Optical signal transmission apparatus and optical signal transmission method
An optical signal transmission apparatus includes a modulation unit which modulates a transmission signal, a training signal sequence generation unit which generates a plurality of signal sequences having power concentrated in a plurality of different frequency bands, at least one of an amplitude and a phase of the plurality of signal sequences being modulated, as a training signal sequence, a signal multiplexing unit which appends the training signal sequence to the transmission signal, and an electro-optical conversion unit which converts a signal sequence obtained by appending the training signal sequence to the transmission signal into an optical signal and transmits the optical signal.
1. An optical signal transmission apparatus comprising:
a modulation unit which modulates a transmission signal;
a training signal sequence generation unit which generates a training signal sequence by generating a plurality of signal sequences which have power concentrated in a plurality of different frequency bands and subsequently modulating at least one of an amplitude and a phase of the plurality of signal sequences;
a signal multiplexing unit which appends the training signal sequence to the transmission signal; and
an electro-optical conversion unit which converts a signal sequence obtained by appending the training signal sequence to the transmission signal into an optical signal and transmits the optical signal.
2. The optical signal transmission apparatus according to claim 1 , wherein the training signal sequence generation unit comprises:
a basic signal sequence generation unit which generates a specific frequency band signal in which a frequency component having higher power than a data sequence is concentrated only in a specific frequency band;
a modulation sequence generation unit which generates a modulation sequence for modulating the frequency component; and
a multiplier which multiplies an output sequence of the basic signal sequence generation unit by an output sequence of the modulation sequence generation unit.
3. The optical signal transmission apparatus according to claim 2 , wherein the modulation sequence generation unit modulates at least one of the amplitude and the phase so that a power component that is present in the specific frequency band of the specific frequency band signal and is higher than that of the data sequence is subjected to frequency spreading.
4. The optical signal transmission apparatus according to claim 3 , wherein the modulation sequence generation unit generates the modulation sequence based on estimation precision of a transmission path parameter and a performance deterioration factor in at least one of an analog device and a propagation path.
5. The optical signal transmission apparatus according to claim 4 , wherein the modulation sequence generation unit generates a sequence which changes at a time interval of a main signal symbol of N symbols as the modulation sequence, and adjusts a degree of modulation of the frequency component of the specific frequency band signal by setting a value of N based on the estimation precision of the transmission path parameter and the performance deterioration factor in at least one of the analog device and the propagation path and changing a modulation rate of the generated modulation sequence.
6. The optical signal transmission apparatus according to claim 2 , wherein the modulation sequence generation unit generates the modulation sequence based on an effective pass bandwidth of cross-phase modulation, which is a non-linear optical effect of a transmission path, and a baud rate of a main signal.
7. The optical signal transmission apparatus according to claim 2 , wherein the modulation sequence generation unit modulates at least one of the amplitude and the phase so that a power component that is present in the specific frequency band of the specific frequency band signal and is higher than that of a data sequence is not subjected to frequency spreading.
8. The optical signal transmission apparatus according to claim 7 , wherein the modulation sequence generation unit modulates at least one of the amplitude and the phase so that power of the training signal sequence is equal to or less than power of the data sequence.
9. The optical signal transmission apparatus according to claim 1 , wherein the training signal sequence generation unit generates the training signal sequence by performing modulation in which at least one of the amplitude and the phase is different between first polarization and second polarization which are different from each other.
10. The optical signal transmission apparatus according to claim 9 , wherein the training signal sequence generation unit determines pattern phases and low cycle patterns of training signal sequences in the first polarization and the second polarization so that a correlation between the first polarization and the second polarization is lowest in a pattern obtained by calculating a product or exclusive OR of the training signal sequences in the first polarization and the second polarization.
11. The optical signal transmission apparatus according to claim 1 , wherein the training signal sequence generation unit generates the training signal sequence from M candidate points when multi-level modulation of an M level is performed on the transmission signal.
12. The optical signal transmission apparatus according to claim 11 , wherein the training signal sequence generation unit generates the training signal sequence by limiting phase modulation serving as polarization scrambling to 90 degrees.
13. The optical signal transmission apparatus according to claim 11 , wherein when the multi-level modulation of the M level is performed on the transmission signal, the training signal sequence generation unit selects candidate points which are smaller in number than M and are symmetrical with respect to an origin from among the M candidate points and generates the training signal sequence using the selected candidate points.
14. The optical signal transmission apparatus according to claim 1 , further comprising a training signal determination unit which determines the training signal sequence in accordance with a parameter of a required condition,
wherein the training signal determination unit determines the training signal sequence by performing clipping on an initial sequence for generation of the training signal sequence using a frequency filter which simulates a shape of a frequency spectrum of the training signal sequence satisfying the required condition.
15. The optical signal transmission apparatus according to claim 14 , wherein the training signal determination unit makes initial sequences for generation of the training signal sequence different between the first polarization and the second polarization.
16. The optical signal transmission apparatus according to claim 14 , wherein the training signal determination unit performs a hard decision in accordance with a modulation scheme of the transmission signal on the training signal sequence subjected to the clipping by the frequency filter.
17. The optical signal transmission apparatus according to claim 16 , wherein the training signal determination unit iterates the hard decision in accordance with the clipping by the frequency filter and the modulation scheme of the transmission signal.
18. An optical signal transmission method comprising:
modulating a transmission signal;
generating a training signal sequence by generating a plurality of signal sequences having power concentrated in a plurality of different frequency bands and subsequently modulating at least one of an amplitude and a phase of the plurality of signal sequences;
appending the training signal sequence to the transmission signal; and
converting a signal sequence obtained by appending the training signal sequence to the transmission signal into an optical signal and transmitting the optical signal.