Multipath anti-interference processing method for response signals

Abstract

This invention discloses a multipath anti-interference processing method for response signals, mainly addressing the problems of low correlation and low anti-multipath effectiveness in existing technologies that use filters to add phase, resulting in low correlation between the stripped direct path signal and the local signal. The implementation scheme is as follows: the radar-received response signal is split into two paths. One path uses Hilbert transform and phase inversion to transform the received signal from a sine signal to a cosine signal; the other path extends the received signal to obtain an in-phase sine signal. A symmetrical multiplier-adder-subtractor structure is used to obtain a sine wave of the difference between two angles, a cosine wave of the difference between two angles, and a sine wave of the sum of two angles from the two signals and the local signal using trigonometric function formulas. A correlation peak is obtained by correlating the sine wave of the sum of two angles with the local sine wave. The correlation peak is then separated to extract the direct path. The direct path signal extracted by this invention exhibits excellent correlation with the local signal and ideal anti-multipath effectiveness, making it suitable for processing target angle flicker caused by multipath effects.

Description

Technical Field

[0001] This invention belongs to the field of radar detection technology, and specifically relates to a multipath anti-interference processing method, which can be used to process target angle scintillation caused by multipath effects. Background Technology

[0002] The radar and transponder constitute an interrogation-response secondary radar system. The transponder is mounted on the aircraft, and the radar is located on the ground. The radar periodically transmits interrogation signals to the transponder. The transponder receives the interrogation signals, judges and processes them, generates a response signal, and replies to the radar. Based on the arrival time and content of the response signal, the radar measures the three-dimensional data of the aircraft's distance, azimuth, and pitch angle relative to the radar.

[0003] When a target aircraft is descending from low altitude to the ground, the electromagnetic waves of the transponder's response signal not only reach the radar directly but also illuminate the ground. After reflection or scattering, the signal reaches the radar again. Each cycle's response signal travels through multiple paths to the receiving radar, and the phase of the response signal differs along each path; this phenomenon is called the "multipath effect." When the radar operates in monopulse angle measurement mode, the normalized error signal can be obtained by dividing the "pitch difference beam" signal by the "sum beam" signal. The target's pitch angle can then be calculated based on this error signal. Due to the multipath effect, the received radar signal attenuates and waveforms overlap, causing jitter in both the "pitch difference beam" and "sum beam" signals during signal processing. This jitter leads to fluctuations in both the normalized error signal and the measured target pitch angle, ultimately causing antenna jitter or even target loss. This results in angular flicker in the angle measurement, leading to errors in the calculated target pitch angle.

[0004] Existing multipath interference mitigation methods typically employ multipath separation techniques, using hardware such as narrowband filters, bandpass filters, multipliers, adders, and integrators to separate the received multipath signals into independent signal paths. Correlation with the local signal is then performed to select the first arriving signal path, i.e., the direct path, from all paths. A pseudo-random code signal, such as an m-sequence code, is used, with a symbol width equal to Δ. Different time delays of the same pseudo-random code are uncorrelated. One period M(t) of the m-sequence code is used to modulate a sinusoidal carrier signal sinx, forming a response signal M(t)sinx, which is transmitted. The radar receives signals from multiple paths, with the direct path signal being M(t)sinx0. Assuming that the time difference between adjacent paths is equal to Δ, the signal received by the radar from the Kth path is M(t-KΔ)sinx. K .

[0005] According to the trigonometric function product-to-sum formula, the radar multiplies its own generated local signal M(t)sinθ with the received direct path signal M(t)sinx0, takes the difference between the two phases θ and x0 (θ-x0), and obtains the first intermediate variable after narrowband filtering. The first intermediate variable Multiplying this by the direct path signal M(t)sinx0, and taking the sum of the two phases (θ-x0) and x0 (θ-x0+x0), then bandpass filtering this result in the second intermediate variable. The second intermediate variable The correlation between the signal and the local signal M(t)sinθ is found to be the highest, resulting in a correlation peak. The direct path signal is then separated, and subsequent angle measurement operations are only performed on the direct path signal, achieving results that resist interference from other multiple paths.

