JP5975736B2 - Optical communication system and optical communication method - Google Patents

Description

  The present invention relates to an optical communication system and an optical communication method for performing communication using an optical fiber as a transmission line by using, for example, an optical subcarrier based on OFDM (Orthogonal Frequency Division Multiplexing).

  Conventionally, a baseband signal digitally modulated by OFDM is up-converted by a transmission light source and transmitted, and a baseband signal obtained by down-converting received light by a local light source is digitally demodulated by OFDM. An OFDM communication system is known (see, for example, Patent Document 1).

  In this optical OFDM communication system, a pilot signal having a known transmission waveform is assigned to each of two subcarriers in a transmitter, and an FFT (Fast Fourier Transform) process is performed on a received baseband signal in a receiver. I do.

  Further, in this optical OFDM communication system, the frequency positions of two pilot signals are estimated from the spectrum intensity obtained by the FFT processing, and the frequency deviation of the local light source and the clock frequency deviation are individually determined from this frequency, The chromatic dispersion of the optical fiber is estimated from the difference in signal arrival time.

  Also, a method of constantly transmitting one pilot signal to the center portion of the baseband, constantly tracking and compensating the light source frequency and phase, and suppressing the nonlinear effect of the optical fiber in a WDM (Wavelength Division Multiplexing) system Has been proposed (see, for example, Non-Patent Document 1).

International Publication No. 2010/134321 Pamphlet

T.A. Kobayashi, et al. , “45.2 Tb / s C-band WDM transmission over 240 km using 538 Gb / s PDM-64QAM single carrier FDM signal with digital pilot tone,” PostdelineT 13. C. 6). pdf

However, the prior art has the following problems.
In Patent Document 1, the spectrum peak frequency of the pilot signal is obtained by FFT processing. Here, since the FFT process is a discrete-time process of FFT frame length N for N consecutive values for each sampling period Ts [s], spectrum information directly obtained by the FFT process is also 1 / (Ts · N) [ [Hz] is the frequency resolution of the subcarrier interval. Patent Document 1 discloses a process for obtaining peak frequency information finer than the subcarrier interval from the obtained spectrum weight information.

  On the other hand, in order to perform OFDM demodulation processing, it is theoretically necessary to set the frequency error to half or less of the subcarrier interval, and in practice, it is necessary to set it to several percent or less of the subcarrier interval. However, in the method of Patent Document 1, the amount of calculation required for processing using spectrum weight information is large, and even if processing using this weight information is taken into account, fine peak frequency information of several percent or less of the subcarrier interval is stabilized. There is a problem that it is difficult to obtain.

  Note that the necessary frequency resolution can be obtained by increasing the FFT frame length N in the FFT processing circuit for obtaining the spectrum peak frequency of the pilot signal by 16 times, for example. In this case, the time of the FFT frame can be obtained. The length is also 16 times. Therefore, there is a problem that the time resolution of the spectrum is greatly lowered, and as a result, the frequency tracking speed and accuracy are lowered.

  When the FFT frame length N is set to 16 times, for example, the calculation amount per FFT frame in the FFT processing circuit is about 16 log 16 times (about 44 times), and the calculation amount per sample time is also log 16 times. (About 2.8 times). Therefore, there is a problem that the circuit scale and power consumption become enormous.

  In addition, the method of Patent Document 1 has a problem that the circuit scale and power consumption increase because it is necessary to individually estimate the frequency shift of the local light source, the clock frequency shift, and the chromatic dispersion of the optical fiber.

  Further, in Patent Document 1, in order to stably obtain the spectrum peak frequency of a pilot signal, it is necessary not to transmit a subcarrier carrying a client payload signal transmitted simultaneously with the pilot signal, or at least sufficiently away from the pilot signal. It is necessary not to transmit the payload subcarrier up to the frequency position. Therefore, there is a problem that the charging efficiency of payload subcarriers carrying actual communication data is lowered.

  Further, in the method of Non-Patent Document 1, it is expected that the light source frequency and phase are accurately followed and compensated, but there is a problem that no countermeasure method is disclosed for the clock frequency deviation. There is.

