anywhere. So the entire spectrum becomes overcrowded and we are in a demand to access the spectrum. At the same time nearly 70% of the allocated spectrum is not utilized properly. The unused spectrum creates white spaces or spectrum hole. In this paper, we propose full cognitive radio systems which perform all the four functions like spectrum sensing, management, sharing, and mobility. Moreover, underlay is also comprised with cognition functions. The concept of Cognitive Radio (CR) is introduced for even use of available spectrum, less blocking probability and low interference.

cognitive radio, sharing, hand-off, fuzzy inference system (FIS), underlay, overlay, power spectral density (PSD).