Beidou user machine high-precision time service and positioning method based on low-orbit high-stability reference

Abstract

The invention discloses a Beidou user machine high-precision time service and positioning method based on a low-orbit high-stability reference, and relates to the field of vehicle-mounted electronic communication. The method comprises the following steps: firstly, receiving a low-orbit satellite time service signal through an SBOX, generating a high-stability time service reference signal through anti-interference enhancement and delay compensation, and transmitting the high-stability time service reference signal to a Beidou user machine; the Beidou user machine calibrates drifting and fluctuation of an original time service signal of the Beidou user machine according to a low-orbit high-stability time service reference, Beidou high-precision and low-orbit high-stability time service output is achieved through double-source fusion, and finally high-precision positioning calculation is completed and packaged into CAN data; and finally, the information is transmitted to a vehicle-mounted information unit through a vehicle-mounted CAN bus, so that navigation and position reporting are realized. According to the invention, the high stability of the low earth orbit satellite and the high precision of the Beidou are complemented and cooperated, the time service precision and continuity are considered through Kalman filtering fusion and extended Kalman positioning solution, the problems of insufficient stability and poor equipment collaboration of a traditional Beidou user machine are solved, and the high stability and precision requirements of military and commercial use are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of vehicle-mounted electronic communication, in particular to a Beidou user machine high-precision timing and positioning method based on a low-orbit high-stability reference. BACKGROUND

[0002] With the increasing demand for intelligent collaborative operation of military vehicles and the development of networked and automatic driving technologies for commercial vehicles, higher and higher requirements are put forward for the precision, reliability and stability of the vehicle-mounted positioning and timing system. The timing precision directly determines the synchronization of multi-device collaboration and the effectiveness of positioning data, and the positioning reliability affects the implementation of core functions such as vehicle navigation, trajectory tracking and remote scheduling. In particular, in the scenarios of military vehicle battlefield collaboration and precise scheduling of commercial vehicles, high-precision timing and stable positioning have become a necessity.

[0003] Low-orbit satellites have the advantages of low orbit, short signal link and multi-satellite coverage, and their timing signals have small delay fluctuations and high continuous reception rates. Currently, vehicle positioning and timing mainly rely on Beidou user machines receiving Beidou satellite signals, but the application of Beidou user machines in existing technologies has obvious defects. Beidou satellites are medium-high orbit satellites, which have high absolute timing accuracy when working alone, but are affected by various factors during transmission. Moreover, their signal transmission path is long, and in scenarios such as urban high-rise dense areas, mountainous areas, tunnels and underground garages, signals are easily blocked or attenuated, and may also be disturbed by the surrounding electromagnetic environment, resulting in the inability of Beidou user machines to stably receive signals, and thus causing positioning failure and timing interruption. In the military scenario, these errors or interruptions will cause the vehicle to lose navigation guidance and time synchronization, resulting in asynchronous execution of action instructions by multiple combat vehicles and aiming and positioning deviation of weapon systems, which seriously affects the battlefield operational effectiveness. In the commercial vehicle field, it will cause inconsistent time stamps in the trajectory records of each vehicle in large vehicle fleet scheduling and asynchronous environment perception and path planning of autonomous driving vehicles, increasing the scheduling risk and safety hazards. SUMMARY

[0004] To solve the above technical problems, the present application proposes a Beidou user machine high-precision timing and positioning method based on a low-orbit high-stability reference, the specific steps of which are as follows: S1: The SBOX receives low-orbit satellite timing signals and performs anti-interference enhancement processing to obtain anti-interference low-orbit satellite timing signals , and then performs delay compensation on to obtain delay-calibrated low-orbit satellite stable timing signals T1, and encapsulates T1 as a timing data frame for transmission to the Beidou user machine; The low-orbit satellite timing signal is a timing signal related to a low-orbit satellite broadcast, containing a second pulse PPS signal, UTC timestamp information and satellite ephemeris auxiliary data; further comprising the following sub-steps: S11: Start the low-orbit satellite signal receiving module of SBOX and configure parameters; The low-orbit satellite signal receiving module is a core functional unit built-in SBOX (vehicle-mounted satellite communication terminal), containing a low-orbit satellite dedicated receiving antenna and a low-orbit satellite signal receiving chip, a signal preprocessing unit.

[0005] The low-orbit satellite dedicated receiving antenna is a signal receiving component adapted to low-orbit timing satellite signals; the low-orbit satellite signal receiving chip converts the radio frequency signals received by the low-orbit satellite dedicated receiving antenna into electrical signals that can be processed by subsequent modules; Start the low-orbit satellite dedicated receiving antenna and the low-orbit satellite signal receiving chip, wherein the antenna gain of the low-orbit satellite dedicated receiving antenna is ≥15dB; then configure the core parameters, set the receiving frequency band to 1575.42MHz, which is the commonly used center frequency band of low-orbit timing satellites, matching the satellite transmission end frequency band standard; in order to avoid interference false triggering capture, the signal capture threshold needs to be lower than the interference power 60dB, only when the power of the received signal exceeds the signal capture threshold, it is determined as an effective satellite signal; if the signal power is lower than the signal capture threshold, it is determined as an interference signal; Preferably, the low-orbit satellite dedicated receiving antenna selects an 8-way array antenna composed of 8 uniformly arranged microstrip elements, the 8 elements are linearly arranged, and the array signal processing technology is used to realize the enhancement of the signal in a specific direction and the suppression of the interference signal, and the antenna gain G is set to 18dB to ensure signal capture; the high-performance signal receiving chip model selects ADI AD9361, which supports 1550MHz-1610MHz frequency band.

[0006] At the same time, the anti-interference preprocessing function of the SBOX low-orbit satellite signal receiving module is started, through the filtering and amplification processing of the signal preprocessing unit, it is ensured that the low-orbit satellite timing signal has a high signal-to-noise ratio and purity before entering the subsequent processing.

[0007] The signal preprocessing unit is responsible for performing preliminary filtering and amplification processing of electrical signals. After the low-orbit satellite signal receiving module is started, the signal preprocessing unit starts working and performs preliminary processing on the digital signals output by the low-orbit satellite signal receiving chip; specifically, bandwidth limiting filtering is adopted, the filtering bandwidth B=2MHz, and the filtering function is FIR low-pass filtering, the unit impulse response h(n)= , where n is the sampling point index of the discrete time series, representing the nth discrete sampling time in the FIR low-pass filtering process, and the value is a non-negative integer; Fs is the sampling rate of the low-orbit satellite signal receiving module.

[0008] FIR low-pass filtering can effectively suppress interference signals outside the frequency band, ensuring the purity of the received signal; and the filtered signal can be appropriately amplified to improve the signal strength, facilitating subsequent signal processing and analysis.

[0009] S12: The low-orbit satellite captures and receives the low-orbit satellite timing signal according to the configured parameters, and performs anti-interference enhancement processing on the timing signal to obtain the anti-interference low-orbit satellite timing signal. The low-Earth orbit satellite signal receiving module captures the timing signal broadcast by the low-Earth orbit satellite according to the configured parameters. The timing signal includes a pulse-per-second (PPS) signal, UTC timestamp information, and satellite ephemeris auxiliary data. To address directional electromagnetic interference in the vehicle environment, an adaptive beamforming algorithm using a dedicated low-orbit satellite receiving antenna is employed. The core of the algorithm is the MVDR (Minimum Variance Distortionless Response) criterion. First, a received data vector is constructed by receiving signals through eight antennas. ,in This represents the signal at the m-th sampling point of the k-th antenna. Next, calculate the covariance matrix R= E[] represents the expected value, and H represents the conjugate transpose; Solving the beamforming weight vector based on the MVDR criterion ,in The direction of low-orbit satellite signal incidence The guiding vector, j is the imaginary unit, and d is the spacing between antenna elements. This refers to the incident angle of a low-orbit satellite. Furthermore, the antenna element spacing d = λ / 2 = 0.095m, where λ is the wavelength corresponding to the center frequency of the low-orbit satellite timing signal, and λ = = ≈0.19m; the incident angle of the low-orbit satellite It is calculated using real-time ephemeris data.

[0010] Finally, the received data vector is weighted by the weight vector W. After weighted processing, the interference-resistant low-Earth orbit satellite timing signal is obtained. The above processing effectively suppresses the gain in the direction of interference signals while preserving the direction of low-Earth orbit satellite signals. Increase the signal gain and eliminate signal interference.

[0011] The essence of the MVDR criterion is to ensure the direction of the useful signal. Under the premise of constant gain, the total power of the array output is minimized. The resulting covariance matrix R precisely quantifies the statistical characteristics of the total power. Therefore, the weight vector solved in this step can accurately suppress the signal in the direction of interference and enhance the gain in the direction of useful signal, thus achieving the purpose of anti-interference.

[0012] S13: Timing signal from low-Earth orbit satellites after interference suppression Extract the timing parameters of the low-Earth orbit satellite, calculate the signal transmission delay based on the timing parameters, and perform delay compensation to obtain the stable timing signal T1 of the low-Earth orbit satellite after delay calibration; Firstly, the signal separation unit built into the vehicle-mounted satellite communication terminal is used to separate the low-orbit satellite timing signal after interference suppression. Extract the core timing parameters, including: the rising edge time of the low-orbit satellite PPS signal. (Unit: ns, time base: BeiDou system time), the time value corresponding to the original UTC timestamp. (Unit: ns) and satellite ephemeris auxiliary data; Furthermore, the long-term frequency stability of the high-precision isothermal crystal oscillator is better than 1× It provides a short-term stable time reference and outputs a 1PPS signal with a pulse width of 100ns.

[0013] Next, the high-precision temperature-controlled crystal oscillator built into the SBOX is activated; the 1PPS signal output by the temperature-controlled crystal oscillator is used as a reference. The time interval measurement unit in the low-orbit satellite signal receiving module is used to measure... Compared with reference benchmark Time difference between 100 sets of time difference data were continuously measured, and random errors were eliminated using a moving average algorithm to obtain the average time difference. ,and The measurement accuracy is ≤50ps; Preferably, the time interval measurement unit is integrated into the low-orbit satellite signal receiving chip, model TDC-GP22, with a measurement accuracy of 10ps.

