A multi-target ddma demodulation method based on sub-band unit accumulation

Abstract

The application 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 2D FFT processing of distance dimension and Doppler dimension is performed on the received signals. Then, the multi-target DDMA demodulation method based on sub-band unit accumulation is used for demodulation, and the characteristics are that under each angle domain, the whole RV-MAP is copied, the energy of each unit cell of all sub-bands is recorded, and energy accumulation of cyclic shift with a length of the number of transmitting antennas is performed to obtain the sub-band group energy of each unit. Then, the maximum accumulated energy of each unit sub-band group is found, threshold judgment is performed according to the energy to obtain the correct sub-band where the target is located. Finally, the real distance and speed of the target are calculated according to the distance formula and the speed formula. The method provided by the application can well process the case that the traditional method cannot be applied to the multi-target scene.

Description

Technical Field

[0001] This invention belongs to the field of radar signal processing technology, specifically relating to a multi-target DDMA demodulation method based on sub-band unit accumulation. Background Technology

[0002] Traditional vehicle-mounted MIMO signals mostly use Time Division Multiple Access (TDMA-MIMO) transmission. Its principle involves alternating signal transmissions from different single antennas, resulting in inefficient use of time resources. This limits TDMA waveforms to short-range, low-resolution radar applications. Slow Time MIMO, on the other hand, is a special system where the waveforms of different array elements are orthogonal throughout the coherent accumulation time, and individual pulses are coherent. Doppler Frequency Division Multiple Access (DDMA) waveforms effectively overcome the shortcomings of TDMA. Unlike TDMA, where single antennas work alternately, DDMA allows all transmitting antennas to transmit simultaneously, but each antenna's signal is subject to a specific frequency offset. This artificial frequency offset separates the signals from different antennas in the Doppler domain; this separation is called DDMA demodulation. Without DDMA demodulation, velocity ambiguity occurs. Currently, commonly used DDMA demodulation algorithms are based on Empty-band demodulation. This method performs well for single-target velocity calculations; however, for multi-target scenarios, Empty-band DDMA may not demodulate correctly. Therefore, research on DDMA demodulation algorithms is of great significance in the field of vehicle-mounted millimeter-wave radar signal processing. Summary of the Invention

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

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

[0005] Initialize system parameters, including: number of transmit and receive antennas, LFMCW waveform parameters, target parameters, and number of sampling points for each channel.

[0006] S2. Constructing an onboard DDMA-MIMO signal model:

[0007] Based on the system parameters in step S1, construct the transmit and echo signal models for DDMA-MIMO.

[0008] S3, Distance-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, i.e., RV-MAP.

[0010] S4, DDMA demodulation:

[0011] On RV-MAP, a multi-target DDMA demodulation method based on sub-band unit accumulation is used to deblur the velocity.

[0012] S5. Solve for target information:

[0013] Based on the distance and speed calculation formulas, the distance and speed of the target can be calculated.

[0014] Furthermore, the specific method for step S1 is as follows:

[0015] Initialize system parameters, including: number of transmit antennas Number of receiving antennas LFMCW waveform sweep time The starting frequency of the LFMCW waveform The slope of the LFMCW waveform Number of sweep cycles Target distance Target speed Target perspective Number of sampling points in the distance dimension and Doppler sampling points .

[0016] Furthermore, the specific method for step S2 is as follows:

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

[0018]

[0019] in Indicates the first Doppler frequency offset of the root transmitting antenna.

[0020] DDMA waveforms are waveforms that can be orthogonalized after Doppler processing at the receiving end, relying on... The changes achieve orthogonality in the Doppler domain. Consider dividing the entire Doppler pulse repetition frequency (PRF) into... There are 3 orthogonal sub-repetition frequency channels, each with a bandwidth of 1. ,So for

[0021]

[0022] To address the speed ambiguity issue in DDMA-MIMO, an empty band is first introduced to alter the Doppler frequency offset of each transmit antenna. The number of empty bands introduced... The selection depends on the number of transmitting antennas. And the number of Doppler domain sampling points currently configured 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 point, the... Doppler frequency offset of the root transmitting antenna for

[0023]

[0024] When constructing the target echo signal, the first The echo signal received by the root receiving antenna is The sum of the echoes of the transmitted signals from the root transmitting antennas. Ignoring amplitude attenuation, the... The received echo signal from the root receiving antenna is

[0025]

[0026] in This indicates the time delay of the radar signal transmitted back after passing through the target.

[0027] Interact the echo signal with a frequency of After the single-frequency signal is mixed and low-pass filtered, the baseband complex signal model obtained by removing the carrier frequency is as follows:

[0028]

[0029] Furthermore, the specific method for step S3 is as follows:

[0030] After obtaining the target mixing data based on the DDMA-MIMO mechanism, firstly, an FFT is performed on each pulse individually to generate range-dimensional data. Then, an FFT is performed on the data in each range cell, i.e., an FFT is performed in the Doppler dimension to obtain the velocity-dimensional data. After completing this one two-dimensional FFT, the range-Doppler spectrum of the environment and target obtained by the radar in this frame can be obtained, i.e., RV-MAP. In each angular domain, the size of the RV-MAP matrix is... .

