CORS service method for improving positioning performance and safety performance of Beidou terminal

Abstract

The invention relates to a CORS service method for improving positioning performance and safety performance of a Beidou terminal, and belongs to the technical field of GNSS positioning. The Beidou terminal requests the CORS service, and in the cold start state, the CORS service center selects whether to send the ephemeris data according to the user request so as to improve the cold start efficiency of the terminal; after the big dipper terminal achieves rough position calculation, the terminal carries out grid code coding on the rough position, meanwhile, encryption is carried out through an encryption algorithm, and the encrypted rough position is sent to a CORS service center; after receiving the request of the Beidou terminal, the CORS service center decodes the grid code encoding information, searches the corresponding virtual observed quantity according to the approximate position, and broadcasts the virtual observed quantity to the Beidou terminal; and after the Beidou terminal receives the virtual observed quantity, grid point coordinates and observed quantity of the virtual observed quantity are decoded, and high-precision real-time positioning is realized. The method is short in positioning time, saves the communication flow overhead, and reduces the exposure risk of the position of the Beidou terminal.

Description

Technical Field

[0001] The present invention belongs to the technical field of GNSS positioning, and particularly relates to a CORS service method for improving the positioning performance and security performance of Beidou terminals. Background Technique

[0002] The Global Navigation Satellite System (GNSS) generally refers to all satellite navigation systems, including global, regional, and enhanced satellite navigation systems.

[0003] The GNSS satellite positioning continuously operating reference stations (CORS) system is a practical distributed network system integrating various technologies such as GNSS navigation and positioning technology, surveying and mapping geographic information technology, modern communication technology, and computer technology. It consists of a data communication subsystem, a reference station network subsystem, a data processing and control subsystem, and a user application subsystem.

[0004] The CORS system mainly realizes the calculation of Beidou high-precision positioning differential correction numbers based on network differential / network RTK technology. Network RTK, also known as multi-station RTK, is a new technology established in recent years on the basis of conventional RTK (single-station RTK). Usually, multiple (generally three or more) GNSS reference stations (CORS stations) are established in a region to form a network coverage (CORS network) for this region. The observations (pseudorange, carrier phase observations, etc.) of the GNSS reference stations are transmitted to the solution server of the CORS service center (the CORS service center aggregates the GNSS reference station observation data and has the CORS service solution ability) through wired or wireless networks. Taking one or more of these reference stations as a reference, GNSS differential information is calculated. When a Beidou terminal sends a request to the service center, the service center selects the virtual grid point that is most conducive to realizing the high-precision solution of the Beidou terminal according to the approximate position (longitude, latitude, and elevation three-dimensional information) of the Beidou terminal, and broadcasts the virtual grid point observations (virtual pseudorange, carrier phase observations, etc.), so as to realize the positioning method for real-time high-precision solution of GNSS users in this area.

[0005] Information of similar products:

[0006] Utility model patent: A new type of CORS integrated service system, patent number CN204539203U. The data communication subsystem of this utility model uses a dedicated high-speed optical fiber ADSL for transmission, and the remote terminal subsystem and the user service subsystem are bidirectionally connected through wireless and wired networks, thereby improving the transmission speed and data processing speed and supporting user remote operation response.

[0007] Invention patent: A GNSS decimeter differential positioning method based on a virtual grid, patent number CN107422351A. This invention patent proposes a GNSS decimeter differential positioning method based on a virtual grid, which divides the pseudo-range differential correction information into grids and broadcasts it in a broadcast form. Users determine which grid they are in based on their approximate location and select the required correction information for pseudo-range differential correction. This method reduces server pressure, is not limited by the number of terminal users, solves the problem of concurrent users going online, and provides a solution for a large number of decimeter-level GNSS differential positioning services.

