WO2022176005A1 - 光受信装置及び周波数オフセット補償方法 - Google Patents
光受信装置及び周波数オフセット補償方法 Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/61—Coherent receivers
- H04B10/616—Details of the electronic signal processing in coherent optical receivers
- H04B10/6164—Estimation or correction of the frequency offset between the received optical signal and the optical local oscillator
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
- H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
- H04B10/077—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using a supervisory or additional signal
- H04B10/0775—Performance monitoring and measurement of transmission parameters
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/61—Coherent receivers
Definitions
- the present invention relates to an optical receiver and a frequency offset compensation method.
- An optical receiver to which a conventional optical digital coherent reception system is applied receives signal light transmitted by an optical transmitter, and combines the received signal light with local oscillation light generated by a local oscillation light source (hereinafter also referred to as "local light”). ) to generate a beat component between the electric field component of the signal light and the electric field component of the local light.
- local light generated by a local oscillation light source
- the signal light received by the optical receiver is, for example, signal light modulated by the polarization multiplexing QPSK (Quadrature Phase Shift Keying) method
- QPSK Quadrature Phase Shift Keying
- the optical receiver After separating the signal light into the X-polarized wave and the Y-polarized wave, the optical receiver generates the beat components of the respective polarized waves, thereby generating the I component and the Q component of the X polarized wave and the I component of the Y polarized wave. Detect the Q component.
- the optical receiver photoelectrically converts the generated beat component to generate four analog electrical signals corresponding to the I component and Q component of the X polarized wave and the I component and Q component of the Y polarized wave, respectively.
- Each of the four analog electric signals is converted into a digital electric signal by an ADC (Analog-to-Digital Converter), and the converted digital signal is transmitted after compensation for deterioration etc. by a digital signal processing circuit. demodulated to data.
- ADC Analog-to-Digital Converter
- phase rotation and noise called frequency offset occur in the received signal received by the optical receiver.
- the phase rotation due to the frequency offset is, for example, when QPSK modulation is performed in the optical transmission device, as shown in FIG. It means that the phases of the symbols 201, 202, 203, and 204 rotate and move to the phases of the symbols 201a, 202a, 203a, and 204a, respectively.
- the digital signal processing circuit of the optical receiver is provided with a frequency offset compensation circuit, and the frequency offset amount is estimated using the frequency offset compensation circuit. Based on the estimated frequency offset amount, the frequency offset compensating circuit rotates the phase in the direction opposite to the direction of rotation due to the frequency offset, so that the symbols 201a, 202a, 203a, and 204a are changed as shown in FIG. 16(c). The phase can be restored to that of the original symbols 201, 202, 203, 204, compensating for signal quality degradation due to frequency offset.
- FIG. 1 the range of the frequency offset that can be estimated is -B/2 or more and +B/2 or less, where B is the baud rate of the signal light, that is, the symbol rate. Therefore, the estimable range differs depending on the symbol rate B.
- the range of the frequency offset amount that can be estimated is sufficient in the range of -B/2 or more and +B/2 or less.
- An object of the present invention is to provide a technology capable of performing frequency offset compensation at low cost.
- One aspect of the present invention includes a local oscillation light source that generates local oscillation light, a signal light having a symbol rate of B generated by optically modulating transmission data, the received signal light, and the local oscillation light source.
- a receiving unit that performs digital coherent reception by interfering with the local oscillation light generated by and converts the signal light into an electrical digital signal and outputs it, wherein the electrical band range is from -Be to +Be and a digital signal processing unit for demodulating the transmission data from the digital signal output from the receiving unit, wherein the digital signal processing unit comprises the signal light and the estimating a frequency offset amount occurring in the digital signal in a range of -B/2 or more and +B/2 or less according to the frequency difference between the local oscillation light and the digital signal based on the estimated frequency offset amount; By compensating the frequency offset for the signal, the frequency offset amount in the range of -B/2 or more and +B/2 or less is compensated, and the frequency range of less than -B/2 and more than +B/2
- a local oscillation light source generates local oscillation light
- a receiving unit whose electrical band ranges from ⁇ Be to +Be and Be>B/2 optically modulates transmission data.
- the signal light having the symbol rate B generated by the above is received, and the received signal light and the local oscillation light generated by the local oscillation light source are caused to interfere with each other to perform digital coherent reception to electrically convert the signal light.
- a frequency offset compensation unit included in a digital signal processing unit that converts the digital signal into a digital signal and outputs it, and demodulates the transmission data from the digital signal output from the reception unit, is provided to compensate for the difference between the signal light and the local oscillation light estimating a frequency offset amount occurring in the digital signal according to the frequency difference in a range of -B/2 or more and +B/2 or less; and frequency offset compensation for the digital signal based on the estimated frequency offset amount.
- the frequency offset amount in the range of -B / 2 or more and +B / 2 or less is compensated, and in the case of the frequency offset amount in the range of less than -B / 2 and in the range of more than +B / 2, the symbol rate
- This is a frequency offset compensation method for compensating so as to leave a frequency offset amount that is an integral multiple of B.
- the frequency stability requirements for the light source of the optical transmitter used to generate the signal light are relaxed, and the frequency can be obtained at a low cost. It becomes possible to perform offset compensation.
- FIG. 1 is a block diagram showing the configuration of an optical transmission system according to a first embodiment
- FIG. FIG. 2 is a diagram showing reception bands of the optical receiver of the first embodiment
- FIG. 4 is a block diagram showing the internal configuration of a frequency offset compensator according to the first embodiment
- FIG. 4 is a flow chart showing the flow of processing by the frequency offset compensator of the first embodiment
- It is a figure explaining the calculation process of the frequency offset amount in 1st Embodiment.
- FIG. 4 is a diagram for explaining frequency offset compensation by the frequency offset compensator of the first embodiment
- 7 is a graph showing the relationship between each of an estimated frequency offset amount and a post-compensation frequency offset amount and an actual frequency offset amount in the first embodiment
- It is a figure which shows the simulation result using the optical receiver of 1st Embodiment.
- 2 is a block diagram showing the configuration of an optical transmission system according to a second embodiment
- FIG. 9 is a block diagram showing the internal configuration of a residual frequency offset compensator according to the second embodiment
- FIG. 10 is a diagram illustrating a process of calculating a residual frequency offset amount in the second embodiment
- FIG. 9 is a flow chart showing the flow of processing by a residual frequency offset compensator according to the second embodiment; 9 is a flow chart showing the flow of processing by a signal quality determination unit and a transmission wavelength change instruction unit according to the second embodiment; It is a figure explaining how to set the threshold referred to in the signal quality determination part of 2nd Embodiment.
