CN116471003A - Frequency synchronization method utilizing coherent clock system in high-speed data transmission - Google Patents
Frequency synchronization method utilizing coherent clock system in high-speed data transmission Download PDFInfo
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- CN116471003A CN116471003A CN202310161927.2A CN202310161927A CN116471003A CN 116471003 A CN116471003 A CN 116471003A CN 202310161927 A CN202310161927 A CN 202310161927A CN 116471003 A CN116471003 A CN 116471003A
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- 229910052701 rubidium Inorganic materials 0.000 description 1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/02—Speed or phase control by the received code signals, the signals containing no special synchronisation information
- H04L7/033—Speed or phase control by the received code signals, the signals containing no special synchronisation information using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop
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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
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2575—Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
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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
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
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Abstract
The invention discloses a frequency synchronization method utilizing a coherent clock system in high-speed data transmission, which can provide high-precision time-frequency reference transmission and 10Gbps data stream transmission, and a device structure thereof. The invention uses high-speed modulator to generate radio frequency signal, and receives the signal of opposite end, uses carrier tracking technique to recover radio frequency carrier, uses signal processing algorithm to obtain frequency discrimination phase discrimination value in digital domain, the local end sends the frequency discrimination phase discrimination value to the far end, the far end uses local value and opposite end value to realize joint phase discrimination, then sends into loop filter, loop filter outputs voltage control signal, the far end uses voltage control signal to regulate voltage controlled crystal oscillator, to realize frequency synchronization of the far end and the local end. The method can realize the functions of single-fiber single-wavelength bidirectional time-frequency synchronization and high-speed data transmission, can fully utilize the optical wavelength resources of the optical fiber transmission system, saves the optical wavelength resources compared with the traditional method, and has higher frequency synchronization precision.
Description
Technical Field
The invention relates to the field of distributed detection, is suitable for a sparse deployment cross-region distributed detection system, and provides high-precision time-frequency reference transmission and 10Gbps data stream transmission. Only a single optical fiber channel is occupied, the integrated realization of the functions of time frequency and data transmission is realized, and the frequency synchronization precision and the ten-thousand-megabyte data transmission bandwidth of the magnitude of 1E-13@s are realized.
Background
When the deployment range of the distributed detection system is expanded across regions, the matched construction of a brand new optical fiber network can bring extremely high cost. Deployment of fiber optic networks by current operators is an important way to achieve cross-regional deployment and is also a key technical research direction. Investigation has shown that the operator network generally comprises a two-level architecture of a metropolitan area network and a wide area backbone network. Metropolitan area networks are used in cities, and coverage ranges are generally tens to hundreds of kilometers, and are divided into a core layer, a convergence layer and an access layer. Wide area backbones are used to aggregate multiple metropolitan area networks covering cities, regions, provinces, or even countries ranging from hundreds to thousands of kilometers. The base optical fiber network of the operators is fully utilized, and the distributed detection system can realize hundreds of kilometers coverage.
According to the traditional optical fiber time-frequency transmission and data transmission method, 3 independent bidirectional channels are occupied by the transmission of 3 services of time, frequency and high-speed data, and the requirement of a single detection node on the number of optical fiber channels reaches 6 channels. The invention envisages that by means of an optical network deployed by an operator, single-fiber single-wavelength bidirectional time-frequency synchronization and high-speed data transmission functions are realized. The optical wavelength resource of the optical fiber transmission system can be fully utilized, and the optical fiber transmission system has the characteristics of picosecond time synchronization precision and 10Gbps data transmission bandwidth.
There are some worth of experience to be borrowed with respect to the integrated implementation of time, frequency, high-speed data 3 services. For example, the inter-satellite laser calibration synchronization link, IEEE1588v2 protocol, white rabbit protocol, etc., but has a small gap from the target. The inter-satellite laser calibration synchronous link and the IEEE1588v2 protocol adopt a mode of loading a time stamp in a data frame, and the ns-level time synchronization is completed while the two-way communication is performed, so that the frequency transmission function is avoided; the white rabbit protocol uses second pulse and time scale data as time standard carrier and 125MHz data clock as frequency standard carrier, the frequency synchronization precision is 1E-11@s magnitude, and the difference is larger than the 1E-13@s magnitude required by the distributed detection system.
