A method and system for generating broadcast ephemeris accuracy parameters

Abstract

The present application relates to a kind of broadcast ephemeris precision parameter generation method and system.The generation method includes: input broadcast ephemeris and precise ephemeris in data input module, and store in database;Extract the broadcast ephemeris and precise ephemeris in the database, and it is used to calculate satellite broadcast orbit and clock error in error calculation module;In error fitting module, using quadratic difference method to evaluate broadcast clock difference precision;In coefficient extraction module, the fitting is carried out to the clock error, to extract the first term coefficient of clock difference fitting;According to the first term coefficient, in grade conversion module, select the constant value suitable for Beidou three satellite navigation system, as the satellite clock frequency offset precision SISA oc1 of Beidou three satellite navigation system;And the grade conversion algorithm of satellite clock frequency offset precision index SISAI oc1 ;And according to the grade conversion algorithm, precision parameter is generated in precision parameter generation module.The present application first proposes the determination method of user grade conversion formula of broadcast ephemeris precision parameter SISA oc1 , and improves the broadcast value of broadcast ephemeris precision parameter SISAI ocb , realizes the zero time envelope of SISA oc Parameter to satellite along radial error, can reduce the system integrity risk event caused by unreasonable text parameter broadcast value.

Description

Technical Field

[0001] This invention relates to the field of navigation and positioning technology for Global Navigation Satellite System (GNSS), and particularly to a method and system for generating broadcast ephemeris accuracy parameters. Background Technology

[0002] GNSS provides users with precise positioning, navigation, and timing services. Accuracy, integrity, continuity, and availability are the four key performance characteristics of GNSS services, with integrity representing the reliability of the service provided. As the accuracy of GNSS services continues to improve and its application scope expands, the integrity of the system, which is crucial for user safety, is receiving increasing attention, especially in user sectors involving life safety, such as civil aviation and autonomous driving, which place high demands on the integrity performance of GNSS services.

[0003] GNSS provides users with satellite position and clock bias information through broadcast ephemeris. Users can determine their own position and time using the position and clock bias information of four or more satellites; this process is known as GNSS positioning and timing service. The position and clock bias information broadcast by each satellite is calculated by the GNSS operation and control system through information processing. This includes unmodeled errors in data processing and prediction errors in orbits and satellite clocks. The navigation system needs to inform users of the error magnitude or level of the satellite position and clock bias information in the broadcast ephemeris by broadcasting the accuracy parameters of each satellite. This allows users to directly obtain the accuracy of the broadcast ephemeris of different satellites, identify abnormal satellites, and thus improve the service safety performance of the navigation system.

[0004] The accuracy parameters of broadcast ephemeris generally reflect the standard deviation of satellite orbit and clock errors in the broadcast ephemeris. GNSS integrity service performance requirements necessitate ensuring that the accuracy parameters of the broadcast ephemeris can confidently encompass the spatial signal errors of the broadcast ephemeris with a certain probability. For example, current GPS system service performance specifications require that the projection of the spatial signal error of the satellite broadcast ephemeris onto the worst-case user direction exceed 4.42 times the URA (User Range Accuracy), while the probability of the system not issuing an alarm should be less than 10%. -5 That is, a 4.42 times URA threshold can encompass the projection of the satellite broadcast ephemeris spatial signal error in the worst-case user direction with a 99.999% probability. The BeiDou Global Navigation Satellite System has also committed to the International Civil Aviation Organization that the probability of a single satellite's spatial signal error exceeding 4.42 times SISA (Signal In Space Accuracy) is less than 10%. -5That is, the envelope capability of 4.42 times SISA for spatial signal error should be greater than 99.999%. As shown in the following formula, (1) In equation (1), URE represents probability, and URE represents User Range Error.

[0005] Currently, the broadcast ephemeris accuracy parameters broadcast in broadcast messages by various Global Navigation Satellite Systems (GNSS) are not the same, as shown in Table 1.

[0006] Table 1. Broadcast ephemeris accuracy parameters of various global satellite navigation systems In the LNAV messages broadcast on L1 signals, the US GPS system uses the "URAI" parameter to represent the integrated user distance accuracy level based on broadcast ephemeris orbit and clock bias. In the CNAV messages broadcast on L5 signals, it uses... Four precision parameters represent the precision of the broadcast ephemeris, among which The three parameters represent the user distance accuracy level, which is independent of the elevation angle. This indicates the level of accuracy of user distance related to altitude angle caused by orbital and clock bias parameters in the broadcast ephemeris. The European Galileo system uses this term in INAV / FNAV messages. "Parameters represent the comprehensive spatial signal accuracy level of the broadcast ephemeris orbit and clock bias parameters. The Chinese BeiDou-3 satellite navigation system (BDS-3) uses..." Four parameters represent the accuracy of the broadcast ephemeris, among which The prediction accuracy level represents the ratio of the satellite's orbital tangential to its normal direction, and is converted through the level to... (This represents the standard deviation of the error of the track tangent plane). This indicates the accuracy level of space signals related to clock bias, which is obtained by refining the clock bias to obtain the accuracy level of satellite orbit radial distance and clock bias prediction. This is achieved through level conversion... The three parameters represent the accuracy of satellite orbit radial deviation and satellite clock fixed deviation, satellite clock frequency offset accuracy, and satellite clock frequency drift accuracy, respectively.

