A satellite navigation on-orbit autonomous programming anti-interference method and system

Abstract

The present invention relates to the field of satellite navigation technology, and specifically discloses a satellite navigation on-orbit autonomous programming anti-interference method and system, including obtaining a mixed signal, the mixed signal including a navigation satellite broadcast signal and a narrowband interference signal; constructing a multi-band signal library; passing the mixed signal through a bandpass filter, judging whether the bandpass filter can restore the navigation satellite broadcast signal, if the navigation satellite broadcast signal can be restored, broadcasting the navigation satellite broadcast signal to the user; if the navigation satellite broadcast signal cannot be restored, calling the multi-band signal library based on on-orbit autonomous programming, autonomously selecting the frequency point with the largest difference from the narrowband interference signal frequency point in the multi-band signal library as the navigation satellite broadcast signal, and broadcasting the navigation satellite broadcast signal to the user. The method intelligently adjusts the time-frequency characteristics of the navigation signal from the multi-band signal library according to the real-time interference situation, thereby avoiding the interference signal and ensuring the normal operation of the GNSS system.

Description

Technical Field

[0001] The present invention relates to the field of satellite navigation technology, and in particular to an on-orbit autonomous programming anti-interference method and system for satellite navigation. Background Art

[0002] The positioning, navigation and timing functions of the Global Navigation Satellite System (GNSS) serve the world and play an important role in various fields. This makes the security of the GNSS system particularly important and also makes it a possible target of attack. For example, GNSS signals are vulnerable to various interference attacks, including suppression interference such as narrowband interference and broadband interference, as well as deceptive interference such as generative interference and forwarding interference. These interferences may cause the GNSS system to provide inaccurate or tampered navigation information, threatening the continuity, integrity, and reliability of the GNSS system and directly affecting the service performance of the entire system, posing a potential threat to users.

[0003] On-orbit programming technology has been used to solve various problems such as rapid on-orbit data processing, redefining satellite functions, rapid data uploading, and reconstruction of signal spectrum resources. For example, Qiao Kai et al. published an analysis of the development trend of on-board intelligent information processing technology and some thoughts in Space Return and Remote Sensing [J], which used on-orbit programming technology to achieve on-board data compression, intelligent information processing, and other tasks, effectively reducing the downlink data rate. Zhang Heng et al. published a design and implementation of DSP on-orbit programming based on 1553B [J] in Guidance and Fuze, which used a digital signal processor to realize satellite function update, upgrade, and reconstruction, greatly improving the utilization efficiency of the satellite. Yang et al. published a paper on Detection of Interference Constraint Violation Based on Heterogeneous Data Fusion in Satellite-Earth on IEEE Access. IntegratedNetworks designs a spatial-temporal spectrum sharing strategy, taking into account the distance between primary and secondary users, and calculating the idle frequency band set of secondary users to achieve heterogeneous spectrum resource sharing. Existing work has insufficient development of on-orbit programming technology for spectrum resources, and more innovations are made in data compression, data processing, software-defined satellites, etc. Although Yang et al. designed a strategy for sharing heterogeneous spectrum resources, they utilized it from the perspective of idle spectrum resources, and did not consider how to deal with co-frequency interference when the current signal is subject to co-frequency interference. Summary of the invention

[0004] In view of the above problems, an object of the present invention is to provide a satellite navigation on-orbit autonomous programming anti-interference method, which, through autonomous on-orbit programming, intelligently adjusts the time-frequency characteristics of the navigation signal from a preset multi-band signal library according to the real-time interference situation, thereby avoiding interference signals and ensuring the normal operation of the GNSS system, thereby improving the system's adaptability to signal interference caused by factors such as electromagnetic interference, and further enhancing the robustness of the system.

[0005] The second object of the present invention is to provide a satellite navigation on-orbit autonomous programming anti-interference system.

