CN116318500A - Airborne optical fiber time-frequency transmission system and method - Google Patents
Airborne optical fiber time-frequency transmission system and method Download PDFInfo
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- CN116318500A CN116318500A CN202211636222.3A CN202211636222A CN116318500A CN 116318500 A CN116318500 A CN 116318500A CN 202211636222 A CN202211636222 A CN 202211636222A CN 116318500 A CN116318500 A CN 116318500A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
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- H—ELECTRICITY
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- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2589—Bidirectional transmission
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- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0682—Clock or time synchronisation in a network by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
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Abstract
The invention discloses an airborne optical fiber time-frequency transmission system and a method, wherein the system comprises the following steps: a master node for distributing time-frequency information to slave nodes, and a plurality of slave nodes for receiving the time-frequency information and realizing signal phase stabilization and time synchronization, wherein: the master node includes: the device comprises a first B code generation module, a first time interval counter, a digital logic module, a first electro-optic conversion module and a first photoelectric conversion module; the slave node includes: the device comprises a second photoelectric conversion module, a delay adjustment module, a second time interval counter, a carrier recovery and phase locking module and a second B code generation module. The invention directly recovers the frequency information from the B code transmitted by the master node, and does not independently transmit the reference clock, and not only realizes the frequency transmission function, but also realizes the bidirectional time comparison function of the master node and the slave node on the same optical fiber link. Reducing system complexity, volume and weight.
Description
Technical Field
The invention relates to the technical field of time synchronization, in particular to an airborne optical fiber time-frequency transmission system and method.
Background
In radar, communication navigation, electronic warfare systems, it is necessary to transmit synchronization time information at each node. The time-frequency transfer is an important component of the time-frequency system, which determines the highest accuracy of the time-frequency application. The optical fiber clock time frequency transmission is one of main research directions of high-precision time frequency transmission, and is also one of time service means with highest transmission precision at present. The airborne platform has strict limits on equipment volume and weight, if signal transmission cables are used as transmission media of time information among all nodes, the signal transmission cables have extremely high consumption on internal space, load, energy consumption and the like of an airplane, and the optical fibers are suitable for being used as the transmission media of the airplane platform due to the physical characteristics of small volume, light weight and the like.
For the airborne platform, the optical fiber time-frequency transmission on the airborne platform has the following characteristics:
the master node is used for accurately transmitting the frequency signal to the slave node, and the time comparison and synchronization between the master node and the slave node are also required to be executed; time-frequency transfer needs to be implemented between a single master node and tens of slave nodes.
All compensation and synchronization functions are realized in the main node by the traditional time-frequency transmission system, so that the main node is huge and bulkier, and the size requirement of airborne equipment is not met. Moreover, all synchronization devices are concentrated on the master node, and when the master node fails, the time synchronization of all slave nodes is affected, so that the reliability of the whole system is reduced.
Disclosure of Invention
The invention aims to provide an airborne optical fiber time-frequency transmission system and an airborne optical fiber time-frequency transmission method, which are used for further improving the reliability of the system.
In order to realize the tasks, the invention adopts the following technical scheme:
an on-board fiber optic time-frequency delivery system, comprising:
a master node for distributing time-frequency information to slave nodes, and a plurality of slave nodes for receiving the time-frequency information and realizing signal phase stabilization and time synchronization, wherein:
the master node includes:
the first B code generation module is used for generating a B code signal;
a first time interval counter for measuring the time interval between the local second pulse of the master node and the second pulse transmitted from the slave node;
the digital logic module is used for switching on or switching off the code stream superposition function of the main node;
the first electro-optical conversion module is used for modulating the code stream of the B code signal on an optical carrier wave so as to convert the electric signal into an optical signal;
the first photoelectric conversion module is used for converting the optical signal sent by the second photoelectric conversion module of the node into an electric signal and sending the electric signal to the digital logic module;
the slave node includes:
the second photoelectric conversion module is used for converting the optical signal output by the first photoelectric conversion module into an electric signal and transmitting the electric signal to the delay adjustment module;
the second electro-optical conversion module is used for converting the B code signal output by the second B code generation module into an optical signal;
the delay adjustment module is used for carrying out time delay on the electric signal output by the second photoelectric conversion module;
a second time interval counter for measuring the time interval between the local second pulse of the slave node and the second pulse transmitted from the master node;
the carrier recovery and phase locking module is used for recovering the carrier and locking the slave node crystal oscillator on the carrier;
the second B code generation module is used for generating a B code signal; wherein the B-code signal uses the recovered carrier as a clock reference.
