The present invention relates to a method and an apparatus for implementing Listen-Before-Talk. According to an embodiment of the present invention, if the channel assessment does not stop at a boundary of the first symbol, the preamble comprises at least a first part, and if the channel assessment stops at the boundary of the first symbol, the preamble comprises a second part. And the first part is transmitted on a remaining portion of the first symbol until the end of the first symbol, and the second part is transmitted on at least one symbol following the first symbol. Besides, the data is transmitted to the receiving device in at least one symbol in the subframe in which the preamble transmission ends.