CN112713953B - Time synchronization device, system and method - Google Patents
Time synchronization device, system and method Download PDFInfo
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- CN112713953B CN112713953B CN202011487134.2A CN202011487134A CN112713953B CN 112713953 B CN112713953 B CN 112713953B CN 202011487134 A CN202011487134 A CN 202011487134A CN 112713953 B CN112713953 B CN 112713953B
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- H04J3/0635—Clock or time synchronisation in a network
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- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
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Abstract
The invention discloses a time synchronization device, a system and a method, belonging to the field of optical fiber time synchronization, comprising a near end A, an optical fiber link and a far endB; the near end A sends the optical pulse signal and receives the optical signal of loopback and feedbacks the optical signal multiplexing from the optical fiber link, the optical signal transmitted from far end B is transmitted to the photoelectric detector and changed into the electric signal and sent to the time measuring module, carry on the time difference, the control module judges the transmission time T from near end A to far end B according to the random numberABAnd the compensated signal is modulated and sent to an optical fiber link and transmitted to a far end B. The far end B respectively realizes time synchronization with the near end A through the beam splitter and carries out time delay to form a loopback signal; meanwhile, the control module delays the clock source signal to obtain a feedback signal; and the beam combiner multiplexes the loopback signal and the feedback signal and transmits the signals to the optical fiber link. The invention can accurately compensate the transmission time and improve the reliability of the system.
Description
Technical Field
The invention belongs to the technical field of optical fiber time synchronization, and particularly relates to a time synchronization device, a time synchronization system and a time synchronization method.
Background
Currently, the time synchronization system commonly used mainly includes a satellite time synchronization system and a fiber time synchronization system.
The satellite time synchronization system is a time synchronization system which uses a satellite to transmit standard time signals, and has the following advantages: the satellite can send standard time signals with high precision, the coverage range can reach the world, the satellite time synchronization receiver is convenient, cheap and fast, and the precision of the satellite time synchronization can meet the requirement of most people on the time synchronization. However, since satellite signals are transmitted from space, the space environment is more complex than the ground environment, which also causes the satellite signals to be interfered by various factors in the space environment, and the signals are weak when being transmitted to the ground, even because some areas are not within the coverage of the satellite, so that the signals cannot be received in these areas.
Since the seventies of the twentieth century, with the increasing practical use of optical fibers, optical fibers have attracted more and more attention because of their excellent characteristics of transmitting signals and the popularity of optical networks. The optical fiber has the following advantages: the method has the advantages of large bandwidth, low loss, small temperature coefficient, low manufacturing cost, high stability, long relay distance and strong anti-interference capability. The optical fiber time synchronization is a novel high-precision time transmission means, and has the specific advantages of optical fiber transmission signals. The optical fiber time synchronization mainly sends out a pulse per second, wherein the pulse per second is fixedly generated and has a certain pulse width. By comparing the pulse per second, the time difference between the two places can be calculated by using a corresponding algorithm, so that the calibration is carried out.
In 2015, a system for synchronizing frequency and time together is realized by Shanghai optical precision mechanical research institute of Chinese academy of sciences, and when the length of an optical fiber is 50km, the time synchronization precision is 1.6 ps; at a fiber length of 110km, the time synchronization accuracy was 30 ps. In 2016, the institute of communication, west ampere, in a fiber optic time synchronization system, receives pulse-per-second signals by using an FPGA, and simultaneously, internally synchronizes the pulse-per-second signals and generates time codes for transmission, wherein the final time synchronization precision is 11.8 ns. In 2016, the university of polacrkov AGH technology used a single-fiber two-way loopback system, and after time compensation was performed by controlling a pair of low-noise precisely matched delay lines, the time synchronization precision was about 2ps after 615km transmission. In 2017, a transmission delay compensation scheme of an accurate optical fiber based on a clock counter and an electronic variable delay line is tested by the university of liberty military scientist, and after 100km of optical fiber, the time synchronization precision is 66.7 ps.
In the classical loop-back time synchronization system, there is a basic assumption: the round-trip optical fiber link is symmetrical, i.e. the transmission time of the optical fiber link from the near end to the far end is the same as the transmission time of the optical fiber link from the far end to the near end. However, based on this, there is a risk that the delay caused by channel asymmetry is too large.
Under normal conditions, the round-trip time T of the entire link is:
in the formula, LAB(LBA) Is the length of the fiber link from the near end A (far end B) to the far end B (near end A), c is the speed of light in vacuum, n0Is the refractive index of the optical fiber.
In the case of time delay caused by channel asymmetry, if the distance from the near end a to the far end B is lengthened by m meters, and the distance from the far end B to the near end a is shortened by m meters, the round trip time of the whole link is still T, but the signal from the near end a to the far end B will be transmitted through the link by more than m meters, and the caused time error T iserrComprises the following steps:
for example, when m is 1 meter, the delay caused by channel asymmetry can reach an effect of 5 ns.
Disclosure of Invention
The invention provides a time synchronization device, a time synchronization system and a time synchronization method for solving the defects of the existing scheme, which can find the time delay caused by the asymmetry of a channel, identify and eliminate the time delay and improve the reliability of a time synchronization system.
