CN112713953B - Time synchronization device, system and method - Google Patents

Abstract

The invention discloses a time synchronization device, system and method, belonging to the field of optical fiber time synchronization, comprising a near-end A, an optical fiber link and a far-end B; The signal and the feedback optical signal are multiplexed, and the optical signal transmitted from the far end B is transmitted to the photodetector and converted into an electrical signal, and then sent to the time measurement module for time difference. For the transmission time T _AB of the remote B, after compensation, the signal is modulated and sent to the optical fiber link, and then transmitted to the remote B. The signal sent by the far-end B from the near-end A passes through the beam splitter to achieve time synchronization with the near-end A, and delays to form a loopback signal; at the same time, the control module delays the clock source signal to obtain the feedback signal; The beamer multiplexes the loopback signal and the feedback signal and transmits it to the fiber link. The invention can accurately compensate the transmission time and improve the reliability of the system.

Description

A time synchronization device, system and method

technical field

The invention belongs to the technical field of optical fiber time synchronization, in particular to a time synchronization device, system and method.

Background technique

At present, the more commonly used time synchronization systems mainly include satellite time synchronization systems and optical fiber time synchronization systems.

The satellite time synchronization system is a time synchronization system that uses satellites to transmit standard time signals. Satellite time synchronization has the following advantages: satellites can send high-precision standard time signals, and the coverage can reach the world, and the satellite time synchronization receiver is convenient, Inexpensive, fast, and the accuracy of satellite time synchronization can already meet the needs of most people for time synchronization. However, since the satellite signal is sent from space, the space environment is more complex than the ground environment, which also causes the satellite signal to be interfered by various factors in the space environment, and the signal will be weaker when it reaches the ground. , and even some areas cannot receive signals because they are not in the coverage area of the satellite.

The optical fiber time synchronization system is a time synchronization system that uses optical fibers to transmit standard time signals. Since the 1970s, as optical fibers have become more and more widely used and entered the practical stage, optical fibers have become more and more widely used because of their excellent characteristics of signal transmission and optical network. With the popularization, optical fiber-based high-precision time transfer has begun to receive more and more attention. Optical fiber has the following advantages: large bandwidth, low loss, small temperature coefficient, low cost, high stability, long relay distance and strong anti-interference ability. Optical fiber time synchronization is a new type of high-precision time transfer method, which has the unique advantages of optical fiber transmission signals. Optical fiber time synchronization mainly transmits the second pulse, which is a pulse with a certain pulse width that is generated every second and has a certain pulse width. By comparing the second pulse, the corresponding algorithm can be used to calculate the time difference between the two places for calibration.

In 2015, the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences realized a frequency and time synchronization system. When the fiber length is 50km, the time synchronization accuracy is 1.6ps; when the fiber length is 110km, the time synchronization accuracy is 30ps. In 2016, Xi'an Institute of Communications used FPGA to receive the second pulse signal in the optical fiber time synchronization system, and at the same time, the second pulse signal was synchronized internally and the time code was generated for transmission. The final time synchronization accuracy was 11.8ns. In 2016, AGH University of Science and Technology in Krakow, Poland used a single-fiber bidirectional loopback system. After time compensation was performed by controlling a pair of low-noise and precisely matched delay lines, the time synchronization accuracy was about 2ps after 615km of transmission. In 2017, the PLA University of Science and Technology experimented with a transmission delay compensation scheme based on a clock counter and an electronic variable delay line for precise optical fibers. After 100 km of optical fibers, the time synchronization accuracy was 66.7ps.

In the classic loopback time synchronization system, there is a basic assumption: the round-trip optical fiber link is symmetrical, that is, 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. Same time. However, based on this, there is a risk of excessive delay caused by channel asymmetry.

Under normal circumstances, the round-trip time T of the entire link is:

In the formula, L _AB (L _BA ) is the length of the fiber link from the near end A (distal end B) to the far end B (the near end A), c is the speed of light in vacuum, and n ₀ is the refractive index of the fiber.

In the case of delay caused by channel asymmetry, if the distance from near-end A to far-end B is increased by m meters, and the distance from far-end B back to near-end A is shortened by m meters, then the round-trip time of the entire link It is still T, but the signal from the near-end A to the far-end B will be transmitted through the m-meter link, and the time error T _err caused is:

For example, when m is 1 meter, the time delay caused by the asymmetry of the channel can reach the influence of 5ns.

SUMMARY OF THE INVENTION

In order to solve the shortcomings of the existing solutions, the present invention provides a time synchronization device, system and method, which can find the time delay caused by channel asymmetry, identify and eliminate the time delay, and improve the reliability of the time synchronization system.

