Simulated on-orbit test method and system for low-orbit satellite time-frequency equipment

Abstract

The invention belongs to the technical field of satellites. The invention provides a simulated in-orbit test method and system for low-orbit satellite time-frequency equipment. According to the embodiment of the invention, a reference atomic clock provides a reference basis for a GNSS navigation signal simulator, a time interval counter and a phase noise analyzer; the GNSS navigation signal simulator provides a Beidou / GNSS analog signal and an SSR (Simple Sequence Repeat) correction number for the satellite time frequency equipment; the satellite time frequency device completes real-time precise orbit determination and clock correction calculation of the low-orbit satellite by using the received Beidou / GNSS analog signal and the SSR correction number, and controls and regulates a built-in local atomic clock according to a calculated clock correction sequence; and respectively carrying out time precision and frequency stability test and analysis on the second 1PPS signal and the second 10MHz signal through a time interval counter and a phase noise analyzer. The low-orbit satellite in-orbit test can be simulated in the initial stage, and real-time calculation of in-orbit satellite test data can be realized.

Description

Technical Field

[0001] The disclosed embodiments relate to the field of satellite technology, and in particular to a method and system for simulating on-orbit testing of low-orbit satellite time and frequency equipment. Background Art

[0002] In recent years, with the rapid development of low-orbit satellite Internet, the demand for the number of low-orbit satellites has exploded, and micro-small, low-cost satellites have become the current development trend. Satellite time and frequency equipment is the core element of low-orbit Internet, and is the basis for generating a unified time and frequency benchmark, achieving high-precision time synchronization and autonomous timekeeping. Facing massive low-orbit satellite nodes, how to build micro-small time and frequency equipment with both high performance and low SWaP-C (volume, weight, power consumption and cost) is the key to the construction of low-orbit satellite Internet.

[0003] The onboard BeiDou / GNSS (Global Navigation Satellite System) time transfer and clock control technology has the characteristics of real-time, global coverage and high precision, and is an important means to improve the performance of satellite time and frequency equipment. The comprehensive on-orbit environmental evaluation of low-orbit satellite time and frequency equipment is an indispensable part of verifying the satellite time and frequency performance. However, it is difficult to implement on-orbit satellite testing in the initial stage, and it is difficult to realize real-time calculation of on-orbit satellite test data.

[0004] Therefore, it is necessary to improve one or more problems existing in the above-mentioned related technical solutions.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] The purpose of the embodiments of the present disclosure is to provide a simulated on-orbit testing method and system for low-orbit satellite time and frequency equipment, thereby overcoming one or more problems caused by the limitations and defects of related technologies at least to a certain extent.

[0007] According to a first aspect of an embodiment of the present disclosure, a method for simulating on-orbit testing of a low-orbit satellite time and frequency device is provided, the method comprising: Generate a time frequency reference signal; wherein the time frequency reference signal is a first 10 MHz signal; Generate the first 1PPS signal based on the time frequency reference signal; generate the Beidou / GNSS simulation signal according to the Beidou / GNSS precise ephemeris, Beidou / GNSS precise clock error, Beidou / GNSS broadcast ephemeris and the dynamic low-orbit satellite position data of the low-orbit satellite; store the SSR correction number file; wherein the SSR correction number file includes the SSR correction number; Perform real-time precise orbit determination and clock error calculation based on BeiDou / GNSS analog signals and SSR correction numbers to generate a precise clock error sequence, and steer and regulate the built-in local atomic clock based on the precise clock error sequence to output the second 10MHz signal and the second 1PPS signal; Taking the time frequency reference signal as a reference, performing a frequency stability test on the first 10 MHz signal and the second 10 MHz signal to obtain frequency stability test data; Taking the time frequency reference signal as a reference, measuring the time accuracy of the first 1PPS signal and the second 1PPS signal to obtain time accuracy test data; The frequency stability test data and time accuracy test data are analyzed to obtain the time and frequency performance test results of satellite time and frequency equipment in a simulated on-orbit environment.

