Disclosure of Invention
The invention aims to provide a speed ambiguity-resolving method and system based on a TDM MIMO radar.
In order to achieve the purpose, the invention provides the following scheme:
a speed deblurring method based on a TDM MIMO radar comprises the following steps:
collecting target data through a TDM MIMO automobile radar; the TDM MIMO automotive radar comprises a plurality of receiving antennas and a plurality of transmitting antennas;
performing distance FFT and Doppler FFT processing on the target data to obtain virtual antenna array data of a target;
calculating a phase calibration matrix based on the virtual antenna array data;
calibrating the virtual antenna array of the actual target based on the phase calibration matrix to obtain a calibrated virtual antenna array; the calibrated virtual antenna array comprises a calibrated transmitting antenna sequence and a calibrated receiving antenna array;
respectively carrying out phase angle solving and unwrapping processing on the calibrated transmitting antenna sequence and the calibrated receiving antenna array to obtain a transmitting antenna phase sequence and a receiving antenna phase sequence;
respectively calculating the average value of the phase difference of the adjacent transmitting antennas and the average value of the phase difference of the adjacent receiving antennas on the basis of the transmitting antenna phase sequence and the receiving antenna phase sequence;
calculating phase change according to the estimated value of the target speed; the estimated value of the target speed is determined by the Doppler FFT processing result of the target data;
calculating an expansion coefficient of the target speed based on the average of the phase differences of the adjacent transmitting antennas, the average of the phase differences of the adjacent receiving antennas and the phase change;
and resolving the ambiguity of the target speed based on the expansion coefficient to obtain the actual target speed.
Alternatively, by the formula phiTX(j)=unwrap(angle(STX(j))),1≤j≤NRXPerforming phase angle solving and unwrapping processing on the calibrated transmitting antenna sequence to obtain a transmitting antenna phase sequence;
by the formula phiRX(i)=unwrap(angle(SRX(i))),1≤i≤NTXPerforming phase angle solving and unwrapping processing on the calibrated receiving antenna array to obtain a receiving antenna phase sequence;
wherein phi isTX(j) Representing the phase sequence, S, of the ith transmit antennaTX(j) Representing the calibrated transmit antenna sequence, NRXIndicating the number of receiving antennas, phiRX(i) Representing the phase sequence of the jth receiving antenna, SRX(i) Representing the calibrated sequence of receiving antennas, NTXIndicating the number of transmit and receive antennas.
Optionally, the mean value of the phase differences of the adjacent transmitting antennas istThe calculation formula is as follows:
optionally, the mean value of the phase differences of the adjacent receiving antennas isrThe calculation formula is as follows:
optionally, the phase change isdetThe calculation formula of (a) is as follows:
wherein v isdetDenotes the estimated value of the target speed, lambda denotes the operating wavelength of the TDM MIMO automotive radar, TcRepresenting the period of the chirp, NTXIndicating the number of transmit and receive antennas.
Optionally, the expansion coefficient n is calculated as follows:
wherein, NTXIndicating the number of transmitting and receiving antennas, phidetIndicates a change in phase, phirMeans, phi, representing phase differences of adjacent receiving antennastRepresenting the average of the phase differences of adjacent transmit antennas.
Alternatively, the calculation formula of the target actual speed v is as follows:
v=vdet+2round(n)vmax
wherein v isdetAn estimated value representing a target velocity, n represents an expansion coefficient, vmaxRepresenting the target speed maximum.
