Communication system, receiver, equalization signal processing circuit, method, and non-transitory computer readable medium

1. An equalization signal processing circuit comprising:

a filter group configured to include a plurality of filters connected in series along a signal path of a reception signal being coherent-received, the plurality of filters including a plurality of non-linear distortion compensation filters configured to compensate for non-linear distortion included in the reception signal and one or more linear distortion compensation filters configured to compensate for linear distortion included in the reception signal;

at least one memory storing instructions; and

at least one processor configured to execute the instructions to:

adaptively control, by using an error back propagation method, a filter coefficient of at least some of a plurality of non-linear distortion compensation filters and the linear distortion compensation filter, based on a difference between an output signal being output from the filter group and a predetermined value of the output signal.

2. The equalization signal processing circuit according to claim 1 , wherein the plurality of non-linear distortion compensation filters include an intra-transmitter non-linear distortion compensation filter configured to compensate for non-linear distortion occurring in a transmitter, and an intra-receiver non-linear distortion compensation filter configured to compensate for non-linear distortion occurring in a receiver.

3. The equalization signal processing circuit according to claim 2 , wherein, in the filter group, the intra-receiver non-linear distortion compensation filter is arranged before the intra-transmitter non-linear distortion compensation filter.

4. The equalization signal processing circuit according to claim 3 , wherein

the one or more linear distortion compensation filters include an intra-transmitter linear distortion compensation filter configured to compensate for linear distortion occurring in the transmitter, and an intra-receiver linear distortion compensation filter configured to compensate for linear distortion occurring in the receiver, and,

in the filter group, the intra-receiver linear distortion compensation filter is arranged after the intra-receiver non-linear distortion compensation filter and before the intra-transmitter linear distortion compensation filter, and the intra-transmitter linear distortion compensation filter is arranged before the intra-transmitter non-linear distortion compensation filter.

5. The equalization signal processing circuit according to claim 4 , wherein

the one or more linear distortion compensation filters further include at least one of a wavelength dispersion compensation filter, a polarization separation filter, or a carrier phase compensation filter, and,

in the filter group, at least one of the wavelength dispersion compensation filter, the polarization separation filter, or the carrier phase compensation filter are arranged between the intra-receiver linear distortion compensation filter and the intra-transmitter linear distortion compensation filter.

6. The equalization signal processing circuit according to claim 1 , wherein the non-linear distortion compensation filter includes a deep neural network (DNN), a convolutional neural network (CNN), or a Volterra filter.

7. The equalization signal processing circuit according to claim 6 , wherein the non-linear distortion compensation filter further includes a linear filter being connected in parallel with the DNN, the CNN, or the Volterra filter, adds an output of the DNN, the CNN, or the Volterra filter and an output of the linear filter, and outputs the added result as an output signal.

8. A receiver comprising:

the equalization signal processing circuit according to claim 1 ; and

a detector configured to coherent-receive a signal transmitted from a transmitter via a transmission path.

9. The receiver according to claim 8 , wherein a plurality of non-linear distortion compensation filters include an intra-transmitter non-linear distortion compensation filter configured to compensate for non-linear distortion occurring in the transmitter, and an intra-receiver non-linear distortion compensation filter configured to compensate for non-linear distortion occurring in a receiver.

10. The receiver according to claim 9 , wherein, in a filter group, the intra-receiver non-linear distortion compensation filter is arranged before the intra-transmitter non-linear distortion compensation filter.

11. The receiver according to claim 8 , wherein the non-linear distortion compensation filter includes a deep neural network (DNN), a convolutional neural network (CNN), or a Volterra filter.

12. A communication system comprising:

a transmitter configured to transmit a signal via a transmission path; and

the receiver according to claim 8 .

13. The communication system according to claim 12 , wherein a plurality of non-linear distortion compensation filters include an intra-transmitter non-linear distortion compensation filter configured to compensate for non-linear distortion occurring in the transmitter, and an intra-receiver non-linear distortion compensation filter configured to compensate for non-linear distortion occurring in the receiver.

14. The communication system according to claim 13 , wherein, in a filter group, the intra-receiver non-linear distortion compensation filter is arranged before the intra-transmitter non-linear distortion compensation filter.

15. The communication system according to claim 12 , wherein the non-linear distortion compensation filter includes a deep neural network (DNN), a convolutional neural network (CNN), or a Volterra filter.

16. An equalization signal processing method comprising:

calculating a loss function, based on a difference between an output signal being output from a filter group in which a plurality of filters connected in series along a signal path of a reception signal being coherent-received are included, the plurality of filters including a plurality of non-linear distortion compensation filters configured to compensate for non-linear distortion included in the reception signal and one or more linear distortion compensation filters configured to compensate for linear distortion included in the reception signal, and a predetermined value of the output signal; and

adaptively controlling, by using an error back propagation method, a filter coefficient of at least some of a plurality of non-linear distortion compensation filters and the linear distortion compensation filter, based on the loss function.

17. A non-transitory computer readable medium storing a program for causing a processor to execute processing of:

calculating a loss function, based on a difference between an output signal being output from a filter group in which a plurality of filters connected in series along a signal path of a reception signal being coherent-received are included, the plurality of filters including a plurality of non-linear distortion compensation filters configured to compensate for non-linear distortion included in the reception signal and one or more linear distortion compensation filters configured to compensate for linear distortion included in the reception signal, and a predetermined value of the output signal; and

adaptively controlling, by using an error back propagation method, a filter coefficient of at least some of a plurality of non-linear distortion compensation filters and the linear distortion compensation filter, based on the loss function.