- FIG. 11 is a block diagram showing another configuration example of the optical transmission system of the second embodiment; It is a figure explaining a frequency offset.
- FIG. 1 is a block diagram showing the configuration of an optical transmission system A according to the first embodiment, which is one embodiment of the present invention.
- connection lines indicated by dashed-dotted lines are optical lines through which optical signals are propagated, and other connection lines are electric lines through which electrical signals are propagated.
- An optical transmission system A includes an optical receiver 1 and an optical transmitter 2 .
- the optical receiver 1 and the optical transmitter 2 are connected via an optical transmission line 3 .
- An optical fiber transmission line for example, is applied to the optical transmission line 3 .
- the optical transmitter 2 includes a light source such as an LD (Laser Diode) that generates signal light.
- the optical transmitter 2 modulates transmission data, which is an electrical digital signal, using, for example, the polarization multiplexing QPSK method, generates signal light, and transmits the generated signal light to the optical receiver 1 through the optical transmission line 3. do.
- the optical receiver 1 includes a local oscillation light source 11 , a receiver 12 and a digital signal processor 13 .
- the local oscillation light source 11 is, for example, an LD, and generates a local signal, which is local oscillation light with a predetermined wavelength ⁇ .
- the receiver 12 includes a polarization phase diversity receiver 21 and an AD (Analog-to-Digital) converter 22 .
- the polarization phase diversity receiver 21 is connected to the optical transmission line 3, receives the signal light at the symbol rate B transmitted by the optical transmission device 2 through the optical transmission line 3, performs digital coherent reception, and receives the received signal light. Convert to electrical analog signal.
- the polarization phase diversity receiver 21 separates the received signal light into X polarized waves and Y polarized waves.
- the polarization phase diversity receiver 21 causes each of the separated X-polarized and Y-polarized signal lights to interfere with a local signal generated by the local oscillation light source 11, so that the electric field component E S of the signal light and the local signal to generate the beat component of the electric field component E LO of .
- the polarization phase diversity receiver 21 detects the X-polarized I component and Q component and the Y-polarized I component and Q component from the generated beat component.
- the polarization phase diversity receiver 21 photoelectrically converts four optical signals corresponding to the detected X-polarized I component and Q component and the Y-polarized I component and Q component, respectively, into four electrical analog signals. Generate a signal.
- the AD converter 22 includes four ADCs 22-1, 22-2, 22-3, and 22-4 corresponding to the I component and Q component of the X polarized wave and the I component and Q component of the Y polarized wave, respectively.
- Each of the ADCs 22-1, 22-2, 22-3, and 22-4 captures the corresponding electrical analog signal generated by the polarization phase diversity receiver 21, and converts the captured analog signal into an electrical digital signal. Convert.
- the receiving band of the receiving unit 12 ranges from “ ⁇ -Be” to " ⁇ +Be” as shown in Fig. 2.
- the electrical band Be and the symbol rate B, there is a relationship that the electrical band Be exceeds half the symbol rate B, that is, Be>B/2.
- the digital signal processing unit 13 includes a clock recovery unit 23, a polarization dispersion compensation unit 24, a chromatic dispersion compensation unit 25, a frequency offset compensation unit 26, a phase compensation unit 27, and a demodulation unit 28.
- the clock recovery unit 23 is, for example, a sampling frequency compensation circuit.
- the clock recovery unit 23 recovers the sampling frequency caused by the difference in the reference clock between the optical transmitter 2 and the optical receiver 1, for example, the oscillation frequency error of the crystal oscillators provided in the optical transmitter 2 and the optical receiver 1. compensate for the difference.
- the clock recovery unit 23 performs compensation on the four digital signals output from each of the ADCs 22-1, 22-2, 22-3, and 22-4, and then combines the four digital signals.
- the polarization dispersion compensator 24 compensates for the polarization dispersion generated while propagating through the optical transmission line 3 for the digital signal coupled by the clock recovery unit 23 .
- the chromatic dispersion compensator 25 compensates for the chromatic dispersion that occurs during propagation through the optical transmission line 3 with respect to the digital signal that has undergone polarization dispersion compensation by the polarization dispersion compensator 24 .
- the frequency offset compensating unit 26 estimates the frequency offset amount in the range of -B/2 or more and +B/2 or less based on the training symbol sequence included in the digital signal chromatic dispersion compensated by the chromatic dispersion compensating unit 25. .
- the estimated frequency offset amount is also referred to as an estimated frequency offset amount.
- the frequency offset compensator 26 performs frequency offset compensation on the digital signal based on the estimated frequency offset amount. More specifically, the frequency offset compensator 26 applies phase rotation to each symbol included in the digital signal in a direction opposite to the direction of rotation due to the frequency offset in accordance with the estimated frequency offset amount. Perform offset compensation.
- the frequency offset compensator 26 has the internal configuration shown in FIG.
- the frequency offset compensator 26 includes a frequency offset amount estimator 31 and a compensation processor 32 .
- the frequency offset amount estimator 31 includes a timing detector 41 , a delay device 42 , a complex conjugator 43 , a multiplier 44 , a vector averager 45 , a declinator 46 and a calculator 47 .
- a digital signal that has undergone chromatic dispersion compensation by the chromatic dispersion compensator 25 has a preamble portion in which a predetermined training symbol sequence is written, and a payload portion that follows the preamble.
- a data sequence corresponding to transmission data transmitted by the optical transmission device 2 is written in the payload portion.
- the timing detector 41 detects the head position of the training symbol sequence from the preamble portion of the digital signal.
- a delay device 42 delays the received symbol by one symbol period T and outputs the delayed symbol.
- a complex conjugate 43 generates a complex conjugate of the acquired symbols.
- the multiplier 44 performs differential detection by multiplying the two captured symbols to calculate a vector.
- the vector averager 45 calculates the vector average by calculating the total sum of a predetermined number of N vectors.
- N is the number of symbols to be averaged and is predetermined within the range of the sequence length of the training symbol sequence.
- a declinator 46 calculates the declination of the vector average.
- the calculation unit 47 calculates the estimated frequency offset amount ⁇ f est based on the vector-averaged declination angle calculated by the declinator 46 .
- the compensation processor 32 performs frequency offset compensation on the digital signal based on the estimated frequency offset amount ⁇ f est calculated by the calculator 47 .
- the phase compensator 27 detects a phase offset component, which is the phase difference between the signal light and the local signal light, based on the digital signal frequency offset-compensated by the frequency offset compensator 26 .
- the phase compensator 27 performs phase compensation by removing the detected phase offset component from the digital signal frequency offset compensated by the frequency offset compensator 26 .
