PPP-B2b enhancement-based LEO on-orbit real-time precision orbit and clock error determination method and system

Abstract

The invention discloses an LEO on-orbit real-time precision orbit and clock error determination method and system based on PPP-B2b enhancement, and belongs to the technical field of low-orbit satellite high-precision autonomous orbit determination and clock error estimation. According to the method, enhanced information broadcasted by Beidou No.3 B2b signals is used for correcting a BDS-3 / GPS satellite orbit and clock correction, under the support of the regional BDS-3 / GPS enhanced information, when a new BDS-3 / GPS tracking satellite exists, before measurement updating, the inter-epoch clock correction variable quantity obtained through calculation by using a carrier phase time difference method is used as two orbit determination filtering clock correction parameters for constraint, so that the measurement accuracy is improved. In-orbit real-time separation of receiver clock error and non-difference floating point ambiguity parameters is carried out; and finally, substituting an LEO precision orbit output by orbit determination filtering and a non-difference floating point ambiguity parameter into a phase observation equation to calculate the precision clock error of the BDS-3 / GPS receiver. The method is suitable for the situation that only regional GNSS enhancement information support exists, and the influence of orbital maneuver is small.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-precision autonomous orbit determination and clock error estimation for low-orbit satellites, and specifically relates to a method and system for determining the LEO on-orbit real-time precise orbit and clock error based on PPP-B2b enhancement. Background Art

[0002] In recent years, with the increasing number of scientific missions of low-orbit satellites, many scientific missions have put forward higher and higher requirements on the orbit and clock error of low-orbit satellite platforms in terms of real-time performance, accuracy and reliability. Spaceborne GNSS has become the main technical means for high-precision orbit determination of low-orbit satellites due to its advantages such as continuous observation, high accuracy, low cost and power consumption, small size and light weight. Although the precise orbit determination of low-orbit satellites based on GNSS can reach the centimeter level through post-processing, it is heavily dependent on post-precision ephemeris and precise clock error products, so the timeliness is not high.

[0003] Since the BeiDou-3 (BDS-3) system was announced to be completed and put into operation in July 2020, in addition to providing high-quality and reliable positioning, navigation and timing services to users around the world, it also provides users with free static centimeter-level and dynamic decimeter-level precise point positioning (PPP) services. Among them, the PPP-B2b signal is used as a data broadcast channel to broadcast enhanced information such as the precise orbit and clock correction numbers of BDS-3 and other GNSS satellites through the BeiDou-3 GEO satellite to provide services to users.

[0004] However, BDS-3 PPP-B2b is currently mainly used in low-dynamic navigation and positioning application scenarios in the Asia-Pacific region. For high-dynamic low-orbit satellite scenarios, there is only regional GNSS enhancement information, which poses certain challenges to autonomous orbit determination data processing methods. In addition, low-orbit satellites inevitably have orbital maneuvers due to scientific mission requirements, and traditional simplified dynamics autonomous orbit determination methods cannot guarantee the accuracy and continuity of real-time orbits and clock errors during orbital maneuvers.

[0005] At present, the existing technologies are mainly focused on improving the orbit accuracy of low-orbit satellites, and there are relatively few studies on the real-time clock error estimation of low-orbit satellites. Therefore, there is an urgent need for a data processing method for on-orbit real-time autonomous orbit determination and clock error estimation of on-board GNSS of low-orbit satellites that only have regional augmentation information and are not affected by orbital maneuvers. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a method and system for determining LEO on-orbit real-time precise orbit and clock error based on PPP-B2b enhancement. The present invention can be used in situations where only regional GNSS enhancement information is supported and is less affected by orbital maneuvers.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The method for determining the LEO on-orbit real-time precise orbit and clock error based on PPP-B2b enhancement includes the following steps:

[0009] (1) Receive GNSS navigation signals and PPP-B2b enhancement signals through the GNSS receiving antenna;

[0010] (2) Filter, amplify, down-convert and sample GNSS navigation signals and PPP-B2b enhancement signals;

[0011] (3) Capture and track digital intermediate frequency signals through baseband signal processing, output GNSS raw observation data, including pseudorange, carrier phase, Doppler data, and output GNSS raw navigation messages and PPP-B2b messages;

[0012] (4) Parse the GNSS broadcast ephemeris and orbit and clock correction information PPP-B2b SSR from the GNSS original navigation message and PPP-B2b message respectively, match the PPP-B2b SSR with the GNSS broadcast ephemeris, and then correct the orbit and clock error calculated by the GNSS broadcast ephemeris to obtain real-time precise ephemeris;

[0013] (5) Complete the filtering estimation of the precise orbit in real time on orbit, and obtain the three-dimensional position and velocity of the low-orbit satellite in the Earth-centered Earth-fixed system, as well as the undifferenced floating-point ambiguity parameters of each satellite;

[0014] (6) Estimating precise clock errors in real time on orbit;

[0015] (7) Real-time ultra-short-term prediction of precise orbit and clock error on-orbit.

