CN113285757B - Frequency division multiplexing high-precision optical fiber time transmission system and method - Google Patents
Frequency division multiplexing high-precision optical fiber time transmission system and method Download PDFInfo
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 50
- 230000005540 biological transmission Effects 0.000 title claims abstract description 43
- 238000000034 method Methods 0.000 title claims abstract description 24
- 230000003287 optical effect Effects 0.000 claims abstract description 21
- 238000012546 transfer Methods 0.000 claims abstract description 15
- 239000000969 carrier Substances 0.000 claims abstract description 10
- 238000006243 chemical reaction Methods 0.000 claims abstract description 8
- 238000011084 recovery Methods 0.000 claims description 4
- 230000002457 bidirectional effect Effects 0.000 abstract description 16
- 239000000835 fiber Substances 0.000 abstract description 6
- 230000001360 synchronised effect Effects 0.000 abstract description 2
- 230000007547 defect Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000011161 development Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000002401 inhibitory effect Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000002354 daily effect Effects 0.000 description 1
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Classifications
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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
- H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
- H04B10/2537—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to scattering processes, e.g. Raman or Brillouin scattering
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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
- H04B10/25752—Optical arrangements for wireless networks
- H04B10/25758—Optical arrangements for wireless networks between a central unit and a single remote unit by means of an optical fibre
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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
- H04B10/548—Phase or frequency modulation
- H04B10/556—Digital modulation, e.g. differential phase shift keying [DPSK] or frequency shift keying [FSK]
- H04B10/5561—Digital phase modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2668—Details of algorithms
- H04L27/2681—Details of algorithms characterised by constraints
- H04L27/2688—Resistance to perturbation, e.g. noise, interference or fading
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
- H04L27/2691—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation involving interference determination or cancellation
Abstract
The invention provides a frequency division multiplexing high-precision optical fiber time transmission system and a method. The time codes containing timing signals, time information and control information at two ends are loaded on radio frequency carriers with different frequencies through phase modulation, and are transmitted to each other through the same optical fiber link and the same wavelength through electro-optical conversion. The two ends respectively convert the received optical signals into electric signals, recover the time codes from the opposite ends through the phase demodulation of the corresponding carrier waves, further decode and recover timing signals, time information and control information, measure the time interval between the local timing signals and the recovered opposite end timing signals, calculate and obtain the real-time clock difference of the two ends by utilizing the bidirectional time comparison principle, and realize time transfer. The frequency division multiplexing high-precision optical fiber time transfer method combines the synchronous wave same-fiber bidirectional transmission and the phase modulation frequency division multiplexing, and simultaneously realizes high-precision and high-stability optical fiber time transfer.
Description
Technical Field
The invention relates to the technical field of high-precision time transmission, in particular to a frequency division multiplexing high-precision optical fiber time transmission system and a method.
Background
Time is taken as the most basic physical quantity, and the requirements on time service precision are also higher and higher along with the rapid development of the fields of navigation, aerospace, communication, electric power and the like in the modern society of informatization. The time frequency with high accuracy and high stability is a crucial resource in the national strategy, and the demand for high-accuracy time transfer in daily life is also increasing. The performance of the time-frequency system is an important embodiment of the development and comprehensive strength of national science and technology.
Time transfer based on unidirectional IRIG systems has been widely used in everyday life, as the system is only suitable for short range time service without taking into account delays in the transmission process. In order to achieve time accuracy of nanosecond order or even higher, satellite-based time service systems and fiber-based time service systems are mainly used at present. Satellite time service is quite mature in technology, but has the defects of complex structure, high cost, long comparison time, poor safety, poor reliability and the like. The optical fiber transmission has the advantages of low loss, large bandwidth, high stability, safety, reliability, wide coverage and the like, and has great potential for realizing high-precision time transmission. The current high-precision optical fiber time transfer schemes mainly include a loop-back method (Round trip) and a two-way time comparison method (two way). Both are based on the symmetry of bidirectional transmission to eliminate the optical fiber transmission delay and the optical fiber transmission delay change caused by factors such as temperature and stress. The existing co-fiber wavelength division multiplexing bidirectional transmission can effectively inhibit the influence of backward scattering noise, but the inconsistency of bidirectional transmission wavelengths breaks the bidirectional transmission symmetry, requires complex link calibration, and limits time transfer performance and cost; the same fiber and same wave bidirectional transmission is adopted to ensure the symmetry of bidirectional transmission, but the backward scattering noise severely limits the improvement of time transmission performance.
