CN113285757A - Frequency division multiplexing high-precision optical fiber time transmission and system and method - Google Patents
Frequency division multiplexing high-precision optical fiber time transmission and system and method Download PDFInfo
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- 230000005540 biological transmission Effects 0.000 title claims abstract description 55
- 239000013307 optical fiber Substances 0.000 title claims abstract description 52
- 238000000034 method Methods 0.000 title claims abstract description 21
- 230000002457 bidirectional effect Effects 0.000 claims abstract description 18
- 230000003287 optical effect Effects 0.000 claims abstract description 18
- 239000000969 carrier Substances 0.000 claims abstract description 12
- 238000006243 chemical reaction Methods 0.000 claims abstract description 12
- 238000012546 transfer Methods 0.000 claims description 11
- 239000000835 fiber Substances 0.000 claims description 6
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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
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- 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
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Abstract
The invention provides a frequency division multiplexing high-precision optical fiber time transmission system and a method. 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 mutually 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 end through phase demodulation of corresponding carriers, further decode and recover timing signals, time information and control information, measure the time intervals of local timing signals and the recovered opposite end timing signals, calculate the real-time clock difference of the two ends by utilizing a bidirectional time comparison principle, and realize time transmission. The frequency division multiplexing high-precision optical fiber time transmission method combines the optical fiber bidirectional transmission and the phase modulation frequency division multiplexing, and simultaneously realizes the optical fiber time transmission with high accuracy and high stability.
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 the most basic physical quantity, and in the modern society of information, with the rapid development of fields such as navigation, aerospace, communication, electric power and the like, the requirement on time service precision is higher and higher. The time frequency with high accuracy and high stability is a vital resource in national strategy, and the demand of daily life for high-precision time transmission is increasing day by day. The performance of the time frequency system is an important embodiment of the development and comprehensive strength of the national science and technology.
Time transfer based on a one-way IRIG system is widely applied in daily life, and the system is only suitable for short-distance time service because delay in a transmission process is not considered. In order to achieve nanosecond-level or even higher time precision, a satellite-based time service system and an optical fiber-based time service system are mainly used at present. Although the satellite time service technology is quite mature, the satellite time service technology 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. At present, the high-precision optical fiber time transmission scheme mainly comprises a loopback 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 variation caused by factors such as temperature and stress. The existing same-fiber wavelength division multiplexing bidirectional transmission can effectively inhibit the influence of back scattering noise, but the inconsistency of bidirectional transmission wavelength destroys the symmetry of bidirectional transmission, requires complex link calibration, and limits the time transfer performance and cost; the same-fiber same-wave bidirectional transmission can ensure the symmetry of the bidirectional transmission, but the backscattering noise seriously limits the improvement of the time transfer performance.
The invention patent of patent document CN111948686A discloses a time synchronization method and device for each processing center in a navigation enhancement system, comprising: sending local clock error products to other processing centers in the navigation enhancement system at regular time, and receiving the clock error products sent by a plurality of processing centers; calculating a difference between a local time reference and a system time reference from a local clock error product and the received plurality of clock error products; and updating the local clock error product according to the difference between the local time reference and the system time reference. The invention can ensure the unification of time reference used by broadcasting products in each processing center in the navigation enhancement system and provide stable navigation enhancement service for users. However, the above scheme cannot simultaneously ensure the symmetry of the bidirectional transmission and suppress the influence of the backward rayleigh scattering noise.
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 frequency division multiplexing high-precision optical fiber time transmission system provided by the invention 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 combiner-splitter, an optical receiving module, a phase demodulator, a time decoder and a time interval measuring module which are sequentially connected, and the combiner-splitter of the near-end module and the far-end module is connected through an optical fiber.
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 at the same wavelength.
Preferably, the local clock outputs a timing signal, a locally measured one-way clock difference, time information and control information to a time encoder for encoding.
