A transmitter sets a time length, determines a time point at which phases of frequency signals coincide within a range of the time length, defines a determined time point as a time reference point, aligns the phases of the frequency signals based on the time reference point, combines phase-aligned frequency, and transmits combined frequency signals to a receiver by the time length as the communication signals. The receiver receives the communication signals, extracts the phases of the frequency signals, obtains a time point at which the phases coincide, and determines an obtained time point as the time reference point.