A real-time state space expression product evaluation method

Abstract

The present invention proposes an evaluation method for a real-time state space expression product, which belongs to the field of satellite navigation and positioning. In view of the fact that the current evaluation methods of state space expression products all belong to the post-evaluation mode, the present invention proposes an evaluation method for real-time state space expression products based on user ranging error (User Range Error, URE). In the case where the coordinates of the reference station are accurately known, this method fully considers the influence of the satellite orbit, clock error, code deviation and ionospheric product provided by the state space expression product, and obtains the user ranging error by calculating the pseudorange error to achieve real-time quantitative evaluation of the state space expression product, providing users with a reliable evaluation method when selecting state space expression products for satellite positioning services.

Description

Technical Field

[0001] The invention belongs to the field of satellite navigation and positioning, and in particular to an evaluation method for a real-time state space expression product. Background Art

[0002] As a performance indicator for evaluating satellite navigation systems, spatial signal accuracy reflects the impact of the deviation of the navigation message broadcast by the satellite on user ranging. The method for evaluating spatial signal accuracy is the ephemeris data method (Bottom-Up method), which uses precise ephemeris as a reference value to evaluate the accuracy of the broadcast ephemeris service. Since precise ephemeris products are generally available only after 14 days. In real-time conditions, the pseudo-range observation method (Top-Down method) is used, which uses a reference station with known precise coordinates to calculate the user pseudo-range error through real-time observation data and broadcast ephemeris to evaluate the spatial signal accuracy in real time. As a major error source, the user pseudo-range error includes the error sources of the satellite end (satellite orbit error, satellite clock error), the space end error (tropospheric error and ionospheric error) and the ground end error (receiver clock error and multipath error).

[0003] In order to meet the demand for real-time high-precision positioning, the International GNSS Service (IGS) has developed and released a protocol based on the Radio Technical Commission for Maritime Services (RTCM) and uses the Internet transport of RTCM via Internet Protocol (NTRIP) to provide state space representation (SSR) products for satellite navigation systems including GPS, BeiDou, GLONASS and Galileo. The state space representation products mainly provide satellite orbits, clock errors, code deviations, phase deviations and real-time ionospheric products based on broadcast ephemeris. At present, there are international institutions including the German Federal Office of Cartography and Geodesy (Bundesamt für Kartographie und Many institutions, including BKG, the European Space Agency (ESA), the French National Space Research Center (CNES), Wuhan University (WHU), and the Chinese Academy of Sciences (CAS), provide real-time spatial state expression products. The quality of real-time spatial state expression products directly affects the accuracy of real-time high-precision positioning. At present, the quality assessment of these real-time spatial state expression products is based on the method of spatial signal accuracy for post-analysis. There is no unified standard method for real-time assessment. Summary of the invention

[0004] The purpose of the present invention is to provide a real-time state space expression product evaluation method to solve the problem that the quality of the space state products broadcast by each analysis center cannot be evaluated in real time. Based on this technology, a reliable evaluation method can be provided for users to select state space expression products for satellite positioning services, and the optimal state space expression product can be selected for satellite positioning services.

[0005] The technical solution to achieve the purpose of the present invention is:

[0006] A method for evaluating a real-time state space expression product comprises the following steps:

[0007] Step 1), select a site with known precise coordinates as a reference site to receive satellite observation data in real time;

[0008] Step 2), secondly, receiving and analyzing in real time the state space expression product of the analysis center that needs to be evaluated in real time;

[0009] Step 3), calculating the geometric distance from the satellite to the reference station based on the satellite broadcast ephemeris, the real coordinates of the measuring station and the state space expression product provided by the analysis center;

[0010] Step 4), calculate the corresponding pseudorange correction based on the pseudorange observation data of the reference station and the state space expression product of the analysis center;

[0011] Step 5), calculating the pseudorange error of each satellite in sight according to the geometric distance from the satellite to the reference station and the corrected pseudorange obtained in step 3) and step 4);

[0012] Step 6), continue to observe, count the pseudo-range errors of each satellite and each frequency point calculated in step 5), and take the set value as the URE for the final result evaluation standard.

