Estimation device, estimation method, and program

Abstract

This estimation device comprises: a difference derivation unit that derives a first power difference between a positive-side frequency component and a negative-side frequency component of a reception signal or derives a second power difference between a positive-side time component and a negative-side time component of the reception signal; and an offset estimation unit that estimates a frequency offset value for the reception signal on the basis of the first power difference or the second power difference. The estimation device can further comprise a compensation unit that compensates for frequency offset by using the frequency offset value. The compensation unit can compensate for the frequency offset of the reception signal on the basis of a predetermined offset value when there is a plurality of frequency offset value candidates.

Description

[Technical Field]

[0001] The present invention relates to an estimation device, an estimation method, and a program. [Background technology]

[0002] In digital coherent optical communications, the frequency of the laser light used for transmission may be matched with the frequency of the laser light (local oscillator) used for reception, and homodyne reception may be performed in the receiving device. Typically, the deviation (frequency offset value) between the frequency of the laser light used for transmission and the frequency of the laser light used for reception is within a range of ±5 GHz. For example, the standard "400ZR" established by the standardization organization "OIF (The Optical Internetworking Forum)" specifies a range of ±3.6 GHz.

[0003] In demodulating a received signal, it is necessary to estimate the frequency offset value of the received signal and compensate for the frequency offset based on the frequency offset estimation result. For example, the frequency offset value is estimated using the fourth power algorithm, which utilizes the distribution characteristics of a Quadrature Phase Shift Keying (QPSK) signal. Therefore, the frequency offset value is often estimated after the frequency offset is compensated for using an adaptive filter (see Non-Patent Documents 1, 2, and 3). Here, the frequency offset value is estimated within the applicable range of the adaptive filter. Therefore, the estimable frequency offset range is approximately 5 GHz when a 100 Gbit / s-class coherent DSP (Digital Signal Processor)-LSI (Large Scale Integrated circuit) is used.

[0004] In recent years, digital coherent optical communications have been applied not only to medium-distance applications such as intercity and long-distance applications such as intercontinental, but also to short-distance applications such as within data centers. Especially in short-distance applications, it is important that communication equipment is small and inexpensive. Therefore, there is a demand for lasers installed in communication equipment to be small and inexpensive. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] I. Fatadin and SJ Savory, "Compensation of Frequency Offset for 16-QAM Optical Coherent Systems Using QPSK Partitioning," in IEEE Photonics Technology Letters, vol. 23, no. 17, pp. 1246-1248, Sept. 1, 2011, doi: 10.1109 / LPT.2011.2158994. [Non-patent document 2] M. Selmi, Y. Jaouen and P. Ciblat, "Accurate digital frequency offset estimator for coherent PolMux QAM transmission systems," 2009 35th European Conference on Optical Communication, 2009, pp.1-2. [Non-patent document 3] Q. Yan, L. Liu and X. Hong, "Blind Carrier Frequency Offset Estimation in Coherent Optical Communication Systems With Probabilistically Shaped M-QAM," in Journal of Lightwave Technology, vol. 37, no. 23, pp. 5856-5866, 1 Dec.1, 2019, doi: 10.1109 / JLT.2019.2940770. Summary of the Invention [Problem to be solved by the invention]

[0006] However, the frequency offset of an optical signal generated using a small and inexpensive laser is wider than that of an optical signal generated using a large or expensive laser, and is, for example, several tens of GHz. When the frequency offset of an electrical signal (received signal) converted from a received optical signal is wide, there is a problem in that it is not possible to estimate the wide frequency offset occurring in the frequency of the received signal using a receiving device with a simple configuration.

[0007] In view of the above circumstances, an object of the present invention is to provide an estimation device, an estimation method, and a program that are capable of estimating a wide range of frequency offsets that occur in the frequency of a received signal using a receiving device with a simple configuration. [Means for solving the problem]

[0008] One aspect of the present invention is an estimation device including: a difference derivation unit that derives a first power difference between a positive-side frequency component and a negative-side frequency component of a received signal, or a second power difference between a positive-side time component and a negative-side time component of the received signal; and an offset estimation unit that estimates a frequency offset value of the received signal based on the first power difference or the second power difference.

[0009] One aspect of the present invention is an estimation method executed by an estimation device, the estimation method including the steps of deriving a first power difference between a positive frequency component and a negative frequency component of a received signal, or deriving a second power difference between a positive time component and a negative time component of the received signal, and estimating a frequency offset value of the received signal based on the first power difference or the second power difference.

[0010] One aspect of the present invention is a program for causing a computer to execute the steps of deriving a first power difference between a positive frequency component and a negative frequency component of a received signal, or deriving a second power difference between a positive time component and a negative time component of the received signal, and estimating a frequency offset value of the received signal based on the first power difference or the second power difference. [Effects of the Invention]

[0011] According to the present invention, it is possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a communication system in a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of a demodulation unit in the first embodiment. [Figure 3] FIG. 3 is a diagram illustrating an example of a frequency spectrum of a received signal in the first embodiment. [Figure 4] FIG. 4 is a diagram illustrating an example of the relationship between a frequency offset and a power difference in the first embodiment. [Figure 5] 5 is a flowchart showing an example of the operation of the receiving device in the first embodiment. [Figure 6] FIG. 10 is a diagram illustrating an example of the configuration of a demodulation unit in the second embodiment. [Figure 7] FIG. 11 is a diagram illustrating an example of the configuration of a demodulation unit in the third embodiment. [Figure 8]FIG. 13 is a diagram illustrating an example of the configuration of a demodulation unit in a fourth embodiment. [Figure 9] FIG. 13 is a diagram illustrating an example of the configuration of a demodulation unit in the fifth embodiment. [Figure 10] FIG. 20 is a diagram illustrating an example of the configuration of a demodulation unit in the sixth embodiment. [Figure 11] FIG. 20 is a diagram illustrating an example of the configuration of a demodulation unit in the seventh embodiment. [Figure 12] FIG. 20 is a diagram illustrating an example of the configuration of a demodulation unit in the eighth embodiment. [Figure 13] FIG. 13 is a diagram illustrating an example of the configuration of a demodulation unit in the ninth embodiment. [Figure 14] FIG. 23 is a diagram illustrating an example of the configuration of a demodulation unit in the tenth embodiment. [Figure 15] FIG. 23 is a diagram illustrating an example of the configuration of a demodulation unit in the eleventh embodiment. [Figure 16] FIG. 23 is a diagram illustrating an example of the configuration of a demodulation unit in the twelfth embodiment. [Figure 17] FIG. 23 is a diagram illustrating an example of the configuration of a demodulation unit in the thirteenth embodiment. [Figure 18] FIG. 23 is a diagram illustrating an example of the configuration of a demodulation unit in the fourteenth embodiment. [Figure 19] FIG. 23 is a diagram illustrating an example of the configuration of a demodulation unit in the fifteenth embodiment. [Figure 20] FIG. 23 is a diagram illustrating an example of the configuration of a demodulation unit in the sixteenth embodiment. [Figure 21] FIG. 23 is a diagram illustrating an example of a frequency spectrum of a received signal in the seventeenth embodiment. [Figure 22] FIG. 23 is a diagram illustrating an example of a peak of a power difference in the seventeenth embodiment. [Figure 23] 23 is a flowchart showing an example of the operation of the receiving device in the seventeenth embodiment. [Figure 24] FIG. 23 is a diagram illustrating an example of the dependency of the power difference on the FFT size (number of samples) in the seventeenth embodiment. [Figure 25] FIG. 23 is a diagram illustrating an example of a data table for each roll-off value of the Nyquist filter in the seventeenth embodiment. [Figure 26] FIG. 2 is a diagram illustrating an example of a hardware configuration of a receiving device in each embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. (First embodiment) 1 is a diagram showing an example of the configuration of a communication system 1a in the first embodiment. The communication system 1a is a system that communicates using optical signals. The communication system 1a includes a transmitter 2, an optical fiber 3, one or more (for example, four) amplifiers 4, and a receiver 5. Here, the communication system 1a includes the optical fiber 3 and the amplifier 4 as a transmission path for the optical signal.

[0014] First, the transmitting device 2 will be described. The transmitting device 2 includes an interface 21, a transmission signal processing unit 22, a modulator driver group 23, and an optical transmitter 24. The transmission signal processing unit 22 includes a framer 221, an error correction coding unit 222, a modulator 223, and a digital-to-analog converter group 224. The optical transmitter 24 includes a laser diode 241, an X-polarized wave optical converter 242, a Y-polarized wave optical converter 243, and a polarization beam combiner 244.

[0015] The interface 21 is an electrical interface on the client (user) side and outputs a client signal (user signal) to be transmitted to a transmission signal processing unit 22.

[0016] The transmission signal processing unit 22 is a functional unit that performs predetermined processing on the client signal to be transmitted. The framer 221 converts the client signal into a transmission signal in a predetermined frame format. The error correction coding unit 222 performs predetermined error correction coding processing on the transmission signal.

[0017] The modulation unit 223 performs a predetermined modulation process on the transmission signal that has been error-correction coded. The digital-to-analog converter group 224 (DAC: Digital to analog converter) converts the modulated transmission signal (analog signal) into a digital transmission signal (X-polarized I-channel signal "XI", X-polarized Q-channel signal "XQ", Y-polarized I-channel signal "YI", and Y-polarized Q-channel signal "YQ"). The modulator driver group 23 (optical modulator driver amplifier) ​​amplifies the power of the digital (electrical) transmission signal.

