Method for improving ranging accuracy of inter-satellite ranging system for two-way time comparison

Abstract

The application relates to a ranging precision improvement method of an inter-satellite ranging system for two-way time comparison. The method comprises the following steps: first and second satellites establish a two-way link and complete pre-synchronization; the first satellite sequentially transmits a measurement frame and multiple data frames in each second period according to a fixed time sequence, and the first bit of the measurement frame is strictly aligned with a local PPS; the second satellite receives all the frames, acquires high-precision time stamps of the frame headers through symbol timing synchronization, and determines the frame serial numbers; pseudo distances are directly calculated for the measurement frame, and pseudo distances are calculated for the data frames after frame serial number compensation; the pseudo distances of all the frames in the second period are collected, averaged as comprehensive pseudo distances, and framed to the next measurement frame which is transmitted to the first satellite; the comprehensive pseudo distances are exchanged by both sides to calculate the inter-satellite distance. The method breaks through the clock resolution limit, utilizes all transmission frames for statistical averaging, significantly reduces the measurement discreteness, and greatly improves the ranging precision without changing the original system.

Description

Technical Field

[0001] This application relates to the fields of satellite communication and inter-satellite measurement technology, and in particular to a method for improving the ranging accuracy of an inter-satellite ranging system oriented towards two-way time comparison. Background Technology

[0002] With the development of satellite navigation and communication technologies, the accuracy of inter-satellite link measurements has become a key factor restricting the improvement of system performance. Two-way time comparison technology is currently one of the most accurate methods for long-distance time synchronization and distance measurement. Its basic principle is as follows: satellites A and B participating in the comparison use their respective equipment to send measurement signals at the edge of their local PPS and receive measurement signals from each other; by exchanging pseudorange measurement values ​​and equipment delay calibration values, the inter-satellite clock difference and distance can be calculated.

[0003] In inter-satellite ranging systems, an integrated data and measurement approach is typically employed. In existing technologies, only measurement frames are used for ranging, obtaining one pseudorange value per second, while data frames are only used for data transmission and are not utilized.

[0004] However, the existing method has the following drawbacks: ranging accuracy depends on clock resolution. For example, when the system clock is 100MHz, one clock cycle of 10ns corresponds to a distance resolution of about 3 meters, which cannot meet the requirements for higher accuracy. At the same time, ranging is performed using only one measurement frame per second, resulting in large dispersion of measurement results. It is necessary to perform multiple measurements over a long period of time to obtain stable statistical results, which limits the further improvement of ranging accuracy. Summary of the Invention

[0005] Therefore, it is necessary to provide a method for improving the ranging accuracy of inter-satellite ranging systems that can overcome clock resolution limitations, make full use of all transmission frames, and significantly reduce the dispersion of ranging results, in order to address the above-mentioned technical problems.

[0006] A method for improving ranging accuracy in an inter-satellite ranging system for two-way time comparison, wherein the inter-satellite ranging system includes a first satellite and a second satellite, both of which include a transmitter and a receiver, and both the transmitter and receiver are synchronized with a local pulse-per-second (PPS) signal, including: The first and second satellites establish a two-way communication link and complete the initial time pre-synchronization. The transmitting end of the first satellite sends measurement frames and multiple data frames sequentially in each second cycle according to a preset fixed timing sequence. The start of the first bit of the measurement frame is strictly aligned with the rising edge of the local PPS signal. The length of all data frames is the same as that of the measurement frames, and the transmission time of each frame is fixed. The receiver of the second satellite receives all frames sent by the first satellite, performs frame synchronization detection on each frame, and obtains the high-precision timestamp corresponding to the frame header of each frame. The receiver of the second satellite determines the frame number of each received frame within the corresponding second period; The receiver of the second satellite determines the type of the current frame. If the current frame is a measurement frame, the pseudorange measurement value of the current frame is directly calculated based on the high-precision timestamp. If the current frame is a data frame, the pseudorange value of the current frame is calculated after compensating the high-precision timestamp for the frame sequence number based on the frame number of the data frame in the corresponding second period and the fixed transmission duration of each frame. After the current second cycle ends, the receiver of the second satellite collects the pseudorange values ​​corresponding to all frames in the current second cycle, performs statistical processing on the pseudorange values, and obtains the comprehensive pseudorange value for the current second cycle. The transmitter of the second satellite will frame the integrated pseudorange values ​​into the measurement frame of the next second cycle and send it to the first satellite; The first and second satellites exchanged their combined pseudorange values ​​and calculated the distance between the two satellites.

