Satellite-ground time synchronization high-precision measurement and control responder time delay measurement system and method

Abstract

The invention discloses a satellite-ground time synchronization high-precision measurement and control responder time delay measurement system and method. The system comprises a measurement and control responder, a measurement and control ground detector, a GNSS antenna and a GNSS timing system. The measurement and control responder is responsible for sending a telemetry signal with a sending timestamp Txi; the measurement and control ground detector receives a telemetry signal sent by the measurement and control responder and marks a receiving timestamp Tdi when receiving a telemetry frame header; the GNSS antenna is installed in an outdoor open area, is connected to the measurement and control ground detector through a radio frequency coaxial cable, and transmits the received navigational star information to the measurement and control ground detector. The GNSS timing system is built in the measurement and control ground detector, and solves the current time in real time according to the telemetry signal and navigation star information received by the measurement and control ground detector. A high-precision timestamp is provided through the GNSS timing system, and the accuracy of time delay measurement is ensured.

Description

Technical Field

[0001] The present invention belongs to the field of satellite measurement and control technology, and specifically relates to a high-precision measurement system and method for measurement of telemetry and control transponder delay for satellite-ground time synchronization. The system is used to accurately measure the telemetry downlink delay (ΔTsy) of the measurement and control transponder during satellite measurement and control subsystem testing, thereby calibrating the satellite-ground time difference and improving the accuracy of satellite time synchronization. Background Art

[0002] In traditional TT&C transponder delay measurement methods, ground stations usually use an indirect calculation scheme based on ground clock synchronization. The process is as follows:

[0003] 1. Ground equipment maintains local clocks through atomic clocks or crystal oscillators, which are not synchronized with satellite time in real time;

[0004] 2. Obtain fixed values ​​of the station equipment delay (△Tsb) and transmission delay (R / C) through offline calibration;

[0005] 3. Use the formula △Tsy=Tdi-Txi-△Tdm-△Tsb-R / C to indirectly calculate the transponder delay.

[0006] Where, △Tsy: time delay of onboard telemetry equipment.

[0007] Tdi: The time stamp of the corresponding station in the i-th frame of telemetry data.

[0008] Txi: The onboard time corresponding to the i-th telemetry frame.

[0009] △Tdm: When calculating the satellite-ground difference, since the on-board time sampling moment is the leading edge of the highest bit of the satellite time, and the time stamp sampling of the telemetry frame received on the ground is at the trailing edge of the frame synchronization code 1ACFFC1D, the corrected △Tdm is 1.953125ms (the code rate is 16384bps).

[0010] △Tsb: Telemetry demodulation delay of ground equipment at the measurement station.

[0011] R / C: Data transmission delay in space; R is the actual distance between the satellite and the ground station, and C is the speed of light.

[0012] Limitations:

[0013] 1. Clock drift error: The ground equipment and satellite clocks are not synchronized in real time. Clock deviations accumulate over long periods of operation, resulting in a decrease in the accuracy of timestamps (Tdi, Txi);

[0014] 2. Poor adaptability to dynamic scenarios: R / C relies on satellite orbit prediction data, and the error is significant when the on-orbit dynamic distance changes (the actual measurement error can reach more than ±10μs);

[0015] 3. Multi-parameter coupling: The formula depends on multiple parameters such as △Tsb, △Tdm, R / C, etc. The superposition of errors limits the measurement accuracy of △Tsy (typical error ≥ 50μs).

[0016] 4. Complex delay measurement: Existing solutions require complex calibration processes and rely on the collaborative work of multiple external devices, increasing system complexity and maintenance costs.

[0017] 5. Poor real-time performance: During the delay measurement process, the existing system is often unable to obtain high-precision timestamps in real time, resulting in delayed measurement results and affecting the timeliness of satellite time calibration. Summary of the Invention

[0018] In response to the problems existing in the prior art, the present invention provides a high-precision measurement system and method for satellite-ground time synchronization of measurement and control transponder delay, and proposes a dual optimization solution of "GNSS time synchronization + dynamic code rate adaptation":

[0019] GNSS time synchronization:

[0020] 1. Receive navigation satellite signals through the GNSS antenna, calculate and synchronize to Beijing time in real time, and eliminate the long-term deviation between the ground clock and satellite time;

[0021] 2. The accuracy of timestamps (Tdi, Txi) is improved to microsecond level to avoid error accumulation caused by clock drift.

