Method for determining numbers of bits allocated to subcarriers and optical transmission system
A bit allocation method is used in an optical transmission system that transmits multicarrier signals of different wavelengths in wavelength division multiplexing. Frequency characteristics of subcarriers included in the multicarrier signals are different between the respective multicarrier signals. The method includes: measuring transmission characteristics of the subcarriers included in corresponding multicarrier signals at different subcarrier frequencies; and determining a number of bits to be allocated to each of the subcarriers included in each of the multicarrier signals based on the transmission characteristics measured at the different subcarrier frequencies.
1. A bit allocation method used in an optical transmission system in which a first wavelength channel that transmits a first multicarrier signal including a plurality of subcarriers arranged in a specified subcarrier frequency range and a second wavelength channel that transmits a second multicarrier signal including a plurality of subcarriers arranged in the subcarrier frequency range are multiplexed, transmission characteristics of the second wavelength channel being different from transmission characteristics of the first wavelength channel, the bit allocation method comprising:
measuring transmission characteristics of subcarriers included in the first multicarrier signal in a first subcarrier frequency range within the subcarrier frequency range;
measuring transmission characteristics of subcarriers included in the second multicarrier signal in a second subcarrier frequency range that is different from the first subcarrier frequency range within the subcarrier frequency range; and
determining 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 subcarriers included in the first multicarrier signal measured in the first subcarrier frequency range and the transmission characteristics of the subcarriers included in the second multicarrier signal measured in the second subcarrier frequency range.
2. The bit allocation method according to claim 1 , further comprising
generating common transmission characteristics by combining the transmission characteristics of the first multicarrier signal measured in the first subcarrier frequency range and the transmission characteristics of the second multicarrier signal measured in the second subcarrier frequency range, wherein
both of the number of bits to be allocated to each of the subcarriers included in the first multicarrier signal and the number of bits to be allocated to each of the subcarriers included in the second multicarrier signal are determined based on the common transmission characteristics.
3. The bit allocation method according to claim 1 , wherein
a number of subcarriers that belong to the first subcarrier frequency range is the same as a number of subcarriers that belong to the second subcarrier frequency range, and
the measuring process for the first subcarrier frequency range is performed in parallel with the measuring process for the second subcarrier frequency range.
4. The bit allocation method according to claim 1 , wherein
when a difference in the transmission characteristics between the first multicarrier signal and the second multicarrier signal in the second subcarrier frequency range is larger than a difference in the transmission characteristics between the first multicarrier signal and the second multicarrier signal in the first subcarrier frequency range, and when the transmission quality of the first multicarrier signal is higher than the transmission quality of the second multicarrier signal,
the transmission characteristics of the subcarriers included in the first multicarrier signal are measured within the first subcarrier frequency range, and
the transmission characteristics of the subcarriers included in the second multicarrier signal are measured within the second subcarrier frequency range.
5. The bit allocation method according to claim 1 , wherein
when the first multicarrier signal and the second multicarrier signal are transmitted in a wavelength band of 1.3 μm in wavelength division multiplexing, and when the second subcarrier frequency range is higher than the first subcarrier frequency range, and when a wavelength of the first wavelength channel is shorter than a wavelength of the second wavelength channel,
the transmission characteristics of the subcarriers included in the first multicarrier signal are measured within the first subcarrier frequency range, and
the transmission characteristics of the subcarriers included in the second multicarrier signal are measured within the second subcarrier frequency range.
6. The bit allocation method according to claim 1 , further comprising
generating first corrected transmission characteristics from the transmission characteristics of the second multicarrier signal measured in the second subcarrier frequency range according to a characteristic of an optical transmission line through which the first and second multicarrier signals are transmitted;
generating first individual transmission characteristics indicating the transmission characteristics for the first multicarrier signal by combining the transmission characteristics of the first multicarrier signal measured in the first subcarrier frequency range and the first corrected transmission characteristics;
generating second corrected transmission characteristics from the transmission characteristics of the first multicarrier signal measured in the first subcarrier frequency range according to the characteristic of the optical transmission line; and
generating second individual transmission characteristics indicating the transmission characteristics for the second multicarrier signal by combining the second corrected transmission characteristics and the transmission characteristics of the second multicarrier signal measured in the second subcarrier frequency range, wherein
the number of bits to be allocated to each of the subcarriers included in the first multicarrier signal is determined in accordance with the first individual transmission characteristics and the number of bits to be allocated to each of the subcarriers included in the second multicarrier signal is determined in accordance with the second individual transmission characteristics.
7. 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.