Synchronization Strategy for Distributed Wireless Power Transfer with Periodic Frequency and Phase Synchronization

This letter analyzes the optimal transmission period to maximize the time-averaged received power using a distributed microwave power transfer (DMPT) system. DMPT requires periodic phase and frequency synchronization. The received power is maximized immediately after synchronization because the received signals from the transmitters are coherent. However, the received power gradually degrades owing to the phase drift caused by the frequency offset of the phase-locked loop (PLL) on the transmitters. Therefore, if the power transmission period is considerably long, the time-averaged received power decreases. To design the synchronization interval, we formulated the expected value of the time-averaged received power. The expected value assists in selecting PLL elements and estimating the received power before hardware implementation of the transmitters, thus enabling the rapid design of DMPT systems.