Time service method and system based on communication satellite and storage medium

Abstract

The invention discloses a time service method and system based on a communication satellite and a storage medium, and the method comprises the following steps: S1, a central station sends a time service signal to a user terminal through a downlink of the communication satellite, and receives a signal returned by the user terminal through an uplink of the communication satellite; s2, calculating the sum of time delays of a downlink and an uplink according to satellite ephemeris information; s3, constructing an ionosphere delay correction model by using the frequency proportional relation of the signals in the downlink and the uplink; s4, according to the downlink time delay, combining the time delay sum, the current layer delay correction model, the satellite ephemeris data and the equipment time delay, calculating the clock difference of the user terminal, and correcting to complete time service; according to the method, nanosecond time service with low cost and wide coverage can be realized by using the existing communication satellite.

Description

Technical Field

[0001] The present invention relates to satellite timekeeping, and in particular to a timekeeping method, system and storage medium based on communication satellites. Background Art

[0002] Current precise timekeeping systems rely greatly on the capabilities of the Global Navigation Satellite System (GNSS) such as large-area coverage, high performance, high reliability, and high availability. The satellite navigation system is vulnerable to environmental shielding or electromagnetic interference, and there are significant uncertainties in its availability and service capabilities.

[0003] Current timekeeping methods can be divided into two categories: land-based and space-based. Shortwave timekeeping, low-frequency time code timekeeping, longwave timekeeping, etc. belong to land-based timekeeping methods. The transmitting stations of these timekeeping systems are located on the ground, generally with a small coverage range and an accuracy of 1 ms to 1 μs. Space-based timekeeping is mainly one-way timekeeping based on satellite navigation systems. High-precision time comparison systems such as GNSS Common View (GNSS CV) and Two Way Satellite Time and Frequency Transfer (TWSTFT) can obtain time synchronization accuracy at the nanosecond level, but cannot be directly used for timekeeping, and have high costs and limited user capacity.

[0004] The Beidou satellite navigation system can achieve one-way timekeeping through the Radio Determination Satellite Service (RDSS) and one-way timekeeping through the Radio Navigation Satellite Service (RNSS). The one-way timekeeping accuracy of RNSS is about dozens of nanoseconds, and the one-way timekeeping accuracy of RDSS is in the order of hundreds of nanoseconds. Beidou RDSS two-way timekeeping is one of the methods with the highest timekeeping accuracy in the Beidou system, with a timekeeping accuracy of about 20 ns, but this method uses an active mode and has limited user capacity.

[0005] That is, GNSS CV, TWSTFT, and the Beidou satellite navigation system can achieve high-precision timekeeping, but these technologies all require leasing GEO communication satellites, the timekeeping schemes are complex and not universal, the equipment is complex, and the economic cost is high. Summary of the Invention

[0006] Object of the Invention: The object of the present invention is to provide a timekeeping method, system and storage medium based on communication satellites that can utilize existing communication satellites to achieve low-cost wide-coverage nanosecond-level timekeeping.

[0007] Technical Solution: A timekeeping method based on communication satellites according to the present invention includes the following steps:

[0008] S1. The central station sends a timing signal to the user terminal via the downlink of the communication satellite and receives the signal returned by the user terminal via the uplink of the communication satellite;

[0009] S2. Calculate the sum of the delays of the downlink and the uplink according to the satellite ephemeris information;

[0010] S3. Construct an ionospheric delay correction model using the frequency ratio relationship of the signals in the downlink and the uplink;

[0011] S4. According to the downlink delay, combined with the sum of the delays, the ionospheric layer delay correction model, the satellite ephemeris data and the device delay, calculate the clock error of the user terminal for correction to complete timing.

[0012] Based on the above technical solution, the two-way communication between the communication satellite, the central station and the user terminal can eliminate the asymmetric error. Based on the two-way signal frequency ratio relationship, constructing an ionospheric error calculation model can eliminate the ionospheric layer error. Then, according to the sum of the delays of the downlink and the uplink, the satellite ephemeris data and the device delay, the clock error of the user terminal can be accurately calculated, and the timing of the user terminal can be corrected according to the clock error, thus completing high-precision timing.

[0013] The timing system based on a communication satellite according to the present invention includes:

[0014] A signal transceiver module: used to enable the central station to send a timing signal to the user terminal via the downlink of the communication satellite and receive the signal returned by the user terminal via the uplink of the communication satellite;

[0015] A delay calculation module: used to calculate the sum of the delays of the downlink and the uplink according to the satellite ephemeris information;

[0016] A correction module: used to construct an ionospheric delay correction model using the frequency ratio relationship of the signals in the downlink and the uplink;

[0017] A timing module: used to calculate the clock error of the user terminal for correction to complete timing according to the downlink delay, combined with the sum of the delays, the ionospheric layer delay correction model, the satellite ephemeris data and the device delay.