The time synchronization device comprises a near end A, an optical fiber link and a far end B.
The near end A consists of a first clock source, a first random number module, a first control module, a delay compensation module, a first light pulse sending module, a first multiplexing module, a first photoelectric detector and a time measuring module;
the first control module is simultaneously connected with a first clock source, a first random number module, a time measuring module and a delay compensation module;
the first clock source generates a pulse-per-second signal and a local clock signal, and the random number generated by the first random digital module is simultaneously provided for the first control module;
the first multiplexing module is simultaneously connected with the first optical pulse sending module and the optical fiber link, multiplexes an optical pulse signal sent by the first optical pulse sending module and an optical signal received from the optical fiber link on one optical fiber, and transmits the optical signal from the optical fiber link to the first photoelectric detector;
the optical signal received by the optical fiber link comprises a loopback signal and a feedback signal which are sent from a far end B;
the first photoelectric detector converts the multiplexed optical signal into an electric signal after detection and sends the electric signal to the time measurement module, the time measurement module makes difference between the converted loopback electric signal and the converted feedback electric signal and a local clock signal received from the first control module respectively, and sends two difference results to the first control module;
the first control module judges according to the random number: looping back the signal, feeding back the time difference between the signal and the local time of the near end A, and calculating the transmission time T from the near end A to the far end BAB；
The first control module transmits the time TABThe second pulse signal is sent to a delay compensation module for delay compensation, and the compensated second pulse signal is sent to a first optical pulse sending module; the first optical pulse sending module modulates the delayed pulse-per-second electrical signal into an optical pulse signal and sends the optical pulse signal to the first multiplexing module, and then the optical pulse signal is sent to the optical fiber link to form a closed loop circuit of the sending end.
The far end B consists of a second clock source, a second random number module, a second control module, a second optical pulse sending module, a beam combiner, a delay module, a second photoelectric detector, a beam splitter and a second multiplexing module;
the second control module is simultaneously connected with a second clock source, a second random number module, a second light pulse sending module, a second photoelectric detector and a delay module.
The second clock source generates a pulse-per-second signal, the random number generated by the second random digital module is shared with the random number of the first random number module, and the pulse-per-second signal and the shared random number are sent to the second control module;
the second multiplexing module receives an optical signal in the optical fiber link and sends the optical signal to the beam splitter, and the optical signal is a signal which is sent to the optical fiber link through the first multiplexing module, wherein the first optical pulse sending module in the near end A modulates a delayed pulse-per-second electrical signal into an optical pulse signal.
The beam splitter divides the signal into two beams according to the proportion: one beam is transmitted to a second photoelectric detector, is converted into an electric signal after detection, is transmitted to a second control module, and is recovered to a timing signal to realize time synchronization with a near end A; and the other beam of optical signal is sent to a delay module to delay the optical signal to form a loopback signal, the delay time is controlled by a second control module, and then the loopback signal is sent to a beam combiner.
The second control module delays the pulse-per-second electrical signal provided by the second clock source and sends the delayed pulse-per-second electrical signal to the second optical pulse sending module, and the second optical pulse sending module modulates the received delayed electrical signal into an optical signal to form a feedback signal and sends the feedback signal to the beam combiner;
the beam combiner combines the feedback signal and the loopback signal into a beam of light and sends the beam of light to the second multiplexing module, and the second multiplexing module multiplexes the beam-combined optical signal and an optical signal received from the optical fiber link on one optical fiber for transmission to form a closed loop circuit at a receiving end.
The second control module needs to control the delay time of the loopback signal and also needs to control the delay time of the feedback signal, judges whether the loopback signal or the feedback signal is selected according to the shared random number, and then controls different delay times of the loopback signal and the feedback signal to form the sending sequence of the loopback signal and the feedback signal.
The time synchronization system has the following specific working principle:
firstly, a loop back signal and a feedback signal sent by a far end B are received by a near end A through an optical fiber link, and the two signals are transmitted to a first photoelectric detector together with an optical pulse signal sent by a first optical pulse sending module;
the first photoelectric detector is converted into an electric signal and sends the electric signal to the time measuring module, the time measuring module makes difference between the converted loopback electric signal and the converted feedback electric signal and a local clock signal respectively, and sends two difference results to the first control module;
the first control module judges according to the random number: the signal is looped back and the signal is,the time difference between the feedback signal and the local time of the near end A is respectively calculated, and the transmission time T from the near end A to the far end B is calculatedAB；
The first control module transmits the time TABThe optical pulse signal is sent to a delay compensation module for delay compensation, then sent to a first optical pulse sending module, modulated into an optical pulse signal and sent to an optical fiber link through a first multiplexing module;
the second multiplexing module of the far-end B receives the optical signal in the optical fiber link and sends the optical signal to the beam splitter, and the beam splitter divides the signal into two beams according to the proportion: one beam is transmitted to a second photoelectric detector, is converted into an electric signal after detection, is transmitted to a second control module, and is recovered to a timing signal to realize time synchronization with a near end A; and the other beam of optical signal is sent to a delay module to delay the optical signal to form a loopback signal, and then is sent to a beam combiner.