[0007] The GPS system provides a mapping relationship between the user distance accuracy level URAI and the user distance accuracy URA in the LNAV message in the interface control file, as shown in formula (2): (2) It also clearly specifies the four precision parameters broadcast in CNAV messages. The calculation method is as follows.

[0008] URA ED Take URAI ED The upper limit of the hierarchical relationship. URA ED Take URAI ED The conversion relationship is shown in Table 2.

[0009] Table 2 URAI ED Index Relationship Table URA NED0 Take URAI NED0 The upper limit of the hierarchical relationship. URA NED0 Take URAI NED0 The conversion relationship is shown in Table 3.

[0010] Table 3 URAI NED0 Index Relationship Table The calculation formula is as follows: (3) (4) comprehensive Computable The formula is as follows: (5) In equation (5), t i It is the observation time, t o This is the reference time for the message. When used by users, the level value of the broadcast ephemeris accuracy parameter is converted into a specific real value for calculating the positioning protection level and evaluating navigation and positioning accuracy.

[0011] The Galileo system provides a method for calculating the Spatial Signal Accuracy (SISA) in INAV / FNAV messages in its interface control file. SISA is taken as the upper limit of the SISAI level relationship. The conversion relationship between SISA and SISAI is shown in Table 4.

[0012] Table 4 SISAI Index Relationship Table Although the GPS and Galileo systems provide user algorithms for broadcast ephemeris accuracy parameters in their interface control files, they do not provide system implementation algorithms for these parameters, and there are no relevant references in academic literature.

[0013] Reference [1] proposes a BeiDou broadcast ephemeris accuracy parameter based on prior information adjustment. The parameter processing algorithm works as follows: Step 1, while the orbit determination system predicts the orbit and clock error parameters, the prediction variance is transferred in parallel using the transfer matrix to provide the covariance matrix of the predicted orbit and clock error parameters for each prediction epoch. Then, based on the predicted orbit and clock error covariance information, the prediction accuracy of the satellite's predicted orbit and clock error is calculated. Predicted values; Step 2, using post-processing to obtain precise orbit and clock bias products, compare the predicted orbit and clock bias from the broadcast ephemeris to calculate the prediction error of the orbit and clock bias. The predicted value is adjusted to obtain Step 3: Utilize global laser observation data to perform error verification on the satellite's precise orbit products. Based on the laser verification results, [the following steps are taken]. Loose coupling adjustment is performed to obtain the final navigation message. Broadcast parameters.

[0014] Because the BeiDou-3 satellite navigation system employs an independent two-way time synchronization system between satellites and ground stations, and processes satellite orbit and clock bias information independently, its broadcast ephemeris spatial signal error characteristics differ from those of the GPS and Galileo systems. While its satellite ephemeris accuracy is high, its clock bias parameter accuracy is slightly lower. Therefore, a different parameter system was used in the design of the broadcast ephemeris accuracy parameters compared to GPS and Galileo. Due to the relatively short service time, the user algorithm for the broadcast ephemeris accuracy parameters still requires further validation. Currently, the official BeiDou interface control documents do not yet provide a user algorithm for the broadcast ephemeris accuracy parameters.

[0015] This paper proposes a system implementation algorithm and a user application algorithm suitable for the broadcast ephemeris accuracy parameters of the BeiDou-3 satellite navigation system, which is of great significance for improving the integrity service performance of the BeiDou-3 satellite navigation system.

[0016] The technology for generating spatial signal accuracy of broadcast ephemeris includes two aspects: first, how to accurately predict the spatial signal accuracy of broadcast ephemeris; and second, due to the limitation of satellite broadcast message bandwidth, it is necessary to design a user conversion algorithm to convert the spatial signal accuracy of broadcast ephemeris into a spatial signal accuracy index before broadcasting it through satellite broadcast messages.

[0017] For the spatial signal accuracy prediction algorithm of Beidou broadcast ephemeris, reference [1] gives a processing algorithm. This algorithm has three calculation steps, the calculation process is relatively complicated, and the ability to identify systematic errors in the observation data is low. The calculation results are prone to being idealized, which may cause the risk of missing envelope.

[0018] Since the official BeiDou interface control document has not yet provided the algorithm for user-defined broadcast ephemeris accuracy parameters, directly using the four accuracy parameters from the GPS system CNAV message would be problematic. The user-used algorithm calculates the broadcast ephemeris accuracy of the BeiDou system and evaluates it accordingly. The ability to enclose orbital plane errors, and Envelope capability for orbital radial and clock error.

[0019] The formula for the error envelope is: (6) (7) in, It is the integrity risk coefficient, according to The parameter must meet the envelope index requirement of 99.999%, and the value is 4.42. These represent the radial, tangential, and normal errors between the orbit calculated from the broadcast ephemeris and the precise orbit. The numerator is the second difference between the difference between the broadcast clock error and the precision clock error. The premise for statistical analysis is that the satellite is healthy (satellite health status identifier Hs=0). This indicates the total number of evaluation points.

[0020] Using broadcast ephemeris data from the BeiDou-3 satellite navigation system B1C signal broadcast from January to June 2023, an assessment revealed that certain time periods... The parameters do not adequately cover the radial error of the satellite (orbit radial error and clock error), failing to meet SISA's commitment to a space signal error envelope capability greater than 99.999%. The envelope probability of the satellite's radial error is shown in Table 5.