[0008] Further, the step of generating a BeiDou / GNSS simulation signal according to BeiDou / GNSS precise ephemeris, BeiDou / GNSS precise clock error, BeiDou / GNSS broadcast ephemeris and dynamic low-orbit satellite position data of a low-orbit satellite includes: According to the Beidou / GNSS precise ephemeris, Beidou / GNSS precise clock error, Beidou / GNSS broadcast ephemeris and the dynamic low-orbit satellite position data of the low-orbit satellite, the inter-satellite distance between the low-orbit satellite and the Beidou / GNSS satellite is obtained, and the time delay is obtained according to the inter-satellite distance; The transmission time of Beidou / GNSS satellite signals is adjusted according to the delay, the Beidou / GNSS broadcast ephemeris is corrected using the transmission time after the delay adjustment, and a dynamic satellite motion trajectory is simulated according to the corrected Beidou / GNSS broadcast ephemeris to obtain simulated Beidou / GNSS broadcast ephemeris data; The simulated Beidou / GNSS broadcast ephemeris data is compiled into telegram information, and the telegram information is modulated at an intermediate frequency and up-converted at a radio frequency to obtain a Beidou / GNSS simulation signal.

[0009] Further, the steps of performing real-time precise orbit determination and clock error calculation according to Beidou / GNSS analog signals and SSR correction numbers to generate a precise clock error sequence, and driving and regulating the built-in local atomic clock according to the precise clock error sequence to output a second 10MHz signal and a second 1PPS signal include: Based on the frequency signal generated by the built-in local atomic clock, it receives Beidou / GNSS analog signals to obtain observation data and broadcast ephemeris information; Use observation data, broadcast ephemeris information and SSR correction numbers to perform real-time precise orbit determination and clock error calculation to obtain a precise clock error sequence; The frequency difference is calculated based on the difference in the precision clock difference sequence per second, and the frequency adjustment amount is calculated based on the clock difference and the frequency difference. The local atomic clock is then driven and regulated based on the frequency adjustment amount to output a second 10MHz signal and a second 1PPS signal.

[0010] Further, the step of performing a frequency stability test on the first 10 MHz signal and the second 10 MHz signal with the time frequency reference signal as a reference to obtain frequency stability test data includes: The frequency stability test is performed using the first 10 MHz signal of the time-frequency reference signal as a reference, the second 10 MHz signal as an input signal, and the first 10 MHz signal as a reference signal to obtain frequency stability test data.

[0011] Further, the step of measuring the time accuracy of the first 1PPS signal and the second 1PPS signal with reference to the time frequency reference signal to obtain time accuracy test data includes: Taking the first 10MHz signal of the time frequency reference signal as a reference, the first 1PPS signal as a start signal, and the second 1PPS signal as a stop signal, the time difference between the first 1PPS signal and the second 1PPS signal is measured to obtain accuracy test data.

[0012] Furthermore, the first 1PPS pulse per second signal generated by the reference frequency source is generated according to the input time frequency reference signal, and the second 1PPS pulse per second signal generated by the measured frequency source is generated according to the second 10 MHz signal driven by the local atomic clock.

[0013] According to a second aspect of an embodiment of the present disclosure, a simulated on-orbit test system for a low-orbit satellite time and frequency device is provided, the system comprising: A reference atomic clock is used to generate a time frequency reference signal; wherein the time frequency reference signal is a first 10 MHz signal; The GNSS navigation signal simulator is used to generate the first 1PPS signal based on the time frequency reference signal; generate the Beidou / GNSS simulation signal according to the Beidou / GNSS precise ephemeris, Beidou / GNSS precise clock error, Beidou / GNSS broadcast ephemeris and the dynamic low-orbit satellite position data of the low-orbit satellite; store the SSR correction number file; wherein the SSR correction number file includes the SSR correction number; Satellite time and frequency equipment, used to perform real-time precise orbit determination and clock error calculation based on Beidou / GNSS analog signals and SSR correction numbers to generate a precise clock error sequence, and to steer and regulate the local atomic clock built into the satellite time and frequency equipment based on the precise clock error sequence to output a second 10MHz signal and a second 1PPS signal; A phase noise analyzer, used to perform a frequency stability test on the first 10 MHz signal and the second 10 MHz signal with the time-frequency reference signal as a reference, so as to obtain frequency stability test data; A time interval counter, used to measure the time accuracy of the first 1PPS signal and the second 1PPS signal with reference to the time frequency reference signal, so as to obtain time accuracy test data; The PC is used to analyze the frequency stability test data and the time accuracy test data to obtain the time and frequency performance test results of the satellite time and frequency equipment in a simulated on-orbit environment.

