Enhanced white rabbit time synchronization system and method based on frequency transmission

Abstract

The invention discloses an enhanced white rabbit time synchronization system and method based on frequency transmission. The system comprises a reference source, a white rabbit master node, a white rabbit slave node, a frequency transmission master end, a frequency transmission slave end, a transmission link and a jitter elimination processing module. According to the invention, on the basis of a white rabbit link, a frequency transmission link constructed based on an optical fiber frequency transmission technology is added, so that high-precision transmission of a reference signal can be realized by using the frequency transmission link; the clock signals output by the white rabbit link and the frequency transmission link are combined to compensate the clock signal output by the frequency transmission link, and the compensated clock signal output by the frequency transmission link is used as a target clock signal during time synchronization; according to the mode, the jitter of the clock signal during the time synchronization based on the rabbit technology can be optimized, so that the short-term stability during the time synchronization based on the rabbit technology can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of time synchronization, and in particular to an enhanced White Rabbit time synchronization system and method based on frequency transfer. Background Art

[0002] The contents in this section merely provide background information related to the present invention and may not constitute prior art.

[0003] The White Rabbit (WR) time synchronization protocol was originally developed by the European Organization for Nuclear Research to provide a reliable and accurate time synchronization system for its Large Hadron Collider. White Rabbit technology is an expansion of the Precision Time Protocol (PTP). In view of the limitations of PTP, it uses a combination of synchronous Ethernet and all-digital dual-mixing phase-detection technology to improve the synchronization accuracy of existing network time synchronization technology by an order of magnitude, achieving sub-nanosecond synchronization accuracy. At the same time, White Rabbit technology also has the advantages of good compatibility, low cost, and easy expansion. It has been applied in many high-energy physics and astronomy-related experimental devices around the world.

[0004] Although the White Rabbit technology can achieve high synchronization accuracy of sub-nanoseconds, it performs poorly in short-term performance indicators. The master and slave nodes of the White Rabbit technology are connected by optical fiber and transmit timestamp information, relying on FPGA chips to mark timestamp information at the physical layer. The receiving frequency of the White Rabbit slave station depends on the clock recovery module inside the FPGA to extract the clock signal from the data. Since the complete clock edge is not retained in the data and is limited by the performance of the FPGA, the recovered clock signal has large jitter. These jitters will cause the short-term stability of the White Rabbit technology to be poor, making it unable to meet some applications with high short-term stability requirements. Summary of the invention

[0005] In view of this, the first object of the present invention is to provide an enhanced White Rabbit time synchronization system based on frequency transfer, in order to overcome the technical problem that the clock signal used in the known White Rabbit technology to achieve time synchronization has large jitter, resulting in poor short-term stability. The second object of the present invention is to provide a time synchronization method using the time synchronization system.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The present invention discloses an enhanced Baitu time synchronization system based on frequency transfer, comprising a reference source, a Baitu master node, a Baitu slave node, a frequency transfer master end, a frequency transfer slave end, a transmission link and a de-jitter processing module;

[0008] The reference source is configured to provide a reference signal;

[0009] The White Rabbit master node and the White Rabbit slave node are connected via the transmission link to form a White Rabbit link; the White Rabbit link is configured to receive a reference signal provided by the reference source and output a first clock signal based on the reference signal;

[0010] The frequency transfer master end and the frequency transfer slave end are connected via the transmission link to form a frequency transfer link; the frequency transfer link is configured to receive a reference signal provided by the reference source and output a second clock signal based on the reference signal; the second clock signal has a phase difference with the first clock signal;

[0011] The de-jitter processing module is configured to receive the first clock signal and the second clock signal to obtain a phase difference between the first clock signal and the second clock signal;

[0012] The de-jitter processing module is also configured to compensate the second clock signal based on the phase difference to obtain a target clock signal.

[0013] Further, the process of the de-jitter processing module compensating the second clock signal based on the phase difference is:

[0014] The de-jitter processing module performs average fitting on the phase difference signal between the first clock signal and the second clock signal to obtain a phase difference fitting value, and then phase-shifts the second clock signal based on the phase difference fitting value to use the phase-shifted second clock signal as the target clock signal.

[0015] Furthermore, the de-jitter processing module includes:

[0016] a phase detector configured to receive the first clock signal and the second clock signal and obtain a phase difference between the first clock signal and the second clock signal;

[0017] The FPGA includes a signal processing module; the signal processing module is configured to perform an average fitting process on a phase difference signal between the first clock signal and the second clock signal to obtain a phase difference fitting value;

[0018] The delay chip is configured to receive the second clock signal and the phase difference fitting value, and to phase-shift the second clock signal based on the phase difference fitting value.

