Radar-based target velocity estimation method, and apparatus therefor

Abstract

A radar-based target velocity estimation method, and an apparatus therefor are disclosed. The radar-based target velocity estimation method comprises the steps of: (a) transmitting a radar transmission chirp signal and receiving a reception chirp signal reflected from a target; (b) multiplying the reception chirp signal by the transmission chirp signal, removing a high-frequency component through a low-pass filter, and then performing sampling through an analog-to-digital converter (ADC), and differently applying sampling periods along a time axis so as to generate a virtual chirp signal; and (c) Fourier-transforming the virtual chirp signal, and estimating the distance and velocity of the target by using the Fourier transform result.

Description

Radar-based target velocity estimation method and apparatus

[0001] The present invention relates to a radar-based target velocity estimation method and apparatus.

[0002]

[0003] Radar systems can estimate the distance and velocity of a target using radio waves. These systems utilize various waveforms, such as continuous wave (CW) or pulse waveforms, to extract information about the target. Among these waveforms, Frequency Modulated Continuous Wave (FMCW) features a characteristic where frequency increases linearly over time and provides superior range resolution compared to pulse Doppler waveforms due to its high pulse compression ratio. For this reason, FMCW radar systems are widely used in various fields, including aircraft, ships, vehicles, and drones.

[0004] In particular, high-speed ramping techniques are primarily adopted in recent automotive radar systems, where hundreds of FMCW waveforms are transmitted as a single bundle. In conventional radar systems, the distance and speed of a target can be estimated immediately by applying the Fourier Transform (FT) to the sampled data after the received waveform is demodulated. In these high-speed FMCW radar systems, speed estimation relies on the phase difference between adjacent waveforms. In this situation, the phase difference between two adjacent waveforms If it exceeds, Doppler ambiguity occurs during the velocity estimation process. As a result, there is a problem in that targets moving beyond the detectable velocity range are inaccurately estimated due to Doppler ambiguity.

[0005] Various studies have been conducted to extend the detectable velocity range, such as methods to extend the detectable velocity range in linear FMCW radars by utilizing previously ignored higher-order phase components, methods using multiple consecutive measurements with varying interval lengths to resolve Doppler ambiguity in short-chirp FMCW radar systems, and methods to resolve velocity ambiguity by leveraging the characteristics of Multiple Input Multiple Output (MIMO) radars. While these conventional techniques have resolved the Doppler non-ambiguity problem, they have the disadvantage of requiring the use of modified signal formats different from previous ones or the addition of complex computational steps.

[0006]

[0007] The present invention is intended to provide a radar-based target velocity estimation method and an apparatus thereof.

[0008] In addition, the present invention aims to provide a radar-based target velocity estimation method and apparatus capable of improving the detectable velocity range of a target by estimating the target's velocity using the distance to the target without changing the radar system.

[0009] In addition, the present invention is intended to provide a radar-based target speed estimation method and apparatus capable of adjusting a detectable speed range based on a selective sampling method.

[0010]

[0011] According to one aspect of the present invention, a radar-based target velocity estimation method is provided.

[0012] According to one embodiment of the present invention, a radar-based target velocity estimation method may be provided, comprising: (a) transmitting a radar transmission chirp signal and receiving a reception chirp signal reflected from a target; (b) generating a virtual chirp signal by multiplying the reception chirp signal with the transmission chirp signal, removing high-frequency components through a low-pass filter, and then sampling through an analog-to-digital converter (ADC), wherein different sampling periods are applied along the time axis; and (c) performing a Fourier transform on the virtual chirp signal and estimating the distance and velocity of a target using the result of the Fourier transform.

[0013] Step (b) above generates a virtual chirp signal by applying different sampling periods along the time axis according to an optional sampling method, wherein the optional sampling method is either a descending sampling method or an ascending sampling method.

[0014] The above step (b) can generate the virtual chirp signal by dynamically changing the sampling period according to the distance estimated for the target at a previous time point.

[0015] The above virtual chirp signal is generated by the following mathematical formula,

[0016]

[0017] Here, represents the index, amplitude, and slope of the virtual chirp signal of the selected sample, respectively, and represents the sampling frequency, and in the case of the rise method , in the case of the descent method It is represented as, and c represents the speed of light, represents distance, and represents speed, represents the carrier frequency, represents the sampling interval between samples, and represents the duration of the virtual chirp signal.