[0022] Dynamic bit rate adaptation:

[0023] 1. Automatically correct △Tdm according to the telemetry code rate (such as 16384bps, 8192bps), replacing the traditional fixed value mode;

[0024] 2. Supports dynamic adjustment of code rate on orbit to adapt to complex measurement and control scenarios.

[0025] The present invention solves the problems in the prior art by optimizing the system architecture and algorithm, and achieves the following objectives:

[0026] 1. High-precision time synchronization: The GNSS timing system provides high-precision timestamps to ensure the accuracy of delay measurements.

[0027] 2. Simplified measurement process: By integrating GNSS antennas and measurement and control ground inspection, the delay measurement process is simplified, reducing system complexity and maintenance costs.

[0028] 3. Strong real-time performance: The system can obtain high-precision timestamps in real time, ensuring the real-time performance of delay measurement and improving the timeliness of satellite time calibration.

[0029] 4. Strong adaptability to dynamic scenarios: The GNSS module uses the PTP protocol and NTP enhanced algorithm to calculate Beijing time and implement local clock calibration. It calculates △Tdm through a table lookup method or formula calculation method to achieve real-time adaptation of the code rate, improving measurement accuracy and adaptability to dynamic scenarios.

[0030] The technical solution of the present invention is: a high-precision measurement system for satellite-ground time synchronization of measurement and control transponder delay measurement, comprising a measurement and control transponder, a measurement and control ground detector, a GNSS antenna and a GNSS timing system;

[0031] The measurement and control transponder is responsible for sending a telemetry signal with a sending timestamp Txi;

[0032] The measurement and control ground detector receives the telemetry signal sent by the measurement and control transponder and adds a receiving timestamp Tdi when receiving the telemetry frame header;

[0033] The GNSS antenna is installed in an open outdoor area and connected to the measurement and control ground inspection via a radio frequency coaxial cable to transmit the received navigation star information to the measurement and control ground inspection;

[0034] The GNSS timing system is built into the ground monitoring system, and the current time is calculated in real time based on the telemetry signal and navigation satellite information received by the ground monitoring system. The calculation formula is:

[0035] △Tsy=Tdi-Txi-△Tdm-△Tsb

[0036] Wherein, △Tsy is the onboard telemetry equipment delay, Tdi is the station time stamp corresponding to the i-th frame of telemetry data, Txi is the onboard time corresponding to the i-th frame of telemetry, △Tdm is the correction value corresponding to the telemetry code rate, and △Tsb is the telemetry demodulation delay of the station ground equipment.

[0037] Furthermore, the clock calculation and calibration method of the GNSS timing system is as follows: by receiving the navigation satellite signal (such as Beidou B1I, GPS L1C / A) transmitted by the GNSS antenna, the satellite time mark is analyzed and converted to Beijing time; using PTP (Precision Time Protocol) or NTP enhanced algorithm (such as NTPv4), the local clock is synchronized to the GNSS timing system, with a synchronization error of ≤1μs;

[0038] The calibration logic is as follows: the GNSS timing system outputs a 1PPS (pulse per second) signal once per second as a time reference; the local clock counter is reset on the rising edge of the 1PPS signal and compensated for clock drift through a phase-locked loop (PLL); when the timestamp Tdi is recorded, the transmission link delay (such as the fixed delay of the coaxial cable) is automatically compensated.

[0039] Furthermore, the ΔTdm correction method of the dynamic code rate adaptation module in the GNSS timing system is as follows:

[0040] Method 1: Lookup table method: Pre-store the △Tdm values ​​corresponding to different code rates and embed them in the FPGA or firmware of the measurement, control and ground detection system; when receiving the telemetry frame, index the corresponding △Tdm value according to the frame header rate identifier;

[0041] Bit rate (bps) △Tdm (ms) 8192 3.90625 16384 1.953125 32768 0.9765625

[0042] Method 2: Real-time calculation method: △Tdm calculation formula: △Tdm=N_Bytes / Ftc×8×1000, where Ftc is the telemetry code rate and N_Bytes is the number of time stamp bits and the telemetry frame header length.

