KR100899545B1 - All-in-view time transfer by use of code and carrier phase measurements of GNSS satellites - Google Patents

Abstract

The present invention relates to a high-precision time transmission method using global navigation satellites (GNSS) global observation. More specifically, the difference between the GNSS navigation system time and the local time maintained by the earth station can be calculated with sub-nanosecond precision. The present invention relates to a high precision time transmission method.

Method of transmitting time using the GNSS satellite full observation method according to the present invention comprises the steps of: receiving all GNSS satellite data, storing GNSS satellite data, and securing GNSS satellite position information corresponding to the observed time (S10); Removing abnormal data on the secured GNSS satellite position information and performing preprocessing for each satellite session (S20); Performing precise time transmission between earth stations for each satellite through real-time or post-processing format for each GNSS data measurement time, and averaging the precision time transmission result to determine a final time comparison value (S30); Creating a time transmission timing table by repeatedly applying the time transmission performance and determining the final time comparison value (S30); and offsetting the time difference between the GNSS satellite systems by offsetting the result of time transmission, 13 and 14, characterized in that it comprises a step (S50) of performing a time transmission.

GNSS satellites, time transmission, full observation, code and carrier

Description

All-in-view time transfer by use of code and carrier phase measurements of GNSS satellites}

1A is a conceptual diagram of a navigation satellite using simultaneous observation method according to the related art.

1B is a conceptual diagram of a navigation satellite all-observation method according to the related art.

2 is a schematic diagram of a configuration of an earth station receiving apparatus according to the present invention;

3 is a flow chart of a time transmission method using the entire navigation satellite observation method according to the present invention.

<Description of the symbols for the main parts of the drawings>

11: GNSS satellite,

12: satellite signal,

13: Earth Station A,

14: Earth Station B,

21: multichannel GNSS receiver,

22: time interval counter,

23: RF Distribution Amplifier

24: external frequency source,

25: computer equipment.

The present invention relates to a high-precision time transmission method using global navigation satellites (GNSS) global observation. More specifically, the difference between the GNSS navigation system time and the local time maintained by the earth station can be calculated with sub-nanosecond precision. The present invention relates to a high precision time transmission method.

The use of satellite visual comparison technology is increasing in the fields of basic science, surveying, transportation, communications, seismic prediction, and space science. At this time, the International Atomic Time and the World Coordinated Time (UTC) are also used by the Pyongyang Bureau to use time / frequency comparison technology using satellites to compare the high accuracy of standard time between countries.

At this time, the most important method of measurement is accurate measurement of propagation delay time by transmission media such as coaxial line, free space, and optical fiber. In the one-way method, a time signal of an earth station is received and used to compare with a user's watch. In the case of terrestrial visual comparison, the propagation delay time increases due to multiple reflections of the signal between the epidermis and the ground from the earth station to the user. In contrast, when a satellite signal is used, the propagation delay time varies depending on the position of the satellite, the ionosphere, and the state of the atmosphere. Therefore, the accuracy of visual comparison depends on how accurately the propagation delay time is corrected.

1A is a conceptual diagram of a simultaneous navigation method using a navigation satellite according to the related art. As shown in FIG. 1A, a user receives a common satellite signal 12 from earth stations A and B 13 and 14 and compares the times. Therefore, since the simultaneous measurement method simultaneously receives the common satellite signal 12, it is true that the error due to the delay time is reduced. However, in this time transmission, as the baseline distance between the two earth stations 13 and 14 to be compared increases, the number of simultaneously observed satellites 11 decreases. In addition, when the distance is more than a certain distance, the simultaneous observation of the satellite 11 disappears and the time transmission is impossible. Even if the observed satellite 11 is present, it has a low satellite relief, and the influence of other transmission delays, including convective delay, becomes severe, thereby greatly reducing the accuracy of visual transmission.

1B is a conceptual diagram of a navigation satellite all-observation method according to the related art. When using the total observation method as described above, the time difference is first obtained for the time of the GNSS system by using the data of all the satellites 11 observed at each of the two earth stations 13 and 14 performing the time comparison. Thereafter, the time difference between the GNSS system time and the earth stations 13 and 14 is further differentiated to enable time transmission regardless of the baseline distance between the earth stations 13 and 14. Since this method is not simultaneous observation, the problem of disappearing the satellite 11 simultaneously observed does not occur. In addition, since the problem of low satellite relief does not occur, it is effective for high precision time transmission.

