A Beidou global timing accuracy evaluation method

Abstract

The present invention discloses a BeiDou global timing accuracy assessment method, which belongs to the field of satellite timing. The method comprises the following steps: a user station uses original observation data and broadcast ephemeris to perform BDS global timing, and obtains the difference between its receiver clock and the broadcast ephemeris BDT benchmark as a first clock error; the difference between the user station receiver clock and the BDT benchmark of a B2b product is calculated as a second clock error; when the user station is located in the Asia-Pacific region, the second clock error is obtained by directly obtaining the PPP clock error calculated by the B2b product; when the user station is located in a non-Asia-Pacific region, a measuring station in the Asia-Pacific region is selected as a reference station, and the time difference between the BDT benchmark of the B2b product and the clock error benchmark corresponding to the precise orbit and clock error products of other institutions is obtained, and the time difference of the user station is corrected based on the PPP clock error calculated by the precise orbit and clock error products of the other institutions to obtain the second clock error; and the timing accuracy of the BDS system is assessed by calculating the difference between the first and second clock errors, so that accurate and reliable assessment can be performed on a global scale.

Description

Technical Field

[0001] The present invention belongs to the field of satellite timing, and in particular relates to a Beidou global timing accuracy assessment method. Background Art

[0002] Time is one of the seven fundamental physical quantities in nature and a crucial component of human civilization. It is also the most precisely measured and widely used physical quantity of all, playing a crucial role in fundamental scientific research, the stable operation of the national economy, and national defense. Currently, commonly used timing methods include internet timing, satellite timing, long and short wave timing, and telephone timing. Of these, satellite timing, with its all-weather availability, high accuracy, and ease of implementation, has become the most widely used method for precision timing.

[0003] Monitoring and evaluating satellite timing accuracy is a crucial foundation for ensuring the quality of satellite timing services. Real-time monitoring and regular post-evaluation of satellite navigation system timing accuracy ensure the reliability of these services, which is crucial for promoting the continued development and widespread application of satellite navigation technology.

[0004] Satellite timing uses navigation satellites as the timing reference source. Users receive satellite signals, correct the satellite clock error, and obtain the difference between local time and satellite navigation system time. When analyzing the accuracy of satellite timing, traditional methods require users to directly or indirectly synchronize local time to a standard time signal (such as UTC (Coordinated Universal Time), (NTSC, National Time Service Center Chinese Academy Of Sciences)) or a satellite navigation system time signal before monitoring and evaluating satellite timing accuracy. For example, the timing performance evaluation method based on the standard time UTC measured by the user end proposed by Liu Ying is based on the following principles: Figure 1As shown, the reference time is the actual UTC obtained using the fast UTC file published by the BIPM (International Bureau of Weights and Measures), which is based on the international time comparison link of the National Time Service Center of the Chinese Academy of Sciences. This method obviously has limitations: for general users, it is difficult to obtain standard time and satellite system time. Therefore, this method can only be implemented at satellite navigation system control stations or stations with external standard time. Some scholars have also evaluated the accuracy of satellite navigation timing using station clock products published by various institutions as a benchmark. For example, Zhang Dazhong analyzed the timing accuracy of single-satellite BDS (BeiDou Navigation Satellite System) satellites in GEO (geostationary Earth orbit), IGSO (inclined geosynchronous orbit), and MEO (medium Earth orbit) at the XIA1 and SHA1 stations, using the clock error files of the BeiDou Analysis Center (CGS) of the China Academy of Surveying and Mapping as a benchmark. However, this method is only applicable to the observation stations included in the clock error files of various institutions, and ordinary users cannot directly evaluate and analyze the calculated clock error information.