[0008] The CORS service provides a differential correction data source for Beidou terminals. However, the existing CORS system usually has the following defects when interacting with the terminals: ① The application scenarios of the terminals are not fully considered, and only the grid point observations or correction numbers are broadcast in a fixed manner. The initial positioning time is relatively long in the terminal cold start scenario; ② The terminal's traffic requirements are not considered, and the service is usually broadcast at the frequency of the user's GGA broadcast, which consumes a lot of communication resources; ③ The terminal interacts with the terminal in a two-way interactive manner (Ntrip protocol), and the terminal exposes its approximate location at the meter level, posing a potential location security risk.

[0009] The patent of this invention aims to solve the above-mentioned technical problems and provide a CORS service system that improves the positioning performance and security performance of Beidou terminals. Summary of the invention

[0010] 1. Technical issues to be resolved

[0011] The technical problem to be solved by the present invention is how to provide a CORS service method for improving the positioning performance and safety performance of Beidou terminals, so as to solve the problems that the initialization positioning time is long in the cold start scenario of the existing CORS service terminal, a large amount of communication resources are consumed, and there are potential location security risks.

[0012] (II) Technical solution

[0013] In order to solve the above technical problems, the present invention proposes a CORS service method for improving the positioning performance and security performance of Beidou terminals, and the method comprises the following steps:

[0014] S1. Build a certain number of reference stations or CORS stations with known coordinates in the service area to provide mesh coverage for the service area, thereby building a ground CORS network.

[0015] S2. Divide the service area into virtual grids, perform integrity check on the Beidou observation data of each reference station, calculate the actual three-dimensional coordinates of each grid point, and interpolate or extrapolate the virtual observation value of each grid point based on the reference station data around the grid point. The grid point coordinates in the virtual observation value are processed by grid code encoding and encrypted by encryption algorithm.

[0016] S3. The Beidou terminal requests the CORS service. In the cold start state, the CORS service center selects whether to send ephemeris data according to the user's request to improve the cold start efficiency of the terminal.

[0017] S4. After the Beidou terminal achieves rough position solution, the terminal encodes the rough position into grid codes, encrypts it through an encryption algorithm, and sends the encrypted rough position to the CORS service center.

[0018] S5. After receiving the request from the Beidou terminal, the CORS service center decodes the grid code encoding information, searches for corresponding virtual observables based on the rough position, and broadcasts the virtual observables to the Beidou terminal.

[0019] S6. After receiving the virtual observables, the Beidou terminal decodes the grid point coordinates and observables of the virtual observables to achieve high-precision real-time positioning.

[0020] (III) Beneficial effects

[0021] The present invention proposes a CORS service method for improving the positioning performance and security performance of the Beidou terminal. The CORS service system described in the present invention supports the broadcast of ephemeris services, adopts an ephemeris aggregation algorithm of multi-modal and multi-subnet fusion, can provide full-galaxy and different ephemeris combination schemes, and optimizes the positioning effect in scenarios such as cold start; provides a high-precision service broadcast frequency option, and the terminal can select the service update frequency according to the positioning scenario requirements to save communication traffic overhead; the high-precision service coding adds a regional grid field and encrypts it through an encryption algorithm. The Beidou terminal side and the CORS service center side adopt a unified encoding and decoding strategy, and the regional grid is used instead of the rough position during the interaction process to reduce the risk of exposing the position of the Beidou terminal.

[0022] Compared with the prior art, the technical solution proposed by the present invention adds an ephemeris service in the CORS service. There is no need to assist in improving the positioning speed through the A-GNSS service, which can not only save the R & D investment of enterprises in the A-GNSS service, but also achieve the effect of rapid positioning of the Beidou terminal in cold start. The initialization positioning duration can be improved from 20s - 30s to within 6s; a service broadcast frequency selection strategy is provided, which can provide different broadcast frequency options such as 1s, 5s, 10s, 20s, etc., and can save 5 times, 10 times, 20 times, etc. of communication traffic correspondingly; the high-precision service coding adds a regional grid field and encrypts the service coding through the AES algorithm, further reducing the risk of exposing the terminal position. Description of the drawings

[0023] Figure 1 It is the ephemeris broadcast process in the cold start scenario of the Beidou terminal.