[0007] The above-mentioned method for improving the ranging accuracy of inter-satellite ranging systems for two-way time comparison achieves full reuse of all transmitted frames per second by determining the frame sequence number of the received frame within a second period and distinguishing the frame type, directly calculating the pseudorange for the measurement frame and calculating the pseudorange after compensating the frame sequence number of the data frame. By statistically processing the pseudorange values ​​of all frames within a second period to obtain a comprehensive pseudorange value and exchanging them to calculate the inter-satellite distance, the method significantly reduces the dispersion of the measurement results using the principle of statistical noise reduction, while greatly shortening the measurement time required to achieve the target statistical accuracy. Moreover, the entire scheme does not require changing the original two-way time comparison ranging system or adding additional hardware equipment, resulting in extremely low modification costs and compatibility with existing integrated data measurement inter-satellite link systems. Attached Figure Description

[0008] Figure 1 This is a flowchart illustrating a method for improving the ranging accuracy of an inter-satellite ranging system oriented towards two-way time comparison in one embodiment. Figure 2 This is a schematic diagram of the sending end processing flow in one embodiment; Figure 3 This is a schematic diagram of the receiving end processing flow in one embodiment; Figure 4 This is a schematic diagram of the physical layer transmission frame timing in another embodiment; Figure 5 This is an internal structural diagram of a computer device in one embodiment. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0010] In one embodiment, such as Figure 1 As shown, a method for improving the ranging accuracy of an inter-satellite ranging system for two-way time comparison is provided. The inter-satellite ranging system includes a first satellite and a second satellite, both of which include a transmitter and a receiver. Both the transmitter and receiver are synchronized with a local pulse-per-second (PPS) signal. The method includes the following steps: Step 102: The first satellite and the second satellite establish a two-way communication link and complete the initial time pre-synchronization. The transmitting end of the first satellite sends a measurement frame and multiple data frames in each second cycle according to a preset fixed timing sequence. The first bit of the measurement frame is strictly aligned with the rising edge of the local PPS signal. The length of all data frames is the same as that of the measurement frames, and the transmission time of each frame is fixed.

[0011] This step corresponds to Figure 2 The transmitting end processing flow is shown below. After the bidirectional communication link is established, the initial clock difference between the two satellites is obtained through the first bidirectional time comparison. This clock difference is used to adjust the local time scale, completing the initial pre-synchronization, eliminating the initial clock difference between the two satellites, and ensuring the accuracy of subsequent measurements. The first bit of the measurement frame is strictly aligned with the local PPS signal, providing a unified time reference for all frames within the entire second cycle. All data frames have the same length as the measurement frames and a fixed transmission time, ensuring that the frame transmission sequence has strict periodicity, providing the prerequisite for subsequent ranging using data frames. During idle periods, the transmitting end sends empty frames or other payload data to maintain an uninterrupted link, ensuring the continuity of the measurement process.

[0012] Step 104: The receiver of the second satellite receives all frames sent by the first satellite, performs frame synchronization detection on each frame, and obtains the high-precision timestamp corresponding to the frame header of each frame; the receiver of the second satellite determines the frame sequence number of each received frame within the corresponding second period; the receiver of the second satellite determines the type of the current frame. If the current frame is a measurement frame, the pseudorange measurement value of the current frame is directly calculated based on the high-precision timestamp; if the current frame is a data frame, the pseudorange value of the current frame is calculated after frame sequence number compensation of the high-precision arrival timestamp based on the frame sequence number of the data frame within the corresponding second period and the fixed transmission duration of each frame.

