Multi-target DDMA demodulation method based on sub-band unit accumulation

Abstract

The invention belongs to the technical field of radar signal processing, and particularly relates to a multi-target DDMA demodulation method based on sub-band unit accumulation. Firstly, initial parameters of a radar system are initialized, then a DDMA-MIMO signal model is constructed according to the system parameters, and then distance dimension and Doppler dimension 2DFFT processing is carried out on received signals. The method is characterized in that in each angle domain, the whole RV-MAP is copied, energy of each cell of all sub-bands is recorded, energy accumulation of cyclic shift with the length equal to the number of transmitting antennas is executed, and sub-band group energy of each unit is obtained. And then finding the maximum accumulated energy of each unit sub-band group, and performing threshold judgment according to the energy to obtain a correct sub-band where the target is located. And finally, calculating the real distance and speed of the target according to a distance formula and a speed formula. The method provided by the invention can well deal with the situation that a traditional method cannot be suitable for a multi-target scene.

Description

Technical Field

[0001] The invention belongs to the technical field of radar signal processing, and in particular relates to a multi-target DDMA demodulation method based on sub-band unit accumulation. Background Art

[0002] Most traditional vehicle-mounted MIMO signals use the transmission form of time division multiple access, namely TDMA-MIMO. Its principle is to use different single antennas to transmit signals alternately. Time resources are not well utilized, so TDMA waveforms are mostly used in short-range, low-resolution radar application scenarios. Slow-time MIMO is a special system. The waveforms of different array elements are orthogonal during the entire coherent accumulation time, and the single pulses are coherent. Among them, the Doppler frequency division multiple access (DDMA) waveform can well make up for the above shortcomings of TDMA. Unlike the alternating operation of single antennas under the TDMA waveform, all transmitting antennas transmit at the same time under the DDMA waveform system, but a specific frequency offset is added to the signal of each transmitting antenna. Through this artificially offset frequency, the signals of different transmitting antennas are separated in the Doppler domain. This separation is called DDMA demodulation. If DDMA demodulation is not performed, speed ambiguity will occur. The currently commonly used DDMA demodulation algorithm is the DDMA demodulation algorithm based on Empty-band. This method has a good speed resolution effect for a single target. However, for multi-target scenarios, the DDMA demodulation algorithm based on Empty-band may not be able to perform correct demodulation. Therefore, studying the DDMA demodulation algorithm is of great significance in the field of vehicle-mounted millimeter-wave radar signal processing. Summary of the invention

[0003] The purpose of the present invention is to provide a multi-target DDMA demodulation method based on sub-band unit accumulation for a vehicle-mounted DDMA-MIMO radar system and for multi-target detection. The method comprises the following steps:

[0004] S1. Build the vehicle-mounted DDMA-MIMO system and initialize the system parameters:

[0005] Initialize system parameters, including the number of transmitting and receiving antennas, LFMCW waveform parameters, target parameters, and the number of sampling points for each channel.

[0006] S2. Constructing the vehicle-mounted DDMA-MIMO signal model:

[0007] According to the system parameters in step S1, the transmission signal and echo signal model of DDMA-MIMO is constructed.

[0008] S3, Range-Doppler 2D-FFT:

[0009] The obtained vehicle-mounted DDMA-MIMO signal model is processed by 2D-FFT in the range dimension and Doppler dimension to obtain the range-Doppler spectrum, namely, RV-MAP.

[0010] S4, DDMA demodulation:

[0011] On RV-MAP, a multi-objective DDMA demodulation method with sub-band unit accumulation is used to deambiguate the velocity.

[0012] S5. Calculate target information:

[0013] According to the distance and speed calculation formula, the distance and speed of the target are calculated.

[0014] Furthermore, the specific method of step S1 is:

[0015] Initialize system parameters, including: number of transmitting antennas M, number of receiving antennas N, sweep time T of LFMCW waveform c , the starting frequency f0 of the LFMCW waveform, the slope μ of the LFMCW waveform, the number of sweep cycles K, the target distance r, the target speed v, the target angle θ, the number of sampling points P in the distance dimension r and the number of Doppler sampling points P v .

