A high-precision TT&C transponder time delay measurement system and method for satellite-ground time synchronization

Abstract

The application discloses a kind of high-precision measurement and control responder time delay measurement systems and methods of star-ground time synchronization, including measurement and control responder, measurement and control ground detection, GNSS antenna and GNSS time correction system;The measurement and control responder is responsible for sending telemetry signal with sending time stamp Txi;The measurement and control ground detection receives the telemetry signal sent by the measurement and control responder, and when receiving telemetry frame header, it is marked with receiving time stamp Tdi;The GNSS antenna is installed in outdoor open area, is connected to the measurement and control ground detection by radio frequency coaxial cable, and transmits the received navigation star information to the measurement and control ground detection;The GNSS time correction system is built-in in measurement and control ground detection, and according to the telemetry signal and navigation star information received by measurement and control ground detection, current time is solved in real time. High-precision time stamp is provided by GNSS time correction system, to ensure the accuracy of time delay measurement.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of satellite TT&C (Telemetry, Tracking and Command), and particularly relates to a high-precision TT&C transponder time delay measurement system and method for satellite-ground time synchronization, which is used for accurately measuring telemetry downlink time delay (△Tsy) of a TT&C transponder in a satellite TT&C subsystem test, calibrating satellite-ground time difference, and improving satellite time synchronization precision. BACKGROUND

[0002] In a traditional TT&C transponder time delay measurement method, a ground station usually adopts an indirect calculation scheme based on ground clock synchronization, and the process is as follows:

[0003] 1. The ground equipment maintains a local clock through an atomic clock or a crystal oscillator, and is not real-time synchronized with a satellite time.

[0004] 2. Fixed values of a station equipment time delay (△Tsb) and a transmission time delay (R / C) are obtained through offline calibration.

[0005] 3. The transponder time delay is indirectly calculated by using a formula △Tsy=Tdi-Txi-△Tdm-△Tsb-R / C.

[0006] Wherein, △Tsy: satellite telemetry equipment time delay.

[0007] Tdi: a station time mark corresponding to the i-th frame of telemetry data.

[0008] Txi: satellite time corresponding to the i-th frame of telemetry.

[0009] △Tdm: When calculating the satellite-ground time difference, since the satellite time sampling time is the leading edge of the highest bit of the satellite time, and the station receives the telemetry frame time mark sampling is behind the frame synchronization code 1ACFFC1D, therefore, △Tdm is corrected to 1.953125 ms (code rate is 16384 bps).

[0010] △Tsb: telemetry demodulation time delay of the station ground equipment.

[0011] R / C: data transmission time delay in space; R takes the actual distance value 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 the satellite clock are not real-time synchronized, and the clock deviation accumulates under long-term operation, resulting in a decrease in the precision of the time stamp (Tdi, Txi);

[0014] 2. Poor adaptability to dynamic scenarios: R / C needs to rely on satellite orbit prediction data, and the error is significant when the distance changes dynamically in orbit (the actual measurement error can be up to ±10 μs or more);

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

[0016] 4. Time delay measurement is complex: The existing scheme needs a complex calibration process and relies on the cooperative work of multiple external devices, increasing the complexity and maintenance cost of the system.

[0017] 5. Poor real-time performance: In the time delay measurement process, the existing system often cannot obtain high-precision timestamps in real time, resulting in lagging measurement results and affecting the timeliness of satellite time calibration. SUMMARY

[0018] To solve the problems in the prior art, the present application provides a high-precision TT&C transponder time delay measurement system and method for satellite-ground time synchronization, and proposes a dual optimization scheme of "GNSS time system synchronization + dynamic code rate adaptation":

[0019] GNSS time system synchronization:

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

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

[0022] Dynamic code 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. Support dynamic adjustment of code rate on orbit, adapting to complex TT&C scenarios.

[0025] The present application optimizes the system architecture and algorithm to solve the problems in the prior art. The following purposes are achieved:

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

[0027] 2. Simplify the measurement process: By integrating the GNSS antenna and the TT&C ground detector, the time delay measurement process is simplified, reducing the complexity and maintenance cost of the system.