- the constellation of the transmission data is reproduced in the data series included in the payload of the digital signal.
- the demodulator 28 demodulates the transmission data from the transmission data constellation reproduced in the data series included in the digital signal phase-compensated by the phase compensator 27 .
- FIG. 4 is a flow chart showing the flow of processing by the frequency offset compensator 26. As shown in FIG.
- the chromatic dispersion compensator 25 outputs the chromatic dispersion compensated digital signal to the frequency offset compensator 26 .
- the digital signal chromatic dispersion compensated by the chromatic dispersion compensator 25 is split into two inside the frequency offset compensator 26 , one of which is sent to the frequency offset amount estimator 31 and the other to the compensation processor 32 .
- the timing detector 41 of the frequency offset amount estimator 31 takes in one of the two-branched digital signals (step S1).
- the timing detector 41 detects the head position of the training symbol sequence from the preamble portion of the captured digital signal.
- the timing detection unit 41 reads a training symbol sequence from the digital signal based on the detected leading position of the training symbol sequence, and sequentially outputs a plurality of symbols included in the read training symbol sequence one symbol at a time for each symbol period T. (step S2).
- a r (t) be the symbol at time t in the training symbol sequence
- time t be the time of every symbol period T.
- the symbol a r (t) sequentially output from the timing detector 41 is branched into two, one of which is sent to the multiplier 44 and the other to the delay device 42 .
- a delay device 42 takes in the other symbol branched into two.
- a delay unit 42 delays the received symbol by one symbol period T and outputs it.
- the complex conjugate 43 generates a complex conjugate of the symbols output by the delay device 42 and outputs it to the multiplier 44 .
- the multiplier 44 performs differential detection by multiplying one of the two-branched symbols by the complex conjugate symbol of the symbol delayed by one symbol period T output from the complex conjugator 43 to obtain the following equation (1 ) is calculated (step S3 ).
- the vector A r (t) can be approximated by an expression for the phase component, exp, as shown in equation (1).
- the first term in the brackets of exp is the modulation component
- the second term is the frequency offset component
- the third term is the phase noise component.
- the vector averager 45 takes in the vector A r (t) calculated and output by the multiplier 44, and calculates a predetermined number of N vectors A r (t) out of the taken vector A r (t).
- a vector average is calculated by calculating the sum (step S4).
- the vector average of the vectors A r (t) calculated by the vector averager 45 is described as " ⁇ NA r (t)".
- each of the plurality of symbols included in the training symbol sequence has a phase of " ⁇ " when the vector average ⁇ NA r (t) is calculated after differential detection when no frequency offset occurs. are differentially encoded in the optical transmitter 2 in advance.
- the direction of the vector average ⁇ NA r (t) indicated by reference numeral 55 is the direction along the real number axis, that is, the direction of the phase “ ⁇ ”. be the direction.
- the declinator 46 calculates the declination angle of the vector average ⁇ NA r (t) calculated and output by the vector averager 45, that is, arg( ⁇ NA r (t)).
- the declinator 46 outputs the declination angle of the calculated vector average ⁇ NA r (t) to the calculator 47 (step S5).
- the calculation unit 47 takes in the argument of the vector average ⁇ NA r (t) output by the declinator 46 .
- the phase noise which is the third term of the phase component of the vector A r (t) becomes almost "0".
- the calculation unit 47 performs the calculation shown in the following equation (2), and sets the calculation result as the estimated frequency offset amount ⁇ f est .
- the calculation shown in the following equation (2) is a calculation of subtracting " ⁇ " from the argument of the vector average ⁇ NA r (t) and then dividing by 2 ⁇ T.
- the calculation unit 47 outputs the estimated frequency offset amount ⁇ f est to the compensation processing unit 32 (step S6).
- the compensation processing unit 32 takes in the other digital signal branched into two and the estimated frequency offset amount ⁇ f est output by the calculation unit 47 .
- the compensation processing unit 32 performs frequency offset compensation on the received digital signal based on the received estimated frequency offset amount ⁇ f est .
- the compensation processor 32 outputs the frequency offset-compensated digital signal to the phase compensator 27 (step S7).
- the wavelength difference between the signal light received by the optical receiving device 1 and the local light output by the local oscillation light source 11, that is, the actual frequency offset amount ⁇ f is included in the range of ⁇ B/2 or more and +B/2 or less. If not, the frequency offset amount estimating section 31 can only estimate in the range of -B/2 or more and +B/2 or less, which means that the frequency offset amount is estimated incorrectly.
- the frequency offset amount estimator 31 sets "-B/4" as the estimated frequency offset amount ⁇ f est . will be calculated.
- the compensation processing unit 32 performs compensation by adding phase rotation of "+B/4" in the opposite direction.
- This process of frequency offset compensation will be described by taking symbol 52 included in the vector average ⁇ NA r (t) of the training symbol sequence shown in FIG. 6(b) as an example.
- Symbol 52 has a frequency offset of “+3B/4” indicated by the dashed-dotted arrow 62 .
- the frequency offset amount indicated by reference numeral 63 will be referred to as a post-compensation frequency offset amount ⁇ fc .
- An arbitrary symbol 71 of the data series included in the digital signal after the above frequency offset compensation has been performed on the digital signal in which the frequency offset of the frequency offset amount ⁇ f +3B/4 is generated, and the symbol 71 adjacent to the symbol 71
- m is an integer satisfying m ⁇ 0, that is, 0 or a natural number.
- the post-compensation frequency offset amount ⁇ fc is always an integral multiple of the symbol rate B as shown in equation (3). After the elapse of one symbol period T, the symbol phase rotates by 2m ⁇ , and the phase difference between adjacent symbols becomes "0". can. However, if the frequency offset amount ⁇ f exceeds the reception band of the receiver 12, the band of the electrical analog signal captured by the ADCs 22-1 to 22-4 will be outside the reception band. Therefore, since the ADCs 22-1 to 22-4 cannot convert analog signals into digital signals, the frequency offset amount ⁇ f that can be received by the optical receiver 1 is limited within the range of the reception band of the receiver 12.
- FIG. 7 is a graph showing the relationship between each of the estimated frequency offset amount ⁇ f est and the post-compensation frequency offset amount ⁇ f c and the actual frequency offset amount ⁇ f.
- the horizontal axis indicates the actual frequency offset amount ⁇ f normalized by the symbol rate B
- the vertical axis indicates the estimated frequency offset amount ⁇ f est normalized by the symbol rate B.
- the dashed line in the graph indicates the case where the estimated frequency offset amount ⁇ f est and the actual frequency offset amount ⁇ f match.