[0018] The computer-readable storage medium storing one or more programs according to the present invention includes one or more programs including instructions, and when the instructions are executed by a computing device, the computing device is caused to execute any of the above methods.

[0019] Beneficial effects: Compared with the prior art, the remarkable effects of the present invention are as follows: By conducting two-way communication between the communication satellite, the central station, and the user terminal, the asymmetric error can be eliminated. Based on the proportional relationship between the two-way signal frequencies, an ionospheric error calculation model is constructed to eliminate the current layer error. Then, according to the sum of the time delays of the downlink and the uplink, the satellite ephemeris data, and the device time delay, the clock error of the user terminal can be accurately calculated. Based on the clock error, the timing of the user terminal can be corrected, thereby completing high-precision nanosecond-level timing. Moreover, the entire method is implemented based on a communication satellite, without the need to rent additional expensive equipment, and the cost is low. Description of the Drawings

[0020] Figure 1 It is a schematic diagram of signal transmission. Detailed Embodiments

[0021] As shown in the figure, the timing method based on a communication satellite according to the present invention includes the following steps:

[0022] S1. The central station sends a timing signal to the user terminal through the downlink of the communication satellite and receives the signal returned by the user terminal through the uplink of the communication satellite;

[0023] The communication satellite timing consists of a central station, a user terminal, and a communication satellite. The communication satellite communication link consists of a downlink and an uplink. The downlink is that the central station transmits a timing signal with a frequency of C1 to the communication satellite, and the transponder on the communication satellite forwards the S1 frequency band signal to the user terminal; the uplink is that the user terminal transmits a signal with a frequency C2 to the communication satellite, and the transponder on the communication satellite forwards it as an S2 frequency band signal to the central station.

[0024] S2. Calculate the sum of the time delays of the downlink and the uplink according to the satellite ephemeris information;

[0025] Assume that the timing signal broadcast by the central station at time t0. The time delay of the signal from the central station through the communication satellite to the user terminal can be measured, that is, the downlink time delay, which can be written as:

[0026]

[0027] In the formula, the superscript 1 represents that the signal goes from the central station to the communication satellite in the uplink, and the superscript 2 represents that the signal goes from the communication satellite to the user terminal in the downlink; c represents the central station, and r represents the user terminal. τ 1 is the position r where the central station transmits the signal at time t0 c (t0) to the position r of the communication satellite when it receives the signal at t1 s (t1) The geometric distance time delay between them, τ 1 =|r c (t0)-r s (t1)| / c, where c is the speed of light; τ2 The position r of the communication satellite at the signal retransmission moment t2 s to the position r of the user terminal at the signal reception moment t3 s (t3), the geometric distance time delay, τ 2 =|r s (t2)-r r (t3)| / c; and are respectively the ionospheric delays of the central station C1-band signal to the communication satellite and the communication satellite retransmitting the S1-band to the user terminal, I c and I r are respectively the ionospheric delay parameters of the central station and the user terminal, f C1 and f S1 are the C1 and S1 band frequencies; and are respectively the tropospheric delays at the central station and the user terminal; and are the Sagnac effect corrections caused by the earth's rotation, ω is the earth's angular velocity of rotation, (X c ,Y c ), (X s ,Y s ) and (X r ,Y r ) are respectively the rectangular coordinates of the central station c, the user terminal r and the communication satellite s. and are respectively the time delays of the central station signal transmitting equipment, the communication satellite C / S transponder time delay and the user terminal receiving and processing the S-band signal delay; τ rclk is the clock error of the user terminal; ε r is the observation noise and multipath effect delay of the user terminal.

[0028] and can be obtained from the communication satellite broadcast information. The user terminal also obtains the position and speed of the communication satellite from the broadcast information for calculating the geometric distance time delay τ 1 and τ 2 . Let

[0029]

[0030] Then the clock error of the user terminal is:

[0031]

[0032] Similarly, the uplink time delay

[0033]

[0034] In the formula, the superscript 3 indicates that the signal travels from the user terminal to the communication satellite in the uplink; the superscript 4 indicates that the signal travels from the communication satellite to the central station in the downlink; τ 3 is the geometric distance delay τ between the position r r (t4) of the user terminal's signal transmission time t4 and the position r s (t5) of the communication satellite when receiving the signal t5: τ 3 = |r r (t4) - r s (t5)| / c;

[0035] τ 4 is the geometric distance delay between the position r s (t6) of the communication satellite at the signal retransmission time t6 and the position r c (t7) of the central station at the signal reception time t7: τ 4 = |r c (t6) - r s (t7)| / c

