A method for detecting and alarming living bodies in vehicles based on millimeter-wave radar

Abstract

The present invention relates to the field of radar electronics technology, specifically a method for detecting and alarming a live person in a vehicle based on millimeter-wave radar, comprising the following steps: comparing the normal human respiratory and heart rate range with the detected signal frequency range: an adult's heart rate is between 1Hz and 1.6Hz, and their respiratory rate is between 0.2Hz and 0.4Hz, while a child's heart rate is between 1.7Hz and 2.2Hz, and their respiratory rate is between 0.5Hz and 0.7Hz; starting detection after the vehicle is locked, determining whether the signal matches a child's heart rate and respiratory rate to determine whether a child has been left in the vehicle; if the signal matches a child's heart rate and respiratory rate, a child is detected and a graded alarm is issued. The present invention distinguishes between children and adults based on the difference between a child's respiratory and heart rate and an adult's respiratory and heart rate, thereby triggering an alarm in a targeted manner, thereby achieving the goal of triggering an alarm only when a child is detected to be left behind, thereby reducing the alarm frequency.

Description

Technical Field

[0001] The present invention relates to the field of radar electronic technology, and in particular to a method for detecting and alarming a living body in a vehicle based on millimeter-wave radar. Background Art

[0002] Every summer, babies are left behind in cars and die. These tragedies serve as a wake-up call, and in-car liveness detection has become a new requirement for automakers. With advances in millimeter-wave radar technology, its application for liveness detection has gradually gained traction. To address this issue, major automakers are developing liveness detection radars.

[0003] Application No. 202111188031.0 "A millimeter-wave vehicle occupancy and occupancy monitoring system and method based on life characteristics" includes a vehicle-mounted control system, a door lock detection module, a 79GHz radar module, a communication alarm module, and a window control module, wherein: the door lock detection module detects whether the door is in a locked state when the vehicle is turned off, and transmits the door status information to the vehicle-mounted control system; the vehicle-mounted control system receives the door status information sent by the door lock detection module, and sends an instruction to control the 79GHz radar module to start occupancy and occupancy detection, and controls the communication alarm module and the window control module according to the radar detection results. This patent uses millimeter-wave radar to detect whether there is someone in the car, which is more robust and can resist interference from external factors. When it detects that there is someone in the car after the engine is turned off, it immediately issues an alarm to remind surrounding people and the driver, thereby realizing occupancy and occupancy monitoring in the car.

[0004] While the aforementioned patent can detect live objects inside a vehicle, errors can still occur due to external interference such as cell phone vibrations and fan rotation. Furthermore, the system cannot distinguish between adults and children. Adults are capable of resolving their own difficulties, so the alarm should only be triggered if a child is left behind. For children, keeping the windows closed is equally important to prevent harm to others. Children, however, often sit in child seats, face forward or backward, or are covered in blankets, which further increases the requirements for radar penetration and resolution. Summary of the Invention

[0005] In response to the above technical problems, the present invention proposes a method for in-vehicle liveness detection and alarm based on millimeter-wave radar, which triggers the alarm only when a child is detected to be left behind, thereby reducing the alarm frequency and making it more targeted.

[0006] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0007] A method for detecting and alarming a living body in a vehicle based on a millimeter-wave radar comprises the following steps:

[0008] (1) Use millimeter-wave radar to send signals to living targets and receive target and noise echo signals every 50ms;

[0009] (2) Perform a 1D range FFT on the received echo signal to obtain 32 signals divided by distance. Then perform a 2D Doppler FFT on the echo signal to obtain the target's velocity and angle information.

[0010] (3) Performing CFAR detection on the echo signal by filtering out noise and clutter signals through windowing, and sending the CFAR detected signal in 8-bit form to a computer for phase analysis to restore the signal waveform;

[0011] (4) Perform spectrum analysis on the restored waveform and convert the phase-time spectrum into a frequency-time spectrum through a digital filter and FFT;

[0012] (5) removing other interfering signals by using a windowing and phasor mean cancellation algorithm, separating the respiratory and heartbeat signals from the signal by using a wavelet separation algorithm, reconstructing the waveforms of the separated signals, and estimating the frequencies of the respiratory and heartbeat signals;

[0013] (6) Compare the normal human respiratory and heart rate range with the detected signal frequency range: the heart rate of an adult is 1Hz to 1.6Hz, and the respiratory rate is 0.2Hz to 0.4Hz; the heart rate of a child is 1.7Hz to 2.2Hz, and the respiratory rate is 0.5Hz to 0.7Hz, and the information is stored in the system;

[0014] (7) After the vehicle is locked, the detection begins, and the signal is judged to be consistent with the child's heartbeat and breathing rate, thereby determining whether there is a child left in the vehicle;

[0015] (8) If the signal is determined to be consistent with the heart rate and breathing rate of a child, a child is left in the vehicle and a graded alarm is issued;

[0016] (9) If the signal is determined not to match the heart rate and breathing rate of the child, then there is no child left in the vehicle.

