CN113093141A - Multi-carrier frequency LFMCW radar signal synthesis processing method - Google Patents

Multi-carrier frequency LFMCW radar signal synthesis processing method Download PDF

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CN113093141A
CN113093141A CN202110390637.6A CN202110390637A CN113093141A CN 113093141 A CN113093141 A CN 113093141A CN 202110390637 A CN202110390637 A CN 202110390637A CN 113093141 A CN113093141 A CN 113093141A
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CN113093141B (en
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韩壮志
李豪欣
刘利民
李琦
解辉
高振斌
刘贺雄
尹园威
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Hebei University of Technology
Army Engineering University of PLA
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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Abstract

The invention discloses a multi-carrier frequency LFMCW radar signal synthesis processing method, and relates to the technical field of radar signal processing methods. The method is based on the characteristics of the multi-carrier frequency LFMCW slow time dimension signal, realizes Doppler frequency compensation by resampling the signal through Keystone transformation, and compensates the phase by using a method of obtaining the phase difference through cross correlation, thereby completing the coherent synthesis processing of the multi-carrier frequency LFMCW radar signal on the slow time dimension. Simulation results show that the effectiveness and high gain of the novel method can ensure higher output signal-to-noise ratio gain even under the condition that the signal-to-noise ratio is-30 dB.

Description

Multi-carrier frequency LFMCW radar signal synthesis processing method
Technical Field
The invention relates to the technical field of radar signal processing methods, in particular to a multi-carrier frequency LFMCW radar signal synthesis processing method.
Background
As a radar signal format which has appeared in recent years, a multi-carrier frequency radar has attracted attention because it has advantages such as frequency diversity, a wide ranging range, high distance resolution, a high target detection probability, and suppression of doppler sensitivity. For the processing of multi-carrier frequency radar signals, the traditional processing method is to synthesize detection data after each radar performs target detection, such as a weighted minimum mean square error algorithm, but because the method does not fully utilize the energy of radar transmission signals, the detection performance of a receiver cannot be improved.
To solve this problem, signal level synthesis processing needs to be implemented on the multi-carrier frequency radar to achieve efficient energy utilization. In the prior art, a space-domain bandwidth synthesis method is proposed, in which each path of signal is spliced into an LFM signal with a large bandwidth, but the method requires that the bandwidth of the modulation band of each path of antenna is not less than the frequency difference between the antennas, so that the method is not applicable to signals with small bandwidth of the modulation band; in the prior art, a non-coherent accumulation signal synthesis processing method is also provided, and multi-frequency point data is subjected to non-coherent accumulation in a speed domain; in addition, the prior art provides an interpolation synthesis method, which synthesizes range-doppler images of various radars through difference fusion; in addition, in the prior art, a synthetic processing method based on two-dimensional correlation processing and phase compensation is provided for a multi-frequency external radiation source radar. These methods synthesize the finally processed spectrum image on the range-doppler spectrum of each detection frequency signal, and their essence is the process of processing each signal separately, and do not achieve the purpose of processing after synthesizing the signal.
Disclosure of Invention
The invention aims to solve the technical problem of how to provide an effective multi-carrier frequency LFMCW radar signal synthesis processing method capable of obtaining high gain.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a multi-carrier frequency LFMCW radar signal synthesis processing method is characterized by comprising the following steps:
respectively carrying out fast time dimension FFT processing on echo beat signals of different carrier frequencies to obtain a located distance unit;
determining one path of signals as reference signals, and converting the Doppler frequency of the slow time dimension signals corresponding to other carrier frequencies into the Doppler frequency same as the reference signals by using Keystone conversion;
performing cross-correlation processing on the slow time dimension signal after Keystone transformation and a reference slow time dimension signal respectively to obtain a phase difference, and compensating the phase difference;
directly synthesizing the multipath slow time dimensional signals subjected to Keystone conversion and cross-correlation processing to obtain synthesized signals;
performing slow time dimension FFT processing on the synthesized signal to obtain a speed unit where a target is located;
and finding out the position of the maximum value in the two-dimensional frequency spectrum, estimating the distance and the speed of the target, and realizing distance-speed decoupling.
