Optical transmission system, transmission apparatus, receiving apparatus and method for device characteristic estimation
A transmission apparatus causes a digital-to-analog conversion unit to perform digital-to-analog conversion on transmission signals pre-equalized by using a compensation filter, then converts electrical signals into optical signals, and outputs the optical signals. A receiving apparatus converts the received optical signals into received electrical signals, then performs analog-to-digital conversion, and demodulates the received signals. A scale estimation unit calculates a slope near an amplitude 0 in a correlation between an amplitude distribution of the pre-equalized transmission signals and an amplitude distribution of the received signals. A scale unit scales amplitude of the received signals on the basis of the calculated slope. A coefficient estimation unit calculates a filter coefficient of the compensation filter on the basis of the pre-equalized transmission signals and the scaled received signals. An output amplitude level determination unit determines output levels of the transmission signals from the digital-to-analog conversion unit on the basis of a correlation between distributions of amplitudes of non-pre-equalized and pre-equalized transmission signals.
1 . An optical transmission system comprising:
a transmission apparatus; and
a receiving apparatus, wherein:
the transmission apparatus includes
a pre-equalizer that performs pre-equalization on digital transmission signals by using a compensation filter,
a digital-to-analog converter that converts the digital transmission signals which have been pre-equalized from digital signals into analog signals, so as to output analog transmission signals, and
an electrical-to-optical converter that converts the analog transmission signals from electrical signals into optical signals so as to output optical transmission signals;
the receiving apparatus includes
a receiver that receives the optical transmission signals which have been output from the output unit electrical-to-optical converter, converts the optical transmission signals from the optical signals into the electrical signals so as to output analog received signals,
an analog-to-digital converter that converts the analog received signals from the analog signals into the digital signals so as to output digital received signals, and
a demodulator that demodulates the digital received signals; and
the optical transmission system further includes
a scale estimation processor that calculates a slope near an amplitude 0 in a correlation between an amplitude distribution of the digital transmission signals which have been pre-equalized by the pre-equalizer and an amplitude distribution of the digital received signals,
a scale processor that scales an amplitude of the digital received signals on the basis of the slope which has been calculated by the scale estimation processor,
a coefficient estimation processor that calculates a filter coefficient of the compensation filter on the basis of the digital transmission signals which have been pre-equalized by the pre-equalizer and the digital received signals which have been scaled by the scale processor, and
an output amplitude level determination processor that determines an output level of the analog transmission signals output from the digital-to-analog converter on the basis of a correlation between a distribution of amplitudes of the digital transmission signals before being pre-equalized by the pre-equalizer and a distribution of amplitudes of the digital transmission signals which have been pre-equalized by the pre-equalizer.
2 . A transmission apparatus comprising:
a pre-equalizer that performs pre-equalization on digital transmission signals by using a compensation filter;
a digital-to-analog converter that converts the digital transmission signals which have been pre-equalized from digital signals into analog signals so as to output analog transmission signals;
an electrical-to-optical converter that converts the analog transmission signals from electrical signals into optical signals so as to output optical transmission signals; and
an output amplitude level determination processor that determines output levels of the analog transmission signals output from the digital-to-analog converter on the basis of a correlation between a distribution of amplitudes of the digital transmission signals before being pre-equalized by the pre-equalizer and a distribution of amplitudes of the digital transmission signals which have been pre-equalized by the pre-equalizer.
3 . The transmission apparatus according to claim 2 , wherein:
a receiving apparatus that has received the optical transmission signals which have been output from the electrical-to-optical converter converts the received optical transmission signals from the optical signals into the electrical signals so as to output received signals and scales the received signals on the basis of a slope near an amplitude 0 in a correlation between an amplitude distribution of the digital transmission signals which have been pre-equalized by the pre-equalizer and an amplitude distribution of the received signals; and
the pre-equalizer sets, to the compensation filter, a filter coefficient calculated on the basis of the digital transmission signals which have been pre-equalized by the pre-equalizer and the received signals which have been scaled.
4 . The transmission apparatus according to claim 2 , further comprising
a clipper that clips the digital transmission signals which have been pre-equalized by the pre-equalizer at the output levels which have been determined by the output amplitude level determination processor.
5 . The transmission apparatus according to claim 4 , further comprising
a scale processor that scales the digital transmission signals before being pre-equalized by the pre-equalizer on the basis of a ratio clipped by the clipper.
6 . A receiving apparatus comprising:
a converter that receives optical transmission signals which have been output from a transmission apparatus and converts the received optical transmission signals from optical signals ef into electrical signals so as to output analog received signals;
an analog-to-digital converter that converts the analog received signals from analog signals into digital signals so as to output digital received signals;
a demodulator that demodulates the digital received signals;
a scale estimation processor that calculates a slope near an amplitude 0 in a correlation between an amplitude distribution of transmission signals which have been pre-equalized by a pre-equalizer of the transmission apparatus by using a compensation filter and an amplitude distribution of the digital received signals;
a scale processor that scales an amplitude of the digital received signals on the basis of the slope which has been calculated by the scale estimation processor; and
a coefficient estimation processor that calculates a filter coefficient of the compensation filter on the basis of the transmission signals which have been pre-equalized by the pre-equalizer and the digital received signals which have been scaled by the scale processor.