A signal transmission method includes: processing, by a base station, a first baseband signal, a second baseband signal, a third baseband signal, and a fourth baseband signal by using a VAM matrix, to obtain four processed signals; performing precoding processing on the four processed signals to obtain four coded signals; and sending the four coded signals to a mobile terminal by using four radio frequency ports. The four radio frequency ports are in a one-to-one correspondence with the four coded signals. A first processed signal is the same as a third processed signal, a second processed signal is the same as a fourth processed signal. The first processed signal is obtained by performing superposition on the first baseband signal and the third baseband signal, and the second processed signal is obtained by performing superposition on the second baseband signal and the fourth baseband signal.