On Ergodic Sum Capacity of Fading Channels in OFDMA-Based Cognitive Radio Networks

Abstract

An orthogonal frequency-division multiple access (OFDMA)-based cognitive radio network (CRN) is considered where cognitive radio users (CRUs) can only access the frequency bands not being occupied by primary users (PUs) while keeping the cross-channel interference to each PU under a specified threshold. In this paper, we investigate the ergodic sum capacity of all CRUs in OFDMA-based networks and consider the constraints on the long-term transmit power of all CRUs, the long-term interference thresholds of PUs, and the statistical proportional fairness of all CRUs. In OFDMA-based CRNs, the number of available subchannels is smaller than that of CRUs in some OFDM symbol durations. To deal with this time-varying nature of available spectrum resource and achieve the ergodic sum capacity of all CRUs, we propose an optimal resource-allocation algorithm under the given constraints. Simulation results show that the proposed algorithm can achieve substantial capacity gains for CRUs over the traditional resource-allocation algorithm and maintain the statistical proportional rate constraints of all CRUs.