Power allocation with min-rate guarantee for OFDM-based cognitive radio systems

In this paper, the power allocation problem is investigated with min-rate guarantee in OFDM-based cognitive radio (CR) system, which is formulated as maximizing the weighted capacity under the total-power, sum-interference, and min-rate constraints. Although the problem can be equivalently transformed into a convex one, and be solved by using the standard software packages, the computational complexity of numerical iteration to find the optimal solution is usually excessively high for the practical implementation. Therefore, a suboptimal algorithm is proposed to reduce the computational intensity. Its basic idea is to select the secondary user (SU), whose achieved rate currently is the farthest from the corresponding min-rate requirement, and if possible, reallocate sufficient power to the SU until the min-rate is reached at each iteration. Simulation results show the proposed algorithm can obtain the near-optimal capacity performance. In addition, the min-rate requirements for SU and the interference protection for primary users are perfectly satisfied as well.