[0013] This step corresponds to Figure 3 The receiver processing flow is shown below. Frame synchronization detection is used to accurately identify the frame header position of each received frame, which is the basis for obtaining an accurate timestamp. Obtaining the high-precision timestamp corresponding to the frame header of each frame specifically includes: performing symbol timing synchronization processing on the received signal to obtain an integer sampling point index and fractional interval; calculating the high-precision timestamp based on the integer sampling point index and fractional interval, thus completely breaking through the limitation of resolution by the system clock frequency.

[0014] In a specific embodiment of this system, the sampling rate is 8MHz, corresponding to a sampling interval of 125ns. Therefore, the minimum time resolution is 125ns / 4096, which is approximately 0.03ns, completely breaking through the 10ns resolution limit of a 100MHz system clock.

[0015] Then, determine the frame sequence number of each received frame within the corresponding second period. Based on the high-precision timestamp corresponding to the frame header of the received frame, determine the second period to which the frame belongs. Based on the number of frames received within the second period, assign frame sequence numbers sequentially. The measurement frame is the first frame sent in each second period, and its frame sequence number is 1. The frame sequence numbers of subsequent data frames are sequentially increased to 2, 3, ..., N, where N is the total number of frames transmitted within each second period.

[0016] The type of the current frame is determined as follows: frames with a sequence number of 1 are measurement frames, and all other frames with a sequence number greater than 1 are data frames. For measurement frames, since their transmission time is strictly aligned with the rising edge of the local PPS and the reference time is 0, the high-precision timestamp is directly used as the pseudorange measurement value for this frame.

[0017] For data frames, their length is the same as that of measurement frames, and the time for transmitting each frame is also fixed. Therefore, the transmission delay of a data frame can be determined simply by knowing its position within one second. That is, assuming the time required to transmit one frame is t, the frame sequence number transmitted within one second is n, and the timestamp of the collected frame header is m, the transmission delay of this frame can be calculated as m-(n-1).

[0018] Step 106: After the current second cycle ends, the receiver of the second satellite collects the pseudorange values ​​corresponding to all frames in the current second cycle, performs statistical processing on the pseudorange values, and obtains the comprehensive pseudorange value of the current second cycle. The transmitter of the second satellite frames the integrated pseudorange value into the measurement frame of the next second cycle and sends it to the first satellite.

[0019] This step corresponds to Figure 4 The diagram shows the timing of the physical layer transmission frames. Traditional schemes only utilize the measurement frame with frame number 1 within each second cycle for ranging; the rest... N -1 data frames were completely unused. This invention utilizes all transmission frames within 1 second (including 1 measurement frame and N-1 data frames) for ranging, significantly increasing the measurement sample size. Specifically: For a given measurement, after 512 consecutive measurements using the traditional method, the standard deviation was 64.024 cm. If 8 measurements were performed per second and averaged, the 512 measurements could be completed in just 64 seconds, reducing the standard deviation to 24.39 cm. If 16 measurements were performed per second and averaged, the 512 measurements could be completed in just 32 seconds, reducing the standard deviation to 15.99 cm. The disadvantages of the traditional method are firstly, its limitation by clock accuracy, and secondly, the large dispersion of pseudorange results per second due to the 1-second measurement interval.