Meanwhile, after delaying the pulse-per-second electrical signal provided by the second clock source, the second control module sends the delayed pulse-per-second electrical signal to the second optical pulse sending module to be modulated into an optical signal, so as to form a feedback signal and send the feedback signal to the beam combiner;
the beam combiner combines the feedback signal and the delay signal into a beam of light and sends the beam of light to the second multiplexing module, and the second multiplexing module transmits the combined beam of light signals to the optical fiber link to form a closed loop circuit.
And the second control module judges the sending sequence of the loopback signal and the feedback signal according to the shared random number.
The time synchronization method comprises the following specific steps:
step one, when the timing information of the first clock source is effective, the first control module controls the delay compensation module to delay the second pulse generated by the local clock source for 1-TABThen, the light pulse is sent to a first light pulse sending module;
TABis the one-way time from the proximal end a to the distal end B;
step two, the first optical pulse sending module delays the time by 1-TABModulating the second pulse signal after the time into an optical signal, and sending the optical signal to a far end B through an optical fiber link;
the modulated optical signal contains local timing information.
After the far end B receives the optical pulse signal sent by the near end A, the second multiplexing module sends the optical pulse signal to the beam splitter;
the beam splitter splits the optical pulse signal into two parts: one beam is transmitted to a second photoelectric detector and converted into an electric signal through detection, and a timing signal synchronous with the near end A is recovered to realize time synchronization with the near end A; another light signal is sent to a delay module to carry out delay T on the light signald1Then forming a loop back signal and sending the loop back signal to the beam combiner;
step four, simultaneously, when the timing information of the second clock source is valid, the second control module delays the second pulse electric signal provided by the second clock source by time Td2And then the optical pulse is sent to a second optical pulse sending module.
Step five, the second light pulse sending module delays the time Td2The second pulse electrical signal is modulated into an optical signal to form a feedback signal, and the feedback signal is sent to the beam combiner.
And step six, the beam combiner sends the loopback signal and the feedback signal to the optical fiber link through the second multiplexing module and returns the loopback signal and the feedback signal to the near end A.
The second control module judges the sending sequence of the feedback signal and the loopback signal according to the random number provided by the second random number module to control the delay time Td1And Td2。
The transmission sequence includes two types: when T isd1Less than Td2The time loop signal arrives first, and the feedback signal arrives later; when T isd1Greater than Td2The time feedback signal arrives first, and the time feedback signal arrives after the signal is looped back;
step seven, the near end A receives the loopback optical signal and the feedback optical signal sent by the far end B through the first multiplexing module, converts the loopback optical signal and the feedback optical signal into a loopback electric signal and a feedback electric signal through the first photoelectric detector, and sends the loopback electric signal and the feedback electric signal to the time measuring module;
and step eight, the time measurement module measures the arrival time of the loopback electric signal and the feedback electric signal, makes difference with the local time respectively, and sends the two difference measurement results to the first control module.
Step nine, the first control module performs the control according to the randomNumber, distinguishing the arrival time of the looped back signal in the difference measurement result from the local time difference TRLTime difference T between arrival time of feedback signal and local timeFL(ii) a And further obtaining the one-way time T from the near end A to the far end BAB。
Wherein: t isRL＝TAB+Td1+TBA，TFL＝T1+Td2+TBA
T1Is the time difference, T, between the first clock source and the second clock sourced1Delay, T, of looped-back signal for second control moduled2Delay of the feedback signal for the second control module, TABOne-way time, T, from proximal A to distal BBAIs the one-way travel time from the distal end B to the proximal end a.
Step ten, adjusting the time delay of the first optical pulse sending module to 1-TABThrough TABThe time arrives at the far end B and is synchronized with the next second pulse of the first clock source module at the near end a.
Compared with the prior art, the invention has the following advantages:
(1) a time synchronization device, a system and a method are provided, wherein at a near end A of a sending end, one-way transmission time from the near end A to a far end B can be accurately obtained through a specific data processing method of a time measurement module and a first control module, and the accuracy of time compensation is ensured.
(2) A time synchronization device, a system and a method are provided, wherein a feedback signal is generated at a receiving end remote end B through an independent second clock source module, so that the stability of the generation of the feedback signal is ensured, and the influence is not easy to occur. The loopback signal is delayed and generated by a delay module controlled by the second control module, and the sending sequence is judged by using a shared random number by combining the near end A and the far end B, so that the loopback signal and the feedback signal can be accurately distinguished by two parties and cannot be distinguished by a third party.
(3) A time synchronization device, system and method, in signal transmission, when feedback signal and loopback signal are transmitted in optical fiber channel, the physical characteristics such as pulse width, wavelength, etc. are consistent, except near end A and far end B of both communication parties, the two can not be distinguished, thus enhancing the safety of the system.
(4) The invention provides a time synchronization device, a time synchronization system and a time synchronization method, which overcome the defect of the traditional loopback time synchronization method on the assumption of the symmetry of a transmission link, can accurately compensate the transmission time from a near end A to a far end B, and improve the reliability of the system.
