Abstract__-__With the advancements in telecommunication,it is generally believed that we are getting short of spectrum. If we look at frequency usage chart it is practically viewed that spectrum usage is concentrated at some portion while some of frequency bands are left unutilized, means actually we have spectrum abundance problem lies in spectrum management policies. Cognitive radio technology provides the efficient way to utilize the electromagnetic spectrum. Physical layer of cognitive radio provides the facility to sense spectrum to determine the spectrum holes. Literature has presented various techniques to sense the spectrum but still there is room for researchers in this field. This paper provides the implementation issues for several spectrum sensing techniques and performance analysis for energy detection, matched filter detection, cyclotationary feature based detection and eigenvalue based detection.Index Terms -Cognitive Radios, AWGN, eigenvalues and eigenfunctions, radio spectrum management, wireless networks.