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

[0029] 4. Strong dynamic scene adaptability: GNSS module adopts PTP protocol and NTP enhanced algorithm to calculate Beijing time, and realizes local clock calibration; through table lookup method or formula calculation method to solve △Tdm, realize real-time adaptation of code rate, improve the measurement accuracy and dynamic scene adaptability.

[0030] The technical scheme of the application is: a high-precision measurement and control transponder time delay measurement system for satellite-ground time synchronization, comprising a measurement and control transponder, a measurement and control ground detector, a GNSS antenna and a GNSS time calibration 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 stamps a receiving timestamp Tdi when receiving the telemetry frame header;

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

[0034] The GNSS time calibration system is built-in in the measurement and control ground detector, and calculates the current time in real time according to the received telemetry signal and navigation satellite information, and the calculation formula is:

[0035] △Tsy=Tdi-Txi-△Tdm-△Tsb

[0036] Wherein, △Tsy is the time delay of the telemetry equipment on the satellite, Tdi is the time stamp of the i-th frame of telemetry data, Txi is the time on the satellite 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 time delay of the ground station equipment.

[0037] Further, the clock solving and calibration method of the GNSS time calibration 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 stamp is analyzed and converted into Beijing time; PTP (Precision Time Protocol) or NTP enhanced algorithm (such as NTPv4) is adopted to synchronize the local clock to the GNSS time calibration system, and the synchronization error is ≤1μs;

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

[0039] Further, the △Tdm correction method of the dynamic code rate adaptation module in the GNSS time calibration system is as follows:

[0040] Method one, table lookup method: prestore different code rate corresponding △Tdm value, embedded in the FPGA or firmware of the ground control station; when receiving the telemetry frame, according to the frame header rate identifier index to obtain the corresponding △Tdm value;

[0041]

[0042] Method two, real-time calculation method: △Tdm calculation formula: △Tdm=N_Bytes / Ftc×8×1000, wherein, Ftc is the telemetry code rate, N_Bytes is the bit number of time mark bit telemetry frame header length.

[0043] Further, the calculation method of △Tsb in the GNSS time synchronization system is as follows: △Tsb is the inherent property of the ground equipment of the station, which is obtained by calibration and basically does not change with time. The calibration steps are as follows:

[0044] 1, the standard telemetry signal source is connected with the ground equipment of the station by wire, and 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 time stamp (Txi), and the ground station receives the telemetry signal and marks a receiving time stamp (Tdi);

[0046] 3, then △Tsb can be obtained: △Tsb=Tdi-Txi-△Tdm-△Tsy0, wherein △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 application also provides a high-precision time delay measurement method for a satellite-ground time synchronization telemetry transponder, and the specific method is as follows:

[0048] Step one, the telemetry transponder is responsible for sending a telemetry signal with a sending time stamp Txi;

[0049] Step two, the ground control station receives the telemetry signal sent by the telemetry transponder, and marks a receiving time stamp Tdi when receiving the telemetry frame header;

[0050] Step three, the GNSS antenna is installed in an outdoor open area and connected to the ground control station through a radio frequency coaxial cable to transmit the received navigation star information to the ground control station;

[0051] Step four, the GNSS time synchronization system built-in the ground control station is used to calculate the current time in real time according to the telemetry signal and the navigation star information received by the ground control station, and the calculation formula is:

[0052] △Tsy=Tdi-Txi-△Tdm-△Tsb

[0053] Wherein, △Tsy is the time delay of the on-board telemetry device, Tdi is the time mark of the corresponding station in the i-th frame of telemetry data, Txi is the on-board 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 time delay of the ground station equipment.

[0054] The beneficial effects of the present application are to provide a high-precision measurement system and method for the time delay of a TT&C transponder in satellite-ground time synchronization:

[0055] 1. Structural advantages:

[0056] The integrated GNSS antenna and TT&C ground station simplifies the system structure, reduces complexity and maintenance costs.

[0057] The GNSS time synchronization system is built into the TT&C ground station, providing high-precision time information to ensure the accuracy of the time stamp.