However, this whole observation method alone does not improve the resolution of the visual information. Thus, it can be effective in achieving precision of several orders of magnitude but does not achieve precision of several orders of magnitude.

The present invention has been made to solve the above problems, and by using the navigation satellite efficiently, it is possible to transmit precise time anywhere on earth regardless of the baseline distance, and the accuracy of the transmitted time is less than nanosecond The goal is to be at the level of.

In order to achieve the above object, in the present invention, the data table from the GNSS satellite is divided into a pre-processing step and a post-processing step to repeat the post-processing step to prepare a timing table for visual information transmitted from the satellite. Another purpose.

Other objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and the preferred embodiments associated with the accompanying drawings.

Method of transmitting time using the GNSS satellite full observation method according to the present invention comprises the steps of: receiving all GNSS satellite data, storing GNSS satellite data, and securing GNSS satellite position information corresponding to the observed time (S10); Removing abnormal data on the secured GNSS satellite position information and performing preprocessing for each satellite session (S20); Performing precise time transmission between earth stations for each satellite through real-time or post-processing format for each GNSS data measurement time, and averaging the precision time transmission result to determine a final time comparison value (S30); By repeating the application of time transmission and determining the final time comparison (S30), a time transmission timing table is created (S40), and the time transmission results are differentially offset to offset the time difference between the GNSS satellite systems and the two earth stations (13). And performing time transmission between (14).

In the present invention, in order to enable visual transmission anywhere, the most important factor is to calibrate to the sub-nanosecond level for all factors contributing to the error of visual information. Such error factors include satellite position, receiver antenna position, Ionizing layer and convective layer delay T, carrier phase unknown constant (N), and the like.

In this case, the distance between the GNSS satellite 11 and the earth stations 13 and 14 becomes an important factor. To measure this, triangulation techniques are used. The triangulation technique requires knowing the positions S1 and S2 of the satellites 11 on a two-dimensional plane and the distance between the earth stations 13 and 14. Then, the positions of the earth stations 13 and 14 refer to the points that meet when the arc is drawn at a distance of the radius R1 and R2 based on the position of the satellite 11. In other words, the description is now based on the two-dimensional plane, but the same technique is applied to the three-dimensional space. That is, distance measurement is performed by knowing the distance between earth stations 13 and 14 with respect to three satellites 11, and drawing three spheres from three satellites.

At this time, when the geometric distance is calculated, it is possible to calculate the error of the process from which the time is transmitted. These errors include the error due to the ionosphere, the error due to the convective layer (Tm (el)), the satellite clock error (δt ^S ), and the earth station receiver clock error (δt _R ). , _Pseudorange noise (ε _ψ ) and carrier phase noise (ε _φ ).

The cause of such an error is described in detail as follows. Errors caused by the ionosphere are errors caused by electrons and ions existing between 50 km and 1000 km above the ground. At this time, radio waves below 100 MHz are reflected from the ionosphere, but radio waves above VHF pass. However, since the accuracy of transmission by the carrier is 100 times or more than the transmission by the C / A code or P code described above, the time transmission accuracy is improved. L1 and L2 waves exist in such a carrier wave. Since the L1 wave is 1.575 GHz and the L2 wave is 1.228 GHz, all carrier waves can penetrate the ionizing layer. However, the propagation delay time is proportional to the total number of electrons and inversely proportional to the square of the frequency. At this time, in the case of the C / A code or P code, the propagation time is delayed in proportion to the total number of electrons in the pass path. On the other hand, in the case of the carrier described above, a time leading phenomenon occurs at the same size.

As a method of correcting such an error, a method of compensating for time delay error using a difference in arrival times of L1 and L2 carriers is used. The ionosphere model used to correct the ionosphere delay is the klobuchar type. Using this, about 50% error correction effect can be obtained, and nanosecond level error correction is possible.

In the model according to the present invention, a method of eliminating such ionospheric errors will be discussed. And we will focus on how to eliminate the error except for this ionospheric error.

