Missile-borne double-base forward-looking SAR time-frequency synchronization method based on direct waves

Abstract

The invention provides a missile-borne bistatic forward-looking SAR time-frequency synchronization method based on direct waves, and the method comprises the steps: carrying out the data demodulation of a received direct wave signal, and carrying out the distance compression of the demodulated direct wave signal; extracting a peak signal with the maximum amplitude of each sampling pulse in the direct wave matrix after distance compression to form a peak signal vector, and performing Doppler centroid estimation on the peak signal vector; performing polynomial fitting on peak position historical data corresponding to peak signals in each sampling pulse, extracting linear components, eliminating deviations corresponding to Doppler centroids, obtaining an offset rate of a linear time synchronization error, and compensating the linear time synchronization error according to the offset rate; the peak phase of the peak signal is subtracted, deviation corresponding to the Doppler centroid is eliminated, an estimated value of the fixed frequency synchronization error is obtained, and the fixed frequency synchronization error is compensated according to the estimated value. According to the method, the time-frequency synchronization error between missile-borne double-base foresight SAR platforms can be effectively eliminated, and high-quality imaging in the whole guidance process is guaranteed.

Description

Technical Field

[0001] The present application belongs to the technical field of time-frequency synchronization processing, and in particular to a missile-borne bistatic forward-looking SAR time-frequency synchronization method based on direct waves. Background Art

[0002] Synthetic Aperture Radar (SAR) can not only work in all-day and all-weather conditions, but also effectively identify camouflaged objects and penetrate cover. Missile-borne SAR technology that combines SAR with missiles is a hot topic in current SAR research. The combination of seeker and SAR gives the seeker the advantages of SAR, improves its full-time detection capability, and has strong autonomy and anti-interference capabilities in battlefields with complex environments. However, a single-base platform cannot perform forward imaging and cannot identify targets directly in front of the platform, so it cannot meet the needs of modern battlefields.

[0003] Missile-borne bistatic forward-looking SAR is a radar system that places the receiver and transmitter separately on two missile platforms. In this system, the transmitting platform is responsible for transmitting radar signals to the target area, while the receiving platform passively captures the reflected signals and processes the received signals to generate two-dimensional high-resolution SAR images.

[0004] The dual-base SAR system can transmit and receive multiple targets at one time, obtain target scattering information from multiple angles, improve the accuracy of target identification, and more easily discover hidden targets, thus improving the platform's reconnaissance capability. At the same time, it is also very suitable for multi-missile formation operations, which can improve strike capabilities and cope with more complex battlefield environments. Usually, the dual-base SAR system adopts the "long-range transmission and short-range reception" working mode, and has natural anti-interference and stealth characteristics. Compared with the single-base SAR system, the dual-base SAR system adds a carrying platform, which means that the dual-base SAR system needs to add modules such as time-frequency synchronization and data link, which increases the complexity of system design. Among them, the time-frequency synchronization problem will affect the imaging quality and the accuracy of target positioning, which is the primary problem that the dual-base system needs to solve.

[0005] Existing time-frequency synchronization technologies are mainly divided into three categories: independent synchronization method, third-party synchronization method, and synchronous link synchronization method. Among them, the independent synchronization method refers to the use of a high-stability frequency source by the sender and receiver, and the synchronization is achieved solely by relying on the consistency and high stability of the frequency source. It has high requirements for the frequency source and is usually difficult to achieve. Third-party synchronization refers to the use of the pps signal provided by satellites such as GPS and Beidou as a synchronization reference. This method is mainly used to process the clock difference between the sender and receiver, and this synchronization method has high requirements for positioning accuracy and is not suitable for high-speed mobile platforms. The synchronous link synchronization method includes a two-way link synchronization method, which requires establishing a communication link between the transmitter and the receiver and sending synchronization signals to each other. This method has high synchronization accuracy, but it will destroy the passive characteristics of the receiver, and the system cost is high. It is usually used for cooperative satellite platforms and is not suitable for missile-borne platforms. Summary of the invention

[0006] In view of this, the present application aims to propose a missile-borne bistatic forward-looking SAR time-frequency synchronization method based on direct waves, so as to solve the problem of eliminating the inherent time-frequency synchronization error between missile-borne bistatic platforms and achieving time-frequency synchronization between missile-borne bistatic platforms.

