Base station differential observation data checking calculation method for terminal RTK positioning

Abstract

A base station differential observation data checking calculation method for terminal RTK positioning comprises the following steps: 1) according to a GNSS pseudo-range observation equation, giving a pseudo-range pre-test residual error of each satellite; 2) averaging the pseudo-range pre-test residual error # imgabs0 # of n satellites: if avg is less than or equal to an empirical threshold value 1, indicating that differential observation data is matched with a base station coordinate; and 3) checking the data quality, giving a phase observation equation # imgabs2 # # imgabs3 #, performing linear expansion to obtain epoch difference, and performing least square solution. Gross error detection is carried out according to the magnitude of a residual value after a satellite carrier and pseudo-range epoch difference verification: for the pseudo-range observed quantity of the ith satellite, if VP, i, postgt; if the empirical threshold value is 2, the gross error exists, and the gross error is marked and eliminated; for the carrier wave observed quantity of the ith satellite, if V phi, i, postgt; if the empirical threshold value is 3, cycle slip exists, and the cycle slip is marked and eliminated. The method is higher in calculation efficiency, is suitable for a gross error detection algorithm of single-frequency, double-frequency and even multi-frequency carrier waves and pseudo-range observed quantities, and can improve the fixed rate and the positioning precision of a whole RTK positioning system.

Description

Technical Field

[0001] The present invention relates to the field of satellite navigation and positioning technology. Specifically, the present invention relates to terminal RTK (Real-time Kinematic) carrier phase differential positioning under a global satellite positioning system (GNSS). More specifically, the present invention relates to a terminal RTK carrier phase differential observation data verification algorithm under a global satellite positioning system. The algorithm can be combined with real-time dynamic differential to meet the real-time positioning requirements in different scenarios (open spaces, urban roads, boulevards, urban canyons, etc. under vehicle-mounted positioning). Background Art

[0002] In the terminal RTK (Real-time Kinematic) carrier phase differential positioning under the Global Satellite Positioning System (GNSS), the verification of base station differential observation data is an important link to ensure the stable and reliable operation of the RTK positioning system. However, there are few studies related to the quality verification of base station observation data in the existing data. RTK (Real-time Kinematic) positioning technology is a real-time dynamic positioning technology based on carrier phase observation values. It can provide real-time three-dimensional positioning results of the measuring station in a specified coordinate system (illustration) with centimeter-level accuracy.

[0003] RTK (Real-time Kinematic Differential Kinematics) is a high-precision global positioning system that uses two receivers (base station and mobile station) to measure the time of satellite arrival and calculate the position. The significant advantage of this technology is its extremely high accuracy. Using the traditional GPS system, the position accuracy may be around 10 meters, while using RTK, the accuracy can reach centimeter or sub-centimeter levels. This technology not only provides a few centimeters or even higher accuracy, but also has good robustness and reliability in different environments, making it widely used in fields that require high precision, such as aviation, urban planning, etc.

[0004] GNSS observation gross error refers to the measurement deviation whose absolute value exceeds the tolerance when a series of observations are made under the same observation conditions. This error is a type of measurement error, usually referring to an observation error whose absolute value is greater than 3 times the mean error, including errors caused by carelessness in indoor and outdoor work. Measurement data containing gross errors must never be used because their absolute value exceeds the measurement deviation tolerance. The existence of gross errors will seriously affect the accuracy and reliability of navigation positioning, so it is very important to deal with them effectively. The gross errors in GNSS observation data mainly include jumps, pulse interference and periodic interference. The existence of these gross errors will seriously affect the accuracy and reliability of navigation positioning.

[0005] GNSS cycle slips refer to the jump or interruption of the whole cycle count caused by the loss of satellite signal lock in the carrier phase measurement of the Global Navigation Satellite System (GNSS) technology. This phenomenon is usually called "cycle slips". The causes of cycle slips may include temporary loss of satellite signal lock due to obstacles, external interference, poor dynamic conditions of the receiver, etc. Correctly detecting and recovering from cycle slips is one of the very important and must-solve problems in carrier phase measurement.

[0006] In actual projects, base station differential observation data is broadcast to end users through the network in the form of RTCM protocol encoding. When switching base stations, new base station coordinates and new differential observation data may be sent to users in different data packets at different times, so there is a problem of mismatch between the sent base station coordinates and base station observation data. At present, the commonly used method is to use the least squares method to match the base station observation data and base station coordinates, but this method has the problems of complex algorithms and large amount of calculations. For hardware platforms with limited computing power in chips or other hardware platforms, using this method will occupy more computing power resources.