[0016] Furthermore, the specific method of step (4) is:

[0017] Parse the PPP-B2b message to obtain the satellite mask, satellite orbit correction number, and satellite clock correction number;

[0018] Parse the GNSS original navigation message to obtain the GNSS broadcast ephemeris;

[0019] Use the SSR version number to synchronize and match the satellite mask, satellite orbit correction number and satellite clock correction number, use the mask version number to synchronize and match the satellite mask and satellite clock correction number, and use the mask information to parse the satellite number of the satellite clock correction number, use the correction number version number to synchronize and match the satellite orbit correction number and satellite clock correction number, and use the IODN in the satellite orbit correction number to match the GNSS broadcast ephemeris;

[0020] After the matching is completed, the satellite orbit correction number and satellite clock correction number are used to calculate the real-time precise orbit and clock error, and obtain the real-time precise ephemeris.

[0021] Furthermore, the specific method of step (5) is:

[0022] (501) Two orbit determination filters based on kinematic orbit determination and based on simplified dynamic orbit determination are run simultaneously; wherein the filter state quantities of the two orbit determination filters based on kinematic orbit determination and based on simplified dynamic orbit determination are:

[0023]

[0024] In the formula, and are the filter state quantities based on kinematic orbit determination and simplified dynamic orbit determination, respectively. and for The three-dimensional position and velocity of the low-orbit satellite at any moment; and They are BDS-3 / GPS receiver clock error parameters, is the receiver clock rate parameter, is the atmospheric drag coefficient, is the solar pressure coefficient, are the empirical accelerations in the radial, tangential and normal directions of the orbit, The first of the two arrays The elements are The ambiguity parameters to be estimated for m BDS-3 satellites and n GPS satellites observed by the low-orbit satellite at the moment, The first of the two arrays The elements are The ephemeris errors of m BDS-3 satellites and n GPS satellites observed by low-orbit satellites at the moment along their respective signal propagation paths;

[0025] Depending on whether there is PPP-B2b augmentation information support, the ephemeris error along the BDS-3 / GPS signal propagation path is The piecewise random walk process is used for modeling;

[0026] (502) When updating the time, the satellite position is predicted in one step using the carrier phase time difference method based on the kinematic orbit determination, and the satellite position is predicted in one step using the low-orbit satellite orbit dynamics method based on the simplified dynamic orbit determination;

[0027] (503) When there is a new BDS-3 / GPS tracking satellite, before the measurement update, the inter-epoch clock error variation obtained by the carrier phase time difference method is used as a virtual observation value to constrain the two orbit determination filter clock error parameters. The on-orbit real-time orbit determination filter model with additional TDCP clock error constraints is obtained as follows:

[0028] (7)

[0029] In the formula, and are the Kalman filter state and observation, respectively. and are the state transfer matrix and the observation matrix respectively, and are system noise and observation noise respectively, for Time has come The change in BDS-3 / GPS receiver clock error between epochs calculated by the carrier phase time difference method; and They are Moment and BDS-3 / GPS receiver clock error parameters in the moment filter state;

[0030] The extended Kalman filter is used to measure and update equation (7) to obtain the precise orbit and non-differenced floating-point ambiguity of the low-orbit satellite, thereby decoupling and separating the receiver clock error and non-differenced floating-point ambiguity parameters in real time on orbit;

[0031] (504) After obtaining the results of orbit determination based on kinematics and orbit determination based on simplified dynamics, when it is detected and determined that the low-orbit satellite has an orbital maneuver, the result of kinematic orbit determination is output; otherwise, the result of simplified dynamics orbit determination is output.

[0032] Furthermore, the specific method of step (6) is:

[0033] (601) Substituting the three-dimensional position and velocity of the low-orbit satellite in the Earth-centered Earth-fixed system obtained in step (5) and the undifferenced floating-point ambiguity parameters of each satellite that have been decoupled from the receiver clock error as known values ​​into the carrier phase observation equation to solve the precise clock error of the low-orbit satellite receiver;

[0034] Among them, the BDS-3 satellite and The clock error of the low-orbit satellite BDS-3 / GPS receiver at the current epoch calculated from the ionosphere-free combined phase observations of the GPS satellites is expressed as:

[0035] (8)

[0036] In the formula, and The current epoch time is BDS-3, Ionosphere-free combined phase observations of GPS satellites and Calculated clock error parameters of low-orbit satellite BDS-3 / GPS; and The signal transmission time is BDS-3, The three-dimensional position of the GPS satellites in the Earth-centered Earth-fixed coordinate system; and Respectively BDS-3, Undifferenced floating point ambiguities of GPS satellites; and Respectively BDS-3, Phase winding error correction of GPS satellites; and Respectively BDS-3, Relativistic error correction of GPS satellites; and Respectively BDS-3, The geometric distance between the phase center of the transmitting antenna and the phase center of the receiving antenna of a GPS satellite, and:

[0037] , ,

[0038] , , They are the low-orbit satellite at the current epoch, BDS-3, The three-dimensional position of the GPS satellites in the Earth-centered Earth-fixed coordinate system;

[0039] (602) Calculate the mean and variance of the receiver precision clock error sequence, and construct the error limit condition with the mean and variance. When the receiver precision clock error of a channel exceeds the error limit, it is considered that the carrier phase observation value of this channel has a gross error and does not participate in the final receiver precision clock error calculation;

