A Path Compensation Method for Time Reversal Pulse Compression

Abstract

A path compensation method for time-reversal pulse compression, step 1, the initial signal s ori (t) is injected into the time reversal system to obtain the response signal s res (t); Step 2, intercept the response signal s of two decay time constants res (t), and then time-flip to s res (‑t), and recorded as the inversion signal s rev (t) = s res (‑t); Step 3, select the amplitude value of the maximum path of the inversion signal as A 0 =max{|A i |}, and the path of the inversion signal is compensated and corrected to A 0 , the compensated inversion signal can be expressed as #imgabs0#Step 4, injecting or radiating the compensated inversion signal into the time reversal system through the receiving port, which can generate pulse compression at the initial position and obtain the same pulse waveform as the initial signal; used in the time reversal pulse compression system, the inversion signal is usually an oscillation attenuation signal; improves the pulse compression efficiency and the gain of the time reversal pulse compression system; has the characteristics of simple method, easy implementation, and can effectively improve the time reversal pulse compression gain.

Description

Technical Field

[0001] The invention belongs to the fields of radar, communication and high-power microwave technology, and in particular relates to a path compensation method for time-reversal pulse compression. Background Art

[0002] Time reversal technology is a method of reconstructing the original waveform at the initial position by flipping the system response signal in time and then inputting it into the system. It has the characteristics of time-space synchronous focusing. During the inversion process, this technology can compress wide pulse signals into narrow pulse signals in the time domain, and has a certain compression gain. Therefore, it has many potential applications in radar, communication, and high-power microwaves. If the flipped response signal is used directly, its compression gain is limited to a certain extent because the signal has the characteristics of attenuated oscillation. In order to improve the pulse compression gain, the inversion signal needs to be corrected and compensated.

[0003] The time inversion process is a phase compensation process. Therefore, the phase of the inversion signal should not be changed during the processing of the inversion signal. In inversion pulse compression, the amplitude of the inversion signal is usually required to be uniform. Therefore, the existing compensation methods include the amplitude spectrum iteration method. This method requires a large number of inverse Fourier transforms, which is not only time-consuming to calculate but also has convergence problems. In addition, there are relatively simple single-bit methods and exponential compensation methods. Both methods can improve the pulse compression gain. However, the single-bit method over-compensates, which seriously affects the pulse compression efficiency. The exponential amplification method does not compensate for the fluctuation characteristics of the oscillation signal, which affects the further improvement of the compression gain. This is not conducive to the application and promotion of time reversal pulse compression technology. Summary of the invention

[0004] In order to overcome the deficiencies of the existing technologies and methods, the purpose of the present invention is to propose a path compensation method for time reversal pulse compression, which utilizes a multipath channel model with attenuation crosstalk characteristics to maximize the amplitude of the inversion signal on the path, thereby achieving uniformity of the inversion signal amplitude; the method is simple, easy to implement, and can effectively improve the time reversal pulse compression gain.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a path compensation method for time reversal pulse compression, comprising the following steps:

[0006] Step 1: The initial signal s ori (t) is injected into the time reversal system to obtain the response signal s res (t), where t represents time;

[0007] Step 2: intercept the response signal s of two decay time constants res(t), and then time-flip to s res (-t), and recorded as the inversion signal s rev (t) = s res (-t);

[0008] Step 3: Select the maximum path amplitude value in the inversion signal as A 0 =max{|A i |}, and correct the amplitude values ​​of all remaining paths in the inversion signal to A 0 , thus, the compensated inversion signal can be expressed as where τ i is the delay of the ith path, m is the number of paths;

[0009] Step 4, injecting or radiating the compensated inversion signal into the time reversal system through a receiving port, which can generate pulse compression at the initial position and obtain a pulse waveform identical to the initial signal.

[0010] The beneficial effects of the present invention are:

[0011] Compared with the prior art, the time reversal path compensation method is very simple and achieves the purpose of improving the pulse compression gain while ensuring a certain compression efficiency.

[0012] The present invention aims at the characteristics of the system response signal, based on the multipath channel model theory of attenuation crosstalk, and establishes a path compensation method to achieve energy compensation for paths with smaller amplitudes, thereby increasing the peak amplitude of the inversion and reconstruction signal. The path compensation method is to compensate the path of the response function.