[0019] Further, the frequency transmission main end includes a frequency multiplier, a first mixer, a second mixer, a third mixer, a first frequency divider, a proportional integral controller, a voltage controlled oscillator, a first laser tube, a first photoelectric tube and a first optical isolator;

[0020] The frequency transmission slave end includes a second photoelectric tube, a second frequency divider, a second laser tube and a second optical isolator;

[0021] The input end of the frequency multiplier is connected to the reference source, and the output end of the frequency multiplier is connected to the input ends of the first mixer and the second mixer respectively;

[0022] The input end of the first mixer is also connected to the output end of the voltage controlled oscillator, the output end of the first mixer is connected to the input end of the first frequency divider; the output end of the first frequency divider is connected to the output end of the third mixer;

[0023] The input end of the second mixer is also connected to the output end of the first photoelectric tube, and the output end of the second mixer is connected to the input end of the third mixer;

[0024] The output end of the third mixer is connected to the input end of the proportional-integral controller, and the output end of the proportional-integral controller is connected to the input end of the voltage-controlled oscillator;

[0025] The output end of the voltage controlled oscillator is also connected to the input end of the first laser tube, and the output end of the first laser tube is connected to the transmission link via the first optical isolator; the input end of the first photoelectric tube is connected to the transmission link via the first optical isolator;

[0026] The input end of the second photoelectric tube is connected to the transmission link via the second optical isolator, and the output end of the second photoelectric tube is connected to the input end of the second frequency divider;

[0027] The second frequency divider has a first output terminal and a second output terminal, the first output terminal of the second frequency divider is connected to the input terminal of the second laser tube, and the second output terminal of the second frequency divider is suitable for outputting the second clock signal;

[0028] The output end of the second laser tube is connected to the transmission link via the second optical isolator.

[0029] Furthermore, the first frequency divider and the second frequency divider are both 1 / 4 frequency dividers.

[0030] Further, the transmission link includes a first wavelength division multiplexer, a second wavelength division multiplexer and an optical fiber link;

[0031] The first wavelength division multiplexer and the second wavelength division multiplexer are symmetrically arranged, and the first wavelength division multiplexer and the second wavelength division multiplexer are connected via the optical fiber link;

[0032] The first wavelength division multiplexer is connected to the White Rabbit master node and the frequency transfer master end respectively; the second wavelength division multiplexer is connected to the White Rabbit slave node and the frequency transfer slave end respectively.

[0033] On the other hand, the present invention discloses a time synchronization method, using the enhanced White Rabbit time synchronization system based on frequency transfer described above, the method comprising:

[0034] The reference source provides reference signals to the White Rabbit link and the frequency transfer link respectively, the White Rabbit link outputs a first clock signal based on the reference signal provided by the reference source, and the frequency transfer link outputs a second clock signal based on the reference signal provided by the reference source;

[0035] Performing phase detection on the first clock signal and the second clock signal to obtain a phase difference between the first clock signal and the second clock signal;

[0036] The second clock signal is compensated based on the phase difference to obtain a target clock signal.

[0037] Further, the process of compensating the second clock signal based on the phase difference is:

[0038] The phase difference signal between the first clock signal and the second clock signal is averaged and fitted to obtain a phase difference fitting value, and then the second clock signal is phase-shifted based on the phase difference fitting value to use the phase-shifted second clock signal as the target clock signal.

[0039] The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0040] The time synchronization system disclosed in the present invention, by adding a frequency transfer link constructed based on optical fiber frequency transfer technology on the basis of the White Rabbit link, can use the frequency transfer link to achieve high-precision transmission of reference signals. On this basis, the White Rabbit link and the clock signal output by the frequency transfer link are combined to compensate for the clock signal output by the frequency transfer link, and the clock signal output by the frequency transfer link and compensated is used as the target clock signal when performing time synchronization. This method is conducive to optimizing the jitter of the clock signal when performing time synchronization based on the White Rabbit technology, thereby helping to improve the short-term stability when performing time synchronization based on the White Rabbit technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A schematic structural diagram of an enhanced White Rabbit time synchronization system based on frequency transfer provided by an embodiment of the present invention;

[0042] Figure 2A schematic diagram of the structure of a reference source and a frequency transfer link provided by an embodiment of the present invention;

[0043] Figure 3 A schematic diagram of the structure of a de-jitter processing module provided in an embodiment of the present invention.