Further, the onboard optical fiber time-frequency transmission system provides time-frequency information for a plurality of slave nodes through one master node.
Further, when the system operates, a time division multiplexing mode is adopted to respectively conduct bidirectional time comparison and frequency transmission.
Furthermore, a polling mode is adopted to realize the time comparison function between a single master node and a plurality of slave nodes.
An on-board fiber time-frequency delivery method, comprising:
step 1, in the initial stage, respectively inputting a first B code generation module, a second B code generation module and generated B code signals into a first electro-optic conversion module and a second electro-optic conversion module, converting the B code signals into optical signals, and sending the optical signals to a first photoelectric conversion module and a second photoelectric conversion module at opposite ends; the first and second photoelectric conversion modules at opposite ends modulate the code stream of the B code signal on an optical carrier wave to be converted into an electric signal, and then the electric signal is respectively transmitted by the opposite ends by taking the node second pulse as a start and the second pulse transmitted by the opposite ends as a stop, and the first and second time interval counters are used for measuring the time interval T 1 And T 2 Calculate the clock difference (T) 1 -T 2 ) 2; according to the clock difference of the two nodes, the slave node compensates the clock difference of the two nodes by adjusting an adjustable delay line in the delay adjustment module and changing the delay of the output electric signal so as to achieve the aim of synchronizing the clocks of the two nodes;
step 2, after bidirectional time comparison and synchronization, the master node uses a first time interval counter to measure the time interval between the local second pulse and the second pulse from the slave node, inputs the time interval into a first electro-optical conversion module and sends the time interval to the slave node, and at the moment, the code stream superposition function is closed through a digital logic module, namely, the B code stream generated by the master node through a first B code generation module and the code stream generated by the slave node through a second B code generation module are not converted through a second photoelectric conversion module, and then logic OR operation is executed according to the bit; the method comprises the steps of recording a B code stream generated by a first B code generating module and a B code stream generated by a second B code generating module as a code 1 and a code 2 respectively;
step 3, after the slave node receives the time interval through the second photoelectric conversion module, the slave node sends the code to the master node through the second photoelectric conversion module, and the code is input into the digital logic module after being converted into an electric signal by the master node through the first photoelectric conversion module;
step 4, the digital logic module of the master node is regulated, the code stream superposition function of the master node is started, namely logic OR operation is carried out on the codes 1 and 2, and a new code stream output by the digital logic module is input into the first electro-optical conversion module to be converted into an optical signal, and the optical signal is sent to the slave node; the optical signal is input into the second photoelectric conversion module, converted into an electrical signal and then input into the delay adjustment module, and the delay adjustment module has a pulse width test function and a delay adjustment function; the slave node obtains the information of the link delay change according to the pulse width change of the code stream;
step 5, after the link delay change is measured, adjusting an electrically adjustable delay line in the delay adjustment module to compensate the link delay change;
and 6, inputting the electric signal subjected to delay compensation into a carrier recovery and phase locking module, demodulating the electric signal by the carrier recovery and phase locking module, constructing a phase locking loop by taking the demodulated carrier signal as a reference, and phase locking the slave node crystal oscillator on the carrier, thereby realizing the transmission from the master node to the slave node frequency.
Further, when the code 1 and the code 2 are overlapped by opening the code stream overlapping function at the digital logic module of the main node, the rising edges of the first zone bit of the code 1 and the code 2 can be close, and the time interval of the falling edges of the code 1 and the code 2 is controlled within 10 ns.
