CN111600628A - Narrowband Interference Suppression Method with Adaptive Filtering Existing Doppler First-Order Rate of Change - Google Patents

Abstract

The invention discloses an adaptive filtering narrowband interference suppression method with a Doppler first-order change rate, which belongs to the technical field of communication. The implementation method of the invention is as follows: the receiving end of the communication system inputs the received signal to the ADC module, and after the signal received by the communication receiving end is subjected to analog-to-digital conversion, digital down-conversion, low-pass filtering and extraction modules, the data is obtained after decimation. It is transmitted to the demodulation module; the initial frequency offset and the first-order rate of change of the frequency offset are estimated by the fractional Fourier transform, and the estimated value is used to compensate the value output by the extraction module, and the signal is interpolated Then, the time-domain adaptive filtering anti-jamming processing is performed to realize the time-domain adaptive filtering anti-jamming when there is a Doppler first-order change rate, and improve the anti-jamming performance of the communication system. The invention utilizes the LMS adaptive filtering method to perform time-domain anti-interference on the communication signal after frequency offset and frequency offset first-order change rate compensation, and has a simple structure and is easy to implement.

Description

Narrowband Interference Suppression Method with Adaptive Filtering Existing Doppler First-Order Rate of Change

technical field

The invention belongs to the technical field of communication, and relates to an adaptive filtering narrowband interference suppression method with a Doppler first-order change rate.

Background technique

Direct Sequence Spread Spectrum (DSSS) is to expand the spectrum of the transmitted signal with pseudo-random sequences to improve the reliability of the communication system. It is widely used in the fields of military and civilian communications. Although the direct sequence spread spectrum technology has a certain anti-interference ability, when the interference intensity exceeds the processing gain of the spread spectrum signal, the interference suppression algorithm must be used to ensure the performance of the system.

The interference suppression algorithm is divided into transform domain anti-interference and time domain anti-interference. The transform domain anti-interference algorithm converts the time domain signal into a transform domain signal through transformation, and the complex filtering and convolution operations in the time domain become multiplication operations in the transform domain. Simple and easy to engineer. However, the hardware resource consumption is relatively large during implementation; in the case where the hardware resources are more constrained, the time-domain anti-jamming algorithm is generally selected, and the time-domain adaptive filtering narrowband interference suppression technology based on the least mean square (LMS) algorithm is commonly used. Time-domain anti-jamming algorithm. In the direct sequence spread spectrum system, the signal bandwidth is large, the pseudo-random sequence is close to the ideal autocorrelation and cross-correlation, and the correlation between the sampling points of the signal is very small, so it is extremely difficult to estimate the following information based on the previous information. The bandwidth of the narrowband interference signal is narrower than that of the spread spectrum signal, and the correlation between the sampling points is very strong. Therefore, the principle of time-domain anti-jamming technology is to use the correlation of the narrowband interference signal to predict it, and then subtract it, thereby improving the system performance.

However, when the received signal has a Doppler frequency offset and the Doppler frequency offset still has a first-order transformation rate, the narrowband interference signal changes from a stationary signal to a non-stationary signal, and its autocorrelation function becomes a time-varying function. When the frequency offset change caused by the Le change rate is much larger than the symbol rate, the interference becomes unpredictable, which will seriously affect the time-domain anti-jamming performance. Therefore, it is very necessary to design a narrowband interference suppression method for LMS adaptive filtering in the presence of Doppler and Doppler first-order transform rate.

SUMMARY OF THE INVENTION

In view of the defects in the prior art: in the presence of Doppler and Doppler first-order rate of change, the time-domain adaptive filtering narrowband interference suppression method cannot correctly estimate the interference situation, which seriously affects the time-domain anti-interference performance. The technical problem to be solved by the adaptive filtering narrowband interference suppression method with the first-order Doppler change rate disclosed in the present invention is: in the case of the first-order Doppler change rate, the fractional-order Fourier transform is used to suppress the received signal. Search for Doppler and Doppler first-order rate of change, perform Doppler and Doppler first-order rate-of-change compensation for the communication system, and then perform time-domain adaptive filtering for narrowband interference suppression to improve the anti-interference performance of the communication system .

