Abstract: A tap-coefficient control circuit sets the tap coefficient converged by the second tap coefficient updater as an initial value of the tap coefficient in the first digital filter which is to be updated by the first tap coefficient updater, arranges the tap coefficients converged by the second tap coefficient updater in descending order of contribution degree to the convergence operation of tap coefficient update in the first tap coefficient updater, judges the tap coefficient not less than upper specified number to be valid and the tap coefficient less than the specified number to be invalid, and sets the tap coefficient of the first digital filter corresponding to the tap coefficient judged to be invalid to zero not to be used in a calculation of the first tap coefficient updater until a next judgment result is made.

Abstract: First compensation circuitry includes a first digital filter compensating a phase difference between a phase of a symbol of a received signal and a sampling timing, and first filter coefficient calculation circuitry calculating a filter coefficient of the first digital filter as a first filter coefficient. Second filter coefficient calculation circuitry calculates, as a second filter coefficient, a filter coefficient for adaptive equalization that compensates distortion due to temporally changing polarization dispersion, based on an output of the first digital filter. Coefficient combination circuitry combines the first filter coefficient and the second filter coefficient. Second compensation circuitry includes a second digital filter which uses a filter coefficient combined by the coefficient combination circuitry and performs a compensation of the phase difference between the phase of the symbol of the received signal and the sampling timing, and a process of the adaptive equalization at the same time.

Abstract: First compensation circuitry includes a first digital filter compensating a phase difference between a phase of a symbol of a received signal and a sampling timing, and first filter coefficient calculation circuitry calculating a filter coefficient of the first digital filter as a first filter coefficient. Second filter coefficient calculation circuitry calculates, as a second filter coefficient, a filter coefficient for adaptive equalization that compensates distortion due to temporally changing polarization dispersion, based on an output of the first digital filter. Coefficient combination circuitry combines the first filter coefficient and the second filter coefficient. Second compensation circuitry includes a second digital filter which uses a filter coefficient combined by the coefficient combination circuitry and performs a compensation of the phase difference between the phase of the symbol of the received signal and the sampling timing, and a process of the adaptive equalization at the same time.