A low-orbit communication link-based satellite-to-ground RTK positioning method

Abstract

The application discloses a kind of star-ground RTK positioning methods based on low-orbit communication link, comprising: low-orbit satellite is used as reference station in RTK positioning algorithm, and the information such as orbit position and attitude of low-orbit satellite on-board Beidou / GNSS observation value is used as RTK enhancement information, user terminal constantly listens and receives the RTK enhancement information that low-orbit satellite is broadcast through communication link, and corresponding RTK enhancement information is detected, then decoding is carried out according to message type and is stored;Beidou / GNSS receiver of user terminal is simultaneously received and handled to obtain Beidou / GNSS observation data;RTK enhancement information and Beidou / GNSS observation value are used to construct double-difference pseudorange and carrier phase observation equation, and the real-time, high-precision position information of user terminal is obtained;Station star single-difference observation equation is established, and satellite end clock difference is eliminated, when low-orbit satellite receives the precise clock error information that ground is noted, user receiver end clock difference is accurately estimated, and station star time synchronization is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of navigation positioning, and particularly relates to a satellite-ground RTK positioning method based on a low-orbit communication link. BACKGROUND

[0002] RTK (Real-time Kinematic) positioning technology, i.e. dynamic differential positioning technology, is a real-time high-precision positioning method realized based on carrier phase differential technology. The basic principle is that the monitoring station uses the correction data of the reference station to correct errors, so that the positioning accuracy of the monitoring station is more accurate. Among them, the three-dimensional coordinates of the reference station are fixed and very accurate within the observation time. The specific implementation method of the RTK technology is as follows: first, the reference station needs to be selected in an open and good view place, and a GNSS receiver is set up at the reference station, so that the receiver can observe the visible GNSS satellite all day long without interruption, and the observed carrier phase correction data is sent to the monitoring station in real time through the data link; similarly, a GNSS receiver is also set up at the monitoring station, which uses the carrier phase correction data broadcast by the reference station and the observation data of the current GNSS satellite to perform difference to correct the positioning error in real time, thereby improving the accuracy of the positioning coordinate value. Due to the characteristics of high precision, real-time, all-weather, etc., the RTK technology has been widely used in precision measurement applications, such as geological disaster monitoring, construction safety monitoring, etc.

[0003] However, the baseline distance between the monitoring station and the reference station greatly affects the accuracy of the traditional RTK positioning. For example, when the baseline length between the monitoring station and the reference station is less than 10 kilometers, most of the atmospheric errors can be eliminated by using the correction data of the reference station and the observation data of the monitoring station for difference; however, if the baseline length between the monitoring station and the reference station is greater than 10 kilometers, the ionospheric delay and some other atmospheric errors are difficult to be eliminated in the difference, so that the error becomes large and the positioning accuracy decreases. Therefore, the traditional RTK technology is highly dependent on ground stations, and it is extremely difficult to establish a ground station in some remote areas, which cannot meet the needs of space full coverage, high-quality monitoring, etc.

[0004] In recent years, low-orbit satellites have become a new research hotspot, and some commercial companies have proposed several LEO (Low Earth Orbit) constellation plans to build a global low-orbit constellation, such as Space X Starlink, One Web in the United States and Hongyan plan in China, etc. Low-orbit satellites not only can provide network services, but also can emit navigation signals, and low-orbit satellites have the advantages of low emission cost, large signal strength, small propagation delay, low transmission loss, etc. Therefore, low-orbit satellites can realize low-cost, high-coverage, near-real-time navigation services in the future, but a relatively complete service system has not been formed at present, and it cannot be widely used. SUMMARY

[0005] To solve the above technical problems, the application provides a star-ground RTK positioning method based on a low-orbit communication link, which is based on low-orbit satellite GNSS observation data and user GNSS observation data, uses low-orbit satellite precise orbit products, and uses a user terminal to take the low-orbit satellite as a reference station to perform RTK differential solution, so as to eliminate receiver clock bias and satellite clock bias, solve the problem that a traditional RTK needs to be highly dependent on a ground reference station, and achieve the purpose of real-time and high-precision positioning of the user terminal.

[0006] To achieve the above purpose, the application provides a star-ground RTK positioning method based on a low-orbit communication link, which comprises the following steps: taking a low-orbit satellite as a reference station in an RTK positioning algorithm, taking star-borne Beidou / GNSS observation values, orbit positions and attitudes and other information of the low-orbit satellite as RTK enhancement information, constantly monitoring and receiving RTK enhancement information broadcast by the low-orbit satellite through a communication link, and decoding and storing the RTK enhancement information according to a message type when the corresponding RTK enhancement information is detected.