The time synchronization device includes a near-end A, an optical fiber link and a far-end B.

The near-end A is composed 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 photodetector and a time measurement module;

The first control module is simultaneously 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 second pulse signal and a local clock signal, and the random number generated by the first random number module is simultaneously provided to the first control module;

The first multiplexing module simultaneously connects the first optical pulse sending module and the optical fiber link, multiplexes the optical pulse signal sent by the first optical pulse sending module and the optical signal received from the optical fiber link on one optical fiber, and multiplexes the optical pulse signal sent by the first optical pulse sending module and the optical signal received from the optical fiber link on one optical fiber, the optical signal from the optical fiber link is transmitted to the first photodetector;

The optical signal received by the optical fiber link includes the loopback signal and feedback signal sent from the remote B;

The first photodetector converts the multiplexed optical signal into an electrical signal after detection and sends it to the time measurement module, and the time measurement module separates the converted loopback electrical signal and the feedback electrical signal with the local clock signal received from the first control module. Do the difference, and send the two difference results to the first control module;

The first control module judges according to the random number: the loopback signal, the time difference between the feedback signal and the local time of the near-end A respectively, and calculates the transmission time T _AB from the near-end A to the far-end B;

The first control module sends the transmission time T _AB to the delay compensation module for delay compensation, and sends the compensated second pulse signal to the first optical pulse sending module; the first optical pulse sending module sends the delayed second pulse signal to the first optical pulse sending module. The signal is modulated into an optical pulse signal and sent to the first multiplexing module, and then sent to the optical fiber link to form a closed-loop circuit at the sending end.

Remote 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 photodetector, a beam splitter and a second multiplexing module composition;

The second control module is simultaneously connected to the second clock source, the second random number module, the second optical pulse sending module, the second photodetector and the delay module.

The second clock source generates a second pulse signal, the random number generated by the second random number module is shared with the random number of the first random number module, and the second pulse signal and the shared random number are jointly sent to the second control module;

The second multiplexing module receives the optical signal in the optical fiber link and sends it to the beam splitter. The optical signal is that the first optical pulse sending module in the near-end A modulates the delayed second-pulse electrical signal into an optical pulse signal and passes through the first multiplexing module. The signal sent by the module into the fiber optic link.

The beam splitter divides the signal into two beams according to the proportion: one beam is sent to the second photodetector, converted into an electrical signal after detection, and sent to the second control module, and the timing signal is recovered to achieve time synchronization with the near-end A; A beam of optical signal is sent to the delay module to delay the optical signal to form a loopback signal, the delay time is controlled by the second control module, and then sent to the beam combiner.

The second control module delays the second pulse electrical signal provided by the second clock source and sends it to the second optical pulse sending module. The second optical pulse sending module modulates the received delayed electrical signal into an optical signal to form a feedback signal sent to the combiner;

The beam combiner combines the feedback signal and the loopback signal into a beam of light and sends it to the second multiplexing module. The second multiplexing module multiplexes the combined optical signal and the optical signal received from the optical fiber link in one optical fiber. Up transmission, forming a closed-loop circuit at the receiving end.

Since the second control module needs to control the delay time of the loopback signal, it also needs to control the delay time of the feedback signal, judge whether the loopback signal or the feedback signal is selected according to the shared random number, and then control the loopback signal A different delay time from the feedback signal forms the sending sequence of the two.

The specific working principle of the time synchronization system is as follows:

First, the near-end A receives the loopback signal and the feedback signal sent by the far-end B through the optical fiber link, and these two signals are transmitted to the first photodetector together with the optical pulse signal sent by the first optical pulse sending module;

The first photodetector is converted into an electrical signal and sent to the time measurement module. The time measurement module makes a difference between the converted loopback electrical signal and the feedback electrical signal and the local clock signal respectively, and sends the two difference results to the first control module. ;

The first control module judges according to the random number: the loopback signal, the time difference between the feedback signal and the local time of the near-end A respectively, and calculates the transmission time T _AB from the near-end A to the far-end B;

The first control module sends the transmission time T _AB to the delay compensation module for delay compensation, and then sends it to the first optical pulse sending module, and modulates it into an optical pulse signal and sends it to the optical fiber link through the first multiplexing module;

The second multiplexing module of remote B receives the optical signal in the optical fiber link and sends it to the beam splitter. The beam splitter divides the signal into two beams according to the proportion: one beam is sent to the second photodetector, and is converted into electrical energy after detection. The signal is sent to the second control module, and the timing signal is recovered to achieve time synchronization with the near-end A; another optical signal is sent to the delay module to delay the optical signal to form a loopback signal, and then send it to the beam combiner.

