CN113281732A - MIMO radar target positioning method and system based on space-time coding - Google Patents
MIMO radar target positioning method and system based on space-time coding Download PDFInfo
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Abstract
The invention discloses a space-time coding-based MIMO radar target positioning method and system, belonging to the field of target detection positioning, wherein the method comprises the following steps: modulating the initial phase of the linear frequency modulation signal by utilizing a space-time block code and then transmitting the signal, wherein the signal is reflected by a target object and then received by a receiving antenna; respectively mixing the signal received by each receiving antenna with the signal transmitted by the first transmitting antenna to obtain a baseband signal, and sequentially sampling, extracting, recombining and space-time decoding the baseband signal to obtain a corresponding decoded signal; combining the decoding signals to construct a space-time two-dimensional virtual array signal, and sequentially performing two-dimensional smoothing and combination on the space-time two-dimensional virtual array signal to obtain a space-time joint virtual sub-array signal; constructing a spectrum function of the space-time joint virtual subarray signal; and calculating the maximum value of the spectrum function, and positioning the target object according to the distance and the azimuth angle corresponding to the maximum value. The angle estimation precision can be improved, the clutter background is cleaner, the target detection is facilitated, and the positioning precision is improved.
Description
Technical Field
The invention belongs to the field of target detection and positioning, and particularly relates to a space-time coding-based MIMO radar target positioning method and system.
Background
The multi-target positioning technology has wide applications, such as intelligent transportation, indoor positioning, and the like. Compared with detection technologies such as infrared rays, laser, ultrasonic waves and the like, the radar is hardly influenced by weather, has the characteristics of all weather and all day time, and has certain penetrating power. The radar also has stable multi-target positioning performance in scenes with low visibility, such as fire scenes, foggy weather and the like.
The multiple-input multiple-output (MIMO) radar is a multi-antenna combined transceiving system, and has the advantages of high resolution, flexible beam design, target flicker resistance, interference resistance and the like due to the technologies of waveform diversity, space diversity, time diversity and the like. Generally, MIMO radar requires that transmission waveforms are orthogonal to each other and have good auto-correlation and cross-correlation characteristics, but it is not easy to design a plurality of waveforms satisfying this condition. The existing MIMO radar positioning technology generally designs a better orthogonal waveform through a special method to meet the positioning requirement, but the method has higher complexity and needs to consume a large amount of hardware resources; in terms of signal processing, a conventional positioning method based on the MIMO radar is generally performed in two steps, that is, a distance of a target is estimated through Fast Fourier Transform (FFT), and an angle of the target is estimated through digital beam forming or a one-dimensional spectrum estimation algorithm, so as to position the target. However, such methods have the disadvantages of poor angular resolution, low positioning accuracy, and the like.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, the invention provides a space-time coding-based MIMO radar target positioning method and system, aiming at improving the angular resolution, enabling the clutter background to be cleaner and being beneficial to target detection, thereby improving the positioning precision.
In order to achieve the above object, according to an aspect of the present invention, there is provided a space-time coding based MIMO radar target positioning method, including: s1, modulating the initial phase of the linear frequency modulation signal by utilizing a space-time block code, transmitting the modulated linear frequency modulation signal by utilizing a transmitting antenna of the MIMO radar, and receiving the linear frequency modulation signal by a receiving antenna of the MIMO radar after the linear frequency modulation signal is reflected by a target object; s2, mixing the signal received by each receiving antenna with the linear frequency modulation signal transmitted by the first transmitting antenna of the MIMO radar to obtain a corresponding baseband signal, and sequentially sampling, extracting, recombining and space-time decoding the baseband signal to obtain a corresponding decoded signal; s3, combining the decoded signals to construct a space-time two-dimensional virtual array signal, and sequentially performing two-dimensional smoothing and combination on the space-time two-dimensional virtual array signal to obtain a space-time joint virtual subarray signal; s4, constructing a spectrum function of the space-time joint virtual subarray signal, wherein the spectrum function is related to the distance and the azimuth angle of the target object relative to the MIMO radar; and S5, calculating the maximum value of the spectrum function, and positioning the target object according to the distance and the azimuth angle corresponding to the maximum value.
