The rapid growth in wireless communication systems has made the problem of under-utilization of spectrum. To solve this problem the concept of Cognitive Radio (CR) emerged, the main goal of which is to provide adaptability to wireless transmission through Dynamic Spectrum Access (DSA) so that the utilization of the frequency spectrum can be enhanced without losing the benefits associated with spectrum allocation. To sense existence of licensed user, energy detection based spectrum sensing technique is used over different wireless fading channels.