  Further, in Non-Patent Document 1, there is a problem that the amount of calculation increases because it is necessary to always perform time domain processing including complex integration on the pilot signal separately from the FFT processing.

  The present invention has been made in order to solve the above-described problems, and includes SC-FDM (Single Carrier-Frequency Division Multiplexing) and IFDM (Interleaved Frequency Division Multiplexing). An object of the present invention is to provide an optical communication system and an optical communication method capable of efficiently estimating and compensating for the frequency or phase deviation of a light source and a clock source in an optical communication system including a method such as Localized OFDM.

An optical communication system according to the present invention is an optical communication system in which a transmitter and a receiver communicate with each other using an optical fiber as a transmission path, and the transmitter includes a pilot signal generation unit that generates a plurality of pilot signals; A mapping unit that maps a signal input to the transmitter to a subcarrier frequency and accommodates it as a multi-level signal together with a pilot signal, a signal modulation unit that converts the multi-level signal to a frequency domain complex value, and a frequency domain complex value Generates a Fourier transform unit for converting to a time domain complex value, a first clock unit for generating a transmission clock, a DA conversion unit for sampling the time domain complex value with a transmission clock and converting it to an analog baseband signal, and a transmission light source A first light source unit, and an optical modulation unit that up-converts the analog baseband signal into a transmission optical signal by the transmission light source. The receiver includes a second light source unit that generates a local light source, an optical demodulation unit that down-converts a transmission optical signal into an analog baseband signal by the local light source, a second clock unit that generates a local clock, An analog to baseband signal is sampled with a local clock and converted to a time domain digital signal, an AD converter for converting the time domain digital signal to a frequency domain complex value, and a pilot selected from the frequency domain complex value A deviation estimation unit that estimates a phase deviation of the light source based on the signal and obtains a complex equalization coefficient by linear approximation; a compensation unit that calculates a complex product based on the frequency domain complex value and the complex equalization coefficient; It is equipped with.

The optical communication method according to the present invention is an optical communication method executed by an optical communication system in which a transmitter and a receiver communicate with each other using an optical fiber as a transmission path, and a pilot that generates a plurality of pilot signals. A signal generation step, a mapping step of mapping a signal input to the transmitter to a subcarrier frequency and accommodating the signal as a multilevel signal together with a pilot signal, a signal modulation step of converting the multilevel signal into a frequency domain complex value, A Fourier transform step for converting a frequency domain complex value to a time domain complex value, a first clock generation step for generating a transmission clock, and a DA conversion step for sampling the time domain complex value with a transmission clock and converting it to an analog baseband signal A first light source generation step for generating a transmission light source, and an analog baseband signal Modulation step of up-converting the transmission optical signal into a transmission optical signal by a transmission light source, a second light source generation step of generating a local light source, and an optical demodulation step of down-converting the transmission optical signal into an analog baseband signal by the local light source A second clock generation step for generating a local clock, an AD conversion step for sampling an analog baseband signal with the local clock and converting it into a time domain digital signal, and converting the time domain digital signal into a frequency domain complex value A signal demodulating step, estimating a phase deviation of the light source based on a pilot signal selected from the frequency domain complex value, and obtaining a complex equalization coefficient by linear approximation, a frequency domain complex value and complex equalization And a compensation step for calculating a complex product based on the coefficient.

According to the optical communication system and the optical communication method according to the present invention, the deviation estimation unit is generated by the pilot signal generation unit and accommodated as a multilevel signal together with the signal input to the transmitter, and is based on signal modulation and transmission clock. After sampling, up-conversion with the transmission light source, down-conversion with the local light source, sampling with the local clock, and signal demodulation, the phase deviation is estimated based on the pilot signal selected from the frequency domain complex value, and complex by linear approximation. Find the equalization coefficient.
Therefore, the frequency or phase deviation of the light source and the clock source can be efficiently estimated and compensated.

