CN109347776B - A Differential Phase Amplitude Ratio Optical Communication Signal Modulation Format Recognition Method - Google Patents

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

A Differential Phase Amplitude Ratio Optical Communication Signal Modulation Format Recognition Method

technical field

The invention relates to an optical communication signal modulation format identification method with differential phase amplitude ratio, and belongs to the technical field of modulation identification.

Background technique

In order to meet the increasing global IP service capacity requirements, optical networks are developing from traditional fixed networks to flexible and adaptive elastic optical network architectures. The research shows that the multi-level combined amplitude and phase modulation (MQAM) format can realize the transmission of signals with variable bit rate by changing M3 through hardware configuration. For an elastic optical network with flexible switching of multiple modulation formats, the optical receiver needs to have the ability to adaptively and blindly identify different modulation formats, so as to provide the receiver with subsequent digital signal processing, such as carrier phase noise estimation and frequency offset compensation. Necessary modulation format information.

Therefore, optical communication signal modulation format identification technology has attracted much attention. In 2015, some researchers proposed a modulation format blind identification technology based on the calculation of the peak-to-average power ratio (PAPR): after the coherent light receiving data is subjected to analog-to-digital conversion, dispersion and polarization mode dispersion equalization, the peak-to-average power ratio (PAPR) of the data is calculated. , and identify the modulation format through the correspondence between optical signal-to-noise ratio (OSNR) and PAPR. This method requires prior knowledge of the OSNR of the optical signal. In recent years, deep learning (DL) is a hot research field. DL-based MFI methods have also been proposed. Some researchers have proposed a convolutional neural network modulation format recognition algorithm based on constellation diagram analysis, but its disadvantage is that it is bundled with the carrier phase noise recovery algorithm, which limits the application range of this method. Some researchers also proposed to use Deep Neural Networks (DNN) to identify the distribution pattern of signal amplitude histogram for modulation format identification. However, in these DL methods, extensive training datasets and huge computational effort are required. For the method of identifying the modulation format based on the normalized amplitude of the normalized distribution function (CDF) curve, a reference CDF of all possible modulation formats needs to be established as a database in advance.

The present application intends to identify the three most commonly used formats in coherent optical transmission systems: QPSK, 16QAM and 64QAM by calculating differential phase distribution ratio (DPDR) and average amplitude ratio (AAR).

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the technical defects of high complexity and high OSNR requirement in the existing optical communication signal modulation format identification method, and propose a differential phase amplitude ratio optical communication signal modulation format identification method.

The core idea of this method is: based on the differential phase distribution ratio DPDR and the average amplitude ratio AAR, and define the modulation format identification factor R: the product of DPDR and AAR, to distinguish whether the signal modulation format is QPSK, 16QAM or 64QAM.

A receiver based on a differential phase-amplitude ratio optical communication signal modulation format identification method mainly includes 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 adaptive compensation unit, and a modulation unit. A format adaptive identification module, an adaptive equalization unit, a carrier phase recovery unit, and a judgment and decoding unit;

Among them, the modulation format adaptive identification module is also called the 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 equalization unit is connected with the dispersion compensation unit; the dispersion compensation unit is connected with the clock recovery unit, 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 adaptive The equalization unit is connected; the 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 a modulation format of an optical communication signal with a differential phase amplitude ratio, that is, a working process of a receiver, comprising the following steps:

Step A, performing coherent detection on the input optical communication signal to be detected in the coherent detection unit;

Step B, carry out front-end equalization in the front-end equalization unit to the signal output by the coherent detection of step A;

Step C, perform dispersion compensation in the dispersion compensation unit on the output signal after the front-end equalization of step B;

Step D, performing clock recovery on the signal after the dispersion compensation in Step C in a clock recovery unit;

Step E, carry out carrier frequency offset compensation in the frequency offset compensation unit to the signal recovered by the clock of step D;

Among them, the signal after carrier frequency offset compensation can be expressed as (1):

Among them, An represents the amplitude of the signal _Sn after the carrier frequency offset compensation, j represents the unit of the imaginary part, an _n represents the modulation phase of the signal after the carrier frequency offset compensation; θ _n represents the phase noise of the signal after the carrier frequency offset compensation; _N represents The total number of sampling points; n represents the number of sampling points, and its value ranges from 1 to N; when the laser line width is less than 10MHz, the phase noise difference of adjacent symbols is considered to be approximately equal, that is, θ _n+1 ≈ θ _n , so , the phase difference between adjacent symbols of the signal after carrier frequency offset compensation is approximately:

Step F, calculate AAR and DPDR in the MFI module based on the signal output after the frequency offset compensation in step E;

Among them, AAR represents the average amplitude ratio, and DPDR represents the differential phase distribution ratio;

The calculation expression of AAR is as follows (2):

Among them, γ _n =max(A _n ,A _n+1 )/min(A _n ,A _n+1 ); max(A _n ,A _n+1 ) represents the _ratio of An and A _n+1 The larger one, min(A _n , A _n+1 ); represents the smaller one of An and A _{n +1} ;

The calculation expression of DPDR is as follows (3):

为真则Θ＝1，否则Θ＝0；其中，ξ为阈值，ξ需要进行优化选择，优化选择的标准是将不同信噪比光信号的调制格式区分开来；Among them, if

If true, Θ=1, otherwise Θ=0; where ξ is the threshold, and ξ needs to be optimally selected, and the criterion for optimal selection is to distinguish the modulation formats of optical signals with different signal-to-noise ratios;

