Research On Power Allocation Algorithm In Cognitive Radio Systems Based On OFDM

As the rapid development of contemporary wireless communications, wireless spectrum resources have become more and more scarce, the traditional fixed static wireless spectrum allocation models and strategies cannot provide more available spectrum bandwidth and higher spectrum efficiency for the development of future wireless communication. Cognitive radio is one of the key technologies to implement dynamic opportunistic spectrum access and solve the shortage of wireless spectrum resources effectively. Orthogonal frequency division multiplexing technique has the advantages of the higher spectrum efficiency and resisting multipath interference of frequency selective fading, which make it to be an ideal technology to realize cognitive radio system.Power allocation is not only the core technology in traditional orthogonal frequency division multiplexing systems but also the important means of spectrum analysis and decision in radio cognitive system. In cognitive radio system, it also needs to further the research of power distribution to achieve the maximization of channel capacity of cognitive users’ communication links. This article does the transmission power allocation algorithm research on account of the modulating sub-carriers of orthogonal frequency division multiplexing in IEEE802.11a down-link of cognitive radio system. Main contents are as follows:1. This article analyses the classic water-filling power allocation algorithm of the traditional orthogonal frequency division multiplexing systems, introduces the power allocation algorithm of iterative partitioned water-filling based on distance model, and does simulation and analysis on the two kinds of water-filling power allocation algorithms.2. On account of cognitive radio system based on orthogonal frequency division multiplexing, this article proposed a power allocation algorithm complying with the power function distribution of transmission power of the cognitive users on the in-band carrier frequency, and also does the simulation and analysis, achieves the maximum channel capacity in the cognitive users’in-band carrier frequency without affecting the quality of the licensed users’ communication.3. It rises more demanding constraints on the basis of the original constraint conditions as for the less demanding constraints appearing in the above power allocation algorithms, such as the constraints on the total transmission power of the cognitive users, the introduction of the licensed user’s power control parameters and so on, then obtains an optimization algorithm on transmission power allocation, and does simulation and analysis about the algorithm, achieves the maximization of channel capacity in the in-band carrier frequency of the cognitive theoretically.