1 is a block configuration diagram illustrating an optical communication system according to a first embodiment of the present invention. (A)-(c) is explanatory drawing which shows the phase deviation characteristic in the optical communication system which concerns on Embodiment 1 of this invention. FIG. 2 is a block configuration diagram illustrating a deviation estimation circuit of FIG. 1. FIG. 4 is a block configuration diagram illustrating a primary interpolation processing unit in FIG. 3. It is a block block diagram which illustrates another deviation estimation circuit of FIG. It is a block block diagram which illustrates the optical communication system which concerns on Embodiment 2 of this invention. It is a block block diagram which illustrates the deviation estimation circuit of FIG. It is a block block diagram which illustrates the optical communication system which concerns on Embodiment 3 of this invention. It is a block block diagram which illustrates the deviation estimation circuit of FIG. It is a block block diagram which illustrates the optical communication system which concerns on Embodiment 4 of this invention. It is a block block diagram which illustrates the deviation estimation circuit of FIG. It is a block block diagram which illustrates the optical communication system which concerns on Embodiment 5 of this invention. It is a block block diagram which illustrates the deviation estimation circuit of FIG. It is a block block diagram which illustrates the optical communication system which concerns on Embodiment 6 of this invention. It is a block block diagram which illustrates the deviation estimation circuit of FIG.

  Hereinafter, preferred embodiments of an optical communication system and an optical communication method according to the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts will be described with the same reference numerals.

Embodiment 1 FIG.
1 is a block diagram illustrating an optical communication system according to Embodiment 1 of the present invention. In FIG. 1, this optical communication system is an optical communication system in which a transmitter 1 and a receiver 2 communicate with each other using an optical fiber 3 as a transmission path.

  Transmitter 1 includes FEC Enc (Forward Error Correction Encoder) & SC Map (SubCarrier Mapper), Mod (Modulator AdiDrC), IDFT (Inverse Distributor), and IDFT (Inverse Distributor). Converter 15, first CLK (CLocK) 16, Opt Mod (Optical Modulator) 17, and first LD (Laser Diode) 18.

  The receiver 2 includes an Opt DeMod (Optical DeModulator) 21, a second LD 22, an ADC (Analog Digital Converter) 23, a second CLK 24, a DFT (Discrete Fourier Transform) 25, a Frame Sync 27, a deviation 28, a Frame Sync 27, a deviation circuit 28, a Frame Sync 27 ) 29 and FEC Dec (Decoder) & SC DeMap (DeMapper) 30.

  The FEC Enc & SC Map 11 adds an FEC redundancy code to the input client payload data sequence (Din) by FEC Enc. Further, FEC Enc & SC Map 11 generates a client payload data sequence to which an FEC redundant code is added by an SC Map on an OFDM frame having an OFDM subcarrier frequency and a time axis as a pilot signal generator (not shown). Multi-level multiplex accommodation with a pilot signal (Pilot).

  Mod12 is provided for each subcarrier frequency, and multilevel information accommodated by FEC Enc & SC Map11 is converted into, for example, QPSK (quaternary phase shift keying: Quadrature Phase Shift Keying) or 16QAM (16-value quadrature amplitude modulation: Quadrature). (Amplitude Modulation) is converted to a frequency domain complex value.

  The IDFT 13 converts the frequency domain complex value converted by Mod 12 into a time domain complex value. CP Add14 adds CP to the time domain complex value converted by IDFT13. The DAC 15 samples the time domain complex value to which the CP is added by the transmission clock generated at the first CLK 16 and converts it into an analog baseband signal.

  The Opt Mod 17 up-converts the analog baseband signal changed by the DAC 15 into a transmission optical signal using the light generated in the first LD 18 as a transmission light source. The transmission optical signal is transmitted to the receiver 2 using the optical fiber 3 as a transmission path.

  The Opt DeMod 21 down-converts the transmission optical signal transmitted through the optical fiber 3 into an analog baseband signal using the light generated by the second LD 22 as a local light source. The ADC 23 samples the analog baseband signal by the local clock generated by the second CLK 24 and converts it into a time domain digital signal.

  The DFT 25 converts the time domain digital signal converted by the ADC 23 into a frequency domain complex value, and at the same time, removes the CP portion of the time domain digital signal by the frame synchronization function of the Frame Sync 26. In place of the DFT 25, an FFT may be used.

The deviation estimation circuit 27 estimates a phase deviation based on the pilot signal selected from the frequency domain complex value converted by the DFT 25, and obtains an equalization coefficient sequence C _k (complex equalization coefficient) by linear approximation.

