Distributed electromagnetic monitoring system and method for abnormal signal direction finding and positioning

Abstract

The invention provides a distributed electromagnetic monitoring system and method for abnormal signal direction finding and positioning. The system comprises a distributed electromagnetic spectrum monitoring subsystem and a GNSS time synchronization system. The distributed electromagnetic spectrum monitoring subsystem comprises a preset number of distributed antennas, a network switch and an operation terminal; the preset number of distributed antennas are distributed at preset positions of a target detection area, and original electromagnetic signals are collected, packaged and then sent to the operation terminal; the network switch provides stable data transmission for the distributed antenna and the operation terminal; the operation terminal is used for processing and analyzing the collected electromagnetic signals, performing instruction configuration on parameters of the whole system, and realizing correlation analysis and direction finding positioning of the signals; and the GNSS time synchronization system is used for realizing the clock synchronization function of the distributed antenna through a preset clock taming method. According to the invention, the accuracy of signal positioning is improved through the high-precision time delay estimation and time synchronization technology.

Description

Technical Field

[0001] This document relates to the field of electromagnetic monitoring technology, and in particular to a distributed electromagnetic monitoring system and method for abnormal signal direction finding and positioning. Background Art

[0002] The earliest application field of spectrum monitoring system is aviation, represented by the spectrum monitoring system IMDS (Interference Monitoring Detection System). The system consists of multiple monitoring aircraft and ground monitoring stations, which can continuously monitor the electromagnetic spectrum information of aviation communications in real time, and issue real-time alarms for illegal signals and abnormal interference signals to ensure the safety of aviation communications. In recent years, my country has made great progress and remarkable achievements in spectrum monitoring and direction finding technology and equipment. From a technical point of view, my country has made great progress in the field of radio spectrum monitoring, covering relevant units in the military and civilian fields.

[0003] However, the existing electromagnetic spectrum monitoring system mainly uses a multi-element antenna array, which is composed of multiple groups of antennas. The direction finding and positioning is performed by calculating the angles of arrival of signals from different antennas. It is not only bulky, inconvenient to carry and deploy, and has poor concealment, but also expensive and unsuitable for large-scale promotion and application. In the field of radio spectrum management, there is a commonly used positioning algorithm TDOA (Time Difference of Arrival), which collects the time when electromagnetic signals arrive at different monitoring terminals, and performs time-distance conversion for intersection positioning. The positioning error of this method is heavily dependent on the time synchronization accuracy of each monitoring terminal and the delay error of the electromagnetic signal reaching each monitoring terminal, and has the following disadvantages:

[0004] 1. Since the monitoring terminals are relatively independent devices, crystal oscillators are usually used as the clock source of the entire board, which makes the frequencies of the devices different, resulting in the inability to achieve accurate time synchronization between different nodes. If the time between different nodes is not synchronized, it is extremely difficult to accurately locate the signal source by receiving information such as the strength, time, and frequency of the signal.

[0005] 2. The propagation speed of electromagnetic signals is close to the speed of light. When using the TDOA algorithm for positioning, the delay error requirement is relatively high, usually at the nanosecond level. If the delay error of the signal reaching different monitoring devices is high, it will seriously affect the accuracy of signal positioning, and even make it impossible to perform intersection positioning.

[0006] Therefore, the present application provides a distributed electromagnetic monitoring system and method for abnormal signal direction finding and positioning to solve the above technical problems. Summary of the invention

[0007] The present application provides a distributed electromagnetic monitoring system and method for abnormal signal direction finding and positioning, aiming to solve the above-mentioned problems.

[0008] The present application provides a distributed electromagnetic monitoring system for abnormal signal direction finding and positioning, including:

[0009] Distributed electromagnetic spectrum monitoring subsystem and GNSS time synchronization system;

[0010] The distributed electromagnetic spectrum monitoring subsystem includes: a preset number of distributed antennas, a network switch and an operation terminal;

[0011] The preset number of distributed antennas are distributed at preset positions in the target detection area, collect the original electromagnetic signals, package them and send them to the operation terminal, wherein each distributed antenna includes a receiving antenna;

[0012] The network switch provides stable data transmission for the distributed antenna and the operation terminal;

[0013] The operation terminal is used to process and analyze the collected electromagnetic signals, configure the parameters of the entire system, and realize signal correlation analysis and direction finding and positioning;

[0014] The GNSS time synchronization system is used to implement the clock synchronization function of the distributed antenna through a preset clock training method.

