CN109347776B - Method for identifying modulation format of optical communication signal with differential phase-to-amplitude ratio - Google Patents

Method for identifying modulation format of optical communication signal with differential phase-to-amplitude ratio Download PDF

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CN109347776B
CN109347776B CN201811416115.3A CN201811416115A CN109347776B CN 109347776 B CN109347776 B CN 109347776B CN 201811416115 A CN201811416115 A CN 201811416115A CN 109347776 B CN109347776 B CN 109347776B
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杨爱英
郭芃
谭庆照
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Beijing Institute of Technology BIT
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0012—Modulated-carrier systems arrangements for identifying the type of modulation
    • 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
    • H04B10/612—Coherent receivers for optical signals modulated with a format different from binary or higher-order PSK [X-PSK], e.g. QAM, DPSK, FSK, MSK, ASK
    • 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
    • H04B10/6161—Compensation of chromatic dispersion
    • 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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Abstract

The invention relates to a method for identifying a modulation format of an optical communication signal with a differential phase-to-amplitude ratio, and belongs to the technical field of modulation identification. The method comprises the following steps: step A, carrying out coherent detection, front end equalization, dispersion compensation, clock recovery and carrier frequency offset compensation on an input optical communication signal to be detected; step B, calculating AAR and DPDR in an MFI module; step C, calculating a modulation format identification factor R; step D, identifying the optical signal modulation format of the output of the step A; step E, carrying out self-adaptive equalization according to the optical signal modulation format; f, carrier phase recovery is carried out; and G, judging and decoding. The method can identify the modulation format of the optical signal without carrier recovery when the OSNR is not less than 12 dB; a large amount of training data sets and complex calculation are not needed; when the input signal OSNR is not less than 12dB, three modulation modes of QPSK, 16QAM and 64QAM can be identified.

