Key Technology Study On Resourse Allocation And Management For Cognitive Radio System

With the rapid development of the wireless communication technology, the frequency resource becomes more and more insufficient. The traditional static wireless frequency management makes much frequency in idle state in usual, which limits the usage efficiency of the frequency resource. Cognitive radio is considered an effective method, which employs spare frequency effectively and solves the insufficiency problem of the wireless frequency. Cognitive radio network can sense the wireless frequency environment intelligently and search for available frequency automatically. Therefore cognitive radio pioneers a new way to enhance the frequency utilization efficiency.Cognitive radio system is based on dynamic frequency access. So resource allocation and management is a pivotal technology and research hotspot. The paper makes deep research in frequency allocation, power control and access control of cognitive radio system. The main innovation results are as follows:1. Research on subcarrier allocation of cognitive radio NC-OFDM system based on graph coloring model. The paper improves the current graph model based on channel allocation and builds the subcarrier allocation model adapted to cognitive radio NC-OFDM system. Based on the improved model, the paper applies the rand algorithm and the existing distribution greedy algorithm for subcarrier allocation in cognitive radio NC-OFDM system. Also the paper introduces the max-min algorithm in multiuser OFDM system and proposes the max-min algorithm adapted to cognitive radio NC-OFDM system, which can not only obtains better throughput performance but good fairness performance.2. Research on power allocation in cognitive radio system based on interference temperature model. In the existing power control based on interference temperature some problems exist. For example, some methods are too simple to attain the optimal solution, and also some have too large computation amount. Aimed at the disadvantage of the existing methods, the paper proposes an optimal power allocation algorithm adapted to uplink cognitive radio OFDM system which has low computation complexity and can maximize the user transmission rate. The algorithm applies the zero-setting iterative water-filling algorithm repeatedly until the optimal power allocation is achieved. The mathematical derivation proves the optimization performance of the algorithm, which is also verified by the simulation result. At the same time the simulation result indicates that the computation complexity of the algorithm reduces by over 50% compared with the gradient method.3. Research on the dynamic resource allocation in cognitive radio system in the condition of non real time service. Currently a lot of document researches on the static resource allocation in cognitive radio system, but because of the time and space change of the available frequency, the static allocation method can’t realize the efficient frequency utilization. The paper researches on dynamic subcarrier and power allocation in cognitive radio system in the condition of non real time service based on overlay and underlay sharing mode. Firstly we build and analyze the model of the subcarrier state based on POMDP theory. Then under the overlay and underlay mode we research on the dynamic resource allocation in cognitive radio system. Under the overlay mode we allocate the idle subcarrier to cognitive user dynamically and control the access probability of cognitive users to spare subcarrier to maximize the system throughput and guarantee the QoS (Quality of Service) requirement of users. The simulation results indicate that the throughput performance of dynamic allocation algorithm is better than static allocation and CSMA access method. Under the underlay mode, first we allocate power dynamically by limiting the cognitive user power only when the primary user arrives. Then we allocate the subcarriers dynamically according to the access probability of cognitive users in each subcarrier states to maximize the system throughput in the precondition of guaranteeing the minimal rate requirement of cognitive users. The simulation results show that the associated subcarrier and power allocation algorithm can attain obvious throughput performance plus.4. Research on access control in cognitive radio system in the condition of real time service. Aimed at the system with buffer mechanism and without buffer mechanism respectively, we build the system state model by continuous time Markov chain and analyze the block probability, forced termination probability and throughput performance respectively. Then we propose the access probability controlling algorithm to satisfy the limitation of the user forced termination probability and also maximize the system throughput. The analysis results indicate that in the system with access probability control, the access probability of users and system throughput are enlarged with the forced termination probability limitation and the largest access probability under the forced termination probability is the access probability value able to maximize the system throughput. Therefore in conclusion the satisfaction of user forced termination probability limitation sacrifices the system throughput performance. Also the results show that the introduction of the buffer mechanism can reduce the forced termination of users and enhance the access probability of users and system throughput performance.