[0031] Furthermore, the specific method for step S4 is as follows:

[0032] The introduction of the empty band in step S2 divides the entire RV-MAP uniformly along the Doppler domain into There are 1 sub-bands, each sub-band having a length of 1. When performing target mapping, a sequence will appear starting from the correct target location and continuing to the right. The target appears in each sub-band (if it exceeds the first sub-band) If there are multiple sub-bands, then the next sub-band will continue to appear. The correct target's left side will then be continuously... Subbands without a target fall in (if it exceeds the first subband, it continues from the last subband), and the energy of a subband without a target falling in must be lower than the others. The energy of a subband into which a target signal falls.

[0033] In each angle domain, the entire RV-MAP is copied, resulting in a new RV-MAP of size [size missing]. The energy of each cell is used It means that among them Indicates distance index, Indicates Doppler index, Indicates the subband index. The cumulative energy of each subband unit group. as follows

[0034]

[0035] Find the greatest energy and the corresponding sub-band index

[0036]

[0037] in A function that takes the maximum value; This indicates the subband index corresponding to the subband group with the highest accumulated energy.

[0038] use As input to the detector, a value related to the average background noise energy of the RV-MAP is used as the threshold. Then the detector output can be expressed as:

[0039]

[0040] In the original size On the RV-MAP, based on the sub-band unit accumulated energy exceeding the threshold The target's subband index is used to obtain the correct subband where the target is located. The distance and Doppler index values ​​of the other subband cells are set to 0, thus obtaining the final RV-MAP.

[0041] Furthermore, the specific method of step S5 is as follows:

[0042] Record the distance index values ​​on the demodulated RV-MAP where the energy is not zero. and Doppler index value Based on the distance and velocity calculation formulas, the correct distance and velocity of the target are calculated. The formulas are as follows:

[0043]

[0044] in Represents distance unit, ; Represents velocity unit, .in, Indicates the bandwidth of the transmitted signal. Indicates the duration of the transmitted signal.

[0045] Compared to existing technologies and traditional Empty-band-based DDMA demodulation algorithms, this invention provides a multi-target DDMA demodulation method based on subband cell accumulation. Traditional Empty-band-based DDMA demodulation algorithms are suitable for single-target scenarios or multi-target scenarios where the velocities are within the same subband; however, they are prone to velocity calculation errors in other scenarios. Using the algorithm provided by this invention, in multi-target scenarios, regardless of whether the targets are in the same or different subbands, this invention can accurately calculate the target's velocity. Attached Figure Description

[0046] Figure 1 This is a flowchart of a multi-target DDMA demodulation method based on subband unit accumulation according to the present invention.

[0047] Figure 2 This is a diagram of DDMA-MIMO signal transmission in step S2.

[0048] Figure 3 The flowchart for distance-Doppler 2D-FFT in step S3.

[0049] Figure 4 This is the RV-MAP image after distance-Doppler 2D-FFT in step S3.

[0050] Figure 5 This is a schematic diagram of a multi-target DDMA demodulation method for subband unit accumulation in step S4.

[0051] Figure 6 The RV-MAP after step S4 uses the Empty-band-based DDMA demodulation algorithm.

[0052] Figure 7The RV-MAP is the result of the multi-target DDMA demodulation method accumulated using the sub-band unit in step S4. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0054] like Figure 1 The flowchart shown illustrates a multi-target DDMA demodulation method based on subband unit accumulation, comprising the following steps:

[0055] S1. Initialize system parameters:

[0056] Initialize system parameters, including: number of transmit and receive antennas, LFMCW waveform parameters, target parameters, and number of sampling points for each channel. A three-transmit, four-receive MIMO system is used here, and the LFMCW waveform sweep time is... The starting frequency of the LFMCW waveform is [number] seconds. Hz, slope of LFMCW waveform The number of frequency sweep cycles is 512. The distance (meters), velocity (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.

[0057] S2. Constructing an onboard DDMA-MIMO signal model:

[0058] Based on the system parameters in step S1, with an empty band number of 1, a DDMA-MIMO transmit and echo signal model is constructed. The DDMA-MIMO radar signal transmission diagram is shown below. Figure 2 As shown.

[0059] S3, Distance-Doppler 2D-FFT:

[0060] The distance-Doppler 2D-FFT flowchart for step S3 is as follows: Figure 3 As shown, the obtained vehicle-mounted DDMA-MIMO signal model is processed by 2D-FFT in the range dimension and Doppler dimension to obtain the RV-MAP. Figure 4 As shown.