Further, the pulse width test function of the delay adjustment module can be realized by TDC measurement or a charge pump phase demodulation circuit.
Further, if the pulse width is measured by the TDC, the rising edge of the first flag bit Pr is used as the door opening signal of the TDC, and the falling edge of the first flag bit Pr is used as the door closing signal of the TDC, a time interval value can be measured, the average value is measured for multiple times to obtain the time interval value, and the difference between the time interval value and the initial time interval value is compared to obtain the link delay variation to be compensated.
Further, if the charge pump phase detection circuit is adopted, the output voltage is in direct proportion to the pulse width, and the output voltage is continuously variable; in this way a continuously regulated control voltage is obtained which, when applied to the analogue electrically variable delay line, results in a fine compensation without steps.
Compared with the prior art, the invention has the following technical characteristics:
the invention completes the time-frequency transmission of a single master node and a plurality of slave nodes by using the time delay measurement and compensation technology based on the B code pulse width change, the time division multiplexing technology, the polling technology and the like, and is suitable for the airborne environment. The invention can achieve the following effects:
1. the slave node realizes the functions of master-slave time pair and synchronization, and reduces the weight and the volume of the master node.
2. Because the time-frequency transmission function is dispersed into each slave station, each master-slave transmission link does not affect each other, and when a certain link fails, only the transmission function module of the slave node on the link needs to be replaced, so that the reliability and maintainability of the whole system are improved.
3. The frequency information is directly recovered from the B code transmitted by the master node, instead of independently transmitting the reference clock, and the frequency transmission function is realized and the bidirectional time comparison function of the master node and the slave node is realized on the same optical fiber link. Reducing system complexity, volume and weight.
Drawings
FIG. 1 is a schematic diagram of the basic principle of an on-board fiber optic time-frequency delivery system;
FIG. 2 is a master-slave time synchronization execution link flow diagram;
FIG. 3 is a schematic diagram of a principle of measuring link delay variation based on pulse width variation;
fig. 4 is a schematic diagram of a principle of a master-slave link delay compensation technique.
The reference numerals in the figures illustrate: the device comprises a first B code generation module, a first time interval counter, a digital logic module, a first photoelectric conversion module, a second photoelectric conversion module, a delay adjustment module, a second time interval counter, a carrier recovery and phase lock module, a first time interval counter, a second time interval counter, a carrier recovery and phase lock module and a second B code generation module.
Detailed Description
The invention provides a novel airborne optical fiber time-frequency transmission system and a novel airborne optical fiber time-frequency transmission method, wherein the comparison and synchronization functions between a master node and each slave node are realized by the slave nodes, so that the volume of the master node is greatly reduced. Moreover, since the transfer function is dispersed into each slave station, each master-slave transfer link does not affect each other, and when a certain link fails, only the transfer function module of the slave node on the link needs to be replaced, so that the reliability and maintainability of the whole system are improved.
Referring to the drawings, the technical scheme of the invention is as follows:
an on-board fiber optic time-frequency delivery system, comprising: a master node for distributing time-frequency information to slave nodes, and a plurality of slave nodes for receiving the time-frequency information and realizing signal phase stabilization and time synchronization, wherein:
the master node includes:
a first B code generating module 1, configured to generate an IRIG-B code signal (hereinafter referred to as B code signal);
a first time interval counter 2 for measuring the time interval between the local second pulse of the master node and the second pulse transmitted from the slave node;
the digital logic module 3 is used for switching on or switching off the code stream superposition function of the main node;
a first electro-optical conversion module 4, configured to modulate the code stream of the B-code signal on an optical carrier, thereby converting an electrical signal into an optical signal;
the first photoelectric conversion module 5 is used for converting the optical signal sent from the second photoelectric conversion module of the node into an electric signal and sending the electric signal to the digital logic module;
the slave node includes:
the second photoelectric conversion module 6 is used for converting the optical signal output by the first photoelectric conversion module into an electric signal and transmitting the electric signal to the delay adjustment module;
the second electro-optical conversion module 7 is used for converting the B code signal output by the second B code generation module into an optical signal;
the delay adjustment module 8 is used for delaying the time of the electric signal output by the second photoelectric conversion module 7;
a second time interval counter 9 for measuring the time interval between the local second pulse of the slave node and the second pulse transmitted from the master node;
the carrier recovery and phase locking module 10 is used for recovering the carrier and locking the slave node crystal oscillator on the carrier;
a second B code generation module 11 for generating a B code signal; wherein the B-code signal uses the recovered carrier as a clock reference.