The further technical scheme is that the fast time dimension FFT processing method comprises the following steps:
suppose with fsSampling K channels of signals for sampling frequency, wherein each channel of receiving antenna receives echo signals of M frequency modulation periods, the number of sampling points in each frequency modulation period is N, FFT processing is carried out on beat signals of each frequency modulation period, and the frequency domain signals of the mth frequency modulation period can be obtained as follows:
Figure BDA0003016572150000021
from the above, the fast time dimension FFT yields a signal frequency of
Figure BDA0003016572150000022
Reflecting the distance channel where the target is located; frequency domain signal Sm,k(f) At frequency fm,kTo obtain the spectral peak:
Figure BDA0003016572150000023
analysis of the above formula yields: sm,k(fm,k) Can be regarded as a signal with T as a sampling period, the time independent variable is mT, and the frequency is mT
Figure BDA0003016572150000024
The Doppler frequency is used for reflecting the speed information of the target;
wherein: f. ofkThe radar has carrier frequency B, frequency T, frequency modulation slope, R, speed of light, v, M0, M.
A further technical solution is that the method for converting the doppler frequency of the slow time dimension signal corresponding to another carrier frequency into the same doppler frequency as the reference signal by using the Keystone transform is as follows:
for a multi-carrier-frequency radar signal, a 1 st path of emission signal is assumed as a reference signal, and a fast time dimension FFT spectrum peak value is as follows:
Figure BDA0003016572150000031
the frequency of the signal can be obtained as
Figure BDA0003016572150000032
With an amplitude of
Figure BDA0003016572150000033
For transmission carrier frequency fkThe fast time dimension FFT spectrum peak result of the echo beat signal of (2) can be expressed as:
Figure BDA0003016572150000034
namely Sk(f) Can be regarded as corresponding to the frequency of
Figure BDA0003016572150000035
In order to
Figure BDA0003016572150000036
The discrete signals obtained by sampling at the sampling interval have different doppler frequencies caused by different carrier frequencies of the transmitted signals, and can be considered as the difference caused by sampling a signal with the same frequency at different intervals; thus, can be to Sk(f) Performing resampling to obtain
Figure BDA0003016572150000037
Correcting the originally different Doppler frequency to be the same Doppler frequency as the reference signal; the transformation is performed by using a sinc interpolation method, and the formula is expressed as follows:
Figure BDA0003016572150000038
wherein, S '(m') is sampled data after Keystone transformation, and after the transformation, the slow time dimension signals corresponding to different echoes have the same doppler frequency, and the signal form is:
Figure BDA0003016572150000039
if the K-path signals are directly synthesized, the obtained synthesized signals are:
Figure BDA00030165721500000310
from the above equation, although the matching of the doppler frequency can be realized by the Keystone transform, the matching is due to the fact that
Figure BDA00030165721500000311
The phase of the part being related to the transmitted signalThe phase of the converted slow time dimension signal can not be kept consistent with the carrier frequency, and if there is a phase difference during the synthesis
Figure BDA00030165721500000312
(wherein n ═ 0, ± 1, ± 2.) is satisfied
Figure BDA00030165721500000313
(wherein
Figure BDA00030165721500000314
) The composite signal is then:
Figure BDA00030165721500000315
at this time, the phase of the transformed slow time dimension signal is the same as the phase of the reference signal.
The further technical scheme is that the phase difference compensation method comprises the following steps:
and (3) solving the cross correlation between the slow time dimension signal after Keystone transformation and a reference signal, wherein the obtained cross correlation function is as follows:
Figure BDA0003016572150000041
namely, the phase difference between the slow time dimension signal after Keystone transformation and the reference signal is:
Figure BDA0003016572150000042
the initial phase difference of the slow time dimension signals with the same Doppler frequency can be obtained by the formula; therefore, after the Keystone transform is used for compensating the frequency, the slow time dimension signals and the reference signals are subjected to cross-correlation processing to obtain the phase difference, and the phase difference is compensated, so that the synchronization of the signal phase is realized; the compensated signal is kept consistent with the phase of the reference signal, and the compensated signal and the reference signal are synthesized to obtain a synthesized signal, wherein the synthesized signal has the form:
Figure BDA0003016572150000043
and performing FFT processing on the synthesized slow time dimension signal to estimate the motion speed of the target.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in: the method is based on the characteristics of the multi-carrier frequency LFMCW slow time dimension signal, realizes Doppler frequency compensation by resampling the signal through Keystone transformation, and compensates the phase by using a method of obtaining the phase difference through cross correlation, thereby completing the coherent synthesis processing of the multi-carrier frequency LFMCW radar signal on the slow time dimension. Simulation results show that the effectiveness and high gain of the novel method can ensure higher output signal-to-noise ratio gain even under the condition that the signal-to-noise ratio is-30 dB.