At the same time, the second control module delays the second pulse electrical signal provided by the second clock source, and sends it to the second optical pulse sending module to modulate it into an optical signal to form a feedback signal and send it to the beam combiner;

The beam combiner combines the feedback signal and the delayed signal into a beam of light and sends it to the second multiplexing module, and the second multiplexing module transmits the combined optical signal to the optical fiber link to form a closed-loop circuit.

The above-mentioned second control module judges the sending order of the loopback signal and the feedback signal according to the shared random number.

The specific steps of the time synchronization method are as follows:

Step 1: When the timing information of the first clock source is valid at the near-end A, the first control module controls the delay compensation module to delay the second pulse generated by the local clock source by 1-T _AB before sending it to the first optical pulse transmission. module;

T _AB is the one-way time from the near end A to the far end B;

Step 2, the first optical pulse sending module modulates the second pulse signal after a delay of 1-T _AB time into an optical signal, and sends it to the remote B through the optical fiber link;

The modulated optical signal contains local timing information.

Step 3: After the remote 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 divides the optical pulse signal into two parts: one beam is sent to the second photodetector and converted into an electrical signal after detection, and the timing signal synchronized with the near-end A is recovered to achieve time synchronization with the near-end A; the other beam of light The signal is sent to the delay module to delay the optical signal by T _d1 to form a loopback signal, which is sent to the beam combiner;

Step 4: At the same time, when the timing information of the second clock source is valid at the remote end B, the second control module sends the second pulse-per-second electrical signal provided by the second clock source after a delay time T _d2 to the second optical pulse sending module.

Step 5. The second optical pulse sending module modulates the second pulse electrical signal after the delay time T _d2 into an optical signal, forms a feedback signal, and sends it to the beam combiner.

Step 6: The beam combiner sends the loopback signal and the feedback signal to the optical fiber link through the second multiplexing module and returns to the near-end A.

The second control module determines 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 times T _d1 and T _d2 .

There are two transmission sequences: when T _d1 is less than T _d2 , the loopback signal arrives first, and the feedback signal arrives later; when T _d1 is greater than T _d2 , the feedback signal arrives first, and the loopback signal arrives later;

Step 7: 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 it into the loopback electrical signal and the feedback electrical signal through the first photodetector, and sends it to the time measurement module ;

Step 8: The time measurement module measures the arrival times of the loopback electrical signal and the feedback electrical signal, makes a difference with the local time respectively, and sends the two difference measurement results to the first control module.

Step 9, the first control module distinguishes the arrival time of the loopback signal in the travel measurement result and the local time difference T _RL according to the random number, and the arrival time of the feedback signal and the local time difference T _FL ; And further obtain from the near-end A to One-way time T _AB of far end B.

Where: T _RL =T _AB +T _d1 +T _BA , T _FL =T ₁ +T _d2 +T _BA

T1 is the time difference between the _first clock source and the second clock source, _Td1 is the delay of the loopback signal by the second control module, _Td2 is the delay of the feedback signal by the second control module, and _TAB is the One-way time from A to far-end B, T _BA is the one-way transmission time from far-end B to near-end A.

Step 10: Adjust the time delay of the first optical pulse sending module to 1-TAB, after reaching the remote end _B after the time of _TAB , it is just synchronized with the next second pulse of the first clock source module of the near end A.

Compared with the prior art, the present invention has the following advantages:

(1) A time synchronization device, system and method, at the near-end A of the transmitting end, the one-way transmission from the near-end A to the far-end B can be accurately obtained through the specific data processing method of the time measurement module and the first control module time, ensuring the accuracy of time compensation.

(2) A time synchronization device, system and method, in which a feedback signal is generated at the remote end B of the receiving end through an independent second clock source module, which ensures the stability of the generation of the feedback signal and is not easily affected. The loopback signal is delayed and generated by the delay module controlled by the second control module, and the shared random number is used in combination with the near-end A and the far-end B to determine the sending order, which can ensure the accuracy of the loopback signal and the feedback signal by both parties. Distinguish and not be distinguished by a third party.

(3) A time synchronization device, system and method. In signal transmission, when the feedback signal and the loopback signal are transmitted in the optical fiber channel, the physical characteristics such as pulse width and wavelength are consistent, except for the near-end of both communication parties. It is impossible to distinguish between A and remote B, which enhances the security of the system.

