Self-Organizing Directional Wireless Backbone Networks
Davis, Christopher C
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Directional wireless communications is emerging as a viable, cost-effective technology for rapidly deployable broadband wireless communication infrastructures. This technology provides extremely high data rates through the use of narrow-beam free space optical (FSO) and/or radio-frequency (RF) point-to-point links. The use of directional wireless communications to form flexible backbone networks, which provide broadband connectivity to capacity-limited wireless networks or hosts, promises to circumvent the scalability limitations of traditional wireless networks. The main challenge in the design of directional wireless backbone (DWB) networks is to assure robustness and survivability in a dynamic wireless environment. DWB networks must assure highly available broadband connectivity and be able to regain connectivity in the face of loss or degradation. This dissertation considers the use of topology control to provide assured connectivity in dynamic environments. Topology control is defined as the autonomous network capability to dynamically reconfigure its physical topology. In the case of DWB networks, the physical topology can be reconfigured through 1) redirection of point-to-point links and/or 2) reposition of backbone nodes. Coverage and connectivity are presented as the two most important issues in DWB-based networks. The aim of this dissertation is to provide initial designs for scalable self-organized DWB networks, which could autonomously adapt their physical topology to maximize coverage to terminals or hosts while maintaining robust backbone connectivity. This dissertation provides a novel approach to the topology control problem by modeling communication networks as physical systems where network robustness is characterized in terms of the system's potential energy. In our model, communication links define physical interactions between network nodes. Topology control mechanisms are designed to mimic physical systems' natural reaction to external excitations which drive the network topology to energy minimizing configurations based on local forces exerted on network nodes. The potential energy of a communications network is defined as the total communications energy usage for a given target performance. Accurate link physics models that take into account the variation of the wireless channel due to atmospheric attenuation, turbulence-induced fading, node mobility, and different antenna patterns have been developed in order to characterize the behavior of the potential energy stored at each wireless link in the network. The net force at each backbone node is computed as the negative gradient of the potential energy function at the node's location. Mobility control algorithms are designed to reposition backbone nodes in the direction of the net force. The algorithms developed are completely distributed, show constant time complexity and produce optimal solutions from local interactions, thus proving the system's self-organizing capability.