Optimal power allocation for real-time services in OFDM-based cognitive radio systems

In this paper, the adaptive power allocation problem on the downlink of a multiuser orthogonal frequency division multiplexing (OFDM) based cognitive radio (CR) systems with real-time (RT) services is investigated. The objective is to minimize the total transmit power of all CR users with satisfying the minimum bit rate requirements for RT services and limiting the interference to primary users´ (PUs) bands below a given threshold. The problem is formulated using convex optimization method and an optimal algorithm is proposed by efficient iteration to search the optimal solution, and the performance of the proposed algorithm is also estimated and compared with that of other methods by numerical simulations.