[0007] In actual engineering, methods based on GF (Geometry-Free) combination (ionospheric staggered combination) and MW (WideLane) combination are often used to detect cycle slips of base station carrier observations. However, since the GF combination requires the carrier observations to be dual-frequency, the GF combination is not suitable for single-frequency data. In addition, the GF combination is an ionospheric residual combination. During the active period of the ionosphere, the ionospheric residual may be large, which often leads to false carrier cycle slips.

[0008] The MW combination is a combination of dual-frequency carrier and pseudorange observations, which is also not applicable to single-frequency carrier data. In addition, the MW combination includes pseudorange observations, which usually have a higher noise level than carrier phase observations, which makes it difficult for the MW combination to detect small cycle slips.

[0009] Therefore, there are gross errors in the base station differential observation data. Measurement data containing gross errors cannot be used and must be discovered and eliminated by formulating effective operating procedures and verification methods.

[0010] However, the cycle slip detection methods based on GF combination and MW combination are currently unable to effectively detect the gross errors in the pseudo-range observations. At the same time, insufficient quality verification of base station differential observation data will lead to a decrease in the fixation rate and positioning accuracy of the RTK positioning system.

[0011] The fixation rate of the RTK positioning system refers to the proportion of the GNSS receiver that successfully solves high-precision position information within a certain period of time. The fixed state refers to when the GNSS receiver successfully solves high-precision position information. The fixation success rate of the RTK system is also one of the important indicators for evaluating its performance. The fixation success rate directly reflects the system's ability to maintain stable and high-precision positioning in various environments. Through continuous technological innovation and optimization, the RTK system can provide reliable high-precision positioning services in various complex environments, thereby meeting the needs of high-precision positioning in different fields. Summary of the invention

[0012] In order to solve the problems of large computing power consumption, inaccurate cycle slip detection, and inability to effectively detect the gross error of pseudorange in the existing RTK base station observation data verification algorithm, the present invention aims to provide a base station differential observation data verification algorithm for terminal RTK positioning under a global satellite positioning system. According to the base station observation data verification method for terminal RTK positioning under a global satellite positioning system of the present invention, accurate and efficient gross error detection of pseudorange and carrier observation quantities is achieved.

[0013] The technical solution of the present invention is as follows:

[0014] 1. According to the GNSS pseudorange observation equation, the pseudorange pre-verification residual of each satellite is given:

[0015] First, the GNSS pseudorange observation equation is given:

[0016]

[0017] Among them, P j s is the pseudo-range observation output by the receiver; j is the frequency number, which is used to distinguish different frequency points; ρ s is the geometric distance from the receiver to the satellite s, in m; c is the speed of light, in m / s; δT is the receiver clock error, in s; δT s is the satellite clock error, in seconds; is the ionospheric delay from the receiver to the satellite s at frequency j, in meters; Trop s is the tropospheric delay from the receiver to the satellite s, in meters; is the pseudorange observation noise from the receiver to the satellite s at frequency j, in m;

[0018] The base station coordinates are obtained through the network in the format defined by the RTCM protocol, and the satellite coordinates and satellite clock error δT s It can be calculated by ephemeris. At this time, P in formula (1) j s , ρ s , cδTs All are known, and the pseudorange pre-test residual can be written as:

[0019]

[0020] 2. The pseudo-range prior residuals of all n satellites Find the mean:

[0021]

[0022] If avg>thre1 (threshold 1), it means that the base station coordinates and the observation data do not match, and this package of base station differential observation data is discarded. If avg≤thre1, it means that the differential observation data matches the base station coordinates, and the observation data quality check can be performed.

[0023] Here, thre1 is generally set as an empirical threshold of 100m, because according to formula (2), the pseudo-range pre-test residual It includes ionospheric delay, tropospheric delay, receiver clock error and pseudorange observation noise. The ionospheric delay and tropospheric delay are generally in the order of several meters to tens of meters, the base station receiver clock error is generally in the order of ten meters at most, and the pseudorange observation noise is generally in the decimeter level. The accumulated error of these errors will not reach the order of one hundred meters, while the distance between adjacent base stations is more than a kilometer, which will be reflected in the pseudorange residual and cause kilometer-level errors. Therefore, the threshold is set to 100m to detect whether the differential observation data matches the base station coordinates.

[0024] 3. After matching the differential observation data with the base station coordinates, the observation data quality is checked.