[0024] Figure 2It is a two-way interaction flow chart between the Beidou terminal and the Beidou CORS service center. Specific implementation manner

[0025] To make the objectives, content and advantages of the present invention clearer, the following further describes in detail the specific implementation manner of the present invention with reference to the accompanying drawings and embodiments.

[0026] This invention patent belongs to the technical field of GNSS positioning, and mainly provides methods for improving the capabilities in the directions of CORS service systems, Beidou terminal positioning performance, security performance, etc.

[0027] The present invention proposes a CORS service method for improving the positioning performance and security performance of Beidou terminals, and the method includes the following steps:

[0028] S1. Build a certain number of reference stations (or CORS stations) with known coordinates within the service area to cover the service area in a mesh pattern, thereby building a ground CORS network;

[0029] S2. Divide the service area into virtual grids, check the integrity of the Beidou observation data of each reference station, calculate the actual three-dimensional coordinates of each grid point, and interpolate or extrapolate the virtual observables of each grid point based on the data of the reference stations around the grid point. The grid point coordinates in the virtual observables are encoded by grid codes and encrypted through an encryption algorithm;

[0030] S3. When the Beidou terminal requests CORS services, in the cold start state, the CORS service center decides whether to send ephemeris data according to the user request to improve the cold start efficiency of the terminal;

[0031] S4. After the Beidou terminal achieves a rough position solution, the terminal encodes the rough position with grid codes and encrypts it through an encryption algorithm, and sends the encrypted rough position to the CORS service center;

[0032] S5. After receiving the request from the Beidou terminal, the CORS service center decodes the grid code encoded information, searches for the corresponding virtual observables based on the rough position, and broadcasts the virtual observables to the Beidou terminal;

[0033] S6. After receiving the virtual observables, the Beidou terminal decodes the grid point coordinates and observables of the virtual observables to achieve high-precision real-time positioning.

[0034] Embodiment 1:

[0035] Another technical solution of the present invention is that on the basis described above, in step S1, a ground CORS network is built within the service area. Specifically, during the construction, in addition to mainly considering the distance between stations and trying to form a Delaunay triangulation network to avoid setting up stations in a straight line, factors such as the distribution of the user group and convenience for construction and maintenance should also be considered. Taking the realization of network differential in China as an example, 50 CORS ground stations are deployed across the country.

[0036] Another technical solution of the present invention is that on the basis described above, in step S2, virtual grid division and numbering are carried out within and around the coverage area of the CORS network, and the numbers are distinguishable and unique. Taking China as an example, if decimeter / sub-meter-level satellite positioning enhancement services are to be provided, the regional grid division can adopt a grid division mode of 5°×5°, with the latitude range from 20°N to 50°N and the longitude range from 75°E to 130°E, and a total of 42 grid points can be divided. The longitude and latitude and numbers of the national grid points are shown in Table 1, and the grid point codes are encrypted through the AES algorithm; the virtual observations of each grid point are interpolated or extrapolated based on the data of the CORS stations around the grid points;

[0037] For grid point i, at least 3 CORS station data around it are selected, assumed to be stations a, b, and c, and the comprehensive errors at these stations can be obtained. Taking station a as an example, if satellite ι is observed, its comprehensive error is:

[0038]

[0039] where ρ is the pseudorange observation value and R is the geometric distance between the grid point and the satellite.

[0040] Through formula (1), the comprehensive error of station b can be obtained and the comprehensive error of station c Then the comprehensive error at grid point i is interpolated,

[0041]

[0042] where a a , a b , a c are interpolation coefficients.

[0043] The observation data of virtual grid point i. Taking the pseudorange observation value as an example, with the coordinates of grid point i known, the geometric distance from grid point i to satellite 1 can be obtained and then the pseudorange observation value at the virtual grid point is simulated:

[0044]

[0045] The comprehensive error correction number of grid point i is:

[0046]

[0047] Another technical solution of the present invention is based on the above, and step S3 includes:

[0048] When the Beidou terminal is in the cold start state, it requests the CORS service. For the ephemeris service, user accounts are divided into two types: those that broadcast ephemeris and those that do not. After authenticating the user, if the user account type is one that does not broadcast ephemeris, no ephemeris broadcast judgment is made; otherwise, subsequent conditional judgments are made.