[0040] If the current low-orbit satellite receives a total of BDS-3 and GPS satellites, then the formula (8) is used to calculate The current low-orbit satellite BDS-3 precise clock error sequence and The current low-orbit satellite GPS precise clock error sequence ; Then, the mean value and standard deviation of the low-orbit satellite precise clock error sequence are calculated by the following formula:

[0041] (9)

[0042] in, and are the average values ​​of the BDS-3 / GPS precise clock error sequence of the low-orbit satellite, and are the standard deviations of the BDS-3 / GPS precision clock error series of low-orbit satellites;

[0043] (603) After excluding the channels with gross errors that exceed the limit, recalculate the mean of the receiver precision clock error sequence composed of all channels with qualified limits, and use the mean as the final BDS-3 / GPS receiver precision clock error.

[0044] Furthermore, in step (7), for the precise orbit, the dynamical orbit integral is used for prediction; for the precise clock error, the clock error-clock rate two-dimensional model is used for prediction, and the time interval of the ultra-short-term prediction is set to 1 minute.

[0045] The LEO on-orbit real-time precise orbit and clock determination system based on PPP-B2b enhancement includes:

[0046] A GNSS receiving antenna (1), used for receiving GNSS navigation signals and PPP-B2b enhancement signals;

[0047] A radio frequency front-end module (2) is used to filter, amplify, down-convert and sample GNSS navigation signals and PPP-B2b enhancement signals;

[0048] The baseband signal processing module (3) is used to realize the capture and tracking of the digital intermediate frequency signal, output the original GNSS observation data, including pseudorange, carrier phase, Doppler data, and output the original GNSS navigation message and PPP-B2b message;

[0049] The real-time precise ephemeris calculation module (4) parses the GNSS broadcast ephemeris and orbit and clock correction information PPP-B2b SSR from the GNSS original navigation message and the PPP-B2b message, matches the PPP-B2b SSR with the GNSS broadcast ephemeris, and then corrects the orbit and clock error calculated by the GNSS broadcast ephemeris to obtain the real-time precise ephemeris;

[0050] A real-time precise orbit estimation module (5) is used to complete the filtering estimation of the precise orbit in real time on orbit, and obtain the three-dimensional position and velocity of the low-orbit satellite in the Earth-centered Earth-fixed system, as well as the undifferenced floating-point ambiguity parameters of each satellite;

[0051] A real-time precise clock error estimation module (6), used to estimate the precise clock error in real time on orbit;

[0052] The precise clock error prediction module (7) is used to complete the ultra-short-term prediction of precise orbit and clock error in real time on orbit.

[0053] The beneficial effects of the present invention compared with the prior art are:

[0054] (1) The orbit determination filter of the present invention takes into account the ephemeris error along the BDS-3 / GPS signal propagation path. This parameter adopts a piecewise random walk model, which is suitable for the situation where low-orbit satellites can only obtain regional enhancement information.

[0055] (2) The present invention detects and determines whether the low-orbit satellite has orbital maneuvers by comparing the differences between the results based on kinematic orbit determination (KOD) and the results based on simplified dynamics orbit determination (RDOD), and then outputs the optimal orbit determination result that is not affected by the orbital maneuvers.

[0056] (3) The present invention takes the low-orbit satellite orbit and carrier phase ambiguity as known values, and inversely calculates the receiver's precise clock error through the carrier phase observation equation, while taking into account the impact of channel gross errors on the final receiver's precise clock error.

[0057] (4) The present invention uses the regional BeiDou-3 PPP-B2b augmentation information to improve the orbit determination and clock error estimation accuracy of low-orbit satellites in the Asia-Pacific region. At the same time, the method of the present invention can also be extended to the augmentation information broadcast by other navigation systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a schematic diagram of the principle of a LEO on-orbit real-time precise orbit and clock error determination system based on PPP-B2b enhancement in an embodiment of the present invention. DETAILED DESCRIPTION

[0059] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0060] The on-orbit real-time precise orbit and clock determination method for LEO based on PPP-B2b enhancement is applied on low-orbit satellites to correct the orbit and clock of BDS-3 / GPS satellites using the enhanced information broadcast by BeiDou-3 B2b signal. With the support of regional BDS-3 / GPS enhanced information, when there are new BDS-3 / GPS tracking satellites, before the measurement update, the inter-epoch clock error variation calculated by the time-differenced carrier phase (TDCP) method is used as the two orbit determination filter clock error parameters for constraint, and the receiver clock error and non-difference floating ambiguity parameters are separated in real time on-orbit; finally, the LEO precise orbit and non-difference floating ambiguity parameters output by the orbit determination filter are substituted into the phase observation equation to calculate the precise clock error of the BDS-3 / GPS receiver.