[0017] Preferably, the millimeter wave radar in step (1) is a four-transmit four-receive 60G millimeter wave radar.

[0018] Preferably, the specific process of performing 1D distance fft on the received echo signal in step (2) is:

[0019] (1) Perform one-dimensional Fourier transform to convert the signal into a distance-time spectrum;

[0020] (2) Perform static clutter removal to remove the static background and obtain the original echo signal;

[0021] (3) Divide the signal into 32 units based on distance.

[0022] Preferably, the analysis in step (3) is performed using an analysis algorithm.

[0023] Preferably, the process of removing other interference signals by the phasor mean cancellation algorithm in step (5) is as follows: first, all received pulses are averaged to obtain a reference received pulse, and then the target echo signal is obtained by subtracting the reference received pulse from each beam of received pulses.

[0024] Preferably, the expression of the reference received pulse is:

[0025]

[0026] Among them, i is the fast time dimension sampling point, and m is the slow time dimension time sampling point.

[0027] Preferably, the hierarchical alarm in step (eight) specifically includes a first-level alarm, a second-level alarm, and a third-level alarm.

[0028] Preferably, the first-level alarm is: 10 seconds after locking the car, the horn and headlights sound an alarm, the alarm mode is different from other alarms, and it lasts for 60 seconds or until the alarm is lifted. If the system still determines that a child is present, it will enter the second-level alarm after 10 minutes regardless of whether the alarm is lifted or not.

[0029] Preferably, the second-level alarm is: turn on the air conditioner in the car, close the windows, maintain a comfortable temperature for people, and control the flow of air in and out; at the same time, send a message reminder to the car owner through the Internet or SMS. If it is still determined that a child is present after 20 minutes, the third-level alarm will be entered regardless of whether the alarm is released or not.

[0030] Preferably, the three-level alarm is: both the first and second level alarms are activated, and a call for help is sent to a third party (medical institution, firefighter, etc.) via the Internet or text message, and the alarm is lifted by opening the car door or connecting the mobile phone to the car's Bluetooth or WiFi.

[0031] The beneficial effects of the present invention are:

[0032] 1) Compared with existing cameras and infrared detection methods, the present invention is more reliable and has a higher monitoring success rate, filling a gap in market demand and is a new means;

[0033] 2) The present invention distinguishes children from adults based on the difference in their respiratory and heart rates, thereby triggering an alarm in a targeted manner, thereby achieving the goal of triggering an alarm only when a child is detected to be left behind, thereby reducing the frequency of alarms;

[0034] 3) The present invention can realize multi-person detection and occupancy detection, and has certain anti-interference ability and penetration. The graded alarm not only meets the safety of the people in the car, but also ensures that the owner and relevant personnel can understand the situation in the car at the first time, and solve the problem of people being trapped in the car. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0036] Figure 1 This is a flow chart of radar echo signal processing in the present invention;

[0037] Figure 2 This is a flow chart of the hierarchical alarm mechanism in the present invention. DETAILED DESCRIPTION

[0038] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below with reference to the accompanying drawings and embodiments.

[0039] like Figure 1 As shown, a method for detecting and alarming a living body in a vehicle based on a millimeter-wave radar is described, and the specific steps are as follows:

[0040] (1) Radar Transmitted Signal: A four-transmitter, four-receiver 60GHz millimeter-wave radar transmits the signal. Every 50 milliseconds, the radar receives all echo signals, including target and noise clutter, and performs a one-dimensional Fourier transform to convert the signal into a range-time spectrum. Static clutter removal and background noise removal are then performed to obtain the original echo signal, which is then divided into 32 signal units based on distance.

[0041] (2) Doppler demodulation is performed on the processed signals to obtain the frequency and velocity of each signal. The rise and fall of the chest during breathing and the pulsation of the heart during heartbeat are reflected on the radar as changes in relative distance. Due to the different periods and amplitudes, these changes can be distinguished and represented as the sum of a series of harmonics.

[0042] (3) CFAR (Constant False Alarm Ratio) (CFAR) detection is performed on the signal, using the average power value as the threshold to filter out radar clutter and external noise within each range cell. After CFAR detection, the signal's noise power is further reduced. The CFAR-detected signal is then sent to a computer in 8-bit format for phase analysis. The signal is then reconstructed using an analysis algorithm, resulting in a phase-time spectrum signal.