[0018] The optical transmitter 24 is a device that transmits an optical signal. A laser diode 241 (LD: Laser Diode) outputs laser light of a predetermined frequency to an X-polarized light converter 242 and a Y-polarized light converter 243. The X-polarized light converter 242 uses the laser light to generate an X-polarized polarized wave in accordance with an X-polarized I-channel signal and an X-polarized Q-channel signal. The Y-polarized light converter 243 uses the laser light to generate a Y-polarized polarized wave in accordance with a Y-polarized I-channel signal and a Y-polarized Q-channel signal.

[0019] The polarization beam combiner 244 combines polarized waves whose polarization planes are orthogonal to each other. That is, the polarization beam combiner 244 combines an X-polarized polarized wave and a Y-polarized polarized wave. The polarization beam combiner 244 transmits the combined polarized wave optical signal to the receiving device 5 via a transmission path. In the transmission path, an optical fiber 3 transmits the optical signal. In the transmission path, an amplifier 4 amplifies the power of the optical signal.

[0020] Next, the receiving device 5 will be described. The receiving device 5 includes an optical receiver 51, a transimpedance amplifier group 52, a received signal processing unit 53, and an interface 54. The optical receiver 51 includes a local oscillator 511, a signal extraction circuit 512, and a detector 513. The received signal processing unit 53 includes an analog-to-digital converter group 531, a demodulation unit 532a, an error correction decoding unit 533, and a framer 534.

[0021] The optical receiver 51 is a device that receives an optical signal. A local oscillator 511 (LO) outputs local light (laser light) of a predetermined frequency to a signal extraction circuit 512. The signal extraction circuit 512 is a circuit (functional unit) that extracts the received signal, and is, for example, a 90-degree optical hybrid circuit. The 90-degree optical hybrid circuit includes a polarization beam splitter (PBS). The signal extraction circuit 512 mixes the optical signal received by the polarization beam splitter with the local light output from the local oscillator 511. In this way, the signal extraction circuit 512 extracts the in-phase component (I) and quadrature component (Q) of the electric field from the received optical signal.

[0022] The detector 513 detects the I-channel and Q-channel signals of X-polarized light and the I-channel and Q-channel signals of Y-polarized light from the mixing result (extraction result). The detector 513 is, for example, a balanced photodetector. The detector 513 outputs a current reception signal (electrical signal) corresponding to the detection result to an analog-to-digital converter group 531 (ADC: Analog to digital converter).

[0023] The transimpedance amplifier group 52 converts the current of the received signal output from the detector 513 into a voltage. Based on the conversion result, the transimpedance amplifier group 52 outputs the received signal to the received signal processing unit 53. The received signal processing unit 53 performs predetermined signal processing on the received signal. The analog-to-digital converter group 531 converts the received signal (analog signal) corresponding to the voltage into a digital received signal.

[0024] The demodulator 532a performs a predetermined demodulation process on the digital received signal. Here, the demodulator 532a (estimation device) estimates a frequency offset value in the received signal. The demodulator 532a (compensation device) compensates for the frequency offset in the received signal based on the estimated frequency offset value. The demodulator 532a also demodulates the received signal by performing predetermined signal processing. This predetermined signal processing is, for example, polarization separation and frequency characteristic compensation using adaptive equalization, chromatic dispersion compensation, or phase compensation.

[0025] The error correction decoder 533 performs a predetermined error correction decoding process on the demodulated received signal. The framer 534 converts the received signal into a client signal (user signal) based on the frame format of the received signal. The interface 54 is an electrical interface on the client (user) side. The interface 54 outputs the received client signal (user signal) to a user device (not shown).

[0026] Next, the demodulation unit 532a will be described. 2 is a diagram showing an example of the configuration of a demodulation unit 532a in the first embodiment. The demodulation unit 532a includes a fast Fourier transform unit 500, a positive-side band-pass filter 501a, a negative-side band-pass filter 502a, a power derivation unit 503a, a power derivation unit 504a, a difference derivation unit 505, an offset estimation unit 506, a compensation unit 507a, and a signal demodulation unit 508.

[0027] In the first embodiment, in the positive and negative frequency domains with frequency "0" as the reference (domain boundary), each band-pass filter is used for the positive frequency component and the negative frequency component, and the frequency offset value of the received signal is estimated. The compensation unit 507a performs processing to compensate for the frequency offset of the received signal on the output of the fast Fourier transform unit 500.

[0028] The fast Fourier transform unit 500 acquires the digital received signal from the analog-to-digital converter group 531. The fast Fourier transform unit 500 performs a fast Fourier transform on the digital received signal, thereby converting the acquired received signal into a received signal in the frequency domain.

[0029] Positive-side band-pass filter 501a extracts positive-side frequency components from the received signal in the frequency domain. Positive-side band-pass filter 501a outputs the extracted positive-side frequency components to power derivation unit 503a. Negative-side band-pass filter 502a extracts negative-side frequency components from the received signal in the frequency domain. Negative-side band-pass filter 502a outputs the extracted negative-side frequency components to power derivation unit 504a.

[0030] Fig. 3 is a diagram showing an example of the frequency spectrum (power spectrum) of a received signal in the first embodiment. The modulation rate of the received signal shown in Fig. 3 is, for example, 60 GBd. When the frequency offset value is "0 GHz", the power spectrum of the positive-side frequency components and the power spectrum of the negative-side frequency components are almost symmetrical with the frequency "0 GHz" as the axis. In contrast, when the frequency offset value is other than "0 GHz" (for example, 6 GHz), the power spectrum of the positive-side frequency components and the power spectrum of the negative-side frequency components are asymmetrical with the frequency "0 GHz" as the axis.

[0031] Returning to FIG. 2, the description of the exemplary configuration of the demodulation unit 532a continues. The power derivation unit 503a derives the power value of the power spectrum of the extracted positive side frequency component. In order to suppress noise, the power derivation unit 503a may acquire the extracted positive side frequency component multiple times. The power derivation unit 503a may perform averaging processing on the positive side frequency component acquired multiple times. The averaging processing may be a simple averaging processing, or may be averaging processing using a forgetting factor "ρ". The averaging processing using a forgetting factor "ρ" for the positive side frequency component is expressed, for example, as in Equation (1).

[0032]

number

[0033] Here, "F abs+ "(f)" represents the average of the squares of the absolute values ​​of the positive frequency components acquired multiple times (averaged positive frequency components). abs+ (f)" represents the square of the absolute value of the positive frequency component acquired once. The power value of the power spectrum of the positive frequency component "P + " is expressed, for example, as in equation (2).

[0034]

number

[0035] The power derivation unit 504a derives the power value of the power spectrum of the extracted negative frequency components. In order to suppress noise, the power derivation unit 504a may obtain the square of the absolute value of the extracted negative frequency components multiple times. The power derivation unit 504a may perform averaging processing on the square of the absolute value of the negative frequency components obtained multiple times. The averaging processing in which a forgetting factor "ρ" is used for the square of the absolute value of the negative frequency components is expressed as shown in Equation (3).

[0036]

number

[0037] Here, "F abs- "F' (f)" represents the average of the squares of the absolute values ​​of the negative frequency components acquired multiple times (averaged negative frequency components). abs- (f)" represents the square of the absolute value of the negative frequency component acquired once. The power value of the power spectrum of the negative frequency component, "P - " is expressed as equation (4).

[0038]

number

[0039] The difference derivation unit 505 calculates the power value “P + ” and the power value of the power spectrum of the negative frequency component “P - The difference (power difference) between the power difference "P diff " is expressed as equation (5).

[0040]

number

[0041] The offset estimation unit 506 estimates a frequency offset value of the received signal based on the derived power difference (first power difference). The offset estimation unit 506 estimates the frequency offset value of the received signal based on, for example, a predetermined conversion formula and the derived power difference. The offset estimation unit 506 may estimate the frequency offset value of the received signal based on, for example, a predetermined data table and the derived power difference. In this data table, frequency offset values ​​and power differences are associated with each other based on, for example, previous measurement results.

[0042] The compensation unit 507a (compensation circuit) receives the frequency domain received signal as input from the fast Fourier transform unit 500. The compensation unit 507a receives the estimated frequency offset value as input from the offset estimation unit 506. The compensation unit 507a compensates for the frequency offset of the received signal based on the estimated frequency offset value. The compensation unit 507a outputs the received signal with the frequency offset compensated for to the signal demodulation unit 508. The signal demodulation unit 508 performs a predetermined demodulation process on the received signal with the frequency offset compensated for. The signal demodulation unit 508 outputs the demodulated received signal to the error correction decoding unit 533.

[0043] 4 is a diagram showing an example of the relationship between the frequency offset value and the power difference in the first embodiment. Data representing the relationship between the frequency offset value and the power difference is stored in a predetermined storage unit of the demodulation unit 532a, for example, in the form of a data table. In the data table, a power difference of "0" is associated with a frequency offset value of "0".

[0044] Next, an example of the operation of the receiving device 5 will be described. 5 is a flowchart showing an example of operation of the receiving device 5 in the first embodiment. The difference derivation unit 505 derives a power difference between the positive-side frequency component and the negative-side frequency component of the received signal (step S101). The offset estimation unit 506 estimates a frequency offset value of the received signal based on the power difference between the positive-side frequency component and the negative-side frequency component (step S102). The compensation unit 507a compensates for the frequency offset using the estimated frequency offset value (step S103).

[0045] As described above, the difference derivation unit 505 derives a power difference (first power difference) between the positive frequency component and the negative frequency component of the received signal (electrical signal) converted from the received optical signal. The offset estimation unit 506 estimates a frequency offset value of the received signal based on the first power difference. The compensation unit 507a compensates for the frequency offset of the received signal using the frequency offset value.

