A Minimum Channel Switch Routing Protocol for Cognitive Radio Ad Hoc Networks We propose a new local spectrum knowledge-based minimum channel switch routing (MCSR) protocolfor cognitive radio ad hoc networks (CRAHNs). CRAHNs have a mix of primary users (PUs) who own a licensed spectrum and secondary users (SUs) who do not own a channel. SUs attempt to make use of the licensed channels owned by the PUs when the latter are not active. We model a network of SUs with links in whose neighborhood there exists at least one unused PU channel. Each SU chooses a preferred PU channel – the channel that is available for a majority of the nodes in its neighborhood. Nevertheless, nodes along an SU-SU path may have to undergo channel switches to complete transmission and reception. MCSR aims at minimizing the number of channel switches per hop along an SU-SU path, the protocol prefers to use paths that would incur fewer switches per hop. MCSR models the weight of an SU-SU edge as 0 if the two end nodes of the edge have the same preferred PU channel or as 1 otherwise, and chooses the SU-SU path whose sum of edge weights is the minimum. We compare the performance of MCSR with that of a minimum hop-based shortest path routing (SPR)protocol in a CRAHN environment. We observe MCSR to incur a relatively lower percentage of switches per hop, but the tradeoff is a slight increase in the average hop count per path.