KR101642094B1 - METHOD FOR PERFORMING TIME SYNCHRONIZATION OF low earth orbit satellites AND APPARATUS THEREOF - Google Patents

METHOD FOR PERFORMING TIME SYNCHRONIZATION OF low earth orbit satellites AND APPARATUS THEREOF Download PDF

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KR101642094B1
KR101642094B1 KR1020150152181A KR20150152181A KR101642094B1 KR 101642094 B1 KR101642094 B1 KR 101642094B1 KR 1020150152181 A KR1020150152181 A KR 1020150152181A KR 20150152181 A KR20150152181 A KR 20150152181A KR 101642094 B1 KR101642094 B1 KR 101642094B1
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reference signal
time
clock
satellites
generated
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KR1020150152181A
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김현철
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엘아이지넥스원 주식회사
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/22—Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/10—Artificial satellites; Systems of such satellites; Interplanetary vehicles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/10—Artificial satellites; Systems of such satellites; Interplanetary vehicles
    • B64G1/1014—Navigation satellites

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  • Remote Sensing (AREA)
  • Aviation & Aerospace Engineering (AREA)
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  • Astronomy & Astrophysics (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
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Abstract

The present invention relates to a method and a device thereof to perform the visual synchronization of low earth orbit satellites. The method includes: a step of receiving a first or second reference signal for synchronization from multiple satellites or ground station; a step of selecting one final reference signal among the first reference signals when receiving the first reference signals from the satellites, generating a third reference signal, including a corrected reference time, by correcting the reference time by using the selected final reference signal, and transmitting the generated third reference signal to the satellites; and a step of transmitting the third reference signal to multiple neighboring satellites. The control part receives the second reference signal from the ground station if the control part is not able to receive the first reference signal for a predetermined time.

Description

METHOD FOR PERFORMING TIME SYNCHRONIZATION OF LOW EARTH ORBIT SATELLITES AND APPARATUS THEREOF FIELD OF THE INVENTION [0001]

More particularly, the present invention relates to a method and apparatus for performing time synchronization of a low orbit satellite group that selectively uses a reference signal from a nearby satellite or a ground station.

It is not possible to perform accurate time synchronization in a special case in which a satellite navigation device such as a GPS (Global Positioning System), GLONASS, Galileo, or the like can not be used.

When synchronous operation is performed in the ground station, a delay error due to the synchronization signal delay and the atmospheric delay occurs, and when the signal synchronization is performed for the satellite group in the ground station, a different delay error may occur.

In case of low-earth orbit satellite, contact time in ground station is very short and continuous synchronization is impossible. In addition, when the reference satellite is used, the satellite speed is very fast in the low orbit, and if there is not the same orbit, the shaded region for the signal of the reference satellite occurs, so that the satellite located in the shaded region can not be synchronized.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and it is an object of the present invention to provide an apparatus and a method for receiving reference signals from a plurality of satellites or ground stations located nearby and selecting one of the received reference signals, And a base station for broadcasting a reference signal including its own clock, a reference time, and its own orbit information by correcting the own clock and the reference time, and a method and apparatus for performing time synchronization of a low orbit satellite group.

However, the objects of the present invention are not limited to those mentioned above, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a method of performing time synchronization of a low earth orbit satellite group, comprising: receiving a first reference signal or a second reference signal for synchronization from a plurality of satellites or a ground station; Receiving a first reference signal from the plurality of satellites, selecting one of the received first reference signals and correcting the reference time using the selected final reference signal, Generating a third reference signal including the third reference signal and transmitting the generated third reference signal to the plurality of satellites; And transmitting the generated third reference signal to a plurality of satellites located in the periphery, wherein when the control unit does not receive the first reference signal for a predetermined time, the control unit receives a second reference signal from the ground station .

Preferably, the controlling step selects a reference signal that satisfies at least one of the first reference signals received from the ground station, the number of hops, and whether to perform the most recent synchronization as the one final reference signal .

Preferably, the controlling step selects the reference signal having the smallest number of hops among the received first reference signals as the one final reference signal.

