  For decades, wireless energy transfer and harvesting remained of focused
attention in the research community, but with limited practical applications.
Recently, with the development of fifth-generation (5G) mobile technology, the
concept of dedicated radio-frequency (RF) charging promises to support the
growing market of wearable devices. In this work, we shed light on the
potential of wireless RF power transfer by elaborating upon feasible system
parameters and architecture, emphasizing the basic trade-offs behind
omni-directional and directional out-of-band energy transmission, providing
system-level performance evaluation, as well as discussing open challenges on
the way to sustainable wireless-powered wearables. The key aspects highlighted
in this article include system operation choices, user mobility effects, impact
of network and user densities, as well as regulatory issues. Ultimately, our
research targets to facilitate the integration of wireless RF charging
technology into the emerging 5G ecosystem.