[0006] The narrower or steeper the passband of a filter, the greater the implementation cost. Its passband may not achieve the ideal rectangle, and spurious components within the passband will pass through the filter along with the desired signal, reducing the amplitude of the desired signal. This reduces the signal-to-noise ratio of the received signal. After the signal passes through the filter, a phase β, the first intermediate variable, is added. The theoretical value of the phase is (θ-x0), but after passing through the narrowband filter, the actual value of the first intermediate variable becomes... Its phase becomes (θ-x0+β), and the actual value of the second intermediate variable becomes

[0007] In multipath separation technology, the signals of multiple paths are processed separately, and the obtained second intermediate variable is correlated with the local signal to obtain a correlation peak. The second intermediate variable of the direct path has the strongest correlation with the local signal, so the direct path obtains the correlation peak first in each cycle. In each cycle, after outputting the first correlation peak, the output of subsequent correlation peaks in the same cycle is masked, thus separating multiple paths and identifying the direct path.

[0008] Because a phase β is added after processing the direct path signal, the actual value of the second intermediate variable becomes At this point, the second intermediate variable... The correlation between the local signal M(t)sinθ and the radar signal will decrease, resulting in a time broadening and amplitude reduction of the correlation peak. This affects the radar's ranging and angle measurement accuracy and reduces its anti-multipath performance. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of the existing technology by proposing a multipath anti-interference processing method for response signals, thereby improving the anti-multipath interference performance and simultaneously improving the signal-to-noise ratio of the received signal.

[0010] The technical concept of this invention is as follows: The radar received signal is split into two paths. One path uses Hilbert transform and phase inversion to convert the received signal from a sine wave to a cosine wave. The other path delays the received signal to obtain a sinusoidal signal in phase. A symmetrical multiplier and adder / subtractor structure is used, with the two paths operating in parallel. Based on trigonometric function formulas, the sine and cosine waves of the difference between two angles are first calculated, and then the sine wave of the sum of the two angles is calculated. By correlating the sine wave of the sum of the two angles with the local sine wave, the correlation peak is obtained, thus separating the direct path signal from multiple path signals. The implementation steps include the following:

[0011] (1) Use one period of the m-sequence code as the pseudo-random code in the response signal, and use the pseudo-random code to modulate the sinusoidal carrier to form the modulation signal S(t) = M(t)sinx, where M(t) is the m-sequence code with a value of ±1, t is the time, x is the phase of the carrier signal, x = ωt, and ω is the angular frequency of the sinusoidal carrier signal;

[0012] (2) The response signal is transmitted via multiple paths. The radar receives the response signal transmitted through multiple paths and obtains the path signal. In the formula, K is a positive integer including 0, representing one of multiple paths. When K = 0, it is the direct path for the response signal to reach the radar. P K x is the amplitude of the signal received along the Kth path, Δ is the width of one symbol of the m-sequence, KΔ is the delay time of the Kth path relative to the direct path, and x K It is the phase of the signal received along the Kth path. ω K It is the angular frequency of the signal received along the Kth path. It is the random phase of the signal received along the Kth path;

[0013] (3) The radar generates an m-sequence code M(t-KΔ), and the numerically controlled oscillator NCO generates a cosine wave cosθ and a sine wave sinθ, which are multiplied by the m-sequence code M(t-KΔ) respectively to obtain the generated local cosine wave signal A(t)=M(t-KΔ)cosθ and the local sine wave signal C(t)=M(t-KΔ)sinθ, where θ=ωt+φ, and φ is the initial phase of the local oscillator;

[0014] (4) Radar receives signal D for the Kth path K (t)=P K M(t-KΔ)sinx K Perform two-way processing:

[0015] For the received signal D K (t) Perform Hilbert transform and inversion to obtain the cosine signal B. K (t)=P K M(t-KΔ)cosx K, as the cosine signal generated by the first path;

[0016] For the received signal D K (t) Delay by time a to obtain the in-phase sinusoidal signal D K (t)=P K M(t-KΔ)sinx K , which is the in-phase sinusoidal signal generated by the second channel, where a is equal to the time required for the first channel to perform the Hilbert transform and inversion;

[0017] (5) Obtain the cosine wave signal E K (t) and the sinusoidal signal F K (t);

[0018] The local cosine wave signal A(t), the local sine wave signal C(t), and the cosine wave signal B are used to generate the local cosine wave signal A(t), the local sine wave signal C(t), and the local cosine wave signal B(t). K (t), In-phase sinusoidal signal D K (t) Substituting into the trigonometric function formula for the difference of two cosine angles: cosθ×cosx0+sinθ×sinx0=cos(θ-x0), we can calculate the difference between the two phases (θ-x0). K The cosine wave signal E) K (t);

[0019] The local cosine wave signal A(t), the local sine wave signal C(t), and the cosine wave signal B are used to generate the local cosine wave signal A(t), the local sine wave signal C(t), and the local cosine wave signal B(t). K (t), In-phase sinusoidal signal D K (t) Substituting into the trigonometric function formula for the difference of two sinusoidal angles: sinθ×cosx0-cosθ×sinx0=sin(θ-x0), we can calculate the difference between the two phases (θ-x0). K The sinusoidal signal F K (t);

[0020] (6) The cosine signal B K (t), In-phase sinusoidal signal D K (t), sinusoidal signal F K (t), cosine wave signal E K (t) Substituting into the trigonometric formula for the sum of two sine angles: sinθ×cosx0+cosθ×sinx0=sin(θ+x0), we can calculate the two phases (θ-x). K ) and x K The sum of (θ-x) K +x K The sinusoidal signal G K (t);

[0021] (7) The two phases (θ-x) K ) and x K The sum of (θ-x) K +xK The sinusoidal signal G K Multiplying C(t) by the local sinusoidal signal C(t) yields the correlation between the two signals. Then, integrate the peaks to obtain the relevant peaks of the Kth path;

[0022] (8) After outputting the first relevant peak in each cycle, the output of subsequent relevant peaks in the current cycle is masked, thus separating multiple paths and extracting the direct path.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1) The signal has excellent correlation and ideal anti-multipath performance.

[0025] This invention uses multiplication, addition, and subtraction operations to calculate the sine wave signal of the difference between two angles, the cosine wave signal of the difference between two angles, and the sine wave signal of the sum of two angles. This eliminates the need for narrowband filters and bandpass filters used in existing technologies. Furthermore, the sine wave signal of the sum of two angles has excellent correlation with the local sine wave signal, and its anti-multipath performance is ideal.

[0026] 2) The symmetrical structure effectively suppresses spurious components and improves the signal-to-noise ratio of the received signal.

[0027] This invention employs a symmetrical structure using multipliers and adders / subtractors. While completely removing stray components, the resulting sinusoidal signal, the sum of two angles, exhibits a significantly larger amplitude compared to the first and second intermediate variable signals in existing technologies. Increasing it to 1 effectively improves the signal-to-noise ratio of the received signal. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the principle of the present invention;

[0029] Figure 2 This is a schematic diagram illustrating the implementation of the present invention. Detailed Implementation

[0030] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0031] This example replaces the narrowband and bandpass filters used in the prior art with trigonometric function operations to improve the correlation between the received signal and the local sine wave signal and improve the signal-to-noise ratio of the received signal, thereby obtaining a sine wave signal that is the sum of the two angles, thus achieving the purpose of stripping away the direct path signal.

