Low earth orbit satellite composite code shift keying signal receiving and processing method based on extension overlapping

Abstract

The invention relates to the application field of low-earth-orbit satellite navigation enhancement and low-earth-orbit satellite precision single-point positioning, and provides a low-earth-orbit satellite composite code-shift keying signal receiving and processing method based on extension overlapping. According to the method, the engineering implementation requirement of the composite code-shift keying signal is met, the signal modulation characteristic of the composite code-shift keying signal is fully utilized, and rapid synchronization of the signal is realized based on a low-speed message signal of the composite code-shift keying signal; secondly, replacing traditional coherent matched filtering with FFT (Fast Fourier Transform) conversion which is easier to engineer by using a principle of replacing time domain convolution with frequency domain multiplication, so as to reduce the complexity of cyclic correlation; and finally, code phases of mapping data bits are expanded and overlapped, so that the parallelism of related processing is improved, the number of coherent matching times is reduced, and the calculation efficiency is improved.

Description

Technical Field

[0001] The invention relates to the application fields of low-orbit satellite navigation enhancement and low-orbit satellite precise single-point positioning, and proposes a low-orbit satellite composite code shift keying (MCSK) signal receiving and processing method based on extended overlap. Background Art

[0002] As an important space-time infrastructure in the information age, the Global Navigation Satellite System (GNSS) plays an important role in the military, industry, science, consumption and other fields. With the continuous deepening of the application of satellite navigation systems, the current global satellite navigation system can no longer meet the needs of users for centimeter-level positioning accuracy in scenarios such as unmanned platforms and intelligent driving. With the vigorous development of low-orbit constellations, the precise point positioning (PPP) technology based on low-orbit satellite navigation enhancement has become the most promising solution. Precise point positioning technology requires users to be able to obtain the precise orbit and precise clock error of the satellite through real-time solution of the precise ephemeris in the navigation message. In order to achieve real-time broadcasting of precise ephemeris data, the message rate must reach the order of several thousand bits per second, which is much higher than the current message rate of one hundred bits per second used by GNSS. In order to improve the message broadcast rate on the basis of achieving signal system compatibility, the composite code shift keying modulation that combines pseudorange measurement and message rate has become the mainstream choice of signal modulation technology in low-orbit satellite navigation enhancement. The composite code shift keying signal combines the measurement synchronization signal of the low-speed message and the message transmission signal of the high-speed message. The signal can complete both signal measurement and high-speed message transmission. The composite code shift keying signal will become the main signal modulation mode for precise point positioning services in the next generation of satellite navigation systems represented by low-orbit satellite navigation enhancement. The signal realizes data bit mapping through the offset of the pseudo code phase and uses the autocorrelation characteristics of the spread spectrum code for multi-value transmission of the message. On the basis of not changing the original navigation signal structure, the high information rate message broadcasting of the precise point positioning high-precision service is directly realized. However, while the composite code shift keying signal brings high-bandwidth message transmission rate, it comes at the cost of increasing the complexity of signal reception. When receiving the composite code shift keying modulated signal, in addition to completing the synchronous tracking of the signal, the receiver also needs to traverse and calculate the correlation values ​​of various mapped data bit code phases to realize message information demodulation. However, the traditional satellite navigation signal processing method has certain limitations when receiving and processing composite code shift keying signals.

[0003] 1. Direct time domain correlation is used to receive and process composite code shift keying signals. For the signal's mapped data bit code phase, a correlator that is multiple times the mapped data bit code phase needs to be set for correlation identification to achieve the acquisition of the correlation value of the mapped data bit code phase. The principle of this method is simple, but the number of correlators required increases exponentially compared to the number of traditional signal tracking methods. This method requires a large amount of hardware logic resources, has a long average correlation processing time, low computational efficiency, and weak engineering implementation;

[0004] 2. Use coherent matched filtering to receive and process composite code shift keying signals. According to the code phase of the signal's mapped data bits, set a matched filter group with the same number of mapped bits to match and correlate the signal, and select the code phase corresponding to the maximum output of the matched filter group as the demodulation of the transmitted symbol. The number of matched filter groups used in this method is determined by the number of mapped bits. It is a two-dimensional array scale correlated matched filter. As the number of mapped bits increases, the amount of matching correlation calculations will increase linearly. Therefore, correlated matched filtering is mostly suitable for theoretical research. As the number of mapped bits increases, the scale of the matched filter is difficult to implement in programmable logic devices.

