  Resonant Beam Charging (RBC) is the Wireless Power Transfer (WPT) technology,
which can provide high-power, long-distance, mobile, and safe wireless charging
for Internet of Things (IoT) devices. Supporting multiple IoT devices charging
simultaneously is a significant feature of the RBC system. To optimize the
multi-user charging performance, the transmitting power should be scheduled for
charging all IoT devices simultaneously. In order to keep all IoT devices
working as long as possible for fairness, we propose the First Access First
Charge (FAFC) scheduling algorithm. Then, we formulate the scheduling
parameters quantitatively for algorithm implementation. Finally, we analyze the
performance of FAFC scheduling algorithm considering the impacts of the
receiver number, the transmitting power and the charging time. Based on the
analysis, we summarize the methods of improving the WPT performance for
multiple IoT devices, which include limiting the receiver number, increasing
the transmitting power, prolonging the charging time and improving the
single-user's charging efficiency. The FAFC scheduling algorithm design and
analysis provide a fair WPT solution for the multi-user RBC system.