[0044] Icons: 10-reference source, 20-White Rabbit master node, 30-White Rabbit slave node, 40-frequency transfer master end, 41-frequency multiplier, 42-first mixer, 43-second mixer, 44-third mixer, 45-first frequency divider, 46-proportional integral controller, 47-voltage controlled oscillator, 48-first laser tube, 49-first photoelectric tube, 410-first optical isolator, 50-frequency transfer slave end, 51-second photoelectric tube, 52-second frequency divider, 53-second laser tube, 54-second optical isolator, 60-transmission link, 61-first wavelength division multiplexer, 62-second wavelength division multiplexer, 63-optical fiber link, 70-de-jitter processing module, 71-phase detector, 72-analog-to-digital converter, 73-delay chip, 74-signal processing module. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described in conjunction with specific implementation methods below. The same figure marks in the accompanying drawings represent the same components. It should be noted that the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] Compared to the embodiments shown in the drawings, feasible embodiments within the scope of the present invention may have fewer components, other components not shown in the drawings, different components, differently arranged components, or differently connected components, etc. In addition, two or more components in the drawings may be implemented in a single component, or a single component shown in the drawings may be implemented as multiple separate components.

[0047] In order to overcome the technical problem that the clock signal used in the known White Rabbit technology to achieve time synchronization has large jitter, resulting in poor short-term stability. The present invention provides an enhanced White Rabbit time synchronization system based on frequency transfer (hereinafter referred to as "time synchronization system" for ease of explanation). The time synchronization system combines the White Rabbit technology with the optical fiber frequency transfer technology and realizes the transmission of signals and data based on the wavelength division multiplexing technology. It is expected to construct an enhanced White Rabbit time synchronization optical fiber network that can achieve synchronization accuracy of several kilometers, hundreds of picoseconds, and stability of tens of picoseconds.

[0048] Among them, the fiber optic frequency transfer technology described in the present invention is a high-precision frequency signal transmission method, which can directly transmit frequency signals without relying on additional clock recovery circuits, thereby reducing signal distortion and the introduction of noise. Compared with the White Rabbit technology, the fiber optic frequency transfer technology performs well in short-term stability and can reach a level far higher than the White Rabbit technology. At the same time, both the fiber optic frequency transfer technology and the White Rabbit technology are based on optical fiber media to realize the transmission of signals and data, so optical fiber wavelength division multiplexing technology can be used to use different wavelength channels to transmit optical fiber frequencies and WR.

[0049] Figure 1 FIG. 2 shows the overall architecture of an exemplary time synchronization system disclosed in an embodiment of the present invention. Figure 1 As shown, the time synchronization system disclosed in the present invention may include a reference source 10, a White Rabbit master node 20, a White Rabbit slave node 30, a frequency transfer master end 40, a frequency transfer slave end 50, a transmission link 60 and a de-jitter processing module 70.

[0050] In some embodiments, the reference source 10 is used to provide a reference signal. For example, the reference source 10 can be a 10 MHz atomic clock that can provide a 10 MHz reference signal. The reference signal provided by the reference source 10 is divided into two paths, and is used as the input of the white rabbit link and the frequency transfer link to be described below.

[0051] In some embodiments, the White Rabbit master node 20 and the White Rabbit slave node 30 are connected via a transmission link 60 to form a White Rabbit link. The round-trip transmission of signals and data between the White Rabbit master node 20 and the White Rabbit slave node 30 is implemented based on the transmission link 60.

[0052] Furthermore, the White Rabbit link is configured to receive a reference signal provided by a reference source 10 and output a first clock signal based on the reference signal.

[0053] Specifically, when the reference signal provided by the reference source 10 reaches the White Rabbit link, the reference signal provided by the reference source 10 can be received by the White Rabbit master node 20, and then the White Rabbit master node 20 obtains a standard reference signal based on the reference signal through a phase-locked loop. For example, for a 10MHz reference signal provided by a 10MHz atomic clock, after receiving the 10MHz reference signal, the White Rabbit master node 20 can perform a phase-locked loop on the reference signal to achieve 12.5 times the frequency, so as to obtain a 125MHz standard reference signal required by Gigabit Ethernet.

[0054] Secondly, the White Rabbit master node 20 transmits the standard reference signal to the White Rabbit slave node 30 via the transmission link 60, and the White Rabbit slave node 30 can recover the first clock signal and output the first clock signal. Figure 1 clk_RX shown in .

[0055] It is worth noting that the process of forming a White Rabbit link by cooperating with the White Rabbit master node 20, the transmission link 60 and the White Rabbit slave node 30, and using the White Rabbit link to recover the first clock signal based on the reference signal provided by the reference source 10 belongs to the prior art and will not be described in detail here. In addition, it is known that the jitter of the first clock signal recovered based on the White Rabbit link is relatively large, about 100 picoseconds.