[0007] A Beidou / GNSS receiver of the user terminal receives and processes Beidou / GNSS observation data simultaneously; the RTK enhancement information and the Beidou / GNSS observation values are used to construct double-difference pseudorange and carrier phase observation equations, and then real-time and high-precision position information of the user terminal is obtained.

[0008] A station-satellite single-difference observation equation is established to eliminate satellite clock bias, when the low-orbit satellite receives precise clock bias information annotated on the ground, the user receiver clock bias is further accurately estimated, and station-satellite time synchronization is realized.

[0009] Optionally, the method that the user terminal constantly monitors and receives RTK enhancement information broadcast by the low-orbit satellite through a communication link, and decodes and stores the RTK enhancement information according to a message type when the corresponding RTK enhancement information is detected, comprises the following steps:

[0010] The user terminal obtains a binary RTK enhancement information data stream through the communication link, and completes decoding of the RTK enhancement information according to a frame definition and a data structure of the RTK enhancement information;

[0011] The user terminal monitors an RTK enhancement information frame header from a communication module, once the RTK enhancement information is detected, the corresponding RTK enhancement information is decoded according to different message types, and verification is completed;

[0012] After decoding and verification are completed, RTK enhancement information stored in the terminal is updated according to an epoch time of the RTK enhancement information.

[0013] Optionally, the method for constructing double-difference pseudo-range and carrier phase observation equations using the RTK enhancement information and the Beidou / GNSS observation values comprises: a user terminal obtaining double-frequency carrier and pseudo-range observation data of a current epoch from a Beidou / GNSS receiver;

[0014] According to a current epoch, the matching enhancement information of the current observation epoch is obtained from the RTK enhancement information stored in the positioning terminal;

[0015] The positioning terminal constructs double-difference pseudo-range and carrier phase observation equations according to the above information, and performs filtering real-time estimation on the positioning terminal and other parameters, and outputs the real-time terminal position obtained by solving.

[0016] Optionally, the matching enhancement information of the current observation epoch comprises space-borne Beidou / GNSS observation data, low-orbit satellite orbit position, and low-orbit satellite attitude.

[0017] Optionally, the method for realizing station-satellite time synchronization comprises:

[0018] The station-satellite single-difference observation equation is established to eliminate satellite clock error and obtain the delay amount between the user terminal receiver and the low-orbit satellite system; when the low-orbit satellite receives the navigation enhancement information such as precise ephemeris and clock error information, regional / global atmospheric delay model, etc. through the uplink injection of the ground station, the clock error correction number determined in the navigation enhancement information is used to keep the low-orbit satellite local time consistent with the Beidou / GNSS system time, and the relative time synchronization of the low-orbit constellation is realized by using the inter-satellite link; the delay amount data between the user terminal receiver and the low-orbit satellite system is used to further accurately estimate the receiver clock error of the user terminal, and the real-time and high-precision positioning of the user terminal is realized.

[0019] Optionally, the method for establishing the station-satellite single-difference observation equation is:

[0020]

[0021] wherein, respectively represent the difference value of the pseudo-range observation values of the user terminal receiver and the low-orbit satellite, and the difference value of the carrier phase observation values of the user terminal receiver and the low-orbit satellite, the subscripts u, l, IF represent the ground user terminal receiver, the low-orbit satellite and the ionosphere-free combination, and the superscript a represents the number of the numbered GNSS satellite, represents the difference value of the geometric distance between the navigation satellite and the center of mass of the user terminal and the low-orbit satellite, c is the speed of light in vacuum, and Δδt u,l represents the clock error between the user terminal and the low-orbit satellite, λ IF represents the signal wavelength, T u a represents the tropospheric delay of the user terminal, a difference between a whole number ambiguity of the user terminal and the low-orbit satellite, and respectively represent a difference between a multipath effect and observation noise of a pseudo-range of the user terminal and the low-orbit satellite, and a difference between a multipath effect and observation noise of a carrier phase of the user terminal and the low-orbit satellite.

[0022] Technical effects of the present application:

[0023] (1) The present application solves the problem that the traditional RTK technology highly depends on ground base stations by using the on-board Beidou / GNSS observation value of the low-orbit satellite and the Beidou / GNSS observation value of the user terminal for double-difference solution, and can meet the needs of spatial full coverage, high-quality monitoring and the like in some remote areas where it is not easy to establish base stations.

