Beidou / GNSS Multi-Constellation Precise Point Time Service Integrity Monitoring Method

Abstract

The present invention belongs to the field of satellite navigation technology and discloses a Beidou / GNSS multi-constellation precise single-point timing integrity monitoring method, comprising the following steps: a first step, pre-allocation of integrity prior probability; a second step, determining a maximum fault order; a third step, determining a fault subset; a fourth step, constructing a weighted matrix; a fifth step, calculating a receiver clock error and constructing a test quantity; a sixth step, calculating a receiver clock error test threshold and discriminating the test quantity; a seventh step, calculating a receiver clock error protection level; and an eighth step, discriminating availability. The present invention fills the research gap of existing timing integrity monitoring algorithms for multi-constellation precise single-point timing monitoring, solves the problem of multiple faults occurring in multi-constellation timing, and improves the reliability of multi-constellation joint timing.

Description

Technical Field

[0001] The present invention belongs to the field of satellite navigation technology, and in particular relates to a BeiDou / GNSS multi-constellation precise single-point timing integrity monitoring method. Background Art

[0002] GNSS receivers typically have the ability to perform autonomous integrity monitoring, known as Receiver Autonomous Integrity Monitoring (RAIM). This is an integrity monitoring method implemented at the GNSS receiver level. Compared to other types of integrity monitoring, RAIM is simple to implement, low-cost, and requires no external information. It can also monitor and assess the actual conditions of the user receiver, such as multipath and signal interference. It is the last line of defense for monitoring the normal provision of GNSS positioning, navigation, and timing (PNT) services, and plays a crucial role in the research and application of satellite navigation integrity monitoring.

[0003] GNSS receivers' low cost, ease of use, and excellent performance make them crucial for GNSS timing services, finding applications in a wide range of sectors, from basic utilities, telecommunications, and finance and securities to various engineering technologies and even modern space and high-tech sectors. While the BeiDou navigation system currently boasts a timing accuracy of 20ns, its inherent vulnerabilities can compromise timing performance and even disrupt unified time distribution across global networks in industries like communications, transportation, and finance, creating significant challenges.

[0004] Although many studies have been conducted on the development and research of RAIM algorithms based on various threats encountered in the GNSS positioning process, there are few RAIM algorithms based on timing services (TRAIM). The shortcomings are mainly reflected in the following aspects: (1) The existing TRAIM algorithms are mainly based on simulation results, and the availability of GNSS observations is not verified; (2) The existing TRAIM measured data results are only for a single satellite navigation system and are not suitable for multi-system joint timing; (3) The current TRAIM algorithms based on measured data can only monitor the occurrence of a single fault and cannot monitor multiple faults. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a BeiDou / GNSS multi-constellation precise single-point timing integrity monitoring method to solve the problems in the prior art. The technical solution adopted by the present invention is:

[0006] The BeiDou / GNSS multi-constellation precise single-point timing integrity monitoring method includes the following steps:

[0007] The first step is to pre-allocate the integrity prior probability;

[0008] The second step is to determine the maximum fault order;

[0009] The third step is to determine the fault subset;

[0010] The fourth step is to construct the weighted matrix;

[0011] Step 5: Calculate the receiver clock error and construct the test quantity;

[0012] Step 6: Calculate the receiver clock error test threshold and use it to determine the test quantity;

[0013] Step 7: Calculate the receiver clock error protection level;

[0014] Step 8: Determine availability.

[0015] The present invention has the following beneficial effects:

[0016] (1) The present invention is innovative in the field of receiver timing integrity algorithm research. Different from the existing single-constellation timing integrity monitoring algorithm, the present invention proposes a multi-constellation joint precise single-point timing integrity monitoring algorithm, filling the research gap in this field;

[0017] (2) The present invention is reliable in application. When multi-constellation joint timing and positioning is performed, there are many constellations and a sharp increase in the number of satellites. At this time, the failure mode is complex and there is a possibility of multiple failures. The existing timing integrity algorithm can only monitor a single failure mode. The present invention can monitor the occurrence of multiple failures, thereby ensuring the reliability of multi-constellation timing.

