Time-frequency synchronization method and device for distributed SAR (Synthetic Aperture Radar)

Abstract

The invention provides a distributed SAR time-frequency synchronization method and device. The method comprises the following steps: determining a local pseudo range of a satellite in a distributed SAR system relative to a Beidou satellite navigation system; and adjusting a reference frequency source signal corresponding to a satellite in the distributed SAR system based on a Beidou satellite navigation system to obtain a reference frequency source signal. And the first satellite opens the inter-satellite link according to the reference frequency source signal corresponding to the first satellite. And sending a first local pseudo range corresponding to the first satellite to a second satellite in the distributed SAR system based on the inter-satellite link. A clock difference of the second satellite relative to the first satellite is determined based on the second local pseudorange and the first local pseudorange. And adjusting the frequency of a voltage-controlled constant-temperature crystal oscillator of the second satellite based on the clock difference. According to the method provided by the invention, time-frequency synchronization between satellites can be realized simply and efficiently at low cost.

Description

Technical Field

[0001] The present application relates to the field of aerospace technology, and in particular to a time-frequency synchronization method and device for a distributed SAR. Background Art

[0002] With the continuous development of science and technology, people are more and more eager to explore the sky. Spaceborne interferometric synthetic aperture radar (InSAR) has become an important technology for people to explore the sky. Compared with the traditional single-platform single-system heavy-track interferometric SAR, distributed SAR adopts a single-transmit dual-receive or single-transmit multiple-receive working mode. The time baseline of the acquired interferometric data is zero, which eliminates the time decorrelation source and the atmospheric decorrelation source, which is conducive to improving the accuracy of generating high-precision digital elevation model (DEM).

[0003] Since the transmitter and receiver of distributed SAR are located on different satellite platforms, the measurement of high-precision DEM information requires the support of three synchronization technologies: time synchronization, space synchronization, and phase synchronization. Time synchronization refers to the synchronization between the timing pulses and the transmission pulses and echo sampling windows between different satellite platforms. Most of the existing satellite platforms use the method of taming the crystal oscillator with a clock to achieve time synchronization. The method of taming the crystal oscillator with a clock uses the second pulse output by the navigation GPS as the time reference, combined with the high stability characteristics of the clock, and uses a taming algorithm to calibrate the local clock source. This method has a high implementation cost and is difficult to implement.

[0004] Therefore, how to simply perform time-frequency synchronization on a distributed SAR system has become a technical problem that those skilled in the art need to solve urgently. Summary of the invention

[0005] Based on the above problems, the present application provides a time-frequency synchronization method and device for a distributed SAR, which realizes the time-frequency synchronization of a distributed SAR system through a simple method and at low cost.

[0006] The present application provides a time-frequency synchronization method for a distributed SAR, the method comprising the following steps: Determine the local pseudorange of satellites in the distributed SAR system relative to the Beidou satellite navigation system based on the Beidou satellite navigation system; Based on the Beidou satellite navigation system, a reference frequency source signal corresponding to a satellite in the distributed SAR system is adjusted to obtain a reference frequency source signal; A first satellite in the distributed SAR system starts an intersatellite link using a reference frequency source signal corresponding to the first satellite; Sending a first local pseudorange corresponding to the first satellite to a second satellite in the distributed SAR system based on the intersatellite link; Determine a clock difference of the second satellite relative to the first satellite based on a second local pseudorange corresponding to the second satellite and the first local pseudorange; The frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite is adjusted based on the clock difference.

[0007] In a possible implementation, adjusting the reference frequency source signal corresponding to the satellite in the distributed SAR system based on the Beidou satellite navigation system to obtain the reference frequency source signal includes: Providing a reference frequency source signal for the satellite clock through a voltage-controlled constant temperature crystal oscillator; Obtaining a local pseudorange of the satellite relative to the BeiDou navigation satellite system; Calculate the local pseudorange based on the Kalman filter algorithm to determine the phase difference, frequency drift rate and frequency difference between the reference frequency source signal of the satellite and the Beidou navigation satellite signal; Determine a frequency adjustment amount of the reference frequency source signal relative to the Beidou frequency signal based on the phase difference, the frequency drift rate and the frequency difference; The reference frequency source signal is adjusted based on the frequency adjustment amount to obtain a navigation disciplined reference frequency source signal.