As described above, in order to measure an accurate time delay, not only the geometric distance ρ of the satellite 11 and the earth stations 13 and 14, but also the measured distance when the receiver clock error δt ^R is present A clock error should be included. The distance measured in consideration of this is called the weft distance (Ψ _IF ).

[Equation 1] shows the pseudo distance and the distance by the carrier.

From here,

Ψ _IF : pseudorange with ionospheric error eliminated

Φ _IF : term multiplied by the carrier phase and the wavelength from which the ionospheric error is removed,

ρ: geometric distance between the observed satellite and the earth station,

T: convective layer error,

m (el): convective error mapping function with embossment,

λΝ: term multiplied by a carrier phase unknown integer and the wavelength,

c: beam,

δt ^S : Satellite clock error,

δt _R : Earth station receiver clock error,

ε _Ψ : pseudorange noise,

ε _Φ : Carrier phase noise.

Then, it is necessary to calculate the geometric distance (ρ) among the elements included in the pseudoranges measured at this time. The method of calculating the geometric distance has been described above.

The measurement method of the earth station receiver clock error (δt _R ) to be extracted in the present invention is as follows. That is, it can be obtained by removing the remaining terms of the right side except for the earth station receiver clock error (δt _R ). In order to correct the error in the order of the right side, in order to calculate the geometric distance between the navigation satellite 11 and the earth stations 13 and 14, the precision orbital force provided by the International GNSS Service (IGS) is required. In the case of such precision orbital force, position and visual accuracy are known to be 0.1 nanoseconds. The satellite clock error (δt ^s ) is calculated for the International GNSS Service Time (IGST), an IGS an in-house software package, named GV4.

Convective error T is the error that occurs in the troposphere, which is the lowest part of the atmosphere and the temperature decreases as the altitude increases. This convective layer error occurs because the GNSS satellite signal 12 is out of the speed of the vacuum light due to the troposphere. Therefore, it can be said that the speed of the radio wave is changed depending on the conditions such as air pressure, temperature, humidity. In the case of such convective layer error (T), unlike the aforementioned ionospheric error, the same time delay occurs in the code and the carrier. This convective error characteristic affects frequencies up to 15 GHz but is not affected by frequency differences. The effects of tropospheric errors can be separated into delays due to dry components and delays due to wet components. The error due to wet components in the troposphere error is 3 cm per hour, but it is difficult to predict. However, errors due to dry components can be predicted. The convective error can be calculated by the mapping function m (el). That is, the product of the mapping function and the convective error is used to calculate the delay time. Such convective error can be calculated using statistical estimation techniques such as weighted least-squares method for the observed data using the mapping function. At this time, the carrier phase noise ε _φ and the pseudo distance noise ε _Ψ are assumed after Gaussian white noise without bias.

In the present invention, the positioning of the GNSS satellite 11 should be made first as a method for correcting such an error. Then the calculation of the geometrical distance ρ is made and the preprocessing proceeds. The preprocessing process can be called a calibration in the range of 100㎱ to 10㎲, which is the process of removing the abnormal data and preprocessing the data for each satellite session. Such abnormal data includes data with cycle slip and low satellite relief.

And the more precise process, the post-processing process is performed in parallel with the real-time processing process. Such a visual system may calculate a time transmission result using statistical estimation in real time or in post-processing form, depending on the type of operation. The Kalman filter, the Extended Kalman filter, and the square root information filter may be used for the real-time calculation.

The Kalman filter does not have to remember all the individual values when there is a lot of data to be processed. When calculating the nth average, the Kalman filter does not have any problem. Will be available. This process is called iterative data processing, which is a very simple means of obtaining the nth average. Therefore, using the Kalman filter, it is possible to calculate time for visual data in real time.

The extended Kalman filter for nonlinear equations is applied after linearizing the nonlinear equations using Taylor series expansion. The only difference is the shape of the transform coefficient due to the linearization of the nonlinearity.

In addition, a weighted least-squares method, Bayesian estimation, or maximum probability estimation may be used for the post-processing technique. As described above, when using the estimation technique, the carrier clock error, carrier unknown distance, convective delay distance, and reception antenna position correction can be applied.