[0014] The technical solution provided by the embodiments of the present disclosure may have the following beneficial effects: In the embodiments of the present disclosure, through the above-mentioned simulated on-orbit test method and system of the low-orbit satellite time and frequency equipment, the reference atomic clock provides a reference benchmark for the GNSS navigation signal simulator, time interval counter and phase noise analyzer; the GNSS navigation signal simulator provides the satellite time and frequency equipment with Beidou / GNSS simulation signals and SSR corrections; the satellite time and frequency equipment uses the received Beidou / GNSS simulation signals and SSR corrections to complete the real-time precise orbit determination and clock error solution of the low-orbit satellite, and drives and regulates the built-in local atomic clock according to the solved clock error sequence; the second 1PPS signal and the second 10MHz signal output by the satellite time and frequency equipment are tested for time accuracy and frequency stability through the time interval counter and phase noise analyzer, and the test data are analyzed. Not only can the satellite be tested on-orbit in the initial stage, but also the real-time calculation of the on-orbit satellite test data can be realized.

[0015] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification are used to explain the principles of the present disclosure. Obviously, the accompanying drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0017] Figure 1 A step diagram showing a method for simulating on-orbit testing of a low-orbit satellite time-frequency device in an exemplary embodiment of the present disclosure; Figure 2 A schematic diagram showing the structure of a simulated on-orbit test system for a low-orbit satellite time and frequency device in an exemplary embodiment of the present disclosure is shown; Figure 3 A structural block diagram of a satellite time and frequency device in an exemplary embodiment of the present disclosure is shown; Figure 4 A schematic diagram showing frequency stability evaluation in an exemplary embodiment of the present disclosure; Figure 5 A schematic diagram showing time accuracy evaluation in an exemplary embodiment of the present disclosure; Figure 6 A graph showing the results of frequency stability in an exemplary embodiment of the present disclosure; Figure 7 A result graph showing time accuracy in an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION

[0018] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in a variety of forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that the disclosure will be more comprehensive and complete and to fully convey the concepts of the example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0019] In addition, the accompanying drawings are only schematic illustrations of the present disclosure and are not necessarily drawn to scale. The same reference numerals in the figures represent the same or similar parts, and their repeated description will be omitted. Some of the block diagrams shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software form, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontroller devices.

[0020] In this example implementation, a method for simulating on-orbit testing of a low-orbit satellite time and frequency device is first provided, and the method can be applied to a terminal device. Figure 1 As shown in , the method may include the following steps: Step S101: Generate a time-frequency reference signal; wherein the time-frequency reference signal is a first 10 MHz signal; Step S102: Generate a first 1PPS signal based on the time frequency reference signal; generate a Beidou / GNSS simulation signal according to the Beidou / GNSS precise ephemeris, Beidou / GNSS precise clock error, Beidou / GNSS broadcast ephemeris and the dynamic low-orbit satellite position data of the low-orbit satellite; store the SSR correction number file; wherein the SSR correction number file includes the SSR correction number; Step S103: Perform real-time precise orbit determination and clock error calculation according to the Beidou / GNSS analog signal and the SSR correction number to generate a precise clock error sequence, and drive and regulate the built-in local atomic clock according to the precise clock error sequence to output a second 10MHz signal and a second 1PPS signal; Step S104: taking the time frequency reference signal as a reference, performing a frequency stability test on the first 10 MHz signal and the second 10 MHz signal to obtain frequency stability test data; Step S105: Taking the time frequency reference signal as a reference, measuring the time accuracy of the first 1PPS signal and the second 1PPS signal to obtain time accuracy test data; Step S106: Analyze the frequency stability test data and the time accuracy test data to obtain the time and frequency performance test results of the satellite time and frequency equipment in a simulated on-orbit environment.

[0021] Through the above-mentioned simulated on-orbit test method of low-orbit satellite time and frequency equipment, the reference atomic clock provides a reference benchmark for the GNSS navigation signal simulator, satellite time and frequency equipment and phase noise analyzer; the GNSS navigation signal simulator provides Beidou / GNSS simulation signals and SSR corrections for the satellite time and frequency equipment; the satellite time and frequency equipment uses the received Beidou / GNSS simulation signals and SSR corrections to complete the real-time precise orbit determination and clock error solution of the low-orbit satellite, and drives and regulates the built-in local atomic clock according to the solved clock error sequence; the second 1PPS signal and the second 10MHz signal output by the satellite time and frequency equipment are tested for time accuracy and frequency stability through the time interval counter and phase noise analyzer, and the test data are analyzed. Not only can the on-orbit test of the satellite be simulated in the initial stage, but also the real-time calculation of the on-orbit satellite test data can be realized.

[0022] Next, we will refer to Figure 1 Each step of the above method in this example implementation is described in more detail.

[0023] In step S101, a time-frequency reference signal is generated; wherein the time-frequency reference signal is a first 10 MHz signal.