[0008] In a possible implementation manner, adjusting the frequency of a voltage-controlled oven-controlled crystal oscillator of the second satellite based on the clock difference includes: Continuously correcting the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite so that the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite is synchronized with the reference frequency source signal of the first satellite; The adjustment is completed when the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite reaches a stable state.

[0009] In a possible implementation, the local pseudorange is determined by the following formula:

[0010] Wherein, P represents the local pseudorange, the coordinates of the satellite in the Beidou satellite navigation system are (x, y, z), the position of the Beidou satellite navigation system is (X, Y, Z), c is the speed of light, It is determined based on the clock difference between the reference frequency source signal corresponding to the satellite and the Beidou frequency signal.

[0011] The present application also provides a time-frequency synchronization device for a distributed SAR, the device comprising the following modules: a pseudorange module, for determining the local pseudorange of the satellite in the distributed SAR system relative to the Beidou satellite navigation system based on the Beidou satellite navigation system; a first adjustment module, for adjusting the reference frequency source signal corresponding to the satellite in the distributed SAR system based on the Beidou satellite navigation system to obtain a reference frequency source signal; A link module, used for a first satellite in the distributed SAR system to start an inter-satellite link using a reference frequency source signal corresponding to the first satellite; A sending module, configured to send a first local pseudorange corresponding to the first satellite to a second satellite in the distributed SAR system based on the intersatellite link; a clock difference determination module, configured to determine a clock difference of the second satellite relative to the first satellite based on a second local pseudorange corresponding to the second satellite and the first local pseudorange; The second adjustment module is used to adjust the frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite based on the clock difference.

[0012] In a possible implementation manner, the first adjustment module is specifically configured to: Providing a reference frequency source signal for the satellite clock through a voltage-controlled constant temperature crystal oscillator; Obtaining a local pseudorange of the satellite relative to the BeiDou navigation satellite system; Calculate the local pseudorange based on the Kalman filter algorithm to determine the phase difference, frequency drift rate and frequency difference between the reference frequency source signal of the satellite and the Beidou navigation satellite signal; Determine a frequency adjustment amount of the reference frequency source signal relative to the Beidou frequency signal based on the phase difference, the frequency drift rate and the frequency difference; The reference frequency source signal is adjusted based on the frequency adjustment amount to obtain a navigation disciplined reference frequency source signal.

[0013] In a possible implementation manner, the second adjustment module is specifically configured to: Continuously correcting the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite so that the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite is synchronized with the reference frequency source signal of the first satellite; The adjustment is completed when the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite reaches a stable state.

[0014] The present application also provides an electronic device, the electronic device comprising a processor and a memory: The memory is used to store a computer program and transmit the computer program to the processor; The processor is used to execute the steps of the above-mentioned distributed SAR time-frequency synchronization method according to the instructions in the computer program.

[0015] The present application also provides a computer-readable storage medium, which is used to store a computer program. When the computer program is executed by an electronic device, the steps of the time-frequency synchronization method of the distributed SAR are implemented.

[0016] Compared with the prior art, this application has the following beneficial effects: Compared with the traditional method of training crystal oscillators with a clock, the method provided by the present application uses the Beidou satellite navigation system to adjust the frequency source signal, avoiding high-cost hardware requirements and complex communication links. This not only reduces the initial investment of the equipment, but also reduces the maintenance cost, making the application of the distributed SAR system more economical and practical. The present application achieves high-precision time and frequency synchronization through a local pseudo-range measurement frame mutual transmission determination method based on the Beidou satellite navigation system and the inter-satellite link. Compared with the synchronization error problem caused by system complexity in the prior art, the solution of the present application can provide a more stable and consistent frequency signal in a simpler way, significantly improving the accuracy of DEM generation. Since the present application no longer relies on a complex motor drive structure or an additional communication link, the overall structure of the system is simplified. This simplification reduces the difficulty of designing, manufacturing and maintaining the equipment. Through timely frequency and time synchronization, the efficiency of data acquisition and processing is significantly improved. Compared with the data processing delay caused by inaccurate synchronization in the prior art, the present application can realize real-time data transmission and processing, providing more efficient support for subsequent analysis and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0018] Figure 1 A flow chart of a time-frequency synchronization method for a distributed SAR provided in an embodiment of the present application; Figure 2 A schematic diagram of the relationship between the clock difference and pseudorange measurement frames in inter-satellite communication provided in an embodiment of the present application; Figure 3 A schematic diagram of the timing relationship between a two-way distance and clock measurement between two satellites provided in an embodiment of the present application; Figure 4 A time-frequency synchronization system for a distributed SAR provided in an embodiment of the present application; Figure 5A schematic diagram of the structure of a time-frequency synchronization device for a distributed SAR provided in an embodiment of the present application. DETAILED DESCRIPTION