[0021] Table 5 CNAV1 Message SISA Parameter Error Envelope Capability (%) Taking C32 and C23 satellites as examples, the envelope time series of SISA parameters with respect to error is as follows: Figure 1 , Figure 2 As shown in the figures, the upper subplot shows the envelope result of the SISAoe parameter on the orbital tangent plane error, and the lower subplot shows the envelope result of the SISAoc parameter on the orbital radial and clock error. The curve at the top of the subplot represents 4.42 times the SISA parameter (alarm threshold), and the curve at the bottom of the subplot represents the orbital and clock error prediction errors in the broadcast ephemeris.

[0022] Therefore, it is evident that the user conversion algorithm for the broadcast ephemeris accuracy parameters of the GPS system is not applicable to the broadcast ephemeris accuracy parameters of the BeiDou-3 satellite navigation system.

[0023] There is a lack of relevant literature research on the implementation algorithm of spatial signal accuracy parameters of broadcast ephemeris of foreign satellite navigation systems. The calculation method of SISA integrity parameters given in Reference [1] for Beidou system is relatively complicated and is not sensitive to systematic errors in the data, which is prone to the risk of missing envelope.

[0024] The BeiDou-3 satellite navigation system has not yet provided a user algorithm for the spatial signal accuracy (SISA) of broadcast ephemeris. If the user algorithm for URA parameters in the GPS system CNAV message is directly referenced, the calculated satellite orbit radial and clock error accuracy parameters cannot accurately reflect the satellite clock error and the satellite clock error drift rate. This will result in insufficient envelope capability of the satellite orbit radial and clock error accuracy parameters for the satellite's radial error (i.e., orbit radial error and clock error), causing system integrity risk events and affecting the operational service integrity performance of the BeiDou-3 satellite navigation system. Summary of the Invention

[0025] To address some or all of the problems in the existing technology, this invention provides a method for generating broadcast ephemeris accuracy parameters, which includes the following steps: Enter the broadcast ephemeris and precise ephemeris in the data input module and store them in the database; Extract the broadcast ephemeris and precise ephemeris from the database and use them in the error calculation module to calculate the satellite broadcast orbit and clock error; The quadratic difference method is used in the error fitting module to evaluate the accuracy of broadcast clock errors; In the coefficient extraction module, the clock error is fitted to extract the coefficients of the first-order term of the clock error fitting. Based on the coefficient of the first term, a constant value suitable for the BeiDou-3 satellite navigation system is selected in the level conversion module as the satellite clock frequency offset accuracy of the BeiDou-3 satellite navigation system. With satellite clock frequency offset accuracy index The level conversion algorithm; and Accuracy parameters are generated in the accuracy parameter generation module according to the level conversion algorithm.

[0026] Furthermore, the calculation of satellite broadcast orbit and clock error in the error calculation module includes: The formula for converting BDST to GPST is as follows: (8) in, and These represent the GPS and BDS time bases, respectively. Perform PCO and TGD corrections; Convert the broadcast orbit error in the XYZ coordinate system to a value in the satellite orbit coordinate system.

[0027] Furthermore, the implementation of PCO and TGD corrections includes: The satellite position coordinate reference point of the broadcast ephemeris is transformed from the phase center to the barycenter using the following formula: (9) in, and These represent the satellite phase center coordinates and mass center coordinates for the broadcast ephemeris, respectively. This represents the transformation matrix from the satellite coordinate system to the Earth-centered Earth-fixed coordinate system. PCO corrections used in broadcast ephemeris calculations; Calculate the clock error deviation caused by the inconsistency between the precision clock error and the broadcast clock error in the Z-direction PCO. , (10) in, and These represent the Z-PCO values ​​of the satellite antenna used in the orbit calculations for broadcast ephemeris and precise ephemeris, respectively. The execution time group delay correction formula is as follows: (11) Where dt represents the broadcast clock bias after group delay correction. and These represent the frequencies of the B1I and B3I signals in the BeiDou Navigation Satellite System, respectively. Indicates satellite broadcast clock bias, This indicates the hardware delay parameter of the B1I signal broadcast in real time by the BeiDou Navigation Satellite System.

[0028] Furthermore, the conversion of the broadcast orbit error in the XYZ coordinate system to a value in the satellite orbit coordinate system includes: The conversion formula is as follows: (12) in, This represents the error vector between the coordinates calculated from the broadcast ephemeris and the coordinates provided by the precise ephemeris. , Given by the following formula, (13) in, and These respectively represent calculations based on broadcast ephemeris. The satellite's three-dimensional coordinates and velocity at any given time.

[0029] Furthermore, the method of using quadratic difference to evaluate the broadcast clock error accuracy in the error fitting module includes: Use the following formula to evaluate the accuracy of broadcast clock errors. (14) (15) in, For a certain epoch, the first i The precise clock bias of each satellite, The first calculated for broadcast ephemeris under the same epoch i The clock bias of a satellite - For the same epoch i The first difference between the precision clock error of a satellite and the broadcast ephemeris clock error. It is the average of the first difference of all satellites in the same epoch of the entire system; using this average as a benchmark, the second difference sequence is obtained by subtracting from the first difference, thus eliminating the system bias caused by the different benchmarks of different clock products to all satellites in the constellation.

[0030] Furthermore, based on the coefficient of the first term, a constant value suitable for the BeiDou-3 satellite navigation system is selected in the level conversion module as the satellite clock frequency offset accuracy of the BeiDou-3 satellite navigation system. With satellite clock frequency offset accuracy index The level conversion algorithms include: The maximum value among all linear coefficients is selected and calculated using the following formula. Comparison of changes (16) in, Values ​​range from 0 to 7. N Values ​​range from 1 to 14.