[0006] The first technical solution adopted by the present invention is: a satellite navigation on-orbit autonomous programming anti-interference method, comprising the following steps:

[0007] S100: Acquire a mixed signal, where the mixed signal includes a navigation satellite broadcast signal and a narrowband interference signal;

[0008] S200: Build a multi-band signal library;

[0009] S300: Pass the mixed signal through a bandpass filter to determine whether the bandpass filter can restore the navigation satellite broadcast signal. If so, the navigation satellite broadcast signal is broadcast to the user. If not, call a multi-band signal library based on on-orbit autonomous programming, and autonomously select a frequency point with the largest difference from the narrowband interference signal frequency point in the multi-band signal library as the navigation satellite broadcast signal, and broadcast the navigation satellite broadcast signal to the user.

[0010] Preferably, the step S100 comprises: directly superimposing the navigation satellite broadcast signal spectrum and the narrowband interference signal spectrum to obtain a mixed signal.

[0011] Preferably, the multi-band signal library includes signal bands of GPS, GLONASS, Galileo, BDS and signal bands of satellite communications.

[0012] Preferably, the bandpass filter in step S300 is a Butterworth filter.

[0013] Preferably, judging whether the bandpass filter can restore the navigation satellite broadcast signal in step S300 includes:

[0014] Determine whether the frequency spectrum of the signal after passing through the bandpass filter is the same as the frequency spectrum of the navigation satellite broadcast signal. If they are the same, it is determined that the bandpass filter can restore the navigation satellite broadcast signal; if they are not the same, it is determined that the bandpass filter cannot restore the navigation satellite broadcast signal.

[0015] Preferably, step S300 also includes: determining whether the frequency spectra of the filtered signal and the signal broadcast by the navigation satellite are the same by calculating the residual value of the filtered signal and the signal broadcast by the navigation satellite; if the residual value is less than a set threshold, determining that the frequency spectra of the filtered signal and the signal broadcast by the navigation satellite are the same; if the residual value is greater than or equal to the set threshold, determining that the frequency spectra of the filtered signal and the signal broadcast by the navigation satellite are not the same.

[0016] Preferably, the residual value is calculated by the following formula:

[0017] ;

[0018] In the formula, RMSE is the residual value between the filtered signal and the signal broadcast by the navigation satellite; The signal after filtering is i The spectrum value at the time; Broadcasting signals for navigation satellites i The spectrum value at the moment; n is the time step.

[0019] Preferably, the step S300 includes:

[0020] When the current navigation satellite signal is interfered with, the on-orbit autonomous programming selects the frequency point with the largest difference from the current navigation satellite signal broadcast frequency point in the multi-band signal library, and determines whether the frequency point with the largest difference from the current navigation satellite signal broadcast frequency point is the frequency point called last time. If not, it will be used as the frequency point for the next call.

[0021] Preferably, the step S300 further includes:

[0022] If the current navigation satellite signal broadcast frequency is at a low frequency, after being interfered, the navigation satellite signal will jump from the current frequency to the highest frequency in the multi-band signal library to defend against narrowband interference; at this time, the current navigation satellite signal broadcast frequency is high frequency. If it is detected again that the current navigation satellite signal is attacked, the on-orbit autonomous programming is used to change the signal frequency from high frequency to medium frequency; if it is still attacked after changing to medium frequency, the on-orbit autonomous programming is continued to be used to call the multi-band signal library to send the minimum value of the remaining signal frequency sequence to the satellite as a new signal broadcast, and the signal becomes low frequency at this time; if it is attacked again, it will change from low frequency to medium frequency, and then from medium frequency to high frequency in turn, and this cycle will be repeated;

[0023] The intermediate frequency is the median of the remaining signal frequency sequence after removing the signal frequency points that have been called in the multi-band signal library.