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The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a flow chart of a method according to an embodiment of the invention;
FIG. 2 is a time-frequency diagram of a transmitted signal and an echo signal according to an embodiment of the present invention;
FIG. 3a is a graph of the results of the Keystone transformation in an embodiment of the present invention;
FIG. 3b is a graph of results after Keystone transformation in an embodiment of the present invention;
FIG. 4a is a diagram of the results before cross-correlation processing in an embodiment of the present invention;
FIG. 4b is a diagram of the results of cross-correlation processing in an embodiment of the present invention;
FIG. 5a is a graph showing the results of the direct synthesis method in the example of the present invention;
FIG. 5b is a graph showing the results of the synthesis method proposed in the example of the present invention;
FIG. 6 is a graph of output SNR gain versus SNR for an embodiment of the present invention;
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.
Generally, as shown in fig. 1, an embodiment of the present invention discloses a method for synthesizing and processing a multi-carrier-frequency LFMCW radar signal, which includes the following steps:
step 1: and respectively carrying out fast time dimension FFT processing on the echo beat signals of different carrier frequencies to obtain the located distance units.
Step 2: and determining one path of signals as reference signals, and changing the Doppler frequency of the slow time dimension signals corresponding to other carrier frequencies into the same Doppler frequency as the reference signals by utilizing Keystone transformation.
Step 3: and respectively carrying out cross-correlation processing on the slow time dimension signal after Keystone transformation and the reference slow time dimension signal to obtain the phase difference of the signals, and compensating the phase difference.
Step 4: and directly synthesizing the multipath slow time dimensional signals subjected to Keystone transformation and cross-correlation processing to obtain synthesized signals.
Step 5: and carrying out slow time dimension FFT processing on the synthesized signal to obtain a speed unit where the target is located.
Step 6: and finding out the position of the maximum value in the two-dimensional frequency spectrum, estimating the distance and the speed of the target, and realizing distance-speed decoupling.
The above method is described in detail below with reference to the following specific contents:
multi-carrier frequency LFMCW radar signal model:
the multi-carrier frequency LFMCW radar adopts a multi-transmitting and multi-receiving mode, and the number of transmitting antennas and the number of receiving antennas are the same. At a sending end, different antennas transmit LFMCW signals of different carrier frequencies, and the frequency modulation bandwidth and the frequency modulation period of the signals are the same. At the receiving end, different antennas respectively receive the corresponding echo signals, and frequency mixing and low-pass filtering processing are carried out.
Assuming that a transmitting end transmits K different carrier frequency signals to detect a target, fig. 2 illustrates a time-frequency relationship diagram of a K-th transmitting signal and an echo signal. Wherein f iskAnd B is a transmission bandwidth, T is a frequency modulation period, and the frequency modulation slope mu is B/T.
Ideally, the signal form of the k-th transmission signal in the m-th frequency modulation period is as follows:
Figure BDA0003016572150000061
if a uniform-speed moving target is provided, the initial distance between the target and the radar is R, and the moving speed is v, the time delay between the echo signal and the transmitting signal is as follows:
Figure BDA0003016572150000062
namely, the expression of the echo signal reflected from the target is:
Figure BDA0003016572150000063
mixing the received echo signal with the transmitted signal, taking into account the fact, ignoring the relation c2(c is the speed of light), and since v < c, the target echo beat signal of the mth frequency modulation period can be obtained as:
Figure BDA0003016572150000064
as can be seen from equation (3), the frequency f of the beat signalm,kThe composition of the three components is characterized by comprising three components,
Figure BDA0003016572150000065
this term is the frequency difference caused by the distance between the target and the radar;
Figure BDA0003016572150000066
this term is the doppler frequency due to the motion of the target, the magnitude of which is related to the target velocity and the carrier frequency of the transmitted signal; last item
Figure BDA0003016572150000067
Is the frequency component due to the distance the target moves during multiple cycles. At the same time, beat signal Sm,kThere are also two phase factors in (t)
Figure BDA0003016572150000071
And
Figure BDA0003016572150000072
the values of which are also related to the carrier frequency of the transmitted signal. It can be seen that there is a coupling between range and velocity due to the presence of doppler frequency; because the carrier frequencies of the transmitted signals are different, the frequencies and the phases of the echo beat signals are different, and therefore the signal synthesis processing is difficult.