[0046] This makes it possible to estimate a wide range of frequency offsets that occur in the frequency of a received signal using a receiver with a simple configuration, and even when a small, inexpensive laser that is prone to wide frequency offsets is used in the receiver configuration, highly reliable optical communications can be achieved.

[0047] (Second embodiment) The second embodiment is mainly different from the first embodiment in that the compensation unit compensates for the frequency offset of the received signal by adjusting the frequency of the local light of the local oscillator. The second embodiment will be described focusing on the differences from the first embodiment.

[0048] 6 is a diagram showing an example of the configuration of a demodulation unit 532b in the second embodiment. The demodulation unit 532b includes a fast Fourier transform unit 500, a positive-side band-pass filter 501b, a negative-side band-pass filter 502b, a power derivation unit 503b, a power derivation unit 504b, a difference derivation unit 505, an offset estimation unit 506, a signal demodulation unit 508, and a laser frequency control unit 600b. The laser frequency control unit 600b may be implemented in, for example, a signal processing circuit inside the demodulation unit 532b, or may be implemented in, for example, an FPGA (Field Programmable Gate Array) (not shown) outside the demodulation unit 532b.

[0049] In the second embodiment, a bandpass filter is used for each of the positive and negative frequency components in the frequency domain to estimate the frequency offset value of the received signal. The laser frequency control unit 600b adjusts the frequency of the local light of the local oscillator 511 to compensate for the frequency offset of the received signal.

[0050] The estimated frequency offset value is input to the laser frequency control unit 600b (compensation circuit) from the offset estimation unit 506. The laser frequency control unit 600b compensates for the frequency offset of the received signal based on the estimated frequency offset value. The laser frequency control unit 600b adjusts the frequency of the local light of the local oscillator 511 based on the estimated frequency offset value. As a result, the fast Fourier transform unit 500 outputs the received signal, whose frequency offset has been compensated, to the signal demodulation unit 508.

[0051] The demodulation unit 532b may further include a compensation unit (not shown) separate from the laser frequency control unit 600b at a stage subsequent to the fast Fourier transform unit 500. The compensation unit (not shown) separate from the laser frequency control unit 600b may perform highly accurate compensation processing for frequency offset on the received signal output from the fast Fourier transform unit 500.

[0052] As described above, the difference derivation unit 505 derives the power difference (first power difference) between the positive frequency component and the negative frequency component of the received signal (electrical signal) converted from the received optical signal. The offset estimation unit 506 estimates the frequency offset value of the received signal based on the first power difference. The laser frequency control unit 600b (compensation unit) compensates for the frequency offset of the received signal by adjusting (feeding back) the frequency of the local light of the local oscillator 511.

[0053] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0054] (Third embodiment) The third embodiment is mainly different from the first embodiment in that a bandpass filter is used in the time domain to estimate the frequency offset value of the received signal. The third embodiment will be described focusing on the differences from the first embodiment.

[0055] 7 is a diagram illustrating an example of the configuration of a demodulation unit 532c in the third embodiment. The demodulation unit 532c includes a positive-side band-pass filter 501c, a negative-side band-pass filter 502c, a power derivation unit 503c, a power derivation unit 504c, a difference derivation unit 505, an offset estimation unit 506, a compensation unit 507c, and a signal demodulation unit 508.

[0056] In the third embodiment, a band-pass filter is used for each of the positive and negative time components in the time domain to estimate the frequency offset value of the received signal. The compensation unit 507c performs a process of compensating for the frequency offset of the received signal in the time domain (time series) on the output of the analog-to-digital converter group 531.

[0057] Positive-side band-pass filter 501c extracts positive-side time components from the received signal in the time domain (time series). Positive-side band-pass filter 501c outputs the extracted positive-side time components to power derivation unit 503c. Negative-side band-pass filter 502c extracts negative-side time components from the received signal in the time domain (time series). Negative-side band-pass filter 502c outputs the extracted negative-side time components to power derivation unit 504c.

[0058] The power derivation unit 503c derives the power value of the power spectrum of the extracted positive time component. The power derivation unit 504c derives the power value of the power spectrum of the extracted negative time component. The difference derivation unit 505 derives the power value of the power spectrum of the positive time component, "P + ” and the power value of the power spectrum of the negative time component “P - " and the frequency offset value of the received signal (second power difference). The offset estimation unit 506 estimates the frequency offset value of the received signal based on the derived power difference (second power difference).

[0059] The compensation unit 507c (compensation circuit) receives a time-domain (time-series) received signal from the analog-to-digital converter group 531. The compensation unit 507c receives an estimated frequency offset value from the offset estimation unit 506. The compensation unit 507c compensates for the frequency offset of the received signal based on the estimated frequency offset value. The compensation unit 507c outputs the received signal with the frequency offset compensated for to the signal demodulation unit 508.

[0060] As described above, the difference derivation unit 505 derives a power difference (second power difference) between the positive time component and the negative time component of the received signal (electrical signal) converted from the received optical signal. The offset estimation unit 506 estimates a frequency offset value of the received signal based on the second power difference. The compensation unit 507c compensates for the frequency offset of the received signal using the frequency offset value.

[0061] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0062] (Fourth embodiment) The fourth embodiment is mainly different from the second embodiment in that a bandpass filter is used in the time domain to estimate the frequency offset value of the received signal. The fourth embodiment will be described focusing on the differences from the second embodiment.

[0063] 8 is a diagram showing an example of the configuration of a demodulation unit 532d in the fourth embodiment. The demodulation unit 532d includes a positive-side band-pass filter 501c, a negative-side band-pass filter 502d, a power derivation unit 503d, a power derivation unit 504d, a difference derivation unit 505, an offset estimation unit 506, a signal demodulation unit 508, and a laser frequency control unit 600d. The laser frequency control unit 600d may be implemented in, for example, a signal processing circuit inside the demodulation unit 532d, or may be implemented in, for example, an FPGA (not shown) outside the demodulation unit 532d.

[0064] In the fourth embodiment, a frequency offset value of the received signal is estimated by using bandpass filters for the positive and negative time components in the time domain. The laser frequency control unit 600d compensates for the frequency offset of the received signal by adjusting (feeding back) the frequency of the local light of the local oscillator 511.

[0065] Positive-side band-pass filter 501d extracts positive-side time components from the received signal in the time domain (time series). Positive-side band-pass filter 501d outputs the extracted positive-side time components to power derivation unit 503d. Negative-side band-pass filter 502d extracts negative-side time components from the received signal in the time domain (time series). Negative-side band-pass filter 502c outputs the extracted negative-side time components to power derivation unit 504d.

[0066] The power derivation unit 503d derives the power value of the power spectrum of the extracted positive time component. The power derivation unit 504d derives the power value of the power spectrum of the extracted negative time component. The difference derivation unit 505 derives the power value of the power spectrum of the positive time component, "P +” and the power value of the power spectrum of the negative time component “P - " and derives a difference (power difference) between the received signal and the power difference (second power difference). The offset estimation unit 506 estimates the frequency offset value of the received signal based on the derived power difference (second power difference). The laser frequency control unit 600d adjusts the frequency of the local light of the local oscillator 511 based on the estimated frequency offset value. As a result, the analog-to-digital converter group 531 outputs the received signal, the frequency offset of which has been compensated, to the signal demodulation unit 508.

[0067] The demodulation unit 532d may further include a compensation unit (not shown) separate from the laser frequency control unit 600d, at a stage subsequent to the analog-to-digital converter group 531. The compensation unit (not shown) separate from the laser frequency control unit 600d may perform highly accurate compensation processing for frequency offset on the reception signal output from the analog-to-digital converter group 531.

[0068] As described above, the difference derivation unit 505 derives the power difference (second power difference) between the positive time component and the negative time component of the received signal (electrical signal) converted from the received optical signal. The offset estimation unit 506 estimates the frequency offset value of the received signal based on the second power difference. The laser frequency control unit 600d (compensation unit) compensates for the frequency offset of the received signal by adjusting (feeding back) the frequency of the local light of the local oscillator 511.

[0069] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0070] (Fifth embodiment) The fifth embodiment is mainly different from the first embodiment in that a low-pass filter is used to estimate the frequency offset value of the received signal. The fifth embodiment will be described focusing on the differences from the first embodiment.

[0071] 9 is a diagram illustrating an example of the configuration of a demodulation unit 532e in the fifth embodiment. The demodulation unit 532e includes a fast Fourier transform unit 500, a power derivation unit 503e, a power derivation unit 504e, a difference derivation unit 505, an offset estimation unit 506, a compensation unit 507e, a signal demodulation unit 508, a positive shift unit 509e, a negative shift unit 510e, a low-pass filter 514e, and a low-pass filter 515e.

[0072] In the fifth embodiment, a frequency offset value of a received signal is estimated by using low-pass filters for positive and negative frequency components in the frequency domain. A compensation unit 507e performs a process of compensating for the frequency offset of the received signal on the output of the fast Fourier transform unit 500.

[0073] The positive shift unit 509e shifts the frequency domain received signal output from the fast Fourier transform unit 500 in the positive or negative direction by a predetermined frequency. This predetermined frequency is determined in advance so that the low-pass filter 514e can extract the positive frequency component from the shifted frequency domain received signal.

[0074] The negative shift unit 510e shifts the frequency domain received signal output from the fast Fourier transform unit 500 in the negative or positive direction by a predetermined frequency. This predetermined frequency is determined in advance so that the low-pass filter 515e can extract negative frequency components from the shifted frequency domain received signal.