[0043] Furthermore, the calculation method of △Tsb in the GNSS timing system is as follows: △Tsb is an inherent property of the ground equipment at the station, obtained through calibration, and basically does not change with time. The calibration steps are as follows:

[0044] 1. Connect the standard telemetry signal source to the ground equipment of the measuring station via wire. The time delay △Tsy0 of the standard telemetry signal source is known.

[0045] 2. The standard telemetry signal source sends a telemetry signal with a sending timestamp (Txi). After the measuring station receives the telemetry signal, it adds a receiving timestamp (Tdi).

[0046] 3. Then △Tsb can be obtained: △Tsb = Tdi-Txi-△Tdm-△Tsy0, where △Tdm is the correction value corresponding to the telemetry code rate, which can be obtained by the above table lookup or calculation method.

[0047] The present invention also provides a method for measuring the time delay of a high-precision measurement and control transponder with satellite-ground time synchronization. The specific method is as follows:

[0048] Step 1: The measurement and control transponder is responsible for sending a telemetry signal with a sending timestamp Txi;

[0049] Step 2: The measurement and control ground detector receives the telemetry signal sent by the measurement and control transponder and adds a receiving timestamp Tdi when receiving the telemetry frame header;

[0050] Step 3: Install the GNSS antenna in an open outdoor area, connect it to the measurement and control ground station via a radio frequency coaxial cable, and transmit the received navigation star information to the measurement and control ground station;

[0051] Step 4: Use the GNSS timing system built into the ground station to calculate the current time in real time based on the telemetry signal and navigation satellite information received by the ground station. The calculation formula is:

[0052] △Tsy=Tdi-Txi-△Tdm-△Tsb

[0053] Wherein, △Tsy is the onboard telemetry equipment delay, Tdi is the station time stamp corresponding to the i-th frame of telemetry data, Txi is the onboard time corresponding to the i-th frame of telemetry, △Tdm is the correction value corresponding to the telemetry code rate, and △Tsb is the telemetry demodulation delay of the station ground equipment.

[0054] The beneficial effects of the present invention are: providing a high-precision satellite-to-ground time synchronization delay measurement system and method for measurement of transponder time;

[0055] 1. Structural advantages:

[0056] The integration of GNSS antenna and measurement and control ground detection simplifies the system structure and reduces complexity and maintenance costs.

[0057] The GNSS timing system is built into the measurement, control and ground inspection system, providing high-precision timing information to ensure the accuracy of timestamps.

[0058] It supports high-precision synchronization in scenarios without ground-based atomic clocks, reducing system deployment costs.

[0059] 2. Functional advantages:

[0060] Improved accuracy: Through GNSS time synchronization, the timestamp error is ≤1μs, and the △Tsy measurement accuracy is improved to the microsecond level.

[0061] It has strong real-time performance and can obtain high-precision timestamps in real time, improving the timeliness of satellite time calibration.

[0062] The delay measurement process is simplified and the reliability and stability of the system are improved.

[0063] This method can ensure that the timestamp (Tdi) and satellite time (Txi) are based on the same time system (Beijing time), eliminating the deviation between the satellite and ground clocks.

[0064] 3. Innovative Advantage 1: GNSS high-precision time synchronization:

[0065] The GNSS antenna receives navigation satellite signals in real time, and the measurement, control and ground inspection obtains Beijing time through calculation, calibrates the local clock, and ensures that the timestamp (Tdi) accuracy reaches the microsecond level.

[0066] Eliminate Tdi errors caused by clock drift in traditional equipment.

[0067] 4. Innovative advantage 2: Delay separation algorithm:

[0068] Based on the formula △Tsy=Tdi-Txi-△Tdm-△Tsb, the transponder delay is directly separated and calculated.

[0069] Through the real-time input of known parameters (△Tdm, △Tsb) and high-precision time stamps (Tdi, Txi), △Tsy can be quickly calculated.

[0070] 5. Innovation Advantage 3: Dynamic Environmental Adaptability:

[0071] By using the dynamic bit rate adaptation function, dynamic bit rate switching can be achieved (such as adjusting the telemetry frame rate during a mission), avoiding the errors caused by the fixed △Tdm in traditional solutions.