[0056] In some embodiments, the frequency transfer master end 40 and the frequency transfer slave end 50 are connected via a transmission link 60 to form a frequency transfer link based on optical fiber frequency transfer technology. The round-trip transmission of signals and data between the frequency transfer master end 40 and the frequency transfer slave end 50 is implemented based on the transmission link 60.

[0057] Furthermore, the frequency transfer link is configured to receive a reference signal provided by the reference source 10, and output a second clock signal based on the reference signal. The second clock signal has a phase difference with the first clock signal. The second clock signal is also Figure 1 clk_remote as shown in .

[0058] It can be understood that the frequency transfer link composed of the frequency transfer master end 40, the frequency transfer slave end 50 and the transmission link 60 is a link constructed based on optical fiber frequency transfer technology. This link can achieve high-precision transmission of the reference signal. The jitter of the second clock signal generated thereby is at the level of tens of picoseconds, which is much better than the jitter of the first clock signal obtained based on the White Rabbit link.

[0059] In some embodiments, the de-jitter processing module 70 is configured to receive a first clock signal from the White Rabbit link and a second clock signal from the frequency transfer link, and perform phase detection on the first clock signal and the second clock signal to obtain a phase difference between the first clock signal and the second clock signal.

[0060] Furthermore, the de-jitter processing module 70 is further configured to compensate the second clock signal based on the phase difference between the first clock signal and the second clock signal, so that the phase of the second clock signal is consistent with the first clock signal, so as to obtain a target clock signal that can replace the first clock signal. The target clock signal is also the compensated second clock signal.

[0061] In other words, after obtaining the phase difference between the first clock signal and the second clock signal through the de-jitter processing module 70, the de-jitter processing module 70 can compensate the second clock signal based on the phase difference between the first clock signal and the second clock, so that the phase of the second clock signal is consistent with the first clock signal, thereby optimizing the phase of the second clock signal and obtaining the target clock signal. The target clock signal can replace the first clock signal as the final clock signal for time synchronization.

[0062] Among them, the process of the de-jitter processing module 70 compensating the second clock signal based on the phase difference between the first clock signal and the second clock can be: the de-jitter processing module 70 performs average fitting on the phase difference signal between the first clock signal and the second clock signal to obtain a phase difference fitting value, and then, phase-shifts the second clock signal based on the phase difference fitting value to use the phase-shifted second clock signal as the target clock signal.

[0063] It is worth noting that the time synchronization system constructed in the above manner will not affect the compatibility of the original White Rabbit link, and at the same time it is conducive to optimizing the jitter of the clock signal when performing time synchronization based on the White Rabbit technology, thereby helping to improve the short-term stability of time synchronization based on the White Rabbit technology.

[0064] In some embodiments, in combination with the foregoing, both the fiber-optic frequency transmission technology and the White Rabbit technology are technologies that realize signal and data transmission based on optical fiber media. Therefore, a transmission link 60 can be constructed based on wavelength division multiplexing technology, so that the transmission link 60 can be used as a channel for signal and data transmission between the White Rabbit master node 20 and the White Rabbit slave node 30, and can also be used as a channel for signal and data transmission between the frequency transmission master end 40 and the frequency transmission slave end 50.

[0065] like Figure 1 As shown, the transmission link 60 includes a first wavelength division multiplexer 61, a second wavelength division multiplexer 62 and an optical fiber link 63. The first wavelength division multiplexer 61 and the second wavelength division multiplexer 62 are symmetrically arranged and connected to each other through the optical fiber link 63.

[0066] Among them, the first wavelength division multiplexer 61 is respectively connected to the White Rabbit master node 20 and the frequency transfer master end 40, so as to receive signals and data from the White Rabbit master node 20 and the frequency transfer master end 40 through the first wavelength division multiplexer 61, and transmit signals and data from the White Rabbit slave node 30 to the White Rabbit master node 20 through the first wavelength division multiplexer 61, and transmit signals and data from the frequency transfer slave end 50 to the frequency transfer master end 40.

[0067] Correspondingly, the second wavelength division multiplexer 62 is connected to the White Rabbit slave node 30 and the frequency transfer slave end 50 respectively, so as to receive signals and data from the White Rabbit slave node 30 and the frequency transfer slave end 50 through the second wavelength division multiplexer 62, and transmit signals and data from the White Rabbit master node 20 to the White Rabbit slave node 30 through the second wavelength division multiplexer 62, and transmit signals and data from the frequency transfer master end 40 to the frequency transfer slave end 50.

[0068] In some embodiments, the frequency transfer master end 40 and the frequency transfer slave end 50 can be constructed in the manner described below but is not limited to the manner described below, so that the frequency transfer link composed of the frequency transfer master end 40, the frequency transfer slave end 50, and the transmission link 60 can output a high and stable second clock signal based on the reference signal provided by the reference source 10.