[0007] To achieve the above purpose, the technical solution of this application is implemented as follows: In a first aspect, the present application provides a missile-borne bistatic forward-looking SAR time-frequency synchronization method based on direct waves, comprising: Performing data demodulation on the received direct wave signal, and performing distance compression on the demodulated direct wave signal; Extracting the peak signal with the largest amplitude of each sampling pulse in the direct wave matrix after range compression to form a peak signal vector, and performing Doppler centroid estimation on the peak signal vector by using an amplitude correlation method; Performing polynomial fitting on the peak position historical data corresponding to the peak signal in each sampling pulse, extracting the linear component to obtain a linear quantity, removing the deviation corresponding to the Doppler centroid from the linear quantity, obtaining the offset rate of the linear time synchronization error, and compensating the linear time synchronization error in the direct wave matrix and the echo matrix according to the offset rate; The peak phase of the peak signal is differentiated, and an estimated value of the fixed frequency synchronization error is obtained according to the peak phase difference value and the Doppler centroid estimate value, and the fixed frequency synchronization error in the direct wave matrix and the echo matrix is ​​compensated according to the estimated value.

[0008] In the second aspect, based on the same inventive concept, the present application also provides a missile-borne bistatic forward-looking SAR time-frequency synchronization system based on direct waves, comprising: A signal processing module is configured to perform data demodulation on the received direct wave signal and perform distance compression on the demodulated direct wave signal; A signal extraction module is configured to extract a peak signal with the largest amplitude of each sampling pulse in the direct wave matrix after range compression to form a peak signal vector, and perform Doppler centroid estimation on the peak signal vector by an amplitude correlation method; A first compensation module is configured to perform polynomial fitting on the peak position historical data corresponding to the peak signal in each sampling pulse, extract the linear component to obtain a linear quantity, remove the deviation corresponding to the Doppler centroid from the linear quantity, obtain the offset rate of the linear time synchronization error, and compensate the linear time synchronization error in the direct wave matrix and the echo matrix according to the offset rate; The second compensation module is configured to differenciate the peak phase of the peak signal, obtain an estimated value of the fixed frequency synchronization error based on the peak phase difference value and the Doppler centroid estimate, and compensate for the fixed frequency synchronization error in the direct wave matrix and the echo matrix based on the estimated value.

[0009] In a third aspect, based on the same inventive concept, the present application also provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the method described in the first aspect is implemented.

[0010] In a fourth aspect, based on the same inventive concept, the present application also provides a non-transitory computer-readable storage medium, wherein the non-transitory computer-readable storage medium stores computer instructions, and the computer instructions are used to enable the computer to execute the method described in the first aspect.

[0011] Compared with the prior art, the missile-borne bistatic forward-looking SAR time-frequency synchronization method based on direct waves described in this application has the following beneficial effects: The direct wave-based missile-borne bistatic forward-looking SAR time-frequency synchronization method described in the present application can effectively eliminate the time-frequency synchronization error between missile-borne bistatic forward-looking SAR platforms, ensure high-quality imaging throughout the guidance process, and lay a solid foundation for the subsequent extraction of image information. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings: Figure 1 This is a flow chart of a method for time-frequency synchronization of a missile-borne bistatic forward-looking SAR based on direct waves as described in an embodiment of the present application; Figure 2 This is a schematic diagram of the structure of a missile-borne bistatic forward-looking SAR time-frequency synchronization system based on direct waves according to an embodiment of the present application; Figure 3 This is a schematic diagram of the hardware structure of the electronic device described in the embodiment of the present application. DETAILED DESCRIPTION

[0013] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0014] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present application should be the usual meanings understood by people with ordinary skills in the field to which the present application belongs. The "first", "second" and similar words used in the embodiments of the present application do not represent any order, quantity or importance, but are only used to distinguish different components. "Including" or "comprising" and similar words mean that the elements or objects appearing in front of the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0015] In order to eliminate the inherent time-frequency synchronization error between missile-borne bistatic platforms, this embodiment proposes a missile-borne bistatic forward-looking SAR time-frequency synchronization method based on direct waves, which can eliminate the time-frequency synchronization error between the bistatic platforms and achieve high-quality imaging and precision guidance throughout the guidance process. In order to achieve time and frequency synchronization of the missile-borne bistatic forward-looking SAR platform, a synchronization link is first established between the two platforms for transmitting and receiving direct waves. The receiver extracts the time-frequency synchronization error from the received direct wave signal and compensates the echo matrix, thereby achieving time-frequency synchronization of the missile-borne bistatic platform.

