CN117492037A - A transformation domain threshold-free narrowband interference suppression method for satellite navigation - Google Patents

Abstract

The present invention relates to the technical field of satellite navigation, and in particular, to a method for suppressing narrowband interference in satellite navigation receiving equipment. A transform domain threshold-free narrowband interference suppression method for satellite navigation, which is characterized by including the following steps: (1) data packet windowing processing: (2) time domain data conversion transform domain processing; (3) frequency domain spectral lines Perform normalization; (4) Transform the domain data back to the time domain. The narrow-band interference of satellite navigation is suppressed through transform domain threshold-free anti-interference processing, which overcomes the difficulty in determining the interference decision threshold in the existing technology. It can not only reduce the implementation complexity of anti-interference processing, but also improve the robustness. It can be used To provide interference protection capabilities for satellite navigation receiving equipment.

Description

A transformation domain threshold-free narrowband interference suppression method for satellite navigation

Technical field

The present invention relates to the technical field of satellite navigation, and in particular, to a method for suppressing narrowband interference in satellite navigation receiving equipment.

Background technique

The detection and elimination of electromagnetic interference has always been a hot and key issue in the application of Global Navigation Satellite System (GNSS). From the source, electromagnetic interference can be divided into unintentional interference and malicious interference. The most commonly mentioned malicious interference is a device called PPDs (Personal Privacy Devices). This is a small, cheap jammer that only requires a few watts of transmission power to interfere with several kilometers or even dozens of Satellite navigation receiving equipment within a kilometer range. Among the incidents of interference with civilian (such as civil aviation) satellite navigation that occurred at home and abroad, it was eventually found that many times it was caused by truck drivers installing and turning on PPDs interference equipment on the vehicle cigarette lighter in order to avoid the company's location monitoring.

There are currently a variety of technologies that can eliminate or reduce the impact of electromagnetic interference on satellite navigation receivers. The basic principle is to use the difference in signal characteristics between electromagnetic interference and satellite navigation signals to identify and eliminate electromagnetic interference. For example, transform domain anti-interference technology uses the difference in bandwidth between the two (electromagnetic interference and satellite navigation signals) to effectively suppress narrowband interference. The airspace anti-interference technology based on array antennas utilizes the difference in the incident directions of the two to achieve interference identification and suppression. The polarization anti-interference technology based on polarization-sensitive antennas uses the difference in polarization methods to realize interference identification and suppression. The latter two anti-interference technologies require the use of array antennas or polarization-sensitive antennas, which increase the size, power consumption and implementation cost of the receiver. Therefore, they are mainly used in some high-end (military) receivers. Transform domain anti-interference technology can be implemented in general satellite navigation receivers through software upgrades, so it is widely used.

The basic process of transform domain anti-interference technology is: (1) Fourier transform is performed on the AD sampling data of the satellite navigation receiver to obtain the frequency domain spectral lines; (2) All spectral lines are compared with the interference decision threshold one by one. If the spectrum If the line exceeds the threshold, it is set to zero; (3) The processed spectral line is transformed back to the time domain by inverse Fourier transform. The selection of the interference judgment threshold is particularly critical in the entire anti-interference process. Choosing a threshold that is too large can easily cause missed alarms, leading to incomplete elimination of interference. Choosing a threshold that is too small can easily cause false alarms, causing useful satellite navigation signals to be mistakenly eliminated. , both situations will deteriorate the anti-interference performance and even cause the receiver to fail to work properly. The determination of the interference decision threshold is closely related to the level of thermal noise in the receiver AD sampling data. However, the level of thermal noise in the AD sampling data is generally not fixed, but dynamically changes with factors such as the temperature of the environment and the receiver AGC gain. How to determine the interference decision threshold in domain anti-interference technology has always been a difficult issue in this field.

Contents of the invention

In order to overcome the shortcomings of the existing technology, the present invention provides a threshold-free narrowband interference suppression method for satellite navigation in the transform domain. Different from the traditional method, the method of the present invention does not need to set any parameters, especially does not need to set a threshold, so it can not only reduce the resistance The implementation complexity of interference processing can also improve the robustness, and can also achieve interference suppression effects similar to traditional methods, which can provide narrowband interference protection capabilities for various satellite navigation receiving equipment.

The technical solution of the present invention provides a transform domain threshold-free satellite navigation narrowband interference suppression method, which is characterized in that it includes the following steps:

(1) Data grouping and windowing processing:

Suppose the AD sampling data of the satellite navigation receiving device is x(n), where n is the index of the sampling data, and the values are 1, 2, 3,…. The above sampled data are grouped according to index order, and each L piece of data is divided into one group. Then the mth group of data contains a total of L pieces of sampled data, as follows: Grouped data The corresponding relationship with the original sampling data x(n) is as follows:

The mth group of data is windowed according to the following formula:

Among them, y(k,m) is the m-th group of data after windowing, and w(k) is the window function of length L. The purpose of windowing is to reduce spectrum leakage caused by data truncation. The types of window functions include rectangular window, Hamming window, Blackman window, etc. Its specific mathematical expression is common knowledge in the field of digital signal processing and will not be discussed here. Repeat.