[0024] The second technical solution adopted by the present invention is: a satellite navigation on-orbit autonomous programming anti-interference system, including a signal acquisition module, a signal library construction module and an anti-interference module;

[0025] The signal acquisition module is used to acquire a mixed signal, wherein the mixed signal includes a navigation satellite broadcast signal and a narrowband interference signal;

[0026] The signal library construction module is used to construct a multi-band signal library;

[0027] The anti-interference module is used to pass the mixed signal through a bandpass filter to determine whether the bandpass filter can restore the navigation satellite broadcast signal. If the navigation satellite broadcast signal can be restored, the navigation satellite broadcast signal is broadcast to the user; if the navigation satellite broadcast signal cannot be restored, a multi-band signal library is called based on on-orbit autonomous programming, and a frequency point with the largest difference from the narrowband interference signal frequency point is autonomously selected in the multi-band signal library as the navigation satellite broadcast signal, and the navigation satellite broadcast signal is broadcast to the user.

[0028] Beneficial effects of the above technical solution:

[0029] (1) The present invention aims at narrowband interference, which is more likely to occur in the space segment. When the satellite in orbit is suppressed by narrowband interference, it can adjust the time-frequency characteristics of the navigation signal from a preset multi-band signal library intelligently according to the real-time interference situation through autonomous programming in orbit, thereby avoiding the interference signal and ensuring the normal operation of the GNSS system, thereby improving the system's adaptability to signal interference caused by factors such as electromagnetic interference and further enhancing the robustness of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic flow chart of an on-orbit autonomous programming anti-interference method for satellite navigation provided by an embodiment of the present invention;

[0031] Figure 2 A schematic diagram of a frequency variation rule for calling a multi-band signal library provided by an embodiment of the present invention;

[0032] Figure 3 A schematic structural diagram of an on-orbit autonomous programming anti-interference system for satellite navigation provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The following detailed description of the embodiments of the present invention is further described in detail in conjunction with the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to exemplarily illustrate the principles of the present invention, but cannot be used to limit the scope of the present invention, that is, the present invention is not limited to the preferred embodiments described, and the scope of the present invention is defined by the claims.

[0034] In the description of the present invention, it should be noted that, unless otherwise specified, “plurality” means two or more than two; the terms “first”, “second”, etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance; for ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0035] Embodiment 1

[0036] like Figure 1 As shown, an embodiment of the present invention provides a satellite navigation on-orbit autonomous programming anti-interference method, comprising the following steps:

[0037] S100: Acquire a mixed signal, where the mixed signal includes a navigation satellite broadcast signal and a narrowband interference signal;

[0038] The navigation satellite broadcast signal spectrum and the narrowband interference signal spectrum are directly superimposed to obtain a mixed signal;

[0039] Narrowband interference is implemented towards the satellites in orbit, so that the signal broadcast by the navigation satellite is mixed with the interference signal to form a mixed signal, that is, the mixed signal includes the signal broadcast by the navigation satellite and the narrowband interference signal.

[0040] S200: Build a multi-band signal library;

[0041] Taking into account that the user end can receive signals of the four major satellite navigation systems of GNSS, the present invention adds the signal frequency bands of the four major GNSS, namely GPS, GLONASS, Galileo and BDS (Beidou Satellite Navigation System), to the multi-band signal library; in addition, based on the existing thought system of communication and navigation integration, the signal frequency bands used by communication satellites can be used in emergency situations, and users can also receive communication satellite signals, so the signal frequency bands of satellite communications are also added to the multi-band signal library to form a multi-band signal library as shown in Table 1, so that the satellite can continue to broadcast signals to users by changing the signal frequency through autonomous in-orbit programming after being interfered; the multi-band signal library is preset on the navigation payload of the satellite; Table 1 shows the signal frequency bands and corresponding frequency values ​​of some preset multi-band signal libraries.

[0042] Table 1 Preset multi-band signal library

[0043]

[0044] The present invention constructs a multi-band signal library to maximize the range of navigation signal selection while avoiding mutual interference with other electronic devices.