[0016] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0017] See also Figure 1 As shown, this embodiment provides a missile-borne bistatic forward-looking SAR time-frequency synchronization method based on direct waves, which specifically includes the following steps: Step S101: demodulate the received direct wave signal and perform distance compression on the demodulated direct wave signal.

[0018] Step S102: extract the peak signal with the largest amplitude of each sampling pulse in the direct wave matrix after range compression to form a peak signal vector, and perform Doppler centroid estimation on the peak signal vector by using an amplitude correlation method.

[0019] Step S103, perform polynomial fitting on the peak position historical data corresponding to the peak signal in each sampling pulse (the data is positioned as: the slant distance corresponding to each peak signal, that is, the distance data of the radar signal from the transmitter to the receiver), extract the linear component to obtain the linear quantity, remove the deviation corresponding to the Doppler centroid from the linear quantity, obtain the offset rate of the linear time synchronization error, and compensate the linear time synchronization error in the direct wave matrix and the echo matrix according to the offset rate.

[0020] Step S104, subtract the peak phase of the peak signal, and obtain an estimated value of the fixed frequency synchronization error based on the peak phase difference value and the Doppler centroid estimate value, and compensate the fixed frequency synchronization error in the direct wave matrix and the echo matrix based on the estimated value.

[0021] The missile-borne bistatic forward-looking SAR time-frequency synchronization method based on direct waves described in this embodiment can eliminate the synchronization error between the missile transmitting and receiving platforms. The transmitter of the irradiation missile transmits the direct wave, and the receiver of the attack missile passively receives the direct wave signal and solves the time-frequency synchronization error. Under the condition of considering the system cost, this method can retain the passive characteristics of the reception and eliminate the time-frequency synchronization error between platforms, thereby realizing high-resolution, high-quality imaging and precise guidance throughout the guidance process.

[0022] The time-frequency synchronization method includes a time synchronization processing method and a frequency synchronization processing method. The two processing processes are specifically explained as follows.

[0023] For the time synchronization processing method, the method includes: Step 1: The receiver demodulates the received direct wave signal, wherein the model of the direct wave signal after demodulation by the receiver is: (1) In the formula, Indicates distance to fast time, Indicates the slow time in azimuth. is the carrier frequency, is the frequency modulation slope, is the propagation delay of the direct wave from the transmitter to the receiver, is the time synchronization error.

[0024] It can be observed from equation (1) that the time synchronization error can be estimated by the delay time of the adjacent direct wave signal or echo signal during the propagation process. Because the direct wave signal can be regarded as a one-way echo signal containing only one point target and with a very high signal-to-noise ratio, the effect of using the direct wave signal to estimate the time synchronization error is more obvious.

[0025] Step 2: performing distance compression on the demodulated direct wave signal; Among them, the linear part of the peak position history after the direct wave range compression contains two key information: first, the drift rate of the linear time synchronization error, and second, the Doppler centroid. Obviously, to obtain the drift rate of the linear time synchronization error, it is only necessary to remove the influence of the Doppler centroid in the range migration.

[0026] Step 3, extracting the peak signal with the largest amplitude of each sampling pulse in the direct wave matrix after range compression to form a peak signal vector; Step 4: Perform polynomial fitting on the peak position historical data corresponding to the peak signal in each sampling pulse to extract its linear component and obtain a linear quantity; Step 5: Using the amplitude correlation method to estimate the Doppler centroid of the peak signal vector generated in step 2; Step 6: Eliminate the deviation caused by the Doppler centroid (i.e., the Doppler centroid estimate) from the linear quantity obtained in step 4, and then obtain the drift rate of the linear time synchronization error; Step 7: Compensate the linear time synchronization error in the direct wave matrix and the echo matrix according to the offset rate.

[0027] For the frequency synchronization processing method, the method includes: Step 1: The receiver demodulates the received direct wave signal, wherein the model of the direct wave signal with a fixed frequency synchronization error after demodulation by the receiver is: (2) In the formula, represents the pulse duration, is the propagation delay of the direct wave from the transmitter to the receiver, represents the frequency modulation slope, is the transmitter carrier frequency, is the pulse repetition period, is the initial phase, where , is the receiver local oscillator, Indicates fixed frequency synchronization error.