[0043] (4) All signals are passed through a designed digital filter to remove clutter and noise outside the required range, and the phase spectrum is converted into a frequency spectrum through an FFT. The zero-frequency DC component is filtered out by subtracting the average amplitude of each signal to obtain the signal to be processed.

[0044] Not all 32 signals have frequencies, so focus on the few signals in the frequency spectrum. The principle of the phasor mean cancellation algorithm is that the distance from the stationary target to the radar antenna is constant, and the time delay of the stationary target on each beam of received pulses is also constant. The reference received pulse can be obtained by averaging all received pulses, and then the target echo signal can be obtained by subtracting the reference received pulse from each beam of received pulses. The core idea is to calculate the mean and make a difference. The implementation process is: first, average all received pulses to obtain the reference received pulse, and then subtract the reference received pulse from each beam of received pulses to obtain the target echo signal. The expression of the reference received pulse is:

[0045]

[0046] Among them, i is the fast time dimension (distance dimension) sampling point, m is the slow time dimension (speed dimension) time sampling point, and the formula of the phasor mean cancellation algorithm is:

[0047] R[m,n]=R[m,n]-C[m].

[0048] The optimal feature of the phasor mean cancellation algorithm is that it does not weaken the target's amplitude, but it keeps background noise relatively clean and preserves micro-Doppler information relatively intact, completely maintaining a high signal-to-noise ratio for the target. It also effectively preserves human vital signals.

[0049] Waveforms are separated using a wavelet separation algorithm. The biggest challenge with windowed Fourier transforms is window size. For time-varying, non-stationary signals, small windows are suitable for high frequencies, while large windows are suitable for low frequencies. However, the window in the Fourier transform is fixed, so this method has limitations when processing. The wavelet transform primarily addresses the issue of the Fourier transform window being fixed. The Fourier transform function is relatively fixed, while the function used in wavelet analysis is flexible and variable. The function used in wavelet basis analysis is selected to achieve a resolution of the signal at a scale of 0.15 Hz after separation.

[0050] (6) Compare the normal human respiratory and heartbeat frequency range with the detected signal frequency range: the heart rate of an adult is between 1Hz and 1.6Hz, and the respiratory rate is between 0.2Hz and 0.4Hz. The heart rate of a child is between 1.7Hz and 2.2Hz, and the respiratory rate is between 0.5Hz and 0.7Hz. The difference in the respiratory and heartbeat ranges between adults and children can be distinguished. The core of frequency resolution lies in the sampling frequency Fs divided by the number of FFT points N. The radar sampling time is 100ms, the sampling frequency is 10Hz, and the number of FFT points is 64, so the frequency resolution is 10 / 64, which is about 0.15Hz. The respiratory and heartbeat waveforms are reconstructed from the separated signals, and the frequency of the reconstructed waveforms is estimated. The system compares the frequency range with the one reserved in the car and starts detecting when the car is locked. It judges whether the signal matches the heart rate and breathing rate of the child to determine whether there is a child left in the car. If the signal matches the heart rate and breathing rate of the child, there is a child left in the car and a graded alarm is issued. If the signal does not match the heart rate and breathing rate of the child, there is no child left in the car.

[0051] Alarm process such as Figure 2 As shown, the alarm is graded. When the vehicle is locked, the radar begins operating. If it determines a child is inside and the doors are closed, the system enters the first-level alarm mode 10 seconds after locking the vehicle. The horn and lights sound an alarm, and the alarm mode must be distinguished from other alarms. This alarm lasts for 60 seconds or until it is cleared. If a child is still detected (regardless of whether it is cleared or not), the system enters the next level of alarm after 10 minutes.

[0052] After entering the second level of alarm, the car's air conditioning is turned on, windows are closed, and air flow is controlled to maintain a comfortable temperature. A reminder message is sent to the driver via the Internet or text message. If a child is still detected after 20 minutes (regardless of whether the alarm is released or not), the next level of alarm is entered.

[0053] If all doors are still closed, the system will enter the third level alarm. Both the first and second level alarms will be activated, and a call for help will be sent to a third party (medical institution, firefighter, etc.) via the Internet or SMS.

[0054] To cancel the alarm, you can open the car door or connect your phone to the car's Bluetooth or Wi-Fi and confirm the cancellation.