[0075] The low-pass filter 514e extracts positive frequency components from the shifted frequency domain received signal. The low-pass filter 514e outputs the extracted positive frequency components to the power derivation unit 503e. The low-pass filter 515e extracts negative frequency components from the shifted frequency domain received signal. The low-pass filter 515e outputs the extracted negative frequency components to the power derivation unit 504e.

[0076] The power derivation unit 503e derives the power value of the power spectrum of the extracted positive frequency component, and the power derivation unit 504e derives the power value of the power spectrum of the extracted negative frequency component.

[0077] The difference derivation unit 505 calculates the power value “P + ” and the power value of the power spectrum of the negative frequency component “P - The offset estimation unit 506 estimates the frequency offset value of the received signal based on the derived power difference.

[0078] The compensating unit 507e compensates for the frequency offset of the received signal based on the estimated frequency offset value. The compensating unit 507e outputs the received signal with the frequency offset compensated for to the signal demodulating unit 508. The signal demodulating unit 508 performs a predetermined demodulation process on the received signal with the frequency offset compensated for. The signal demodulating unit 508 outputs the received signal with the demodulated process performed to the error correction decoding unit 533.

[0079] As described above, in the frequency domain, the low-pass filter 514e is used for the positive frequency component, and the low-pass filter 515e is used for the negative frequency component, thereby estimating the frequency offset value of the received signal. The compensation unit 507e performs processing to compensate for the frequency offset of the received signal on the output of the fast Fourier transform unit 500.

[0080] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0081] (Sixth embodiment) The sixth embodiment is mainly different from the fifth embodiment in that the compensation unit compensates for the frequency offset of the received signal by adjusting the frequency of the local light of the local oscillator. The sixth embodiment will be described focusing on the differences from the fifth embodiment.

[0082] 10 is a diagram showing an example of the configuration of a demodulation unit 532f in the sixth embodiment. The demodulation unit 532f includes a fast Fourier transform unit 500, a power derivation unit 503f, a power derivation unit 504f, a difference derivation unit 505, an offset estimation unit 506, a signal demodulation unit 508, a positive shift unit 509f, a negative shift unit 510f, a low-pass filter 514f, a low-pass filter 515f, and a laser frequency control unit 600f. The laser frequency control unit 600f may be implemented in, for example, a signal processing circuit inside the demodulation unit 532f, or may be implemented in, for example, an FPGA (not shown) outside the demodulation unit 532f.

[0083] In the sixth embodiment, a frequency offset value of the received signal is estimated by using low-pass filters for the positive frequency component and the negative frequency component in the frequency domain. The laser frequency control unit 600f compensates for the frequency offset of the received signal by adjusting the frequency of the local light of the local oscillator 511.

[0084] The estimated frequency offset value is input to the laser frequency control unit 600f (compensation circuit) from the offset estimation unit 506. The laser frequency control unit 600f compensates for the frequency offset of the received signal based on the estimated frequency offset value. The laser frequency control unit 600f adjusts the frequency of the local light of the local oscillator 511 based on the estimated frequency offset value. As a result, the fast Fourier transform unit 500 outputs the received signal, whose frequency offset has been compensated, to the signal demodulation unit 508.

[0085] The demodulation unit 532f may further include a compensation unit (not shown) separate from the laser frequency control unit 600f at a stage subsequent to the fast Fourier transform unit 500. The compensation unit (not shown) separate from the laser frequency control unit 600f may perform highly accurate compensation processing for frequency offset on the received signal output from the fast Fourier transform unit 500.

[0086] As described above, in the frequency domain, low-pass filter 514f is used for the positive frequency component, and low-pass filter 515f is used for the negative frequency component, to estimate the frequency offset value of the received signal. Laser frequency control unit 600f (compensation unit) adjusts the frequency of the local light of local oscillator 511 to compensate for the frequency offset of the received signal.

[0087] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0088] (Seventh embodiment) The seventh embodiment is mainly different from the fifth embodiment in that a low-pass filter is used in the time domain to estimate the frequency offset value of the received signal. The seventh embodiment will be described focusing on the differences from the fifth embodiment.

[0089] 11 is a diagram showing an example of the configuration of a demodulation unit 532g in the seventh embodiment. The demodulation unit 532g includes a power derivation unit 503g, a power derivation unit 504g, a difference derivation unit 505, an offset estimation unit 506, a compensation unit 507g, a signal demodulation unit 508, a positive shift unit 509g, a negative shift unit 510g, a low-pass filter 514g, and a low-pass filter 515g.

[0090] In the seventh embodiment, a frequency offset value of the received signal is estimated by using low-pass filters for the positive and negative time components in the time domain. A compensation unit 507g performs a process of compensating for the frequency offset of the received signal on the output of the analog-to-digital converter group 531.

[0091] The positive shift unit 509g shifts the time domain (time series) received signal output from the analog-to-digital converter group 531 in the positive or negative direction by a predetermined frequency. This predetermined frequency is determined in advance so that the low-pass filter 514g can extract the positive frequency component from the shifted time domain received signal.

[0092] The negative shift unit 510g shifts the time domain (time series) received signal output from the analog-to-digital converter group 531 by a predetermined frequency in the negative or positive direction. This predetermined frequency is determined in advance so that the low-pass filter 515g can extract negative frequency components from the shifted time domain received signal.

[0093] The low-pass filter 514g extracts positive frequency components from the shifted time-domain received signal. The low-pass filter 514g outputs the extracted positive frequency components to the power derivation unit 503g. The low-pass filter 515g extracts negative frequency components from the shifted time-domain received signal. The low-pass filter 515g outputs the extracted negative frequency components to the power derivation unit 504g.

[0094] The power derivation unit 503g derives the power value of the power spectrum of the extracted positive frequency component.The power derivation unit 504g derives the power value of the power spectrum of the extracted negative frequency component.

[0095] The difference derivation unit 505 calculates the power value “P + ” and the power value of the power spectrum of the negative frequency component “P - The offset estimation unit 506 estimates the frequency offset value of the received signal based on the derived power difference.

[0096] The compensating unit 507g compensates for the frequency offset of the received signal based on the estimated frequency offset value. The compensating unit 507g outputs the received signal with the frequency offset compensated for to the signal demodulating unit 508. The signal demodulating unit 508 performs a predetermined demodulation process on the received signal with the frequency offset compensated for. The signal demodulating unit 508 outputs the received signal with the demodulated process performed to the error correction decoding unit 533.

[0097] As described above, in the time domain, the frequency offset value of the received signal is estimated using low-pass filter 514g for the positive time component and low-pass filter 515g for the negative time component. Compensation unit 507g performs processing to compensate for the frequency offset of the received signal on the output of analog-to-digital converter group 531.

[0098] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0099] (Eighth embodiment) The eighth embodiment is mainly different from the sixth embodiment in that a low-pass filter is used in the time domain to estimate the frequency offset value of the received signal. The eighth embodiment will be described mainly focusing on the differences from the sixth embodiment.

[0100] 12 is a diagram showing an example of the configuration of a demodulation unit 532h in the eighth embodiment. The demodulation unit 532h includes a power derivation unit 503h, a power derivation unit 504h, a difference derivation unit 505, an offset estimation unit 506, a signal demodulation unit 508, a positive shift unit 509h, a negative shift unit 510h, a low-pass filter 514h, a low-pass filter 515h, and a laser frequency control unit 600h. The laser frequency control unit 600h may be implemented in, for example, a signal processing circuit inside the demodulation unit 532h, or may be implemented in, for example, an FPGA (not shown) outside the demodulation unit 532h.

[0101] In the eighth embodiment, a frequency offset value of the received signal is estimated by using low-pass filters for the positive and negative time components in the time domain. The laser frequency control unit 600h compensates for the frequency offset of the received signal by adjusting the frequency of the local light of the local oscillator 511.

[0102] The positive shift unit 509h shifts the time domain (time series) received signal output from the analog-to-digital converter group 531 in the positive or negative direction by a predetermined frequency. This predetermined frequency is determined in advance so that the low-pass filter 514h can extract the positive frequency component from the shifted time domain received signal.

[0103] The negative shift unit 510h shifts the time domain (time series) received signal output from the analog-to-digital converter group 531 by a predetermined frequency in the negative or positive direction. This predetermined frequency is determined in advance so that the low-pass filter 515h can extract negative frequency components from the shifted time domain received signal.

[0104] The low-pass filter 514h extracts positive frequency components from the shifted time-domain received signal. The low-pass filter 514h outputs the extracted positive frequency components to the power derivation unit 503h. The low-pass filter 515h extracts negative frequency components from the shifted time-domain received signal. The low-pass filter 515h outputs the extracted negative frequency components to the power derivation unit 504h.

[0105] The power derivation unit 503h derives the power value of the power spectrum of the extracted positive time component. The power derivation unit 504h derives the power value of the power spectrum of the extracted negative time component. The difference derivation unit 505 derives the power value of the power spectrum of the positive time component, "P + ” and the power value of the power spectrum of the negative time component “P - " and derives a difference (power difference) between the received signal and the frequency offset value. The offset estimation unit 506 estimates the frequency offset value of the received signal based on the derived power difference. The laser frequency control unit 600h adjusts the frequency of the local light of the local oscillator 511 based on the estimated frequency offset value. As a result, the analog-to-digital converter group 531 outputs the received signal, whose frequency offset has been compensated for, to the signal demodulation unit 508.

[0106] The demodulation unit 532h may further include a compensation unit (not shown) separate from the laser frequency control unit 600h, at a stage subsequent to the analog-digital converter group 531. The compensation unit (not shown) separate from the laser frequency control unit 600h may perform highly accurate compensation processing for frequency offset on the reception signal output from the analog-digital converter group 531.

