CN110212990B - Signal receiving method for coherent optical communication - Google Patents

Signal receiving method for coherent optical communication Download PDF

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CN110212990B
CN110212990B CN201910349459.5A CN201910349459A CN110212990B CN 110212990 B CN110212990 B CN 110212990B CN 201910349459 A CN201910349459 A CN 201910349459A CN 110212990 B CN110212990 B CN 110212990B
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signal
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carrier phase
phase noise
recovery
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杨彦甫
向前
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Shenzhen Graduate School Harbin Institute of Technology
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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
    • H04B10/6165—Estimation of the phase of the received optical signal, phase error estimation or phase error correction

Abstract

The invention provides a signal receiving method of coherent optical communication, which comprises the steps of generating a level signal through an arbitrary waveform generator, then leading the level signal into an IQ modulator for photoelectric modulation, generating Gaussian white noise through a noise source with variable power, mixing the Gaussian white noise and a modulated optical signal through an optical coupler, carrying out data acquisition on signal light and local oscillator light through a data acquisition oscilloscope after passing through a band-pass optical filter, processing the acquired electrical signal through a subsequent offline digital signal processing module, and sequentially carrying out low-pass filtering, resampling, clock recovery, signal equalization, frequency offset estimation, carrier recovery and error code judgment on the acquired electrical signal through the digital signal processing module. The invention has the beneficial effects that: the coherent optical communication signal receiving method has the advantages of transparent modulation format and large line width tolerance.