[0069] Combination Figure 2 As shown, the frequency transmission master end 40 may include a frequency multiplier 41, a first mixer 42, a second mixer 43, a third mixer 44, a first frequency divider 45, a proportional integral controller 46, a voltage controlled oscillator 47, a first laser tube 48, a first photoelectric tube 49, and a first optical isolator 410. The frequency transmission slave end 50 may include a second photoelectric tube 51, a second frequency divider 52, a second laser tube 53, and a second optical isolator 54.

[0070] At the frequency transfer main end 40, the input end of the frequency multiplier 41 is connected to the reference source 10, and the output end of the frequency multiplier 41 is respectively connected to the input ends of the first mixer 42 and the second mixer 43. The frequency multiplier 41 is used to receive the reference signal provided by the reference source 10, and amplify the frequency of the reference signal by a predetermined multiple to obtain a signal output to the first mixer 42 and the second mixer 43; for example, the frequency multiplier 41 in the present invention can be used to amplify the frequency of the reference signal by 20 times, that is, assuming that the reference source 10 provides a 10MHz reference signal, the frequency multiplier 41 outputs a 200MHz signal to the first mixer 42 and the second mixer 43.

[0071] The input end of the first mixer 42 is also connected to the output end of the voltage controlled oscillator 47, and the output end of the first mixer 42 is connected to the input end of the first frequency divider 45. The first mixer 42 is used to mix and filter the signal from the frequency multiplier 41 and the signal from the voltage controlled oscillator 47 to obtain a signal output to the first frequency divider 45.

[0072] The output end of the first frequency divider 45 is connected to the input end of the third frequency mixer 44 . The first frequency divider 45 is used to divide the frequency of the signal from the first frequency mixer 42 to obtain a signal output to the third frequency mixer 44 .

[0073] The input end of the second mixer 43 is also connected to the output end of the first photoelectric tube 49, and the output end of the second mixer 43 is connected to the input end of the third mixer 44. The second mixer 43 is used to mix and filter the signal from the frequency multiplier 41 and the signal from the first photoelectric tube 49 to obtain a signal output to the third mixer 44.

[0074] The output end of the third mixer 44 is connected to the input end of the proportional-integral controller 46. The third mixer 44 is used to mix and filter the signal from the first frequency divider 45 and the signal from the second mixer 43 to obtain a signal output to the proportional-integral controller 46.

[0075] The output end of the proportional-integral controller 46 is connected to the input end of the voltage-controlled oscillator 47 . The proportional-integral controller 46 is used to process the signal from the third mixer 44 and then output it to the voltage-controlled oscillator 47 .

[0076] The output end of the voltage controlled oscillator 47 is also connected to the input end of the first laser tube 48. The voltage controlled oscillator 47 is used to transmit signals to the first mixer 42 as well as to transmit signals to the first laser tube 48.

[0077] The output end of the first laser tube 48 is connected to the transmission link 60, specifically the first wavelength division multiplexer 61, via the first optical isolator 410. The first laser tube 48 is used to transmit the signal from the voltage controlled oscillator 47 to the frequency transfer slave end 50, specifically the second photoelectric tube 51 of the frequency transfer slave end 50, via the transmission link 60. Under the action of the first optical isolator 410, the first laser tube 48 can only transmit signals to the transmission link 60, and cannot receive signals transmitted by the transmission link 60.

[0078] The input end of the first photoelectric tube 49 is connected to the transmission link 60, specifically the first wavelength division multiplexer 61, via the first optical isolator 410. The first photoelectric tube 49 is used to receive the signal transmitted from the frequency transfer slave end 50 via the transmission link 60, specifically the signal from the second laser tube 53. Under the action of the first optical isolator 410, the first photoelectric tube 49 can only receive the signal transmitted by the transmission link 60, and cannot transmit the signal to the transmission link 60.

[0079] At the frequency transfer slave end 50, the input end of the second phototube 51 is connected to the transmission link 60, specifically the second wavelength division multiplexer 62, via the second optical isolator 54, and the output end of the second phototube 51 is connected to the input end of the second frequency divider 52. The second phototube 51 is used to receive the signal from the frequency transfer master end 40 transmitted via the transmission link 60, specifically the signal from the first laser tube 48, and output the signal to the second frequency divider 52. Under the action of the second optical isolator 54, the second phototube 51 can only receive the signal transmitted by the transmission link 60, and cannot transmit the signal to the transmission link 60.

[0080] The second frequency divider 52 has a first output end and a second output end, the first output end of the second frequency divider 52 is connected to the input end of the second laser tube 53, and the second output end of the second frequency divider 52 is suitable for outputting a second clock signal. The second frequency divider 52 is used to divide the frequency of the signal from the second photoelectric tube 51, and the second frequency divider 52 can transmit the divided signal to the second laser tube 53 through the first output end, or output the signal as the second clock signal through the second output end.

