Satellite clock performance evaluation method based on inter-satellite link construction reference time reference

Abstract

The invention relates to the technical field of radar information, in particular to a satellite clock performance evaluation method for constructing a reference time benchmark based on an inter-satellite link, which comprises the following steps of: 1, collecting GNSS inter-satellite bidirectional pseudo-range observation data, establishing a bidirectional pseudo-range observation equation, reducing to the same target moment to obtain an inter-satellite relative clock error, and calculating the inter-satellite relative clock error; reducing to a main clock on a selected main satellite to obtain a clock difference of each clock relative to the initial time reference; step 2, fitting a polynomial clock error parameter by using the accumulated satellite clock error data with a certain arc length, deducting the clock error parameter from the satellite clock error epochwise, and calculating to obtain a clock error residual error; step 3, the alron variance of each satellite clock is calculated by using the clock error residual error, the stability of each clock is evaluated, and then the weight of each satellite clock is determined; 4, constructing a space-based time reference based on the clock error residual error obtained in the step 2 and the satellite clock weight determined in the step 3; and step 5, evaluating the performance of the satellite clocks based on the clock difference of each satellite clock under the space-based time reference.

Description

Technical Field

[0001] The present invention relates to the technical field of high-precision time and frequency technology of the Global Navigation Satellite System (GNSS), and specifically to a method for evaluating the performance of satellite clocks based on constructing a reference time benchmark through inter-satellite links. Background Art

[0002] GNSS can provide all-weather and all-time positioning, navigation, and timing (PNT) services to various users around the world, and has played a huge role in various fields such as financial services, transportation, aerospace, agricultural production, power transmission, disaster reduction and relief, weather forecasting, environmental monitoring, scientific research, and national defense and military. Satellite clocks provide time and frequency benchmarks for navigation satellites and are important core payloads. Their performance characteristics such as frequency stability, drift rate, and accuracy directly affect the positioning and timing accuracy of GNSS and the performance of PNT services. Accurately evaluating and analyzing the on-orbit performance of satellite clocks is of great significance for mastering the PNT service capabilities of the system and carrying out performance improvement. Currently, GNSS satellite clocks mainly include high-precision rubidium clocks, cesium clocks, and hydrogen clocks, and their daily frequency stability can reach the order of E-15. In order to achieve high-precision evaluation of satellite clocks, it is necessary to select atomic clocks or clock groups with higher performance as reference benchmarks. Generally, high-performance ground atomic clock groups for establishing or maintaining the GNSS system time are selected as reference benchmarks.

[0003] However, using ground atomic clock groups to evaluate the performance of satellite clocks has the following deficiencies: First, ground atomic clock groups are generally concentrated in a single ground station or distributed in multiple ground stations, and ground natural disasters (such as earthquakes and floods) or human sabotage (such as cyberattacks) will have an impact; second, in order to achieve full-arc monitoring of GNSS satellite clock differences, it is generally necessary to build a globally distributed ground station network to achieve time synchronization between the ground time benchmark and the satellites, which has a large dependence on the layout of the ground station network; third, the space-ground time synchronization means based on the space-ground observation link need to pass through the atmosphere, and are affected by atmospheric delay, observation environment errors, observation noise, etc. Moreover, there are differences in the propagation paths of different space-ground observation links, resulting in different degrees of errors, which affect the space-ground time synchronization accuracy. The above deficiencies limit the accurate evaluation of high-performance satellite clocks.

[0004] In view of the above problems, the present invention proposes a method for evaluating the performance of satellite clocks based on constructing a reference time benchmark through inter-satellite links. The inter-satellite link technology of navigation satellites can achieve the overall network time synchronization of the GNSS constellation only through high-precision measurements between satellites without the support of ground stations, and does not depend on the layout of the ground station network. Its measurement does not pass through the atmosphere, is less affected by the space environment, and has high time synchronization accuracy. Through remote phase comparison of inter-satellite links, high-performance on-board atomic clocks of the entire GNSS constellation can be unified into a clock group to construct a high-precision space-based time reference benchmark for satellite clock performance evaluation. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for evaluating the performance of satellite clocks based on an inter-satellite link to construct a reference time benchmark, so as to solve the problems raised in the above background technology.