Drawings
FIG. 1 is a schematic diagram of a time synchronization system according to the present invention;
FIG. 2 is a flow chart of a method of time synchronization of the present invention;
FIG. 3 is a graph of the present invention when the loopback signal is sent before the feedback signal, i.e., Td1<Td2The optical fiber time synchronization working process schematic diagram;
FIG. 4 is a graph of the present invention when the loopback signal is sent out after the feedback signal, i.e., Td1>Td2The working process of the optical fiber time synchronization is shown schematically.
Detailed Description
The present invention will be described in further detail and with reference to the accompanying drawings so that those skilled in the art can understand and practice the invention.
The invention discloses a time synchronization device, a system and a method, which add feedback signals and simultaneously introduce the randomness of random numbers, and specifically comprise the following steps: the near end A sends an optical pulse signal containing local timing information to the far end B through an optical fiber link; the far end B receives the optical pulse signal sent by the near end A, and one part of the optical pulse signal is used for detection to realize time synchronization with the near end A; the other part forms a loopback signal through time delay and returns the loopback signal to the sending end; the far end B delays the signal generated by the clock source of the far end B to form a feedback signal, the sending sequence of the loopback signal and the feedback signal is formed by different delays, and the loopback signal and the feedback signal are sequenced and determined by random numbers; the near end A measures the time of the received loopback signal and the feedback signal, accurately analyzes the signal and the time difference between the signals according to the consistent random number shared by the two parties, and compensates the time delay, thereby achieving the effects of finding the time delay caused by the channel asymmetry and removing the influence of the time delay.
The time synchronization device, as shown in fig. 1, includes a near end a, a fiber link, and a far end B.
The near end A consists of a first clock source, a first random number module, a first control module, a delay compensation module, a first light pulse sending module, a first multiplexing module, a first photoelectric detector and a time measuring module;
the first control module is simultaneously connected with a first clock source, a first random number module, a time measuring module and a delay compensation module;
the first clock source generates a pulse-per-second signal and a local clock signal, and the random number generated by the first random digital module is simultaneously provided for the first control module; the first control module controls the adjustment of the time delay according to the random number.
The first random number module is in a classical form or a quantum form;
the first multiplexing module is simultaneously connected with the first optical pulse sending module and the optical fiber link, and multiplexes an optical pulse signal sent by the first optical pulse sending module and an optical signal received from the optical fiber link on one optical fiber and transmits the optical pulse signal and the optical signal to the first photoelectric detector;
the optical signal received by the optical fiber link comprises a loopback signal and a feedback signal which are sent from a far end B;
the first photoelectric detector converts the multiplexed optical signal into an electric signal after detection and sends the electric signal to the time measurement module, the time measurement module makes difference between the converted loopback electric signal and the converted feedback electric signal and a local clock signal received from the first control module respectively, and sends two difference results to the first control module;
the time measuring module is used for measuring time information such as time difference between the received signal time and local time;
the first control module judges according to the random number: the time difference between the loopback signal and the local time of the near end A and the time difference between the feedback signal and the local time of the near end A are calculated, and the transmission time T from the near end A to the far end B is calculatedAB；
Since it is for the pulse arriving at the distal end B and the proximal endA is synchronous, and the first control module transmits time TABThe second pulse signal is sent to a delay compensation module for delay compensation, and the compensated second pulse signal is sent to a first optical pulse sending module; the first optical pulse sending module modulates the delayed second pulse electrical signal into an optical pulse signal and sends the optical pulse signal to the first multiplexing module, and then the optical pulse signal is sent to the optical fiber link to form a closed loop circuit of the sending end.
The delay compensation module is used for controlling the delay of the pulse per second, so that the far end B and the near end A are time-synchronized.
The far end B consists of a second clock source, a second random number module, a second control module, a second optical pulse sending module, a beam combiner, a delay module, a second photoelectric detector, a beam splitter and a second multiplexing module;
the second control module is simultaneously connected with a second clock source, a second random number module, a second light pulse sending module, a second photoelectric detector and a delay module.
The second clock source generates a pulse-per-second signal, the second random number module is used for providing the same random number as the first random number module of the near end A, and the random number generated by the second random number module is shared with the random number of the first random number module; the second pulse signal and the shared random number are jointly sent to a second control module;
the sharing of random numbers is realized by quantum key distribution and other modes;
the second control module controls the sending sequence of the loopback signal and the feedback signal according to the random number;
the second multiplexing module receives an optical signal in the optical fiber link and sends the optical signal to the beam splitter, and the optical signal is a signal which is sent to the optical fiber link through the first multiplexing module, wherein the first optical pulse sending module in the near end A modulates a delayed pulse-per-second electrical signal into an optical pulse signal.
The beam splitter divides the signal into two beams according to the proportion: one beam is transmitted to a second photoelectric detector, is converted into an electric signal after detection, is transmitted to a second control module, and is recovered to a timing signal to realize time synchronization with a near end A; and the other beam of optical signal is sent to a delay module to delay the optical signal to form a loopback signal, the delay time is controlled by a second control module, and then the loopback signal is sent to a beam combiner.