[0013] This method only compensates for the amplitude of the signal on the smaller path, and does not change the parameters such as the rising edge and period of the signal on the path. Therefore, during the inversion process, the signal can still return along the original path and generate superposition reconstruction at the initial position. In addition, this method compensates for the attenuation and superposition drop in the forward response of the path, thereby improving the compensation efficiency and obtaining a better compression gain.

[0014] The inversion signal feature of the method of the present invention is to compensate all signals on the inversion path to the same amplitude value as the maximum path signal, thereby increasing the energy of the inversion signal and effectively increasing the main lobe amplitude of the reconstructed signal. The method is derived based on the multipath channel model theory and can compensate for the attenuation and superposition drop characteristics of the forward response. Under the condition of ensuring appropriate compression efficiency, the time reversal pulse compression gain can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of a typical time reversal system.

[0016] Figure 2 Time domain waveform of the inverted signal after compensation.

[0017] Figure 3 Waveform diagram for uncompensated time-reversal reconstruction.

[0018] Figure 4 This is the waveform of time-reversal reconstruction after compensation. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below in conjunction with specific embodiments and drawings.

[0020] A path compensation method for time reversal pulse compression comprises the following steps:

[0021] Step 1: The initial signal s ori (t) is injected into the time reversal system to obtain the response signal s res (t), where t represents time;

[0022] Step 2: intercept the response signal s of two decay time constants res (t), and then time-flip to s res (-t), and recorded as the inversion signal s rev (t) = s res (-t);

[0023] Step 3: Select the maximum path amplitude of the inversion signal as A 0 =max{|A i |}, and the amplitude values ​​of all remaining paths of the inversion signal are compensated and corrected to A 0 , thus, the compensated inversion signal can be expressed as where τ i is the delay of the ith path, m is the number of paths;

[0024] Step 4, injecting or radiating the compensated inversion signal into the time reversal system through a receiving port, which can generate pulse compression at the initial position and obtain a pulse waveform identical to the initial signal.

[0025] The present invention is mainly used in a time reversal pulse compression system, in which the inversion signal is usually an oscillating attenuation signal. In order to improve the pulse compression efficiency, the path amplitude is corrected according to a multipath channel model with attenuation crosstalk characteristics to compensate for the adverse effects of attenuation and crosstalk in the path response, thereby improving the gain of the time reversal pulse compression system.

[0026] 1. Basic Principles of Electromagnetic Time Reversal Pulse Compression

[0027] 1) Time reversal

[0028] The time reversal theory can be obtained from a forward excitation and reverse inversion process of the system, that is, its inversion reconstruction process can be expressed as follows:

[0029] s rec (t) = s rev (t)*h(t)=s ori (t)*h(t)*h(-t) (3)

[0030] In the formula, s ori (t), s rev (t) and s rec (t) are respectively represented as the initial signal, the inversion signal and the reconstruction signal; h(t) is the impulse response function of the system. Under ideal conditions, the autocorrelation function of the impulse response function satisfies: h(t)*h(-t)=δ(t). That is to say, under ideal conditions, there is s rec (t) = s ori (t). However, in actual situations, due to system loss, crosstalk and other characteristics, s rec (t)≠s ori (t).

[0031] 2) Multipath channel model

[0032] According to the multipath channel model, considering the diffusion, scattering and loss characteristics of electromagnetic waves during propagation, crosstalk and attenuation will occur in electromagnetic waves propagating on different paths. The impulse response function of the multipath channel can be defined as:

[0033]

[0034] In the formula, is the attenuation coefficient vector of the path, where the i-th coefficient k i (t) describes the time attenuation characteristics of the propagation signal on the i-th path (including the superposition effect of the spatial path); the matrix A(t) is the correlation matrix of the electromagnetic wave propagation between each path, which describes the crosstalk characteristics of the electromagnetic wave propagation between the paths and can be expressed as

[0035]

[0036] Among them, a ij (t) represents the correlation of the electromagnetic wave on the i-th path propagating to the j-th path. is a singular function vector, which can be expressed as

[0037]

[0038] Among them, τ i is the response delay time of the i-th path (i.e., the flight time of the path); T represents the transpose of the vector.