Further, the onboard optical fiber time-frequency transmission system provides time-frequency information for a plurality of slave nodes through one master node.
Furthermore, in order to obtain a smoother control process, the system is prone to compensating the link delay by using an analog electrical adjustable delay line, and the control quantity is continuous, so that a step-shaped control process caused by delay stepping (about 10 ps) of the digital control electrical adjustable delay line is avoided.
The airborne optical fiber time-frequency transmission method suitable for the airborne optical fiber time-frequency transmission system comprises the following steps of:
step 1, in the initial stage after starting up, B code signals generated by the first and second B code generating modules 1 and 11 are respectively input into the first and second electro-optical conversion modules 4 and 7 to be converted into optical signals, and the optical signals are sent to the first and second electro-optical conversion modules 5 and 6 at opposite ends (namely, a master node sends the optical signals to a slave node, and the slave node sends the optical signals to the master node); the first and second photoelectric conversion modules 5 and 6 at opposite ends modulate the code stream of the B code signal on the optical carrier wave to be converted into an electric signal, and then the second pulse transmitted by the opposite ends is taken as a stop, and the first and second time interval counters 2 and 9 are used for measuring the time interval T of the second pulse 1 And T 2 Calculate the clock difference (T) 1 -T 2 ) 2; according to the clock difference of the two nodes, the slave node compensates the clock difference of the two nodes by adjusting an adjustable delay line in the delay adjustment module 8 and changing the delay of an output electric signal (time pulse signal), so as to achieve the aim of synchronizing the clocks of the two nodes.
And 2, after bidirectional time comparison and synchronization, the master node uses the first time interval counter 2 to measure the time interval between the local second pulse and the second pulse from the slave node, inputs the time interval into the first electro-optical conversion module 4 and sends the time interval to the slave node, and at the moment, the digital logic module 3 turns off the code stream superposition function, namely, the B code stream (abbreviated as code 1) generated by the master node through the first B code generation module 1 and the code stream (abbreviated as code 2) generated by the slave node through the second B code generation module 11 are not subjected to conversion by the second photoelectric conversion module, and then logic OR operation is carried out according to bits, namely, the superposition operation of two columns of code streams is not carried out.
And 3, after the slave node receives the time interval through the second photoelectric conversion module 6, the slave node sends the code 2 to the master node through the second photoelectric conversion module 7, and the code 2 is converted into an electric signal through the first photoelectric conversion module 5 by the master node and then is input into the digital logic module 3.
Step 4, the digital logic module 3 of the main node is regulated, the code stream superposition function of the main node is started, namely logic or operation is carried out on the codes 1 and 2, and a new code stream (electric signal) output by the digital logic module 3 is input into the first electric-to-optical conversion module 4 to be converted into an optical signal, and the optical signal is sent to the slave node; the optical signal is input into the second photoelectric conversion module 6 to be converted into an electric signal and then is input into the delay adjustment module 8, the delay adjustment module 8 has a pulse width test function and a delay adjustment function, and the pulse width test function can be realized by a TDC measurement circuit or a charge pump phase discrimination circuit; the slave node obtains the information of the link delay change of the master-slave node according to the pulse width change of the code stream.