- the estimated frequency offset amount ⁇ f est is estimated in the range of ⁇ 0.5 or more and 0.5 or less, that is, the range of ⁇ B/ or more and +B/2 or less. It can be seen that
- the horizontal axis indicates the actual frequency offset amount ⁇ f normalized by the symbol rate B
- the vertical axis indicates the post-compensation frequency offset amount ⁇ fc normalized by the symbol rate B.
- FIG. 8(a) shows the bit error rate (hereafter referred to as "BER” (hereafter referred to as “BER") in a simulation of receiving a digital signal having several frequency offsets ⁇ f in the optical receiver 1 of the first embodiment. Bit Error Rate)).
- BER bit error rate
- the polarization phase diversity receiver 21 included in the receiving unit 12 is configured to perform phase diversity reception for simplification.
- a state in which an optical amplifier is placed in front of the optical receiver 1, that is, a configuration in which received light received by the optical receiver 1 is amplified by the optical amplifier is assumed.
- Numerical conditions for the simulation are as follows.
- the wavelength of the signal light is "1550 nm”
- the baud rate that is, the symbol rate B is "12.5 Gbaud”
- the sampling rate of the ADCs 22-1 to 22-4 is "50 GS/s”
- the electrical The band Be is "22 GHz”.
- B/2 is 6.25 GHz, satisfying Be>B/2.
- the gain of the optical amplifier is "20.0 dB”
- the noise figure is "6.0 dB”
- the received power of the signal light received by the receiver 12 of the optical receiver 1 is ) is “ ⁇ 43.5 dBm”.
- the horizontal axis indicates the actual frequency offset amount ⁇ f normalized by the symbol rate B, and the vertical axis indicates the BER.
- the frequency offset amount ⁇ f corresponding to the position of the circle mark present on the line graph shown in FIG. 8A is the frequency offset amount ⁇ f of the signal light given as a calculation parameter.
- the normalized frequency offset amount ⁇ f indicated by reference numeral 81 is in the range of -1.5 to 1.5, good BER characteristics are obtained, and -0. It can be seen that good BER characteristics are obtained even when the frequency offset amount ⁇ f exceeds the range of 5 or more and +0.5 or less, that is, the range of -B/2 or more and +B/2 or less.
- the local oscillation light source 11 generates local oscillation light.
- the receiving unit 12 receives signal light having a symbol rate B generated by optically modulating transmission data and having an electric band range of ⁇ Be to +Be, where Be>B/2.
- the digital signal processing unit 13 demodulates transmission data from the digital signal output by the receiving unit 12 .
- the frequency offset compensating unit 26 provided in the digital signal processing unit 13 reduces the amount of frequency offset generated in the digital signal according to the frequency difference between the signal light and the local oscillation light to -B/2 or more and +B/2 or less.
- the frequency offset amount in the range of -B/2 or more and +B/2 or less is compensated, and -B
- compensation is performed so that the frequency offset amount of integral multiples of the symbol rate B is left.
- the estimable range of the frequency offset amount estimator 31 becomes narrow.
- the frequency offset amount can be adjusted to an integral multiple of the symbol rate B, that is, ⁇ (m+1)B. (However, m is an integer satisfying m ⁇ 0). In this case, when one symbol period T elapses, a phase rotation of 2m ⁇ is added to the next symbol, and the phase difference with the adjacent symbol becomes "0", enabling demodulation.
- the estimation range of the frequency offset amount is -B/2 or more and +B/2 or less, where B is the symbol rate.
- B is the symbol rate.
- the optical receiver 1 uses the conventional frequency offset method, it is possible to reduce manufacturing costs. Even if the symbol rate B becomes low, it is possible to demodulate signal light with frequency offsets in the range of less than -B/2 and in the range of more than +B/2. It is possible to relax the requirement of frequency stability required for the light source used at the time, and to reduce the cost required for manufacturing the optical transmitter 2 .
- the optical transmitter 2 corresponds to a transmitter provided in an ONU (Optical Network Unit) of the access network
- the optical receiver 1 corresponds to , corresponds to a coherent receiver provided in an OLT (Optical Line Terminal) of an access network.
- the transmitters provided in the ONUs of the access network are cheaper than the transmitters used in the core network.
- the coherent receiver provided in the OLT can be shared by a plurality of users, so it can be costly, and high-performance equipment can be applied.
- the symbol rate B generally used in access networks is assumed to be, for example, 10 GBaud to 25 GBaud.
- the core network for example, signals of 25 GBaud to 60 GBaud are used. Therefore, when a signal with a symbol rate B of 10 GBaud to 25 GBaud is received using a receiver capable of receiving signals of 25 GBaud to 60 GBaud used in the core network, the electrical band Be of the receiver is changed from 25 GBaud to 60 GBaud. >B/2.
- the estimable frequency offset amount is in the range of -5 GBaud or more and +5 GBaud or less.
- 10 GBaud is, for example, XGS-PON (Passive Optical Network), NG (Next Generation)-PON2, 10G-EPON (Ethernet (registered trademark)-PON), etc.
- 25 GBaud is, for example, This is the case of 50G-PON and the like.
- 25 GBaud is, for example, the case of DP (Dual-Polarization)-QPSK 100 Gbps
- 60 GBaud is the case of DP-16 QAM (Quadrature Amplitude Modulation) 400 Gbps.
- FIG. 9 is a block diagram showing the configuration of the optical transmission system Aa according to the second embodiment. Also in FIG. 9, the connection lines indicated by the dashed-dotted lines are optical lines through which optical signals propagate, and the other connection lines are electric lines through which electrical signals propagate.
- the same components as those of the optical transmission system A of the first embodiment are denoted by the same reference numerals, and different configurations will be described below.
- the band limitation causes quality degradation in the received signal. Therefore, an estimation error occurs in the estimated frequency offset amount ⁇ f est calculated by the frequency offset amount estimating section 31 included in the frequency offset compensating section 26 .
- the estimated error amount is detected, and the detected estimated error amount is used as an index indicating the degree of signal quality deterioration. It is determined whether or not it is close to the 12 electric band Be.
- the wavelength of the signal light is changed.
- the optical transmission system Aa includes an optical receiver 1a, an optical transmitter 2a, and an optical transmission line 3 and a communication line 4 that connect the optical receiver 1a and the optical transmitter 2a.
- the communication line 4 is shown as an electric line, like the optical transmission line 3, it may be an optical line.
- the optical transmission device 2a has the same configuration as the optical transmission device 2 of the first embodiment. A configuration is provided for changing the wavelength of the light source used when generating the light.
- the optical receiver 1a includes a local oscillation light source 11, a receiver 12, and a digital signal processor 13a.
