In the last few years, there has been enormous improvement in mobile communication services.

Due to this rapid growth in the field of communications, the demand for wireless spectrum has

increased rapidly. In the early days in order to remove the interference problem, the spectrum

was assigned statically. To assign the spectrum statically, the fixed spectrum assignment policy

was used. Due to the fixed spectrum assignment policy, the spectrum was not efficiently utilized

and remained vacant most of the time. The study by Federal Communications Commission

(FCC) shows that the spectrum is available but its usage is not efficient. Such kind of spectrum

inefficiency can be overcome by the use of Cognitive Radio.-In the last few years, there has been enormous improvement in mobile communication services.

Due to this rapid growth in the field of communications, the demand for wireless spectrum has

increased　rapidly. In the early days　in　order to remove the　interference problem, the spectrum

was assigned statically. To assign the spectrum statically, the fixed spectrum assignment policy

was used. Due to the fixed spectrum assignment policy, the spectrum was not efficiently utilized

and　remained　vacant　most　of　the　time.　The　study　by　Federal　Communications　Commission

(FCC) shows that the spectrum is available but its usage is not efficient. Such kind of spectrum

inefficiency can be overcome by the use of Cognitive Radio.