**6. Conclusion**

**Figure 8.** Successful packet delivery ratio, Ch = 5.

20 Cognitive Radio

**Figure 9.** Successful packet delivery ratio, Ch = 10.

**Figure 10.** Average number of used channels for broadcast per node.

In this chapter, the problem of reliable broadcast in ad hoc CRNs is addressed. Due to the spatial variation in spectrum availability, different CR nodes might sense different idle channels, which can partition the network into different clusters. By jointly representing the spectrum availability and the network local topology as a bipartite graph, the problem of connecting different CR nodes can be mapped to the problem of set cover. An intelligent algorithm is developed, which guarantees a distributed reliable selection of the broadcast channel with a facilitative channel switching facility where primary user activity is detected without the need for frequent reselection. It has been shown through simulation results that the only way to provide a reliable broadcast that considers the spatial variation of spectrum availability is through connecting different local topologies in the absence of a common control channel.