[0018] (3) The present invention is universal and flexible in multi-constellation joint timing. Different regions of the world have different user needs, and the available constellations are different. The present invention is applicable to the selection of observation constellations and changes in the number of constellations. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0020] The following is a combination of the embodiments of the present invention Figure 1 , the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0021] like Figure 1The present invention aims to propose a BeiDou / GNSS multi-constellation precise single-point timing integrity monitoring method. Specifically, considering the important application of multi-system timing in high-precision PNT services, and taking into account the inter-system deviation of multi-constellation joint timing, a multi-constellation pseudo-range joint timing integrity monitoring method based on GNSS pseudo-range observations is proposed. This method fills the research gap of the existing timing integrity monitoring algorithm for multi-constellation precise single-point timing monitoring, solves the problem of multiple faults in multi-constellation timing, and improves the reliability of multi-constellation joint timing. The method includes the following steps:

[0022] The first step is to pre-allocate the integrity prior probability: the integrity prior probability includes the probability of hazardous misleading information PHMI (Probability of Hazardous Misleading Information), the continuity risk probability P FA , Unmonitored fault integrity risk probability P fault_thres Since there is a system bias when estimating the receiver clock difference in multiple constellations, each system must estimate the corresponding receiver clock difference. Therefore, the above integrity prior probability is evenly distributed to each constellation in the multi-constellation timing. Among them, PHMI specifies the probability that the clock error exceeds the timing protection level (TPL) but no alarm is issued in time, P FA is the false alarm probability, P fault_thres is the probability of unmonitored failure integrity risk.

[0023] The second step is to determine the maximum fault order: the maximum fault order N fault_max Indicates the maximum fault order that needs to be detected when the sum of the probabilities of higher-order fault modes is less than the probability of unmonitored fault integrity risk. In the present invention, the maximum fault order N corresponding to constellation j needs to be calculated separately. j,fault_max . N j,fault_max The definition is as follows:

[0024] N j,fault_max =max{r∈1,…,N j,sat |P j,not_monitored ≤P j,fault_thres} (16)

[0025] The sum of the undetected high-order fault probabilities of constellation j is P j,not_monitored It can also be regarded as (N j,fault_max +1) and the sum of the probabilities of higher-order failure modes, which needs to be less than the unmonitored failure integrity risk probability P assigned to constellation j j,fault_thres For example, the sum of the probabilities of second-order and higher-order faults is:

[0026]

[0027] P no_fault represents the probability of no failure, which can be expressed as P j,event,i It means the probability of a satellite or constellation failure.

[0028] The third step is to determine the fault subset: the fault subset is the set of all fault modes that need to be monitored. Since the number of fault subsets increases explosively with the increase of the fault order, it is still necessary to exclude redundant fault modes after determining the maximum fault order. According to the maximum fault order, all fault modes are obtained by permutation and combination, and unobservable fault modes are excluded. The exclusion rule is that the number of satellites in the fault-tolerant subset is less than (3+N) in both the fixed coordinate and fixed coordinate solution modes. const )、(1+N const ) are deleted from the list, and the total probability of unobservable failure modes P j,unobservable Add to the probability of unmonitored failure, N const is the number of constellations currently observed. Then, all fault modes are sorted in ascending order of fault order and descending order of fault mode probability, and the top N faultmode failure mode, and the remaining failure mode probabilities Add to the unmonitored fault probability to obtain the updated unmonitored fault probability P j,not_monitored,new , so that it still satisfies:

[0029]

[0030] The first k fault modes are the fault subsets that need to be monitored.

[0031] The fourth step is to construct the weight matrix. Use the integrity support message (ISM) to construct the fault-free full set weight matrix W j (0) and the weight matrix W of the fault-tolerant subset k j (k) :

[0032]

[0033] in is the pseudo-range covariance matrix for evaluating the integrity of constellation j, which is a diagonal matrix. The elements on the main diagonal are the user ranging accuracy variance of satellite i in the constellation. Tropospheric delay variance and user elevation angle error variance The sum is expressed as:

[0034]

[0035] The weight matrix W of the fault-tolerant subset k corresponding to each failure mode j (k) It can be expressed as:

[0036]

[0037] The fifth step is to calculate the receiver clock error and construct the test quantity. In this invention, the classical weighted least squares method is used to estimate the clock error of the full set of fault-free receivers. and the receiver clock error of fault-tolerant subset k The fault-free clock error estimation matrix is:

[0038]

[0039] Among them G j is the observation matrix of the receiver clock error solution of constellation j. The clock error estimation matrix of fault-tolerant subset k can be expressed as:

[0040]

[0041] The receiver clock errors of the full set without faults and the fault-tolerant subset k are calculated based on the clock error estimation matrix. The calculation method is as follows:

[0042]

[0043] Then the k-clock difference test quantity of the fault-tolerant subset is defined as:

[0044]

[0045] The sixth step is to calculate the receiver clock error test threshold and use it to determine the test quantity. The receiver clock error test threshold is used to monitor the continuity risk. The continuity risk budget P of constellation j is j,FA Evenly distribute to the fault-tolerant subset of each failure mode. Test threshold is defined as:

[0046]

[0047] Where H0 is a fault-free scenario, the test quantity obeys the mean of zero, and is the standard deviation Gaussian distribution. Therefore, the calculation method of the test quantity can be given:

[0048]

[0049] where K fa,j is the threshold of the standard normal distribution obeyed by the test quantity of constellation j, S is the fault-free clock error estimation matrix, C j,acc The pseudo-range covariance matrix for evaluating accuracy is a diagonal matrix, and the main diagonal elements are calculated as follows:

[0050]

[0051] in, is the user ranging error variance.

[0052] If the clock error test quantity satisfies:

[0053]

[0054] Then the fault-tolerant subset k passes the test. The test amount is judged for each fault-tolerant subset of the fault subset. If all fault-tolerant subsets meet condition (14), the subsequent process of the algorithm can be solved. Otherwise, the faulty satellites of the fault-tolerant subsets that do not meet the condition are eliminated, and the third step is returned to restart the test until all fault-tolerant subsets meet condition (14).

[0055] Step 7: Calculate the receiver clock protection level (TPL). The TPL defined in this invention refers to the probability that the error between the full set of fault-free receiver clock errors and the true clock error exceeds the TPL and does not exceed the PHMI indicator requirements, provided that the receiver clock error test values of all fault-tolerant subsets pass the test threshold. That is:

[0056]

[0057] According to the constraints of formula (15), the equation is mathematically transformed to give the receiver clock error protection level TPL of constellation j: j Calculation method:

[0058]

[0059] in are the maximum deviation of fault-tolerant subset k and the standard deviation of receiver clock error estimation, respectively.

[0060] Step 8: Determine availability. TAL stands for Timing Alert Limit (TAL), which is the upper limit of the acceptable receiver clock error. The determination rules are as follows:

[0061] TPL j ≤TAL (32)

[0062] When the receiver clock error protection level of constellation j is less than TAL, TRAIM is declared valid and subsequent receiver clock error calculation can be performed. Otherwise, it is declared invalid and an alarm is issued to the user.

[0063] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various deformations, modifications, and substitutions made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. BeiDou / GNSS multi-constellation precise single-point timing integrity monitoring method, characterized by: The following steps are involved: The first step is to pre-allocate the integrity prior probability: assign the integrity prior probability to each constellation in the multi-constellation timing system. The second step is to determine the maximum fault order; The third step is to determine the fault subset: according to the maximum fault order, all fault modes are obtained by permutation and combination, and unobservable fault modes are excluded; The fourth step is to construct the weighted matrix; Step 5: Calculate the receiver clock error and construct the test quantity; Step 6: Calculate the receiver clock error test threshold and use the judgment test quantity to eliminate the faulty satellites in the fault-tolerant subset that do not meet the conditions, and return to step 3 to restart the test until the test quantity is met. Step 7: Calculate the receiver clock error protection level; Step 8: Determine availability: When the receiver clock error protection level is no greater than the timing alarm threshold, TRAIM is declared valid and subsequent receiver clock error calculation can be performed; otherwise, it is declared invalid.

2. The BeiDou / GNSS multi-constellation precise single point timing integrity monitoring method according to claim 1, characterized in that: In the first step, the integrity prior probability includes the probability of dangerous misleading information, the probability of continuity risk, and the probability of unmonitored fault integrity risk.

3. The BeiDou / GNSS multi-constellation precise single point timing integrity monitoring method according to claim 1, characterized in that: In the second step, the maximum fault order N corresponding to each constellation j is calculated respectively. j,fault_max , which is expressed as follows: N j,fault_max =max{r∈1,…,N j,sat |P j,not_monitored ≤P j,fault_thres } (1) Among them, P j,not_monitored is the sum of the undetected high-order fault probabilities of constellation j, P j,fault_thres is the unmonitored fault integrity risk probability assigned to constellation j.