Description

Method for identifying modulation format of optical communication signal with differential phase-to-amplitude ratio
Technical Field
The invention relates to a method for identifying a modulation format of an optical communication signal with a differential phase-to-amplitude ratio, and belongs to the technical field of modulation identification.
Background
To meet the increasing global IP traffic capacity demand, optical networks are evolving from traditional fixed networks to flexible and adaptive resilient optical network architectures. Research shows that the multi-system amplitude-phase joint modulation (MQAM) format can realize the transmission of signals with variable bit rates by changing M3 through hardware configuration. For an elastic optical network with flexibly switched multiple modulation formats, an optical receiver needs to have the capability of adaptively and blindly identifying different modulation formats, so that necessary modulation format information is provided for subsequent digital signal processing of the receiver, such as carrier phase noise estimation and frequency offset compensation.
Therefore, optical communication signal modulation format identification techniques are of interest. In 2015, researchers proposed a modulation format blind identification technique based on calculating peak-to-average power ratio (PAPR): after analog-to-digital conversion, dispersion and polarization mode dispersion equalization are carried out on coherent light receiving data, the peak-to-average power ratio (PAPR) of the data is calculated, and the modulation format is identified through the corresponding relation between the optical signal-to-noise ratio (OSNR) and the PAPR. This method requires prior knowledge of the OSNR of the optical signal. In recent years, Deep Learning (DL) is a popular research area. A DL-based MFI method is also proposed. Researchers propose a convolutional neural network modulation format recognition algorithm based on constellation diagram analysis, and the disadvantage is that the convolutional neural network modulation format recognition algorithm is bound with a carrier phase noise recovery algorithm, so that the application range of the method is limited. Researchers have also proposed using Deep Neural Networks (DNNs) that identify signal amplitude histogram distribution patterns for modulation format identification. However, extensive training data sets and huge computational effort are required in these DL methods. The method of identifying modulation formats based on normalized amplitude of a normalized distribution function (CDF) curve requires that reference CDFs for all possible modulation formats be pre-established as a database.
The present application intends to identify the three most commonly used formats in coherent optical transmission systems by calculating a Differential Phase Distribution Ratio (DPDR) and an Average Amplitude Ratio (AAR): QPSK, 16QAM, and 64 QAM.
Disclosure of Invention
The invention aims to overcome the technical defects of high complexity and high OSNR requirement of the existing optical communication signal modulation format identification method, and provides an optical communication signal modulation format identification method with a differential phase-to-amplitude ratio.
The method has the core idea that based on the differential phase distribution ratio DPDR and the average amplitude ratio AAR, a modulation format identification factor R is defined: the product of DPDR and AAR to distinguish whether the signal modulation format is QPSK, 16QAM, or 64 QAM.
A receiver supported by the method for identifying the modulation format of an optical communication signal with a differential phase-to-amplitude ratio mainly comprises a coherent detection unit, a front-end equalization unit, a dispersion compensation unit, a clock recovery unit, a frequency offset compensation unit, a frequency offset self-adaptive compensation unit, a modulation format self-adaptive identification module, a self-adaptive equalization unit, a carrier phase recovery unit and a judgment and decoding unit;
the modulation format adaptive identification module is also called as MFI module;
the connection relationship of each module and unit in the receiver is as follows:
a coherent detection unit and a front end equalization unit; the front end equalizing unit is connected with the dispersion compensation unit; the dispersion compensation unit is connected with the clock recovery unit, and the clock recovery unit is connected with the frequency offset compensation unit; the frequency offset compensation unit is connected with the MFI module; the MFI module is connected with the self-adaptive equalization unit; the self-adaptive equalization unit is connected with the carrier phase recovery unit; the carrier phase recovery unit is connected with the judgment and decoding unit;
a method for identifying modulation format of optical communication signal with differential phase-amplitude ratio, namely the working process of receiver, includes the following steps:
step A, carrying out coherent detection on an input optical communication signal to be detected in a coherent detection unit;
b, performing front-end equalization on the signal output by the coherent detection in the step A in a front-end equalization unit;
c, performing dispersion compensation on the output signal subjected to front end equalization in the step B in a dispersion compensation unit;
d, performing clock recovery on the signal subjected to dispersion compensation in the step C in a clock recovery unit;
e, carrying out carrier frequency offset compensation on the signal recovered by the clock in the step D in a frequency offset compensation unit;
the carrier frequency offset compensated signal can be expressed as (1):
Figure BDA0001879515240000021
wherein A isnRepresenting the carrier frequency offset compensated signal SnJ denotes the imaginary unit, anRepresenting the modulation phase of the signal after the carrier frequency offset compensation; thetanRepresenting the phase noise of the carrier frequency offset compensated signal; n represents the total number of sampling points; n represents the serial number of the sampling point, and the value range of N is 1 to N; when the laser linewidth is less than 10MHz, the phase noise difference of adjacent symbols is considered to be approximately equal, i.e. θn+1≈θnTherefore, the phase difference between adjacent symbols of the signal after carrier frequency offset compensation is approximately:
Figure BDA0001879515240000022
step F, calculating AAR and DPDR in an MFI module based on the signal output after the frequency offset compensation in the step E;
