Satellite navigation message monitoring system based on inter-satellite measurement

Abstract

The invention generally relates to the technical field of navigation satellites, and provides a satellite navigation message monitoring system based on inter-satellite measurement. The system is configured to perform the following actions: performing inter-satellite ranging on navigation satellites; and monitoring a satellite navigation message according to an inter-satellite distance measurement result, the satellite navigation message comprising ephemeris parameters and clock difference parameters, the step of monitoring the ephemeris parameters comprises the following steps: calculating a first geometric distance between the first satellite and the second satellite at the current moment according to the ephemeris parameters of the first satellite and the second satellite; calculating a second geometric distance between the first satellite and the second satellite at the current moment according to the inter-satellite distance measurement results of the first satellite and the second satellite; and judging the reasonability of the ephemeris parameter at the current moment by comparing the first geometric distance with the second geometric distance.

Description

Technical Field

[0001] The present invention generally relates to the technical field of navigation satellite technology. Specifically, the present invention relates to a satellite navigation message monitoring system based on inter-satellite measurement. Background Art

[0002] In a navigation satellite system, since the ground control facilities of the GPS navigation system are spread all over the world, the health status of global GPS navigation satellites can be monitored in real time, and faults can be disposed of and restored in time, so as to ensure the continuity of the navigation service of the GPS navigation system.

[0003] The Beidou satellite navigation system is an independent global satellite navigation system in China. When a navigation signal fault occurs to a Beidou satellite overseas due to factors such as single-event upset in space or interference and countermeasure, the navigation signal can only be set to unavailable first, and it can only be disposed of and restored after the Beidou satellite re-enters the country, which will directly affect the continuity and availability of the navigation service provided by the Beidou satellite. Therefore, it is necessary to carry out autonomous integrity monitoring on satellite navigation signals.

[0004] In satellite navigation signals, the satellite navigation message is a very important one. The satellite navigation message is broadcast by a navigation satellite to a user, and it can describe the operating state parameters of the navigation satellite. The operating state parameters may include system time, ephemeris, almanac, correction parameters of the satellite clock, health status of the navigation satellite, and ionospheric delay model parameters, etc. The operating state parameters can provide time information to the user. Using the operating state parameters, the position coordinates and speed of the navigation satellite can be calculated, and the user's own position coordinates and speed can be calculated through multi-satellite positioning. Therefore, Beidou satellites can independently verify the satellite navigation message in the space segment to make up for the shortcoming that the Beidou satellite navigation system does not have global monitoring stations, and can also more quickly restore the normal service of navigation satellites with navigation signal faults.

[0005] Currently, the effective duration of each group of satellite navigation messages is usually 1 hour. Since there is a certain time gap in the process from the generation to the actual broadcast of the satellite navigation message, the message for the next hour can be checked in advance. On the premise of ensuring the reasonableness and effectiveness of the message for the previous hour, the reasonableness of the parameters of the message for the next hour can be verified by using the message for the previous hour, so as to realize the advance monitoring of the satellite navigation message to be broadcast.

[0006] However, the current advance monitoring of satellite navigation messages is only a one-time monitoring before the message is broadcast and takes effect. If errors such as single-event upset occur at the message source during the message encoding and broadcast process of the satellite navigation message, resulting in parameter errors, these errors will not be detected at this time. Summary of the Invention

[0007] To at least partially solve the above problems in the prior art, the present invention proposes

[0008] A satellite navigation message monitoring system based on inter-satellite measurement, characterized in that it includes a first satellite and a second satellite, wherein the first satellite is the satellite to be evaluated, and the first satellite and the second satellite store the message parameters being broadcast, and store the ranging information and message parameter information obtained by establishing links with other satellites; the system is configured to perform the following actions:

[0009] Perform inter-satellite ranging on navigation satellites; and

[0010] Monitor the satellite navigation message according to the result of inter-satellite ranging, the satellite navigation message includes ephemeris parameters and clock error parameters, wherein monitoring the ephemeris parameters includes the following steps:

[0011] Calculate the first geometric distance between the first satellite and the second satellite at the current moment according to the ephemeris parameters of the first and second satellites;