If pulse width is measured through the TDC, the rising edge of the first flag bit Pr can be used as a door opening signal of the TDC, the falling edge of the first flag bit Pr can be used as a door closing signal of the TDC, a time interval value can be measured, in order to reduce the influence of signal edge jitter on a measurement result, a method of measuring an average value for a plurality of times is generally adopted to obtain the time interval value, and the difference value between the time interval value and the initial time interval value is compared, so that the link delay variation quantity to be compensated can be obtained; if the charge pump phase discrimination circuit is adopted, the output voltage is in direct proportion to the pulse width, and the output voltage is continuously variable. In this way, a continuously regulated control voltage is obtained, although a specific pulse width value cannot be obtained. When the control voltage is applied to the analog electrically variable delay line, a fine compensation effect without steps can be obtained. The principle of measuring the link delay variation according to the pulse width variation is shown in fig. 3.
When the code 1 and the code 2 are overlapped by opening the code stream overlapping function at the digital logic module 3 of the main node, the rising edges of the first zone bits of the code 1 and the code 2 can be close, and the time interval of the falling edges of the code 1 and the code 2 can be controlled within 10ns, so that the pulse width measurement of a new code stream after the overlapping of two columns of code streams is facilitated, and the change of the pulse width can naturally reflect the change of the unidirectional time delay of a link from the slave node to the main node.
And step 5, after the link delay change is measured, adjusting an electrically adjustable delay line in the delay adjustment module 8 to compensate the link delay change.
And 6, inputting the electric signal subjected to delay compensation into a carrier recovery and phase locking module 10, demodulating the electric signal by the carrier recovery and phase locking module 10, constructing a phase locking loop by taking the demodulated carrier signal as a reference, and phase locking the slave node crystal oscillator on the carrier, thereby realizing the transmission from the master node to the slave node frequency. The phase-locked loop realizes loose phase locking, namely the locking process is slower, and the transition process of delay adjustment can be properly shielded, so that the influence of the delay compensation process on the short stability of the crystal oscillator signal is avoided.
Further, when the system operates, the two-way time comparison and the frequency transmission are respectively carried out in a time division multiplexing mode in consideration of possible conflicts between the two modes of time comparison and frequency transmission.
Furthermore, considering the problem of resource occupation when the time comparison is carried out between the master node and the plurality of slave nodes, the time comparison function between a single master node and the plurality of slave nodes is realized by adopting a polling mode, so that only one time interval measuring unit can be adopted, hardware resources are greatly saved, and the equipment volume is smaller.
Examples:
the invention can be applied to an airborne environment, and one main node transmits time-frequency information to a plurality of sub-nodes.
Since all slave nodes have the same structure, only one slave node is described, and the method is equally applicable to other slave nodes, as shown in fig. 1, and the system includes: the system comprises a master node for distributing time-frequency information to slave nodes, and a plurality of slave nodes for receiving the time-frequency information and realizing signal phase stabilization and time synchronization.
Wherein the master node comprises: the device comprises a B code generation module 1, a time interval counter 2, a digital logic module 3, an electro-optical conversion module 4 and a photoelectric conversion module 5. The slave node includes: the photoelectric conversion module 6, the electro-optical conversion module 7, the delay adjustment module 8, the time interval counter 9, the carrier recovery and phase locking module 10 and the B code generation module 11.
The invention discloses an airborne optical fiber time-frequency transmission method of an airborne optical fiber time-frequency transmission system, which comprises the following steps:
step 1, in the starting stage after starting up, B code signals generated by a B code generating module 1/11 of a master/slave node are respectively input into an electro-optical conversion module 4 and 7 to be converted into optical signals and sent to an opposite terminal, the opposite terminal photoelectric conversion modules 5 and 6 convert the optical signals into electric signals, the two nodes respectively take the second pulse of the node as start, the second pulse transmitted by the opposite terminal is stop, and the time interval T is measured by using time interval counters 2 and 9 1 And T 2 Calculate the clock difference (T) 1 -T 2 )/2. And then the slave node compensates the clock difference of the two nodes by adjusting the delay adjusting module 8 so as to achieve the aim of synchronizing the clocks of the two nodes. The synchronization execution link is shown in fig. 2. For clock skew within 10ns, the amount of delay required for clock skew compensation is produced by an electrically adjustable delay line. For clock differences greater than 10ns, a delay amount having a value that is an integer multiple of the carrier period (100 mhz,10 ns) is generated by directly intervening in the encoding process of the time code. The remaining Zhong Chazhi is then passed to an electrical delay adjustment module to compensate.