(4) A time synchronization device, system and method, the method provided by the present invention overcomes the defect of the assumption of the symmetry of the transmission link in the traditional loopback time synchronization method, and can accurately synchronize the transmission link from the near end A to the far end. The transmission time of the terminal B is compensated, which improves the reliability of the system.

Description of drawings

Fig. 1 is the structural representation of a kind of time synchronization system of the present invention;

Fig. 2 is the flow chart of a kind of time synchronization method of the present invention;

3 is a schematic diagram of the present invention when the loopback signal is sent out before the feedback signal, that is, T _d1 <T _d2 optical fiber time synchronization working process;

FIG. 4 is a schematic diagram of the time synchronization working process of the optical fiber when the loopback signal is sent after the feedback signal, that is, T _d1 >T _d2 according to the present invention.

Detailed ways

In order to facilitate the understanding and implementation of the present invention by those of ordinary skill in the art, the present invention will be further described in detail and in-depth below with reference to the accompanying drawings.

The invention discloses a time synchronization device, system and method, which adds the randomness of a feedback signal and introduces random numbers at the same time. ; Far-end B receives the optical pulse signal sent by near-end A, part of which is used for detection to achieve time synchronization with near-end A; the other part is delayed to form a loopback signal and returned to the sender; far-end B uses its own clock source The generated signal is delayed to form a feedback signal, and the sequence of sending the loopback signal and the feedback signal is formed by different delays, which are determined by random numbers; the near-end A measures the time of the received loopback signal and the feedback signal , according to the consistent random number shared by both parties and accurately analyze the signal and the time difference between the signals, and compensate for the delay, so as to find the delay caused by the asymmetry of the channel and remove its influence.

The above-mentioned time synchronization device, as shown in FIG. 1 , includes a near-end A, an optical fiber link and a far-end B.

The near-end A is composed 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 photodetector and a time measurement module;

The first control module is simultaneously 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 second pulse signal and a local clock signal, and the random number generated by the first random number module is simultaneously provided to the first control module; the first control module controls the adjustment of the delay according to the random number.

The first random number module is in a classical form or a quantum form;

The first multiplexing module connects the first optical pulse sending module and the optical fiber link at the same time, and multiplexes the optical pulse signal sent by the first optical pulse sending module and the optical signal received from the optical fiber link on one optical fiber, and transmits it to the optical fiber. a first photodetector;

The optical signal received by the optical fiber link includes the loopback signal and feedback signal sent from the remote B;

The first photodetector converts the multiplexed optical signal into an electrical signal after detection and sends it to the time measurement module, and the time measurement module separates the converted loopback electrical signal and the feedback electrical signal with the local clock signal received from the first control module. Do the difference, and send the two difference results to the first control module;

The time measurement module is used to measure time information such as the time difference between the received signal time and the local time;

The first control module determines 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, and calculates the transmission time T _AB from the near-end A to the far-end B ;

In order to synchronize the pulse arriving at the far end B with the near end A, the first control module sends the transmission time T _AB to the delay compensation module for delay compensation, and sends the compensated second pulse signal to the 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 it to the first multiplexing module, and then sends it to the optical fiber link to form a closed-loop circuit at the sending end.

The delay compensation module is used to control the delay of the second pulse, so that the far end B and the near end A achieve time synchronization.

Remote 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 photodetector, a beam splitter and a second multiplexing module composition;

The second control module is simultaneously connected to the second clock source, the second random number module, the second optical pulse sending module, the second photodetector and the delay module.

The second clock source generates a second pulse signal, the second random number module is used to provide 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 the same as the random number of the first random number module. Sharing; the second pulse signal and the shared random number are jointly sent to the second control module;

Shared random numbers are realized through quantum key distribution, etc.;

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 the optical signal in the optical fiber link and sends it to the beam splitter. The optical signal is that the first optical pulse sending module in the near-end A modulates the delayed second-pulse electrical signal into an optical pulse signal and passes through the first multiplexing module. The signal sent by the module into the fiber optic link.

The beam splitter divides the signal into two beams according to the proportion: one beam is sent to the second photodetector, converted into an electrical signal after detection, and sent to the second control module, and the timing signal is recovered to achieve time synchronization with the near-end A; A beam of optical signal is sent to the delay module to delay the optical signal to form a loopback signal, the delay time is controlled by the second control module, and then sent to the beam combiner.

The second control module delays the second pulse electrical signal provided by the second clock source and sends it to the second optical pulse sending module. The second optical pulse sending module modulates the received delayed electrical signal into an optical signal to form a feedback signal sent to the combiner;

The loopback signal is consistent with the feedback signal wavelength, pulse width and other parameters.

