CN116990794A - MIMO radar target detection method and device based on DDMA waveform modulation - Google Patents

MIMO radar target detection method and device based on DDMA waveform modulation Download PDF

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CN116990794A
CN116990794A CN202310920909.8A CN202310920909A CN116990794A CN 116990794 A CN116990794 A CN 116990794A CN 202310920909 A CN202310920909 A CN 202310920909A CN 116990794 A CN116990794 A CN 116990794A
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target
sub
ddma
distance
hypothesis
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王帅
王雨
李佩佩
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Chengdu Nalei Technology Co ltd
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Chengdu Nalei Technology Co ltd
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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
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/003—Bistatic radar systems; Multistatic radar systems
    • 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
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/06—Systems determining position data of a target
    • G01S13/42—Simultaneous measurement of distance and other co-ordinates
    • 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
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
    • G01S7/415—Identification of targets based on measurements of movement associated with the target

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Radar Systems Or Details Thereof (AREA)

Abstract

The invention discloses a MIMO radar target detection method and device based on DDMA waveform modulation, wherein the method comprises the following steps: receiving an echo signal of a DDMA waveform transmitted by a MIMO radar system, and sequentially performing distance dimension FFT calculation and speed dimension FFT calculation to obtain a distance Doppler data matrix; dividing the space domain to be searched into a plurality of sub-spaces, sequentially carrying out cyclic hypothesis test of a distance Doppler data matrix on each sub-space, wherein the cyclic hypothesis test of the distance Doppler data matrix comprises cyclic hypothesis transmitting antenna sequences, constructing a virtual MIMO array for DBF, and judging whether target signals exist in the corresponding directions of each sub-space according to the DBF result of the virtual MIMO array obtained by each cyclic hypothesis. The invention has the advantages of simple implementation method, low cost, good weak target detection performance, long detection distance, low report missing rate and the like.

Description

MIMO radar target detection method and device based on DDMA waveform modulation
Technical Field
The invention relates to the technical field of radar target detection, in particular to a MIMO radar target detection method and device based on DDMA waveform modulation.
Background
MIMO (Multiple-Input Multiple-Output )Out) radar is a waveform that transmits diversity synchronously with a plurality of transmitting antennas while receiving echo signals using a plurality of receiving antennas. The virtual channel number of the radar can be increased through the MIMO technology, so that the detection performance of the radar is improved. For a containing N Tx Root transmitting antenna, N Rx MIMO radar systems with multiple receive antennas, which may be formed into an N using appropriate antenna layouts and wave designs Tx ×N Rx By doing the reception DBF (Digital Beam Forming ) on the received signal in the desired direction, the detection gain of the system in the desired direction can be improved. In order to form a virtual antenna array, the transmitting end must be able to transmit N in a certain dimension Tx The waveforms of the transmitting antennas are multiplexed, and the receiving end must be able to multiplex N in the same dimension after receiving the waveforms Tx The waveforms of the root transmit antennas are separated.
DDMA (Doppler multiple access) is a method in which signals from different transmitting antennas are separated in the Doppler domain by transmitting all transmitting antennas simultaneously, and each transmitting antenna's signal is shifted by a specific frequency. All transmit antennas (N) can be implemented in a MIMO radar using DDMA (doppler multiple access) Tx Root) is transmitted simultaneously, compared with the traditional TDMA (time division multiple access) mode, the transmission time of one pulse can be reduced, and under the condition of the same transmission signal time, the detection gain of the virtual antenna DBF can be ensured. In DDMA, the target signal needs to be detected at the receiving end, and then different transmitting antennas need to be separated at the receiving end, that is, the sequence of the transmitting antennas needs to be determined at the receiving end, and before the sequence of the transmitting antennas is not determined, the virtual antenna DBF cannot be performed, but only the DBF of the receiving channel can be performed. Therefore, the premise of using the DDMA is that the target signal can be analyzed in the target signal detection stage, otherwise, the DBF gain of the transmitting antenna cannot be reflected.
In the prior art, when a DDMA method is adopted in a MIMO radar, echo signals are generally accumulated in a pulse mode, and since transmission antennas are not separated, only a receiving channel DBF can be performed at this time, then a detection algorithm is used to detect a two-dimensional data matrix after receiving the DBF, transmission is decoupled according to detected values, and a sequence of the transmission antennas is determined for a signal processing algorithm such as a subsequent angle measurement. For the target with stronger echo signals, target signal detection can be realized through pulse accumulation gain and receiving channel DBF gain, so that different transmitting antenna sequences are determined, and then algorithm processing such as angle measurement is performed by using a virtual array. However, for targets with weaker echo signals (possibly with smaller target RCS, or with a longer target distance from the radar system, etc.), the DBF signal gain through the pulse accumulation and reception channels is still insufficient to enable detection of the target signal, i.e. the target signal cannot be detected during the target detection phase, so that different transmit antennas cannot be separated, and subsequent algorithm processing cannot be performed. In conclusion, the MIMO radar system adopts DDMA to detect weak targets, the detection distance of the system is relatively short, and the radar system has the risk of missing report.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the technical problems existing in the prior art, the invention provides the MIMO radar target detection method and device based on DDMA waveform modulation, which have the advantages of simple implementation method, low cost, good weak target detection performance, long detection distance and low missing report rate.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a MIMO radar target detection method based on DDMA waveform modulation includes the steps:
receiving echo signals of DDMA waveforms transmitted by a MIMO radar system, and sequentially performing distance dimension FFT (fast Fourier transform) calculation and speed dimension FFT calculation to obtain a distance Doppler data matrix;
dividing the space domain range to be searched into a plurality of sub-spaces, sequentially carrying out cyclic hypothesis test on the distance Doppler data matrix on each sub-space, wherein the cyclic hypothesis test on the distance Doppler data matrix comprises cyclic hypothesis transmitting antenna sequences, constructing a virtual MIMO array for DBF, and judging whether target signals exist in the corresponding directions of each sub-space according to the DBF result of the virtual MIMO array obtained by each cyclic hypothesis.