[0024] Specifically, the time frequency reference signal is a first 10 MHz signal. The GNSS navigation signal simulator generates a first 1PPS pulse per second signal using the time frequency reference signal as a reference.

[0025] In step S102, a first 1PPS signal is generated based on the time frequency reference signal; a Beidou / GNSS simulation signal is generated according to the Beidou / GNSS precise ephemeris, Beidou / GNSS precise clock difference, Beidou / GNSS broadcast ephemeris and the dynamic low-orbit satellite point data of the low-orbit satellite; and an SSR correction number file is stored; wherein the SSR correction number file includes the SSR correction number.

[0026] Specifically, the GNSS navigation signal simulator uses the reference atomic clock as the time and frequency reference, calculates the satellite-to-ground distance between the low-orbit satellite and the Beidou / GNSS satellite based on the dynamic low-orbit satellite position data of the low-orbit satellite, the Beidou / GNSS precise ephemeris and the Beidou / GNSS precise clock difference, and uses the satellite-to-ground distance to calculate the delay. The launch time of the Beidou / GNSS satellite is adjusted according to the delay, and the Beidou / GNSS broadcast ephemeris is corrected using the launch time of the Beidou / GNSS satellite. Then, the corrected Beidou / GNSS broadcast ephemeris is used to simulate the trajectory of the corresponding Beidou / GNSS satellite. Repeatedly adjust the ephemeris information of the corresponding Beidou / GNSS satellite, use the corrected Beidou / GNSS broadcast ephemeris to compile it into a telegram message, and modulate and up-convert it to obtain the Beidou / GNSS simulation signal. The GNSS navigation signal simulator stores the SSR correction number file downloaded from the ICG official website.

[0027] In step S103 to step S106, real-time precise orbit determination and clock error solution are performed according to the Beidou / GNSS simulation signal and the SSR correction number to generate a precise clock error sequence, and the built-in local atomic clock is driven and regulated according to the precise clock error sequence to output a second 10MHz signal and a second 1PPS signal; with the time-frequency reference signal as a reference, a frequency stability test is performed on the first 10MHz signal and the second 10MHz signal to obtain frequency stability test data; with the time-frequency reference signal as a reference, a time accuracy measurement is performed on the first 1PPS signal and the second 1PPS signal to obtain time accuracy test data; the frequency stability test data and the time accuracy test data are analyzed to obtain the time and frequency performance test results of the satellite time and frequency equipment in a simulated on-orbit environment.

[0028] Specifically, the satellite time and frequency equipment receives Beidou / GNSS analog signals through its own navigation and orbit determination processing receiver, and receives SSR correction numbers through the network cable; the satellite time and frequency equipment uses the internal local atomic clock as a reference, and performs real-time precise orbit determination and precise clock error calculation based on the received observation data and broadcast ephemeris information and SSR correction numbers. The clock error is the clock error between the internal atomic clock (i.e., the local atomic clock) and the reference atomic clock. The clock error sequence is then used to accurately control and regulate the local atomic clock to achieve time synchronization with the high-performance reference atomic clock, achieve the purpose of accurate tracing, and output high-performance second 10MHz signal and second 1PPS signal. The phase noise analyzer and time interval counter test the second 10MHz signal and the second 1PPS signal with the reference atomic clock as a reference.

[0029] It should be noted that, although the steps of the method in the present disclosure are described in a specific order in the accompanying drawings, this does not require or imply that the steps must be performed in this specific order, or that all the steps shown must be performed to achieve the desired results. Additionally or alternatively, some steps may be omitted, multiple steps may be combined into one step for execution, and / or one step may be decomposed into multiple steps for execution, etc. In addition, it is also easy to understand that these steps may be, for example, executed synchronously or asynchronously in multiple modules / processes / threads.

