Narrowband anti-interference threshold determination method based on iterative computation

Abstract

The invention discloses a narrowband anti-interference threshold determination method based on iterative computation, which comprises the following steps of: 1, performing N-point FFT (Fast Fourier Transform) computation on a received zero intermediate frequency time domain signal to obtain a frequency spectrum data sequence XK of the signal; 2, performing m times of iterative operation on the spectrum data sequence XK obtained in the step 1, and determining an accurate threshold value; step 3, obtaining a new spectrum data sequence XK'according to the spectrum data sequence XK in the step 1 and the threshold value in the step 2; and step 4, carrying out IFFT on the XK'calculated in the step 3 to obtain time domain data after interference suppression. The method is simple in algorithm and easy to implement, and does not need complex arithmetic operation.

Description

Technical Field

[0001] The invention belongs to the technical field of interference suppression of direct sequence spread spectrum systems, and relates to a method for determining a narrowband anti-interference threshold based on iterative calculation. Background Art

[0002] Direct Sequence Spread Spectrum (DSSS) technology is widely used in satellite navigation and other fields due to its good concealment and ability to resist multipath and multiple access interference. However, during operation, the DSSS system will be subject to interference from the natural environment or man-made interference. When it exceeds the system spread spectrum gain, additional interference suppression measures are required to ensure the normal operation of the system. One of the conventional narrowband interference suppression technologies in spread spectrum systems is frequency domain narrowband anti-interference technology, which is widely used due to its simple and direct design and fast suppression speed.

[0003] The basic idea of ​​the frequency domain narrowband anti-interference algorithm is to use digital processing technology to process the signal spectrum according to the different spectrum characteristics of the useful signal and the interference signal, so as to effectively suppress interference and retain the useful signal. The specific method is to detect the spectrum position of the interference by performing FFT on the received signal, which will show a peak value higher than the spread spectrum signal spectrum, remove or attenuate these spectrum lines, and then restore them to the time domain signal through inverse transformation to suppress interference. The process is as follows: Figure 1 shown.

[0004] Among them, the commonly used amplitude spectrum mean multiplied by a pre-set threshold parameter T is used as the threshold value for judging interference, and the frequency point greater than the threshold is considered to be the frequency point where interference exists. This method is relatively simple to determine the interference location, but it requires the threshold value to be relatively accurate, otherwise it will cause misjudgment. If the threshold is too high, it is easy to miss some interference, and if the threshold is too low, it is easy to cause false detection and misdetect useful signals as interference. Summary of the invention

[0005] (I) Purpose of the invention

[0006] The purpose of the present invention is to solve the problem of setting a threshold parameter T to determine the presence of interference in the prior art, and to propose a narrowband anti-interference threshold determination method based on iterative calculation, which uses an iterative algorithm to accurately calculate the theoretical threshold value, thereby avoiding the above-mentioned shortcomings of missing interference information and misdetecting useful information.

[0007] (II) Technical solution

[0008] In order to solve the above technical problems, the present invention provides a method for determining a narrowband anti-interference threshold based on iterative calculation, wherein the processing starts after the receiving end down-converts the received time domain signal to a zero intermediate frequency, and specifically comprises the following steps:

[0009] Step 1: Perform N-point FFT calculation on the received zero intermediate frequency time domain signal to obtain the signal's spectrum data:

[0010] The input zero-IF time domain signal sequence is represented as xn={x1,x2,...,x n},n=1,2,...,N;

[0011] The spectrum data sequence after N-point FFT is expressed as XK={X1,X2,...,X k}, k = 1, 2, ..., N;

[0012] Step 2: Perform m iterations on the spectrum data sequence XK obtained in step 1 to determine the precise threshold value, specifically:

[0013] Step 2.1 sets the initial threshold value Th_cmp and the initial increase or decrease value Th_inc. Generally;

[0014] Step 2.2: Compare the spectrum data values ​​obtained in step 1 with the threshold value Th_cmp in turn, and count the number of under_cnt values ​​below the threshold value Th_cmp;

[0015] Step 2.3: Compare the under_cnt calculated in step 2.2 with the preset useful signal number threshold R th By contrast, if under_cnt is higher than the threshold R th If under_cnt is lower than the threshold R, adj_low is set to 1. th Then adj_high is set to 1, and one iteration operation is completed;

[0016] Step 2.4 updates the threshold value Th_cmp and the increase / decrease value Th_inc, specifically: according to the result of step 2.3, if adj_high is 1, Th_cmp+Th_inc is used as the threshold value of the next iteration, and Th_inc / 2 is used as the increase / decrease value of the next iteration; if adj_low is 1, Th_cmp-Th_inc is used as the threshold value of the next iteration, and Th_inc / 2 is used as the increase / decrease value of the next iteration;

[0017] Step 2.5: Repeat steps 2.2-2.4 until the maximum number of iterations m is reached. The final calculated Th_cmp is the accurate threshold value.

