Error and Integrity Assessment via Motion Prediction

Abstract

The invention relates to a method for error and integrity assessment during positioning, the method comprising recording position values (P ‑N , P ‑2 , P ‑1 ) by means of time-discrete transmission time measurements via a satellite navigation system and calculating the clock error of the receiver, recording a first pseudorange at a later point in time by means of time-discrete transmission time measurements via a satellite navigation system, extrapolating the position value (P'0) of the receiver at the later point in time based on a trajectory reproducing the previous movement path of the receiver, and extrapolating the clock error of the receiver at the later point in time based on a certain number of clock errors calculated before the later point in time, determining the distance (r'0) between the extrapolated position value (P'0) of the receiver and the position of a satellite (S0) of the satellite navigation system at the later point in time, wherein a quality measure of the availability of positioning using the satellite is obtained by constructing a second pseudorange based on the sum of the determined distance (r'0) and the extrapolated clock error at the later point in time, and comparing the second pseudorange with the first pseudorange.

Description

Technical Field

[0001] The present invention relates to a method for error and integrity evaluation during positioning, as well as a control device and a computer program product for executing the method. Background Art

[0002] Nowadays, a vehicle's absolute geographic location can be determined using a Global Navigation Satellite System (GNSS) receiver, hereinafter also referred to as a GNSS measurement. Furthermore, the vehicle's relative motion can be determined, for example, using inertial sensors (IMUs) and odometry (ODO) sensors installed in the vehicle.

[0003] Firstly, the Global Navigation Satellite System (GNSS) measures the receiver's position via a flight time measurement, also known as code ranging. Secondly, the receiver's velocity can be measured via the Doppler shift.

[0004] In the sensor fusion framework, global navigation satellite system (GNSS) measurements, inertial sensor (IMU) measurements, and odometry (ODO) sensor measurements can be fused to obtain more accurate and high-availability positioning. Sensor fusion is usually implemented using a Kalman filter or a particle filter.

[0005] Known methods for measuring GNSS errors include receiver autonomous integrity monitoring (RAIM) and fault detection and elimination (FDE). The practical application here is that during GNSS measurements, more than four satellite signals are often available. At least six satellites must be available for fault detection and elimination. Furthermore, methods such as code-subtraction carrier and double-delta correlators can be used to detect GNSS multipath transmission.

[0006] GNSS measurements in vehicles are subject to sporadic errors that cannot be detected with the current state of the art. This limits the confidence level and, therefore, the integrity of the position measurements made with GNSS.

[0007] Positioning, hereinafter referred to as determining both slowly varying and rapidly varying errors, is understood to include the detection of errors in both position determination and velocity or acceleration determination. Rapidly varying measurement errors are primarily caused by so-called non-line-of-sight (NLOS) propagation paths of radio signals, particularly in mobile receivers, but also by errors in Global Navigation Satellite Systems (GNSS) satellites, such as random hardware errors and software errors, such as unusually rapid clock drift.

[0008] The non-line-of-sight radio (NLOS) signals are caused by the reflection and scattering of radio signals in the surrounding environment immediately adjacent to the receiver, such as in a building. Here, different overlapping possibilities of unwanted non-line-of-sight radio (NLOS) signals and desired direct line-of-sight radio signals (LOS) can be distinguished. Most of these overlapping possibilities are described by the term multipath propagation.

[0009] In the fused filter method, errors in the corresponding sensors involved can lead to incorrect positioning. Here, in addition to the non-line-of-sight radio (NLOS) signals of the global satellite navigation system (GNSS), drift and offset in inertial sensors and offset in odometers are all possible causes of errors. The Kalman filter solution in particular shows an unwanted error transmission over time.

