Distributed beamforming is an energy-efficient wireless communication technique that allows cooperative nodes to transmit a common message to a receiver. This paper investigates carrier synchronization for distributed beamforming in large-scale wireless networks. In order to pursue less timeslots for synchronization, we present a time-slotted round-trip carrier synchronization protocol exploiting the broadcast nature of the wireless links with master-slave architecture among transmitters. Numerical simulations are presented and the results indicate that this protocol can achieve longer valid communication time for beamforming.