  Hereinafter, k is an integer from −N / 2 to + N / 2-1 when the FFT frame length N is an even number, and − (N−1) / when the FFT frame length N is an odd number. It is assumed that it is an integer from 2 to + (N−1) / 2, and represents a subcarrier number corresponding to the subcarrier frequency. That is, k is expressed as kε−N / 2 + 1, −N / 2 + 2,..., −1, 0, 1,.

The compensation unit 28 is composed of a plurality of integrators provided for each subcarrier number, and is converted by the DFT 25 and input to the frequency domain complex value input for each subcarrier number. The deviation estimation circuit 27 calculates the subcarrier. Based on the equalization coefficient sequence C _k input for each number, a complex product is calculated.

  The DeMod 29 is provided for each subcarrier number, and converts the complex product calculated by the compensation unit 28 into a multilevel signal by determination using a corresponding demodulation method such as QPSK or 16QAM. The FEC Dec & SC DeMap 30 removes FEC redundant codes and corrects errors using the FEC Dec, and obtains a received payload data sequence (Dout) using the SC DeMap.

  2A to 2C are explanatory diagrams showing phase deviation characteristics in the optical communication system according to Embodiment 1 of the present invention. The upper part of FIGS. 2A to 2C highlights the effect of frequency deviation in the optical OFDM reception spectrum, and the lower part of FIGS. 2A to 2C shows the sub-frames for each OFDM frame. The relationship between carrier phase fluctuation (DELTA) phi and a subcarrier frequency is shown.

  2A shows the case where only the light source frequency deviation is given, FIG. 2B shows the case where only the clock frequency deviation is given, and FIG. 2C shows the light source frequency deviation and The case where the clock frequency deviation is given simultaneously is shown. From FIG. 2, as the subcarrier frequency increases, the frequency deviation (α) of the subcarrier caused by the frequency deviation of the sampling clock increases, while the frequency deviation (β) of the light source increases with respect to all subcarriers. You can see that it works uniformly.

  FIG. 3 is a block diagram illustrating the deviation estimation circuit 27 of FIG. In FIG. 3, the deviation estimation circuit 27 includes a declination extraction unit 201, a differentiation unit 202, a primary interpolation processing unit 203, an integration unit 204, and a complex coefficient conversion 205.

  In FIG. 3, two pilot signals are assigned to symmetrical positions represented by subcarrier numbers -M and + M. 2 is obtained from the frequency domain complex value corresponding to the pilot signal input to the deviation estimation circuit 27, and the frequency deviations α and β in FIG. Can be obtained.

FIG. 4 is a block diagram illustrating the primary interpolation processing unit 203 in FIG. The primary interpolation processing unit 203 is an arithmetic circuit that obtains Δφ _k from the frequency deviations α and β. As shown in FIG. 4, the primary interpolation processing unit 203 can be efficiently configured with only an adder / subtracter without using a product operation circuit with a large circuit scale.

As described above, according to the first embodiment, the deviation estimation unit is generated by the pilot signal generation unit and is accommodated as a multi-level signal together with the signal input to the transmitter, signal modulation, sampling by a transmission clock, Phase conversion is estimated based on the pilot signal selected from the frequency domain complex value through up-conversion by the transmission light source, down-conversion by the local light source, sampling by the local clock, and signal demodulation, and complex equalization by linear approximation Find the coefficient.
Therefore, the frequency or phase deviation of the light source and the clock source can be efficiently estimated and compensated.

  In Embodiment 1 described above, two pilot signals are assigned to symmetrical positions represented by subcarrier numbers -M and + M. However, the present invention is not limited to this.

  FIG. 5 is a block diagram illustrating another deviation estimation circuit 27 of FIG. In FIG. 5, the primary interpolation processing unit 203A has a least square method processing unit. By using the least squares processing unit, it is possible to deal with three or more pilot signals, pilots arranged on asymmetric subcarrier frequencies, or any plurality of pilot signals, and it is possible to improve compensation accuracy. .