And 2, after bidirectional time comparison and synchronization, the master node measures the time interval between the local second pulse and the second pulse from the slave node by using the time interval counter 2, then inputs the time interval value into the electro-optical conversion module 4 to be converted into an optical signal, and then sends the optical signal to the slave node, and at the moment, the code stream (abbreviated as code 1) sent by the master node and the code stream (abbreviated as code 2) sent by the slave node and returned by the slave node are not subjected to logical OR operation according to bits, namely the overlapping operation of the two columns of code streams is not executed.
And 3, after receiving the time interval value and inputting the time interval value into the photoelectric conversion module 6 to be converted into an electric signal, the slave node changes the delay output by the code 2 by adjusting the delay adjustment module 8, then inputs the code 2 into the photoelectric conversion module 7 to be converted into an optical signal, and then sends the optical signal to the master node, and after the optical signal is converted into the electric signal by the photoelectric conversion module 5 of the master node, the electric signal is input into the digital logic module 3.
And 4, adjusting the digital logic module 3 of the master node, starting the code stream superposition function of the master node, namely executing logic OR operation, and converting the electric signal output by the digital logic module 3 into an optical signal by the electric-optical conversion module 4 and sending the optical signal to the slave node, wherein the optical signal is input into the photoelectric conversion module 6 and is input into the delay adjustment module 8 after being converted into the electric signal, the delay adjustment module 8 has a pulse width test function and a delay adjustment function, and the pulse width test function can be realized by a TDC or charge pump phase detection circuit.
When two columns of code streams are overlapped at the main node by adjusting the delay adjusting module 8, the rising edge of the first flag bit Pr of the two columns of code streams can be close, and the time interval of the falling edge of the first flag bit Pr and the falling edge of the first flag bit Pr can be controlled within 10ns, so that Pr pulse width measurement of a new code stream after the two columns of code streams are overlapped is facilitated, and the change of the pulse width can naturally reflect the change of the unidirectional time delay of a link from the slave node to the main node.
Step 5, after the single-pass delay variation of the link is measured, the adjustable delay line in the delay adjustment module 8 can be used for compensating the delay variation of the link. In order to obtain a smoother control process, the scheme is prone to using an analog electrical adjustable delay line, and the control quantity is continuous, so that a step-shaped control process caused by delay stepping (about 10 ps) of the digital control electrical adjustable delay line is avoided, in order to ensure that the delay change can be accurately measured, a same type of electrical delay line needs to be additionally arranged on a slave node, the slave node is located on a backward path, and the slave node and the electrical delay line of a forward path are subjected to the same control voltage, as shown in fig. 3. When the delay compensation amounts of the current and the backward paths are very close, the delay compensation effect of the forward path can be accurately reflected on Pr pulse width, the subsequent measurement can be accurate, and the principle of the delay compensation technology is shown in figure 4.
And 6, inputting the signal subjected to delay compensation into a carrier recovery and phase locking module 10, constructing a phase locking loop by taking the carrier signal demodulated from the slave node as a reference, and locking the slave node crystal oscillator on the phase locking loop, thereby realizing frequency transmission. The phase-locked loop realizes loose phase locking, namely the locking process is slower, and the transition process of delay adjustment can be properly shielded, so that the influence of the delay compensation process on the short stability of the crystal oscillator signal is avoided. The frequency signal output by the carrier recovery and phase lock module 10 can be used as a reference clock of the B code generation module 11 for generating a B code signal synchronized with the master node at the slave node.
When the phase stabilizing function is executed, since the code 1 and the code 2 are overlapped, at the moment, we cannot send time interval information to the slave node by the master node, and then the time comparison needs to be time-shared with the delay compensation. The slave node checks whether the device address in the code stream matches with the own address, and when the addresses match, the received code stream is used for bidirectional time comparison, otherwise, the received code stream is used for frequency transmission. Because the time alignment is performed at a low frequency, usually several tens of minutes, and the execution time is usually less than 1 second, the link delay changes very little (subpicoseconds) within such a short time and does not exceed the error range of delay compensation, so that the time-sharing execution time alignment does not have a significant effect on the frequency transfer function.
