Method of processing radio navigation signals generated by satellites
By determining the real amplitude distribution pattern of GNSS signals in the frequency domain and setting a threshold, components exceeding the threshold are filtered out or removed, thus solving the problem of Gaussian noise power separation in GNSS signals and improving signal processing efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2021-06-22
- Publication Date
- 2026-03-27
AI Technical Summary
Existing technologies struggle to effectively separate Gaussian noise power from GNSS signals, especially when receiver resources are limited, as the intensity of interference signals is far greater than that of noise, affecting signal processing performance.
By converting the signal to the frequency domain using complex Fourier transform, the amplitude distribution of the real part is determined, a threshold is set and components exceeding the threshold are filtered out or removed, and the time domain signal is recovered by combining complex inverse transform, thus achieving interference cancellation.
It simplifies resource requirements, improves the efficiency of extracting useful GNSS signals from interference signals, and reduces the requirements for receiver resources.
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Figure CN115735139B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present invention relates to global navigation satellites, and more particularly to a method and device for processing signals in a global navigation satellite system. BACKGROUND
[0002] In global navigation satellite systems (GPS, GLONASS, etc.), interference rejection is a fundamental element of the performance of these systems.
[0003] More specifically, a global navigation satellite receiver implements a correlation between a measurement signal (hereinafter referred to as GNSS signal) (from a satellite) and a replica signal, and implements processing operations that make it possible to reduce the interference in the measurement signal before correlating the measurement signal with the replica signal. These processing operations are generally referred to as pre-correlation interference cancellation processing operations.
[0004] For certain types of pre-correlation interference cancellation processing, in order to separate, on the one hand, the GNSS signal buried in the noise, and on the other hand, the interference having a power higher than the Gaussian noise, it is necessary to estimate the Gaussian noise power. Such separation is used in particular in frequency cut type or amplitude blocking type frequency filtering techniques, for which a good estimate of the Gaussian noise power is essential.
[0005] Such an estimate of the Gaussian noise power is not easy, especially for receiving GNSS signals. Indeed, all these signals will be present simultaneously; among them, the interference is 100 to 1000 times stronger than the noise, and the noise itself is 1000 times stronger than the GNSS signal.
[0006] Furthermore, in the case of a GNSS receiver, given the miniaturization of the receiver, it is necessary to estimate this Gaussian noise power using a small number of digital resources. SUMMARY
[0007] The present invention makes it possible to separate the useful GNSS signal from the interference in a simple manner.
[0008] To this end, according to a first aspect, the invention proposes a method for processing a radio navigation signal from a satellite, the method comprising the following steps implemented in a processing unit of a radio navigation receiver:
[0009] - converting the radio navigation signal into the frequency domain by complex Fourier transform, so as to obtain a frequency radio navigation signal comprising a real part I and an imaginary part Q, the real part I having an amplitude I 2 associated with the frequency;
[0010] - determining the amplitude I 2the distribution law;
[0011] determining an amplitude for cancelling the real component of the distribution function, the amplitude defining a threshold value;
[0012] processing the frequency radio navigation signal to filter out components having an amplitude greater than the determined threshold value.
[0013] Advantageously, the application is completed by the following features, taken individually or in any technically feasible combination thereof.
[0014] Processing the frequency radio navigation signal can comprise frequency cut, the processing comprising removing components having an amplitude greater than the determined threshold value.
[0015] Processing the frequency radio navigation signal can comprise amplitude blanking.
[0016] Determining the distribution law comprises obtaining a histogram of the amplitudes of the real components.
[0017] The method further comprises converting, by inverse complex Fourier transform, the frequency radio navigation signal from which components having an amplitude greater than the determined threshold value have been removed, into the time domain to obtain a processed radio navigation signal.
[0018] According to a second aspect, the application also relates to a computer program product comprising program code instructions for executing the steps of the method according to the first aspect of the application when the program is run on a computer.
[0019] The fact of considering only the real part in the method makes it possible to obtain a method requiring fewer resources than a solution based on the real and imaginary parts. BRIEF DESCRIPTION OF DRAWINGS
[0020] Other characteristics, aims and advantages of the application will appear from the following description, which is merely exemplary and non-limiting, and should be understood with reference to the appended drawings in which:
[0021] Figure 1 a receiver according to the application is shown receiving a signal from a satellite;
[0022] Figure 2 a method according to the application is shown for processing a signal from a satellite;
[0023] Figure 3a and 3b a representation of a frequency signal acquired during a method according to the application is shown.
[0024] In all the drawings, similar elements have the same reference signs. DETAILED DESCRIPTION
[0025] Figure 1 A radio navigation receiver 1, hereinafter referred to as GNSS receiver, is shown. The GNSS receiver comprises a receiving unit 11 configured to acquire radio navigation signals (hereinafter referred to as GNSS signals) from satellites SAT, for example of the GPS or GLONASS type, and to convert them into digital GNSS signals. The receiving unit 11 comprises, among other elements, an antenna A and an analog-to-digital converter (not shown) to acquire a digital signal S at the output of the receiving unit 11. The receiving unit 11 also comprises other elements, which will not be described in greater detail here, as they are well known to the person skilled in the art.
[0026] The GNSS receiver 1 also comprises a processing unit 2. The receiving unit 11 transmits the digitized GNSS signals S, hereinafter referred to as GNSS signals, to the processing unit 2. The processing unit 2 is composed of one or more processors that will make it possible to implement different processing operations.
[0027] The received digitized GNSS signals comprise the useful signals emitted by the satellites SAT, the Gaussian white noise and the interferences to be eliminated.