[0020] The method of this application, for measurement frames, is used both for measurement and to transmit measurement information such as pseudorange measured within the current second to the other end. For data frames, their length is the same as the measurement frames, and the transmission time for each frame is also fixed. Therefore, knowing the position of the data frame within one second is sufficient to determine the transmission delay of the data frame. That is, assuming the time required to transmit one frame is... t The sequence number of the frames transmitted within 1 second of this frame is n The timestamp of the collected frame header is m Therefore, the transmission delay of this frame can be calculated as follows: m -( n -1). The advantage of this scheme is that it reduces the number of measurements by 10% within the same time frame. N Next, N The process of processing the measurement results and using them as the measurement result for the current second can greatly reduce data dispersion. For scenarios requiring multiple consecutive measurements, it can shorten the measurement time, effectively reduce the dispersion of measurement results, and improve ranging accuracy.

[0021] The arithmetic mean of the pseudorange values ​​corresponding to all frames within the current second period is taken, and this arithmetic mean is used as the comprehensive pseudorange value for the current second period. According to basic statistical laws, the standard deviation of the measurement result is inversely proportional to the square root of the number of measurements; therefore, increasing the sample size can effectively reduce the dispersion of the measurement results.

[0022] The transmitter of the second satellite frames the calculated composite pseudorange value and other measurement information into a measurement frame for the next second cycle, and sends it to the first satellite at the first rising edge of the first PPS of that second cycle. The first satellite uses the exact same processing procedure as the second satellite to calculate its own measured composite pseudorange value, and then frames and sends it to the second satellite.

[0023] Step 108: The first and second satellites exchange their combined pseudorange values ​​and calculate the distance between the two satellites.

[0024] Let the composite pseudorange value measured by the first satellite be composite pseudorange_A, and the composite pseudorange value measured by the second satellite be composite pseudorange_B. Let the transmission delay of the first satellite be τ_A (transmission) and the reception delay be τ_A (reception). Let the transmission delay of the second satellite be τ_B (transmission) and the reception delay be τ_B (reception). All these equipment delays can be obtained in advance through ground calibration. Since both satellites transmit measurement signals at the same time and travel along the same spatial propagation path, their round-trip propagation delays are approximately equal. Therefore, the inter-satellite distance R is: R = (Comprehensive pseudorange_A + Comprehensive pseudorange_B - τ_A transmission - τ_A reception - τ_B transmission - τ_B reception) × c / 2, where c represents the speed of light.

[0025] Since the composite pseudorange value has undergone statistical smoothing, its random error is significantly smaller than that of a single pseudorange measurement, thus improving the accuracy of the final calculated distance. This method achieves a breakthrough in ranging accuracy through improvements at the signal processing level without altering the original bidirectional comparison system and hardware architecture. It boasts low engineering implementation cost and good compatibility.

[0026] In the above method, firstly, a high-precision timestamp corresponding to the frame header of each frame is obtained. This technique does not rely on integer period counting of the system's working clock, but rather interpolates fractional intervals between sampling points through symbolic timing synchronization, thereby achieving sub-nanosecond time resolution. This directly breaks through the physical limitations of clock resolution, fundamentally solving the constraint of clock resolution on ranging accuracy and improving the timestamp accuracy of a single measurement by more than three orders of magnitude. Secondly, all frames transmitted by the first satellite are received, the frame sequence number of each received frame within the corresponding second period is determined, pseudorange is directly calculated for the measurement frames, and pseudorange is calculated after frame sequence number compensation for data frames. The pseudorange values ​​corresponding to all frames within the current second period are collected and statistically processed to obtain the comprehensive pseudorange. This transforms data frames, which are only used for transmission in traditional techniques, into effective ranging samples, increasing the number of effective ranging measurements per second from 1 to [missing information]. N Then, random noise is reduced by statistical averaging. Based on the statistical principle that variance is inversely proportional to sample size, the standard deviation of the comprehensive pseudorange is reduced to that of the single pseudorange. This application solves the dual technical problems of limited accuracy resolution and large dispersion of measurement results by combining two innovative technologies: high-precision timestamps and full-frame statistical averaging, without changing the original two-way comparison system and hardware costs.