Furthermore, the number of the target objects is one or more, the maximum values correspond to the target objects one to one, and in S5, each target object is located according to the distance and the azimuth angle corresponding to each maximum value.
Further, the modulated chirp signal transmitted by the transmitting antenna in S1 is:
wherein,
the method comprises the steps that a modulated chirp signal transmitted by a pth transmitting antenna in an mth sweep frequency period is represented, P is 1,2, …, P is 1,2, …, M is represented, P is the number of transmitting antennas in the MIMO radar, M is the number of sweep frequency periods, M is larger than or equal to P, t is time, j is an imaginary number unit, f is f0Is the starting frequency, mu is the slope of the sweep,
the phase of the modulated chirp signal transmitted by the pth transmitting antenna in the mth sweep period after space-time coding.
Further, in the step S2, the baseband signal is sequentially sampled, extracted, recombined and processedThe space-time decoding includes: sampling each baseband signal respectively, wherein the number of sampling points in each sweep frequency period is L; extracting the nth sampling point in each frequency sweep period of each baseband signal and recombining to form a recombination matrix with the size of QxM
Q is the number of receiving antennas in the MIMO radar, and M is the number of sweep frequency periods; for each recombination matrix
Performing space-time decoding to obtain corresponding decoded signal
Further, the recombination matrix
And decoding the signal
Respectively as follows:
wherein phi is a space-time coding matrix, K is the number of the target objects, and betai、θiAnd riRespectively, the reflection coefficient, azimuth angle and distance of the ith target object, aR(θi) A vector is directed to the receiving array corresponding to the ith target object,
the emitting array corresponding to the ith target object is guided to a vector aT(θi) J is an imaginary unit, ωr(ri)＝4πμri/cfs，ωr(ri) Is the phase associated with the ith target object distance, μ is the slope of the sweep, c is the speed of light, fsIn order to be able to sample the rate,
in order to be a noise term, the noise term,
the phase of the modulated chirp signal transmitted by the pth transmitting antenna in the mth sweep period after space-time coding is 1,2, …, P, M is 1,2, …, M, P is the number of transmitting antennas in the MIMO radar, and M is the number of sweep periods.
Further, the combining the decoded signals to construct a space-time two-dimensional virtual array signal in S3 includes: vectorizing each decoded signal column respectively to obtain a corresponding spatial virtual array output signal; and sequentially arranging and recombining the space virtual array output signals to form the space-time two-dimensional virtual array signals.
Further, the sequentially performing two-dimensional smoothing and combining on the space-time two-dimensional virtual array signal in S3 to obtain a space-time joint virtual sub-array signal includes: performing two-dimensional smoothing on the space-time two-dimensional virtual array signal to obtain a plurality of sub-arrays; and converting each subarray into a corresponding column vector, and sequentially arranging and recombining the column vectors to form the space-time joint virtual subarray signal.
Still further, the spectral function is:
wherein, PMUSIC(r, θ) is the spectral function, r is the distance, θ is the azimuth angle, a (r, θ)HA conjugate transpose matrix of a steering vector a (r, theta) of the space-time joint virtual sub-matrix,
function(s)
j is an imaginary unit, ωr(r) is the phase, ω, related to the distanceθ(theta) is the phase associated with the azimuth, Y is the column smoothing size of the two-dimensional smoothing, X is the row smoothing size of the two-dimensional smoothing,
denotes kronecker product, UNAnd carrying out singular value decomposition on the space-time joint virtual subarray signal to obtain a noise subspace.