[0019] As described above, most existing satellite platforms use the method of taming the crystal oscillator with a clock to achieve time synchronization. The method uses the second pulse output by the navigation GPS as the time reference, combined with the high stability of the clock, and uses a taming algorithm to calibrate the local clock source. This method has a high implementation cost and is difficult to implement.

[0020] After research, it was found that if the method of taming the crystal oscillator with a clock is chosen, at least the number of clocks corresponding to the number of satellites in the distributed SAR system must be equipped. In order to deal with possible problems such as clock damage, more clocks need to be put into use. First, the price of the clock itself is relatively high. Secondly, taming the crystal oscillator with a clock requires a corresponding taming crystal oscillator system, which makes the cost too high.

[0021] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0022] It is understandable that the method provided in the present application can be applied to a processing device, which is a processing device that can adjust the reference frequency source signal corresponding to the satellite in the distributed SAR system based on the Beidou satellite navigation system to obtain a reference frequency source signal, for example, a terminal device or server that can determine the local pseudorange of the satellite in the distributed SAR system relative to the Beidou satellite navigation system based on the Beidou satellite navigation system. The method provided in the present application can be executed independently by a terminal device or a server, and can also be applied to a network scenario where a terminal device and a server communicate, and is executed in cooperation with a terminal device and a server. Among them, the terminal device can be a computer, a mobile phone or other device. The server can be understood as an application server or a Web server. In actual deployment, the server can be an independent server or a cluster server.

[0023] Figure 1 This is a flow chart of a time-frequency synchronization method for a distributed SAR provided in the present application, the method comprising the following steps: S101: Determine local pseudoranges of satellites in a distributed SAR system relative to the Beidou satellite navigation system based on the Beidou satellite navigation system.

[0024] The processing equipment can determine the local pseudo-range of satellites in the distributed SAR system relative to the Beidou satellite navigation system based on the Beidou satellite navigation system. Pseudo-range is the distance from the GPS observation station to the satellite obtained by GPS observation. Since the influence of "synchronization error between satellite clock and receiver clock" has not been corrected, the measured distance contains the clock error factor, so it is called pseudo-range.

[0025] In one possible implementation, the processing device may obtain the coordinates of the Beidou satellite navigation system in the satellite. Then, the position of the satellite relative to the Beidou satellite navigation system is determined based on the Beidou satellite navigation system. The processing device determines the local pseudorange of the satellite based on the coordinates of the Beidou satellite navigation system in the satellite, the position of the satellite relative to the Beidou satellite navigation system, and the frequency difference between the reference frequency source signal corresponding to the satellite and the Beidou frequency signal. Specifically, the local pseudorange can be determined by the following formula:

[0026] Wherein, P represents the local pseudorange, the coordinates of the satellite in the Beidou satellite navigation system are (x, y, z), and the position of the Beidou satellite navigation system is (X, Y, Z). is the speed of light, It is determined based on the clock difference between the reference frequency source signal corresponding to the satellite and the Beidou frequency signal.

[0027] S102: Adjust the reference frequency source signal corresponding to the satellite in the distributed SAR system based on the Beidou satellite navigation system to obtain a reference frequency source signal.

[0028] The processing device adjusts the reference frequency source signal corresponding to the satellite in the distributed SAR system based on the Beidou satellite navigation system to obtain a reference frequency source signal.

[0029] In a possible implementation, the processing device can provide a reference frequency source signal for the satellite's clock through a voltage-controlled constant temperature crystal oscillator. The voltage-controlled constant temperature crystal oscillator is a constant temperature crystal oscillator whose frequency can be controlled by voltage. The processing device can then obtain the Beidou frequency signal corresponding to the clock of the Beidou satellite navigation system. The phase difference, frequency drift rate, and frequency difference between the reference frequency source signal and the Beidou frequency signal are determined based on the Kalman filter algorithm. The processing device can then determine the frequency adjustment amount of the reference frequency source signal relative to the Beidou frequency signal based on the phase difference, frequency drift rate, and frequency difference. The processing device finally adjusts the reference frequency source signal based on the frequency adjustment amount to obtain a reference frequency source signal.

