Low-orbit satellite navigation enhanced signal capturing method based on high and medium orbit assistance

Abstract

The invention relates to the field of satellite navigation and low-orbit satellite service application, and provides a low-orbit satellite navigation enhanced signal capturing method based on high and middle orbit assistance. According to the method, the signal features and enhancement application modes of the navigation enhancement signals are fully analyzed for meeting the requirement for engineering implementation of receiving and processing of the low-orbit satellite navigation enhancement signals, and dynamic estimation and correction of the low-orbit satellite navigation enhancement signals are achieved in a high-and-medium-orbit constellation space-time information assisting mode. Therefore, the dynamic pressure, the time pressure and the logic resource pressure of signal capture are reduced. High-sensitivity and high-resolution capture processing of low-orbit high-dynamic signals is realized by matching with a two-dimensional correlation capture method of frequency domain zero-fill segmentation matched filtering, carrier Doppler and pseudo code phases of the signals are obtained through peak judgment, and finally, capture processing work of high-dynamic low-orbit satellite navigation enhanced signals is realized. The method is of great significance to development of a low-orbit satellite navigation enhanced receiver and construction of a high, medium and low-orbit collaborative navigation constellation in China.

Description

Technical Field

[0001] The present invention relates to the field of satellite navigation and low-orbit satellite service applications, and proposes a low-orbit satellite navigation enhanced signal acquisition method based on high and medium orbit assistance. Background Art

[0002] As an important space-time infrastructure in the information age, the Global Navigation Satellite System (GNSS) can provide high-quality positioning, navigation and timing services to users around the world, and plays an important supporting role in the military, industrial, scientific, financial, consumer and other fields. In recent years, with the continuous expansion of satellite navigation application services and the increasing demand for satellite navigation services from users, high-performance navigation services with high precision and strong robustness as the goal are gradually becoming standard. Various navigation augmentation systems and technologies such as Precise Point Positioning (PPP), Real-time Kinematic Carrier Phase Differential (RTK), Ground-Based Augmentation System (GBAS), and Satellite-Based Augmentation System (SBAS) have made great progress. However, on the road of satellite navigation enhancement development, these navigation augmentation systems and technologies have the problems of "fragmentation" and "patch" construction, and all have certain limitations, which cannot meet the needs of the vast number of users around the world for high-performance navigation services.

[0003] Low-orbit satellite constellations move fast and at low cost. Using them as space-based platforms for satellite navigation enhancement and high-precision services can achieve global coverage without relying on dense ground stations, and achieve real-time convergence of navigation signal enhancement and high-precision services. It is expected to solve the bottleneck of current high-performance navigation services and become an important development direction for the next generation of satellite navigation systems. With the vigorous development of large-scale low-orbit constellations such as Iridium, Starlink, OneWeb, and Telesat, navigation enhancement applications based on low-orbit satellites have become the most promising solution for future navigation enhancement and high-precision services. At present, various low-orbit satellite constellations make full use of the advantages of low-orbit constellations' global coverage, strong signal landing power, and rapid convergence of high-precision positioning to deploy satellite navigation signal enhancement and precision enhancement and other satellite navigation application services, and improve the system performance and comprehensive service capabilities of satellite navigation.

[0004] Low-orbit satellite navigation enhancement is a space-based navigation signal source based on a low-orbit constellation. The signal fully utilizes the advantages of the low-orbit constellation's proximity to the earth, small signal spatial attenuation, and strong ground transmission power to achieve satellite navigation enhancement. Through satellite navigation enhancement, user positioning accuracy and anti-interference capabilities are enhanced, thereby improving the high-performance service capabilities of the satellite navigation system. While fully enjoying the advantages of low-orbit satellite signals with small spatial attenuation and fast changes in constellation geometric configuration, the high dynamics and increased radial Doppler of low-orbit satellite navigation enhancement signals have become difficulties in signal capture and processing. Low-orbit satellites have a fast operating speed and a short visible time. If they are faced with the long-term capture brought by high-dynamic signals, it will have a huge impact on the use efficiency of low-orbit satellite navigation signals. Therefore, there are certain limitations in processing the capture and processing of high-dynamic low-orbit satellite navigation enhancement signals according to the traditional satellite navigation signal capture method.