[0025] Assume that at epoch t = i(s), the coordinates of the station (base station) are A(x i ,y i ,z i ), the approximate coordinate is B(x i,0 ,y i,0 ,z i,0 ), the coordinate correction value is (δx i ,δy i ,δz i ), the satellite s coordinates are The phase observation equation is given as:

[0026]

[0027] where ρ s is the geometric distance from the receiver to the satellite s, in m, c is the speed of light, in m / s; δT is the receiver clock error, in s; δT s is the satellite clock error, in seconds; is the ionospheric delay from the receiver to the satellite s at frequency j, in meters; Trop s is the tropospheric delay from the receiver to the satellite s, in meters; is the integer ambiguity of satellite s frequency j; is the carrier observation noise from the receiver to satellite s at frequency j, in m.

[0028] 4. Linearly expand (3) at point B to obtain:

[0029]

[0030] In the formula,

[0031]

[0032] x i,0 ,y i,0 , z i,0 is the approximate coordinate, δx i ,δy i ,δz i is the coordinate correction value,

[0033] is the geometric distance from the receiver to the satellite (i = 1, 2, 3..., n, n is the number of visible satellites),

[0034] l i,0 , m i,0 , n i,0 They represent the direction cosine vectors from the satellite to the base station,

[0035] The direction cosine vector from satellite to base station is used to represent the directional relationship between the satellite and the base station in the geometric positioning method.

[0036] According to the present invention, for the base station coordinates, at epoch t=i, the corresponding coordinate correction is 0, and formula (4) can be reduced to:

[0037]

[0038] According to the present invention, similarly, at epoch t=i+1(s), the coordinates of the station (base station) are C(x i+1 ,y i+1 ,z i+1 ), the approximate coordinate is D(x i+1,0 ,y i+1,0 ,z i+1,0 ), coordinate correction value (δx i+1 ,δy i+1 ,δz i+1 ), the satellite s coordinates are Similarly, linear expansion of (3) at point D yields:

[0039]

[0040] According to the present invention, the delay variation of the ionosphere and troposphere in adjacent epochs is very small, and the satellite clock error changes slowly. If there is no cycle slip, the integer ambiguity remains unchanged, and formulas (6)-(5) can be obtained:

[0041]

[0042] make And from the above formula we get:

[0043]

[0044] Respectively represent t

[0045] = phase observation equation at time i (frequency j), represents the (frequency j) carrier phase difference.

[0046] According to the present invention, the epoch difference formula of the pseudorange observation is similarly as follows:

[0047]

[0048] According to the present invention, n satellites (n>4) are observed simultaneously, and formula (8) is written in the matrix form of n satellites:

[0049]

[0050] The above formula is abbreviated as V φ,prio =AX. Theoretically, the coordinates of the base station at epoch i and i+1 remain unchanged, so the coordinate correction value (δx i+1 ,δy i+1 ,δz i+1 )=0, and combine it with the above equation to get the equation:

[0051]

[0052] Based on the constraint equation of the above formula, using the least squares formula:

[0053] X=(A T PA) -1 (A T PV φ,prio )(13)

[0054] The coordinate correction can be accurately obtained.

[0055] According to the present invention, further by the formula: V φ,post =HX-V φ,prio (14)

[0056] Find the posterior residual of the carrier observation,

[0057] Combined with formula (9) and (10), the pseudo-range residual after verification is obtained in the same way:

[0058] V P,post =HX-V P,prio (15).

[0059] The pseudorange post-verification residual value refers to the difference between the actual measured pseudorange and the theoretically calculated pseudorange during the pseudorange measurement process. This difference reflects the precision and accuracy of the pseudorange measurement and is one of the important indicators for evaluating the quality of pseudorange measurement. Pseudorange measurement is a technology used to measure the distance between the measuring station and the satellite in satellite navigation systems such as the Global Positioning System (GPS). The distance measured by this method contains clock errors and atmospheric refraction delays, so it is called pseudorange. The accuracy of pseudorange measurement is affected by many factors, including the propagation delay of satellite signals, the accuracy of the receiver clock, atmospheric conditions (such as the influence of the ionosphere and troposphere), and multipath effects. These factors will cause a difference between the measured pseudorange and the true distance, that is, the pseudorange post-verification residual value. In order to reduce this difference and improve the accuracy of pseudorange measurement, a series of measures need to be taken, such as using a higher-precision clock, improving the signal processing algorithm, and calibrating the influence of atmospheric conditions.

[0060] According to the present invention, gross error detection is finally performed based on the size of the residual value of the carrier and pseudorange verification of each satellite:

[0061] For the pseudo-range observation of the i-th satellite, if |V P,i,post |>empirical threshold 2, it means that there is a gross error in the pseudorange observation, which is marked and removed.