[0015] The present application provides a distributed electromagnetic monitoring method for abnormal signal direction finding and positioning, comprising:

[0016] Distribute a preset number of distributed antennas at preset positions in the target detection area, collect raw electromagnetic signals, package them and send them to the operation terminal, and use the GNSS time synchronization system to achieve the clock synchronization function of the distributed antennas through a preset clock taming method, wherein each distributed antenna includes a receiving antenna;

[0017] Providing stable data transmission for the distributed antenna and the operation terminal through a network switch;

[0018] The collected electromagnetic signals are processed and analyzed through the operating terminal, and the parameters of the entire system are configured with instructions to achieve signal correlation analysis and direction finding and positioning.

[0019] The distributed antenna device used in the present invention has only one receiving antenna. Unlike the existing electromagnetic spectrum monitoring system that contains a multi-element antenna array, the system has a wider monitoring range, stronger anti-destruction ability, lower cost, and is convenient for large-scale promotion and use. The distributed electromagnetic monitoring method for abnormal signal direction finding and positioning provided by the present invention realizes local clock synchronization through the GNSS time synchronization system to improve positioning accuracy, and realizes the estimation error at the sampling point level through the time delay estimation technology of the timing acquisition and CAF (Cross Ambiguity Function) algorithm. When performing positioning, there is no need for synchronization between unknown nodes and reference nodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate one or more embodiments of this specification 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 recorded in this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0021] Figure 1 A schematic diagram of a distributed electromagnetic monitoring system for abnormal signal direction finding and positioning according to an embodiment of the invention;

[0022] Figure 2 This is an architecture diagram of a distributed electromagnetic monitoring system for abnormal signal direction finding and positioning according to an embodiment of the present invention;

[0023] Figure 3 A GNSS tractable state transition diagram according to an embodiment of the present invention;

[0024] Figure 4 This is a schematic diagram of the positioning and orientation algorithm principle of an embodiment of the present invention;

[0025] Figure 5 This is a working deployment diagram of a distributed electromagnetic monitoring system for abnormal signal direction finding and positioning according to an embodiment of the present invention;

[0026] Figure 6 The present invention is a flow chart of a distributed electromagnetic monitoring method for abnormal signal direction finding and positioning according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solutions in one or more embodiments of this specification, the following will be combined with the drawings in one or more embodiments of this specification to clearly and completely describe the technical solutions in one or more embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on one or more embodiments of this specification, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this document.

[0028] Glossary

[0029] GNSS System:

[0030] The GNSS system consists of: space segment (satellite), ground control segment and user segment (user equipment);

[0031] The space part (satellite), which is mainly composed of multiple navigation satellites, is one of the core components of the GNSS system. Navigation satellites continuously send out radio frequency signals, which contain time information and the satellite's own position information. The user equipment receives these signals and combines them with the auxiliary data of the ground control part to calculate the user's location. The number of satellites and orbital layout of different GNSS systems are different.

[0032] The ground control part is mainly responsible for processing satellite signals and generating navigation data. It includes several ground monitoring stations and data processing centers. The ground monitoring station is responsible for receiving satellite signals and monitoring the working status of the satellite, while the data processing center is responsible for generating navigation data and uploading it to the satellite. The ground control part ensures the accuracy and reliability of satellite signals, thereby ensuring the accuracy of user positioning.

[0033] The user part (user equipment) mainly refers to various GNSS receivers, including handheld, vehicle-mounted, marine and other types of receivers. These receivers receive satellite signals and process them to calculate the user's position, speed, time and other information. Modern GNSS receivers also have multiple functions, such as navigation, positioning, timing, etc., and are widely used in military, civil, scientific research and other fields.

[0034] System Example

[0035] According to an embodiment of the present invention, a distributed electromagnetic monitoring system for abnormal signal direction finding and positioning is provided. Figure 1 Schematic diagram of a distributed electromagnetic monitoring system for abnormal signal direction finding and positioning according to an embodiment of the invention. Figure 2 This is a diagram of the architecture of a distributed electromagnetic monitoring system for abnormal signal direction finding and positioning according to an embodiment of the present invention. Figure 1 and Figure 2 As shown, the distributed electromagnetic monitoring system for abnormal signal direction finding and positioning according to the embodiment of the present invention specifically includes:

[0036] Distributed electromagnetic spectrum monitoring subsystem 10 and GNSS time synchronization system 12;

[0037] The distributed electromagnetic spectrum monitoring subsystem includes: a preset number of distributed antennas 101, a network switch 102 and an operation terminal 103;

[0038] The preset number of distributed antennas 101 are distributed at preset positions in the target detection area, collect the original electromagnetic signals, package them and send them to the operation terminal, wherein each distributed antenna 101 includes a receiving antenna;

[0039] The distributed antenna 101 in the embodiment of the present invention includes: an FPGA development module, a multi-mode GNSS module, an AD board, and a single receiving antenna, which are respectively deployed at multiple locations in the target monitoring area to collect original electromagnetic signals.

