A wide-area ultra-sparse MIMO radar system near-field angle measurement method

Abstract

The present application provides a wide-area ultra-sparse MIMO radar system near-field angle measurement method for realizing the distance azimuth-elevation two-dimensional amplitude comparison method for measuring the angle of the target in the near-field condition, and the signal between each radar node is combined in space-distance three-dimensional to obtain the output signal after combination; the center position of the channel with the maximum amplitude is taken as the space position of the target, the distance unit number corresponds to the target distance, the joint beam pattern of the beam center is solved by fixing the target distance; the two-dimensional Gaussian function is used to approximate the normalized joint beam pattern; the normalized pattern fitted by the two-dimensional Gaussian function is mapped to the sine space to obtain the azimuth-elevation adjacent beam channel echo amplitude difference, so as to calculate the position coordinates of the target in the sine space, and finally the position coordinates are mapped to the azimuth-elevation two-dimensional, so that the real coordinates of the target in the near-field angle measurement can be obtained more accurately.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of radar communication, and particularly relates to a wide-area ultra-sparse MIMO radar system near-field angle measurement technology. BACKGROUND

[0002] MIMO radar can be divided into antenna co-located MIMO radar and distributed MIMO radar. When the transmission waveforms of each antenna of the antenna co-located MIMO radar or each node of the distributed MIMO radar are orthogonal to each other, the signals in any direction in space will not cancel or add, and coverage of the detection space can be achieved. After receiving the return signals, according to the orthogonal characteristics of the signals, signal separation can be performed on the received signals from different transmission nodes by using matched filtering. According to the transmission path and the transmission signals, the output signals after matched filtering can be phase compensated and summed, that is, “joint beam forming” is performed. Compared with the traditional phased array, the joint beam has the advantages of narrow main lobe and low side lobe.

[0003] The existing method for simultaneously multi-beam amplitude comparison angle measurement of MIMO radar is for the co-located antenna MIMO radar system using a uniform linear array. The simultaneously multi-beam coverage required for detecting the space is designed to intersect at the half-power point. After detecting the target, the amplitudes of the signals received by the two beam channels are compared to determine the target angle. See document: He Xi. MIMO radar detection and estimation theory research [D]. University of Electronic Science and Technology of China, 2010. This method mainly forms simultaneously multi-beam coverage in a certain space θ min and θ max to perform amplitude comparison angle measurement in one dimension. For the specific application scenario of the co-located antenna MIMO radar system using a uniform linear array, the target angle measurement effect has a small error, but it is not suitable for the near-field angle measurement scenario of the wide-area ultra-sparse MIMO radar system. SUMMARY

[0004] In view of the defects of the existing simultaneously multi-beam amplitude comparison angle measurement method, such as the limited use scene of the uniform linear array MIMO radar system, the present application provides a wide-area ultra-sparse MIMO radar system near-field angle measurement method.

[0005] The technical scheme adopted by the present application to solve the above technical problems is a wide-area ultra-sparse MIMO radar system near-field angle measurement method for realizing distance azimuth-elevation two-dimensional amplitude comparison angle measurement of a target in a near-field condition, which specifically comprises the following steps:

[0006] Step 1, after receiving the return signals of the wide-area distributed MIMO radar, digital beam synthesis DBF is first performed in the node under the far-field condition, and then signal separation is performed on the received signals from different transmission nodes after matched filtering, and then pulse accumulation is performed;

[0007] Step 2, design the multi-beam channel pointing, determine the distance cell size according to the received sampling rate;

[0008] Step 3, under the near-field condition, the signal between each radar node is spatial-distance three-dimensional synthesized to obtain the output signal after synthesis, wherein the space is composed of azimuth-elevation two dimensions, and the specific is:

[0009] For each position belonging to the search space Determine the corresponding number of transmitting distance cells k T , the number of receiving distance cells k R , and the spatial steering vector under the near-field condition Select The distance cell pulse accumulation echo data Get the spatial-distance three-dimensional synthesis result Wherein, r is the distance dimension variable, θ is the azimuth dimension variable, is the elevation dimension variable, the superscript T represents the transmission, the superscript R represents the reception, Indicates the Kronecker product, and the superscript H represents the transpose of the matrix;

[0010] Step 4, find the beam channel with the largest amplitude in all the beam channels that detect the target as the main beam channel, and the two adjacent angle channels that need to be compared in amplitude, record the pulse number and distance cell number corresponding to the maximum amplitude value;