[0005] 1. The dynamic expansion of low-orbit satellite navigation enhancement signals is more than ten times that of traditional satellite navigation signals. If traditional navigation signal acquisition methods such as time domain, frequency domain, and matched filtering are used, the signal search frequency domain range is large and the acquisition time is long, which will form an irreconcilable contradiction with the visible time of low-orbit satellites;

[0006] 2. In the face of the high-dynamic capture requirements of low-orbit satellite navigation enhancement signals, expanding the two-dimensional correlation search range in the code domain and frequency domain is the only way to achieve engineering implementation. However, the way of expanding the two-dimensional correlation search results in a huge overhead of hardware logic resources, low computing efficiency, and weak engineering implementation.

[0007] 3. When capturing high-dynamic signals of low-orbit satellite navigation enhancement, no matter what capture method is used, the frequency domain loss caused by signal dynamics will become an inevitable problem in signal capture. When traditional navigation signal capture methods capture high-dynamic low-orbit satellite navigation enhancement signals, the reduced sensitivity caused by frequency domain loss will directly restrict the application scenarios of low-orbit satellite navigation enhancement;

[0008] How to achieve the capture and processing of high-dynamic low-orbit satellite navigation enhancement signals is the design basis for satellite navigation receivers to process low-orbit satellite navigation enhancement signals and is the key to realizing low-orbit satellite navigation enhancement applications. Solving the engineering implementation difficulties of high-dynamic capture and processing of low-orbit satellite navigation enhancement signals is of great significance to promoting the systematic integration and application of high, medium and low-orbit satellite navigation. Research on high-dynamic capture and processing methods for low-orbit satellite navigation enhancement signals is of great significance to the development of low-orbit satellite navigation enhancement receivers and the construction of my country's high, medium and low-orbit collaborative navigation constellations, while improving the accuracy, integrity, availability and anti-interference capabilities of my country's integrated navigation, positioning and timing (PNT) service system. Summary of the invention

[0009] The method of the present invention mainly aims at the problems of large Doppler frequency shift and short visibility time of low-orbit satellite navigation enhancement signals, and innovatively utilizes the navigation enhancement working mode of low-orbit satellites to solve the engineering implementation difficulties such as long signal capture time, low capture sensitivity and large logic resource overhead caused by Doppler frequency shift in the capture process of high dynamic signals. It provides an engineering solution for the development of low-orbit satellite navigation receivers and the system construction of high, medium and low orbit collaborative navigation.

[0010] The present invention fully analyzes the signal characteristics and application modes of low-orbit satellite navigation enhancement signals, and uses the existing high and medium orbit satellite navigation constellations and traditional navigation signal capture processing as a basis to propose a low-orbit satellite navigation enhancement signal capture method based on high and medium orbit assistance. The method makes full use of the prior space-time information of high and medium orbit satellites to estimate the signal Doppler of low-orbit satellites, thereby realizing high-dynamic capture of low-orbit satellite enhancement signals.

[0011] The technical solution adopted by the present invention is:

[0012] A method for capturing enhanced signals of low-orbit satellite navigation based on high and medium orbit assistance comprises the following steps:

[0013] (1) Receive all visible satellite navigation signals in space, convert them into baseband signals through the RF front end, and then sample the baseband signals to obtain digital satellite navigation baseband signals;

[0014] (2) According to the satellite navigation signal reception and processing mode, the high-mid orbit satellite navigation enhancement signal in the digital satellite navigation baseband signal is sequentially captured and tracked, and the message is demodulated and the positioning is solved;

[0015] (3) Based on the positioning solution processing results, the receiver is positioned to obtain the receiver's time, position and satellite almanac information;

[0016] (4) Performing time synchronization for capturing low-orbit satellite navigation enhancement signals based on time information, determining the satellite number and satellite position of visible low-orbit satellites based on the satellite almanac, and performing Doppler dynamic prediction of low-orbit satellite navigation enhancement signals using the satellite position of the low-orbit satellite and the receiver position;

[0017] (5) After completing the Doppler dynamic prediction of the low-orbit satellite navigation enhancement signal, the frequency domain zero-filling segmented matched filtering capture method is used to perform a two-dimensional correlation capture search in the code domain and frequency domain on the low-orbit satellite navigation enhancement signal, and the carrier Doppler and pseudo-code phase of the signal are obtained through frequency domain peak judgment, finally completing the capture and processing of the low-orbit satellite navigation enhancement signal.