[0018]

[0019] According to another embodiment of the present invention, a radar-based target velocity estimation method may be provided, comprising: a step of receiving a received signal reflected from a target; a step of sampling the received signal using an analog-to-digital converter (ADC), wherein the sampling period is dynamically changed according to the previously detected distance of the target to sample the received signal through the analog-to-digital converter (ADC); and a step of processing the sampled signal to estimate the distance and velocity of the target at a current time.

[0020]

[0021] According to another aspect of the present invention, a radar system that performs a radar-based target velocity estimation method is provided.

[0022] According to one embodiment of the present invention, a radar system may be provided comprising: a receiver that receives a received chirp signal reflected from a target for a transmitted radar transmitted chirp signal; a mixer that multiplies the received chirp signal with the transmitted chirp signal; a low-pass filter that removes high-frequency components from the signal output from the mixer and outputs a baseband signal; an analog-to-digital converter (ADC) that samples the baseband signal and generates a virtual chirp signal by applying different sampling periods along a time axis; and a processor that performs a Fourier transform on the virtual chirp signal and estimates the distance and velocity of a target using the result of the Fourier transform.

[0023] The analog-to-digital converter (ADC) generates a virtual chirp signal by applying different sampling periods along the time axis according to an optional sampling method, wherein the optional sampling method is either a descending sampling method or an ascending sampling method.

[0024] The analog-to-digital converter (ADC) can generate the virtual chirp signal by dynamically changing the sampling period according to the distance estimated for the target at a previous time point.

[0025]

[0026] By providing a radar-based target velocity estimation method and apparatus according to one embodiment of the present invention, the detectable velocity range of a target can be improved by estimating the velocity of a target using the distance of the target without changing the radar system.

[0027] In addition, the present invention can adjust the detectable speed range based on a selective sampling method.

[0028]

[0029] FIG. 1 is a flowchart illustrating a conventional target detection method.

[0030] FIG. 2 is a drawing illustrating a multi-chirp according to an embodiment of the present invention.

[0031] FIG. 3 is a diagram illustrating a target detectable speed range according to an embodiment of the present invention.

[0032] Figure 4 is a diagram showing a distance-Doppler map.

[0033] FIG. 5 is a flowchart illustrating a radar-based target velocity estimation method according to an embodiment of the present invention.

[0034] FIG. 6 is a drawing illustrating a sampling method according to an embodiment of the present invention.

[0035] FIG. 7 is a diagram illustrating the detectable speed when estimating a target speed according to a conventional method and an embodiment of the present invention.

[0036] FIGS. 8 and 9 are diagrams comparing Doppler spectra according to a simulation scenario according to a conventional method and an embodiment of the present invention.

[0037] FIG. 10 is a diagram comparing the speed estimation results according to the prior art and an embodiment of the present invention.

[0038] FIG. 11 is a block diagram schematically illustrating the configuration of a radar system according to one embodiment of the present invention.

[0039] FIG. 12 is a drawing illustrating the architecture of a radar system according to one embodiment of the present invention.

[0040]

[0041] As used in this specification, singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "composed" or "comprising" should not be interpreted as necessarily including all of the various components or steps described in the specification, and should be interpreted as meaning that some of the components or steps may be excluded, or that additional components or steps may be included. Furthermore, terms such as "...part," "module," etc., as used in the specification refer to a unit that processes at least one function or operation, which may be implemented in hardware or software, or a combination of hardware and software.

[0042] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

[0043]

[0044] FIG. 1 is a flowchart illustrating a conventional target detection method, FIG. 2 is a diagram illustrating a multi-chirp according to an embodiment of the present invention, FIG. 3 is a diagram illustrating a target detection speed range according to an embodiment of the present invention, and FIG. 4 is a diagram illustrating a distance-Doppler map.

[0045] In step 110, the radar system (100) transmits a radar transmission signal.

[0046] In one embodiment of the present invention, it is assumed that the radar system (100) is an FMCW radar system. An FMCW radar system estimates the distance and velocity information of a target using a waveform having a frequency that changes linearly over time. Assuming a chirp signal of the FMCW radar signal, the transmitted signal can be represented as Equation 1.