[0011] Step 5, take the center position of the channel with the maximum amplitude as the spatial position of the target, and the distance cell number as the target distance, and fix the target distance to obtain the beam center The joint beam pattern θ b is the beam center elevation angle, is the beam center azimuth angle;

[0012] Step 6, through the direction pattern of the joint beam, the half-power beam width of the azimuth dimension and the elevation dimension is respectively solved;

[0013] Step 7, a two-dimensional Gaussian function is used to approximate the normalized joint beam pattern, that is Wherein, α, β are Gaussian parameters, e is a natural constant, and they are respectively obtained through the beam half-power width of the direction and elevation dimension;

[0014] Step 8, through the relationship between the two dimensions u, v of the two-dimensional Gaussian function Map the normalized direction pattern fitted by the two-dimensional Gaussian function to the sine space, respectively solve the echo amplitude difference of the adjacent beam channels in the azimuth and elevation dimensions, and then solve the position coordinates of the target in the sine space. Mapping to the azimuth-elevation two dimensions can obtain the real coordinates of the near-field angle measurement target.

[0015] In step 2 above, when designing simultaneous multi-beam channel pointing, existing methods, when determining the range-azimuth-elevation interval to be searched, strictly require the intersection of two adjacent beams in the azimuth-elevation interval at the half-power point to achieve full spatial coverage, resulting in a large computational load. Preferably, this invention uses a sparser search interval division method, no longer strictly requiring the intersection of two adjacent beams in the azimuth-elevation interval at the half-power point. During spatial synthesis, full coverage of the search spatial domain is no longer required. The interval spacing is flexibly selected based on the required detection spatial domain size and the system's computational capacity, appropriately widening the synthesized beam spacing to reduce signal processing computation and improve real-time performance. For the range interval, R... cell The distance intervals are uniformly discretized. The distance interval is determined based on the receiving sampling rate f. s Determined, i.e., R cell =c / 2f s c is the speed of light.

[0016] Specifically, step 4 above determines the three beam channels that need to be compared in amplitude. That is, the beam channel with the largest amplitude among all beam channels that detect the target is selected as the main beam channel. The two adjacent angle channels that need to be compared in amplitude are selected as follows: after selecting the main beam channel based on the maximum echo amplitude, select one adjacent azimuth channel and one elevation channel.

[0017] Preferably, step 6 above determines the half-power beamwidth θ in the azimuth and elevation dimensions. 3dB , Specifically, this refers to: the joint beam pattern After normalization, the magnitude is calculated to obtain the amplitude pattern of the joint beam. exist The position is obtained as θ 3dB , The position yields the half-power beamwidth in the elevation dimension.

[0018] Preferably, step 7 above uses a two-dimensional Gaussian function to approximate the normalized radiation pattern to simplify the calculation; specifically, this is achieved by setting the Gaussian parameters. The normalized direction pattern is fitted as follows:

[0019] Preferably, in step 8 above, the normalized directional pattern fitted by the two-dimensional Gaussian function is obtained through a relational analysis. Mapped to sinusoidal space, specifically:

[0020]

[0021] In this context, subscript 1 represents the cell with the largest echo amplitude, and subscripts 2 and 3 represent the cells adjacent to the cell with the largest echo amplitude in the pitch and azimuth dimensions, respectively.t ,v t represents the position coordinates of the target in the two-dimensional u,v space under the two-dimensional sinusoidal space, and ΔA 12 , ΔA 13 respectively represent the difference between the output signal amplitude of the beam channel corresponding to the cell with the maximum echo amplitude and the output signal amplitude of the beam channel corresponding to the adjacent cell in the elevation dimension and the azimuth dimension.

[0022] The beneficial effect of the present application is that a range-azimuth-elevation three-dimensional space synthesis method under near-field conditions is innovatively proposed, a normalized joint beam pattern is fitted by a two-dimensional Gaussian function, and then a more accurate target position is solved by constructing an equation group by using the amplitude difference of the main beam channel and the adjacent azimuth and elevation angle channels. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a flowchart of the method of the present application.

[0024] Figure 2 is an embodiment schematic diagram.

