Communication system, optical transceiver, control method by communication system, and control method by optical transceiver

1. A communication system comprising:

a first optical transceiver including

a transmission signal processor configured to generate a multi-valued pulse amplitude modulation signal including a fixed bit pattern,

a first optical transmitter configured to convert the multi-valued pulse amplitude modulation signal into an optical transmission signal to transmit the optical transmission signal,

a first optical receiver configured to receive an optical adjustment signal that is transmitted from a second optical transceiver to reproduce an adjustment signal from the optical adjustment signal, and

a first controller configured to control the transmission signal processor, the first optical transmitter, and the first optical receiver; and

the second optical transceiver configured to communicate with the first optical transceiver, the second optical transceiver including

a second optical receiver configured to receive the optical transmission signal to convert the received optical transmission signal into a received signal,

a received-signal processor configured to measure a bit error rate of the received signal, based on the fixed bit pattern,

a second optical transmitter configured to convert the adjustment signal that includes measurement information indicating the bit error rate, into the optical adjustment signal to transmit the optical adjustment signal, and

a second controller configured to control the second optical receiver, the received-signal processor, and the second optical transmitter,

wherein the first controller is configured to

extract the measurement information indicating the bit error rate, from the reproduced adjustment signal, and

control the transmission-signal processor based on the extracted measurement information indicating the bit error rate, to adjust light power at each multi-valued pulse amplitude modulation level of the optical transmission signal.

2. An optical transceiver for communicating with a second optical transceiver via an optical fiber, the optical transceiver comprising:

an optical receiver configured to

receive, from the second optical transceiver, (i) a first optical transmission signal and (ii) a first optical adjustment signal that includes measurement information indicating a bit error rate that is measured by the second optical transceiver,

convert the received first optical transmission signal into a first received signal, and

reproduce a first adjustment signal from the received first optical adjustment signal;

a received-signal processor configured to measure a bit error rate of the first received signal, based on a fixed bit pattern;

a transmission signal processor configured to generate a multi-valued pulse amplitude modulation signal including the fixed bit pattern;

an optical transmitter configured to

convert the multi-valued pulse amplitude modulation signal into a second optical transmission signal,

transmit the second optical transmission signal to the second optical transceiver,

convert, into a second optical adjustment signal, a second adjustment signal that includes measurement information indicating the bit error rate that is measured by the received-signal processor, and

transmit the second optical adjustment signal to the second optical transceiver; and

a controller configured to

control the optical receiver, the received-signal processor, the transmission signal processor, and the optical transmitter,

extract, from the first adjustment signal reproduced by the optical receiver, the measurement information indicating the bit error rate that is measured by the second optical transceiver, and

control the transmission signal processor based on the extracted measurement information indicating the bit error rate, to adjust light power at each multi-valued pulse amplitude modulation level of the second optical transmission signal.

3. A control method by a communication system including a first optical transceiver and a second optical transceiver that communicates with the first optical transceiver, the control method comprising:

generating, by the first optical transceiver, a multi-valued pulse amplitude modulation signal including a fixed bit pattern;

converting, by the first optical transceiver, the multi-valued pulse amplitude modulation signal into an optical transmission signal to transmit the optical transmission signal;

receiving, by the first optical transceiver, an optical adjustment signal that is transmitted from the second optical transceiver to reproduce an adjustment signal from the optical adjustment signal;

receiving, by the second transceiver, the optical transmission signal to convert the received optical transmission signal into a received signal;

measuring, by the second transceiver, a bit error rate of the received signal, based on the fixed bit pattern;

converting, by the second transceiver, the adjustment signal that includes measurement information indicating the bit error rate, into the optical adjustment signal to transmit the optical adjustment signal;

extracting, by the first transceiver, the measurement information indicating the bit error rate, from the reproduced adjustment signal; and

adjusting, by the first transceiver, optical power at each multi-valued pulse amplitude modulation level of the optical transmission signal to be transmitted to the second optical transceiver, based on the extracted measurement information indicating the bit error rate.

4. A control method by an optical transceiver that communicates with a second optical transceiver, the control method comprising:

receiving (i) a first optical transmission signal and (ii) a first optical adjustment signal that includes measurement information indicating a bit error rate that is measured by the second optical transceiver;

converting the received first optical transmission signal into a first received signal, and

reproducing a first adjustment signal from the received first optical adjustment signal;

measuring a bit error rate of the first received signal, based on a fixed bit pattern;

generating a multi-valued pulse amplitude modulation signal including the fixed bit pattern;

converting the multi-valued pulse amplitude modulation signal into a second optical transmission signal;

transmitting the second optical transmission signal to the second optical transceiver;

converting, into a second optical adjustment signal, a second adjustment signal that includes measurement information indicating a measured bit error rate;

extracting the measurement information indicating the bit error rate measured by the second optical transceiver, from the reproduced first adjustment signal; and

adjusting optical power at each multi-valued pulse amplitude modulation level of the second optical transmission signal, based on the extracted measurement information indicating the bit error rate.