CN114598392B - High-precision synchronization method between multi-dimensional optical modulator branches - Google Patents
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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
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
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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
- H04B10/6161—Compensation of chromatic dispersion
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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
- H04B10/66—Non-coherent receivers, e.g. using direct detection
- H04B10/69—Electrical arrangements in the receiver
- H04B10/697—Arrangements for reducing noise and distortion
- H04B10/6971—Arrangements for reducing noise and distortion using equalisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0682—Clock or time synchronisation in a network by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
Abstract
The invention discloses a high-precision synchronization method between branches of a multidimensional light modulator, which comprises the following steps: modulating the signal and inserting a pilot signal to obtain a transmitting signal; receiving a transmitting signal and carrying out equalization compensation on the received transmitting signal to obtain a compensated signal; performing wavelet analysis on the compensated signal, and estimating to obtain delay information; and carrying out delay compensation on the received transmitting signal according to the delay information, and finishing signal judgment. By using the invention, the synchronization of each branch of the multidimensional optical modulation can be realized, so that the synchronization precision of the existing high baud rate optical communication system is improved. The invention is used as a high-precision synchronization method between the branches of the multidimensional optical modulator, and can be widely applied to the fields of optical communication and signal processing.
Description
Technical Field
The invention relates to the field of optical communication and signal processing, in particular to a high-precision synchronization method between branches of a multidimensional optical modulator.
Background
Currently, with the rapid increase of global data traffic, the demand for high baud rate, high-capacity optical communication systems has been significantly increased. In order to meet the current high-speed and high-capacity data flow demands, researchers continuously research on the basic theory of ultra-large-capacity optical transmission and novel transmission technology. For a single-path optical signal, the transmission rate of information can be increased by modulating the intensity, phase, frequency, and polarization of the optical carrier. Multidimensional optical modulation is usually implemented by using a plurality of parallel modulators at a transmitting end, and modulating a plurality of branch signals to each dimension of an optical carrier and then transmitting the branch signals together in an optical fiber, so that the system capacity is effectively improved. In multidimensional modulation, each branch signal is usually required to keep high-precision timing synchronization, so that demodulation can be performed by using a correlation algorithm in a receiver.
In practical system procedures, the different propagation paths of the various branches (e.g., different cables) result in a relative delay between each branch. The signals with different rates have different time delay sensitivity to the branch signals, and the signals with high rates have higher sensitivity to the relative time delay between the branch signals due to the short symbol period. The common delay estimation technology cannot directly obtain the synchronization of signals among all branches, has limited application scenes, and cannot be applied to delay estimation among all branches of a multi-dimensional optical modulator.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a high-precision synchronization method among branches of a multidimensional optical modulator, which can realize synchronization of each branch of the multidimensional optical modulator so as to improve the synchronization precision of the existing high-baud rate optical communication system.
The first technical scheme adopted by the invention is as follows: the high-precision synchronization method between the multi-dimensional optical modulator branches comprises the following steps:
modulating the signal and inserting a pilot signal to obtain a transmitting signal;
receiving a transmitting signal and carrying out equalization compensation on the received transmitting signal to obtain a compensated signal;
performing wavelet analysis on the compensated signal, and estimating to obtain delay information;
and carrying out delay compensation on the received transmitting signal according to the delay information, and finishing signal judgment.
Further, the step of modulating the signal and inserting a pilot signal to obtain a transmission signal specifically includes:
modulating a random sequence in the signal to obtain a modulated signal;
and inserting a preset single-frequency pilot signal into a modulator branch and processing the modulated signal to generate a transmitting signal.
Further, the step of receiving the transmission signal and performing equalization compensation on the received transmission signal to obtain a compensated signal specifically includes:
receiving a transmit signal based on the receiving end;
performing IQ amplitude imbalance equalization and orthogonalization normalization on the received transmitting signals to obtain first compensation signals;
performing dispersion and nonlinear compensation on the first compensation signal to obtain a second compensation signal;
and carrying out signal clock recovery, frequency offset estimation and phase recovery on the second compensation signal to obtain a compensated signal.