The purpose of the present invention is achieved through the following technical solutions.

The invention discloses an adaptive filtering narrow-band interference suppression method with a Doppler first-order change rate. The receiving end of the communication system inputs the received signal to the ADC module, and the signal received by the communication receiving end undergoes analog-to-digital conversion and digital downlinking. After the frequency conversion, low-pass filtering and decimation modules, the data obtained after decimation is transmitted to the demodulation module; the initial frequency offset of the signal and the first-order change rate of the frequency offset are estimated by the fractional Fourier transform, and the estimated frequency is used. The value compensates the value output by the extraction module, and then performs time-domain adaptive filtering and anti-interference processing after the signal is interpolated, so as to realize the time-domain adaptive filtering anti-interference when there is a Doppler first-order change rate, and improve the communication system. Anti-interference performance.

The adaptive filtering narrowband interference suppression method with the Doppler first-order change rate disclosed in the present invention includes the following steps:

Step 1: The receiving end of the communication system inputs the received signal to the ADC module, and the quadrature down-conversion module performs digital down-conversion processing on the digital signal output by the ADC to obtain I and Q quadrature baseband data, and converts the I and Q into positive The baseband data is transmitted to the low-pass filter module;

In step 1, the received signal r(t) at the receiving end of the communication system is expressed as formula (1):

为初始相位、N为扩频码长度、h(t)为成型波形、T_c为一个扩频码的码片持续时间、c为扩频码向量。Among them, f _c is the carrier frequency, and Δf is the frequency offset. Since there is a Doppler first-order rate of change, the frequency offset Δf is a function that changes with time,

is the initial phase, N is the length of the spreading code, h(t) is the shaping waveform, T _c is the chip duration of a spreading code, and c is the spreading code vector.

In step 2, the low-pass filter module performs low-pass filtering on the I, Q quadrature baseband data, and then transmits the filtered I, Q quadrature baseband data to the extraction module;

The implementation method of step 2 is: the low-pass filter module performs low-pass filtering on the I and Q quadrature baseband data, and the discrete signal after the low-pass filtering is expressed as:

不随时间变化，因此公式(2)变换为：where c is the spreading code of the nth sampling point, d is the transmitted signal, T _smp is the sampling interval, and f _smp is the sampling rate. Due to the initial phase

does not change with time, so formula (2) transforms into:

s(n)=Ac(n)d(n)exp(j2πΔf(nT _smp )nT _smp ) ⑶

将经过滤波之后的I、Q正交基带数据s(n)传输给抽取模块。in

The filtered I, Q quadrature baseband data s(n) are transmitted to the decimation module.

Step 3, the extraction module extracts the filtered I, Q quadrature baseband data s(n) to obtain data s'(n), and transmits s'(n) to the demodulation module;

Preferably, in step 3, the filtered I, Q quadrature baseband data s(n) is extracted to twice the chip rate to obtain the signal s'(n).

Step 4. The demodulation module uses the fractional Fourier transform to search and estimate the frequency offset and the frequency offset transformation rate of the extracted I, Q orthogonal baseband data s'(n), and then obtain the frequency offset according to the estimation. Compensate the extracted I, Q orthogonal baseband data with the frequency offset conversion rate, and transmit the compensated I, Q orthogonal baseband data to the time-domain anti-jamming module;

Step four includes the following five steps:

Step 4.1. Store the extracted I and Q quadrature baseband data s'(n) output in step 3 into the memory in the demodulation modulation process, and then store the frequency offset and the first-order change rate of the frequency offset after estimating the frequency offset. The data in the memory is read out for compensation;

Step 4.2. While performing step 4.1, take the rotation angle α as a variable and perform fractional Fourier transform on the input discrete signal of N points with d as the step of the data s'(n) output in step 3.