[0025] Figure 3 is a position map of the target under near-field and radar. DETAILED DESCRIPTION

[0026] The following is a theoretical proof of the model of the near-field MIMO radar system, M is the total number of transmitting nodes, N is the total number of receiving nodes, m and n are the serial numbers of the transmitting nodes and the receiving nodes respectively, r is the distance dimension variable, θ is the azimuth dimension variable, is the elevation dimension variable, the superscript T represents transmission, and the superscript R represents reception:

[0027] Let s1(t), s2(t),..., s m (t),..., s M (t) be the baseband signals transmitted by each node, and after adding a carrier frequency signal, they are denoted as:

[0028]

[0029] The superscript ~ represents a frequency band signal, f s is the receiving sampling rate, and t is the time variable.

[0030] Considering the existence of receiver noise, the target baseband echo signal received by the nth receiving node is

[0031]

[0032] ξ mn is the amplitude of the signal transmitted by the mth transmitting node and received by the nth receiving node, u n (t) is the receiver noise, τ mThe path delay of the signal transmitted by the mthtransmitting node, τ n The path delay of the signal received by the nthreceiving node, d n Denote the distance from the nthreceiving node to the center of the array in the global coordinate system, f dm Denote the Doppler shift of the transmitting path of the mthreceiving node; according to the radar equation, the amplitude ξ of the signal transmitted by the mthtransmitting node received by the nthreceiving node mn Can be expressed as

[0033]

[0034] P T Denote the transmitting power, λ denotes the transmitting wavelength, σ mn The scattering coefficient of the path, Denote the antenna transmitting pattern gain of the mthtransmitting node, The position of the mthtransmitting node;

[0035] Consider the multi-pulse case, T p The set pulse period, the pulse repetition frequency PRF is:

[0036]

[0037] Let the total number of pulses be Q, and the qth, q = 1, 2,..., Q pulse signal received by the nthradar receiving node be written as

[0038]

[0039] Where t ∈ [0, T p ].

[0040] The following is a proof of the two-dimensional amplitude comparison angle finding theory:

[0041] Suppose the target is between the adjacent three beams. Calculate the projection positions of the three beams in the sine space as (u i , v i ), i = 1, 2, 3, subscript 1 denotes the cell with the largest echo amplitude, 2 and 3 denote the cells adjacent to the elevation and azimuth of the cell with the largest echo amplitude, respectively. The projection of the target in the two-dimensional sine space is denoted as (u t , v t ), where

[0042]

[0043] For simple operation, a two-dimensional Gaussian function is used to approximate the joint beam pattern

[0044]

[0045] The output signal amplitudes of the three beam channels are A1, A2 and A3,

[0046]

[0047] The above two equations are solved simultaneously to obtain:

[0048]

[0049]

[0050] The equation group can be constructed:

[0051]

[0052] That is:

[0053]

[0054] In actual engineering problems, the sinusoidal space projection of the target can be obtained by solving the above binary equation, and then the position of the target is obtained.

[0055] The following is an analysis of the influence of beam distribution on the amount of calculation:

[0056] The coherent results of each beam channel are obtained by coherent synthesis of the matched filtering results of MN (M and N are the numbers of transmitting and receiving nodes) channels, so MN complex multiplication and addition operations are required for one beam channel, and if K beam channels are designed, 8MNK floating point operations are required in total, and if the radar system is a multi-pulse, 8MNKQ floating point operations are required in total, so the amount of calculation is related to the number of beam channels.

[0057] Since the joint beam of the MIMO radar system is a needle-shaped beam, if the multiple beams formed at the same time strictly intersect at a 3dB width, a huge amount of calculation resources will be consumed. Therefore, appropriately relaxing the beam interval during searching can reduce the number of beams to be searched, thereby reducing the amount of calculation and improving the real-time performance of signal processing.

[0058] The specific embodiments of the present application will be described in detail below in combination with the method flowchart attached in the specification.

[0059] As shown in the present application, a wide-area ultra-sparse MIMO radar system near-field angle measurement method specifically includes the following steps: Figure 1 Step 1, after receiving the wide-area distributed MIMO radar echo signal, DBF is performed for a certain radar node in the far-field case, in order to simultaneously obtain the target azimuth-elevation information, the radar node should be a radar array, as shown in

[0060] Figure 2

[0061] ​​In the scenario of a battle formation, let the coordinates of the center of the battle formation be (x... c ,y c ,z c ), Let x be the coordinates of each receiving array element. t ,y t ,z t () represents the target location coordinates.

[0062] Then the signal B formed by the beamforming of N receiving array elements is expressed as:

[0063]

[0064] Among them, W n The weight matrix for DBF processing, d represents the direction vector from the target to the center of the array. n It is expressed as the distance from array element n to the center of the array surface in the global coordinate system.