[0005] In July 2020, my country completed construction of the independently developed and operated BeiDou Navigation Satellite System (BDS-3), marking a new phase in the development of my country's satellite navigation system. This means the BDS system can provide high-precision, highly reliable positioning, navigation, and timing services to a wide range of users around the world, 24 / 7. BeiDou global timing involves users performing standard single-point positioning (SPP) with the BDS system based on observed pseudorange information and broadcast ephemeris. This allows users to simultaneously obtain both user station coordinates and the receiver clock error based on the BeiDou Time (BDT) reference clock error in the broadcast ephemeris. This higher-precision receiver clock error, based on BDT, is required for evaluating and analyzing BeiDou global timing accuracy. The BDS-3 system adds Precise Point Positioning (PPP) services. It broadcasts PPP-B2b correction signals to China and surrounding areas via three GEO satellites. The satellite clock corrections in this signal, like those in the Beidou broadcast ephemeris, are referenced to the same time period as BDT. Therefore, the PPP-B2b signal provides a new method for monitoring and evaluating Beidou's global timing accuracy. Users can use the PPP-B2b signal to perform single-station PPP and use this PPP clock error as a benchmark for analyzing and evaluating Beidou's global timing accuracy. However, this method only applies to areas covered by the PPP-B2b signal (i.e., China and surrounding areas). For Beidou-3 to provide global timing services, global monitoring and evaluation of Beidou's timing accuracy is necessary.

[0006] Therefore, how to evaluate the timing accuracy of BDS-3 users outside the scope of PPP-B2b services has become a technical problem that needs to be solved urgently. Summary of the Invention

[0007] In order to solve the above problems existing in the prior art, the present invention provides a BeiDou global timing accuracy assessment method. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0008] A BeiDou global timing accuracy assessment method, comprising:

[0009] The user station uses the acquired raw observation data and broadcast ephemeris to perform BDS global timing, and obtains the difference between the user station receiver clock and the broadcast ephemeris BDT benchmark as the first clock difference;

[0010] Calculate the difference between the user station's receiver clock and the B2b product's BDT reference as the second clock error. When the user station is located in the Asia-Pacific region, the user station obtains the second clock error by directly obtaining the B2b precise orbit and clock product and calculating the PPP clock error. When the user station is located outside the Asia-Pacific region, select a station in the Asia-Pacific region as a reference station to obtain the time difference between the B2b product's BDT reference and the clock error reference corresponding to the precise orbit and clock error product of another institution. Use this time difference to correct the PPP clock error calculated by the user station based on the precise orbit and clock error product of another institution to obtain the second clock error.

[0011] The BDS system timing accuracy of the user station is evaluated by calculating the difference between the first clock difference and the second clock difference.

[0012] Beneficial effects of the present invention:

[0013] In the BeiDou global timing accuracy assessment method provided by the embodiments of the present invention, for user stations in the Asia-Pacific region, the B2b product broadcast by the BDS system's GEO satellites is received. A dual-frequency, ionospheric-free solution is used to calculate the difference between the user station's receiver clock and the BDT reference of the B2b product. This difference is then used as a benchmark to assess the difference between the user station's receiver clock and the broadcast ephemeris BDT reference, calculated using the BeiDou timing solution. For user stations outside the Asia-Pacific region, the accuracy of BeiDou timing results cannot be assessed because they cannot receive the BDS system's B2b product. The present invention introduces a station in the Asia-Pacific region as a reference station, calculates the PPP clock difference between the reference station and the user station by using the BDS system satellite orbit and clock products of other institutions, and solves the PPP clock difference based on the B2b product at the reference station. The PPP clock difference time difference calculated by different orbit and clock products is determined by the reference station, and corrected to the PPP clock difference value of the user station, thereby obtaining the PPP clock difference of the user station based on the B2b product. The difference between the local clock of the user station obtained by the Beidou global timing and the BDT can be evaluated, and the Beidou global timing accuracy evaluation based on the B2b product can be realized. Therefore, the method proposed by the present invention breaks the PPP-B2b service area limitation and can realize accurate and reliable monitoring and evaluation of Beidou timing accuracy on a global scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the principle of the Beidou timing performance evaluation method based on the standard time UTC measured by the user end in the existing technology;

[0015] Figure 2 A flowchart of a BeiDou global timing accuracy assessment method provided by an embodiment of the present invention;

[0016] Figure 3This is a schematic diagram of the BDS timing accuracy evaluation principle based on the B2b product for user stations in the Asia-Pacific region in an embodiment of the present invention;

[0017] Figure 4 This is a schematic diagram of the BDS system timing accuracy evaluation principle based on the B2b product for non-Asia-Pacific user stations in an embodiment of the present invention;

[0018] Figure 5 This is a diagram showing the difference in PPP timing between SEPT stations based on different products in the experiment of this invention.

