CN107607937A - Radar target distance-finding method based on time reversal - Google Patents

Abstract

The invention discloses a radar target distance measurement method based on time inversion, which solves the problem of accurate radar target distance measurement in a multipath environment. The implementation steps are: generate the radar transmission signal to obtain the echo data; perform time inversion on the echo data to obtain the time-inversion signal; set the distance search range, calculate the virtual channel model corresponding to different distance points, and transmit the time-inversion signal to the corresponding virtual channel model. The channel obtains the time-inverse echo signal; constructs the comparison signal, and calculates the correlation coefficient between the time-inverse echo signal and the comparison signal; finds the distance corresponding to the maximum correlation coefficient among all correlation coefficients, which is the target distance. The present invention reverses the time of the echo data and transmits it to the virtual channel, focuses the direct wave and the multipath wave in time, uses the multipath information to make the time-inverse echo corresponding to the real distance highly correlated with the comparison signal, and realizes Accurate ranging of targets, low cost, suitable for various delay multipath situations, used for distance measurement of low-altitude radar points on the sea surface.

Description

Radar Target Ranging Method Based on Time Reversal

technical field

The invention belongs to the technical field of radar, and in particular relates to target distance measurement, in particular to a method for target distance measurement based on time inversion, which can be used for distance measurement of low-altitude point targets on the sea surface.

Background technique

When the radar measures the distance of the target in the low-altitude environment of the sea surface, it will be affected by the multipath effect, that is, the echo signal received by the radar includes the direct wave signal from the target and the multipath wave signal reflected from the sea surface. At this time, if the traditional matched filter method is used for distance measurement, the radar will obtain the distance information of multiple paths at the same time. Due to the interference of multipath signals, the radar will mistakenly detect multiple false targets, so that the real distance of the target cannot be accurately measured. information.

In view of the influence of multipath effect on radar target range measurement in low-altitude sea environment, the existing methods mainly suppress multipath signals from two aspects of airspace and time domain to obtain the real distance information of the target. In terms of air space, by changing the antenna placement strategy, the direct wave signal and the multipath signal arrive at the antenna almost at the same time, or the ground plane antenna is designed to block the multipath signal from below the antenna. The two methods in the airspace need to be implemented by setting up antennas, and the implementation cost is relatively high. In the time domain, the use of narrow correlation technology allows the receiver to use a wider pre-correlation bandwidth and a narrower lead-lag correlator interval, but its application range is limited, and it is only suitable for the suppression of medium and long delay multipath.

Affected by the multipath effect, the matched filtering method in the prior art will detect false targets by mistake, but suppressing multipath through the method of space domain and time domain has problems such as high cost and limited scope of application.

Contents of the invention

The object of the present invention is to address the deficiencies of the above methods, and propose a more accurate time-reversal-based ranging method for low-altitude point targets on the sea surface, using multipath information to measure the target.

The present invention is a radar target ranging method based on time inversion, which is characterized in that the multipath information is used to measure the target, including the following steps:

(1) The radar generates the emission signal s _t (t), and obtains the radar echo data s _r (t).

(2) Perform time inversion processing on the echo data s _r (t) to obtain the time inversion signal s _r ^* (-t), where ^* is the conjugate symbol.

(3) Calculate the radar time back echo signal S _TR ,

(4) Calculate the Pearson correlation coefficient according to the transmitted signal s _t (t) and the time-inverse echo signal S _TR .

4a) Construct a comparison signal s _t ^* (-t) from the transmitted signal s _t (t).

4b) Calculate the Pearson correlation coefficient ρ of each echo in the time-inverse echo signal S _TR and the comparison signal s _t ^* (-t).

(5) Find the largest correlation coefficient among all Pearson correlation coefficients ρ, and its corresponding distance is the distance of the target, and complete the target ranging.

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

1. In a multipath environment, the traditional matched filter method will be interfered by multipath signals and cannot accurately measure the distance of the target. The invention reverses the time of the echo signal and resends it to the virtual channel, and uses the correlation property of the time-inverse echo signal to measure the target distance information more accurately.

Second, in order to weaken the impact of multipath effects on ranging, the traditional method adopts the method of suppressing multipath effects. The invention transmits the time-reverse signal into the virtual channel, and at the distance of the real target, the direct wave signal and the multi-path signal in the time-reverse echo will produce a focusing effect in time. The invention uses multipath information to measure the real distance of the target. The method of the invention has low cost and is applicable to various delay multipath situations.

Description of drawings

Fig. 1 is the realization flowchart of the present invention.