[0005] How to reduce the difficulty of implementing the composite code shift keying signal reception and processing and improve the computational efficiency of signal processing has become the key to restricting the large-scale application of low-orbit satellite navigation precision point positioning services. Solving the difficulties of optimizing and engineering the composite code shift keying signal reception and processing algorithm will realize the industrialization and promotion of low-orbit satellite precision point positioning services. The composite code shift keying signal reception and processing method is of great significance to the industrialization and promotion of high-precision reception and processing and precision point positioning services for low-orbit satellite navigation enhancement. Summary of the invention

[0006] The present invention is particularly suitable for the engineering implementation of receiving and processing of a low-orbit satellite high-precision receiver when receiving a downlink composite code shift keying signal of a low-orbit satellite precise single-point positioning service. Mainly aiming at the problems and difficulties of random mapping of data bit code phase in the reception and demodulation of composite code shift keying signals, a method for receiving and processing low-orbit satellite composite code shift keying signals based on extended overlap is proposed. This method innovatively proposes a solution of frequency domain correlation and extended overlap fusion to reduce the complexity of the composite code shift keying signal reception and processing process, and provides an engineering-implementable solution for the design of high-precision positioning receivers and precise single-point positioning service applications for low-orbit satellite navigation enhancement.

[0007] The technical solution adopted by the present invention is:

[0008] A method for receiving and processing a low-orbit satellite composite code shift keying signal based on extended overlap comprises the following steps:

[0009] (1) receiving a composite code shift keying signal from a low-orbit satellite, converting the signal into a baseband signal through a radio frequency front end, and then sampling the baseband signal to obtain a digital composite code shift keying baseband signal, wherein the digital composite code shift keying baseband signal includes a low-speed navigation message signal and a high-speed navigation message signal;

[0010] (2) Correlate, capture and track the low-speed navigation message signal, complete the measurement and synchronization of the low-speed navigation message signal, and realize the synchronization of the digital composite code shift keying baseband signal;

[0011] (3) performing FFT conversion on the synchronized digital composite code shift keying baseband signal, converting it into the frequency domain and storing it, and grouping the mapped data bit code phase of the local high-speed telegram pseudo code;

[0012] (4) performing arithmetic addition on one group of mapped data bit code phases to complete the expansion and overlap of the mapped data bit code phases, performing FFT conversion and taking complex conjugation on the expanded and overlapped mapped data bit code phases, and then multiplying the conjugated result with the stored signal FFT conversion result and taking IFFT to complete the expansion and overlap cyclic correlation of the mapped data bit code phases of the local high-speed telegram pseudo code;

[0013] (5) Perform peak detection on the result of the extended overlapped cyclic correlation according to the set threshold value. If a peak value exceeding the threshold value is detected, the mapped data bit code phase corresponding to the signal exists in the extended overlapped group, and step (6) is executed. If no peak value is detected, the mapped data bit code phase corresponding to the signal does not exist in the extended overlapped group, and step (4) is returned to select another group of mapped data bit code phases until the selected mapped data bit code phases for all groups are completed.

[0014] (6) Expand the mapping data bit code phase corresponding to the existing signal, then perform FFT conversion on each code phase independently, and perform circular correlation with the stored signal FFT conversion result to determine the mapping data bit code phase corresponding to the signal, obtain the mapping data bit information, perform high-speed telegram decoding on the mapping data bit information, and finally complete the reception and processing of the composite code shift keying signal.

[0015] Compared with the traditional composite code shift keying signal processing method in the background art, the present invention has the following advantages:

[0016] 1. The composite code shift keying signal processing method of the present invention uses the signal's own low-speed telegram signal to complete signal synchronization, has a low degree of dependence on external signals, is easy to implement, and greatly improves the engineering feasibility of composite code shift keying signal reception and processing.

[0017] 2. The present invention uses the idea that frequency domain multiplication is equivalent to time domain convolution to perform cyclic correlation calculations, which greatly reduces the scale and amount of calculation of the correlator for code phase identification in composite code shift keying signal processing, occupies less resources, and improves the calculation efficiency by 45%, providing an engineering feasible solution for composite code shift keying signal reception and processing.

[0018] 3. The present invention innovatively introduces code phase expansion and overlapping technology, and realizes code phase expansion and overlapping of multi-dimensional mapping data bit code phase by group addition, thereby realizing dimensionality reduction processing of mapping data bit code phase, thereby improving the parallelism of related processing; without increasing logical resources, it improves the computational efficiency of mapping data bit code phase detection, and provides an efficient solution for composite code shift keying signal processing.