Disclosure of Invention
The invention provides that when various clock systems (reference clock, AD clock, DA clock, intermediate frequency receiving and transmitting local oscillator and radio frequency receiving and transmitting local oscillator) in the high-speed modulator and demodulator have phase coherence and phase noise is low enough, the high-precision frequency discrimination and phase discrimination required by frequency transmission can be realized in a digital domain by utilizing the coherent clock system, and the equivalent performance of analog frequency transmission can be realized by utilizing a digital phase locking technology. On the basis of frequency synchronization, the high-precision ranging frames are embedded in the data stream to further realize time synchronization.
The invention adopts the technical scheme that:
a frequency synchronization method using a coherent clock system in high-speed data transmission comprises the following steps:
(1) Generating broadband intermediate frequency signals at the local end and the far end respectively, modulating the intermediate frequency signals onto a radio frequency carrier in an up-conversion mode, modulating the radio frequency signals onto optical signals, coupling the optical signals into an optical fiber channel, and transmitting the optical signals to the opposite end;
(2) The local end and the remote end mutually receive the optical signals of the opposite end, recover the emergent frequency signals, recover the emergent frequency carrier waves by utilizing the carrier wave tracking technology, and then carry out frequency mixing, low-pass filtering and integral cleaning with the local radio frequency carrier waves in a digital domain to obtain frequency discrimination phase discrimination values;
(3) The local end frames and modulates the local frequency discrimination phase discrimination value to a radio frequency carrier wave, sends the radio frequency carrier wave to a far end, carries out joint phase discrimination by utilizing the far end frequency discrimination value and the received frequency discrimination value of the opposite end at the far end, and then carries out loop filtering on the far end joint phase discrimination value to obtain a voltage control signal of the voltage-controlled crystal oscillator;
(4) The remote end regulates and controls the voltage-controlled crystal oscillator by utilizing the voltage control signal to realize the frequency synchronization of the remote end and the local end, and the local end detects the frequency synchronization state by utilizing the combined phase discrimination result.
Further, the step (2) specifically includes the following steps:
the local end and the far end mutually receive the optical signals of the opposite end, recover the emergent frequency signals, perform quadrature down-conversion on the emergent frequency signals, and respectively perform digital AGC on the down-converted signals of the I path and the Q path; non-coherent accumulation is carried out on the I path and Q path baseband signals obtained by the digital AGC, then FFT processing is carried out, frequency estimation is carried out by utilizing the generated FFT operation value signals, and frequency deltaf is estimated; simultaneously extracting carrier errors, extracting tracking errors, obtaining error frequency control words cw_err, carrying out carrier phase compensation by using delta f and cw_err, carrying out phase discrimination by using carrier signals after phase compensation to obtain frequency discrimination phase discrimination values, carrying out complex multiplication operation on I-path baseband signals and Q-path baseband signals obtained through digital AGC and carrier signals after phase compensation, taking generated real part data as I-path data, and taking generated imaginary part data as Q-path data; and the carrier error extraction is adjusted according to the I-path and Q-path data after complex multiplication operation, and soft decision and error correction decoding are carried out at the same time, so that the original data stream is recovered.
Further, in the step (3), the far end performs joint phase discrimination by using the far-end frequency discrimination phase discrimination value and the received frequency discrimination phase discrimination value of the opposite end, and then loop filtering is performed on the far-end joint phase discrimination value to obtain a voltage control signal of the voltage-controlled crystal oscillator; the method specifically comprises the following steps:
the remote end utilizes the frequency discrimination phase discrimination value of the remote end and the frequency discrimination phase discrimination value of the received opposite end to carry out comprehensive processing to obtain the phase difference of signals at the two ends, designs the filtering rate and the loop bandwidth according to the system requirement to obtain specific loop parameters, and utilizes the phase difference and the loop parameters to obtain the voltage control signal of the voltage-controlled crystal oscillator through correlation operation.
Compared with the prior art, the invention has the following advantages:
the method can realize the functions of single-fiber single-wavelength bidirectional time-frequency synchronization and high-speed data transmission, can fully utilize the optical wavelength resources of an optical fiber transmission system, has the characteristics of picosecond-level time synchronization precision and 10Gbps data transmission bandwidth, saves the optical wavelength resources compared with the traditional method, and has higher frequency synchronization precision.
Drawings
Fig. 1 is a view showing the constitution of the apparatus of the present invention.
Fig. 2 is a diagram of a high-speed modulator design based on a coherent clock train.
Fig. 3 is a high speed demodulator design.
Fig. 4 is a diagram of a single fiber bi-directional transmission link design.
Detailed Description
The technical solution of the present invention will be described in more detail with reference to the accompanying drawings and examples, but the scope of the present invention is not limited thereto. As shown in fig. 1, the present embodiment is composed of a digital phase detector & control unit, an electro-optical modulator, a photodetector, a circulator, a long-distance optical fiber, and the like.
