Robust topology control in multi-hop cognitive radio networks

The opening of under-utilized spectrum creates the opportunity of substantial performance improvement through cognitive radio techniques. However, the real network performance may be limited since unlicensed users must vacate and switch to other available spectrum if the current spectrum is reclaimed by the licensed (primary) users. During spectrum switching, network partitions may occur since multiple links may be affected if they use the channel reclaimed by the primary users. In this paper, we address this problem through robust topology control, where channels are assigned to minimize channel interference while maintaining network connectivity when primary users appear. The problem is proved to be NP-hard and a sufficient condition for a robust channel assignment is derived. To solve this problem, we first propose centralized algorithms which can reduce the channel interference while satisfying the robustness constraints. Moreover, we derive its performance bound on channel interference and its computational overhead through theoretical analysis. Then, we propose distributed algorithms based on channel hopping techniques, and prove their correctness. Simulation results show that our solutions outperform existing interference-aware approaches substantially when primary users appear and achieve similar performance at other times.