The invention patent of CN111948686A discloses a time synchronization method and a device, which are used for each processing center in a navigation enhancement system, and comprise the following steps: the method comprises the steps of regularly sending local clock error products to other processing centers in the navigation enhancement system and receiving the clock error products sent by a plurality of processing centers; calculating the difference between the local time reference and the system time reference according to the local clock difference product and the received clock difference products; and updating the local clock difference product according to the difference between the local time reference and the system time reference. The invention can ensure the unification of the time references used by each processing center for broadcasting the products in the navigation enhancement system and provide stable navigation enhancement service for users. However, the above scheme cannot ensure the symmetry of bidirectional transmission and suppress the influence of backward rayleigh scattering noise at the same time.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a frequency division multiplexing high-precision optical fiber time transmission system and a method.
The invention provides a frequency division multiplexing high-precision optical fiber time transfer system, which comprises a near-end module and a far-end module, wherein the near-end module and the far-end module respectively comprise a local clock, a time encoder, a phase modulator, an optical transmitting module, a combining and branching device, an optical receiving module, a phase demodulator, a time decoder and a time interval measuring module which are sequentially connected, and the combining and branching devices of the near-end module and the far-end module are connected through optical fibers.
Preferably, the time codes of the near end and the far end are loaded on radio frequency carriers with different frequencies through phase modulation, and the time codes are recovered through phase demodulation of the corresponding radio frequency carriers.
Preferably, the phase modulated signals carrying the time signals at the near end and the far end are transmitted bi-directionally over the same optical fiber and at the same wavelength.
Preferably, the local clock outputs a timing signal, the locally measured unidirectional clock difference, time information and control information to a time encoder for encoding.
The frequency division multiplexing high-precision optical fiber time transmission method based on the frequency division multiplexing high-precision optical fiber time transmission system provided by the invention comprises a near-end to far-end unidirectional time transmission step, wherein the near-end to far-end unidirectional time transmission step comprises the following steps of:
a near-end time code generation step: the near end encodes a timing signal output by the local clock, a locally measured unidirectional clock error, time information and control information to generate a time code;
a near-end phase modulation step: the generated time code is relative to frequency f 1 The radio frequency carrier signal of (2) is phase modulated, and the phase modulated carrier signal produced by phase modulation is loaded into the wavelength lambda through electro-optical conversion 1 Is transmitted to the far end through the optical fiber;
and (3) a remote recovery step: the far end photoelectrically converts the optical signal received from the optical fiber from the near end, and the carrier frequency of the converted electric signal is f 1 And then decoding the recovered time code to extract timing signals, locally measured unidirectional clock differences, time information and control information.
Preferably, the method further comprises a step of transmitting the far-end to near-end unidirectional time, and the step of transmitting the far-end to near-end unidirectional time comprises the following steps:
a remote time code generation step: the remote end encodes a timing signal output by the local clock, a locally measured unidirectional clock difference, time information and control information to generate a time code;
a remote phase modulation step: the time code generated by the far end is f to the frequency 2 The radio frequency carrier signal of (2) is phase modulated, and the phase modulated carrier signal produced by phase modulation is loaded into the wavelength lambda through electro-optical conversion 1 Is transmitted to the near end through the same optical fiber;
proximal recovery step: the near end photoelectrically converts the far-end optical signal received from the optical fiber, and the carrier frequency of the converted electric signal is f 2 And then decoding the recovered time code to extract timing signals, locally measured unidirectional clock differences, time information and control information.