The second control module delays the second pulse electrical signal provided by the second clock source and then sends the second pulse electrical signal to the second optical pulse sending module, and the second optical pulse sending module modulates the received delayed electrical signal into an optical signal to form a feedback signal and sends the feedback signal to the beam combiner;
the loopback signal is consistent with parameters such as wavelength, pulse width and the like of the feedback signal.
The beam combiner combines the feedback signal and the delay signal into a beam of light and sends the beam of light to the second multiplexing module, and the second multiplexing module multiplexes the beam-combined optical signal and an optical signal received from the optical fiber link on one optical fiber for transmission to form a closed loop circuit of a receiving end.
The second control module needs to control the delay time of the loopback signal and also needs to control the delay time of the feedback signal, judges the sending sequence of the loopback signal and the feedback signal according to the shared random number, and controls and adjusts the delay time according to the sending sequence.
The time synchronization system has the following specific working principle:
firstly, a loop back signal and a feedback signal sent by a far end B are received by a near end A through an optical fiber link, and the two signals are transmitted to a first photoelectric detector together with an optical pulse signal sent by a first optical pulse sending module;
the first photoelectric detector is converted into an electric signal and sends the electric signal to the time measuring module, the time measuring module respectively makes a difference between the converted loopback electric signal and the converted feedback electric signal and a local clock signal, and sends two difference results to the first control module;
the first control module judges according to the random number: the time difference between the loopback signal and the local time of the near end A and the time difference between the feedback signal and the local time of the near end A are calculated, and the transmission time T from the near end A to the far end B is calculatedAB；
The first control module transmits the time TABThe optical pulse signals are sent to a time delay compensation module for time delay compensation, then sent to a first optical pulse sending module, modulated into optical pulse signals, and sent to an optical fiber chain through a first multiplexing moduleIn the road;
the second multiplexing module of the far-end B receives the optical signal in the optical fiber link and sends the optical signal to the beam splitter, and the beam splitter divides the signal into two beams according to the proportion: one beam is transmitted to a second photoelectric detector, is converted into an electric signal after detection, is transmitted to a second control module, and is recovered to a timing signal to realize time synchronization with a near end A; and the other beam of optical signal is sent to a delay module to delay the optical signal to form a loopback signal, and then the loopback signal is sent to a beam combiner.
Meanwhile, after delaying the pulse-per-second electrical signal provided by the second clock source, the second control module sends the delayed pulse-per-second electrical signal to the second optical pulse sending module to be modulated into an optical signal, so as to form a feedback signal and send the feedback signal to the beam combiner;
the beam combiner combines the feedback signal and the delay signal into a beam of light and sends the beam of light to the second multiplexing module, and the second multiplexing module transmits the combined beam of light signals to the optical fiber link to form a closed loop circuit.
And the second control module judges the sending sequence of the loopback signal and the feedback signal according to the shared random number.
The time synchronization method comprises the steps that firstly, a near end A sends an optical pulse signal containing local timing information (such as 1PPS,5PPS and the like) to a far end B through an optical fiber link when the time information of a local clock source is effective; receiving a loopback signal and a feedback signal looped back by a far end B, wherein the two signals judge the arrangement sequence of the two signals in a random number mode shared by the two parties, and the parameters of the loopback signal and the feedback signal, such as wavelength, pulse width and the like, are consistent; then, the far-end B receives the optical pulse signal sent by the near-end A, one part of the optical pulse signal is used for detecting and recovering a time signal synchronous with the near-end A, the other part of the optical pulse signal is sent back to the near-end A to form a loopback signal, the far-end B generates a feedback signal when the time information of the clock source is effective, and the other part of the optical pulse signal sends another feedback signal; the sequence of sending the loopback signal and the feedback signal is performed according to the random number agreed by both parties. Finally, the near end A measures the time of the received loop back signal and feedback signal and adjusts the time delay of the system for sending light pulse to 1-TABThrough TABTime to the far end B and synchronized with the next second pulse of the near end a; clock source of near-end A and far-end BThe frequencies being equal but with a fixed time difference T1。
As shown in fig. 2, the specific steps are as follows:
step one, when the timing information of a first clock source 1-1 is valid, a near end A sends local timing information to a first control module 1-3, and the first control module 1-3 controls a delay compensation module 1-4 to delay time 1-T of a second pulse generated by a local clock sourceABThen, the light pulse is sent to a first light pulse sending module 1-5;
TABis the one-way time from the proximal end a to the distal end B; the first control module 1-3 measures the time T from the near end A to the far end B according to the time measuring module 1-6ABControlling the delay compensation module 1-4 to perform delay compensation 1-TAB；
Step two, the first optical pulse sending module 1-5 and the first multiplexing module 1-7 delay 1-TABModulating the second pulse signal after the time into an optical signal, and sending the optical signal to a far end B through an optical fiber link;
the modulated optical signal contains local timing information.