[0019] Figure 6 This is a sequence diagram of clock difference values ​​based on PPP-B2b obtained by two methods at the GAMG station in the experiment of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0021] The BeiDou Service Performance Specification defines timing accuracy as the statistical difference between the time determined by users using public service signals and the BDT. Therefore, users need to obtain accurate BDT for evaluation, but BDT and its related standard time signals (such as UTC (NTSC)) are difficult to accurately obtain. Traditional methods currently assess timing accuracy at stations connected to external standard time signals, or employ other evaluation benchmarks for timing accuracy analysis, such as station clock error products generated by analysis agencies or the 1pps signal output by base station receivers.

[0022] Using traditional methods, users have difficulty obtaining BDT and related standard time signals, such as UTC (NTSC). Furthermore, when using station clock products generated by various analysis agencies as a benchmark, the stations of ordinary users are not included in the clock product's station list. Analyzing user station timing using the 1pps signal output by the base station receiver as a benchmark is prohibitively expensive, making it difficult for users to conveniently assess their own BDS timing accuracy using this method.

[0023] The latest B2b signal reference time is BDT, and the PPP clock difference time reference calculated by users based on B2b products is also BDT, which is the same as the time base of Beidou global timing. Therefore, the PPP clock difference calculated by users based on B2b products can be used as the benchmark for Beidou global timing accuracy evaluation. However, due to the limited coverage of the B2b signal, it is impossible to directly implement Beidou global timing accuracy monitoring and evaluation.

[0024] In view of the above problems, the embodiment of the present invention provides a BeiDou global timing accuracy evaluation method, such as Figure 2 As shown, the method may include the following steps:

[0025] S1, the user station uses the acquired raw observation data and broadcast ephemeris to perform BDS global timing, and obtains the difference between the user station receiver clock and the broadcast ephemeris BDT benchmark as the first clock difference;

[0026] S2: Calculate the difference between the user station's receiver clock and the B2b product's BDT reference as the second clock error. When the user station is located in the Asia-Pacific region, the user station obtains the second clock error by directly obtaining the B2b precise orbit and clock product and calculating the PPP clock error. When the user station is located outside the Asia-Pacific region, select a station in the Asia-Pacific region as a reference station to obtain the time difference between the B2b product's BDT reference and the clock error reference corresponding to the precise orbit and clock error product of another institution. Use this time difference to correct the PPP clock error calculated by the user station based on the precise orbit and clock error product of another institution to obtain the second clock error.

[0027] S3: Evaluate the timing accuracy of the BDS system of the user station by calculating the difference between the first clock difference and the second clock difference.

[0028] To facilitate understanding of the embodiments of the present invention, the following describes the cases where the user station is located in the Asia-Pacific region and the case where the user station is located in a non-Asia-Pacific region.

[0029] (1) The user station is located in the Asia-Pacific region;

[0030] See Figure 3 understand, Figure 3 This is a schematic diagram of the BDS timing accuracy evaluation principle based on the B2b product for user stations in the Asia-Pacific region in an embodiment of the present invention;

[0031] The specific process can be divided into the following steps:

[0032] Step A1: The user station uses the acquired raw observation data and broadcast ephemeris to perform BDS global timing, and obtains the difference between the user station receiver clock and the broadcast ephemeris BDT reference as the first clock difference;

[0033] Step A1 corresponds to step S1. The user station observes the BDS satellite to obtain the original observation data (i.e. Figure 3 At the same time, the user station can obtain the broadcast ephemeris. By using these two to perform BDS global timing, the difference between the user station receiver clock and the broadcast ephemeris BDT reference can be obtained, which can be expressed as:

[0034] (1);

[0035] in, Represents the difference between the user station receiver clock and the broadcast ephemeris BDT reference, as the first clock difference; Indicates the user station receiver clock; Indicates the broadcast ephemeris BDT reference.

