Massive MIMO with Radio Stripes for Indoor Wireless Energy Transfer

TL;DR

This paper explores using massive MIMO with radio stripes for indoor wireless energy transfer, optimizing power delivery to IoT devices while managing electromagnetic exposure and system efficiency.

Contribution

It introduces novel precoding techniques and an analytical framework for EMF control in indoor massive MIMO WET systems, addressing power minimization and safety.

Findings

EMF exposure can be controlled more easily at higher frequencies.

Training is not critical for the indoor system performance.

MRT/SCA precoders are effective for few UEs, suitable for TDMA.

Abstract

Radio frequency wireless energy transfer (WET) is a promising solution for powering autonomous Internet of Things (IoT) deployments. In this work, we leverage energy beamforming for powering multiple user equipments (UEs) with stringent energy harvesting (EH) demands in an indoor distributed massive multiple-input multiple-output system. Based on semi-definite programming, successive convex approximation (SCA), and maximum ratio transmission (MRT) techniques, we derive optimal and sub-optimal precoders aimed at minimizing the radio stripes' transmit power while exploiting information of the power transfer efficiency of the EH circuits at the UEs. Moreover, we propose an analytical framework to assess and control the electromagnetic field (EMF) radiation exposure in the considered indoor scenario. Numerical results show that i) the EMF radiation exposure can be more easily controlled at higher frequencies at the cost of a higher transmit power consumption, ii) training is not a very critical factor for the considered indoor system, iii) MRT/SCA-based precoders are particularly appealing when serving a small number of UEs, thus, especially suitable for implementation in a time domain multiple access (TDMA) scheduling framework, and iv) TDMA is more efficient than spatial domain multiple access (SDMA) when serving a relatively small number of UEs. Results suggest that additional boosting performance strategies are needed to increase the overall system efficiency, thus making the technology viable in practice.