After the far end B receives the optical pulse signal sent by the near end A, the second multiplexing module 2-9 sends the optical pulse signal to the beam splitter 2-8;
the beam splitter 2-8 splits the optical pulse signal into two parts according to a certain ratio (e.g. 50: 50): one beam is transmitted to a second photoelectric detector 2-7 and converted into an electric signal after detection, the electric signal is transmitted to a control module 2-3 of a far end B, a timing signal synchronous with a near end A is recovered at the far end B, and time synchronization with the near end A is realized; the other beam of optical signal is sent to a delay module 2-6 for carrying out delay T on the optical signald1Then forming a loop back signal, and sending the loop back signal to the beam combiner 2-5;
step four, simultaneously, when the timing information of the second clock source 2-1 is valid, the second control module 2-3 of the far end B delays the second pulse electrical signal provided by the second clock source 2-1 by the time Td2And then transmitted to the second optical pulse transmitting module 2-4.
Step five, the second optical pulse sending module 2-4 delays the time Td2The second pulse electrical signal is modulated into an optical signal to form a feedback signal, and the feedback signal is sent to the beam combiner 2-5。
Step six, the beam combiner 2-5 sends the loopback signal and the feedback signal to the optical fiber link through the second multiplexing module 2-9 and returns to the near end A.
The second control module 2-3 judges the sending sequence of the feedback signal and the loopback signal according to the random number provided by the second random number module 2-2, so that the delay module 2-6 controls the delay time Td1And Td2。
step seven, the near end A receives the loopback optical signal and the feedback optical signal sent by the far end B through the first multiplexing module 1-7, converts the loopback optical signal and the feedback optical signal into a loopback electric signal and a feedback electric signal through the first photoelectric detector 1-8, and sends the loopback electric signal and the feedback electric signal to the time measuring module 1-6;
and step eight, the time measurement modules 1 to 6 measure the arrival time of the loopback electric signal and the feedback electric signal, respectively make difference with the local time, and send the two difference measurement results to the first control module 1 to 3.
Ninthly, after the first control module 1-3 determines the sequence of the loopback signal and the feedback signal according to the random number of the first random number module 1-2, distinguishing the time difference T between the arrival time of the loopback signal and the local time in the difference measurement resultAB+Td1+TBATime difference T between arrival time of feedback signal and local time1+Td2+TBA(ii) a And further obtaining the one-way time T from the near end A to the far end BAB。
T1Is the time difference, T, between the first clock source and the second clock sourced1Delay, T, of looped-back signal for second control moduled2Delay of the feedback signal for the second control module, TABOne-way time, T, from proximal A to distal BBAIs the one-way travel time from the distal end B to the proximal end a.
Step ten, adjusting the time delay of the first optical pulse sending module to 1-TABThrough TABTime arrives farEnd B is then just synchronized with the next second pulse of the first clock source module at the near end a.
The following presents a schematic time synchronization operation diagram of an embodiment with reference to the embodiment and fig. 3, where the embodiment is implemented on the premise of the time synchronization method of the present invention, and a detailed implementation manner and a specific workflow are provided, but the scope of the present invention is not limited to the following embodiments.
In fig. 3 and 4, T, R, RT of the pulses indicate a transmission pulse, a reception pulse, and a reception and transmission pulse, respectively, and the corresponding reference numerals are assigned to the respective pulses. In the figure, the clock source of the near-end A is taken as a time reference by default, and the clock source of the far-end B and the clock source of the near-end A do not synchronously have a time difference T1But both frequencies are the same.
When the time synchronization just starts, the working flow of the loopback signal is as follows: the near end A sends a pulse TA1 to the far end B through the optical fiber link, the far end B receives the signal and loops the signal to the near end A, and the near end A can calculate the loop time T of the whole systemAB+TBAAt a time delay of 1- (T)AB+TBA) After/2 a second sync pulse TA2 is sent; the feedback signal work flow is as follows: when the clock source second pulse of the far-end B is effective, the far-end B sends a feedback signal TB1, the feedback signal TB1 is transmitted through an optical fiber link and reaches the near-end A, and the near-end A compares the local time of the near-end A to obtain the transmission time T1+TBA。
When the loopback signal is sent before the feedback signal, i.e. Td1<Td2As shown in FIGS. 3 for 1-2 s. The loop-back signal working process comprises the following steps: the optical pulse TA2 sent by the near end A passes through T after being transmitted by the optical fiber linkABThe time reaches the far end B after being transmitted, and the far end B delays the time by Td1Then forms a loop back signal to return to the near end A. The near end A is compared with the local time to obtain the difference T between the loopback signal and the local timeRLIs TAB+Td1+TBA(ii) a The feedback signal work flow is as follows: the far end B passes through T when the clock source pulse is effectived2Sending a feedback pulse TB2 after delaying, comparing the near end A with the local time to obtain the difference T between the loopback signal and the local time when the TB2 pulse reaches the near end AFLIs T1+Td2+TBAAnd then calculating the one-way transmission time T from the near end A to the far end BABAnd delays 1-TAB before sending a pulse TA 3.