Two-dimensional FFT
And for the distance-velocity coupling phenomenon existing in the LFMCW radar, two-dimensional FFT is adopted for processing. Suppose with fsSampling K channels of signals for sampling frequency, wherein each channel of receiving antenna receives echo signals of M frequency modulation periods, the number of sampling points in each frequency modulation period is N, FFT processing is carried out on beat signals of each frequency modulation period, and the frequency domain signals of the mth frequency modulation period can be obtained as follows:
Figure BDA0003016572150000073
from equation (4), the fast time dimension FFT yields a signal frequency of
Figure BDA0003016572150000074
It reflects the eyeThe distance channel is marked. Frequency domain signal Sm,k(f) At frequency fm,kTo obtain the spectral peak:
Figure BDA0003016572150000075
analytical formula (5) gives: sm,k(fm,k) Can be regarded as a signal with T as a sampling period, the time independent variable is mT, and the frequency is mT
Figure BDA0003016572150000076
The target distance estimation method is a Doppler frequency method and reflects the speed information of a target, so that the distance and the speed of the target can be solved by using two-dimensional FFT, and if the receiving end accumulates echo beat signals of M frequency modulation periods, N-point FFT processing can be performed on the beat signals of each period to estimate the target distance, namely fast time dimension FFT; and then performing M-point FFT on the frequency spectrum signals with different frequency modulation periods in the same distance unit to estimate a target speed, namely a slow time dimension FFT, so as to realize decoupling of the target distance and the speed.
When the two-dimensional FFT is used for solving the target distance and speed, theoretically, the frequency resolution corresponding to the fast time-dimensional FFT is
Figure BDA0003016572150000077
The maximum unambiguous velocity measurable by the FFT in the slow time dimension corresponds to a Doppler frequency of
Figure BDA0003016572150000078
While
Figure BDA0003016572150000079
This is always true. This shows that, for multiple signals of different carrier frequencies, the difference in doppler frequency does not affect the range channel where the target is located, i.e., the signals can still be guaranteed to be on the same range channel. For the FFT result in the slow time dimension, the velocity channels corresponding to different doppler frequencies are also different. Therefore, in order to realize the synthesis processing of the multiple carrier frequency signals, the consistency of the speed channels needs to be ensured.
New method for synthesizing and processing multi-carrier frequency LFMCW radar signal
If the same velocity channel is to be ensured, the same Doppler frequency is required. When processing multi-carrier frequency signals, firstly, FFT processing is carried out on each path of signals in a fast time dimension, and then frequency compensation is carried out on the signals in a slow time dimension, so that the purpose of synthesizing the multi-carrier frequency signals is achieved, and effective detection on targets is realized.
Keystone transform compensated Doppler frequency
In order to realize the consistency of the Doppler frequency of the signals, Keystone transformation is adopted to process the signals in the slow time dimension. For a multi-carrier-frequency radar signal, a 1 st path of emission signal is assumed as a reference signal, and a fast time dimension FFT spectrum peak value is as follows:
Figure BDA0003016572150000081
the frequency of the signal can be obtained as
Figure BDA0003016572150000082
With an amplitude of
Figure BDA0003016572150000083
For transmission carrier frequency fkThe fast time dimension FFT spectrum peak result of the echo beat signal of (2) can be expressed as:
Figure BDA0003016572150000084
namely Sk(f) Can be regarded as corresponding to the frequency of
Figure BDA0003016572150000085
In order to
Figure BDA0003016572150000086
The discrete signals sampled for the sampling interval have different Doppler frequencies due to different carrier frequencies of the transmitted signal, which can be considered to be for the same frequencyThe difference caused by sampling the signal at different intervals. Thus, can be to Sk(f) Performing resampling to obtain
Figure BDA0003016572150000087
The originally different doppler frequency is corrected to the same doppler frequency as the reference signal. This resampling process is the process of the Keystone transform, and the present application uses the sinc interpolation method for the transformation, and the formula is expressed as:
Figure BDA0003016572150000088
wherein, S '(m') is sampled data after Keystone transformation, and after the transformation, the slow time dimension signals corresponding to different echoes have the same doppler frequency, and the signal form is:
Figure BDA0003016572150000091
if the K-path signals are directly synthesized, the obtained synthesized signals are:
Figure BDA0003016572150000092
from the equation (10), although the matching of the doppler frequency can be realized by the Keystone transform, the doppler frequency is uniform because of the Keystone transform
Figure BDA0003016572150000093
The phase of the part is related to the carrier frequency of the transmitted signal, the phase of the converted slow time dimension signal can not be kept consistent, and if a phase difference exists during the synthesis
Figure BDA0003016572150000094
(wherein n ═ 0, ± 1, ± 2.) is satisfied
Figure BDA0003016572150000095
(wherein
Figure BDA0003016572150000096
) The composite signal is then:
Figure BDA0003016572150000097
at this time, the phase of the transformed slow time dimension signal is the same as that of the reference signal, and theoretically, the gain of the output signal-to-noise ratio after the synthesis processing can be improved by 10log10(K) dB. When in use
Figure BDA0003016572150000098
In time, the phases of the slow time-dimension signals are still different, and energy cannot be effectively accumulated during signal synthesis, which leads to loss of an output signal-to-noise ratio.