In order to improve the computing efficiency, the length L of each group of data is taken as an exponential multiple of 2. Typical values such as 256, 512, and 1024 are commonly used in actual engineering implementation.

(2) Time domain data transformation transformation domain processing:

Fourier transform is performed on the windowed grouped data and converted to the transform domain. For the mth group of data, the conversion process is carried out as follows:

Among them, Y(i,m) is the frequency domain spectrum line obtained after converting the time domain data to the transform domain, and its value is a complex number.

(3) Normalize the frequency domain spectral lines:

All frequency domain spectral lines are normalized. For the mth group of frequency domain spectral lines, the normalization process is carried out as follows:

Among them, the function Re(·) represents taking the real part of a complex number, and the function Im(·) represents taking the imaginary part of a complex number. The normalization process of frequency domain spectral lines can eliminate outliers and effectively achieve the interference suppression function.

(4) Convert the transform domain data back to the time domain:

The inverse Fourier transform is performed on the normalized frequency domain spectral lines to convert the data from the transform domain back to the time domain. For the mth group of normalized frequency domain spectral lines, the conversion process is carried out as follows:

In the formula, z(k,m) is the time domain grouped data after interference suppression. The final anti-interference output data z(n) can be obtained by splicing the time domain grouped data.

Because for any positive integer n, there are positive integers m and k, such that n=(m-1)L+k holds, so the corresponding relationship between z(n) and z(k,m) can be expressed by the following formula:

z(k,m)=z((m-1)L+k)=z(n),

z(n) is the data after interference suppression according to the method of the present invention, and is output to the back-end capture and tracking module for further processing.

It can be seen from the above steps that the narrowband interference suppression process provided by the method of the present invention does not need to set a threshold, nor does it need to determine whether each frequency domain spectral line is interference.

The beneficial effects of the present invention are: it suppresses satellite navigation narrowband interference through transform domain threshold-free anti-interference processing, overcomes the difficulty in determining the interference decision threshold existing in the existing technology, and can not only reduce the implementation complexity of the anti-interference processing, but also It can improve the robustness and can be used to provide interference protection capabilities for satellite navigation receiving equipment.

Description of drawings

Figure 1 is a flow chart of a transform domain threshold-free satellite navigation narrowband interference suppression method provided by the present invention;

Figure 2 is the signal spectrum diagram before narrowband interference suppression;

Figure 3 is a signal spectrum diagram obtained after narrowband interference suppression using traditional methods;

Figure 4 is a signal spectrum diagram obtained after narrowband interference suppression using the method of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the drawings and examples.

Figure 1 is a flow chart of a transform domain threshold-free satellite navigation narrowband interference suppression method provided by the present invention. As shown in the figure, it includes the following steps:

Step S11, data grouping window processing:

Suppose the AD sampling data of the satellite navigation receiving device is x(n), where n is the index of the sampling data, and the values are 1, 2, 3,…. The above sampled data are grouped according to index order, and each L piece of data is divided into one group. Then the mth group of data contains a total of L pieces of sampled data, as follows: Grouped data The corresponding relationship with the original sampling data x(n) is as follows:/>

The mth group of data is windowed according to the following formula:

Among them, y(k,m) is the m-th group of data after windowing, and w(k) is the window function of length L. Types of window functions include rectangular windows, Hamming windows, Blackman windows, etc. Their specific mathematical expressions are common knowledge in the field of digital signal processing and will not be described again here.

Step S12, time domain data conversion domain processing:

Fourier transform is performed on the windowed grouped data and converted to the transform domain. For the mth group of data, the conversion process is carried out as follows:

Among them, Y(i,m) is the frequency domain spectrum line obtained after converting the time domain data to the transform domain, and its value is a complex number.

Step S13, normalize the frequency domain spectral lines:

All frequency domain spectral lines are normalized. For the mth group of frequency domain spectral lines, the normalization process is carried out as follows:

Among them, the function Re(·) represents taking the real part of a complex number, and the function Im(·) represents taking the imaginary part of a complex number.

Step S14, the transform domain data is converted back to the time domain:

The inverse Fourier transform is performed on the normalized frequency domain spectral lines to convert the data from the transform domain back to the time domain. For the mth group of normalized frequency domain spectral lines, the conversion process is carried out as follows:

In the formula, z(k,m) is the time domain grouped data after interference suppression. The final anti-interference output data z(n) can be obtained by splicing the time domain grouped data.