[0012] Calculate the second geometric distance between the first satellite and the second satellite at the current moment according to the inter-satellite ranging result of the first and second satellites; and

[0013] Judge the rationality of the ephemeris parameters at the current moment by comparing the first and second geometric distances;

[0014] The first and second satellites broadcast satellite navigation messages and the first satellite establishes an inter-satellite link with the second satellite as the transmitter and receiver respectively for ranging; wherein

[0015] The moments when the first and second satellites broadcast satellite navigation messages closest to the current moment T0 are respectively represented as the first moment T1 and the second moment T2;

[0016] The message transfer moment when the first satellite as the transmitter establishes an inter-satellite link with the second satellite to complete ranging closest to the current moment T0 is represented as the third moment T3; and

[0017] The message transfer moment when the first satellite as the receiver establishes an inter-satellite link with the second satellite to complete ranging closest to the current moment T0 is represented as the fourth moment T4;

[0018] Wherein the ephemeris parameters in the satellite navigation message broadcast by the first satellite at the first moment T1 and the ephemeris parameters in the satellite navigation message broadcast by the second satellite at the second moment T2 are used for orbit extrapolation to calculate the positions of the first satellite and the second satellite at the current moment, and calculate the first geometric distance between the first satellite and the second satellite at the current moment;

[0019] Calculate the second geometric distance between the first satellite and the second satellite at the current moment according to the inter-satellite link ranging result between the first satellite and the second satellite at the third moment T3 and the fourth moment T4;

[0020] Provide a geometric distance difference threshold value, wherein when the difference between the first geometric distance and the second geometric distance is greater than the geometric distance difference threshold value, it is determined that the ephemeris parameters are abnormal at the current moment.

[0021] In an embodiment of the present invention, it is stipulated that the time interval between the initial moment and the first to fourth moments is less than or equal to 1 minute.

[0022] In an embodiment of the present invention, it is stipulated that monitoring the clock difference parameters includes the following steps:

[0023] Calculate the first clock difference between the first satellite and the second satellite at the current moment according to the clock difference parameters of the first and second satellites;

[0024] Calculate the second clock difference between the first satellite and the second satellite at the current moment according to the inter-satellite ranging results of the first and second satellites; and

[0025] Judge the rationality of the clock difference parameters at the current moment by comparing the first and second geometric distances.

[0026] In an embodiment of the present invention, it is stipulated that the clock difference between the first satellite and the second satellite at the current moment is calculated by using the clock difference parameters in the satellite navigation message broadcast by the first satellite at the first moment T1 and the clock difference parameters in the satellite navigation message broadcast by the second satellite at the second moment T2, and the first clock difference between the first satellite and the second satellite at the current moment is calculated.

[0027] In an embodiment of the present invention, it is stipulated that the second clock difference between the first satellite and the second satellite at the current moment is calculated according to the inter-satellite link ranging results between the first satellite and the second satellite at the third moment T3 and the fourth moment T4.

[0028] In an embodiment of the present invention, it is stipulated that a clock difference threshold value is provided, wherein when the difference between the first clock difference and the second clock difference is greater than the clock difference threshold value, it is determined that the clock difference parameters are abnormal at the current moment.

[0029] The present invention has at least the following beneficial effects: The present invention provides a satellite navigation message monitoring system based on inter-satellite measurement, which can monitor the ephemeris parameters and clock difference parameters broadcast by navigation satellites, can judge the rationality of the ephemeris clock difference parameters broadcast by satellites in real time, and avoid the satellite from broadcasting incorrect message parameters. This method is applicable to avoiding errors that may occur in the whole process of message generation, transmission, and broadcast of the ground operation control system and satellite system.