[0040] The distributed antenna first collects the original electromagnetic signal through the receiving antenna and converts it into a digital signal, then packages the data and transmits it to the operation terminal through the optical fiber network and network switch. The transmitted data mainly includes: 1) electromagnetic signal data: electromagnetic signal data after encoding and compression processing, which are digitized electromagnetic signals collected from sensors; 2) acquisition device information: such as device identifier, location information, sampling rate, etc.; 3) timestamp information: contains accurate time information, recording the specific time point of data collection.

[0041] The network switch 102 provides stable data transmission for the distributed antenna 101 and the operation terminal 103;

[0042] The operation terminal 103 is used to process and analyze the collected electromagnetic signals, configure the parameters of the entire system, and implement signal correlation analysis and direction finding and positioning. The operation terminal 103 is specifically used for:

[0043] The delay estimation technology based on timing acquisition and CAF algorithm is used to reduce the delay estimation error of signals reaching multiple distributed antennas;

[0044] In one embodiment of the present invention, the operation terminal adopts a delay estimation technology based on timed acquisition and CAF algorithm, and ensures that multiple distributed antennas can synchronously collect electromagnetic signal data by continuously issuing instructions for collecting signals in full seconds through the operation terminal, and then uses the CAF algorithm to calculate the correlation between electromagnetic signals collected by multiple distributed antennas in the same time period to achieve the estimation error at the sampling point level and determine whether two signal data are from the same signal source. After the signal data is correlated, the TDOA (Time Difference of Arrive) algorithm is used for positioning based on high-precision delay estimation and clock synchronization, thereby achieving high-precision electromagnetic signal direction finding and positioning.

[0045] A preset distributed positioning and orientation algorithm is used to achieve directional positioning based on distributed antenna units.

[0046] The distributed antenna in the embodiment of the present invention is different from the existing multi-antenna array receiving unit. In order to realize distributed reception of signals, each distributed antenna device of the present invention contains only one receiving antenna, and the signal is located and direction-finded by delaying the reception of the same signal at different antennas. Specifically, the signal is first decomposed, and the correlation between the two signals is calculated based on the similarity relationship between the signals received by multiple antennas and the function of the relative displacement τ. Finally, when the TDOA algorithm is used, there is no need for synchronization between the unknown nodes and the reference nodes, but time synchronization between the reference nodes is required. More importantly, due to the distributed deployment, the system has a wider monitoring range and stronger anti-destruction capability, and does not require the use of a multi-antenna array, so the cost is low and it is convenient for large-scale promotion and use.

[0047] The distributed positioning and orientation algorithm in the embodiment of the present invention can not only realize directional positioning based on distributed antenna units, but also provide a basic idea for subsequent multi-source heterogeneous signal fusion.

[0048] Figure 4 This is a schematic diagram of the positioning and orientation algorithm principle of an embodiment of the present invention. Figure 4 It can be seen that the main working principle of the positioning and orientation algorithm of the embodiment of the present invention is as follows:

[0049] Step 1: Assume that there are different receiving antenna units A, B, C, etc. Each receiving unit contains only one receiving antenna, and their deployment is as follows: Figure 5 As shown in the figure, the signal is first decomposed, and then the CAF algorithm is used to perform feature correlation analysis on the signal.

[0050] Step 2: The correlation coefficient quantitatively describes the similarity or dependence between two signals. Therefore, the cross-correlation function is a measure of the similarity or dependence between two signals that are displaced from each other. It is a function of the relative displacement τ of the two signals. Therefore, it can not only be used to determine whether a signal exists, but also to measure the arrival time of the signals and the distance between them. Then the correlation between the two signals is calculated.

