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Keeping Energy-Neutral Devices Operational: a Coherent Massive Beamforming Approach

Jarne Van Mulders, Bert Cox, Benjamin J. B. Deutschmann, Gilles Callebaut, Lieven de Strycker, Liesbet Van der Perre

TL;DR

This work investigates powering energy-harvesting ESLs in a retail setting via RF wireless power transfer using a distributed antenna array of $L=351$ antennas operating at $868\mathrm{MHz}$ under regulatory constraints. It compares three provisioning strategies—Option 1 baseline with a single element per ESL, Option 2 non-coherent multi-element transmission, and Option 3 fully coherent transmission—evaluating total transmit power and charging efficiency. Results indicate that coherent beamforming can yield substantial gains but may still violate ETSI limits when scaling to hundreds of ESLs; non-coherent schemes can become more practical as device counts grow. The study outlines future directions including beamsharing, multi-beam strategies, reciprocity-based calibration, real-world validation on the Techtile REINDEER testbed, and potential frequency shifts (e.g., to $917.5\mathrm{MHz}$) to enable higher allowed transmit power.

Abstract

Keeping the batteries on the shelf: this is the holy grail for low-cost Internet of Things (IoT) nodes. In this paper we study the potential of radio frequency (RF)-based wireless power transfer implementing coherent beamforming with many antennas to realize this ambitious target. We optimize the deployment of the antennas to charge electronic shelf labels (ESLs), considering actual regulatory constraints. The results confirm the feasibility to create power spots that are sufficient to keep the high density of battery-less devices operational.

Keeping Energy-Neutral Devices Operational: a Coherent Massive Beamforming Approach

TL;DR

This work investigates powering energy-harvesting ESLs in a retail setting via RF wireless power transfer using a distributed antenna array of antennas operating at under regulatory constraints. It compares three provisioning strategies—Option 1 baseline with a single element per ESL, Option 2 non-coherent multi-element transmission, and Option 3 fully coherent transmission—evaluating total transmit power and charging efficiency. Results indicate that coherent beamforming can yield substantial gains but may still violate ETSI limits when scaling to hundreds of ESLs; non-coherent schemes can become more practical as device counts grow. The study outlines future directions including beamsharing, multi-beam strategies, reciprocity-based calibration, real-world validation on the Techtile REINDEER testbed, and potential frequency shifts (e.g., to ) to enable higher allowed transmit power.

Abstract

Keeping the batteries on the shelf: this is the holy grail for low-cost Internet of Things (IoT) nodes. In this paper we study the potential of radio frequency (RF)-based wireless power transfer implementing coherent beamforming with many antennas to realize this ambitious target. We optimize the deployment of the antennas to charge electronic shelf labels (ESLs), considering actual regulatory constraints. The results confirm the feasibility to create power spots that are sufficient to keep the high density of battery-less devices operational.
Paper Structure (10 sections, 3 equations, 2 figures, 1 table)

This paper contains 10 sections, 3 equations, 2 figures, 1 table.

Table of Contents

  1. Introduction
  2. System design and methodology
  3. Deployment Scenario
  4. Energy Requirements
  5. Coherent Massive Beamforming to Boost Efficiency
  6. Option 1, Multiple Radio Elements with a Single Antenna
  7. Option 2, Non-coherent transmission by multiple distributed radio elements
  8. Option 3: Coherent transmission by multiple distributed transmitters
  9. Results
  10. Conclusion and future work

Figures (2)

  • Figure 1: 3D representation of a supermarket aisle with 351 antennas transmitting on 868MHz. The orange digits represent the antenna numbering.
  • Figure 2: Evaluation of both SISO, non-coherent and coherent charging cases in relation to the number of within a aisle for the closest and furthest locations and with patch antennas.