Description

Signal receiving method for coherent optical communication
Technical Field
The present invention relates to optical communications, and in particular, to a signal receiving method for coherent optical communications.
Background
With the development and rapid deployment of technologies and services such as cloud computing, internet of things, unmanned driving and the like, network traffic demands have presented a burst-type and unpredictable development mode. To accommodate this highly dynamic network traffic demand, variable bandwidth transmitters capable of adaptive modulation format and transmission rate adjustment are becoming the primary technology to support this demand. However, dynamic switching of modulation formats brings a series of challenges to the digital signal processing part of the receiving end, for example: how to achieve carrier phase recovery without knowing any modulation information. The carrier phase noise is mainly caused by the phase difference between the signal light and the local oscillator light, which causes serious distortion of the signal.
Therefore, in order to adapt to the next generation flexible optical network development, it is necessary to provide a carrier recovery scheme with transparent modulation format and large line width tolerance.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a signal receiving method for coherent optical communication.
The invention provides a signal receiving method of coherent optical communication, which generates a level signal through an arbitrary waveform generator, then introduces the level signal into an IQ modulator for photoelectric modulation, generates Gaussian white noise through a noise source with variable power, mixes the Gaussian white noise and a modulated optical signal through an optical coupler, acquires data through a data acquisition oscilloscope after passing through a band-pass optical filter, processes the acquired electrical signal through a subsequent off-line digital signal processing module, and sequentially performs low-pass filtering, resampling, clock recovery, signal equalization, frequency offset estimation, carrier recovery and error code judgment on the acquired electrical signal by the digital signal processing module, wherein the carrier recovery is a modulation format transparent carrier recovery method based on 4-order statistic minimization, and the method specifically comprises the following processes: after the effects of dispersion, polarization rotation, frequency offset, etc. are fully compensated, the received signal is represented as follows:
r(n)＝s(n)ejθ(n)+ξ(n) (1)
wherein r (n) and s (n) represent the received signal and the ideal transmitted signal, respectively, θ (n) represents the carrier phase noise, which is described as a mean of 0 and a variance of 2 π Δ ν TsOf (2) accumulated random Gaussian noise, Δ ν and TsRepresenting the laser linewidth and the time interval between adjacent symbols, respectively, in addition to ξ (n) being an additional white gaussian additive noise:
as shown in equation (1), the carrier phase noise is described as a linear superposition of the IQ component of the transmitted signal, expressed as follows:
Figure GDA0002612232050000021
where I and Q represent the real and imaginary parts of the signal, respectively, Y and X represent the IQ component matrix of the received and transmitted signal, respectively, W is the linear mixing matrix, and ξ is the IQ component matrix of white noise, so the compensation scheme is described by equation (3), i.e.: multiplying the received Y signal by an inverse linear mixing matrix:
Figure GDA0002612232050000022
where Z is the recovered signal, M is the inverse mixing matrix,
Figure GDA0002612232050000031
the carrier phase noise is estimated, the carrier phase recovery of the signal is realized by minimizing the kurtosis of the recovered signal, since M is a unitary matrix, the variance of the received signal is a constant c, and the cost function based on the minimized kurtosis is expressed as follows:
Figure GDA0002612232050000032
where E () represents the expectation over a time window, to achieve dynamic carrier phase noise tracking, a sliding window of length L is substituted for the expected operation to compute the 4 th order statistic of the signal, so the cost function J is further simplified as follows:
Figure GDA0002612232050000033
estimated carrier phase noise by deriving the estimated phase noise from equation (5)
Figure GDA0002612232050000035
The update is as follows:
Figure GDA0002612232050000034
where μ is the update step size.
The invention has the beneficial effects that: by the scheme, the coherent optical communication signal receiving method has the advantages of being transparent in modulation format and large in line width tolerance.
Drawings
Fig. 1 is a simulation model diagram of a signal receiving method of coherent optical communication according to the present invention.
Fig. 2 is a graph comparing the bit error rate Vs osnr of the present invention with the prior art.
Figure 3 is a graph comparing osnr penalty Vs laser linewidth for the present invention and prior art schemes.
Detailed Description
The invention is further described with reference to the following description and embodiments in conjunction with the accompanying drawings.
As shown in fig. 1, a coherent optical communication signal receiving method includes generating a level signal by an arbitrary waveform generator, then introducing the level signal into an IQ modulator for performing optical-electrical modulation, generating white gaussian noise by a noise source with variable power, mixing the white gaussian noise and a modulated optical signal by an optical coupler, performing data acquisition by a data acquisition oscilloscope after passing through a band-pass optical filter, processing an acquired electrical signal by a subsequent offline digital signal processing module, and sequentially performing low-pass filtering, resampling, clock recovery, signal equalization, frequency offset estimation, carrier recovery and error code decision on the acquired electrical signal by the digital signal processing module, where carrier recovery is a modulation format transparent carrier recovery method based on 4-order statistic minimization, and specifically includes the following processes: after the effects of dispersion, polarization rotation, frequency offset, etc. are fully compensated, the received signal may represent the following:
r(n)＝s(n)ejθ(n)+ξ(n) (1)
where r (n) and s (n) represent the received signal and the ideal transmitted signal, respectively, and θ (n) represents the carrier phase noise. In general, phase noise is generally described as a mean of 0 and a variance of 2 π Δ ν TsOf (2) accumulated random Gaussian noise, Δ ν and TsRepresenting the laser linewidth and the time interval between adjacent symbols, respectively, except that ξ (n) is an additional white gaussian additive noise.
As shown in equation (1), the carrier phase noise can also be described as a linear superposition of the IQ components of the transmitted signal, expressed as follows:
Figure GDA0002612232050000041
where the real and imaginary parts of the I and Q signals, Y and X represent the IQ component matrices of the received and transmitted signals, respectively, W is the linear mixing matrix and ξ is the IQ component matrix of white noise.
The compensation scheme can therefore be described by equation (3), namely: multiplying the received Y signal by an inverse linear mixing matrix:
Figure GDA0002612232050000051
where Z is the recovered signal, M is the inverse mixing matrix,
Figure GDA0002612232050000052
is the estimated carrier phase noise.
Based on blind source separation theory, the mixed signals tend to be in normalized gaussian distribution with kurtosis of 0, however, the kurtosis of the modulation format commonly used in the optical communication system tends to be negative, so carrier phase recovery of the signals can be realized by minimizing the kurtosis of the recovered signals, since M is a unitary matrix, the variance of the received signals is a constant c, and the cost function based on the minimized kurtosis can be expressed as follows:
Figure GDA0002612232050000053
where E () represents a desire within a time window.
To achieve dynamic carrier phase noise tracking, a sliding window of length L is used to calculate the 4 th order statistic of the signal instead of the desired operation, so the cost function J can be further simplified as follows:
Figure GDA0002612232050000054
by evaluating equation (5)Calculating phase noise to derive estimated carrier phase noise
Figure GDA0002612232050000056
The following may be updated:
Figure GDA0002612232050000055
where μ is the update step size.
Fig. 1 is a simulation model of coherent optical communication according to an embodiment of the present invention, which includes the following specific processes:
the arbitrary waveform generator generates a level signal commonly used in 28GS/s QPSK/16QAM/64QAM and the like, and then the level signal is introduced into an IQ modulator for photoelectric modulation. Next, white gaussian noise is generated by a variable power noise source and the white noise and the modulated optical signal are mixed by an optical coupler. After passing through the band-pass optical filter, the signal light and the local oscillator light are subjected to data acquisition through the data acquisition oscilloscope, and the acquired electric signals pass through the subsequent off-line digital signal processing module. The digital signal processing module mainly comprises low-pass filtering, resampling, clock recovery, signal equalization, frequency offset estimation, carrier recovery and error code judgment. Then, the disclosed existing scheme and the invention scheme are used for carrier recovery of signals, and the optical signal ratio cost and the laser line width tolerance of the two schemes are compared by adjusting the laser line width and the noise source power.
As shown in fig. 2 and 3, in fig. 2, (a) QPSK, (b)16QAM and (c)64QAM, and in fig. 3, (a) QPSK, (b)16QAM and (c)64QAM, the bit error rates of the two schemes are a function of the optical signal-to-noise ratio. The osnr sensitivity of the signal in a back-to-back scenario is used to calculate the osnr implementation cost of the two schemes. At a target error rate of 7% FEC, existing schemes require approximately 0.4dB and 2.12dB optical signal-to-noise ratio penalties for 16QAM and 64QAM signals. The OSNR penalty required by the present invention is only 0.2dB and 1.1dB OSNR penalty for the same error code requirement. Compared with the prior scheme, the invention saves the optical signal-to-noise ratio of 0.2dB and 1.02dB for 16QAM and 64 QAM.
Second, the osnr penalty of both schemes varies with the laser linewidth. Both schemes have a relatively small optical signal-to-noise ratio penalty when the laser linewidth is small. As the laser linewidth increases, there is a significant difference in the osnr penalty of the two schemes. Under the condition of 1dB optical signal-to-noise ratio cost, for QPSK/16QAM/64QAM signals, the invention can respectively tolerate the maximum laser line width of 4MHz,1MHz and 100KHz, which is 4 times of the existing scheme. The reason that the performance of the existing scheme is poor under the condition of the maximum laser line width is mainly that the cost function is also based on the statistical characteristics of signals, a large estimation error occurs to the fast time-varying phase noise when the phase noise estimation is carried out by using a single symbol, and the estimation accuracy of the phase noise is easily influenced by the ASE noise.
The modulation format transparent carrier recovery method based on 4-order statistic minimization has the advantages of low optical signal-to-noise ratio cost and large line width tolerance, and is a carrier phase recovery scheme with a transparent modulation format and large line width tolerance.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims (1)