[0065]

[0066]

[0067] ||·||2 is the 2-norm.

[0068] At this point, the signals from each node after DBF processing are subjected to matched filtering to separate the signals from different transmitting nodes, and then pulse accumulation is performed.

[0069] Step 2: Wide-area distributed radar systems use sparsely distributed radar nodes, and signal propagation does not meet far-field conditions. Because the propagation delay differences along different target paths cannot be ignored under near-field conditions, this affects the range cells and echo signal phase, thus impacting the coherent synthesis of the target signal. Therefore, a space-range joint search approach is adopted to effectively synthesize the target signal under near-field conditions. The range-azimuth-elevation interval to be synthesized is determined, i.e., the azimuth interval [θ...]. min ,θ max Pitch range and distance interval [r min ,r max The azimuth and elevation intervals can be freely selected based on computational and storage requirements. To save on computational and storage costs, it is not necessary to intersect two adjacent beams at the half-power point; the angle interval can be flexibly selected according to actual needs and resources. The range intervals are then uniformly discretized at certain intervals.

[0070] Distance unit R cell Set as:

[0071]

[0072] Wherein, the receiving sampling rate is fs At this time, it is convenient to correspond the distance unit number with the sampling point number.

[0073] Step 3, space-distance synthesis is performed, and the flow is as follows:

[0074] (1) For each belonging to the search space The corresponding space steering vector is calculated, such as Figure 3 is the position map of the target under the near field and the radar.

[0075] Then The distance between the mth transmitting node with the position of can be written as

[0076]

[0077] Under the near field condition, the signal received by the radar node is a spherical wave, and the steering vector is

[0078]

[0079] (2) Calculate the distance from the target coordinate to each transceiving node:

[0080]

[0081] Where, p is the target coordinate, R m , R n are the distances from the target to the mth transmitting node and the nth receiving node, respectively, p m , p n are the coordinates of the mth transmitting node and the nth receiving node, respectively, and the distance from the point to each transceiving node is calculated

[0082]

[0083] The distance unit number corresponding to each transceiving path is calculated

[0084]

[0085] round represents the rounding operation.

[0086] (4) According to the distance unit number, the corresponding distance unit (sampling point number) data is selected, and the distance unit in which is located after pulse accumulation of the echo data MN, which can be represented as a MNx1 vector, denoted as

[0087] (5) According to the space steering vector synthesis, the obtained space-distance joint synthesis result is denotes the Kronecker product.

[0088] Step 4: Select the beam channel with the largest amplitude among all the beam channels that detect the target as the main beam channel, and record its corresponding pulse number, range cell number and maximum amplitude. Fix this pulse number and find the maximum amplitude of the adjacent azimuth and elevation beam channels under this pulse.

[0089] Step 5: Assume the target coordinates are... in r is the center of the main channel beam obtained in step 4. t To record the distance corresponding to the distance unit, this distance is fixed, and the beam center can be calculated. Joint beam pattern

[0090] Step 6: Perform joint beam pattern analysis After normalization, the magnitude is calculated to obtain the amplitude pattern of the joint beam. Find the half-power point of the joint beam in both the azimuth and elevation dimensions, that is, let Where, θ=θ b +θ 3dB , Calculate the half-power beamwidth θ in the azimuth and elevation dimensions respectively. 3dB ,

[0091] Step 7: Use a two-dimensional Gaussian function to approximate the normalized radiation pattern, i.e. To simplify the calculation, where θ b ,β b Therefore, for the joint beam center, α and β are unknown parameters, through... Can be launched

[0092] Step 8: Through relationships Normalized pattern of fitting a two-dimensional Gaussian function Mapping to sinusoidal space yields F(u,v). Let the radiation pattern of the main beam channel be F1(u,v), and the radiation patterns of adjacent azimuth and elevation beam channels be F2(u,v) and F3(u,v), respectively. Calculate the echo amplitude difference ΔA between adjacent beam channels in the azimuth and elevation dimensions. 12 =lnF1(u t ,v t )-lnF2(u t ,v t ), ΔA 13 =lnF1(u t ,v t )-lnF3(u t ,v t ), by solving the system of equations

[0093]

[0094] in

[0095]

[0096] (u1,v1), (u2,v2), and (u3,v3) are the coordinates of the center of the main beam channel, the adjacent azimuth beam channel, and the adjacent elevation beam channel after being mapped to sinusoidal space, respectively.