- the digital signal processing unit 13a includes a clock recovery unit 23, a polarization dispersion compensation unit 24, a chromatic dispersion compensation unit 25, a frequency offset compensation unit 26, a residual frequency offset compensation unit 26a, a phase compensation unit 27, a demodulation unit 28, and a signal quality determination unit. It has a section 91 and a transmission wavelength change instructing section 92 .
- the residual frequency offset compensation unit 26a has the same configuration as the frequency offset compensation unit 26 except that the output destination of the calculation unit 47 is connected to the compensation processing unit 32 and the signal quality determination unit 91. with the configuration of
- a frequency offset amount estimator 31 included in the residual frequency offset compensator 26a estimates a residual frequency offset amount ⁇ fn based on the digital signal frequency offset-compensated by the frequency offset compensator 26 based on the estimated frequency offset amount ⁇ f est .
- the residual frequency offset amount ⁇ f n is the estimated error amount included in the estimated frequency offset amount ⁇ f est calculated by the frequency offset amount estimating section 31 of the frequency offset compensating section 26, as described above.
- the estimated frequency offset amount ⁇ f est is expressed as the sum of the actual frequency offset amount ⁇ f and the residual frequency offset amount ⁇ fn , which is the estimated error amount.
- the above equation (3) is expressed as the following equation (4).
- the post-compensation frequency offset amount ⁇ fc also includes the residual frequency offset amount ⁇ fn .
- FIG. 11 shows the vector of the residual frequency offset compensator 26a when the frequency offset compensated digital signal based on the estimated frequency offset amount ⁇ f est is given to the frequency offset amount estimator 31 of the residual frequency offset compensator 26a.
- 3 is a diagram showing three symbols included in the vector average ⁇ NA r (t) output by the averager 45 on the complex plane.
- FIG. 11A shows the vector average ⁇ NA r ( t).
- the direction will indicate the direction of the vector average ⁇ NA r (t).
- FIG. 11B shows the vector average when the post-compensation frequency offset amount ⁇ f c is ⁇ f c ⁇ 0, ⁇ (m+1)B, that is, the residual frequency offset amount ⁇ f n having a value other than 0 is superimposed. It is the figure which showed ⁇ NA r (t).
- the direction indicated by reference numeral 55a is the direction having an inclination corresponding to the residual frequency offset amount ⁇ fn . Therefore, by using the deflection angle of the vector averager 45 of the residual frequency offset compensator 26a, the residual frequency offset amount ⁇ fn can be calculated in the range of -B/2 or more and +B/2 or less.
- the signal quality determining section 91 is connected to the calculating section 47 of the frequency offset amount estimating section 31 of the residual frequency offset compensating section 26a and takes in the residual frequency offset amount ⁇ fn calculated by the calculating section 47 .
- the signal quality determination unit 91 uses the captured residual frequency offset amount ⁇ f n as an index indicating the degree of deterioration of the signal quality of the digital signal, and determines the digital signal based on the residual frequency offset amount ⁇ f n and a predetermined threshold value. Determine whether the signal quality is degraded.
- the transmission wavelength change instruction unit 92 is connected to the communication line 4, and when the signal quality determination unit 91 determines that the signal quality of the digital signal is degraded, the transmission wavelength change instruction unit 92 transmits signal light to the optical transmission device 2a through the communication line 4. transmits an instruction signal instructing to change the wavelength of the
- FIG. 12 is a flow chart showing the flow of processing by the residual frequency offset compensator 26a.
- the residual frequency offset compensator 26a takes in the digital signal for which the frequency offset compensation has been performed by the frequency offset compensator 26 (step Sa1).
- steps Sa2 to Sa6 the same processing as steps S2 to S6 shown in FIG. 4 is performed by the frequency offset amount estimator 31 of the residual frequency offset compensator 26a.
- step Sa6 it is not the estimated frequency offset amount ⁇ f est but the residual frequency offset amount ⁇ f n that is calculated and output by the computing unit 47 .
- the compensation processing unit 32 of the residual frequency offset compensating unit 26a takes in the other two-branched digital signal and the residual frequency offset amount ⁇ fn calculated and output by the computing unit 47 of the residual frequency offset compensating unit 26a.
- the compensation processing unit 32 of the residual frequency offset compensating unit 26a performs frequency offset compensation on the received digital signal based on the received residual frequency offset amount ⁇ fn .
- the compensation processing unit 32 of the residual frequency offset compensating unit 26a outputs the frequency offset-compensated digital signal to the phase compensating unit 27 (step Sa7).
- FIG. 13 is a flow chart showing the flow of processing by the signal quality judgment section 91 and the transmission wavelength change instruction section 92.
- the signal quality determining unit 91 determines the residual frequency offset amount ⁇ fn calculated and output by the calculating unit 47 of the frequency offset amount estimating unit 31 of the residual frequency offset compensating unit 26a in the process of step Sa6 of the flowchart shown in FIG. Take in (step Sa10).
- the process of step Sa10 is a process performed in parallel with the process of step Sa7 in FIG.
- the signal quality determination unit 91 uses the acquired residual frequency offset amount ⁇ f n as an index indicating the degree of deterioration of the signal quality of the digital signal, and determines whether the absolute value of the residual frequency offset amount ⁇ f n is equal to or greater than a predetermined threshold. (step Sa11).
- step Sa11, No determines that the signal quality of the digital signal is not degraded and performs processing. exit.
- step Sa11, Yes determines that the signal quality of the digital signal is degraded. and outputs a transmission instruction signal to the transmission wavelength change instruction section 92 .
- the transmission wavelength change instruction unit 92 Upon receiving the transmission instruction signal from the signal quality determination unit 91, the transmission wavelength change instruction unit 92 transmits a wavelength change instruction signal instructing to change the wavelength of the signal light to the optical transmission device 2a via the communication line 4. (step Sa13), and the process ends.
- the optical transmitter 2a Upon receiving the wavelength change instruction signal from the transmission wavelength change instruction unit 92 via the communication line 4, the optical transmitter 2a changes the wavelength of the signal light.
- the wavelength change amount may be a fixed amount that is predetermined in the optical transmission device 2a to the extent that the wavelength of the signal light is finely adjusted, or may be determined according to the wavelength of the signal light at that time. It may be a variable amount determined by the optical transmitter 2a.
- the optical receiver 1a may notify the optical transmitter 2a of the amount of change in wavelength corresponding to the magnitude of the absolute value of the residual frequency offset amount ⁇ fn in the following manner.
- the signal quality determination unit 91 stores in its internal storage area a table that defines the amount of change in wavelength for each range of absolute values of the residual frequency offset amount ⁇ fn .
