A transmission device includes: an acquiring unit acquires LTF parameters, and acquires a start position I of allocated subcarriers, where the LTF parameters include a frequency domain transform parameter and a time domain transform parameter that are required for generating an LTF sequence; a frequency domain transform unit performs, according to the frequency domain transform parameter and the start position I, a frequency domain transform on an LTF basic sequence to obtain an LTF symbol; a time domain transform unit performs, according to the time domain transform parameter, a time domain transform on the LTF symbol to obtain the LTF sequence; and a sending unit adds the LTF sequence to a first data frame, and sends the first data frame to a second device, so that the second device determines the LTF basic sequence according to the LTF sequence and performs channel estimation according to the LTF basic sequence.