Figure 2 is a graph of ranging results obtained by using the matched filtering method under the set target and environmental parameters.

Fig. 3 is a distance measurement result diagram obtained by using the method of the present invention under the set target and environment parameters.

Detailed ways

Below in conjunction with accompanying drawing, the present invention is described in detail:

Example 1

When the radar performs target ranging in the low-altitude environment on the sea surface, the traditional method performs matched filter processing on the echo, which is affected by the multipath effect. Get the distance to the real target. Aiming at this current situation, the present invention conducts research, and specifically proposes a low-cost ranging method applicable to low-altitude point targets on the sea surface with various delays and multipaths.

The present invention is a radar target ranging method based on time inversion. With reference to Fig. 1, the multipath information is used to measure the target, including the following steps:

(1) The radar generates the emission signal s _t (t), and obtains the radar echo data s _r (t).

(2) Perform time inversion processing on the echo data s _r (t) to obtain the time inversion signal s _r ^* (-t), where ^* is the conjugate symbol.

(3) Establish the virtual channel model of the radar to different distances and transmit the time-reverse signal to these virtual channels, carry out the distance search, and calculate the radar time-reverse echo signal S _TR .

(4) Calculate the Pearson correlation coefficient according to the transmitted signal s _t (t) and the time-inverse echo signal S _TR .

4a) Construct the comparison signal s _t ^* (-t) according to the transmitted signal s _t (t), and perform time conjugate inversion on the transmitted signal.

4b) Calculate the Pearson correlation coefficient ρ of each echo in the time-inverse echo signal S _TR and the comparison signal s _t ^* (-t).

(5) Find the largest correlation coefficient among all Pearson correlation coefficients ρ, and its corresponding distance is the distance of the target, and complete the target ranging.

In the low-altitude sea environment, if affected by multipath signals, the traditional matched filtering method will detect multiple false targets and cannot accurately measure the real distance of the target. The present invention reverses the time of the echo signal and obtains the time-inverse echo signal, and by calculating the Pearson correlation coefficient of the time-inverse echo signal and the comparison signal, finds out the distance corresponding to the largest correlation coefficient, and can accurately measure the distance of the target. real distance.

Example 2

The radar target ranging method based on time inversion is the same as embodiment 1, and the reverse echo signal S _TR is calculated when the radar is obtained as described in the step (3) of the present invention, specifically comprising:

3a) Select the distance range R, and select different distances in the distance range R in ascending order as search points.

3b) According to the environmental parameters and radar parameters, establish the direct wave and multipath wave virtual channel model H from the radar to these search points.

3c) Transmit the time-reverse signal s _r ^* (-t) into the direct wave and multipath wave virtual channel H, and obtain the corresponding time-reverse echo signal S _TR , which is used to calculate and compare the Pearson correlation coefficient of the signals.

Among them, the search distance range R=[R ₁ ... R _k ... R _n ], R ₁ is the initial search distance, R _k is the real distance of the target, R _n is the final search distance, satisfying R ₁ <R _k < R _n , the virtual channel model is expressed as H=[H ₁ ... H _k ... H _n ], where H ₁ , H _k , and H _n are the virtual channel models corresponding to R ₁ , R _k , and R _n respectively. Signal S _TR ＝[s _TR1 (t) … s _TRk (t) …s _TRn (t)], where s _TR1 (t), s _TRk (t), s _TRn (t) are R ₁ , R _k , The time-reverse echo signal corresponding to R _n .

Usually the distance range R is selected for the real distance R _k of the target, and R _k can be roughly estimated first to set a rough search range.

Example 3

The radar target ranging method based on time inversion is the same as in embodiment 1-2, step 3c) transmit the time-reversal signal s _r ^* (-t) into the direct wave and multipath wave virtual channel H, and obtain the corresponding time-return signal The wave signal S _TR includes the following steps:

According to the channel transmission response function h k (t) of the direct wave and the channel transmission response function h _k ′(t) of the multipath wave, when the real distance _{R k of} the target is found, the time-inverse echo signal at this time is :

Where s _t ^* (-t) is the contrast signal, ^* is the conjugate symbol, is a convolution operation, the virtual channel model corresponding to R _k is H _k =[h _k (t)+h _k ′(t)], η _k is the complex electromagnetic scattering coefficient of the multipath wave channel, and τ _k is the direct wave channel delay , τ _k ′ is the multipath wave channel delay, and N(t) is Gaussian white noise signal. When the radar parameters, environment parameters and target position are determined, all the above parameters can be determined.

