Methods for using radar sensors in motor vehicles, radar sensors and motor vehicles

Abstract

A method for using a radar sensor (14) in a motor vehicle (10), wherein, in SAR measurement mode, objects including stationary objects (12) are located at high angular resolution according to the synthetic aperture principle, characterized in that the same radar sensor (14) operates in the SAR measurement mode and the Doppler measurement mode at staggered or simultaneous times, wherein, in the Doppler measurement mode, the relative velocity of objects including moving objects is measured at a greater time resolution than that in the SAR measurement mode.

Description

Technical Field

[0001] This invention relates to a method for a radar sensor used in a motor vehicle, in which, in SAR measurement mode, objects, including stationary objects, are located with high angular resolution based on the synthetic aperture principle. Background Technology

[0002] Radar systems used to measure the distance, relative speed, and positioning angle of objects are used in motor vehicles for various auxiliary functions, such as safety functions (e.g., automatic collision warning or collision avoidance) and comfort functions (e.g., automatic parking space search). An example of a method for operating SAR radar sensors in a motor vehicle is described in DE 199 12 370 A1.

[0003] The synthetic aperture principle allows for exceptionally precise angular measurements of a radar sensor in motion by combining radar measurements from different local locations to create a large antenna aperture. This synthetic aperture is achieved because the transmitting and receiving antennas are located at different positions at each individual radar measurement due to the movement of the vehicle and the radar sensor. Therefore, the received radar echoes can be processed as if a large antenna aperture existed along the vehicle's trajectory. Consequently, a significantly greater angular resolution can be achieved compared to antenna arrays with physical apertures limited by installation constraints.

[0004] To analyze and process the measured radar signal according to the synthetic aperture principle, the motion of the radar sensor itself must be known, i.e., the vehicle's trajectory must be known. This trajectory is the input parameter of the SAR analysis and processing algorithm and represents the basis for SAR image calculation. According to the analysis and processing algorithm, the precise trajectory is measured, or the trajectory is estimated based on the measured vehicle speed, where a linear trajectory is assumed.

[0005] Generally, conventional SAR analysis and processing algorithms assume that the radar's surrounding environment is stationary. However, there are also schemes that extend SAR analysis and processing to non-stationary radar surrounding environments by correcting for moderate motion of the target.

[0006] Radar sensors typically transmit at frequencies of around 24 GHz or 77 GHz. SAR analysis and processing generally do not depend on the specific frequency modulation method used. The maximum available bandwidth for frequency modulation is typically below 4 GHz, and in most cases, it is on the order of 0.5 GHz.

[0007] A commonly used modulation method in radar systems for motor vehicles is FMCW modulation (Frequency Modulated Continuous Wave) with "Fast-Chirp-Modulation," in which multiple linear frequency ramps with the same gradient pass sequentially. After low-pass filtering, the mixing of the currently transmitted and received signals generates a low-frequency (schwebung) signal whose frequency is proportional to the distance between the located object and the target. The system is typically designed such that, at the typical relative velocity of the target, the Doppler effect-induced fraction of the strab frequency is negligible. Thus, with appropriate parameter selection, unique and definitive distance information is obtained. Subsequently, the Doppler displacement and therefore the relative velocity can be determined by observing the phase evolution of the (complex)distance signal across the multiple ramps. Distance and velocity measurements can be performed independently, for example, using a two-dimensional fast Fourier transform.

[0008] Fast linear frequency modulation (FLM) can also be used in SAR radar sensors. Spacing measurements can then be performed in the same manner as in classic FMCW radar. However, the Doppler analysis processing across the frequency ramp is replaced by SAR analysis processing, so that instead of obtaining a Doppler measurement, an angle measurement is obtained under the assumption of a stationary target and with knowledge of the vehicle's own motion.

[0009] For SAR analysis and processing, various algorithms are known in the literature. For applications in the field of motor vehicles, the following algorithm is preferred: this algorithm requires certain restrictions on the direction of the driving trajectory; however, it can efficiently and in real time calculate SAR images by leveraging the data processing capabilities available in motor vehicles.

[0010] Since angular resolution depends on the aperture size and therefore on the length of the trajectory traversed within a measurement cycle (which is proportional in some respects to the product of speed and time), temporal resolution is necessarily limited in SAR analysis with high angular resolution. Therefore, SAR radar sensors are particularly suitable for applications where the surrounding environment to be detected has only low dynamics. Conversely, for detecting highly dynamic driving situations, radar sensors designed for classical measurement principles are used, particularly capable of measuring relative speed with high temporal and velocity resolution. Summary of the Invention

[0011] The objective of this invention is to enable a simple radar system to be used for a wider range of measurement tasks.

[0012] According to the present invention, this task is accomplished by operating the same radar sensor in staggered or simultaneous SAR measurement mode and Doppler measurement mode, wherein, in Doppler measurement mode, the relative velocity of objects, including moving objects, is measured at a greater time resolution than that in SAR measurement mode.

[0013] Therefore, this invention allows the same radar sensor to be used not only for measurement tasks requiring high angular resolution, but also for measurement tasks involving the detection of more dynamic situations and thus requiring higher temporal resolution, i.e., a greater number of repetitions of the measurement process per unit time. In this way, enhanced functionality can be achieved with minimal hardware cost, especially considering that enhanced functionality is already achievable with a single radar sensor. Compared to systems with independent radar sensors, the following advantages are also obtained: avoidance of interference between radar signals.