Further, the cyclic hypothesis transmitting antenna sequence includes cyclic hypothesis that some Doppler units in all Doppler units contain a target signal, and extracting each Doppler unit hypothesized to contain the target signal to obtain a hypothesized transmitting antenna sequence.
Further, the constructing the virtual MIMO array for DBF includes:
searching corresponding receiving channel data according to the transmitting antenna data obtained according to the transmitting antenna sequence obtained by each hypothesis;
according to the determined receiving channel arrangement sequence of the searched receiving channel data, constructing a corresponding virtual MIMO array;
and performing DBF on the target signal vector of the virtual MIMO array according to the pointing angle of the current sub-airspace to obtain a synthesized value for output.
Further, the determining whether the target signal exists in the direction corresponding to each sub-airspace according to the virtual MIMO array DBF result obtained by each cycle hypothesis includes: and judging the synthesized value obtained by each hypothesis, if a plurality of synthesized values are larger than a preset threshold, judging that a target signal exists in the corresponding sub-space domain direction, and determining the position in the sub-space domain where the first transmitting antenna is located according to the position of the maximum value of the synthesized values, namely determining the sequence of the transmitting antennas.
Further, the number of times of hypothesis detection in the loop hypothesis test is N Chirp ，N Chirp For the doppler cell length, one transmit antenna channel order is assumed at a time.
Further, the dividing the space domain to be searched into a plurality of sub-space domain ranges, wherein the number of the divided sub-space domains is N th The sub-airspace direction angle is theta i ＝-θ+[(i-1)Δθ,iΔθ]Sub-spatial space interval is[-θ,+θ]For the space domain range to be searched, θ i I=1, 2, …, N for the i-th sub-airspace directional angle th 。
Further, the sequentially performing a distance dimension FFT calculation and a velocity dimension FFT calculation to obtain a distance doppler data matrix includes:
carrying out one-dimensional distance dimension FFT calculation on each receiving channel of the echo signal to obtain a one-dimensional distance matrix;
and carrying out pulse accumulation and two-dimensional speed dimension FFT calculation on each distance unit in the distance matrix to obtain the distance Doppler data matrix.
Performing angle measurement according to the constructed virtual MIMO array and the detected target signal;
further, the cyclic detection further comprises angle measurement according to the constructed virtual MIMO array and the detected target signals, and whether the detected target signals are real targets is confirmed according to the corresponding relation between the angle measurement results and the pointing angle ranges of the corresponding sub-airspaces.
Further, according to the corresponding relationship between the angle measurement result and the pointing angle range of the corresponding sub-airspace, determining whether the detected target signal is a real target includes: if the angle measurement result of the target signal is within the pointing angle range of the corresponding sub-airspace, judging the target signal as a real target; and if the angle measurement result of the target signal is not in the pointing angle range of the corresponding sub-airspace, judging that the target signal is a false target.
A MIMO radar target detection apparatus based on DDMA waveform modulation, comprising a processor and a memory for storing a computer program for execution by the processor to perform a method as described above.
Compared with the prior art, the invention has the advantages that:
1. according to the invention, the airspace range is divided into a plurality of sub airspace ranges in the airspace range to be searched, the cyclic hypothesis test of the distance Doppler data matrix is sequentially carried out on all Doppler units corresponding to each distance unit of each sub airspace range, so that different hypothesized transmitting antenna sequences are allocated to all target signals in advance, then target signal vectors of a virtual MIMO array are correspondingly constructed, when the cyclic hypothesis condition is met, the echo signals can be overlapped with the DBF pointing gain of the virtual MIMO array, when the target signals are weaker, the signal-to-noise ratio (SNR) of the weak echo signal targets is improved due to the overlapped DBF gain of the virtual MIMO array, and therefore, the position and the transmitting antenna sequence of the weak echo target signals can be effectively found from Doppler domains, the problem that the target signals cannot be detected in the distance-Doppler data matrix for weaker echo signals in the DDMA mode in the traditional MIMO radar system is solved, the weak target detection performance in the DDMA mode of the MIMO radar is greatly improved, and the miss detection probability is reduced.
2. The method can improve the detection capability of the MIMO radar system on the weak echo signal target on the basis of the consistency of hardware and the existing DDMA waveform modulation method, can reduce the minimum RCS detection lower limit under the condition of the same target detection distance, and can improve the furthest target detection distance under the condition of the same target RCS, thereby ensuring the detection performance of the whole radar system.
Drawings
Fig. 1 is a schematic diagram of the structure and data processing principle of a MIMO radar in a specific application embodiment.
Fig. 2 is a schematic diagram of MIMO virtual array equivalent transmit-receive digital beam synthesis in a specific application embodiment.