[0028] Step 2: Perform distance compression on the demodulated direct wave signal, wherein the demodulated direct wave signal after distance compression is: (3) In the formula, is the signal bandwidth. , it can be seen from the formula that when When the pulse pressure reaches the maximum value, the signal phase is only One item. It can be seen from the expression of The linear component of contains the Doppler centroid of the direct wave and the fixed frequency synchronization error. To obtain the fixed frequency synchronization error, just remove The influence of the Doppler centroid in the linear component of .

[0029] Step 3, extract the peak signal with the largest amplitude of each sampling pulse in the direct wave matrix after range compression, form a peak signal vector, and make a difference in the peak phase; Among them, subtracting the phase at the peak of the pulse pressure can be obtained: (4) in, is the instantaneous Doppler frequency of the direct wave. Within the time when two adjacent direct waves are transmitted, the relative distance between the transmitter and the receiver changes too much, which will cause phase entanglement. and There is a linear relationship between them, but only the phase after winding can be obtained. It is difficult to directly obtain the linear relationship between the two. Rewrite equation (4) as follows: (5) In the formula, is the unknown winding number, express exist The main value part in the bistatic SAR system. As described above, based on the current frequency accuracy level of the oscillation source, ambiguity usually does not occur between pulses, so there is no need to consider the phase winding phenomenon.

[0030] Step 4: perform Doppler centroid estimation on the peak signal vector in step 3 using the amplitude correlation method; Step 5: Subtract the Doppler centroid estimate from the peak phase difference in step 2 to obtain an estimate of the fixed frequency synchronization error; Step 6: Compensate the fixed frequency synchronization error in the direct wave matrix and the echo matrix according to the estimated value of the fixed frequency synchronization error.

[0031] Compared with the two-way link synchronization method, the method described in this embodiment can effectively eliminate the synchronization error while retaining the passive characteristics of the receiver, so that its anti-interference ability and stealth characteristics are not destroyed; compared with the third-party synchronization method, the method described in this embodiment does not rely on high-precision positioning results and is more suitable for processing time-frequency synchronization errors between high-speed maneuvering platforms; compared with the independent synchronization method, the method described in this embodiment does not require a high-stability frequency source and can maintain a low system cost. Therefore, this method can effectively eliminate the time-frequency synchronization error between missile-borne dual-base forward-looking SAR platforms, ensure high-quality imaging throughout the guidance process, and lay a solid foundation for the subsequent extraction of image information.

[0032] It should be noted that the above describes some embodiments of the present application. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the above embodiments and still achieve the desired results. In addition, the processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0033] Based on the same inventive concept, corresponding to any of the above-mentioned embodiments and methods, an embodiment of the present application further provides a missile-borne bistatic forward-looking SAR time-frequency synchronization system based on direct waves.

[0034] like Figure 2 As shown, the missile-borne bistatic forward-looking SAR time-frequency synchronization system based on direct waves includes: The signal processing module 11 is configured to perform data demodulation on the received direct wave signal and perform distance compression on the demodulated direct wave signal; The signal extraction module 12 is configured to extract the peak signal with the largest amplitude of each sampling pulse in the direct wave matrix after range compression to form a peak signal vector, and perform Doppler centroid estimation on the peak signal vector by an amplitude correlation method; The first compensation module 13 is configured to perform polynomial fitting on the peak position historical data corresponding to the peak signal in each sampling pulse, extract the linear component to obtain the linear quantity, remove the deviation corresponding to the Doppler centroid from the linear quantity, obtain the offset rate of the linear time synchronization error, and compensate the linear time synchronization error in the direct wave matrix and the echo matrix according to the offset rate; The second compensation module 14 is configured to differenciate the peak phase of the peak signal, obtain an estimated value of the fixed frequency synchronization error based on the peak phase difference value and the Doppler centroid estimate, and compensate the fixed frequency synchronization error in the direct wave matrix and the echo matrix based on the estimated value.

[0035] For the convenience of description, the above system is described by dividing the functions into various modules. Of course, when implementing the embodiments of the present application, the functions of each module can be implemented in the same or multiple software and / or hardware.