According to another aspect of the present invention, there is provided a MIMO radar target positioning system based on space-time coding, including: the modulation and transmission module is used for modulating the initial phase of the linear frequency modulation signal by utilizing a space-time block code, transmitting the modulated linear frequency modulation signal by utilizing a transmitting antenna of the MIMO radar, and receiving the linear frequency modulation signal by a receiving antenna of the MIMO radar after the linear frequency modulation signal is reflected by a target object; the receiving and decoding module is used for respectively mixing the signal received by each receiving antenna with the linear frequency modulation signal transmitted by the first transmitting antenna of the MIMO radar to obtain a corresponding baseband signal, and sequentially sampling, extracting, recombining and space-time decoding the baseband signal to obtain a corresponding decoding signal; the combined construction module is used for combining the decoding signals to construct a space-time two-dimensional virtual array signal, and sequentially performing two-dimensional smoothing and combination on the space-time two-dimensional virtual array signal to obtain a space-time joint virtual subarray signal; the spectrum function constructing module is used for constructing a spectrum function of the space-time joint virtual subarray signal, and the spectrum function is related to the distance and the azimuth angle of the target object relative to the MIMO radar; and the positioning module is used for calculating the maximum value of the spectrum function and positioning the target object according to the distance and the azimuth angle corresponding to the maximum value.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained: the space-time coding is utilized to carry out phase coding on the transmitting signals of a plurality of transmitting antennas of the MIMO radar in a plurality of periods, so that space diversity and time diversity gain can be obtained simultaneously, each transmitting waveform in a long time easily meets the orthogonal condition, a good orthogonal waveform is easily designed, and the practical application is facilitated; in the aspect of signal processing, each signal is separated by performing space-time decoding on a received baseband signal, so that the cross correlation among transmitted waveforms can be greatly reduced or even eliminated, and the estimation performance of positioning parameters is improved; the constructed space-time two-dimensional virtual array signal is subjected to space-time two-dimensional smoothing, and the distance and the azimuth angle of a target object can be estimated simultaneously by a space spectrum estimation technology, so that one-step positioning is realized, and the angular resolution and the positioning precision are improved; the positioning method can simultaneously estimate the distances and the azimuth angles of a plurality of target objects, and has higher positioning efficiency; compared with the traditional method, the MIMO radar target positioning method based on the space-time coding has higher angular resolution, cleaner clutter background, is beneficial to target detection, has higher positioning precision and is easy to realize.
Drawings
Fig. 1 is a flowchart of a space-time coding-based MIMO radar target positioning method according to an embodiment of the present invention;
FIG. 2 is a diagram of a real object scene provided in an embodiment of the present invention;
FIG. 3 is a schematic diagram of two-dimensional smooth partitioning according to an embodiment of the present invention;
FIG. 4A is a diagram of the positioning effect of a conventional two-step Fourier transform estimation method;
FIG. 4B is a diagram illustrating a positioning effect of the method according to the embodiment of the present invention;
fig. 5 is a block diagram of a space-time coding based MIMO radar target positioning system according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
In the present application, the terms "first," "second," and the like (if any) in the description and the drawings are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order.
Fig. 1 is a flowchart of a space-time coding based MIMO radar target positioning method according to an embodiment of the present invention. Referring to fig. 1, with reference to fig. 2 to fig. 4B, a detailed description is given of the space-time coding based MIMO radar target location method in this embodiment, where the method includes operation S1-operation S5.
Operation S1 is to modulate the initial phase of the chirp signal using the space-time block code, and transmit the modulated chirp signal using a transmitting antenna of the MIMO radar, where the chirp signal is reflected by a target object and then received by a receiving antenna of the MIMO radar.
In this embodiment, the transceiving arrays of the MIMO radar are, for example, uniform linear arrays, which are disposed in parallel, the numbers of the transmitting antennas and the receiving antennas are P and Q, respectively, the interval between the receiving antennas is d, and the interval between the transmitting antennas is Qd, where d is λ/2, and λ is the wavelength corresponding to the central carrier frequency. The modulated chirp signal transmitted by the pth transmit antenna during the mth sweep period in operation S1
Comprises the following steps:
wherein P is 1,2, …, P, M is 1,2, …, M, P is the number of transmitting antennas in the MIMO radar, M is the number of sweep periods, M is equal to or greater than P, t is time, j is an imaginary unit, f is f0Is the starting frequency, mu is the slope of the sweep,
the phase of the modulated chirp signal transmitted by the pth transmitting antenna in the mth sweep period after space-time coding,
the selection of the phase encoding vector should ensure that the phase encoding vectors of the transmitting antennas are orthogonal to each other.