Cross correlation compensation phase
Although the Keystone transform compensates the doppler frequency of the signal, it still cannot achieve signal phase synchronization and ensure effective utilization of signal energy. Therefore, further aiming at the problem that the initial phases of the slow time dimension signals are different, the compensation of the initial phases is realized by adopting cross correlation. And (3) solving the cross correlation between the slow time dimension signal after Keystone transformation and a reference signal, wherein the obtained cross correlation function is as follows:
Figure BDA0003016572150000099
namely, the phase difference between the slow time dimension signal after Keystone transformation and the reference signal is:
Figure BDA00030165721500000910
the initial phase difference of the slow time dimension signals with the same Doppler frequency can be obtained by the equation (13). Therefore, after the frequency is compensated by the Keystone transform, the slow time-dimensional signals and the reference signal are cross-correlated to obtain the phase difference, and the phase difference is compensated, so that the signal phase is synchronized. The compensated signal is kept consistent with the phase of the reference signal, and the compensated signal and the reference signal are synthesized to obtain a synthesized signal, wherein the synthesized signal has the form:
Figure BDA0003016572150000101
the FFT processing is carried out on the synthesized slow time dimension signal, the movement speed of the target can be estimated, and the output signal-to-noise ratio gain of 10log10(K) dB can be obtained theoretically.
Results and analysis of the experiments
In the simulation experiment, 4 paths of transmitting signals are arranged on the radar, carrier frequencies are respectively 24GHz, 24.5GHz, 25GHz and 25.5GHz, carrier frequency differences of the transmitting signals of adjacent antennas are respectively 0.5GHz, frequency modulation periods are respectively T (100 us), and frequency modulation bandwidth is B (150 MHz).
Signal synthesis processing method effectiveness analysis
In order to analyze the effectiveness of the provided signal synthesis processing method, experimental simulation sets that the signal-to-noise ratios of four paths of beat signals are all-15 dB, the initial distance of a target is 100m, and the initial speed of the target is 13 m/s. Fig. 3a and fig. 3b are output results before and after the four-path signal slow time dimension signal Keystone transformation, respectively. It can be seen that before the Keystone transform is performed, the result cannot be guaranteed to be on the same speed unit after the two-dimensional FFT due to the difference of doppler frequencies; after Keystone conversion processing, Doppler frequency is compensated, and the speed units are consistent. Fig. 4a and fig. 4b are output results before and after performing the cross-correlation processing, respectively, and it can be seen by comparison that the output signal-to-noise ratio before the cross-correlation processing is low; after the phase is compensated by cross-correlation, the output signal-to-noise ratio is obviously improved. Fig. 5a and 5b are output results processed by the direct synthesis method and the proposed new synthesis method, respectively, and it can be analyzed that when the direct synthesis method is used, coherent synthesis cannot be realized due to doppler frequency difference and phase difference, the processed results are represented as a plurality of points on a distance-velocity two-dimensional spectrum, and output signal-to-noise ratio is low; when the new synthesis method is adopted for processing, the multi-carrier frequency signals are effectively synthesized, the target position signals are represented as one point on the two-dimensional frequency spectrum, and the output signal-to-noise ratio is high.
