Signal processing device, signal processing method, receiver, and optical communication system

A signal processing method for processing reception signals of optical signals received by a receiver when the optical signals transmitted from a transmitter are propagated to the receiver via a plurality of paths, the signal processing method comprising:

• calculating signal-to-noise ratios of the optical signals that have been propagated through the respective paths, the signal-to-noise ratios being based on propagation distances of the optical signals in the respective paths, intensities of the optical signals transmitted from the transmitter, and intensities of noise with respect to the optical signals transmitted from the transmitter;
• adjusting amplitudes of the reception signals of the optical signals that have been propagated through the respective paths, using the corresponding signal-to-noise ratios calculated;
• and
• combining the reception signals whose amplitudes have been adjusted.

A receiver comprising:

• a plurality of receivers to receive optical signals that have been propagated through a plurality of respective paths through which the optical signals transmitted from a transmitter are propagated, and to output reception signals of the respective optical signals;
• signal-to-noise ratio calculating circuitry to calculate signal-to-noise ratios of the optical signals received by the respective receivers, the signal-to-noise ratios being based on propagation distances of the optical signals in the respective paths, intensities of the optical signals transmitted from the transmitter, and intensities of noise with respect to the optical signals transmitted from the transmitter;
• amplitude adjusting circuitry to adjust amplitudes of the reception signals output from the respective receivers, using the corresponding signal-to-noise ratios calculated by the signal-to-noise ratio calculating circuitry;
• and
• signal combining circuitry to combine the reception signals whose amplitudes have been adjusted by the amplitude adjusting circuitry.