[0030] Furthermore, in this exemplary embodiment, a simulated on-orbit test system for low-orbit satellite time and frequency equipment is also provided. Figure 2 As shown in , the system may include a reference atomic clock, a GNSS navigation signal simulator, a satellite time and frequency device, a phase noise analyzer, a time interval counter and a PC. Among them: A reference atomic clock is used to generate a time frequency reference signal; wherein the time frequency reference signal is a first 10 MHz signal; The GNSS navigation signal simulator is used to generate the first 1PPS signal based on the time frequency reference signal; generate the Beidou / GNSS simulation signal according to the Beidou / GNSS precise ephemeris, Beidou / GNSS precise clock error, Beidou / GNSS broadcast ephemeris and the dynamic low-orbit satellite position data of the low-orbit satellite; store the SSR correction number file; wherein the SSR correction number file includes the SSR correction number; Satellite time and frequency equipment, used to perform real-time precise orbit determination and clock error calculation based on Beidou / GNSS analog signals and SSR correction numbers to generate a precise clock error sequence, and to steer and regulate the local atomic clock built into the satellite time and frequency equipment based on the precise clock error sequence to output a second 10MHz signal and a second 1PPS signal; A phase noise analyzer, used to perform a frequency stability test on the first 10 MHz signal and the second 10 MHz signal with the time-frequency reference signal as a reference, so as to obtain frequency stability test data; A time interval counter, used to measure the time accuracy of the first 1PPS signal and the second 1PPS signal with reference to the time frequency reference signal, so as to obtain time accuracy test data; The PC is used to analyze the frequency stability test data and the time accuracy test data to obtain the time and frequency performance test results of the satellite time and frequency equipment in a simulated on-orbit environment.

[0031] In a specific embodiment, the specific use process of the simulated on-orbit test system of the low-orbit satellite time and frequency equipment of the present application includes: 1. Generate the first 1PPS second pulse signal based on the reference atomic clock as the time frequency reference signal of the GNSS navigation signal simulator.

[0032] The reference atomic clock provides a reference benchmark for the GNSS navigation signal simulator and test equipment. The reference atomic clock can be a hydrogen atomic clock, which is not specifically limited here. The reference benchmark here can also be a cesium atomic clock or the national standard time UTC (NTSC).

[0033] In addition, the time frequency reference signal is a first 10 MHz signal. Taking the time frequency reference signal as a reference, a first 1PPS pulse per second signal is generated for time accuracy measurement. 2. Generate Beidou / GNSS simulation signal through external input Beidou / GNSS precise ephemeris, Beidou / GNSS precise clock difference, Beidou / GNSS broadcast ephemeris and dynamic low-orbit satellite point data of low-orbit satellite, and store the GNSS enhancement information downloaded from the IGS official website, that is, the SSR correction number, in the GNSS navigation signal simulator.

[0034] The GNSS navigation signal simulator uses the reference atomic clock as the time and frequency reference. It calculates the satellite-to-ground distance between the low-orbit satellite and the Beidou / GNSS satellite based on the dynamic low-orbit satellite position data of the low-orbit satellite, the Beidou / GNSS precise ephemeris and the Beidou / GNSS precise clock difference, and uses the satellite-to-ground distance to calculate the delay. The launch time of the Beidou / GNSS satellite is adjusted according to the delay, and the Beidou / GNSS broadcast ephemeris is corrected using the launch time of the Beidou / GNSS satellite. Then, the corrected Beidou / GNSS broadcast ephemeris is used to simulate the trajectory of the corresponding Beidou / GNSS satellite. Repeatedly adjust the ephemeris information of the corresponding Beidou / GNSS satellite, use the corrected Beidou / GNSS broadcast ephemeris to compile it into a telegram, and modulate and up-convert it to obtain the Beidou / GNSS simulation signal. The GNSS navigation signal simulator stores the SSR correction number downloaded from the IGS official website and sends it to the satellite time and frequency equipment through the network port. Among them, SSR corrections are GNSS enhancement information, including orbital clock corrections, code deviations, phase deviations and other products based on Beidou / GNSS broadcast ephemeris. SSR corrections can also be obtained through real-time collection, reception, storage and processing of time and frequency reference stations, IGS or iGMAS ground tracking stations in China or distributed globally.

[0035] The number of simulated satellites is more than 4. The more simulated satellites, the more accuracy can be guaranteed. The specific number needs to be determined by the number of Beidou satellites and the number of channels of the GNSS navigation signal simulator. The number of channels is the maximum number of satellites that can be broadcast.

[0036] The corrected Beidou / GNSS satellite data is compiled into telegram information, and the simulated Beidou / GNSS signal is obtained through intermediate frequency modulation and RF up-conversion. The output power is set and sent to the satellite time and frequency equipment through the RF cable for solution.

[0037] Optionally, the radio frequency conversion is to up-convert the modulated baseband signal to a radio frequency band.

[0038] The GNSS navigation signal simulator of the present application supports multi-system and multi-frequency simulation of BDS / GPS / GLONASS / GALILEO. The BDS system supports B1I, B2I, B3I, B1C, B2a, and B2b; the GPS system supports L1CA, L1C, L2C, and L5I; the GALILEO system supports E1, E5a, and E5b; the GLONASS system supports G1 and G2, and the supported frequency is 1176.45GHz~1561.098GHz.