The specific implementation steps are as follows:
(1) Generating broadband intermediate frequency signals at the local end and the far end respectively, modulating the intermediate frequency signals onto a radio frequency carrier by utilizing a high-speed modulator in an up-conversion way, modulating the radio frequency signals onto optical signals by utilizing an electro-optical modulator, coupling the optical signals into an optical fiber channel, and transmitting the optical signals to the opposite end;
as shown in fig. 2, the high-speed modulator of this embodiment receives multiple paths of parallel data of the detection sensor node, firstly sends the parallel data to the encoder for encoding, then sends the encoded and shaped filtered data to the DA conversion module for converting the encoded and shaped filtered data to analog signals, sends the analog signals to the quadrature modulator for quadrature modulation after analog low-pass filtering and operational amplification, and finally sends the outgoing frequency signals in an up-conversion mode.
The 20GHz intermediate frequency carrier is used as a high-frequency side tone obtained after frequency multiplication of a frequency standard (10 MHz/100 MHz) signal, and carries the characteristic of a frequency standard signal. And a fixed time delay is introduced through the photoelectric conversion-optical fiber transmission-electro-optical conversion process, and the carrier is separated on an electric domain after the carrier is recovered, so that the carrier is not mutually influenced with data transmission.
(2) The local end and the far end mutually receive the optical signals of the opposite end by utilizing a photoelectric detector, recover the emergent frequency signals, recover the emergent frequency carrier wave by utilizing a carrier tracking technology in a high-speed demodulator, then carry out frequency mixing, low-pass filtering and integral cleaning with the local radio frequency carrier wave in a digital domain to obtain a frequency discrimination phase discrimination value,
as shown in fig. 3, the processing procedure of the high-speed demodulator is as follows:
the local end and the far end mutually receive the optical signals of the opposite end, recover the emergent frequency signals, perform quadrature down-conversion on the emergent frequency signals, and respectively perform digital AGC on the down-converted signals of the I path and the Q path; non-coherent accumulation is carried out on the I path and Q path baseband signals obtained by the digital AGC, then FFT processing is carried out, frequency estimation is carried out by utilizing the generated FFT operation value signals, and frequency deltaf is estimated; simultaneously extracting carrier errors, extracting tracking errors, obtaining error frequency control words cw_err, carrying out carrier phase compensation by using delta f and cw_err, carrying out phase discrimination by using carrier signals after phase compensation to obtain frequency discrimination phase discrimination values, carrying out complex multiplication operation on I-path baseband signals and Q-path baseband signals obtained through digital AGC and carrier signals after phase compensation, taking generated real part data as I-path data, and taking generated imaginary part data as Q-path data; and the carrier error extraction is adjusted according to the I-path and Q-path data after complex multiplication operation, and soft decision and error correction decoding are carried out at the same time, so that the original data stream is recovered.
(3) The local frequency and phase discrimination values are framed and modulated to radio frequency carrier waves by a high-speed modulator, and then are transmitted to a far end after electro-optical modulation, the far end comprehensively processes the frequency and phase discrimination values of the far end and the received frequency and phase discrimination values of an opposite end in a combined phase discriminator to obtain phase differences of signals at the two ends, the filtering rate and the loop bandwidth of a loop filter are designed according to the system requirements, specific loop parameters are obtained, and voltage control signals of the voltage-controlled crystal oscillator are obtained through correlation operation by the phase differences and the loop parameters.
(4) The remote end regulates and controls the voltage-controlled crystal oscillator by utilizing the voltage control signal to realize the frequency synchronization of the remote end and the local end, and the local end detects the frequency synchronization state by utilizing the combined phase discrimination result.
As shown in fig. 4, the single fiber bi-directional transmission link is designed as follows:
the main end DA outputs a radio frequency signal to be connected to the main end optical transmitting unit, the radio frequency signal is electro-optically converted into an optical signal, the optical signal is output to the long-distance optical fiber through the main station optical circulator bidirectional transmission port, the optical signal transmitted to the slave end is output to the slave end optical receiving unit through the slave end optical circulator bidirectional transmission port, and the slave end optical receiving unit is electro-optically converted into a radio frequency signal to be output to the slave end AD unit. And the secondary end DA unit outputs radio frequency signals, and the radio frequency signals are converted into radio frequency signals by the secondary end light emitting unit, the secondary end light circulator, the long-distance optical cable, the main end light circulator and the main end light receiving unit and are output to the main end AD unit.