[0049] Identify whether there is location information in the GGA uploaded by the user. If there is location information, no ephemeris is broadcast. If the GGA is empty, the ephemeris is broadcast to the user once, and the broadcast constellation is optional, with the default being the same as the constellation combination of the observables.

[0050] Since the ephemeris validity period of each constellation is not less than 30 minutes, if the terminal device is normal, broadcasting the ephemeris once can achieve the effect of shortening the positioning time in the cold start scenario. Considering that the ephemeris broadcast may fail due to reasons such as network, the positioning situation within 10 s after the ephemeris broadcast is judged. If the terminal achieves positioning during this process, the ephemeris broadcast is terminated. If positioning is not achieved, the ephemeris is broadcast one more time, and then the ephemeris broadcast ends.

[0051] If the terminal does not position for a long time, the user account will be removed from the platform as an invalid account, so there is no need to broadcast the ephemeris to it again. The process is as Figure 1 shown.

[0052] Regarding the ephemeris broadcast, in the case of multi-constellation combination, the number of satellites is relatively large (more than 40 can be exceeded), and the size of the ephemeris of each satellite is about 500 bit. The amount of data broadcast within 1 s is relatively large, so the ephemeris is broadcast in 2 s.

[0053] Regarding the generation of the ephemeris, since the user's location is unknown, a multi-modal multi-subnet fusion ephemeris calculation algorithm is adopted, that is, the ephemeris data of multiple constellations, multiple subnets, and multiple base stations of the fusion service platform are fused to ensure the integrity of the satellite ephemeris to a greater extent. However, this will cause the problem of an increase in the number of satellites. Therefore, through the ephemeris screening strategy, invalid ephemeris are removed in a timely manner to ensure the timeliness of the satellite ephemeris.

[0054] Another technical solution of the present invention is based on this. In step S4, after the Beidou terminal realizes the approximate position calculation, the terminal encodes the approximate position into a grid code. The approximate position encoding of the terminal is the same as that in step S2. According to the corresponding relationship between the longitude, latitude, and number in Table 1 of the approximate position, when encoding the approximate position, it is encrypted through an encryption algorithm at the same time, and the encrypted approximate position is sent to the CORS service center.

[0055] Table 1 Grid point numbers and corresponding longitude and latitude

[0056]

[0057] Another technical solution of the present invention is based on this. In step S5, after the CORS service center receives the request from the Beidou terminal, it decodes the grid code encoding information, searches for the corresponding virtual observables according to the approximate position, refers to the RTCM standard, and virtualizes the observation values of each satellite system for all grid points, and broadcasts them to the user respectively according to the virtual observation value broadcast format in Table 2: For different satellite systems, different message numbers can be defined. For example, the virtual pseudorange observation values of GPS can be defined to be sent by message number 1178 in the above format, and the virtual pseudorange observation values of BDS can be defined to be sent by message number 1179. When using the satellite-based augmentation system to broadcast differential information, in order to reduce the amount of information broadcast by the satellite, the comprehensive error information can be broadcast in the format imitating the virtual pseudorange, see the comprehensive error correction number broadcast format in Table 3.

[0058] Table 2 Virtual Observation Value Broadcast Format

[0059]

[0060] Note: Ns represents the number of satellites; n is the number of padding digits.

[0061] Table 3 Comprehensive Error Correction Number Broadcast Format

[0062]

[0063] Note: Ns: represents the number of satellites; n is the number of padding digits.

[0064] The specific update frequency of the broadcast data can be specifically determined according to actual positioning accuracy requirements, communication bandwidth, broadcast data volume, etc.