[0058] Supports high-precision synchronization in the absence of ground atomic clocks, reducing system deployment costs.

[0059] 2. Functional advantages:

[0060] Improved accuracy: Through GNSS time synchronization, the time stamp error is less than or equal to 1 microsecond, and the △Tsy measurement accuracy is improved to the microsecond level.

[0061] Strong real-time performance, capable of obtaining high-precision time stamps in real time, improving the timeliness of satellite time calibration.

[0062] Simplified time delay measurement process, improved system reliability and stability.

[0063] This method can realize the time stamp (Tdi) and satellite time (Txi) based on the same time system (Beijing time), eliminating the clock bias between the satellite and the ground.

[0064] 3. Innovation advantage 1: GNSS high-precision time synchronization:

[0065] The GNSS antenna receives navigation satellite signals in real time, and the TT&C ground station obtains Beijing time by solving and calibrates the local clock to ensure that the time stamp (Tdi) accuracy reaches the us level.

[0066] Eliminates the Tdi error caused by clock drift in traditional equipment.

[0067] 4. Innovation advantage 2: Time delay separation algorithm:

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

[0069] By inputting known parameters (△Tdm, △Tsb) and high-precision timestamps (Tdi, Txi) in real time, △Tsy can be solved quickly.

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

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

[0072] It adapts to multi-task scenarios (such as low-rate telemetry frames + high-rate remote control commands) to improve system flexibility. Attached Figure Description

[0073] Figure 1 This is a block diagram of a telemetry and control transponder delay measurement system.

[0074] Figure 2 This is a flowchart for time delay measurement. Detailed Implementation

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

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

[0077] 1. Telemetry and Control Transponder: Responsible for sending telemetry signals with a transmission timestamp (Txi).

[0078] 2. Telemetry, Control and Detection: Receive telemetry signals and add a reception timestamp (Tdi) when the telemetry frame header is received.

[0079] 3. GNSS antenna: placed outdoors, connected to the telemetry, tracking and monitoring system via radio frequency coaxial cable, to receive navigation satellite information and provide high-precision time and stability information.

[0080] 4. GNSS time synchronization system: Built into the telemetry, tracking, and command (TT&C) system, it calculates the current time in real time and provides high-precision time synchronization information for TT&C.

[0081] System connection relationships:

[0082] 1. The telemetry and control transponder is connected to the telemetry and control ground detection via wired / wireless connection. The telemetry and control transponder sends telemetry signals with a transmission timestamp (Txi).

[0083] 2. The GNSS antenna is connected to the telemetry, tracking, and command (TT&C) ground detection system via an RF coaxial cable to receive navigation satellite information and provide high-precision timing information.

[0084] 3. GNSS time calibration system is built in the TT&C ground station, which can calculate the current time and provide high-precision time information for the TT&C ground station to ensure the accuracy of the receiving time stamp (Tdi).

[0085] 4. The TT&C ground station stamps the receiving time stamp (Tdi) when receiving the telemetry frame header, and calculates the transponder time delay (△Tsy) according to the known △Tsb and the calculated △Tdm.

[0086] As shown in Figure 2 the system working principle:

[0087] Step 1: The TT&C transponder is responsible for sending telemetry signals with a sending time stamp Txi;

[0088] Step 2: The TT&C ground station receives the telemetry signals sent by the TT&C transponder, and stamps the receiving time stamp Tdi when receiving the telemetry frame header;

[0089] Step 3: The GNSS antenna is installed in an outdoor open area and connected to the TT&C ground station through a radio frequency coaxial cable to transmit the received navigation satellite information to the TT&C ground station;

[0090] Step 4: The GNSS time calibration system built in the TT&C ground station calculates the current time in real time according to the received telemetry signals and navigation satellite information, and the calculation formula is:

[0091] △Tsy = Tdi - Txi - △Tdm - △Tsb

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

[0093] Clock calculation and calibration of GNSS time calibration system: The GNSS time calibration system is built in the TT&C ground station, which can analyze the satellite time stamp and convert it into Beijing time by receiving the navigation satellite signals (such as Beidou B1I and GPS L1C / A) transmitted by the GNSS antenna. The local clock is synchronized to the GNSS time calibration system by using PTP (Precision Time Protocol) or NTP enhanced algorithm (such as NTPv4), and the synchronization error is ≤1μs; the calibration logic is that the GNSS time calibration system outputs a 1PPS (second pulse) signal once a second as a time reference; the local clock counter is reset at the rising edge of 1PPS, and the clock drift is compensated through a phase-locked loop (PLL); when the time stamp (Tdi) is recorded, the transmission link delay (such as the fixed time delay of coaxial cable) is automatically compensated.

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

[0095] Table lookup method: Pre-store the △Tdm values corresponding to different code rates (such as Table 1), and embed them in the FPGA or firmware of the telemetry ground station; when receiving a telemetry frame, index the corresponding △Tdm value according to the frame header rate identifier (such as 2-bit rate code).

[0096] Table 1: Code rate and △Tdm correspondence table

[0097]

[0098] Real-time calculation method: △Tdm calculation formula: △Tdm = N_Bytes / Ftc x 8 x 1000, where Ftc is the telemetry code rate (bps), N_Bytes is the bit number (Byte) of the time mark bit of the frame header length. Example: when the code rate is 16384bps, △Tdm = (32 / 16384) x 1000 = 1.953125ms.

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

[0100] 1. Hardware deployment:

[0101] Install the GNSS antenna in an open outdoor area and connect it to the telemetry ground station through a low-loss RF coaxial cable (such as LMR-400);

[0102] The telemetry transponder is directly connected to the telemetry ground station through a cable / wireless connection.

[0103] 2. Time synchronization process:

[0104] After the telemetry ground station is started, the GNSS time calibration module calculates the Beijing time in real time and calibrates the local clock;

[0105] Timestamp marking logic: trigger Tdi recording at the telemetry frame header (synchronization code trailing edge).

[0106] 3. Time delay calculation example:

[0107] Let Txi be the satellite time 1000.000s (converted to Beijing time), Tdi be 1000.035s, △Tdm = 1.953ms (Ftc = 16384bps, N_Bytes = 4Bytes), and △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 time calibration module synchronization process is implemented as follows:

[0110] 1. GNSS antenna receives Beidou B1I signal, outputs 1PPS pulse and NMEA-0183 time message;

[0111] 2. The measurement and control ground station parses UTC time in NMEA message and converts it into Beijing time;

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

[0113] For this system, a dynamic code rate adaptation scenario is as follows:

[0114] 1. The task requires code rate to switch from 16384bps to 32768bps:

[0115] 2. The measurement and control ground station detects the telemetry frame header rate identifier (such as "10" represents 16384bps, "11" represents 32768bps, and detects that it changes from "10" to "11");

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

[0117] The best use state is as follows:

[0118] Best use state 1: In the pre-launch test of the satellite measurement and control subsystem and the ground station, the system is used to measure the transponder time delay to ensure the time synchronization between the on-orbit satellite and the ground station.

[0119] Best use state 2: In the pre-launch test of the satellite measurement and control subsystem and the ground station, the system is used to measure the transponder time delay to ensure the time synchronization between the on-orbit satellite and the ground station.

[0120] Best use state 3: After the satellite measurement and control subsystem is upgraded or maintained, the system is used to measure the time delay to verify the performance and accuracy of the system.