[0024] (2) The present application can obtain higher positioning accuracy by using double positioning of the low-orbit satellite and the ground, and the accuracy can even reach centimeter level in open areas, thereby greatly improving work efficiency and realizing real-time and high-precision navigation and positioning of the user.

[0025] (3) The low-orbit navigation enhancement information broadcast in the present application further includes an atmospheric delay model parameter, so that the convergence speed of navigation and positioning of the user terminal is accelerated, and the measurement and positioning time is greatly saved.

[0026] (4) The present application takes the low-orbit satellite as a reference station, and does not need to establish a fixed reference station, thereby saving manpower and material resources and reducing costs.

[0027] (5) The application of the present application can drive the development of low-orbit satellite related industries and promote economic growth. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of the present application illustrated in the drawings and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0029] Fig. 1 a flowchart of a star-ground RTK positioning method based on a low-orbit communication link according to an embodiment of the present application;

[0030] Fig. 2 a principle structure diagram of a positioning service system taking a low-orbit satellite as an RTK algorithm reference station according to an embodiment of the present application. DETAILED DESCRIPTION

[0031] It should be noted that the embodiments and features in the embodiments in the present application can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0032] It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described herein can be executed in an order different from that shown.

[0033] As shown in Figs. 1-2 The embodiment provides a low-orbit communication link-based satellite-ground RTK positioning method, which comprises a Beidou / GNSS constellation, a low-orbit satellite constellation, and a user terminal, and the specific steps are as follows.

[0034] (1) The low-orbit satellite is used as a reference station in the RTK positioning algorithm, and the onboard Beidou / GNSS observation value, orbit position, and attitude information of the low-orbit satellite are used as RTK enhancement information. The user terminal continuously monitors and receives the RTK enhancement information broadcast by the low-orbit satellite through the communication link, and once the corresponding RTK enhancement information is detected, the message type is decoded and stored.

[0035] (2) The Beidou / GNSS receiver of the user terminal simultaneously receives and processes the Beidou / GNSS observation data. The RTK enhancement information and the Beidou / GNSS observation value are used to construct double-difference pseudorange and carrier phase observation equations. Then, the real-time and high-precision position information of the user terminal is obtained.

[0036] (3) The station-satellite single-difference observation equation is established to eliminate the satellite clock error. When the low-orbit satellite receives the precise clock error information on the ground, the user receiver clock error can be further accurately estimated to realize station-satellite time synchronization.

[0037] Further, the specific method of step (1) is as follows:

[0038] (101) The user terminal obtains the binary RTK enhancement information data stream through the communication link, and decodes the RTK enhancement information according to the frame definition and data structure of the RTK enhancement information.

[0039] (102) The user terminal monitors the RTK enhancement information frame header from the communication module, and once the RTK enhancement information is detected, the corresponding RTK enhancement information is decoded according to different message types, and the verification is completed.

[0040] (103) After decoding and verification, the RTK enhancement information stored in the terminal is updated according to the epoch time of the RTK enhancement information.

[0041] Further, the specific method of the user terminal for constructing double-difference pseudorange and carrier phase observation equations is as follows:

[0042] (201) The user terminal obtains the double-frequency carrier and pseudorange observation data of the current epoch from the Beidou / GNSS receiver.

[0043] (202) According to the current epoch, the positioning terminal stores the RTK enhancement information matched with the current observation epoch, including satellite-based Beidou / GNSS observation data, low-orbit satellite orbit position, low-orbit satellite attitude, etc.

[0044] (203) The positioning terminal constructs double-difference pseudorange and carrier phase observation equations according to the above information, and filters the positioning terminal and other parameters to estimate in real time, and outputs the real-time terminal position obtained by solving.

[0045] (204) Taking a low-orbit satellite as an example, first, the GNSS observation equation of the user terminal and the low-orbit satellite is established:

[0046]

[0047] Wherein, P, L represent pseudorange and carrier phase observation values respectively, and subscripts u, l represent ground user terminal receiver and low-orbit satellite respectively, and superscripts a, b represent different numbered GNSS satellites, and represent the geometric distance between the navigation satellite and the user terminal and the low-orbit satellite center, c is the speed of light in vacuum, δt u , δt l , δt a represent the clock error of the user terminal, low-orbit satellite and navigation satellite respectively, λ represents the signal wavelength, represent the ionospheric delay of the user terminal and the low-orbit satellite respectively, represent the user terminal troposphere delay, represent the integer ambiguity of the user terminal and the low-orbit satellite respectively, and represent the sum of the multipath effect and observation noise of pseudorange and carrier phase respectively.