[0045] S300: passing the mixed signal through a bandpass filter to determine whether the bandpass filter can restore the navigation satellite broadcast signal; if so, broadcasting the navigation satellite broadcast signal to the user; if not, calling a multi-band signal library based on on-orbit autonomous programming, autonomously selecting a frequency point with the largest difference from the frequency point of the narrowband interference signal in the multi-band signal library as the navigation satellite broadcast signal, and broadcasting the navigation satellite broadcast signal to the user;

[0046] The mixed signal is passed through a bandpass filter, such as a Butterworth filter; after the mixed signal passes through the bandpass filter, it is determined whether the spectrum of the filtered signal is the same as the spectrum of the broadcast signal of the navigation satellite; if they are the same, it is determined that the bandpass filter can restore the navigation satellite broadcast signal; if they are not the same, it is determined that the bandpass filter cannot restore the navigation satellite broadcast signal; the residual of the filtered signal and the navigation satellite broadcast signal can be calculated by the following formula for comparative analysis (i.e., to determine whether they are the same):

[0047] ;

[0048] In the formula, RMSE is the residual value between the filtered signal and the navigation satellite broadcast signal. When the residual value is <0.1, it is considered that the spectrum of the filtered signal and the navigation satellite broadcast signal is the same, that is, it is considered that the navigation satellite broadcast signal can be recovered; The signal after filtering is i The spectrum value at the time; Broadcasting signals for navigation satellites i The spectrum value at the moment; n is the time step.

[0049] If the navigation satellite broadcast signal can be restored, it will be broadcast to the user; if the navigation satellite broadcast signal cannot be restored, the frequency point with the largest difference from the narrowband interference signal frequency point will be autonomously selected from the preset multi-band signal library as the navigation satellite broadcast signal, thereby avoiding the implementation of narrowband interference.

[0050] When the multi-band signal library is called by autonomous programming on-orbit, in principle, the frequency with the largest difference from the interfered signal frequency is selected as the new broadcast signal. However, in actual scenarios, the narrowband interference signal may also change dynamically. After the navigation satellite is autonomously programmed to reselect the frequency, the narrowband interference signal will adjust the frequency according to the updated broadcast signal frequency and interfere again. In view of the situation where the interference frequency point of narrowband interference dynamically changes, the present invention designs an on-orbit autonomous programming anti-interference mechanism to dynamically avoid interference signals.

[0051] The rules for calling the multi-band signal library based on on-orbit autonomous programming (i.e. calling the multi-band signal library based on on-orbit autonomous programming) are:

[0052] When the current navigation satellite broadcast signal is interfered, the on-orbit autonomous programming selects the frequency point with the largest difference from the current navigation satellite broadcast signal frequency point in the multi-band signal library, and determines whether the frequency point with the largest difference from the current navigation satellite broadcast signal frequency point is the frequency point called last time. If not, it is used as the frequency point for the next call. The pseudo code is as follows:

[0053] ;

[0054] in, is the frequency of the multi-band signal library, , Select the frequency for the current moment, The frequency selected for the last call, Select a frequency for the next call.

[0055] like Figure 2 As shown in the figure, the on-orbit autonomously programmed anti-interference mechanism includes: assuming that the current navigation satellite broadcast signal frequency is at "low frequency", after being interfered with, the navigation satellite broadcast signal jumps from the current frequency to the highest frequency in the multi-band signal library to defend against narrowband interference. Such a jump with the maximum amplitude can ensure that the jump can achieve better anti-interference effect and prolong the time of interference signal detection, preventing multiple jumps from causing instability in navigation services.

[0056] The current navigation satellite signal broadcast frequency belongs to "high frequency". If it is detected again that the current navigation satellite signal is under attack, the on-orbit autonomous programming is used to change the navigation satellite signal broadcast frequency from "high frequency" to "medium frequency". The "medium frequency" at this time can be defined as: the median of the signal frequency sequence after removing the signal frequency points that have been called in the preset multi-band signal library (if the total number is an even number, the frequency value corresponding to the value of the total number divided by two is selected); if it is still attacked after changing to the medium frequency, the multi-band signal library is still called by autonomous programming to send the minimum value of the remaining signal frequency sequence to the satellite as a new signal broadcast. At this time, the signal becomes "low frequency"; then, according to the above definition of "medium frequency", it can change from "low frequency" to "medium frequency" and then from "medium frequency" to "high frequency", and this is a cycle.