[0030] It is understandable that there may be multiple satellites in the distributed SAR system, and each satellite in the distributed SAR system may execute the steps corresponding to S101 to adjust the reference frequency source signal of the satellite to obtain a reference frequency source signal.

[0031] In a possible implementation manner, satellites in the distributed SAR system that need to perform inter-satellite time and frequency synchronization execute steps corresponding to S101.

[0032] When adjusting the reference frequency source signal, the frequency adjustment amount can be converted into a voltage, and the voltage is applied to the voltage-controlled constant temperature crystal oscillator to achieve the adjustment of the reference frequency source signal.

[0033] S103: The first satellite in the distributed SAR system starts an inter-satellite link using a reference frequency source signal corresponding to the first satellite.

[0034] The first satellite in the distributed SAR system starts the intersatellite link with the reference frequency source signal corresponding to the first satellite. The intersatellite link refers to the link used for communication between satellites. In the intersatellite link, each satellite will become a node of the space network, so that the communication signal can be transmitted according to the required optimal path. The difference between the intersatellite link and the general up / down link is that both ends of the link are satellites. The intersatellite link can be a laser link or a millimeter wave such as a Ka-band link. The first satellite can be the main satellite in the distributed SAR system.

[0035] S104: Sending a first local pseudorange corresponding to the first satellite to a second satellite in the distributed SAR system based on an inter-satellite link.

[0036] The processing device sends a first local pseudorange corresponding to the first satellite to a second satellite in the distributed SAR system based on an intersatellite link. The second satellite may be a slave satellite in the distributed SAR system.

[0037] S105: Determine a clock difference of the second satellite relative to the first satellite based on a second local pseudorange corresponding to the second satellite and the first local pseudorange.

[0038] The processing device may determine a clock difference of the second satellite relative to the first satellite based on a second local pseudorange corresponding to the second satellite and the first local pseudorange.

[0039] Figure 2 A schematic diagram of the relationship between the clock difference and pseudo-range measurement frame in inter-satellite communication provided in an embodiment of the present application. Figure 2 In the example, the master satellite A can be the first satellite and the slave satellite B can be the second satellite. The master satellite A and the slave satellite B independently send transmission frames to each other through the intersatellite link, and the two satellites are not required to transmit carriers and clocks in the same manner. The two satellites calculate the local pseudorange in time form at the time when the local transmission frame header is sent, and embed it in the local transmission frame and send it to each other. The local pseudorange measurement values ​​in the transmission frames of the master satellite A and the slave satellite B are all local pseudoranges sampled at the time when the current frame is sent. The two satellites can calculate the clock difference of the distance between the two satellites by settling the pseudoranges in the information frames of each other and the pseudorange values ​​given by their respective tracking loops.

[0040] by Figure 2 For example, in the Nth frame, the corresponding rectangle of (1) represents the frame header of the Nth transmission frame sent by the master satellite A, and (2) represents the local pseudorange inserted in the Nth transmission frame sent by the master satellite A. Slave satellite B receives the Nth transmission frame sent by the master satellite A, (3) represents the frame header of the Nth transmission frame sent by the master satellite A received by slave satellite B, and (4) represents the local pseudorange inserted in the Nth transmission frame received by slave satellite B.

[0041] Figure 2 The rectangle corresponding to (5) in the figure sent by satellite B represents the frame header of the Nth transmission frame sent by satellite B, and (6) represents the local pseudorange inserted in the Nth transmission frame sent by satellite B. (7) represents the frame header of the Nth transmission frame sent by satellite B received by master satellite A, and (8) represents the local pseudorange inserted in the Nth transmission frame sent by slave satellite B received by master satellite A.