Preferably, the controlling step may include: an orbit measuring step of measuring the orbit information of the one final reference signal when the one final reference signal is selected; A delay error determination step of calculating a delay time based on the measured own orbit information and the orbit information of the satellite that transmitted the selected final reference signal and setting the reference time using the calculated delay time; An error correcting step of calculating a start time of a reference clock using the set delay time and the reference time and generating a reference clock according to a start time of the calculated reference clock; And a clock generating step of synchronizing the self clock generated in accordance with the generated reference clock.

Preferably, the step of controlling includes transmitting the second reference signal generated by generating the second reference signal including the reference clock, the reference time, and the own orbit information to a plurality of satellites located in the periphery And a control unit.

According to another aspect of the present invention, there is provided an apparatus for performing time synchronization in a low orbit satellite group, including: a signal receiver for receiving a first reference signal or a second reference signal for synchronization from a plurality of satellites or a ground station; Receiving a first reference signal from the plurality of satellites, selecting one of the received first reference signals and correcting the reference time using the selected final reference signal, And to transmit the generated third reference signal to the plurality of satellites; And a signal transmitter for transmitting the generated third reference signal to a plurality of satellites located in the periphery, wherein, when the first reference signal is not received for a preset time, Signal is received.

Preferably, the control unit selects, as the one final reference signal, a reference signal that satisfies at least one of whether or not the first reference signals are transmitted from the ground station, the number of hops, .

Preferably, the control unit selects the reference signal having the smallest number of hops among the received first reference signals as the one final reference signal.

Preferably, the control unit includes: a trajectory measuring unit for measuring the trajectory information of the one final reference signal; A delay error determination unit for calculating a delay time based on the measured own orbit information and the orbit information of the satellite that transmitted the selected final reference signal and setting the reference time using the calculated delay time; An error corrector configured to calculate a start time of a reference clock using the set delay time and the reference time and to generate a reference clock according to a start time of the calculated reference clock; And a clock generator for synchronizing a self clock generated in accordance with the generated reference clock.

Preferably, the control unit controls to transmit the second reference signal generated by generating the second reference signal including the reference clock, the reference time, and the own orbit information to a plurality of satellites located in the vicinity .

Accordingly, the present invention receives reference signals from a plurality of satellites or ground stations located nearby, selects one of the received reference signals, corrects its own clock and reference time using the selected reference signal, And the reference signal including the own clock, the reference time, and the own orbit information of the low-orbit satellite can be quickly broadcasted.

Further, since the present invention can quickly synchronize the entire satellite group using the reference signal received from the surrounding satellites, it is possible to perform an immediate business operation.

Further, since the present invention can overcome the propagation disturbance with respect to the reference signal from the ground station, it is possible to synchronize its own clocks.

Further, since the present invention can overcome the irregular delay time due to the waiting of the reference signal from the ground station, it is possible to perform more precise synchronization.

1 is a diagram illustrating a method of performing time synchronization in a low orbit satellite group according to an embodiment of the present invention.
2 is a block diagram illustrating an apparatus for performing time synchronization in a low orbit satellite group according to an embodiment of the present invention.
3 is a view for explaining the principle of time synchronization according to an embodiment of the present invention.

Hereinafter, a method and an apparatus for performing time synchronization of a low orbit satellite according to an embodiment of the present invention will be described with reference to the accompanying drawings. The present invention will be described in detail with reference to the portions necessary for understanding the operation and operation according to the present invention.

In describing the constituent elements of the present invention, the same reference numerals may be given to constituent elements having the same name, and the same reference numerals may be given thereto even though they are different from each other. However, even in such a case, it does not mean that the corresponding component has different functions according to the embodiment, or does not mean that the different components have the same function. It should be judged based on the description of each component in the example.

In particular, the present invention receives reference signals from a plurality of satellites or ground stations located nearby, selects one of the received reference signals, corrects its own clock and reference time using the selected reference signal, A new method of broadcasting a reference signal including its own clock, reference time, and its own orbit information is proposed.

1 is a diagram illustrating a method of performing time synchronization in a low orbit satellite group according to an embodiment of the present invention.

As shown in FIG. 1, the apparatus for performing time synchronization of the low-earth orbit satellite according to the present invention can confirm whether or not reference signals for synchronization are received from a plurality of nearby satellites (S101).

At this time, the apparatus for time synchronization waits for a preset time and confirms whether or not the reference signal is received from the surrounding satellite.