[0057] The present invention is based on a multi-band signal library and an on-orbit programming strategy for autonomously selecting anti-interference frequencies to ensure that the selected frequencies can avoid interference frequencies to the greatest extent.

[0058] Embodiment 2

[0059] like Figure 3 As shown, an embodiment of the present invention provides a satellite navigation on-orbit autonomous programming anti-interference system, including a signal acquisition module, a signal library construction module and an anti-interference module;

[0060] The signal acquisition module is used to acquire a mixed signal, wherein the mixed signal includes a navigation satellite broadcast signal and a narrowband interference signal;

[0061] The signal library construction module is used to construct a multi-band signal library;

[0062] The anti-interference module is used to pass the mixed signal through a bandpass filter to determine whether the bandpass filter can restore the navigation satellite broadcast signal. If the navigation satellite broadcast signal can be restored, the navigation satellite broadcast signal is broadcast to the user; if the navigation satellite broadcast signal cannot be restored, a multi-band signal library is called based on on-orbit autonomous programming, and a frequency point with the largest difference from the narrowband interference signal frequency point is autonomously selected in the multi-band signal library as the navigation satellite broadcast signal, and the navigation satellite broadcast signal is broadcast to the user.

[0063] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed in the embodiments of the present invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0064] In the embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0065] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0066] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0067] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard disks, ROM, RAM, magnetic disks, or optical disks.

[0068] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A satellite navigation on-orbit autonomous programming anti-interference method, characterized in that: The following steps are involved: S100: Acquire a mixed signal, where the mixed signal includes a navigation satellite broadcast signal and a narrowband interference signal; S200: Build a multi-band signal library; S300: passing the mixed signal through a bandpass filter to determine whether the bandpass filter can restore the navigation satellite broadcast signal; if the navigation satellite broadcast signal can be restored, broadcasting the navigation satellite broadcast signal to the user; If the navigation satellite broadcast signal cannot be restored, the multi-band signal library is called based on the on-orbit autonomous programming, and a frequency point with the largest difference from the narrowband interference signal frequency point is autonomously selected from the multi-band signal library as the navigation satellite broadcast signal, and the navigation satellite broadcast signal is broadcast to the user; Wherein, the step S300 includes: After the current navigation satellite broadcast signal is interfered, the on-orbit autonomous programming selects the frequency point with the largest difference from the current navigation satellite broadcast signal frequency point in the multi-band signal library, and determines whether the frequency point with the largest difference from the current navigation satellite broadcast signal frequency point is the frequency point called last time, and if not, uses it as the frequency point called next time; If the current navigation satellite signal broadcast frequency is at a low frequency, after being interfered, the navigation satellite signal will jump from the current frequency to the highest frequency in the multi-band signal library to defend against narrowband interference; at this time, the current navigation satellite signal broadcast frequency is high frequency. If it is detected again that the current navigation satellite signal is attacked, the on-orbit autonomous programming is used to change the signal frequency from high frequency to medium frequency; if it is still attacked after changing to medium frequency, the on-orbit autonomous programming is continued to be used to call the multi-band signal library to send the minimum value of the remaining signal frequency sequence to the satellite as a new signal broadcast, and the signal becomes low frequency at this time; if it is attacked again, it will change from low frequency to medium frequency, and then from medium frequency to high frequency in turn, and this cycle will be repeated; The intermediate frequency is the median of the remaining signal frequency sequence after removing the signal frequency points that have been called in the multi-band signal library.

2. The satellite navigation on-orbit autonomous programming anti-interference method according to claim 1 is characterized in that: The step S100 includes: directly superimposing the navigation satellite broadcast signal spectrum and the narrowband interference signal spectrum to obtain a mixed signal.

