Subcarrier Allocation Based on Water-Filling Level in OFDMA-Based Cognitive Radio Networks

Cognitive radio makes it possible for an unlicensed user to access a spectrum unoccupied by the licensed user. In this paper, the resource allocation is investigated for OFDMA-based cognitive radio networks. Considering the characteristics of cognitive radio and OFDMA, an improved water-filling power allocation scheme is proposed under the interference temperature constraints. Based on the improved water-filling power allocation, the subcarrier allocation algorithms for both downlink and uplink are proposed. In these algorithms, the subcarriers are allocated to the users with the best channel quality initially and then adjusted to improve the system performance. The subcarrier adjustment rules are obtained by strict theoretical deduction. Finally, the performance of the proposed subcarrier allocation algorithms is investigated by numerical results.