[0014] The signal transmission delay, including ionospheric delay, is calculated by combining low-Earth orbit satellite ephemeris data extracted from Y(k). Tropospheric delay and geometric delay Final total delay These delay errors cause the received time to lag behind the actual satellite launch time. Without compensation, this directly introduces errors at the nanosecond (ns) to microsecond (μs) level, failing to meet the fusion requirements of BeiDou user terminals. Therefore, a calibration algorithm is used to compensate for the delay in the low-Earth orbit (LEO) satellite timing signal. This is achieved by using a calibration algorithm unit (integrated within the signal preprocessing unit) in the LEO satellite signal receiving module to adjust the timing signal of Y(k). and After delay compensation and calibration, the stable timing signal T1 of the low-Earth orbit satellite satisfies the following condition: the rising edge time of the PPS signal in T1... The time value corresponding to the UTC timestamp of T1 = - Ensure that the accuracy of T1 is ≤100ns.

[0015] The above processing eliminates the delay error generated during the process of low-orbit satellite timing signal transmission from satellite to vehicle-mounted satellite communication terminal reception, suppresses delay fluctuations, and keeps the delay fluctuation of the obtained T1 within 10ps, ensuring the stability of the timing reference.

[0016] S14: Transmit the delayed-calibrated high-precision timing signal from the low-Earth orbit satellite. The data is encapsulated into a timing data frame and transmitted to the BeiDou user terminal. The SPI high-speed interface is used as the transmission channel, and the SPI interface is configured in master mode; preferably, the transmission rate of the SPI is set to 10Mbps to ensure transmission redundancy.

[0017] High-precision timing signals from low-orbit satellites after delay calibration Encapsulated as a time synchronization data frame, the time synchronization data frame includes a frame header and a timestamp field (i.e., ... The frame consists of UTC time (in ns), checksum, and frame trailer; the checksum is obtained using the CRC-16 checksum algorithm.

[0018] SBOX sends the encapsulated timing data frame to the SPI slave interface of the Beidou user terminal through the SPI interface, and at the same time, it uses the status bits of the SPI to provide feedback on the transmission status, and uses feedback codes to indicate normal or abnormal transmission.

[0019] S1 improves signal reliability through parameter configuration of the low-orbit satellite signal receiving module and adaptive beamforming algorithm; ensures output accuracy through high-precision temperature-controlled crystal oscillator and delay compensation; and guarantees real-time performance through SPI high-speed interface, providing a highly stable and interference-resistant timing reference source for BeiDou user terminals to calibrate the drift of the original BeiDou timing signal.

[0020] S2: The BeiDou user terminal receives the timing data frame, extracts T1 from the timing data frame as a high-stability timing reference, and extracts BeiDou satellite data to form the original BeiDou timing signal T2; then, based on T1, it performs drift calibration and stability compensation on T2 to obtain the compensated original BeiDou timing signal. ; Integration of T1 and To obtain a high-precision and stable fused timing signal Based on High-precision positioning calculations are performed to obtain high-precision vehicle positioning data. Finally, and Encapsulation is performed to obtain CAN-encapsulated timing and positioning data frames; The original BeiDou timing signal is an autonomous timing signal generated by the BeiDou user terminal after receiving BeiDou medium- and high-orbit satellite positioning and timing signals, and after acquisition, tracking, and parameter calculation; further, it includes the following sub-steps: S21: The Beidou user terminal receives and verifies the timing data frame transmitted by SBOX, extracts T1 from the timing data frame as a high-stability timing reference, and starts its own Beidou satellite signal reception and data extraction to obtain the original Beidou timing signal T2. The Beidou user terminal receives timing data frames sent by the vehicle-mounted satellite communication terminal through the matching SPI interface and performs CRC-16 verification to ensure data validity. If the CRC-16 check fails, the BeiDou user terminal sends a retransmission request to the SBOX. If the retransmission fails, the BeiDou user terminal records the fault type and temporarily uses its own original BeiDou timing signal as a substitute for the high-stability timing reference T1.

[0021] The high-stability time reference refers to a highly reliable time reference standard used by BeiDou user terminals after validity verification to calibrate their own time signals, support the generation of fused time signals, and perform high-precision positioning calculations.

[0022] Furthermore, the maximum number of retransmissions for the retransmission request is set to 3, and the timeout period is set to 100μs.

[0023] Then, the BeiDou satellite receiving antenna built into the BeiDou user terminal is activated to receive the positioning and timing signals broadcast by BeiDou medium and high orbit satellites, and the radio frequency signal is converted into an intermediate frequency signal by the radio frequency front end.

[0024] Furthermore, the BeiDou satellite receiving antenna has a gain of 15dB and a receiving frequency band of 1561.098MHz and 1207.14MHz; the intermediate frequency of the intermediate frequency signal is 46MHz; and the low-noise amplifier of the radio frequency front end has a gain of 40dB and a noise figure ≤1.5dB.

[0025] The intermediate frequency signal is then sampled and converted into a digital signal using an ADC with a sampling rate of 20MHz. The BeiDou signal processing module of the BeiDou user terminal performs FFT accelerated correlation calculations based on the BeiDou spreading code and the digital intermediate frequency signal, traversing the carrier frequency offset and code phase offset. When the correlation peak exceeds 6 times the noise power, it is determined that the acquisition is successful.

[0026] Furthermore, the BeiDou spreading code has a rate of 1.023MHz and is a B1C code; the carrier frequency offset has a traversal range of ±5kHz and a traversal step size of 100Hz; and the code phase offset has a traversal range of 0~10229 chips and a traversal step size of 1 chip.

[0027] Simultaneously, the BeiDou user terminal initiates a 1Hz delay-locked loop to track the phase of the spreading code. The code tracking loop generates three local spreading codes—Early, Prompt, and Late—and performs correlation operations with the received spreading code to obtain three correlation output values ​​E, P, and L. The error signal ℇ is then calculated. The phase of the local spreading code is adjusted in real time to ensure that the instantaneous tributary correlation output P always remains at its maximum value. The phase offset of the local code relative to the received code, after time conversion, is the accurate code delay measurement. (Unit: ns). Complete signal acquisition and tracking, and extract ephemeris data from BeiDou medium and high orbit satellites; Simultaneously, the carrier tracking loop synchronously tracks the carrier phase, and measures the carrier phase at M consecutive sampling times. (Sampling interval 150ns, ADC sampling rate 20 MHz) Perform the following integration: Due to the short period of time The mean approaches 0, and Using constant integers, the integral result is fitted to obtain the integer ambiguity of the i-th Beidou medium-high orbit satellite. .

[0028] Furthermore, the ephemeris data of the BeiDou medium and high orbit satellites includes the position coordinates of the N successfully captured BeiDou high orbit satellites. (i=1,2,...,N), satellite clock bias Klobuchar ionospheric model coefficients and BDT (BeiDou system time) - UTC bias parameters ;in, This refers to the instantaneous position coordinates of the i-th Beidou medium-high orbit satellite in the Earth's inertial coordinate system.

[0029] Based on the extracted ephemeris data of BeiDou medium- and high-orbit satellites, the BeiDou signal processing module calculates the pseudorange measurement value of the i-th satellite. Where c is the speed of light 3 × 108 m / s, The pseudorange measurement value of the i-th Beidou medium-high orbit satellite The deviation from the actual straight-line distance between the satellite and the BeiDou user terminal is essentially the sum of all error sources during the pseudorange measurement process; the pseudorange measurement value It is an estimated value including errors, obtained by the BeiDou user terminal measuring the distance from the i-th BeiDou medium-high orbit satellite to itself.

[0030] The pseudorange error Including ionospheric delay error and tropospheric delay error The ephemeris data from BeiDou's medium and high orbit satellites will broadcast Klobuchar ionospheric model coefficients A and B. BeiDou user terminals will then combine this data with their own latitude... Longitude λ, substituting it into the Klobuchar model formula ))( (For model reference latitude) The environmental sensors built into the BeiDou user terminal collect real-time local air pressure (P), temperature (T), and water vapor pressure (e), combined with satellite elevation angles. (Calculated from ephemeris data), substituted into the Saastamoinen tropospheric delay model formula get . It is the sum of the ionospheric delay error and the tropospheric delay error mentioned above, that is = + This corrects the discrepancy between the propagation time and the actual distance.

[0031] Simultaneously, the BeiDou signal processing module extracts the carrier phase measurement value of the i-th BeiDou medium-high orbit satellite. ,in The wavelength of the BeiDou B1C band signal. This represents the actual straight-line distance between the satellite and the BeiDou user terminal. For integer ambiguity, The measured carrier phase error.

[0032] Based on the signal tracking and parameter calculation results, the BeiDou signal processing module further generates its own original timing signal T2: first, the precise code delay measurement value output by the code tracking loop. (Unit: ns), combined with satellite clock bias Correcting the actual code delay = - This value is the signal propagation time. = Secondly, the BDT time of the current launch signal of the i-th Beidou medium-high orbit satellite is analyzed from the navigation message. Then the BDT time for the BeiDou user terminal to receive the corresponding signal is = + ; Subsequently, for at least 4 valid satellites Weighted fusion is performed to obtain the average BDT time. Finally, combining the navigation message... ,Will Convert to UTC timestamp At the same time The rising edge is defined as the exact second, generating a 1PPS signal with a pulse width of 100ns. , UTC timestamp With 1PPS signal The system integrates these components to form BeiDou's own original timing signal T2.

[0033] Furthermore, the aforementioned The weighting criteria for weighted fusion are as follows: when the satellite signal-to-noise ratio (SNR) is ≥ 40dB, the weight of the corresponding satellite is set to 0.8; when the satellite signal-to-noise ratio (SNR) is ≤ 30dB and < 40dB, the weight of the corresponding satellite is set to 0.5; when the satellite signal-to-noise ratio (SNR) is < 30dB, the data of that satellite is discarded.

[0034] S22: The BeiDou user terminal compensates for its own original timing signal T2 based on the highly stable timing reference T1 to obtain the compensated original BeiDou timing signal. ; The rising edge time of the PPS signal is obtained from the high-stability timing reference T1. Time value corresponding to UTC timestamp , by As a synchronization reference, the time difference between the rising edge of PPS and the rising edge of T1 of 50 sets of BeiDou raw timing signals T2 was continuously measured. (k=1,2,...,50), and using the moving average algorithm Eliminate random errors.