In the presence of the Doppler first-order frequency offset first-order rate of change, the Doppler frequency offset is a time-varying function, which is expressed as follows:

为频偏一阶变化率，因此步骤三中抽取后的数据表示为下式：where Δf ₀ is the initial frequency offset,

is the first-order rate of change of frequency offset, so the extracted data in step 3 is expressed as the following formula:

where T _d is the decimation interval, and the formula for fractional Fourier transform is as follows:

Where α=pπ/2, α∈(-π,π], after traversing α, a two-dimensional plane is obtained;

Step 4.3, search the two-dimensional plane obtained in step 4.2 to obtain the coordinates of the peak point

计算得到初始频偏及频偏一阶变化率。Step 4.4, obtain the coordinates of the peak point through step 4.3

Calculate the initial frequency offset and the first-order rate of change of the frequency offset.

The estimation formulas of the initial frequency offset and the first-order rate of change of the frequency offset are as follows:

Step 4.5, read out the data stored in step 4.1 and use the initial frequency offset and the first-order change rate of frequency offset estimated in step 4.4 to perform frequency offset on the extracted I, Q quadrature baseband data s'(n); After compensation, it is transmitted to the time-domain anti-jamming module;

Step 5: After inputting the frequency offset compensated data into the adaptive filter module for time-domain narrowband interference suppression, the data after narrowband interference suppression is transmitted to the interpolation module;

The fifth step includes the following two steps:

Step 5.1, calculate the response of the data output in step 4.5 through the adaptive filter y(n)=w ^T (n)x(n), where x(n) is the input of the adaptive filter, and w(n) is the adaptive filter The tap coefficient of the filter, y(n) is the output of the adaptive filter, and the interference suppression output e(n)=x(n)-y(n) is obtained.

Step 5.2, update the adaptive filter tap coefficients for the interference suppression output e(n) output in step 5.1, and return to step 5.1.

Preferably, step 5.2 chooses to use the least mean square (LMS) adaptive filtering narrowband anti-interference method, wherein the adaptive filter tap coefficient update method in step 5.2 is: w(n+1)=w(n)+μe( n)x(n), where μ is the update step size.

Step 6: Interpolate the output signal after interference suppression in step 5 to complete narrowband anti-jamming processing, that is, realize time-domain adaptive filtering narrowband interference suppression in the presence of Doppler and Doppler first-order rate of change, and improve Anti-jamming performance of communication systems.

Beneficial effects:

1. The adaptive filtering narrowband interference suppression method with the Doppler first-order change rate disclosed in the present invention, in the presence of the Doppler first-order change rate, the Doppler and The Doppler first-order rate of change is searched, and the Doppler and Doppler rate of change of the communication system are compensated, and then the time-domain adaptive filtering is performed to suppress narrow-band interference to improve the anti-interference performance of the communication system.

2. The adaptive filtering narrowband interference suppression method with the Doppler first-order rate of change disclosed in the present invention uses the LMS adaptive filtering method to perform time-domain immunity on the communication signal after frequency offset and frequency offset first-order rate of change compensation. interference, simple structure, low complexity and easy implementation.

3. The adaptive filtering narrowband interference suppression method with the Doppler first-order change rate disclosed in the present invention reduces the resource consumption when the anti-interference algorithm is implemented by extracting the communication signal to twice the chip rate.

Description of drawings

1 is a flowchart of a time-domain adaptive filtering narrowband interference suppression method with a Doppler first-order transform rate of the present invention;

Fig. 2 is the principle block diagram of the time-domain adaptive filtering narrow-band interference suppression method with Doppler first-order transformation rate of the present invention;

Fig. 3 is the principle block diagram of demodulation module in the present invention's existence Doppler first-order transform rate time-domain adaptive filtering narrow-band interference suppression method;

4 is a schematic block diagram of a time-domain anti-jamming module in a time-domain adaptive filtering narrowband interference suppression method with a Doppler first-order transformation rate according to the present invention.