[0027] In one embodiment, obtaining the high-precision timestamp corresponding to the frame header of each frame includes: The received signal is subjected to symbol timing synchronization processing to obtain an integer sampling point index and a fractional interval. A high-precision timestamp is then calculated based on the integer sampling point index and the fractional interval. ; in, For high-precision timestamps, Integer sample point index, For fractional intervals, The sampling interval is denoted as .

[0028] Specifically, symbol timing synchronization is introduced, and interpolation techniques are used to estimate the optimal sampling time between sampling points to obtain fractional intervals. This allows the timestamp accuracy to break through the limitations of the sampling interval, providing high-quality single-measurement samples for subsequent multi-frame averaging.

[0029] In one embodiment, in an FPGA implementation, the fractional interval Quantified as High-precision timestamp The calculation formula is .

[0030] Specifically, this quantization method represents fractional intervals as 12-bit binary numbers, achieving a minimum time resolution of 125ns / 4096 ≈ 0.03ns. In hardware implementation, it is only necessary to... As a fixed-point decimal used in calculations, it consumes low resources and is easy to pipeline design.

[0031] In one embodiment, determining the frame sequence number of each received frame within the corresponding second period includes: The second period to which the received frame belongs is determined based on the high-precision timestamp corresponding to the frame header of the received frame. Based on the number of frames received within the second period, frame sequence numbers are assigned sequentially, with the frame sequence number of the measurement frame being 1, and the frame sequence numbers of subsequent data frames increasing sequentially.

[0032] Specifically, because the transmission time of measurement frames is strictly aligned with PPS, the PPS at the transmitting end starts at 0; data frames follow immediately, and their sequence numbers can be naturally obtained according to the receiving order. For example, transmissions per second... N Frame, then frame number n =1,2,..., N This allocation method is simple and reliable, requiring no additional signaling overhead. It enables the receiver to uniquely determine the position of each data frame within a second, providing accurate information for subsequent frame sequence number compensation. n This avoids compensation errors caused by sequence number misalignment, ensuring that each data frame can be correctly converted into a valid pseudorange sample.

[0033] In one embodiment, based on the frame sequence number of the data frame within the corresponding second period and the fixed transmission duration of each frame, the pseudorange value of the current frame is calculated after frame sequence number compensation of the high-precision arrival timestamp, including: Based on the frame sequence number of the data frame within the corresponding second period and the fixed transmission duration of each frame, the pseudorange value of the current frame is calculated after frame sequence number compensation of the high-precision arrival timestamp: The pseudorange measurement of the data frame = the high-precision arrival timestamp of the data frame. ,in, n The frame number of the data frame within the current second. The fixed duration required to transmit one frame.

[0034] Specifically, since only the measurement frame is aligned with the PPS, the transmission time of the data frame relative to the PPS is... The data frame arrival timestamp recorded by the receiver contains a fixed delay. To ensure it has the same physical meaning as the pseudorange of the measurement frame—the pure propagation delay of the signal from the transmitting antenna to the receiving antenna—this delay must be subtracted. This compensation formula converts the data frame into an effective ranging observation with minimal computational cost—a single subtraction. Compared to simply using the measurement frame, this embodiment increases the number of ranging samples per second from 1 to N. Based on the averaging effect, the ranging random error is reduced to [percentage missing]. .

[0035] In one embodiment, statistical processing is performed on the pseudorange value to obtain a comprehensive pseudorange value for the current second period, including: Take the arithmetic mean of the pseudorange values ​​corresponding to all frames within the current second period, and use the arithmetic mean as the comprehensive pseudorange value for the current second period.

[0036] Specifically, the arithmetic mean is the simplest and most effective statistical processing method, suitable for situations where all measurements are independent and identically distributed, and the noise follows a zero-mean distribution. Since the propagation delay of each frame is the same, and errors such as receiving channel noise and timing jitter are independent, the noise is reduced to its original value. .