[0036] The system of the above embodiment is used to implement the corresponding method in any of the above embodiments, and has the beneficial effects of the corresponding method embodiment, which will not be repeated here.

[0037] Based on the same inventive concept, corresponding to any of the above-mentioned embodiments and methods, an embodiment of the present application also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the method described in any of the above embodiments is implemented.

[0038] Figure 3 A more specific schematic diagram of the hardware structure of an electronic device provided in this embodiment is shown, and the device may include: a processor 1010, a memory 1020, an input / output interface 1030, a communication interface 1040, and a bus 1050. The processor 1010, the memory 1020, the input / output interface 1030, and the communication interface 1040 are connected to each other through the bus 1050 in the device.

[0039] The processor 1010 can be implemented by a general-purpose CPU (Central Processing Unit), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of this specification.

[0040] The memory 1020 may be implemented in the form of ROM (Read Only Memory), RAM (Random Access Memory), static storage device, dynamic storage device, etc. The memory 1020 may store an operating system and other application programs. When the technical solutions provided in the embodiments of this specification are implemented by software or firmware, the relevant program codes are stored in the memory 1020 and are called and executed by the processor 1010.

[0041] The input / output interface 1030 is used to connect the input / output module to realize information input and output. The input / output module can be configured in the device as a component (not shown in the figure), or it can be externally connected to the device to provide corresponding functions. The input device may include a keyboard, a mouse, a touch screen, a microphone, various sensors, etc., and the output device may include a display, a speaker, a vibrator, an indicator light, etc.

[0042] The communication interface 1040 is used to connect a communication module (not shown) to realize communication interaction between the device and other devices. The communication module can realize communication through wired means (such as USB, network cable, etc.) or wireless means (such as mobile network, WIFI, Bluetooth, etc.).

[0043] The bus 1050 includes a path that transmits information between the various components of the device (eg, the processor 1010 , the memory 1020 , the input / output interface 1030 , and the communication interface 1040 ).

[0044] It should be noted that, although the above device only shows the processor 1010, the memory 1020, the input / output interface 1030, the communication interface 1040 and the bus 1050, in the specific implementation process, the device may also include other components necessary for normal operation. In addition, it can be understood by those skilled in the art that the above device may also only include the components necessary for implementing the embodiments of the present specification, and does not necessarily include all the components shown in the figure.

[0045] The electronic device of the above embodiment is used to implement the corresponding method in any of the above embodiments, and has the beneficial effects of the corresponding method embodiment, which will not be described in detail here.

[0046] Based on the same inventive concept, corresponding to any of the above-mentioned embodiments, the present application also provides a non-transitory computer-readable storage medium, wherein the non-transitory computer-readable storage medium stores computer instructions, and the computer instructions are used to enable the computer to execute the method described in any of the above embodiments.

[0047] The computer-readable medium of this embodiment includes permanent and non-permanent, removable and non-removable media, and information storage can be implemented by any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, read-only compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassettes, tape disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device.

[0048] The computer instructions stored in the storage medium of the above embodiments are used to enable the computer to execute the method described in any of the above embodiments, and have the beneficial effects of the corresponding method embodiments, which will not be repeated here.

[0049] A person skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present application (including the claims) is limited to these examples. In line with the concept of the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0050] In addition, to simplify the description and discussion, and in order not to make the embodiments of the present application difficult to understand, the known power / ground connections to the integrated circuit (IC) chip and other components may or may not be shown in the provided drawings. In addition, the device may be shown in the form of a block diagram to avoid making the embodiments of the present application difficult to understand, and this also takes into account the fact that the details of the implementation of these block diagram devices are highly dependent on the platform on which the embodiments of the present application are to be implemented (that is, these details should be fully within the scope of understanding of those skilled in the art). Where specific details (e.g., circuits) are set forth to describe exemplary embodiments of the present application, it is obvious to those skilled in the art that the embodiments of the present application can be implemented without these specific details or with changes in these specific details. Therefore, these descriptions should be considered illustrative rather than restrictive.

[0051] Although the present application has been described in conjunction with specific embodiments of the present application, many alternatives, modifications and variations of these embodiments will be apparent to those skilled in the art from the foregoing description. For example, other memory architectures (e.g., dynamic RAM (DRAM)) may use the discussed embodiments.

