System design study for energy-neutral devices interacting with the RadioWeaves infrastructure
Creators: name: Deutschmann, Benjamin
name: Buyle, Chesney
name: Cox, Bert
name: Delabie, Daan
name: Graber, Maximilian
name: Wildnig, Thomas
name: Witrisal, Klaus
name: Mühlmann, Ulrich
Publisher: name: Zenodo
Year: 2023
Subjects: RF
WPT
array near field
energy neutral devices
DMIMO

description: This deliverable examines the fundamental performance limits of a RadioWeaves infrastructure with respect to the interaction with energy neutral (EN) devices. In particular, the maximum regulatory-compliant power budget and achievable initial access distance are derived, and backscatter communication schemes and data rates are discussed. While batteryless ultra high frequency (UHF) radio frequency identification (RFID) tags exhibit read-ranges limited to a few meters and data rates in the kbit/s range, we demonstrate that RadioWeaves pushes these performance indicators by orders of magnitude. We define an efficiency model that reflects the losses incurring in every individual building block of a complete wireless power transfer (WPT) system. Major gains are expected to be made in the RF-to-RF link due to the massive antenna deployment in a RadioWeaves infrastructure. Existing channel models do not sufficiently model array gains and signal amplitudes for radio frequency (RF) WPT in geometry-based environment models. Therefore, we derive a channel model capable of representing RF WPT in a physically correct manner such that the RF-to-RF transmission efficiency is accurately modeled. The channel model is verified by means of synthetic aperture measurements with a vector network analyzer (VNA), where results of both measurements and simulations show a close correspondence. With the ability of conducting realistic simulations, we have analyzed exemplary RadioWeaves deployments and found that this future distributed radio infrastructure shows several beneficial properties regarding regulatory compliance. Based on our findings, we derive the maximum regulatory-compliant power budget of EN devices at various sub-10 GHz bands. Building upon the expertise on state-of-the-art RFID technology that is available within the REINDEER consortium, we are able to compute the achievable initial access distances for EN devices. Furthermore, we already propose a first initial access scheme and reveal how beam diversity can be exploited to overcome impairments due to strong multipath propagation. Our system analysis is rounded-off with a discussion of transponder architectures and performance evaluations thereof. Circuit-level simulations and RF measurements hint at typical efficiency limits of integrated transponder designs and reveal demanding design challenges (e.g., matching an antenna to a nonlinear rectifier impedance) that require particular attention for a high overall system efficiency. With the WPT channel model derived and measurement procedures defined, we have set the stage for algorithmic developments which will strongly build on the realistic synthetic and measured data from our simulation framework and measurement testbeds, respectively. These algorithms will be published in the REINDEER deliverable D4.2 [1]. Our findings in this document reveal that many of the achievable gains of RadioWeaves rely on its geometric environmentawareness. Therefore, our algorithms for WPT will have a strong connection to algorithms for position estimation and environment learning that will be covered in deliverable D3.3 [2].