Research Of Slow-moving Cognitive User Spectrum Reallocation Algorithm Based On Graph Theory

Cognitive Radio was expected to improve spectrum efficiency and solve theproblem of spectrum shortage. A lot of research on spectrum allocation algorithm hasbeen done but most of them only considered primary allocation, which is difficult toadapt to complex radio environment and moving users. The thesis studied spectrumreallocation algorithm of slow-moving cognitive users. The thesis considered influenceof authorized users’ working mode switch and cognitive users’ mobility, reducedcommunication overhead and performance loss.Firstly, the thesis analyzed relation of spectrum allocation algorithm and graphtheory, introduced related knowledge of graph theory, and then gave a detailedexplanation of math basement of coloring model and relationship between coloringtheory and cognitive radio system, and also studied theoretical basis andimplementation method of Maximal Independent Set algorithm. Mobility management,including location management and handover control, is analyzed. Mobility models arealso introduced. This thesis also analyzed reallocation strategy based on game theoryand graph theory.Secondly, this thesis had research on mobility model aiming at open zone andurban street blocks, that is, random walking model and Manhattan street model. Thethesis considered memory factors and proposed memory walk model and improvedstreet model because of consideration of actual situation. Prediction algorithm for thesemodel are proposed to predict topcity of net in the future, which may lead to allocationresult with foreseeability, and avoid interference before next allocation. Simulationproved that prediction algorithm performed well. Influence on authorized users’working-mode switch is studied, and influence area is proposed to reduce computationalcomplexity of useable spectrum list when working mode switched.In the end, aiming at working-mode switching authorized users and movingcognitive users, periodic part spectrum reallocation is proposed, its detail process is alsointroduced. According to data from mobility model and prediction algorithm, periodicspectrum reallocation is done in three ways, including total reallocation, subgraphreallocation and node reallocation. System performance, such as system utility, fairness,communication overhead and performance loss of reallocation are compared. MISalgorithm and greedy algorithm are used to allocate spectrum. Result of simulationproved advantages of part reallocation.