Constructing a Robust Topology for Reliable Communications in Multi-Channel Cognitive Radio Ad Hoc Networks

In multi-channel CRAHNs, the spectrum efficiency can be improved via spectrum reutilization by secondary users. However, unpredictable transmission interruptions may occur when primary users reclaim their channels, resulting in the partition of the CRAHN and the failure of the end-to-end transmission. Therefore, in CRAHNs, considering the activities of primary users, how to maintain a connected network topology is fundamental in ensuring reliable secondary communications. Even though one licensed channel is reclaimed by a PU, multiple SUs may be affected. The situation gets even worse when multiple channels are reclaimed simultaneously. In this article, we elaborate on k-channel connectivity in the context of multi-channel CRAHNs. We first introduce the preliminaries of topology connectivity with the focus on the k-channel connectivity and then discuss the challenges of robust topology control by guaranteeing the k-channel connectivity in both interweave mode and underlay mode. After reviewing the recent research on topology control algorithms, we propose a distributed k-channel connectivity algorithm in underlay mode to minimize the number of required channels while satisfying the k-channel connectivity and conflict-free property. Next, we illustrate the potential benefits of k-channel connectivity through simulation results. Finally, possible directions for future research are pointed out in the conclusions.