Fig. 3 is a schematic diagram of the structural principle of DDMA in a specific application embodiment.
Fig. 4 is a schematic diagram of the DDMA waveform modulation effect employed in the present embodiment.
Fig. 5 is a schematic diagram of the results of DDMA on four transmit antennas in a specific application example.
Fig. 6 is a schematic diagram of the result of null-interval DDMA on four transmit antennas in a specific application embodiment.
Fig. 7 is a schematic diagram of a flow chart for implementing MIMO radar target detection based on DDMA waveform modulation in the present embodiment.
Fig. 8 is a flowchart of the cyclic hypothesis testing process for the sub-airspace according to the present embodiment.
Figure 9 is a schematic of a range-doppler two-dimensional spectrum of a strong echo signal target obtained in a specific application embodiment.
Figure 10 is a schematic of a range-doppler two-dimensional spectrum of a weak echo signal target obtained in a specific application embodiment.
Fig. 11 is a schematic diagram of a doppler frequency domain spectrum corresponding to a range bin and a space domain where a target is located, which is obtained in a specific application embodiment.
Fig. 12 is a DBF pattern corresponding to 11 ° directed by the virtual MIMO array obtained in the specific application embodiment.
Fig. 13 is a schematic diagram of the detection result of the virtual array DBF synthesized data after the doppler cell cycle hypothesis obtained in the specific application example.
Fig. 14 is a schematic view of MIMO goniometry results obtained in a specific application example.
Detailed Description
The invention is further described below in connection with the drawings and the specific preferred embodiments, but the scope of protection of the invention is not limited thereby.
As shown in fig. 1, in the MIMO radar, the transmit beam forming is equivalently implemented at the receiving end, and the transmit-receive array is assumed to be co-located, so that the transmit array includes N T Each array element has an array element interval d T The receiving array comprises N R Each array element has an array element interval d R . The signals transmitted by the MIMO radar are mutually orthogonal, the orthogonal signals are subjected to power superposition in space, when the signals are reflected back and received by the receiving array, the orthogonal signals can be separated through matched filtering, namely, one receiving array element can obtain a plurality of outputs after passing through a group of matched filtering groups, and the output of each matched filter maintains the relative phase relation among the transmitting array elements, so that the MIMO radar can perform equivalent transmitting beams at the receiving end.
To form a virtual beam pointing in a particular direction, a set of weight vectors w are used s The output of the matched filter bank will be weighted, assuming w s Can be expressed as:
wherein,,is the nth r N-th receive array element pair t The corresponding weight vector coefficients are output by matched filtering of the transmitting signals, wherein n r ＝0,1,...,N R -1，n t ＝0,1,...,N T -1。
According to airspace beam forming theory and matched filtering theory, the weight vector w s For a particular direction, w is set to maximize the output SNR in that direction s The value should be:
wherein the method comprises the steps ofIs Kronecker product, w T And w R Weight vectors s representing virtual transmit and receive beamforming, respectively T (θ 0 ) For transmitting steering vectors s R (θ 0 ) To receive the steering vector, the beam is directed at θ 0 ，w T (θ 0 ) Can be expressed as:
w R (θ 0 ) Can be expressed as:
as shown in fig. 2, the MIMO virtual array equivalent transceiving DBF first performs receive beam forming, and the receive beam is directed to θ 0 In the direction, all receiving array elements output by w for the same transmitting signal matched filtering R (θ 0 ) Weighted summation, equivalent transmit beamforming is performed on the receive beamformed output, i.e., by w T (θ 0 ) The receive beamformed outputs are weighted summed. MIMO radar receiving and transmitting combined partyThe directivity diagram is equivalent to the product of the receiving directivity diagram and the transmitting directivity diagram, and the MIMO equivalent receiving directivity diagram can form a narrower main beam, which can be equivalent to a length N T N R A pattern formed by a uniform linear array.
The MIMO radar of DDMA is a radar which uses echo signals from the same target, different transmitting antennas (T x ) Different positions phi are occupied on the Doppler frequency of the target, so that multiplexing of Doppler domains is realized, as shown in figure 3. The speed value detected in the echo formed by the next target under the irradiation of signals of different transmitting antennas in the DDMA waveform is different, and the signals of different transmitting antennas can be separated at the receiving end by utilizing the difference of the speed for one target.
Assuming that the MIMO system radar adopts DDMA waveform modulation, the radar system comprises N Tx Root transmitting antenna, N Rx Root receiving antenna, N chirp Pulse-by-pulse and single pulse period T c . For the transmitting antenna k, the phase shift ω added on the adjacent pulse (Chirp) k The following are provided:
where n=n Tx Specific waveform modulation is shown in fig. 4,respectively represent N Tx Root transmitting antenna, N chirp Indicating the number of pulses.
In the DDMA mode, different Chirp of the same transmitting antenna have added DDMA frequency offset besides Doppler frequency shift generated by target motion, namely the phase shift difference between two adjacent transmitting antenna pulses is as follows:
for the same target, the Doppler frequency difference in the echoes generated by two adjacent transmitting antennas is as follows:
the corresponding speed difference is:
wherein V is max Is the maximum velocity value of the echo signal.
From the above derivation, the maximum non-ambiguous speed interval of the radar becomes 1/N of the original speed interval caused by DDMA waveform modulation Tx In the echo generated by two adjacent transmitting antenna signals, the corresponding Doppler units differ(typically an integer).