[0042] Figure 3 A schematic diagram of the timing relationship between a two-way distance and clock measurement between two satellites provided in an embodiment of the present application, Figure 3 In the example, the two communication satellites are master satellite A and slave satellite B. express The local pseudorange corresponding to the primary star A at this moment, express The local pseudorange corresponding to star B at this moment. express The spatial delay of the radio wave between the phase centers of the antennas of the master satellite A and the slave satellite B at a given moment. express The spatial delay of the radio wave between the phase centers of the antennas of the master satellite A and the slave satellite B at a given moment. express The clock difference between the master satellite A and the slave satellite B at the moment. , , and They represent the delays of master satellite A sending, slave satellite B receiving, slave satellite B sending, and master satellite A receiving respectively.

[0043] according to Figure 3 The relationship between the inter-satellite distance and the clock difference between the master satellite A and the slave satellite B is obtained as follows:

[0044]

[0045] The above two equations are the local measured pseudo-range values ​​of the master satellite A and the slave satellite B. c represents the speed of light. This pseudo-range includes the influence of the true distance, clock error and other measurement errors. Based on these two equations, the expressions of the clock error between the two satellites and the distance between the satellites can be obtained as follows:

[0046]

[0047] in, represents the carrier phase ranging value, c represents the speed of light, represents the two-way path propagation delay difference, is the delay difference of the receiving and sending channels from satellite B, is the delay difference between the receiving and transmitting channels of the main satellite A. In the distributed SAR system, since the distance between the spacecraft is relatively short and the relative speed is not large, the measurement error caused by motion can be ignored when the distance and clock error are decoupled by the two-way ranging method, that is, , so the above formula can be rewritten as:

[0048] In this way, the clock difference of slave satellite B relative to master satellite A can be determined.

[0049] S106: Adjust the frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite based on the clock difference.

[0050] The processing device adjusts the frequency of the voltage-controlled constant temperature crystal oscillator of the second satellite based on the clock difference. In a possible implementation, the processing device can continuously correct the oscillation frequency emitted by the voltage-controlled constant temperature crystal oscillator of the second satellite to make it continuously close to the reference frequency source signal corresponding to the first satellite until a stable state is reached.

[0051] In a possible implementation, the processing device may continuously correct the oscillation frequency of the voltage-controlled oven crystal oscillator of the second satellite so that the oscillation frequency of the voltage-controlled oven crystal oscillator of the second satellite is synchronized with the reference frequency source signal of the first satellite. When the oscillation frequency of the voltage-controlled oven crystal oscillator of the second satellite reaches a stable state, the frequency of the voltage-controlled oven crystal oscillator of the second satellite is adjusted.

[0052] Compared with the traditional method of training crystal oscillators with a clock, the method provided by the present application uses the Beidou satellite navigation system to adjust the frequency source signal, avoiding high-cost hardware requirements and complex communication links. This not only reduces the initial investment of the equipment, but also reduces the maintenance cost, making the application of the distributed SAR system more economical and practical. The present application achieves high-precision time and frequency synchronization through a local pseudo-range measurement frame mutual transmission determination method based on the Beidou satellite navigation system and the inter-satellite link. Compared with the synchronization error problem caused by system complexity in the prior art, the solution of the present application can provide a more stable and consistent frequency signal in a simpler way, significantly improving the accuracy of DEM generation. Since the present application no longer relies on a complex motor drive structure or an additional communication link, the overall structure of the system is simplified. This simplification reduces the difficulty of designing, manufacturing and maintaining the equipment. Through timely frequency and time synchronization, the efficiency of data acquisition and processing is significantly improved. Compared with the data processing delay caused by inaccurate synchronization in the prior art, the present application can realize real-time data transmission and processing, providing more efficient support for subsequent analysis and application.

[0053] This application also provides a Figure 4 The time-frequency synchronization system of the distributed SAR shown in the figure includes a master satellite A (first satellite) and slave satellites B, C and D (at least one second satellite). The first satellite and the at least one second satellite are located in the same plane, and the at least one second satellite performs a satellite mission with the first satellite as the center point.

[0054] This application also provides a Figure 5 The schematic structural diagram of the distributed SAR time-frequency synchronization device shown in FIG. 5 includes the following modules: The pseudorange module 501 is used to determine the local pseudoranges of the satellites in the distributed SAR system relative to the Beidou satellite navigation system based on the Beidou satellite navigation system; The first adjustment module 502 is used to adjust the reference frequency source signal corresponding to the satellite in the distributed SAR system based on the Beidou satellite navigation system to obtain a reference frequency source signal; A link module 503 is used for a first satellite in the distributed SAR system to start an inter-satellite link using a reference frequency source signal corresponding to the first satellite; A sending module 504, configured to send a first local pseudorange corresponding to the first satellite to a second satellite in the distributed SAR system based on the intersatellite link; A clock difference determination module 505, configured to determine a clock difference of the second satellite relative to the first satellite based on a second local pseudorange corresponding to the second satellite and the first local pseudorange; The second adjustment module 506 is configured to adjust the frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite based on the clock difference.