The beam combiner combines the feedback signal and the delayed signal into a beam of light and sends it to the second multiplexing module. The second multiplexing module multiplexes the combined optical signal and the optical signal received from the optical fiber link on one optical fiber. Up transmission, forming a closed-loop circuit at the receiving end.

Since the second control module needs to control the delay time of the loopback signal, it also needs to control the delay time of the feedback signal, judge the sending order of the loopback signal and the feedback signal according to the shared random number, and delay the delay according to the sending order. Time control adjustment.

The specific working principle of the time synchronization system is as follows:

First, the near-end A receives the loopback signal and the feedback signal sent by the far-end B through the optical fiber link, and these two signals are transmitted to the first photodetector together with the optical pulse signal sent by the first optical pulse sending module;

The first photodetector is converted into an electrical signal and sent to the time measurement module. The time measurement module makes a difference between the converted loopback electrical signal and the feedback electrical signal and the local clock signal respectively, and sends the two difference results to the first control module. ;

The first control module determines 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, and calculates the transmission time T _AB from the near-end A to the far-end B ;

The first control module sends the transmission time T _AB to the delay compensation module for delay compensation, and then sends it to the first optical pulse sending module, and modulates it into an optical pulse signal and sends it to the optical fiber link through the first multiplexing module;

The second multiplexing module of remote B receives the optical signal in the optical fiber link and sends it to the beam splitter. The beam splitter divides the signal into two beams according to the proportion: one beam is sent to the second photodetector, and is converted into electrical energy after detection. The signal is sent to the second control module, and the timing signal is recovered to achieve time synchronization with the near-end A; another optical signal is sent to the delay module to delay the optical signal to form a loopback signal, and then send it to the beam combiner.

At the same time, the second control module delays the second pulse electrical signal provided by the second clock source, and sends it to the second optical pulse sending module to modulate it into an optical signal to form a feedback signal and send it to the beam combiner;

The beam combiner combines the feedback signal and the delayed signal into a beam of light and sends it to the second multiplexing module, and the second multiplexing module transmits the combined optical signal to the optical fiber link to form a closed-loop circuit.

The above-mentioned second control module judges the sending order of the loopback signal and the feedback signal according to the shared random number.

The time synchronization method is as follows: First, when the time information of the local clock source is valid, the near-end A sends an optical pulse signal containing the local timing information (such as 1PPS, 5PPS, etc.) to the far-end B through the optical fiber link; The loopback signal and feedback signal looped back by end B. These two signals are used to judge the arrangement order of the two signals by means of random numbers shared by both parties, and the parameters such as the wavelength and pulse width of the loopback signal and the feedback signal are consistent; Then, the far end B receives the optical pulse signal sent by the near end A, part of which is used for detection to recover the time signal synchronized with the near end A, and the other part is sent back to the near end A to form a loopback signal, and the far end B is at the clock source When the time information of the loopback signal is valid, a feedback signal is generated, and another feedback signal is sent; the order of sending the loopback signal and the feedback signal is carried out according to the random number agreed by both parties. Finally, the near-end A measures the time of the received loopback signal and the feedback signal, and _adjusts the time delay of the optical pulse sent by the system to 1- _TAB . Second pulse synchronization; the clock source frequency of near-end A and far-end B is the same, but there is a fixed time difference T ₁ .

As shown in Figure 2, the specific steps are as follows:

Step 1: When the timing information of the first clock source 1-1 is valid, the near-end A sends the local timing information to the first control module 1-3, and the first control module 1-3 controls the delay compensation module 1-4 to After the second pulse generated by the local clock source is delayed by 1-T _AB , it is sent to the first optical pulse sending module 1-5;

T _AB is the one-way time from the near-end A to the far-end B; the first control module 1-3 controls the delay compensation module 1 according to the time T _AB from the near-end A to the far-end B measured by the time measurement module 1-6 -4 for delay compensation 1-T _AB ;

Step 2, the first optical pulse sending module 1-5 and the first multiplexing module 1-7 modulate the second pulse signal after a delay of 1-T _AB time into an optical signal, and send it to the remote end B through the optical fiber link;

The modulated optical signal contains local timing information.

Step 3. After the remote 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 divides the optical pulse signal into two parts according to a certain ratio (such as 50:50): one beam is sent to the second photodetector 2-7 and converted into an electrical signal after detection, and then sent to the control module of the remote B 2-3. The timing signal synchronized with the near-end A is recovered at the far-end B to achieve time synchronization with the near-end A; another optical signal is sent to the delay module 2-6 to delay the optical signal by T _d1 to form The loopback signal is sent to the beam combiner 2-5;

Step 4: At the same time, when the timing information of the second clock source 2-1 is valid, the second control module 2-3 of the remote end B sends the pulse-per-second electrical signal provided by the second clock source 2-1 after a delay time T _d2 . to the second optical pulse sending module 2-4.