The space-time coding based MIMO radar target positioning method is described by taking the application scenario shown in fig. 2 as an example. For example, an IWR1843 millimeter wave radar is selected as the MIMO radar, and the number of transmitting antennas and the number of receiving antennas are 2 and 4, respectively; 3 static target objects are arranged in a scene, the target object 1 and the target object 2 are both placed at a position 5m away from a radar, the angles formed by the target object 1 and the target object 2 in the vertical direction of the radar are respectively 0 degree and 15 degrees, the target object 3 (a flower bed) is arranged at the other side, the distance from the radar is 6.5m, and the angle formed by the target object 1 and the target object 2 in the vertical direction of the radar is 25 degrees; the initial frequency of the radar work is 77GHz, the termination frequency is 79.73GHz, the modulation frequency is 80 MHz/mus, and the sampling rate is 10 MHz. For the application scenario shown in fig. 2, in operation S1, a space-time block code is used to perform initial phase modulation on two frequency-swept periodic chirp signals, where the phase modulation matrix is
Operation S2 is to mix the signal received by each receiving antenna with the chirp signal transmitted by the first transmitting antenna of the MIMO radar to obtain a corresponding baseband signal, and perform sampling, extraction, recombination, and space-time decoding on the baseband signal in sequence to obtain a corresponding decoded signal.
Operation S2 includes sub-operation S21-sub-operation S24, according to an embodiment of the invention.
In sub-operation S21, the signals received by each receiving antenna are mixed with the chirp signal transmitted by the first transmitting antenna of the MIMO radar, respectively, to obtain corresponding baseband signals.
In sub-operation S22, each baseband signal is sampled, where the number of sampling points in each sweep period is L and the number of sweep periods is M.
In a sub-operation S23, the nth sample point of each baseband signal in each sweep period is extracted and recombined to form a recombined matrix with dimension Q × M
In this embodiment, the signals sampled from the baseband signals may be combined in sub-operation S22 to obtain a matrix of Q × ML
Matrix array
The q-th row of (a) represents the corresponding baseband signal for the q-th receive antenna. Slave matrix
The n, n + L, n +2L, the
The recombination matrix obtained in sub-operation S23
Comprises the following steps:
wherein Φ is a space-time coding matrix:
wherein K is the number of the target objects; beta is ai、θiAnd riRespectively the reflection coefficient, azimuth angle and distance of the ith target object; a isR(θi) Steering vector of receiving array corresponding to ith target object，
The emitting array corresponding to the ith target object is guided to a vector aT(θi) The transpose matrix of (a) is,
j is an imaginary unit, ωr(ri)＝4πμri/cfs，ωr(ri) Is the phase associated with the ith target object distance, m is the slope of the sweep, c is the speed of light, fsIs the sampling rate; omegaθ(θi)＝2pf0d sinθiC is the phase associated with the azimuth of the ith target object, d is the receive antenna spacing;
in order to be a noise term, the noise term,
the phase of the modulated chirp signal transmitted by the pth transmitting antenna in the mth sweep period after space-time coding is 1,2, …, P, M is 1,2, …, M, P is the number of transmitting antennas in the MIMO radar, and M is the number of sweep periods.
In sub-operation S24, for each reorganization matrix
Performing space-time decoding to obtain corresponding decoded signal
Decoding a signal
Comprises the following steps:
wherein,
is the decoded noise term. Taking the number of sampling points L in each sweep period as 256 as an example, for the application scenario shown in fig. 2, a 4 × 512 matrix is obtained
And will matrix
Splitting into 256 4 x 2 recombination matrices
Further, for each recombination matrix
Decoding is performed, decoding matrix
Operation S3, the decoding signals are combined to construct a space-time two-dimensional virtual array signal, and the space-time two-dimensional virtual array signal is sequentially subjected to two-dimensional smoothing and combining to obtain a space-time joint virtual sub-array signal.
