The cooperation among cognitive users (CUs) is considered as an efficient means to improve the primary user (PU) sensing in cognitive radio environment. Almost all previous related works employ the cooperation among CUs for PU activity detection whereas in this paper, the notions of cooperation among PUs and CUs are applied. This is achieved by allocating the available PU power among OFDMA subcarriers with two objectives 1. Guaranteed spectral efficiency to PU 2. Maximize detection of PU presence to a CU. The dynamic nature of channel parameters significantly improves the detection probability of CU with a minor reduction in PU's spectral efficiency. Analysis shows that a reduction of 5% spectral efficiency could be utilized to gain more than 15% in terms of the correct detection probability. The convexity of the formulated problem is analyzed. Finally, we propose deploying our scheme with CU collaborative sensing schemes to improve the detection probability in the low signal-to-noise ratio regions.
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