[0032] Reference Figure 1 The principle of multipath anti-interference processing for response signals in this example is as follows:

[0033] The radar-received response signal is split into two paths. One path uses Hilbert transform and phase inversion to convert the received signal from a sine wave to a cosine wave. The other path delays the received signal to obtain an in-phase sine wave. A symmetrical multiplier-adder-subtractor structure is used to perform parallel operations on these two paths. Based on trigonometric function formulas, the sine wave of the difference between two angles, the cosine wave of the difference between two angles, and the sine wave of the sum of two angles are calculated. By correlating the sine wave of the sum of two angles with the local sine wave, the correlation peak is obtained, thus separating the direct path signal from the multiple path signals.

[0034] Reference Figure 2 The implementation steps of the multipath anti-interference processing method for the response signal in this example are as follows:

[0035] Step 1: Generate a response signal modulated with a pseudo-random code.

[0036] One period of the m-sequence code is used as the pseudo-random code in the response signal. The pseudo-random code is used to modulate the sinusoidal carrier to form the modulation signal S(t) = M(t)sinx, where M(t) is the m-sequence code with a value of ±1, t is time, x is the phase of the carrier signal, x = ωt, and ω is the angular frequency of the sinusoidal carrier signal.

[0037] Step 2: The radar receives signals from multiple paths.

[0038] The response signal is transmitted via multiple paths. The radar receives the response signal transmitted through multiple paths and obtains the path signal. In the formula:

[0039] K is a positive integer including 0, representing one of multiple paths. When K = 0, it is a direct path for the response signal to reach the radar. P K Δ is the amplitude of the signal received along the Kth path, Δ is the width of one symbol of the m-sequence, and KΔ is the delay time of the Kth path relative to the direct path. It is the phase of the signal received along the Kth path, ω K It is the angular frequency of the signal received along the Kth path. It is the random phase of the signal received along the Kth path.

[0040] Step 3: The radar generates a pair of orthogonal signals.

[0041] 3.1) The radar delays the initial phase of the m-sequence generator by KΔ to generate the m-sequence code M(t-KΔ);

[0042] 3.2) The numerically controlled oscillator (NCO) generates cosine waves (cosθ) and sine waves (sinθ).

[0043] 3.3) Multiply the cosine wave cosθ with the m-sequence code M(t-KΔ) to obtain the local cosine wave signal A(t)=M(t-KΔ)cosθ;

[0044] 3.4) Multiply the sine wave sinθ with the m-sequence code M(t-KΔ) to obtain the local sine wave signal C(t)=M(t-KΔ)sinθ, where θ=ωt+φ, and φ is the initial phase of the local oscillator;

[0045] The local cosine wave signal and the local sine wave signal constitute a pair of orthogonal signals.

[0046] Step 4, the radar receives the signal D from the Kth path. K (t) Perform two-way processing.

[0047] 4.1) Based on the path signal S obtained from the radar K (t), to obtain the received signal D of the Kth path. K (t):

[0048] D K (t)=P K M(t-KΔ)sinx K ;

[0049] 4.2) Regarding the received signal D K (t) Perform Hilbert transform and inversion to obtain the cosine signal B. K (t)=P K M(t-KΔ)cosx K , as the cosine signal generated by the first path;

[0050] 4.3) Regarding the received signal D K (t) Delay by time a to obtain the in-phase sinusoidal signal D K (t)=P K M(t-KΔ)sinx K , which is the in-phase sinusoidal signal generated by the second channel, where a is equal to the time required for the first channel to perform the Hilbert transform and inversion.

[0051] Step 5: Calculate the cosine wave signal E representing the difference between the two angles. K (t) and the sinusoidal signal F of the difference between the two angles. K (t).