[0035] Considering the inherent system delay of signal processing within the BeiDou user terminal (Determined in advance through calibration experiments), the following linear compensation is applied to T2 to calibrate its timing drift: The original timing signal of Beidou after compensation Significantly reduces the BeiDou timing signal after synchronization. The time deviation between the time reference and the highly stable time reference T1.

[0036] S23: Beidou user terminal integration T1 and The state prediction is iteratively updated to obtain a high-precision, stable fused timing signal. ; The BeiDou user terminal uses the Kalman filter algorithm to fuse T1 and By suppressing single-source timing errors through state prediction and observation updates, high-precision timing output can be achieved.

[0037] Define state variables ,in The time value at time k. The timing drift rate is the rate at which the timing signal changes over time.

[0038] The observation equation is , where the observation vector Observation matrix Observation noise Follows a normal distribution R is the observation noise covariance, based on T1 and Error statistics, R=diag([ ]).

[0039] Then, the Kalman filter update iteration is performed according to the following process (1)-(6): (1) Initialization phase: At the 0th moment of filter start, i.e., k=0, the initial optimal state is determined. and the initial covariance matrix Initial state ,in Take the average of T1 and T2'. Set to 0; initial covariance matrix = ; (2) Prediction phase: Based on the optimal state at time k-1 Covariance Matrix Calculate the predicted state and prediction covariance at time k; based on The predicted state is obtained by mapping the optimal timing value and drift rate from the previous time step to the current time step using the state transition matrix F, thus reflecting the temporal continuity of the timing state without observation data correction; where the state transition matrix is... ,in The filter period; based on Predict covariance, combined with The uncertainty of the predicted state is updated by summing the process noise covariance Q. (3) Residual calculation stage: based on the observation vector at the current time. and predicted state Calculate the observation residuals ; (4) Kalman gain update stage: Calculate the Kalman gain This enhances the correction effect of observation data; (5) State update phase: based on Perform optimal state correction using Kalman gain. Weighted residuals For the predicted state Make corrections to obtain the optimal time synchronization state at the current moment; and based on Perform covariance update, where I is a 2-order identity matrix; (6) Iteration Termination and Mode Judgment: The above (1)-(5) processes are performed according to the filtering cycle. Repeat the iteration until five consecutive optimal states are reached. When the change in the value satisfies the preset Kalman convergence condition, the filter is determined to be convergent. Preferably, the preset Kalman convergence condition is set to , .

[0040] After the filtering converges, the first element of the optimal state vector is extracted as the fused timing signal, i.e. To obtain a high-precision and stable fused timing signal If T1 fails, it automatically switches to single-source timing mode. In this mode, the state equation and observation equation retain only the T2' related terms, i.e., the observation vector. The observation matrix H = [1, 0] ensures the continuity of time synchronization.

[0041] Through S23 and S24, the Kalman filter algorithm suppresses the drift fluctuation of T2, preserving the absolute high precision of BeiDou. By fusing T1 and T2', a high-precision and highly stable fused timing signal is finally obtained. .

[0042] S24: BeiDou user terminal combined with high-precision, stable fusion timing signal Achieve high-precision positioning calculation and obtain high-precision vehicle positioning data. ; by Using time as the reference, according to the formula Correct the pseudorange measurement value of the i-th Beidou medium-high orbit satellite to obtain the pseudorange observation value. To eliminate pseudorange error caused by timing deviation; among which For T2 and Time deviation; and according to the formula The carrier phase measurement value of the i-th BeiDou medium-high orbit satellite is corrected to obtain the carrier phase observation value, and the carrier phase error is corrected simultaneously. After correction... and Keep time synchronized.

[0043] The positioning calculation unit of the BeiDou user terminal uses EKF (Extended Kalman Filter) to achieve three-dimensional positioning. The three-dimensional position coordinates of the vehicle in the Earth's inertial coordinate system are obtained by performing EKF iterative calculation. The units are all in meters, where , , These represent the position components of the vehicle in the x-axis, y-axis, and z-axis directions of the Earth's inertial coordinate system. The x-axis points to the vernal equinox; the y-axis lies in the Earth's equatorial plane and is perpendicular to the x-axis, forming a right-handed coordinate system with the x-axis and z-axis; the z-axis coincides with the Earth's rotation axis and represents the vehicle's spatial position related to its altitude.

[0044] S25: BeiDou user terminal provides high-precision, stable fusion timing signals. With vehicle high-precision positioning data The data is encapsulated to obtain a CAN-encapsulated timing and positioning data frame; The CAN data encapsulation unit encapsulates data according to the automotive CAN 2.0B protocol. The encapsulated data includes: frame header, frame ID, data length, etc. (UTC timestamp, format YYYY-MM-DD HH:MM:SS.sssssssss, converted to hexadecimal) (Units are all in m, with 3 decimal places, in hexadecimal representation), checksum, frame tail; the frame ID is a preset unique identifier frame ID, and the data length is denoted as N bytes; Multi-source data fusion can improve the accuracy and reliability of the system. The Kalman filter algorithm has good error suppression effects in time series data fusion, and the extended Kalman filter can effectively solve nonlinear positioning problems. This step uses low-orbit satellites to provide a highly stable timing reference, calibrating the drift and fluctuations of the original BeiDou timing signal, and solving the instability problem caused by obstruction and electromagnetic interference when BeiDou operates alone. After fusion... It retains the absolute high precision of BeiDou and has the high stability of low orbit, meeting the rigid requirements of high-precision and stable synchronization for military vehicle combat coordination and commercial vehicle autonomous driving.

[0045] S3: The Beidou user terminal sends a CAN-encapsulated timing and positioning data frame to the vehicle CAN bus. The vehicle CAN bus performs anti-interference processing and forwards the anti-interference processed CAN-encapsulated timing and positioning data frame to the vehicle information unit. The vehicle information unit verifies and decapsulates the CAN-encapsulated timing and positioning data frame, extracts the timing and positioning data, and completes navigation and location reporting based on the timing and positioning data. The vehicle information unit is the core control unit in the vehicle system responsible for receiving, processing, and applying timing and positioning data; further, it includes the following sub-steps: S31: The Beidou user terminal sends a CAN-encapsulated timing and positioning data frame to the vehicle CAN bus, and the vehicle CAN bus then forwards the CAN-encapsulated timing and positioning data frame to the vehicle information unit. Start the built-in CAN controller of the Beidou user terminal and configure the core parameters that are compatible with the vehicle CAN bus; Preferably, the baud rate of the CAN controller is set to 500kbps, the sampling point is set to 87.5% to balance the transmission rate and anti-interference capability, reduce bit errors caused by signal reflection, and the synchronization jump width (SJW) is set to 1TQ (Time Quantum) to ensure bus synchronization stability.

[0046] The Beidou user terminal will send the CAN-encapsulated timing and positioning data frames to the vehicle's CAN bus via its built-in CAN transceiver. Simultaneously, the Beidou user terminal records the data transmission time. If the Beidou user terminal does not receive a bus acknowledgment signal within 100μs, it will trigger a retransmission mechanism. The number of retransmissions, N ≤ 3, is determined by the formula... = 50μs×(N+1) Dynamically adjusted; Furthermore, when N=1 =100μs, N=2 =150μs, to avoid bus conflicts; if it still fails after 3 retransmissions, the Beidou user terminal records a fault code indicating CAN transmission failure and reports it to the vehicle information unit.

[0047] The vehicle CAN bus uses differential signal transmission to forward the timing and positioning data frames encapsulated in CAN to the vehicle information unit. According to the CAN bus standard, the differential voltage range is set to 2V~3.5V, which can effectively suppress common-mode interference in the vehicle environment. The vehicle CAN bus is equipped with 120Ω terminating resistors at both ends to match the characteristic impedance of the bus, reduce signal reflection, and improve signal integrity.

[0048] The bus gateway associated with the vehicle CAN bus starts the data filtering function, which, based on preset rules, only allows the frame ID that is the unique identifier of the timing and positioning data frame to pass through, filters out irrelevant data, controls the bandwidth utilization of the vehicle CAN bus, and ensures the real-time transmission of timing and positioning data.

[0049] S32: The vehicle information unit receives the CAN-encapsulated timing and positioning data frame, verifies and decapsulates the CAN-encapsulated timing and positioning data frame, and extracts the timing data and positioning data. The vehicle information unit starts its built-in CAN receiver module, configures the parameters exactly the same as the CAN controller, and sets the reception filtering conditions, that is, only receives CAN data frames with the frame ID being the unique identifier frame ID of the timing and positioning data frame and a data length of N bytes, and filters out other irrelevant frames to reduce the load on the information processing unit.

[0050] The CAN receiving module of the vehicle information unit monitors the vehicle CAN bus data in real time through the matching CAN transceiver. When the CAN receiving module detects a data frame that meets the conditions, it triggers the interrupt reception mechanism and transmits the data to the information processing unit of the vehicle information unit within 50μs to ensure that the data is not lost.

[0051] The information processing unit of the vehicle information unit first performs CRC check on the CAN-encapsulated timing and positioning data frame to verify whether the frame ID and data length conform to the CAN-encapsulated timing and positioning data frame. If they do not conform, the frame is determined to be invalid.

[0052] Then, the information processing unit decapsulates the CAN-encapsulated timing and positioning data frame according to the S26 encapsulation format as follows: extracting the fused timing signal. As timekeeping data, convert hexadecimal to decimal, unit: ns; extract... , and As positioning data, convert hexadecimal to decimal, unit m, and retain 3 decimal places.

[0053] If the verification fails, a retransmission request is sent to the BeiDou user terminal. If the number of failures exceeds 5, an alarm is triggered.

[0054] S33: The onboard information unit supports navigation and location reporting functions based on the extracted timing and positioning data; For navigation functions: The information processing unit of the onboard information unit processes the extracted positioning data into the vehicle's three-dimensional positioning coordinates in the Earth's inertial coordinate system. The coordinates are converted to geographic coordinates in the WGS-84 geodetic coordinate system. The information processing unit performs the conversion using the following projection algorithm: longitude ,latitude ,in The longitude of the central meridian. For reference latitude, , Here are the coordinates of the projection origin, and N is the radius of curvature of the Earth ellipsoid, calculated from the WGS-84 ellipsoid parameters. , where a is the semi-major axis of the ellipsoid and e is the eccentricity of the ellipsoid; The information processing unit of the vehicle information unit overlays the converted geographic coordinates onto a 1:10000 electronic map, and generates a driving trajectory based on five consecutive sets of positioning data (with a time interval of 100ms). The trajectory error is determined by the information processing unit according to a formula. calculate; At the same time, the information processing unit of the vehicle information unit combines the preset route coordinates ( , , )to( , , ), through the distance formula The vehicle's deviation distance from the preset route is calculated in real time, and a deviation alarm is triggered by the on-board information unit when d > 5m.