[0061] Specifically, the method comprises the following steps:

[0062] (1) Receive BDS-3 / GPS navigation signals and PPP-B2b enhanced signals through the GNSS receiving antenna;

[0063] (2) The RF front-end module completes the filtering, amplification, down-conversion and sampling (A / D conversion) of the BDS-3 / GPS navigation signal and the PPP-B2b enhanced signal;

[0064] (3) Complete the capture and tracking of digital intermediate frequency signals through the baseband signal processing module, output BDS-3 / GPS original observation data, including pseudorange, carrier phase, Doppler, etc., and output BDS-3 / GPS original navigation messages and PPP-B2b messages;

[0065] (4) Through the real-time precise ephemeris calculation module, the BDS-3 / GPS broadcast ephemeris and orbit and clock correction information (PPP-B2b SSR) are parsed from the BDS-3 / GPS original navigation message and PPP-B2b message respectively, the PPP-B2b SSR is matched with the GPS / BDS-3 broadcast ephemeris, and then the orbit and clock error calculated by the BDS-3 / GPS broadcast ephemeris are corrected to obtain the real-time precise ephemeris.

[0066] When parsing the PPP-B2b message, focus on parsing information type 1 (satellite mask), information type 2 (satellite orbit correction number), and information type 4 (satellite clock correction number) in the PPP-B2b message.

[0067] When matching PPP-B2b SSR with BDS-3 / GPS broadcast ephemeris, use the SSR version number (IOD SSR) to synchronize and match information types 1, 2, and 4, use the mask version number (IODP) to synchronize and match information types 1 and 4, and use the mask information to parse the satellite number of information type 4, use the correction number version number (IOD Corr) to synchronize and match information types 2 and 4, and use the IODN in information type 2 to match BDS-3 / GPS broadcast ephemeris.

[0068] After the matching is completed, the real-time precise orbit and clock correction are calculated using information type 2 (satellite orbit correction number) and information type 4 (satellite clock correction number). The specific calculation process refers to the precise point positioning service signal PPP-B2b ICD document, which will not be repeated here.

[0069] (5) The real-time precise orbit estimation module is used to complete the filtering estimation of the precise orbit in real time on-orbit. The specific method is as follows:

[0070] (501) Two orbit determination filters based on kinematics orbit determination (KOD) and reduced-dynamic orbit determination (RDOD) are run simultaneously. The orbit determination filter state includes the ephemeris error along the BDS-3 / GPS signal propagation path. The ephemeris error is modeled using a piecewise random walk model, and its random process noise is set according to the extreme value range of the ephemeris error change rate.

[0071] Among them, the filter state quantities of the two orbit determination filters based on kinematic orbit determination and simplified dynamics orbit determination are selected as:

[0072] (1)

[0073] In the formula, and They are the filter state quantities based on kinematic orbit determination (KOD) and simplified dynamic orbit determination (RDOD), and for The three-dimensional position and velocity of the LEO satellite at this moment; and They are BDS-3 / GPS receiver clock error parameters, is the receiver clock rate parameter; is the atmospheric drag coefficient, is the solar pressure coefficient, are the empirical accelerations of the orbital radial (R), tangential (T), and normal (N); They are The ambiguity parameters to be estimated for m BDS-3 satellites and n GPS satellites observed by the LEO satellite at the moment, They are The ephemeris errors of m BDS-3 satellites and n GPS satellites observed by the LEO satellite at this moment along their respective signal propagation paths.

[0074] Ephemeris error along the BDS-3 / GPS signal propagation path It can be calculated by the following formula:

[0075] (2)

[0076] In the formula, is the three-dimensional position of the low-orbit satellite in the Earth-centered Earth-fixed coordinate system; For the true three-dimensional position and clock error of BDS-3 / GPS satellite, the three-dimensional position and clock error of BDS-3 / GPS satellite calculated by the final precise ephemeris and clock error products released by IGS can usually be used as the reference truth value; is the three-dimensional position and clock error of the BDS-3 / GPS satellite calculated by the BDS-3 / GPS broadcast ephemeris or PPP-B2b SSR correction, and c is the speed of light;

[0077] Ephemeris error along the BDS-3 / GPS signal propagation path It has been shown that it can be modeled using a random walk process:

[0078] (3)

[0079] In the formula, is the three-dimensional position of the low-orbit satellite in the Earth-centered Earth-fixed coordinate system; For the true three-dimensional position and clock error of BDS-3 / GPS satellites, the three-dimensional position and clock error of BDS-3 / GPS satellites calculated from the final precise ephemeris and clock error products released by IGS can usually be used as the reference truth value; The three-dimensional position and clock error of the BDS-3 / GPS satellite calculated from the BDS-3 / GPS broadcast ephemeris or PPP-B2b SSR correction;

[0080] and They are Moment and The ephemeris error along the BDS-3 / GPS signal propagation path at the moment, is the epoch time interval, is a white noise sequence with zero mean, represents the variance of the variable, for The process noise variance is They are zero-mean white noise sequences The power spectral density of is the random process noise.

[0081] When the satellite is continuously tracking normally, The initial variance According to The maximum value of the random process noise is set and The power spectral density of By setting a suitable random model, If part of the ephemeris error along the BDS-3 / GPS signal propagation path can be absorbed, the corresponding real-time orbit determination accuracy will also be greatly improved.