[0052] The embodiments of the present application are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present application should be included in the scope of protection of the present application.

Claims

1. A missile-borne bistatic forward-looking SAR time-frequency synchronization method based on direct waves, characterized in that: include: Performing data demodulation on the received direct wave signal and performing distance compression on the demodulated direct wave signal; Extracting the peak signal with the largest amplitude of each sampling pulse in the direct wave matrix after range compression to form a peak signal vector, and performing Doppler centroid estimation on the peak signal vector by using an amplitude correlation method; Performing polynomial fitting on the peak position historical data corresponding to the peak signal in each sampling pulse, extracting the linear component to obtain a linear quantity, removing the deviation corresponding to the Doppler centroid from the linear quantity, obtaining the offset rate of the linear time synchronization error, and compensating the linear time synchronization error in the direct wave matrix and the echo matrix according to the offset rate; The peak phase of the peak signal is differentiated, and an estimated value of the fixed frequency synchronization error is obtained according to the peak phase difference value and the Doppler centroid estimate value, and the fixed frequency synchronization error in the direct wave matrix and the echo matrix is ​​compensated according to the estimated value.

2. The method according to claim 1, characterized in that: The step of performing data demodulation on the received direct signal comprises: The receiver demodulates the received direct wave signal, where the demodulated direct wave signal model is: ； In the formula, Indicates distance to fast time, Indicates the slow time in azimuth. Indicates the carrier frequency, represents the frequency modulation slope, represents the propagation delay of the direct wave from the transmitter to the receiver, Indicates the time synchronization error.

3. The method according to claim 1, characterized in that Also includes: Among them, the model of the direct wave signal with fixed frequency synchronization error after demodulation by the receiver is: ； In the formula, represents the pulse duration, represents the propagation delay of the direct wave from the transmitter to the receiver, represents the frequency modulation slope, Indicates the transmitter carrier frequency, represents the pulse repetition period, represents the initial phase, where , represents the receiver local oscillator, Indicates fixed frequency synchronization error.

4. The method according to claim 3, characterized in that The demodulated direct wave signal after distance compression is: ； In the formula, represents the signal bandwidth, , The linear components of contain the Doppler centroid of the direct wave and the fixed frequency synchronization error.

5. The method according to claim 4, characterized in that The peak phase of the peak signal is subtracted, include: Among them, subtracting the phase at the peak of the pulse pressure can be obtained: ； In the formula, represents the instantaneous Doppler frequency of the direct wave, within the emission time of two adjacent direct waves, and the above formula is rearranged as: ； In the formula, represents the unknown winding number, express exist The main value part within.

6. The method according to claim 1, characterized in that The step of obtaining an estimated value of a fixed frequency synchronization error according to a peak phase difference value and a Doppler centroid estimated value comprises: The peak phase difference value is subtracted from the Doppler centroid estimate to obtain an estimate of the fixed frequency synchronization error.

7. A missile-borne bistatic forward-looking SAR time-frequency synchronization system based on direct waves, characterized in that: include: A signal processing module is configured to perform data demodulation on the received direct wave signal and perform distance compression on the demodulated direct wave signal; A signal extraction module is configured to extract a peak signal with the largest amplitude of each sampling pulse in the direct wave matrix after range compression to form a peak signal vector, and perform Doppler centroid estimation on the peak signal vector by an amplitude correlation method; A first compensation module is configured to perform polynomial fitting on the peak position historical data corresponding to the peak signal in each sampling pulse, extract the linear component to obtain a linear quantity, remove the deviation corresponding to the Doppler centroid from the linear quantity, obtain the offset rate of the linear time synchronization error, and compensate the linear time synchronization error in the direct wave matrix and the echo matrix according to the offset rate; The second compensation module is configured to differenciate the peak phase of the peak signal, obtain an estimated value of the fixed frequency synchronization error based on the peak phase difference value and the Doppler centroid estimate, and compensate for the fixed frequency synchronization error in the direct wave matrix and the echo matrix based on the estimated value.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the method according to any one of claims 1 to 6 is implemented.

9. A non-transitory computer-readable storage medium, characterized in that: in, The non-transitory computer-readable storage medium stores computer instructions, and the computer instructions are used to cause a computer to execute the method according to any one of claims 1 to 6.

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