[0072] Adapt to multi-task scenarios (such as low-rate telemetry frames + high-rate remote control commands) to improve system flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 This is the block diagram of the time delay measurement system for the measurement and control transponder;

[0074] Figure 2 This is the delay measurement flow chart. DETAILED DESCRIPTION

[0075] The present invention will be further described below with reference to the accompanying drawings.

[0076] like Figure 1 As shown in the figure, a high-precision measurement system for satellite-ground time synchronization of telemetry and control transponder delay measurement mainly includes the following components:

[0077] 1. TT&C transponder: responsible for sending telemetry signals with a sending timestamp (Txi).

[0078] 2. Measurement and control ground detection: Receive telemetry signals and add a receiving timestamp (Tdi) when the telemetry frame header is received.

[0079] 3. GNSS antenna: Placed outdoors, connected to the measurement and control ground inspection system via a radio frequency coaxial cable, receives navigation star information, and provides high-precision time information.

[0080] 4. GNSS timing system: Built into the measurement, control and ground inspection system, it calculates the current time in real time and provides high-precision time information for the measurement, control and ground inspection system.

[0081] System connection relationship:

[0082] 1. The measurement and control transponder is connected to the measurement and control ground detection through wired / wireless connection, and the measurement and control transponder sends a telemetry signal with a sending timestamp (Txi).

[0083] 2. The GNSS antenna is connected to the measurement and control ground inspection system through a radio frequency coaxial cable to receive navigation star information and provide high-precision time information.

[0084] 3. The GNSS timing system is built into the measurement, control and ground inspection system to calculate the current time in real time and provide high-precision time information for the measurement, control and ground inspection system to ensure the accuracy of the received timestamp (Tdi).

[0085] 4. The measurement and control ground detection adds a receiving timestamp (Tdi) when receiving the telemetry frame header, and calculates the transponder delay (△Tsy) based on the known △Tsb and the calculated △Tdm.

[0086] like Figure 2 As shown, the system works as follows:

[0087] Step 1: The measurement and control transponder is responsible for sending a telemetry signal with a sending timestamp Txi;

[0088] Step 2: The measurement and control ground detector receives the telemetry signal sent by the measurement and control transponder and adds a receiving timestamp Tdi when receiving the telemetry frame header;

[0089] Step 3: Install the GNSS antenna in an open outdoor area, connect it to the measurement and control ground station via a radio frequency coaxial cable, and transmit the received navigation star information to the measurement and control ground station;

[0090] Step 4: Use the GNSS timing system built into the ground station to calculate the current time in real time based on the telemetry signal and navigation satellite information received by the ground station. The calculation formula is:

[0091] △Tsy=Tdi-Txi-△Tdm-△Tsb

[0092] Wherein, △Tsy is the onboard telemetry equipment delay, Tdi is the station time stamp corresponding to the i-th frame of telemetry data, Txi is the onboard time corresponding to the i-th frame of telemetry, △Tdm is the correction value corresponding to the telemetry code rate, and △Tsb is the telemetry demodulation delay of the station ground equipment.

[0093] Clock calculation and calibration of the GNSS timing system: The TT&C system has a built-in GNSS timing system. It receives navigation satellite signals (such as Beidou B1I and GPS L1C / A) transmitted by GNSS antennas, analyzes the satellite time scale, and converts it to Beijing Time. It uses PTP (Precision Time Protocol) or an enhanced NTP algorithm (such as NTPv4) to synchronize the local clock to the GNSS timing system, with a synchronization error of ≤1μs. The calibration logic is as follows: The GNSS timing system outputs a 1PPS (pulse per second) signal once per second as the time reference. The local clock counter is reset on the rising edge of the 1PPS signal, and a phase-locked loop (PLL) is used to compensate for clock drift. When recording the timestamp (Tdi), the transmission link delay (such as the fixed delay of the coaxial cable) is automatically compensated.

[0094] △Tdm correction of the dynamic code rate adaptation module: achieved by selecting one of the following two methods.

[0095] Table lookup method: Pre-store the △Tdm values ​​corresponding to different code rates (as shown in Table 1) and embed them in the FPGA or firmware of the measurement, control and ground detection system. When receiving the telemetry frame, index the corresponding △Tdm value based on the frame header rate identifier (such as a 2-bit rate code).