The invention also provides a speed ambiguity-resolving system based on the TDM MIMO radar, which comprises:
the target data acquisition module is used for acquiring target data through the TDM MIMO automobile radar; the TDM MIMO automotive radar comprises a plurality of receiving antennas and a plurality of transmitting antennas;
the processing module is used for carrying out distance FFT and Doppler FFT processing on the target data to obtain virtual antenna array data of a target;
a phase calibration matrix calculation module for calculating a phase calibration matrix based on the virtual antenna array data;
the calibration module is used for calibrating the virtual antenna array of the actual target based on the phase calibration matrix to obtain a calibrated virtual antenna array; the calibrated virtual antenna array comprises a calibrated transmitting antenna sequence and a calibrated receiving antenna array;
the antenna phase sequence determining module is used for respectively carrying out phase angle solving and unwrapping processing on the calibrated transmitting antenna sequence and the calibrated receiving antenna array to obtain a transmitting antenna phase sequence and a receiving antenna phase sequence;
the mean value calculation module of the adjacent antenna phase difference is used for respectively calculating the mean value of the adjacent transmitting antenna phase difference and the mean value of the adjacent receiving antenna phase difference based on the transmitting antenna phase sequence and the receiving antenna phase sequence;
the phase change calculation module is used for calculating phase change according to the estimated value of the target speed; the estimated value of the target speed is determined by the Doppler FFT processing result of the target data;
an expansion coefficient calculation module, configured to calculate an expansion coefficient of the target speed based on the average of the phase differences between the adjacent transmitting antennas, the average of the phase differences between the adjacent receiving antennas, and the phase change;
and the target actual speed determining module is used for performing deblurring on the target speed based on the expansion coefficient to obtain the target actual speed.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention accurately estimates the real speed value of any angle target by fully utilizing the phase value of the virtual antenna array, enlarges the maximum speed measurement range of the TDM MIMO automobile radar, achieves the same speed measurement range as that of a single transmitting antenna, and simultaneously ensures the accuracy of azimuth angle estimation. The method has low calculation complexity, does not need to calculate the angle FFT for multiple times, and then compares peak values to carry out speed expansion; the speed of the target at any angle can be expanded, and the target is not limited to the target right in front of the radar.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a speed ambiguity-resolving method and system based on a TDM MIMO radar.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
The specific position of a radar target is generally determined by radial distance, azimuth angle and pitch angle, and the TDM MIMO automobile radar comprises N in the horizontal direction for accurately measuring the azimuth angle information of the targetTXA transmitting antenna and NRXA receiving antenna; there will also be a small number of transmit antennas in the vertical direction to measure the pitch angle information of the target. In order to accurately estimate the actual speed of the target, the invention uses an antenna array in the horizontal direction to perform speed ambiguity resolution.
In the TDM MIMO automotive radar, the transmitting antenna and the receiving antenna array generally adopt an equally spaced design pattern, as shown in fig. 2, NTXThe distance between every two adjacent antennas in each transmitting antenna is dt,NRXThe distance between every two adjacent antennas in each receiving antenna is dr. To NTXA transmitting antenna numbered 1 to NTX(ii) a To NRXA receiving antenna numbered 1 to NRX. In practical design, the spacing between some adjacent receiving antennas may be set to other values to realize a larger number of virtual antenna arrays, and this part of data may not be used or may be subjected to additional processing, which does not affect the present invention.
The MIMO automobile radar under the TDM working mode realizes the orthogonality of the transmitting antenna in time, NTXNumber 1 to number N of transmitting antennaTXSequential emission, NRXThe receiving antennas simultaneously receive the echo of each transmitting antenna to form NTX×NRXThe echo signal array of (1).
The radar carries out frequency mixing processing on the transmitting signal and the receiving signal to obtain an intermediate frequency signal, and then the intermediate frequency signal is sampled by the ADC to obtain a discrete signal sequence. TDM MIMO steamThe radar of the vehicle is in a chirp period TCInternal sampling NRangeSub, NTXThe transmitting antennas transmit signals in sequence in a cycle; one frame carries out NDopplerThe secondary circulation is used for achieving the purpose of speed measurement. One frame of radar data may be represented as NRange×NDoppler×NTX× NRXThe four-dimensional array of (1).
In NRangePerforming distance FFT processing on the dimension, and distinguishing targets in the radial distance; index Ind of a certain distancerIf the FFT result of the lower distance has a peak value, the target exists at the distance, and the specific distance value can be calculated by the distance index, wherein Ind is more than or equal to 1r≤NRange. After the distance FFT processing, N under each distance index is obtainedDopplerDimension is processed by Doppler FFT with a certain Doppler index InddIf a peak value exists in the Doppler FFT result, the target with the corresponding speed exists, and the specific speed value can be calculated by the Doppler index, wherein Ind is more than or equal to 1d≤NDoppler. For range-Doppler two-dimensional data, a certain range-Doppler index (Ind)r,Indd) If there is a peak, it indicates that there is a target with corresponding speed at the distance, and N of the targetTX×NRXVirtual antenna array data is thus available.
As shown in fig. 1, the speed deblurring method based on the TDM MIMO radar provided by the present invention includes:
step 101: collecting target data through a TDM MIMO automobile radar; the TDM MIMO automotive radar includes a plurality of receive antennas and a plurality of transmit antennas.