[0036] For the processing procedure of step A1, please refer to the relevant technical understanding and will not be described in detail here.

[0037] Step A2: Calculate the difference between the user station receiver clock and the BDT reference of the B2b product as the second clock difference;

[0038] Step A1 corresponds to step S2. When evaluating the timing accuracy of the BDS system, the user station is located in the Asia-Pacific region. By receiving the B2b precise orbit clock product (B2b product) broadcast by the BDS system GEO satellite, the BDS-3 system dual-frequency ionospheric elimination solution can be used to calculate the difference between the user station receiver clock and the BDT reference of the B2b product, such as Figure 3 For the specific processing process, please refer to the relevant technical understanding.

[0039] Therefore, when the user station is located in the Asia-Pacific region, the calculation process of the second clock difference is expressed as follows:

[0040] (2);

[0041] in, The difference between the user station receiver clock and the BDT reference of the B2b product is used as the second clock difference; Indicates the user station receiver clock; Represents the BDT benchmark for B2b products.

[0042] Step A3: Evaluate the BDS system timing accuracy of the user station by calculating the difference between the first clock difference and the second clock difference.

[0043] Step A3 corresponds to step S3. Specifically, the difference between the first clock difference and the second clock difference is calculated, which can be expressed as:

[0044] (3);

[0045] in, represents the first clock error; represents the second clock error; represents the difference between the first clock difference and the second clock difference.

[0046] After calculating the difference between the first clock difference and the second clock difference, the timing accuracy of the BDS system of the user station can be evaluated. The specific process will not be described in detail here.

[0047] It can be seen that user stations in the Asia-Pacific region can directly use PPP technology based on the B2b product to obtain the difference between the user station receiver clock and the BDT benchmark of the B2b product, and use this as a benchmark to evaluate the Beidou timing results.

[0048] (2) The user station is located outside the Asia-Pacific region;

[0049] When user stations outside the Asia-Pacific region cannot receive the BDS system's B2b product, it is impossible to evaluate the accuracy of Beidou timing results in these areas. To address this problem, the present invention introduces a station in the Asia-Pacific region as a reference station to indirectly calculate the difference between the user station receiver clock and the BDT reference of the B2b product.

[0050] See Figure 4 understand, Figure 4 This is a schematic diagram of the principle of BDS system timing accuracy evaluation based on B2b products for user stations outside the Asia-Pacific region in an embodiment of the present invention;

[0051] The specific process can be divided into the following steps:

[0052] Step B1: The user station uses the acquired original observation data and broadcast ephemeris to perform BDS global timing, and obtains the difference between the user station receiver clock and the broadcast ephemeris BDT reference as the first clock difference;

[0053] Step B1 corresponds to S1, and the execution process is exactly the same as step A1. Referring to formula (1), the difference between the user station receiver clock and the broadcast ephemeris BDT reference can be obtained, that is, the first clock difference The specific process will not be described here.

[0054] Step B2, calculating the difference between the user station receiver clock and the BDT reference of the B2b product as the second clock difference;

[0055] Step B2 corresponds to step S2. When the user station is located outside the Asia-Pacific region, the calculation process of the second clock difference includes the following steps:

[0056] Step B21: The reference station performs dual-frequency ionospheric elimination combination of the BDS system based on the acquired original observation data, the B2b precise orbit and clock products, and the precise orbit and clock products of other institutions. The PPP clock difference between the receiver clock of the reference station and the clock reference corresponding to the precise orbit and clock products of other institutions is calculated, as well as the PPP clock difference between the receiver clock of the reference station and the BDT reference of the B2b product. The difference between the two PPP clock difference values ​​is calculated to obtain the time difference between the BDT reference of the B2b product and the clock reference corresponding to the precise orbit and clock products of other institutions.