[0037] In one embodiment, the symbol timing synchronization processing of the received signal includes: Calculate the interpolation value based on the current fraction interval and the integer part; calculate the timing error signal using the interpolation value; smooth the timing error signal to generate a control signal; and update the fraction interval according to the control signal using the interpolation controller. and integer sample point index .

[0038] Specifically, smoothing the timing error signal to generate a control signal includes: using a second-order proportional-integral (PI) loop filter, whose discrete-time recursive equation is: ; in ; . For loop bandwidth, The damping coefficient is... For loop gain, the damping factor is typically used. The loop filter can smooth noise in the timing error signal, generate a stable control signal, and ensure the convergence and stability of the timing synchronization loop.

[0039] In one embodiment, calculating the interpolation value based on the current fractional interval and the integer part includes: The interpolation value is calculated based on the current fractional interval and the integer part: ; in, It depends on the fractional interval The filter coefficients, Integer sample point index, For the first The value of each sampling point, It is the half-length parameter of the interpolation filter.

[0040] Specifically, by designing the filter coefficients as The polynomial function can calculate interpolated values ​​at arbitrary fractional intervals in real time without storing a large number of coefficient tables, making it very suitable for FPGA implementation. High-precision interpolation can be achieved with only a small number of multipliers and adders. This embodiment enables the symbol timing synchronization loop to dynamically adjust the interpolation phase within each symbol period, achieving accurate tracking of the optimal sampling time of continuous waveforms. This is one of the core technologies for overcoming clock resolution limitations.

[0041] In one embodiment, calculating the timing error signal using the interpolation includes: For the k The timing error signal is calculated using the interpolation of the given symbols as follows: ; in, and They are the first n I-channel and Q-channel baseband signals at each sampling point The symbol sampling period, i.e., the interpolation period. It is the first The ideal sampling time for each symbol It is the first and the The intermediate moment of a symbol.

[0042] Specifically, the timing error is estimated by using the difference between the middle sampling point of each symbol and the sampling points of the preceding and following symbols, which avoids complex data decision-making or pilot assistance, reduces the implementation complexity, and at the same time ensures the linear range and convergence speed of timing error detection.

[0043] In one embodiment, the fractional interval is quantized into 4096 equally spaced discrete values, with a minimum time resolution of [missing value]. .

[0044] Specifically, this quantization precision meets the requirements of high-precision ranging without excessively consuming hardware resources. Compared to floating-point arithmetic, fixed-point quantization is more suitable for pipelined processing in FPGAs, ensuring that the symbol timing loop can be updated within each sampling period, achieving real-time synchronization.

[0045] It should be understood that, although Figure 1 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order in which these steps are executed, and they can be performed in other orders. Figure 1 At least some of the steps in the process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.

[0046] In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as follows: Figure 5 As shown, the computer device includes a processor, memory, network interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The network interface is used for communication with external terminals via a network connection. When the computer program is executed by the processor, it implements a method for improving the ranging accuracy of an inter-satellite ranging system oriented towards two-way time comparison. The display screen can be an LCD screen or an e-ink screen. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad mounted on the computer device casing, or an external keyboard, touchpad, or mouse.