Embodiment 2. FIG.
FIG. 6 is a block diagram illustrating an optical communication system according to Embodiment 2 of the present invention. In FIG. 6, the compensation unit 28 is arranged in the previous stage of the deviation estimation circuit 27. That is, the deviation estimation circuit 27 and the compensation unit 28 are configured as a feedback loop.

  FIG. 7 is a block diagram illustrating the deviation estimation circuit 27 of FIG. In FIG. 7, a subtracting unit 202A is provided instead of the differentiating unit 202. Further, the primary interpolation processing unit 203B has loop filters having different characteristics with respect to the frequency deviations α and β. By applying loop filters having different characteristics, the phase variation characteristics inherent to the clock source device such as the VCO and the light source device such as the temperature controller and the bias current controller that control the oscillation frequency of the LD are Optimal loop response characteristics can be obtained.

  As described above, according to the second embodiment, by configuring the deviation estimation circuit and the compensation unit as a feedback loop, the wavelength dispersion of the optical fiber can be compensated simultaneously with the frequency or phase deviation of the light source and the clock source. it can.

Embodiment 3 FIG.
FIG. 8 is a block diagram illustrating an optical communication system according to Embodiment 3 of the present invention. In FIG. 8, the deviation estimation circuit 27 performs feedback control on the frequency of the local light source of the second LD 22 and the frequency of the local clock of the second CLK 24.

  FIG. 9 is a block configuration diagram illustrating the deviation estimation circuit 27 of FIG. In FIG. 9, the primary interpolation processing unit 203C has loop filters having different characteristics with respect to the frequency deviations α and β. By applying loop filters having different characteristics, optimum loop response characteristics can be obtained for different phase fluctuation characteristics of the clock source and the light source, as in the second embodiment.

  As described above, according to the third embodiment, the deviation estimation circuit performs feedback control on the frequency of the local light source of the second LD and the frequency of the local clock of the second CLK, so that the frequency synchronization possible range is achieved. Can be taken widely.

Embodiment 4 FIG.
FIG. 10 is a block diagram illustrating an optical communication system according to Embodiment 4 of the present invention. In FIG. 10, the deviation estimation circuit 27 feeds back the signal g _k after the equalization processing with the equalization coefficient sequence C _k in the compensation unit 28.

FIG. 11 is a block diagram illustrating the deviation estimation circuit 27 of FIG. In FIG. 11, the deviation estimation circuit 27 includes a deviation calculation unit 206 in addition to FIG. 5. Deviation calculation unit 206 obtains deviation γ _k based on signal g _k after equalization processing in compensation unit 28 and complex value Γ _k corresponding to a known pilot signal, and outputs it to complex coefficientization 205. As a result, the equalization coefficient C _k including the clock frequency and the light source frequency compensation can be obtained.

  As described above, according to the fourth embodiment, the deviation estimation circuit feeds back the signal after the equalization processing in the compensation unit, thereby simultaneously compensating for the chromatic dispersion and frequency gain characteristics of the optical fiber. .

Embodiment 5 FIG.
In the above Patent Document 1, optical signals transmitted by a plurality of optical OFDM transmitters are multiplexed via an optical coupler and received by a single optical OFDM receiver. PON (Passive Optical Network) -OFDM In the uplink, since the necessary pilot signal source is, for example, 100 times, there is a problem that a reduction in payload subcarrier filling efficiency becomes serious.

  In order to effectively implement the method of Non-Patent Document 1, it is necessary to place the pilot signal in the center of the transmission baseband, but in the uplink of PON-OFDM composed of a plurality of transmitters. There is a problem in that the degree of freedom of subcarrier band allocation is reduced, and the charging efficiency of payload subcarriers that are actually allocated to the PON uplink is reduced. Therefore, Embodiment 5 of the present invention shows a method for solving these problems.

  FIG. 12 is a block configuration diagram illustrating an optical communication system (PON system) according to the fifth embodiment of the invention. In FIG. 12, the deviation estimation circuit 27 performs feedback control on the transmission clock of the first CLK16 and the frequency of the transmission light source of the first LD 18 for each transmitter (for example, for each of the transmitters 1A and 1B).