[0055] For the location reporting function: the information processing unit of the vehicle information unit encapsulates the location reporting frame according to the military communication protocol GJB 2077-94. The location reporting frame includes a frame header, vehicle number, and... Geographic longitude L, geographic latitude B, altitude Frame end; The information processing unit of the vehicle information unit first uses the extracted timing data Perform synchronization calibration on the local clock with a calibration period of 1ms to ensure the accuracy of the local clock is consistent with... Consistent; the instant the information processing unit completes the full encapsulation of the location report frame and sends the transmission command to its built-in communication module, the local clock's UTC timestamp at that moment is immediately acquired and recorded as [data missing]. The communication module first The data is sent back to the information processing unit for storage, and then the radio frequency transmission operation of the location report frame is performed. The information processing unit will collect With extraction Substitute into the formula Calculate the reporting delay to ensure that the location data obtained by the command center matches the actual location of the vehicle in real time.

[0056] Furthermore, if If the latency exceeds 50ms, a self-check of the communication module is triggered to investigate reasons such as excessive encapsulation time or radio frequency link congestion. The vehicle information unit reports to the command center periodically through its built-in communication module according to the reporting cycle.

[0057] The CAN bus features strong anti-interference capabilities, stable transmission, low cost, and adaptability to complex in-vehicle environments, conforming to industry standards for in-vehicle data transmission. This step ensures timely and accurate data transmission through parameter optimization and verification mechanisms, effectively delivering the high-precision timing and positioning data fused from the front end to downstream in-vehicle information units. This provides data support for core functions such as military navigation, location reporting, and commercial vehicle dispatching, realizing the practical application of the technical solution.

[0058] The beneficial effects of the high-precision timing and positioning method of Beidou user terminal based on low-orbit high-stability reference are as follows: (1) After receiving the low-orbit satellite signal, the SBOX adopts the MVDR adaptive beamforming algorithm to actively suppress directional interference in the complex electromagnetic environment of the vehicle, and at the same time constructs a highly stable and anti-interference low-orbit timing reference signal; at the same time, the Beidou user terminal introduces the low-orbit satellite signal as an auxiliary stable timing source to generate the optimal time reference; when any signal source fails, it switches to the single-source working mode, and uses the extended Kalman filter to maintain short-term positioning output by relying on motion state prediction when the satellite signal is briefly and completely lost; moreover, through differential signal transmission, terminal impedance matching to suppress common-mode interference and dynamic adjustment retransmission mechanism, it ensures that each data frame can be reliably delivered to the application unit in the harsh electrical environment of the vehicle. In military scenarios, vehicles can maintain navigation guidance and time synchronization in complex environments such as urban street fighting and mountain warfare, avoiding asynchronous combat commands and weapon aiming deviations caused by time interruption, thus improving the effectiveness of battlefield collaborative combat. In commercial vehicle scenarios, when passing through long tunnels or driving in densely populated high-rise areas, the trajectory tracking will not be interrupted due to the loss of Beidou signal. The environmental perception and path planning of autonomous vehicles will remain continuous, greatly reducing scheduling risks and safety hazards. 2) Extended Kalman filter predicts motion state when satellite signals are completely lost. It can not only maintain short-term positioning output, but also continuously iterate and optimize motion parameters such as vehicle speed and acceleration, providing more accurate dynamic reference for autonomous driving path planning, reducing decision deviations caused by positioning interruption, and further improving driving smoothness and safety. (3) The MVDR adaptive beamforming algorithm's ability to suppress directional electromagnetic interference is not only suitable for vehicle environments, but also can resist interference from complex electromagnetic scenarios, enabling the system to be applied to special operation vehicles across boundaries, expanding the applicable scenario boundaries of the technical solution. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the overall workflow of the BeiDou user terminal high-precision timing and positioning method based on a low-orbit, high-stability benchmark according to the present invention. Detailed Implementation

[0060] To provide a further understanding of the purpose, features, and functions of the present invention, detailed descriptions are provided below with reference to specific embodiments.

[0061] likeFigure 1 As shown, the high-precision timing and positioning method for BeiDou user terminals based on a low-orbit, high-stability benchmark includes: S1: SBOX receives low-Earth orbit satellite timing signals and performs anti-interference enhancement processing to obtain anti-interference low-Earth orbit satellite timing signals. And then Delay compensation is performed to obtain the delayed-calibrated low-Earth orbit satellite stable timing signal T1, and T1 is encapsulated into a timing data frame and transmitted to the BeiDou user terminal; this includes the following sub-steps: S11: Start the SBOX low-Earth orbit satellite signal receiving module and configure the parameters; The low-orbit satellite signal receiving module is a core functional unit built into the SBOX (vehicle-mounted satellite communication terminal), which includes a dedicated low-orbit satellite receiving antenna, a low-orbit satellite signal receiving chip, and a signal preprocessing unit.

[0062] Activate the dedicated low-Earth orbit (LEO) satellite receiving antenna and the LEO satellite signal receiving chip, wherein the antenna gain of the dedicated LEO satellite receiving antenna is ≥15dB; then configure the core parameters, setting the receiving frequency band to 1575.42MHz, which is the commonly used center frequency band for LEO timing satellites and matches the satellite transmitter frequency band standard; to avoid interference-induced false acquisition, the signal acquisition threshold needs to be lower than the interference power by 60dB;

[0063] At the same time, the anti-interference preprocessing function of the SBOX low-orbit satellite signal receiving module is enabled. Through the filtering and amplification processing of the signal preprocessing unit, the low-orbit satellite timing signal has a high signal-to-noise ratio and purity before entering the subsequent processing.

[0064] The signal preprocessing unit is responsible for performing preliminary filtering and amplification. After the low-Earth orbit (LEO) satellite signal receiving module is started, the signal preprocessing unit begins operation, performing preliminary processing on the digital signal output from the LEO satellite signal receiving chip; specifically, bandwidth-limited filtering is used, with a filter bandwidth B = 2MHz, and the filtering function is an FIR low-pass filter with a unit impulse response h(n) = , where n is the sampling point index of the discrete time series, representing the nth discrete sampling time in the FIR low-pass filtering process, and the value is a non-negative integer; Fs is the sampling rate of the low-orbit satellite signal receiving module.

[0065] The signal acquisition threshold Pth is set to -120dBm; to achieve distortion-free signal sampling, the sampling rate Fs of the low-orbit satellite signal receiving module is set to 100MHz.

[0066] S12: The low-Earth orbit (LEO) satellite acquires and receives LEO satellite timing signals according to the configured parameters, and performs anti-interference enhancement processing on the timing signals to obtain anti-interference LEO satellite timing signals. ; The low-Earth orbit (LEO) satellite signal receiving module captures the timing signal broadcast by the LEO satellite according to the configured parameters. The timing signal includes a pulse-per-second (PPS) signal, UTC timestamp information, and satellite ephemeris auxiliary data (the ephemeris auxiliary data includes the LEO satellite position). , , )); To address directional electromagnetic interference in the vehicle environment, an adaptive beamforming algorithm using a dedicated low-orbit satellite receiving antenna is employed. The core of the algorithm is the MVDR (Minimum Variance Distortionless Response) criterion. First, a received data vector is constructed by receiving signals through eight antennas. ,in This represents the signal at the m-th sampling point of the k-th antenna. Next, calculate the covariance matrix R= = H represents the conjugate transpose; beamforming weight vector is solved based on the MVDR criterion. ,in The direction of low-orbit satellite signal incidence The guiding vector, j is the imaginary unit, and d is the spacing between antenna elements. This refers to the incident angle of a low-orbit satellite. The antenna element spacing d = λ / 2 = 0.095m, where λ is the wavelength corresponding to the center frequency of the low-orbit satellite timing signal, and λ = = ≈0.19m; the incident angle of the low-orbit satellite It is calculated using real-time ephemeris data.

[0067] Finally, the received data vector is weighted by the weight vector W. After weighted processing, the interference-resistant low-Earth orbit satellite timing signal is obtained. .

[0068] S13: Timing signal from low-Earth orbit satellites after interference suppression Extract the timing parameters of the low-Earth orbit satellite, calculate the signal transmission delay based on the timing parameters, and perform delay compensation to obtain the stable timing signal T1 of the low-Earth orbit satellite after delay calibration; Firstly, the signal separation unit built into the vehicle-mounted satellite communication terminal is used to separate the low-orbit satellite timing signal after interference suppression. Extract the core timing parameters, including: the rising edge time of the low-orbit satellite PPS signal. (Unit: ns, time base: BeiDou system time), the time value corresponding to the original UTC timestamp. (Unit: ns) and satellite ephemeris auxiliary data; The high-precision isothermal crystal oscillator has a long-term frequency stability better than 1× It provides a short-term stable time reference and outputs a 1PPS signal with a pulse width of 100ns.

[0069] Next, the high-precision temperature-controlled crystal oscillator built into the SBOX is activated; the 1PPS signal output by the temperature-controlled crystal oscillator is used as a reference. The time interval measurement unit in the low-orbit satellite signal receiving module is used to measure... Compared with reference benchmark Time difference between 100 sets of time difference data were continuously measured, and random errors were eliminated using a moving average algorithm to obtain the average time difference. ,and The measurement accuracy is ≤50ps; The time interval measurement unit is integrated into the low-orbit satellite signal receiving chip, model TDC-GP22, with a measurement accuracy of 10ps.