[0031] By traversing the range of constant values ​​and considering the statistical characteristics of the coefficients of the first-order term fitted to the satellite clock error of the BeiDou-3 satellite navigation system, a suitable constant value for the BeiDou satellite navigation system is selected as the satellite clock frequency offset accuracy of the BeiDou-3 satellite navigation system. With satellite clock frequency offset accuracy index The level conversion algorithm.

[0032] Furthermore, generating the accuracy parameters in the accuracy parameter generation module includes: The formula for generating the accuracy parameter is as follows: (19) (20) in Indicates the satellite clock frequency offset accuracy index. Indicates the frequency offset accuracy of the satellite clock. This indicates the radial and fixed deviation accuracy index of the satellite orbit.

[0033] The present invention also provides a system for generating broadcast ephemeris accuracy parameters, the system comprising the following modules: The data input module is configured to input broadcast ephemeris and precise ephemeris, and store them in the database; An error calculation module is configured to extract the broadcast ephemeris and precise ephemeris from the database and to calculate satellite broadcast orbit and clock error therein; The error fitting module is configured to use a quadratic difference method to evaluate the accuracy of broadcast clock errors. A coefficient extraction module is configured to perform fitting on the clock error to extract the coefficients of the first-order term of the clock error fitting. The level conversion module is configured to select a constant value suitable for the BeiDou-3 satellite navigation system from the coefficients of the first-order term, and use this constant value as the satellite clock frequency offset accuracy of the BeiDou-3 satellite navigation system. With satellite clock frequency offset accuracy index The level conversion algorithm; and The accuracy parameter generation module is configured to generate accuracy parameters therein according to the level conversion algorithm.

[0034] The present invention also provides a computer system, comprising: A processor, configured to execute machine-readable instructions; and A memory configured to store machine-readable instructions that, when executed by a processor, perform the steps of the precision parameter generation method.

[0035] The present invention also provides a computer-readable storage medium storing machine-readable instructions thereon, which, when executed by a processor, perform the steps of the precision parameter generation method.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention proposes for the first time broadcast ephemeris accuracy parameters. The method for determining the user level conversion formula was improved, and the broadcast ephemeris accuracy parameters were refined. The broadcast value of the parameter is implemented. The zero-order missing envelope of the parameters relative to the radial error of the satellite can reduce system integrity risks caused by unreasonable message parameter broadcast values. Attached Figure Description

[0037] To further illustrate the above and other advantages and features of the various embodiments of the present invention, a more specific description of the various embodiments of the present invention will be presented with reference to the accompanying drawings. It is to be understood that these drawings depict only typical embodiments of the invention and are therefore not intended to limit its scope. In the drawings, identical or corresponding parts will be indicated by identical or similar reference numerals for clarity.

[0038] Figure 1 A schematic diagram of the error envelope results for the SISAoe and SISAoc parameters of the C32 satellite is shown. Figure 2 A schematic diagram of the error envelope results for the SISAoe and SISAoc parameters of the C23 satellite is shown. Figure 3 A flowchart illustrating a method for generating broadcast ephemeris precision parameters according to an embodiment of the present invention is shown. Figure 4 This diagram illustrates the trend of the maximum value of the first-order term coefficient of the clock error fitting of each satellite in the BeiDou-3 satellite navigation system over one hour. Figure 5 This shows the generation of formula (16) when N=4 in the BeiDou-3 satellite navigation system. A diagram illustrating the trend of parameter changes; Figure 6 This shows the generation of formula (16) when N=14 in the BeiDou-3 satellite navigation system. A diagram illustrating the trend of parameter changes; Figure 7 This shows the generation of formula (16) when N=10 in the BeiDou-3 satellite navigation system. A diagram illustrating the trend of parameter changes; and Figure 8 A schematic diagram of a broadcast ephemeris accuracy parameter generation system according to an embodiment of the present invention is shown. Detailed Implementation

[0039] In the following description, the invention is described with reference to various embodiments. However, those skilled in the art will recognize that the embodiments may be practiced without one or more specific details or in conjunction with other alternatives and / or additional methods or components. In other instances, well-known structures or operations are not shown or described in detail so as not to obscure the inventive points of the invention. Similarly, for illustrative purposes, specific numbers and configurations are set forth to provide a comprehensive understanding of embodiments of the invention. However, the invention is not limited to these specific details.

[0040] In this specification, references to "an embodiment" or "this embodiment" mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. The phrase "in one embodiment" appearing throughout this specification does not necessarily refer to the same embodiment in all instances.

[0041] It should be noted that the embodiments of the present invention describe the method steps in a specific order; however, this is only for illustrating the specific embodiment and not for limiting the order of the steps. On the contrary, in different embodiments of the present invention, the order of the steps can be adjusted according to actual needs.

[0042] In this invention, the modules of the system according to the invention can be implemented using software, hardware, firmware, or a combination thereof. When a module is implemented using software, its function can be implemented through computer program flow. For example, the module can be implemented using code segments (such as code segments in languages ​​like C and C++) stored in a storage device (such as a hard disk, memory, etc.), wherein the corresponding function of the module can be implemented when the code segment is executed by a processor. When a module is implemented using hardware, its function can be implemented by setting a corresponding hardware structure. For example, the module's function can be implemented by hardware programming a programmable device such as a field-programmable gate array (FPGA), or by designing an application-specific integrated circuit (ASIC) that includes multiple transistors, resistors, capacitors, and other electronic devices. When a module is implemented using firmware, the module's function can be written into a read-only memory such as an EPROM or EEPROM in the form of program code, and the corresponding function of the module can be implemented when the program code is executed by a processor. In addition, some functions of the module may need to be implemented by separate hardware or by working in cooperation with the hardware. For example, the detection function is implemented by a corresponding sensor (such as a proximity sensor, accelerometer, gyroscope, etc.), the signal transmission function is implemented by a corresponding communication device (such as a Bluetooth device, infrared communication device, baseband communication device, Wi-Fi communication device, etc.), the output function is implemented by a corresponding output device (such as a display, speaker, etc.), and so on.