According to the invention, the frequency division multiplexing high-precision optical fiber time transmission method based on the frequency division multiplexing high-precision optical fiber time transmission system 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:
a near-end time code generating step: the near end encodes a timing signal output by a local clock, a locally measured one-way clock difference, time information and control information to generate a time code;
a near-end phase modulation step: the generated time code has a frequency f1The radio frequency carrier signal is phase-modulated, and the phase-modulated carrier signal generated by phase modulation is loaded to the wavelength lambda through electro-optical conversion1And transmitted to the far end via the optical fiber;
a remote recovery step: the far end carries out photoelectric conversion on the optical signal received from the optical fiber from the near end, and the carrier frequency f of the converted electrical signal is1The time code is recovered by phase demodulation, and then the recovered time code is decoded to extract the timing signal, the locally measured one-way clock error, the time information and the control information.
Preferably, the method further comprises a far-end to near-end unidirectional time transmission step, wherein the far-end to near-end unidirectional time transmission step comprises:
a remote time code generating step: the remote end encodes a timing signal output by the local clock, the locally measured one-way clock difference, the time information and the control information to generate a time code;
a far-end phase modulation step: the time code generated at the remote end has a frequency f2The radio frequency carrier signal is phase-modulated, and the phase-modulated carrier signal generated by phase modulation is loaded to the wavelength lambda through electro-optical conversion1And transmitted to the near end through the same optical fiber;
a near-end recovery step: the near end performs photoelectric conversion on the optical signal received from the optical fiber from the far end, and performs carrier frequency f on the converted electric signal2The time code is recovered by phase demodulation, and then the recovered time code is decoded to extract the timing signal, the locally measured one-way clock error, the time information and the control information.
Preferably, the timing signal comprises a 1PPS signal.
Preferably, the method further comprises a clock difference acquiring step:
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 to obtain the one-way clock difference measured by the near end, and adds the one-way clock difference into the time code to be transmitted to the far end;
the far end measures the time interval between the timing signal output by the local clock and the timing signal received by the near end, namely the one-way clock difference measured by the far end, and adds the one-way clock difference into the time code to be transmitted to the near end;
the near end and the far end respectively calculate the clock error of the two ends by utilizing a bidirectional comparison principle according to the locally measured one-way clock error and the one-way clock error received from the opposite end.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention carries out bidirectional transmission through the same optical fiber and the same wavelength by phase modulation signals carrying time signals at two ends, ensures the symmetry of bidirectional optical fiber transmission, and solves 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.
2. The time codes at two ends of the invention are loaded on the 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 the back scattering noise.
3. According to the invention, through the combination of phase modulation frequency division multiplexing and same-fiber same-wave bidirectional transmission, the symmetry of time delay of a bidirectional time transmission link is ensured, the influence of backscattering on the quality of a transmission signal is effectively inhibited, the accuracy and stability of optical fiber time transmission are obviously improved, the link calibration is not required, and the implementation and operation and maintenance costs are reduced.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
fig. 1 is a schematic diagram of a system for frequency division multiplexing high-precision optical fiber time transfer.
