CN108196269B - Detection method of weak harmonic interference signal in satellite navigation anti-jamming antenna system - Google Patents

Abstract

The invention provides a method for detecting weak harmonic interference signals in a satellite navigation anti-interference antenna system, which adopts coherent accumulation of frequency spectrum energy as a check quantity and adaptively calculates a decision threshold to detect the weak harmonic interference signals in the satellite navigation anti-interference antenna system. Compared with a manual detection and identification method, the method has the characteristics that the detection threshold is determined in a self-adaptive mode on the basis of the sampling data by carrying out automatic detection processing on the original digital signals sampled by each channel in the system, and the detection probability of weak harmonic signals in the system can be effectively improved.

Description

Detection method of weak harmonic interference signal in satellite navigation anti-jamming antenna system

technical field

The invention belongs to the field of satellite navigation anti-jamming, and relates to a method for detecting weak harmonic interference signals inside a satellite navigation anti-jamming antenna system.

Background technique

At present, the satellite navigation anti-jamming antenna system is the key equipment to protect the satellite navigation receiver to work normally in the complex electromagnetic environment. In order to make the performance of the satellite navigation anti-jamming antenna system reach the optimal value of the design, it is necessary to accurately detect and eliminate the factors that affect the system performance in the system design, production and debugging process.

The satellite navigation anti-jamming antenna system is mainly composed of four parts: receiving array antenna, low noise amplifier, multi-channel radio frequency components and digital signal processing components. Due to the processing technology and the working characteristics of the analog components, there are different degrees of weak harmonic interference signals in each channel of the satellite navigation anti-jamming antenna system. The satellite navigation anti-jamming algorithm suppresses the weak harmonic interference signal inside the system as the external interference signal incident from a certain direction or multiple directions, so it will consume part of the processing freedom of the anti-jamming algorithm and affect the anti-jamming algorithm. Maximum number of anti-interference and maximum interference suppression capability.

At present, the detection of weak harmonic interference inside the satellite navigation anti-jamming antenna system is mainly to observe and analyze the output signals of each module such as low-noise amplifiers and multi-channel RF components by using instrumentation tools such as spectrum analyzers during the debugging process. Engineers use the real-time observation or maximum hold function of the spectrum analyzer to manually observe the spectrum of the output signal of each module to detect and identify weak harmonic interference signals within the system. For weak harmonic interference signals whose power is close to or weaker than system noise, manual detection and identification can easily lead to missed detection.

SUMMARY OF THE INVENTION

In order to overcome the deficiencies of the prior art, the present invention provides a method for detecting weak harmonic interference signals inside a satellite navigation anti-jamming antenna system, which adopts the coherent accumulation of spectrum energy as a test quantity, and adaptively calculates a judgment threshold for the satellite navigation anti-jamming antenna system. The detection of internal weak harmonic interference signals can effectively improve the detection probability of weak harmonic signals in the system.

The technical scheme adopted by the present invention to solve its technical problem comprises the following steps:

The first step is to collect and store the digital signal output by the analog-to-digital converter of the satellite navigation anti-jamming antenna with a set duration of T milliseconds in the absence of external electromagnetic interference, and the corresponding number of data points stored in each channel L=T×F _s ×10 ³ , where F _s is the sampling frequency of the analog-to-digital converter;

Assuming that the satellite navigation anti-jamming antenna system includes M channels, the collected and stored data forms a matrix with a dimension of L×M, and the data in the i-th column of the matrix is denoted as x(i)=[x ₀ , x ₁ ,..., x _L-1 ] ^T ;

第k(k＝1,2,…K)个子数据块记为x_k(i)；The second step is to divide the data vector x(i) into overlapping sub-data segments. The length of each sub-data block is N, and the value of N is set to a positive integer power of 2. Between two adjacent sub-data blocks The overlap ratio is set to 50%, the total number of sub-blocks

The kth (k=1,2,...K) sub-data block is denoted as x _k (i);

The third step is to construct a vector y with a size of N×1 dimension, and initialize each element in y to 0, which is represented as y ₀ =0;