[0030] In the technical solution of the present invention, through the adoption of algorithms such as orbit extrapolation algorithm, algorithm defined based on the clock error parameter itself, inter-satellite link measurement model, ranging epoch reduction, etc., combined with the characteristics of the satellite navigation message itself, the data can be dimensionally reduced, and complex ephemeris parameters and clock error parameters can be transformed into one-dimensional threshold judgment. The method is simple and effective; the method of the present invention provides the possibility of real-time monitoring in the order of minutes, meets the requirements of rapid and real-time monitoring of satellites, and at the same time provides ideas and solutions for the expansion of the on-board integrity monitoring ability; and the method of the present invention is applicable to the failure of the uplink injection link, does not depend on the control of the ground station, can achieve autonomous judgment within the constellation, and can effectively reduce the unplanned interruption index of the satellite. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] To further clarify the advantages and features possessed by and other in each embodiment of the present invention, a more specific description of each embodiment of the present invention will be presented with reference to the accompanying drawings. It can be understood that these drawings only depict typical embodiments of the present invention and will not be considered as limiting its scope. In the drawings, for clarity, the same or corresponding components will be denoted by the same or similar reference numerals.

[0032] Figure 1 FIG. shows a schematic diagram of establishing an inter-satellite link for a navigation satellite in an embodiment of the present invention.

[0033] Figure 2 FIG. shows a schematic flow diagram of monitoring the ephemeris parameters of a satellite navigation message in an embodiment of the present invention.

[0034] Figure 3 FIG. shows a schematic flow diagram of monitoring the clock error parameters of a satellite navigation message in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] It should be noted that the components in each drawing may be exaggerated for illustration purposes and are not necessarily to scale correctly. In each drawing, the same or functionally identical components are provided with the same reference numerals.

[0036] In the present invention, unless otherwise specified, "arranged on...", "arranged above...", and "arranged on top of..." do not exclude the existence of an intermediate object between the two. In addition, "arranged on or above..." only represents the relative positional relationship between two components, and in certain cases, such as when the product direction is reversed, it can also be converted to "arranged under or below...", and vice versa.

[0037] In the present invention, each embodiment is only intended to illustrate the solution of the present invention and should not be construed as restrictive.

[0038] In the present invention, unless otherwise specified, the quantifiers "a" and "one" do not exclude scenarios with multiple elements.

[0039] It should also be noted here that, in the embodiments of the present invention, for the sake of clarity and simplicity, only a part of the components or assemblies may be shown. However, those of ordinary skill in the art can understand that, under the teaching of the present invention, the required components or assemblies can be added according to specific scenario needs. Additionally, unless otherwise stated, the features in different embodiments of the present invention can be combined with each other. For example, a certain feature in the second embodiment can be used to replace the corresponding or functionally identical or similar feature in the first embodiment, and the resulting embodiment also falls within the scope of the disclosure or the scope of the record of this application.

[0040] It should also be noted here that within the scope of the present invention, terms such as "identical", "equal", and "equal to" do not mean that the two values are absolutely equal, but allow for a certain reasonable error. That is to say, these terms also cover "substantially identical", "substantially equal", and "substantially equal to". By analogy, in the present invention, terms indicating directions such as "perpendicular to" and "parallel to" also cover the meanings of "substantially perpendicular to" and "substantially parallel to".

[0041] In addition, the numbering of the steps of each method of the present invention does not limit the execution order of the method steps. Unless otherwise specified, the method steps can be executed in different orders.

[0042] The present invention will be further elaborated below in conjunction with the specific embodiments with reference to the accompanying drawings.

[0043] The present invention provides a method for monitoring satellite navigation messages based on inter-satellite measurement. Through this method, navigation satellites can independently utilize the limited on-board data resources to monitor satellite navigation messages and achieve autonomous judgment of the rationality of message parameters, which can include two parts: pre-monitoring and real-time monitoring. Pre-monitoring can monitor the rationality of the message parameters to be broadcast in the next hour before the satellite navigation message is updated every hour; real-time monitoring can detect the rationality of the message parameters being broadcast during the broadcast of the satellite navigation message in the current hour.

[0044] The message parameters may include ephemeris parameters and clock offset parameters. During the monitoring of the ephemeris parameters and clock offset parameters, it is meaningless to simply perform a threshold judgment on a single parameter. Therefore, it is necessary to perform dimensionality reduction processing on the multi-dimensional parameters composed of the latest ephemeris message parameters and clock offset parameters to obtain a set of one-dimensional results, and finally set a reasonable error threshold according to engineering requirements to determine the rationality of the message parameters.

