Spectrum underlay-based water-filling algorithm in cognitive radio networks

Under the constraint of the interference power for the primary user and the overall transmission power for the cognitive user, we mainly investigate the spectrum sharing problems in a cognitive radio network. According to the interference constraint of the primary user and the water-filling power of the cognitive user, we obtain a monotonic function about the water-level, and then propose a novel power allocation algorithm based on the water-filling theorem. Through which we can not only protect the primary user´s QoS, but also obtain the optimal communication utility for the cognitive user. Theory analysis shows that the proposed algorithm can significantly reduce the complexity. Simulation results verify the feasibility and validity of the proposed algorithm.