An Efficient Spectrum-Sharing Algorithm for Multiuser OFDM Based Cognitive Radio Systems

Abstract

As the vigorous development of wireless communications technology, there are more and more users accessing the wireless networks, and the spectrum scarcity becomes a severe problem, especially when the high data throughput is required. It was indicated by the Federal Communications Commission (FCC) of the United States that the utilization efficiency is less than 30% of the allocated spectrum in the country. Cognitive radio (CR) is a technology that can enable an intelligent device to sense its surrounding environment, identify idle spectrums, and use them for data transmission dynamically, thereby increasing the spectrum utilization. The main idea of CR is that the secondary users (SUs) can use idle spectrums of the primary users (PUs), but they must satisfy the transmitted power constraints for avoiding interference to PUs. One of the most significant studies in CR is how to quickly allocate idle spectrums appropriately to SUs for maximizing the spectrum efficiency as well as the system capacity. In this thesis, we propose an efficient power allocation algorithm for spectrum sharing in multiuser orthogonal frequency division multiplexing (OFDM) based CR systems. The proposed algorithm is derived by using the Lagrange multipliers to solve the optimization problem subject to 1) the power constraint on each subcarrier of SUs represented by the interference temperature limit (ITL) of PUs and 2) the total power constraint on each SU. As compared to related works for spectrum sharing, the proposed approach achieves a higher system capacity with acceptable computational complexity.