[0036] and are the ionospheric delays of the user terminal's C2 - band signal to the communication satellite and the communication satellite's retransmission of the S2 - band signal to the central station respectively. I c and I r are the corresponding ionospheric delay parameters of the central station and the user terminal respectively. f C2 and f S2 are the frequencies of the C2 and S2 bands. It is known that f C2 = f C1 , f S2 = f S1 ;

[0037] and are the corrections for the Sagnac effect caused by the earth's rotation, which are and

[0038]

[0039] and are the delays of the central station receiving and processing the S - band signal, the delay of the communication satellite's C / S transponder, and the delay of the user terminal's signal transmitting device respectively; ε c is the observation noise and multipath effect delay of the central station receiver.

[0040] Therefore, the time delay between the central station transmitting the timing signal forward and receiving the reverse signal transmitted by the user terminal, that is, the sum of the time delays between the downlink and the uplink

[0041]

[0042] There is no τ in formula (5) rclk , because it is eliminated through the two-way link, and the specific reasons are as follows:

[0043] Link 1: The central station c to the user terminal r via the communication satellite:

[0044]

[0045] Link 2: The receiver r to the central station c via the satellite:

[0046]

[0047] Adding the above two formulas gives:

[0048]

[0049] Among them, and are respectively the time when the central station transmits the signal in the downlink and the clock offset of the central station transmitting the signal, and are respectively the time when the user terminal receives the signal in the downlink and the clock offset of the user terminal, and are respectively the time when the user terminal transmits the signal in the uplink and the clock offset of the user terminal, and are respectively the time when the central station receives the signal in the uplink and the clock offset of the central station receiving the signal; the τ to be solved in this application rclk is essentially or (the two are essentially the same); for the same central station and user terminal, there is

[0050]

[0051] And the user terminal transmits the signal simultaneously when it receives the signal, so it can be approximately considered that

[0052] Combining the above formula gives:

[0053]

[0054] That is, the clock offset is eliminated through the two-way link.

[0055] S3. Construct an ionospheric delay correction model using the frequency ratio relationship of signals in the downlink and uplink;

[0056] Taking the geometric delay τ 1 +τ 2 of the downlink from the central station to the user receiver as the parameter to be estimated, based on the symmetry between the downlink and the uplink, it is assumed that the geometric delay of the downlink is equal to that of the uplink, that is, the geometric delay of the downlink is half of the geometric delay of the two-way link:

[0057]

[0058] There is no ε c and ε r in formula (6) because they cancel each other out in the two-way link and the residual value can be ignored.

[0059] Substituting formula (6) into formula (1), the clock error τ rclk

[0060]

[0061] of the user receiver can be obtained. In the formula, the tropospheric delay is eliminated, and the ionospheric delay needs to be corrected using the model; time delay calibration is performed on each device and stored in the central station for time delay correction.

[0062] In formula (7), it is assumed that the geometric delay of the downlink is half of the geometric delay of the two-way link. However, in the actual working environment, the geometric delay of the downlink is not equal to that of the uplink, which will introduce an error of dozens of nanoseconds.

[0063] Therefore, taking the ionospheric delay as the parameter to be estimated, using the frequency ratio relationship between the outbound signal and the inbound signal, constructing an ionospheric calculation model, obtaining the ionospheric delay through two-way ranging calculation, and then calculating the clock error of the user receiver. Using formula (5), the ionospheric delay can be obtained:

[0064]

[0065] Let

[0066]

[0067] Then

[0068]

[0069] Compare the ionospheric delay calculation formula

[0070]

[0071] Due to the existence of (α is the proportionality coefficient), then

[0072]

[0073] Substituting Equation (12) into Equation (10), we can obtain:

[0074]

[0075] Equation (13) is the ionospheric delay correction model.

[0076] S4. According to the downlink time delay, combined with the sum of geometric time delays, the current layer delay correction model, satellite ephemeris data, and equipment time delay, calculate the clock error of the user terminal for correction to complete time synchronization.

[0077] Considering that the tropospheric delay is related to the location and satellite elevation angle and is not related to the frequency, there is:

[0078] Therefore, Equation (13) can be further simplified to:

[0079]

[0080] Substituting Equation (14) into Equation (3), the clock error of the user receiver can be obtained as:

[0081]

[0082] In the formula, After calculation at the ground central station, all equipment time delays in the calculation formula include the transmission and reception time delays of the central station, the satellite transponder time delay, and the transmission and reception time delays of the user terminal. The equipment time delay is obtained from the satellite broadcast information. It is sent to the user terminal for correction through the downlink to obtain accurate time synchronization.