[0006] To achieve the above purpose, the present invention provides the following technical solutions: A method for evaluating the performance of satellite clocks based on an inter-satellite link to construct a reference time benchmark, comprising the following steps: Step 1, Inter-satellite time synchronization processing observation model: Use on-board inter-satellite link observation equipment to collect GNSS inter-satellite two-way pseudorange observation data, establish a two-way pseudorange observation equation, reduce it to the same target time to obtain the inter-satellite relative clock difference, and then reduce it to the master clock on the selected master satellite to obtain the clock difference of each clock relative to the initial time benchmark; Step 2, Clock difference residual calculation: Use the accumulated satellite clock difference data of a certain arc length to fit the polynomial clock difference parameters, and subtract the clock difference parameters from the satellite clock difference epoch by epoch to calculate the clock difference residual; Step 3, Satellite clock weighting: Use the clock difference residual to calculate the Allan variance of each satellite clock, evaluate the stability of each clock, and then determine the weight of each satellite clock; Step 4, Construct a space-based time benchmark based on the clock difference residual obtained in Step 2 and the satellite clock weights determined in Step 3; Step 5, Evaluate the performance of the satellite clock based on the clock difference of each satellite clock under the space-based time benchmark.

[0007] Preferably, the two-way pseudorange observation equation in Step 1 is as follows: (1); In formula (1): A and B respectively represent satellite A and satellite B; and respectively represent the one-way pseudorange observation quantities of B transmitting to A and A transmitting to B; 、 respectively represent and the ranging times; 、 respectively represent and the signal emission times; 、 respectively represent the three-dimensional position vectors of satellite A at the ranging time and satellite B at the ranging time ; 、 respectively represent the three-dimensional position vectors of satellite B at the signal emission time and satellite A at the signal emission time ; 、 respectively represent the three-dimensional position vectors of satellite A at the ranging time and satellite B at the ranging moment satellite clock error; 、 respectively represent the satellite clock errors of satellite B at the signal transmission moment and satellite A at the signal transmission moment satellite clock error; 、 respectively represent the receiving delay and transmitting delay of the inter-satellite link equipment of satellite A; 、 respectively represent the receiving delay and transmitting delay of the inter-satellite link equipment of satellite B; is the speed of light; is the measurement noise and other unmodeled errors; 、 are respectively the modelable error corrections for the ranging values of B transmitting to A receiving and A transmitting to B receiving.

[0008] Preferably, the reduction to the same target moment in step 1 to obtain the inter-satellite relative clock error specifically includes: Reduce the two-way pseudorange observation in formula (1) to the same target moment , and the reduction formula is as follows: (2); In formula (2) 、 are respectively the one-way pseudorange measurement values of B transmitting to A receiving and A transmitting to B receiving reduced to the target moment ; 、 are respectively the three-dimensional position vectors of satellite A and satellite B at the target moment ; 、 are respectively the satellite clock errors of satellite A and satellite B at the target moment ; and are the ranging correction values calculated according to the predicted ephemeris and satellite clock parameters, and the calculation method is: (3); Subtract the two formulas in formula (2) to eliminate the satellite position information, and obtain the inter-satellite relative clock error: (4).

[0009] Preferably, the further reduction to the master clock on the selected master satellite in step 1 to obtain the clock error of each clock relative to the initial time reference specifically includes: The initial time reference is established with equal weights, and the clock errors of each on-board clock are reduced to this time reference to obtain the clock error of each clock relative to the initial time reference : (5); (6); Equation (5) is the time of the clock face reading. Among them is the initial time reference 、 are the clock face readings, i and j are the clock numbers , and i is the master clock number is the number of clocks participating in establishing the time scale

[0010] Preferably, the calculation method of the clock error residual in step 2 is as follows (7); In Equation (7) 、 、 are the zero-order, first-order, and second-order term coefficients of time respectively is the fitting reference time

[0011] Preferably, the calculation method of the Allan variance in step 3 is as follows (8); In Equation (8) is the clock error phase data is the number of samples is the smoothing time is the sampling interval is the smoothing factor That is, the measurement time is the number of data

[0012] Preferably, the specific steps of determining the weights of each satellite clock in step 3 include The weight determination method is as follows (9); is the normalized weight of each satellite clock is an empirical constant is the th satellite clock at the smoothing time of Allan variance

[0013] Preferably, the space-based time reference in step 4 is calculated by the relative clock error method with the initial time reference, and its expression is (10); The clock error of each clock under the space-based time reference is (11); The frequency stability of the satellite clock is evaluated by using the clock offset of each clock under the space-based time reference through formula (8).