[0096] Table 1: Code rate and ΔTdm correspondence table

[0097] Bit rate (bps) △Tdm (ms) 8192 3.90625 16384 1.953125 32768 0.9765625

[0098] Real-time calculation method: △Tdm calculation formula: △Tdm = N_Bytes / Ftc × 8 × 1000, where Ftc is the telemetry bit rate (bps), N_Bytes is the number of time stamp bits (bytes), and the telemetry frame header length. Example: When the bit rate is 16384 bps, △Tdm = (32 / 16384) × 1000 = 1.953125 ms.

[0099] Take a specific deployment system solution as an example, as follows:

[0100] 1. Hardware deployment:

[0101] Install the GNSS antenna in an open outdoor area and connect it to the measurement and control ground inspection system via a low-loss RF coaxial cable (such as LMR-400);

[0102] The measurement and control transponder is directly connected to the measurement and control ground detection via cable / wireless mode.

[0103] 2. Time synchronization process:

[0104] After the ground monitoring system is started, the GNSS timing module calculates Beijing time in real time and calibrates the local clock.

[0105] Timestamp logic: triggers Tdi recording at the telemetry frame start (trailing edge of the synchronization code).

[0106] 3. Delay calculation example:

[0107] Assume Txi is the satellite time 1000.000s (converted to Beijing time), Tdi is 1000.035s, △Tdm=1.953ms (Ftc=16384bps, N_Bytes =4 Bytes), △Tsb=0.5ms;

[0108] Substitute into the formula: △Tsy=1000.035-1000.000-0.001953-0.0005 =32.547ms.

[0109] For this system, the GNSS timing module synchronization process is implemented as follows:

[0110] 1. The GNSS antenna receives BeiDou B1I signals and outputs 1PPS pulses and NMEA-0183 time messages;

[0111] 2. The measurement and control ground detection analyzes the UTC time in the NMEA message and converts it to Beijing time;

[0112] 3. The local clock counter is reset on the rising edge of 1PPS, and the clock phase is adjusted through PLL to achieve ±0.5μs synchronization accuracy.

[0113] For this system, an example of a dynamic bit rate adaptation scenario is as follows:

[0114] 1. The task requires the bit rate to be switched from 16384bps to 32768bps:

[0115] 2. The telemetry frame header rate identifier of the measurement and control ground detection (e.g. "10" indicates 16384bps, "11" indicates 32768bps, and a change from "10" to "11" is detected);

[0116] 3. Update the parameters of the delay calculation formula and output the corrected △Tsy.

[0117] The best usage conditions are as follows:

[0118] Optimal use condition 1: During the docking test between the measurement and control subsystem and the ground station before satellite launch, use this system to measure the transponder delay to ensure time synchronization between the in-orbit satellite and the ground station.

[0119] Optimal use condition 2: Use this system to measure transponder delays during desktop joint testing of the measurement and control subsystem before satellite launch to ensure time synchronization between the on-orbit satellite and the ground station.

[0120] Optimal use condition 3: After the satellite tracking and control subsystem is upgraded or maintained, use this system to perform delay measurements to verify the system's performance and accuracy.

[0121] Through the above optimal usage conditions, this system can ensure the time synchronization accuracy between the satellite and the ground station, and improve the reliability and stability of the satellite measurement and control system.

[0122] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A high-precision satellite-to-ground time synchronization transponder delay measurement system, characterized by: Including measurement and control transponder, measurement and control ground detection, GNSS antenna and GNSS timing system; The measurement and control transponder is responsible for sending a telemetry signal with a sending timestamp Txi; The measurement and control ground detector receives the telemetry signal sent by the measurement and control transponder and adds a receiving timestamp Tdi when receiving the telemetry frame header; The GNSS antenna is installed in an open outdoor area and connected to the measurement and control ground inspection via a radio frequency coaxial cable to transmit the received navigation star information to the measurement and control ground inspection; The GNSS timing system is built into the ground monitoring system, and the current time is calculated in real time based on the telemetry signal and navigation satellite information received by the ground monitoring system. The calculation formula is: △Tsy=Tdi-Txi-△Tdm-△Tsb Wherein, △Tsy is the onboard telemetry equipment delay, Tdi is the station time stamp corresponding to the i-th frame of telemetry data, Txi is the onboard time corresponding to the i-th frame of telemetry, △Tdm is the correction value corresponding to the telemetry code rate, and △Tsb is the telemetry demodulation delay of the station ground equipment.