Step G, calculate the product of AAR and DPDR in the MFI module, and call it the modulation format identification factor R;

Step G is specifically expressed as formula (4):

R=η(ξ) γ (4)

Step H, identify the optical signal modulation format for the signal output by the carrier frequency offset compensation unit in step E based on the calculated modulation format identification factor:

If R is less than 13, the optical signal modulation format is QPSK;

If R is greater than or equal to 13 and less than 28, the optical signal modulation format is 16QAM;

If R is greater than or equal to 28, the optical signal modulation format is 64QAM;

Step 1, according to the optical signal modulation format identified in step H, carry out adaptive equalization in the adaptive equalization unit;

Step J, carry out carrier phase recovery in the carrier phase recovery unit to the result of step H adaptive equalization output;

In step K, the result of the carrier phase recovery output in step J is judged and decoded in the judgment and decoding unit.

beneficial effect

Compared with the prior art, a method for identifying a modulation format of an optical communication signal with a differential phase amplitude ratio proposed by the present invention has the following beneficial effects:

1. This method can identify the optical signal modulation format when the OSNR is not less than 12dB, and does not require carrier recovery;

2. This method does not require a large number of training data sets and complex calculations;

3. The experimental and simulation results of this method show that when the OSNR of the input signal is not less than 12dB, the proposed method can identify three modulation modes: QPSK, 16QAM and 64QAM.

Description of drawings

1 is a system block diagram and a connection relationship based on a method for identifying a modulation format of an optical communication signal with a differential phase amplitude ratio according to the present invention;

Fig. 2 is the system setting and scene when a kind of optical communication signal modulation format identification method of differential phase amplitude ratio of the present invention is concretely implemented;

Fig. 3 is the simulation result of step F when a kind of optical communication signal modulation format identification method of differential phase amplitude ratio of the present invention is concretely implemented;

FIG. 4 is a simulation result of step G of a method for identifying a modulation format of an optical communication signal based on a differential phase-to-amplitude ratio of the present invention.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

Example 1

This embodiment describes the specific implementation of the optical communication signal modulation format identification method using the differential phase amplitude ratio described in the present invention.

FIG. 1 is a system block diagram and connection relationship based on a method for identifying a modulation format of an optical communication signal based on a differential phase-to-amplitude ratio; FIG. 2 is a system design during specific implementation.

In Figure 2, at the transmitting end, the continuous wave laser, namely the CW Laser, is controlled by the IQ modulator, namely

IQMod, modulation; in the IQ modulator, the I-channel and Q-channel signals are modulated by two random bit sequences generated by an arbitrary waveform generator; the emitted laser signal is 1550nm, with a line width of 5kHz.

The IQ modulator generates three modulation signals of 10G baud rate, QPSK, 16QAM and 64QAM, respectively. The transmit power is 0dBm. This signal is transmitted through 100k standard optical fiber. The transmitted optical signal is amplified by the first erbium-doped fiber amplifier EDFA 1, and mixed with the spontaneous emission optical noise generated by the second erbium-doped fiber amplifier EDFA 2 through a 3dB coupler.

Among them, 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 optical noise power of spontaneous emission generated by the EDFA 2 is changed by adjusting the optical attenuator Att.

After the transmitted optical signal is mixed with spontaneous emission optical noise, the optical signal of the identified modulation format is coupled with the local oscillator laser into the optical mixer; the mixing is performed in the optical mixer, and then the detector is balanced for coherence demodulation.

Fig. 3 is the simulation result of AAR in step F when the optical communication signal modulation format identification method of differential phase amplitude ratio of the present invention is specifically implemented; it can be seen from Fig. 3 that for different modulation methods, the calculated average amplitude ratio has been able to A good distinction is made between the three modulation methods.

In order to further improve the discrimination performance, the modulation format identification factor R is introduced, and the simulation results are shown in Figure 4.

FIG. 4 is a simulation result of a method for identifying a modulation format of an optical communication signal based on a differential phase-to-amplitude ratio according to the present invention. Specifically used in back-to-back systems.

It can be clearly seen from FIG. 4 that the modulation format identification factor R can well distinguish the optical signals of the three modulation modes, even when OSNR=10dB, it can still be clearly distinguished.

The above descriptions are only the preferred embodiments of the present invention, and the present invention should not be limited to the contents disclosed in the embodiments and the accompanying drawings. All equivalents or modifications accomplished without departing from the disclosed spirit of the present invention fall into the protection scope of the present 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):

wherein A is_nRepresenting the carrier frequency offset compensated signal S_nJ denotes the imaginary unit, a_nRepresenting the modulation phase of the signal after the carrier frequency offset compensation; theta_nRepresenting 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. θ_n+1≈θ_nTherefore, the phase difference between adjacent symbols of the signal after carrier frequency offset compensation is approximately:

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):

wherein, γ_n＝max(A_n,A_n+1)/min(A_n,A_n+1)；max(A_n,A_n+1) Is represented by A_nAnd A_n+1The larger of the twoMin (A)_n,A_n+1) Is represented by A_nAnd A_n+1The smaller of the two;

the calculation expression of DPDR is as follows (3):

wherein, if

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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