[0070] The signal transmission delay, including ionospheric delay, is calculated by combining low-Earth orbit satellite ephemeris data extracted from Y(k). Tropospheric delay and geometric delay Geometric delay R is the straight-line distance between the low-orbit satellite and the vehicle-mounted SBOX, determined by the satellite position in the ephemeris data ( , , ) and the initial positioning position of SBOX ( , , )Calculations show that c is the speed of light 3 × m / s; Ionospheric delay The calculation is performed using the Klobuchar model, and the formula is as follows: )), where A and B are Klobuchar model coefficients (provided by ephemeris data). The latitude of SBOX The reference latitude for the Klobuchar model; Tropospheric delay The calculation is performed using the Saastamoinen model, and the formula is as follows: Where P is the local air pressure, T is the local temperature, and e is the local water vapor pressure, which is collected in real time by the built-in sensor of SBOX; Final Total Delay These delay errors cause the recorded time at the received moment to lag behind the actual satellite launch time. Delay compensation is performed on the low-Earth orbit (LEO) satellite timing signal using a calibration algorithm. This calibration algorithm is integrated into the signal preprocessing unit within the LEO satellite signal receiving module and applies it to Y(k). and After delay compensation and calibration, the stable timing signal T1 of the low-Earth orbit satellite satisfies the following condition: the rising edge time of the PPS signal in T1... The time value corresponding to the UTC timestamp of T1 = - Ensure that the accuracy of T1 is ≤100ns.

[0071] S14: Transmit the delayed-calibrated high-precision timing signal from the low-Earth orbit satellite. The data is encapsulated into a timing data frame and transmitted to the BeiDou user terminal. The SPI high-speed interface is used as the transmission channel, and the SPI interface is configured in master mode. Preferably, the SPI transmission rate is set to 10 Mbps to ensure transmission redundancy.

[0072] High-precision timing signals from low-orbit satellites after delay calibration Encapsulated as a time synchronization data frame, the time synchronization data frame includes a frame header and a timestamp field (i.e., ... UTC time (in ns), checksum, and frame trailer; The checksum is derived using the CRC-16 check algorithm, and the check formula is CRC-16= The initial value is 0xFFFF, and it performs check calculations on all data except the checksum and the frame tail.

[0073] SBOX sends the encapsulated timing data frame to the SPI slave interface of the Beidou user terminal through the SPI interface, and at the same time, it uses the status bits of the SPI to provide feedback on the transmission status, and uses feedback codes to indicate normal or abnormal transmission.

[0074] S1 enhances signal reliability through parameter configuration of the low-Earth orbit satellite signal receiving module and adaptive beamforming algorithm; ensures output accuracy through high-precision temperature-controlled crystal oscillator and delay compensation; and guarantees real-time performance through SPI high-speed interface. It provides a high-precision, interference-resistant auxiliary timing source for BeiDou user terminals.

[0075] S2: The BeiDou user terminal receives the timing data frame, extracts T1 from the timing data frame as a high-stability timing reference, and extracts BeiDou satellite data to form the original BeiDou timing signal T2; then, based on T1, it performs drift calibration and stability compensation on T2 to obtain the compensated original BeiDou timing signal. ; Integration of T1 and To obtain a high-precision and stable fused timing signal Based on High-precision positioning calculations are performed to obtain high-precision vehicle positioning data. Finally, and The data is encapsulated to obtain a CAN-encapsulated timing and positioning data frame; this includes the following sub-steps: S21: The Beidou user terminal receives and verifies the timing data frame transmitted by SBOX, extracts T1 from the timing data frame as a high-stability timing reference, and starts its own Beidou satellite signal reception and data extraction to obtain the original Beidou timing signal T2. The Beidou user terminal receives timing data frames sent by the vehicle-mounted satellite communication terminal through the matching SPI interface, and ensures data validity through the following verification mechanism: (1) The frame verification unit first performs frame header and frame tail matching verification. If they do not match, the frame is directly determined to be invalid. (2) If the frame header and frame trailer match, perform CRC-16 check, with an initial value of 0xFFFF, and iterate through each byte of data other than the checksum and frame trailer: ,in ); (3) If the CRC-16 check result is consistent with the check code in the data frame, and the transmission status feedback code indicates that the transmission is normal, then the Beidou user terminal extracts T1 from the timing data frame and uses T1 as the high-stability timing reference. (4) If the verification fails or the status feedback code indicates a transmission abnormality, the Beidou user terminal sends a retransmission request to the SBOX. If the retransmission fails, the Beidou user terminal records the fault type and temporarily uses its own original Beidou timing signal as a substitute for the high-stability timing reference T1.

[0076] The maximum number of retransmissions for the retransmission request is set to 3, and the timeout period is set to 100μs.

[0077] Then, the BeiDou satellite receiving antenna built into the BeiDou user terminal is activated to receive the positioning and timing signals broadcast by BeiDou medium and high orbit satellites, and the radio frequency signal is converted into an intermediate frequency signal by the radio frequency front end.

[0078] The BeiDou satellite receiving antenna has a gain of 15dB and a receiving frequency band of 1561.098MHz and 1207.14MHz; the intermediate frequency of the intermediate frequency signal is 46MHz; the low-noise amplifier of the radio frequency front end has a gain of 40dB and a noise figure ≤1.5dB.

[0079] The intermediate frequency signal is then sampled and converted into a digital signal using an ADC with a sampling rate of 20MHz. The BeiDou signal processing module of the BeiDou user terminal performs FFT accelerated correlation calculations based on the BeiDou spreading code and the digital intermediate frequency signal, traversing the carrier frequency offset and code phase offset. When the correlation peak exceeds 6 times the noise power, it is determined that the acquisition is successful.

[0080] The BeiDou spreading code has a rate of 1.023MHz and is a B1C code. The carrier frequency offset has a traversal range of ±5kHz and a traversal step size of 100Hz. The code phase offset has a traversal range of 0~10229 chips and a traversal step size of 1 chip.

[0081] Simultaneously, the BeiDou user terminal initiates a 1Hz delay-locked loop to track the phase of the spreading code. The code tracking loop generates three local spreading codes—Early, Prompt, and Late—and performs correlation operations with the received spreading code to obtain three correlation output values ​​E, P, and L. The error signal ℇ is then calculated. The phase of the local spreading code is adjusted in real time to ensure that the instantaneous tributary correlation output P always remains at its maximum value. The phase offset of the local code relative to the received code, after time conversion, is the accurate code delay measurement. (Unit: ns). Complete signal acquisition and tracking, and extract ephemeris data from BeiDou medium and high orbit satellites; Simultaneously, the carrier tracking loop synchronously tracks the carrier phase, and measures the carrier phase at M consecutive sampling times. (Sampling interval 150ns, ADC sampling rate 20 MHz) Perform the following integration: Due to the short period of time The mean approaches 0, and Given a constant integer, fit the integral result as follows: Finally, the integer ambiguity of the i-th Beidou medium-high orbit satellite is obtained. .

[0082] The ephemeris data of the BeiDou medium and high orbit satellites includes the position coordinates of N successfully captured BeiDou high orbit satellites. (i=1,2,...,N), satellite clock bias Klobuchar ionospheric model coefficients and BDT (BeiDou system time) - UTC bias parameters .in, This refers to the instantaneous position coordinates of the i-th Beidou medium-high orbit satellite in the Earth's inertial coordinate system.

[0083] Based on the extracted ephemeris data of BeiDou medium- and high-orbit satellites, the BeiDou signal processing module calculates the pseudorange measurement value of the i-th satellite. Where c is the speed of light 3 × 10 8 m / s, The pseudorange measurement value of the i-th Beidou medium-high orbit satellite The deviation from the actual straight-line distance between the satellite and the BeiDou user terminal is essentially the sum of all error sources during the pseudorange measurement process; the pseudorange measurement value It is an estimated value including errors, obtained by the BeiDou user terminal measuring the distance from the i-th BeiDou medium-high orbit satellite to itself.

[0084] The pseudorange error Including ionospheric delay error and tropospheric delay error The ephemeris data from BeiDou's medium and high orbit satellites will broadcast Klobuchar ionospheric model coefficients A and B. BeiDou user terminals will then combine this data with their own latitude... Longitude λ, substituting it into the Klobuchar model formula ))( (For model reference latitude) The environmental sensors built into the BeiDou user terminal collect real-time local air pressure (P), temperature (T), and water vapor pressure (e), combined with satellite elevation angles. (Calculated from ephemeris data), substituted into the Saastamoinen tropospheric delay model formula get . It is the sum of the ionospheric delay error and the tropospheric delay error mentioned above, that is = + This corrects the discrepancy between the propagation time and the actual distance.

[0085] Simultaneously, the BeiDou signal processing module extracts the carrier phase measurement value of the i-th BeiDou medium-high orbit satellite. ,in The wavelength of the BeiDou B1C band signal. This represents the actual straight-line distance between the satellite and the BeiDou user terminal. For integer ambiguity, The measured carrier phase error.

[0086] Based on the signal tracking and parameter calculation results, the BeiDou signal processing module further generates its own original timing signal T2: first, the precise code delay measurement value output by the code tracking loop. (Unit: ns), combined with satellite clock bias Correcting the actual code delay = - This value is the signal propagation time. = Secondly, the BDT time of the current launch signal of the i-th Beidou medium-high orbit satellite is analyzed from the navigation message. Then the BDT time for the BeiDou user terminal to receive the corresponding signal is = + ; Subsequently, for at least 4 valid satellites Weighted fusion is performed to obtain the average BDT time. Finally, combining the navigation message... ,Will Convert to UTC timestamp (The format is YYYY-MM-DD HH:MM:SS.sssssssss), and at the same time... The rising edge is defined as the exact second, generating a 1PPS signal with a pulse width of 100ns. , UTC timestamp With 1PPS signal The system integrates these components to form BeiDou's own original timing signal T2.

[0087] The pair The weighting criteria for weighted fusion are as follows: when the satellite signal-to-noise ratio (SNR) is ≥ 40dB, the weight of the corresponding satellite is set to 0.8; when the satellite signal-to-noise ratio (SNR) is ≤ 30dB and < 40dB, the weight of the corresponding satellite is set to 0.5; when the satellite signal-to-noise ratio (SNR) is < 30dB, the data of that satellite is discarded.

[0088] S22: The BeiDou user terminal compensates for its own original timing signal T2 based on the highly stable timing reference T1 to obtain the compensated original BeiDou timing signal. ; The rising edge time of the PPS signal is obtained from the high-stability timing reference T1. Time value corresponding to UTC timestamp , by As a synchronization reference, the time difference between the rising edge of PPS and the rising edge of T1 of 50 sets of BeiDou raw timing signals T2 was continuously measured. (k=1,2,...,50), and using the moving average algorithm Eliminate random errors.