Step 5: The second optical pulse sending module 2-4 modulates the second pulse electrical signal after the delay time T _d2 into an optical signal, forms a feedback signal, and sends it to the beam combiner 2-5.

Step 6: The beam combiner 2-5 sends the loopback signal and the feedback signal to the optical fiber link back to the near-end A through the second multiplexing module 2-9.

The second control module 2-3 determines 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 times T _d1 and T _d2 .

The random numbers 0 and 1 correspond to two transmission sequences respectively: when T _d1 is less than T _d2 , the loopback signal arrives first, and the feedback signal arrives later; when T _d1 is greater than T _d2 , the feedback signal arrives first, and the loopback signal arrives later;

Step 7: 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, and converts it into the loopback electrical signal and the feedback electrical signal through the first photodetector 1-8 , sent to time measurement modules 1-6;

Step 8: The time measurement modules 1-6 measure the arrival times of the loopback electrical signal and the feedback electrical signal, make differences with the local time respectively, and send the two difference measurement results to the first control module 1-3.

Step 9. 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, it distinguishes the arrival time of the loopback signal in the travel measurement result and the local time difference T. _AB +T _d1 +T _BA , the time difference between the arrival time of the feedback signal and the local time T ₁ +T _d2 +T _BA ; and further obtain the one-way time T _AB from the near end A to the far end B .

T1 is the time difference between the _first clock source and the second clock source, _Td1 is the delay of the loopback signal by the second control module, _Td2 is the delay of the feedback signal by the second control module, and _TAB is the One-way time from A to far-end B, T _BA is the one-way transmission time from far-end B to near-end A.

Step 10: Adjust the time delay of the first optical pulse sending module to 1-TAB, after reaching the remote end _B after the time of _TAB , it is just synchronized with the next second pulse of the first clock source module of the near end A.

A schematic diagram of the time synchronization work of the embodiment is shown below in conjunction with the embodiment and FIG. 3. The embodiment is implemented on the premise of the time synchronization method of the present invention, and provides a detailed implementation manner and a specific work flow, but the protection scope of the present invention is not limited to Limited to the following examples.

In Figures 3 and 4, T, R, and RT in the pulses respectively represent sending pulses, receiving pulses, and receiving and sending pulses, and the corresponding labels are under each pulse. In the figure, the clock source of near-end A is used as the time reference by default. The clock source of far-end B and the clock source of near-end A are not synchronized and there is a time difference T ₁ , but the two have the same frequency.

At the beginning of time synchronization, the loopback signal workflow is: Near-end A sends a pulse TA1 to far-end B through the optical fiber link, and far-end B receives the signal and loops it back to near-end A, then near-end A can Calculate the loopback time T _AB +T _BA of the entire system, and send the second synchronization pulse TA2 after a delay of 1-(T _AB +T _BA )/2; the feedback signal workflow is: remote B is in its clock source When the second pulse is valid, the feedback signal TB1 is sent, transmitted through the optical fiber link, and arrives at the near-end A. By comparing the near-end A with its local time, the transmission time can be obtained as T ₁ +T _BA .

When the loopback signal is sent out before the feedback signal, that is, T _d1 <T _d2 , as shown in 1-2s in FIG. 3 . The workflow of the loopback signal is: after the optical pulse TA2 sent by the near-end A is transmitted through the optical fiber link, it reaches the far-end B after the time of TAB transmission, and the far-end _B delays it by T _d1 to form a loopback signal and returns. Proximal A. Comparing the near-end A and the local time, the difference T _RL between the loopback signal and the local time is T _AB +T _d1 +T _BA ; the feedback signal workflow is: when the clock source pulse of the far-end B is valid, after the delay of T _d2 Send the feedback pulse TB2, when the TB2 pulse reaches the near-end A, the near-end A and the local time are compared to obtain the loopback signal and the local time difference T _FL is T ₁ +T _d2 +T _BA , and then calculate from the near-end A to The one-way transmission time T _AB of the remote end B, and the pulse TA3 is sent after a delay of 1-TAB.

