Metric-based taxonomy of routing protocols for cognitive radio ad hoc networks

Cognitive radio (CR) technology is introduced to solve the problem of spectrum under-utilization in wireless networks by opportunistically exploiting portions of the spectrum temporarily vacated by licensed primary users. Devices with cognitive capabilities can be networked to create cognitive radio ad hoc networks (CRAHNs) that face many challenges in different layers due to the flexibility in the spectrum access process. In this paper, we present a survey of recent routing solutions in CRAHNs. We start by listing routing challenges associated with the CRAHNs. We then present different routing protocols that are designed for CRAHNs, they can be classified according to the routing metric into six main categories: delay based, link stability based, throughput based, location based, energy-aware, and combined or multi-metric protocols that either combine many metrics together or use different metrics according to some specific rules. Finally, possible future research directions are discussed.