[0047] Those skilled in the art will understand that Figure 5 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0048] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0049] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0050] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for improving ranging accuracy in an inter-satellite ranging system for two-way time comparison, wherein the inter-satellite ranging system includes a first satellite and a second satellite, each of which includes a transmitter and a receiver, and both the transmitter and receiver are synchronized with a local pulse-per-second (PPS) signal, characterized in that... include: The first and second satellites established a two-way communication link and completed the initial time pre-synchronization. The transmitter of the first satellite transmits measurement frames and multiple data frames sequentially in each second cycle according to a preset fixed timing sequence. The first bit of the measurement frame is strictly aligned with the rising edge of the local PPS signal. All data frames have the same length as the measurement frames, and the transmission time of each frame is fixed. The receiver of the second satellite receives all frames sent by the first satellite, performs frame synchronization detection on each frame, and obtains the high-precision timestamp corresponding to the frame header of each frame. The receiver of the second satellite determines the frame number of each received frame within the corresponding second period; The receiver of the second satellite determines the type of the current frame. If the current frame is a measurement frame, the pseudorange measurement value of the current frame is directly calculated based on the high-precision timestamp. If the current frame is a data frame, the pseudorange value of the current frame is calculated after compensating the high-precision timestamp based on the frame sequence number of the data frame in the corresponding second period and the fixed transmission duration of each frame. After the current second cycle ends, the receiver of the second satellite collects the pseudorange values ​​corresponding to all frames in the current second cycle, performs statistical processing on the pseudorange values, and obtains the comprehensive pseudorange value of the current second cycle. The transmitter of the second satellite frames the integrated pseudorange value into the measurement frame of the next second cycle and sends it to the first satellite; The first and second satellites exchange their combined pseudorange values ​​and calculate the distance between the two satellites. Specifically, based on the frame sequence number of the data frame within the corresponding second period and the fixed transmission duration of each frame, the pseudorange value of the current frame is calculated after frame sequence number compensation of the high-precision arrival timestamp, including: Based on the frame sequence number of the data frame within the corresponding second period and the fixed transmission duration of each frame, the pseudorange value of the current frame is calculated after frame sequence number compensation of the high-precision arrival timestamp: The pseudorange measurement of the data frame = the high-precision arrival timestamp of the data frame - ( n -1)× ,in, n The frame number of the data frame within the current second. The fixed duration required to transmit one frame; The pseudorange values ​​are statistically processed to obtain the comprehensive pseudorange value for the current second period, including: Take the arithmetic mean of the pseudorange values ​​corresponding to all frames within the current second period, and use the arithmetic mean as the comprehensive pseudorange value for the current second period.

2. The method according to claim 1, characterized in that, Obtain the high-precision timestamp corresponding to the frame header of each frame, including: The received signal is subjected to symbol timing synchronization processing to obtain an integer sampling point index and a fractional interval. A high-precision timestamp is then calculated based on the integer sampling point index and the fractional interval. in, For high-precision timestamps, Integer sample point index, For fractional intervals, The sampling interval is denoted as .

3. The method according to claim 1, characterized in that, Determine the frame sequence number of each received frame within the corresponding second period, including: The second period to which the received frame belongs is determined based on the high-precision timestamp corresponding to the frame header of the received frame. Based on the number of frames received within the second period, frame sequence numbers are assigned sequentially, with the frame sequence number of the measurement frame being 1, and the frame sequence numbers of subsequent data frames increasing sequentially.

4. The method according to claim 2, characterized in that, The symbol timing synchronization processing of the received signal includes: Calculate the interpolation value based on the current fraction interval and the integer part; calculate the timing error signal using the interpolation value; smooth the timing error signal to generate a control signal; and update the fraction interval according to the control signal using the interpolation controller. and integer sample point index .

5. The method according to claim 4, characterized in that, The interpolation is calculated based on the current fractional interval and the integer part, including: The interpolation value is calculated based on the current fractional interval and the integer part. in, It depends on the fractional interval The filter coefficients, Integer sample point index, For the first The value of each sampling point, It is the half-length parameter of the interpolation filter.

6. The method according to claim 5, characterized in that, The timing error signal is calculated using the interpolation, including: For the k The timing error signal is calculated using the interpolation of the given symbols as follows: in, and They are the first n I-channel and Q-channel baseband signals at each sampling point The symbol sampling period, i.e., the interpolation period. It is the first The ideal sampling time for each symbol It is the first and the The intermediate moment of a symbol.

7. The method according to claim 5, characterized in that, The fractional intervals are quantized into 4096 equally spaced discrete values, with a minimum time resolution of [missing value]. .

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