Further, the step of performing signal clock recovery, frequency offset estimation and phase recovery on the second compensation signal to obtain a compensated signal specifically includes:
carrying out signal clock recovery on the second compensation signal, and synchronizing a sampling clock of a receiving end with a transmitting end to obtain a first synchronization signal;
and carrying out frequency offset estimation and phase recovery on the first synchronous signal, and keeping the frequency and the phase of the signal light of the receiving end consistent with the intrinsic light to obtain a compensated signal.
Further, the step of performing wavelet analysis on the compensated signal to obtain delay information by estimation specifically includes:
performing wavelet transformation on the compensated signal, selecting window control frequency resolution and time domain resolution precision, and obtaining a time-frequency analysis chart of the pilot signal;
acquiring frequency domain information and time domain information according to a time-frequency analysis chart of the pilot signal;
and integrating the frequency domain information and the time domain information, and estimating to obtain delay information.
Further, the wavelet transform is formulated as follows:
in the above formula, f (t) represents a compensation signal,the wavelet function basis is represented for scale transformation and time delay expansion, a represents the transformation coefficient of the scale transformation, and tau represents the time delay shift amount.
Further, the step of performing delay compensation on the received transmitting signal according to the delay information and completing signal judgment specifically includes:
compensating corresponding branches of the received transmitting signals according to the delay information to obtain third compensating signals;
demodulating the third compensation signal to obtain a demodulation signal;
and judging the demodulation signal based on a preset judgment rule.
The method has the beneficial effects that: the invention inserts a single-frequency pilot signal into the transmitting end of the optical communication system, and performs wavelet transformation of the signal at the receiving end, thereby obtaining a local time-frequency diagram of the signal and estimating the delay of the high-baud rate signal transmission system with high precision. In addition, the frequency of the pilot signal, the sampling rate of the system and the up-sampling multiple in the DSP process can be dynamically controlled to obtain the required delay precision, so that the problem of low precision of the traditional correlation-based delay estimation algorithm is solved.
Drawings
FIG. 1 is a flow chart of the steps of a method for high precision synchronization between branches of a multi-dimensional optical modulator according to the present invention;
FIG. 2 is a schematic diagram of a multi-dimensional optical modulator structure;
FIG. 3 illustrates different wavelets for different frequencies in accordance with an embodiment of the present invention;
FIG. 4 is a time-frequency analysis chart of wavelet transform of a signal at a receiving end according to an embodiment of the present invention;
fig. 5 is a time domain diagram of wavelet transform of pilot signals at a receiving end according to an embodiment of the present invention;
fig. 6 is an enlarged partial view of a second frequency discontinuity in accordance with an embodiment of the present invention;
fig. 7 is a top view of different frequency resolution wavelet transforms of a receiving end pilot signal in accordance with an embodiment of the present invention.
Detailed Description
The invention will now be described in further detail with reference to the drawings and to specific examples. The step numbers in the following embodiments are set for convenience of illustration only, and the order between the steps is not limited in any way, and the execution order of the steps in the embodiments may be adaptively adjusted according to the understanding of those skilled in the art.
Referring to fig. 2, the multi-dimensional optical modulator modulates a plurality of branch signals to each dimension of an optical carrier and transmits the branch signals in an optical fiber, thereby effectively improving the system capacity.
Referring to fig. 1, the present invention provides a high-precision synchronization method between branches of a multidimensional optical modulator, which comprises the following steps:
s1, modulating a signal and inserting a pilot signal to obtain a transmitting signal;
s1.1, carrying out signal modulation on a random sequence in a signal to obtain a modulated signal;
specifically, in order to transmit data with larger capacity in a limited bandwidth in optical communication, a transmitted random sequence is firstly subjected to signal modulation, in a related optical communication system, for convenience of signal equalization of a receiving end, a signal is subjected to 16QAM modulation, and the signal is transmitted by an IQ modulator of a transmitting end.
S1.2, inserting a preset single-frequency pilot signal into a modulator branch and processing a modulation signal to generate a transmitting signal.
