Transmission device and selection method for modulation scheme

1. A transmission device comprising:

a memory; and

a processor coupled to the memory and configured to:

acquire a polarization mode dispersion value of a plurality of wavelengths of a polarization-multiplexed optical signal having a wavelength;

multiply a mean value of the polarization mode dispersion values of the wavelengths by a prescribed ratio, to thereby calculate a maximum value of the polarization mode dispersion value that is temporally varied; and

select a multi-level modulation scheme of the polarization-multiplexed optical signal based on an index value of transmission quality of the polarization-multiplexed optical signal and the maximum value.

2. The transmission device according to claim 1 , wherein the processor is configured to:

acquire the index value of a plurality of multi-level modulation schemes; and

correct the index value in each of the multi-level modulation schemes based on a polarization mode dispersion value of the polarization-multiplexed optical signal having the wavelength with a prescribed value, and the maximum value, to thereby select the multi-level modulation scheme from the corrected index value.

3. The transmission device according to claim 1 , further comprising: a transmitter configured to transmit the polarization-multiplexed optical signal for acquiring a polarization mode dispersion value to a transmission path, wherein the processor is configured to change the wavelength of the polarization-multiplexed optical signal at a prescribed interval, and change a transmission band of a wavelength filter on the transmission path based on the wavelength.

4. The transmission device according to claim 3 , wherein the prescribed interval is set based on autocorrelation of a polarization mode dispersion value related to the wavelength.

5. The transmission device according to claim 1 , wherein

the processor is configured to change the wavelength of the polarization-multiplexed optical signal at a prescribed interval while avoiding a wavelength that another polarization-multiplexed optical signal is using.

6. The transmission device according to claim 5 , wherein the prescribed interval is set based on autocorrelation of a polarization mode dispersion value related to the wavelength.

7. A selection method for a modulation scheme that a transmission device executes, the selection method comprising:

acquiring a polarization mode dispersion value of a plurality of wavelengths of a polarization-multiplexed optical signal having a wavelength;

multiplying a mean value of the polarization mode dispersion values of the wavelengths by a prescribed ratio, to thereby calculate a maximum value of the polarization mode dispersion value that is temporally varied; and

selecting a multi-level modulation scheme of the polarization-multiplexed optical signal based on an index value of transmission quality of the polarization-multiplexed optical signal and the maximum value.

8. The selection method according to claim 7 , further comprising:

acquiring the index value in a plurality of multi-level modulation schemes; and

correcting the index value in each of the multi-level modulation schemes based on a polarization mode dispersion value of the polarization-multiplexed optical signal having the wavelength with a prescribed value, and the maximum value, to thereby select the multi-level modulation scheme from the corrected index value.

9. The selection method according to claim 7 , further comprising:

transmitting the polarization-multiplexed optical signal for acquiring a polarization mode dispersion value to a transmission path;

changing the wavelength of the polarization-multiplexed optical signal at a prescribed interval; and changing a transmission band of a wavelength filter on the transmission path based on the wavelength.

10. The selection method according to claim 9 , wherein the prescribed interval is set based on autocorrelation of a polarization mode dispersion value related to the wavelength.

11. The selection method according to claim 9 , further comprising:

changing the wavelength of the polarization-multiplexed optical signal at a prescribed interval while avoiding a wavelength that another polarization-multiplexed optical signal is using.

12. The selection method according to claim 11 , wherein the prescribed interval is set based on autocorrelation of a polarization mode dispersion value related to the wavelength.