Subcarrier and Power Allocation for Multiuser OFDM-based Cognitive Radio Uplink Systems

Cognitive radio (CR) technology is designed to enhance the spectrum efficacy by allowing the secondary user to use the unoccupied frequency bands which belong to the primary user. A problem of maximization in the capacity of the secondary users subject to the power and mutual interference constraints is discussed in multiuser OFDM-based CR uplink systems. A modulation order limitation on each subcarrier is also considered. The proposed allocation scheme is developed based on a well-designed indicator which is composed of three terms with parameters related to the amount of power, interference, and other adjustable coefficients. The allocation strategy assigns subcarriers to users and allocates power to subcarriers by utilizing the proposed indicator. The scheme outperforms the existing schemes shown in the simulation results. In order to further improve the performance, a refinement approach is applied after the proposed allocation strategy. The proposed allocation schemes further outperform the existing schemes as revealed in the simulation results.