Detailed ways

In order to describe in detail the technical content, achieved objects and effects of the present invention, the technical solutions in this embodiment will be described clearly and completely below with reference to the embodiments and the accompanying drawings. Obviously, the described embodiments are part of the present invention. , not all examples. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

In the direct sequence spread spectrum system, the correlation characteristics of narrowband interference are much stronger than the signal itself. The basis of the anti-interference algorithm of time domain adaptive filter is based on this strong correlation of narrowband interference. The interference is estimated in the state of superposition of narrowband interference and deleted in the time domain. The correlation of narrowband interference is affected in the presence of Doppler and Doppler first-order rate of change and must be compensated for.

As shown in FIG. 1 and FIG. 2 , the time-domain adaptive filtering narrowband interference suppression method disclosed in this embodiment in the presence of Doppler and Doppler first-order transform rate, the specific implementation steps are as follows:

Step 1: The receiving end of the communication system inputs the received signal to the ADC module, and the quadrature down-conversion module performs digital down-conversion processing on the digital signal output by the ADC to obtain I and Q quadrature baseband data, and converts the I and Q into positive The baseband data is transmitted to the low-pass filter module;

The received signal r(t) is expressed as follows

为初始相位、N为扩频码长度、h(t)为成型波形、T_c为一个扩频码的码片持续时间、c为扩频码向量。Among them, f _c is the carrier frequency, and Δf is the frequency offset. Since there is a first-order Doppler rate of change, the frequency offset Δf is a function that changes with time,

is the initial phase, N is the length of the spreading code, h(t) is the shaping waveform, T _c is the chip duration of a spreading code, and c is the spreading code vector.

In step 2, the low-pass filter module performs low-pass filtering on the I and Q quadrature baseband data, and the discrete signal after the low-pass filtering is expressed as;

不随时间变化，因此上式可以变为：where c is the spreading code of the nth sampling point, d is the transmitted signal, T _smp is the sampling interval, and f _smp is the sampling rate. Due to the initial phase

does not change with time, so the above formula can be changed to:

s(n)=Ac(n)d(n)exp(j2πΔf(nT _smp )nT _smp ) (10)

将经过滤波之后的I、Q正交基带数据s(n)传输给抽取模块。in

The filtered I, Q quadrature baseband data s(n) are transmitted to the decimation module.

Step 3: The extraction module extracts the filtered I, Q quadrature baseband data s(n) to obtain data s'(n), and transmits s'(n) to the demodulation module. In order to reduce the difficulty of anti-aliasing filter design and improve the signal-to-noise in the working frequency band, oversampling will be performed when AD sampling the received signal. When adaptive filtering suppresses interference, it will also damage useful signals, and if the signal sampling rate is too large, it will consume a lot of hardware resources during demodulation and time-domain anti-interference. Therefore, the signal is extracted to 2 times the chip rate, and the extraction The data after that is as follows:

s'(n)=Ac(n)d(n)exp(j2πΔf(nT _d )nT _d ) (11)

T_c为一个码片的时间，将经过抽取之后的数据传输给解线调模块。in

T _c is the time of one chip, and the extracted data is transmitted to the demodulation module.