Next, if the reference signals are received as a result of the confirmation, the apparatus for time synchronization can select one of the received first reference signals (S102).

At this time, when the final reference signal is selected, the apparatus for time synchronization can determine whether or not to use the final reference signal in consideration of the synchronization reference (ground or self), the number of hops, the synchronization time, That is, the time synchronization apparatus proceeds with the synchronization using the final reference signal selected at the time of the synchronization determination, and otherwise selects another reference signal.

On the other hand, if the reference signals are not received as a result of the confirmation, the apparatus for time synchronization performs the setting of the reference satellite as the reference satellite (S111) and confirm whether the second reference signals are received from the ground station (S112).

At this time, the apparatus for time synchronization waits for a preset time and confirms whether or not the reference signal is received from the ground station.

That is, if the second reference signal is received, the apparatus for time synchronization selects the received second reference signal as a final reference signal and performs synchronization using the selected final reference signal.

Alternatively, if the second reference signal is not received, the apparatus for time synchronization performs a second reference signal including the reference clock, the reference time, the measured own orbit information, and the number of hops, And transmits the second reference signal to a plurality of satellites located in the vicinity (S107, S108).

In this case, the number of hops included in the second reference signal is set to the number of hops to increase the number of hops included in the previously received final reference signal by one and to include the increased value in the second reference signal.

Next, the apparatus for time synchronization may calculate a delay time based on its own orbit information and the orbit information of a satellite transmitting the selected final reference signal (S103), and set a reference time based on the calculated delay time S104).

Next, the apparatus for time synchronization may calculate the start time of the reference clock using the calculated delay time and the reference time, and generate a reference clock according to the calculated start time of the reference clock (S105).

Next, the apparatus for time synchronization may synchronize its own clock generated in accordance with the generated reference clock (S106).

Next, the apparatus for time synchronization generates a third reference signal including the previously generated reference clock, the set reference time, the measured own orbit information, and the number of hops (S107) (S108).

In this case, the number of hops included in the third reference signal is set to a number of hops to increase the number of hops included in the previously received final reference signal by one and to include the increased value in the third reference signal.

2 is a block diagram illustrating an apparatus for performing time synchronization in a low orbit satellite group according to an embodiment of the present invention.

2, the apparatus 200 for performing time synchronization of the low earth orbit satellite group according to the present invention may include a signal receiving unit 210, a signal transmitting unit 220, and a controller 230.

The signal receiving unit 210 may receive a synchronization signal for synchronization from a ground station or receive reference signals for synchronization from a plurality of satellites located within a predetermined number of hops.

At this time, the reference signal includes information on whether the information is information that is generated from the transmission side information generating the reference signal, for example, information generated from itself or information received from the ground, a self clock of the transmission side, a reference time, And the like.

The signal transmitting unit 220 may transmit a synchronization signal or a reference signal to a plurality of satellites in the vicinity.

When receiving the first reference signal from a plurality of nearby satellites, the controller 230 corrects the reference time using one of the first reference signals received from the plurality of satellites, And transmit the generated third reference signal or broadcast the third reference signal.

If the first reference signal is not received from a plurality of satellites for a predetermined time, the control unit 230 sets itself as a reference satellite, receives the second reference signal from the ground station, Synchronization can be performed. That is, the controller 230 may transmit or broadcast a third reference signal including the corrected reference time by correcting the reference time using the second reference signal.

3 is a view for explaining the principle of time synchronization according to an embodiment of the present invention.

As shown in FIG. 3, in the asynchronous case where it is impossible to receive navigation satellite information, the low orbit satellite group transmits or receives a synchronous signal or a reference signal from a plurality of satellites located at least around one hop, Signal or reference signal.

For example, even if a satellite is located in a shadow area where radio waves do not reach from a reference satellite, synchronization can be achieved by receiving a synchronization signal or a reference signal from the surrounding satellite.

The control unit 230 may include a trajectory measurement unit 231, a delay error determination unit 232, an error correction unit 233, a clock generator 234, and the like.

Of course, the synchronization can be performed using the first reference signal or the second reference signal. Since the synchronization process is the same, the following description will be made using the first reference signal.

The orbit measuring unit 231 can measure its own orbit information. For example, a satellite laser ranging system capable of measuring precise orbit information can be used.