Taking four transmitting antennas as an example, when DDMA is not used, the non-fuzzy speed interval of the radar is [ -V max ,V max ]After DDMA is adopted, the interval is equally divided into four sub-intervals of A, B, C and D with equal length, and the non-fuzzy speed interval of the radar is [ -V max /4,V max /4]. Corresponding to the same target, the echo signals of the four transmitting antennas respectively fall into the four intervals, and the velocity value difference V of the echo signals corresponding to the two adjacent transmitting antennas max /2. As shown in fig. 5, where (a) corresponds to case 1: when V is more than or equal to 0 and V is less than or equal to V max /2,Tx 1 Falling in zone C, (b) corresponds to case 2: when V is>V max V is equal to or less than V and is equal to or less than 2 max ,Tx 1 Falling in zone D, (c) corresponds to case 3: when V is more than or equal to-V max And V is less than or equal to-V max /2,Tx 1 Falling in zone a, (d) corresponds to case 4: when V is>-V max 2 and V<0, tx1 falls in zone B. As can be seen from the graph, when 0.ltoreq.V.ltoreq.V max At/2 Tx 1 /Tx 2 /Tx 3 /Tx 4 The echo signals of the (B) will fall into the subinterval C/D/A/B respectively, the speed is not blurred at this time, and after the target signal is detected, tx can be separated out once according to the sequence of C/D/A/B 1 /Tx 2 /Tx 3 /Tx 4 I.e. DDMA demodulation. However, if the velocity V of the echo signal exceeds the range (e.g., 2/3/4 of the cases corresponding to (b), (c), and (d)), tx 1 /Tx 2 /Tx 3 /Tx 4 The corresponding relation between the sub-interval C/D/A/B is changed, and at the moment, different transmitting antenna positions cannot be separated through the positions of the sub-interval, namely DDMA speed blurring is generated, and other methods are needed to complete DDMA demodulation.
If the number N of the non-ambiguous speed subintervals of the DDMA waveform is set to be N not equal to N in the above formula (5) Tx (selection of N and N) Tx Number of pulses N chirp Related, the number N of pulses is to be ensured chirp Is an integer multiple of the number N of subintervals), by increasing the null subintervals (subbands) such that N Tx When the signal of the root transmitting antenna is mapped to the N subintervals, no target signal mapping occurs in the null subintervals. On the basis of four transmitting antennas, 2 null intervals (null sub-bands) are added, and the non-fuzzy speed interval [ -V ] of the radar is adopted max ,V max ]Is divided into six sub-intervals of equal length, wherein the maximum non-blurring speed corresponding to each sub-interval is V max 3, as shown in fig. 6, wherein (a) corresponds to case 1: when V is more than or equal to 0 and V is less than or equal to V max /3,Tx 1 Falling in zone D; (b) corresponds to case 2: when V is>V max V is not more than 2V and/3 max /3,Tx 1 Falling in the E area; (c) corresponds to case 3: when V is>2V max V is not less than V and is not more than 3 max ,Tx 1 Falling in zone F; (d) corresponds to case 4: when V is more than or equal to-V max And V is less than or equal to-2V max /3,Tx 1 Falling in the zone A; (e) corresponding case 5: when V is>-2Vmax/3 and V is less than or equal to-V max /3，Tx 1 Falling in the zone B; (f) corresponds to case 6: when V is>-V max 3 and V<0，Tx 1 Falls in zone C. For a target signal, tx 1 /Tx 2 /Tx 3 /Tx 4 The echo signals of the antenna fall into four continuous circulation continuous subintervals in turn, and no echo signals corresponding to the transmitting antennas are arranged on the remaining two empty subintervals.
As can be seen from FIG. 6, the actual speed of the target is at the overall non-ambiguous speedInterval [ -V max ,V max ]There are six possibilities (Tx 1 Falling within a subinterval of A/B/C/D/E/F). If it can be determined that there is no signal in any two of the six subintervals (fig. 6 (a) is a B, C subinterval, (b) is a C, D subinterval, (c) is a D, E subinterval, (d) is a E, F subinterval, (e) is a A, F subinterval, and (f) is a A, B subinterval), it can be determined what belongs to one of six possible types, i.e., it can be determined that:
1)Tx 1 /Tx 2 /Tx 3 /Tx 4 corresponding subinterval numbers (transmit antenna sequences);
2) The actual speed of the target lies in which sub-interval of the entire non-ambiguous speed interval (speed defuzzification).
To sum up, the DDMA method needs to find out the subinterval not containing the target signal in all the subintervals, and if the echo signal is weak (when the radar reflection cross-sectional area RCS is small or the target is far away from the radar system), the null subinterval and the subinterval containing the target signal cannot be identified in the range-doppler data matrix through the detection algorithm. If the space is increased, N is Tx When the signals of the root transmitting antenna are mapped to N subintervals, the situation that no target signal is mapped in the null subintervals can occur, and if the signals of the signals in each subinterval can be determined, the sequence of the transmitting antenna can be determined, so that speed disambiguation is realized.