[0039] Optionally, the GNSS navigation signal simulator has two signal output ports. The adjustable power range of the small signal port is -80~-160dBm, and the output power range of the large signal port is -20dBm~-100dBm; the output power can be adjusted according to demand.

[0040] 3. Generate a precise clock error sequence based on the BeiDou / GNSS analog signal and SSR correction number, and steer and regulate the local atomic clock based on the precise clock error sequence to output 10MHz signal and 1PPS signal.

[0041] like Figure 3 The figure shows the schematic diagram of the structure of the satellite time and frequency equipment. The navigation orbit determination processing receiver in the satellite time and frequency equipment uses the internal atomic clock as the time and frequency reference, and completes the acquisition tracking and channel decoding by receiving the above-mentioned GNSS signals, and outputs the observation data and broadcast ephemeris information, and then completes the precise orbit determination and clock error solution according to the received SSR correction number, thereby obtaining the clock error sequence. Among them, the observation data includes dual-frequency carrier pseudorange observation data, pseudorange and Doppler frequency shift and other information; the broadcast ephemeris information includes satellite orbit parameters and clock error and other information.

[0042] Optionally, the navigation and orbit determination processing receiver supports systems and frequencies including BDS B1C / B2a, GPSL1 / L5 and GalileoE1 / E5 signals. The number of channels for each frequency is not less than 12, the pseudorange accuracy (1σ) is better than 0.2m, the carrier phase accuracy (1σ) is better than 2mm, and the chip computing power inside the receiver supports orbit determination and clock error solution once every 1s, where the time and frequency reference refers to the 10MHz signal.

[0043] 4. The control module in the satellite time and frequency equipment steers and regulates the local atomic clock by processing the clock error sequence output by the navigation and orbit determination receiver.

[0044] Optionally, the local atomic clock here uses a rubidium atomic clock, and the control and regulation mainly calculates the frequency difference through the clock difference data per second. The frequency difference here refers to the frequency deviation between the local rubidium clock and the hydrogen atomic clock in the test system. Then the frequency of the rubidium atomic clock is adjusted by the clock difference and frequency difference, thereby reducing the clock difference, and when the clock difference is close to zero deviation, the frequency is adjusted to be consistent with the hydrogen atomic clock, thus achieving time frequency synchronization.

[0045] Optionally, the time frequency signal here refers to the second 10MHz and the second 1PPS, wherein the frequency performance is tested by the phase noise analyzer for the second 10MHz signal, and the time accuracy is tested by the time interval counter for the second 1PPS signal output after taming and the first 1PPS signal output by the GNSS navigation signal simulator. In addition, both the phase noise analyzer and the time interval counter require a hydrogen atomic clock as a frequency reference, and the phase noise analyzer compares the frequency deviation of the second 10MHz signal after taming and the first 10MHz signal of the hydrogen atomic clock; while the time interval counter tests the time difference between the second 1PPS after taming and the first 1PPS output by the GNSS navigation signal simulation source, thereby calculating the time accuracy.

[0046] Specifically, the frequency phase comparison method is mainly used to measure the frequency fluctuation of the rubidium atomic clock after training. The output signals of the measured frequency source (the local rubidium atomic clock of the satellite time and frequency equipment) and the reference frequency source (hydrogen atomic clock) are added to the corresponding input terminals of the phase noise analyzer, and the change in the phase difference between the two signals is continuously recorded. The frequency stability of the rubidium atomic clock for 1 second, 10 seconds, and 100 seconds is calculated by Allan variance. Allan variance is defined as a commonly used frequency stability analysis method by the IEEE standard. It converges for most frequency noises. The calculation formula of Allan variance is as follows: (2) Where: Indicates the basic sampling interval, usually 1s, is the Allan variance, Refers to The data value of the sample, Refers to The data value of the sample, is the number of sampling groups.

[0047] like Figure 4 As shown, this is a schematic diagram of frequency stability evaluation.

[0048] Further, such as Figure 5The figure shows a schematic diagram of time accuracy evaluation, and the evaluation method is specifically introduced. The time accuracy is measured by the time ratio method. The time ratio method uses the second 1PPS second pulse signal generated by the measured frequency source and the first 1PPS second pulse signal generated by the reference frequency source as the start signal and stop signal of the time interval counter, respectively, to measure the time difference between the two pulse signals. The time interval counter measures the time difference between the two 1PPS signals, outputs a set of clock difference data every second, stores it in the PC, and calculates its standard deviation. The standard deviation calculation formula is as follows:

[0049] Where: Indicates the basic sampling interval, usually 1s, is the standard deviation, Refers to The data value of the sample, is the sample mean, is the number of sampling points.