Operation S3 includes sub-operation S31-sub-operation S34, according to an embodiment of the invention.
In sub-operation S31, each decoded signal is vectorized to obtain a corresponding spatial virtual matrix output signal:
wherein,
outputs signals for the PQ cell spatial virtual array,
is the steering vector of the virtual array and,
is a virtual signal noise term.
In sub-operation S32, the spatial virtual array output signals are sequentially arranged and recombined to form a space-time two-dimensional virtual array signal. Arranging L space virtual array output signals into a PQ multiplied by L matrix to obtain a space-time two-dimensional virtual array signal Z, namely
For the application scenario shown in fig. 2, first, 256 4 × 2 recombination matrices obtained in operation S2 are combined
Performing column vectorization to obtain 256 8 × 1 vectors
And then the 256 vectors are used
The arrangement forms an 8 x 256 matrix Z, i.e. a space-time two-dimensional virtual array signal.
In sub-operation S33, the space-time two-dimensional virtual array signal is two-dimensionally smoothed to obtain a plurality of sub-arrays. The space-time two-dimensional virtual array signal is divided into (PQ +1-X) (L +1-Y) sub-arrays of size X × Y, which is the space-time two-dimensional smooth window size, as shown in fig. 3.
In sub-operation S34, each sub-array is converted into a corresponding column vector, and the column vectors are sequentially arranged and recombined to form a space-time joint virtual sub-array signal. Converting the output signals of each subarray into XY X1 column vector signals, and arranging and combining the column vector signals to obtain a space-time joint virtual subarray signal with the size of XY X (PQ +1-X) (L + 1-Y).
For the application scenario shown in fig. 2, first, space-time two-dimensional smoothing is performed on the matrix Z obtained in sub-operation S32, where the size of each sub-array is, for example, 6 × 100, and the total number of sub-arrays is 471. Then converting the input signals of each sub array into 600 × 1 column vector signals, and finally arranging and combining the column vector signals to obtain a space-time joint virtual sub array signal with the size of 600 × 471.
And operation S4, a spectral function of the space-time joint virtual subarray signal is constructed, and the spectral function is related to the distance and azimuth angle of the target object relative to the MIMO radar.
Singular value decomposition is carried out on the space-time joint virtual subarray signal to obtain a signal subspace USSum noise subspace UNThen constructing a spectral function PMUSIC(r,θ)：
Where r is the distance, θ is the azimuth angle, a (r, θ)HIs a conjugate transpose matrix of the steering vector a (r, theta) of the space-time joint virtual sub-matrix,
function(s)
j is an imaginary unit, ωr(r) is the phase, ω, related to the distanceθ(theta) is the phase associated with the azimuth, Y is the column smoothing size of the two-dimensional smoothing, X is the row smoothing size of the two-dimensional smoothing,
denotes kronecker product, UNAnd carrying out singular value decomposition on the space-time joint virtual subarray signal to obtain a noise subspace.
Operation S5 is to calculate a maximum of the spectral function and locate the target object according to the distance and azimuth corresponding to the maximum.
Specifically, values of the spectrum function at different distances r and azimuth angles theta are calculated, a maximum value of the spectrum function is found, and the distance r and the azimuth angle theta corresponding to the maximum value are estimated values of the distance and the azimuth angle of each target object relative to the MIMO radar.
In this embodiment of the present invention, the number of the target objects is one or more, the maximum values correspond to the target objects one to one, and the position of each target object is determined according to the distance and the azimuth angle corresponding to each maximum value in operation S5.
Referring to fig. 4A and 4B, schematic diagrams of a conventional two-dimensional fourier transform two-step estimation method and a positioning performance of the space-time coding-based MIMO radar target positioning method in the embodiment of the present invention are respectively shown, and it can be known from comparison between fig. 4A and 4B that, compared with the conventional method, the position of a target object in the embodiment of the present invention is clear and distinguishable, the angular resolution is greatly improved, clutter interference is greatly reduced, and subsequent target detection is facilitated.
