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Electromagnetic aspects of ESPAR and digitally controllable scatterers with a look at low-complexity algorithm design

Abstract : The thesis focuses on the idea of exploiting the spatial domain (as opposed to the exploitation of the time-frequency resource) of wireless environments from two fronts: a) ESPAR antennas (standing for Electronically Steerable Parasitic Array Radiator) as a potential inexpensive alternative to conventional multi-antenna architectures (inexpensive in relation to the number of radio frequency front-ends these conventional architectures are often assumed to be provided with), and b) the study of reactively loaded arrays to deliver controllable scattering as a mean of adding degrees of freedom to the propagation environment itself. The latter is achieved here via digitally controllable scatterers (DCS).Particularly, the thesis focuses on the goal of better conditioning optimization problems as means of proposing low-complexity algorithms. Therefore, one key aspect is the required balance between the accuracy and complexity of the adopted electromagnetic models.Thus, it is appropriate to highlight the importance given to the interface between electromagnetism and the signal characterization. More specifically, both ESPAR and DCS require the understanding of electromagnetic (EM) phenomena that is not fully accounted for through conventional link-level descriptions. More importantly, the latter is proof of the need to join the approaches of two related research communities to cope with the scarcity of resources that is only expected to grow in the decades to come. In fact, the document is mostly positioned from the view of someone with a background in telecommunications (unlike pure electromagnetism) with looks at enlightening the underlying EM mechanisms. It is roughly composed of three parts, namely: fundamentals, the ESPAR antenna and digitally controllable scatterers. In fact, the aim of having one part of the document dedicated purely to fundamentals is to describe the EM phenomena while highlighting all relevant details to the remaining two.The part "fundamentals" begins with Maxwell's equations (and their convenient solution for far-field radiation problems) all the way to the well-known (y=hx+n) signal characterization. As the seemingly least appropriate description to work with, but most complete characterization of the EM phenomena, Maxwell's equations are the basis that link our mathematical description to the very same reality. Thus, the objective of this part is to expose the connection between fields and signals, as well as to open the door to questioning the conventional transmitter-receiver signal model. The latter becomes one of the most exciting outcomes of this project in line with the research-related aim of challenging our vision to expand our understanding of a problem.To continue, the second part is dedicated to the ESPAR antenna as a preamble of what is meant by "questioning the conventional transmitter-receiver signal model". Particularly, ESPAR obliges us to depart from the abstract signal space in which traditional multi-antenna link-level characterizations are depicted. As a contribution of this work, it will be shown how a local approximation of the system model offers an alternative view. Notably, through such an approximation of the system model, a computationally-efficient solution to the non-trivial problem of channel-based adaptation of the radiation characteristics of ESPAR is found.Last, but not least, the third part deals with digitally controllable scatterers as a mean of improving energy efficiency. Such an exciting concept has gained significant attention in the recent years and, in a sense, opens the door to a radically different way to conceive communication problems. Even though these devices are in their infancy, it is not difficult for me to imagine how the decades to come could be marked by the massification of this technology.
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  • HAL Id : tel-02611257, version 2

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Juan Bucheli Garcia. Electromagnetic aspects of ESPAR and digitally controllable scatterers with a look at low-complexity algorithm design. Networking and Internet Architecture [cs.NI]. Institut Polytechnique de Paris, 2020. English. ⟨NNT : 2020IPPAT004⟩. ⟨tel-02611257v2⟩

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