Preferably, the timing signal comprises a 1PPS signal.
Preferably, the method further comprises the step of clock difference acquisition:
the near end measures the time interval between the timing signal output by the local clock and the timing signal received from the far end, obtains the unidirectional clock difference measured by the near end, adds the unidirectional clock difference into the time code and transmits the unidirectional clock difference to the far end;
the remote end measures the time interval between the timing signal output by the local clock and the timing signal received by the near-remote end, namely the unidirectional clock difference measured by the remote end, and adds the unidirectional clock difference into a time code to be transmitted to the near-end;
the near end and the far end calculate the clock difference at the two ends by utilizing the two-way comparison principle according to the locally measured one-way clock difference and the one-way clock difference received from the opposite end respectively.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the invention, the phase modulation signals with the time signals at the two ends are transmitted in a bidirectional way through the same optical fiber and the same wavelength, so that the symmetry of bidirectional optical fiber transmission is ensured, and the defects of the existing optical fiber time transmission scheme in the aspects of simultaneously ensuring the symmetry of bidirectional transmission and inhibiting the influence of backward Rayleigh scattering noise are overcome.
2. The time codes at the two ends of the invention are loaded on radio frequency carriers with different frequencies through phase modulation, and the time codes are recovered through phase demodulation of the corresponding radio frequency carriers, thereby effectively inhibiting the interference of backward scattering noise.
3. The invention combines phase modulation frequency division multiplexing and same-fiber same-wave bidirectional transmission, effectively inhibits the influence of backward scattering on the quality of transmission signals while guaranteeing the symmetry of the bidirectional time transmission link, remarkably improves the accuracy and stability of the time transmission of the optical fiber, does not need link calibration, and reduces the implementation and operation cost.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:
fig. 1 is a schematic diagram of a frequency division multiplexing high-precision optical fiber time transfer method system.
Fig. 2 is a schematic diagram of a time encoding and decoding and carrier phase modulation and demodulation process of a frequency division multiplexing high-precision optical fiber time transfer method.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications could be made by those skilled in the art without departing from the inventive concept. These are all within the scope of the present invention.
As shown in fig. 1 and fig. 2, the present invention provides a frequency division multiplexing high-precision optical fiber time transmission system and a method, and fig. 1 is a schematic diagram of frequency division multiplexing high-precision optical fiber time transmission based on the present invention. The near end and the far end are connected through an optical fiber link, so that time transmission between the near-end local clock and the far-end local clock is realized. With reference to fig. 2, the specific working process is as follows:
(1) Proximal to distal unidirectional time transmission
The 1PPS timing signal and the reference frequency signal output by the near-end local clock enter a time coding module, and the time coding module carries out B code coding on the 1PPS timing signal, the time information and the control information time signal and outputs the B code coding to the phase modulation module; in the phase modulation module, a reference frequency signal output by a near-end local clock is converted into a frequency f through a phase-locked loop 1 Is input with a frequency f 1 The carrier signal is subjected to BPSK phase modulation (the 0 phase of a high-level selected carrier is time coded, and the 180 phase is low-level selected), and the BPSK phase modulated carrier signal is output to the optical transmitting module; the near-end optical transmitting module modulates the input BPSK phase modulation carrier signal into light with the wavelength lambda, and inputs the light into an optical fiber through a two-port optical combiner/divider (such as an optical coupler or a circulator) to be transmitted to the far end; the far-end optical receiving module receives signals in the optical fiber through the two-port optical multiplexer/splitter, recovers near-end BPSK phase modulation carrier signals through photoelectric conversion, and outputs the near-end BPSK phase modulation carrier signals to the phase demodulation module; phase demodulation recovers the near-end carrier wave f through a COSTAS phase-locked loop 1 Recovering the near-end time code B code from the recovered carrier wave and the phase modulation BPSK signal; the far-end time decoding module decodes the recovered near-end time coding B code to recover 1PPS, time information and control information; the remote interval counter measures the recovered 1PPS and the remote local clock output 1PPS interval.
