Subcarrier and power allocation schemes for multiuser OFDM-based cognitive radio systems

This paper proposes suboptimal schemes for subcarrier allocation with associated power loading mechanism for the orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems that achieve performance close to the optimal scheme but with relatively lesser complexity. The objective is to maximize the CR users´ transmission capacity by adjusting the power allocation across the subcarriers so that the total power remains within the power budget and imposes interference within a permissible threshold limit to the primary user (PU) band. The suboptimal triangular and Gaussian power loading schemes as suggested here have been compared with the optimal scheme and with the uniform power loading technique. Numerical results show that the proposed algorithm is able to achieve performance close to the optimal scheme and much better than the uniform power loading technique while satisfying the interfering constraints to PU.