[0016] Furthermore, the specific method of step S2 is:

[0017] First, a target model based on the DDMA-MIMO system is constructed. Under the DDMA-MIMO system, all transmitting antennas transmit simultaneously, and the signal of each transmitting antenna is Doppler frequency offset so that the signals of different transmitting antennas are separated in the Doppler domain. According to the system parameters set in step S1, the waveform of the mth transmitting antenna is

[0018]

[0019] where f m Represents the Doppler frequency offset of the mth transmitting antenna.

[0020] The DDMA waveform is a waveform that can be orthogonalized after Doppler processing at the receiving end. m The change of (k-1)T achieves orthogonality in the Doppler domain. Consider dividing the entire Doppler pulse repetition frequency PRF into M orthogonal sub-repetition frequency channels, and the bandwidth of each channel is Then f m for

[0021]

[0022] In order to solve the problem of DDMA-MIMO speed ambiguity, an empty band is first introduced to change the Doppler frequency offset of each transmitting antenna. band The selection should be based on the number of transmitting antennas M and the number of Doppler domain sampling points P currently configured. v Taking all factors into consideration, it is necessary to ensure that the number of Doppler units allocated to each sub-band is an integer. At this time, the Doppler frequency offset f of the mth transmitting antenna is m for

[0023]

[0024] When constructing the target echo signal, the echo signal received by the nth receiving antenna is the sum of the echoes of the transmitted signals of the M transmitting antennas. Without considering the amplitude attenuation, the echo signal received by the nth receiving antenna is

[0025]

[0026] Where t represents the echo delay of the radar signal transmitted by the target.

[0027] The echo signal is mixed with a single-frequency signal with a frequency of f0 and then low-pass filtered to remove the carrier frequency to obtain the baseband complex signal model:

[0028]

[0029] Furthermore, the specific method of step S3 is:

[0030] After obtaining the target mixing data based on the DDMA-MIMO mechanism, first perform FFT on each pulse to generate the distance dimension data, and then perform FFT on the data on each distance unit, that is, perform FFT in the Doppler dimension to obtain the velocity dimension data. After completing such a two-dimensional FFT, the range-Doppler spectrum of the environment and the target obtained by the radar in this frame time, that is, RV-MAP, can be obtained. In each angle domain, the size of the matrix RV-MAP is P r ×P v .

[0031] Furthermore, the specific method of step S4 is:

[0032] Step S2 introduces the empty band, which evenly divides the entire RV-MAP into M+E band subbands, each subband has a length of P s =P v / (M+E bandWhen performing target mapping, the target will appear in M-1 consecutive sub-bands on the right starting from the correct target position (if it exceeds the M+E band sub-bands, it will continue to appear from the first sub-band). The left side of the correct target is continuous E band The sub-band where no target falls (if it exceeds the first sub-band, it will continue to appear from the last sub-band), and the energy of the sub-band where no target falls must be lower than the energy of the remaining M sub-bands where target signals fall.

[0033] In each angle domain, the entire RV-MAP is copied so that the size of the new RV-MAP is P r ×2P v , the energy of each cell is expressed as S(r i ,v i ,sb i )(1≤r i ≤P r ,1≤v i ≤P s ,1≤sb i ≤M+E band ), where ri represents the distance index, vi represents the Doppler index, and sbi represents the subband index. The accumulated energy S of each subband unit group G (r i ,v i ,sb i )as follows

[0034]

[0035] Find the maximum energy S max , and the corresponding subband index S index

[0036] S max =max(S G (r i ,v i ,sb i ),S G (r i ,v i ,sb i +1),…,S G (r i ,v i ,sb i +M))

[0037] S index =p

[0038] Wherein, represents the function to obtain the maximum max(·) value; p represents the subband index corresponding to the accumulated subband group with the highest energy.

[0039] Use S max =S G (r i ,v i ,p) as the input of the detector, and use the value related to the average background noise energy value of RV-MAP as the threshold T, then the output of the detector can be expressed as:

[0040]

[0041] In the original size P r ×P v On the RV-MAP, the correct sub-band where the target is located is obtained according to the sub-band index corresponding to the target whose sub-band unit accumulated energy is higher than the threshold T, and the distance and Doppler index value position energy corresponding to the remaining sub-band units are set to 0 to obtain the final RV-MAP.