[0051] Step 3: After classifying the signal data, use the TDOA (Time Difference of Arrive) algorithm for positioning. When using the TDOA algorithm, there is no need for synchronization between the unknown node and the reference node, but time synchronization between the reference nodes is required. Compared with the TOA algorithm, the complexity of positioning calculation can be simplified. Its positioning principle is as follows Figure 4 As shown. A, B, C, and D are all reference nodes, and O is an unknown node. A and B are selected as a group, and C and D are selected as a group, respectively, as the two foci of the hyperbola. Point O is on one branch of the two hyperbolas, and the two hyperbolas intersect at one point, which is the position of point O, that is, the position of the abnormal signal.

[0052] The GNSS time synchronization system 12 is used to implement the clock synchronization function of the distributed antennas through a preset clock training method.

[0053] The GNSS time synchronization system 12 in the embodiment of the present invention is specifically used to calibrate the frequency of the local oscillator, that is, to synchronize the output second pulse of the local oscillator, to ensure that the local second signal is highly synchronized with the second signal output by the GNSS receiver, and to combine the long-term stability of the GNSS receiver output signal with the short-term stability of the constant temperature crystal oscillator to achieve synchronization between the local time and the standard time. At the same time, the GNSS serial port outputs the Universal Time Coordinated (UTC) time information corresponding to the second pulse. After extracting the precise time information, the local clock is synchronized with the second pulse, thereby achieving high-precision unification of the local time and the UTC time, and realizing the function of clock taming, such as Figure 3 The GNSS tractable state transition diagram of the embodiment of the present invention is shown. Figure 3 It can be seen that the GNSS clock training method in the embodiment of the present invention specifically includes:

[0054] The present invention uses the clock error historical data of the local clock to build a model to obtain the characteristic parameters of the local clock, and then calculates the clock control adjustment amount according to the characteristic parameters to adjust the local clock accordingly. The clock error model of the chip-scale atomic clock (CSAC) can be expressed as follows:

[0055]

[0056] Among them, t 0 is the starting time of clock difference measurement; a 0 is the initial phase deviation between CSAC and the reference signal; a 1 is the initial frequency deviation between CSAC and the reference signal; a 2 is the frequency drift rate of the CSAC itself, also known as the aging rate; ∈(t) is the random error caused by frequency noise. By using the least squares method, a can be solved 0 、a 1 and a 2 result.

[0057] The clock adjustment methods are divided into phase modulation and frequency modulation. Phase modulation can make the local clock phase jump directly to the preset phase value, but frequent phase modulation will cause the phase discontinuity and frequency mutation of the clock output signal, reducing the stability of the local clock. According to the characteristics of phase modulation and frequency modulation, the present invention selects to adjust the phase of CSAC when the clock difference between CSAC and the receiver is large, so that the clock difference converges quickly; and adopts frequency adjustment when the clock difference is small, so that the clock difference converges slowly. Through the formula It can be seen that the final result of frequency modulation is to adjust the phase of the CSAC output signal, but this method will not destroy the continuity of the signal. is the relative frequency deviation, Δτ is the clock frequency of CSAC in the time interval T 0 Difference change.

[0058] Since there is a large phase deviation between CSAC and the receiver at the initial moment, it is necessary to phase adjust CSAC to complete coarse phase synchronization. After coarse phase synchronization, the main factor affecting the CSAC clock error is frequency offset, so the adjustment method used in subsequent steps is frequency adjustment. At the same time, when CSAC starts working, there is a frequency offset that drives its clock error with the GNSS system time to change toward zero, and the offset needs to be eliminated by frequency modulation. After eliminating the above two initial deviations, the global navigation system specification oscillator (GNSSDO) has entered a relatively stable operating state, which is called phase fine synchronization, and subsequent clock driving operations will always be performed in this state. Among them, the ping-pong algorithm is used to drive the CSAC in the phase fine synchronization state to control the clock error between the CSAC and the GNSS system time within a certain range.

[0059] When the GNSS receiver loses lock, it will output an abnormal 1PPS signal, which will affect the clock taming process. To address this issue, in the phase fine synchronization state, the current clock error measurement value will be used to determine whether the receiver has lost lock. If the current clock error is detected to be a singular value, the receiver is determined to have lost lock, and the receiver is restarted. After waiting for 35 seconds, it will re-enter the phase fine synchronization state and resume the clock taming operation.