In an open field or a microwave darkroom environment, the TDM MIMO automobile radar is used for collecting static target data at a certain distance in front of the automobile radar.
Step 102: and performing distance FFT and Doppler FFT processing on the target data to obtain virtual antenna array data of the target.
Step 103: a phase calibration matrix is calculated based on the virtual antenna array data.
Over-distance FFT sumObtaining N of the target after Doppler FFT processingTX×NRXVirtual antenna array data Scalib. Selecting antenna pair data S of transmitting antenna 1-receiving antenna 1calib(1,1) as a reference, a phase calibration matrix is calculated:
the matrix is used to calibrate the phase values of the virtual antenna array to compensate for amplitude and phase mismatches caused by antenna path length mismatch, inter-chip differences, antenna coupling, etc.
Step 104: calibrating the virtual antenna array of the actual target based on the phase calibration matrix to obtain a calibrated virtual antenna array; the calibrated virtual antenna array comprises a calibrated transmitting antenna sequence and a calibrated receiving antenna array.
The TDM MIMO automobile radar obtains four-dimensional array data in an actual working environment, and distance and speed values of a plurality of actual targets are obtained after constant false alarm screening. The resulting speed values may be ambiguous due to the speed ambiguity associated with the TDM mode of operation. Virtual antenna array data S for real targetvirtualProcessing is carried out to obtain a real speed value of the target, and the virtual antenna array data is calibrated according to the calibration matrix obtained in the step 103:
S(i,j)=Svirtual(i,j)×phasecalib(i,j),1≤i≤NTX,1≤j≤NRX (2)
step 105: and respectively carrying out phase angle solving and unwrapping processing on the calibrated transmitting antenna sequence and the calibrated receiving antenna array to obtain a transmitting antenna phase sequence and a receiving antenna phase sequence.
All receiving antenna sequences S for the ith transmitting antennaRX(i)=[S(i,1)S(i,2)…S(i,NRX)]And performing phase angle solving and unwrapping operations to obtain a phase sequence of the receiving antenna:
φRX(i)=unwrap(angle(SRX(i))),1≤i≤NTX (3)
all transmitting antenna sequences S for the jth receiving antennaTX(i)=[S(1,j)S(2,j)…S(NTX,j)]And performing phase angle solving and unwrapping operations to obtain a phase sequence of the transmitting antenna:
φTX(j)=unwrap(angle(STX(j))),1≤j≤NRX (4)
the phase sequence obtained after the processing is shown in fig. 5 and 6, and an example is a 12-transmission 8-reception automotive radar. The different colors in the figure represent 12 different transmitting antennas, and the same color represents 8 receiving antennas corresponding to the same transmitting antenna. FIG. 5 is a phase sequence of the object moving in front of Lei Dazheng; fig. 6 is a phase sequence with the target at an angle to the radar.
Step 106: and respectively calculating the average value of the phase difference of the adjacent transmitting antennas and the average value of the phase difference of the adjacent receiving antennas on the basis of the transmitting antenna phase sequence and the receiving antenna phase sequence.
Calculating the transmitting antenna sequence phi in turnTX(j) And (3) solving the average value of the phase difference values of the adjacent antennas to obtain the average value of the phase difference values of the adjacent transmitting antennas:
calculating in sequence a sequence of receiving antennas phiRX(i) And (3) solving the average value of the phase difference values of the adjacent antennas to obtain the average value of the phase difference values of the adjacent receiving antennas:
step 107: calculating phase change according to the estimated value of the target speed; the estimate of the target velocity is determined from the doppler FFT processing of the target data.
Based on the Doppler FFT result of the target data, a predicted value v of the target speed can be obtaineddetThe velocity being caused by the time interval between two chirps of the same transmit antennaThe phase difference change is:
step 108: and calculating the expansion coefficient of the target speed based on the average value of the phase differences of the adjacent transmitting antennas, the average value of the phase differences of the adjacent receiving antennas and the phase change.
As shown in fig. 3, when the target moves in front of the radar at a speed v and the angle between the target and the radar is θ, for all receiving antennas of the same transmitting antenna, the echo between two adjacent receiving antennas has drsin θ, which corresponds to the phase change of the receiving antenna:
where λ is the operating wavelength of the radar and can be represented by λ = c/fcIs obtained, c is the speed of light, fcIs the operating frequency of the radar.
