Cognitive radio networks (CRNs) are a promising solution to the channel (spectrum) congestion problem nowadays. Primary users (PUs) in CRNs are privileged users, for whom there should be no interference. Each secondary user (SU) or node in a CRN Efficient Virtual Backbone Construction without a Common Control Channel in Cognitive Radio Networks is capable of sensing the available channels, and can make opportunistic use of them without causing interference with primary users. When a PU begins to occupy a channel, SUs on that channel need to quit immediately. Hence, the dynamics of channel availability makes it difficult to carry out end-to-end data transport in CRNs. For example, in Fig. 1, there are two PUs, Tx and Rx. There is a data transmission route, consisting of three SUs, S1, S2, and S3. When the link between PU Tx and Rx is active, the links between the three SUs may be broken if they use the same channel as the two PUs. Therefore, the endto- end data transmission from Efficient Virtual Backbone Construction without a Common Control Channel in Cognitive Radio Networks S1 to S3 is unstable A practical scenario is that the two PUs in Fig. 1 are TV towers, and the SUs here are wireless devices using IEEE 802.22. If a node in a CRN wants to reach another node that is multiple hops away, two problems arise. First, the node needs to calculate the route to the destination node. However, the high dynamics of channel availability makes it costly to collect informationfrom other nodes and construct a routing path. Second, even if the route is built, the links on the route are unstable. When the dynamic channels on a link of the Efficient Virtual Backbone Construction without a Common Control Channel in Cognitive Radio Networks route become unavailable, the route is broken. To solve the problem of broken routes caused by unstable links, we can make use of the virtual backbone structure. A virtual backbone consists of a connected subset of nodes in the network where every node is either in the subset, or is a neighbor of a node in the subset. We use area to refer to a backbone node and the nodes attached to it. If a virtual backbone is constructed for a CRN, the backbone nodes can calculate area routes for end-to-end communications. An area route means a set of areas that would be passed in order to reach the destination. For example, in Fig. 2, each node is either a backbone node or is attached to a backbone node. Efficient Virtual Backbone Construction without a Common Control Channel in Cognitive Radio Networks A1 denotes an area, which includes the backbone node and its attached nodes. Nodes on the borders are called gateway nodes. The source node S wants to reach the destination node D, which is located in another area. The backbone node that S is attached to calculates an area route for S, which is Moreover, the virtual ackbone can solve the unstable link problem, because with the area route, a packet can be sent to any node in the next-hop area. This is much more robust than the case with the route consisting of nodes, where a packet must be sent to the next-hop node. Therefore, the influence of unpredictable channel availability is reduced.