A quadrature signaling based cooperative scheme for Cognitive Radio Networks

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. The closed-form solution is derived. Numerical results demonstrate that, with the proposed cooperative strategy, the PU can achieve optimal performance and the SU can gain transmission opportunities through cooperation.