[0043] The existing BeiDou-3 satellite navigation system does not provide a user algorithm for the spatial signal accuracy (SISA) of broadcast ephemeris. Directly referencing the URA parameter user algorithm in the GPS system's CNAV message results in insufficient envelope capability of the calculated satellite orbit radial and clock error accuracy parameters for the satellite's radial error, potentially leading to system integrity risks and affecting the operational service integrity performance of the BeiDou-3 satellite navigation system. This invention proposes a system implementation algorithm and user algorithm applicable to the spatial signal accuracy parameters of the BeiDou-3 satellite navigation system's broadcast ephemeris. This algorithm accurately expresses the spatial signal accuracy of the satellite navigation system. While meeting the message reservation size for the spatial signal accuracy parameters in the broadcast ephemeris, it improves the envelope capability of the broadcast ephemeris's spatial signal accuracy parameters for satellite tangential plane errors and radial errors, thus addressing system integrity risks caused by unreasonable broadcast message parameter values ​​even when the actual satellite spatial signal error is within the normal range.

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0045] Figure 3 A flowchart illustrating a method for generating broadcast ephemeris precision parameters according to an embodiment of the present invention is shown. Figure 3 As shown, the method for generating broadcast ephemeris precision parameters includes the following steps: First, the broadcast ephemeris and precise ephemeris are input into the data input module and stored in the database. Global Navigation Satellite System (GNSS) satellite ephemeris are divided into predicted ephemeris and post-processed ephemeris. Predicted ephemeris is also known as broadcast ephemeris. Post-processed ephemeris is also known as precise ephemeris.

[0046] Next, the broadcast ephemeris and precise ephemeris are extracted from the database and used in the error calculation module to calculate the satellite broadcast orbit and clock error. This step includes: First, the BeiDou-3 satellite navigation system (BDS-3) broadcasts ephemeris time reference BDS time (BDST), while the precise ephemeris time system is GPS time (GPST). The conversion formula from BDST to GPST is as follows: (8) in, and These represent the GPS and BDS time bases, respectively. Furthermore, due to their different starting epochs, BDST and GPST differ by 1356 weeks.

[0047] Next, corrections such as PCO (Phase Center Offset) and TGD (Timing Group Delay) are performed.

[0048] The satellite position coordinate reference points for calculating precise ephemeris and broadcast ephemeris are the satellite's center of mass and the antenna's phase center, respectively. Evaluating the orbital accuracy of broadcast ephemeris requires correcting the satellite antenna's phase center, which necessitates converting the coordinate reference point from the phase center to the center of mass. The conversion formula is as follows: (9) in, and These represent the satellite phase center coordinates and mass center coordinates for the broadcast ephemeris, respectively. This represents the transformation matrix from the satellite coordinate system to the Earth-centered Earth-fixed coordinate system. The PCO correction value used in broadcast ephemeris calculation.

[0049] Both precision clock bias and broadcast clock bias absorb most of the satellite antenna Z-PCO. When using precision clock bias to evaluate broadcast clock bias, it is necessary to eliminate the clock bias deviation caused by the inconsistency in the Z-direction PCO of the satellite antennas used in the two clock bias products. , (10) in, and These represent the Z-PCO values ​​of the satellite antenna used in the orbit calculations for broadcast ephemeris and precise ephemeris, respectively.

[0050] BDS's current precision clock bias products are based on the B1I / B3I ionospheric-free combination calculation, with B3I as the reference frequency for its broadcast clock bias solution. When comparing the two, the hardware delay inconsistencies absorbed in the clock bias must be considered. Time group delay correction needs to be performed, using the following formula: (11) Where dt represents the broadcast clock bias after group delay correction. and These represent the frequencies of the B1I and B3I signals in the BeiDou Navigation Satellite System, respectively. Indicates satellite broadcast clock bias, This represents the hardware delay parameter of the B1I signal broadcast in real time by BDS.

[0051] After the above corrections, the orbital position and clock bias calculated from the broadcast ephemeris are consistent with the reference standards for orbit and clock bias in the precise ephemeris product. The difference between the two represents the prediction error of the satellite broadcast orbit and broadcast clock bias. The broadcast orbit error in the XYZ coordinate system is then converted to a value in the RTN coordinate system (satellite orbit coordinate system, radial, transverse, normal). The conversion formula is as follows: (12) in, This represents the error vector between the coordinates calculated from the broadcast ephemeris and the coordinates provided by the precise ephemeris. , Given by the following formula, (13) in, and These respectively represent calculations based on broadcast ephemeris. The satellite's three-dimensional coordinates and velocity at any given time.