In order to weaken the impact of multipath effect on ranging, the multipath effect can be suppressed by changing the antenna placement or using narrow correlation technology. The invention performs time inversion on the echo signal to obtain the time inversion signal, and retransmits the time inversion signal into the virtual channel for distance search. If the position of the real distance of the target is searched, the direct wave and multipath signals in the time-reverse echo will produce a focusing effect in time, and the correlation coefficient between the time-reverse echo and the contrast signal will produce a maximum value at this time. The invention utilizes the multipath information to promote a higher correlation between the time-reverse echo and the comparison signal at the real distance of the target, thereby realizing the target distance measurement. Moreover, the method of the present invention is applicable to various delay multipath situations, and the cost is low.

Example 4

The radar target ranging method based on time inversion is the same as that in Embodiment 1-3

In order to realize the purpose of ensuring ranging accuracy in a multipath environment, the technical solution adopted in the present invention includes the following steps:

(1) Generate the radar emission signal s _t (t), and obtain the radar echo data s _r (t).

(2) Perform time inversion processing on the echo data s _r (t) to obtain the time inversion signal s _r ^* (-t), where ^* is the conjugate symbol. The time-reversal operation performs conjugate inversion of the echo data in time, and this operation makes the direct wave and multipath signals in the time-reversal echo produce a focusing effect in time.

(3) Calculate the time-inverse signal echo S _TR :

3a) Select a distance range R, and take each distance within the distance range R in sequence as a search point.

3b) According to the environmental parameters and radar parameters, establish the direct wave and multipath wave channel model H from the radar to these search points.

3c) Transmit the time-reversed signal s _r ^* (-t) into the virtual channel H of the direct wave and the multipath wave, and obtain the corresponding time-reversed signal echo S _TR .

Among them, the distance range R=[R ₁ ,...,R _k ,...,R _n ], R ₁ is the initial search distance, R _k is the real distance of the target, R _n is the final search distance, and the virtual channel model H= [H ₁ ... H _k ... H _n ], H ₁ , H _k , and H _n are the virtual channel models corresponding to R ₁ , R _k , and R _n respectively, and the time-reverse signal echo S _TR = [s _TR1 (t) ... s _TRk (t) … s _TRn (t)], s _TR1 (t), s _TRk (t), s _TRn (t) are the time-reverse signal echoes corresponding to R ₁ , R _k , and R _n respectively.

(4) Measure the distance of the target according to the transmitted signal s _t (t) and the time-reverse signal echo S _TR :

4a) Construct the comparison signal s _t ^* (-t) according to the transmitted signal s _t (t), that is, perform time-domain conjugate inversion on the transmitted signal.

4b) Calculating the Pearson correlation coefficient ρ of each echo in the counter-echo signal S _TR and the comparison signal s _t ^* (-t).

The Pearson correlation coefficient of any two signals s ₁ (t) and s ₂ (t) is ρ and satisfies the following relationship:

Where cov[s ₁ (t), s ₂ (t)] is the covariance of signal s ₁ (t) and s ₂ (t), var[s ₁ (t)] is the variance of signal s ₁ (t), var[s ₂ (t)] is the variance of the signal s ₂ (t).

Since the present invention performs time inversion operation on the echo data, the correlation coefficient between the signal corresponding to the real target distance and the comparison signal in the time-inverse echo signal S _TR is the largest, and the distance corresponding to the maximum value is found among all correlation coefficients ρ as The true distance to the target.

A more detailed example is given below to further illustrate the present invention:

Example 5

The radar target ranging method based on time inversion is the same as embodiment 1-4, with reference to Fig. 1, the concrete realization steps of the present invention are as follows:

Step 1: Generate the radar emission signal s _t (t), and obtain the radar echo data s _r (t):

in is the convolution symbol, h _k (t) is the direct wave channel transmission response function, h _k ′(t) is the multipath wave channel transmission response function, n(t) is the receiver noise signal, which can be regarded as Gaussian white noise signal . τ _k is the direct wave channel delay, η _k is the complex electromagnetic scattering coefficient of the multipath wave channel, and τ _k ′ is the multipath wave channel delay.

Step 2: Perform time inversion processing on the radar echo data s _r (t) to obtain the time inversion signal s _r ^* (-t):

s _r ^* (-t)＝s _t ^* (-t-τ _k )+η _k ^* s _t ^* (-t-τ _k ′)+n ^* (-t)

where ^* is the conjugate symbol.

Step 3: Calculate the time-inverse echo signal S _TR :

3a) Select the distance range R, and take different distances in the distance range R in order of small to large as search points.