[0089] Considering the inherent system delay of signal processing within the BeiDou user terminal (Determined beforehand through calibration experiments), T2 is compensated for linearly as follows: The original timing signal of Beidou after compensation .

[0090] S23: Beidou user terminal integration T1 and The state prediction is iteratively updated to obtain a high-precision, stable fused timing signal. ; The BeiDou user terminal uses the Kalman filter algorithm to fuse T1 and By suppressing single-source timing errors through state prediction and observation updates, high-precision timing output can be achieved.

[0091] Define state variables ,in The time value at time k. The timing drift rate is the rate at which the timing signal changes over time.

[0092] The observation equation is , where the observation vector Observation matrix Observation noise Follows a normal distribution R is the observation noise covariance, based on T1 and Error statistics, R=diag([ ]).

[0093] Then, the Kalman filter update iteration is performed according to the following process (1)-(6): (1) Initialization phase: At the 0th moment of filter start, i.e., k=0, the initial optimal state is determined. and the initial covariance matrix Initial state ,in Take the average of T1 and T2'. Set to 0; initial covariance matrix = A larger initial variance is used to accommodate the state uncertainty at the start of the filter.

[0094] (2) Prediction phase: Based on the optimal state at the previous time step, i.e., time step k-1. Covariance Matrix Calculate the predicted state and predicted covariance at the current time, i.e., time k. Based on The predicted state is obtained by mapping the optimal timing value and drift rate from the previous time step to the current time step using the state transition matrix F, thus reflecting the temporal continuity of the timing state without observation data correction; where the state transition matrix is... ,in The filter period is set to 1ms. based on Predict covariance, combined with The uncertainty of the predicted state is updated by adding the process noise covariance Q. The process noise Q is introduced to compensate for possible random variations in the timing drift rate.

[0095] (3) Residual calculation stage: based on the observation vector at the current time. and predicted state Calculate the observation residuals Residual This reflects the relationship between observed values ​​T1, T2' and predicted values. The greater the deviation, the greater the gap between the predicted state and the actual observation, and the stronger the correction is required.

[0096] (4) Kalman gain update stage: Calculate the Kalman gain If the prediction covariance is small, it indicates that the prediction is reliable. Therefore, the Kalman gain is small, which reduces the correction weight of the observation data. If the observation noise covariance is small, it indicates that the observation is reliable. Therefore, the Kalman gain is large, which enhances the correction effect of the observation data and ensures that the correction process takes into account both the continuity of prediction and the accuracy of observation.

[0097] (5) State update phase: based on Perform optimal state correction using Kalman gain. Weighted residuals For the predicted state Make corrections to obtain the optimal time synchronization state at the current moment; and based on Covariance updates are performed, where I is a second-order identity matrix. The covariance of the optimal state is updated using Kalman gain and the observation matrix to reduce the uncertainty of subsequent predictions and ensure the stability of the filtering process.

[0098] (6) Iteration Termination and Mode Judgment: The above (1)-(5) processes are performed according to the filtering cycle. = Repeat the iteration every 1ms until 5 consecutive optimal states are reached. The change in quantity satisfies , When the filter converges, it is determined that the filter has converged.

[0099] After the filtering converges, the first element of the optimal state vector is extracted as the fused timing signal, i.e. To obtain a high-precision and stable fused timing signal Simultaneously, the accuracy monitoring unit of the Beidou user terminal verifies in real time. The time deviation is the difference from the ideal timing signal, ensuring an accuracy of ≤1ms. If T1 fails, it automatically switches to single-source timing mode. In this mode, the state equation and observation equation retain only the T2' related terms, i.e., the observation vector. The observation matrix H = [1, 0] ensures the continuity of time synchronization.

[0100] S24: BeiDou user terminal combined with high-precision, stable fusion timing signal Achieve high-precision positioning calculation and obtain high-precision vehicle positioning data. ; by Using time as the reference, according to the formula Correct the pseudorange measurement value of the i-th Beidou medium-high orbit satellite to obtain the pseudorange observation value. To eliminate pseudorange error caused by timing deviation; among which For T2 and Time deviation; and according to the formula The carrier phase measurement value of the i-th BeiDou medium-high orbit satellite is corrected to obtain the carrier phase observation value, and the carrier phase error is corrected simultaneously. After correction... and Keep time synchronized.

[0101] The positioning calculation unit of the BeiDou user terminal uses EKF (Extended Kalman Filter) to achieve three-dimensional positioning and defines a state vector. , in the form of Where x, y, z represent the vehicle's position. For vehicle speed; Process noise covariance ; Observation equations Based on pseudorange and carrier phase, specifically , where the observation function for: ( (for BeiDou user terminal clock bias) . To observe the noise, it follows a normal distribution. ,in To observe the noise covariance, based on and The error statistics were obtained; Perform EKF iterations according to the following process (1)-(5): (1) EKF initialization: First, complete the initialization of the EKF core parameters and initialize the state vector to obtain :in For the initial vehicle position estimate, priority is given to using BeiDou satellite ephemeris data and initial pseudorange from S22. The preliminary calculation results are obtained by solving the simultaneous equations of the pseudorange of the three satellites: The calculation yields the result; if no rough calculation data is available, the default setting is the initial installation position calibrated by the Beidou user terminal at the factory. Initially set to 0.

[0102] Initialization of the covariance matrix The initial variance of the position component is set to 100, corresponding to the error range of the rough position calculation; the variance of the velocity component is set to 1 to accommodate the uncertainty of the initial state.

[0103] (2) EKF prediction stage: The core is to calculate the predicted position at the current time based on the optimal position and velocity at the previous time step, specifically including: based on Prior estimates of the state vector are obtained by performing state prediction. ,in ( (where the matrix is ​​a 3rd order identity matrix), the mapping logic for the state vector is as follows: , , (velocity component) (It remains unchanged), that is, by using the optimal position and speed of the previous moment, the predicted position of the current moment is calculated, which reflects the continuity of vehicle movement.

[0104] Based on Perform covariance prediction to obtain a prior estimate of the covariance. Process noise introduces a small variance into the position component to simulate random disturbances in vehicle motion, ensuring that the predicted position does not deviate from the actual motion range.

[0105] (3) Linearize the observation function: Since the observation function The square root containing the position component is a nonlinear function and requires prior estimation of the state vector. The core of linearization is to establish a linear mapping between the state vector and the observation value through the Jacobian matrix J, which provides a mathematical basis for position correction. A Jacobian matrix J with a dimension of 2N×6 is constructed.

[0106] In the 2N×6 Jacobian matrix J, N represents the number of effective BeiDou medium and high orbit satellites, and 2N corresponds to N pseudorange observations. and N carrier phase observations 6 corresponds to the state vector The six components of J; each row of J corresponds to the partial derivative of an observation with respect to the state vector (all partial derivatives are in...). (values ​​are taken at the location), where the velocity component is... It has no direct effect on pseudorange and carrier phase, and its partial derivative is always 0. The complete matrix form is as follows:

[0107] Based on Taylor expansion, the observation function exist The linear approximation for the vicinity is h(X)≈ This transforms nonlinear problems into linear equations; in actual calculations, the EKF update formula is directly used. Subsequently, the position component in the state vector is corrected using Kalman gain.

[0108] (4) EKF update stage: based on the linearized observation equation, combined with the corrected observation values ​​( ), calculate residuals ,in residual It reflects the difference between the observed value corresponding to the predicted position and the actual observed value, and iteratively corrects the predicted position based on the residual; Next, calculate the Kalman gain. : And update the predicted state to obtain the optimal posterior estimated state of the state vector. , The focus is on correcting the position component in the state vector, i.e. as well as ; The first row of the gain matrix corresponds to the corrected weights in the x-direction, making the corrected position closer to the true value; finally, the covariance is also updated. ( (As a 6th-order identity matrix), reducing the variance of the position components reflects the reduced uncertainty of the corrected position.

[0109] (5) Iterative convergence and ( Extraction: Repeat the above process (1)-(4) at a period of 1ms until the change of position components in 5 consecutive iterations meets the requirement. 0.01m 0.01m and When the value is 0.02m, it indicates that the estimated position is close to the actual position of the vehicle, and the filter has converged.

[0110] At this point, the converged state vector is extracted. The first three components, namely The coordinate system is Earth inertial coordinate system 1, which is consistent with the satellite ephemeris coordinate system 1, ensuring the universality of positioning data. Finally, the three-dimensional position coordinates of the vehicle in Earth inertial coordinate system are obtained. The units are all in meters, where , and These represent the position components of the vehicle in the x-axis, y-axis, and z-axis directions of the Earth's inertial coordinate system. The x-axis points to the vernal equinox; the y-axis lies in the Earth's equatorial plane and is perpendicular to the x-axis, forming a right-handed coordinate system with the x-axis and z-axis; the z-axis coincides with the Earth's rotation axis and represents the vehicle's spatial position related to its altitude.

[0111] S25: BeiDou user terminal provides high-precision, stable fusion timing signals. With vehicle high-precision positioning data The data is encapsulated to obtain a CAN-encapsulated timing and positioning data frame; The CAN data encapsulation unit encapsulates data according to the automotive CAN 2.0B protocol. The encapsulated data includes: frame header, frame ID, data length, etc. (UTC timestamp, format YYYY-MM-DD HH:MM:SS.sssssssss, converted to hexadecimal) , , ( The units are all in m, with 3 decimal places, and represented in hexadecimal; check code, frame tail; the frame ID is a preset unique identifier frame ID, and the data length is denoted as N bytes; S3: The Beidou user terminal sends a CAN-encapsulated timing and positioning data frame to the vehicle CAN bus. The vehicle CAN bus performs anti-interference processing and forwards the anti-interference processed CAN-encapsulated timing and positioning data frame to the vehicle information unit. The vehicle information unit verifies and decapsulates the CAN-encapsulated timing and positioning data frame, extracts the timing and positioning data, and completes navigation and location reporting based on the timing and positioning data. This includes the following sub-steps: S31: The Beidou user terminal sends a CAN-encapsulated timing and positioning data frame to the vehicle CAN bus, and the vehicle CAN bus then forwards the CAN-encapsulated timing and positioning data frame to the vehicle information unit. Start the CAN controller built into the Beidou user terminal and configure the core parameters for compatibility with the vehicle CAN bus: set the baud rate of the CAN controller to 500kbps, the sampling point to 87.5% to balance the transmission rate and anti-interference capability, reduce bit errors caused by signal reflection, and set the synchronization jump width (SJW) to 1TQ (Time Quantum) to ensure bus synchronization stability.