[0052] Next, the quadratic difference method is used in the error fitting module to evaluate the broadcast clock bias accuracy. After calculating the clock bias errors of all satellites, differences in the time scale and reference realization exist between different clock bias products. Ignoring this effect would result in the same deviation for all satellites within the constellation. Therefore, taking into account time system differences, satellite antenna PCO and TGD corrections, the following formula is used to evaluate the broadcast clock bias accuracy. (14) (15) in, For a certain epoch, the first i The precise clock bias of each satellite, The first calculated for broadcast ephemeris under the same epoch i The clock bias of a satellite - For the same epoch i The first difference between the precision clock error of a satellite and the broadcast ephemeris clock error. It is the average of the first difference of all satellites in the same epoch of the entire system. Using this average as a benchmark, the second difference sequence is obtained by subtracting it from the first difference, thus eliminating the systematic bias caused by the different benchmarks of different clock products to all satellites in the constellation.

[0053] Next, in the coefficient extraction module, the clock error is fitted to extract the first-order coefficients of the clock error fitting. Fitting is performed on a 1-hour basis for each satellite. First-order or second-order fitting is selected based on whether the predicted age in the broadcast ephemeris is greater than 26 hours, and the first-order coefficients of the clock error fitting for each satellite are extracted.

[0054] Next, based on the first-order term coefficient, a constant value suitable for the BeiDou-3 satellite navigation system is selected in the level conversion module as the satellite clock frequency offset accuracy of the BeiDou-3 satellite navigation system. With satellite clock frequency offset accuracy index The level conversion algorithm.

[0055] For the coefficients of the first-order terms of each extracted satellite clock bias fitting, the maximum value among all the first-order coefficients is selected and calculated using the following formula. Comparison of changes (16) in, Values ​​range from 0 to 7. N Values ​​range from 1 to 14.

[0056] By traversing the range of constant values ​​and considering the statistical characteristics of the coefficients of the first-order term fitted to the satellite clock error of the BeiDou-3 satellite navigation system, a suitable constant value for the BeiDou satellite navigation system is selected as the satellite clock frequency offset accuracy of the BeiDou-3 satellite navigation system. With satellite clock frequency offset accuracy index The level conversion algorithm.

[0057] Because the coefficient of the first term is too small, the change in clock difference over 1 hour (3600 seconds) is compared, as shown in Table 6.

[0058] Table 6 shows the formula (16) generated. Statistical results of parameter changes over 1 hour Figure 4 This diagram illustrates the trend of the maximum value of the first-order coefficient of the clock bias fitting for each satellite of the BeiDou-3 satellite navigation system over one hour. Figure 4 As shown, the maximum value of the first-order coefficient of the clock error fitting of each satellite in the BeiDou-3 satellite navigation system, which is also the maximum value of the BDS-3 evaluation value, is 1.658 meters, and the minimum value, which is also the minimum value of the BDS-3 evaluation value, is 0.766 meters.

[0059] Figure 5 This shows the BeiDou-3 satellite navigation system. When the formula (16) is generated A diagram illustrating the trend of parameter changes. (Example) Figure 5 As shown, when When the value is 0~7, The values ​​are all greater than the maximum value of the BDS-3 evaluation (1.658 meters), verifying the current BDS calculation. The formula is not applicable.

[0060] Figure 6 This shows the BeiDou-3 satellite navigation system. When the formula (16) is generated A diagram illustrating the trend of parameter changes. (Example) Figure 6 As shown, when When the value is 0~7, The values ​​were all less than the minimum value of the BDS-3 assessment (0.766 meters), verifying that the calculation was performed by directly referring to the GPS system URANed1 calculation formula. The actual data calculation results are not applicable to BDS-3.

[0061] Choose the appropriate N value corresponding The value should satisfy: when When the value is between 0 and 7, its maximum value is greater than the maximum value among all satellite coefficient values. (The maximum value of the BDS-3 assessment is 1.658 meters), and the minimum value is less than the minimum of all the maximum values ​​of the satellite coefficients. (The minimum value of the BDS-3 assessment is 0.766 meters), while ensuring that the maximum value is not exceeded. The parameters have redundancy and relatively small values, leaving room for future system upgrades. The BDS-3 evaluation's maximum / minimum conditions meet the requirements. N The value ranges from 6 to 10. Considering the redundancy and the condition of taking a small value, the value is determined. , that is Figure 7 As shown. Also, a reminder to update the broadcast ephemeris. Values ​​can be determined using the same method for other systems. N value.

[0062] The maximum sum of the RMS values ​​of orbital radial error and clock error among all satellites in the RTN coordinate system is selected as the maximum value. The minimum limit, based on the statistical results of the BDS system from January to June 2023, is shown in Table 7. The minimum limit is 0.953 meters (i.e., the sum of Radial MEO 0.198 meters and Clock IGSO 0.755 meters). Refer to Table 3 for broadcast information. The minimum level should be -2. Therefore, users can convert levels accordingly. The calculated value should be 1.2 meters.

[0063] Table 7. BDS-3 Satellite Orbit and Clock Error RMS Values / m Finally, based on the level conversion algorithm, the accuracy parameters are generated in the accuracy parameter generation module.

[0064] Based on the selected level conversion algorithm, the basic integrity message accuracy parameters of the BDS-3 system are generated using the following formula: (17) =1.2( (18) Therefore, the formula for generating broadcast ephemeris accuracy parameters provided by this invention patent is as follows: (19) (20) in Indicates the satellite clock frequency offset accuracy index. Indicates the frequency offset accuracy of the satellite clock. This indicates the radial and fixed deviation accuracy index of the satellite orbit.