Among them, the distance range R=[R ₁ ,...,R _k ,...,R _n ], satisfying the relationship R ₁ <R _k <R _n , R ₁ is the initial search distance, R _k is the real distance of the target, R _n is the final search distance.

3b) According to the environmental parameters and radar parameters, establish the direct wave and multipath wave virtual channel model H from the radar to these search points:

H＝[H ₁ ... H _k ... H _n ]

H _k ＝[h _k (t)+h _k '(t)]

where H ₁ , H _k , and H _n are the channel models corresponding to R ₁ , R _k , and R _n respectively, h _k (t) is the channel transmission response function of the direct wave, and h _k ′(t) is the channel of the multipath wave Transfer response function.

3c) Transmit the time-reverse signal s _r ^* (-t) into the direct wave and multipath wave virtual channel H, and obtain the corresponding time-reverse echo signal S _TR :

S _TR ＝[s _TR1 (t) … s _TRk (t) … s _TRn (t)]

Among them, s _TR1 (t), s _TRk (t), s _TRn (t) are the time-inverse echo signals corresponding to R ₁ , R _k , and R _n respectively, s _t ^* (-t) is the comparison signal, and ^* is conjugate symbol, is the convolution operation, η _k is the multipath wave channel complex electromagnetic scattering coefficient, τ _k is the direct wave channel delay, τ _k ′ is the multipath wave channel delay, N(t) is the noise signal.

Step 4: Calculate the Pearson correlation coefficient according to the transmitted signal s _t (t) and the time-inverse echo signal S _TR .

4a) Construct a comparison signal s _t ^* (-t) from the transmitted signal s _t (t).

4b) Calculating the Pearson correlation coefficient ρ of each echo in the counter-echo signal S _TR and the comparison signal s _t ^* (-t).

Step 5: Since the echo signal is time-reversed and re-transmitted to different virtual channels, the Pearson correlation coefficient of the time-inverse echo and the comparison signal corresponding to the real distance of the target is the largest, among all the Pearson correlation coefficients Find the largest correlation coefficient in ρ, and its corresponding distance is the real distance of the target, thus realizing the accurate ranging of the target.

In a multi-path environment, the traditional matched filter ranging method cannot accurately measure the distance, and false targets will be detected by mistake. However, the present invention performs time inversion on the echo signal and resends it to the virtual channel, and uses time inversion The correlation property of the wave accurately measures the target distance information. In order to weaken the influence of multipath effect on distance measurement, the traditional method adopts the method of suppressing multipath effect, but the present invention uses multipath information for distance measurement, and the cost is low, and it is applicable to various delayed multipath situations.

The technical effects of the present invention will be further described through simulation experiments and data.

Example 6

The radar target ranging method based on time inversion is the same as in Embodiments 1-5, and the present invention further verifies the target ranging performance in a multipath environment through the following simulation.

(1) Experimental scene:

Under the same environmental parameters and radar parameters, the traditional matched filter ranging method and the radar target ranging method based on time inversion of the present invention are respectively used for simulation experiments.

(2) Experimental content and analysis of experimental results:

Experimental conditions: Simulate the distance measurement of low-altitude point targets on the sea surface in the computer, and set the environmental parameters and radar parameters as shown in the table below.

In the case of the above parameters, only the influence of one multipath on single target ranging is considered, the transmitted signal is in the horizontal polarization mode, and the traditional matched filter method is used for ranging, and the ranging result diagram is shown in Figure 2, where the horizontal The coordinates are distance values, and the ordinate is the normalized matched filter amplitude. It can be seen from Figure 2 that due to the influence of the multipath effect, two peaks appear in the matched filter ranging result graph. Target.

Under the same simulation conditions, the radar target ranging method based on time inversion of the present invention is used for ranging, and the ranging result diagram is obtained as shown in Figure 3, wherein the abscissa is the distance value, and the ordinate is the normalized correlation coefficient. It can be seen from Figure 3 that the distance value corresponding to the maximum value of the correlation coefficient is the target distance. The distance corresponding to the peak point of the correlation coefficient in the figure is 30000m, and the measured target distance is 30000m, which is the same as the real distance of the target. In order to accurately measure the target distance, the error of the ranging result is extremely small.

