Communication apparatus, communication system, communication method, and non-transitory computer readable medium

A communication system comprising:

• a transmitter capable of transmitting a plurality of types of quadrature amplitude-modulated signals and adding error correction codes to the quadrature amplitude-modulated signals;
• a receiver configured to demodulate the received quadrature amplitude-modulated signals;
• and
• a controller;
• where in the controller comprises;
• at least one memory storing instructions;
• and
• at least one processor configured to execute the instructions to:
• change, for each of the quadrature amplitude-modulated signals to be transmitted, the number of bits of the error correction code to be added thereto, and
• change the number of bits of the error correction code in such a way that margins in regard to performance from the reception Q-value as transmission quality at an OSNR condition of each of the quadrature amplitude-modulated signals to a FEC correction limit are substantially equal to each other,
• wherein the FEC correction limit is a maximum value of a bit error rate before FEC coding, and
• wherein the maximum value satisfies the requirement that the Q value≥17 dB after the FEC coding.

A communication method comprising:

• adding an error correction code to a quadrature amplitude-modulated signal;
• changing the number of bits of the error correction code according to a type of the quadrature amplitude-modulated signal;
• and
• transmitting a plurality of types of quadrature amplitude-modulated signals, and
• change the number of bits of the error correction code in such a way that margins in regard to performance from the reception Q-value as transmission quality at an OSNR condition of each of the quadrature amplitude-modulated signals to a FEC correction limit are substantially equal to each other,
• wherein the FEC correction limit is a maximum value of a bit error rate before FEC coding, and
• wherein the maximum value satisfies the requirement that the Q value≥17 dB after the FEC coding.