The Study Of The Resourceallocationalgorithm In Ofdm-based Cognitive Radio Systems

Recently with the rapid development of the wireless communication,the spectrum resource is increasingly scarce. The present fixed allocation for spectrum often brings up uneven distribution of spectral resource, and even a waste of it. Cognitive radio has emerged as a hot topic in wireless communication in recent years. By detection the spectrum usage of licensed users, adaptively adjust the communication parameters, Cognitive radio users opportunistically choose free spectrum to transmit. And spectrum allocation is one of the most challenging and crucial problems in cognitive radio. A nice scheme of spectrum access and power allocation should increase the system capacity while guaranteeing the quality of services.This thesis focuses on the study of spectrum allocation in cognitive radio system. Firstly, the thesis introduces the research background of cognitive radio, the concept of radio resource management (RRM), channel allocation and power control. And we analyze the character of RRM in cognitive radio systems. Then analysis of resource allocation model and associasted algorithms in the traditional multi-user OFDM system is presented.And introduce the resource allocation model and associated algorithms in multi-user OFDM-based cognitive radio system.At last, we simulate two classic algorithms and analyze their performance. A novel algorithm of adaptive subchannel, bit and power allocation for the multiuser OFDM-based cognitive radio system is proposed. We formulate the resource allocation problem as a multidimensional 0-1 knapsack problem and adopt a low-complexity algorithm to solve it.The proposed algorithm not only considers the mutual interference (MI) between primary users(PU) and secondary users(SU), but also accommodates SUs'bandwidth demand, and satisfies each secondary user's Quality of Service (QoS) requirement under the constraint of primary users'interference power limits. Simulation results show that, in comparison with RC (Reduced Complexity) algorithm, the proposed algorithm can decrease complexity and increase the system capacity while satisfying each user's QoS requirment.Under the constraints of both primary users'interference power limits and secondary users'transmission power limits for OFDM-based cognitive radio system, a multi-user resource allocation algorithm is presented based on dual decomposition in this thesis. In the algorithm lagrange multiplier problem is decomposed into sub-problems through dual decomposition. By solving the subproblems, we can obtain the optimal power and sub-carriers allocation. Besides, in order to satisfy distributed network structure, a distribution allocation algorithm is put forward, which meets the needs of a more realistic communications environment. The proposed algorithm not only realizes the target of maximum system capacity in the context of satisfying each SU's rate allocation weight but also guarantees the normal communications between PUs. Simulation results show that the performance of proposed algorithms increase with the increasing of SUs' transmission power and PUs'interference power. The convergence of the proposed algorithm is also proved by simulation.