When the loopback signal is sent out after the feedback signal, that is, T _d1 >T _d2 , as shown in 1-2s in FIG. 4 . The workflow of the loopback signal is: after the optical pulse TA2 sent by the near-end A is transmitted through the optical fiber link, it reaches the far-end B after the time of TAB transmission, and the far-end _B delays it by T _d1 to form a loopback signal and returns. Proximal A. Comparing the near-end A and the local time, the difference T _RL between the loopback signal and the local time is T _AB +T _d1 +T _BA ; the feedback signal workflow is: when the clock source pulse of the far-end B is valid, after the delay of T _d2 Send the feedback pulse TB2, when the TB2 pulse reaches the near-end A, the near-end A and the local time are compared to obtain the loopback signal and the local time difference T _FL is T ₁ +T _d2 +T _BA , and then calculate from the near-end A to The one-way transmission time T _AB of the remote end B, and the pulse TA3 is sent after a delay of 1-TAB.

Claims (5)

1. A time synchronization device, characterized in that it comprises 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 A near-end A composed of a photodetector and a time measurement module; and 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, and a second photodetector A remote B composed of a splitter, 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, the loopback optical signal and the feedback optical signal received from the optical fiber link on one optical fiber, and is converted by the detection of the first photodetector The loopback electrical signal and the feedback electrical signal are sent to the time measurement module; the loopback optical signal and the feedback optical signal are the signals sent from the remote B through the optical fiber link; The time measurement module makes a difference between the loopback electrical signal and the feedback electrical signal respectively and the local clock signal sent from the first clock source, and sends the two difference results to the first control module; The first control module determines the time difference T _RL between the loopback electrical signal and the local time, and the time difference T _FL between the feedback electrical signal and the local time according to the random number sent by the first random number module, and further calculates the distance from the near end A to the far end. Transmission time T _AB of terminal B; wherein, T _RL =T _AB +T _d1 +T _BA , T _FL =T ₁ +T _d2 +T _BA ; T ₁ is the time difference between the first clock source and the second clock source, T _d1 is the delay of the second control module to the loopback signal, T _d2 is the delay of the second control module to the feedback signal, and T _BA is the one-way transmission time from the far end B to the near end A; Then, the transmission time T _AB is sent to the delay compensation module for delay compensation, and the compensated second pulse signal is sent to the first optical pulse sending module, modulated into an optical pulse signal, and sent to the optical fiber link to form a transmission closed-loop circuit at the end; The second multiplexing module receives the optical signal in the optical fiber link and sends it to the beam splitter. The beam splitter divides the signal into two beams according to the proportion: one beam is sent to the second photodetector, and after detection, it is converted into an electrical signal and sent to the second beam splitter. The second control module recovers the timing signal to achieve time synchronization with the near-end A; another optical signal is sent to the delay module to delay the optical signal to form a loopback signal, and then send it to the beam combiner; The second control module delays the second pulse electrical signal provided by the second clock source, sends it to the second optical pulse sending module to modulate it into an optical signal, and forms a feedback signal and sends it to the beam combiner; The second control module needs to control the delay time of the loopback signal, and also control the delay time of the feedback signal, judge whether the loopback signal or the feedback signal is selected according to the shared random number, and then control the loopback signal and the feedback signal. The different delay times of the feedback signals form the sending order of the two; The beam combiner combines the feedback signal and the loopback signal into a beam of light and sends it to the second multiplexing module. The second multiplexing module multiplexes the combined optical signal and the optical signal received from the optical fiber link in one optical fiber. Up transmission, forming a closed-loop circuit at the receiving end. 2. A time synchronization device according to claim 1, wherein the first control module is simultaneously connected to the first clock source, the first random number module, the time measurement module and the delay compensation module; the first The clock source generates a second pulse signal and a local clock signal, and the random number generated by the first random number module is simultaneously provided to the first control module. 3. A time synchronization device according to claim 1, wherein the second control module is simultaneously connected to a second clock source, a second random number module, a second optical pulse sending module, and a second photodetector The second clock source generates a second pulse signal, the random number generated by the second random number module is shared with the random number of the first random number module, and the second pulse signal and the shared random number are jointly sent to the second control module. 