Cutting Last Wires for Mobile Communications by Microwave Power Transfer

Abstract: The advancements in microwave power transfer (MPT) over past decades have enabled wireless power transfer over long distances. The latest breakthroughs in wireless communication, namely massive MIMO, small cells and millimeter-wave communication, make wireless networks suitable platforms for implementing MPT. This can lead to the elimination of the "last wires" connecting mobile devices to the grid for recharging, thereby tackling a long-standing ICT grand challenge. Furthermore, the seamless integration between MPT and wireless communication opens a new area called wirelessly powered communications (WPC) where many new research directions arise e.g., simultaneous information-and-power transfer, WPC network architectures, and techniques for safe and efficient WPC. This article provides an introduction to WPC by describing the key features of WPC, shedding light on a set of frequently asked questions, and identifying the key design issues and discussing possible solutions.

• The paper explores achieving wirelessly powered communications using microwave power transfer to potentially eliminate mobile device charger wires.
• It details technical methods like power and adaptive beamforming with large antenna arrays, suggesting significant power transfer distance increases are possible.
• The research discusses mobile architectures with RF energy harvesters, SWIPT configurations, challenges like signal loss and safety, and future research directions.

Wireless Powering of Mobile Devices Through Microwave Power Transfer

The paper "Cutting Last Wires for Mobile Communications by Microwave Power Transfer" by Kaibin Huang and Xiangyun Zhou presents a comprehensive exploration of microwave power transfer (MPT) as a means to achieve wirelessly powered communications (WPC). This research proposes the potential elimination of the last physical tether—charger wires—for mobile devices, a significant challenge in information and communications technology (ICT).

Overview of Microwave Power Transfer and Wirelessly Powered Communications

MPT has witnessed significant advancements due to long-distance wireless power transfer capabilities, supported by progressive technologies in massive MIMO, small-cell, and millimeter-wave communication. These advances imply that MPT could effectively cut the necessity of wired charging. The authors present wirelessly powered communication (WPC) as a new area of research, highlighting its potential in fields such as simultaneous wireless information-and-power transfer (SWIPT), network architectures, and safety techniques for WPC.

Technical Insights and Numerical Results

The paper explores the technical prerequisites and methodologies for achieving efficient MPT, including power beamforming, channel estimation, and adaptive beamforming to ensure safety and high power-transfer efficiencies. Specifically, the utilization of large-scale antenna arrays and efforts towards beam sharpness advancement show promise in improving power-transfer systems. Higher frequencies like 60 GHz allow for ultra-sharp beamforming, potentially scaling power-transfer distances significantly, with numerical simulations suggesting a 25-fold increase from current capabilities at 2.4 GHz.

The authors also present practical scenarios and address frequently asked questions, such as the short-range nature of power transmission compared to information transmission. Mixers, rectennas, and circuit designs within mobile devices are optimized for effective microwave energy harvesting, considering form-factor constraints and the power consumption profiles of current mobile devices.

Mobile Architecture and SWIPT Configurations

The paper describes a mobile architecture supporting WPC, where inclusion of RF energy harvesters permits energy storage for device transceivers. The researchers elaborate on SWIPT configurations with detailed system designs such as integrated, closed-loop, and decoupled SWIPT, emphasizing their varying applicability and practical challenges, especially regarding network coverage and operational viability.

Challenges and Safety Considerations

While MPT presents a path toward removing charging cables, the paper addresses inherent challenges such as high propagation losses and safety issues. Retrodirective beam control, efficient pilot signal design, and safe power density measures are proposed to mitigate health concerns associated with exposure to high-density beams. Theoretical limits are explored under constraints imposed by international standards (e.g., FCC and ICNIRP) on exposure to microwave radiation.

Implications and Future Directions

This research underscores the theoretical and practical implications of integrating MPT into wireless communication networks. It marks a shift towards truly mobile communications and opens discussions on advanced network design protocols, cognitive WPC, cooperative clustering of power beacons/base stations, and relay-assisted communications—all pivotal in reaching the goal of untethered device autonomy.

In conclusion, while the integration of WPC and SWIPT technologies offers promising avenues for enhancing mobile device independence from physical power connections, it demands further investigation into network architectures, safety protocols, and efficient power transmission techniques. With continued research and development, the mobile ecosystem can anticipate a transformative step toward seamless and reliable wireless power solutions.