Date Added: Nov 2012
A two-phase cooperative framework in Cognitive Radio Networks (CRNs), whereby the Secondary Users (SUs) can fully exploit the transmission opportunities through cooperation with Primary Users (PUs), is proposed. Specifically, the SU cooperates with the active PU to improve the PU's utility. As a reward, the period of time when the PU is inactive, is allocated to the cooperating SU for its own transmissions. During the cooperation, the PU and the cooperating SU use Quadrature Amplitude Modulation (QAM) to attain orthogonal signaling to cooperate efficiently, while the SU selects the optimal power allocation coefficient to maximize the performance of the PU, when its own transmission requirement is satisfied. The SU selection and power allocation determination procedure is formulated as a nonlinear optimization problem.