A method includes: generating a physical layer protocol data unit PPDU, where the PPDU includes a data field; and sending the PPDU to a first station and a second station, where the first station is a station that does not support receiving a midamble, and the second station is a station that supports receiving the midamble. A second data field transmitted on a second resource unit allocated to the second station includes a midamble subfield. A first data field transmitted on a first resource unit allocated to the first station includes a useful information subfield. The useful information subfield includes useful data information, and the useful information subfield is located before a first OFDM symbol corresponding to the midamble subfield.