wherein, AAR represents the average amplitude ratio, DPDR represents the differential phase distribution ratio;
the calculation expression of AAR is as follows (2):
Figure BDA0001879515240000023
wherein, γn＝max(An,An+1)/min(An,An+1)；max(An,An+1) Is represented by AnAnd An+1The larger of the two, min (A)n,An+1) (ii) a Is represented by AnAnd An+1The smaller of the two;
the calculation expression of DPDR is as follows (3):
Figure BDA0001879515240000031
wherein, if
Figure BDA0001879515240000032
If yes, theta is 1, otherwise theta is 0, wherein ξ is a threshold, ξ needs to be optimized and selected, and the standard of the optimized selection is to distinguish modulation formats of optical signals with different signal-to-noise ratios;
step G, calculating the product of AAR and DPDR in the MFI module, and calling the product as a modulation format identification factor R;
step G is specifically expressed as formula (4):
R＝η(ξ)·γ (4)
step H, identifying the modulation format of the optical signal for the signal output by the carrier frequency offset compensation unit in the step E based on the calculated modulation format identification factor:
if R is less than 13, the modulation format of the optical signal is QPSK;
if R is greater than or equal to 13 and less than 28, the modulation format of the optical signal is 16 QAM;
if R is greater than or equal to 28, the modulation format of the optical signal is 64 QAM;
step I, carrying out self-adaptive equalization in a self-adaptive equalization unit according to the optical signal modulation format identified in the step H;
step J, carrying out carrier phase recovery on the result of the self-adaptive equalization output in the step H in a carrier phase recovery unit;
and step K, judging and decoding the result output by the carrier phase recovery in the step J in a judging and decoding unit.
Advantageous effects
Compared with the prior art, the method for identifying the modulation format of the optical communication signal with the differential phase-to-amplitude ratio has the following beneficial effects:
1. the method can identify the modulation format of the optical signal when the OSNR is not less than 12dB, and does not need carrier recovery;
2. the method does not need a large amount of training data sets and complex calculation;
3. the experiment and simulation results of the method show that when the OSNR of the input signal is not less than 12dB, the proposed method can identify three modulation modes of QPSK, 16QAM and 64 QAM.
Drawings
FIG. 1 is a system diagram and connection relationship based on the method for identifying modulation format of optical communication signal with differential phase-to-amplitude ratio according to the present invention;
FIG. 2 is a diagram of system setup and scenario for an embodiment of a method for identifying modulation formats of optical communication signals with differential phase-to-amplitude ratios of the present invention;
FIG. 3 is a simulation result of step F when the method for identifying modulation format of optical communication signal with differential phase-to-amplitude ratio according to the present invention is implemented;
fig. 4 is a simulation result of step G of the method for identifying modulation format of optical communication signal with differential phase-to-amplitude ratio according to the present invention.
Detailed Description
The invention is further described with reference to the following detailed description and accompanying drawings.
Example 1
This embodiment describes a specific implementation of the method for identifying modulation format of optical communication signal by using the differential phase-amplitude ratio according to the present invention.
FIG. 1 is a system diagram and connection relationship based on the method for identifying modulation format of optical communication signal with differential phase-to-amplitude ratio according to the present invention; fig. 2 shows the system design in an implementation.
In fig. 2, at the transmitting end, a continuous wave Laser, CW Laser, is modulated by an IQ modulator, i.e.
IQMOD; in an IQ modulator, an I path signal and a Q path signal are modulated by two random bit sequences generated by an arbitrary waveform generator; the emitted laser signal is 1550nm and the line width is 5 kHz.
The IQ modulator respectively generates QPSK, 16QAM and 64QAM modulation signals with the rate of 10 Gbaud, the transmitting power is 0dBm, and the signals are transmitted through a 100k standard optical fiber. The transmitted optical signal is amplified by the first erbium-doped fiber amplifier EDFA 1 and is mixed with spontaneous emission optical noise generated by the second erbium-doped fiber amplifier EDFA 2 through the 3dB coupler.
Wherein the signal-to-noise ratio of the measured optical signal is measured by the spectrometer OSA. In order to change the signal-to-noise ratio of the measured optical signal, the magnitude of the spontaneous emission optical noise power generated by the EDFA 2 is changed by adjusting the optical attenuator Att.
The transmitted optical signal and the spontaneous radiation optical noise are mixed to form an optical signal with an identified modulation format, and the optical signal and the local oscillator laser are coupled into an optical mixer; the mixing is performed in an optical mixer and then the coherent demodulation is performed by a balanced detector.
FIG. 3 is a simulation result of AAR in step F when the method for identifying modulation format of optical communication signal with differential phase-to-amplitude ratio according to the present invention is implemented; as can be seen from fig. 3, the calculated average amplitude ratio can be used for better distinguishing the three modulation modes.
In order to further improve the distinguishing performance, a modulation format identification factor R is introduced, and the simulation result is shown in fig. 4.
Fig. 4 is a simulation result of the method for identifying the modulation format of the optical communication signal with a differential phase-to-amplitude ratio according to the present invention. The method is particularly applied to a back-to-back system.
As is apparent from fig. 4, the modulation format recognition factor R can well distinguish the optical signals of the three modulation schemes, and can still clearly distinguish the optical signals even when the OSNR is 10 dB.
While the foregoing is directed to the preferred embodiment of the present invention, it is not intended that the invention be limited to the embodiment and the drawings disclosed herein. Equivalents and modifications may be made without departing from the spirit of the disclosure, which is to be considered as within the scope of the invention.