[0065] Another technical solution of the present invention is based on this. In step S6, it decodes the grid point coordinates and observables of the virtual observables, and realizes high-precision real-time positioning through the RTD positioning algorithm.

[0066] The data interaction process between the Beidou terminal and the CORS service center in steps S4 to S6 is as Figure 2 shown.

[0067] The CORS service system described in the present invention supports the broadcast of ephemeris services. It adopts a multi-modal and multi-subnet fusion ephemeris aggregation algorithm, which can provide full-galaxy and different ephemeris combination schemes, and optimize the positioning effect in scenarios such as cold start. It provides high-precision service broadcast frequency options, and the terminal can select the service update frequency according to the positioning scenario requirements, saving communication traffic overhead. The high-precision service coding adds a regional grid field and is encrypted through an encryption algorithm. The Beidou terminal side and the CORS service center side adopt a unified encoding and decoding strategy, and the regional grid is used instead of the approximate location during the interaction process, reducing the risk of Beidou terminal location exposure.

[0068] Compared with the prior art, the technical solution proposed in the present invention adds ephemeris services in the CORS service. There is no need to assist in improving the positioning speed through A-GNSS services. It can not only save the R & D investment of enterprises in A-GNSS services, but also achieve the effect of rapid positioning of Beidou terminals in cold start. The initialization positioning duration can be improved from 20s - 30s to within 6s. It provides a selectable strategy for service broadcast frequency, and can provide different broadcast frequency options such as 1s, 5s, 10s, 20s, etc., which can save 5 times, 10 times, 20 times, etc. of communication traffic correspondingly. The high-precision service coding adds a regional grid field, and the service coding is encrypted through the AES algorithm, further reducing the risk of terminal location exposure.

[0069] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A CORS service method for improving the positioning performance and security performance of Beidou terminals, characterized in that The method includes the following steps: S1. Build a certain number of reference stations or CORS stations with known coordinates within the service area to conduct mesh coverage of the service area, thereby building a ground CORS network; S2. Divide the service area into virtual grids, check the integrity of the Beidou observation data of each reference station, calculate the actual three-dimensional coordinates of each grid point, and interpolate or extrapolate the virtual observables of each grid point based on the data of the reference stations around the grid point. The grid point coordinates in the virtual observables are encoded by grid codes and encrypted through an encryption algorithm; S3. The Beidou terminal requests CORS services. In the cold start state, the CORS service center decides whether to send ephemeris data according to the user's request to improve the cold start efficiency of the terminal; S4. After the Beidou terminal achieves rough position solution, the terminal encodes the rough position by grid codes and encrypts it through an encryption algorithm, and sends the encrypted rough position to the CORS service center; S5. After receiving the request from the Beidou terminal, the CORS service center decodes the grid code encoding information, searches for the corresponding virtual observables according to the rough position, and broadcasts the virtual observables to the Beidou terminal; S6. After receiving the virtual observables, the Beidou terminal decodes the grid point coordinates and observables of the virtual observables to achieve high-precision real-time positioning.

2. The CORS service method for improving the positioning performance and security performance of Beidou terminals according to claim 1, characterized in that, In S1, when building a ground CORS network within the service area, in addition to mainly considering the distance between stations, trying to form a Delaunay triangulation network and avoiding setting up stations in a straight line, the distribution of the user group and factors facilitating construction and maintenance should also be considered.

3. The CORS service method for improving the positioning performance and security performance of Beidou terminals according to claim 1, characterized in that, In S2, virtual grid division and numbering are carried out within and around the coverage area of the CORS network, and the numbering is distinguishable and unique; for the Chinese region, if decimeter / sub-meter-level satellite positioning augmentation services are to be provided, the regional grid division adopts a 5°×5° grid division mode, with the latitude range of 20°N to 50°N and the longitude range of 75°E to 130°E. There are a total of 42 grid points in the division, and the grid point codes are encrypted through the AES algorithm; the virtual observation values of each grid point are interpolated or extrapolated based on the data of the CORS stations around the grid point.