[0083] The time synchronization system based on a communication satellite according to the present invention includes:

[0084] A signal transceiver module: used to enable the central station to send a time synchronization signal to the user terminal through the downlink of the communication satellite and receive the signal returned by the user terminal through the uplink of the communication satellite;

[0085] A time delay calculation module: used to calculate the sum of the downlink and uplink time delays according to the satellite ephemeris information;

[0086] A correction module: used to construct an ionospheric delay correction model by using the frequency ratio relationship of the signals in the downlink and uplink;

[0087] A time synchronization module: used to calculate the clock error of the user terminal for correction to complete time synchronization according to the downlink time delay, combined with the sum of time delays, the current layer delay correction model, satellite ephemeris data, and equipment time delay.

[0088] A computer-readable storage medium storing one or more programs, the one or more programs including instructions that, when executed by a computing device, cause the computing device to perform any of the above methods.

Claims

1. A timing method based on a communication satellite, characterized in that: The following steps are involved: S1, the central station sends a timing signal to the user terminal through the downlink of the communication satellite, and receives the signal returned by the user terminal through the uplink of the communication satellite; S2. Calculate the sum of the downlink and uplink delays based on the satellite ephemeris information; S3, constructing an ionospheric delay correction model using the frequency ratio relationship of the signals in the downlink and uplink; S4. According to the downlink delay, combined with the sum of the delays, the current layer delay correction model, the satellite ephemeris data and the equipment delay, the clock error of the user terminal is calculated and corrected to complete the timing.

2. The timing method based on communication satellite according to claim 1, characterized in that: The downlink is a C1 frequency band signal transmitted by the central station, which is forwarded as an S1 frequency band signal to the user terminal via the communication satellite.

3. The timing method based on communication satellite according to claim 2, characterized in that: The uplink transmits a C2 frequency band signal to the user terminal, which is forwarded as an S2 frequency band signal to the central station via the communication satellite.

4. The timing method based on communication satellite according to claim 3, characterized in that: The ionospheric delay correction model is: in, and are the ionospheric delays from the central station to the communication satellite and from the communication satellite to the user terminal in the downlink, respectively; is the sum of the geometric delays of the downlink and uplink, is the tropospheric delay of the signal during the i-th transmission process; α is the proportional coefficient; Among them, τ i is the geometric delay in the i-th transmission process; is the Sagnac effect correction caused by the Earth's rotation during the i-th transmission process, and They represent the transmission signal delay and reception signal delay of the central station in the downlink and uplink, respectively. and are the communication satellite transponder delays in the downlink and uplink, respectively. and are the user terminal receiving signal delay and transmitting signal delay in the downlink and uplink respectively.

5. The timing method based on communication satellite according to claim 4, characterized in that: The calculation formula of α is: Among them, f C1 and f C2 are the frequencies of signals transmitted from the central station and user terminal to the communication satellite in the downlink and uplink, respectively, S1 and f S2 These are the signal frequencies transmitted by communication satellites to user terminals and central stations in the downlink and uplink, respectively.

6. The timing method based on communication satellite according to claim 5, characterized in that: The clock error calculation formula of the user terminal is: τ rclk is the clock difference of the user terminal, is the downlink delay; Among them, τ 1 is the geometric delay generated by the central station transmitting the signal to the communication satellite receiving the signal in the downlink, τ 2 The geometric delay generated when the communication satellite transmits the signal to the user terminal receiving the signal; and They are respectively the Sagnac effect correction caused by the earth's rotation during the downlink signal from the central station to the communication satellite and from the communication satellite to the user terminal.

7. The timing method based on communication satellite according to claim 1, characterized in that: The device delay in step S4 includes the central station transmission and reception delay, the satellite transponder delay and the user terminal transmission and reception delay, and the device delay is obtained from the satellite broadcast information.

8. The timing method based on communication satellite according to claim 1, characterized in that: The satellite ephemeris information in step S2 includes the position, velocity and Sagnac effect correction parameters of the communication satellite.

9. A timing system based on a communication satellite, characterized in that: include: Signal transceiver module: used to enable the central station to send timing signals to the user terminal through the downlink of the communication satellite, and receive the signal returned by the user terminal through the uplink of the communication satellite; Delay calculation module: used to calculate the sum of downlink and uplink delays based on satellite ephemeris information; Correction module: used to construct an ionospheric delay correction model using the frequency ratio relationship of the downlink and uplink signals; Timing module: It is used to calculate the clock error of the user terminal and correct it to complete the timing according to the downlink delay, the sum of the delays, the current layer delay correction model, the satellite ephemeris data and the equipment delay.

10. A computer-readable storage medium storing one or more programs, characterized in that: The one or more programs include instructions which, when executed by a computing device, cause the computing device to perform any one of the methods according to claims 1 to 8.

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