[0048] (205) Construct an ionosphere-free combination model to eliminate the influence of ionospheric delay, and establish a combination observation equation:

[0049]

[0050] Wherein, subscript IF represents ionosphere-free combination.

[0051] (206) First, low-orbit / user single-difference calculation is performed, and then the observation results of two GNSS satellites are differentiated to obtain a double-difference observation equation:

[0052]

[0053] Wherein, Δ represents the difference between the observation values of two navigation satellites, represents the difference between the observation values of low-orbit and user.

[0054] (207)To perform Taylor expansion as follows:

[0055]

[0056] where, R 3×1 = [ΔX u ΔY u ΔZ u ] T .

[0057] The initial approximate position of the user terminal is set as The correction term is ΔR u = [ΔX u ΔY u ΔZ u ], the superscript 0 indicates the result calculated using the approximate position of the user, and respectively represent the unit vector from the approximate position of the user terminal to the navigation satellite and the unit vector from the low earth orbit satellite to the navigation satellite.

[0058] (208)After linearization of the double-difference observation equation of step (206) using step (207), the following linearized observation equation is obtained:

[0059]

[0060] where, is the optimal estimation of the double-difference ambiguity in the last iteration, is the error of the double-difference ambiguity, The parameters are calculated as follows:

[0061]

[0062]

[0063] where, represents the dry delay, which can be obtained using a troposphere model; m df is the projection function of the dry delay; is the troposphere parameter to be estimated, including the troposphere wet delay Z W , the north-south troposphere gradient parameter F ns , the east-west troposphere gradient parameter F ew , and the azimuth angle α. The projection function of the wet component and the projection function of the troposphere gradient part can be obtained using the troposphere projection function.

[0064] (209)The above steps are the calculation process of a single low-orbit satellite. When the entire low-orbit satellite is used, the following combined observation equation is obtained:

[0065]

[0066] (210)The tropospheric delay model in step (208) is substituted into and arranged to obtain the following combined observation equation:

[0067]

[0068] wherein subscript l represents the low-orbit satellite number, ranging from 1 to m, and there are m low-orbit satellites; superscripts a1 and b1 represent two GNSS satellites, the former represents a reference satellite, and the latter ranges from 1 to n, and there are n non-reference satellites; Δ(Z D m df ) a1,b1 represents the dry delay inter-satellite single difference; represents the inter-satellite single difference of the tropospheric parameter to be estimated.

[0069] (211)For the combined observation equation in step (210), the parameters to be estimated are represented as:

[0070]

[0071] wherein, there are n unknowns, there are m×n unknowns, ΔR u there are 3 unknowns, and there are 2mn equations in total.

[0072] (212)The combined observation equation in step (210) is solved using the observation data of multiple navigation satellites, and the least squares optimal solution is obtained through multiple iterations, so as to determine the user terminal position coordinates. The original observation equation is converted into the least squares form as follows:

[0073] B=HA

[0074] wherein,

[0075]

[0076]

[0077]

[0078] (213)The least squares optimal solution formula is as follows, wherein X is the parameter to be estimated; Y is the observation value; G is the coefficient matrix; and W is the weight matrix, which can be determined by the satellite elevation angle weight model:

[0079]

[0080] Further, the method for eliminating satellite clock bias and receiver clock bias and realizing station-satellite time synchronization is as follows:

[0081] (301) Establish a station-satellite single-difference observation equation, which can eliminate the satellite clock bias, so as to obtain the delay between the user terminal receiver and the low-orbit satellite system. According to steps (204) and (205), the station-satellite single-difference observation equation is as follows:

[0082]

[0083] As can be seen from the above formula, after the single-difference calculation of the Beidou / GNSS observation data of the user terminal receiver and the on-board Beidou / GNSS observation data of the low-orbit satellite, the clock bias of the low-orbit satellite is eliminated, and the delay between the user terminal receiver and the low-orbit satellite system is obtained.

[0084] (302) When the low-orbit satellite receives the navigation enhancement information such as precise ephemeris and clock bias information, regional / global atmospheric delay model and the like through the uplink, the clock bias correction number determined in the navigation enhancement information is used to keep the low-orbit satellite local time consistent with the Beidou / GNSS system time, and the relative time synchronization of the low-orbit constellation is realized by using the inter-satellite link. Then, the delay data between the user terminal receiver and the low-orbit satellite system obtained in step (301) is used to further accurately estimate the receiver clock bias of the user terminal, so as to realize the real-time and high-precision positioning of the user terminal.