[0057] It is understood by those skilled in the art that the base station can observe the GEO satellite to obtain the original observation data and obtain the B2b precise orbit clock error product (see Figure 4 The PPP-B2b product in [1] is included in the PPP-B2b product, as well as precise orbit and clock products from other institutions. The precise orbit and clock products from other institutions are described using the GFZ's ex-post orbit and clock products as an example. For ease of understanding, this will be used in the subsequent explanations.

[0058] The PPP clock difference between the receiver clock of the reference station and the clock difference product of the precise orbit and clock error of other institutions is expressed as follows:

[0059] (4);

[0060] in, represents the PPP clock difference between the receiver clock of the reference station and the posterior orbit and clock difference product of GFZ, The clock reference corresponding to the GFZ's post-orbit and clock products; Represents the receiver clock of the reference station.

[0061] The PPP clock difference between the receiver clock of the reference station and the BDT reference of the B2b product is expressed as follows:

[0062] (5);

[0063] in, Indicates the PPP clock difference between the receiver clock of the reference station and the BDT reference of the B2b product; Represents the BDT benchmark for B2b products.

[0064] By subtracting formula (4) from formula (5), we can obtain the time difference between the BDT reference of the B2b product and the clock reference corresponding to the precise orbit and clock products of other institutions. The calculation formula is expressed as:

[0065] (6);

[0066] in, It represents the time difference between the BDT reference of the B2b product and the clock reference corresponding to the precise orbit and clock products of other institutions.

[0067] Step B22: The user station calculates the PPP clock error based on the precise orbit and clock error products of the other institutions;

[0068] Please refer to Figure 4The user station can also obtain the same precise orbit and clock products as the base station, and use the BDS-3 system's dual-frequency ionospheric elimination to calculate the PPP clock error.

[0069] The PPP clock error calculated by the user station based on the precise orbit and clock error products of other institutions is expressed as follows:

[0070] (7);

[0071] in, Represents the PPP clock error calculated by the user station based on the precise orbit and clock products of other institutions; Indicates the user station receiver clock.

[0072] Step B23: Use the time difference to correct the PPP clock difference calculated by the user station based on the precise orbit and clock products of other institutions to obtain the second clock difference.

[0073] Specifically, the time difference is used to correct the PPP clock difference calculated by the user station based on the precise orbit and clock products of other institutions to obtain the second clock difference, which is expressed by the formula:

[0074] (8);

[0075] It can be seen that by calculating the PPP clock error of the user station based on the precise orbit and clock error products of other institutions The time difference between the BDT reference of the B2b product and the clock reference corresponding to the precise orbit and clock products of other institutions The difference, was offset, obtained That is the second clock difference.

[0076] Step B3: Evaluate the BDS system timing accuracy of the user station by calculating the difference between the first clock difference and the second clock difference.

[0077] Step B3 corresponds to step S3. Calculate the difference between the first clock difference and the second clock difference, which can be expressed as:

[0078] (9);

[0079] Same as formula (3), represents the first clock error; represents the second clock error; represents the difference between the first clock difference and the second clock difference.

[0080] As can be seen, for user stations outside the Asia-Pacific region, the present invention introduces reference stations within the B2b coverage area and another precise orbit clock product. By calculating the PPP clock error based on the B2b product and the other precise product at the reference station, the time difference between the two time bases can be determined. The PPP clock error based on the other precise product is then calculated at the user station. The PPP clock error obtained at the user station is then corrected to the BDT reference, allowing analysis of the BeiDou Global Timing Service at the user station.

