Towards the 1G of Mobile Power Network: RF, Signal and System Designs to Make Smart Objects Autonomous

Bruno Clerckx1, Alessandra Costanzo2, Apostolos Georgiadis3, and Nuno Borges Carvalho4 1Imperial College London, UK, 2University of Bologna, Italy, 3Heriot-Watt University, UK, 4University of Aveiro, Portugal
Email: b.clerckx@imperial.ac.uk, alessandra.costanzo@unibo.it, A.Georgiadis@hw.ac.uk, nbcarvalho@ua.pt

Thanks to the quality of the technology and the existence of international standards, wireless communication networks (based on radio-frequency RF radiation) nowadays underpin the global functioning of our societies. The pursuit towards higher spectral efficiency has been around for about 4 decades, with 5G expected in 2020. 5G and beyond will see the emergence of trillions of low-power autonomous wireless devices for applications such as ubiquitous sensing through an Internet of Things (IoT). Wireless is however more than just communications. For very short range, wireless power via Inductive Power Transfer is a reality with available products and standards (Wireless Power Consortium, Power Matters Alliance, Alliance for Wireless Power, Rezence). Wireless Power via RF (as in wireless communication) on the other hand could be used for longer range via two different ways, commonly referred to as wireless energy harvesting (WEH) and (far- field or radiative) wireless power transfer/transmission (WPT). While WEH assumes RF transmitters are exclusively designed for communication purposes whose ambient signals can be harvested, WPT relies on dedicated sources designed exclusively for wireless power delivery. Wireless Power via RF has long been regarded as a possibility for energising low- power devices, but it is only recently that it has become recognised as feasible. Indeed, according to [Hemour:2014], at a fixed computing load, the amount of requested energy falls by a factor of two every year and a half due to the evolution of the electrical efficiency of computer technology. This explains why relying on wireless power to perform meaningful computation tasks at reasonable distances only became feasible in the last few years and justifies this recent interest in wireless power.
Recent research advocates that the future of wireless networking goes beyond conventional communication-centric transmission. In the same way as wireless (via RF) has disrupted mobile communications for the last 40 years, wireless (via RF) will disrupt the delivery of mobile power. However, current wireless networks have been designed for communication purposes only. While mobile communication has become a relatively mature technology, currently evolving towards its fifth generation, the development of mobile power is in its infancy and has not even reached its first generation. Not a single standard on mobile power and far-field WPT exists. Despite being subject to regulations on exposure to electromagnetic fields as wireless communication, wireless power brings numerous new opportunities. It enables proactive and controllable energy replenishment of devices for genuine mobility so that they no longer depend on centralised power sources. Hence, no wires, no contact, no (or at least reduced) batteries (and therefore smaller, lighter and compact devices), an ecological solution with no production/maintenance/disposal of trillions of batteries, a prolonged lifetime and a perpetual, predictable and reliable energy supply as opposed to ambient energy-harvesting technologies (solar, thermal, vibration). This is very relevant in future networks with ubiquitous and autonomous low-power and energy limited devices, device-to-device communications and the Internet-of-Things (IoT) with massive connections.
Interestingly, radio waves carry both energy and information simultaneously. Nevertheless, traditionally, energy and information have been treated separately and have evolved as two independent fields in academia and industry, namely wireless power and wireless communication, respectively. This separation has for consequences that 1) current wireless networks pump RF energy into the free space (for communication purposes) but do not make use of it for energizing devices and 2) providing ubiquitous mobile power would require the deployment of a separate network of dedicated energy transmitters. Imagine instead a wireless network where information and energy flow together through the wireless medium. Wireless communication, or Wireless Information Transfer (WIT), and WPT would refer to two extreme strategies respectively targeting communication-only and power-only. A unified Wireless Information and Power Transfer (WIPT) design would have the ability to softly evolve in between those two extremes to make the best use of the RF spectrum/radiations and network infrastructure to communicate and energize, and hence outperform traditional systems relying on a separation of com

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