[0052] 5.1) Combine the local cosine wave signal A(t), the local sine wave signal C(t), and the cosine signal B. K (t), In-phase sinusoidal signal D K (t) Substituting into the trigonometric function formula for the difference of two cosine angles: cosθ×cosx0+sinθ×sinx0=cos(θ-x0), we can calculate the difference between the two phases (θ-x0). K The cosine wave signal E) K (t):

[0053] E K (t)=A(t)×B K (t)+C(t)×D K (t)

[0054] =M(t-KΔ)cosθ×P K M(t-KΔ)cosx K +M(t-KΔ)sinθ×P K M(t-KΔ)sinx K

[0055] =P K cos(θ-x K );

[0056] 5.2) Combine the local cosine wave signal A(t), the local sine wave signal C(t), and the cosine signal B. K (t), In-phase sinusoidal signal D K (t) Substituting into the trigonometric function formula for the difference of two sinusoidal angles: sinθ×cosx0-cosθ×sinx0=sin(θ-x0), we can calculate the difference between the two phases (θ-x0). K The sinusoidal signal F K (t);

[0057] F K (t)=C(t)×B K (t)-A(t)×D K (t)

[0058] =M(t-KΔ)sinθ×P K M(t-KΔ)cosx K -M(t-KΔ)cosθ×P K M(t-KΔ)sinx K

[0059] =P K sin(θ-x K ).

[0060] Step 6: Calculate the sine wave signal G, which is the sum of the two angles. K (t).

[0061] The cosine signal B K (t), In-phase sinusoidal signal D K (t), sinusoidal signal F K (t), cosine wave signal E K (t) Substituting into the trigonometric formula for the sum of two sine angles: sinθ×cosx0+cosθ×sinx0=sin(θ+x0), we can calculate the two phases (θ-x). K ) and xK The sum of (θ-x) K +x K The sinusoidal signal G K (t);

[0062]

[0063] Step 7, for the sine wave signal G, which is the sum of the two angles K Find the correlation between (t) and the local sinusoidal signal C(t).

[0064] 7.1) The two phases (θ-x) K ) and x K The sum of (θ-x) K +x K The sinusoidal signal G K Multiplying C(t) by the local sinusoidal signal C(t) yields the correlation between the two signals.

[0065]

[0066] 7.2) Correlation Integrating, we obtain the correlation peak of the Kth path.

[0067] Step 8: Separate multiple paths and extract the direct path.

[0068] Let K = 0, D K (t) represents the direct path signal;

[0069] In each cycle, the direct path signal D K (t) is processed sequentially through two parallel processing paths and trigonometric function operations to obtain a sine wave signal G, which is the sum of two angles. K (t), the sinusoidal signal G K (t) has the strongest correlation with the local sine wave signal C(t), and the correlation peak is obtained first in each cycle;

[0070] After outputting the first relevant peak in each cycle, the output of subsequent relevant peaks in the same cycle is blocked. In this way, multiple paths are separated and the direct path is extracted.

