Optimal Spectrum Allocation of Improving Connectivity Robustness in Cognitive Radio Ad-Hoc Networks

In cognitive radio ad-hoc networks (CRAHN), we can change the network topology through flexible spectrum allocation. In this regard, even though CRAHN is not prone to single points of failure, its network performance is entirely dependent on node connectivity. However, the existing solutions mainly focus on the connections between certain nodes, without fully considering the overall network connectivity. To this end, to avoid a large number of connection failures caused by local damage, it is necessary of improving system connectivity performance from a global perspective when allocating available spectrum. As such, we explore the relationship between spectrum allocation and global connectivity of CRAHN, and then propose a robust optimization scheme using optimal spectrum allocation (ROUOS). This scheme aims to create new connections in the connectivity vulnerable areas through spectrum allocation. Specifically, we establish a spectrum allocation model including available spectrum matrix, bandwidth benefit matrix, interference constraint matrix, communication connection matrix, alternate channel vector and optimal allocation matrix. After that, based on the connectivity quantitative index in [11], we design a network benefit function to measure the gain effect of different spectrum allocation solutions on network connectivity. Finally, we select the spectrum allocation solution (i.e., adding communication links) that most effectively improves network connectivity. Simulation results show that, compared to the benchmark scheme, our proposed ROUOS scheme increases the second smallest eigenvalue of the graph Laplacian matrix from 0.09 to 0.29, significantly enhancing the robustness of topological connectivity.