In addition, at the master node, because bidirectional time comparison is performed with tens of slave nodes, in order to save space resources, the time interval between the local second pulse and the second pulse from a certain slave node can be measured in turn, so that only one time interval measuring unit can be adopted, hardware resources are saved greatly, and the equipment is smaller in size. To implement this time alignment of polling, a different device address needs to be defined for each node, and since the number of nodes is typically not more than 100, the address length is defined as one byte. The master node maintains a slave node address list, after a new slave node is added in the system, the slave node transmits its own device address to the master node, and then the master node decodes the address from the code stream and stores the address in the address list, and the address corresponds to the receiving port of the code stream. In the comparison process, the master node obtains a code stream signal from a certain slave node, then generates a demodulation second, and then measures the time interval between the demodulation second and the current second. The master station loads the time interval data into the time information field after generating the B code, and then attaches the device address of the slave node to the time information field. The code stream signal is sent to all slave nodes, when the slave node with the address mismatch receives the B code, the comparison data generated in the master node is not extracted from the code stream, and when the slave node with the address mismatch receives the B code, the comparison data generated in the master node is extracted from the code stream, so that the clock difference between the slave node and the master node is calculated, and the clock synchronization operation is performed. In the process that the comparison data of the slave nodes are sent to the master node, the master node can distinguish which slave node the code stream comes from because the communication link from the master node to the slave node is one-to-one, so that after the stable communication link is established, no additional device address is needed when the slave node codes.
The above embodiments are only for illustrating the technical solution of the present application, and are not limiting thereof; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced equally; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application, and are intended to be included in the scope of the present application.
Claims (9)
1. An on-board fiber optic time-frequency delivery system, comprising:
a master node for distributing time-frequency information to slave nodes, and a plurality of slave nodes for receiving the time-frequency information and realizing signal phase stabilization and time synchronization, wherein:
the master node includes:
a first B code generation module (1) for generating a B code signal;
a first time interval counter (2) for measuring the time interval between the local second pulse of the master node and the second pulse transmitted from the slave node;
the digital logic module (3) is used for switching on or switching off the code stream superposition function of the main node;
a first electro-optical conversion module (4) for modulating a code stream of the B-code signal on an optical carrier, thereby converting an electrical signal into an optical signal;
the first photoelectric conversion module (5) is used for converting the optical signal sent by the second photoelectric conversion module of the node into an electric signal and sending the electric signal to the digital logic module;
the slave node includes:
the second photoelectric conversion module (6) is used for converting the optical signal output by the first photoelectric conversion module (4) into an electric signal and transmitting the electric signal to the delay adjustment module (8);
the second electro-optical conversion module (7) is used for converting the B code signal output by the second B code generation module into an optical signal;
the delay adjustment module (8) is used for carrying out time delay on the electric signal output by the second photoelectric conversion module (7);
a second time interval counter (9) for measuring the time interval between the local second pulse of the slave node and the second pulse transmitted from the master node;
the carrier recovery and phase locking module (10) is used for recovering the carrier and locking the slave node crystal oscillator on the carrier;
a second B-code generation module (11) for generating a B-code signal; wherein the B-code signal uses the recovered carrier as a clock reference.
2. The on-board fiber optic time-frequency transfer system of claim 1, wherein the on-board fiber optic time-frequency transfer system provides time-frequency information to a plurality of slave nodes via a master node.
3. The system of claim 1, wherein the system is configured to perform bidirectional time alignment and frequency transfer in a time division multiplexing manner.
4. The on-board fiber optic time-frequency transfer system of claim 1, wherein the time alignment function between a single master node and a plurality of slave nodes is implemented by polling.
