Abstract: A transmitter inverts polarities of some symbols in a to-be-sent signal based on a target frequency, so that power of a to-be-sent signal at the target frequency is suppressed. The transmitter may flexibly adjust the power spectrum of the to-be-sent signal based on an actual frequency of interference or noise, so that the to-be-sent signal does not overlap the interference or the noise in frequency, and a receiver can effectively filter out the interference or the noise and cause no impairment to the signal from the transmitter. The transmitter further sends identification information to the receiver, so that the receiver performs inverse transformation of power spectrum adjustment on a received signal based on the identification information, to restore the original signal that is before the transmitter performs power spectrum adjustment.