After distance dimension FFT and speed dimension FFT are carried out on echo signals of DDMA waveforms transmitted by a MIMO radar system, the space domain is divided into a plurality of sub-space domain ranges in a space domain range to be searched, cyclic hypothesis test of a distance-Doppler data matrix is sequentially carried out on all Doppler units corresponding to each distance unit of each sub-space domain range, namely, cyclic hypothesis is carried out on that some Doppler units in all Doppler units contain target signals, different transmitting antenna sequences are allocated to all target signals in advance, namely, the assumption of the transmitting antenna sequences is realized, then a target signal vector of a virtual MIMO array is correspondingly constructed, under the condition that the assumption is established, the output signals can be superposed with the DBF gains of the transmitting antennas of the DDMA, and the target signal echo gains of the virtual MIMO array can be improved by carrying out DBF on the target signal vectors of the virtual MIMO array. When the target signal is weak, by comparing the DBF results of each hypothesis, it can be determined whether the target signal exists in each sub-spatial direction and each distance unit, and the order in which the target signal is in the sub-interval (i.e., the transmitting antenna order). The method can still accurately detect the target signal in the weaker echo signal, determine the transmitting antenna sequence of the weak target signal in the corresponding DDMA echo, ensure the DBF gain of the transmitting antenna, solve the problem that the target signal cannot be detected in the distance-Doppler data matrix for the weaker echo signal in the DDMA mode in the traditional MIMO radar system, greatly improve the weak target detection performance in the DDMA mode of the MIMO radar, and reduce the detection omission ratio.
As shown in fig. 7, the steps of the MIMO radar target detection method based on DDMA waveform modulation in this embodiment include:
s01, radar echo signals of DDMA waveforms transmitted by the MIMO radar system are received, and distance dimension FFT calculation and speed dimension FFT calculation are sequentially carried out to obtain a distance Doppler data matrix.
S101, performing one-dimensional distance dimension FFT calculation on each receiving channel of the echo signals to obtain a one-dimensional distance matrix.
S102, performing two-dimensional velocity-dimension FFT calculation on each distance unit in the distance matrix to obtain a distance Doppler data matrix.
The pulse accumulation is to combine multiple pulses of the same range gate to improve the target signal-to-noise ratio (SNR), and is realized by performing FFT calculation on all the pulses of the same range unit. And sequentially performing distance dimension FFT calculation and speed dimension FFT calculation on the radar echo signals of the DDMA waveforms transmitted by the MIMO radar system to obtain a distance Doppler data matrix containing distance information and speed information.
S02, checking a circulation hypothesis: dividing the space domain to be searched into a plurality of sub-spaces, sequentially carrying out cyclic hypothesis test of a distance Doppler data matrix on each sub-space, wherein the cyclic hypothesis test of the distance Doppler data matrix comprises cyclic hypothesis transmitting antenna sequences, constructing a virtual MIMO array for DBF, and judging whether target signals exist in the directions corresponding to each sub-space according to the DBF results of the virtual MIMO array obtained by each cyclic hypothesis.
In the present embodiment, the spatial range to be searched is [ - θ, +θ]Divided into N th A sub-airspace with a pointing angle ofSub-spatial space->In the space domain range to be searched [ -theta, +theta]Sequentially aiming at each sub-airspace theta i A cyclic hypothesis test of the range-doppler data matrix is performed to cyclically hypothesize the target coordinate information, i.e. to cyclically hypothesize the transmit antenna order including cyclically hypothesizing the target signal spatial coordinate information, cyclically hypothesizing the range cell locations, and cyclically hypothesizing the transmit antenna order, each hypothesis including a transmit antenna channel order.
In this embodiment, the cyclic assumption specifically includes the following transmit antenna sequences: and circularly supposing that part of Doppler units in all Doppler units contain target signals, extracting Doppler units supposing to contain the target signals, and obtaining supposing transmitting antenna sequences so as to allocate different transmitting antenna sequences to all the target signals. The hypothesis test is mainly to respectively carry out cyclic hypothesis on all Doppler units corresponding to each distance unit, and to assume that some Doppler units in all Doppler units contain target signals, then extract Doppler units which are assumed to contain target signals, wherein the number of the extracted Doppler units is the number N of transmitting antenna channels Tx . Specific hypothesis detection times in the cyclic hypothesis test are N Chirp ，N Chirp Is the Doppler unit length.
In this embodiment, constructing a virtual MIMO array for DBF includes:
searching corresponding receiving channel data according to the transmitting antenna data obtained according to the transmitting antenna sequence obtained by each hypothesis;
according to the found receiving channel arrangement sequence determined by the receiving channel data, constructing a corresponding virtual MIMO array, wherein the MIMO array is a target signal vector array;
and performing DBF on the target signal vector of the virtual MIMO array according to the pointing angle of the current sub-airspace to obtain a synthesized value for output.
The size of the target signal vector of the virtual MIMO array constructed by the method is specifically N Tx *N Rx Wherein N is Tx For transmitting the number of antenna channels, N Rx For the number of receive channels. For a virtual array DBF of a certain spatial angle, the composite signal has 10 log10 (N Tx ×N Rx ) dB detection gain.