[0039] 3) Time reversal model

[0040] Usually, the impulse response signal oscillates violently, and the time interval between two adjacent paths is much smaller than the decay time constant of the system. The decay coefficient k of the path i and the correlation coefficient a ij It can be considered as a constant. According to the convolution theorem, the reconstructed signal s rec (t) can be expressed as:

[0041]

[0042] It can be seen that the model can represent the characteristics of the time reversal reconstructed signal, which has the characteristics of the time main lobe and noise side lobe and is symmetrical.

[0043] 4) Path compensation

[0044] In practical applications, the oscillation waveform of the system impulse response function is usually used to represent its response path. In this case, the multipath channel model can be expressed as:

[0045]

[0046] In the formula, A i is the i-th duration τ i The amplitude of the impulse response signal on the path. Under the action of the initial signal, the path decomposition expression of the system response signal can be expressed as

[0047]

[0048] Path amplitude A caused by attenuation, superposition, etc. i It is oscillating and decaying. Therefore, in order to improve the performance of time reversal pulse compression, it is necessary to compensate for the loss attenuation and superposition drop of the path in pulse compression. Therefore, the compensated inversion signal can be expressed as:

[0049]

[0050] In the formula, c i is the compensation coefficient of the signal on the i-th path. Therefore, this method is also called the path compensation method;

[0051] In pulse compression, the amplitude of the inverted signal is usually uniform. In this case, the signals on all paths can be compensated to the maximum value, and the compensation coefficient c of each path is i It can be expressed as:

[0052]

[0053] In the formula, c iis a constant. It is related to the attenuation and superposition fluctuation characteristics of the path, and both are greater than or equal to 1. In this case, the compensated inversion signal can be expressed as:

[0054]

[0055] In the formula, A 0 is the maximum amplitude of the response signal. It can be seen that this method is very simple, and it only changes the amplitude of the signal on the path, and does not change the characteristics of the signal such as the rising edge, period and time shift;

[0056] According to the multipath channel model, the time reversal process can return the inverted signal to the initial position along the original path. For the compensated inverted signal, its reconstructed signal can be expressed as:

[0057]

[0058] It can be seen that the path compensation method does not change the attenuation and crosstalk characteristics of the path, so the original signal can still be reconstructed.

[0059] In addition, this method only compensates for the crosstalk and attenuation of the path in the forward response, but does not compensate for the attenuation and crosstalk in the inversion process. Therefore, the sidelobe noise signal is asymmetric.

[0060] 2. Application Example

[0061] Considering the characteristics of the time reversal system and the computational simulation requirements, a typical quasi-two-dimensional time reversal cavity system is constructed, such as Figure 1 As shown in the figure, the cavity size is 875mm×700mm×43.18mm, and both ports are BJ26 waveguide ports. In addition, the initial signal is a Gaussian modulated pulse signal with a carrier frequency of 2.4GHz and a pulse width of 3ns. Figure 2 is the inversion signal after compensation. Figure 3 and Figure 4 They are respectively the reconstructed signals obtained by time inversion of the above two inversion signals. Among them, the compensated reconstructed main lobe is about 3.5 times that of the uncompensated reconstructed main lobe. It can be seen that the path compensation method can effectively improve the time reversal pulse compression gain.

[0062] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A path compensation method for time reversal pulse compression, characterized in that: The following steps are involved: Step 1: The initial signal s ori (t) is injected into the time reversal system to obtain the response signal s res (t), where t represents time; Step 2: intercept the response signal s of two decay time constants res (t), and then time-flip to s res (-t), and recorded as the inversion signal s rev (t) = s res (-t); Step 3: Select the maximum path amplitude value in the inversion signal as A0=max{|A i |}, and the amplitude values ​​of all remaining paths in the inversion signal are corrected and compensated to A0. Therefore, the compensated inversion signal can be expressed as where s ori is the initial signal, τ i is the delay of the ith path, and m is the number of paths; Step 4, injecting or radiating the compensated inversion signal into the time reversal system through the receiving port, can generate pulse compression at the initial position and obtain a pulse waveform identical to the initial signal.

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