In this letter, we propose a new synchronous duplexing scheme for a long distance wireless backhaul system. In conventional time-division duplexing, a backhaul system can transmit its data only after the transmission of the opposite backhaul system is finished. Thus, any propagation delay caused by long distances leads to a long guard time. However, in our proposed scheme, both local and remote backhaul systems transmit their down and up-link data to each other simultaneously. Thus, even for a long propagation delay, the time for which the channel is not used, which is called the feedback delay, can be effectively reduced. We conduct a mathematical analysis to derive the theoretical efficiency of the proposed scheme and show simulation results indicating the superiority of the proposed scheme in terms of synchronization error and propagation delay.