A clutter map constant false alarm rate detection method based on DDMA-MIMO

Abstract

The application belongs to the technical field of radar detection, and particularly relates to a clutter map constant false alarm detection method based on DDMA-MIMO. In a measured scene, 2D-FFT processing of Doppler and distance dimensions is performed on data of the n+1th frame under the DDMA-MIMO system to obtain a range-Doppler spectrum (i.e. RV-MAP). In order to avoid velocity ambiguity, the RV-MAP is demodulated based on the Empty-band DDMA method. In this process, in order to reduce the influence of scene clutter on detection performance, the clutter map of the nth frame is combined with the demodulated data of the n+1th frame to perform constant false alarm detection (CFAR), and finally, the clutter map of the n+1th frame is updated in combination with the RV-MAP of the n+1th frame and the clutter map of the nth frame. Through measured data verification, after the traditional CFAR algorithm is performed, targets and clutter and noise are retained in the RV-MAP, while after the clutter map constant false alarm detection method is adopted, more clutter data is filtered out, and target data is retained. At the same time, due to the filtering of the clutter data, the target detection rate is improved.

Description

A clutter map constant false alarm rate detection method based on DDMA-MIMO Technical Field

[0001] This invention belongs to the field of radar signal processing technology, specifically relating to a clutter map constant false alarm rate detection method based on DDMA-MIMO. Background Technology

[0002] Constant false alarm rate (CFAR) detection exhibits excellent detection performance when the number of reference cells and the uniform width of clutter are matched, making it an important component of radar signal processing systems. However, for clutter with drastic variations in clutter intensity across range and azimuth, and a narrow uniform width, such as ground object clutter, the CFAR loss increases rapidly as the number of reference cells decreases, rendering traditional CFAR unsuitable. Clutter map CFAR processing, on the other hand, iteratively processes echo samples from previous scans over time to estimate the current clutter background intensity, achieving CFAR detection. Therefore, it is suitable for spatially non-uniform but temporally stable clutter. Clutter map CFAR processing has wide applications in radar moving target detection, enhancing the detection performance of radar signal processing systems. Summary of the Invention

[0003] The purpose of this invention is to provide a clutter map constant false alarm rate (CFAR) detection method based on DDMA-MIMO for vehicle-mounted DDMA-MIMO radar systems, in order to improve their target detection performance. The method includes the following steps:

[0004] S1. Initialize system parameters:

[0005] Initialize system target parameters and clutter parameters. The target parameters include target range, target velocity, and target angle. The clutter parameters include radar altitude above the ground and limitations on the clutter introduction range.

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

[0007] The vehicle-mounted DDMA-MIMO signal model includes target modeling and clutter modeling. Based on the target parameters and clutter parameters in step S1, the DDMA-MIMO transmit and echo signals are constructed.

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

[0009] The obtained echo signal of the vehicle-mounted DDMA-MIMO 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-MIMO demodulation:

[0011] Because all radar transmitting antennas transmit signals simultaneously under the DDMA-MIMO system, if demodulation is not performed after 2D-FFT, velocity ambiguity will occur, making it impossible to obtain the correct velocity of the target.

[0012] S5, Clutter Map Constant False Alarm Rate Detection:

[0013] The Nitzberg clutter map CFAR algorithm is used to filter out clutter, leaving only the target parameters on the RV-MAP to achieve target detection.

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

[0015] Initialize system target parameters and clutter parameters, wherein the target parameters include: target range. Target speed and target angle The clutter parameters include: the radar's altitude above the ground. The range of clutter introduction is within and Between, among Indicates the initial distance at which clutter is introduced. This indicates the distance at which clutter is introduced.

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

[0017] First, a transmission signal based on the DDMA-MIMO system is constructed. In the DDMA-MIMO system, all transmitting antennas transmit simultaneously, and the signal from each transmitting antenna is Doppler frequency offset so that the signals from different transmitting antennas are separated in the Doppler domain. Assume the MIMO radar is... hair Received, and the waveform adopts linear frequency modulated continuous wave (LFM), then the first The waveform of the root transmitting antenna is

[0018]

[0019] in Indicates the first One sweep frequency cycle, total One sweep cycle, Indicates the center frequency of radar operation, Indicates the modulation slope of the LFM signal, Indicates the sweep period of the LFM signal, 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 10 ... for ,So for

[0021]

[0022] 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

[0023]

[0024] in This indicates the time delay of the radar signal transmitted back after passing through the target.