[0071] The above description is merely a specific example of the present invention and does not constitute any limitation on the present invention. Obviously, those skilled in the art, after understanding the content and principles of the present invention, may make various modifications and changes in form and details without departing from the principles and structure of the present invention. However, these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A method for multipath interference rejection processing of a response signal, characterized by, The method comprises the following steps: (1) using a period of m sequence code as a pseudo-random code in a response signal, modulating a sinusoidal carrier with the pseudo-random code to form a modulated signal S(t)=M(t)sinx, wherein M(t) is an m sequence code with values of ±1, t is time, x is a phase of the carrier signal, x=ωt, and ω is an angular frequency of the sinusoidal carrier signal; (2) The multi-path transmission of the response signal, the radar receives the response signal transmitted through multiple paths, and the path signal is In the formula, K is a positive integer including 0, representing one of the multiple paths, K = 0 is the direct path of the response signal directly reaching the radar, P K is the amplitude of the Kth path received signal, Δ is a symbol width of the m sequence, KΔ is the delay time of the Kth path relative to the direct path, x K is the phase of the Kth path received signal, ω K is the angular frequency of the Kth path received signal, is the random phase of the Kth path received signal; (3) the radar generates an m sequence code M(t-KΔ), a numerically controlled oscillator (NCO) generates a cosine wave cosθ and a sine wave sinθ, and the m sequence code M(t-KΔ) is multiplied with the cosine wave cosθ and the sine wave sinθ respectively to obtain a generated local cosine wave signal A(t)=M(t-KΔ)cosθ and a generated local sine wave signal C(t)=M(t-KΔ)sinθ, wherein θ=ωt+φ, and φ is an initial phase of a local oscillator; (4) Radar receives signal D on the Kth path K (t) = P K M(t - KΔ) sin x K Two-way processing is performed: D(t) = D(t) - D(t - KΔ) cos x K (t) = P(t) - P(t - KΔ) cos x K (t) = P(t) - P(t - KΔ) cos x K M(t - KΔ) cos x K , as the cosine signal generated by the first path; D K (t) = D(t - aΔ) K (t) = P(t - aΔ) K M(t - KΔ) sin x K , as the in-phase sinusoidal signal generated by the second path, where a is equal to the time consumed by the first path to perform the Hilbert transform and inversion. (5) obtain a cosine wave signal E K (t) and a sine wave signal F K (t); The local cosine wave signal A(t), the local sine wave signal C(t), and the cosine wave signal B are used to generate the local cosine wave signal A(t), the local sine wave signal C(t), and the local cosine wave signal B(t). K (t), In-phase sinusoidal signal D K (t) Substituting into the trigonometric function formula for the difference of two cosine angles: cosθ×cosx0+sinθ×sinx0=cos(θ-x0), we can calculate the difference between the two phases (θ-x0). K The cosine wave signal E) K (t); The local cosine wave signal A(t), the local sinusoidal signal C(t), the cosine signal B K (t), the in-phase sinusoidal signal D K (t) are substituted into the sinusoidal two-angle-difference trigonometric function formula: sinθ×cosx0-cosθ×sinx0=sin(θ-x0), to calculate the sinusoidal signal F K (t) of the difference (θ-x0) of the two phases K ; (6) The cosine signal B K (t), In-phase sinusoidal signal D K (t), sinusoidal signal F K (t), cosine wave signal E K (t) Substituting into the trigonometric formula for the sum of two sine angles: sinθ×cosx0+cosθ×sinx0=sin(θ+x0), we can calculate the two phases (θ-x). K ) and x K The sum of (θ-x) K +x K The sinusoidal signal G K (t); (7) The two phases (θ-x) K ) and x K The sum of (θ-x) K +x K The sinusoidal signal G K Multiplying C(t) by the local sinusoidal signal C(t) yields the correlation between the two signals. Then, integrate the peaks to obtain the relevant peaks of the Kth path; (8) after outputting the first obtained correlation peak in each period, the output of subsequent correlation peaks in the period is shielded, so that multiple paths are separated and the direct path is stripped.

2. The method of claim 1, wherein: The first obtained correlation peak in step (8) refers to a first correlation peak obtained by sequentially processing a direct path signal received by the radar through two parallel processes, trigonometric function operations, correlation calculation and integration.

3. The method of claim 1, wherein: The cosine wave signal E(t) of the difference (θ - x) of the two phases obtained in step (5) K ) is expressed as follows: K (t), represents as follows: E K (t) = A(t) x B K (t) + C(t) x D K (t) = M(t - KΔ) cos θ x P K M(t - KΔ) cos θ K + M(t - KΔ) sin θ x P K M(t - KΔ) sin θ K = P K cos(θ - x K ).

4. The method of claim 1, wherein: The sinusoidal signal F(t) of the difference (θ - x K ) of the two phases in step (5) is expressed as follows: K (t) = sin(θ - x F K (t) = C(t) x B K (t) - A(t) x D K (t) = M(t - KΔ) sin θ x P K M(t - KΔ) cos θ K - M(t - KΔ) cos θ x P K M(t - KΔ) sin θ K = P K sin(θ - x K ).

5. The method of claim 1, wherein: In step (6), two phases (θ-x) are obtained. K ) and x K The sum of (θ-x) K +x K The sinusoidal signal G K (t), represented as follows:

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