(2) Remote-to-near unidirectional time transmission
Similarly, the 1PPS timing signal and the reference frequency signal output by the remote local clock enter a time coding module, and the time coding module carries out B code coding on the 1PPS timing signal, the time information and the control information time signal and outputs the B code coding to the phase modulation module; in the phase modulation module, the reference frequency signal output by the remote local clock is converted into a frequency f by a phase-locked loop 2 Is input with a frequency f 2 The carrier signal is subjected to BPSK phase modulation (the 0 phase of a high-level selected carrier is time coded, and the 180 phase is low-level selected), and the BPSK phase modulated carrier signal is output to the optical transmitting module; far-end lightThe transmitting module modulates the input BPSK phase modulation carrier signal to light with the wavelength lambda, and inputs the light into an optical fiber through a two-port optical combiner/divider (such as an optical coupler or a circulator) to be transmitted to a far end; the near-end optical receiving module receives signals in the optical fiber through the two-port optical multiplexer/splitter, recovers near-end BPSK phase modulation carrier signals through photoelectric conversion and outputs the near-end BPSK phase modulation carrier signals to the phase demodulation module; phase demodulation recovers the far-end carrier wave f through a COSTAS phase-locked loop 2 Recovering the remote time code B code from the recovered carrier wave and the phase modulation BPSK signal; the near-end time decoding module decodes the recovered near-end time coding B code to recover 1PPS, time information and control information; the near-end interval counter measures the recovered 1PPS and the far-end local clock output 1PPS interval.
(3) Real-time clock difference calculation
The near end measures the time interval between the timing signal (such as 1 PPS) output by the local clock and the timing signal (such as 1 PPS) received from the far end, obtains the unidirectional clock difference measured by the near end and transmits the unidirectional clock difference to the far end; the far end measures the time interval between the timing signal (such as 1 PPS) output by the local clock and the timing signal (such as 1 PPS) received by the near end, namely the unidirectional clock difference measured by the far end, and transmits the unidirectional clock difference to the near end; the near end and the far end calculate the clock difference at the two ends by utilizing the two-way comparison principle according to the locally measured one-way clock difference and the one-way clock difference received from the opposite end respectively.
The phase modulation signals carrying time signals at two ends of the invention are transmitted bidirectionally through the same optical fiber and the same wavelength, thereby ensuring the symmetry of the bidirectional optical fiber transmission. The time codes containing timing signals, time information and control information at two ends are loaded on radio frequency carriers with different frequencies through phase modulation, and are transmitted to each other through the same optical fiber link and the same wavelength through electro-optical conversion. The two-end distribution converts the received optical signal into an electric signal, the opposite end is recovered through phase demodulation of the corresponding carrier wave to obtain time codes, the recovered timing signal, time information and control information are further decoded, the time interval between the local timing signal and the recovered opposite end timing signal is measured, the two-end real-time clock difference is calculated by utilizing a two-way time comparison principle, and time transfer is realized. The frequency division multiplexing high-precision optical fiber time transfer method combines the synchronous wave same-fiber bidirectional transmission and the phase modulation frequency division multiplexing, and simultaneously realizes high-precision and high-stability optical fiber time transfer. The time codes at the two ends are loaded on radio frequency carriers with different frequencies through phase modulation, and the time codes are recovered through phase demodulation of the corresponding radio frequency carriers, so that interference of backward scattering noise is effectively restrained.
The foregoing describes specific embodiments of the present invention. It is to be understood that the invention is not limited to the particular embodiments described above, and that various changes or modifications may be made by those skilled in the art within the scope of the appended claims without affecting the spirit of the invention. The embodiments of the present application and features in the embodiments may be combined with each other arbitrarily without conflict.