Fig. 2 is a schematic diagram of time encoding and decoding and carrier phase modulation and demodulation processes of a frequency division multiplexing high-precision optical fiber time transmission 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 invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
As shown in fig. 1 and fig. 2, the present invention provides a system and a method for frequency division multiplexing high-precision optical fiber time transfer, and fig. 1 is a schematic diagram of frequency division multiplexing high-precision optical fiber time transfer based on the present invention. The near end and the far end are connected through an optical fiber link, and time transmission between the near end local clock and the far end local clock is achieved. With reference to fig. 2, the specific working process is as follows:
(1) near-end to far-end one-way 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 performs B code coding on the 1PPS timing signal, the time information and the control information time signal and outputs the signals to a 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 by a phase-locked loop1Of the input B-code signal to a frequency f1The carrier signal is subjected to BPSK phase modulation (the high level of time coding selects the 0 phase of the carrier, the low level selects the 180 phase), and the BPSK phase modulation carrier signal is output to the light emitting module; the near-end optical transmitting module modulates the input BPSK phase modulation carrier signal into light with the wavelength of lambda, and inputs the light into an optical fiber through a two-port optical multiplexer/demultiplexer (such as an optical coupler or a circulator) and sends the light to a far end; the far-end light receiving module receives signals in the optical fiber through the two-port optical multiplexer/splitter, restores the BPSK phase modulation carrier signals of the near end through photoelectric conversion and outputs the signals to the phase demodulation module; phase demodulation to recover near-end carrier f through COSTAS phase-locked loop1Then, the recovered carrier wave and phase modulation BPSK signal are used to recover the time coding B code of the near end; the far-end time decoding module decodes the recovered near-end time coding B code to recover 1PPS, time information and control information; remote time interval counter measurementRecovered 1PPS and 1PPS time interval of the far-end local clock output.
(2) Far-end to near-end one-way time transmission
Similarly, a 1PPS timing signal and a reference frequency signal output by the remote local clock enter a time coding module, and the time coding module performs B code coding on the 1PPS timing signal, time information and a control information time signal and outputs the signals to a phase modulation module; in the phase modulation module, a reference frequency signal output by a remote local clock is converted into a frequency f by a phase-locked loop2Of the input B-code signal to a frequency f2The carrier signal is subjected to BPSK phase modulation (the high level of time coding selects the 0 phase of the carrier, the low level selects the 180 phase), and the BPSK phase modulation carrier signal is output to the light emitting module; the far-end optical transmission module modulates the input BPSK phase modulation carrier signal into light with the wavelength of lambda, and inputs the light into an optical fiber through a two-port optical multiplexer/demultiplexer (such as an optical coupler or a circulator) and sends the light to a far end; the near-end light receiving module receives signals in the optical fiber through the two-port optical multiplexer/splitter, restores a near-end BPSK phase modulation carrier signal through photoelectric conversion and outputs the near-end BPSK phase modulation carrier signal to the phase demodulation module; phase demodulation for recovering remote carrier f through COSTAS phase-locked loop2Then, the recovered carrier wave and phase modulation BPSK signal are used to recover the remote time coding B code; the time decoding module at the near end decodes the recovered time coding B code at the near end to recover 1PPS, time information and control information; the time interval counter at the near end measures the time interval of the recovered 1PPS and the 1PPS output by the far end local clock.
(3) Real-time clock error calculation
The near end measures the time interval between the timing signal (such as 1PPS) output by the local clock and the timing signal (such as 1PPS) received from the far end to obtain the one-way clock difference measured by the near end and transmits the one-way clock difference to the far end; the far end measures the time interval between the timing signal (such as 1PPS) output by the local clock and the timing signal (such as 1PPS) received by the near end and the far 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 respectively calculate the clock error of the two ends by utilizing a bidirectional comparison principle according to the locally measured one-way clock error and the one-way clock error received from the opposite end.
The phase modulation signals carrying time signals at two ends of the optical fiber transmission device are transmitted in two directions through the same optical fiber and the same wavelength, so that the symmetry of the two-way optical fiber transmission is ensured. 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 mutually transmitted to each other through the same optical fiber link and the same wavelength through electro-optical conversion. The two ends are distributed to convert the received optical signals into electric signals, the opposite end is recovered through phase demodulation of corresponding carriers to obtain time codes, timing signals, time information and control information are further recovered through decoding, the time intervals of the local timing signals and the recovered opposite end timing signals are measured, real-time clock errors at the two ends are calculated by utilizing a two-way time comparison principle, and time transmission is achieved. The frequency division multiplexing high-precision optical fiber time transmission method combines the optical fiber bidirectional transmission and the phase modulation frequency division multiplexing, and simultaneously realizes the optical fiber time transmission with high accuracy and high stability. 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 the interference of the back scattering noise is effectively inhibited.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (8)
1. The frequency division multiplexing high-precision optical fiber time transmission system 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 combiner-splitter, an optical receiving module, a phase demodulator, a time decoder and a time interval measuring module which are sequentially connected, and the combiner-splitter of the near-end module and the far-end module is connected through optical fibers.
