Robust Relay Selection and Power Allocation for OFDM-Based Cooperative Cognitive Radio Networks

In this paper, we study the robust relay selection and power allocation problems for orthogonal frequency division multiplexing (OFDM) based cooperative cognitive radio networks (CRNs) with channel uncertainties. The objective is to maximize the capacity of the cooperative CRN, which is subject to the interference threshold constraints of primary users (PUs) and the total transmit power limitation of secondary user (SU) and relays. We describe all possible channel uncertainties with ellipsoid set and interval set. The robust relay selection and power allocation problems are formulated as semi-infinite programming (SIP) problems, respectively. We convert the SIP problems into their equivalent convex optimization problems with the worst-case approach, which can be solved by the Lagrange dual decomposition method. Simulation results show that the proposed robust relay selection and power allocation algorithm can strictly guarantee the quality of service of PUs under channel uncertainties.