[0107] As described above, in the time domain, the low-pass filter 514h is used for the positive time component, and the low-pass filter 515h is used for the negative time component, thereby estimating the frequency offset value of the received signal. The laser frequency control unit 600h (compensation unit) adjusts the frequency of the local light of the local oscillator 511 to compensate for the frequency offset of the received signal.

[0108] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0109] (Ninth embodiment) The ninth embodiment is mainly different from the first embodiment in that positive frequency components and negative frequency components are alternately acquired in the frequency domain. The ninth embodiment will be described focusing on the differences from the first embodiment.

[0110] 13 is a diagram illustrating an example of the configuration of a demodulation unit 532i in the ninth embodiment. The demodulation unit 532i includes a fast Fourier transform unit 500, a positive-side band-pass filter 501i, a negative-side band-pass filter 502i, a power derivation unit 503i, a difference derivation unit 505, an offset estimation unit 506, a compensation unit 507i, a signal demodulation unit 508, and switches 516i-1 and 516i-2.

[0111] In the ninth embodiment, positive and negative frequency components are alternately acquired in the frequency domain, and a frequency offset value of the received signal is estimated by using bandpass filters for the positive and negative frequency components in the frequency domain. The compensation unit 507i performs a process of compensating for the frequency offset of the received signal on the output of the fast Fourier transform unit 500.

[0112] The switches 516i-1 and 516i-2 alternately input the frequency domain received signal output from the fast Fourier transform unit 500 to the positive side band-pass filter 501i and the negative side band-pass filter 502i.

[0113] The positive-side band-pass filter 501i extracts positive-side frequency components from the received signal in the frequency domain. The positive-side band-pass filter 501i outputs the extracted positive-side frequency components to the power derivation unit 503i. The negative-side band-pass filter 502i extracts negative-side frequency components from the received signal in the frequency domain. The negative-side band-pass filter 502i outputs the extracted negative-side frequency components to the power derivation unit 503i.

[0114] When the extracted positive-side frequency components are input to the power derivation unit 503i, the power derivation unit 503i derives the power value of the power spectrum of the extracted positive-side frequency components.When the extracted negative-side frequency components are input to the power derivation unit 503i, the power derivation unit 503i derives the power value of the power spectrum of the extracted negative-side frequency components.

[0115] The difference derivation unit 505 calculates the power value “P + ” and the power value of the power spectrum of the negative frequency component “P - " and derives a difference (power difference) between the received signal and the offset estimating unit 506. The offset estimating unit 506 estimates a frequency offset value of the received signal based on the derived power difference. The compensating unit 507i compensates for the frequency offset of the received signal based on the estimated frequency offset value. The compensating unit 507i outputs the received signal with the frequency offset compensated to the signal demodulating unit 508.

[0116] As described above, switch 516i alternately outputs frequency components to positive-side band-pass filter 501i and negative-side band-pass filter 502i. In the frequency domain, the positive-side band-pass filter 501i is used for the positive frequency components, and the negative-side band-pass filter 502i is used for the negative frequency components, thereby estimating the frequency offset value of the received signal. Compensation unit 507i performs a process of compensating for the frequency offset of the received signal on the output of fast Fourier transform unit 500.

[0117] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0118] (Tenth embodiment) The tenth embodiment is mainly different from the second embodiment in that positive frequency components and negative frequency components are alternately acquired in the frequency domain. The tenth embodiment will be described focusing on the differences from the second embodiment.

[0119] 14 is a diagram showing an example of the configuration of a demodulation unit 532j in the tenth embodiment. The demodulation unit 532j includes a fast Fourier transform unit 500, a positive-side band-pass filter 501j, a negative-side band-pass filter 502j, a power derivation unit 503j, a difference derivation unit 505, an offset estimation unit 506, a signal demodulation unit 508, switches 516j-1 and 516j-2, and a laser frequency control unit 600j. The laser frequency control unit 600j may be implemented in, for example, a signal processing circuit inside the demodulation unit 532j, or may be implemented in, for example, an FPGA (not shown) outside the demodulation unit 532j.

[0120] In the tenth embodiment, positive and negative frequency components are alternately acquired in the frequency domain, and a frequency offset value of the received signal is estimated by using bandpass filters for the positive and negative frequency components in the frequency domain. The laser frequency control unit 600j compensates for the frequency offset of the received signal by adjusting the frequency of the local light of the local oscillator 511.

[0121] The estimated frequency offset value is input to the laser frequency control unit 600j (compensation circuit) from the offset estimation unit 506. The laser frequency control unit 600j compensates for the frequency offset of the received signal based on the estimated frequency offset value. The laser frequency control unit 600j adjusts the frequency of the local light of the local oscillator 511 based on the estimated frequency offset value. As a result, the fast Fourier transform unit 500 outputs the received signal, whose frequency offset has been compensated, to the signal demodulation unit 508.

[0122] The demodulation unit 532j may further include a compensation unit (not shown) separate from the laser frequency control unit 600j at a stage subsequent to the fast Fourier transform unit 500. The compensation unit (not shown) separate from the laser frequency control unit 600j may perform highly accurate compensation processing for frequency offset on the received signal output from the fast Fourier transform unit 500.

[0123] As described above, switch 516j alternately outputs frequency components to positive-side band-pass filter 501j and negative-side band-pass filter 502j. In the frequency domain, positive-side band-pass filter 501j is used for positive frequency components, and negative-side band-pass filter 502j is used for negative frequency components, thereby estimating the frequency offset value of the received signal. Laser frequency control unit 600j (compensation unit) adjusts the frequency of the local light of local oscillator 511 to compensate for the frequency offset of the received signal.

[0124] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0125] (Eleventh embodiment) The eleventh embodiment is mainly different from the third embodiment in that positive time components and negative time components are alternately acquired in the time domain. The eleventh embodiment will be described focusing on the differences from the third embodiment.

[0126] 15 is a diagram illustrating an example of the configuration of a demodulation unit 532k in the 11th embodiment. The demodulation unit 532k includes a positive-side band-pass filter 501k, a negative-side band-pass filter 502k, a power derivation unit 503k, a difference derivation unit 505, an offset estimation unit 506, a compensation unit 507k, a signal demodulation unit 508, and switches 516k-1 and 516k-2.

[0127] In the eleventh embodiment, positive and negative time components are alternately acquired in the time domain, and a frequency offset value of the received signal is estimated by using bandpass filters for the positive and negative time components in the time domain. The compensation unit 507k performs a process of compensating for the frequency offset of the received signal on the output of the analog-to-digital converter group 531.

[0128] The switch 516k-1 and the switch 516k-2 alternately input the time domain received signal output from the analog-to-digital converter group 531 to the positive side band-pass filter 501k and the negative side band-pass filter 502k.

[0129] The positive-side band-pass filter 501k extracts positive-side time components from the received signal in the time domain (time series). The positive-side band-pass filter 501k outputs the extracted positive-side time components to the power derivation unit 503k. The negative-side band-pass filter 502k extracts negative-side time components from the received signal in the time domain (time series). The negative-side band-pass filter 502k outputs the extracted negative-side time components to the power derivation unit 503k.

[0130] The power derivation unit 503k derives the power value of the power spectrum of the extracted positive time component. The power derivation unit 503k derives the power value of the power spectrum of the extracted negative time component. The difference derivation unit 505 derives the power value of the power spectrum of the positive time component, "P + ” and the power value of the power spectrum of the negative time component “P - The offset estimation unit 506 estimates the frequency offset value of the received signal based on the derived power difference.

[0131] The compensation unit 507k (compensation circuit) receives a time-domain (time series) received signal from the analog-to-digital converter group 531. The compensation unit 507k receives an estimated frequency offset value from the offset estimation unit 506. The compensation unit 507k compensates for the frequency offset of the received signal based on the estimated frequency offset value. The compensation unit 507k outputs the received signal with the frequency offset compensated for to the signal demodulation unit 508.

[0132] As described above, switch 516k alternately outputs the time component to positive-side band-pass filter 501k and outputs the time component to negative-side band-pass filter 502k. In the time domain, the positive-side band-pass filter 501k is used for the positive time component, and the negative-side band-pass filter 502k is used for the negative time component, to estimate the frequency offset value of the received signal. Compensation unit 507k performs a process of compensating for the frequency offset of the received signal on the output of analog-to-digital converter group 531.

[0133] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0134] (Twelfth embodiment) The twelfth embodiment is mainly different from the fourth embodiment in that positive time components and negative time components are alternately acquired in the time domain. The twelfth embodiment will be described focusing on the differences from the fourth embodiment.

[0135] 16 is a diagram showing an example of the configuration of a demodulation unit 532l in the twelfth embodiment. The demodulation unit 532l includes a positive-side band-pass filter 501l, a negative-side band-pass filter 502l, a power derivation unit 503l, a difference derivation unit 505, an offset estimation unit 506, a signal demodulation unit 508, switches 516l-1 and 516l-2, and a laser frequency control unit 600l. The laser frequency control unit 600l may be implemented in, for example, a signal processing circuit inside the demodulation unit 532l, or may be implemented in, for example, an FPGA (not shown) outside the demodulation unit 532l.

[0136] In the twelfth embodiment, positive and negative time components are alternately acquired in the time domain, and a frequency offset value of the received signal is estimated by using bandpass filters for the positive and negative time components in the time domain. The laser frequency control unit 600l compensates for the frequency offset of the received signal by adjusting the frequency of the local oscillator light of the local oscillator 511.

[0137] The switches 516l-1 and 516l-2 alternately input the time domain received signal output from the fast Fourier transform unit 500 to the positive side band pass filter 501l and the negative side band pass filter 502l.