[0047]

[0048] Here, and represents the amplitude, carrier frequency, bandwidth, and chirp duration of the transmitted signal, respectively.

[0049] In step 115, the radar system (100) receives a signal (received signal) that is reflected by the target from the transmitted signal. The transmitted signal reaches the target, and some of it is reflected back to the radar system. The target is at a distance speed at When moving, the received signal received by the radar system can be represented as Equation 2.

[0050]

[0051] Here, represents the amplitude of the received signal, and c represents the speed of light.

[0052] In step 120, the radar system (100) multiplies the received signal with the transmitted signal and then passes it through a low-pass filter (LPF) to remove high-frequency components and generates a baseband signal.

[0053] This can be expressed as a mathematical formula, as in mathematical formula 3.

[0054]

[0055] In step 125, the radar system (100) samples the baseband signal through an analog-to-digital converter (ADC) and converts it into a digital signal (hereinafter referred to as a bit signal). This can be represented as Equation 4.

[0056]

[0057] Here, represents the sampling interval between two samples, and N s represents the number of samples.

[0058] A multi-chirp signal transmits multiple chirps as a bundle, as illustrated in FIG. 2. Similar to single chirp transmission, a multi-chirp signal can also be processed through a mixer, a low-pass filter, and an analog-to-digital converter (ADC).

[0059] When multiple chirps are transmitted (m>1), the received signal can be represented as in Equation 5.

[0060]

[0061] Here, N c represents the number of chirps.

[0062] In step 130, the radar system (100) estimates the distance and velocity of the target by signal processing (Discrete Fourier Transform (DFT)) the sampled signal (bit signal). The result of the Discrete Fourier Transform can be expressed as Equation 6.

[0063]

[0064] Here, and represents the index in the frequency domain.

[0065] At time t, the distance and velocity of the target are Peaks can be found within and estimated using peak detection algorithms such as CFAR or CLEAN algorithms.

[0066] Conventional FMCW radar systems have a detectable velocity range based on the duration of a single chirp waveform. It is determined by. The speed of the target between adjacent chirps Assuming movement to, the phase change between the two chirps due to the target's movement is It can be expressed as follows. Therefore, the velocity of the target is estimated by measuring the phase difference between the two chirps.

[0067] In this case, the clearly estimable speed range is It is defined as, and as shown in FIG. 3, the phase is If it exceeds, ambiguity arises in the speed estimation.

[0068] As a result, the detectable speed range of the conventional target can be expressed as Equation 7.

[0069]

[0070] thus, This becomes the maximum detectable speed.

[0071] Considering the chirp duration and wavelength used in vehicle radar systems, generally, the chirp duration in a vehicle radar system is 30 from 50 It is between, and when using the frequency band from 76 GHz to 81 GHz, the wavelength is 0.0039 m / s to 0.0037 m / s. In this case, the detectable speed range of a conventional vehicle radar system is between 18.5 m / s and 32.5 m / s.

[0072] Figure 4 shows the detection results for targets moving at 20 m / s and 50 m / s at a distance of 25 m, respectively, when the radar system operates at its maximum detectable speed of 32.5 m / s. As shown in Figure 4 (a), both distance and speed can be accurately estimated when the target is within the maximum detectable speed range. However, as shown in Figure 4 (b), when the target moves beyond the radar system's detectable speed, accurate speed estimation is impossible due to Doppler ambiguity.

[0073]

[0074] FIG. 5 is a flowchart illustrating a radar-based target velocity estimation method according to an embodiment of the present invention, FIG. 6 is a diagram illustrating a sampling method according to an embodiment of the present invention, FIG. 7 is a diagram illustrating detectable velocity when estimating target velocity according to a conventional method and an embodiment of the present invention, FIG. 8 and FIG. 9 are diagrams comparing Doppler spectra according to simulation scenarios according to a conventional method and an embodiment of the present invention, and FIG. 10 is a diagram comparing velocity estimation results according to a conventional method and an embodiment of the present invention.

[0075] In step 510, the radar system (100) transmits a radar signal and detects the target distance using the received signal reflected from the target. Here, it is assumed that the target distance is detected in the same way as described in FIG. 1.