[0112] The Beidou user terminal will send the CAN-encapsulated timing and positioning data frames to the vehicle's CAN bus via its built-in CAN transceiver. Simultaneously, the Beidou user terminal records the data transmission time. If the Beidou user terminal does not receive a bus acknowledgment signal within 100μs, it will trigger a retransmission mechanism. The number of retransmissions, N ≤ 3, is determined by the formula... = 50μs×(N+1) Dynamically adjusted; When N=1 =100μs, N=2 =150μs, to avoid bus conflicts; if it still fails after 3 retransmissions, the Beidou user terminal records a fault code indicating CAN transmission failure and reports it to the vehicle information unit.

[0113] The vehicle CAN bus uses differential signal transmission to forward the timing and positioning data frames encapsulated in CAN to the vehicle information unit. According to the CAN bus standard, the differential voltage range is set to 2V~3.5V, which can effectively suppress common-mode interference in the vehicle environment. The vehicle CAN bus is equipped with 120Ω terminating resistors at both ends to match the characteristic impedance of the bus, reduce signal reflection, and improve signal integrity.

[0114] The bus gateway associated with the vehicle CAN bus starts the data filtering function, which, based on preset rules, only allows the frame ID that is the unique identifier of the timing and positioning data frame to pass through, filters out irrelevant data, controls the bandwidth utilization of the vehicle CAN bus, and ensures the real-time transmission of timing and positioning data.

[0115] S32: The vehicle information unit receives the CAN-encapsulated timing and positioning data frame, verifies and decapsulates the CAN-encapsulated timing and positioning data frame, and extracts the timing data and positioning data. The vehicle information unit starts its built-in CAN receiver module, configures the parameters exactly the same as the CAN controller, and sets the reception filtering conditions, that is, only receives CAN data frames with the frame ID being the unique identifier frame ID of the timing and positioning data frame and a data length of N bytes, and filters out other irrelevant frames to reduce the load on the information processing unit.

[0116] The CAN receiving module of the vehicle information unit monitors the vehicle CAN bus data in real time through the matching CAN transceiver. When the CAN receiving module detects a data frame that meets the conditions, it triggers the interrupt reception mechanism and transmits the data to the information processing unit of the vehicle information unit within 50μs to ensure that the data is not lost.

[0117] The information processing unit of the vehicle information unit first performs the following checks on the CAN-encapsulated timing and positioning data frame: verifying whether the frame ID and data length conform to the CAN-encapsulated timing and positioning data frame; if not, it is determined to be an invalid frame; and using the standard check formula CRC-32=X³²+X² 6 +X²³+X²²+X¹ 6 +X¹²+X¹¹+X¹ 0 +X 8 +X 7 +X 5 +X 4 +X²+X+1, with an initial value of 0xFFFFFFFF, iterates through the data bytes other than the checksum and frame tail one by one. If the checksum result matches the checksum in the CAN-encapsulated timing and positioning data frame, it is considered valid.

[0118] Then, the information processing unit decapsulates the CAN-encapsulated timing and positioning data frame according to the S26 encapsulation format as follows: extracting the fused timing signal. As timekeeping data, convert hexadecimal to decimal, unit: ns; extract... , and As positioning data, convert hexadecimal to decimal, unit m, and retain 3 decimal places.

[0119] If the verification fails, a retransmission request is sent to the BeiDou user terminal. If the number of failures exceeds 5, an alarm is triggered.

[0120] S33: The onboard information unit supports navigation and location reporting functions based on the extracted timing and positioning data; S33: The onboard information unit supports navigation and location reporting functions based on the extracted timing and positioning data; For navigation functions: The information processing unit of the onboard information unit processes the extracted positioning data into the vehicle's three-dimensional positioning coordinates in the Earth's inertial coordinate system. The coordinates are converted to geographic coordinates in the WGS-84 geodetic coordinate system. The information processing unit performs the conversion using the following projection algorithm: longitude ,latitude ,in The longitude of the central meridian. For reference latitude, , Here are the coordinates of the projection origin, and N is the radius of curvature of the Earth ellipsoid, calculated from the WGS-84 ellipsoid parameters. , where a is the semi-major axis of the ellipsoid and e is the eccentricity of the ellipsoid; The information processing unit of the vehicle information unit overlays the converted geographic coordinates onto a 1:10000 electronic map, and generates a driving trajectory based on five consecutive sets of positioning data (with a time interval of 100ms). The trajectory error is determined by the information processing unit according to a formula. calculate; At the same time, the information processing unit of the vehicle information unit combines the preset route coordinates ( , , )to( , , ), through the distance formula The vehicle's deviation distance from the preset route is calculated in real time, and a deviation alarm is triggered by the on-board information unit when d > 5m.

[0121] For the location reporting function: the information processing unit of the vehicle information unit encapsulates the location reporting frame according to the military communication protocol GJB 2077-94. The location reporting frame includes a frame header, vehicle number, and... Geographic longitude L, geographic latitude B, altitude Frame end; The information processing unit of the vehicle information unit first uses the extracted timing data Perform synchronization calibration on the local clock with a calibration period of 1ms to ensure the accuracy of the local clock is consistent with... Consistent; the instant the information processing unit completes the full encapsulation of the location report frame and sends the transmission command to its built-in communication module, the local clock's UTC timestamp at that moment is immediately acquired and recorded as [data missing]. The communication module first The data is sent back to the information processing unit for storage, and then the radio frequency transmission operation of the location report frame is performed. The information processing unit will collect With extraction Substitute into the formula Calculate the reporting delay to ensure that the location data obtained by the command center matches the actual location of the vehicle in real time.

[0122] Furthermore, if If the latency exceeds 50ms, a self-test of the communication module is triggered to investigate reasons for excessive delays, such as excessive encapsulation time or radio frequency link congestion. The vehicle information unit reports according to the reporting cycle using its built-in communication module. The system reports to the command center every 5 seconds. The reporting period can be modified by a CAN command issued by the command center. After receiving the command, the information processing unit reconfigures the reporting timer parameters of the communication module to complete the period adjustment.

[0123] The present invention has been described in the above-described embodiments; however, these embodiments are merely examples for implementing the present invention. It must be noted that the disclosed embodiments do not limit the scope of the present invention. Conversely, any modifications and refinements made without departing from the spirit and scope of the present invention are within the scope of patent protection of the present invention.

Claims

1. A high-precision time synchronization and positioning method for BeiDou user terminals based on a low-orbit, high-stability benchmark, characterized in that: Includes the following steps: S1: SBOX receives low-Earth orbit satellite timing signals and performs anti-interference enhancement processing to obtain anti-interference low-Earth orbit satellite timing signals. ; then Delay compensation is performed to obtain the low-orbit satellite stable timing signal T1 after delay calibration, and T1 is encapsulated into a timing data frame and transmitted to the Beidou user terminal. The low-Earth orbit satellite timing signal is broadcast by the low-Earth orbit satellite and includes timing-related signals such as second pulse (PPS) signal, UTC timestamp information, and satellite ephemeris auxiliary data. The SBOX is a vehicle-mounted satellite communication terminal with a built-in low-orbit satellite signal receiving module; the low-orbit satellite signal receiving module includes a dedicated low-orbit satellite receiving antenna, a low-orbit satellite signal receiving chip, and a signal preprocessing unit. The low-Earth orbit (LEO) satellite-specific receiving antenna is a signal receiving component adapted to LEO timing satellite signals; the LEO satellite signal receiving chip converts the radio frequency signals received by the LEO satellite-specific receiving antenna into electrical signals that can be processed by subsequent modules. The signal preprocessing unit is responsible for performing preliminary filtering and amplification of the electrical signals; S2: The BeiDou user terminal receives the timing data frame, extracts T1 from the timing data frame as a high-stability timing reference, and extracts BeiDou satellite data to form BeiDou's own original timing signal T2; Then, based on T1, drift calibration and stability compensation are performed on T2 to obtain the compensated original BeiDou timing signal. ; Integration of T1 and To obtain a high-precision and stable fused timing signal Based on High-precision positioning calculations are performed to obtain high-precision vehicle positioning data. Finally, and Encapsulation is performed to obtain CAN-encapsulated timing and positioning data frames; The high-stability time reference refers to a highly reliable time reference standard used by BeiDou user terminals after validity verification to calibrate their own time signals, support the generation of fused time signals, and perform high-precision positioning calculations. The original timing signal of BeiDou itself is an autonomous timing signal generated by the BeiDou user terminal after receiving the positioning and timing signal of BeiDou medium and high orbit satellites, and after acquisition, tracking and parameter calculation. The vehicle high-precision positioning data Let be the three-dimensional position coordinates of the vehicle in the Earth's inertial coordinate system, where , and These represent the position components of the vehicle in the x-axis, y-axis, and z-axis directions of the Earth's inertial coordinate system. The x-axis points to the vernal equinox; the y-axis lies in the Earth's equatorial plane and is perpendicular to the x-axis, forming a right-handed coordinate system with the x-axis and z-axis; the z-axis coincides with the Earth's rotation axis and represents the vehicle's spatial position related to its altitude. S3: The Beidou user terminal sends a CAN-encapsulated timing and positioning data frame to the vehicle CAN bus. The vehicle CAN bus performs anti-interference processing and forwards the anti-interference processed CAN-encapsulated timing and positioning data frame to the vehicle information unit. The vehicle information unit verifies and decapsulates the CAN-encapsulated timing and positioning data frame, extracts the timing and positioning data, and completes navigation and location reporting based on the timing and positioning data. The vehicle information unit is the core control unit in the vehicle system responsible for receiving, processing, and applying timing and positioning data.