[0081] The output end of the second laser tube 53 is connected to the transmission link 60, specifically the second wavelength division multiplexer 62, via the second optical isolator 54. The second laser tube 53 is used to transmit the signal from the second frequency divider 52 to the frequency transmission main end 40, specifically the first photoelectric tube 49, via the transmission link 60. Under the action of the second optical isolator 54, the second laser tube 53 can only transmit signals to the transmission link 60, and cannot receive signals transmitted by the transmission link 60.

[0082] In some embodiments, the first frequency divider 45 and the second frequency divider 52 are both 1 / 4 frequency dividers.

[0083] For example, in the present invention, the reference source 10 provides a 10MHz reference signal, the frequency multiplier 41 amplifies the frequency of the reference signal and outputs a 200MHz signal, the voltage-controlled oscillator 47 outputs a 500MHz signal, the first mixer 42 outputs a 300MHz signal, the second mixer 43 outputs a 75MHz signal, the first photoelectric tube 49 outputs a 125MHz signal to the second mixer 43, and the signal divided by the second frequency divider 52 is a 125MHz signal. That is, in the frequency transfer link composed of the frequency transfer master end 40, the frequency transfer slave end 50 and the transmission link 60 disclosed in the present invention, the frequencies of the signals transmitted through the transmission link 60 and traveling back and forth between the frequency transfer master end 40 and the frequency transfer slave end 50 are 500MHz and 125MHz respectively.

[0084] Specifically, the principle of the frequency transfer link composed of the frequency transfer master end 40, the frequency transfer slave end 50 and the transmission link 60 outputting a high and stable second clock signal based on the reference signal provided by the reference source 10 is as follows:

[0085] Assumption: The reference signal provided by reference source 10 is V ref ; The signal output by the voltage controlled oscillator 47 is V0.

[0086] Then, the reference signal V ref It is expressed as:

[0087]

[0088] In the above formula: ω ref The signal V ref Angular frequency; The signal V ref The initial phase of; t is the time.

[0089] The signal V0 output by the voltage controlled oscillator 47 is expressed as:

[0090]

[0091] In the above formula: ω0 is the angular frequency of signal V0; is the initial phase of signal V0; t is time.

[0092] When the signal V0 output by the voltage controlled oscillator 47 is transmitted to the frequency transmission slave end 50 via the first laser tube 48 and the transmission link 60, the light delay is assumed to be τ, and the signal received by the frequency transmission slave end 50 is assumed to be V remote , then the frequency transfer signal V received from terminal 50 remote Expressed as:

[0093]

[0094] The signal V remote After being divided by four by the second frequency divider 52 of the frequency transfer slave terminal 50, the divided signal is returned to the frequency transfer master terminal 40 via the transmission link 60. Assume that the signal received by the frequency transfer master terminal 40 is V back , then the signal V back Expressed as:

[0095]

[0096] On this basis, let the reference signal V ref The signal V0 is mixed and filtered by the first mixer 42 and divided by four by the first frequency divider 45 to output a signal V1. Then the signal V1 is expressed as:

[0097]

[0098] Assume that the reference signal V ref And the signal V back The signal output after mixing and filtering by the second mixer 43 is V2, and the signal V2 is expressed as:

[0099]

[0100] Assume that the signal V3 is the signal output after the signal V1 and the signal V2 are mixed and filtered by the third mixer 44, then the signal V3 is expressed as:

[0101]

[0102] The signal V3 is processed by the proportional-integral controller 46 to obtain a control signal, which is fed back to the voltage-controlled oscillator 47. The signal V0 output by the voltage-controlled oscillator 47 is corrected to obtain:

[0103] V3≈0

[0104] At this time, we can get:

[0105]

[0106] Substituting this formula into the signal V remote The expression of can be obtained:

[0107]

[0108] It can be seen from the above formula that the reference signal V provided by the reference source 10 is transmitted by using the frequency transmission link composed of the frequency transmission master end 40, the frequency transmission slave end 50 and the transmission link 60 disclosed in the present invention. ref , realizing the final output signal V of the frequency transfer link remote Locked to the reference signal V ref In this way, the link noise caused by the transmission link 60 is compensated, thereby achieving high-precision transmission of the frequency signal.

[0109] In some embodiments, the de-jitter processing module 70 can be constructed in the manner described below, but is not limited to the manner described below, so that the de-jitter processing module 70 can obtain the phase difference between the first clock signal and the second clock signal, perform average fitting on the phase difference signal to obtain a phase difference fitting value, and shift the phase of the second clock signal based on the phase difference fitting value to obtain a target clock signal.