Specifically, in order to demodulate and determine the signal at the receiving end, a synchronization head needs to be inserted into the signal to synchronize the signal, and a simple synchronization head cannot effectively synchronize due to the fact that multiplexing technology is applied to mix multiple signals, so that a synchronization sequence is designed. Assuming that four paths of signals (I1, Q1, I2, Q2) are mixed in the optical communication system, for the purpose of applying the signal to wavelet transform analysis of time-frequency characteristics at a receiving end, a single-frequency pilot signal of different frequencies with the same time interval is inserted before signals of a plurality of branches are modulated to each dimension of an optical carrier. The frequency of the pilot signal for each modulator arm is different for the same time interval of the pilot signal, in order to show that four different arms are distinguished, sinusoidal signals of different frequencies need to be inserted. Since the delay to be estimated is of the order of 10ps, the frequency at which the pilot is inserted is preferably a high frequency signal, which is advantageous for improving the accuracy of delay estimation, four frequencies are taken here as 10GHz,8GHz,5GHz and 4GHz, respectively. Since there is only one single frequency signal per leg in a pilot time interval, it is preferable to synthesize a single signal, i.e. a superposition of different frequency single frequency signals containing all legs in a pilot time interval.
The transmission signal is transmitted through the IQ modulator.
S2, receiving a transmitting signal and carrying out equalization compensation on the received transmitting signal to obtain a compensated signal;
specifically, after the signal is transmitted through a channel, the signal received by the receiving end firstly carries out a series of equalization compensation of a conventional optical communication system, such as IQ imbalance equalization and orthogonalization normalization, dispersion and nonlinear compensation, clock recovery, frequency offset estimation, phase compensation and the like of the signal, so as to obtain a compensated signal.
S2.1, receiving a transmission signal based on a receiving end;
s2.2, performing IQ amplitude imbalance equalization and orthogonalization normalization on the received transmitting signals to obtain first compensation signals;
specifically, the IQ amplitude imbalance means that the IQ two paths of signals pass through a channel from a transmitting end to a receiving end, the amplitude of the IQ two paths of signals is changed from the original ratio, the algorithm is required to perform balance compensation, the phase orthogonalization means that the two paths of signals are orthogonal to each other before transmission, the two paths of signals are not intersected during reception, and the orthogonalization means that the two paths of non-orthogonal signals are orthogonal to each other.
S2.3, performing dispersion and nonlinear compensation on the first compensation signal to obtain a second compensation signal;
specifically, after the signal passes through the optical fiber channel, a dispersion effect and a nonlinear effect are generated and are mainly expressed as pulse signal broadening, and adjacent pulse signals are affected, so that signal damage in the signal transmission process is caused, and dispersion compensation and nonlinear compensation are required.
S2.4, carrying out signal clock recovery, frequency offset estimation and phase recovery on the second compensation signal to obtain a compensated signal.
Specifically, the three-step equalization compensation algorithm is prepared for the subsequent wavelet transform.
S2.4.1, carrying out signal clock recovery on the second compensation signal, and synchronizing a sampling clock of the receiving end with the transmitting end to obtain a first synchronization signal;
s2.4.2, performing frequency offset estimation and phase recovery on the first synchronous signal, and keeping the frequency and the phase of the signal light of the receiving end consistent with the intrinsic light to obtain a compensated signal.
Specifically, the purpose of signal clock recovery is to synchronize the sampling clock of the receiver with the transmitter, avoid missing the optimal sampling point and bring sampling errors, and the purpose of frequency offset estimation and phase recovery is to keep the frequency and phase of the signal light and the intrinsic light of the receiving end consistent, so that the coherent receiver can recover the original signal conveniently.
S3, carrying out wavelet analysis on the compensated signal, and estimating to obtain delay information;
s3.1, performing wavelet transformation on the compensated signal, and selecting a window to control the frequency resolution and the time domain resolution precision to obtain a time-frequency analysis chart of the pilot signal;
specifically, the local time-frequency diagram of the signal is obtained through wavelet transformation, so that the time delay of each branch can be intuitively obtained, parameters can be dynamically adjusted, and the precision is improved.
The wavelet transform is formulated as follows:
in the above formula, f (t) represents a compensation signal,the wavelet function basis is represented for scale transformation and time delay expansion, a represents the transformation coefficient of the scale transformation, and tau represents the time delay shift amount.
S3.2, acquiring frequency domain information and time domain information according to a time-frequency analysis chart of the pilot signal;
and S3.3, integrating the frequency domain information and the time domain information, and estimating to obtain delay information.