[0010] The above-mentioned global satellite navigation system (GNSS) fault detectors, namely Receiver Autonomous Integrity Monitoring (RAIM) and Fault Detection and Exclusion (FDE), are in principle limited to the isolated observation of global satellite navigation system (GNSS) signals, which limits the detection of the same type of errors (common mode faults). In addition, if multiple satellites are disturbed simultaneously, Receiver Autonomous Integrity Monitoring (RAIM) and Fault Detection and Exclusion (FDE) will show detection weaknesses. Summary of the Invention

[0011] Therefore, the basis of the task of the present invention is to achieve improved error and integrity assessment during positioning. Here, it should also preferably be achieved that rapidly changing errors in global satellite navigation system (GNSS) measurements are detected, especially errors caused by multipath propagation and / or inertial sensor measurements or odometer measurement errors, and thereby the integrity of the determined vehicle position is improved.

[0012] The task is solved by the features of the independent claims. Preferred further improvements are the subject of the dependent claims. The claims hereby become part of the description by express reference.

[0013] According to one aspect of the present invention, a method for error and integrity assessment during positioning includes recording position values by time-discrete transmission time measurements with the aid of a satellite navigation system and calculating the clock error of the receiver. For each of these measurements, the position value preferably includes a position specification in a three-dimensional coordinate system, which is determined by measuring the transmission time of the global satellite navigation system (GNSS) signal and multiplying it by the speed of light. Preferably, a history of the position values is stored so that it can be used in subsequent method steps.

[0014] The transmission time measurement, often also referred to as code ranging or pseudorange, preferably refers to the measurement of the time difference elapsed between the emission of a Global Navigation Satellite System (GNSS) signal from the satellite antenna phase center and the reception of the signal at the receiving antenna phase center. However, the interval between the two obtained by multiplying by the speed of light has a large inaccuracy due to the lack of synchronization of the satellite and receiver clocks. In addition to the carrier signal and the ephemeris data of the satellite, the Global Navigation Satellite System (GNSS) signal also includes a code, which is also included in the receiver and indicates the degree of offset of the receiver synchronized with the received satellite code. This offset corresponds to the measured transmission time.

[0015] If decisive inaccurate factors are included, the pseudorange generally refers to the measured spacing between the satellite and the receiver. Due to the large value of the speed of light, even a small clock error will cause a large deviation in the transmission time measurement, which also applies to the position values recorded by time-discrete transmission time measurements. Mathematically, the pseudorange PR at time point i can be described by PR_i = r_i + e_RecClock_i + e_other_i + e_MP_i, where r_i is the actual spacing between the satellite and the receiver, e_RecClock_i is the receiver clock error, e_other_i is other errors such as ionospheric error, noise error, and satellite clock error, and e_MP_i is, for example, an error that rapidly changes at each corresponding time point i, such as multipath error or non-line-of-sight (NLOS) error. The error e_RecClock is calculated or estimated mathematically in the receiver after each pseudorange measurement. The error term can take both positive and negative values.

[0016] Another step of the method according to the present invention includes recording a first pseudorange at a later time point, preferably at the current time point, by means of a satellite navigation system through time-discrete transmission time measurement. If four Global Navigation Satellite System (GNSS) satellites are available, the clock error can be determined in a known manner. The clock error is preferably converted into a distance obtained by multiplying the time difference corresponding to the clock error by the speed of light. Using the first pseudorange, a comparison parameter obtained by measurement can be obtained.

[0017] For comparison, a prediction parameter, i.e., a second pseudorange, is provided. To this end, the position value of the receiver assigned to the later time point is extrapolated based on the trajectory, i.e., the trajectory is logically continued for a time step. The trajectory reproduces the previous movement path of the receiver continuously or for discrete time points. In addition, the clock error at the later time point is extrapolated based on the course of the clock error so far. This is achieved based on a certain number of clock errors calculated before the later time point, where the certain number of clock errors is variable or can be determined once.

[0018] In addition, the method further includes determining the distance between the extrapolated position value of the receiver and the position of a satellite of the satellite navigation system at a later time point. As described above, the position values recorded by time-discrete transmission time measurements form the basis for the extrapolated position values. Thus, the extrapolated position values, i.e., the estimated position values assigned to a later time point, constitute one end of the actual distance, and the other end is constituted by a satellite, for example, a satellite with a known position from the transmitted ephemeris data. The satellite preferably refers to an arbitrarily selected satellite that can be used for direct signal transmission.