Because for any positive integer n, there are positive integers m and k, so that n=(m-1)L+k holds, so the corresponding relationship between z(n) and z(k,m) can be expressed by the following formula:

z(k,m)＝z((m-1)L+k)＝z(n)

z(n) is the data after interference suppression according to the method of the present invention, and is output to the back-end capture and tracking module for further processing.

In this embodiment, the radio frequency front-end bandwidth of the navigation receiving equipment is 20MHz, AD sampling adopts orthogonal sampling method, and the sampling rate is 20.48MHz. The sampled data includes Beidou B3I signal, receiver thermal noise and narrow-band interference. The center frequency of the Beidou B3I signal is 1268.52MHz, and the carrier-to-noise ratio is 44dBHz. The center frequency of the narrowband interference is consistent with the Beidou B3I signal, the interference bandwidth is 1MHz, and the interference power is 60dB greater than the Beidou B3I signal power. Comparing Figure 2 with Figure 3 and Figure 4, it can be seen that both the traditional method and the method of the present invention effectively suppress narrow-band interference. The traditional method produces a deep null at the position of the interference spectrum line, while the method of the present invention suppresses the interference spectrum line. Normalized to the noise floor level. Furthermore, after capturing and tracking the signal after anti-interference, and using traditional methods for interference suppression, it is estimated that the carrier-to-noise ratio of the Beidou B3I signal is 43.3dBHz. The carrier-to-noise ratio obtained by the method of the present invention is 42.7dBHz, and the anti-interference performance is similar. It should be noted that in this embodiment, when the traditional method is used for narrowband interference suppression, the value of the interference decision threshold is optimized multiple times to obtain better anti-interference performance, while the method of the present invention does not require threshold setting. , the implementation complexity is lower and more robust.

The above description of the preferred embodiments of the present invention is included to illustrate the technical features of the present invention in detail. It is not intended to limit the content of the invention to the specific forms described in the embodiments. Other modifications and modifications may be made based on the gist of the content of the present invention. Variations are also protected by this patent. The gist of the present invention is defined by the claims rather than by the detailed description of the embodiments.

Claims (4)

1. A method for inhibiting narrow-band interference of threshold-free satellite navigation in a transform domain is characterized by comprising the following steps:

(1) Windowing of data packets:

setting AD sampling data of the satellite navigation receiving equipment as x (n), wherein n is an index of the sampling data, and the values are 1, 2, 3 and …; grouping the sampled data according to an index sequence, wherein each L data is divided into one group, and the m-th group of data contains L sampled data respectively: packetized dataThe correspondence with the original sample data x (n) is as follows:

windowing is carried out on the data in the m group according to the following formula:

wherein y (k, m) is the m-th group of data after windowing, and w (k) is a window function with the length L;

(2) Time domain data-to-transform domain processing:

performing Fourier transform on the windowed packet data, and converting the windowed packet data into a transform domain; for the mth set of data, the conversion process proceeds as follows:

wherein Y (i, m) is a frequency domain spectral line obtained after the time domain data is converted into a transform domain, and the value of Y (i, m) is complex;

(3) Normalizing the frequency domain spectral line:

normalizing all the frequency domain spectral lines, and for the m-th group of frequency domain spectral lines, normalizing according to the following formula:

wherein, the function Re (·) represents taking the real part of the complex number, and the function Im (·) represents taking the imaginary part of the complex number;

(4) Transform domain data is transferred back to the time domain:

and performing inverse Fourier transform on the normalized frequency domain spectral line, and converting the data from a transform domain back to a time domain. For the m-th normalized frequency domain spectrum line, the conversion process is performed according to the following formula:

wherein z (k, m) is time domain packet data after interference suppression, and the time domain packet data is spliced to obtain final anti-interference output data z (n).

2. The transform domain threshold-free satellite navigation narrowband interference suppression method of claim 1, wherein the window function is of a type of rectangular window, hamming window, or blackman window.

3. The method for suppressing interference in a narrow band of a transform-domain threshold-free satellite navigation according to claim 1 or 2, wherein the length L of each group of data is an exponential multiple of 2, and typically 256, 512 or 1024 are used in practical engineering implementation.

4. A method of transform-domain threshold-free satellite navigation narrowband interference suppression according to claim 3, characterized in that the transform-domain data is transformed back into the time domain, for any positive integer n, there are positive integers m and k such that n= (m-1) l+k holds, so that the correspondence of z (n) to z (k, m) can be represented by:

z(k,m)＝z((m-1)L+k)＝z(n)，

z (n) is the data after interference suppression by the method of the invention, and is output to the capturing and tracking module at the back end for further processing.