Claims (5)
1. The frequency division multiplexing high-precision optical fiber time transmission method is characterized by comprising a near-end to far-end unidirectional time transmission step, wherein the near-end to far-end unidirectional time transmission step comprises the following steps of:
a near-end time code generation step: the near end encodes a timing signal output by the local clock, a locally measured unidirectional clock error, time information and control information to generate a time code;
a near-end phase modulation step: the generated time code is relative to frequencyf 1 The radio frequency carrier signal of (2) is phase modulated, and the phase modulated carrier signal produced by phase modulation is loaded into the wavelength lambda through electro-optical conversion 1 Is transmitted to the far end through the optical fiber;
and (3) a remote recovery step: the far end photoelectrically converts the optical signal received from the optical fiber from the near end, and the carrier frequency of the converted electric signal isf 1 Recovering the time code by the phase demodulation of the clock signal, and decoding the recovered time code to extract a timing signal, a locally measured unidirectional clock error, time information and control information;
the method further comprises a step of transmitting the far-end to the near-end unidirectional time, and the step of transmitting the far-end to the near-end unidirectional time comprises the following steps:
a remote time code generation step: the remote end encodes a timing signal output by the local clock, a locally measured unidirectional clock difference, time information and control information to generate a time code;
a remote phase modulation step: remotely generated time code versus frequency off 2 The radio frequency carrier signal of (2) is phase modulated, and the phase modulated carrier signal produced by phase modulation is loaded into the wavelength lambda through electro-optical conversion 1 Is transmitted to the near end through the same optical fiber;
proximal recovery step: the near end photoelectrically converts the far-end optical signal received from the optical fiber, and the carrier frequency of the converted electric signal isf 2 And then decoding the recovered time code to extract timing signals, locally measured unidirectional clock differences, time information and control information.
2. The method of frequency division multiplexed high precision optical fiber time transfer of claim 1, wherein the timing signal comprises a 1PPS signal.
3. The method for frequency division multiplexing high-precision optical fiber time transfer according to claim 1, further comprising the step of clock skew acquisition:
the near end measures the time interval between the timing signal output by the local clock and the timing signal received from the far end, obtains the unidirectional clock difference measured by the near end, adds the unidirectional clock difference into the time code and transmits the unidirectional clock difference to the far end;
the remote end measures the time interval between the timing signal output by the local clock and the timing signal received from the near end, obtains the unidirectional clock difference measured by the remote end, adds the unidirectional clock difference into the time code and transmits the unidirectional clock difference to the near end;
the near end and the far end calculate the clock difference at the two ends by utilizing the two-way comparison principle according to the locally measured one-way clock difference and the one-way clock difference received from the opposite end respectively.
4. A frequency division multiplexing high-precision optical fiber time transmission system for realizing the frequency division multiplexing high-precision optical fiber time transmission method according to any one of claims 1 to 3, which is characterized by comprising a near-end module and a far-end module, wherein the near-end module and the far-end module respectively comprise a local clock, a time encoder, a phase modulator, an optical transmitting module, a combining and branching device, an optical receiving module, a phase demodulator, a time decoder and a time interval measuring module which are sequentially connected, and the combining and branching devices of the near-end module and the far-end module are connected through optical fibers;
the time codes of the near end and the far end are loaded on radio frequency carriers with different frequencies through phase modulation, and the time codes are recovered through phase demodulation of the corresponding radio frequency carriers;
the phase modulation signals carrying time signals at the near end and the far end are transmitted in two directions through the same optical fiber and the same wavelength.
5. The system of claim 4, wherein the local clock output timing signal, the locally measured unidirectional clock differential, the time information and the control information are sent to a time encoder for encoding.
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| CN113645004B (en) * | 2021-10-14 | 2021-12-17 | 成都金诺信高科技有限公司 | Comparison method of high-precision bidirectional time-frequency comparison system based on pulse width modulation |
| CN115225246B (en) * | 2022-07-11 | 2023-12-01 | 北京邮电大学 | Phase modulation bidirectional time synchronization device, method and system |
| CN115225247B (en) * | 2022-07-11 | 2023-12-01 | 北京邮电大学 | Phase modulation loop-back time synchronization device, method and system |
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