[0082] Due to the limitation of regional tracking network, PPP-B2b can only be used in Asia-Pacific region. For low-orbit satellites, only when the sub-satellite point is in Asia-Pacific region can it receive PPP-B2b augmentation information matching GPS / BDS-3 observations. Other regions can only use BDS-3 / GPS broadcast ephemeris because there is no PPP-B2b augmentation information. Therefore, further, according to different situations of whether there is PPP-B2b augmentation information support, the ephemeris error along the BDS-3 / GPS signal propagation path is calculated. The piecewise random walk process is used for modeling, that is, In the case of regional PPP-B2b enhanced information support (without regional PPP-B2b enhanced information support, recorded as case 1), the random process noise is: , when there is only BDS-3 / GPS broadcast ephemeris (without regional PPP-B2b enhancement information support, recorded as working condition 0), the random process noise is .in, and The specific values ​​are based on the conditions 1 and 0 respectively. The rate of change is roughly set, for example, if the rate of change ranges between positive and negative 1, the corresponding random process noise is set to 1.

[0083] (502) When updating the time, the satellite position is predicted in one step using the carrier phase time difference method based on the kinematic orbit determination (KOD), and the satellite position is predicted in one step using the low-orbit satellite orbit dynamics method based on the simplified dynamic orbit determination (RDOD).

[0084] The carrier phase time difference method is to calculate the difference between the phase observation values ​​of the previous and next epochs when there is no cycle slip in the carrier phase observation value, and the carrier phase difference observation value between epochs can be obtained:

[0085] (4)

[0086] In the formula, is the carrier phase difference observation value between epochs; They are Moment and The non-differenced carrier phase observation value at time; is the change in geometric distance between epochs, which is related to both the LEO position and the BDS-3 / GPS navigation satellite position between epochs; and are the changes of receiver clock error and navigation satellite clock error between epochs respectively; is the phase winding correction variation between epochs; is the change in correction of relativistic effect between epochs; is the variation of multipath and observation noise; within a very short observation time interval, the errors such as the variation of BDS-3 / GPS satellite position / clock difference between epochs calculated by BDS-3 / GPS ephemeris (broadcast ephemeris or real-time precise ephemeris after its PPP-B2b correction) are at the same order of magnitude as the phase noise (about mm level), and can therefore be basically ignored.

[0087] Taking a single BDS-3 / GPS system as an example, if the number of BDS-3 / GPS satellites observed continuously reaches 4 or more, the position / clock difference change between LEO satellite epochs is ,in, is the component of the position change between epochs of the LEO satellite in the three axes in the Earth-centered Earth-fixed system, are the changes of BDS-3 / GPS receiver clock errors between epochs.

[0088] The least squares method can be used to solve it, which can be expressed as:

[0089] (5)

[0090] In the formula, is the epoch difference observation coefficient matrix; is the residual vector of epoch difference observations; is the weight matrix of epoch difference observations.

[0091] Based on the kinematic orbit determination (KOD), the TDCP method is used to predict the satellite position in one step, that is,

[0092] (6)

[0093] In the formula, They are The components of the three axes of the LEO satellite in the Earth-centered Earth-fixed system at this moment, They are The weight of the three axes of the LEO satellite in the Earth-centered Earth-fixed system at this moment.

[0094] Based on simplified dynamical orbit determination (RTOD), the satellite position is predicted using dynamical orbit integrals when the time is updated. This process is well known in the industry and will not be described in detail here.

[0095] (503) Before the measurement update, the inter-epoch clock error variation calculated by the time difference of carrier phase (TDCP) method is used as a virtual observation value to constrain the two orbit determination filter clock error parameters, and the receiver clock error and non-difference floating point ambiguity parameters are separated in real time on orbit.

[0096] Because the time difference carrier phase (TDCP) method eliminates the ambiguity parameters by taking the difference between the carrier phase observations of two consecutive epochs, the high-precision position and clock difference changes between epochs can be solved by least squares estimation, so the solved clock difference changes are independent of the ambiguity parameters and directly reflect the actual changes of the receiver clock. The accuracy of the solved clock difference changes is related to factors such as the noise of the carrier phase observations, multipath errors, BDS-3 / GPS real-time ephemeris errors, and satellite geometric distribution, and can usually obtain cm or even mm level accuracy.

[0097] In order to achieve the decoupling of LEO phase clock error and ambiguity parameters, based on the real-time precise orbit determination filter model, when the newly tracked satellite-borne BDS-3 / GPS observations are involved in the filtering orbit determination, the inter-epoch clock error variation calculated by TDCP is used as a constraint equation to participate in the filtering solution. Therefore, the on-orbit real-time orbit determination filter model with additional TDCP clock error constraints is as follows:

[0098] (7)

[0099] In the formula, and are the Kalman filter state quantity and observation quantity respectively; and They are the state transfer matrix and the observation matrix respectively; and are system noise and observation noise respectively; for Time has come The time is the change of BDS-3 / GPS receiver clock error between epochs calculated by the TDCP method using equation (5); and They are Moment and BDS-3 / GPS receiver clock error parameters in the moment filtering state.