Claims (2)

1. A method for identifying modulation format of optical communication signal with differential phase amplitude ratio comprises a receiver used in the method mainly comprises a coherent detection unit, a front end equalization unit, a dispersion compensation unit, a clock recovery unit, a frequency offset compensation unit, a frequency offset self-adaptive compensation unit, a modulation format self-adaptive identification module, a self-adaptive equalization unit, a carrier phase recovery unit and a judgment and decoding unit;
the modulation format adaptive identification module is also called as MFI module;
the connection relationship of each module and unit in the receiver is as follows:
the coherent detection unit is connected with the front end equalization unit; the front end equalizing unit is connected with the dispersion compensation unit; the dispersion compensation unit is connected with the clock recovery unit, and the clock recovery unit is connected with the frequency offset compensation unit; the frequency offset compensation unit is connected with the MFI module; the MFI module is connected with the self-adaptive equalization unit; the self-adaptive equalization unit is connected with the carrier phase recovery unit; the carrier phase recovery unit is connected with the judgment and decoding unit;
the method for identifying the modulation format of the optical communication signal, namely the working process of the receiver, is characterized in that: the method comprises the following steps:
step A, carrying out coherent detection on an input optical communication signal to be detected in a coherent detection unit;
b, performing front-end equalization on the signal output by the coherent detection in the step A in a front-end equalization unit;
c, performing dispersion compensation on the output signal subjected to front end equalization in the step B in a dispersion compensation unit;
d, performing clock recovery on the signal subjected to dispersion compensation in the step C in a clock recovery unit;
e, carrying out carrier frequency offset compensation on the signal recovered by the clock in the step D in a frequency offset compensation unit;
the carrier frequency offset compensated signal can be expressed as (1):
Figure FDA0002420913040000011
wherein A isnRepresenting the carrier frequency offset compensated signal SnJ denotes the imaginary unit, anRepresenting the modulation phase of the signal after the carrier frequency offset compensation; thetanRepresenting the phase noise of the carrier frequency offset compensated signal; n represents the total number of sampling points; n represents the serial number of the sampling point, and the value range of N is 1 to N; when the laser linewidth is less than 10MHz, the phase noise difference of adjacent symbols is considered to be approximately equal, i.e. θn+1≈θnTherefore, the phase difference between adjacent symbols of the signal after carrier frequency offset compensation is approximately:
Figure FDA0002420913040000021
step F, calculating AAR and DPDR in an MFI module based on the signal output after the frequency offset compensation in the step E;
wherein, AAR represents the average amplitude ratio, DPDR represents the differential phase distribution ratio;
the calculation expression of AAR is as follows (2):
Figure FDA0002420913040000022
wherein, γn＝max(An,An+1)/min(An,An+1)；max(An,An+1) Is represented by AnAnd An+1The larger of the twoMin (A)n,An+1) Is represented by AnAnd An+1The smaller of the two;
the calculation expression of DPDR is as follows (3):
Figure FDA0002420913040000023
wherein, if
Figure FDA0002420913040000024
If yes, theta is 1, otherwise theta is 0, wherein ξ is a threshold, ξ needs to be optimized and selected, and the standard of the optimized selection is to distinguish modulation formats of optical signals with different signal-to-noise ratios;
step G, calculating the product of AAR and DPDR in the MFI module, and calling the product as a modulation format identification factor R;
step G is specifically expressed as formula (4):
R＝η(ξ)·γ (4)
step H, identifying the modulation format of the optical signal for the signal output by the carrier frequency offset compensation unit in the step E based on the calculated modulation format identification factor;
step I, carrying out self-adaptive equalization in a self-adaptive equalization unit according to the optical signal modulation format identified in the step H;
step J, carrying out carrier phase recovery on the result of the self-adaptive equalization output in the step I in a carrier phase recovery unit;
and step K, judging and decoding the result output by the carrier phase recovery in the step J in a judging and decoding unit.
2. The method of claim 1 for identifying a modulation format of an optical communication signal having a differential phase-to-amplitude ratio, wherein: step H, specifically:
if R is less than 13, the modulation format of the optical signal is QPSK;
if R is greater than or equal to 13 and less than 28, the modulation format of the optical signal is 16 QAM;
if R is greater than or equal to 28, the optical signal modulation format is 64 QAM.
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