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The intensification in the number of mobile subscribers over the preceding years leads to a situation of the Voice-oriented, data-oriented wireless telephony. It is now point in time to explore new demands and to find the new ways to broaden the mobile concepts. The Cognitive Radio (CR) is one of the essential steps that initiate the solution towards these problems. Then also there are lot of challenges associated to Cognitive Radio in the area of operational field and implementation in Real world. In this paper we tried to give the ideas about the voyage of Cognitive Radio from evolution to challenges experienced with respect to Physical Layer.