[0081] In summary, the BeiDou global timing accuracy assessment method provided by the embodiments of the present invention allows user stations in the Asia-Pacific region to receive the B2b product broadcast by the BDS system's GEO satellites. A dual-frequency, ionospheric-free solution is used to calculate the difference between the user station's receiver clock and the BDT reference of the B2b product. This difference is then used to assess the difference between the user station's receiver clock and the broadcast ephemeris BDT reference, calculated using the B2b product. However, for user stations outside the Asia-Pacific region, the accuracy of BeiDou timing results cannot be assessed because they cannot receive the BDS system's B2b product. The present invention introduces a survey station in the Asia-Pacific region as a reference station, and uses the BDS system satellite orbit and clock products of other institutions and PPP B2b products to calculate the PPP clock error of the reference station, and determines the time difference between the clock error benchmark of the orbit clock error product of other institutions and the BDT benchmark of the PPP B2b product, and then corrects it to the PPP clock error of the user station, thereby obtaining the PPP clock error of the user station based on the B2b product. The difference between the local clock of the user station obtained by the Beidou global timing and the BDT can be evaluated, and the Beidou global timing accuracy evaluation based on the B2b product can be realized. Therefore, the method proposed by the present invention breaks the PPP-B2b service area limitation and can realize accurate and reliable monitoring and evaluation of Beidou timing accuracy on a global scale.

[0082] In order to facilitate understanding of the effectiveness of the method of the present invention, relevant experimental verification is carried out below.

[0083] The experiment of the present invention uses SEPT as the reference station and GAMG station as the user station for verification. Both SEPT and GAMG stations can receive B2b products. The reliability of the method of the present invention is verified by comparing the two single-frequency timing accuracy evaluation results.

[0084] In order to clarify the difference between the PPP clock errors calculated for B2b products and those generated by institutions such as GFZ, the PPP clock errors were first calculated at SEPT based on B2b products and GFZ products respectively. The obtained clock errors were the SEPT clock error based on BDT_B2b (BDT benchmark for B2b products) and the SEPT clock error based on the GFZ product clock error benchmark. The above two clock error results are shown in Figure 2. Figure 5 As shown, Figure 5This is a diagram showing the differences in PPP timing between SEPT stations based on different products in the experiment of this invention. It can be seen that due to the different time bases of the GFZ product and the B2b product, the receiver clock errors obtained by calculating the GFZ precise orbit and clock error products show obvious jumps every day.

[0085] There are two single-frequency timing accuracy evaluation methods: the first one is to refer to the BDS timing accuracy evaluation steps based on B2b products for stations in the Asia-Pacific region, that is, to use the GAMG station clock error calculated by the dual-frequency ionospheric elimination point solution of the B2b product as the benchmark to evaluate the BDS timing results of the station; the second one is to use the BDS timing accuracy evaluation steps based on B2b products outside the Asia-Pacific region, and obtain the BDS timing results through the reference station. Time difference with the GFZ product clock reference , correct the PPP clock error calculated by the user station based on the precise orbit and clock error products of other institutions to the clock error between the user station receiver and The clock error is calculated and the BDS timing accuracy of the user station is analyzed. The essence of the two methods is that the user station obtains a high-precision receiver clock based on different methods. Clock difference , Figure 6 This figure shows the clock difference sequence based on PPP-B2b obtained by the two methods at the GAMG station in the experiment of the present invention; the figure shows the clock difference sequence based on PPP-B2b obtained by the two methods at the GAMG station. The mean of the difference sequence is 0.16ns and the STD is 0.09ns, which fully demonstrates the feasibility of the method of the present invention.

[0086] This study, conducted by the National Timing Center's iGMAS Analysis Center, used a multi-day experiment using the BeiDou-3 system's B2b product. The results showed that within the Asia-Pacific region, the mean of the clock difference sequence obtained using PPP-B2b using two methods was 0.16 ns, with an STD of 0.09 ns. This method can be extended to stations worldwide, enabling global monitoring and assessment of BDS timing accuracy based on B2b products. This addresses the technical challenge of effectively assessing BeiDou timing accuracy outside the BeiDou-3 PPP-B2b service area.