4. The CORS service method for improving the positioning performance and security performance of Beidou terminals according to claim 1, characterized in that, In S2, for grid point i, select the data of at least 3 CORS stations around it, assumed to be stations a, b, and c, to obtain the comprehensive errors at these stations. If station a observes satellite ι, its comprehensive error is: where ρ is the pseudorange observation value and R is the geometric distance between the grid point and the satellite; The comprehensive error of survey station b is obtained through formula (1). and the comprehensive error of survey station c Then, the comprehensive error at grid point i is interpolated. Among them, a a , a b , a c is an interpolation coefficient; Observation data of the virtual grid point i: Given the coordinates of grid point i, the geometric distance from grid point i to satellite 1 can be obtained. Furthermore, the pseudorange observation value at the virtual grid point is simulated: The comprehensive error correction number of grid point i is:

5. The CORS service method for improving the positioning performance and security performance of Beidou terminals according to any one of claims 1-4, characterized in that, S3 includes: When the Beidou terminal requests CORS services in the cold start state, for the ephemeris service, user accounts are divided into two types: broadcasting ephemeris and not broadcasting ephemeris. Judge the authenticated users. If the user account type is not broadcasting ephemeris, no ephemeris broadcast judgment is made. Otherwise, subsequent conditional judgments are made; Identify whether there is position information in the GGA uploaded by the user. If there is position information, no ephemeris is broadcast. If the GGA is empty, broadcast the ephemeris to the user once. The broadcast constellation is optional, and the default is the same as the constellation combination of the observables. Since the validity period of the ephemeris of each constellation is not less than 30 minutes, if the terminal device is normal, broadcasting the ephemeris once can achieve the effect of shortening the positioning time in the cold start scenario. Considering that the ephemeris broadcast may fail due to possible network reasons, the positioning situation within 10 s after the ephemeris broadcast is added is judged. If the terminal achieves positioning during this process, the ephemeris broadcast is terminated. If the positioning is not achieved, the ephemeris is broadcast one more time and then the ephemeris broadcast ends.

6. The CORS service method for improving the positioning performance and security performance of a Beidou terminal according to claim 5, wherein, If the terminal fails to be positioned for a long time, the user account will be removed from the platform as an invalid account, so there is no need to broadcast the ephemeris to it again.

7. The CORS service method for improving the positioning performance and security performance of Beidou terminals according to claim 5, characterized in that, Regarding the broadcast of the ephemeris, in the case of multi-constellation combination, the number of satellites is large, and the size of the ephemeris of each satellite is about 500 bit. The amount of data broadcast within 1 s is large, so the ephemeris is broadcast in 2 s.

8. The CORS service method for improving the positioning performance and security performance of Beidou terminals according to claim 5, characterized in that, Regarding the generation of the ephemeris, a multi-modal multi-subnet fusion ephemeris calculation algorithm is adopted, that is, the ephemeris data of multiple constellations, multiple subnets, and multiple base stations of the fusion service platform are fused, and the invalid ephemeris is removed in time through the ephemeris screening strategy to ensure the timeliness of the satellite ephemeris.

9. The CORS service method for improving the positioning performance and security performance of Beidou terminals as described in claim 5, characterized in that, In S5, after receiving the request from the Beidou terminal, the CORS service center decodes the grid code encoding information, searches for the corresponding virtual observables according to the approximate position, refers to the RTCM standard, and virtualizes the observation values of each satellite system for all grid points, and broadcasts them to the user in the format of the virtualized observation value broadcast: for different satellite systems, different message numbers can be defined; when using the satellite-based augmentation system to broadcast differential information, in order to reduce the amount of information broadcast by the satellite, the comprehensive error information is broadcast in the format of imitating the virtual pseudorange.

10. The CORS service method for improving the positioning performance and security performance of Beidou terminals according to claim 9, characterized in that, In S6, the grid point coordinates and observables of the virtual observables are decoded, and high-precision real-time positioning is achieved through the RTD positioning algorithm.

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