In the present embodiment, in the cyclic hypothesis test process, after determining a transmitting antenna channel sequence for each hypothesis, the channel sequence is determined according to the receiving channels (the number of channels is N Rx ) Constructing a virtual MIMO array echo target signal vector according to the arrangement sequence, and then directing the angle theta according to the sub-airspace i And performing virtual MIMO array DBF on the virtual MIMO array target signal vector. And combining and detecting the circulated data, wherein if the assumption is simultaneously satisfied, the corresponding data has the maximum value, so that whether the target signal exists or not and the transmitting antenna sequence of the target signal can be determined. In this embodiment, determining whether a target signal exists in a direction corresponding to each sub-space domain according to a virtual MIMO array DBF result obtained by each cycle hypothesis includes: and judging the composite value obtained by each hypothesis, if a plurality of composite values are larger than a preset threshold value, judging that a target signal exists in the corresponding sub-space domain direction, and determining the position of the first transmitting antenna in the sub-space domain according to the position of the maximum value of the composite values, namely determining the sequence of the transmitting antennas.
In a specific application embodiment, as shown in fig. 8, the detailed steps of the loop hypothesis testing include:
s201, the airspace range to be searched is [ -theta, +theta]Cycling, wherein the cycling step isNumber of cycles N th The ith sub-airspace range is: θ i ＝-θ+[(i-1)Δθ,iΔθ]The midline is 0 DEG, theta i I=1, 2, …, N for the i-th sub-airspace directional angle th ；
S202, for all distance unit ranges [1, M]Cycling, wherein the cycling step is 1, the cycling times are M, and the jth distance unit is R j ；
S203, for all Doppler unit ranges [1, N Chirp ]Performing transmission antenna sequence hypothesis cycle, and performing cycle step 1 and cycle number N Chirp The kth Doppler unit order isWherein N is Eb And the number of empty sub-airspace is represented. When a selected Doppler unit sequence value exceeds the pulse number N Chirp Then subtracting N from the sequential value Chirp A representation;
s204, searching corresponding receiving channel data for the transmitting antenna data circularly obtained in the S203, and constructing a virtual MIMO array vector (the vector size is [1, N Tx *N Rx ]) And performs virtual MIMO array DBF (DBF steering vector size is: [1, N Tx *N Rx ]) Obtaining a synthesized value;
s205, circularly executing the steps S203 and S204 to obtain a group of N-length Chirp Selecting the highest target signal from the combined values by adopting a detection algorithm, if the target signal is detected, determining the corresponding Doppler unit sequence and the transmitting antenna sequence; if the target signal is not detected, the loop is skipped, and the process proceeds to step S202 to perform the next loop.
According to the method and the device, target signal detection of overlapping transmitting antenna gains can be completed by combining cyclic hypothesis detection and MIMO virtual array DBF, so that target signals can be detected in the whole airspace range finally, doppler unit positions and transmitting antenna sequences of the target signals in each sub airspace range are determined, and detection performance of a radar system on weak signal targets (radar reflection sectional area sigma is smaller or targets are far away from the radar system) is effectively improved.
The present embodiment includes, but is not limited to, performing multiple loop hypothesis testing on range-doppler echo signal spectrum data of a MIMO radar system to improve overall detection performance of the radar system.
And S03, performing angle measurement according to the constructed virtual MIMO array and the detected target signals, and determining whether the detected target signals are real targets according to the corresponding relation between the angle measurement results and the pointing angle ranges of the corresponding sub-airspaces.
In addition to distance and speed, the angle of the target relative to the radar is an important amount of information characterizing the target, whereas the target signal detected according to step S02 may contain false targets since it contains only distance, speed information. In the embodiment, after detecting the target signal in step S02, angle measurement is further performed according to the virtual MIMO array and the detected target signal, the angle measurement search interval is the coverage area of the sub-airspace angle, and whether the detected target signal is a real target is finally confirmed by using the angle measurement result, if the target signal angle measurement result is within the pointing angle range of the corresponding sub-airspace, the target signal is determined to be the real target; if the angle measurement result of the target signal is not in the pointing angle range of the corresponding sub-airspace, the target signal is judged to be a false target, the accuracy of target detection can be further improved, false alarms caused by misjudgment are restrained, and the false alarm rate is reduced. The angle measurement algorithm can adopt a subspace-based DOA angle estimation algorithm and the like, and the configuration can be specifically selected according to actual requirements.
The embodiment is realized by the steps of ranging [ -theta, +theta ] in the airspace interval to be searched]In the method, the airspace range is divided into a plurality of sub airspace ranges (the number of the sub airspace ranges is N th The sub-airspace direction angle is theta i Sub-space-domain spacing) Sequentially performing distance-Doppler data matrix hypothesis test on each sub-airspace range, and respectively performing cyclic hypothesis on all Doppler units corresponding to each distance unit, namely assuming some Doppler units in all Doppler unitsComprises a target signal, each time the hypothesis comprises a transmitting antenna channel sequence, doppler units which are assumed to comprise the target signal are extracted (the number of the extracted Doppler units is the transmitting antenna channel number N Tx ) According to the arrangement sequence of the receiving channels, an N is constructed Tx *N Rx Is based on the sub-airspace pointing angle theta i Performing virtual MIMO array DBF (DBF pointing angle is set sub-airspace pointing angle theta) on the virtual MIMO array target signal vector i ) Obtaining a composite value, which can increase the target signal echo gain to 10 log10 (N) Tx ) By directing a certain sub-airspace direction theta i R of (2) i N is carried out by a plurality of distance units Chirp Sub-hypothesis by comparing N Chirp The sub-hypothesized composite value may determine the sub-spatial direction, whether the target signal is present on the range bin, and the order in which the target signal is in the sub-interval (transmit antenna order). By applying the method to the whole space domain range [ -theta, +theta]The target signal detection of the superposition transmitting antenna gain can be completed by utilizing the MIMO virtual array DBF, and the detection performance of the radar system on a weak signal target (the radar reflection sectional area sigma is smaller or the target is far away from the radar system) is improved. Finally, angle measurement is carried out according to the detected target signal and the constructed virtual MIMO array, and if the angle measurement result of the target signal is in the pointing angle range of the corresponding sub-airspace, the real existence of the target signal is judged; if the angle measurement result of the target signal is not in the pointing angle range of the corresponding sub-airspace, the false target signal is judged, and the target signal is discarded, so that false alarm caused by misjudgment can be further restrained.