[0019] 4. The present invention does not require supporting environment support, does not require changing the receiver hardware, and does not require external auxiliary signals. It only realizes the composite code shift keying signal reception processing through multi-dimensional domain signal expansion and overlapping processing in terms of signal processing algorithm, and completes the reception and demodulation of high information rate telegrams. The method has low environmental dependence, simple engineering implementation, and strong updatability.

[0020] 5. The present invention solves the engineering application problem of composite code shift keying signal processing by integrating multiple means, and provides a receiver engineering implementation solution for realizing high information rate telegram reception and low-orbit satellite fast and precise single-point positioning services based on composite code shift keying signals for low-orbit satellite navigation; it has a wide range of applications, a high level of achievability, and good engineering implementation and industrial promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention is a flowchart of receiving and processing a low-orbit satellite composite code shift keying signal based on extended overlap according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] Reference Figure 1The present invention mainly aims at the engineering requirements such as the complex algorithm of receiving and processing composite code shift keying signals of low-orbit satellites, large amount of calculation, many hardware logic resource requirements, and low operation efficiency in the implementation process, and makes full use of the signal characteristics of composite code shift keying signals to propose a method for receiving and processing composite code shift keying signals of low-orbit satellites based on extended overlap. The method first completes the reception, frequency conversion and sampling of composite code shift keying signals of space low-orbit satellites, and then performs digital baseband signal processing on them. The signal system advantages of the fusion design of low-speed navigation telegram signals and high-speed navigation telegram signals in composite code shift keying signals are fully utilized to complete the correlation, capture and tracking demodulation of low-speed telegram signals, and obtain the measurement information and synchronization information of composite code shift keying signals. The composite code shift keying signal is then converted and stored in the frequency domain, and the mapped data bit code phase of the local high-speed telegram pseudo code is grouped, and the code phase is extended and overlapped within the group. The code phase after extended overlap is FFT converted and complex conjugate is taken, and then the two FFT conversion results are multiplied and IFFT is taken to complete the cyclic correlation of the extended overlapping code phase. By detecting the peak value of the cyclic correlation result, the extended overlapping group corresponding to the code phase of the mapped data bit in the signal is determined. Then the group is de-expanded and overlapped to obtain the mapped data bit information of the code phase, and finally the data bit information is decoded at a high speed to finally realize the reception and processing of the composite code shift keying signal.

[0023] like Figure 1 As shown, a flowchart of receiving and processing low-orbit satellite composite code shift keying signals based on extended overlap is provided. In the specific embodiment, the composite code shift keying signal MCSK (4, 2, 1) in the low-orbit satellite precise point positioning service is selected as an example for analyzing the receiving and processing method. In the composite code shift keying signal MCSK (4, 2, 1), the code rate is 1.023Mcps, the code length is 1023 chips, the low-speed message is 100bps, and the high-speed message is 2000bps. The steps of the receiving and processing method of the low-orbit satellite composite code shift keying signal based on extended overlap are as follows:

[0024] Step 1: Receive a composite code shift keying signal from a low-orbit satellite in space, convert it into a baseband signal through a radio frequency front end, and then sample the baseband signal to obtain a digital composite code shift keying baseband signal, which includes a low-speed navigation message signal and a high-speed navigation message signal;

[0025] Step 2: Correlate, capture and track the low-speed navigation message signal, complete the measurement and synchronization of the low-speed navigation message signal, and realize the synchronization of the digital composite code shift keying baseband signal;

[0026] Step 3: Build a 1024-point FFT processing module to perform FFT conversion on the 1-millisecond digital composite code shift keying baseband signal after synchronization, convert it to the frequency domain and store the conversion result. At the same time, divide the 16-bit code phase of the local high-speed telegram pseudo code corresponding to MCSK (4,2,1) into 4 groups;

[0027] Step 4: Perform corresponding arithmetic accumulation on the first group of 4 code phases with a code length of 1023 to achieve extended overlap, and finally obtain an extended overlapping code phase with a length of 1023. After zero padding to 1024 points, the extended overlapping code phase is transformed into the frequency domain and complex conjugate is taken using the FFT processing module, and the result is multiplied with the stored signal frequency domain conversion result, and the 1024-point IFFT conversion is performed at the same time to complete the cyclic correlation of the first group of code phases;

[0028] Step 5: Use the normalized preset threshold of 0.65 to perform peak detection on the results of the extended overlap cyclic correlation. If no correlation result exceeds the threshold, it means that there is no mapping data bit code phase corresponding to the signal in the extended overlap group. Repeat the above steps to complete the search for the second group of extended overlap mapping data bit code phases. After the peak value is found in the third group, it is determined that the third group is a group with extended overlap mapping data bit code phases.