[0061] S4, DDMA demodulation:

[0062] A schematic diagram of the multi-target DDMA demodulation method for sub-band unit accumulation in step S4 is shown below. Figure 5 As shown, this method is used to deblur velocity on RV-MAP, and the demodulated RV-MAP is as follows. Figure 7 As shown.

[0063] S5. Solve for target information:

[0064] After demodulation, the distance and velocity of the target are calculated using the distance and velocity calculation formulas.

[0065] RV-MAP after using the multi-target DDMA demodulation method with sub-band unit accumulation is as follows: Figure 7 As shown, compared with the traditional Empty-band-based DDMA demodulation algorithm... Figure 6 In comparison, its advantage lies in the fact that the Empty-band-based DDMA demodulation algorithm can only retain one subband, and for multi-target scenarios in different subbands, velocity calculation failures will always occur. The multi-target DDMA demodulation method based on subband unit accumulation provided by this invention can effectively handle situations where traditional algorithms are not applicable to multi-target scenarios, and correctly calculate the target's distance and velocity.

Claims

1. A multi-target DDMA demodulation method based on subband unit accumulation, characterized in that, Includes the following steps: S1. Construct the vehicle-mounted DDMA-MIMO system and initialize system parameters. System parameters include: number of transmit antennas. Number of receiving antennas LFMCW waveform sweep time The starting frequency of the LFMCW waveform The slope of the LFMCW waveform Number of sweep cycles Target distance Target speed Target perspective Number of sampling points in the distance dimension and Doppler sampling points ; S2. All transmitting antennas in the system transmit simultaneously. The signal from each transmitting antenna is Doppler frequency offset so that the signals from different transmitting antennas are separated in the Doppler domain; based on the system parameters set in step S1, the first... The waveform of the transmitting antenna is as follows: ， in Indicates the first Doppler frequency offset of the root transmitting antenna; The entire Doppler pulse repetition frequency (PRF) is divided into... There are 3 orthogonal sub-repetition frequency channels, each with a bandwidth of 1. ,but for: ， Introducing empty bands alters the Doppler frequency offset of each transmitting antenna; the number of empty bands introduced affects this effect. The selection depends on the number of transmitting antennas. And the number of Doppler domain sampling points currently configured Taking all factors into consideration, it is necessary to ensure that the number of Doppler units allocated to each sub-band is an integer. In this case, the [number of units]th [sub-band]... Doppler frequency offset of the root transmitting antenna for: ， No. The echo signal received by the root receiving antenna is The sum of the echoes from the transmitted signals of the root transmitting antenna: ， in This indicates the time delay of the radar signal transmitted back after passing through the target; The echo signal and the frequency are The baseband complex signal model obtained after low-pass filtering and removal of the carrier frequency from the single-frequency signal mixing is as follows: ； S3, Distance-Doppler 2D-FFT: After obtaining the target mixing data based on the DDMA-MIMO mechanism, firstly, an FFT is performed on each pulse individually to generate range-dimensional data. Then, an FFT is performed on the data in each range cell, i.e., an FFT is performed in the Doppler dimension to obtain the velocity-dimensional data. After completing this one two-dimensional FFT, the range-Doppler spectrum of the environment and target obtained by the radar in this frame can be obtained, i.e., RV-MAP. In each angular domain, the size of the RV-MAP matrix is... ; S4, DDMA demodulation: By introducing the empty band in step S2, the entire RV-MAP is uniformly divided along the Doppler domain. There are 1 sub-bands, each sub-band having a length of 1. When performing target mapping, a sequence of values ​​will appear starting from the correct target location and continuing to the right. The target appears in the sub-band, and the correct target is continuously to the left of it. Subbands with no target falling in, where the energy of the subbands with no target falling in is lower than the others. The energy of a subband into which a target signal falls; In each angle domain, the entire RV-MAP is copied, resulting in a new RV-MAP of size [size missing]. The energy of each cell is used It means that among them , Indicates distance index, Indicates Doppler index, Indicates the subband index; the cumulative energy of each subband unit group. as follows: ， Find the greatest energy and the corresponding sub-band index : ， in This represents a function that takes the maximum value. This indicates the subband index corresponding to the subband group with the highest accumulated energy; use As input to the detector, a value related to the average background noise energy of the RV-MAP is used as the threshold. The detector output is represented as: ， In the original size On the RV-MAP, based on the sub-band unit accumulated energy exceeding the threshold The target's subband index is used to obtain the correct subband where the target is located. The energy of the distance and Doppler index values ​​of the other subband cells is set to 0 to obtain the final RV-MAP. S5. Solve for the target information: Record the distance index values ​​on the demodulated RV-MAP where the energy is not zero. and Doppler index value , , Based on the distance and velocity calculation formulas, the correct distance and velocity of the target can be calculated: ， in Indicates distance resolution. Indicates speed resolution.

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