Specifically, the compensated signal is subjected to wavelet analysis, if fourier transform (FFT) is performed, only four different frequency peaks can be obtained to distinguish four branch signals, and the delay of each branch is insensitive and cannot be effectively estimated. For this purpose two parameters of the signal should be obtained, one with different frequencies to scale the different branches and the other with different random delays for the individual branches. And the FFT is directly performed, only frequency domain information can be obtained, and the time delay of the time domain cannot be estimated accurately. The delay estimates for the various branches of the modulator lie in the different frequency spectrums that occur at different times. The synchronization of signals between the branches of each modulator of the optical communication system is to obtain frequency domain information and time domain delay information of each branch, and the frequency domain information is used for distinguishing different branches. It is difficult to obtain a high precision time domain resolution for each branch signal of the modulator. The wavelet transform may be employed as shown in fig. 4 in order to obtain a high-precision time-domain resolution.
The advantage of wavelet transform is that the appropriate small window can be dynamically selected to control the desired frequency resolution and time domain resolution accuracy. For wavelet transformation, as long as a mother wavelet (such as Morlet wavelet) is determined, the frequency component of a signal can be represented by the scale change of the wavelet, the wavelet basis is determined first, and then the high-frequency component and the low-frequency component of the signal are represented by the scale change of the wavelet. As shown in fig. 3, a high frequency wavelet is selected for the high frequency signal and vice versa. For an optical modulator system, the single frequency signal per branch is relatively high, and the high frequency wavelet should be chosen to obtain high time resolution. Because the frequency domain resolution is only used to distinguish four different branches, a too high resolution is not required. As can be seen from fig. 5 and fig. 6, a signal at the receiving end undergoes wavelet transformation, a peak pulse appears between the discontinuities, and the moment at which the maximum is found by searching for the local maximum. The time of occurrence of different frequencies can be directly read out, so that the relative delay of occurrence of a certain branch signal can be estimated.
Since the delay is randomly unknown, assuming that the sampling rate of the system is 125G sample/s, each symbol time is 8ps, up-sampling is performed 10 times, thus the sampling precision becomes 0.8ps, if the delay generated by the system branch is 10ps, the corresponding delay can be estimated by observing the movement of the peak value of the break point of the branch, and can be estimated to be 9.6ps or 10.4ps, and the error precision is 0.4ps, as shown in fig. 7. The desired accuracy can be obtained by varying the multiple of the up-sampling rate, theoretically the higher the up-sampling, the greater the accuracy of the estimation, but in practice a compromise is made. The synchronization of each branch of the multi-dimensional optical modulator can be obtained through simulation.
And S4, carrying out delay compensation on the received transmitting signal according to the delay information, and finishing signal judgment.
S4.1, compensating corresponding branches of the received transmitting signals according to the delay information to obtain third compensating signals;
s4.2, demodulating the third compensation signal to obtain a demodulation signal;
and S4.3, judging the demodulation signal based on a preset judgment rule.
Specifically, modulation and demodulation are a pair of opposite operations, demodulation of the corresponding format is performed by using what modulation format, demodulation decision of the signal can be performed only after synchronization, and the demodulation decision is not an error signal.
Because the random sequence is changed into the modulated signal, if the pilot frequency is subjected to wavelet transformation to estimate the delay before the modulated signal, the signal synchronously modulated with the transmitting end can be obtained by firstly estimating the delay to compensate the offset number, then the modulated signal subjected to delay compensation is demodulated into the random sequence, and the judgment conditions are as follows: taking binary as an example, a threshold voltage is set, for example, 0.5, more than 0.5 is judged as 1, less than 0.5 is judged as 0, which is a hard decision. Still other soft decisions are decided by euclidean distance.
A multi-dimensional optical modulator inter-arm high precision synchronization system comprising:
the transmitting terminal is used for modulating the signal and inserting a pilot signal to obtain a transmitting signal;
the receiving end is used for receiving the transmitting signal and carrying out equalization compensation on the received transmitting signal to obtain a compensated signal; performing wavelet analysis on the compensated signal, and estimating to obtain delay information; and carrying out delay compensation on the received transmitting signal according to the delay information, and finishing signal judgment.
The content in the method embodiment is applicable to the system embodiment, the functions specifically realized by the system embodiment are the same as those of the method embodiment, and the achieved beneficial effects are the same as those of the method embodiment.