[0097] The solution to the resulting system of equations is the position of the target in sinusoidal space, which can be obtained through mapping.

[0098]

[0099] This allows us to obtain more precise position coordinates of the target after two-dimensional amplitude angle measurement.

[0100] This invention is not limited to the specific embodiments described above; it is also applicable to radar systems with single pulses or concentrated node distribution.

Claims

1. A method for near-field angle measurement of a wide-area ultra-sparse MIMO radar system, characterized in that, Comprising the following steps: Step 1, after receiving the wide-area distributed MIMO radar echo signal, the node first carries out digital beam synthesis under the far-field condition, and then carries out signal separation on the received signals from different transmitting nodes after matching filtering and then carries out pulse accumulation; Step 2, design simultaneous multi-beam channel pointing, determine the distance unit size according to the receiving sampling rate; Step 3, under the near-field condition, the signals between the radar nodes are spatial-distance three-dimensional synthesized to obtain the synthesized output signal, wherein the space is composed of azimuth-elevation two dimensions, and specifically: For each position belonging to the search space Determine its corresponding transmit distance cell number k T , receive distance cell number k R And the spatial steering vector under the near-field condition Select The echo data after pulse accumulation of the distance cell where it is located Get the spatial-distance three-dimensional synthesis result Where r is the distance dimension variable, θ is the azimuth dimension variable, Is the elevation dimension variable, the superscript T represents transmission, and the superscript R represents reception, Indicates the Kronecker product, and the superscript H indicates the transpose of the matrix; Step 4, find out the amplitude maximum beam channel in all the beam channels that detect the target as the main beam channel, and select one azimuth channel and one elevation channel adjacent to the main beam channel as the azimuth-elevation adjacent beam channels to compare the amplitudes, and record the pulse number and distance unit number corresponding to the amplitude maximum value; Step 5, taking the channel center position where the amplitude maximum value is located as the target space position, and taking the distance corresponding to the unit number as the target distance, the beam center is obtained with the target distance fixed Joint beam pattern θ b is the beam center elevation angle, is the beam center azimuth angle; Step 6, through the directivity diagram of the joint beam, the half-power beam width of the azimuth dimension and the elevation dimension is respectively solved; Step 7, a two-dimensional Gaussian function is used to approximate the normalized joint beam pattern, i.e. where α, β are Gaussian parameters, e is the natural constant, and α, β are obtained by the beam half-power width in the azimuth and elevation dimensions, respectively. Step 8, the relationship between the two dimensions u, v of the two-dimensional Gaussian function The normalized direction pattern fitted by the two-dimensional Gaussian function is mapped to the sine space, the difference of echo amplitudes of adjacent beam channels in azimuth and elevation dimensions is respectively calculated, the position coordinates of the target in the sine space are solved, and the real coordinates of the near-field angle measurement target are obtained by mapping to the azimuth-elevation two-dimensional.

2. The method of claim 1, wherein, Step 2: The interval is selected flexibly according to the required detection space and the system's computational capacity when the multi-beam channel is designed to point at the same time; for the distance interval, uniform discretization is performed with R cell as the interval, R cell =c / 2f s , f s is the receiving sampling rate, and c is the speed of light.

3. The method of claim 1, wherein, The azimuth dimension half-power beamwidth θ is determined in step 6 3dB and the elevation dimension half-power beamwidth Specifically, the joint beam pattern is normalized and the amplitude pattern of the joint beam is obtained At the position of the azimuth dimension half-power beamwidth θ is obtained 3dB At the position of the elevation dimension half-power beamwidth is obtained 4. The method of claim 3, wherein, Gaussian parameters 5. The method of claim 1, wherein, The normalized directional pattern of the two-dimensional Gaussian function fit in step 8 is mapped to the sinusoidal space by the relation Specifically, wherein (u1, v1), (u2, v2), (u3, v3) are the coordinates of the center of the main beam channel, the adjacent azimuth dimension beam channel and the adjacent elevation dimension beam channel respectively mapped to the sinusoidal space after the mapping, u t ,v t represents the position coordinates of the target in the two-dimensional u, v space under the two-dimensional sinusoidal space, ΔA 12 , ΔA 13 respectively represent the difference between the output signal amplitude of the beam channel corresponding to the cell with the maximum echo amplitude and the output signal amplitude of the beam channel corresponding to the adjacent cell in the elevation dimension and the azimuth dimension.

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