Signal synthesis output signal-to-noise ratio gain analysis
In order to analyze the output signal-to-noise ratio gain of the provided signal synthesis processing method, the speed of a target is set to be 13m/s by experimental simulation, the initial distance is 100:20:200, the signal-to-noise ratios of four paths of beat signals are all-15 dB, and the first path of signals are used as reference signals. Under different target distances, two processing methods are respectively adopted, each processing method is subjected to 250 Monte Carlo experiments, and the first processing method is directly subjected to synthesis processing after Keystone conversion; the second employs the signal synthesis processing method proposed herein. Let the fast time dimension FFT point number be 512 and the slow time dimension FFT point number be 128. Theoretically, the signal-to-noise ratio gain of 4-path signal synthesis is 10log10(4) 6.0206 dB. The results of the experimental simulation are shown in table 1.
TABLE 1 output signal-to-noise ratio (dB)
High target distance (m) 24GHz 24.5GHz 25GHz 25.5GHz First processing method Second processing method
100 33.1317 33.3450 33.8214 32.2325 27.1950 38.6566
120 33.1300 33.3518 33.8442 32.1957 39.1648 38.6652
140 33.1155 33.3384 33.8281 32.2111 27.1091 38.6580
160 33.1319 33.3473 33.7972 32.1899 27.2401 38.6546
180 33.1390 33.3540 33.8211 32.2202 39.1609 38.6608
200 33.1447 33.3331 33.8103 32.2235 27.1075 38.6611
The data in table 1 show that, for the targets with distances of 100, 140, 160 and 200, because the phases of the signals after the Keystone transformation are different, the output signal-to-noise ratios obtained by the first processing method are all about 27dB, and are reduced compared with the output signal-to-noise ratio of the reference beat signal, which causes the performance reduction of the receiver, and the result shows that the output signal-to-noise ratio cannot be improved only by the Keystone transformation, and is consistent with the theoretical analysis; the output signal-to-noise ratios obtained by the second processing method are all improved, namely, the phases are effectively compensated after cross-correlation processing, and the signal energy is fully utilized. For the target with the initial distance of 120, 180, the reason is that
Figure BDA0003016572150000111
The signal phases are integers, namely the signal phases after Keystone transformation are synchronized, and the signal-to-noise ratio gain obtained by adopting the first processing method is close to the theoretical output signal-to-noise ratio gain; the signal-to-noise ratio gain obtained by adopting the second processing method is also above 5.5dB, and although the gain is reduced compared with a theoretical value, the higher output signal-to-noise ratio gain is still ensured. In practical application, the distance of the moving target is constantly changed, and the phase difference cannot be ensured constantly
Figure BDA0003016572150000112
Is an integer, therefore, the method provided by the invention meets the requirement of practical application.
Influence of noise on signal synthesis processing method
In order to analyze the anti-noise performance of the signal synthesis processing method, the initial distance of a target is set to be 92m and the speed is set to be 13m/s in experimental simulation. The signal-to-noise ratio of the beat signal is-30 dB: 1: 20dB, 250 Monte Carlo simulation experiments are carried out, and the experimental results are shown in figure 6. As can be seen from fig. 6, when the multi-carrier LFMCW signal is processed by the synthesis method proposed herein, the output snr gain decreases as the snr of the received signal increases. The result shows that the method is particularly suitable for multi-carrier frequency signal synthesis processing under the condition of low signal-to-noise ratio, and can effectively improve the processing performance of the system.
In summary, the method compensates the doppler frequency and phase of the slow time dimension signal by using the Keystone transform and the cross correlation, and can complete the multi-channel signal synthesis processing in the slow time dimension. Experimental simulation shows that the method can effectively realize coherent synthesis of multi-carrier frequency signals, still has higher output signal-to-noise ratio gain when the signal-to-noise ratio is-30 dB, and provides a certain reference value for practical engineering application.

Claims (4)

1. A multi-carrier frequency LFMCW radar signal synthesis processing method is characterized by comprising the following steps:
respectively carrying out fast time dimension FFT processing on echo beat signals of different carrier frequencies to obtain a located distance unit;
determining one path of signals as reference signals, and converting the Doppler frequency of the slow time dimension signals corresponding to other carrier frequencies into the Doppler frequency same as the reference signals by using Keystone conversion;
performing cross-correlation processing on the slow time dimension signal after Keystone transformation and a reference slow time dimension signal respectively to obtain a phase difference, and compensating the phase difference;
directly synthesizing the multipath slow time dimensional signals subjected to Keystone conversion and cross-correlation processing to obtain synthesized signals;
performing slow time dimension FFT processing on the synthesized signal to obtain a speed unit where a target is located;
and finding out the position of the maximum value in the two-dimensional frequency spectrum, estimating the distance and the speed of the target, and realizing distance-speed decoupling.