[0045] The present invention is based on the following insights of the inventors: Navigation satellites can receive the latest ephemeris parameters and clock offset parameters injected by ground systems every hour. Among them, the ephemeris parameters can reflect the position state of the navigation satellites. Since navigation satellites usually operate stably along a certain orbit and at a certain speed, the positions of the navigation satellites have a certain predictability and can be extrapolated and predicted based on the ephemeris parameters. The clock offset parameters can reflect the offset of the satellite clock of the navigation satellite relative to the ground clock. Since the space-ground atomic clocks have stable characteristics during stable operation, the clock offset parameters usually do not change significantly.

[0046] Since both the satellite ephemeris and clock offset parameters are system parameters composed of multiple parameters and cannot be directly compared and judged through a single parameter, in order to ensure the correctness of the injection and broadcast of satellite ephemeris and clock offset parameters, in the method of the present invention, the characteristics of the above ephemeris parameters and clock offset parameters can be utilized to convert the ephemeris parameters to be broadcast on the satellite into the orbital position of the satellite, and the clock offset parameters to be broadcast on the satellite into the clock time change information of the satellite clock, and then the parameter rationality is judged.

[0047] The following specifically describes, with reference to the accompanying drawings, the judgment process of the ephemeris parameters and clock offset parameters by the satellite navigation message monitoring method based on inter-satellite measurement in an embodiment of the present invention.

[0048] Figure 1 FIG. shows a schematic diagram of inter-satellite measurement by a navigation satellite in an embodiment of the present invention. As Figure 1 shown, satellite A can be the satellite to be evaluated. Among them, satellite A and satellite B store in real time the message parameters currently being broadcast, and store in real time the ranging information and message parameter information obtained by establishing a link with other navigation satellites.

[0049] The current moment is represented as moment T0. The satellite that recently established an inter-satellite link with satellite A is satellite B. The reference moments of the most recently broadcast messages of the two satellites stored are T1 and T2 respectively. The moment when satellite A most recently established a link with satellite B as the sending end and completed ranging and message transmission is T3, and the moment when satellite A most recently established a link with satellite B as the receiving end and completed ranging and message transmission is T4. (Among them, the time interval between the actual T0 and T4 of the satellite ≤ 1 minute.)

[0050] At moment T0, satellite A can retrieve the message parameters of satellite B at moment T2, the inter-satellite ranging value at moment T3, the inter-satellite ranging value at moment T4, and the message parameters currently being broadcast by satellite A at moment T0 stored. Based on this, satellite A can perform real-time monitoring and rationality judgment on the satellite ephemeris parameters and satellite clock offset parameters.

[0051] Figure 2The figure shows a schematic flow chart of real-time monitoring of satellite ephemeris parameters by navigation satellites based on inter-satellite measurements. Among them, the ephemeris parameters can describe the satellite orbit obtained under a certain fitting interval, and the ephemeris parameters include 18 quasi-Keplerian orbit parameters and 1 satellite orbit type parameter. Under normal circumstances, the update period of the ephemeris parameters is 1 hour, and it is updated at the whole hour of Beidou Time (BDT).

[0052] As Figure 2 shown, satellite A can, according to its own broadcast ephemeris parameters and the received ephemeris parameters of satellite B, uniformly reduce the geometric distance X1 between satellite A and satellite B at a certain moment T0 through orbit extrapolation; further, satellite A can, through inter-satellite ranging, measurement model of the inter-satellite link, and ranging epoch reduction, uniformly reduce the geometric distance X2 between satellite A and satellite B at a certain moment T0; and by comparing the difference between X1 and X2, a threshold can be set according to engineering experience to judge the correctness of the ephemeris parameters.

