Now days due to the rapid advancement and usage of wireless communication technology have made available the key enabling technology name as Cognitive Radio (CR). CR is providing many of advance network services anytime and anywhere even for next generation networks. As cognitive radio have opened many doors of flexible communication, the technology has also provided analyzing and testing methodologies for many of the complex problems those were occurring in history of wireless communication. Such is the issue of spectral crowding.
Due to the rapid increase of wireless communication connectivity has caused crowding of unlicensed spectrum. Spectrum allocation and spectrum sharing was the regulatory techniques to avoid spectral crowding, which was by federal communication commission’s. As spectral efficiency of wireless radio systems is improved and developing, however they are face with increased spectral congestion and network interference. The inflexibility of licensing process increases the inefficiency by assigning complete rights for a frequency band to a primary client. To overcome the spectrum deficiencies and the inefficient utilization of the allocated frequencies, it is necessary to introduce new communication models through which frequency spectrum can be utilized whenever the opening (hole) is available. Thus to resolve the spectrum inefficiency problem, the concept of dynamic spectrum access and cognitive radio is introduced.
The concept of CR was proposed by Mitola in 1998. Such as a radio which is aware of its environment and make decisions accordingly. The important requirement of cognitive radio is to detect a spectrum opening. CR determines which portion of the spectrum is available and detects the presence of licensed users operates in licensed band. Spectrum sensing enables the cognitive radio to detect the spectrum openings.