[0055] In a possible implementation manner, the first adjustment module is specifically configured to: Providing a reference frequency source signal for the satellite clock through a voltage-controlled constant temperature crystal oscillator; Obtaining a local pseudorange of the satellite relative to the BeiDou navigation satellite system; Calculate the local pseudorange based on the Kalman filter algorithm to determine the phase difference, frequency drift rate and frequency difference between the reference frequency source signal of the satellite and the Beidou navigation satellite signal; Determine a frequency adjustment amount of the reference frequency source signal relative to the Beidou frequency signal based on the phase difference, the frequency drift rate and the frequency difference; The reference frequency source signal is adjusted based on the frequency adjustment amount to obtain a navigation disciplined reference frequency source signal.

[0056] In a possible implementation manner, the second adjustment module is specifically configured to: Continuously correcting the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite so that the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite is synchronized with the reference frequency source signal of the first satellite; The adjustment is completed when the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite reaches a stable state.

[0057] The device provided by the present application uses the Beidou satellite navigation system to adjust the frequency source signal, avoiding high-cost hardware requirements and complex communication links. This not only reduces the initial investment of the equipment, but also reduces the maintenance cost, making the application of the distributed SAR system more economical and practical. The present application realizes high-precision time and frequency synchronization through a local pseudo-range measurement frame mutual transmission determination method based on the Beidou satellite navigation system and the inter-satellite link. Compared with the synchronization error problem caused by system complexity in the prior art, the solution of the present application can provide a more stable and consistent frequency signal in a simpler way, significantly improving the accuracy of DEM generation. Since the present application no longer relies on a complex motor drive structure or an additional communication link, the overall structure of the system is simplified. This simplification reduces the difficulty of design, manufacturing and maintenance of the equipment. Through timely frequency and time synchronization, the efficiency of data acquisition and processing is significantly improved. Compared with the data processing delay caused by inaccurate synchronization in the prior art, the present application can realize real-time data transmission and processing, providing more efficient support for subsequent analysis and application.

[0058] An embodiment of the present application also provides a time-frequency synchronization device for a distributed SAR, wherein the device includes a memory and a processor, the memory is used to store instructions or codes, and the processor is used to execute the instructions or codes so that the device performs the steps of the time-frequency synchronization method for a distributed SAR described in any embodiment of the present application.

[0059] In practical applications, the computer-readable storage medium may be any combination of one or more computer-readable media, which may be a computer-readable signal medium or a computer-readable storage medium.

[0060] The computer-readable storage medium may be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device or device, or any combination thereof. More specific examples of computer-readable storage media (a non-exhaustive list) include: an electrical connection with one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof. In the present embodiment, the computer-readable storage medium may be any tangible medium containing or storing a program that may be used by or in conjunction with an instruction execution system, device, or device.

[0061] Computer-readable signal media may include data signals propagated in baseband or as part of a carrier wave, which carry computer-readable program code. Such propagated data signals may take a variety of forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. Computer-readable signal media may also be any computer-readable medium other than a computer-readable storage medium, which may send, propagate, or transmit a program for use by or in conjunction with an instruction execution system, apparatus, or device.

[0062] The program code embodied on the computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

[0063] Computer program code for performing the operations of the present invention may be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code may be executed entirely on the user's computer, partially on the user's computer, as a separate software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0064] It should be noted that each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. The device embodiment described above is merely schematic, in which the unit described as a separate component may or may not be physically separated, and the component prompted as a unit may or may not be a physical unit, that is, it may be located in one place, or it may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative work.