As shown in fig. 4, for all transmitting antennas of the same receiving antenna, the echo path difference between two adjacent transmitting antennas is composed of two parts, one part is the path difference caused by the transmitting antenna spacing, and this part reflects the azimuth angle of the target, and the corresponding phase changes:
another part is the phase change caused by the object motion, and the object moves by vT in the interval time of two adjacent transmitting antennascThis part reflects the velocity change of the target, the corresponding phase change is:
the actual phase change of two adjacent transmit antennas then becomes:
in combination of equations (8) and (11), the adjacent antenna phase change due to velocity is:
when phi isdetWhen the value of (d) exceeds. + -. π, the velocity is blurred. N is used for representing the number of turns of phase ambiguity, namely a speed expansion coefficient, and when the speed expansion coefficient is positive, the speed is positive, namely the target is gradually far away from the radar; when the velocity expansion coefficient is negative, it means that the velocity is negative, i.e., the target gradually approaches the radar. The true phase difference can be expressed as:
φtrue=φdet+2nπ,n∈[1-NTX,NTX-1] (13)
this phase difference can be equated to N in the same cycleTXSum of phase differences of the transmit antennas caused by velocity:
φtrue=NTXφt-v (14)
combining equation (7) and equations (12) to (14), the velocity expansion coefficient can be obtained as:
step 109: and performing deblurring on the target speed based on the expansion coefficient to obtain the target actual speed.
v=vdet+2round(n)vmax (15)
Where round (n) denotes rounding n.
Deblurring results as shown in fig. 7 and 8, taking the car radar of 12-transmission and 8-reception as an example, the fork marks represent the initial doppler FFT results,the circular marks represent deblurring results. Fig. 7 shows the deblurring result when the moving speed of the target changes, and the algorithm can obtain the actual speed. FIG. 8 shows the target at different angles θ1De-blurring result when moving forward at a speed of 10m/s, actual radial velocity v measured by radar1Can be expressed as v1=10cosθ1And the result obtained by the fuzzy algorithm solution is consistent with the theoretical result.
After the accurate speed of the target is obtained, the phase of the virtual antenna array can be compensated, so that a more accurate azimuth angle estimation value is obtained.
According to the invention, the speed expansion coefficient can be obtained by calculating the phase value of the virtual antenna array, so that the current speed is expanded to reach the speed measuring range same as that of a single-transmitting multi-receiving antenna, the problem that the speed measuring range is obviously reduced when the number of transmitting antennas of the TDM MIMO automobile radar is large is solved, and the speeds of targets with different azimuth angles can be accurately expanded.
The invention also provides a speed ambiguity resolving system based on the TDM MIMO radar, which comprises the following components:
the target data acquisition module is used for acquiring target data through the TDM MIMO automobile radar; the TDM MIMO automotive radar comprises a plurality of receiving antennas and a plurality of transmitting antennas;
the processing module is used for carrying out distance FFT and Doppler FFT processing on the target data to obtain virtual antenna array data of a target;
a phase calibration matrix calculation module for calculating a phase calibration matrix based on the virtual antenna array data;
the calibration module is used for calibrating the virtual antenna array of the actual target based on the phase calibration matrix to obtain a calibrated virtual antenna array; the calibrated virtual antenna array comprises a calibrated transmitting antenna sequence and a calibrated receiving antenna array;
the antenna phase sequence determining module is used for respectively carrying out phase angle solving and unwrapping processing on the calibrated transmitting antenna sequence and the calibrated receiving antenna array to obtain a transmitting antenna phase sequence and a receiving antenna phase sequence;
the mean value calculation module of the adjacent antenna phase difference is used for respectively calculating the mean value of the adjacent transmitting antenna phase difference and the mean value of the adjacent receiving antenna phase difference based on the transmitting antenna phase sequence and the receiving antenna phase sequence;
the phase change calculation module is used for calculating phase change according to the estimated value of the target speed; the estimated value of the target speed is determined by the Doppler FFT processing result of the target data;
an expansion coefficient calculation module for calculating an expansion coefficient of the target speed based on the average of the phase differences of the adjacent transmitting antennas, the average of the phase differences of the adjacent receiving antennas, and the phase variation;
and the target actual speed determining module is used for performing deblurring on the target speed based on the expansion coefficient to obtain the target actual speed.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.