Fig. 5 is a block diagram of a space-time coding based MIMO radar target positioning system according to an embodiment of the present invention. Referring to fig. 5, the space-time coding based MIMO radar target positioning system 500 includes a modulation and transmission module 510, a receiving and decoding module 520, a combination construction module 530, a spectrum function construction module 540, and a positioning module 550.
The modulation and transmission module 510 performs, for example, operation S1, to modulate an initial phase of the chirp signal using space-time block coding, and transmit the modulated chirp signal using a transmission antenna of the MIMO radar, where the chirp signal is reflected by a target object and then received by a reception antenna of the MIMO radar.
For example, the receiving and decoding module 520 performs operation S2, and is configured to mix the signal received by each receiving antenna with the chirp signal transmitted by the first transmitting antenna of the MIMO radar to obtain a corresponding baseband signal, and perform sampling, extraction, recombination, and space-time decoding on the baseband signal in sequence to obtain a corresponding decoded signal.
The combination construction module 530 performs, for example, operation S3, to combine the decoded signals to construct a space-time two-dimensional virtual array signal, and sequentially perform two-dimensional smoothing and combination on the space-time two-dimensional virtual array signal to obtain a space-time joint virtual sub-array signal.
The spectral function construction module 540 performs, for example, operation S4, for constructing a spectral function of the space-time joint virtual sub-array signal, the spectral function being related to the range and azimuth of the target object with respect to the MIMO radar.
The positioning module 550 performs, for example, operation S5, to calculate a maximum value of the spectral function and position the target object according to a distance and an azimuth corresponding to the maximum value.
The space-time coding based MIMO radar target location system 500 is used to perform the space-time coding based MIMO radar target location method in the embodiments shown in fig. 1-4B. Please refer to the space-time coding based MIMO radar target positioning method in the embodiments shown in fig. 1-4B, which is not described herein in detail.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (9)
1. A MIMO radar target positioning method based on space-time coding is characterized by comprising the following steps:
s1, modulating the initial phase of the linear frequency modulation signal by utilizing a space-time block code, transmitting the modulated linear frequency modulation signal by utilizing a transmitting antenna of the MIMO radar, and receiving the linear frequency modulation signal by a receiving antenna of the MIMO radar after the linear frequency modulation signal is reflected by a target object;
s2, mixing the signal received by each receiving antenna with the linear frequency modulation signal transmitted by the first transmitting antenna of the MIMO radar to obtain a corresponding baseband signal, and sequentially sampling, extracting, recombining and space-time decoding the baseband signal to obtain a corresponding decoded signal;
s3, combining the decoded signals to construct a space-time two-dimensional virtual array signal, and sequentially performing two-dimensional smoothing and combination on the space-time two-dimensional virtual array signal to obtain a space-time joint virtual subarray signal;
s4, constructing a spectrum function of the space-time joint virtual subarray signal, wherein the spectrum function is related to the distance and the azimuth angle of the target object relative to the MIMO radar;
and S5, calculating the maximum value of the spectrum function, and positioning the target object according to the distance and the azimuth angle corresponding to the maximum value.
2. The method of claim 1, wherein the number of target objects is one or more, the maxima correspond one-to-one to the target objects, and each of the target objects is located according to the distance and azimuth corresponding to each of the maxima at S5.
3. The method according to claim 1 or 2, wherein the modulated chirp signal transmitted by the transmitting antenna in S1 is:
wherein,
the method comprises the steps that a modulated chirp signal transmitted by a pth transmitting antenna in an mth sweep frequency period is represented, P is 1,2, …, P is 1,2, …, M is represented, P is the number of transmitting antennas in the MIMO radar, M is the number of sweep frequency periods, M is larger than or equal to P, t is time, j is an imaginary number unit, f is f0Is the starting frequency, mu is the slope of the sweep,
the phase of the modulated chirp signal transmitted by the pth transmitting antenna in the mth sweep period after space-time coding.