[0076] In step 515, the radar system (100) transmits a radar signal and samples the received signal reflected from the target through an analog-to-digital converter (ADC), but generates a virtual chirp signal by dynamically changing the sampling period along the time axis according to the previously detected target distance.

[0077] I will explain this in more detail.

[0078] The radar system (100) uses a conventional speed estimation method to estimate the speed of a target containing ambiguity. Estimates.

[0079] When using a conventional velocity estimation method, the phase difference between adjacent chirps can be expressed as Equation 8.

[0080]

[0081] Here, o represents the index of the chirp. Therefore, the velocity of the target can be estimated by performing a Fourier transform (FT) in Equation 8.

[0082] The radar system (100) can generate a virtual chirp signal having a longer chirp duration than the existing chirp using a sampling method. Here, the virtual chirp signal should be understood as a sampled signal by dynamically changing the sampling period of the ADC according to the distance of the previously detected target.

[0083] The sampling method consists of two methods: rising sampling and falling sampling, each as illustrated in Figures 6 (a) and (b). As shown in Figure 6, in the case of the rising method, the index of the selected sample increases when the index of the chirp increases. Conversely, in the case of the falling method, the index of the selected sample decreases when the index of the chirp increases.

[0084] The virtual chirp signal composed of the data selected in each method is in (a) of Fig. 6 It is shown as a green chirp, and as a red chirp in Fig. 6(b). The virtual chirp signal can be represented as Equation 9.

[0085]

[0086] If we apply the Fourier Transform (FT) to Equation 10, A frequency value corresponding to can be obtained. Therefore, the speed of the target can be estimated by inputting the target's distance information.

[0087] The detectable speed range of a target according to one embodiment of the present invention can be expressed as Equation 11.

[0088]

[0089] Here, represents the sampling frequency. As shown in Equation 11, the detectable velocity range is related to the distance from the target. In addition, the detectable velocity range is and It is determined by.

[0090] Because the method according to one embodiment of the present invention modifies the signal processing part of a conventional radar system, is not changed. Therefore, the detectable speed range according to one embodiment of the present invention is the remaining two factors and It is determined by.

[0091] first of all, It is related to the chirp duration and sampling interval of conventional radar systems and can determine the span of detectable speeds. In addition, is related to the data sampling method (i.e., rise and fall) and the duration and bandwidth of the virtual chirp. In Equation 11 It appears as a factor that is multiplied by the distance to the target, and can determine how much the detectable speed range changes as the distance changes.

[0092] Therefore, a method for improving the detectable speed of a target according to one embodiment of the present invention and By adjusting parameters, the detectable speed range can be dynamically adjusted to suit various situations.

[0093] In step 520, the radar system (100) processes the virtual chirp signal (DFT) to estimate the distance and velocity of the target.

[0094] A method for enhancing the detectable speed of a radar according to an embodiment of the present invention was simulated based on parameters commonly used in vehicle radar systems. The simulation was performed using the same number of chirps and time samples. However, even in scenarios where the number of chirps and time samples is not the same, the method for enhancing the detectable speed of a radar according to an embodiment of the present invention can be used by sampling the received signal at regular intervals. When estimating the speed using these parameters, the detectable speed range is determined as shown in FIG. 7. In the conventional method, the detectable speed range remains fixed at -32.4 m / s to 32.4 m / s regardless of the distance to the target, which is indicated by the blue line in FIG. 7.

[0095] On the other hand, the range of estimable velocity in the sampling method according to one embodiment of the present invention (when using rising sampling and falling sampling methods) varies linearly with distance, as indicated by the green and red lines in FIG. 7. As shown in FIG. 7, it can be seen that the feature of the method according to one embodiment of the present invention is that the detectable velocity range varies with the distance of the target.

[0096] Simulations were performed in two scenarios. One scenario involves estimating the velocity using a conventional method and an ascending sampling method according to an embodiment of the present invention, and the other scenario involves estimating the velocity using only the ascending sampling method according to an embodiment of the present invention. In the first scenario, a target is moving at a speed of -25 m / s and is located 10 m away. When estimating the velocity of the target using the conventional method, the Doppler spectrum is shown in FIG. 8 (a). Additionally, when estimating the velocity of the target using the method according to an embodiment of the present invention in the same scenario, the Doppler spectrum appears as shown in FIG. 8 (b). As shown in FIG. 8, both the conventional method and the method according to an embodiment of the present invention accurately estimated the velocity of the target to be -25 m / s.