[0053] Specifically, the real-time monitoring of satellite ephemeris parameters by navigation satellites based on inter-satellite measurements and the rationality judgment of ephemeris parameters may include the following steps:

[0054] Step 1: Obtain a set of ephemeris parameters of satellite A being broadcast (ephemeris parameter array 1). Taking the ephemeris parameters broadcast by B1C signal as an example, the ephemeris parameters include 19 parameters;

[0055] Step 2: Obtain a set of the latest ephemeris parameters of satellite B (ephemeris parameter array 2). Taking the ephemeris parameters broadcast by B1C signal as an example, the ephemeris parameters include 19 parameters;

[0056] Step 3: Obtain a set of the latest two-way ranging results between satellite A and satellite B, and record the corresponding ranging times T3 and T4;

[0057] Step 4: Take the current time T0 as the reference time. According to the orbit extrapolation algorithm, respectively calculate the position O 1 (X k1 , Y k1 , Z k1 ) of satellite A and the position O 2 (X k1 , Y k1 , Z k1 ) of satellite B at time T0 according to ephemeris parameter array 1 and ephemeris parameter array 2, and calculate the distance X1 between the positions of the two satellites, that is

[0058] Step 5: Satellite A can uniformly reduce the latest two-way ranging results of Satellite A - B at times T3 and T4 to the current time T0 according to the inter-satellite link measurement model and ranging epoch reduction, and obtain the geometric distance X2 between Satellite A and Satellite B after deducting errors such as ranging error and clock error;

[0059] Step 6: Set a threshold according to engineering data experience. If |X1 - X2| exceeds the threshold, it is determined that the telegram parameters are abnormal; otherwise, it is determined that the telegram parameters are reasonable.

[0060] Figure 3 shows a method for real-time monitoring of satellite clock error parameters of navigation satellites based on inter-satellite measurement in an embodiment of the present invention. The clock error parameters may include t oc , a 0 , a 1 , a 2 . t oc is the reference time of the clock error parameter of this clock, with the unit of second. Under normal circumstances, the update period of the clock error parameter is 1 hour, and it is updated at the BDT whole hour.

[0061] As Figure 3 shown, Satellite A can uniformly reduce the clock errors broadcast by itself and the clock error telegram received from Satellite B to the clock error at a certain time T0, and obtain the clock error Y1 between Satellite A and Satellite B; further, Satellite A can uniformly reduce the clock error between Satellite A and Satellite B at a certain time T0 through inter-satellite ranging via the inter-satellite link measurement model and ranging epoch reduction; and the difference between Y1 and Y2 can be compared, and a threshold can be set according to engineering requirements to judge the correctness of the clock error parameters.

[0062] Specifically, the real-time monitoring of satellite clock error parameters and the rationality judgment of ephemeris parameters based on inter-satellite measurement by navigation satellites may include the following steps:

[0063] Step 1: Obtain a set of clock error parameters being broadcast by Satellite A (clock error parameter array 1). Taking the ephemeris parameters broadcast in B1C signal as an example, the clock error parameters include 4 parameters;

[0064] Step 2: Obtain a set of the latest clock error parameters of Satellite B (clock error parameter array 2). Taking the ephemeris parameters broadcast in B1C signal as an example, the clock error parameters include 4 parameters;

[0065] Step 3: Obtain a set of the latest two-way ranging results of Satellite A - B, and record the corresponding ranging times T3 and T4;

[0066] Step 4: Take the current time T0 as the reference time. According to the definition of clock error parameters, calculate the clock error A of Satellite A at time T0 and the clock error A of Satellite B at time T0 respectively according to clock error parameter array 1 and clock error parameter array 2 1 and the clock error A of Satellite B2 , calculate the clock difference Y1 between satellite A and satellite B, that is, Y1 = A1 - A2;

[0067] Step Five: Satellite A can uniformly reduce the latest two-way ranging results of satellite A - B at times T3 and T4 to the current time T0 according to the inter-satellite link measurement model and ranging epoch reduction, and obtain the clock difference Y2 between satellite A and satellite B after deducting the ranging and ranging errors;

[0068] Step Six: Set a threshold according to the engineering data experience. If |Y1 - Y2| exceeds the threshold, it is determined that the clock difference parameter is abnormal; otherwise, it is determined that the clock difference parameter is reasonable.

[0069] Although the embodiments of the present invention have been described above, it should be understood that they are presented only as examples and not as limitations. It is obvious to those skilled in the relevant art that various combinations, variations, and changes can be made to them without departing from the spirit and scope of the present invention. Therefore, the width and scope of the present invention disclosed herein should not be limited by the above-disclosed exemplary embodiments, but should be defined only by the appended claims and their equivalents.