4. The BeiDou / GNSS multi-constellation precise single point timing integrity monitoring method according to claim 1, characterized in that: In the third step, when eliminating unobservable failure modes, the following steps are included: In the two solution modes of non-fixed coordinates and fixed coordinates, the number of satellites in the fault-tolerant subset is less than (3+N const )、(1+N const ) failure modes are deleted from the list, where N const is the number of constellations currently observed; The sum of the probabilities of unobservable failure modes P j,unobservable Added to the probability of unmonitored failure; Sort all fault modes in ascending order of fault order and descending order of fault mode probability, and select the top N faultmode failure mode, and the remaining failure mode probabilities Add to the unmonitored fault probability to obtain the updated unmonitored fault probability P j,not_monitored,new , so that it satisfies: The first k fault modes are the fault subsets that need to be monitored.

5. The BeiDou / GNSS multi-constellation precise single point timing integrity monitoring method according to claim 1, characterized in that: In the fourth step, the integrity support information is used to construct the fault-free full set weight matrix W j (0) and the weight matrix W of the fault-tolerant subset k j (k) : in is the pseudo-range covariance matrix for evaluating the integrity of constellation j, which is a diagonal matrix. The elements on the main diagonal are the user ranging accuracy variance of satellite i in the constellation. Tropospheric delay variance and user elevation angle error variance The sum is expressed as: The weight matrix W of the fault-tolerant subset k corresponding to each failure mode j (k) Expressed as:

6. The BeiDou / GNSS multi-constellation precise single point timing integrity monitoring method according to claim 1, characterized in that: In the fifth step, the classical weighted least squares method is used to estimate the clock bias of the full set of unfaulted receivers. and the receiver clock error of fault-tolerant subset k The fault-free clock error estimation matrix is: Among them G j is the measurement matrix of the receiver clock error solution for constellation j; The clock error estimation matrix of the fault-tolerant subset k can be expressed as: According to the clock error estimation matrix, the receiver clock errors of the complete fault-free set and the fault-tolerant subset k are calculated respectively. The calculation formula is as follows: Then the k-clock difference test quantity of the fault-tolerant subset is defined as:

7. The BeiDou / GNSS multi-constellation precise single point timing integrity monitoring method according to claim 1, characterized in that: In the sixth step, the receiver clock error test threshold is used to monitor the continuity risk, and the continuity risk probability P of constellation j is j,FA Evenly distribute to the fault-tolerant subset of each failure mode; test threshold is defined as: Where H0 is a fault-free scenario, the test quantity obeys the mean of zero, and is the standard deviation Gaussian distribution, is the receiver clock error, N faultmode is the first N failure modes, N const is the number of constellations currently observed, P FA is the overall continuity risk probability; The calculation formula for the test quantity is: where K fa,j is the threshold of the standard normal distribution obeyed by the test quantity of constellation j, S is the fault-free clock error estimation matrix, C j,acc The pseudo-range covariance matrix for evaluating accuracy is a diagonal matrix, and the main diagonal element calculation formula is: in, is the user ranging error variance; If the clock error test quantity satisfies: Then the fault-tolerant subset k passes the test, and the test amount is judged for each fault-tolerant subset of the fault subset. If all fault-tolerant subsets satisfy formula (14), the subsequent process of the algorithm can be solved. Otherwise, the faulty satellites of the fault-tolerant subsets that do not meet the conditions will be eliminated, and the third step will be returned to restart the test until all fault-tolerant subsets satisfy formula (14).

8. The BeiDou / GNSS multi-constellation precise single point timing integrity monitoring method according to claim 1, characterized in that: In the seventh step, The probability that the error between the clock error of the complete set of receivers without faults and the true clock error exceeds the TPL and does not exceed the PHMI indicator requirements, that is: Perform mathematical transformation to obtain the receiver clock protection level TPL of constellation j j Calculation formula: in are the maximum deviation of the fault-tolerant subset k, the standard deviation of the receiver clock error estimation, and N const is the number of constellations currently observed, is the receiver clock error, is the clock error of the full set of fault-free receivers, TPL is the clock error exceeding the timing protection level, PHMI is the integrity prior probability including the probability of dangerous misleading information, N faultmode These are the top N failure modes.

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