[0097] In addition, a simulation was performed for a second scenario in which a target, whose velocity could not be estimated using conventional methods, was present at a position of 10 m at a velocity of -55 m / s. The Doppler spectrum generated using conventional methods is shown in Fig. 9(a). As shown in Fig. 9(a), accurate velocity estimation was impossible in this scenario because the target's velocity exceeded the detectable range.

[0098] On the other hand, in FIG. 9(b), which is a result obtained using the method according to one embodiment of the present invention, it can be seen that the speed of the target was accurately estimated to be -55 m / s.

[0099] In a method according to one embodiment of the present invention, the estimable velocity range of a target is determined by the distance between the target and the radar system. To intuitively demonstrate the advantages of the method according to one embodiment of the present invention, simulation results were analyzed in which the distance between the target and the radar was fixed and only the target's velocity varied. In the simulation, the target was located at a distance of 5 m, and the velocity varied from 0 m / s to -55 m / s. Additionally, the radar system parameters were the same as in the previous simulation, and a descending sampling method was used. When the target is located at 5 m, the conventional method can estimate a velocity in the range of -32 m / s to 32 m / s, whereas the present invention shows an estimable velocity range shifted from -58.43 m / s to 5.96 m / s as a result. Figures 10 (a) and (b) show the velocity estimation results using the conventional method and the present invention when the target's velocity changes over time. As can be seen in Figure 10 (a), when using the conventional velocity estimation method, it can be seen that velocity ambiguity occurs when the target exceeds the detectable velocity range of the radar system starting from 60 seconds. On the other hand, since the target exists within a detectable speed range over all times, it can be seen that speed estimation is possible without ambiguity, as shown in Fig. 10 (b).

[0100]

[0101] FIG. 11 is a block diagram schematically illustrating the configuration of a radar system according to one embodiment of the present invention, and FIG. 12 is a diagram illustrating the architecture of a radar system according to one embodiment of the present invention.

[0102] Referring to FIG. 11, a radar system (100) according to one embodiment of the present invention comprises a transmitter (1110), a receiver (1120), a mixer (1130), a low-pass filter (LPF) (1140), an analog-to-digital converter (ADC) (1150), a memory (1160), and a processor (1170). The architecture of the radar system (100) is as shown in FIG. 13. Below, the operation of each component will be briefly described, focusing on the components necessary to explain the main argument of the present invention.

[0103] The transmitter (1110) transmits a radar transmission signal (transmission chirp signal).

[0104] The receiver (1120) receives the received signal (received chirp signal) reflected from the target.

[0105] The mixer (1130) multiplies the received chirp signal and the transmitted chirp signal and passes them to the low-pass filter (LPF).

[0106] A low-pass filter (LPF) (1140) removes high-frequency components from the signal transmitted from the mixer (1130) and outputs a baseband signal.

[0107] The analog-to-digital converter (ADC) (1150) samples the baseband signal transmitted from the low-pass filter (LPF) (1140) and outputs the sampled signal.

[0108] Here, the analog-to-digital converter (ADC) (1150) can sample the baseband signal by dynamically changing the sampling period along the time axis. More specifically, the analog-to-digital converter (ADC) (1150) can sample the baseband signal by dynamically changing the sampling period according to the previously detected distance to the target.

[0109] Additionally, the analog-to-digital converter (ADC) (1150) may sample the baseband signal by dynamically changing the sampling period along the time axis according to the sampling method. Here, the sampling methods include rising sampling and falling sampling methods. The sampling methods may be used selectively or both may be used.

[0110] The memory (1160) stores various instructions (or program codes) for performing a radar-based target velocity estimation method according to one embodiment of the present invention.

[0111] A processor (1170) is a means for controlling internal components of a radar system (100) according to one embodiment of the present invention (e.g., a transmitter (1110), a receiver (1120), a mixer (1130), a low-pass filter (LPF) (1140), an analog-to-digital converter (ADC), a memory (1160), etc.).