[0065] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A time-frequency synchronization method for distributed SAR, characterized in that: include: Determine the local pseudorange of satellites in the distributed SAR system relative to the Beidou satellite navigation system based on the Beidou satellite navigation system; Based on the Beidou satellite navigation system, a reference frequency source signal corresponding to a satellite in the distributed SAR system is adjusted to obtain a reference frequency source signal; A first satellite in the distributed SAR system starts an intersatellite link using a reference frequency source signal corresponding to the first satellite; Sending a first local pseudorange corresponding to the first satellite to a second satellite in the distributed SAR system based on the intersatellite link; Determine a clock difference of the second satellite relative to the first satellite based on a second local pseudorange corresponding to the second satellite and the first local pseudorange; The frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite is adjusted based on the clock difference.

2. The method according to claim 1, characterized in that The adjusting the reference frequency source signal corresponding to the satellite in the distributed SAR system based on the Beidou satellite navigation system to obtain the reference frequency source signal comprises: Providing a reference frequency source signal for the satellite clock through a voltage-controlled constant temperature crystal oscillator; Obtaining a local pseudorange of the satellite relative to the BeiDou navigation satellite system; Calculate the local pseudorange based on the Kalman filter algorithm to determine the phase difference, frequency drift rate and frequency difference between the reference frequency source signal of the satellite and the Beidou navigation satellite signal; Determine a frequency adjustment amount of the reference frequency source signal relative to the Beidou frequency signal based on the phase difference, the frequency drift rate and the frequency difference; The reference frequency source signal is adjusted based on the frequency adjustment amount to obtain a navigation disciplined reference frequency source signal.

3. The method according to claim 1, characterized in that The step of adjusting the frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite based on the clock difference comprises: Continuously correcting the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite so that the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite is synchronized with the reference frequency source signal of the first satellite; The adjustment is completed when the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite reaches a stable state.

4. The method according to claim 1, characterized in that: The local pseudorange is determined by the following formula: ; Wherein, P represents the local pseudorange, the coordinates of the satellite in the BeiDou satellite navigation system are (x, y, z), the position of the BeiDou satellite navigation system is (X, Y, Z), c is the speed of light, t s It is determined based on the clock difference between the reference frequency source signal corresponding to the satellite and the Beidou frequency signal.

5. A time-frequency synchronization device for a distributed SAR, characterized in that: include: A pseudorange module, used to determine the local pseudorange of satellites in the distributed SAR system relative to the Beidou satellite navigation system based on the Beidou satellite navigation system; A first adjustment module is used to adjust the reference frequency source signal corresponding to the satellite in the distributed SAR system based on the Beidou satellite navigation system to obtain a reference frequency source signal; A link module, used for a first satellite in the distributed SAR system to start an inter-satellite link using a reference frequency source signal corresponding to the first satellite; A sending module, configured to send a first local pseudorange corresponding to the first satellite to a second satellite in the distributed SAR system based on the intersatellite link; a clock difference determination module, configured to determine a clock difference of the second satellite relative to the first satellite based on a second local pseudorange corresponding to the second satellite and the first local pseudorange; The second adjustment module is used to adjust the frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite based on the clock difference.

6. The device according to claim 5, characterized in that The first adjustment module is specifically used for: Providing a reference frequency source signal for the satellite clock through a voltage-controlled constant temperature crystal oscillator; Obtaining a local pseudorange of the satellite relative to the BeiDou navigation satellite system; Calculate the local pseudorange based on the Kalman filter algorithm to determine the phase difference, frequency drift rate and frequency difference between the reference frequency source signal of the satellite and the Beidou navigation satellite signal; Determine a frequency adjustment amount of the reference frequency source signal relative to the Beidou frequency signal based on the phase difference, the frequency drift rate and the frequency difference; The reference frequency source signal is adjusted based on the frequency adjustment amount to obtain a navigation disciplined reference frequency source signal.

7. The device according to claim 5, characterized in that The second adjustment module is specifically used for: Continuously correcting the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite so that the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite is synchronized with the reference frequency source signal of the first satellite; The adjustment is completed when the oscillation frequency of the voltage-controlled oven-controlled crystal oscillator of the second satellite reaches a stable state.

8. An electronic device, characterized in that: comprising a memory and a processor, wherein: The memory is used to store the computer program; The processor is used to execute the computer program to implement the time-frequency synchronization method of the distributed SAR according to any one of claims 1 to 4.

9. A computer-readable storage medium, characterized in that: Used to store a computer program, wherein when the computer program is executed by a processor, the time-frequency synchronization method for a distributed SAR according to any one of claims 1 to 4 is implemented.

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