Robust Cognitive Algorithms For Fast-Varying Spectrum-Agile Wireless Networks

Abstract

Wireless communications have experienced tremendous growth in the last decade, which has placed significant demand for RF spectrum, leading to spectrum "crunch." Driven by numerous studies that revealed the significant under-utilization of many licensed channels in the VHF and UHF bands, a new paradigm for spectrum sharing has emerged in the past decade. In this paradigm, wireless devices (a.k.a. secondary users) are allowed to operate opportunistically in certain licensed bands without interfering with the licensed users (a.k.a. primary users). The realization of this new communication paradigm necessitates the design of a new generation of smart, adaptable, and programmable radios, called cognitive radios. Enabling opportunistic operation requires addressing various challenges including device coordination, resource allocation, channel monitoring, and various security issues. Specifically, secondary users are particularly vulnerable to node compromise and malicious jamming attacks. In this dissertation, we first develop several rendezvous algorithms for establishing unicast as well as multicast communication links in opportunistic spectrum access networks. The developed rendezvous algorithms are shown to be robust to node compromise attacks. Second, we study the anti-jamming rendezvous problem in the presence of an insider attack. We develop a combinatorial game-theoretic framework to capture the interactions between the rendezvousing nodes and the insider jammer. Third, to account for the dynamism of primary users, we propose novel stochastic resource allocation schemes under channel-quality uncertainty. The proposed schemes support channel bonding and aggregation and account for adjacent channel interference by introducing guard-bands. Fourth, to prevent interference with primary users, we design an optimal spectrum-sensing algorithm that achieves high detection accuracy and low false-alarm rate. Finally, we present an application of using cognitive radios for jamming mitigation in satellite communications. Extensive simulations are conducted to demonstrate the effectiveness and robustness of the proposed algorithms.