[0112] Additionally, the processor (1170) may estimate the distance and speed of the target by processing the signal sampled by the analog-to-digital converter (ADC) (e.g., DFT).

[0113]

[0114] An apparatus and method according to an embodiment of the present invention may be implemented in the form of program instructions that can be executed through various computer means and recorded on a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, etc., either alone or in combination. The program instructions recorded on the computer-readable medium may be those specifically designed and configured for the present invention, or they may be those known and available to a person skilled in the art of computer software. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tapes; optical recording media such as CD-ROMs and DVDs; magneto-optical media such as floptical disks; and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, and flash memory. Examples of program instructions include machine code, such as that generated by a compiler, as well as high-level language code that can be executed by a computer using an interpreter, etc.

[0115] The hardware device described above may be configured to operate as one or more software modules to perform the operation of the present invention, and vice versa.

[0116] The present invention has been described above with reference to its embodiments. Those skilled in the art will understand that the present invention may be implemented in modified forms without departing from the essential characteristics of the invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the invention is defined by the claims, not by the foregoing description, and all variations within the scope of the claims should be interpreted as being included in the invention.

Claims

1. (a) Transmitting a radar transmission chirp signal and receiving a reception chirp signal reflected from a target; (b) a step of generating a virtual chirp signal by multiplying the received chirp signal with the transmitted chirp signal, removing high-frequency components through a low-pass filter, and then sampling through an analog-to-digital converter (ADC), wherein different sampling periods are applied along the time axis; and (c) A radar-based target velocity estimation method comprising the step of performing a Fourier transform on the virtual chirp signal and estimating the distance and velocity of the target using the result of the Fourier transform.

2. In Paragraph 1, The above step (b) is, A virtual chirp signal is generated by applying different sampling periods along the time axis according to the selective sampling method, A radar-based target velocity estimation method characterized in that the above-mentioned selective sampling method is either a descending sampling method or an ascending sampling method.

3. In Paragraph 1, The above step (b) is, A radar-based target velocity estimation method characterized by generating the virtual chirp signal by dynamically changing the sampling period according to the distance estimated for the target at a previous point in time.

4. In Paragraph 1, A radar-based target velocity estimation method characterized by generating the above virtual chirp signal using the following mathematical formula. Here, represents the index, amplitude, and slope of the virtual chirp signal of the selected sample, respectively, and represents the sampling frequency, and in the case of the rise method , in the case of the descent method It is represented as, and c represents the speed of light, represents distance, and represents speed, represents the carrier frequency, represents the sampling interval between samples, and represents the duration of the virtual chirp signal.

5. In Paragraph 4, A radar-based target velocity estimation method characterized by determining the detectable velocity range of the above target using the following mathematical formula.

6. A computer-readable recording medium having program code for performing a method according to any one of claims 1 to 5.

7. A receiver that receives a received chirp signal reflected from a target in response to a transmitted radar transmission chirp signal; A mixer that multiplies the received chirp signal with the transmitted chirp signal; A low-pass filter that removes high-frequency components from the signal output from the above mixer and outputs a baseband signal; An analog-to-digital converter (ADC) that samples the above baseband signal and generates a virtual chirp signal by applying different sampling periods along the time axis; and A radar system comprising a processor that performs a Fourier transform on the virtual chirp signal and estimates the distance and velocity of a target using the result of the Fourier transform.

8. In Paragraph 7, The above analog-to-digital converter (ADC) is, A virtual chirp signal is generated by applying different sampling periods along the time axis according to the selective sampling method, A radar system characterized in that the above-mentioned selective sampling method is either a descending sampling method or an ascending sampling method.

9. In Paragraph 7, The above analog-to-digital converter (ADC) is, A radar system characterized by generating the virtual chirp signal by dynamically changing the sampling period according to the distance estimated for the target at a previous point in time.

10. Step of receiving a signal reflected from the target; A step of sampling the received signal using an analog-to-digital converter (ADC), wherein the sampling period is dynamically changed according to the previously detected distance of the target to sample the received signal through the analog-to-digital converter (ADC); and A radar-based target velocity estimation method comprising the step of processing the sampled signal to estimate the distance and velocity of the target at the current time.

Images