Adaptive equalization circuit, digital coherent receiver, and adaptive equalization method

A digital coherent receiver, comprising:

• a received light processing circuit configured to perform photoelectric conversion and digital conversion of light obtained by mixing signal light and local oscillation light;
• a calculation circuit configured to calculate a noise power of a predetermined training sequence pattern repeatedly included in a first signal obtained by the received light processing circuit, based on a second signal obtained by compensating the predetermined training sequence pattern by a compensation circuit, a channel estimation value based on the second signal, and the predetermined training sequence pattern;
• an average circuit configured to obtain an average value of estimation values of frequency offsets based on the predetermined training sequence pattern having the noise power equal to or smaller than a predetermined power, among estimation values of frequency offsets based on the predetermined training sequence pattern, the compensation circuit being configured to compensate a frequency offset of the predetermined training sequence pattern based on the average value and thereby obtain the second signal;
• an adaptive equalizer configured to perform adaptive equalization processing of the first signal obtained by the received light processing circuit, with a setting value based on the second signal;
• and
• a decode circuit configured to perform decoding based on the first signal resultant from the adaptive equalization processing by the adaptive equalizer.

An adaptive equalization method comprising:

• calculating, by a digital circuit, a noise power of a predetermined training sequence pattern repeatedly included in a first signal, based on a second signal obtained by compensating the predetermined training sequence pattern, a channel estimation value based on the second signal, and the predetermined training sequence pattern;
• obtaining, by the digital circuit, an average value of estimation values of frequency offsets based on the predetermined training sequence pattern each having the noise power equal to or smaller than a predetermined power, among estimation values of frequency offsets based on the predetermined training sequence pattern;
• compensating, by the digital circuit, a frequency offset of the predetermined training sequence pattern based on the average value and thereby obtaining the second signal;
• and
• performing, by the digital circuit, adaptive equalization processing of the first signal with a setting value based on the second signal.