The present invention relates to the field of communications technologies, and discloses a data transmission method, user equipment, a base station, and a system. The method includes: selecting, by user equipment (UE), a preamble sequence, and acquiring an uplink time-frequency resource and a downlink time-frequency resource that are corresponding to the preamble sequence; sending the preamble sequence to a base station, so that the base station decodes the preamble sequence, and determines, according to the decoded preamble sequence, the uplink time-frequency resource and the downlink time-frequency resource that are corresponding to the decoded preamble sequence.