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在认知无线电网络(CRNs)中,次级用户(SUs)在主用户(PUs)取回频谱时必须让出频谱。当PU取回被占用信道时,在相同信道上进行传输的多个SUs会被影响,导致CRNs中的网络切割。因此,如何在考虑主用户活动性的前提下保持CRNs的连通性是一个重要的问题。这篇文章结合功率控制和信道分配,使用最小数目的信道来构造一个双信道连通无冲突拓扑。在第一阶段生成基本拓扑,实现双信道连通。在信道分配阶段,使用图着色理论给每个SU分配信道来实现无冲突传输。针对删除节点后局部冲突图不连通的情况,应用改进的MPH算法,通过给最短路径密集经过的节点分配路径权值,优先考虑通过路径权值大的节点接入已有拓扑,在实现连通之外也减少了路径花费。进一步考虑到如果删除节点后原拓扑被切割为两部分,同时这两部分除去被删除的节点之外不存在其他边相连,那么就无法执行构造Steiner树的算法使其连通,算法失效。针对这种情况,考虑增加次级用户个数。取切割部分点间最短距离的一半位置添加节点,即次级用户,从而实现连通。理论分析和仿真都证明了生成的拓扑能够在任意PU引起的单信道中断下保持网络连通性,减少了所需信道数,减少了网络花费。
In Cognitive Radio Networks (CRNs), secondary users (SUs) have to let the spectrum off when primary users (PUs) retrieve the spectrum. When a PU retrieves an occupied channel, multiple SUs transmitting on the same channel are affected, causing the network to cut in the CRNs. Therefore, how to maintain the connectivity of CRNs considering the activity of the primary user is an important issue. This article, combined with power control and channel allocation, uses a minimum number of channels to construct a two-channel connected conflict-free topology. In the first stage to generate the basic topology, to achieve two-channel connectivity. In the channel allocation phase, the graph coloring theory is used to allocate channels to each SU for collision-free transmission. Aiming at the situation that the local conflict graph is not connected after the node is deleted, an improved MPH algorithm is used to assign the path weights to the nodes that pass the shortest path densely. The nodes with large path weights are prioritized to access the existing topology. Outside also reduces the path cost. Further consider that if the original topology is cut into two parts after the node is deleted and no other edges are connected except the removed nodes, the algorithm for constructing the Steiner tree can not be implemented and the algorithm fails. In view of this situation, consider increasing the number of secondary users. Take the cutting part of the shortest distance between the half of the location to add nodes, that is, secondary users, in order to achieve connectivity. Both theoretical analysis and simulation prove that the generated topology can maintain network connectivity under the single-channel interruption caused by any PU, reduce the number of required channels and reduce the network cost.