Step 4. The demodulation module uses the fractional Fourier transform to search and estimate the frequency offset and the frequency offset transformation rate of the extracted I, Q orthogonal baseband data s'(n), and then obtain the frequency offset according to the estimation. Compensate the extracted I, Q orthogonal baseband data with the frequency offset conversion rate, and transmit the compensated I, Q orthogonal baseband data to the time-domain anti-jamming module;

In the presence of the Doppler first-order rate of change, the Doppler frequency offset is a time-varying function expressed as follows:

为频偏一阶变化率，因此步骤三中抽取后的数据可以表示为下式：where Δf ₀ is the initial frequency offset,

is the first-order rate of change of frequency offset, so the extracted data in step 3 can be expressed as the following formula:

The principle block diagram of the demodulation module is shown in Figure 2. When the data output in step 3 is input into the buffer buffer, the rotation angle α is used as a variable, and d is used as the step size to perform fractional Fourier transformation on the input N-point discrete signal Transform, the formula of fractional Fourier transform is as follows:

然后即可根据下式估计出初始频偏与频偏一阶变化率：where α=pπ/2, α∈(-π,π], traverse α to get a two-dimensional plane; search this two-dimensional plane to get the coordinates of its maximum value

Then the initial frequency offset and the first-order rate of change of the frequency offset can be estimated according to the following formula:

The data in the buffer is read out, the estimated initial frequency offset and the first-order change rate of the frequency offset are used to compensate the data read in the buffer, and then the compensated data is transmitted to the time-domain anti-interference.

Step 5: Input the data output in step 4 into the time-domain adaptive filtering anti-interference module, the schematic diagram of which is shown in Figure 3. Because the LMS adaptive filtering anti-interference method has low computational complexity and is easy to implement, the LMS algorithm is selected. to update the tap coefficients of the adaptive filter. The module input signal x(n) passes through the adaptive filter to obtain the filter output y(n)=w ^T (n)x(n), and the input signal is subtracted from the filter output to obtain the interference suppression output e(n)= x(n)-y(n), on the one hand, the output of the interference suppression is output to the interpolation module for subsequent processing, and on the other hand, the LMS algorithm is used to update the adaptive filter tap system, and the update method is w(n+1) =w(n)+μe(n)x(n), where μ is the update step size.

Step 6: Interpolate the output signal after interference suppression in step 5 to complete narrowband anti-jamming processing, that is, realize time-domain adaptive filtering narrowband interference suppression in the presence of Doppler and Doppler first-order rate of change, and improve Anti-jamming performance of communication systems.

The above-mentioned specific descriptions further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned descriptions are only specific embodiments of the present invention, and are not intended to limit the protection of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (7)

1. there is the adaptive filtering narrowband interference suppression method of Doppler first-order rate of change, it is characterized in that: comprise the steps, Step 1: The receiving end of the communication system inputs the received signal to the ADC module, and the quadrature down-conversion module performs digital down-conversion processing on the digital signal output by the ADC to obtain I and Q quadrature baseband data, and converts the I and Q into positive The baseband data is transmitted to the low-pass filter module; In step 2, the low-pass filter module performs low-pass filtering on the I, Q quadrature baseband data, and then transmits the filtered I, Q quadrature baseband data to the extraction module; Step 3, the extraction module extracts the filtered I, Q quadrature baseband data s(n) to obtain data s'(n), and transmits s'(n) to the demodulation module; Step 4. The demodulation module uses the fractional Fourier transform to search and estimate the frequency offset and the frequency offset transformation rate of the extracted I, Q orthogonal baseband data s'(n), and then obtain the frequency offset according to the estimation. Compensate the extracted I, Q orthogonal baseband data with the frequency offset conversion rate, and transmit the compensated I, Q orthogonal baseband data to the time-domain anti-jamming module; Step 5: After inputting the frequency offset compensated data into the adaptive filter module for time-domain narrowband interference suppression, the data after narrowband interference suppression is transmitted to the interpolation module; Step 6: Interpolate the output signal after interference suppression in step 5 to complete narrowband anti-jamming processing, that is, realize time-domain adaptive filtering narrowband interference suppression in the presence of Doppler and Doppler first-order rate of change, and improve Anti-jamming performance of communication systems. 2. the self-adaptive filtering narrow-band interference suppression method with Doppler first-order rate of change as claimed in claim 1, is characterized in that: in step 1, the reception signal r(t) of the communication system receiving end is expressed as shown in formula (1) Show:

Among them, f _c is the carrier frequency, and Δf is the frequency offset. Since there is a Doppler first-order rate of change, the frequency offset Δf is a function that changes with time,

is the initial phase, N is the length of the spreading code, h(t) is the shaping waveform, T _c is the chip duration of a spreading code, and c is the spreading code vector. 3. the self-adaptive filtering narrowband interference suppression method that there is Doppler first-order rate of change as claimed in claim 2, is characterized in that: step 2 realization method is, low-pass filter module carries out I, Q quadrature baseband data. Low-pass filtering, the discrete signal after low-pass filtering is expressed as:

where c is the spreading code of the nth sampling point, d is the transmitted signal, T _smp is the sampling interval, and f _smp is the sampling rate; since the initial phase

does not change with time, so formula (2) transforms into: s(n)=Ac(n)d(n)exp(j2πΔf(nT _smp )nT _smp ) ⑶ in

The filtered I, Q quadrature baseband data s(n) are transmitted to the decimation module. 4. The adaptive filtering narrowband interference suppression method with Doppler first-order rate of change as claimed in claim 3, wherein step 4 comprises the following five steps, Step 4.1. Store the extracted I and Q quadrature baseband data s'(n) output in step 3 into the memory in the demodulation modulation process, and then store the frequency offset and the first-order change rate of the frequency offset after estimating the frequency offset. The data in the memory is read out for compensation; Step 4.2, while performing step 4.1, use the rotation angle α as a variable for the data s'(n) output in step 3, and use d as the step size to perform fractional Fourier transform on the input N-point discrete signal; In the presence of the Doppler first-order frequency offset first-order rate of change, the Doppler frequency offset is a time-varying function, which is expressed as follows:

where Δf ₀ is the initial frequency offset,

is the first-order rate of change of frequency offset, so the extracted data in step 3 is expressed as the following formula:

where T _d is the decimation interval, and the formula for fractional Fourier transform is as follows:

Where α=pπ/2, α∈(-π,π], after traversing α, a two-dimensional plane is obtained; Step 4.3, search the two-dimensional plane obtained in step 4.2 to obtain the coordinates of the peak point

Step 4.4, obtain the coordinates of the peak point through step 4.3

Calculate the initial frequency offset and the first-order rate of change of frequency offset; The estimation formulas of the initial frequency offset and the first-order rate of change of the frequency offset are as follows:

Step 4.5, read out the data stored in step 4.1 and use the initial frequency offset and the first-order change rate of frequency offset estimated in step 4.4 to perform frequency offset on the extracted I, Q quadrature baseband data s'(n); After compensation, it is transmitted to the time-domain anti-jamming module. 5. The adaptive filtering narrowband interference suppression method with Doppler first-order rate of change as claimed in claim 4, wherein step 5 comprises the following two steps, Step 5.1, calculate the response of the data output in step 4.5 through the adaptive filter y(n)=w ^T (n)x(n), where x(n) is the input of the adaptive filter, and w(n) is the adaptive filter The tap coefficient of the filter, y(n) is the output of the adaptive filter, and the interference suppression output e(n)=x(n)-y(n) is obtained; Step 5.2, update the adaptive filter tap coefficients for the interference suppression output e(n) output in step 5.1, and return to step 5.1. 6. the self-adaptive filtering narrowband interference suppression method that there is Doppler first-order rate of change as claimed in claim 5, is characterized in that: in step 3, the I, Q orthogonal baseband data s (n) after filtering will be extracted The signal s'(n) is obtained at twice the chip rate. 7. The adaptive filtering narrowband interference suppression method with Doppler first-order rate of change as claimed in claim 5, wherein step 5.2 selects and uses least mean square (LMS) adaptive filtering narrowband anti-interference method, wherein step The adaptive filter tap coefficient update method in 5.2 is: w(n+1)=w(n)+μe(n)x(n), where μ is the update step size.

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