[0018] Furthermore, in step (4), the specific process of using the satellite position of the low-orbit satellite and the receiver position to perform Doppler dynamic prediction of the low-orbit satellite navigation enhancement signal is as follows:

[0019] The satellite position and receiver position of the low-orbit satellite are used to obtain the satellite speed and signal arrival angle, and then the Doppler dynamic prediction of the low-orbit satellite navigation enhancement signal is performed according to the following formula:

[0020]

[0021] In the formula, f d is the signal Doppler, V s is the satellite speed, R e is the radius of the Earth,

[0022] R s is the satellite's geocentric height, θ is the signal arrival angle, and f c is the carrier frequency, c is the speed of light;

[0023] The signal Doppler is then converted into dynamic parameters of the local carrier and pseudo code in the satellite navigation signal receiving and processing mode, and the carrier NCO and pseudo code NCO are compensated.

[0024] Furthermore, the specific process of step (5) is as follows:

[0025] (501) After multiplying the low-orbit satellite navigation enhancement signal of length N with the local carrier and performing digital down-conversion, the signal is divided into P equal segments, and enters P partial matched filters to perform correlation matching using the local pseudo code sequence, then N=P*X, where X is the number of correlation points of each matched filter;

[0026] (502) Perform a K-point FFT on the correlation integral results of the matched filter at the same position in each section. If the maximum value after FFT modulus calculation exceeds the set threshold, it is determined that the capture is successful and enters the tracking phase to obtain the carrier Doppler and pseudo code phase of the signal; otherwise, the local pseudo code sequence is moved by one code chip and returns to step (501), finally completing the capture process of the low-orbit satellite navigation enhancement signal.

[0027] Compared with the conventional navigation signal acquisition method in the background art for capturing high-dynamic low-orbit satellite navigation enhancement signals, the present invention has the following advantages:

[0028] 1. Aiming at the enhanced application mode of low-orbit satellite navigation enhancement signals, the present invention innovatively proposes to use the spatiotemporal information of high and medium-orbit satellites to assist the high-dynamic capture of low-orbit satellites, thereby achieving rapid and accurate capture of low-orbit satellite navigation enhancement signals and providing a time guarantee for the service availability of low-orbit satellite navigation enhancement.

[0029] 2. Based on the assistance of high and medium orbit constellation time, position and almanac, the present invention reduces the capture range of high-dynamic low-orbit satellite navigation enhancement signals by more than ten times, reduces the complexity and logic resource scale of high-dynamic low-orbit satellite navigation enhancement signal capture units, improves the signal capture sensitivity, and provides engineering guarantees for the design of low-orbit satellite receivers and the application of low-orbit satellite navigation enhancement services.

[0030] 3. Based on the traditional satellite navigation time domain capture and frequency domain capture, the present invention innovatively proposes a capture method of frequency domain zero-filling segmented matched filtering. Without increasing logic resources, the parallel computing efficiency of signal capture is improved, the frequency domain loss caused by signal dynamics is reduced, the resource usage is small, the computing efficiency is high, and an efficient solution is provided for the capture of high-dynamic low-orbit satellite navigation signals.

[0031] 4. The present invention solves the engineering application problem of high-dynamic capture of low-orbit satellite navigation enhancement signals by means of high- and medium-orbit spatiotemporal information assistance and frequency-domain zero-filling segmented matching filtering fusion, providing a receiver engineering implementation approach for realizing low-orbit satellite navigation enhancement services and low-orbit fusion application services.

[0032] 5. The present invention is applicable to high dynamic signals of all low-orbit satellites, such as low-orbit satellite navigation enhancement, low-orbit precise single-point positioning and low-orbit satellite communications. It has a wide range of applications and has good engineering realization and industrial promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention is a flow chart of low-orbit satellite navigation enhanced signal capture based on high and medium orbit assistance. DETAILED DESCRIPTION

[0034] Reference Figure 1 The present invention mainly aims at the capture problems of low-orbit satellite navigation enhancement signals, such as large dynamic range, wide search frequency domain range, long capture time, and large scale of logical resources occupied by capture. It gives full play to the spatiotemporal information auxiliary advantages of high and medium orbit satellites, integrates the improved method of traditional satellite navigation signal capture and processing, and proposes a low-orbit satellite navigation enhancement signal capture method based on high and medium orbit assistance.