[0025] The modeling of radar clutter signals is based on the range of radar clutter introduction. to and radar altitude Calculate the radar antenna angle corresponding to each clutter element, and divide the ground elements accordingly. Assume that the number of clutter elements after division is... Then the echo data of the clutter cell can be represented as

[0026]

[0027] In the formula The time delay represents the distance between the clutter element and the center of the radar array. Therefore, clutter can be modeled as...

[0028]

[0029] Ultimately, this causes radar clutter signals to be superimposed onto the target echo data.

[0030]

[0031] Furthermore, the specific method for step S3 is as follows:

[0032] After obtaining the target and clutter echo data based on the DDMA-MIMO mechanism, an FFT is first performed on each pulse to generate range dimension 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 dimension data. After completing such a 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.

[0033] Furthermore, the specific method for step S4 is as follows:

[0034] To address the Doppler ambiguity issue in DDMA-MIMO, an Empty-band DDMA demodulation algorithm can be used. Empty-band DDMA involves dividing the Doppler frequency domain into sections when setting the Doppler frequency offset for each transmit antenna. The simple linear form of a channel of equal width is achieved by adding one or two Empty subbands to the number of transmit antennas. The choice of the number of Empty subbands depends on the number of transmit antennas. Considering both the current configured number of Doppler domain sampling points and the overall number of Doppler units allocated to each sub-band, it is necessary to ensure that the number of Doppler units assigned to each sub-band is an integer. At this point, the [number of units]... Doppler frequency offset of the root transmitting antenna for

[0035]

[0036] The introduction of the empty band divides the entire RV-MAP uniformly along the Doppler domain into segments that allow for... In target mapping, a sub-band will appear, starting from the correct target position and extending continuously 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 each sub-band into which the target signal falls. Based on this pattern, we can assume the energy of each sub-band is... ,right The execution length of each sub-band is The energy accumulation of the cyclic shifts yields the energy of each sub-band group.

[0037]

[0038] Find the maximum subband energy Based on the index number of the maximum value Find the target in the first He has a belt.

[0039] Furthermore, the specific method of step S5 is as follows:

[0040] To filter out the influence of stationary clutter in the scene on the target detection, unlike the traditional constant false alarm rate (CFAR) detection algorithm, this method introduces a clutter map approach. The main idea is to combine the sub-band data in the RV-MAP of each frame during radar processing, extract and record the clutter data in the scene in real time, and finally use it for detection and judgment in the current processing frame. Therefore, the dimension of the clutter map is always the same as the sub-band dimension in the RV-MAP after processing in step S4.

[0041] For the first frame of data, the sub-band data set in the RV-MAP obtained after processing in step S4 will be... Assigned to the clutter map data of frame 1 Then proceed to the processing of the second frame.

[0042] Let the first The sub-band data set obtained after processing the frame data in step S4 is the RV-MAP. ,forward The clutter map formed by subband data in frame RV-MAP is Assuming a set The Middle The amplitude at each point is clutter diagram The Middle The amplitude at each point is First, constant false alarm rate (CFAR) detection is performed. The Middle Points Calculate its detection threshold ,in The threshold coefficient is determined by the following formula:

[0043]

[0044] In the formula For false alarm probability, For the current number of frames processed and Forgetting factor. Comparison and The amplitude, if Medium to large If the target exists in the data of that sub-band, then it is determined that the target does not exist; otherwise, it is determined that the target does not exist.

[0045] After the above steps, the target detection process of the clutter map constant false alarm rate algorithm is completed. The next step is to combine it with the previous steps. Frame clutter diagram With the Subband data set in frame RV-MAP and the Frame detection results, iteratively update the first frame. Frame clutter diagram When the first Point at If a frame is not detected and is determined to be a target, the update method is as follows:

[0046]

[0047] If it is detected as a target, the update method is as follows:

[0048]

[0049] The obtained clutter map Used as the first The sub-band data set in RV-MAP obtained after frame step S4 processing The detection and judgment.

[0050] Compared to existing technologies and traditional constant false alarm rate (CFAR) detection algorithms, this invention provides a clutter map-based CFAR CFAR detection method based on DDMA-MIMO. When using traditional CFAR for detection, in environments with strong changes in clutter in range and azimuth, the CFAR loss increases rapidly with the decrease in the number of references, and the obtained CFAR results contain non-target clutter points. However, the clutter map-based CFAR CFAR detection method provided by this invention, in the context of vehicle-mounted DDMA-MIMO, can iteratively process the echo sample values ​​obtained from previous scans over time to estimate the current clutter background intensity, thereby filtering out clutter background from the echo signal and improving the detection performance of the CFAR algorithm. Attached Figure Description

[0051] Figure 1 is a flowchart of a clutter map constant false alarm rate detection method based on DDMA-MIMO according to the present invention.