[0138] Positive-side band-pass filter 501l extracts positive-side time components from the received signal in the time domain (time series). Positive-side band-pass filter 501l outputs the extracted positive-side time components to power derivation unit 503l. Negative-side band-pass filter 502l extracts negative-side time components from the received signal in the time domain (time series). Negative-side band-pass filter 502c outputs the extracted negative-side time components to power derivation unit 504l.

[0139] The power derivation unit 503l derives the power value of the power spectrum of the extracted positive time component. The power derivation unit 504l derives the power value of the power spectrum of the extracted negative time component. The difference derivation unit 505 derives the power value of the power spectrum of the positive time component, "P+ ” and the power value of the power spectrum of the negative time component “P - " and derives a difference (power difference) between the received signal and the frequency offset value. The offset estimation unit 506 estimates the frequency offset value of the received signal based on the derived power difference. The laser frequency control unit 600l adjusts the frequency of the local light of the local oscillator 511 based on the estimated frequency offset value. As a result, the analog-to-digital converter group 531 outputs the received signal, whose frequency offset has been compensated for, to the signal demodulation unit 508.

[0140] The demodulation unit 532l may further include a compensation unit (not shown) separate from the laser frequency control unit 600l, at a stage subsequent to the analog-to-digital converter group 531. The compensation unit (not shown) separate from the laser frequency control unit 600l may perform highly accurate compensation processing for frequency offset on the received signal output from the analog-to-digital converter group 531.

[0141] As described above, switch 516l alternately outputs the time component to positive-side band-pass filter 501l and outputs the time component to negative-side band-pass filter 502l. Positive-side band-pass filter 501l is used for the positive-side time component, and negative-side band-pass filter 502l is used for the negative-side time component, thereby estimating the frequency offset value of the received signal. Laser frequency control unit 600l (compensation unit) adjusts the frequency of the local light of local oscillator 511 to compensate for the frequency offset of the received signal.

[0142] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0143] (Thirteenth embodiment) The thirteenth embodiment is mainly different from the fifth embodiment in that positive frequency components and negative frequency components are alternately acquired in the frequency domain. The thirteenth embodiment will be described focusing on the differences from the fifth embodiment.

[0144] 17 is a diagram showing an example of the configuration of a demodulation unit 532m in the 13th embodiment. The demodulation unit 532m includes a fast Fourier transform unit 500, a power derivation unit 503m, a power derivation unit 504m, a difference derivation unit 505, an offset estimation unit 506, a compensation unit 507m, a signal demodulation unit 508, a positive shift unit 509m, a negative shift unit 510m, a low-pass filter 514m, a low-pass filter 515m, a switch 516m-1, and a switch 516m-2.

[0145] In the thirteenth embodiment, positive and negative frequency components are alternately acquired in the frequency domain, and a low-pass filter is used on the positive and negative frequency components in the frequency domain to estimate the frequency offset value of the received signal. The compensation unit 507m performs processing to compensate for the frequency offset of the received signal on the output of the fast Fourier transform unit 500.

[0146] The switch 516m-1 and the switch 516m-2 alternately input the frequency domain received signal output from the fast Fourier transform unit 500 to the positive shift unit 509m and the negative shift unit 510m.

[0147] The positive shift unit 509m shifts the frequency domain received signal output from the fast Fourier transform unit 500 in the positive or negative direction by a predetermined frequency. This predetermined frequency is determined in advance so that the low-pass filter 514m can extract the positive frequency component from the shifted frequency domain received signal.

[0148] The negative shift unit 510m shifts the frequency domain received signal output from the fast Fourier transform unit 500 in the negative or positive direction by a predetermined frequency. This predetermined frequency is determined in advance so that the low-pass filter 515m can extract negative frequency components from the shifted frequency domain received signal.

[0149] The low-pass filter 514m extracts positive frequency components from the shifted frequency domain received signal. The low-pass filter 514m outputs the extracted positive frequency components to the power derivation unit 503m. The low-pass filter 515m extracts negative frequency components from the shifted frequency domain received signal. The low-pass filter 515m outputs the extracted negative frequency components to the power derivation unit 504m.

[0150] The power derivation unit 503m derives the power value of the power spectrum of the extracted positive frequency component.The power derivation unit 504m derives the power value of the power spectrum of the extracted negative frequency component.

[0151] The difference derivation unit 505 calculates the power value “P + ” and the power value of the power spectrum of the negative frequency component “P - The offset estimation unit 506 estimates the frequency offset value of the received signal based on the derived power difference.

[0152] The compensator 507m compensates for the frequency offset of the received signal based on the estimated frequency offset value. The compensator 507m outputs the received signal with the frequency offset compensated for to the signal demodulator 508. The signal demodulator 508 performs a predetermined demodulation process on the received signal with the frequency offset compensated for. The signal demodulator 508 outputs the received signal with the demodulated signal to the error correction decoder 533.

[0153] As described above, the switch 516m alternately outputs the frequency component to the positive shift unit 509m and outputs the frequency component to the negative shift unit 510m. In the frequency domain, the low-pass filter 517m is used on the positive frequency component and the negative frequency component to estimate the frequency offset value of the received signal. The compensation unit 507m performs a process of compensating for the frequency offset of the received signal on the output of the fast Fourier transform unit 500.

[0154] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0155] (Fourteenth embodiment) The fourteenth embodiment is mainly different from the sixth embodiment in that positive frequency components and negative frequency components are alternately acquired in the frequency domain. The fourteenth embodiment will be described focusing on the differences from the sixth embodiment.

[0156] 18 is a diagram showing an example of the configuration of a demodulation unit 532n in the fourteenth embodiment. The demodulation unit 532n includes a fast Fourier transform unit 500, a power derivation unit 503n, a power derivation unit 504n, a difference derivation unit 505, an offset estimation unit 506, a signal demodulation unit 508, a positive shift unit 509n, a negative shift unit 510n, a low-pass filter 514n, a low-pass filter 515n, switches 516n-1 and 516n-2, and a laser frequency control unit 600n. The laser frequency control unit 600n may be implemented in, for example, a signal processing circuit inside the demodulation unit 532n, or may be implemented in, for example, an FPGA (not shown) outside the demodulation unit 532n.

[0157] In the fourteenth embodiment, positive and negative frequency components are alternately acquired in the frequency domain, and a low-pass filter is used on the positive and negative frequency components in the frequency domain to estimate the frequency offset value of the received signal. The laser frequency control unit 600n compensates for the frequency offset of the received signal by adjusting the frequency of the local light of the local oscillator 511.

[0158] The switches 516n-1 and 516n-2 alternately input the frequency domain received signal output from the fast Fourier transform unit 500 to the positive shift unit 509n and negative shift unit 510n.

[0159] The laser frequency control unit 600n (compensation circuit) receives the estimated frequency offset value from the offset estimation unit 506. The laser frequency control unit 600n compensates for the frequency offset of the received signal based on the estimated frequency offset value. The laser frequency control unit 600n adjusts the frequency of the local light of the local oscillator 511 based on the estimated frequency offset value. As a result, the fast Fourier transform unit 500 outputs the received signal, whose frequency offset has been compensated, to the signal demodulation unit 508.

[0160] The demodulation unit 532n may further include a compensation unit (not shown) separate from the laser frequency control unit 600n at a stage subsequent to the fast Fourier transform unit 500. The compensation unit (not shown) separate from the laser frequency control unit 600n may perform highly accurate compensation processing for frequency offset on the received signal output from the fast Fourier transform unit 500.

[0161] As described above, the switch 516n alternately outputs the frequency component to the positive shift unit 509n and outputs the frequency component to the negative shift unit 510n. In the frequency domain, a low-pass filter 517n is used for the positive frequency component and the negative frequency component to estimate the frequency offset value of the received signal. The laser frequency control unit 600n (compensation unit) adjusts the frequency of the local light of the local oscillator 511 to compensate for the frequency offset of the received signal.

[0162] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0163] (Fifteenth embodiment) The 15th embodiment differs from the 7th embodiment mainly in that positive time components and negative time components are alternately acquired in the time domain. The 15th embodiment will be described focusing on the differences from the 7th embodiment.

[0164] 19 is a diagram showing an example of the configuration of a demodulation unit 532o in the fifteenth embodiment. The demodulation unit 532o includes a power derivation unit 503o, a power derivation unit 504o, a difference derivation unit 505, an offset estimation unit 506, a compensation unit 507o, a signal demodulation unit 508, a positive shift unit 509o, a negative shift unit 510o, a low-pass filter 514o, a low-pass filter 515o, a switch 516o-1, and a switch 516o-2.

[0165] In the fifteenth embodiment, positive and negative time components are alternately acquired in the time domain, and a low-pass filter is used on the positive and negative time components in the time domain to estimate the frequency offset value of the received signal. The compensation unit 507o performs processing to compensate for the frequency offset of the received signal on the output of the analog-to-digital converter group 531.

[0166] The switches 516n-1 and 516n-2 alternately input the time domain received signals output from the analog-to-digital converter group 531 to the positive shift unit 509n and the negative shift unit 510n.

[0167] The positive shift unit 509o shifts the time domain (time series) received signal output from the analog-to-digital converter group 531 in the positive or negative direction by a predetermined frequency. This predetermined frequency is determined in advance so that the low-pass filter 514o can extract the positive frequency component from the shifted time domain received signal.

[0168] The negative shift unit 510o shifts the time domain (time series) received signal output from the analog-to-digital converter group 531 by a predetermined frequency in the negative or positive direction. This predetermined frequency is determined in advance so that the low-pass filter 515o can extract negative frequency components from the shifted time domain received signal.