[0013] Compared with the prior art, the present invention has the following significant advantages:

[0014] The present invention discloses a method for evaluating a real-time state space expression product. First, real-time data observation is performed through a known reference station. Then, the correction number provided by each state space expression product is used to calculate the URE as an evaluation standard. By introducing a known reference station and using each state space expression product to perform real-time URE calculation, a new evaluation method for real-time state space expression products is provided, which solves the problem that real-time state space expression products cannot be evaluated in real time. It can evaluate multi-satellite systems, multiple satellites, and multiple frequency points in real time, and provides an effective quantitative evaluation reference for users when selecting state space expression products for satellite positioning services. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of URE calculation for real-time state space expression product. DETAILED DESCRIPTION

[0016] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0017] The present invention proposes a real-time state space expression evaluation method, which can provide an effective quantitative evaluation reference for users when selecting state space expression products for satellite positioning services. The method specifically includes:

[0018] First, select a reference station with known coordinates as real-time observation data. The reference station can be an IGS reference station located locally or an observation station with accurate coordinates obtained by surveying in advance. Then, by receiving and parsing the state space expression products of various analysis centers, the pseudo-range error of each satellite and each frequency point is calculated in real time. Finally, the URE is obtained by observing and calculating the pseudo-range error over a period of time as an evaluation standard, providing a reference standard for users when selecting state space expression products.

[0019] like Figure 1 This is the URE data processing flow of the real-time state space expression product of the present invention. The specific process is as follows:

[0020] Step 1), first select a site with known coordinates as a reference site to receive satellite observation data in real time;

[0021] Step 2), secondly, receiving and analyzing the state space expression products of each analysis center in real time;

[0022] Step 3) Calculate the geometric distance from the satellite to the reference station based on the satellite broadcast ephemeris, the true coordinates of the station, and the state space expression product provided by the analysis center:

[0023]

[0024] Where Xs is the position of the satellite in the Earth-fixed coordinate system, X r is the position of the measuring station in the earth-fixed coordinate system; c is the speed of light, δt s The satellite clock error is expressed based on the state space product;

[0025] Furthermore, the calculation of the geometric distance from the satellite to the reference station in step 3) includes calculation of satellite orbit coordinates based on the state space expression product and calculation of satellite clock error based on the state space expression product.

[0026] Furthermore, the satellite orbit calculation based on the state-space expression product is calculated based on the orbit correction number and broadcast ephemeris provided by the state-space expression product. The orbit correction number δO contains the correction data of the three components of radial, normal and tangential. The correction error δX of the satellite position is calculated based on these orbit correction numbers, and then the broadcast ephemeris coordinates X are calculated using the broadcast ephemeris broadcast The satellite position corrected by the orbit correction data can be calculated:

[0027] X s =X broedcest -δX (2)

[0028] Among them, X s is the satellite position corrected using orbit correction data; X broedcest is the satellite position calculated using the broadcast ephemeris; δX is the satellite position correction, which is calculated as follows:

[0029] δX=[e radial e along e cross ]δO (3)

[0030] Among them, e radial , e along , e cross They are the correction vectors in the radial, along and cross directions of the satellite orbit. The calculation formula is as follows:

[0031]

[0032]

[0033] e radial =e along ×e cross (6)

[0034] here, r = X broadcast are the velocity and coordinate vector of the satellite broadcast ephemeris position in the Earth's geocentric reference frame. The calculation formula of δO is as follows:

[0035]

[0036] In the above formula, t is the calculation point time, t0 is the reference time of orbit correction information, and δO j , (j={radial, along, cross}) are the orbit correction information and the first-order orbit correction information provided by the state space expression corresponding to the j direction.

[0037] Furthermore, the satellite clock error based on the state space expression product is calculated as follows:

[0038]

[0039] where t broadcast is the clock error parameter of the broadcast ephemeris, δt s is the corrected clock error parameter, and δC is calculated from the clock error correction information provided by the state space expression product:

[0040] δC=C0+C1(t-t0)+C2(t-t0) 2 (9)

[0041] t is the calculation point time, t0 is the reference time provided by the orbit correction information, C i , i = {0, 1, 2} is the quadratic polynomial correction coefficient of the clock error based on the broadcast ephemeris provided by the state space expression.

[0042] Step 4) Calculate the corresponding pseudorange correction based on the pseudorange observation data of the reference station and the state space expression product of the analysis center

[0043]

[0044] Where ρ is the observed pseudorange, dion is the pseudorange ionospheric delay calculated by providing the ionospheric product through the state space expression, and δρ is the code bias provided by the state space expression product;

[0045] Further, the observed pseudorange correction in step 4) includes ionospheric delay correction and pseudorange bias correction;

[0046] Furthermore, the ionospheric delay calculation in step 4) uses the ionospheric spherical harmonic coefficients provided by the state space expression product to sequentially calculate the ionospheric electron content in the zenith direction, the ionospheric electron content at the satellite penetration point, and the ionospheric pseudorange error.