[0042] Furthermore, the specific method of step S5 is:

[0043] Record the distance index value r where the energy on the demodulated RV-MAP is not zero i (1≤r i ≤P r ) and Doppler index value v i (,1≤v i ≤P v ), according to the distance calculation formula and speed calculation formula, calculate the correct distance and speed of the target. The formula is as follows

[0044] R=(r i -1)·R res

[0045] V=(v i -P v / 2)·V res

[0046] Where R res represents the distance unit, V res represents the speed unit, Wherein, B represents the bandwidth of the transmitted signal, and PRT represents the duration of the transmitted signal.

[0047] Compared with the prior art, and compared with the traditional Empty-band-based DDMA demodulation algorithm, the present invention provides a multi-target DDMA demodulation method based on sub-band unit accumulation. The traditional Empty-band-based DDMA demodulation algorithm is suitable for single-target scenarios or multi-target scenarios where the speed is in the same sub-band, and other scenarios are prone to speed calculation errors. Using the algorithm provided by the present invention, in a multi-target scenario, whether the target is in the same sub-band or in different sub-bands, the present invention can well calculate the correct speed of the target. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The present invention is a flow chart of a multi-target DDMA demodulation method based on sub-band unit accumulation.

[0049] Figure 2 This is a DDMA-MIMO signal transmission diagram of step S2.

[0050] Figure 3 This is a flow chart of the range-Doppler 2D-FFT of step S3.

[0051] Figure 4 It is the RV-MAP image after the range-Doppler 2D-FFT in step S3.

[0052] Figure 5 This is a schematic diagram of a multi-target DDMA demodulation method for sub-band unit accumulation in step S4.

[0053] Figure 6 It is the RV-MAP after using the Empty-band based DDMA demodulation algorithm in step S4.

[0054] Figure 7 This is the RV-MAP after the multi-target DDMA demodulation method using sub-band unit accumulation in step S4. DETAILED DESCRIPTION

[0055] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0056] like Figure 1 As shown, a flow chart of a multi-target DDMA demodulation method based on sub-band unit accumulation includes the following steps:

[0057] S1. Initialize system parameters:

[0058] Initialize system parameters, including: the number of transmitting and receiving antennas, LFMCW waveform parameters, target parameters, and the number of sampling points for each channel. Here, a three-transmit and four-receive MIMO system is adopted, the sweep time of the LFMCW waveform is 10e-6 seconds, the starting frequency of the LFMCW waveform is 76.5e9Hz, the slope of the LFMCW waveform is 30e12, the number of sweep cycles is 512, the distance (meters), speed (meters / second), and angle (degrees) of the three targets are (100, -20, 0), (50, 10, 0), and (50, 70, 0), respectively. The number of sampling points in the distance dimension is 256, and the number of sampling points in the Doppler dimension is 512.

[0059] S2. Constructing the vehicle-mounted DDMA-MIMO signal model:

[0060] According to the system parameters of step S1, the number of empty bands is 1, and the DDMA-MIMO transmission signal and echo signal model is constructed. The DDMA-MIMO radar signal transmission diagram is as follows: Figure 2 shown.

[0061] S3, Range-Doppler 2D-FFT:

[0062] The flow chart of the distance-Doppler 2D-FFT in step S3 is as follows: Figure 3 As shown, the vehicle-mounted DDMA-MIMO signal model is processed by 2D-FFT in the distance dimension and Doppler dimension to obtain the RV-MAP as shown in Figure 4 shown.

[0063] S4, DDMA demodulation:

[0064] The schematic diagram of the multi-target DDMA demodulation method of sub-band unit accumulation in step S4 is as follows: Figure 5 As shown, on the RV-MAP, this method is used to deambiguate the speed, and the demodulated RV-MAP is as follows Figure 7 shown.

[0065] S5. Calculate target information:

[0066] After demodulation, the distance and speed of the target are calculated according to the distance and speed calculation formula.

[0067] The RV-MAP after the multi-target DDMA demodulation method using sub-band unit accumulation is as follows Figure 7 As shown in the figure, compared with the traditional DDMA demodulation algorithm based on Empty-band Figure 6Compared with the conventional method, the advantages are: the DDMA demodulation algorithm based on Empty-band can only retain a certain sub-band, and for multi-target scenes in different sub-bands, the speed calculation will always fail. The multi-target DDMA demodulation method based on sub-band unit accumulation provided by the present invention can well handle the situation that the traditional algorithm cannot be applied to the multi-target scene, and correctly calculate the distance and correct speed of the target.