Through the above process, time transmission is performed for the system time or IGST of a specific earth station (13, 14) and a navigation satellite system, and then the same process is performed at another earth station (13, 14) for the same measurement time. Can be done. As a result, the time transmission between the two earth stations 13 and 14 is possible by differentiating the time transmission result between the earth stations 13 and 14 and the navigation satellite system time or IGST. In other words, the results of two time transmissions are obtained after the navigating satellite satellite system time or IGST is offset.

2 is a schematic diagram showing a GNSS receiving system of the earth stations 13 and 14 for time transmission using the entire navigation satellite system, wherein the reference frequency oscillated from an external frequency source 24 including a hydrogen major is connected to the receiver external frequency input terminal. The multi-channel GNSS receiver 21 provides code and carrier data in association with the RF distribution amplifier 23, the time interval counter 22, and the like, in conjunction with the input external frequency.

In the RF distribution amplifier 23, the reference frequency oscillated from the external frequency source 24 is distributed. In addition, the time interval counter 22 calculates a time interval from the input reference frequency. The multi-channel GNSS receiver 21 provides code and carrier data in association with the external frequency from the time interval counter 22. The code and carrier data thus provided are stored in the computer device 25.

When the atomic clock (not shown) information mounted on the GNSS satellite 11 is received using the multi-channel GNSS receiver 21, the signal is transmitted between the signal transmission time of the satellite 11 and the signal reception time of the earth stations 13 and 14. Delay time expressed by Equation 1 occurs. At this time, the code and the carrier phase data are generated based on the delay time calculated by the correlator (not shown) inside the multi-channel GNSS receiver 21 through the code and carrier tracking loop, and stored in the computer device 5 or the like.

3 is a flowchart illustrating a time transmission method using the entire navigation satellite observation method according to the present invention. The earth station 13, 14 selected for time transmission may be provided with an external frequency source 24, an RF distribution amplifier 23, and a multi-channel GNSS receiver 21. Here, the external frequency source 24 provides a reference frequency that is the object of time comparison. An RF distribution amplifier is installed at the receiver external frequency input, and a multichannel GNSS receiver (GNSS) provides code and carrier data. When ready for the receiver in this way, time transmission from the observable satellite 11 takes place. At this time, the position information of the GNSS satellite 11 is first secured using the precision orbital force (S10). As described above, when surveying using the GNSS satellites 11, there are various error factors such as orbital errors of the GNSS satellites 11, clock errors of the receivers 21 and satellites 11, and errors caused by the ion layer and the convective layer. In particular, the position measurement by the GNSS transmits the distance between the GNSS satellite 11 and the receiver 21 and the broadcast orbital force which is the position data of the satellite 11 to the user in the form of a navigation message. It is estimated that the error by 3m prediction is included. Therefore, in the geodetic and surveying fields, it is difficult to obtain the baseline measurement accuracy with high accuracy when measuring the baseline vector using broadcast trajectory force. In order to solve this problem, international joint researches to calculate the precision orbital force of the GNSSS satellite 11 have been actively conducted. In other words, if the precision geodetic / surveying and buildings require precision, such as measuring the deformation and motion of the crust, the precision orbital force of the GNSS satellite 11 is required.

Nowadays, the precision orbital force of the GPS satellite 11 is calculated and supplied to the general user in the international GPS observation network constructed for the study of earth science and position astronomy. IGS operates a GPS observation network of approximately 110 stations around the world to calculate precision orbital forces. In Korea, the Astronomical Observatory GPS Observatory located in Daedeok Research Complex is officially designated as the IGS Core Observatory.

Observation data from each station belonging to IGS are collected into an international data center and processed by each of the seven data analysis centers. Each data analysis center uses different data and algorithms to calculate the GPS precision orbital force. In particular, since the results vary depending on the number and distribution of GPS stations used to calculate the precision orbital force of GPS, the results of the precision orbital force calculated at each center are slightly different. IGS calculates and supplies the final IGS precision orbital force by combining the results of each analysis center. Currently, IGS final precision orbits with a precision of about 5 cm are available to the public over the Internet about 11 days after data is collected at each station. IGS supplies IGS rapid precision orbital force calculated one day after observation for rapid supply of precision orbital force.