[0052] Figure 2 shows the DDMA-MIMO signal transmission diagram in step S2.

[0053] Figure 3 is a schematic diagram of clutter simulation in step S2.

[0054] Figure 4 is a flowchart of the distance-Doppler 2D-FFT process in step S3.

[0055] Figure 5 shows the DDMA-MIMO velocity ambiguity RV-MAP in step S4.

[0056] Figure 6 shows the RV-MAP after DDMA-MIMO demodulation in step S4.

[0057] Figure 7 shows the clutter map constant false alarm detector diagram in step S5.

[0058] Figure 8 shows an RV-MAP using a traditional CFAR.

[0059] Figure 9 shows the RV-MAP using the clutter map constant false alarm rate detection method of the present invention. Detailed Implementation

[0060] 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.

[0061] In practical implementation, the AWR2243 millimeter-wave radar cascade platform manufactured by TI is used, employing a 3-transmit, 4-receive MIMO system with an Empty-band number of 1. Figure 1 shows a flowchart of a clutter map constant false alarm rate (CFAR) detection method based on DDMA-MIMO, including the following steps:

[0062] S1. Initialize system parameters:

[0063] Initialize the system target parameters and clutter parameters. The target parameters include: target distance of approximately 2.7 meters, target speed of approximately 6 meters per second, and target angle of 0 degrees. The clutter parameters include: radar height above the ground of 60 centimeters, and clutter is related to the actual field measurement environment.

[0064] S2. Constructing an onboard DDMA-MIMO signal model:

[0065] Step S2 involves modeling the vehicle-mounted DDMA-MIMO signal, including target modeling and clutter modeling. The radar signal transmission diagram is shown in Figure 2, and the clutter simulation diagram is shown in Figure 3. The DDMA-MIMO transmission signal is then constructed.

[0066] S3, Distance-Doppler 2D-FFT:

[0067] The distance-Doppler 2D-FFT flowchart for step S3 is shown in Figure 4. The obtained vehicle-mounted DDMA-MIMO signal model is processed by 2D-FFT in the distance dimension and Doppler dimension to obtain RV-MAP.

[0068] S4, DDMA-MIMO demodulation:

[0069] Because all radar transmitting antennas transmit signals simultaneously in the DDMA-MIMO system, if demodulation is not performed after 2D-FFT, a velocity ambiguity RV-MAP will appear as shown in Figure 5, resulting in three target velocities. After using the Empty-band-based DDMA demodulation algorithm, since the real target is in sub-band 3, the data from sub-band 3 is retained, resulting in the demodulated RV-MAP shown in Figure 6.

[0070] S5, Clutter Map Constant False Alarm Rate Detection:

[0071] The clutter map constant false alarm rate detector diagram of step S5 is shown in Figure 7. The Nitzberg clutter map CFAR algorithm is used to filter out clutter and retain only the target parameters on the RV-MAP.

[0072] Figure 9 shows the RV-MAP after applying the clutter map constant false alarm rate (CFAR) detection method. Compared with Figure 8, which uses the commonly used traditional CFAR algorithm, its advantages are as follows: After the traditional CFAR algorithm, the target, clutter, and noise are retained in the RV-MAP, while the clutter map CFAR detection method filters out more clutter data and retains the target data. Furthermore, the removal of clutter data improves the target detection rate, which is calculated by dividing the number of targets by the sum of the number of non-targets and the number of targets.