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The satellite clock performance evaluation method based on the inter-satellite link to construct a reference time reference provided by the present invention can achieve autonomous time comparison and synchronization between satellites through the inter-satellite link, reducing the dependence on ground stations; the time-frequency comparison is carried out in space for satellites, avoiding the error accumulation introduced by the atmosphere through the space-ground comparison link; satellites are scattered in space orbits, and the constellation composed of multiple satellites has redundancy. A single satellite failure can maintain the reference benchmark through reconstruction, with strong overall reliability; aiming at the problems that the traditional satellite clock evaluation method has a strong dependence on the ground time reference station network and poor reliability, the present invention creatively realizes the space-based evaluation of satellite clock performance based on the high-precision inter-satellite link of navigation satellites and high-performance spaceborne atomic clocks, improving the evaluation performance of satellite clocks. Description of the Drawings

[0015] Figure 1 It is a flowchart of the satellite clock performance evaluation method based on the inter-satellite link to construct a reference time reference provided by the present invention. Detailed Embodiments

[0016] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0017] Figure 1 It is a flowchart of the satellite clock performance evaluation method based on the inter-satellite link to construct a reference time reference provided by the present invention. As Figure 1 shown, the embodiment of the present invention provides a satellite clock performance evaluation method based on the inter-satellite link to construct a reference time reference, including the following steps: Including the following steps: Step 1, inter-satellite time synchronization processing observation model: Use the on-board inter-satellite link observation equipment to collect GNSS inter-satellite two-way pseudorange observation data, establish a two-way pseudorange observation equation, reduce it to the same target time to obtain the inter-satellite relative clock offset, and then reduce it to the master clock on the selected master satellite to obtain the clock offset of each clock relative to the initial time reference; Step 2, clock offset residual calculation: Use the accumulated satellite clock offset data of a certain arc length to fit polynomial clock offset parameters, and subtract the clock offset parameters from the satellite clock offset epoch by epoch to calculate the clock offset residual; Step 3, satellite clock weighting: Calculate the Allan variance of each satellite clock using the clock error residuals, evaluate the stability of each clock, and then determine the weights of each satellite clock; Step 4, construct a space-based time reference based on the clock error residuals obtained in Step 2 and the satellite clock weights determined in Step 3; Step 5, evaluate the performance of the satellite clock based on the clock error of each satellite clock under the space-based time reference.

[0018] In the method for evaluating the performance of satellite clocks based on an inter-satellite link to construct a reference time reference provided by the present invention, it is assumed that navigation satellites can achieve full constellation connectivity through the inter-satellite link, and high-performance atomic clocks are carried on the satellites, so as to effectively perform long-distance phase comparison between satellites and comprehensively construct a high-precision reference benchmark based on the performance of on-board clocks. In practice, this condition is very easy to meet. Existing navigation systems have achieved full constellation interconnection through the inter-satellite link, and major global satellite navigation systems carry high-precision cesium clocks, rubidium clocks or hydrogen clocks.

[0019] In an embodiment of the present invention, the two-way pseudo-range observation equation in Step 1 is as follows: (1); In Equation (1): A and B respectively represent satellite A and satellite B; and respectively represent the one-way pseudo-range observation values of B transmitting to A and A transmitting to B; 、 respectively represent and the ranging times; 、 respectively represent and the signal transmission times; 、 respectively represent the three-dimensional position vectors of satellite A at the ranging time and satellite B at the ranging time ; 、 respectively represent the three-dimensional position vectors of satellite B at the signal transmission time and satellite A at the signal transmission time ; 、 respectively represent the satellite clock errors of satellite A at the ranging time and satellite B at the ranging time ; 、 respectively represent the satellite clock errors of satellite B at the signal transmission time and satellite A at the signal transmission time ; 、 respectively represent the reception delay and transmission delay of the inter-satellite link equipment of satellite A; and respectively represent the reception delay and transmission delay of the inter-satellite link equipment of satellite B; is the speed of light; is the measurement noise and other unmodeled errors; and are respectively the modelable error corrections for the ranging values of B transmitting to A receiving and A transmitting to B receiving. For inter-satellite ranging, it includes satellite antenna phase center correction and relativistic effect correction. For the ranging between the satellite and the anchoring station, it also includes tropospheric delay correction, station eccentricity correction, tidal correction and other errors, but all can be obtained through accurate modeling.