3. The satellite navigation on-orbit autonomous programming anti-interference method according to claim 1 is characterized in that: The multi-band signal library includes signal bands of GPS, GLONASS, Galileo, BDS and signal bands of satellite communications.

4. The satellite navigation on-orbit autonomous programming anti-interference method according to claim 1, characterized in that: The bandpass filter in step S300 is a Butterworth filter.

5. The satellite navigation on-orbit autonomous programming anti-interference method according to claim 1, characterized in that: The step S300 of determining whether the bandpass filter can restore the navigation satellite broadcast signal includes: Determine whether the frequency spectrum of the signal after passing through the bandpass filter is the same as the frequency spectrum of the navigation satellite broadcast signal. If they are the same, it is determined that the bandpass filter can restore the navigation satellite broadcast signal; if they are not the same, it is determined that the bandpass filter cannot restore the navigation satellite broadcast signal.

6. The satellite navigation on-orbit autonomous programming anti-interference method according to claim 5, characterized in that: The step S300 also includes: determining whether the frequency spectra of the filtered signal and the signal broadcast by the navigation satellite are the same by calculating the residual value of the filtered signal and the signal broadcast by the navigation satellite; if the residual value is less than a set threshold, determining that the frequency spectra of the filtered signal and the signal broadcast by the navigation satellite are the same; if the residual value is greater than or equal to the set threshold, determining that the frequency spectra of the filtered signal and the signal broadcast by the navigation satellite are not the same.

7. The satellite navigation on-orbit autonomous programming anti-interference method according to claim 6, characterized in that: The residual value is calculated by the following formula: Where, RMSE is the residual value between the filtered signal and the navigation satellite broadcast signal; f′ i is the spectrum value of the filtered signal at time i; f i is the spectrum value of the navigation satellite broadcast signal at time i; n is the time step.

8. A satellite navigation on-orbit autonomous programming anti-interference system, characterized in that: It includes signal acquisition module, signal library construction module and anti-interference module; The signal acquisition module is used to acquire a mixed signal, wherein the mixed signal includes a navigation satellite broadcast signal and a narrowband interference signal; The signal library construction module is used to construct a multi-band signal library; The anti-interference module is used to pass the mixed signal through a bandpass filter to determine whether the bandpass filter can restore the navigation satellite broadcast signal, and if the navigation satellite broadcast signal can be restored, broadcast the navigation satellite broadcast signal to the user; If the navigation satellite broadcast signal cannot be restored, the multi-band signal library is called based on the on-orbit autonomous programming, and the frequency point with the largest difference from the narrowband interference signal frequency point is autonomously selected from the multi-band signal library as the navigation satellite broadcast signal, and the navigation satellite broadcast signal is broadcast to the user; The anti-interference module is used to perform the following operations: After the current navigation satellite broadcast signal is interfered, the on-orbit autonomous programming selects the frequency point with the largest difference from the current navigation satellite broadcast signal frequency point in the multi-band signal library, and determines whether the frequency point with the largest difference from the current navigation satellite broadcast signal frequency point is the frequency point called last time, and if not, uses it as the frequency point called next time; If the current navigation satellite signal broadcast frequency is at a low frequency, after being interfered, the navigation satellite signal will jump from the current frequency to the highest frequency in the multi-band signal library to defend against narrowband interference; at this time, the current navigation satellite signal broadcast frequency is high frequency. If it is detected again that the current navigation satellite signal is attacked, the on-orbit autonomous programming is used to change the signal frequency from high frequency to medium frequency; if it is still attacked after changing to medium frequency, the on-orbit autonomous programming is continued to be used to call the multi-band signal library to send the minimum value of the remaining signal frequency sequence to the satellite as a new signal broadcast, and the signal becomes low frequency at this time; if it is attacked again, it will change from low frequency to medium frequency, and then from medium frequency to high frequency in turn, and this cycle will be repeated; The intermediate frequency is the median of the remaining signal frequency sequence after removing the signal frequency points that have been called in the multi-band signal library.

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