  FIG. 13 is a block configuration diagram illustrating the deviation estimation circuit 27 of FIG. In FIG. 12, the deviation estimation circuit 27 selects a pilot signal corresponding to each transmitter, obtains frequency deviations α and β corresponding to each transmitter from the selected pilot signal, and based on the frequency deviations α and β. The feedback manipulated variables α ″ and β ″ are obtained.

  Here, the primary interpolation processing unit 203D has a loop filter for obtaining feedback manipulated variables α ″ and β ″, and the characteristics of the loop filter are set according to the distance to the transmitter. Thereby, it is possible to obtain an optimum loop response characteristic as a system.

  As described above, according to the fifth embodiment, the deviation estimation circuit performs feedback control on the transmission clock of the first CLK and the frequency of the transmission light source of the first LD for each transmitter, so that transmission is performed in the PON system. It is possible to suppress the occurrence of subcarrier collision or interference between transmitters due to a difference in light source and clock frequency between the machines.

Embodiment 6 FIG.
FIG. 14 is a block diagram illustrating an optical communication system according to Embodiment 6 of the present invention. In FIG. 14, the deviation estimation circuit 27 feeds back reliability information (Reliability Info) from the FEC Dec & SC DeMap 30.

FIG. 15 is a block diagram illustrating the deviation estimation circuit 27 of FIG. In FIG. 15, the deviation estimation circuit 27 includes a dither search unit 207 in addition to FIG. The dither search unit 207 obtains the deviation γ _k based on the existing reliability information in the FEC circuit from the FEC Dec & SC DeMap 30 and outputs the deviation γ _k to the complex coefficient 205. Thereby, deviation estimation can be performed simply.

  As described above, according to the sixth embodiment, the deviation estimation circuit feeds back reliability information from the FEC Dec & SC DeMap, so that the wavelength dispersion of the optical fiber as well as the frequency or phase deviation of the light source and the clock source can be obtained. Can be compensated simultaneously.

  1, 1A, 1B transmitter, 2 receiver, 3 optical fiber, 11 FEC Enc & SC Map (mapping unit), 12 Mod (signal modulation unit), 13 IDFT, 14 CP Add, 15 DAC (DA conversion unit), 16 First CLK (first clock part), 17 Opt Mod (light modulation part), 18 First LD (first light source part), 21 Opt DeMod (light demodulation part), 22 Second LD (second light source part), 23 ADC (AD conversion unit), 24 2nd CLK (second clock unit), 25 DFT (signal demodulation unit), 26 Frame Sync, 27 Deviation estimation circuit (deviation estimation unit), 28 Compensation unit, 29 DeMod, 30 FEC Dec & SC DeMap, 201 Declination extraction unit, 202 Differentiation unit, 202A Subtraction unit, 203, 203A, 203B, 203C, 03D 1-order interpolation processing unit, 204 integral unit, 205 complex coefficients of, 206 deviation calculation unit, 207 dither search unit.

Claims (22)