[0035] The method first receives the space satellite navigation signal according to the normal navigation signal processing mode, and converts the frequency into the intermediate frequency signal through the radio frequency front end. After sampling the intermediate frequency signal, it performs orthogonal digital frequency conversion processing to obtain the digital baseband signal, and enters the navigation signal baseband processing flow; secondly, the navigation signal of the high and medium orbit satellite is processed. According to the traditional navigation reception and processing mode, the signal capture and tracking unit of the receiver is started, and the high and medium orbit satellites are sequentially captured and tracked according to the satellite numbers, and the reception and processing of all visible high and medium orbit satellite navigation signals in space are completed; after completing the reception and processing of the high and medium orbit satellites, the high and medium orbit satellites are demodulated and the positioning solution is processed according to the conventional data processing mode, and the time, position and satellite almanac of the receiver in the high and medium orbit constellation working mode are obtained; according to the satellite almanac, it is determined whether there is a visible low-orbit satellite in the receiver's field of view. If there is no low-orbit satellite, the low-orbit satellite navigation enhancement signal capture is not started, and the low-orbit satellite navigation enhancement mode is not entered. If there is a low-orbit satellite, the low-orbit satellite navigation enhancement signal capture mode is started; after starting the low-orbit satellite navigation enhancement signal capture mode, the dynamic Doppler estimation of the low-orbit satellite navigation enhancement signal is completed based on the low-orbit satellite position and the receiver position in the satellite almanac; the dynamic parameters of the carrier and pseudo code NCO in the signal baseband unit are corrected according to the Doppler estimation value, the capture dynamic range of the low-orbit satellite navigation enhancement signal is reduced, the capture time is reduced, and the capture probability is increased; after successfully completing the Doppler estimation correction of the low-orbit satellite navigation enhancement signal, the capture of the signal is started. The signal is searched two-dimensionally in the code domain and the frequency domain by using the capture method of frequency domain zero-filling segmented matched filtering, and the carrier Doppler and pseudo code phase of the signal are obtained by frequency domain peak judgment, and finally the capture and processing of the high-dynamic low-orbit satellite navigation enhancement signal is completed.

[0036] Attached Figure 1 This is a flow chart of low-orbit satellite navigation enhancement signal capture based on high- and medium-orbit assistance. In the specific implementation example, it is assumed that there are 12 high- and medium-orbit navigation satellites and 2 low-orbit navigation enhancement satellites in the field of view, where the signal of the navigation enhancement satellite is 1575.42MHz and the code rate is 10.23Mcps. This is used as an example to analyze the high-dynamic low-orbit satellite navigation enhancement signal capture method. The steps of the high-dynamic low-orbit satellite navigation enhancement signal capture processing method are as follows:

[0037] Step 1: Receive all visible satellite navigation signals in space according to the normal navigation signal processing mode of the receiver, and convert them into intermediate frequency signals through the RF front end. After sampling the intermediate frequency signals, perform orthogonal digital frequency conversion processing to obtain digital satellite navigation baseband signals, and transfer them to the navigation signal baseband processing flow;

[0038] Step 2: Set up the capture unit in the receiver baseband signal processing, and sequentially capture the high- and medium-orbit satellite navigation enhancement signals in the digital satellite navigation baseband signal according to the traditional satellite navigation reception and processing mode, and transfer the captured satellites to tracking processing. After the baseband signal processing of the high- and medium-orbit satellites, the capture and tracking processing of the navigation signals of all 12 visible high- and medium-orbit satellites in space is completed;

[0039] Step 3: After receiving and processing all visible high- and medium-orbit satellites in space, the visible high- and medium-orbit satellites are demodulated and positioned according to the conventional data processing mode. The receiver's positioning is completed based on 12 high- and medium-orbit satellites to obtain the receiver's time, position, and satellite almanac information.