In order to verify the effectiveness of the invention, the simulation experiment of MIMO radar target detection based on DDMA waveform modulation is carried out by adopting the method of the invention in a specific application embodiment, wherein the DDMA stepping phase is set as follows:when the target RCS is 20 square meters (RCS is larger), the target distance radar R=300m, the target relative radar movement speed V=100 km/h, and the target relative radarAt an angle a=11° (strong echo target), a range-doppler two-dimensional spectrum corresponding to the second reception channel is obtained as shown in fig. 9. As can be seen from fig. 9, the distance-doppler two-dimensional spectrum is equally divided into 8 subintervals (6 transmit antennas occupy subintervals+2 null subintervals), and a rectangular frame indicates a position where the target signal falls in the 6 transmit antenna subintervals, and the null subintervals do not include the target signal. For targets with larger RCS, DBF gains can be directly received through pulse accumulation or superposition, and the positions of target signals in each subinterval and the positions of empty subintervals are separated from the range-Doppler frequency spectrum. However, when RCS is 0.1 square meter, the range-doppler two-dimensional spectrum of the target range radar r=500 m (weak echo signal target), as shown in fig. 10, is basically a noise signal, the target signal cannot be found out from the spectrum, and the target signal position and the transmitting antenna sequence cannot be determined by DDMA waveform modulation and demodulation, which may cause target miss.
The invention divides the airspace scanning range [ -15 DEG, 15 DEG ] into 10 sub airspace, the sub airspace cyclic stepping is 3 DEG, the distance unit range [1,1024], the cyclic stepping is 1, and the Doppler unit ranges [1,256] are used for carrying out the transmission antenna sequence assumption cycle. When the range of the sub-airspace search interval is [9 °,12 ° ], and the range search unit is 500 °, the spectrum of the corresponding second receiving channel doppler unit is shown in fig. 11. As can be seen from fig. 11, the target echo signal cannot be found from the noise signal in the doppler frequency domain, and the order of the transmitting antennas cannot be determined. The DBF directional diagram of the virtual MIMO array pointing to the 11-degree position of the airspace is shown in fig. 12, the DBF gain of the virtual MIMO array in the 11-degree direction is 16.8dB, and the virtual MIMO array meets the design theoretical index. After performing cyclic assumption and virtual MIMO array DBF on the 256 Doppler units, obtaining a group of synthetic data with length of 256; the set of data is detected by setting a threshold, and if a plurality of values are larger than the set threshold, the position of the maximum value is the position of the first transmitting antenna in the subspace domain, and the sequence of the transmitting antennas in the corresponding frequency domain is determined.
The result of the virtual array DBF composite data detection after the Doppler cell cycle is assumed is shown in FIG. 13, sinceThe former assumption is that the antenna sequence is not completely aligned, the detection threshold detects 8 times of data, the Doppler unit has the maximum value in 139 th assumption, and then the 139 th Doppler unit can be determined as the coordinate of the target signal falling in the corresponding sub-airspace of the first transmitting antenna. Transmitting antenna T x1 ,T x2 ,T x3 ,T x4 ,T x5 ,T x6 The corresponding Doppler units are respectively: [139,172,203,235,11,43]. Therefore, the method can effectively detect the target signal from the weak echo signal and determine the sequence of the transmitting antenna. Further, according to the position of the detected target signal corresponding to the transmitting antenna sequence in the Doppler domain, MIMO angle measurement is performed, as shown in FIG. 14, the angle measurement result is 10.98 degrees, and the result is equal to the set sub-airspace search interval range [9 degrees, 12 degrees ]]Is substantially identical, the weak target signal currently detected is considered to be a true target signal (true target signal angle is 11). I.e. the false alarm can be further filtered out by combining the angle measurement result.
On the basis of the traditional DDMA, the invention carries out cyclic hypothesis test on airspace, distance domain and Doppler domain by dividing the airspace range to be searched, when cyclic hypothesis conditions are met, echo signals can overlap virtual MIMO array DBF pointing gain, when target echo signals are weak, the Doppler domain position where the target signals are possibly located is circularly hypothesized, and then synthetic data detection is carried out on the hypothesized result, because the overlapped virtual array DBF gain improves the signal-to-noise ratio (SNR) of the target of the weak echo signals, the position (transmitting antenna sub airspace position) and transmitting antenna sequence of the target signals of the weak echo signals can be effectively found from the Doppler domain, and then the detection of the radar system to the weak echo signals can be accurately realized through MIMO angle measurement secondary confirmation, and false alarm brought by interference signals is restrained.
The invention can improve the detection capability of the MIMO radar system on the weak echo signal target on the basis of the consistency of hardware and the existing DDMA waveform modulation, can reduce the minimum RCS detection lower limit under the condition of the same target detection distance, and can improve the furthest detection distance of the target under the condition of the same target RCS, thereby ensuring the detection performance of the whole radar system.