An optical communication system in which a transmitter and a receiver communicate with each other using an optical fiber as a transmission path,
The transmitter is
A pilot signal generator for generating a plurality of pilot signals;
A mapping unit that maps a signal input to the transmitter to a subcarrier frequency and accommodates it as a multi-level signal together with the pilot signal;
A signal modulator for converting the multilevel signal into a frequency domain complex value;
A Fourier transform unit for transforming the frequency domain complex value into a time domain complex value;
A first clock unit for generating a transmission clock;
A DA converter that samples the time-domain complex value with the transmission clock and converts it into an analog baseband signal;
A first light source unit for generating a transmission light source;
An optical modulator that up-converts the analog baseband signal into a transmission optical signal by the transmission light source, and
The receiver
A second light source unit for generating a local light source;
An optical demodulation unit that down-converts the transmission optical signal into an analog baseband signal by the local light source;
A second clock unit for generating a local clock;
Sampling the analog baseband signal with the local clock and converting it into a time domain digital signal;
A signal demodulator for converting the time domain digital signal into a frequency domain complex value;
Based on the pilot signal selected from the frequency domain complex value, a phase estimator of the light source is estimated, and a deviation estimator for obtaining a complex equalization coefficient by linear approximation;
An optical communication system, comprising: a compensation unit that calculates a complex product based on the frequency domain complex value and the complex equalization coefficient. The optical communication system according to claim 1, wherein the mapping unit arranges the two pilot signals at positions corresponding to positive and negative symmetric subcarrier numbers. The optical communication system according to claim 1, wherein the deviation estimation unit controls a frequency of the second light source unit. The optical communication system according to any one of claims 1 to 3, wherein the deviation estimation unit controls a frequency of the second clock unit. The optical communication system according to any one of claims 1 to 4, wherein the deviation estimation unit controls a frequency of the first light source unit. The optical communication system according to any one of claims 1 to 5, wherein the deviation estimation unit controls a frequency of the first clock unit. Comprising a plurality of said transmitters,
The optical communication system according to any one of claims 1 to 4, wherein the deviation estimation unit controls frequencies of the plurality of first light source units. Comprising a plurality of said transmitters,
The optical communication system according to any one of claims 1 to 4, or 7, wherein the deviation estimation unit controls frequencies of the plurality of first clock units. The optical communication system according to claim 1, wherein the deviation estimation unit and the compensation unit constitute a feedback loop . The optical communication system according to claim 1, wherein the deviation estimation unit feeds back a signal after equalization processing in the compensation unit. The receiver further includes an error correction unit that performs error correction on the signal after equalization processing in the compensation unit,
The optical communication system according to claim 1, wherein the deviation estimation unit feeds back reliability information from the error correction unit. An optical communication method executed by an optical communication system in which a transmitter and a receiver communicate with each other using an optical fiber as a transmission path,
A pilot signal generation step of generating a plurality of pilot signals;
A mapping step of mapping a signal input to the transmitter to a subcarrier frequency and accommodating the signal as a multi-level signal together with the pilot signal;
A signal modulation step of converting the multilevel signal into a frequency domain complex value;
A Fourier transform step of transforming the frequency domain complex value to a time domain complex value;
A first clock generation step of generating a transmission clock;
A DA conversion step of sampling the time domain complex value with the transmission clock and converting it to an analog baseband signal;
A first light source generating step for generating a transmission light source;
An optical modulation step of up-converting the analog baseband signal into a transmission optical signal by the transmission light source;
A second light source generating step for generating a local light source;
An optical demodulation step of down-converting the transmission optical signal into an analog baseband signal by the local light source;
A second clock generating step for generating a local clock;
Sampling the analog baseband signal with the local clock and converting it to a time domain digital signal;
A signal demodulation step of converting the time domain digital signal into a frequency domain complex value;
A deviation estimating step for estimating a phase deviation of a light source based on the pilot signal selected from the frequency domain complex value and obtaining a complex equalization coefficient by linear approximation;
A compensation step for computing a complex product based on the frequency domain complex value and the complex equalization coefficient;
An optical communication method comprising: The optical communication method according to claim 12, wherein the mapping step arranges the two pilot signals at positions corresponding to positive and negative symmetric subcarrier numbers. The optical communication method according to claim 12 or 13, wherein the deviation estimating step controls a frequency of a local light source generated in the second light source step. The optical communication method according to any one of claims 12 to 14, wherein the deviation estimation step controls a frequency of a local clock generated in the second clock step. The optical communication method according to any one of claims 12 to 15, wherein the deviation estimation step controls a frequency of the transmission light source generated in the first light source step. The optical communication method according to any one of claims 12 to 16, wherein the deviation estimation step controls a frequency of a transmission clock generated in the first clock step. A plurality of said transmitters are provided;
The deviation estimation step controls a frequency of a transmission light source generated in the first light source step in each of the plurality of transmitters. 16. Optical communication method. A plurality of said transmitters are provided;
The deviation estimation step controls a frequency of a transmission clock generated in the first clock step in each of the plurality of transmitters. 16. The optical communication method according to claim 18. The optical communication method according to claim 12 or 13, wherein the deviation estimation step and the compensation step form a feedback loop . The optical communication method according to claim 12 or 13, wherein the deviation estimation step feeds back the signal after the equalization processing in the compensation step. The signal after the equalization processing in the compensation step further comprises an error correction step for performing error correction,
The optical communication method according to claim 12 or 13, wherein the deviation estimation step feeds back reliability information from the error correction step.

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