Distributed coherence: fundamental building blocks, system concepts, and experimental demonstration

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Over the past two decades, advances in multi-antenna wireless systems have opened up the possibility of tremendous increases in wireless communication throughputs. The practical realization of these increases in real-world wireless networks is constrained by size and cost considerations that limit the number of antennas, especially for mobile devices. This research aims to achieve the gains from multi-antenna techniques in a distributed fashion by having groups of wireless transceivers pool together and cooperatively act like a virtual antenna array. The concept of virtual arrays has broad transformative potential for wireless networks by extending the numerous benefits of multi-antenna systems to networks of single-antenna devices. We will prototype and demonstrate virtual array techniques experimentally on a software-defined radio platform, and we plan to share our implementations as reusable building blocks to stimulate technology transition and to promote interactions between the academic, open-source software community and radio hobbyist communities. The elements of a virtual array have an unknown, typically time-varying, geometry and are driven by independent oscillators, each with stochastic drift; the main technical challenge is in maintaining distributed coherence in the array in the presence of these effects. While this is a very challenging problem, recent results have demonstrated the feasibility of virtual arrays.This research will establish a solid theoretical foundation for distributed coherence and chart a clear path to technology transfer by applying the theory and techniques to the cross-layer design of concept systems based on virtual antenna arrays. Specifically we will develop a state space framework for tracking and prediction of oscillator dynamics and mobility, and scalable architectures for distributed transmission and reception appropriate for large distributed arrays of low-cost single-antenna devices. We will also identify fundamental tradeoffs and scaling laws for virtual arrays. We will apply and integrate the theory and techniques to two concept systems of great societal significance: Distributed base station provides multi-antenna capabilities even for low carrier frequencies where standard antenna arrays would be too bulky (e.g., white space frequencies). Distributed 911, enables a cluster of nodes to communicate with a possibly moving distant rescue vehicle which would be out of range for any one of the nodes. Our goal is to perform design and performance evaluation in sufficient detail to clear conceptual hurdles for implementation.