[0060] In order to reduce the cost of the monitoring system while ensuring the accuracy of direction finding and positioning, the present invention designs a distributed electromagnetic spectrum monitoring system, which consists of three parts: distributed antennas, network switches and operation terminals. Figure 2 As shown, the distributed antenna is a signal monitoring device, which consists of an FPGA development module, a multi-mode GNSS module, an AD board, a single receiving antenna, etc., and is deployed at multiple locations in the target monitoring area to collect original electromagnetic signals; the network switch realizes high-speed and stable data transmission between the distributed antenna and the operation terminal; the operation terminal is used to process and analyze the collected electromagnetic signal data and to configure the parameters of the entire system.

[0061] In order to realize the accurate positioning of abnormal signals, the present invention includes three technologies: a time synchronization system based on GNSS, a time delay estimation technology based on timing acquisition and CAF algorithm, and a positioning and orientation algorithm.

[0062] The GNSS-based time synchronization system combines the long-term stability of the GNSS receiver output signal with the short-term stability of the constant temperature crystal oscillator, and achieves synchronization between local time and standard time in two steps, from coarse adjustment to fine adjustment. After extracting the precise time information, it synchronizes the local clock with the second pulse, thereby achieving high-precision unification of local time and UTC time and realizing the function of clock taming.

[0063] A delay estimation technology based on timed acquisition and CAF algorithm. The operating terminal continuously issues instructions for collecting signals in whole seconds to ensure that multiple distributed antennas can collect electromagnetic signal data at the same time, realize time alignment of different antennas, and then use the CAF algorithm to calculate the correlation of electromagnetic signals received after antenna alignment, realizing the estimation error at the sampling point level, that is, ns level.

[0064] The abnormal signal positioning and orientation method based on the above-mentioned time synchronization and high-precision delay estimation includes: designing different receiving antenna units A, B, C, etc., first decomposing the signal, and then performing feature correlation analysis on the signal. According to the similarity relationship between the two signals and the function of the relative displacement τ, the correlation between the two signals is calculated, and a threshold is set to determine whether the two signal data come from the same abnormal signal source. According to the signal classification information, the TDOA (Time Difference of Arrive) algorithm is used for positioning. When using the TDOA algorithm, synchronization between the unknown node and the reference node is not required, but time synchronization between the reference nodes is required.

[0065] The embodiments of the present invention have the following beneficial effects:

[0066] The distributed antenna device used in the present invention has only one receiving antenna. Unlike the existing electromagnetic spectrum monitoring system that contains a multi-element antenna array, the system has a wider monitoring range, stronger anti-destruction capability, and lower cost, which is convenient for large-scale promotion and use. The distributed electromagnetic monitoring method for abnormal signal direction finding and positioning provided by the present invention realizes local clock synchronization through the GNSS time synchronization system to improve positioning accuracy, and realizes the estimation error at the sampling point level through the time delay estimation technology of the timing acquisition and CAF algorithm, and does not require synchronization between unknown nodes and reference nodes when performing positioning.

[0067] Method Embodiment

[0068] According to an embodiment of the present invention, a distributed electromagnetic monitoring method for abnormal signal direction finding and positioning is provided. Figure 6 Flow chart of a distributed electromagnetic monitoring method for abnormal signal direction finding and positioning according to an embodiment of the present invention. Figure 6 As shown, the distributed electromagnetic monitoring method for abnormal signal direction finding and positioning according to the embodiment of the present invention specifically includes:

[0069] S1. Distribute a preset number of distributed antennas at preset positions in the target detection area, collect original electromagnetic signals, package them and send them to the operation terminal, and use the GNSS time synchronization system to achieve the clock synchronization function of the distributed antennas through a preset clock taming method, wherein each distributed antenna includes a receiving antenna;

[0070] S2. Providing stable data transmission for the distributed antenna and the operation terminal through a network switch;

[0071] S3. Process and analyze the collected electromagnetic signals through the operating terminal, configure the parameters of the entire system, and realize signal correlation analysis and direction finding and positioning.

[0072] The embodiments of the present method correspond one-to-one to the above-mentioned system embodiments. For specific implementation steps, please refer to the contents of the above-mentioned system embodiments and will not be repeated here.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A distributed electromagnetic monitoring system for abnormal signal direction finding and positioning, characterized in that include: Distributed electromagnetic spectrum monitoring subsystem and GNSS time synchronization system; The distributed electromagnetic spectrum monitoring subsystem includes: a preset number of distributed antennas, a network switch and an operation terminal; The preset number of distributed antennas are distributed at preset positions in the target detection area, collect the original electromagnetic signals, package them and send them to the operation terminal, wherein each distributed antenna includes a receiving antenna; The network switch provides stable data transmission for the distributed antenna and the operation terminal; The operation terminal is used to process and analyze the collected electromagnetic signals, configure the parameters of the entire system, and realize signal correlation analysis and direction finding and positioning; The GNSS time synchronization system is used to implement the clock synchronization function of the distributed antenna through a preset clock training method.