[0028] The processing unit 2 comprises a cutting module 20 for cutting the GNSS signals into blocks of samples of predetermined size.
[0029] The processing unit 2 also comprises a time / frequency converter 21 configured to convert the GNSS signals, which are in the time domain, into the frequency domain. In particular, the converter 21 makes it possible to apply a complex Discrete Fourier Transform (DFT).
[0030] After the converter 21, the receiver 1 also comprises an interference elimination module 22 configured to implement a number of processing operations on the frequency signals from the converter 21. The steps of these processing operations will be described in detail later. The module 22 provides the frequency signals, from which the interferences have been eliminated, to a frequency / time converter 23 configured to convert the signals into the time domain. In particular, the converter 23 makes it possible to apply a complex inverse Discrete Fourier Transform to the complex Discrete Fourier Transform applied by the converter 21.
[0031] The time signals are then provided to a correlation unit 24 that makes it possible to apply processing operations to the time signals to provide navigation signals known to the person skilled in the art.
[0032] The processing unit 2 also comprises a memory 25 that makes it possible to store the signals during the different processing operations.
[0033] Figure 2 The method steps for processing GNSS signals from satellites, implemented by processing unit 2, are shown.
[0034] First, receiver 1 receives the signal from the satellite and digitizes it (step 100) to obtain the GNSS signal represented as S.
[0035] The digitized GNSS signal S includes the useful signal transmitted by the SAT satellite, Gaussian white noise, and interference to be eliminated. First, the digitized GNSS signal S is windowed (step 101) and then cut into multiple sample blocks containing several samples. Complex DFT is applied to these samples (step 102) to obtain the frequency signal.
[0036] The window serves to limit spectral diffusion caused by the complex DFT and is associated with time truncation. An example of a window is a Blackman-Harris type window.
[0037] At the end of the complex DFT, the frequency signal consists of N samples indexed from 1 to N, where N is a multiple of 2, for example:
[0038] 256≤N≤1,024.
[0039] In the case of complex DFT, the frequency signal includes a real part (the component in phase I) and an imaginary part (the component in quadrature Q). Furthermore, the signal also includes N samples (denoted as I) describing the real part. i (i=1 to N) and N samples describing the imaginary part (denoted as Q). i ).
[0040] Then, as Figure 2 As shown, the distribution function of the real part amplitude of the frequency signal is determined (step 103). Determining this distribution function includes calculating the real part for each sample I. i amplitude I i 2 And classify them horizontally to obtain a histogram of multiple samples that present a certain amplitude value.
[0041] The step size of the histogram is a constant and, for example, equal to 1.
[0042] exist Figure 3b An example of this distribution function is shown in the figure.
[0043] Based on the obtained distribution function, determine the real part magnitude used to eliminate the distribution function (step 104). The determined magnitude corresponds to a threshold, and samples with a real part magnitude greater than this threshold are considered noise.
[0044] Figure 3aThe real part amplitude as a function of frequency is shown, the corresponding distribution function being shown in Figure 3b
[0045] In this example, the spectrogram represents a GPS C / A signal buried in Gaussian noise in the presence of a CW jammer centered on the frequency L1. The estimate of the noise power is derived from the level at which the histogram is eliminated, here the value is indicated by the threshold = 9.
[0046] Above this threshold are the noise, it can thus be observed that only the low amplitude levels correspond to a signal with only Gaussian noise, since they correspond to Gaussian noise whose distribution follows the law of central normality.
[0047] The frequency signal is then processed to filter out or remove the components whose real part amplitude is greater than the determined threshold (step 105).
[0048] The processed signal is then converted into a time signal by applying a complex inverse DFT -1 to the processed signal (step 106).
[0049] The signal S' is then obtained. This signal S' then makes it possible to obtain the navigation signal S".
[0050] According to one embodiment, the processing of the frequency signal in step 105 can comprise a frequency cut of this signal. This processing comprises eliminating the frequency components whose real part amplitude is greater than the threshold determined in step 104. The elimination of the frequency components is implemented both on the real part and on the imaginary part.
[0051] According to another embodiment, the processing of the frequency signal in step 105 can comprise an amplitude blocking.
[0052] According to this embodiment, unlike the elimination of the frequency components, the amplitude blocking comprises setting the amplitude in the frequency range of the jammer while preserving its phase. The set amplitude value can be chosen so as to maximize the signal-to-noise ratio; to take into account the percentage of frequency components to be processed; to preserve the spectral representation of the signal (advantageous variant) to limit the distortion contribution in the remaining processing.
Claims
1. A method for processing a radio navigation signal from a satellite, the method comprising the following steps implemented in a processing unit (2) of a radio navigation receiver (1): - converting (102) the radio navigation signal into a frequency domain by a complex Fourier transform to obtain a frequency radio navigation signal comprising real and imaginary parts, the real part having an amplitude associated with a frequency; - determining (103) a distribution law of the amplitudes of the real component of the frequency radio navigation signal; - determining (104) a threshold for eliminating the amplitudes of the real component of the distribution function, the amplitudes defining the threshold; - removing (105) the frequency components of the real component of the frequency radio navigation signal having an amplitude greater than the determined threshold; and - converting (106) the frequency radio navigation signal thus obtained into a time domain by an inverse complex Fourier transform, thereby obtaining a processed radio navigation signal.
2. The method of claim 1, wherein, The removing (105) step comprises frequency cut.
3. The method of claim 1 or 2, wherein, The determining (103) of the distribution law comprises obtaining a histogram of the amplitudes of the real component.
4. A computer program product comprising program code instructions for executing the steps of the method according to any one of claims 1 to 3 when the program is executed by a computer.