[0050] 5. The tamed local rubidium atomic clock signal in the satellite time and frequency equipment is output to the phase noise analyzer and time interval counter for performance testing. Finally, the test data is analyzed by a PC.

[0051] In a specific embodiment, a hydrogen atomic clock (VCH-1003M) is used as a reference clock, and the GNSS navigation analog signal device, satellite time and frequency equipment, phase noise analyzer (53100A), time interval counter (SR620) and other equipment are connected according to Figure 2 The test platform was built using the connection method, and the frequency stability and time accuracy of the satellite time and frequency equipment were tested. The test results showed that the frequency stability of the satellite time and frequency equipment was 9.71E-15 per 10,000 seconds, and the time accuracy of the satellite time and frequency equipment was 0.0996ns. Figure 6 and Figure 7 shown.

[0052] Through the above-mentioned simulated on-orbit test method and system for low-orbit satellite time and frequency equipment, the reference atomic clock provides a reference benchmark for the GNSS navigation signal simulator, time interval counter and phase noise analyzer; the GNSS navigation signal simulator provides Beidou / GNSS simulation signals and SSR correction numbers for the satellite time and frequency equipment; the satellite time and frequency equipment uses the received Beidou / GNSS simulation signals and SSR correction numbers to complete the real-time precise orbit determination and clock error solution of the low-orbit satellite, and drives and regulates the built-in local atomic clock according to the solved clock error sequence; the second 1PPS signal and the second 10MHz signal output by the satellite time and frequency equipment are tested for time accuracy and frequency stability through the time interval counter and phase noise analyzer, and the test data are analyzed. Not only can the satellite be tested on-orbit in the initial stage, but also the real-time calculation of the on-orbit satellite test data can be realized.

[0053] Regarding the device in the above embodiment, the specific manner in which each module performs operations has been described in detail in the embodiment of the method, and will not be elaborated here.

[0054] It should be noted that although several modules or units of the device for action execution are mentioned in the above detailed description, this division is not mandatory. In fact, according to the embodiment of the present disclosure, the features and functions of two or more modules or units described above can be concretized in one module or unit. Conversely, the features and functions of a module or unit described above can be further divided into multiple modules or units for concretization. The components displayed as modules or units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the disclosed solution. Those of ordinary skill in the art can understand and implement it without paying creative work.

[0055] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the specification and practicing the invention disclosed herein. This application is intended to cover any modification, use or adaptation of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary techniques in the art that are not disclosed in the present disclosure. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present disclosure are indicated by the appended claims.

Claims

1. A simulated on-orbit test method for low-orbit satellite time and frequency equipment, characterized in that: The method includes: Generate a time frequency reference signal; wherein the time frequency reference signal is a first 10 MHz signal; Generate the first 1PPS signal based on the time frequency reference signal; generate the Beidou / GNSS simulation signal according to the Beidou / GNSS precise ephemeris, Beidou / GNSS precise clock error, Beidou / GNSS broadcast ephemeris and the dynamic low-orbit satellite position data of the low-orbit satellite; store the SSR correction number file; wherein the SSR correction number file includes the SSR correction number; Perform real-time precise orbit determination and clock error calculation based on BeiDou / GNSS analog signals and SSR correction numbers to generate a precise clock error sequence, and steer and regulate the built-in local atomic clock based on the precise clock error sequence to output the second 10MHz signal and the second 1PPS signal; Taking the time frequency reference signal as a reference, performing a frequency stability test on the first 10 MHz signal and the second 10 MHz signal to obtain frequency stability test data; Taking the time frequency reference signal as a reference, measuring the time accuracy of the first 1PPS signal and the second 1PPS signal to obtain time accuracy test data; The frequency stability test data and time accuracy test data are analyzed to obtain the time and frequency performance test results of satellite time and frequency equipment in a simulated on-orbit environment.

