Building k-Protected Routes in Multi-Hop Cognitive Radio Networks

In cognitive radio networks (CRNs), the established communication sessions between secondary users (SUs) may be affected or even get interrupted because the SUs need to relinquish a spectrum when the primary users (PUs) become active again. On detecting PU activities, the SUs on the interrupted links either switch to another link operating on another spectrum fragment using the same one-hop path, or the SUs seek for an alternative multi-hop backup path. In either approach, the communication session is destined to experience a delay or even gets interrupted, which is intolerable to quality of service-sensitive applications such as multimedia streaming or audio/video conferencing. In this paper, we study the problem of building k-protected routes in CRNs. A k-protected route consists of a set of main links with preassigned backup links and backup paths so that the k-protected route is guaranteed to endure k PU appearances without being interrupted. For a CRN, we find a k-protected route for each session request and maximize the number of sessions that the CRN can support. We propose both centralized and distributed algorithms for the k-protected routing problem. Simulation results show that our k-protected routes outperform existing opportunistic spectrum switching approaches regarding delay and interruption rate.