[0100] The extended Kalman filter (EKF) is used to update the measurement of equation (7) to obtain the LEO precise orbit and non-differenced floating point ambiguity.

[0101] (504) After obtaining the results of kinematic orbit determination (KOD) and simplified dynamic orbit determination (RDOD), when it is detected and determined that the low-orbit satellite has an orbital maneuver, the result of kinematic orbit determination (KOD) is output, otherwise the result of simplified dynamic orbit determination (RDOD) is output.

[0102] (6) The precise clock error estimation module is used to estimate the precise clock error in real time on orbit. The specific method is as follows:

[0103] (601) The three-dimensional position and velocity of the low-orbit satellite in the Earth-centered Earth-fixed system output in step (5) and the undifferenced floating-point ambiguity parameters of each satellite are substituted as known values ​​into the carrier phase observation equation to solve the precise clock error of the low-orbit satellite receiver.

[0104] By BDS-3 satellite and The LEO satellite BDS-3 / GPS receiver clock error at the current epoch calculated from the ionosphere-free combined phase observations of the GPS satellites can be expressed as:

[0105] (8)

[0106] In formula (8), and The current epoch time is BDS-3 and Ionosphere-free combined phase observations of GPS satellites and Calculated LEO satellite BDS-3 / GPS clock error parameters; and The signal transmission time is BDS-3 / The three-dimensional position of the GPS satellites in the Earth-centered Earth-fixed coordinate system; , , and Respectively BDS-3 / The geometric distance between the phase center of the transmitting antenna and the phase center of the receiving antenna of a GPS satellite, and They are the LEO satellite at the current epoch and the BDS-3 / The three-dimensional position of the GPS satellites in the Earth-centered Earth-fixed coordinate system; and Respectively BDS-3 / The undifferenced floating point ambiguities of the GPS satellites are estimated by filtering in step (5); and Respectively BDS-3 / GPS satellite phase winding error correction; and Respectively BDS-3 / GPS satellite relativistic error correction.

[0107] (602) Calculate the mean and variance of the receiver precision clock error sequence obtained by the above solution, and construct the limit error condition with the mean and variance. When the receiver precision clock error of a certain channel exceeds the limit error, it is considered that the carrier phase observation value of this channel has a gross error, and therefore does not participate in the final receiver precision clock error calculation.

[0108] If the LEO satellite receives a total of BDS-3 and GPS satellites, then it can be calculated by formula (8): The LEO satellite BDS-3 precise clock error sequence at the current time and The LEO satellite GPS precise clock error sequence at the current time Then, the mean value and standard deviation of the LEO satellite precise clock error sequence can be calculated by the following formula:

[0109] (9)

[0110] in, and are the average values ​​of the LEO satellite BDS-3 / GPS precise clock error sequence, and are the standard deviations of the LEO satellite BDS-3 / GPS precise clock error sequence. Taking BDS-3 as an example, when the LEO satellite precise clock error calculated by a BDS-3 satellite does not meet , the BDS-3 satellite does not participate in the final LEO satellite precise clock error solution.

[0111] (603) After excluding the above-mentioned channels with gross errors exceeding the limit, recalculate the mean of the receiver precision clock error sequence composed of all channels with qualified limits, and use the mean as the final BDS-3 / GPS receiver precision clock error.

[0112] (7) The precise orbit clock error prediction module is used to complete the ultra-short-term prediction of the precise orbit clock error in real time on orbit. Specifically, the dynamic orbit integral is used to predict the precise orbit, and the clock error-clock rate two-dimensional model is used to predict the precise clock error. The ultra-short-term prediction time interval is set to 1 minute.

[0113] In order to implement the above method, we can use Figure 1 The LEO on-orbit real-time precise orbit and clock error determination system based on PPP-B2b enhancement shown includes:

[0114] A GNSS receiving antenna (1), used for receiving GNSS navigation signals and PPP-B2b enhancement signals;

[0115] A radio frequency front-end module (2) is used to filter, amplify, down-convert and sample GNSS navigation signals and PPP-B2b enhancement signals;

[0116] The baseband signal processing module (3) is used to realize the capture and tracking of the digital intermediate frequency signal, output the original GNSS observation data, including pseudorange, carrier phase, Doppler data, and output the original GNSS navigation message and PPP-B2b message;

[0117] The real-time precise ephemeris calculation module (4) parses the GNSS broadcast ephemeris and orbit and clock correction information PPP-B2b SSR from the GNSS original navigation message and the PPP-B2b message, matches the PPP-B2b SSR with the GNSS broadcast ephemeris, and then corrects the orbit and clock error calculated by the GNSS broadcast ephemeris to obtain the real-time precise ephemeris;

[0118] A real-time precise orbit estimation module (5) is used to complete the filtering estimation of the precise orbit in real time on orbit, and obtain the three-dimensional position and velocity of the low-orbit satellite in the Earth-centered Earth-fixed system, as well as the undifferenced floating-point ambiguity parameters of each satellite;

[0119] A real-time precise clock error estimation module (6), used to estimate the precise clock error in real time on orbit;

[0120] The precise clock error prediction module (7) is used to complete the ultra-short-term prediction of precise orbit and clock error in real time on orbit.

