  Green radio communication is an emerging topic since the overall footprint of
information and communication technology (ICT) services is predicted to triple
between 2007 and 2020. Given this research line, energy harvesting (EH) and
wireless power transfer (WPT) networks can be evaluated as promising
approaches. In this paper, an overview of recent trends for future green
networks on the platforms of EH and WPT is provided. By rethinking the
application of radio frequency (RF)-WPT, a new concept, namely green RF-WTP, is
introduced. Accordingly, opening challenges and promising combinations among
current technologies, such as small-cell, millimeter (mm)-wave, and Internet of
Things (IoT) networks, are discussed in details to seek solutions for the
question with how to re-green the future networks?