[0169] The low-pass filter 514o extracts positive frequency components from the shifted time-domain received signal. The low-pass filter 514o outputs the extracted positive frequency components to the power derivation unit 503o. The low-pass filter 515o extracts negative frequency components from the shifted time-domain received signal. The low-pass filter 515o outputs the extracted negative frequency components to the power derivation unit 504o.

[0170] The power derivation unit 503o derives the power value of the power spectrum of the extracted positive frequency component, and the power derivation unit 504o derives the power value of the power spectrum of the extracted negative frequency component.

[0171] The difference derivation unit 505 calculates the power value “P + ” and the power value of the power spectrum of the negative frequency component “P - The offset estimation unit 506 estimates the frequency offset value of the received signal based on the derived power difference.

[0172] The compensating unit 507o compensates for the frequency offset of the received signal based on the estimated frequency offset value. The compensating unit 507o outputs the received signal with the frequency offset compensated for to the signal demodulating unit 508. The signal demodulating unit 508 performs a predetermined demodulation process on the received signal with the frequency offset compensated for. The signal demodulating unit 508 outputs the received signal with the demodulated process performed to the error correction decoding unit 533.

[0173] As described above, switch 516o alternately outputs the time component to positive shift unit 509o and the time component to negative shift unit 510o. In the time domain, low-pass filter 517o is used on the positive and negative time components to estimate the frequency offset of the received signal. Compensation unit 507o compensates for the frequency offset of the received signal on the output of analog-to-digital converter group 531.

[0174] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0175] (16th embodiment) The sixteenth embodiment is mainly different from the eighth embodiment in that positive time components and negative time components are alternately acquired in the time domain. The sixteenth embodiment will be described focusing on the differences from the eighth embodiment.

[0176] 20 is a diagram showing an example of the configuration of a demodulation unit 532p in the sixteenth embodiment. The demodulation unit 532p includes a power derivation unit 503p, a power derivation unit 504p, a difference derivation unit 505, an offset estimation unit 506, a signal demodulation unit 508, a positive shift unit 509p, a negative shift unit 510p, a low-pass filter 514p, a low-pass filter 515p, switches 516p-1 and 516p-2, and a laser frequency control unit 600p. The laser frequency control unit 600p may be implemented in, for example, a signal processing circuit inside the demodulation unit 532p, or may be implemented in, for example, an FPGA (not shown) outside the demodulation unit 532p.

[0177] In the sixteenth embodiment, positive and negative time components are alternately acquired in the time domain, and a low-pass filter is used on the positive and negative time components in the time domain to estimate the frequency offset value of the received signal. The laser frequency control unit 600p compensates for the frequency offset of the received signal by adjusting the frequency of the local light of the local oscillator 511.

[0178] The switches 516p-1 and 516p-2 alternately input the time domain received signals output from the analog-to-digital converter group 531 to the positive shift unit 509p and the negative shift unit 510p.

[0179] The positive shift unit 509p shifts the time domain (time series) received signal output from the analog-to-digital converter group 531 by a predetermined frequency in the positive or negative direction. This predetermined frequency is determined in advance so that the low-pass filter 514p can extract the positive frequency component from the shifted time domain received signal.

[0180] The negative shift unit 510p shifts the time domain (time series) received signal output from the analog-to-digital converter group 531 by a predetermined frequency in the negative or positive direction. This predetermined frequency is determined in advance so that the low-pass filter 515p can extract negative frequency components from the shifted time domain received signal.

[0181] The low-pass filter 514p extracts positive frequency components from the shifted time-domain received signal. The low-pass filter 514p outputs the extracted positive frequency components to the power derivation unit 503p. The low-pass filter 515p extracts negative frequency components from the shifted time-domain received signal. The low-pass filter 515p outputs the extracted negative frequency components to the power derivation unit 504p.

[0182] The power derivation unit 503p derives the power value of the power spectrum of the extracted positive time component. The power derivation unit 504p derives the power value of the power spectrum of the extracted negative time component. The difference derivation unit 505 derives the power value of the power spectrum of the positive time component, "P + ” and the power value of the power spectrum of the negative time component “P - " and derives a difference (power difference) between the received signal and the frequency offset value. The offset estimation unit 506 estimates the frequency offset value of the received signal based on the derived power difference. The laser frequency control unit 600p adjusts the frequency of the local light of the local oscillator 511 based on the estimated frequency offset value. As a result, the analog-to-digital converter group 531 outputs the received signal, whose frequency offset has been compensated for, to the signal demodulation unit 508.

[0183] The demodulation unit 532p may further include a compensation unit (not shown) separate from the laser frequency control unit 600p, at a stage subsequent to the analog-to-digital converter group 531. The compensation unit (not shown) separate from the laser frequency control unit 600p may perform highly accurate compensation processing for frequency offset on the reception signal output from the analog-to-digital converter group 531.

[0184] As described above, the switch 516p alternately outputs the time component to the positive shift unit 509p and the time component to the negative shift unit 510p. In the time domain, a low-pass filter 517p is used on the positive and negative time components to estimate the frequency offset of the received signal. The laser frequency control unit 600p (compensation unit) adjusts the frequency of the local light of the local oscillator 511 to compensate for the frequency offset of the received signal.

[0185] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0186] (17th embodiment) The seventeenth embodiment is mainly different from the first to sixteenth embodiments in that the frequency offset compensation process is divided and executed. The seventeenth embodiment will be described focusing on the differences from the first to sixteenth embodiments.

[0187] Fig. 21 is a diagram showing an example of the frequency spectrum (power spectrum) of a received signal in the seventeenth embodiment. The modulation rate of the received signal shown in Fig. 21 is, for example, 60 GBd. When the frequency offset value is other than "0 GHz", the power spectrum of the positive frequency component and the power spectrum of the negative frequency component are asymmetric with respect to the frequency "0 GHz".

[0188] Here, the power spectrum of the positive frequency component when the frequency offset value is, for example, 10 GHz is different from the power spectrum of the positive frequency component when the frequency offset value is, for example, 30 GHz. Similarly, the power spectrum of the negative frequency component when the frequency offset value is, for example, 10 GHz is different from the power spectrum of the negative frequency component when the frequency offset value is, for example, 30 GHz.

[0189] FIG. 22 is a diagram showing an example of a peak of the power difference in the seventeenth embodiment. When the estimated value of the frequency offset value exceeds a certain value, the power difference may decrease. In FIG. 22, the estimated value of the frequency offset value is, for example, "2.0×10 10 If the power difference exceeds the threshold, the power difference is reduced.

[0190] When the entire power spectrum of either the positive frequency component or the negative frequency component falls outside the band of the band-pass filter or the low-pass filter, the power of the outlying frequency component becomes 0, and the power difference reaches a peak. Therefore, even if the value of the power difference is the same, the estimated values ​​of the frequency offset value may differ on both sides of the peak of the power difference.

[0191] In a frequency offset value range where the power difference decreases as the frequency offset value increases, the entire power spectrum of one of the positive-side frequency components and the negative-side frequency components falls outside the band of the band-pass filter or the low-pass filter. Also, in a frequency offset value range where the power difference decreases as the frequency offset value increases, a part of the power spectrum of the other of the positive-side frequency components and the negative-side frequency components falls outside the band of the band-pass filter or the low-pass filter.

[0192] If there is no possibility that the frequency offset value of the received signal will be greater than the frequency offset value associated with the peak of the power difference, the compensation unit can compensate for the frequency offset in a lump based on the estimated value of the frequency offset value. For example, if the specifications of the laser light stipulate that the frequency offset value of the laser light will not exceed the frequency offset value associated with the peak of the power difference, the compensation unit can compensate for the frequency offset in a lump based on the estimated value of the frequency offset value. In Figure 22, the frequency offset of the laser is "2.0 x 10 10 If the laser light specifications stipulate that the frequency offset is equal to or less than 3.0 × 10 10 ", but "1.0 × 10 10 Therefore, the estimated frequency offset value is 1.0 × 10 10 Based on this, the compensator can collectively compensate for the frequency offset.

[0193] If there is a possibility that the frequency offset value of the received signal will be larger than the frequency offset value associated with the peak of the power difference, the frequency offset value estimation process and compensation process are performed multiple times. Here, if the frequency offset value of the received signal is smaller than the frequency offset value associated with the peak of the power difference, the power difference will decrease as a result of partial compensation for the frequency offset. On the other hand, if the frequency offset value of the received signal is larger than the frequency offset value associated with the peak of the power difference, the power difference will increase as a result of partial compensation for the frequency offset. Therefore, the offset estimation unit 506 determines whether the frequency offset value of the received signal is larger than the frequency offset value associated with the peak of the power difference based on the results of the estimation process and compensation process performed multiple times.

[0194] In FIG. 22, when the derived power difference is, for example, “7.5”, the candidate frequency offset value is “1.0×10 10 " and "3.0 x 1010 The compensator compensates for the frequency offset by, for example, 6 GHz. That is, the compensator compensates for the frequency offset by, for example, 0.6×10 10 ” to decrease the frequency offset value.

[0195] If the power difference is reduced by compensating for a portion of the frequency offset, the offset estimation unit 506 determines that the frequency offset value of the received signal is smaller than the frequency offset value associated with the peak of the power difference. Based on the determination result, the offset estimation unit 506 selects the smaller candidate "1.0×10 10 The compensation unit selects the selected frequency offset value "1.0×10 10 The frequency offset of the received signal is compensated for based on the above formula.