[0029] Step 6: After determining that the third group of mapped data bit code phases have correlation peaks, the code phases corresponding to the four mapped data bits 0X8, 0X9, 0XA, and 0XB in the third group are de-expanded and overlapped. First, the code phases corresponding to the four mapped data bits are independently padded with zeros and the 1024-point FFT conversion is completed. Then, they are multiplied with the stored signal FFT results and IFFT conversion is completed for circular correlation. Through the peak detection of the four circular correlation results, only the mapped data bit code phase corresponding to 0XA has a correlation peak. Therefore, it is determined that the mapped data bit information in the current signal is 0XA, and the data bit is sent to the high-speed telegram decoding unit for decoding, completing the high-speed telegram demodulation of the signal, and finally realizing the reception and processing of the composite code shift keying signal.

[0030] The working principle of the present invention is as follows:

[0031] The present invention proposes a method for receiving and processing composite code shift keying signals of low-orbit satellites based on extended overlap. This method is oriented to the engineering realization requirements of composite code shift keying signals, makes full use of the signal modulation characteristics of composite code shift keying signals, and realizes rapid synchronization of signals based on its low-speed telegram signal; then, the principle of frequency domain multiplication instead of time domain convolution is used to replace the traditional coherent matched filtering with a more easily engineered FFT conversion, thereby reducing the complexity of cyclic correlation; and then the code phase of the mapped data bit is extended and overlapped, thereby improving the parallelism of the related processing, reducing the number of coherent matching and improving the computational efficiency. This method is based on the synchronization of the signal itself, has a low degree of dependence on external signals, and is convenient to implement based on mature modules, providing a feasible solution for the engineering of composite code shift keying signal reception and processing; at the same time, the extended overlap technology is innovatively introduced to reduce the dimensionality of the multi-dimensional mapped data bit code phase, thereby improving the parallelism of the cyclic correlation without increasing the logic resources, thereby improving the computational efficiency of the mapped data bit code phase. This method solves the high complexity of related processing in the engineering application of composite code shift keying signal processing, and provides an engineering receiver solution for realizing high information rate reception and fast and precise single-point positioning services of low-orbit satellites. This method is applicable to all navigation enhancement receivers and precision single-point service receiving and processing units that receive composite code shift keying signals from low-orbit satellites. It has a wide range of applications, high safety and reliability, and good engineering realization and industrial promotion value. It is of great significance to the engineering realization of high-precision signal reception and processing for low-orbit satellite navigation enhancement and the industrial promotion of precise single-point positioning services.

Claims

1. A method for receiving and processing low-orbit satellite composite code shift keying signals based on extended overlap, characterized in that , including the following steps: (1) receiving a composite code shift keying signal from a low-orbit satellite, converting the signal into a baseband signal through a radio frequency front end, and then sampling the baseband signal to obtain a digital composite code shift keying baseband signal, wherein the digital composite code shift keying baseband signal includes a low-speed navigation message signal and a high-speed navigation message signal; (2) Correlate, capture and track the low-speed navigation message signal, complete the measurement and synchronization of the low-speed navigation message signal, and realize the synchronization of the digital composite code shift keying baseband signal; (3) performing FFT conversion on the synchronized digital composite code shift keying baseband signal, converting it into the frequency domain and storing it, and grouping the mapped data bit code phase of the local high-speed telegram pseudo code; (4) performing arithmetic addition on one group of mapped data bit code phases to complete the expansion and overlap of the mapped data bit code phases, performing FFT conversion and taking complex conjugation on the expanded and overlapped mapped data bit code phases, and then multiplying the conjugated result with the stored signal FFT conversion result and taking IFFT to complete the expansion and overlap cyclic correlation of the mapped data bit code phases of the local high-speed telegram pseudo code; (5) Perform peak detection on the result of the extended overlapped cyclic correlation according to the set threshold value. If a peak value exceeding the threshold value is detected, the mapped data bit code phase corresponding to the signal exists in the extended overlapped group, and step (6) is executed. If no peak value is detected, the mapped data bit code phase corresponding to the signal does not exist in the extended overlapped group, and step (4) is returned to select another group of mapped data bit code phases until the selected mapped data bit code phases for all groups are completed. (6) Expand the mapping data bit code phase corresponding to the existing signal, then perform FFT conversion on each code phase independently, and perform circular correlation with the stored signal FFT conversion result to determine the mapping data bit code phase corresponding to the signal, obtain the mapping data bit information, perform high-speed telegram decoding on the mapping data bit information, and finally complete the reception and processing of the composite code shift keying signal.

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