[0110] Specifically, combined Figure 3 As shown in the figure, the de-jitter processing module 70 may include a phase detector 71 , an analog-to-digital converter 72 , a delay chip 73 and an FPGA, wherein the FPGA includes a signal processing module 74 .

[0111] The input end of the phase detector 71 is connected to the output end of the White Rabbit link and the frequency transfer link respectively, the output end of the phase detector 71 is connected to the input end of the analog-to-digital converter 72, and the output end of the analog-to-digital converter 72 is connected to the input end of the signal processing module 74.

[0112] Among them, the phase detector 71 is configured to receive a first clock signal from the White Rabbit link and a second clock signal from the frequency transfer link, and perform phase detection on the first clock signal and the second clock signal to obtain a phase difference between the first clock signal and the second clock signal, and convert the phase difference signal between the first clock signal and the second clock signal through the analog-to-digital converter 72 and transmit it to the signal processing module 74.

[0113] The signal processing module 74 is configured to perform an average fitting process on the phase difference signal between the first clock signal and the second clock signal to obtain a phase difference fitting value.

[0114] The input end of the delay chip 73 is respectively connected to the output end of the frequency transfer link and the output end of the signal processing module 74. The delay chip 73 is used to receive the second clock signal from the frequency transfer link and the phase difference fitting value from the signal processing module 74, and phase-shift the second clock signal based on the phase difference fitting value so that the phase of the second clock signal is consistent with the phase of the first clock signal, so that the second clock signal after the phase shift is used as the target clock signal, and the target clock signal is output through the delay chip 73 to replace the first clock signal used for time synchronization in the White Rabbit link.

[0115] It can be understood that the jitter of the second clock signal output by the frequency transfer link is at the level of tens of picoseconds. Therefore, by using the phase-shifted second clock signal as the clock signal for time synchronization, it is beneficial to optimize the jitter of the clock signal when time synchronization is performed based on the White Rabbit technology, thereby helping to improve the short-term stability when time synchronization is performed based on the White Rabbit technology.

[0116] On the other hand, the present invention also discloses a time synchronization method, which adopts the enhanced White Rabbit time synchronization system based on frequency transfer described above. Specifically, the method comprises:

[0117] The reference source 10 provides reference signals to the White Rabbit link and the frequency transfer link respectively. The White Rabbit link outputs a first clock signal based on the reference signal provided by the reference source 10, and the frequency transfer link outputs a second clock signal based on the reference signal provided by the reference source 10; wherein there is a phase difference between the first clock signal and the second clock signal.

[0118] The first clock signal and the second clock signal are phase-detected by the de-jitter processing module 70 to obtain the phase difference between the first clock signal and the second clock signal. Subsequently, the de-jitter processing module 70 compensates the second clock signal based on the phase difference between the first clock signal and the second clock signal so that the phase of the second clock signal is consistent with the first clock signal to obtain a target clock signal that replaces the first clock signal. Thereafter, the target clock signal can be used as a clock signal for time synchronization to complete time synchronization.

[0119] In the above method, the process of the de-jitter processing module 70 compensating the second clock signal based on the phase difference between the first clock signal and the second clock can be: the de-jitter processing module 70 performs average fitting on the phase difference signal between the first clock signal and the second clock signal to obtain a phase difference fitting value, and then, phase-shifts the second clock signal based on the phase difference fitting value to use the phase-shifted second clock signal as the target clock signal and replace the first clock signal.

[0120] It is worth noting that the time synchronization method disclosed in the present invention, by adopting the above-mentioned time synchronization system, makes the method at least have the beneficial effects of the above-mentioned time synchronization system, that is, it is conducive to optimizing the jitter of the clock signal when performing time synchronization based on the White Rabbit technology, thereby helping to improve the short-term stability when performing time synchronization based on the White Rabbit technology.

[0121] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An enhanced White Rabbit time synchronization system based on frequency transfer, characterized in that: It includes a reference source, a White Rabbit master node, a White Rabbit slave node, a frequency transfer master end, a frequency transfer slave end, a transmission link and a de-jitter processing module; The reference source is configured to provide a reference signal; The White Rabbit master node and the White Rabbit slave node are connected via the transmission link to form a White Rabbit link; the White Rabbit link is configured to receive a reference signal provided by the reference source and output a first clock signal based on the reference signal; The frequency transfer master end and the frequency transfer slave end are connected via the transmission link to form a frequency transfer link; The frequency transfer link is configured to receive a reference signal provided by the reference source and output a second clock signal based on the reference signal; There is a phase difference between the second clock signal and the first clock signal; The de-jitter processing module is configured to receive the first clock signal and the second clock signal to obtain a phase difference between the first clock signal and the second clock signal; The de-jitter processing module is also configured to compensate the second clock signal based on the phase difference to obtain a target clock signal.