[0121] Through the above best use states, the 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 the preferred embodiment of the present application, it should be noted that for those skilled in the art, without departing from the principles of the present application, can make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A high-precision TT&C transponder time delay measurement system for satellite-ground time synchronization, characterized in that: The telemetry and control transponder, the telemetry and control ground detector, the GNSS antenna and the GNSS time correction system are comprised. The telemetry and control transponder is responsible for sending telemetry signals with sending time stamp Txi. The telemetry and control ground detector receives the telemetry signals sent by the telemetry and control transponder and stamps receiving time stamp Tdi when receiving the telemetry frame header. The GNSS antenna is installed in an outdoor open area and is connected to the telemetry and control ground detector through a radio frequency coaxial cable to transmit the received navigation satellite information to the telemetry and control ground detector. The GNSS time correction system is built in the telemetry and control ground detector and calculates the current time according to the telemetry signals and the navigation satellite information received by the telemetry and control ground detector, with the calculation formula being: △Tsy = Tdi - Txi -△Tdm -△Tsb Wherein, △Tsy is the time delay of the telemetry equipment on the satellite, Tdi is the time stamp of the corresponding station in the i-th frame of telemetry data, Txi is the time on the satellite 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 time delay of the ground equipment of the station. The clock calculation and calibration method of the GNSS time correction system is as follows: the navigation satellite signals transmitted by the GNSS antenna are received, the satellite time stamp is analyzed and converted into Beijing time; the PTP or NTP enhanced algorithm is adopted to synchronize the local clock to the GNSS time correction system, and the synchronization error is less than or equal to 1 μs. The calibration logic is that the GNSS time correction system outputs a 1PPS signal once a second as a time reference; the local clock counter is reset at the rising edge of the 1PPS and compensates for the clock drift through a phase-locked loop; the time stamp Tdi is recorded, and the transmission link delay is automatically compensated. The △Tdm correction method of the dynamic code rate adaptation module in the GNSS time correction system is as follows: Method one: table lookup method: the △Tdm values corresponding to different code rates are pre-stored in the FPGA or firmware embedded in the telemetry and control ground detector; when the telemetry frame is received, the corresponding △Tdm value is obtained according to the frame header rate identifier index; Method two: real-time calculation method: the calculation formula of △Tdm is: △Tdm = N_Bytes / Ftc x 8 x 1000, wherein Ftc is the telemetry code rate, and N_Bytes is the bit number of the time mark bit.

2. A high-precision TT&C transponder time delay measurement method for satellite-ground time synchronization, characterized in that, The specific method is as follows: Step one: the telemetry and control transponder is responsible for sending telemetry signals with sending time stamp Txi; Step two: the telemetry and control ground detector receives the telemetry signals sent by the telemetry and control transponder and stamps receiving time stamp Tdi when receiving the telemetry frame header; Step three: the GNSS antenna is installed in an outdoor open area and is connected to the telemetry and control ground detector through a radio frequency coaxial cable to transmit the received navigation satellite information to the telemetry and control ground detector; Step four: the GNSS time correction system built in the telemetry and control ground detector calculates the current time according to the telemetry signals and the navigation satellite information received by the telemetry and control ground detector, with the calculation formula being: △Tsy = Tdi - Txi -△Tdm -△Tsb Wherein, △Tsy is the time delay of the telemetry equipment on the satellite, Tdi is the time stamp of the corresponding station in the i-th frame of telemetry data, Txi is the time on the satellite 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 time delay of the ground equipment of the station. The clock solution and calibration method of the GNSS timing system is as follows: by receiving the navigation satellite signal transmitted by the GNSS antenna, the satellite time mark is analyzed and converted into Beijing time; the local clock is synchronized to the GNSS timing system by using PTP or NTP enhancement algorithm, and the synchronization error is less than or equal to 1 microsecond; The calibration logic is that the GNSS timing system outputs a 1PPS signal once per second as a time reference; the local clock counter is reset at the rising edge of 1PPS, and the clock drift is compensated through a phase-locked loop; the time stamp Tdi is recorded, and the transmission link delay is automatically compensated; The △Tdm correction method of the dynamic code rate adaptation module in the GNSS timing system is as follows: Method one, table lookup method: prestore the △Tdm values corresponding to different code rates in the FPGA or firmware embedded in the ground control station; when receiving the telemetry frame, the corresponding △Tdm value is obtained according to the frame header rate identifier index; Method two, real-time calculation method: the △Tdm calculation formula is: △Tdm=N_Bytes / Ftc×8×1000, wherein Ftc is the telemetry code rate, and N_Bytes is the bit number of the time mark bit of the telemetry frame header length.

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