- the table when outputting a transmission instruction signal to the transmission wavelength change instructing unit 92, the table is referenced to detect the wavelength change amount corresponding to the magnitude of the absolute value of the residual frequency offset amount ⁇ fn .
- the signal quality determination unit 91 includes the detected amount of wavelength change in a transmission instruction signal and outputs the transmission instruction signal to the transmission wavelength change instruction unit 92 .
- the transmission wavelength change instruction unit 92 includes the wavelength change amount contained in the transmission instruction signal in the wavelength change instruction signal and transmits the wavelength change instruction signal to the optical transmission device 2a.
- the optical transmitter 2a Upon receiving the wavelength change instruction signal, the optical transmitter 2a reads the wavelength change amount included in the received wavelength change instruction signal, and changes the wavelength of the light source according to the read wavelength change amount. As a result, the optical transmitter 2a can change the wavelength of the signal light according to the magnitude of the absolute value of the residual frequency offset amount ⁇ fn .
- the threshold value that the signal quality determination unit 91 refers to in the process of step Sa11 is selected in advance by, for example, the following method.
- the relationship between the actual frequency offset amount ⁇ f normalized by the symbol rate B and the estimated error amount, that is, the absolute value of the residual frequency offset amount ⁇ fn is measured in advance, and a graph as shown in FIG. 14(a) is created. .
- the absolute value of the residual frequency offset amount ⁇ fn corresponding to the frequency offset amount ⁇ f causing signal quality deterioration, ie, the value indicated by reference numeral 101 is selected as the threshold value.
- the average value is calculated from the time-series data of the absolute value of the estimated error amount, that is, the residual frequency offset amount ⁇ fn , which is continuously measured in a steady state, that is, in a state where signal quality is not degraded, and the calculated average value is It may be selected as a threshold.
- the signal quality judging section 91 determines that the residual frequency offset amount ⁇ f n is equal to or greater than the average value of the absolute values of the residual frequency offset amount ⁇ f n in the steady state. When the signal quality is degraded, it is determined that the signal quality is degraded.
- the residual frequency offset compensator 26a corrects the estimated error amount caused by the signal quality degradation, that is, the residual frequency offset amount ⁇ f n is calculated, and the calculated residual frequency offset amount ⁇ fn is used as an index indicating deterioration of signal quality.
- the signal quality determination unit 91 determines whether or not the signal quality is degraded based on the residual frequency offset amount ⁇ fn calculated by the residual frequency offset compensation unit 26a and a predetermined threshold value.
- the transmission wavelength change instruction unit 92 determines that the signal quality determination unit 91 has degraded the signal quality
- the wavelength of the signal light is changed to the optical transmission device 2a.
- a wavelength change instruction signal instructing to change the wavelength is transmitted.
- the optical transmission system Aa of the second embodiment it is possible to adjust the wavelength of the signal light of the optical transmitter 2a in accordance with the quality deterioration of the received signal, thereby improving the reception characteristics. Therefore, by using the configuration of the second embodiment described above, in addition to the effects of the optical transmission system A of the first embodiment, the frequency Stability requirements can be further relaxed, and the cost of the optical transmitter 2a can be reduced.
- frequency offset compensation is performed based on the residual frequency offset amount ⁇ fn , transmission data can be demodulated with higher precision than in the first embodiment.
- the residual frequency offset compensator 26a is also superimposed with an estimation error. Therefore, in order to reduce the estimation error, in the calculation of the vector averager 45 of the residual frequency offset compensator 26a, the value of N, which is the number of symbols to be averaged, is set to By setting the value to a large value, the estimation error superimposed by the residual frequency offset compensator 26a may be reduced, and the estimation accuracy may be improved.
- the timing detection unit 41 of the frequency offset amount estimation unit 31 provided in the residual frequency offset compensation unit 26a does not detect the leading position of the training symbol sequence from the digital signal, but the frequency offset compensation unit The start position of the training symbol sequence in the digital signal detected by the timing detector 41 of the frequency offset amount estimator 31 provided in 26 may be used. In this case, the start position of the training symbol sequence detected by the timing detection unit 41 of the frequency offset amount estimation unit 31 included in the frequency offset compensation unit 26 is determined by the timing detection unit of the frequency offset amount estimation unit 31 included in the residual frequency offset compensation unit 26a. An electric line for notification to notify 41 is required.
- the signal quality determination unit 91 calculates the SNR based on the residual frequency offset amount ⁇ f n , and based on the calculated SNR and a predetermined threshold value for the SNR, It may be determined whether or not the signal quality is degraded.
- the signal quality determination unit 91 may output the determination result to an external device such as a display device connected to the optical receiver 1a.
- the phase compensator 27 may include the residual frequency offset compensator 26a therein.
- FIG. 15 is a block diagram showing the configuration of an optical transmission system Ab, which is another configuration example of the second embodiment. Also in FIG. 15, the connection lines indicated by dashed lines are optical lines through which optical signals propagate, and the other connection lines are electric lines through which electrical signals are propagated.
- the optical transmission system Ab the same components as those of the optical transmission systems A and Aa of the first and second embodiments are denoted by the same reference numerals, and different configurations will be described below.
- the optical transmission system Ab includes an optical receiver 1b, an optical transmitter 2a, and an optical transmission line 3 and a communication line 4 that connect the optical receiver 1b and the optical transmitter 2a.
- the communication line 4 is shown as an electric line also in the optical transmission system Ab, it may be an optical line as in the case of the optical transmission system Aa.
- the optical receiver 1b includes a local oscillation light source 11, a receiver 12, and a digital signal processor 13b.
- the digital signal processing unit 13b includes a clock recovery unit 23, a polarization dispersion compensation unit 24, a chromatic dispersion compensation unit 25, a frequency offset compensation unit 26, a phase compensation unit 27, a demodulation unit 28, a signal quality determination unit 91b, and a transmission wavelength change instruction.
- a portion 92 is provided.
- the signal quality determination unit 91b is connected to the output side of the phase compensation unit 27 and takes in the digital signal phase-compensated by the phase compensation unit 27.
- the signal quality determination unit 91b calculates an error vector amplitude (hereinafter referred to as "EVM" (Error Vector Magnitude)) based on the captured digital signal.
- EVM Error Vector Magnitude
- the signal quality determination unit 91b uses the calculated EVM as an index indicating the degree of deterioration of the signal quality of the digital signal, and determines whether the signal quality of the digital signal is degraded based on the EVM and a predetermined threshold value. do.
- the signal quality determination unit 91 b outputs a transmission instruction signal to the transmission wavelength change instruction unit 92 when determining that the signal quality of the digital signal is degraded.