1. A signal receiving method of coherent optical communication, characterized in that: generating a level signal through an arbitrary waveform generator, then leading the level signal into an IQ modulator for photoelectric modulation, generating Gaussian white noise through a noise source with variable power, mixing the Gaussian white noise and a modulated optical signal through an optical coupler, after the mixture passes through a band-pass optical filter, performing data acquisition on the signal light and a local oscillator light through a data acquisition oscilloscope, processing the acquired electrical signal through a subsequent offline digital signal processing module, and sequentially performing low-pass filtering, resampling, clock recovery, signal equalization, frequency offset estimation, carrier recovery and error code judgment on the acquired electrical signal by the digital signal processing module, wherein the carrier recovery is a modulation format transparent carrier recovery method based on 4-order statistic minimization, and the method specifically comprises the following processes:
after the dispersion, polarization rotation, and frequency offset effects are fully compensated, the received signal represents the following:
r(n)＝s(n)ejθ(n)+ξ(n) (1)
wherein r (n) and s (n) represent the received signal and the ideal transmitted signal, respectively, θ (n) represents the carrier phase noise, which is described as a mean of 0 and a variance of 2 π Δ ν TsOf (2) accumulated random Gaussian noise, Δ ν and TsRepresenting the laser linewidth and the time interval between adjacent symbols, respectively, in addition to ξ (n) being an additional white gaussian additive noise:
as shown in equation (1), the carrier phase noise is described as a linear superposition of the IQ component of the transmitted signal, expressed as follows:
Figure FDA0002612232040000011
where I and Q represent the real and imaginary parts of the signal, respectively, Y and X represent the IQ component matrix of the received and transmitted signal, respectively, W is the linear mixing matrix, and ξ is the IQ component matrix of white noise, so the compensation scheme is described by equation (3), i.e.: multiplying the received Y signal by an inverse linear mixing matrix:
Figure FDA0002612232040000021
where Z is the recovered signal, M is the inverse mixing matrix,
Figure FDA0002612232040000022
is the estimated carrier phase noise;
the carrier phase recovery of the signal is realized by minimizing the kurtosis of the recovered signal, since M is a unitary matrix, the variance of the received signal is constant c, and the cost function based on the minimized kurtosis is expressed as follows:
Figure FDA0002612232040000023
where E () represents the expectation over a time window, to achieve dynamic carrier phase noise tracking, a sliding window of length L is substituted for the expected operation to compute the 4 th order statistic of the signal, so the cost function J is further simplified as follows:
Figure FDA0002612232040000024
estimated carrier phase noise by deriving the estimated phase noise from equation (5)
Figure FDA0002612232040000025
The update is as follows:
Figure FDA0002612232040000026
where μ is the update step size.
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EP3110043A1 (en) * 2015-06-22 2016-12-28 Alcatel Lucent Carrier phase estimation at a coherent optical receiver
CN108683620A (en) * 2018-03-19 2018-10-19 西安电子科技大学 A kind of blind carrier recovering method of anti-phase noise of suitable high-order modulating
WO2018213251A1 (en) * 2017-05-15 2018-11-22 The Board Of Trustees Of The Leland Stanford Junior University Dsp-free coherent receiver
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EP3110043A1 (en) * 2015-06-22 2016-12-28 Alcatel Lucent Carrier phase estimation at a coherent optical receiver
WO2018213251A1 (en) * 2017-05-15 2018-11-22 The Board Of Trustees Of The Leland Stanford Junior University Dsp-free coherent receiver
CN108683620A (en) * 2018-03-19 2018-10-19 西安电子科技大学 A kind of blind carrier recovering method of anti-phase noise of suitable high-order modulating
CN109243483A (en) * 2018-10-17 2019-01-18 西安交通大学 A kind of noisy frequency domain convolution blind source separation method
CN109347561A (en) * 2018-11-06 2019-02-15 聊城大学 A kind of low power high speed rate Dispersion Flattened Fiber Transmission system
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