2. The frequency division multiplexing high accuracy optical fiber time transfer system of claim 1, wherein the time codes of the near end and the far end are loaded onto radio frequency carriers with different frequencies by phase modulation, and the time codes are recovered by phase demodulation of the corresponding radio frequency carriers.
3. The frequency division multiplexed high precision fiber optic time transfer system of claim 1 wherein the phase modulated signals carrying the time signals at the near end and the far end are transmitted bi-directionally over the same fiber at the same wavelength.
4. The frequency division multiplexed high precision fiber optic time transfer system of claim 1, wherein the local clock outputs timing signals, locally measured one-way clock differences, time information, and control information to a time encoder for encoding.
5. A frequency division multiplexing high precision optical fiber time transfer method based on the frequency division multiplexing high precision optical fiber time transfer system of any one of claims 1 to 4, characterized by comprising a near end to far end unidirectional time transmission step, the near end to far end unidirectional time transmission step comprising:
a near-end time code generating step: the near end encodes a timing signal output by a local clock, a locally measured one-way clock difference, time information and control information to generate a time code;
a near-end phase modulation step: the generated time code has a frequency f1The radio frequency carrier signal is phase-modulated, and the phase-modulated carrier signal generated by phase modulation is loaded to the wavelength lambda through electro-optical conversion1And transmitted to the far end via the optical fiber;
a remote recovery step: the far end carries out photoelectric conversion on the optical signal received from the optical fiber from the near end, and the carrier frequency f of the converted electrical signal is1The time code is recovered by phase demodulation, and then the recovered time code is decoded to extract the timing signal, the locally measured one-way clock error, the time information and the control information.
6. The method according to claim 5, further comprising a far-end to near-end unidirectional time transmission step, the far-end to near-end unidirectional time transmission step comprising:
a remote time code generating step: the remote end encodes a timing signal output by the local clock, the locally measured one-way clock difference, the time information and the control information to generate a time code;
a far-end phase modulation step: the time code generated at the remote end has a frequency f2The radio frequency carrier signal is phase-modulated, and the phase-modulated carrier signal generated by phase modulation is loaded to the wavelength lambda through electro-optical conversion1And transmitted to the near end through the same optical fiber;
a near-end recovery step: the near end performs photoelectric conversion on the optical signal received from the optical fiber from the far end, and performs carrier frequency f on the converted electric signal2The time code is recovered by phase demodulation, and then the recovered time code is decoded to extract the timing signal, the locally measured one-way clock error, the time information and the control information.
7. The method of claim 6, wherein the timing signal comprises a 1PPS signal.
8. The method according to claim 5, further comprising the step of obtaining the clock error:
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 to obtain the one-way clock difference measured by the near end, and adds the one-way clock difference into the time code to be transmitted to the far end;
the far end measures the time interval between the timing signal output by the local clock and the timing signal received by the near end, namely the one-way clock difference measured by the far end, and adds the one-way clock difference into the time code to be transmitted to the near end;
the near end and the far end respectively calculate the clock error of the two ends by utilizing a bidirectional comparison principle according to the locally measured one-way clock error and the one-way clock error received from the opposite end.
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| CN115225246A (en) * | 2022-07-11 | 2022-10-21 | 北京邮电大学 | Phase modulation bidirectional time synchronization device, method and system |
| CN115225247A (en) * | 2022-07-11 | 2022-10-21 | 北京邮电大学 | Phase modulation loopback 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 |
| CN115225246B (en) * | 2022-07-11 | 2023-12-01 | 北京邮电大学 | Phase modulation bidirectional time synchronization device, method and system |
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