[0040] Step 4: Based on the time information, the time synchronization of the low-orbit satellite navigation enhancement signal acquisition is performed. The satellite number and satellite position of the visible low-orbit satellite are determined based on the satellite almanac. The satellite position of the low-orbit satellite and the receiver position are used to obtain the satellite running speed and signal arrival angle. Then, the Doppler dynamic prediction of the low-orbit satellite navigation enhancement signal is completed according to the following formula:

[0041]

[0042] Among them, f d is the signal Doppler, V s is the satellite speed, R e is the radius of the Earth,

[0043] R s is the satellite's geocentric height, θ is the signal arrival angle, and f c is the carrier frequency and c is the speed of light.

[0044] After calculation, the orbital Doppler values ​​of the two low-orbit satellites relative to the receiver are +35KHz and -41KHz respectively. Based on the Doppler estimation, the Doppler adjustment of the carrier NCO in the digital frequency conversion processing is corrected respectively. At the same time, the dynamic correction of the pseudo code is calculated based on the Doppler estimation to be 227Hz and 266Hz respectively, and the dynamic adjustment of the pseudo code NCO is corrected synchronously. After the estimation correction, the dynamic capture range of the low-orbit satellite navigation enhancement signal is reduced from ±50KHz to ±5KHz. The dynamic range of the capture search is greatly reduced, the capture time is shortened, and the capture probability is increased;

[0045] Step 5. After completing the Doppler dynamic prediction of the low-orbit satellite navigation enhancement signal, start capturing the signal. In signal capture, in order to cope with the frequency domain loss caused by the dynamics of the signal and improve the capture sensitivity, a frequency domain zero-filled segmented matched filtering capture method is designed based on the traditional navigation signal capture method. A pseudo code period is divided into code segments with a length of 80 code chips and matched with the input signal. Then, 128 matching results are padded with 128 zeros. After 256 data bits are gathered, a 256-point frequency domain peak search is performed to complete the two-dimensional correlation search of the signal code domain and frequency domain, and the signal's carrier Doppler and pseudo code phase are obtained. Finally, the capture, reception and processing of the high-dynamic low-orbit satellite navigation enhancement signal are completed. The frequency domain zero-filled segmented matched filtering process not only improves the signal capture sensitivity and capture frequency resolution, but also reduces the capture logic resource overhead of dynamic signals. The specific process is:

[0046] (501) After multiplying the low-orbit satellite navigation enhancement signal of length N with the local carrier and performing digital down-conversion, the signal is divided into P equal segments, and enters P partial matched filters to perform correlation matching using the local pseudo code sequence, then N=P*X, where X is the number of correlation points of each matched filter;

[0047] (502) Perform a K-point FFT on the correlation integral results of the matched filter at the same position in each section. If the maximum value after FFT modulus calculation exceeds the set threshold, it is determined that the capture is successful and enters the tracking phase to obtain the carrier Doppler and pseudo code phase of the signal; otherwise, the local pseudo code sequence is moved by one code chip and returns to step (501), finally completing the capture process of the low-orbit satellite navigation enhancement signal.

[0048] The working principle of the present invention is as follows:

[0049] The present invention proposes a method for capturing low-orbit satellite navigation enhancement signals based on high and medium orbit assistance. This method is aimed at the engineering realization requirements of low-orbit satellite navigation enhancement signal reception and processing, fully analyzes the signal characteristics and enhancement application mode of the navigation enhancement signal, and uses the spatial and temporal information of high and medium orbit constellations to realize the dynamic estimation and correction of low-orbit satellite navigation enhancement signals, thereby reducing the dynamic pressure, time pressure and logical resource pressure of signal capture. The two-dimensional correlation capture method of frequency domain zero-filled segmented matched filtering is used to realize high-sensitivity and high-resolution capture and processing of low-orbit high-dynamic signals, and the carrier Doppler and pseudo-code phase of the signal are obtained through peak judgment, and finally the capture and processing of high-dynamic low-orbit satellite navigation enhancement signals is realized. This method innovatively proposes a low-orbit dynamic estimation and correction method assisted by high and medium orbit constellations in spatial and temporal space, which solves the difficulty of high-dynamic capture and processing of low-orbit satellite navigation enhancement signals. At the same time, it innovatively designs a two-dimensional search method of frequency domain zero-filled segmented matched filtering, which improves the high sensitivity and high resolution of high-dynamic signal capture. Through the organic fusion of high and medium orbit constellation time and space assistance and frequency domain zero-filling segmented matching filtering, the fast, high-sensitivity and high-resolution capture of low-orbit satellite navigation enhancement signals is achieved, while reducing the scale of logical resources and the amount of calculation for capture processing, occupying less resources and having high calculation efficiency. It provides an engineering solution for the reception and processing of low-orbit satellite navigation enhancement signals and low-orbit satellite navigation enhancement services.