[0019] To obtain a comparison parameter for the first pseudorange from the distance between the extrapolated position value of the receiver and the satellite position, the extrapolated clock error, i.e., the estimated clock error assigned to a later time point, is added to the measured distance. Here, as described above, it is meaningful that the extrapolated clock error is expressed as a distance. Then, the second pseudorange thus obtained is compared with the first pseudorange.

[0020] In other words, in the method according to the present invention, estimates or predictions of the clock error and the receiver position of the receiver are formed and the associated pseudorange is calculated. The predicted pseudorange is compared with the measured pseudorange in order to obtain a better quality measure of the error and integrity of a specific satellite transmission time measurement in a simple, cost-effective, and efficient manner. In particular, rapidly changing errors are identified. Preferably, the method is repeated for other satellites in the satellite navigation system.

[0021] Different from the conventional Fault Detection and Exclusion (FDE) method, the error and integrity assessment performed in the method according to the present invention can be carried out before solving the position equation system, where the position of the receiver is calculated by means of data of multiple satellites, thereby reducing the computational workload.

[0022] Contrary to the code minus carrier method, the error and integrity assessment is independent of the error type of non-line-of-sight radio (NLOS) transmission paths, such as those occurring only in multipath transmissions or multipath transmissions outside the direct signal path.

[0023] The receiver preferably refers to a vehicle, and the receiver is arranged or fixedly installed in the vehicle.

[0024] The trajectory is preferably constructed from a certain number of position values recorded by means of the satellite navigation system by time-discrete transmission time measurements before a later time point and / or extracted from data of surrounding environment detection sensors (especially cameras, radars, and / or lidars). Since it can be updated by motion detection starting from a known absolute position, surrounding environment detection sensors can be used.

[0025] The later time point preferably corresponds to the current time point. In contrast, the recording of the position value and the calculation of the receiver clock error are performed at an earlier time point, i.e., before the later time point. The time points preferably have a uniform interval, i.e., the time-discrete transmission time measurements and preferably the later time point accordingly has the same time spacing from the previous time point. Thus, the later time point is preferably the next step after a specific clock signal in a series of measurement time points. The clock signal preferably corresponds to the sampling rate of the receiver.

[0026] According to a preferred embodiment, in order to extrapolate the position value of the receiver at a later time point, a position value difference is derived from the position value differences of the previously recorded position values. The change from the position value to the position value is considered in order to estimate the position value at the later time point.

[0027] Corresponding to a preferred embodiment, the extrapolation of the position value of the receiver is also based on inertial modeling, measurements of an inertial sensor (IMU), measurements of an odometer sensor, and / or Doppler measurements of satellite navigation. Inertial sensors typically include sensors for measuring acceleration and rotational speed, while an odometer can determine its own position by measuring data of a propulsion system such as wheel speed and / or steering movement.

[0028] According to a preferred embodiment, the extrapolation of the receiver clock error is also based on temperature measurements, stored information about clock drift and / or about the clock quartz, so that the clock error can be determined more precisely.

[0029] As already explained above, the extrapolation of the receiver clock error is preferably performed in the form of a distance value equivalent to the clock error.

[0030] According to a preferred embodiment of the method, when determining the distance (r‘0) between the extrapolated position value (P‘0) of the receiver and the satellite position (S0), the position of the satellite is determined according to the ephemeris data transmitted together with the satellite signal.

[0031] The comparison of the second pseudorange with the first pseudorange preferably includes subtraction. The difference can be stored or transmitted as a variable, or preferably directly used as a starting point for further measures, whereby a response is made to a fault or integrity of the currently determined satellite transmission time measurement. In the case of a large difference, it may be meaningful, for example, to first exclude the satellite from a specific receiver position.

[0032] Relative to a reference value, preferably a high quality measure is assigned to a small difference, a small quality measure is assigned to a large difference, and the corresponding quality measures are determined. Thereby a unified measure is provided for the quality.

[0033] According to a preferred embodiment, indirect received signals, such as those caused by multipath transmission, are examined, where a rapid change of a quality metric relative to a reference value is evaluated as a sign of indirect signal reception.

