Disclosed is an uplink communication method for: receiving data through an mmWave downlink from an mmWave base station; transmitting, to the mmWave base station, an ACK/NACK reply to the data and an mmWave uplink reference signal through an mmWave uplink; receiving, from the mmWave base station, an indicator indicating use of a legacy uplink instead of the mmWave uplink; shortening the length of a legacy TTI to correspond to the length of an mmWave TTI according to the indicator; and communicating with the mmWave base station through the legacy uplink using the shortened legacy TTI.