2. The method for multi-carrier frequency LFMCW radar signal synthesis processing according to claim 1, wherein the fast time dimension FFT processing method is as follows:
suppose with fsSampling K channels of signals for sampling frequency, wherein each channel of receiving antenna receives echo signals of M frequency modulation periods, the number of sampling points in each frequency modulation period is N, FFT processing is carried out on beat signals of each frequency modulation period, and the frequency domain signals of the mth frequency modulation period can be obtained as follows:
Figure FDA0003016572140000011
from the above, the fast time dimension FFT yields a signal frequency of
Figure FDA0003016572140000012
Reflecting the distance channel where the target is located; frequency domain signal Sm,k(f) At frequency fm,kTo obtain the spectral peak:
Figure FDA0003016572140000013
analysis of the above formula yields: sm,k(fm,k) Can be regarded as a signal with T as a sampling period, the time independent variable is mT, and the frequency is mT
Figure FDA0003016572140000014
The Doppler frequency is used for reflecting the speed information of the target;
wherein: f. ofkThe radar has carrier frequency B, frequency T, frequency modulation slope, R, speed of light, v, M0, M.
3. The method for synthesizing a multi-carrier-frequency LFMCW radar signal according to claim 2, wherein the method for transforming the doppler frequency of the slow time dimension signal corresponding to other carrier frequency into the same doppler frequency as the reference signal by using the Keystone transform comprises the following steps:
for a multi-carrier-frequency radar signal, a 1 st path of emission signal is assumed as a reference signal, and a fast time dimension FFT spectrum peak value is as follows:
Figure FDA0003016572140000021
the frequency of the signal can be obtained as
Figure FDA0003016572140000022
With an amplitude of
Figure FDA0003016572140000023
For transmission carrier frequency fkThe fast time dimension FFT spectrum peak result of the echo beat signal of (2) can be expressed as:
Figure FDA0003016572140000024
namely Sk(f) Can be regarded as corresponding to the frequency of
Figure FDA0003016572140000025
In order to
Figure FDA0003016572140000026
The discrete signals obtained by sampling at the sampling interval have different doppler frequencies caused by different carrier frequencies of the transmitted signals, and can be considered as the difference caused by sampling a signal with the same frequency at different intervals; thus, can be to Sk(f) Performing resampling to obtain
Figure FDA0003016572140000027
Correcting the originally different Doppler frequency to be the same Doppler frequency as the reference signal; the transformation is performed by using a sinc interpolation method, and the formula is expressed as follows:
Figure FDA0003016572140000028
wherein, S '(m') is sampled data after Keystone transformation, and after the transformation, the slow time dimension signals corresponding to different echoes have the same doppler frequency, and the signal form is:
Figure FDA0003016572140000029
if the K-path signals are directly synthesized, the obtained synthesized signals are:
Figure FDA00030165721400000210
as is clear from the above formula, when the phase difference is present during the synthesis
Figure FDA00030165721400000211
(wherein n ═ 0, ± 1, ± 2.) is satisfied
Figure FDA00030165721400000212
(wherein
Figure FDA00030165721400000213
) The composite signal is then:
Figure FDA0003016572140000031
at this time, the phase of the transformed slow time dimension signal is the same as the phase of the reference signal.
4. The method for synthesizing and processing the multi-carrier frequency LFMCW radar signal according to claim 3, wherein the phase difference is compensated by the following method:
and (3) solving the cross correlation between the slow time dimension signal after Keystone transformation and a reference signal, wherein the obtained cross correlation function is as follows:
Figure FDA0003016572140000032
namely, the phase difference between the slow time dimension signal after Keystone transformation and the reference signal is:
Figure FDA0003016572140000033
the initial phase difference of the slow time dimension signals with the same Doppler frequency can be obtained by the formula; therefore, after the Keystone transform is used for compensating the frequency, the slow time dimension signals and the reference signals are subjected to cross-correlation processing to obtain the phase difference, and the phase difference is compensated, so that the synchronization of the signal phase is realized; the compensated signal is kept consistent with the phase of the reference signal, and the compensated signal and the reference signal are synthesized to obtain a synthesized signal, wherein the synthesized signal has the form:
Figure FDA0003016572140000034
and performing FFT processing on the synthesized slow time dimension signal to estimate the motion speed of the target.
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