[0196] If the power difference increases due to the compensation of a portion of the frequency offset, the offset estimation unit 506 determines that the frequency offset value of the received signal is larger than the frequency offset value associated with the peak of the power difference. Based on the determination result, the offset estimation unit 506 selects the larger candidate "3.0×10 10 The compensation unit selects the selected frequency offset value "3.0×10 10 The frequency offset of the received signal is compensated for based on the above formula.

[0197] Next, an example of the operation of the receiving device 5 will be described. 23 is a flowchart showing an example of the operation of the receiving device 5 in the seventeenth embodiment. The receiving device 5 in the seventeenth embodiment may correspond to any of the receiving devices 5 in the first to sixteenth embodiments.

[0198] The offset estimation unit 506 estimates a candidate frequency offset value based on the power difference. For example, in FIG. 22, the offset estimation unit 506 estimates a candidate frequency offset value of "1.0×10" associated with the power difference of "7.5". 10 " and candidate "3.0 x 1010 (Step S201). The offset estimation unit 506 determines whether there are multiple candidates for the frequency offset value (Step S202).

[0199] If it is determined that there are multiple frequency offset value candidates (step S202: YES), the compensating unit of the demodulator compensates for the frequency offset based on a predetermined small offset value (e.g., 6 GHz) (step S203). The difference deriving unit 505 derives the power difference of the received signal. The offset estimating unit 506 determines whether the power difference has increased (step S204).

[0200] If it is determined that the power difference has decreased (step S204: NO), the offset estimation unit 506 selects a smaller frequency offset value from the frequency offset value candidates. For example, in FIG. 22, the offset estimation unit 506 selects the candidate “1.0×10 10 " (Step S205).

[0201] If it is determined that the power difference has increased (step S204: YES), the offset estimation unit 506 selects a larger frequency offset value from the frequency offset value candidates. For example, in FIG. 22, the offset estimation unit 506 selects the candidate “3.0×10 10 " (step S206). The compensating unit of the demodulating unit compensates for the frequency offset based on the selected frequency offset value (step S207).

[0202] Next, an example of the dependence of the power difference on the FFT size will be described. 24 is a diagram showing an example of the dependency of the power difference on the FFT size (number of samples) in the seventeenth embodiment. The larger the FFT size in the fast Fourier transform applied to the received signal, the more stable the fluctuation of the power difference becomes. Also, the larger the FFT size, the smaller the size of the frequency component or time component to be averaged becomes.

[0203] However, the larger the FFT size in the fast Fourier transform, the higher the implementation cost. Also, the larger the size of the frequency components or time components to be averaged (the number of averaging), the longer it takes to derive an estimated value of the frequency offset value. Therefore, the implementation cost and estimation time of the FFT size and the number of averaging are determined so that the estimation accuracy of the frequency offset value is equal to or higher than a predetermined accuracy.

[0204] In FIG. 24, a data table with "FFT: 64 samples" and "forgetting factor: 0.01" is adopted as the data table for estimating the frequency offset value, so that the fluctuation of the power difference is sufficiently stable and the size of the frequency component or time component to be averaged is sufficiently small.

[0205] Next, an example of a data table (highly reliable data table) for each roll-off value of the Nyquist filter will be described. The more the shape of the power spectrum is restricted by the bandwidth characteristics of the optical and electrical devices and the roll-off of the Nyquist filter, the more the data table associating frequency offset values ​​with power differences depends on the FFT size.

[0206] 25 is a diagram showing an example of a data table for each roll-off value of the Nyquist filter in the seventeenth embodiment. Even if the same device is used for communication, the data in the data table may differ depending on the shape of the waveform of the received signal. For this reason, it is desirable to create the data table using a signal in the format actually used to estimate the frequency offset value.

[0207] 25 shows examples of data tables created based on different conditions. These data tables have in common that the smaller the power difference, the smaller the frequency offset value. Therefore, whichever data table is used, the frequency offset can be made sufficiently small by repeating the estimation process and compensation process until the power difference becomes sufficiently small.

[0208] As described above, when there are multiple frequency offset value candidates, the compensator compensates for the frequency offset of the received signal based on a predetermined offset value. When the first power difference based on the frequency component or the second power difference based on the time component decreases, the offset estimator 506 selects the smaller frequency offset value from the candidates as the frequency offset value to be used for compensation. When the first power difference based on the frequency component or the second power difference based on the time component increases, the offset estimator 506 selects the larger frequency offset value from the candidates as the frequency offset value to be used for compensation.

[0209] This makes it possible to estimate a wide range of frequency offsets occurring in the frequency of a received signal using a receiving device with a simple configuration.

[0210] (Example of hardware configuration) FIG. 26 is a diagram illustrating an example of the hardware configuration of a receiving device 5 in each embodiment. The receiving device 5 (communication device) includes a processor 6. The processor 6, such as a CPU (Central Processing Unit), executes a program stored in a storage device 8 having a non-volatile recording medium (non-transitory recording medium) and a memory 7, thereby realizing the receiving device 5 as software. The program (computer program) may be recorded on a computer-readable non-transitory recording medium. The program may be a multi-threaded program. Examples of computer-readable non-transitory recording media include portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), and CD-ROMs (Compact Disc Read Only Memory), and storage devices such as hard disks built into computer systems. A communication unit 9 executes predetermined communication processing.

[0211] At least a part of each functional unit of the receiving device 5 may be an analog circuit or a digital circuit. The receiving device 5 may be realized using hardware including an electronic circuit or circuitry using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), an FPGA (Field Programmable Gate Array), etc. The same applies to an example hardware configuration of the transmitting device 2.

[0212] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Industrial Applicability]

[0213] The present invention is applicable to optical communication systems. [Explanation of symbols]

[0214] 1a...communication system, 2...transmitter, 3...optical fiber, 4...amplifier, 5...receiving device, 6...processor, 7...memory, 8...storage device, 9...communication unit, 21...interface, 22...transmitting signal processing unit, 23...modulator driver group, 24...optical transmitter, 51...optical receiver, 52...transimpedance amplifier group, 53...receiving signal processing unit, 54...interface, 221...framer, 222...error correction coding unit, 223...modulation unit, 224...digital-analog converter group, 241...laser diode, 242...X polarization optical converter, 243...Y polarization optical converter, 24 4...Polarization beam combiner, 500...Fast Fourier transform unit, 501a, 501b, 501c, 501d, 501i, 501j, 501k, 501l...Positive band pass filters, 502a, 502b, 502c, 502d, 502i, 502j, 502k, 502l...Negative band pass filters, 503a, 503b, 503c, 503d, 503e, 503f, 503g, 503h, 503i, 503j, 503k, 503l, 503m, 503n, 503o, 503p...Power derivation unit, 504a, 504b, 504c, 504d, 504e, 504f, 504g, 504h... Power derivation unit, 505... Difference derivation unit, 506... Offset estimation unit, 507a, 507c, 507e, 507g, 507i, 507k, 507m, 507o... Compensation unit, 508... Signal demodulation unit, 509e, 509f, 509g, 509h, 509m, 509o, 509p... Positive shift unit, 510e, 510f, 510g, 510h, 510m, 510o, 510p... Negative shift unit, 511... Local oscillator, 512... Signal extraction circuit, 513... Detector, 514e, 514f, 514g, 514h... Low-pass filter, 515e, 515f, 515g ,515h...low-pass filter, 516i, 516j, 516k, 516l, 516m, 516n, 516o, 516p...switch, 517m, 517n, 517o, 517p...low-pass filter, 531...analog-digital converter group, 532a, 532b, 532c, 532d, 532e, 532f, 532g, 532h, 532i, 532j, 532k, 532l, 532m, 532n, 532o, 532p...demodulation unit, 533...error correction decoding unit, 534...framer, 600b, 600d, 600f, 600h, 600j, 600l, 600n,600p...Laser frequency control unit,

Claims

1. A power derivation unit that performs averaging processing using a forgetting factor on positive frequency components and negative frequency components of a received signal, or on positive time components and negative time components of the received signal; a difference derivation unit that derives a first power difference between the positive side frequency component and the negative side frequency component on which the averaging process has been performed, or derives a second power difference between the positive side time component and the negative side time component on which the averaging process has been performed; an offset estimator that estimates a frequency offset value of the received signal based on the first power difference or the second power difference; An estimation device comprising:

2. The estimation device according to claim 1 , further comprising a compensation unit that compensates for a frequency offset of the received signal using the frequency offset value.

3. when there are a plurality of candidates for the frequency offset value, the compensating unit compensates for the frequency offset of the received signal based on a predetermined offset value; The offset estimation unit If the first power difference or the second power difference decreases, selecting a smaller frequency offset value from the candidates as the frequency offset value to be used for compensation; The estimation device according to claim 2 , wherein when the first power difference or the second power difference increases, the larger of the frequency offset values ​​is selected from the candidates as the frequency offset value to be used for compensation.

4. An estimation method executed by an estimation device, performing averaging using a forgetting factor on positive frequency components and negative frequency components of a received signal or on positive time components and negative time components of the received signal; deriving a first power difference between the averaged positive frequency component and the averaged negative frequency component, or deriving a second power difference between the averaged positive time component and the averaged negative time component; estimating a frequency offset value of the received signal based on the first power difference or the second power difference; Estimation methods including:

5. On the computer, performing averaging processing using a forgetting factor on positive frequency components and negative frequency components of a received signal, or on positive time components and negative time components of the received signal; deriving a first power difference between the averaged positive frequency component and the averaged negative frequency component, or deriving a second power difference between the averaged positive time component and the averaged negative time component; estimating a frequency offset value of the received signal based on the first power difference or the second power difference; A program to execute.

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