[0065] This invention is the first to propose broadcast ephemeris accuracy parameters. The method for determining the user level conversion formula was improved, and the broadcast ephemeris accuracy parameters were refined. The broadcast value of the parameter is implemented. The zero-order missing envelope of the parameters relative to the radial error of the satellite can reduce system integrity risks caused by unreasonable message parameter broadcast values.

[0066] This invention also provides a system for generating broadcast ephemeris accuracy parameters. Figure 8 A schematic diagram of a broadcast ephemeris accuracy parameter generation system according to an embodiment of the present invention is shown. Figure 8 As shown, the system includes the following modules: The data input module is configured to input broadcast ephemeris and precise ephemeris, and store them in the database; An error calculation module is configured to extract the broadcast ephemeris and precise ephemeris from the database and to calculate satellite broadcast orbit and clock error therein; The error fitting module is configured to use a quadratic difference method to evaluate the accuracy of broadcast clock errors. A coefficient extraction module is configured to perform fitting on the clock error to extract the coefficients of the first-order term of the clock error fitting. The level conversion module is configured to select a constant value suitable for the BeiDou-3 satellite navigation system from the coefficients of the first-order term, and use this constant value as the satellite clock frequency offset accuracy of the BeiDou-3 satellite navigation system. With satellite clock frequency offset accuracy index The level conversion algorithm; and The accuracy parameter generation module is configured to generate accuracy parameters therein according to the level conversion algorithm.

[0067] In one embodiment of the present invention, a computer system is also provided, comprising a processor and a memory. The processor is configured to execute machine-readable instructions, and the memory is configured to store machine-readable instructions. When the processor executes the machine-readable instructions, it performs the following processing steps: inputting broadcast ephemeris and precise ephemeris into a data input module and storing them in a database; retrieving the broadcast ephemeris and precise ephemeris from the database and using them to calculate satellite broadcast orbit and clock error in an error calculation module; evaluating the broadcast clock error accuracy using a quadratic difference method in an error fitting module; performing fitting on the clock error in a coefficient extraction module to extract the first-order coefficients of the clock error fitting; and selecting a constant value suitable for the BeiDou-3 satellite navigation system in a level conversion module based on the first-order coefficients as the satellite clock frequency offset accuracy of the BeiDou-3 satellite navigation system. With satellite clock frequency offset accuracy index The level conversion algorithm; and the generation of precision parameters in the precision parameter generation module according to the level conversion algorithm.

[0068] The memory includes various media capable of storing machine-readable instructions, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0069] It is understood that, in addition to the memory and processor mentioned above, the computer system described above also includes other hardware and software components not listed in this specification. The specific components can be determined according to the model of the specific data processing equipment in different application scenarios, and will not be listed and described in detail in this specification.

[0070] In one embodiment, a computer-readable storage medium is also provided, on which machine-readable instructions are stored. When executed by a processor, the machine-readable instructions perform the following processing steps: inputting broadcast ephemeris and precise ephemeris into a data input module and storing them in a database; retrieving the broadcast ephemeris and precise ephemeris from the database and using them to calculate satellite broadcast orbit and clock error in an error calculation module; evaluating broadcast clock error accuracy using a quadratic difference method in an error fitting module; performing fitting on the clock error in a coefficient extraction module to extract the first-order coefficients of the clock error fitting; and selecting a constant value suitable for the BeiDou-3 satellite navigation system in a level conversion module based on the first-order coefficients as the satellite clock frequency offset accuracy of the BeiDou-3 satellite navigation system. With satellite clock frequency offset accuracy index The level conversion algorithm; and the generation of precision parameters in the precision parameter generation module according to the level conversion algorithm.

[0071] Although various embodiments of the invention have been described above, it should be understood that they are presented by way of example only and not as limitations. It will be apparent to those skilled in the art that various combinations, modifications, and alterations can be made without departing from the spirit and scope of the invention. Therefore, the breadth and scope of the invention disclosed herein should not be limited by the exemplary embodiments disclosed above, but should be defined solely by the appended claims and their equivalents.

[0072] The following is a list of references cited in this invention: [1] Chen Jinping, Cao Yueling, Guo Rui, et al. Calculation method and performance verification of spatial signal accuracy parameter SISA of Beidou experimental satellite [J]. Acta Geodaetica et Cartographica Sinica, 2018, 47(B12):8. DOI:CNKI:SUN:CHXB.0.2018-S1-001.

Claims

1. A method for generating broadcast ephemeris accuracy parameters, characterized in that, Includes the following steps: Enter the broadcast ephemeris and precise ephemeris in the data input module and store them in the database; Extract the broadcast ephemeris and precise ephemeris from the database and use them in the error calculation module to calculate the satellite broadcast orbit and clock error; The quadratic difference method is used in the error fitting module to evaluate the accuracy of broadcast clock errors; In the coefficient extraction module, the clock error is fitted to extract the coefficients of the first-order term of the clock error fitting. Based on the first-order coefficient, a suitable constant value for the BeiDou-3 satellite navigation system is selected in the level conversion module as the satellite clock frequency offset accuracy (SISA) of the BeiDou-3 satellite navigation system. oc1 With the satellite clock frequency offset accuracy index SISAI oc1 The level conversion algorithm; and Accuracy parameters are generated in the accuracy parameter generation module according to the level conversion algorithm.