T when the loopback signal is sent after the feedback signald1>Td2As shown in FIGS. 4 for 1-2 s. The loop-back signal working process comprises the following steps: the optical pulse TA2 sent by the near end A passes through T after being transmitted by the optical fiber linkABThe time reaches the far end B after being transmitted, and the far end B delays the time by Td1Then forms a loop back signal to return to the near end A. The near end A is compared with the local time to obtain the difference T between the loopback signal and the local timeRLIs TAB+Td1+TBA(ii) a The feedback signal work flow is as follows: the far end B passes through T when the clock source pulse is effectived2Sending a feedback pulse TB2 after delaying, comparing the near end A with the local time to obtain the difference T between the loopback signal and the local time when the TB2 pulse reaches the near end AFLIs T1+Td2+TBAAnd then calculating the one-way transmission time T from the near end A to the far end BABAnd delays 1-TAB before sending a pulse TA 3.
Claims (5)
1. A time synchronizer is characterized by comprising a near end A consisting of a first clock source, a first random number module, a first control module, a delay compensation module, a first optical pulse sending module, a first multiplexing module, a first photoelectric detector and a time measuring module; the far end B consists of a second clock source, a second random number module, a second control module, a second optical pulse sending module, a beam combiner, a delay module, a second photoelectric detector, a beam splitter and a second multiplexing module;
the first multiplexing module multiplexes the optical pulse signal sent by the first optical pulse sending module and the loopback optical signal and the feedback optical signal received from the optical fiber link on an optical fiber, converts the optical pulse signal into a loopback electric signal and a feedback electric signal through the detection of the first photoelectric detector and sends the loopback electric signal and the feedback electric signal to the time measuring module; the loopback optical signal and the feedback optical signal are signals transmitted from a far end B through an optical fiber link;
the time measurement module makes difference between the loop back electric signal and the feedback electric signal and a local clock signal sent from a first clock source respectively, and sends two difference results to the first control module;
the first control module judges the time difference T between the loopback electric signal and the local time according to the random number sent by the first random number moduleRLAnd the time difference T between the feedback electrical signal and the local timeFLAnd further calculates the transmission time T from the near end A to the far end BAB(ii) a Wherein, TRL＝TAB+Td1+TBA，TFL＝T1+Td2+TBA；T1Is the time difference, T, between the first clock source and the second clock sourced1Delay, T, of looped-back signal for second control moduled2Delay of the feedback signal for the second control module, TBAIs the one-way travel time from the distal end B to the proximal end a;
then, the transmission time T is determinedABThe second pulse signal is sent to a first optical pulse sending module, modulated into an optical pulse signal and sent to an optical fiber link to form a closed loop circuit of a sending end;
the second multiplexing module receives optical signals in the optical fiber link and sends the optical signals to the beam splitter, and the beam splitter is divided into two beams of signals according to the proportion: one beam is transmitted to a second photoelectric detector, is converted into an electric signal after detection, is transmitted to a second control module, and is recovered to a timing signal, so that time synchronization with a near end A is realized; the other beam of optical signal is sent to a delay module to delay the optical signal to form a loopback signal, and then the loopback signal is sent to a beam combiner;
the second control module delays the pulse-per-second electrical signal provided by the second clock source, and sends the delayed pulse-per-second electrical signal to the second optical pulse sending module to be modulated into an optical signal, so that a feedback signal is formed and sent to the beam combiner;
the second control module is used for controlling the delay time of the loopback signal and the delay time of the feedback signal, judging whether the loopback signal or the feedback signal is selected according to the shared random number, and controlling different delay times of the loopback signal and the feedback signal to form a sending sequence of the loopback signal and the feedback signal;
the beam combiner combines the feedback signal and the loopback signal into a beam of light and sends the beam of light to the second multiplexing module, and the second multiplexing module multiplexes the beam-combined optical signal and an optical signal received from the optical fiber link on one optical fiber for transmission to form a closed loop circuit at a receiving end.
2. The apparatus for time synchronization of claim 1, wherein the first control module is connected to the first clock source, the first random number module, the time measurement module and the delay compensation module; the first clock source generates a pulse per second signal and a local clock signal, and the random number generated by the first random digital module is provided to the first control module at the same time.
3. The time synchronizer of claim 1, wherein said second control module is connected to a second clock source, a second random number module, a second optical pulse transmitting module, a second photo detector and a delay module; the second clock source generates a pulse-per-second signal, the random number generated by the second random digital module is shared with the random number of the first random number module, and the pulse-per-second signal and the shared random number are sent to the second control module together.