The fourth step is to perform fast Fourier transform on the sub-data block x _k in turn, set the number of fast Fourier transform points to N, the result of the fast Fourier transform is recorded as X _k , and X _k is an N×1-dimensional vector ; Calculate the square of the modulus value of the n-th element X _k (n) in the X _k vector and accumulate it in the n-th element in the vector y, y _k (n)=y _k-1 (n)+|X _k ( n)| ² , n=1,2,...,N;

F_s为采样频率，用y_s表示向量y的第s个子带数据块，s＝1,2,…,S；The fifth step is to divide the vector y into S sub-bands according to the effective working bandwidth B of the satellite navigation system,

F _s is the sampling frequency, and y _s represents the s-th subband data block of the vector y, s=1,2,...,S;

The sixth step is to search for the maximum value d _s in the sub-band data block y _s in turn, and form the maximum value in the S sub-bands into a vector d=[d ₁ ,d ₂ ,...,d _S ] ^T with a size of S×1 ;

The seventh step is to search for the minimum value d _min in the vector d, set the average noise power value P _noise and initialize it to 0, set the counter J and initialize it to 0; judge in turn whether each element y(n) of the vector y is less than d _min , if it is less than d _min , then y(n) is accumulated in P _noise , the counter J counts up by 1, and after all N elements are judged, P _noise /J is calculated and used as the updated value of P _noise ;

上存在干扰，并将f(n)输出。The eighth step is to use twice the P _noise as the decision threshold y _t to perform weak harmonic interference detection, and sequentially determine whether each element y(n) of the vector y is greater than y _t , if y(n)>y _t , Then it is judged that the frequency

There is interference on and f(n) is output.

The beneficial effects of the present invention are: through the coherent accumulation of the spectral capabilities of a plurality of data blocks, the energy of the weak harmonic interference signal inside the satellite navigation anti-jamming antenna system can obtain a coherent accumulation gain, and the weak harmonic interference signal relative to the system thermal noise is improved. signal-to-noise ratio. At the same time, compared with the fixed decision threshold, the adaptive calculation of the decision threshold based on the sampled data can further improve the detection probability of weak harmonic interference in the case of different states of the anti-jamming antenna systems. The invention is suitable for the best performance debugging of the satellite navigation anti-jamming antenna system in the early stage, the system state self-check report, and the like.

Description of drawings

Fig. 1 is the method flow chart of the present invention;

FIG. 2 is a schematic diagram of division of overlapping sub-data blocks.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and embodiments, and the present invention includes but is not limited to the following embodiments.

The implementation steps of the method of the present invention are as follows:

The first step: in the absence of external electromagnetic interference, collect and store the digital signal output by the satellite navigation anti-jamming antenna analog-to-digital converter (A/D) with a duration of T milliseconds (T ≥ 1). The number of stored data points is L, the difference between L and the storage time length T (dimension is milliseconds, denoted as ms) and the sampling frequency of the analog-to-digital converter (A/D) F _s (dimension is megahertz, denoted as MHz) The calculation relationship is:

L=T×F _s ×10 ³ (1)

Assuming that the satellite navigation anti-jamming antenna system includes M channels, the collected and stored data form a matrix with a dimension of L×M. The i-th (i=1,2,...,M) column data of the data matrix is denoted as x(i)=[x ₀ ,x ₁ ,...,x _L-1 ] ^T , and the superscript T is the transpose operator.

Step 2: Divide the data vector x(i) (i=1,2,...,M) into overlapping sub-data segments, and set the length of each sub-data block to N (the value of N is set to a positive value of 2 Integer power, usually set to 1024 or 2048), the overlap rate between two adjacent sub-data blocks is set to 50%, and the total number of sub-data blocks is K. Under the condition of 50% data overlap rate, the relationship between K and N and L is;

为向下取整运算符。第k(k＝1,2,…K)个子数据块记为x_k(i)。in,

is the round-down operator. The kth (k=1, 2, . . . K ) sub-data block is denoted as x _k (i).

Step 3: Construct a vector of size N × 1, denoted as y, and initialize each element in y to 0, which is expressed as:

y ₀ =0 (3)

Among them, the subscript 0 represents the initial state, and the 0 on the right side of the equation represents a column vector containing N 0 elements.