2. The enhanced White Rabbit time synchronization system based on frequency transfer according to claim 1 is characterized in that: The process of the de-jitter processing module compensating the second clock signal based on the phase difference is as follows: The de-jitter processing module performs average fitting on the phase difference signal between the first clock signal and the second clock signal to obtain a phase difference fitting value, and then phase-shifts the second clock signal based on the phase difference fitting value to use the phase-shifted second clock signal as the target clock signal.

3. The enhanced White Rabbit time synchronization system based on frequency transfer according to claim 2 is characterized in that: The de-jitter processing module comprises: a phase detector configured to receive the first clock signal and the second clock signal and obtain a phase difference between the first clock signal and the second clock signal; The FPGA includes a signal processing module; the signal processing module is configured to perform an average fitting process on a phase difference signal between the first clock signal and the second clock signal to obtain a phase difference fitting value; The delay chip is configured to receive the second clock signal and the phase difference fitting value, and to phase-shift the second clock signal based on the phase difference fitting value.

4. The enhanced White Rabbit time synchronization system based on frequency transfer according to claim 1, characterized in that: The frequency transmission main end includes a frequency multiplier, a first mixer, a second mixer, a third mixer, a first frequency divider, a proportional integral controller, a voltage controlled oscillator, a first laser tube, a first photoelectric tube and a first optical isolator; The frequency transmission slave end includes a second photoelectric tube, a second frequency divider, a second laser tube and a second optical isolator; The input end of the frequency multiplier is connected to the reference source, and the output end of the frequency multiplier is connected to the input ends of the first mixer and the second mixer respectively; The input end of the first mixer is also connected to the output end of the voltage controlled oscillator, the output end of the first mixer is connected to the input end of the first frequency divider; the output end of the first frequency divider is connected to the output end of the third mixer; The input end of the second mixer is also connected to the output end of the first photoelectric tube, and the output end of the second mixer is connected to the input end of the third mixer; The output end of the third mixer is connected to the input end of the proportional-integral controller, and the output end of the proportional-integral controller is connected to the input end of the voltage-controlled oscillator; The output end of the voltage controlled oscillator is also connected to the input end of the first laser tube, and the output end of the first laser tube is connected to the transmission link via the first optical isolator; the input end of the first photoelectric tube is connected to the transmission link via the first optical isolator; The input end of the second photoelectric tube is connected to the transmission link via the second optical isolator, and the output end of the second photoelectric tube is connected to the input end of the second frequency divider; The second frequency divider has a first output terminal and a second output terminal, the first output terminal of the second frequency divider is connected to the input terminal of the second laser tube, and the second output terminal of the second frequency divider is suitable for outputting the second clock signal; The output end of the second laser tube is connected to the transmission link via the second optical isolator.

5. The enhanced White Rabbit time synchronization system based on frequency transfer according to claim 4 is characterized in that: The first frequency divider and the second frequency divider are both 1 / 4 frequency dividers.

6. The enhanced White Rabbit time synchronization system based on frequency transfer according to claim 1, characterized in that: The transmission link includes a first wavelength division multiplexer, a second wavelength division multiplexer and an optical fiber link; The first wavelength division multiplexer and the second wavelength division multiplexer are symmetrically arranged, and the first wavelength division multiplexer and the second wavelength division multiplexer are connected via the optical fiber link; The first wavelength division multiplexer is connected to the White Rabbit master node and the frequency transfer master end respectively; the second wavelength division multiplexer is connected to the White Rabbit slave node and the frequency transfer slave end respectively.

7. A time synchronization method, characterized in that: Using the enhanced White Rabbit time synchronization system based on frequency transfer as claimed in any one of claims 1 to 6, the method comprises: The reference source provides reference signals to the White Rabbit link and the frequency transfer link respectively, the White Rabbit link outputs a first clock signal based on the reference signal provided by the reference source, and the frequency transfer link outputs a second clock signal based on the reference signal provided by the reference source; Performing phase detection on the first clock signal and the second clock signal to obtain a phase difference between the first clock signal and the second clock signal; The second clock signal is compensated based on the phase difference to obtain a target clock signal.

8. The time synchronization method according to claim 7, characterized in that: The process of compensating the second clock signal based on the phase difference is: The phase difference signal between the first clock signal and the second clock signal is averaged and fitted to obtain a phase difference fitting value, and then the second clock signal is phase-shifted based on the phase difference fitting value to use the phase-shifted second clock signal as the target clock signal.

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