2. The system according to claim 1, characterized in that The data sent by the distributed antenna to the operation terminal includes: The electromagnetic signal data includes: electromagnetic signal data after encoding and compression processing; The collected device information includes: device identifier, location information, and sampling rate; Timestamp information includes: accurate time information and the specific time point when the data was collected.

3. The system according to claim 1, characterized in that The operation terminal is specifically used for: The delay estimation technology based on timing acquisition and CAF algorithm is used to reduce the delay estimation error of signals reaching multiple distributed antennas; A preset distributed positioning and orientation algorithm is used to achieve directional positioning based on distributed antenna units.

4. The system according to claim 3, characterized in that The delay estimation technology based on timing acquisition and CAF algorithm adopted by the operation terminal specifically includes: The operating terminal continuously issues instructions for collecting signals every second to ensure that the preset number of distributed antennas synchronously collect the original electromagnetic signals, and then uses the CAF algorithm to calculate the correlation between the electromagnetic signals collected by the preset number of distributed antennas in the same time period to achieve the estimation error at the sampling point level.

5. The system according to claim 3, characterized in that The distributed positioning and orientation algorithm adopted by the operation terminal specifically includes: Decompose the received electromagnetic signal to perform feature correlation analysis and obtain the similarity relationship between the two signals; The correlation between the two signals is calculated based on the similarity relationship and mutual function between the two signals, and the correlation is determined by a preset threshold to determine whether the two signal data are derived from the same abnormal signal source, thereby obtaining signal classification information; Positioning is performed using the TDOA algorithm according to the signal classification information.

6. The system according to claim 1, characterized in that The GNSS time synchronization system is specifically used to: combine the long-term stability of the GNSS receiver output signal with the short-term stability of the constant temperature crystal oscillator of the distributed antenna to achieve synchronization of local time with standard time, and at the same time, the GNSS receiver serial port outputs the world coordinated time moment information corresponding to the second pulse, and after extracting the precise time information, synchronizes the local clock together with the second pulse, thereby achieving the unification of local time with the world coordinated time and realizing the clock synchronization function of the distributed antenna.

7. The system according to claim 6, characterized in that The preset clock taming method adopted by the GNSS time synchronization system specifically includes: The clock error model of the chip-level atomic clock is established using the clock error history data of the local clock; Performing phase adjustment on the clock error model at the initial moment to complete coarse synchronization; In the working state, the frequency deviation is eliminated by frequency modulation to enter the phase precise synchronization state.

8. The system according to claim 7, characterized in that The clock error model of the chip-level atomic clock is obtained by formula 1: Among them, t0 is the starting time of the clock error measurement, a0 is the initial phase deviation between the chip-level atomic clock and the reference signal, a1 is the initial frequency deviation between the chip-level atomic clock and the reference signal, a2 is the frequency drift rate of the chip-level atomic clock itself, ∈(t) is the random error caused by frequency noise, and the results of a0, a1 and a2 are calculated by the least squares method.

9. The system according to claim 7, characterized in that The preset clock taming method adopted by the GNSS time synchronization system further includes: in the phase fine synchronization state, judging whether the GNSS receiver is lost by the current clock difference measurement value; if the current clock difference is detected to be a singular value, the GNSS determines that the receiver is lost, restarts the receiver, re-enters the phase fine synchronization state after waiting for a specific time, and resumes the clock taming operation.

10. A distributed electromagnetic monitoring method for abnormal signal direction finding and positioning, characterized in that: include: Distribute a preset number of distributed antennas at preset positions in the target detection area, collect raw electromagnetic signals, package them and send them to the operation terminal, and use the GNSS time synchronization system to achieve the clock synchronization function of the distributed antennas through a preset clock taming method, wherein each distributed antenna includes a receiving antenna; Providing stable data transmission for the distributed antenna and the operation terminal through a network switch; The collected electromagnetic signals are processed and analyzed through the operating terminal, and the parameters of the entire system are configured with instructions to achieve signal correlation analysis and direction finding and positioning.

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