Claims

1. A clutter map constant false alarm rate detection method based on DDMA-MIMO, characterized in that, Includes the following steps: S1. Initialize system parameters: Initialize system target parameters and clutter parameters. The target parameters include: target distance. Target speed and target angle The clutter parameters include: the radar's altitude above the ground. The range of clutter introduction is within and Between, among Indicates the initial distance at which clutter is introduced. This indicates the termination distance of the introduced clutter; S2, Constructing the vehicle-mounted DDMA-MIMO signal model: First, construct the transmission signal based on the DDMA-MIMO system. In 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; Assuming the MIMO radar is... hair Received, and the waveform adopts linear frequency modulated continuous wave (LFM), then the first The waveform of the transmitting antenna is as follows: ,in Indicates the first One sweep frequency cycle, total One sweep cycle, Indicates the center frequency of radar operation, Indicates the modulation slope of the LFM signal, Indicates the sweep period of the LFM signal, Indicates the first The Doppler frequency is offset by the transmitting antenna; the DDMA waveform is processed by Doppler at the receiving end to achieve orthogonal waveforms, 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 10 ... for ， for: 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 first transmitting antenna; neglecting amplitude attenuation, the... The echo signal received by the root receiving antenna is: ,in This represents the echo delay of the radar transmitted signal after passing through the target and returning; while the modeling of radar clutter signals is based on the range of radar clutter introduction. to and radar altitude Calculate the radar antenna angle corresponding to each clutter element, and divide the ground elements accordingly. Assume that the number of clutter elements after division is... The echo data of the clutter cell is represented as follows: In the formula The time delay represents the distance between the clutter element and the center of the radar array; the clutter is modeled as: This ultimately causes radar clutter signals to be superimposed on the target echo data: S3, Range-Doppler 2D-FFT: After obtaining target and clutter echo data based on the DDMA-MIMO mechanism, firstly, FFT is performed on each pulse individually to generate range dimension data, and then FFT is performed on the data in each range cell, i.e., FFT is performed in the Doppler dimension to obtain velocity dimension data; after completing such a two-dimensional FFT, the range-Doppler spectrum of the environment and target obtained by the radar in this frame is obtained, defined as RV-MAP; S4, DDMA-MIMO Demodulation: Using the Empty-band-based DDMA demodulation algorithm, when setting the Doppler frequency offset of each transmitting antenna, the Doppler frequency domain is divided into The simple linear form of a channel of equal width involves adding one or two Empty subbands to the number of transmit antennas. The choice of the number of Empty subbands depends on the number of transmit antennas. Considering the current configuration of the number of Doppler domain sampling points, 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 of the root transmitting antenna for: The introduction of the Empty Band divides the entire RV-MAP uniformly along the Doppler domain into... When mapping targets, a sub-band will appear with the correct target position as the starting point, and the right side will be continuous. The target appears in the sub-band, and the correct target is continuously to the left of it. Subbands fall into the subband without a target, and the energy of a subband falling into the subband without a target must be lower than that of the others. The energy of each sub-band into which the target signal falls; based on this rule, the energy of each sub-band is defined as... ,right The execution length of each sub-band is The energy of each subband group is obtained by accumulating the energy from the cyclic shifts: Find the energy of the largest subband. Based on the index number of the maximum value Find the target in the first Sub-band; S5, Clutter Map Constant False Alarm Rate Detection: Using the Nitzberg clutter map CFAR algorithm, clutter is filtered out, and only the target parameters are retained on the RV-MAP to achieve target detection.

2. The clutter map constant false alarm rate detection method based on DDMA-MIMO according to claim 1, characterized in that, The specific method of S5 is to extract and record clutter data in the scene in real time by combining the sub-band data in the RV-MAP of each frame during radar processing, and finally use it for detection and judgment of the current processing frame. The dimension of the clutter map is always the same as the sub-band dimension of the RV-MAP after processing in step S4. Specifically, for the first frame of data, the sub-band data set of the RV-MAP obtained after processing in step S4 is... Assigned to the clutter map data of frame 1 Then proceed to the processing of the second frame; Let the first The sub-band data set obtained after processing the frame data in step S4 is the RV-MAP. ， ,forward The clutter map formed by subband data in frame RV-MAP is Define a set The Middle The amplitude at each point is clutter diagram The Middle The amplitude at each point is First, constant false alarm rate (CFAR) detection is performed. The Middle Points Calculate its detection threshold ,in Represents the threshold coefficient: In the formula This represents the probability of a false alarm. The current number of frames being processed. Forgetting factor; comparison and The amplitude, if Greater than If the target is not detected, it is determined that the target exists in the sub-band data; otherwise, it is determined that the target does not exist. After completing the target detection, the next step is to combine the previous data... Frame clutter diagram With the Subband data set in frame RV-MAP and the Frame detection results, iteratively update the first frame. Frame clutter diagram When the first Point at If a frame is not detected as a target, the update method is as follows: If it is detected as a target, the update method is as follows: The resulting clutter map Used as the first The sub-band data set in RV-MAP obtained after frame step S4 processing The detection and judgment.

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