  Federated learning (FL), invented by Google in 2016, has become a hot
research trend. However, enabling FL in wireless networks has to overcome the
limited battery challenge of mobile users. In this regard, we propose to apply
unmanned aerial vehicle (UAV)-empowered wireless power transfer to enable
sustainable FL-based wireless networks. The objective is to maximize the UAV
transmit power efficiency, via a joint optimization of transmission time and
bandwidth allocation, power control, and the UAV placement. Directly solving
the formulated problem is challenging, due to the coupling of variables. Hence,
we leverage the decomposition technique and a successive convex approximation
approach to develop an efficient algorithm, namely UAV for sustainable FL
(UAV-SFL). Finally, simulations illustrate the potential of our proposed
UAV-SFL approach in providing a sustainable solution for FL-based wireless
networks, and in reducing the UAV transmit power by 32.95%, 63.18%, and 78.81%
compared with the benchmarks.
