The present application discloses a communication method performed by a relay device. The method includes: receiving a first uplink data frame from a terminal, the first uplink data frame comprising information indicating a first period; determining a length of a first preamble according to the first period and a first time length, the first time length being equal to a length of a third preamble plus a second time length; sending a second downlink data frame to the terminal, the second downlink data frame comprising the first preamble; and receiving a first downlink data frame from a base station, the first downlink data frame comprising a second preamble, wherein a length of the second preamble is less than or equal to each of the length of the first preamble and the length of the third preamble.