[0055] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and description merely illustrate the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for detecting and alarming living things in a vehicle based on millimeter-wave radar, characterized by: The following steps are involved: (1) Use millimeter-wave radar to emit signals to living targets and receive target and noise echo signals every 50ms; (2) Perform a 1D range FFT on the received echo signal to obtain 32 signals divided by distance, and then perform a 2D Doppler FFT to obtain the target's velocity and angle information; (3) Performing CFAR detection on the signal after the 2D Doppler FFT by windowing to remove noise and clutter signals, and sending the CFAR detected signal in 8-bit form to a computer for phase analysis to restore the signal waveform; (4) Perform spectrum analysis on the restored waveform and convert the phase-time spectrum into the frequency-time spectrum through digital filter and FFT; (5) Remove other interfering signals through windowing and phasor mean cancellation algorithms, separate the respiratory and heartbeat signals from the signals through a wavelet separation algorithm, reconstruct the waveforms of the separated signals, and estimate the frequencies of the respiratory and heartbeat signals; (6) Compare the normal human respiratory and heart rate range with the detected signal frequency range: the heart rate of an adult is 1Hz to 1.6Hz, and the respiratory rate is 0.2Hz to 0.4Hz; the heart rate of a child is 1.7Hz to 2.2Hz, and the respiratory rate is 0.5Hz to 0.7Hz, and this information is stored in the system; (7) After the vehicle is locked, the detection begins, and the signal is judged to be consistent with the child's heartbeat and breathing rate, thereby determining whether there is a child left in the vehicle; (8) If the signal is determined to be consistent with a child’s heartbeat and breathing rate, a child is left in the vehicle and a graded alarm is issued; (9) If the signal is determined not to be consistent with the child's heart rate and breathing rate, then there is no child left in the vehicle; The specific process of performing 1D distance fft on the received echo signal in step (2) is as follows: (1) Perform one-dimensional Fourier transform to convert the signal into a distance-time spectrum; (2) Perform static clutter removal to remove the static background and obtain the original echo signal; (3) Divide the signal into 32 units based on distance.

2. The method for detecting and alarming a living body in a vehicle based on millimeter-wave radar according to claim 1, characterized in that: The millimeter-wave radar in step (1) is a four-transmit, four-receive 60G millimeter-wave radar.

3. The method for detecting and alarming a living body in a vehicle based on millimeter-wave radar according to claim 1, characterized in that: In step (3), parsing is performed using a parsing algorithm.

4. The method for detecting and alarming a living body in a vehicle based on millimeter-wave radar according to claim 1, characterized in that: The process of removing other interference signals by the phasor mean cancellation algorithm in step (5) is as follows: first, all received pulses are averaged to obtain a reference received pulse, and then the reference received pulse is subtracted from each beam of received pulses to obtain the target echo signal.

5. The method for detecting and alarming a living body in a vehicle based on millimeter-wave radar according to claim 4, characterized in that: The expression of the reference received pulse is: ； Where C is the clutter estimator, R is the original signal, i is the fast time dimension sampling point, m is the slow time dimension time sampling point, N is the total number of receiving antennas, and the formula of the phasor mean cancellation algorithm is: R[m, n]=R[m, n]-C[m] Where R[m,n] is the original received signal, C[m] is the static clutter estimate, and n is the channel index.

6. The method for detecting and alarming a living body in a vehicle based on millimeter-wave radar according to claim 1, characterized in that: The hierarchical alarm in step (eight) specifically includes a first-level alarm, a second-level alarm, and a third-level alarm.

7. The method for detecting and alarming a living body in a vehicle based on millimeter-wave radar according to claim 6, characterized in that: Level 1 alarm: 10 seconds after locking the car, the horn and lights sound an alarm. The alarm mode is different from other alarms and lasts for 60 seconds or until the alarm is lifted. If the system still determines that a child is present, it will enter level 2 alarm after 10 minutes regardless of whether the alarm is lifted or not.

8. The method for detecting and alarming a living body in a vehicle based on millimeter-wave radar according to claim 7, characterized in that: The second-level alarm is: turn on the air conditioner in the car, close the windows, maintain a comfortable temperature for people, and control the flow of air in and out; at the same time, send a message reminder to the car owner through the Internet or text message. If it is still determined that there is a child after 20 minutes, the third-level alarm will be entered regardless of whether the alarm is released or not.

9. The method for detecting and alarming a living body in a vehicle based on millimeter-wave radar according to claim 8, characterized in that: The three-level alarm is as follows: both the first and second level alarms are activated, and a call for help is sent to a third party via the Internet or text message. The alarm is lifted by opening the car door or connecting the mobile phone to the car's Bluetooth or Wi-Fi.

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