The embodiment also provides a MIMO radar target detection device based on DDMA waveform modulation, which comprises a processor and a memory, wherein the memory is used for storing a computer program, and the processor is used for executing the computer program to execute the method.
The foregoing is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. While the invention has been described with reference to preferred embodiments, it is not intended to be limiting. Therefore, any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present invention shall fall within the scope of the technical solution of the present invention.

Claims (10)

1. The MIMO radar target detection method based on DDMA waveform modulation is characterized by comprising the following steps:
receiving an echo signal of a DDMA waveform transmitted by a MIMO radar system, and sequentially performing distance dimension FFT calculation and speed dimension FFT calculation to obtain a distance Doppler data matrix;
dividing the space domain range to be searched into a plurality of sub-spaces, sequentially carrying out cyclic hypothesis test on the distance Doppler data matrix on each sub-space, wherein the cyclic hypothesis test on the distance Doppler data matrix comprises cyclic hypothesis transmitting antenna sequences, constructing a virtual MIMO array for DBF, and judging whether target signals exist in the corresponding directions of each sub-space according to the DBF result of the virtual MIMO array obtained by each cyclic hypothesis.
2. The DDMA waveform modulation based MIMO radar target detection method of claim 1, wherein the cyclically hypothesizing the transmit antenna order comprises cyclically hypothesizing that some of all the doppler cells contain target signals, extracting the doppler cells hypothesized to contain target signals, and obtaining the hypothesized transmit antenna order.
3. The DDMA waveform modulation based MIMO radar target detection method of claim 1, wherein the constructing a virtual MIMO array for DBF comprises:
searching corresponding receiving channel data according to the transmitting antenna data obtained by the transmitting antenna sequence assumed each time;
according to the determined receiving channel arrangement sequence of the searched receiving channel data, constructing a corresponding virtual MIMO array;
and performing DBF on the target signal vector of the virtual MIMO array according to the pointing angle of the current sub-airspace to obtain a synthesized value for output.
4. The method for detecting a target of a MIMO radar based on DDMA waveform modulation according to claim 3, wherein the determining whether the target signal exists in the direction corresponding to each sub-space domain according to the virtual MIMO array DBF result obtained by each cycle hypothesis comprises: and judging the synthesized value obtained by each hypothesis, if a plurality of synthesized values are larger than a preset threshold, judging that a target signal exists in the corresponding sub-space domain direction, and determining the position in the sub-space domain where the first transmitting antenna is located according to the position of the maximum value of the synthesized values, namely determining the sequence of the transmitting antennas.
5. The DDMA waveform modulation-based MIMO radar target detection method of claim 1, wherein the number of hypothesis detections in the cyclic hypothesis test is N Chirp ，N Chirp For the doppler cell length, one transmit antenna channel order is assumed at a time.
6. The method for detecting a target of a MIMO radar based on DDMA waveform modulation according to any one of claims 1 to 5, wherein the dividing of the spatial range to be searched into a plurality of sub-spatial ranges is N th The sub-airspace direction angle is theta i ＝-θ+[(i-1)Δθ,iΔθ]Sub-spatial space interval is[-θ,+θ]For the space to be searchedRange, θ i I=1, 2, …, N for the i-th sub-airspace directional angle th 。
7. The method for detecting a target of a MIMO radar based on DDMA waveform modulation according to any one of claims 1 to 5, wherein the sequentially performing distance-dimensional FFT computation and velocity-dimensional FFT computation to obtain a distance-doppler data matrix comprises:
carrying out one-dimensional distance dimension FFT calculation on each receiving channel of the echo signal to obtain a one-dimensional distance matrix;
and carrying out pulse accumulation and two-dimensional speed dimension FFT calculation on each distance unit in the distance matrix to obtain the distance Doppler data matrix.
8. The DDMA waveform modulation-based MIMO radar target detection method according to any one of claims 1 to 5, wherein the cyclic detection further comprises performing angle measurement according to the constructed virtual MIMO array and the detected target signal, and determining whether the detected target signal is a real target according to the correspondence between the angle measurement result and the pointing angle range of the corresponding sub-airspace.
9. The method for detecting a target of a MIMO radar based on DDMA waveform modulation according to claim 8, wherein determining whether the detected target signal is a real target according to the correspondence between the angle measurement result and the pointing angle range of the corresponding sub-airspace comprises: if the angle measurement result of the target signal is within the pointing angle range of the corresponding sub-airspace, judging the target signal as a real target; and if the angle measurement result of the target signal is not in the pointing angle range of the corresponding sub-airspace, judging that the target signal is a false target.
10. A MIMO radar target detection apparatus based on DDMA waveform modulation, comprising a processor and a memory for storing a computer program, wherein the processor is configured to execute the computer program to perform the method of any one of claims 1 to 9.
CN202310920909.8A 2023-07-25 2023-07-25 MIMO radar target detection method and device based on DDMA waveform modulation Pending CN116990794A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117452390A (en) * 2023-12-25 2024-01-26 厦门大学 DDMA-MIMO radar speed estimation method

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117452390A (en) * 2023-12-25 2024-01-26 厦门大学 DDMA-MIMO radar speed estimation method
CN117452390B (en) * 2023-12-25 2024-05-03 厦门大学 DDMA-MIMO radar speed estimation method

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