Thus, GNSS codes and carrier data obtained through IGS precision orbital force are removed, and abnormal slips such as satellite signals (12) with cycle slip and low embossment are removed, and unknown parameters to be estimated for each GNSS satellite (11) session and low precision The preprocessing including the primary time transmission is performed (S20). Cycle slip is an error caused by momentarily missing the value of the carrier phase value in the GPS carrier phase tracking circuit. Cycle slip occurs mainly due to signal interruption, high signal noise, and low signal strength by features around the GPS antenna (not shown). The cycle slip is very important in the field of precision position measurement using carrier phase data, so the detection of cycle slip is very important. When the cycle slip is removed, a primary time transmission process with low precision is performed. This low precision refers to the precision of the unit of power. As a result of the primary time transmission process, the error level for the delay time is corrected to some extent in the preprocessing step.

For each GNSS measurement time, statistical estimation of the unknown variable (N) selected in the preprocessing is performed in real time or after processing format to perform precise time transmission between the earth stations (13, 14) for each GNSS satellite (11). And the final time comparison value is determined by averaging this (S30). Since there are some such statistical estimates and different estimations are applied in real time or in a post-processing form, they are omitted here.

By repeatedly applying this time transmission process to other earth stations 13 and 14, which are time transmission targets, it is possible to prepare a timing table for the entire time range for which time transmission is to be performed (S40).

After the time transmission process through the wireless communication between the GNSS satellite 11 and the earth stations 13 and 14 described above is completed and the time table for the entire range is prepared, the time transmission with the other earth stations 13 and 14 is started. do. As such, when the transmission between the other earth stations 13 and 14 is performed and the result is further differentiated, the satellite system time difference is canceled, and the time difference between each earth station 13 and 14 is obtained (S50).

According to the time transmission method according to the present invention, even the earth station equipped with the GNSS reception equipment, including the national time standard organization, by receiving the GNSS satellite signal, it is possible to transmit a high-precision time of nanosecond level regardless of the baseline distance.

This time transmission is a method that can be widely used in various fields such as navigation system, wired / wireless communication network, power transmission control system, electronic commerce, and internet security message transmission, and by using the GNSS satellite 11, which is already provided, time synchronization Increase the utilization of your infrastructure.

In addition, the time transmission method using the navigation satellite is not limited to the baseline distance compared to the time transmission by the conventional simultaneous observation method. In addition, the difference between the earth station and the GNSS satellite system time can be calculated accurately compared to the method using code or navigation message.

Claims (7)

In the time transmission method using the navigation satellite whole observation method, (a) receiving all GNSS satellites 11 data, storing the GNSS satellites 11 data, and securing GNSS satellites 11 position information corresponding to the observed time through IGS precision orbital force (S10); ); (b) removing abnormal data with respect to the secured GNSS satellites (11) position information and performing preprocessing for each of the GNSS satellites (11) sessions (S20); (c) Perform precise time transmission between earth stations 13 and 14 for each GNSS satellite 11 by real-time or post-processing format for each GNSS data measurement time, and compare the final time by averaging the precision time transmission results. Determining a value (S30); (d) creating a time transmission timing table by repeatedly applying the time transmission performance and determining the final time comparison value (S30) (S40); and (e) applying the time transmission results to two or more earth stations 13 and 14, respectively, and then offsetting the time transmission results to offset the time difference between GNSS satellite systems (S50). A time transmission method using satellite full observation method. The method of claim 1, In step (S20), the abnormal data includes a satellite signal having a cycle slip and a low relief. The method of claim 1, In the step S20 of performing the preprocessing for each of the GNSS satellites 11, the preprocessing includes selecting unknown variables to be estimated for each session of the GNSS satellites 11 and primary visual transmission of low precision. Time transmission method using. delete The method of claim 1, When time transmission is performed in real time with respect to the time of the GNSS measurement data, the time transmission method using the navigation satellite full observation method characterized in that the time transmission results can be calculated using a Kalman filter, an extended Kalman filter, or a square root information filter. . The method of claim 1, When post-processing time transmission is performed for the time of the GNSS measurement data, the time transmission method using the full satellite navigation method, characterized in that the time transmission results can be calculated using a weighted least square method, Bayesian estimation method or the maximum probability estimation method. . The method of claim 6, And a time delay error for the carrier undefined constant (N) and the convective delay distance when using the weighted least square method, the Bayesian estimation method, or the maximum probability estimation method.

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