[0018] Step 3: Compare the frequency spectrum data sequence XK obtained in step 1 with the threshold value Th_cmp obtained by iteration in step 2.5. The frequency value greater than Th_cmp is considered to be the frequency point with interference and is set to 0; the frequency value less than Th_cmp retains the original value, and a new frequency spectrum data sequence XK'={X1',X2',...,X k '};

[0019] Step 4: Perform IFFT on XK' calculated in step 3 to obtain the interference-suppressed time domain data xn'={x1',x2',...,x n '}.

[0020] in:

[0021] (1) The maximum number of iterations m can be calculated and set according to the quantization bit width of the input data;

[0022] (2) In general, the initial threshold value Th_cmp is half of the maximum value that can be represented by the quantization bit width of the spectrum data, and the initial increase or decrease value Th_inc is half of the initial threshold value Th_cmp;

[0023] (3) Useful signal number threshold R th The settings can be calculated based on the relative bandwidth of the known narrowband interferers.

[0024] (III) Beneficial effects

[0025] The narrowband anti-interference threshold determination method based on iterative calculation provided by the above technical solution has the following beneficial effects compared with the traditional threshold determination method:

[0026] (1) The algorithm is simple and easy to implement, and does not require complex arithmetic operations;

[0027] (2) As long as the number of iterations is sufficient, the anti-interference threshold value calculated by this method is accurate enough, avoiding the defects of the traditional method of setting the threshold parameter T too high to cause missed detection of interference information and setting the threshold parameter T too low to misdetect useful information. Figure 2 As shown, the method of the present invention has a performance about 1.5 dB better than the low threshold parameter and much better than the high threshold parameter. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of frequency domain anti-interference of a method for determining a narrowband anti-interference threshold based on iterative calculation according to an embodiment of the present invention;

[0029] Figure 2 The figure is a curve diagram showing the variation of the bit error rate with Eb / N0 under different signal-to-noise ratios in the narrowband anti-interference threshold determination method based on iterative calculation in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with the drawings and examples.

[0031] Aiming at the defects of missing interference information and misdetecting useful information by setting a threshold parameter T in the traditional method of judging the existence of interference, the present invention proposes a method for determining a narrowband anti-interference threshold based on iterative calculation.

[0032] Reference Figure 1 As shown, the narrowband anti-interference threshold determination method based on iterative calculation in this embodiment is applied to a narrowband anti-interference example with a relative bandwidth RBW=10% and a signal-to-interference ratio JSR=40dB.

[0033] Step 1. The input zero intermediate frequency time domain signal sequence xn is: [324, -1204, -901, 1651, 213, 1588, 525, -167, 107, -1923, ...,] a total of 512 symbols, the quantization bit width is 16 bits, and the spectrum data sequence XK after 512-point FFT is: [151, 141, 164, 87, 98, 148, 76, 55, ..., 3498, 3515, 2858, 1785, 1291, 1966, 5308, 4693, ..., 159, 150, 190, 131, 129, 63, 78, 91] a total of 512 symbols, the quantization bit width is 16 bits. It can be clearly seen that the larger value is the location of the interference frequency point;

[0034] Step 2: Perform 15 iterations on the spectrum data sequence XK obtained in step 1. The maximum number of iterations is the quantization bit width minus 1. The specific operations are:

[0035] Step 2.1: Set the initial threshold value Th_cmp to 2^15 and the initial increase / decrease value Th_inc to 2^14;

[0036] Step 2.2: Compare the spectrum data values ​​obtained in step 1 with the threshold value 2^15 in turn, and count the number of under_cnt values ​​below the threshold value 2^15, which is 512.

[0037] Step 2.3: Since the relative bandwidth of narrowband interference RBW = 10%, the number of FFT points is 512, so the useful signal number threshold R th It can be set to 512*(1-10%)=461, and the under_cnt calculated in step 2.2 is compared with the preset R th By contrast, if under_cnt is higher than the threshold R th If under_cnt is lower than the threshold R, adj_low is set to 1. th Then adj_high is set to 1, and one iteration operation is completed;

[0038] Step 2.4 updates the threshold value Th_cmp and the increase / decrease value Th_inc. Specifically, according to the result of step 2.3, adj_high is 0 and adj_low is 1, then 2^15-2^14 is used as the threshold value for the next iteration, and 2^13 is used as the increase / decrease value for the next iteration;

[0039] Step 2.5: Repeat steps 2.2-2.4 until the maximum number of iterations reaches 15. The final calculated Th_cmp is 712, which is the precise threshold value.

