A method for fast and efficient data downloading in wireless communications. The method includes ways to download file data of a large size from a server (access point) to a user's client (mobile device) at high speed and efficiency by using both mmWave wireless communication and conventional wireless communication (WiFi, 3G, etc.). A server transmits packetized file data to a client. The file data is transmitted as data packets via mmWave. In parallel, the server transmits check packets (roll-call packets) corresponding to the data packets. As a test at the time of establishing links, the latency for each communication line is measured. The receiver side, upon completion of receiving the check packets, checks whether their corresponding mmWave packets have arrived. If any corresponding mmWave packet has not arrived, it is determined that the mmWave packet has been lost and a retransmission request is immediately returned to the server via WiFi.