Distortion estimation device, receiver, and distortion estimation method

A receiver comprising:

• a detector that coherently receives a polarization-multiplexed signal transmitted from a transmitter via a transmission path;
• and
• a distortion estimation device that detects distortion included in a signal based on the coherently received polarization-multiplexed signal,
• wherein the distortion estimation device comprises at least one memory storing instructions;
• and at least one processor configured to execute the instructions to;
• perform equalization processing on the signal to which nonlinear distortion is applied in at least one of the transmitter, the transmission path, or the receiver, by using an equalization filter that includes an in-receiver distortion compensation filter that compensates for in-receiver distortion occurring in the polarization-multiplexed signal in the receiver, a transmission path distortion compensation filter that compensates for distortion occurring in the polarization-multiplexed signal in the transmission path, and an in-transmitter distortion compensation filter that compensates for in-transmitter distortion occurring in the polarization-multiplexed signal in the transmitter, and
• adaptively control filter coefficients of the in-receiver distortion compensation filter, the transmission path distortion compensation filter, and the in-transmitter distortion compensation filter, and
• detect the in-receiver distortion based on the filter coefficients of the in-receiver distortion compensation filter, and detect the in-transmitter distortion based on the filter coefficients of the in-transmitter distortion compensation filter, after convergence of the filter coefficients.

A distortion estimation method comprising:

• performing equalization processing on a signal to which nonlinear distortion is applied in at least one of a transmitter, a transmission path, or a receiver, the signal being received by the receiver, by using an equalization filter that includes an in-receiver distortion compensation filter that compensates for in-receiver distortion occurring in a polarization-multiplexed signal in the receiver that receives the polarization-multiplexed signal transmitted from the transmitter via the transmission path, a transmission path distortion compensation filter that compensates for distortion occurring in the polarization-multiplexed signal in the transmission path, and an in-transmitter distortion compensation filter that compensates for in-transmitter distortion occurring in the polarization-multiplexed signal in the transmitter;
• adaptively controlling filter coefficients of the in-receiver distortion compensation filter, the transmission path distortion compensation filter, and the in-transmitter distortion compensation filter;
• and
• detecting the in-receiver distortion based on the filter coefficients of the in-receiver distortion compensation filter, and detecting the in-transmitter distortion based on the filter coefficients of the in-transmitter distortion compensation filter, after convergence of the filter coefficients.