Claims

1. A multi-target DDMA demodulation method based on subband unit accumulation, characterized in that: The following steps are involved: S1. Build the vehicle-mounted DDMA-MIMO system and initialize the system parameters, including: the number of transmitting antennas M, the number of receiving antennas N, the sweep time T of the LFMCW waveform c , the starting frequency f0 of the LFMCW waveform, the slope μ of the LFMCW waveform, the number of sweep cycles K, the target distance r, the target speed v, the target angle θ, the number of sampling points P in the distance dimension r and the number of Doppler sampling points P v ; S2. All transmitting antennas in the system transmit simultaneously, and the signal of each transmitting antenna is Doppler frequency offset so that the signals of different transmitting antennas are separated in the Doppler domain; according to the system parameters set in step S1, the waveform of the mth transmitting antenna is obtained as follows: where f m represents the Doppler frequency offset of the mth transmitting antenna; The entire Doppler pulse repetition frequency PRF is divided into M orthogonal sub-repetition frequency channels, and the bandwidth of each channel is Then f m for: The introduction of null bands changes the Doppler frequency offset of each transmitting antenna. For the number of null bands introduced, band The selection should be based on the number of transmitting antennas M and the number of Doppler domain sampling points P currently configured. v Taking all factors into consideration, it is necessary to ensure that the number of Doppler units allocated to each subband is an integer. In this case, the Doppler frequency offset f of the mth transmitting antenna is m for: The echo signal received by the nth receiving antenna is the sum of the echoes of the transmission signals of the M transmitting antennas: Where t represents the echo delay of the radar signal transmitted by the target; After mixing the echo signal with a single-frequency signal with a frequency of f0 and performing low-pass filtering, the baseband complex signal model obtained by removing the carrier frequency is: S3, Range-Doppler 2D-FFT: After obtaining the target mixing data based on the DDMA-MIMO mechanism, first perform FFT on each pulse to generate the distance dimension data, and then perform FFT on the data on each distance unit, that is, perform FFT on the Doppler dimension to obtain the velocity dimension data; after completing such a two-dimensional FFT, the range-Doppler spectrum of the environment and the target obtained by the radar in this frame time, that is, RV-MAP, can be obtained. In each angle domain, the size of the matrix RV-MAP is P r ×P v ; S4, DDMA demodulation: By introducing the empty band in step S2, the entire RV-MAP is evenly divided into M+E band subbands, each subband has a length of P s =P v / (M+E band ), when performing target mapping, the correct target position will be taken as the starting point, and the target will appear in M-1 consecutive sub-bands on the right, and the left side of the correct target will be continuous E band The sub-band has no target falling into it, and the energy of the sub-band with no target falling into it is lower than the energy of the remaining M sub-bands with target signals falling into it; In each angle domain, the entire RV-MAP is copied so that the size of the new RV-MAP is P r ×2P v , the energy of each cell is expressed as S(r i ,v i ,sb i )(1≤r i ≤P r ,1≤v i ≤P s ,1≤sb i ≤M+E band ) represents, where ri represents the distance index, vi represents the Doppler index, and sbi represents the subband index; the cumulative energy S of each subband unit group G (r i ,v i ,sb i )as follows: Find the maximum energy S max , and the corresponding subband index S index S max =max(S G (r i ,v i ,sb i ),S G (r i ,v i ,sb i +1),…,S G (r i ,v i ,sb i +M)) S index =p Wherein, it represents the function that obtains the maximum max(·) value, and p represents the subband index corresponding to the accumulated subband group with the highest energy; Use S max =S G (r i ,v i ,p) as the input of the detector, and the value related to the average background noise energy value of RV-MAP is used as the threshold T. The output of the detector is expressed as: In the original size P r ×P v On the RV-MAP, the correct sub-band where the target is located is obtained according to the sub-band index corresponding to the target whose sub-band unit accumulated energy is higher than the threshold T, and the distance and Doppler index value position energy corresponding to the remaining sub-band units are set to 0 to obtain the final RV-MAP; S5. Calculate the target information: Record the distance index value r where the energy on the demodulated RV-MAP is not zero i and the Doppler index value v i , 1≤r i ≤P r , 1≤v i ≤P v , according to the distance calculation formula and speed calculation formula, calculate the correct distance and speed of the target: R=r i ·R res V=(v i -P v / 2)·V res Where R res Indicates the distance resolution, V res Indicates the speed resolution.

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