In Cognitive radio networks (CRN), secondary users(SUs) can access the unlicensed channel dymanically, but must vacate the spectrum on the appearance of primary users(PUs). Therefore multiple SUs will be affected, which will cause the network partition if there is no other backup channels. We combine power control and channel assignment to construct a bi-channel connected and conflict-free topology with the minimum number of required channels. Based on CGCA algorithm, we propose the improved CGCA algorithm. Particularly, we construct an underlying topology robust against interruption of PUs activities, then we assign channels to each SU according to graph coloring to achieve conflict-free transmission. Note that, the local spanning tree may be not connected after deleting SU nodes. We present the improved MPH algorithm to make it connected, whose philosophy is to give priority to the link on these nodes who have the large path weights, and its been proved that the improved MPH algorithm can achieve connecting the network while reducing the cost. Furthermore, considering that the centralized topology control algorithm will lose efficacy under the circumstance that the original topology will be divided into two parts after deleting the SU nodes by which they are connected with each other. Specifically for this situation we utilize an algorithm of adding SU nodes at the middle of the shortest link between all these edges to make the divided parts connected. Simulation has verified the correctness and effectiveness of the ICGCA algorithm.
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