- the signal quality determination unit 91b uses EVM instead of the residual frequency offset amount ⁇ fn to perform the same processing as steps Sa10 and Sa11 in FIG. 13 performed by the signal quality determination unit 91.
- FIG. 1 the signal quality determination unit 91b uses EVM instead of the residual frequency offset amount ⁇ fn to perform the same processing as steps Sa10 and Sa11 in FIG. 13 performed by the signal quality determination unit 91.
- the wavelength of the signal light of the optical transmission device 2a can be adjusted in accordance with the quality deterioration of the received signal.
- the requirements for the frequency stability of the light source used to generate the signal light included in the optical transmission device 2a can be relaxed. It becomes possible to reduce the cost of 2a.
- the signal quality determination unit 91b calculates the SNR from the calculated EVM, and the signal quality of the digital signal deteriorates based on the calculated SNR and a predetermined threshold value for the SNR. You may make it determine whether it is carrying out.
- the signal quality determination unit 91b may output the determination result to an external device such as a display device connected to the optical receiver 1b.
- the optical receiver 1b may notify the optical transmitter 2a of the amount of change in wavelength corresponding to the magnitude of the EVM. .
- the signal quality determination unit 91b calculates an index indicating signal quality other than EVM based on the captured digital signal, and determines the signal quality of the digital signal based on the calculated index and a predetermined threshold value for the index. is degraded.
- the signal quality determination unit 91 of the optical transmission system Aa described above calculates the EVM from the digital signal phase-compensated by the phase compensation unit 27 like the signal quality determination unit 91b of the optical transmission system Ab, and the residual frequency offset amount ⁇ f n and Both EVM may be used to determine whether the signal quality of the digital signal is degraded, or the signal-to-noise ratio is calculated from both the residual frequency offset amount ⁇ f n and EVM, and Based on the obtained signal-to-noise ratio, it may be determined whether or not the signal quality of the digital signal is degraded.
- the optical transmitters 2 and 2a modulate the transmission data by the polarization multiplexing QPSK method.
- each of the optical receivers 1, 1a, and 1b is modulated by the receiving section 12 corresponding to the modulation scheme of the optical transmitters 2 and 2a facing each other, that is, by the modulation scheme of the optical transmitters 2 and 2a.
- a receiver 12 is provided for converting the signal light into a digital signal.
- the frequency offset amount of the frequency offset amount estimator 31 of the frequency offset compensator 26 included in the optical receivers 1, 1a, and 1b of the first and second embodiments and the frequency offset amount of the residual frequency offset compensator 26a included in the optical receiver 1a As the estimating unit 31, an example using a method based on differential detection shown in Non-Patent Document 3 has been described. If there is, any method may be used, for example, the methods disclosed in Non-Patent Documents 1 and 2 may be used.
- the range of the estimable frequency offset amount is narrower than the range of ⁇ B/2 or more and +B/2 or less, compensation Since the post-frequency offset amount ⁇ f c does not become an integral multiple of the symbol rate B and is affected by phase rotation, such a conventional method cannot be used.
- the polarization phase diversity receiver 10 included in the optical receivers 1, 1a, and 1b of the first and second embodiments may be a receiver that performs only polarization diversity, or performs only phase diversity. It may be a receiver.
- the optical receivers 1, 1a, and 1b of the first and second embodiments described above are provided with the frequency offset compensator 26 after the chromatic dispersion compensator 25. may be provided with a frequency offset compensator 26 .
- the optical receiver 1a may be provided with a frequency offset compensator 26 and a residual frequency offset compensator 26a before the chromatic dispersion compensator 25.
- step Sa11 determination processing using inequality signs with equal signs is performed in the processing shown in step Sa11.
- the present invention is not limited to this embodiment. may be replaced with the determination process.
- the digital signal processing units 13, 13a, and 13b in the above-described embodiments may be realized by computers.
- a program for realizing this function may be recorded in a computer-readable recording medium, and the program recorded in this recording medium may be read into a computer system and executed.
- the "computer system” referred to here includes hardware such as an OS and peripheral devices.
- the term "computer-readable recording medium” refers to portable media such as flexible discs, magneto-optical discs, ROMs and CD-ROMs, and storage devices such as hard discs incorporated in computer systems.
