Method for determining numbers of bits allocated to subcarriers and optical transmission system

An optical transmission system that transmits a first multicarrier signal including a plurality of subcarriers arranged in a specified subcarrier frequency range and a second multicarrier signal including a plurality of subcarriers arranged in the subcarrier frequency range in wavelength division multiplexing from a first optical transmission device to a second optical transmission device, frequency characteristics of subcarriers included in the first multicarrier signal being different from frequency characteristics of subcarriers included in the second multicarrier signal, the optical transmission system comprising:

• first and second transmitters configured to respectively transmit the first and second multicarrier signals to the second optical transmission device, the first and second transmitters being provided in the first optical transmission device;
• a calculator configured to calculate transmission characteristics of the subcarriers included in each of the first and second multicarrier signals, the calculator being provided in the second optical transmission device;
• a bit allocator configured to determine bit allocation indicating numbers of bits to be allocated to the subcarriers included in each of the first and second multicarrier signals in accordance with the transmission characteristics calculated by the calculator;
• and
• a controller configured to control the first and second transmitters in accordance with the bit allocation, the controller being provided in the first optical transmission device, wherein
• a first subcarrier frequency range in the subcarrier frequency range is allocated to the first transmitter,
• a second subcarrier frequency range that is different from the first subcarrier frequency range in the subcarrier frequency range is allocated to the second transmitter,
• the first transmitter transmits probe signals to the second optical transmission device by using subcarriers that belong to the first subcarrier frequency range,
• the second transmitter transmits probe signals to the second optical transmission device by using subcarriers that belong to the second subcarrier frequency range,
• the calculator measures transmission characteristics of the probe signals in the first subcarrier frequency range and transmission characteristics of the probe signals in the second subcarrier frequency range,
• the bit allocator determines a number of bits to be allocated to each of the subcarriers included in the first multicarrier signal and a number of bits to be allocated to each of the subcarriers included in the second multicarrier signal based on the transmission characteristics of the probe signals in the first multicarrier signal measured in the first subcarrier frequency range and the transmission characteristics of the probe signals in the second multicarrier signal measured in the second subcarrier frequency range, and
• the controller controls the first and second transmitters in accordance with the bit allocation.