5. An airborne optical fiber time-frequency transmission method, which is characterized by comprising the following steps:
step 1, in the initial stage, B code signals generated by a first B code generation module (1) and a second B code generation module (11) are respectively input into a first electro-optic conversion module (4) and a second electro-optic conversion module (7) to be converted into optical signals, and the optical signals are sent to a first photoelectric conversion module (5) and a second photoelectric conversion module (6) at opposite ends; the first and second photoelectric conversion modules (5, 6) at opposite ends modulate the code stream of the B code signal on the optical carrier wave to be converted into electric signals, and then the second pulse transmitted by the opposite ends is taken as stop, and the first and second time interval counters (2, 9) are used for measuring the time interval T 1 And T 2 Calculate the clock difference (T) 1 -T 2 ) 2; according to the clock difference of the two nodes, the slave node compensates the clock difference of the two nodes by adjusting an adjustable delay line in a delay adjustment module (8) and changing the delay of an output electric signal so as to achieve the aim of synchronizing the clocks of the two nodes;
step 2, after bidirectional time comparison and synchronization, the master node uses a first time interval counter (2) to measure the time interval between the local second pulse and the second pulse from the slave node, inputs the time interval into a first electro-optical conversion module (4) and sends the time interval to the slave node, and at the moment, a code stream superposition function is closed through a digital logic module (3), namely, the B code stream generated by the master node through a first B code generation module (1) and the code stream generated by the slave node through a second B code generation module (11) are not converted through the second electro-optical conversion module, and then logic OR operation is executed according to bits; the B code stream generated by the first B code generation module (1) and the B code stream generated by the second B code generation module (11) are respectively a code 1 and a code 2;
step 3, after the slave node receives the time interval through the second photoelectric conversion module (6), the slave node sends the code 2 to the master node through the second photoelectric conversion module (7), and the code 2 is input into the digital logic module (3) after the master node converts the code 2 into an electric signal through the first photoelectric conversion module (5);
step 4, the digital logic module (3) of the main node is regulated, the code stream superposition function of the main node is started, namely logic OR operation is carried out on the codes (1) and (2), and a new code stream output by the digital logic module (3) is input into the first electro-optical conversion module (4) to be converted into an optical signal, and the optical signal is sent to the slave node; the optical signal is input into a second photoelectric conversion module (6) to be converted into an electric signal and then is input into a delay adjustment module (8), and the delay adjustment module (8) has a pulse width test function and a delay adjustment function; the slave node obtains the information of the link delay change according to the pulse width change of the code stream;
step 5, after the link delay change is measured, an electrically adjustable delay line in the delay adjustment module (8) is adjusted to compensate the link delay change;
and 6, inputting the electric signal subjected to delay compensation into a carrier recovery and phase locking module (10), demodulating the electric signal by the carrier recovery and phase locking module (10), constructing a phase locking loop by taking the demodulated carrier signal as a reference, and phase locking the slave node crystal oscillator on the carrier, thereby realizing the transmission from the master node to the slave node frequency.
6. The method for transmitting the onboard optical fiber time-frequency according to claim 5, wherein the delay adjustment module (8) is adjusted so that when the code (1) and the code (2) are overlapped by opening the code stream overlapping function at the main node digital logic module (3), rising edges of first flag bits of the code 1 and the code 2 can be close, and a time interval of falling edges of the code 1 and the code 2 is controlled within 10 ns.
7. The method according to claim 5, wherein the pulse width test function of the delay adjustment module (8) can be implemented by TDC measurement or charge pump phase demodulation circuit.
8. The method of claim 5, wherein if pulse width is measured by a TDC, a rising edge of the first flag bit Pr is used as a door opening signal of the TDC, and a falling edge of the first flag bit Pr is used as a door closing signal of the TDC, a time interval value is measured, an average value is measured multiple times, a time interval value is obtained, and a difference value between the time interval value and the initial time interval value is compared to obtain the link delay variation to be compensated.
9. The method of claim 5, wherein if a charge pump phase demodulation circuit is used, the output voltage is proportional to the pulse width and is continuously variable; in this way a continuously regulated control voltage is obtained which, when applied to the analogue electrically variable delay line, results in a fine compensation without steps.
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