Using the traditional matched filter method for target ranging, due to the interference of multipath signals, multiple peaks with similar amplitudes appear in the ranging results, and the radar cannot accurately measure the distance of the target. Using the method of the present invention for distance measurement, the correlation coefficient of a peak in the distance measurement result is much larger than the correlation coefficients at other positions. It is only necessary to find the distance corresponding to the peak, which is the real distance of the target, and is not affected by false targets. . Moreover, the inventive method does not need to set up the antenna, has low cost, and is applicable to situations of different delay multipaths.

To sum up, the present invention discloses a radar target ranging method based on time inversion, which solves the problem of accurate target ranging in a multipath environment. The implementation steps are: 1. Generate the radar transmission signal and obtain the echo data; 2. Perform time inversion on the echo data to obtain the time inversion signal; 3. Set the distance search range and calculate the virtual channel model corresponding to different distance points, Transmit the time-reverse signal into these channels to obtain the time-reverse echo signal; 4. Construct the comparison signal, and calculate the Pearson correlation coefficient of each time-reverse echo signal and the comparison signal; 5. Find the maximum correlation coefficient among all correlation coefficients The corresponding distance is the target distance. The present invention performs time inversion on the echo data and transmits them to the virtual channel to focus the direct wave and multipath wave signals in time, and uses the multipath information to correlate the time-inverse echo corresponding to the real distance with the comparison signal High reliability, so as to achieve accurate ranging of the target, and the cost is low, suitable for various delay multipath situations, and can be used to measure the distance of the target at low altitude points on the sea surface.

The above description is only a specific example of the present invention, and does not constitute any limitation to the present invention. Obviously, for those skilled in the art, after understanding the contents and principles of the present invention, it is possible without departing from the principles and structures of the present invention. Various modifications and changes in form and details are made under the circumstances of the present invention, but these modifications and changes based on the idea of the present invention are still within the protection scope of the claims of the present invention.

Claims (3)

1. a kind of radar target distance-finding method based on time reversal, it is characterised in that surveyed using multi-path information to target Away from, including have the following steps：

(1) radar produces transmission signal s_t(t) radar return data s, is obtained_r(t)；

(2) by echo data s_r(t) time reversal processing, inverted signal s when obtaining are carried out_r ^*(- t), wherein * are conjugate of symbol；

(3) back echo signal S when radar is calculated_TR；

(4) according to transmission signal s_t(t) and when back echo signal S_TR, obtain Pearson correlation coefficient：

4a) according to transmission signal s_t(t) contrast signal s is constructed_t ^*(-t)；

Back echo signal S when 4b) being calculated_TRIn each echo and contrast signal s_t ^*The Pearson correlation coefficient ρ of (- t)；

(5) coefficient correlation of maximum is found in whole Pearson correlation coefficient ρ, its corresponding distance is the distance of target, Complete object ranging.

2. the radar target distance-finding method according to claim 1 based on time reversal, being calculated described in step 3 Back echo signal S during radar_TR, specifically include：

3a) selected distance scope R, each distance is taken to be used as Searching point in order in distance range R；

3b) according to ambient parameter and radar parameter, direct wave and multipath ripple pseudo channel of the radar at these Searching points are established Model H；

3c) by when inverted signal s_r ^*(- t) is transmitted into direct wave and multipath ripple pseudo channel H, back echo signal when corresponding to acquisition S_TR；

Wherein, distance range R=[R₁,…,R_k,…,R_n], R₁For initial detection range, R_kFor the actual distance of target, R_nFor Final detection range, channel model H=[H₁ … H_k … H_n], wherein H₁,H_k,H_nRespectively R₁,R_k,R_nIt is corresponding virtual Channel model, when back echo signal S_TR=[s_TR1(t) … s_TRk(t) … s_TRn(t)], wherein s_TR1(t),s_TRk(t),s_TRn (t) it is respectively R₁,R_k,R_nBack echo signal when corresponding.

3. the radar target distance-finding method according to claim 2 based on time reversal, wherein step 3c) by when inverted signal s_r ^*(- t) is transmitted into direct wave and multipath ripple pseudo channel H, back echo signal S when corresponding to acquisition_TR, enter as follows OK：

According to the transmission receptance function h of direct wave_k(t) and multipath ripple transmission receptance function h '_k(t), when searching R_kDuring position, the when back echo signal obtained now is：

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Wherein s_t ^*(- t) is contrast signal, and * is conjugate of symbol,For convolution algorithm, R_kCorresponding channel model multipath channel models H_k=[h_k(t)+h′_k(t)], η_kFor multipath ripple channel electromagnetic scattering coefficient, τ_kFor direct wave channel time delay, τ '_kBelieve for multipath ripple Road is delayed, and N (t) is noise signal.