[0087] It should be noted that, in the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0088] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims

1. A BeiDou global timing accuracy assessment method, characterized in that: include: The user station uses the acquired raw observation data and broadcast ephemeris to perform BDS global timing, and obtains the difference between the user station receiver clock and the broadcast ephemeris BDT benchmark as the first clock difference; Calculate the difference between the user station's receiver clock and the B2b product's BDT reference as the second clock error. When the user station is located in the Asia-Pacific region, the user station obtains the second clock error by directly obtaining the B2b precise orbit and clock product and calculating the PPP clock error. When the user station is located outside the Asia-Pacific region, select a station in the Asia-Pacific region as a reference station to obtain the time difference between the B2b product's BDT reference and the clock reference corresponding to the precise orbit and clock products of other institutions. Use this time difference to correct the PPP clock error calculated by the user station based on the precise orbit and clock products of other institutions to obtain the second clock error. The precise orbit and clock products of other institutions include the post-orbit and clock products of the GFZ. Evaluating the BDS system timing accuracy of the user station by calculating the difference between the first clock difference and the second clock difference; When the user station is located outside the Asia-Pacific region, the calculation process of the second clock difference includes: The reference station performs dual-frequency ionospheric elimination combination of the BDS system based on the acquired original observation data, the B2b precise orbit and clock products, and the precise orbit and clock products of other institutions, and calculates the PPP clock difference between the receiver clock of the reference station and the clock difference benchmark corresponding to the precise orbit and clock products of other institutions, as well as the PPP clock difference between the receiver clock of the reference station and the BDT benchmark of the B2b product. The difference between the two PPP clock difference values ​​is calculated to obtain the time difference between the B2b product BDT benchmark and the clock difference benchmark corresponding to the precise orbit and clock products of other institutions. The user station calculates the PPP clock error based on the precise orbit and clock error products of the other institutions; The time difference is used to correct the PPP clock difference of the user station calculated based on the precise orbit and clock products of other institutions to obtain the second clock difference.

2. The method according to claim 1, characterized in that The difference between the user station receiver clock and the broadcast ephemeris BDT reference is expressed as: ； in, Represents the difference between the user station receiver clock and the broadcast ephemeris BDT reference, as the first clock difference; represents the user station receiver clock; Indicates the broadcast ephemeris BDT reference.

3. The method according to claim 1, characterized in that When the user station is located in the Asia-Pacific region, the calculation process of the second clock difference is expressed as follows: ； in, The difference between the user station receiver clock and the BDT reference of the B2b product is used as the second clock difference; represents the user station receiver clock; Represents the BDT benchmark for B2b products.

4. The method according to claim 1, wherein The PPP clock difference between the receiver clock of the reference station and the clock difference product of the precise orbit and clock difference of other institutions is expressed as follows: ； in, represents the PPP clock difference between the receiver clock of the reference station and the posterior orbit and clock difference product of GFZ, The clock reference corresponding to the GFZ's post-orbit and clock products; Represents the receiver clock of the reference station.

5. The method according to claim 4, wherein The PPP clock difference between the receiver clock of the reference station and the BDT reference of the B2b product is expressed as: ； in, Indicates the PPP clock difference between the receiver clock of the reference station and the BDT reference of the B2b product; Represents the BDT benchmark for B2b products.

6. The method according to claim 5, wherein The calculation formula for the time difference between the BDT reference of the B2b product and the clock reference corresponding to the precise orbit and clock products of other institutions is expressed as: ； in, It represents the time difference between the BDT reference of the B2b product and the clock reference corresponding to the precise orbit and clock products of other institutions.

7. The method according to claim 6, characterized in that The PPP clock error calculated by the user station based on the precise orbit and clock error products of other institutions is expressed as follows: ； in, represents the PPP clock error calculated by the user station based on the precise orbit and clock error products of other institutions; Indicates the user station receiver clock.

8. The method according to claim 7, characterized in that The time difference is used to correct the PPP clock difference calculated by the user station based on the precise orbit and clock products of other institutions to obtain the second clock difference, which is expressed by the formula: 。 9. The method according to claim 1, characterized in that For the user station, the difference between the first clock difference and the second clock difference is calculated, which can be expressed as: ； in, represents the first clock error; represents the second clock error; represents the difference between the first clock difference and the second clock difference.

Images