- “computer-readable recording medium” means a medium that dynamically retains a program for a short period of time, like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. It may also include something that holds the program for a certain period of time, such as a volatile memory inside a computer system that serves as a server or client in that case. Further, the program may be for realizing a part of the functions described above, or may be capable of realizing the functions described above in combination with a program already recorded in the computer system. It may be implemented using a programmable logic device such as an FPGA (Field Programmable Gate Array).
- FPGA Field Programmable Gate Array
- SYMBOLS 1 ... Optical receiver, 2... Optical transmitter, 3... Optical transmission line, A... Optical transmission system, 12... Receiver, 13... Digital signal processor, 21... Polarization phase diversity receiver, 22... AD converter , 22-1 to 22-4 ADC, 23 Clock recovery unit 24 Polarization dispersion compensation unit 25 Wavelength dispersion compensation unit 26 Frequency offset compensation unit 27 Phase compensation unit 28 Demodulation unit
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Abstract
Description
以下、本発明の実施形態について図面を参照して説明する。図1は、本発明の一実施形態である第1の実施形態による光伝送システムAの構成を示すブロック図である。図1において、一点鎖線で示す接続線は光信号が伝搬する光回線であり、それ以外の接続線は電気信号が伝搬する電気回線である。
次に、第1の実施形態の光受信装置1の周波数オフセット補償部26による処理について説明する。図4は、周波数オフセット補償部26による処理の流れを示すフローチャートである。
光受信装置1が受光する信号光と、局部発振光源11が出力するローカル光との波長差、すなわち実際の周波数オフセット量Δfが、-B/2以上であって+B/2以下の範囲に含まれない場合、周波数オフセット量推定部31は、-B/2以上であって+B/2以下の範囲でしか推定することができないため、誤った周波数オフセット量を推定していることになる。
図9は、第2の実施形態による光伝送システムAaの構成を示すブロック図である。なお、図9においても、一点鎖線で示す接続線は、光信号が伝搬する光回線であり、それ以外の接続線は、電気信号が伝搬する電気回線である。光伝送システムAaにおいて、第1の実施形態の光伝送システムAと同一の構成については、同一の符号を付し、以下、異なる構成について説明する。
図12は、残留周波数オフセット補償部26aによる処理の流れを示すフローチャートである。残留周波数オフセット補償部26aは、周波数オフセット補償部26が周波数オフセット補償したデジタル信号を取り込む(ステップSa1)。ステップSa2~ステップSa6は、図4に示したステップS2~S6と同様の処理が、残留周波数オフセット補償部26aの周波数オフセット量推定部31によって行われる。ただし、ステップSa6において、演算部47が算出して出力するのは、推定周波数オフセット量Δfestではなく、残留周波数オフセット量Δfnである。
図13は、信号品質判定部91と送信波長変更指示部92による処理の流れを示すフローチャートである。信号品質判定部91は、残留周波数オフセット補償部26aの周波数オフセット量推定部31の演算部47が、図12に示したフローチャートのステップSa6の処理において算出して出力する残留周波数オフセット量Δfnを取り込む(ステップSa10)。なお、ステップSa10の処理は、図12のステップSa7の処理と並列に行われる処理である。
図15は、第2の実施形態の他の構成例である光伝送システムAbの構成を示すブロック図である。なお、図15においても、一点鎖線で示す接続線は、光信号が伝搬する光回線であり、それ以外の接続線は、電気信号が伝搬する電気回線である。光伝送システムAbにおいて、第1及び第2の実施形態の光伝送システムA,Aaと同一の構成については、同一の符号を付し、以下、異なる構成について説明する。
Claims (7)
- 局部発振光を生成する局部発振光源と、
送信データを光変調することにより生成されたシンボルレートBの信号光を受光し、受光した前記信号光と、前記局部発振光源が生成する前記局部発振光とを干渉させることによりデジタルコヒーレント受信を行って前記信号光を電気のデジタル信号に変換して出力する受信部であって電気帯域の範囲が-Beから+Beの範囲であってBe>B/2である受信部と、
前記受信部が出力する前記デジタル信号から前記送信データを復調するデジタル信号処理部と、を備え、
前記デジタル信号処理部は、
前記信号光と前記局部発振光との間の周波数差に応じて前記デジタル信号において生じる周波数オフセット量を-B/2以上であって+B/2以下の範囲で推定し、推定した前記周波数オフセット量に基づいて前記デジタル信号に対して周波数オフセット補償することにより、-B/2以上であって+B/2以下の範囲の周波数オフセット量を補償し、かつ-B/2未満の範囲及び+B/2を超える範囲の周波数オフセット量の場合にシンボルレートBの整数倍の周波数オフセット量を残すように補償する周波数オフセット補償部
を備える光受信装置。 - 前記周波数オフセット補償部が周波数オフセット補償した前記デジタル信号における信号品質の劣化度合いを示す指標を検出し、検出した前記信号品質の劣化度合いを示す指標と、予め定められる閾値とに基づいて、前記デジタル信号の信号品質が劣化しているか否かを判定する信号品質判定部
をさらに備える請求項1に記載の光受信装置。 - 前記デジタル信号処理部は、
前記周波数オフセット補償部が周波数オフセット補償した前記デジタル信号において生じている前記周波数オフセット量を-B/2以上であって+B/2以下の範囲で推定し、推定した前記周波数オフセット量を前記デジタル信号に含まれる残留周波数オフセット量とする周波数オフセット量推定部を備え、
前記信号品質判定部は、
前記残留周波数オフセット量を、前記信号品質の劣化度合いを示す指標として、前記デジタル信号の信号品質が劣化しているか否かを判定するか、または、前記残留周波数オフセット量から信号対雑音比を算出し、算出した前記信号対雑音比を前記信号品質の劣化度合いとして、前記デジタル信号の信号品質が劣化しているか否かを判定する、
請求項2に記載の光受信装置。 - 前記デジタル信号処理部は、
前記信号光と前記局部発振光との間の位相差を検出し、検出した位相差に基づいて前記デジタル信号に対して位相補償を行う位相補償部
を備えており、
前記信号品質判定部は、
前記位相補償部が位相補償した前記デジタル信号に基づいてエラーベクトル振幅を算出し、算出した前記エラーベクトル振幅を前記信号品質の劣化度合いを示す指標として、前記デジタル信号の信号品質が劣化しているか否かを判定するか、または、前記エラーベクトル振幅から信号対雑音比を算出し、算出した前記信号対雑音比を前記信号品質の劣化度合いとして、前記デジタル信号の信号品質が劣化しているか否かを判定する、
請求項2又は3に記載の光受信装置。 - 前記信号品質判定部が、前記デジタル信号の信号品質が劣化していると判定した場合、前記送信データを送信した光送信装置に対して前記信号光の波長を変更することを指示する指示信号を送信する送信波長変更指示部
をさらに備える請求項2から4のいずれか一項に記載の光受信装置。 - 前記デジタル信号処理部は、
前記周波数オフセット補償部が周波数オフセット補償した前記デジタル信号において生じている前記周波数オフセット量を-B/2以上であって+B/2以下の範囲で推定し、推定した前記周波数オフセット量を前記デジタル信号に含まれる残留周波数オフセット量とする周波数オフセット量推定部と、
前記残留周波数オフセット量に基づいて、前記周波数オフセット補償部が周波数オフセット補償した前記デジタル信号に対して周波数オフセット補償する補償処理部と、を有する残留周波数オフセット補償部を備える、
請求項1に記載の光受信装置。 - 局部発振光源が、局部発振光を生成し、
電気帯域の範囲が-Beから+Beの範囲であってBe>B/2である受信部が、送信データを光変調することにより生成されたシンボルレートBの信号光を受光し、受光した前記信号光と、前記局部発振光源が生成する前記局部発振光とを干渉させることによりデジタルコヒーレント受信を行って前記信号光を電気のデジタル信号に変換して出力し、
前記受信部が出力する前記デジタル信号から前記送信データを復調するデジタル信号処理部が備える周波数オフセット補償部が、前記信号光と前記局部発振光との間の周波数差に応じて前記デジタル信号において生じる周波数オフセット量を-B/2以上であって+B/2以下の範囲で推定し、推定した前記周波数オフセット量に基づいて前記デジタル信号に対して周波数オフセット補償することにより、-B/2以上であって+B/2以下の範囲の周波数オフセット量を補償し、かつ-B/2未満の範囲及び+B/2を超える範囲の周波数オフセット量の場合にシンボルレートBの整数倍の周波数オフセット量を残すように補償する、
周波数オフセット補償方法。
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JP2019110479A (ja) * | 2017-12-19 | 2019-07-04 | 日本電信電話株式会社 | 光受信装置、光送信装置及び周波数オフセット推定方法 |
JP2020039089A (ja) * | 2018-09-05 | 2020-03-12 | 日本電信電話株式会社 | 光受信装置、光送信装置、及び周波数オフセット推定方法 |
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JP2019110479A (ja) * | 2017-12-19 | 2019-07-04 | 日本電信電話株式会社 | 光受信装置、光送信装置及び周波数オフセット推定方法 |
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