Optimal power allocation and power constraint in OFDM-Based cognitive radio systems

Cognitive Radio (CR), which aims to improve spectrum utilization by accessing the spectrum originally licensed to a primary system, is a promising concept. In cognitive radio system based on orthogonal frequency division multiplexing (OFDM), the optimized algorithms for sub-carrier power allocation share the problems of complex iterative calculation and difficult realization. In this case, a sub-optimal power allocation algorithm based on power function distribution is proposed, to allocate power of in-band subcarrier of cognitive user according to the numerical characteristics of the power function by using a convex optimization numerical method under linear constraint. This algorithm has the advantages of fast calculation speed and easy realization, and reduces the interference for the authorized user brought by the power leakage of the in-band subcarrier of cognitive user appears in the out-of-band. MALAB simulation results show that the proposed scheme maximizes the in-band channel capacity of the cognitive user under the interference threshold of the authorized user and the comparison model the optimal relationship between the limited and unlimited transmit power capacity. Meanwhile, the maximum transmission rate of the existing power allocation scheme is increased within the same condition.