2. The method for generating accuracy parameters according to claim 1, characterized in that, The calculation of satellite broadcast orbit and clock error in the error calculation module includes: The formula for converting BDST to GPST is as follows: T BDS =T GPS -14s Among them, T GPS With T BDS These represent the GPS and BDS time bases, respectively. Perform PCO and TGD corrections; Convert the broadcast orbit error in the XYZ coordinate system to a value in the satellite orbit coordinate system.

3. The method for generating precision parameters according to claim 2, characterized in that, The implementation of PCO and TGD corrections includes: The satellite position coordinate reference point of the broadcast ephemeris is transformed from the phase center to the barycenter using the following formula: in, and A represents the coordinates of the satellite phase center and the centroid of the broadcast ephemeris, respectively. s This represents the transformation matrix from the satellite coordinate system to the Earth-centered Earth-fixed coordinate system. PCO corrections used in broadcast ephemeris calculations; Calculate the clock error deviation caused by the inconsistency between the precision clock error and the broadcast clock error in the Z-direction PCO. in, and These represent the Z-PCO values ​​of the satellite antenna used in orbit calculations for broadcast ephemeris and precise ephemeris, respectively. The execution time group delay correction formula is as follows: Where dt represents the broadcast clock bias after group delay correction, f1 and f3 represent the frequencies of the BeiDou Navigation Satellite System B1I and B3I signals, respectively, and t brd,B3 TGD1 represents the hardware delay parameter of the B1I signal broadcast in real time by the BeiDou Navigation Satellite System, indicating the satellite broadcast clock difference.

4. The method for generating precision parameters according to claim 2, characterized in that, The process of converting the broadcast orbit error in the XYZ coordinate system to a value in the satellite orbit coordinate system includes: The conversion formula is as follows: Where Δr represents the error vector between the coordinates calculated from the broadcast ephemeris and the coordinates provided by the precise ephemeris, Δr=(ΔX,ΔY,ΔZ), e radial e along e cross Given by the following formula, in, and These represent the satellite's three-dimensional coordinates and velocity at time t, calculated based on the broadcast ephemeris.

5. The method for generating precision parameters according to claim 1, characterized in that, The method of using the quadratic difference method to evaluate the broadcast clock error accuracy in the error fitting module includes: Use the following formula to evaluate the accuracy of broadcast clock errors. ΔC=T i -t i -μ Among them, T i Let t be the precise clock bias of the i-th satellite at a certain epoch. i T is the clock bias of the i-th satellite calculated using broadcast ephemeris at the same epoch. i -t i Let μ be the first difference between the precision clock error of the i-th satellite and the broadcast ephemeris clock error at the same epoch. μ is the average of the first differences of all satellites in the entire system at the same epoch. Using this average as a reference, the second difference sequence is obtained by subtracting from the first difference, thus eliminating the system bias caused by the different references of different clock error products to all satellites in the constellation.

6. The method for generating precision parameters according to claim 1, characterized in that, The constant value suitable for the BeiDou-3 satellite navigation system is selected in the level conversion module based on the first-order term coefficient, and is used as the satellite clock frequency offset accuracy (SISA) of the BeiDou-3 satellite navigation system. oc1 With satellite clock frequency offset accuracy index SISAI oc1 The level conversion algorithms include: The SISA is calculated by selecting the maximum value among all linear coefficients and using the following formula. oc1 Comparison of changes Among them, SISAI oc1 The value of N ranges from 0 to 7, and the value of N ranges from 1 to 14. A comprehensive search was conducted across the range of constant values. Based on the statistical characteristics of the coefficients of the first-order term fitted to the satellite clock bias error of the BeiDou-3 satellite navigation system, a suitable constant value was selected as the SISA (Series Indicator of Satellite Clock Frequency Offset) for the BeiDou-3 satellite navigation system. oc1 With satellite clock frequency offset accuracy index SISAI oc1 The level conversion algorithm.

7. The method for generating precision parameters according to claim 1, characterized in that, The generation of accuracy parameters in the accuracy parameter generation module includes: The formula for generating the accuracy parameter is as follows: SIDE oc1 =-log2SISA oc1 -10 SISAI ocb =-2 Among them, SISAI oc1 Indicates the satellite clock frequency offset accuracy index, SISA oc1 Indicates the frequency offset accuracy of satellite clocks, SISA ocb This indicates the radial and fixed deviation accuracy index of the satellite orbit.

8. A system for generating broadcast ephemeris accuracy parameters, characterized in that, Includes the following modules: The data input module is configured to input broadcast ephemeris and precise ephemeris, and store them in the database; An error calculation module is configured to extract the broadcast ephemeris and precise ephemeris from the database and to calculate satellite broadcast orbit and clock error therein; The error fitting module is configured to use a quadratic difference method to evaluate the accuracy of broadcast clock errors. A coefficient extraction module is configured to perform fitting on the clock error to extract the coefficients of the first-order term of the clock error fitting. The level conversion module is configured to select a constant value suitable for the BeiDou-3 satellite navigation system based on the coefficients of the first term, as the satellite clock frequency offset accuracy (SISA) of the BeiDou-3 satellite navigation system. oc1 With satellite clock frequency offset accuracy index SISAI oc1 The level conversion algorithm; and The accuracy parameter generation module is configured to generate accuracy parameters therein according to the level conversion algorithm.

9. A computer system, characterized in that, include: A processor, configured to execute machine-readable instructions; and A memory configured to store machine-readable instructions that, when executed by a processor and / or a graphics card, perform the steps of the method according to any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, It stores machine-readable instructions that, when executed by a processor, perform the steps of the method according to any one of claims 1-7.

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