The delay error determination unit 232 selects one final reference signal among the received first reference signals and calculates a delay time based on the measured orbit information and the orbit information of the satellite that transmitted the selected final reference signal Can be calculated.

The delay error determination unit 232 selects one of the received first reference signals as a final reference signal, and determines a reference signal that satisfies at least one of whether it is transmitted from a ground station, the number of hops, It can be selected as a reference signal.

For example, the delay error determination unit 232 may select a reference signal transmitted from a ground station as a final reference signal from a first one of the received first reference signals, which has generated the reference signal.

As another example, the delay error determination unit 232 may select a reference signal having a small number of hops of the received first reference signals as a final reference signal.

As another example, the delay error determination unit 232 may select the reference signal used when performing the most recent time synchronization among the received first reference signals as a final reference signal.

The delay error determining unit 232 calculates the delay time based on the orbit information of the satellite and the orbit information of the satellite that transmitted the final reference signal by the Euclidean distance formula based on the line of sight and calculates the calculated delay time Based time can be set.

For example, when (x1, y1, z1) is the transmission position of the reference satellite and x2, y2, z2 are reception points of the receiving satellites,

Figure 112015105831086-pat00001
.

(T + d / c) is calculated as the delay time when the reference time of the reference signal is t and the speed of light is c, and the delay time measured by the ground test (T + d / c + t_c) to which t_c is added is set as the reference time of the receiving satellite.

The error corrector 233 calculates the start time of the reference clock using the calculated delay time and the reference time to correct a clock skew in accordance with the clock of the own clock and the received reference time, The reference clock can be generated according to the start time of the reference clock.

The clock generator 234 may synchronize its own clock generated in accordance with the generated reference clock.

The control unit 230 may generate a second reference signal including a reference clock, a reference time, its own orbit information, and a hop count, and may transmit the generated second reference signal to a plurality of satellites located in the vicinity.

At this time, the controller 230 may increase the number of hops included in the previously received final reference signal by one and set the increased value as the number of hops to be included in the second reference signal.

It is to be understood that the present invention is not limited to these embodiments, and all of the elements constituting the embodiments of the present invention described above are described as being combined or operated together. That is, within the scope of the present invention, all of the components may be selectively coupled to one or more of them. In addition, although all of the components may be implemented as one independent hardware, some or all of the components may be selectively combined to perform a part or all of the functions in one or a plurality of hardware. As shown in FIG. In addition, such a computer program may be stored in a computer-readable medium such as a USB memory, a CD disk, a flash memory, etc., and read and executed by a computer, thereby implementing embodiments of the present invention. As the storage medium of the computer program, a magnetic recording medium, an optical recording medium, a carrier wave medium, or the like may be included.

While the invention has been shown and described with reference to certain embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

210:
220: Signal transmitter
230:
231: Orbital measuring unit
232: delay error determination unit
233: error correction unit
234: Clock Generator

Claims (10)