[0020] Furthermore, in an embodiment of the present invention, the obtaining of the inter-satellite relative clock difference by reducing to the same target time in step 1 specifically includes: Reducing the two-way pseudorange observation in formula (1) to the same target time , and the reduction formula is as follows: (2); In formula (2) and are respectively the one-way pseudorange measurement values of B transmitting to A receiving and A transmitting to B receiving reduced to the target time ; and are respectively the three-dimensional position vectors of satellite A and satellite B at the target time ; and are respectively the satellite clock differences of satellite A and satellite B at the target time ; and are the ranging correction values calculated according to the predicted ephemeris and satellite clock parameters, and the calculation method is: (3); Taking the difference between the two formulas in formula (2) to eliminate the satellite position information, and obtaining the inter-satellite relative clock difference: (4).

[0021] Even further, in an embodiment of the present invention, the obtaining of the clock difference of each clock relative to the initial time reference by reducing to the master clock on the selected master star in step 1 specifically includes: The initial time reference is established by equal weights, and the clock differences of each on-board clock are reduced to this time reference to obtain the clock difference of each clock relative to the initial time reference : (5); (6); Equation (5) is the clock face reading time, and is the initial time reference, 、 is the clock face reading, i and j are clock numbers, and i is the master clock number, is the number of clocks participating in establishing the time scale.

[0022] In an embodiment of the present invention, the calculation method of the clock error residual in step 2 is as follows: (7); In Equation (7) 、 、 are the zero-order, first-order, and second-order term coefficients of time respectively, is the fitting reference time.

[0023] In an embodiment of the present invention, the calculation method of the Allan variance in step 3 is as follows: (8); In Equation (8) is the clock error phase data; is the number of samples; is the smoothing time, is the sampling interval, is the smoothing factor; That is, the measurement time is the number of data.

[0024] Furthermore, in an embodiment of the present invention, the specific steps of determining the weights of each satellite clock in step 3 include: The weight determination method is: (9); is the normalized weight of each satellite clock, is the empirical constant, is the th satellite clock's Allan variance at the smoothing time of .

[0025] In an embodiment of the present invention, the space-based time reference in step 4 is calculated by the relative clock error method with the initial time reference, and its expression is: (10); The clock error of each clock under the space-based time reference is: (11); The frequency stability of the satellite clock is evaluated by the clock offset of each clock under the space-based time reference through formula (8).

[0026] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for evaluating the performance of satellite clocks based on constructing a reference time benchmark through inter-satellite links, characterized in that, It includes the following steps: Step 1, Inter-satellite time synchronization processing observation model: Using on-board inter-satellite link observation equipment, collect GNSS inter-satellite two-way pseudorange observation data, establish a two-way pseudorange observation equation, reduce it to the same target time to obtain the inter-satellite relative clock offset, and then reduce it to the master clock on the selected master satellite to obtain the clock offset of each clock relative to the initial time reference; Step 2, Clock offset residual calculation: Use the accumulated satellite clock offset data of a certain arc length to fit polynomial clock offset parameters, subtract the clock offset parameters from the satellite clock offset epoch by epoch, and calculate the clock offset residual; Step 3, Satellite clock weighting: Use the clock offset residual to calculate the Allan variance of each satellite clock, evaluate the stability of each clock, and then determine the weight of each satellite clock; Step 4, Construct a space-based time reference based on the clock offset residual obtained in Step 2 and the satellite clock weights determined in Step 3; Step 5, Evaluate the performance of the satellite clock based on the clock offset of each satellite clock under the space-based time reference.