Step 4: Perform fast Fourier (FFT) transformation on the sub-data blocks x _k (k=1,2,...K) in turn, set the number of fast Fourier transform points to N, and record the result of the fast Fourier transform. is X _k , and X _k is an N×1-dimensional vector. Calculate the square of the modulus value of the nth (n=1,2,...,N) element X _k (n) in the X _k vector and accumulate it in the nth element in the vector y. The calculation expression is:

y _k (n)=y _k-1 (n)+|X _k (n)| ² (4)

Step 5: According to the effective working bandwidth B of the satellite navigation system (dimension is megahertz), the vector y is divided into S sub-bands, and the calculation relationship between the number of sub-bands S, the effective working bandwidth B and the sampling frequency F _s is as follows :

为向下取整运算符。用y_s(s＝1,2,…,S)表示向量y的第s个子带数据块。in,

is the round-down operator. Let y _s (s=1,2,...,S) denote the sth subband data block of the vector y.

Step 6: Search for the maximum value d _s in the sub-band data blocks y _s (s=1,2,...,S) in turn. The search algorithm adopts the "bubble" sorting method, and the maximum value in the S sub-bands is composed of a size is a vector d of S × 1:

d=[d ₁ ,d ₂ ,...,d _S ] ^T (6)

The seventh step: use the "bubble" sorting method to search for the minimum value d _min in the vector d, set the average noise power value P _noise and initialize it to 0, and set the counter J and initialize it to 0. Judging in turn whether each element y(n) (n=1,2,...,N) of the vector y is less than d _min , if it is less than d _min , y(n) is accumulated in P _noise , and the counter J counts Add 1, after all N elements are judged, calculate P _noise /J and use it as the updated value of P _noise .

Step 8: Use twice the P _noise as the judgment threshold y _t to detect weak harmonic interference, and then judge whether each element y(n) (n=1,2,...,N) of the vector y is in turn. greater than y _t , if y(n)>y _t , it is judged that there is interference on the frequency point f(n), and f(n) is output, and f(n) is calculated as follows:

The invention is suitable for detecting weak harmonic interference signals in satellite navigation anti-jamming antenna systems such as GPS, BDS and GLONASS. The specific embodiment of the present invention is described by taking the detection of weak harmonic interference signals in the 4-unit BD2-B3 frequency point anti-jamming antenna system as an example.

Step 1: In the absence of external electromagnetic interference, the digital signal processing mode of the satellite navigation anti-jamming antenna system is used to collect and store the received signals of all 4 channels. The sampling frequency F _s is set to 62MHz, and the sampling duration is 2.1141ms. According to Equation (1) can calculate that the number of signal points L collected and stored by each channel is 131072. Finally, the data stored in the 4 channels forms a matrix of dimension 131072×4.

Step 2: Divide the i-th (i=1,2,...,4) column vector x(i) of the data matrix into overlapping sub-data blocks, set the length of each sub-data block to N is 2048, and the adjacent two The overlap rate between the sub-data blocks is set to 50%, then according to formula (2), the total number of sub-data blocks can be calculated as K is 127. The kth (k=1, 2, . . . 127) sub-data block is denoted as x _k (i). FIG. 2 is a schematic diagram showing the division process of overlapping sub-data blocks.

Step 3: Construct a vector of size 2048×1 dimension, denoted as y, and initialize each element in y to 0.

Step 4: Perform fast Fourier (FFT) transformation on the sub-data blocks x _k (i) (k=1, 2, ... 127) in turn, set the number of fast Fourier transform points to 2048, and set the number of fast Fourier transform points to 2048. The result is denoted as _{X k} , which is a 2048×1-dimensional vector. Calculate the square of the modulus value of the nth (n _{= 1} , 2, .

Step 5: The effective working bandwidth B of the BD2-B3 frequency satellite navigation signal is 20.46MHz. According to formula (5), it is calculated that the vector y can be divided into 30 sub-bands, using y _m (m=1,2,...,30 ) represents the mth subband data block of the vector y.