Receiving a first reference signal or a second reference signal for synchronization from a plurality of satellites or ground stations;
Receiving a first reference signal from the plurality of satellites, selecting one of the received first reference signals and correcting the reference time using the selected final reference signal, Generating a third reference signal including the third reference signal and transmitting the generated third reference signal to the plurality of satellites; And
Transmitting the generated third reference signal to a plurality of satellites located in the vicinity;
, The controlling step
Selecting one of the first reference signals as a final reference signal that satisfies at least one of whether it is transmitted from a ground station, the number of hops,
And receiving a second reference signal from the ground station if the first reference signal is not received for a predetermined time. delete The method according to claim 1,
Wherein the controlling comprises:
And selecting a reference signal having the smallest number of hops among the received first reference signals as the one final reference signal. The method according to claim 1,
Wherein the controlling comprises:
A trajectory measuring step of measuring its own orbit information when the one final reference signal is selected;
A delay error determination step of calculating a delay time based on the measured own orbit information and the orbit information of the satellite that transmitted the selected final reference signal and setting the reference time using the calculated delay time;
An error correcting step of calculating a start time of a reference clock using the set delay time and the reference time and generating a reference clock according to a start time of the calculated reference clock; And
A clock generating step of synchronizing a self clock generated in accordance with the generated reference clock;
Wherein the low-orbit satellite group comprises: 5. The method of claim 4,
Wherein the controlling comprises:
Wherein the control unit controls the second reference signal generated by generating the second reference signal including the reference clock, the reference time, and the own orbit information to be transmitted to a plurality of satellites located in the periphery, How to Perform Time Synchronization of a Group. A signal receiving unit for receiving a first reference signal or a second reference signal for synchronization from a plurality of satellites or ground stations;
Receiving a first reference signal from the plurality of satellites, selecting one of the received first reference signals and correcting the reference time using the selected final reference signal, And to transmit the generated third reference signal to the plurality of satellites; And
A signal transmitter for transmitting the generated third reference signal to a plurality of satellites located in the vicinity;
, Wherein the control unit
Selecting one of the first reference signals as a final reference signal that satisfies at least one of whether it is transmitted from a ground station, the number of hops,
And receives a second reference signal from the ground station when the first reference signal is not received for a predetermined time. delete The method according to claim 6,
Wherein,
And selects the reference signal having the smallest number of hops among the received first reference signals as the one final reference signal. The method according to claim 6,
Wherein,
A trajectory measuring unit for measuring the trajectory information of the one final reference signal;
A delay error determination unit for calculating a delay time based on the measured own orbit information and the orbit information of the satellite that transmitted the selected final reference signal and setting the reference time using the calculated delay time;
An error corrector configured to calculate a start time of a reference clock using the set delay time and the reference time and to generate a reference clock according to a start time of the calculated reference clock; And
A clock generator for synchronizing a self clock generated in accordance with the generated reference clock;
Wherein the low-orbit satellite group comprises: 10. The method of claim 9,
Wherein,
Wherein the control unit controls the second reference signal generated by generating the second reference signal including the reference clock, the reference time, and the own orbit information to be transmitted to a plurality of satellites located in the periphery, A device for performing time synchronization of a group.
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Cited By (3)

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KR20190096665A (en) * 2018-02-09 2019-08-20 한국전자통신연구원 Unmanned vehicle, apparatus for supporting time synchronization between unmanned vehicles and method for the same
KR102506207B1 (en) * 2021-09-16 2023-03-06 한국항공우주연구원 Apparatus and method for time synchronization between a ground station and a satellite
CN117970775A (en) * 2024-04-01 2024-05-03 中国科学院国家授时中心 Standard time timing method and system combining GNSS and LEO satellites

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JPH06308262A (en) * 1993-04-27 1994-11-04 Mitsubishi Electric Corp Time synchronizing device for spacecraft
JP2000131474A (en) * 1998-10-27 2000-05-12 Fujitsu Ltd Time synchronization system, satellite system and ground system applied thereto, time synchronization method and medium with recorded program for execution of method on computer
JP2009294007A (en) * 2008-06-04 2009-12-17 Mitsubishi Electric Corp Time management apparatus and program

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JPH06308262A (en) * 1993-04-27 1994-11-04 Mitsubishi Electric Corp Time synchronizing device for spacecraft
JP2000131474A (en) * 1998-10-27 2000-05-12 Fujitsu Ltd Time synchronization system, satellite system and ground system applied thereto, time synchronization method and medium with recorded program for execution of method on computer
JP2009294007A (en) * 2008-06-04 2009-12-17 Mitsubishi Electric Corp Time management apparatus and program

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Publication number Priority date Publication date Assignee Title
KR20190096665A (en) * 2018-02-09 2019-08-20 한국전자통신연구원 Unmanned vehicle, apparatus for supporting time synchronization between unmanned vehicles and method for the same
KR102208580B1 (en) * 2018-02-09 2021-01-28 한국전자통신연구원 Unmanned vehicle, apparatus for supporting time synchronization between unmanned vehicles and method for the same
KR102506207B1 (en) * 2021-09-16 2023-03-06 한국항공우주연구원 Apparatus and method for time synchronization between a ground station and a satellite
CN117970775A (en) * 2024-04-01 2024-05-03 中国科学院国家授时中心 Standard time timing method and system combining GNSS and LEO satellites
CN117970775B (en) * 2024-04-01 2024-06-11 中国科学院国家授时中心 Standard time timing method and system combining GNSS and LEO satellites

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