[0050] This method is applicable to all low-orbit satellite high-dynamic signals, such as low-orbit satellite navigation enhancement signals, low-orbit precision single-point positioning signals and low-orbit communication signals. It has a wide range of applications, a high level of engineering, and good engineering implementation and industrial promotion value. It is of great significance to the development of low-orbit satellite navigation enhancement receivers and the construction of my country's high, medium and low-orbit collaborative navigation constellations.

Claims

1. A method for capturing enhanced signals of low-orbit satellite navigation based on high and medium orbit assistance, characterized in that: The steps include: (1) Receive all visible satellite navigation signals in space, convert them into baseband signals through the RF front end, and then sample the baseband signals to obtain digital satellite navigation baseband signals; (2) According to the satellite navigation signal reception and processing mode, the high-mid orbit satellite navigation enhancement signal in the digital satellite navigation baseband signal is sequentially captured and tracked, and the message is demodulated and the positioning is solved; (3) Based on the positioning solution processing results, the receiver is positioned to obtain the receiver's time, position and satellite almanac information; (4) Performing time synchronization for capturing low-orbit satellite navigation enhancement signals based on time information, determining the satellite number and satellite position of visible low-orbit satellites based on the satellite almanac, and performing Doppler dynamic prediction of low-orbit satellite navigation enhancement signals using the satellite position of the low-orbit satellite and the receiver position; (5) After completing the Doppler dynamic prediction of the low-orbit satellite navigation enhancement signal, the frequency domain zero-filling segmented matched filtering capture method is used to perform a two-dimensional correlation capture search in the code domain and frequency domain on the low-orbit satellite navigation enhancement signal, and the carrier Doppler and pseudo-code phase of the signal are obtained through frequency domain peak judgment, finally completing the capture and processing of the low-orbit satellite navigation enhancement signal.

2. The method for capturing and processing high-dynamic low-orbit satellite navigation enhancement signals according to claim 1, characterized in that: In step (4), the specific process of using the satellite position of the low-orbit satellite and the receiver position to perform Doppler dynamic prediction of the low-orbit satellite navigation enhancement signal is as follows: The satellite position and receiver position of the low-orbit satellite are used to obtain the satellite speed and signal arrival angle, and then the Doppler dynamic prediction of the low-orbit satellite navigation enhancement signal is performed according to the following formula: In the formula, f d is the signal Doppler, V s is the satellite speed, R e is the radius of the Earth, R s is the satellite's geocentric height, θ is the signal arrival angle, and f c is the carrier frequency, c is the speed of light; The signal Doppler is then converted into dynamic parameters of the local carrier and pseudo code in the satellite navigation signal reception process, and the carrier NCO and pseudo code NCO are compensated.

3. The method for capturing and processing high-dynamic low-orbit satellite navigation enhancement signals according to claim 1, characterized in that: The specific process of step (5) is as follows: (501) After multiplying the low-orbit satellite navigation enhancement signal of length N with the local carrier and performing digital down-conversion, the signal is divided into P equal segments, and enters P partial matched filters to perform correlation matching using the local pseudo code sequence, then N=P*X, where X is the number of correlation points of each matched filter; (502) performing a K-point FFT on the correlation integral result of the matched filter at the same position in each segment. If the maximum value after the FFT modulus exceeds the set threshold, it is determined that the capture is successful and the tracking phase is entered to obtain the carrier Doppler and pseudo code phase of the signal; Otherwise, the local pseudo code sequence is shifted by one chip, and the process returns to step (501), thereby finally completing the capture process of the low-orbit satellite navigation enhancement signal.

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