4. The method according to claim 1 or 2, wherein the sequentially sampling, extracting, recombining and space-time decoding the baseband signal in S2 comprises:
sampling each baseband signal respectively, wherein the number of sampling points in each sweep frequency period is L;
extracting the nth sampling point in each frequency sweep period of each baseband signal and recombining to form a recombination matrix with the size of QxM
Q is the number of receiving antennas in the MIMO radar, and M is the number of sweep frequency periods;
for each recombination matrix
Performing space-time decoding to obtain corresponding decoded signal
5. The method of claim 4, wherein the recombination matrix
And decoding the signal
Respectively as follows:
wherein phi is a space-time coding matrix, K is the number of the target objects, and betai、θiAnd riRespectively, the reflection system of the ith target objectNumber, azimuth and distance, aR(θi) A vector is directed to the receiving array corresponding to the ith target object,
the emitting array corresponding to the ith target object is guided to a vector aT(θi) J is an imaginary unit, ωr(ri)＝4πμri/cfs，ωr(ri) Is the phase associated with the ith target object distance, μ is the slope of the sweep, c is the speed of light, fsIn order to be able to sample the rate,
in order to be a noise term, the noise term,
the phase of the modulated chirp signal transmitted by the pth transmitting antenna in the mth sweep period after space-time coding is 1,2, …, P, M is 1,2, …, M, P is the number of transmitting antennas in the MIMO radar, and M is the number of sweep periods.
6. The method according to claim 1 or 2, wherein the combining the decoded signals to construct a space-time two-dimensional virtual array signal in S3 comprises:
vectorizing each decoded signal column respectively to obtain a corresponding spatial virtual array output signal;
and sequentially arranging and recombining the space virtual array output signals to form the space-time two-dimensional virtual array signals.
7. The method according to claim 1 or 2, wherein the step of S3, sequentially performing two-dimensional smoothing and combining on the space-time two-dimensional virtual array signals to obtain space-time joint virtual sub-array signals, comprises:
performing two-dimensional smoothing on the space-time two-dimensional virtual array signal to obtain a plurality of sub-arrays;
and converting each subarray into a corresponding column vector, and sequentially arranging and recombining the column vectors to form the space-time joint virtual subarray signal.
8. The method of claim 1 or 2, wherein the spectral function is:
wherein, PMUSIC(r, θ) is the spectral function, r is the distance, θ is the azimuth angle, a (r, θ)HA conjugate transpose matrix of a steering vector a (r, theta) of the space-time joint virtual sub-matrix,
function(s)
j is an imaginary unit, ωr(r) is the phase, ω, related to the distanceθ(theta) is the phase associated with the azimuth, Y is the column smoothing size of the two-dimensional smoothing, X is the row smoothing size of the two-dimensional smoothing,
denotes kronecker product, UNAnd carrying out singular value decomposition on the space-time joint virtual subarray signal to obtain a noise subspace.
9. A MIMO radar target positioning system based on space-time coding is characterized by comprising:
the modulation and transmission module is used for modulating the initial phase of the linear frequency modulation signal by utilizing a space-time block code, transmitting the modulated linear frequency modulation signal by utilizing a transmitting antenna of the MIMO radar, and receiving the linear frequency modulation signal by a receiving antenna of the MIMO radar after the linear frequency modulation signal is reflected by a target object;
the receiving and decoding module is used for respectively mixing the signal received by each receiving antenna with the linear frequency modulation signal transmitted by the first transmitting antenna of the MIMO radar to obtain a corresponding baseband signal, and sequentially sampling, extracting, recombining and space-time decoding the baseband signal to obtain a corresponding decoding signal;
the combined construction module is used for combining the decoding signals to construct a space-time two-dimensional virtual array signal, and sequentially performing two-dimensional smoothing and combination on the space-time two-dimensional virtual array signal to obtain a space-time joint virtual subarray signal;
the spectrum function constructing module is used for constructing a spectrum function of the space-time joint virtual subarray signal, and the spectrum function is related to the distance and the azimuth angle of the target object relative to the MIMO radar;
and the positioning module is used for calculating the maximum value of the spectrum function and positioning the target object according to the distance and the azimuth angle corresponding to the maximum value.
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