An Opportunistic Pervasive Networking Paradigm: Multi-hop Cognitive Radio Networks

Cognitive radio networks enable ubiquitous communications both in frequency and time domain, and hence enable opportunistic pervasive communications. Multi-hop cognitive radio networks are appealing to the researchers due to their wide range of application potential in commercial, emergency communication, and military tactical networks. However, the multi-hop nature of the network coupled with the varying spectrum availability owing to the opportunistic spectrum access introduce many design challenges. Medium access control (MAC) layer in multi-hop cognitive radio networks needs to make distributed spectrum sensing and accessing decisions without disturbing the communications of the licensed users, while at the same time determining the communication frequency with the neighboring unlicensed users. Various MAC protocols for multi-hop cognitive radio networks have hitherto been proposed in the literature. In this chapter, we first outline the design challenges for the MAC layer protocols. Subsequently, we describe several MAC protocols proposed for multi-hop cognitive radio networks, emphasizing their strengths and weaknesses. Finally, we point out open research issues with regard to the MAC design of these networks.