Reseach On Topology Control In Cognitive Radio AD Hoc Networks

Mobile Ad Hoc network(MANET) is a Multi-hop wireless communication network composed of a group of wireless nodes without fixed infrastructures. MANET is great flexibility with self-discovery, self-organizing, self-healing features. Through spectrum sensing technology, cognitive radio can dynamic discovery and use available spectrum to improve spectrum utilization and avoid external interference in cognitive wireless networks. CR Ad Hoc networks integrate cognitive radio technology into the mobile Ad Hoc network, so that nodes have sensing ability and learning ability, and are able to use the idle spectrum in regional spatial of network. It solves the problem of scarce spectrum resources and improves the spectrum utilization rate, and increases the capacity of the network.In CR Ad Hoc networks, the factors that affect the network topology are not only the relative position of nodes and transmit power, but also the available channels of nodes. This paper focuses on the CR Ad Hoc networks based on clustering topology management and robust topology control problem, mainly includes the following aspects:First, we introduce the characteristics and key technologies of CR Ad Hoc networks, and then analyze the importance of topology control and compare the difference between traditional Ad Hoc networks and CR Ad Hoc networks.Then,in the networks that nodes are equipped with multiple sets of transceiver, there are some common available channel in the whole network, and nodes can use different channels to communicate with neighboring nodes at the same time. Considering the connectivity of the network, network capacity and robustness of the network topology, we use pre-allocation mechanism, assigning the channel for the transceivers of the nodes before the data sending request arrive. We propose a robust topology control algorithm, where channels are assigned to minimize co-channel interference while maintaining network connectivity when primary users or other external interference appear and maximize network capacity. The simulation results show that RTCA can improve the capacity of the network and maintain network connectivity compared with IATA.Third, in CR Ad Hoc networks that without a common channel, based on the use of cluster structure topology management mechanism, the members in a cluster have common available channel. Nodes in the network establish a cluster structure through distributed information exchange, and the cluster head management or maintenance the cluster through a common control channel within a cluster. The number of common channels in a cluster and the cluster size are two conflicting factors. We need to ensure the stability of the cluster structure, but also increase cluster size and decrease the number of clusters in network. We propose an algorithm that allocates different channels that meet the requirements for control at various clusters in the network, and tradeoff between the number of common channels in a cluster and the cluster size. And the clustering problem is formulated as a bipartite graph problem. The simulation results show that compared with LCA, CTSC can ensure that there are common channels in a cluster and the cluster size is larger.Finally, we summarize the work of this paper and give an expectation to the further research.