Step 6: Search for the maximum value d _m in the sub-band data blocks y _m (m=1, 2, ..., 30) in turn. The search algorithm adopts the "bubble" sorting method, and the maximum value in the 30 sub-bands is composed of dimensions. A vector of size 30×1 d=[d ₁ ,d ₂ ,…,d ₃₀ ] ^T , where the superscript T is the transpose operator.

Step 7: Use the "bubble" sorting method to search for the minimum value d _min in the vector d, set the average noise power value P _noise and initialize it to 0, and set the counter J and initialize it to 0. Judging in turn whether each element y(n) (n=1,2,...,2048) of the vector y is less than d _min , if it is less than d _min , y(n) is accumulated in P _noise , and the counter J counts Add 1, after all 2048 elements are judged, calculate P _noise /J and update the P _noise value.

Step 8: Use twice the P _noise as the decision threshold y _t to perform weak harmonic interference detection, and sequentially determine whether each element y(n) (n=1,2,...,2048) of the vector y is greater than y _t , if y(n)>y _t , it is judged that there is interference on the frequency point f(n), and the weak interference harmonic frequency f(n) is calculated and output according to formula (8). So far, the detection of weak harmonic interference in the i-th channel.

Follow steps 2 to 8 in sequence to complete the detection of weak harmonic interference in all channels.

Claims (1)

1. A method for detecting weak harmonic interference signals in a satellite navigation anti-interference antenna system is characterized by comprising the following steps:

the method comprises the steps of firstly, collecting and storing digital signals output by an analog-to-digital converter of a satellite navigation anti-interference antenna with a set time length of T milliseconds under the condition of no external electromagnetic interference, and storing the number L of data points in each corresponding channel as T multiplied by F_s×10³Wherein F is_sSampling frequency for the analog-to-digital converter;

assuming that the satellite navigation anti-interference antenna system comprises M channels, the acquired and stored data form a matrix with dimension L multiplied by M, and the ith column of data of the matrix is marked as x (i) ([ x)₀,x₁,…,x_L-1]^T；

Secondly, dividing the data vector x (i) into sub-data blocks which are overlapped with each other, wherein the length of each sub-data block is N, the value of N is set to be the positive integer power of 2, the overlapping rate between two adjacent sub-data blocks is set to be 50%, and the total number of the sub-data blocks is

K (k is 1, 2)… K) sub-data blocks denoted x_k(i)；

Thirdly, constructing a vector y with the size of Nx 1 dimension, and initializing each element in y to be 0, wherein y is represented as₀＝0；

Fourthly, sequentially sub-data blocks x_kPerforming fast Fourier transform, setting the number of fast Fourier transform points to be N, and recording the result of the fast Fourier transform as X_k，X_kIs a vector of dimension Nx 1; calculating X_kThe nth element X in the vector_kThe squares of the modulus values of (n) are summed up in the nth element of the vector y, y_k(n)＝y_k-1(n)+|X_k(n)|²，n＝1,2,...,N；

Fifthly, dividing the vector y into S sub-bands according to the effective working bandwidth B of the satellite navigation system,

F_sfor sampling frequency, use y_sThe S-th subband data block, S-1, 2, …, S, representing vector y;

sixthly, the sub-band data block y is searched in sequence_sMaximum value of d_sThe maximum values in the S subbands are combined into a vector d ═ d of size S × 1₁,d₂,…,d_S]^T；

Seventhly, searching the minimum value d in the vector d_minLet the noise mean power value P_noiseAnd initialized to 0, a counter J is designed and initialized to 0; sequentially judging whether each element y (n) of the vector y is smaller than d_minIf it is less than d_minThen y (n) is added to P_noiseAnd (4) performing middle accumulation, adding 1 to the count of the counter J, and calculating P after judging all N elements_noiseA combination of J and P_noiseUpdating the value;

eighth step with P_noiseIs twice as the decision threshold value y_tCarrying out weak harmonic interference detection, and sequentially judging whether each element y (n) of the vector y is larger than y_tIf y (n) > y_tIf yes, the decision is at the frequency point

There is interference and f (n) is output.

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