[0085] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1.A method for satellite-to-ground RTK positioning based on a low-orbit communication link, characterized in that, The method comprises the following steps: The low-orbit satellite is used as a reference station in the RTK positioning algorithm, and the on-board Beidou / GNSS observation value, orbit position and attitude information of the low-orbit satellite are used as RTK enhancement information. The user terminal continuously listens to and receives the RTK enhancement information broadcast by the low-orbit satellite through a communication link, and decodes and stores the corresponding RTK enhancement information according to the message type when the RTK enhancement information is detected; The Beidou / GNSS receiver of the user terminal simultaneously receives and processes Beidou / GNSS observation data; The RTK enhancement information and the Beidou / GNSS observation value are used to construct double-difference pseudo-range and carrier phase observation equations, and then the position information of the user terminal is obtained; A station-satellite single-difference observation equation is established to eliminate the satellite clock error. When the low-orbit satellite receives the precise clock error information annotated on the ground, the clock error of the user receiver is accurately estimated, and the station-satellite time synchronization is realized. The method for constructing double-difference pseudo-range and carrier phase observation equations using the RTK enhancement information and the Beidou / GNSS observation value comprises the following steps: According to the current epoch time, the matching enhancement information is obtained from the RTK enhancement information stored in the positioning terminal; The positioning terminal constructs double-difference pseudo-range and carrier phase observation equations according to the above information, and filters and estimates the positioning terminal and other parameters in real time to output the calculated real-time terminal position. The method for realizing station-satellite time synchronization comprises the following steps: A station-satellite single-difference observation equation is established to eliminate the satellite clock error, and the delay between the user terminal receiver and the low-orbit satellite system is obtained. When the low-orbit satellite receives the precise ephemeris and clock error information annotated on the ground through the uplink by the ground gateway station, the navigation enhancement information of the regional / global atmospheric delay model is used to determine the clock correction number in the navigation enhancement information, so that the local time of the low-orbit satellite is consistent with the Beidou / GNSS system time, and the relative time synchronization of the low-orbit constellation is realized by using the inter-satellite link. The delay data between the user terminal receiver and the low-orbit satellite system is used to accurately estimate the clock error of the user terminal receiver, and the real-time and high-precision positioning of the user terminal is realized. 2.The low earth orbit communication link based RTK positioning method according to claim 1, wherein, The method for continuously listening to and receiving the RTK enhancement information broadcast by the low-orbit satellite through the communication link, and decoding and storing the corresponding RTK enhancement information according to the message type when the RTK enhancement information is detected comprises the following steps: The user terminal obtains the binary RTK enhancement information data stream through the communication link, and decodes the RTK enhancement information according to the frame definition and data structure of the RTK enhancement information; The user terminal monitors the RTK enhancement information frame header from the communication module, and decodes the corresponding RTK enhancement information according to different message types and completes the verification once the RTK enhancement information is detected; After decoding and verification, the RTK enhancement information stored in the terminal is updated according to the epoch time of the RTK enhancement information. 3.The low earth orbit communication link based RTK positioning method according to claim 1, wherein, The matching enhancement information includes on-board Beidou / GNSS observation data, low-orbit satellite orbit position and low-orbit satellite attitude. 4.The low-orbit communication link based satellite-to-ground RTK positioning method according to claim 1, wherein, The method for establishing a station-satellite single-difference observation equation comprises the following steps: ； wherein , respectively represent the difference of the pseudorange observations of the user terminal receiver and the low earth orbit satellite, the difference of the carrier phase observations of the user terminal receiver and the low earth orbit satellite, the index , , respectively represent the ground user terminal receiver, the low earth orbit satellite and the ionosphere-free combination, the index represents the number of the numbered GNSS satellite, represents the difference of the geometric distances between the navigation satellite to the user terminal and to the low earth orbit satellite center of mass, is the speed of light in vacuum, represents the clock bias between the user terminal and the low earth orbit satellite, represents the signal wavelength, represents the tropospheric delay of the user terminal, represents the difference of the integer ambiguities between the user terminal and the low earth orbit satellite, and respectively represent the difference of the multipath effects and the observation noise of the pseudoranges between the user terminal and the low earth orbit satellite, the difference of the multipath effects and the observation noise of the carrier phases between the user terminal and the low earth orbit satellite.

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