[0121] In summary, the present invention uses the enhanced information broadcast by the BeiDou-3 B2b signal to correct the BDS-3 / GPS satellite orbit and clock error. With the support of regional BDS-3 / GPS enhanced information, when there is a new BDS-3 / GPS tracking star, before the measurement update, the inter-epoch clock error variation calculated by the carrier phase time difference method is used as two orbit determination filter clock error parameters for constraint, and the receiver clock error and non-difference floating point ambiguity parameters are separated in real time on orbit; finally, the LEO precise orbit and non-difference floating point ambiguity parameters output by the orbit determination filter are substituted into the phase observation equation to calculate the BDS-3 / GPS receiver precise clock error. The present invention is applicable to situations where only regional GNSS enhanced information is supported, and is less affected by orbit maneuvers.

[0122] The above description is only an embodiment of the present invention, and does not limit the protection scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, is included in the protection scope of the present invention.

Claims

1. A method for determining LEO on-orbit real-time precise orbit and clock errors based on PPP-B2b enhancement, characterized in that: The steps include: (1) Receive GNSS navigation signals and PPP-B2b enhancement signals through the GNSS receiving antenna; (2) Filter, amplify, down-convert and sample GNSS navigation signals and PPP-B2b enhancement signals; (3) Capture and track digital intermediate frequency signals through baseband signal processing, output GNSS raw observation data, including pseudorange, carrier phase, Doppler data, and output GNSS raw navigation messages and PPP-B2b messages; (4) Parse the GNSS broadcast ephemeris and orbit and clock correction information PPP-B2b SSR from the GNSS original navigation message and PPP-B2b message respectively, match the PPP-B2b SSR with the GNSS broadcast ephemeris, and then correct the orbit and clock error calculated by the GNSS broadcast ephemeris to obtain real-time precise ephemeris; (5) Complete the filtering estimation of the precise orbit in real time on orbit, and obtain the three-dimensional position and velocity of the low-orbit satellite in the Earth-centered Earth-fixed system, as well as the undifferenced floating-point ambiguity parameters of each satellite; (6) Estimating precise clock errors in real time on orbit; (7) Real-time ultra-short-term prediction of precise orbit and clock error on-orbit.

2. The method for determining LEO on-orbit real-time precise orbit and clock error based on PPP-B2b enhancement according to claim 1 is characterized in that: The specific method of step (4) is: Parse the PPP-B2b message to obtain the satellite mask, satellite orbit correction number, and satellite clock correction number; Parse the GNSS original navigation message to obtain the GNSS broadcast ephemeris; Use the SSR version number to synchronize and match the satellite mask, satellite orbit correction number and satellite clock correction number, use the mask version number to synchronize and match the satellite mask and satellite clock correction number, and use the mask information to parse the satellite number of the satellite clock correction number, use the correction number version number to synchronize and match the satellite orbit correction number and satellite clock correction number, and use the IODN in the satellite orbit correction number to match the GNSS broadcast ephemeris; After the matching is completed, the satellite orbit correction number and satellite clock correction number are used to calculate the real-time precise orbit and clock error, and obtain the real-time precise ephemeris.

3. The method for determining LEO on-orbit real-time precise orbit and clock error based on PPP-B2b enhancement according to claim 1 is characterized in that: The specific method of step (5) is: (501) Two orbit determination filters based on kinematic orbit determination and based on simplified dynamic orbit determination are run simultaneously; wherein the filter state quantities of the two orbit determination filters based on kinematic orbit determination and based on simplified dynamic orbit determination are: ； In the formula, and are the filter state quantities based on kinematic orbit determination and simplified dynamic orbit determination, respectively. and for The three-dimensional position and velocity of the low-orbit satellite at any moment; and They are BDS-3 / GPS receiver clock error parameters, is the receiver clock rate parameter, is the atmospheric drag coefficient, is the solar pressure coefficient, are the empirical accelerations in the radial, tangential and normal directions of the orbit, The first of the two arrays The elements are The ambiguity parameters to be estimated for m BDS-3 satellites and n GPS satellites observed by the low-orbit satellite at the moment, The first of the two arrays The elements are The ephemeris errors of m BDS-3 satellites and n GPS satellites observed by low-orbit satellites at the moment along their respective signal propagation paths; Depending on whether there is PPP-B2b augmentation information support, the ephemeris error along the BDS-3 / GPS signal propagation path is The piecewise random walk process is used for modeling; (502) When updating the time, the satellite position is predicted in one step using the carrier phase time difference method based on the kinematic orbit determination, and the satellite position is predicted in one step using the low-orbit satellite orbit dynamics method based on the simplified dynamic orbit determination; (503) When there is a new BDS-3 / GPS tracking satellite, before the measurement update, the inter-epoch clock error variation obtained by the carrier phase time difference method is used as a virtual observation value to constrain the two orbit determination filter clock error parameters. The on-orbit real-time orbit determination filter model with additional TDCP clock error constraints is obtained as follows: （7） In the formula, and are the Kalman filter state and observation, respectively. and are the state transfer matrix and the observation matrix respectively, and are system noise and observation noise respectively, for Time has come The change in BDS-3 / GPS receiver clock error between epochs calculated by the carrier phase time difference method; and They are Moment and BDS-3 / GPS receiver clock error parameters in the moment filter state; The extended Kalman filter is used to measure and update equation (7) to obtain the precise orbit and non-differenced floating-point ambiguity of the low-orbit satellite, thereby decoupling and separating the receiver clock error and non-differenced floating-point ambiguity parameters in real time on orbit; (504) After obtaining the results of orbit determination based on kinematics and orbit determination based on simplified dynamics, when it is detected and determined that the low-orbit satellite has an orbital maneuver, the result of kinematic orbit determination is output; otherwise, the result of simplified dynamics orbit determination is output.