[0034] According to another aspect of the invention, a control device is designed to carry out the method.

[0035] The control device preferably has a memory and a processor, where the method is stored in the memory in the form of a computer program, and if the computer program is loaded from the memory into the processor, the processor is designed to carry out the method.

[0036] The computer program of the control device preferably includes program code means which, when the computer program is executed on a computer or the above device, can carry out all steps of the method.

[0037] According to another aspect of the invention, a computer program product includes program code stored on a computer-readable data carrier which, when executed on a data processing device, carries out one of the methods given above. Description of the Drawings

[0038] In conjunction with the following description of the embodiments and in conjunction with the drawings, the above-mentioned characteristics, features and advantages of the invention and the ways and means of achieving them will become clearer and more understandable. Detailed Embodiment

[0039] Figure 1 An exemplary view extending along the spatial axes X, Y showing the movement of a receiver and a satellite and their separation at a particular point in time, where the receiver is contained in a vehicle and the vehicle movement is equivalent to the receiver movement. The reference symbols each include a time index i, where i represents the sampling time point. -N, -2 and -1 represent the respective time points at which past measurements were carried out. In contrast, later time points correspond to the present and are denoted by i = 0. The satellites shown represent arbitrary satellites and occupy positions S -N , S -2 , S -1 and S0.

[0040] The position value corresponds to the receiver position, where P is described by P-N, P-2, and P-1. They are obtained by time-discrete transmission time measurements via satellite navigation systems such as the Navigation Satellite Timing and Ranging Global Positioning System (NAVSTAR GPS), Galileo positioning system, GLONASS positioning system, or Beidou. The vectors u-1, u-2, corresponding to u-(N-1) describe the following position changes, i.e., the position changes correspondingly represent the difference between two position values. In an embodiment, the distances r-N, r-2, r-1 between the receiver and the satellites also change with the position change. For a later time point with i = 0, the position value P0 and the distance r0 from the satellite are determined, from which the first pseudorange is measured as the measured distance by adding the currently measured clock error Δt0.

[0041] Based on the so far position changes, an estimated value u'0 of the subsequent, i.e., the current or the current sampling time point's position change, is estimated by logical continuation. Thereby, an estimated value (usually denoted by an apostrophe here) of the current position value P'0 of the receiver is obtained by means of the motion history. Here, the inertial modeling of the vehicle, the measurements of the inertial sensors, the measurements of the odometer sensors, and the Doppler measurements of the satellite navigation are used as additional information.

[0042] The clock error of the receiver, i.e., the time difference by which the receiver clock deviates from the satellite clock, is also estimated. For this purpose, the time difference Δt'0 is extrapolated using the history of the most recently measured clock error, and for easier further calculation, it is expressed as a range equivalent. In addition, the extrapolation also includes the stored information about the clock drift or the clock quartz and the temperature measurement information.

[0043] In addition, the actual distance r'0 between the satellite and the receiver is calculated based on this estimated information, where the term actual distance means that the distance does not contain any clock error, ionospheric error, or other errors common in satellite measurements, i.e., the distance is calculated as the distance between two points. The second pseudorange is provided by adding the also estimated clock error Δt'0. In addition to the clock error Δt'0, other error parameters can also be added to form the estimated pseudorange, i.e., the second pseudorange, in order to conform to the first pseudorange that may also contain other error parameters such as ionospheric error when necessary. Assuming only the clock error Δt'0 is added, the difference between the first and the second pseudoranges, i.e., |(r'0 + Δt'0) - (r0 + Δt0)|, contains information about the possible rapid change errors caused by, for example, the multipath transmission of the satellite signal, due to the sudden deviation of the measured distance from the distance obtained by extrapolation or estimation. Generally, the magnitude of the difference usually reflects the integrity of the measurement, and the more time steps there are, the better this effect is.