[0062] The noise of pseudorange observation is generally at the decimeter level. Therefore, if the post-verification residual is above 1m, it can be regarded as a gross error. The empirical threshold 2 can be set to 1m.

[0063] According to the present invention, for the carrier observation of the i-th satellite, if |V φ,i,post |>empirical threshold 3, it means that the carrier observation has cycle slips, which are marked and removed.

[0064] The carrier observation noise is at the millimeter level, the carrier wavelengths of different frequencies are between 19cm and 25cm, and the small cycle slips are generally a quarter of a wavelength or larger. Therefore, the empirical threshold 3 of a quarter of a wavelength, about 0.05m, is sufficient to detect cycle slips larger than a quarter of a wavelength.

[0065] According to the base station differential observation data verification algorithm for terminal RTK positioning of the present invention, it is characterized in that:

[0066] The base station differential observation data verification algorithm for terminal RTK positioning is applicable to the gross error detection algorithm of single-frequency, dual-frequency or even multi-frequency carrier and pseudo-range observation quantities.

[0067] Beneficial Effects

[0068] The present invention realizes a base station observation data quality verification algorithm with low computing power consumption and more accurate gross error detection; solves the problems of large computing power consumption, inaccurate cycle slip detection and inability to effectively detect pseudorange gross errors in the existing RTK base station observation data verification algorithm, and proposes a gross error detection algorithm with higher computing efficiency for base station observation data verification, which is suitable for single-frequency, dual-frequency and even multi-frequency carrier and pseudorange observation quantities, thereby achieving a significant improvement in the fixation rate and positioning accuracy of the RTK positioning system. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 This is a flow chart of the base station differential observation data verification algorithm for RTK positioning of the present invention;

[0070] Figure 2 A comparison chart of the horizontal positioning accuracy of the RTK positioning system of the present invention before and after optimization of the base station differential observation data;

[0071] Figure 3 A comparison chart of the fixation rate of the RTK positioning system of the present invention before (left) and after (right) optimization of base station differential observation data. DETAILED DESCRIPTION

[0072] Example

[0073] Taking the data collected from the actual vehicle in Jiading, Shanghai as an example, the following results were obtained by regressing the data using the algorithm without the algorithm of the present invention and the algorithm after optimization by the scheme of the present invention:

[0074] Figure 1 The figure is a flow chart of the base station differential observation data verification algorithm for RTK positioning of the present invention.

[0075] Figure 2 and Figure 3 The comparison diagrams of the positioning accuracy and fixation rate of the RTK positioning system before and after the algorithm optimization described in the present invention are respectively shown. Figure 2 The red curve represents the horizontal error curve of the RTK positioning system before optimization without using the algorithm of the present invention, and the blue curve represents the horizontal error curve of the RTK positioning system after optimization with the algorithm of the present invention. Figure 2 It can be seen that after the optimization of the algorithm of the present invention, the two red flying spots in the red circles in the figure are well suppressed, and the horizontal positioning accuracy is also greatly improved. Figure 3 It can be seen that after the optimization of the algorithm of the present invention, the overall fixation rate of the RTK positioning system is increased by 1.43%.

Claims

1. A base station differential observation data verification algorithm for terminal RTK positioning, characterized in that ； Step 1) According to the GNSS pseudorange observation equation, the pseudorange pre-verification residual of each satellite is given: First, the GNSS pseudorange observation equation is given: in, P j s is the pseudo-range observation output by the receiver; j is the frequency number, which is used to distinguish different frequency points; ρ s is the geometric distance from the receiver to the satellite s, in meters; c is the speed of light, in m / s; δT is the receiver clock error, in seconds; δT s is the satellite clock error, in seconds; is the ionospheric delay from the receiver to the satellite s with frequency j, in meters; Trop s is the tropospheric delay from the receiver to the satellite s, in meters; is the pseudorange observation noise from the receiver to the satellite s at frequency j, in m; The base station coordinates are obtained through the network in the format defined by the RTCM protocol, and the satellite coordinates and satellite clock error δT s It can be calculated by ephemeris. At this time, P in formula (1) j s , ρ s , c, δT s All are known, Pseudorange pre-verification residual (frequency j): Step 2) Assume that there are n satellites, and the pseudo-range residuals of these satellites are Find the mean: If avg>empirical threshold 1, it means that the base station coordinates and the observation data do not match, and this package of base station differential observation data is discarded; If avg ≤ empirical threshold 1, it means that the differential observation data matches the base station coordinates, and the observation data quality check can be performed; Step 3) After matching and checking the differential observation data with the base station coordinates, the quality of the observation data is checked.

2. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 1, characterized in that ； In step 2), set the empirical threshold 1 to 100m.

3. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 1, characterized in that ； In step 3), assume that at epoch t = i(s), the coordinates of the survey (base) station are A(x i ,y i ,z i ), the approximate coordinate is B(x i,0 ,y i,0 ,z i,0 ), the coordinate correction value is (δx i ,δy i ,δz i ), the satellite s coordinates are The phase observation equation is given as: in, ρ s is the geometric distance from the receiver to the satellite s, in meters, c is the speed of light, in m / s; δT is the receiver clock error, in seconds; δT s is the satellite clock error, in seconds; is the ionospheric delay from the receiver to the satellite s at frequency j, in meters; Trop s is the tropospheric delay from the receiver to the satellite s, in meters; is the integer ambiguity of satellite s frequency j; is the carrier observation noise from the receiver to satellite s at frequency j, in m.

4. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 3, characterized in that ； Linearly expand equation (3) at point B and obtain: In the formula, is the geometric distance from the receiver to the satellite (i = 1, 2, 3..., n, n is the number of visible satellites), l i,0 , m i,0 , n i,0 They represent the direction cosine vectors from the satellite to the base station respectively.

5. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 4, characterized in that ； For the base station coordinates, at epoch t=i, the base station coordinates are known, and the corresponding coordinate correction is 0. Formula (4) can be reduced to: It is the phase observation equation at time t=i (frequency j).

6. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 3, characterized in that ； At epoch t=i+1(s), The base station coordinates are C(x i+1 ,y i+1 ,z i+1 ) Assume that the approximate coordinates of the base station at epoch t=i+1(s) are: D(x i+1,0 ,y i+1,0 ,z i+1,0 ), Coordinate correction value (δx i+1 ,δy i+1 ,δz i+1 ), The satellite s coordinates are Linear expansion of (3) at point D yields: It is the phase observation equation at time t=i+1 (frequency j).

7. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 6, characterized in that ； The delay changes of the ionosphere and troposphere in adjacent epochs are very small, and the satellite clock error changes slowly. If there is no cycle slip, the whole cycle ambiguity remains unchanged. Formula (6)-(5) gives make And from the above formula we get: It represents the phase observation equation at time t=i (frequency j), represents the (frequency j) carrier phase difference.

8. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 7, characterized in that ； For the carrier observation of the i-th satellite, if |V φ,i,post |>empirical threshold 3, it means that the carrier observation has cycle slips, which should be marked and removed, and the process goes to claim 14.

9. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 6, characterized in that ； The epoch difference formula of pseudorange observation is as follows: represents the pseudorange prior residual.

10. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 7, characterized in that ； When observing n satellites (n>4) at the same time, formula (8) is written in the matrix form of n satellites:

11. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 10, characterized in that ； The above formula (11) can be simplified as: V φ,prio =AX. Theoretically, the coordinates of the base station at epoch i and i+1 remain unchanged, so the coordinate correction value (δx i+1 ,δy i+1 ,δz i+1 )=0, and combine it with the above equation to get the equation: Based on the constraint equation above, using the least squares formula: X = (A T PA) -1 (A T PV φ,prio )(13)The coordinate correction can be accurately calculated.

12. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 11, characterized in that ； Furthermore, the carrier post-verification residual is calculated from the carrier pre-verification residual: V φ,post =AX-V φ,prio (14) Calculate the post-verification residual of the carrier observation, and combine formula (9) (10) to calculate the post-verification residual of the pseudorange: V P,post =AX-V P,prio (15).

13. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 12, characterized in that ； Finally, gross error detection is performed based on the residual value of each satellite’s carrier and pseudorange verification: For the pseudo-range observation of the i-th satellite, if |V P,i,post |>Experience threshold 2, This indicates that the pseudo-range observation has a gross error, which is marked and removed. P,i,post |≤empirical threshold 2, it means that the pseudorange observation is positive, and the normal data is retained for subsequent RTK positioning solution.

14. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 13, characterized in that ； The empirical threshold 2 is set to 1m.

15. A base station differential observation data verification algorithm for terminal RTK positioning as claimed in claim 12, characterized in that ； For the carrier observation of the i-th satellite, if |V φ,i,post |>empirical threshold 3, it means that the carrier observation has cycle slips, which are marked and removed, and normal data is retained for subsequent RTK positioning solution.

16. The base station differential observation data verification algorithm for terminal RTK positioning according to claim 13, characterized in that: The empirical threshold 3 (thre3) is taken as 4.75-6.25cm, which is a quarter wavelength.

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