Power allocation for orthogonal frequency division multiplexing-based cognitive radio networks with cooperative relays

The power allocation problem in orthogonal frequency division multiplexing-based cognitive radio (CR) networks with cooperative relays has been investigated here, where both the interference to primary users (PUs) and the power budget of the CR network are considered. The authors try to maximise the overall throughput of the CR network within the given constraints. The coupling variables in the formulated problem make it hard to solve, so an iterative optimisation scheme to find out the optimal solution with a controllable complexity is developed. First, the original problem is decomposed into two subproblems that can be solved independently. A fast barrier method has been employed to work out the optimal solution to one of the subproblems with a complexity of O(L²N), where L and N are the number of PUs and subcarriers, respectively. Then, an iterative procedure is developed to solve the other subproblem. Numerical results show that the proposed method can significantly increase the throughput of the CR system, comparing with other representative ones. Furthermore, the proposed algorithm gives a general power optimisation framework for CR networks with cooperative relays.