2. The high-precision timing and positioning method for BeiDou user terminals based on a low-orbit, high-stability benchmark as described in claim 1, is characterized in that... Step S1 also includes the following sub-steps: S11: Start the SBOX low-orbit satellite signal receiving module and configure the parameters; S12: The low-Earth orbit (LEO) satellite acquires and receives LEO satellite timing signals according to the configured parameters, and performs anti-interference enhancement processing on the timing signals to obtain anti-interference LEO satellite timing signals. ; S13: Timing signal from low-Earth orbit satellites after interference suppression Extract the timing parameters of the low-Earth orbit satellite, calculate the signal transmission delay based on the timing parameters, and perform delay compensation to obtain the stable timing signal T1 of the low-Earth orbit satellite after delay calibration; S14: Transmit the delayed-calibrated high-precision timing signal from the low-Earth orbit satellite. The data is encapsulated into a timing data frame and transmitted to the BeiDou user terminal. While activating the dedicated low-orbit satellite receiving antenna and high-performance signal receiving chip in S1, the anti-interference preprocessing function of the SBOX low-orbit satellite signal receiving module is also enabled, and the signal is filtered and amplified through the signal preprocessing unit.

3. The high-precision timing and positioning method for BeiDou user terminals based on a low-orbit, high-stability benchmark as described in claim 2, is characterized in that... In step S12, we obtain During the process, an adaptive beamforming algorithm for low-orbit satellite dedicated receiving antennas is used to address directional electromagnetic interference present in the vehicle environment. First, a received data vector is constructed by receiving signals through a dedicated low-Earth orbit satellite receiving antenna. ; Next, calculate the covariance matrix R= H represents conjugate transpose; Solving the beamforming weight vector based on the MVDR criterion ,in The direction of low-orbit satellite signal incidence The guiding vector, j is the imaginary unit, and d is the spacing between antenna elements. This refers to the incident angle of a low-orbit satellite. Finally, After weighted processing, the interference-resistant low-Earth orbit satellite timing signal is obtained. ; Includes the rising edge time of the PPS signal from low-Earth orbit satellites The time value corresponding to the original UTC timestamp Satellite ephemeris auxiliary data.

4. The high-precision timing and positioning method for BeiDou user terminals based on a low-orbit, high-stability reference as described in claim 1 or 2, characterized in that, The delay in the delay compensation specifically includes ionospheric delay. Tropospheric delay and geometric delay The total delay was calculated. ; and for Y(k) and After delay compensation and calibration, the stable timing signal T1 of the low-Earth orbit satellite satisfies the following condition: the rising edge time of the PPS signal in T1... The time value corresponding to the UTC timestamp of T1 = - .

5. The high-precision timing and positioning method for BeiDou user terminals based on a low-orbit, high-stability benchmark as described in claim 1, characterized in that, Step S2 also includes the following sub-steps: S21: The Beidou user terminal receives and verifies the timing data frame transmitted by SBOX, extracts T1 from the timing data frame as a high-stability timing reference, and starts its own Beidou satellite signal reception and data extraction to obtain the original Beidou timing signal T2. S22: The BeiDou user terminal compensates for its own original timing signal T2 based on the highly stable timing reference T1 to obtain the compensated original BeiDou timing signal. ; S23: Beidou user terminal integration T1 and The state prediction is iteratively updated to obtain a high-precision, stable fused timing signal. ; S24: BeiDou user terminal combined with high-precision, stable fusion timing signal Achieve high-precision positioning calculation and obtain high-precision vehicle positioning data. ; S25: BeiDou user terminal provides high-precision, stable fusion timing signals. With vehicle high-precision positioning data The data is encapsulated to obtain a CAN-encapsulated timing and positioning data frame; The process of obtaining the original BeiDou timing signal T2 is as follows: The BeiDou user terminal starts a delay-locked loop with a loop bandwidth of 1Hz to track the phase of the spreading code and obtains the code delay measurement value. ; Satellite clock bias combined with satellite ephemeris data Correcting the actual code delay = - As signal propagation time = ; Secondly, the BDT time of the current signal launched by the i-th Beidou medium-high orbit satellite is analyzed from the navigation message. Then the BDT time for the BeiDou user terminal to receive the corresponding signal is = + ; Subsequently, for at least 4 valid satellites Weighted fusion is performed to obtain the average BDT time. Finally, combining the navigation message... ,Will Convert to UTC timestamp At the same time The rising edge is defined as the exact second, generating a 1PPS signal with a pulse width of 100ns. , UTC timestamp With 1PPS signal The system integrates these components to form BeiDou's own original timing signal T2.

6. The high-precision timing and positioning method for BeiDou user terminals based on a low-orbit, high-stability benchmark as described in claim 5, is characterized in that... In step S2, the... The weighting criteria for weighted fusion are as follows: when the satellite signal-to-noise ratio (SNR) is ≥ 40dB, the weight of the corresponding satellite is set to 0.8; when the satellite signal-to-noise ratio (SNR) is ≤ 30dB and < 40dB, the weight of the corresponding satellite is set to 0.5; when the satellite signal-to-noise ratio (SNR) is < 30dB, the data of that satellite is discarded.

7. The high-precision timing and positioning method for BeiDou user terminals based on a low-orbit, high-stability reference as described in claim 1 or 5, characterized in that, In step S2, the fusion T1 and To obtain a high-precision and stable fused timing signal The state variables are defined using a Kalman filter update iteration method. ,in The time value at time k. The time drift rate is the rate of change of the time signal over time; the observation equation is... , where the observation vector Observation matrix Observation noise Follows a normal distribution R is the observation noise covariance, based on T1 and Error statistics, R=diag([ ]); Perform the Kalman filter update iteration according to the following process (1)-(6): (1) Initialization phase: At the 0th moment of filter start, i.e., k=0, the initial optimal state is determined. and the initial covariance matrix Initial state ,in Take the average of T1 and T2'. Set to 0; initial covariance matrix = ; (2) Prediction phase: Based on the optimal state at time k-1 Covariance Matrix Calculate the predicted state and prediction covariance at time k; based on The predicted state is obtained by mapping the optimal timing value and drift rate of the previous time step to the current time step through the state transition matrix F, thus obtaining the predicted timing state without observation data correction, which reflects the temporal continuity of the timing state. The state transition matrix is: ,in The filter period; based on Predict covariance, combined with The uncertainty of the predicted state is updated by summing the process noise covariance Q. (3) Residual calculation stage: based on the observation vector at the current time. and predicted state Calculate the observation residuals ; (4) Kalman gain update stage: Calculate the Kalman gain This enhances the correction effect of observation data; (5) State update phase: based on Perform optimal state correction using Kalman gain. Weighted residuals For the predicted state Make corrections to obtain the optimal time synchronization state at the current moment; and based on Perform covariance update, where I is a 2-order identity matrix; (6) Iteration Termination and Mode Judgment: The above (1)-(5) processes are performed according to the filtering cycle. Repeat the iteration until five consecutive optimal states are reached. When the change in the value satisfies the preset Kalman convergence condition, the filter is determined to be convergent. After the filtering converges, the first element of the optimal state vector is extracted as the fused timing signal, i.e. To obtain a high-precision and stable fused timing signal Simultaneously, the accuracy monitoring unit of the Beidou user terminal verifies in real time. If the time deviation fails (T1), the system automatically switches to single-source timing mode. In this mode, the state equation and observation equation retain only the T2' related terms, i.e., the observation vector. The observation matrix H = [1, 0].

8. The high-precision timing and positioning method for BeiDou user terminals based on a low-orbit, high-stability benchmark as described in claim 1, is characterized in that... Step S3 also includes the following sub-steps: S31: The Beidou user terminal sends a CAN-encapsulated timing and positioning data frame to the vehicle CAN bus, and the vehicle CAN bus then forwards the CAN-encapsulated timing and positioning data frame to the vehicle information unit. S32: The vehicle information unit receives the CAN-encapsulated timing and positioning data frame, verifies and decapsulates the CAN-encapsulated timing and positioning data frame, and extracts the timing data and positioning data. S33: The onboard information unit supports navigation and location reporting functions based on the extracted timing and positioning data; In S31, the Beidou user terminal will send the CAN-encapsulated timing and positioning data frame to the vehicle's CAN bus via its built-in CAN transceiver. Simultaneously, the Beidou user terminal records the data transmission time. If the Beidou user terminal does not receive a bus acknowledgment signal within 100μs, a retransmission mechanism is triggered. The number of retransmissions, N ≤ 3, and the retransmission interval is determined by the formula... = 50μs×(N+1) Dynamically adjusted; When N=1 =100μs, N=2 =150μs; If the retransmission fails after 3 attempts, the Beidou user terminal will record a fault code indicating CAN transmission failure and report it to the vehicle information unit.

9. The high-precision timing and positioning method for BeiDou user terminals based on a low-orbit, high-stability reference as described in claim 1 or 8, characterized in that, In step S3, when implementing the navigation function: for the extracted positioning data, the information processing unit of the vehicle information unit will calculate the vehicle's three-dimensional positioning coordinates in the Earth's inertial coordinate system. The geographic coordinates are converted to a geodetic coordinate system by the information processing unit using the following projection algorithm: longitude ,latitude ,in The longitude of the central meridian. For reference latitude, , Here are the coordinates of the projection origin, and N is the radius of curvature of the Earth ellipsoid, calculated from the WGS-84 ellipsoid parameters. , where a is the semi-major axis of the ellipsoid and e is the eccentricity of the ellipsoid; The information processing unit of the vehicle information unit overlays the converted geographic coordinates onto a 1:10000 electronic map, which then generates a driving trajectory based on five consecutive sets of positioning data. The trajectory error is determined by the information processing unit according to a formula. calculate; When implementing the location reporting function: the information processing unit of the vehicle information unit encapsulates a location reporting frame, which includes the vehicle number, Geographic longitude L, geographic latitude B, altitude ; The information processing unit of the vehicle information unit first uses the extracted timing data Perform synchronization calibration on the local clock to ensure its accuracy is consistent with... Consistent; the instant the information processing unit completes the full encapsulation of the location report frame and sends the transmission command to its built-in communication module, the local clock's UTC timestamp at that moment is immediately acquired and recorded as [data missing]. The communication module first The data is sent back to the information processing unit for storage, and then the radio frequency transmission operation of the location report frame is performed. The information processing unit will collect With extraction Substitute into the formula Calculate the reporting delay.

10. The high-precision timing and positioning method for BeiDou user terminals based on a low-orbit, high-stability benchmark according to claim 9, characterized in that, like If the delay exceeds 50ms, the communication module will perform a self-check to investigate the cause of the delay exceeding the limit. The vehicle information unit will report to the command center periodically according to the reporting cycle through its built-in communication module.

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