[0044] Accordingly, the parameter of the difference is a measure of the quality of the transmission time measurement error and integrity of a specific satellite. Higher effectiveness can be obtained for multiple repetitions of the method or for using a larger number of time steps or measurements for the estimation, but it is in principle sensible to seek a compromise in terms of the necessary computing power.

[0045] The method or the corresponding control device can be used in any system such as, for example, a motor vehicle, a drone, an aircraft or a ship.

Claims

1. A method for error and integrity assessment during positioning, the method comprising: - Recording position values (P -N , P -2 , P -1 ) by means of time-discrete transmission time measurements with the aid of a satellite navigation system and calculating the clock error of the receiver, - Recording a first pseudorange at a later time point by means of time-discrete transmission time measurements with a satellite navigation system, - Extrapolating a position value (P'0) of the receiver at a later time point based on a trajectory reproducing a previous movement path of the receiver, and extrapolating a clock error of the receiver at the later time point based on a certain number of clock errors calculated before the later time point, - Determining a distance (r'0) between the extrapolated position value (P'0) of the receiver and the position of a satellite (S0) of the satellite navigation system at the later time point, wherein a quality measure of the availability of positioning using the satellite is obtained by - constructing a second pseudorange based on the sum of the determined distance (r'0) and the extrapolated clock error at the later time point, and - Comparing the second pseudorange with the first pseudorange.

2. The method according to claim 1, wherein The trajectory is constructed from a certain number of position values (P -N , P -2 , P -1 ) recorded prior to a later point in time and / or extracted from data of sensors detecting the surroundings.

3. The method according to claim 2, wherein The ambient detection sensor includes a camera, a radar and / or a lidar.

4. The method according to any one of claims 1 to 3, characterized in that, The later time point corresponds to the current time point, and, in contrast thereto, the recording of the position values (P -N , P -2 , P -1 ) and the calculation of the clock error of the receiver are performed at the previous time point.

5. The method according to claim 4, wherein The recording of the position values (P -N , P -2 , P -1 ) and the calculation of the clock error of the receiver are performed at previous equally spaced time points.

6. The method according to any one of claims 1 to 3, characterized in that In order to extrapolate the position value (P'0) of the receiver at a later point in time, the previously recorded position value (P -N 、P -2 、P -1 ) position value difference (u -1 、u -2 ) to derive the position numerical difference (u'0).

7. The method according to any one of claims 1 to 3, characterized in that, The extrapolation of the position value (P'0) of the receiver is further based on inertial modeling, measurements of inertial sensors, measurements of odometer sensors and / or Doppler measurements of satellite navigation.

8. The method according to any one of claims 1 to 3, characterized in that, The extrapolation of the clock error of the receiver is further based on temperature measurements, stored information about clock drift and / or about clock quartz.

9. The method according to any one of claims 1 to 3, characterized in that, The extrapolation of the clock error of the receiver is performed in the form of a distance value equivalent to the clock error.

10. The method according to any one of claims 1 to 3, characterized in that, When determining the distance (r'0) between the extrapolated position value (P'0) of the receiver and the position of the satellite (S0), the position (S0) of the satellite is determined according to the ephemeris data transmitted together with the satellite signal.

11. The method according to any one of claims 1 to 3, characterized in that, The comparison of the second pseudorange with the first pseudorange includes subtraction.

12. The method according to claim 11, wherein Relative to a reference value, a high quality measure is assigned to a small difference, and a small quality measure is assigned to a large difference and the corresponding quality measure is determined.

13. The method according to claim 11, characterized in that, An indirectly received signal is checked, wherein a rapid change of the quality measure relative to the reference value is evaluated as a sign of indirect signal reception.

14. A control device for performing the method according to any one of claims 1 to 13.

15. The control device according to claim 14, having a memory and a processor, wherein, The method is stored in a memory in the form of a computer program, and if the computer program is loaded from the memory into a processor, the processor is designed to perform the method.

16. The control device according to claim 15, wherein, The computer program includes program code means for performing all steps of the method when the computer program is implemented on a computer or a given device.

17. A computer program product comprising program code stored on a computer-readable data carrier, which program code performs the method according to any one of claims 1 to 13 when implemented on a data processing device.

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