4. A time synchronization system, comprising near-end A, optical fiber link and far-end B, is characterized in that: First, the near-end A receives the loopback signal and the feedback signal sent by the far-end B through the optical fiber link, and together with the optical pulse signal sent by the first optical pulse sending module, it is transmitted to the first photodetector; The first photodetector converts the loopback signal, the feedback signal and the optical pulse signal into electrical signals respectively, and sends them to the time measurement module. Signal difference, and send the two difference results to the first control module; The first control module determines according to the random number: the time difference T _RL between the loopback signal and the local time of the near-end A, and the time difference T _FL between the feedback signal and the local time of the near-end A, and calculates the time difference from the near-end A to the far-end B. The transmission time T _AB is sent to the delay compensation module for delay compensation; wherein, T _RL =T _AB +T _d1 +T _BA , T _FL =T ₁ +T _d2 +T _BA ; T ₁ is the first clock source and the first clock source The time difference between the two clock sources, T _d1 is the delay of the second control module to the loopback signal, T _d2 is the delay of the second control module to the feedback signal, and T _BA is the one-way transmission time from far-end B to near-end A; The first control module controls the delay compensation module to delay the second pulse generated by the local clock source, and then sends it to the first optical pulse sending module, modulates it into an optical pulse signal and sends it to the optical fiber link, and transmits it to the second optical pulse signal of the remote B. The multiplexing module, and then the optical signal is divided into two beams by the beam splitter: one beam is sent to the second control module, and the timing signal is recovered to achieve time synchronization with the near-end A; the other beam of optical signals is sent to the delay module pair. After the optical signal is delayed by T _d1 , a loopback signal is formed and sent to the beam combiner; at the same time, when the timing information of the second clock source is valid at the remote end B, the second control module delays the second pulse electrical signal provided by the second clock source. After the time T _d2 , it is sent to the second optical pulse sending module; the second optical pulse sending module modulates the second pulse electrical signal after the delay time T _d2 into an optical signal, forms a feedback signal, and sends it to the beam combiner; The control module determines 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 times T _d1 and T _d2 ; 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 based on the first control module and the random number based on the second control module are determined by the first random number module and the second random number respectively. module generation; The beam combiner combines the feedback signal and the delayed signal into a beam of light and sends it to the optical fiber link to form a closed-loop circuit. 5. a time synchronization method based on time synchronization system as claimed in claim 4, concrete steps are as follows: Step 1: When the timing information of the first clock source is valid at the near-end A, the first control module controls the delay compensation module to delay the second pulse generated by the local clock source by 1-T _AB before sending it to the first optical pulse transmission. module; T _AB is the one-way time from the near end A to the far end B; Step 2, the first optical pulse sending module modulates the second pulse signal after a delay of 1-T _AB time into an optical signal, and sends it to the remote B through the optical fiber link; The modulated optical signal contains local timing information; Step 3: After the remote 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 divides the optical pulse signal into two parts: one beam is sent to the second photodetector and converted into an electrical signal after detection, and the timing signal synchronized with the near-end A is recovered to achieve time synchronization with the near-end A; the other beam of light The signal is sent to the delay module to delay the optical signal by T _d1 to form a loopback signal, which is sent to the beam combiner; Step 4: At the same time, when the timing information of the second clock source is valid at the remote end B, the second control module sends the pulse-per-second electrical signal provided by the second clock source to the second optical pulse sending module after a delay time T _d2 ; Step 5. The second optical pulse sending module modulates the second pulse electrical signal after the delay time T _d2 into an optical signal, forms a feedback signal, and sends it to the beam combiner; Step 6: The beam combiner sends the loopback signal and the feedback signal to the optical fiber link through the second multiplexing module and returns to the near-end A; The second control module determines the sending order of the feedback signal and the loopback signal according to the random number provided by the second random number module, thereby controlling the delay times T _d1 and T _d2 ; There are two transmission sequences: when T _d1 is less than T _d2 , the loopback signal arrives first, and the feedback signal arrives later; when T _d1 is greater than T _d2 , the feedback signal arrives first, and the loopback signal arrives later; Step 7: 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 it into the loopback electrical signal and the feedback electrical signal through the first photodetector, and sends it to the time measurement module ; Step 8: The time measurement module measures the arrival times of the loopback electrical signal and the feedback electrical signal, and respectively makes a difference with the local clock signal, and sends the two difference measurement results to the first control module; Step 9, the first control module distinguishes the arrival time of the loopback signal in the travel measurement result and the local time difference T _RL according to the random number, and the arrival time of the feedback signal and the local time difference T _FL ; And further obtain from the near-end A to One-way time T _AB of remote B; Where: T _RL =T _AB +T _d1 +T _BA , T _FL =T ₁ +T _d2 +T _BA T1 is the time difference between the _first clock source and the second clock source, _Td1 is the delay of the loopback signal by the second control module, _Td2 is the delay of the feedback signal by the second control module, and _TAB is the One-way time from A to far-end B, T _BA is the one-way transmission time from far-end B to near-end A; Step 10: Adjust the time delay of the first optical pulse sending module to 1-TAB, after reaching the remote end _B after the time of _TAB , it is just synchronized with the next second pulse of the first clock source module of the near end A.

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