In order to reduce the outage probability and enhance the stability of cognitive system, an improved algorithm of spectrum allocation based on classical graph coloring model was proposed. A difference factor of spectrum's idle time and user's request time was introduced. For every cognitive user, the algorithm allocated spectrums according to two factors: the spectrum efficiency and the time difference factor. Cognitive user with greater product value of the two factors was prior. The simulation results show that the outage probability of improved algorithm is far below that of the previous algorithm.%为了降低认知系统的通信中断概率,提高认知系统的稳定性,在经典的图论着色模型基础上提出了一种改进的频谱分配算法.该改进算法引入一个频谱空闲时间和用户请求时间的差值因子,对于每个认知用户,该算法综合考虑频谱效益与时间差因子两个因素来分配频谱.仿真结果表明,改进算法使认知系统的中断概率远低于原算法.
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