A high-precision synchronization device between multi-dimensional optical modulator branches:
at least one processor;
at least one memory for storing at least one program;
the at least one program, when executed by the at least one processor, causes the at least one processor to implement a method of high precision synchronization between branches of a multi-dimensional optical modulator as described above.
The content in the method embodiment is applicable to the embodiment of the device, and the functions specifically realized by the embodiment of the device are the same as those of the method embodiment, and the obtained beneficial effects are the same as those of the method embodiment.
A storage medium having stored therein instructions executable by a processor, characterized by: the processor-executable instructions, when executed by the processor, are for implementing a method of high precision synchronization between branches of a multi-dimensional optical modulator as described above.
The content in the method embodiment is applicable to the storage medium embodiment, and functions specifically implemented by the storage medium embodiment are the same as those of the method embodiment, and the achieved beneficial effects are the same as those of the method embodiment.
While the preferred embodiment of the present invention has been described in detail, the invention is not limited to the embodiment, and various equivalent modifications and substitutions can be made by those skilled in the art without departing from the spirit of the invention, and these modifications and substitutions are intended to be included in the scope of the present invention as defined in the appended claims.
Claims (4)
1. The high-precision synchronization method between the multi-dimensional optical modulator branches is characterized by comprising the following steps of:
modulating the signal and inserting a pilot signal to obtain a transmitting signal;
receiving a transmitting signal and carrying out equalization compensation on the received transmitting signal to obtain a compensated signal;
performing wavelet analysis on the compensated signal, and estimating to obtain delay information;
performing delay compensation on the received transmitting signal according to the delay information, and finishing signal judgment;
the step of receiving the transmitted signal and performing equalization compensation on the received transmitted signal to obtain a compensated signal specifically includes:
receiving a transmit signal based on the receiving end;
performing IQ amplitude imbalance equalization and orthogonalization normalization on the received transmitting signals to obtain first compensation signals;
performing dispersion and nonlinear compensation on the first compensation signal to obtain a second compensation signal;
performing signal clock recovery, frequency offset estimation and phase recovery on the second compensation signal to obtain a compensated signal;
the step of performing wavelet analysis on the compensated signal to obtain delay information by estimation specifically comprises the following steps:
performing wavelet transformation on the compensated signal, selecting window control frequency resolution and time domain resolution precision, and obtaining a time-frequency analysis chart of the pilot signal;
acquiring frequency domain information and time domain information according to a time-frequency analysis chart of the pilot signal;
integrating the frequency domain information and the time domain information, and estimating to obtain delay information;
the step of performing delay compensation on the received transmitting signal according to the delay information and completing signal judgment specifically comprises the following steps:
compensating corresponding branches of the received transmitting signals according to the delay information to obtain third compensating signals;
demodulating the third compensation signal to obtain a demodulation signal;
judging the demodulation signal based on a preset judgment rule;
the frequency of the pilot signal, the sampling rate of the system, and the up-sampling multiple in the DSP process are dynamically controlled to achieve the desired delay accuracy.
2. The method of high precision synchronization between branches of a multidimensional optical modulator according to claim 1, wherein the step of modulating the signal and inserting a pilot signal to obtain a transmission signal comprises:
modulating a random sequence in the signal to obtain a modulated signal;
and inserting a preset single-frequency pilot signal into a modulator branch and processing the modulated signal to generate a transmitting signal.
3. The method of high precision synchronization between branches of a multidimensional optical modulator according to claim 2, wherein the steps of performing signal clock recovery, frequency offset estimation and phase recovery on the second compensation signal to obtain a compensated signal specifically include:
carrying out signal clock recovery on the second compensation signal, and synchronizing a sampling clock of a receiving end with a transmitting end to obtain a first synchronization signal;
and carrying out frequency offset estimation and phase recovery on the first synchronous signal, and keeping the frequency and the phase of the signal light of the receiving end consistent with the intrinsic light to obtain a compensated signal.
4. A method of high precision synchronization between branches of a multi-dimensional optical modulator according to claim 3 wherein the wavelet transform is formulated as follows:
in the above formula, f (t) represents a compensation signal,the wavelet function basis is represented for scale transformation and time delay expansion, a represents the transformation coefficient of the scale transformation, and tau represents the time delay shift amount.
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