2. The method for evaluating the performance of a satellite clock based on constructing a reference time benchmark through an inter-satellite link according to claim 1, wherein The two-way pseudorange observation equation described in Step 1 is as follows: (1)； In formula (1): A and B respectively represent satellite A and satellite B; and respectively represent the one-way pseudorange observables of B transmitting to A and A transmitting to B; and respectively represent and the ranging times; and respectively represent and the signal emission times; and respectively represent the three-dimensional position vectors of satellite A at the ranging time and satellite B at the ranging time ; and respectively represent the three-dimensional position vectors of satellite B at the signal emission time and satellite A at the signal emission time ; and respectively represent the satellite clock biases of satellite A at the ranging time and satellite B at the ranging time ; and respectively represent the satellite clock biases of satellite B at the signal emission time and satellite A at the signal emission time ; and respectively represent the receive delay and transmit delay of the inter-satellite link equipment of satellite A; and respectively represent the receive delay and transmit delay of the inter-satellite link equipment of satellite B; is the speed of light; is the measurement noise and other unmodeled errors; and are respectively the modelable error corrections for the ranging values of B transmitting to A and A transmitting to B.

3. The satellite clock performance evaluation method for constructing a reference time benchmark based on an inter-satellite link according to claim 2, wherein The specific process of reducing to the same target time to obtain the inter-satellite relative clock offset described in Step 1 includes: Reduce the two-way pseudorange observations in Equation (1) to the same target time , and the reduction formula is as follows: (2)； In formula (2) and are the one-way pseudorange measurement values after reduction to the target time for B transmitting and A receiving, and A transmitting and B receiving respectively; The one-way pseudorange measurement values and are the three-dimensional position vectors of satellite A and satellite B at the target time respectively; and are the satellite clock biases of satellite A and satellite B at the target time respectively; and are the ranging correction values calculated according to the predicted ephemeris and satellite clock parameters, and the calculation method is as follows: (3)； Subtract the two equations in Equation (2) to eliminate the satellite position information and obtain the inter-satellite relative clock offset: (4)。 4. The method for evaluating the performance of a satellite clock based on an inter-satellite link to construct a reference time benchmark according to claim 3, wherein, The specific process of reducing to the master clock on the selected master satellite to obtain the clock offset of each clock relative to the initial time reference described in Step 1 includes: The initial time reference is established by equal weights, and the clock offsets of each on-board clock are reduced to this time reference to obtain the clock offset of each clock relative to the initial time reference. : （5）； （6）； In formula (5) is the clock face reading time,[[]] is the initial time reference,[[]] , are the clock face readings, i and j are the clock numbers, , and i is the master clock number, is the number of clocks participating in establishing the time scale.

5. The method for evaluating the performance of a satellite clock based on an inter-satellite link to construct a reference time benchmark according to claim 4, wherein The clock error residual described in Step 2 is calculated as follows: （7）； In formula (7) , , are the zero-order, first-order, and second-order term coefficients of time respectively, is the fitting reference time.

6. The method for evaluating the performance of a satellite clock based on an inter-satellite link to construct a reference time benchmark according to claim 5, wherein The calculation method of the Allan variance described in Step 3 is: （8）； In formula (8) is the clock error phase data; is the number of samples; is the smoothing time, is the sampling interval, is the smoothing factor; That is, the measurement time is the number of data.

7. The method for evaluating the performance of a satellite clock based on constructing a reference time benchmark using an inter-satellite link according to claim 6, wherein The specific process of then determining the weight of each satellite clock described in Step 3 includes: The weight determination method is: （9）； is the normalized weight of each satellite clock, is an empirical constant, is the th satellite clock's Allan variance at the smoothing time of .

8. The method for evaluating the performance of a satellite clock based on an inter-satellite link to construct a reference time benchmark according to claim 7, wherein The space-based time reference described in Step 4 It is calculated by the relative clock difference from the initial time reference, and its expression is: （10）； The clock offset of each clock under the space-based time reference is: （11）； Use the clock offset of each clock under the space-based time reference to evaluate the frequency stability of the satellite clock through Equation (8).

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