[0040] Step 3. Compare the frequency spectrum data sequence XK obtained in step 1 with the threshold value 712 obtained in step 2.5. The frequency values ​​greater than 712 are considered to be the frequency points with interference and are set to 0. The frequency values ​​less than 712 retain the original values. The new frequency spectrum data sequence XK' is [151,141,164,87,98,148,76,55,…,0,0,0,0,0,0,0,0,…,159,150,190,131,129,63,78,91]. It can be seen that the interference data in the middle segment are effectively suppressed.

[0041] Step 4: Perform IFFT on XK' calculated in step 3 to obtain the interference-suppressed time domain data xn': [272, -151, -168, 479, 363, 246, 367, -289, 479, -517, ... ].

[0042] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for determining a narrowband anti-interference threshold based on iterative calculation, characterized in that: The method processing process starts after the receiving end down-converts the received time domain signal to zero intermediate frequency, and includes the following steps: Step 1: Perform N-point FFT calculation on the received zero intermediate frequency time domain signal to obtain the signal spectrum data sequence XK; Step 2: Perform m iterations on the spectrum data sequence XK obtained in step 1 to determine an accurate threshold value; Step 3: Obtain a new spectrum data sequence XK' according to the spectrum data sequence XK in step 1 and the threshold value in step 2; Step 4: Perform IFFT on XK' calculated in step 3 to obtain time domain data with interference suppressed.

2. The method for determining a narrowband anti-interference threshold based on iterative calculation according to claim 1, characterized in that: In step 1, the input zero intermediate frequency time domain signal sequence is represented as xn = {x1, x2, ..., x n }, n = 1, 2, ..., N; the spectrum data sequence after N-point FFT is expressed as XK = {X1, X2, ..., X k },k=1,2,...,N.

3. The method for determining a narrowband anti-interference threshold based on iterative calculation according to claim 2, characterized in that: Step 2 includes the following sub-steps: Step 2.1: Set the initial threshold value Th_cmp and the initial increase / decrease value Th_inc; Step 2.2: Compare the spectrum data sequence obtained in step 1 with the threshold value Th_cmp in turn, and count the number of under_cnt below the threshold value Th_cmp; Step 2.3: Compare the under_cnt calculated in step 2.2 with the preset useful signal number threshold R th By contrast, if under_cnt is higher than the threshold R th , then adj_low is set to 1, if under_cnt is lower than the threshold R th , then adj_high is set to 1, and one iteration operation is completed; Step 2.4 updates the threshold value Th_cmp and the increase / decrease value Th_inc; Step 2.5: Repeat steps 2.2-2.4 until the maximum number of iterations m is reached. The final calculated Th_cmp is the accurate threshold value.

4. The method for determining a narrowband anti-interference threshold based on iterative calculation according to claim 3, characterized in that: In step 2.4, according to the result of step 2.3, if adj_high is 1, Th_cmp+Th_inc is used as the threshold value for the next iteration, and Th_inc / 2 is used as the increase or decrease value for the next iteration; if adj_low is 1, Th_cmp-Th_inc is used as the threshold value for the next iteration, and Th_inc / 2 is used as the increase or decrease value for the next iteration.

5. The method for determining a narrowband anti-interference threshold based on iterative calculation according to claim 4, characterized in that: In step 3, the spectrum data sequence XK obtained in step 1 is compared with the threshold value Th_cmp obtained by iteration in step 2.

5. The frequency value greater than Th_cmp is considered to be the frequency point with interference and is set to 0; the frequency value less than Th_cmp retains the original value, and a new spectrum data sequence XK'={X1',X2',...,X k '}.

6. The method for determining a narrowband anti-interference threshold based on iterative calculation according to claim 5, characterized in that: In step 4, the XK' calculated in step 3 is subjected to IFFT to obtain the interference-suppressed time domain data xn'={x1',x2',...,x n '}.

7. The method for determining a narrowband anti-interference threshold based on iterative calculation according to claim 6, characterized in that: The maximum number of iterations m is calculated and set according to the quantization bit width of the input data.

8. The method for determining a narrowband anti-interference threshold based on iterative calculation according to claim 7, characterized in that: The initial threshold value Th_cmp is half of the maximum value that can be represented by the quantization bit width of the spectrum data, and the initial increase or decrease value Th_inc is half of the initial threshold value Th_cmp.

9. The method for determining a narrowband anti-interference threshold based on iterative calculation according to claim 8, characterized in that: Useful signal number threshold R th The settings can be calculated based on the relative bandwidth of the known narrowband interferers.

10. An application of the narrowband anti-interference threshold determination method according to any one of claims 1 to 9 in the technical field of interference suppression in direct sequence spread spectrum systems.

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