Claims

1. A satellite navigation message monitoring system based on inter-satellite measurement, characterized in that, it includes a first satellite and a second satellite, where the first satellite is the satellite to be evaluated. The first satellite and the second satellite store the message parameters being broadcast, and store the ranging information and message parameter information obtained by establishing a link with other satellites; the system is configured to perform the following actions: Perform inter-satellite ranging on navigation satellites; And Monitor the satellite navigation message according to the result of inter-satellite ranging. The satellite navigation message includes ephemeris parameters and clock offset parameters. Monitoring the ephemeris parameters includes the following steps: Calculate the first geometric distance between the first satellite and the second satellite at the current moment according to the ephemeris parameters of the first and second satellites; Calculate the second geometric distance between the first satellite and the second satellite at the current moment according to the inter-satellite ranging result of the first and second satellites; And Judge the rationality of the ephemeris parameters at the current moment by comparing the first and second geometric distances; The first and second satellites broadcast satellite navigation messages and the first satellite establishes an inter-satellite link with the second satellite as a sending end and a receiving end respectively for ranging; Where The moments when the first and second satellites broadcast satellite navigation messages closest to the current moment T0 are respectively represented as the first moment T1 and the second moment T2; The message transfer moment when the first satellite closest to the current moment T0 establishes an inter-satellite link with the second satellite as a sending end and completes ranging is represented as the third moment T3; And The message transfer moment when the first satellite closest to the current moment T0 establishes an inter-satellite link with the second satellite as a receiving end and completes ranging is represented as the fourth moment T4; Where the ephemeris parameters in the satellite navigation message broadcast by the first satellite at the first moment T1 and the ephemeris parameters in the satellite navigation message broadcast by the second satellite at the second moment T2 are used for orbit extrapolation to calculate the positions of the first satellite and the second satellite at the current moment, and calculate the first geometric distance between the first satellite and the second satellite at the current moment; Calculate the second geometric distance between the first satellite and the second satellite at the current moment according to the inter-satellite link ranging result between the first satellite and the second satellite at the third moment T3 and the fourth moment T4; Provide a geometric distance difference threshold value. When the difference between the first geometric distance and the second geometric distance is greater than the geometric distance difference threshold value, it is judged that the ephemeris parameters at the current moment are abnormal.

2. The satellite navigation message monitoring system based on inter-satellite measurement according to claim 1, characterized in that, The time interval between the initial moment and the first to fourth moments is less than or equal to 1 minute.

3. The satellite navigation message monitoring system based on inter-satellite measurement according to claim 1, characterized in that, Monitoring the clock offset parameters includes the following steps: Calculate the first clock offset difference between the first satellite and the second satellite at the current moment according to the clock offset parameters of the first and second satellites; Calculate the second clock offset difference between the first satellite and the second satellite at the current moment according to the inter-satellite ranging result of the first and second satellites; And Judge the rationality of the clock difference parameter at the current moment by comparing the first and second geometric distances.

4. The satellite navigation message monitoring system based on inter-satellite measurement according to claim 3, wherein, calculate the clock difference between the first satellite and the second satellite at the current moment by using the clock difference parameter in the satellite navigation message broadcast by the first satellite at the first moment T1 and the clock difference parameter in the satellite navigation message broadcast by the second satellite at the second moment T2, and calculate the first clock difference difference between the first satellite and the second satellite at the current moment.

5. The satellite navigation message monitoring system based on inter-satellite measurement according to claim 4, wherein, calculate the second clock difference difference between the first satellite and the second satellite at the current moment according to the ranging result of the inter-satellite link between the first satellite and the second satellite at the third moment T3 and the fourth moment T4.

6. The satellite navigation message monitoring system based on inter-satellite measurement according to claim 5, wherein, provide a threshold for the clock difference difference, and when the difference between the first clock difference difference and the second clock difference difference is greater than the threshold for the clock difference difference, it is judged that the clock difference parameter at the current moment is abnormal.

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