The Research Of Sub-channel Allocation Algorithm In Cognitive Radio

With the fast development of wireless communication technology, the wireless spectrum resource has become indispensable to current information society. However, according to the data provided by Federal Communications Committee in USA, the actual availability of allocated spectrum is only in the range of 15%~85%, which is resulted from the current fixed spectrum-allocating scheme, has greatly resulted in the loss of large amount of spectrum resources and low spectrum availability. Therefore comparing with the scarcity of physical spectrum, it is much more important to have a reasonable spectrum access and allocation scheme. Cognitive radio is regarded as the best solution for low availability of wireless spectrum, it puts forward a dynamic spectrum share framework, which allows cognitive users intelligently to make use of large amounts of free spectrum resources and dynamically finish the channel allocation process, while not affecting the primary user. Hence, it's worthwhile to research the dynamic channel allocation technology in cognitive radio.The Research on sub-channel allocation algorithm in cognitive radio ,which supported by the National Natural Science Fund(N0.60832009)and (N0. 60872017) as well as the Shanghai Key Technology Fund(No. 8511500502) mainly covered four parts:Firstly, the paper generally introduced the channel allocation in cognitive radio,especially, when coming to the model of channel allocation in cognitive radio, it mainly focused on two channel allocation schemes: Channel allocation based on cellular network and distributed network.Secondly, the paper focused on the classic channel allocation algorithms based on graph coloring theory: Greedy algorithm,Fair algorithm,Collaborative Max Sum Bandwidth and Collaborative Max Proportional Fair algorithms. In order to overcome the defects in the classic graph coloring algorithms, the paper proposed an improved graph coloring algorithm. And the simulated results show that the improved algorithm performs better in the aspect of time consuming,the availability of spectrum and the fair ability.Thirdly, the paper analyzed the model and process of traditional power control algorithm. In order to overcome the disadvantages of this power control algorithm, particularly, how to guarantee the quality of service of users when the channel detecting error occurs and how to allocate the channel resources to the cognitive users where the maximum eigenvalue of idle channel matrix is greater than one. The paper put forward a novel quality of service (QoS) Control and rate adjustment channel allocation algorithm. with the methodology that adaptively grouping the cognitive user to the channel set,while introducing QoS control and rate adjust mechanism, so as to assign available channel and power for CU. The simulation results show that the QoS Control and rate adjustment channel allocation algorithm is applicable where the maximum eigenvalue of idle channel matrix is greater than one and protecting the user when channel allocation occurs, meanwhile, obviously improving the availability of spectrum.In the last, the paper researched the combination of OFDM and Cognitive Radio technology. Considering the obvious advantage of OFDM and the unique feature of CR, a novel CR system module based on OFDM was proposed. This system has added the channel detection,channel allocation and power control units into previous Multi-user OFDM module, so as to dynamically accomplish the channel allocation task, meanwhile upholding the availability of the spectrum. On the basis of the novel system module, a channel allocation algorithm based on Multi-user OFDM was proposed. And the paper showed the algorithm into two parts:Sub-carrier allocation and Sub-carrier power allocation. The simulation results show that comparing with the traditional FDMA, the new algorithm based on Multi-user OFDM performs much better in the respect of channel capability,channel availability and fairness in CR network.