The whole optical fiber transmission link realizes single-fiber bidirectional transmission of radio frequency signals by configuring the optical circulator at the master end and the slave end, and ensures symmetry of the optical fiber transmission link.
The frequency synchronization accuracy test is as follows:
during testing, the master end and the slave end are placed at the same place in the form of a long-distance optical fiber disc, and a 10MHz standard frequency signal generated by a rubidium clock and a 10MHz regenerated frequency signal generated by a voltage-controlled VCXO are connected into a frequency synchronization precision testing instrument for measurement, so that an Aren variance curve is obtained. In this embodiment, an optical fiber is not used, and a radio frequency line direct connection mode is adopted, and the frequency synchronization accuracy is shown in the following table.
TABLE 1
| Time | Frequency stability |
| 1s | 3.790e-13 |
| 10s | 1.353e-13 |
| 100s | 1.58e-14 |
| 1000s | 1.74e-15 |
The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any changes or substitutions that may be easily contemplated by those skilled in the art within the scope of the present invention should be included in the present invention.
Claims (3)
1. A method for frequency synchronization using a coherent clock system in high-speed data transmission, comprising the steps of:
(1) Generating broadband intermediate frequency signals at the local end and the far end respectively, modulating the intermediate frequency signals onto a radio frequency carrier in an up-conversion mode, modulating the radio frequency signals onto optical signals, coupling the optical signals into an optical fiber channel, and transmitting the optical signals to the opposite end;
(2) The local end and the remote end mutually receive the optical signals of the opposite end, recover the emergent frequency signals, recover the emergent frequency carrier waves by utilizing the carrier wave tracking technology, and then carry out frequency mixing, low-pass filtering and integral cleaning with the local radio frequency carrier waves in a digital domain to obtain frequency discrimination phase discrimination values;
(3) The local end frames and modulates the local frequency discrimination phase discrimination value to a radio frequency carrier wave, sends the radio frequency carrier wave to a far end, carries out joint phase discrimination by utilizing the far end frequency discrimination value and the received frequency discrimination value of the opposite end at the far end, and then carries out loop filtering on the far end joint phase discrimination value to obtain a voltage control signal of the voltage-controlled crystal oscillator;
(4) The remote end regulates and controls the voltage-controlled crystal oscillator by utilizing the voltage control signal to realize the frequency synchronization of the remote end and the local end, and the local end detects the frequency synchronization state by utilizing the combined phase discrimination result.
2. The method for frequency synchronization using a coherent clock system in high speed data transmission according to claim 1, wherein said step (2) comprises the steps of:
the local end and the far end mutually receive the optical signals of the opposite end, recover the emergent frequency signals, perform quadrature down-conversion on the emergent frequency signals, and respectively perform digital AGC on the down-converted signals of the I path and the Q path; non-coherent accumulation is carried out on the I path and Q path baseband signals obtained by the digital AGC, then FFT processing is carried out, frequency estimation is carried out by utilizing the generated FFT operation value signals, and frequency deltaf is estimated; simultaneously extracting carrier errors, extracting tracking errors, obtaining error frequency control words cw_err, carrying out carrier phase compensation by using delta f and cw_err, carrying out phase discrimination by using carrier signals after phase compensation to obtain frequency discrimination phase discrimination values, carrying out complex multiplication operation on I-path baseband signals and Q-path baseband signals obtained through digital AGC and carrier signals after phase compensation, taking generated real part data as I-path data, and taking generated imaginary part data as Q-path data; and the carrier error extraction is adjusted according to the I-path and Q-path data after complex multiplication operation, and soft decision and error correction decoding are carried out at the same time, so that the original data stream is recovered.
3. The method for frequency synchronization using a coherent clock system in high speed data transmission according to claim 1, wherein in the step (3), the far end performs joint phase demodulation by using a far-end phase demodulation value and a received phase demodulation value of the opposite end, and then performs loop filtering on the far-end joint phase demodulation value to obtain a voltage control signal of the voltage-controlled crystal oscillator; the method specifically comprises the following steps:
the remote end utilizes the frequency discrimination phase discrimination value of the remote end and the frequency discrimination phase discrimination value of the received opposite end to carry out comprehensive processing to obtain the phase difference of signals at the two ends, designs the filtering rate and the loop bandwidth according to the system requirement to obtain specific loop parameters, and utilizes the phase difference and the loop parameters to obtain the voltage control signal of the voltage-controlled crystal oscillator through correlation operation.
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