[0047] The state space expression product divides the ionosphere into k layers (k = 1, 2, ..., n), where the electron content of each ionosphere layer in the zenith direction is calculated as follows:

[0048]

[0049] Where N and M are the order and degree of the ionospheric spherical harmonic coefficients, respectively, and C nm and S nm The spherical harmonic sine and cosine function coefficients of a certain layer are provided for the real-time state space expression product; P nm is the Legendre function of order n and degree m; s Indicates the longitude value of the puncture point. The calculation formulas for the latitude values ​​of the puncture points are as follows:

[0050] λ s =(λ pp +(t-5400)*π / 43200)mod2π (12)

[0051]

[0052] Among them, mod is the remainder function, represents the latitude of the reference station, λ R The station longitude, A represents the satellite azimuth, ψ pp It represents the geocentric angle between the reference station and the ionospheric piercing point, and its calculation formula is:

[0053]

[0054] Where E represents the satellite altitude angle, R e represents the average radius of the Earth, h I represents the height of the ionosphere thin layer, h R Reference station altitude. pp Indicates the puncture point accuracy, and its calculation formula is as follows:

[0055]

[0056] According to the zenith delay of the kth ionosphere layer obtained by formula (12), the slant path delay of this layer on the satellite propagation signal path can be calculated:

[0057]

[0058] Total ionospheric slant delay The pseudo-range ionospheric delay (m) of the ionosphere's effect on the observation of a specific frequency point f (Hz) can be further calculated:

[0059] dion(f)=40.3 / f 2 *STEC*10 16 (17)

[0060] Furthermore, the pseudorange correction in step 4) is to correct the pseudorange observation according to the code deviation product provided by the state space expression product.

[0061] Step 5), the geometric distance from the satellite to the reference station obtained in step 3) and step 4) and corrected pseudorange Calculate the pseudorange error of each satellite seen:

[0062]

[0063] Furthermore, the pseudorange error in step 5) includes GPS L1, L2, L5, BeiDou-2 B1I, B2I, B3I, BeiDou-3 B1I, B3I, B1C, B2a, GLONASS G1, G2 and Galileo E1, E5a, E5b, E6 and other frequencies.

[0064] Step 6), continue observing for a period of time, calculate the pseudorange error of each satellite and each frequency point in turn, and take 95% of the pseudorange error as the URE for the final result evaluation standard.

[0065] In summary, the evaluation method of a real-time state space expression product provided by the present invention adopts the idea of ​​spatial signal accuracy evaluation, and performs real-time corrections on the orbit, clock error, code deviation, ionospheric delay, etc. of the correction number provided by the state space expression product, and performs corrections based on the pseudo-range observation data of the known reference station, and calculates the pseudo-range error of each satellite system to obtain URE as the evaluation standard. This method provides a real-time evaluation method for users to select state space expression products for GNSS positioning services.

[0066] The above are only implementation modes of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for evaluating a product expressing a real-time state space, characterized in that: The steps include: Step 1), select a site with known precise coordinates as a reference site to receive satellite observation data in real time; Step 2), secondly, receiving and analyzing in real time the state space expression product of the analysis center that needs to be evaluated in real time; Step 3), calculating the geometric distance from the satellite to the reference station based on the satellite broadcast ephemeris, the real coordinates of the measuring station and the state space expression product provided by the analysis center; The calculation of the geometric distance from the satellite to the reference station includes the calculation of the satellite orbit coordinates based on the state space expression product and the calculation of the satellite clock error based on the state space expression product; The satellite orbit calculation based on the state-space expression product is calculated based on the orbit correction number and broadcast ephemeris provided by the state-space expression product: the correction error δX of the satellite position is calculated based on the orbit correction number, and then the broadcast ephemeris coordinates X are calculated using the broadcast ephemeris broadcast The satellite position corrected by the orbit correction data can be calculated: X s =X broadcast -δX (1) Among them, X s is the satellite position corrected using orbit correction data; The satellite clock error based on the state space expression product is calculated as follows: where t broadcast is the clock error parameter of the broadcast ephemeris, δt s is the clock error parameter obtained after correction, δC represents the clock error correction number provided by the real-time state space expression product; δC is calculated from the clock correction information provided by the state space expression product: δC=C0+C1(t-t0)+C2(t-t0) 2 (3) Among them C i i = {0, 1, 2} is the state space expression providing the quadratic polynomial correction coefficients based on the broadcast ephemeris, t is the calculation point time, and t0 is the reference time provided by the orbit correction information; Step 4), calculating the corresponding pseudorange correction according to the pseudorange observation data of the reference station and the state space expression product of the analysis center; the observed pseudorange correction includes ionospheric delay correction and pseudorange bias correction; Ionospheric delay: dion(f)=40.3 / f 2 *STEC*10 16 (4) Where f is the ionosphere for a specific frequency, STEC is the total slant delay of the ionosphere; Step 5), calculating the pseudorange error of each satellite in sight according to the geometric distance from the satellite to the reference station and the corrected pseudorange obtained in step 3) and step 4); Step 6), continue to observe, count the pseudo-range errors of each satellite and each frequency point calculated in step 5), and take 95% of the pseudo-range errors as the URE for final result evaluation.

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