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Inefficient use of radio spectrum necessitates the use of cognitive radio technology to exploit the underutilized radio spectrum opportunistically. Spectrum sensing enables cognitive radio user to continuously sense the channel before accessing in order to avoid interference to licensed user and other radio systems. Most of existing research in cognitive radio had been mainly dedicated to the physical layer aspect of the cognitive radio design. Recently, some research efforts were carried out to investigate the impact of physical layer information on upper layer performance. We review the conventional energy detection spectrum sensing, and a cooperative relay diversity-based spectrum sensing using amplify and forward protocol. We also discuss cooperative spectrum sensing where multiuser are involved in spectrum sensing. Finally we briefly present a cross layer design approach proposal for multimedia transmission over cognitive radio networks framework as our work in progress.