  Radiative wireless power transfer (WPT) is a promising technology to provide
cost-effective and real-time power supplies to wireless devices. Although
radiative WPT shares many similar characteristics with the extensively studied
wireless information transfer or communication, they also differ significantly
in terms of design objectives, transmitter/receiver architectures and hardware
constraints, etc. In this article, we first give an overview on the various WPT
technologies, the historical development of the radiative WPT technology and
the main challenges in designing contemporary radiative WPT systems. Then, we
focus on discussing the new communication and signal processing techniques that
can be applied to tackle these challenges. Topics discussed include energy
harvester modeling, energy beamforming for WPT, channel acquisition, power
region characterization in multi-user WPT, waveform design with linear and
non-linear energy receiver model, safety and health issues of WPT, massive MIMO
(multiple-input multiple-output) and millimeter wave (mmWave) enabled WPT,
wireless charging control, and wireless power and communication systems
co-design. We also point out directions that are promising for future research.
