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Scatter radio relaying & applications

Vougioukas Georgios

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Summary

Billions of devices are expected to be wirelessly connected in the foreseeable future. Sustaining such connectivity will require simple, elegant, engineering solutions. Based on backscatter radio principles, this dissertation offers novel, ultra-low-complexity, ultra-low-power, ultra-low-cost solutions, for connectivity in the field of narrowband wireless communications. Methods for achieving wireless communication by “recycling” radio waves, pre-existing in the environment, are offered and analysed. In contrast to generating own signals for transmission, a device (tag) adopting the suggested methods can transmit its information towards any conventional FM radio receiver, by recycling ambient signals from FM radio stations. That way, it is shown that batteryless information transmission can be achieved up to distances of 26 meters, by harvesting energy from the environment. Ultra-low cost prototypes consumed only 24 μWatt in continuous (non duty-cycled) operation. In the case of ambient signals of unknown origin and structure, digital modulation schemes are also offered, accompanied by novel coherent, partially-coherent illumination-agnostic, as well as fully noncoherent, channel-coded or uncoded detection algorithms. It is shown that under certain conditions, modulated and unknown ambient signals, can offer performance gains in the process of recovering tag's information signal, i.e., modulation of the ambient signal may be helpful. The proposed schemes do not require any cooperation with the ambient transmitter. That way, in sharp contrast to prior art, the tags adopting the proposed techniques are receiver-less; ultra-low-complexity and batteryless operation are also facilitated. Exploiting the aforementioned methods, originally intended for solving ambient backscatter communication problems, it is demonstrated for the first time that backscattering tags can also be used in an unorthodox way, for relaying signals in the frequency domain. Scatter radio relaying can be used to solve multi-antenna processing problems: a) blind (i.e., zero-feedback) beamforming, offering power gains in the order of 0.4-3.7 dB, and b) direction of arrival (DoA) estimation, offering error less than 5 degrees with 8 scattering tags. The proposed methods utilize single antenna radios without any requirement for channel feedback, multi-antenna RF front-ends or expensive controllers. The proposed techniques extend the solution space for engineers building wireless devices under power, complexity and cost constraints. Hopefully, this work will amplify the recent interest of the research community on backscatter radio and accelerate efforts towards the wide adoption of backscatter radio relaying in current and future commodity wireless systems, sensors and networks.

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