4. The method for determining LEO on-orbit real-time precise orbit and clock error based on PPP-B2b enhancement according to claim 1 is characterized in that: The specific method of step (6) is: (601) Substituting the three-dimensional position and velocity of the low-orbit satellite in the Earth-centered Earth-fixed system obtained in step (5) and the undifferenced floating-point ambiguity parameters of each satellite that have been decoupled from the receiver clock error as known values ​​into the carrier phase observation equation to solve the precise clock error of the low-orbit satellite receiver; Among them, the BDS-3 satellite and The clock error of the low-orbit satellite BDS-3 / GPS receiver at the current epoch calculated from the ionosphere-free combined phase observations of the GPS satellites is expressed as: （8） In the formula, and The current epoch time is BDS-3, Ionosphere-free combined phase observations of GPS satellites and Calculated clock error parameters of low-orbit satellite BDS-3 / GPS; and are the signal emission times BDS-3, The three-dimensional position of the GPS satellites in the Earth-centered Earth-fixed coordinate system; and Respectively BDS-3, Undifferenced floating point ambiguities of GPS satellites; and Respectively BDS-3, Phase winding error correction of GPS satellites; and Respectively BDS-3, Relativistic error correction of GPS satellites; and Respectively BDS-3, The geometric distance between the phase center of the transmitting antenna and the phase center of the receiving antenna of a GPS satellite, and: ， ， , , They are the low-orbit satellite at the current epoch, BDS-3, The three-dimensional position of the GPS satellites in the Earth-centered Earth-fixed coordinate system; (602) Calculate the mean and variance of the receiver precision clock error sequence, and construct the error limit condition with the mean and variance. When the receiver precision clock error of a channel exceeds the error limit, it is considered that the carrier phase observation value of this channel has a gross error and does not participate in the final receiver precision clock error calculation; If the current low-orbit satellite receives a total of BDS-3 and GPS satellites, then the formula (8) is used to calculate The current low-orbit satellite BDS-3 precise clock error sequence and The current low-orbit satellite GPS precise clock error sequence ; Then, the mean value and standard deviation of the low-orbit satellite precise clock error sequence are calculated by the following formula: （9） in, and are the average values ​​of the BDS-3 / GPS precise clock error sequence of the low-orbit satellite, and are the standard deviations of the BDS-3 / GPS precision clock error series of low-orbit satellites; (603) After excluding the channels with gross errors that exceed the limit, recalculate the mean of the receiver precision clock error sequence composed of all channels with qualified limits, and use the mean as the final BDS-3 / GPS receiver precision clock error.

5. The method for determining LEO on-orbit real-time precise orbit and clock error based on PPP-B2b enhancement according to claim 1, characterized in that: In step (7), for the precise orbit, the dynamical orbit integral is used for prediction; for the precise clock error, the clock error-clock rate two-dimensional model is used for prediction, and the time interval for ultra-short-term prediction is set to 1 minute.

6. The LEO on-orbit real-time precise orbit and clock determination system based on PPP-B2b enhancement is characterized by: include: A GNSS receiving antenna (1), used for receiving GNSS navigation signals and PPP-B2b enhancement signals; A radio frequency front-end module (2) is used to filter, amplify, down-convert and sample GNSS navigation signals and PPP-B2b enhancement signals; The baseband signal processing module (3) is used to realize the capture and tracking of the digital intermediate frequency signal, output the original GNSS observation data, including pseudorange, carrier phase, Doppler data, and output the original GNSS navigation message and PPP-B2b message; The real-time precise ephemeris calculation module (4) parses the GNSS broadcast ephemeris and orbit and clock correction information PPP-B2b SSR from the GNSS original navigation message and the PPP-B2b message, matches the PPP-B2b SSR with the GNSS broadcast ephemeris, and then corrects the orbit and clock error calculated by the GNSS broadcast ephemeris to obtain the real-time precise ephemeris; A real-time precise orbit estimation module (5) is used to complete the filtering estimation of the precise orbit in real time on orbit, and obtain the three-dimensional position and velocity of the low-orbit satellite in the Earth-centered Earth-fixed system, as well as the undifferenced floating-point ambiguity parameters of each satellite; A real-time precise clock error estimation module (6), used to estimate the precise clock error in real time on orbit; The precise clock error prediction module (7) is used to complete the ultra-short-term prediction of precise orbit and clock error in real time on orbit.

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