2. The high-precision satellite-to-ground time synchronization delay measurement system for tracking and controlling transponders according to claim 1, characterized in that: The clock calculation and calibration method of the GNSS timing system is as follows: by receiving the navigation satellite signal transmitted by the GNSS antenna, parsing the satellite time scale and converting it into Beijing time; using the PTP or NTP enhanced algorithm to synchronize the local clock to the GNSS timing system, with a synchronization error of ≤1μs; The calibration logic is as follows: the GNSS timing system outputs a 1PPS signal once per second as a time reference; the local clock counter is reset on the rising edge of the 1PPS signal and compensates for clock drift through a phase-locked loop; when the timestamp Tdi is recorded, the transmission link delay is automatically compensated.

3. The high-precision satellite-to-ground time synchronization delay measurement system for tracking and controlling transponders according to claim 1, characterized in that: The ΔTdm correction method of the dynamic code rate adaptation module in the GNSS timing system is as follows: Method 1: Lookup table method: Pre-store the △Tdm values ​​corresponding to different code rates and embed them in the FPGA or firmware of the measurement, control and ground detection system; when receiving the telemetry frame, index the corresponding △Tdm value according to the frame header rate identifier; Method 2: Real-time calculation method: △Tdm calculation formula: △Tdm=N_Bytes / Ftc×8×1000, where Ftc is the telemetry code rate and N_Bytes is the number of time stamp bits and the telemetry frame header length.

4. A high-precision measurement method for delay of a satellite-ground time-synchronized telemetry and control transponder, characterized in that: The specific method is as follows: Step 1: The measurement and control transponder is responsible for sending a telemetry signal with a sending timestamp Txi; Step 2: The measurement and control ground detector receives the telemetry signal sent by the measurement and control transponder and adds a receiving timestamp Tdi when receiving the telemetry frame header; Step 3: Install the GNSS antenna in an open outdoor area, connect it to the measurement and control ground station via a radio frequency coaxial cable, and transmit the received navigation star information to the measurement and control ground station; Step 4: Use the GNSS timing system built into the ground station to calculate the current time in real time based on the telemetry signal and navigation satellite information received by the ground station. The calculation formula is: △Tsy=Tdi-Txi-△Tdm-△Tsb Wherein, △Tsy is the onboard telemetry equipment delay, Tdi is the station time stamp corresponding to the i-th frame of telemetry data, Txi is the onboard time corresponding to the i-th frame of telemetry, △Tdm is the correction value corresponding to the telemetry code rate, and △Tsb is the telemetry demodulation delay of the station ground equipment.

5. The method for measuring time delay of a high-precision measurement and control transponder with satellite-ground time synchronization according to claim 1, characterized in that: The clock calculation and calibration method of the GNSS timing system is as follows: by receiving the navigation satellite signal transmitted by the GNSS antenna, parsing the satellite time scale and converting it into Beijing time; using the PTP or NTP enhanced algorithm to synchronize the local clock to the GNSS timing system, with a synchronization error of ≤1μs; The calibration logic is as follows: the GNSS timing system outputs a 1PPS signal once per second as a time reference; the local clock counter is reset on the rising edge of the 1PPS signal and compensates for clock drift through a phase-locked loop; when the timestamp Tdi is recorded, the transmission link delay is automatically compensated.

6. The method for measuring time delay of a high-precision measurement and control transponder with satellite-ground time synchronization according to claim 1, characterized in that: The ΔTdm correction method of the dynamic code rate adaptation module in the GNSS timing system is as follows: Method 1: Lookup table method: Pre-store the △Tdm values ​​corresponding to different code rates and embed them in the FPGA or firmware of the measurement, control and ground detection system; when receiving the telemetry frame, index the corresponding △Tdm value according to the frame header rate identifier; Method 2: Real-time calculation method: △Tdm calculation formula: △Tdm=N_Bytes / Ftc×8×1000, where Ftc is the telemetry code rate and N_Bytes is the number of time stamp bits and the telemetry frame header length.

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