4. A time synchronization system comprising a near end a, a fiber link and a far end B, characterized in that:
firstly, a loop back signal and a feedback signal sent by a far end B are received by a near end A through an optical fiber link and are transmitted to a first photoelectric detector together with an optical pulse signal sent by a first optical pulse sending module;
the first photoelectric detector converts the loopback signal, the feedback signal and the optical pulse signal into electric signals respectively and sends the electric signals to the time measuring module, the time measuring module measures the arrival time of the loopback electric signal and the feedback electric signal respectively, then makes difference with the local clock signal respectively and sends two difference results to the first control module;
the first control module judges according to the random number: time difference between loopback signal and local time of near end ATRLAnd the time difference T between the feedback signal and the local time of the near end AFLAnd calculating the transmission time T from the near end A to the far end BABSending the signal to a delay compensation module for delay compensation; wherein, TRL＝TAB+Td1+TBA，TFL＝T1+Td2+TBA；T1Is the time difference, T, between the first clock source and the second clock sourced1Delay, T, of looped-back signal for second control moduled2Delay of the feedback signal for the second control module, TBAIs the one-way travel time from the distal end B to the proximal end a;
the first control module controls the delay compensation module to delay the pulse per second generated by the local clock source, and then sends the delayed pulse per second to the first optical pulse sending module, and the delayed pulse per second is modulated into an optical pulse signal to be sent to the optical fiber link, transmitted to the second multiplexing module at the far end B, and then the optical signal is divided into two beams through the beam splitter: one beam is sent to a second control module, and a timing signal is recovered to realize time synchronization with a near end A; another light signal is sent to a delay module to carry out delay T on the light signald1Then forming a loop back signal and sending the loop back signal to the beam combiner; meanwhile, when the timing information of the second clock source is valid, the second control module delays the time T of the pulse-per-second electrical signal provided by the second clock sourced2Then sending the light pulse to a second light pulse sending module; the second optical pulse transmitting module delays the time by Td2Modulating the second pulse electrical signal into an optical signal to form a feedback signal, and sending the feedback signal to a beam combiner; the second control module judges the sending sequence of the feedback signal and the loopback signal according to the random number provided by the second random number module to control the delay time Td1And Td2；
The random number generated by the second random number module is shared with the random number of the first random number module, wherein the random number according to which the first control module is based and the random number according to which the second control module is based are respectively generated by the first random number module and the second random number module;
the beam combiner combines the feedback signal and the delay signal into a beam of light and sends the beam of light to the optical fiber link to form a closed loop circuit.
5. A time synchronization method based on the time synchronization system of claim 4, comprising the following steps:
step one, when the timing information of the first clock source is effective, the first control module controls the delay compensation module to delay the second pulse generated by the local clock source for 1-TABThen, the light pulse is sent to a first light pulse sending module;
TABis the one-way time from the proximal end a to the distal end B;
step two, the first optical pulse sending module delays the time by 1-TABModulating the second pulse signal after the time into an optical signal, and sending the optical signal to a far end B through an optical fiber link;
the modulated optical signal contains local timing information;
after the far end B receives the optical pulse signal sent by the near end A, the second multiplexing module sends the optical pulse signal to the beam splitter;
the beam splitter splits the optical pulse signal into two parts: one beam is transmitted to a second photoelectric detector and converted into an electric signal through detection, and a timing signal synchronous with the near end A is recovered to realize time synchronization with the near end A; another light signal is sent to a delay module to carry out delay T on the light signald1Then forming a loop back signal and sending the loop back signal to the beam combiner;
step four, simultaneously, when the timing information of the second clock source is valid, the second control module delays the second pulse electric signal provided by the second clock source by time Td2Then sending the light pulse to a second light pulse sending module;
step five, the second light pulse sending module delays the time Td2Modulating the second pulse electrical signal into an optical signal to form a feedback signal, and sending the feedback signal to a beam combiner;
step six, the beam combiner sends the loopback signal and the feedback signal to the optical fiber link through the second multiplexing module and returns the loopback signal and the feedback signal to the near end A;
the second control module judges the sending sequence of the feedback signal and the loopback signal according to the random number provided by the second random number module, thereby controlling the delay time Td1And Td2；
The transmission sequence includes two types: when T isd1Less than Td2The time loop signal arrives first, and the feedback signal arrives later; when T isd1Greater than Td2The time feedback signal arrives first, and the time feedback signal arrives after the signal is looped back;
step seven, the near end A receives the loopback optical signal and the feedback optical signal sent by the far end B through the first multiplexing module, converts the loopback optical signal and the feedback optical signal into a loopback electric signal and a feedback electric signal through the first photoelectric detector, and sends the loopback electric signal and the feedback electric signal to the time measuring module;
step eight, the time measurement module measures the arrival time of the loopback electric signal and the feedback electric signal, makes difference with the local clock signal respectively, and sends the two difference measurement results to the first control module;
step nine, the first control module distinguishes the arrival time of the loopback signal in the difference measurement result and the local time difference T according to the random numberRLTime difference T between arrival time of feedback signal and local timeFL(ii) a And further obtaining the one-way time T from the near end A to the far end BAB；
Wherein: t isRL＝TAB+Td1+TBA，TFL＝T1+Td2+TBA
T1Is the time difference, T, between the first clock source and the second clock sourced1Delay, T, of looped-back signal for second control moduled2Delay of the feedback signal for the second control module, TABOne-way time, T, from proximal A to distal BBAIs the one-way travel time from the distal end B to the proximal end a;
step ten, adjusting the time delay of the first optical pulse sending module to 1-TABThrough TABThe time arrives at the far end B and is synchronized with the next second pulse of the first clock source module at the near end a.
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