The Study Of Theadaptive Resourceallocation Algorithm In OFDM-Based Cognitive Radio Systems

In recent years, with the rapid development of communication technology, the fixed spectrum allocation resulted in a shortage of spectrum resources. A large number of licensed wireless spectrum to be idle, and can not be effectively used. Cognitive radio (CR), with its ability to improve the spectrum utilization by allowing secondary users (SUs) opportunity to access the spectrum which is unused by primary users (PUs), has become the focus of research. Spectrum allocation is one of the most challenging and crucial problems in cognitive radio. A good scheme of resource allocation should increase the system capacity while guaranteeing the quality of services(QoS).This thesis focuses on the study of spectrum resource allocation in CR system. Firstly, we introduce the concept of CR, and deeply study the resource allocation in CR. Secondly, the analysis of resource allocation model and algorithms in the traditional multi-user orthogonal frequency division multiplexing (OFDM) system is presented. And then, we introduce the resource allocation model and algorithms in multi-user OFDM-based cognitive radio system. At last, we simulate some classic algorithms and analyze their performance.A dynamic resource allocation algorithms for OFDM CR systems is presented. This algorithm solves the optimization problem based on maximize the total transmit bit rates of SUs, on one hand, the total transmit power of SUs should below the transmit power constraint, on the other hand, the interference to PUs should under the maximum interference level. We allocate subchannels by an improved Hungarian Algorithm based on a new cost function, then, we allocate the bits and power adaptively based on requirement of SUs. Simulation results show that the proposed algorithm could effectively use spectrum holes and improve the system throughput with the constraint on every PU.We maximize the transmission rate of non-real-time (NRT) service under the QoS requirement of real-time (RT) service, in order to maximize system capacity of secondary users. Thus, a dynamic RA algorithm is proposed. This algorithm solves the optimization problem based on maximizing the total transmit bit rates of SUs, on the one hand, the total transmit power of SUs should below the transmit power constraint, on the other hand, the interference to PUs should under the maximum interference level. Firstly, we convert the Qos requirement of RT service to the rate requirement of RT CRUs, then, we allocate the bits and power adaptively based on requirement of RT CRUs until meet the Qos requirement. At last, the remaining resource is allocated to NRT CRUs. Simulation results show that the proposed algorithm could maximize the system throughput with the constraint on every primary user and the Qos requirement of RT service.