2. The method for simulating on-orbit testing of low-orbit satellite time and frequency equipment according to claim 1, characterized in that: The step of generating a BeiDou / GNSS simulation signal according to BeiDou / GNSS precise ephemeris, BeiDou / GNSS precise clock difference, BeiDou / GNSS broadcast ephemeris and dynamic low-orbit satellite position data of a low-orbit satellite comprises: According to the Beidou / GNSS precise ephemeris, Beidou / GNSS precise clock error, Beidou / GNSS broadcast ephemeris and the dynamic low-orbit satellite position data of the low-orbit satellite, the inter-satellite distance between the low-orbit satellite and the Beidou / GNSS satellite is obtained, and the time delay is obtained according to the inter-satellite distance; The transmission time of Beidou / GNSS satellite signals is adjusted according to the delay, the Beidou / GNSS broadcast ephemeris is corrected using the transmission time after the delay adjustment, and a dynamic satellite motion trajectory is simulated according to the corrected Beidou / GNSS broadcast ephemeris to obtain simulated Beidou / GNSS broadcast ephemeris data; The simulated Beidou / GNSS broadcast ephemeris data is compiled into telegram information, and the telegram information is modulated at an intermediate frequency and up-converted at a radio frequency to obtain a Beidou / GNSS simulation signal.

3. The method for simulating on-orbit testing of low-orbit satellite time and frequency equipment according to claim 2, characterized in that: The steps of performing real-time precise orbit determination and clock error calculation according to BeiDou / GNSS analog signals and SSR correction numbers to generate a precise clock error sequence, and driving and regulating the built-in local atomic clock according to the precise clock error sequence to output a second 10MHz signal and a second 1PPS signal include: Based on the frequency signal generated by the built-in local atomic clock, it receives Beidou / GNSS analog signals to obtain observation data and broadcast ephemeris information; Use observation data, broadcast ephemeris information and SSR correction numbers to perform real-time precise orbit determination and clock error calculation to obtain a precise clock error sequence; The frequency difference is calculated based on the difference in the precision clock difference sequence per second, and the frequency adjustment amount is calculated based on the clock difference and the frequency difference. The local atomic clock is then driven and regulated based on the frequency adjustment amount to output a second 10MHz signal and a second 1PPS signal.

4. The method for simulating on-orbit testing of low-orbit satellite time and frequency equipment according to claim 3, characterized in that: The step of performing a frequency stability test on the first 10 MHz signal and the second 10 MHz signal with reference to the time frequency reference signal to obtain frequency stability test data includes: The frequency stability test is performed using the first 10 MHz signal of the time-frequency reference signal as a reference, the second 10 MHz signal as an input signal, and the first 10 MHz signal as a reference signal to obtain frequency stability test data.

5. The method for simulating on-orbit testing of low-orbit satellite time and frequency equipment according to claim 4, characterized in that: The step of measuring the time accuracy of the first 1PPS signal and the second 1PPS signal with reference to the time frequency reference signal to obtain time accuracy test data includes: Taking the first 10MHz signal of the time frequency reference signal as a reference, the first 1PPS signal as a start signal, and the second 1PPS signal as a stop signal, the time difference between the first 1PPS signal and the second 1PPS signal is measured to obtain time accuracy test data.

6. The method for simulating on-orbit testing of low-orbit satellite time and frequency equipment according to claim 5, characterized in that: The first 1PPS signal of the second pulse generated by the reference frequency source is generated according to the input time frequency reference signal, and the second 1PPS signal of the second pulse generated by the measured frequency source is generated according to the second 10MHz signal driven by the local atomic clock.

7. A simulated on-orbit test system for low-orbit satellite time and frequency equipment, characterized in that: The system includes: A reference atomic clock is used to generate a time frequency reference signal; wherein the time frequency reference signal is a first 10 MHz signal; The GNSS navigation signal simulator is used to generate the first 1PPS signal based on the time frequency reference signal; generate the Beidou / GNSS simulation signal according to the Beidou / GNSS precise ephemeris, Beidou / GNSS precise clock error, Beidou / GNSS broadcast ephemeris and the dynamic low-orbit satellite position data of the low-orbit satellite; store the SSR correction number file; wherein the SSR correction number file includes the SSR correction number; Satellite time and frequency equipment, used to perform real-time precise orbit determination and clock error calculation based on Beidou / GNSS analog signals and SSR correction numbers to generate a precise clock error sequence, and to steer and regulate the local atomic clock built into the satellite time and frequency equipment based on the precise clock error sequence to output a second 10MHz signal and a second 1PPS signal; A phase noise analyzer, used to perform a frequency stability test on the first 10 MHz signal and the second 10 MHz signal with the time-frequency reference signal as a reference, so as to obtain frequency stability test data; A time interval counter, used to measure the time accuracy of the first 1PPS signal and the second 1PPS signal with reference to the time frequency reference signal, so as to obtain time accuracy test data; The PC is used to analyze the frequency stability test data and the time accuracy test data to obtain the time and frequency performance test results of the satellite time and frequency equipment in a simulated on-orbit environment.

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