  Resonant beam communications (RBCom), which adopt oscillating photons between
two separate retroreflectors for information transmission, exhibit potential
advantages over other types of wireless optical communications (WOC). However,
echo interference generated by the modulated beam reflected from the receiver
affects the transmission of the desired information. To tackle this challenge,
a synchronization-based point-to-point RBCom system is proposed to eliminate
the echo interference, and the design for the transmitter and receiver is
discussed. Subsequently, the performance of the proposed RBCom is evaluated and
compared with that of visible light communications (VLC) and free space optical
communications (FOC). Finally, future research directions are outlined and
several implementation challenges of RBCom systems are highlighted.