[0014] Advantageous configurations of the invention are described below.

[0015] In one implementation, the radar sensor can operate in frequency division multiplexing, allowing signal analysis and processing to be performed simultaneously in SAR and Doppler measurement modes, wherein the measurement signals for the different analysis and processing modes are separated from each other based on their frequencies. In another implementation, the radar sensor operates in either SAR or Doppler measurement mode at a given time, and the switching between the two measurement modes is situational or based on a determined time division multiplexing scheme.

[0016] In SAR mode, maximum angular resolution is achieved for objects that are lateral to the vehicle's trajectory, i.e., with a positioning angle on the order of 90° relative to the vehicle's current direction of travel. Conversely, for measurement tasks within the scope of automatic spacing adjustment, collision warning, or collision avoidance, it is particularly critical to measure the distance and relative speed of objects in front of or behind the vehicle (i.e., objects with positioning angles on the order of 0° or 180°). Therefore, radar sensors mounted at the front of the vehicle are preferably configured, either by digital beamforming or by a corresponding design of monostatic or bistatic antenna arrays, such that their positioning area covers not only the forward direction of the vehicle but also the lateral direction on at least one side of the vehicle. Accordingly, radar sensors mounted at the rear of the vehicle should cover at least the reverse direction and one side of the vehicle. Here, the antenna pattern can be designed such that the positioning angle range is 90° or greater, and that greater transmission power is available in the forward or backward directions, thereby enabling the positioning of objects at larger distances, while objects on the side of the vehicle, which are typically only at a smaller distance from the vehicle itself, are of significant importance.

[0017] Switching between measurement modes can be situational. For example, when driving at higher speeds on rural roads or highways, the classic Doppler measurement mode is more likely to be used, while in the case of searching for parking spaces in urban traffic, it can be switched automatically or by driver instruction to identify and measure parking spaces.

[0018] In time-division multiplexing operation, the measurement periods in SAR mode and Doppler mode are interleaved. Here, the relative frequencies of the two measurement modes are used. Again, this can vary depending on the situation. For example, when driving on a multi-lane roadway, Doppler mode is used for most measurement cycles to, for example, perform automatic spacing adjustment, while SAR mode measurement cycles are only occasionally inserted to “side-view” traffic events or stationary traffic in adjacent lanes, or to map the surrounding environment. Conversely, when driving at low speeds, the share of measurement cycles in SAR mode can be increased.

[0019] Since SAR mode is only available while the vehicle is in motion, it can automatically switch to Doppler mode when the vehicle is stationary.

[0020] In one implementation, depending on the measurement task, switching between multiple analysis and processing algorithms in SAR measurement mode and / or Doppler measurement mode can be configured, thereby allowing the selection of the optimal analysis and processing algorithm for each measurement task.

[0021] Typically, measurement modes differ not only in the analysis and processing algorithms but also in the parameters of the hardware used in radar sensors. For example, the transmission frequency, modulation scheme, parameters for digital beamforming, and other operating parameters can be optimized, taking into account the separately selected analysis and processing algorithms.

[0022] In hybrid operation of measurement modes using time-division multiplexing or frequency-division multiplexing, the measurement results obtained in the two measurement modes can also be fused according to the fusion algorithm, especially by means of the following algorithm: the algorithm weights the results obtained in the two measurement modes according to the accuracy or reliability achievable in the measurement mode.

[0023] The subject of this invention is also a radar sensor having analog transmitting and receiving hardware and a digital analysis and processing system, wherein the analog transmitting and receiving hardware and the digital analysis and processing system are configured for SAR measurement mode and Doppler measurement mode. Attached Figure Description

[0024] The following describes the embodiments in further detail with reference to the accompanying drawings.

[0025] The attached diagram shows:

[0026] Figures 1 to 3 A diagram illustrating the principles of SAR measurement is shown;

[0027] Figure 4 A block diagram showing a radar sensor configured for use in the method according to the invention is shown; and

[0028] Figure 5 A timeline of the method according to the present invention is shown. Detailed Implementation

[0029] exist Figure 1 In a Cartesian coordinate system with x and y axes, a motor vehicle 10 traveling at a constant speed along the x-axis is shown at three different moments, occupying different positions x1, x2, and x3 along the x-axis at these three different moments. A stationary object 12 is positioned at coordinate (x0, y0) beside the trajectory traversed by the vehicle 10. The vehicle 10 has a radar sensor 14, shown only schematically here, at its right front. The positioning angle range 16 of this radar sensor covers not only the space in front of the vehicle 10 but also the space beside the vehicle in the y-axis direction. (A mirror-arranged sensor on the other side of the vehicle is not shown here).

[0030] The object 12 is located by radar sensor 14 at each of positions x1, x2, and x3 at different positioning angles α1, α2, and α3. Here, positioning angles α1 to α3 are defined as the angles between the line of sight from radar sensor 14 to object 12 and the forward direction of the vehicle (i.e., the line parallel to axis x passing through the position of radar sensor 14).

[0031] The radar sensor 14 typically has an antenna array with multiple antenna elements arranged side-by-side on a horizontal line. These antenna elements form a defined physical aperture, allowing the positioning angle of the object 12 to be measured based on the phase and amplitude relationships between the signals arriving at two antenna elements, even with limited angular resolution. However, according to the synthetic aperture principle, during the movement of the vehicle 10 along its trajectory from position x1 to position x3, the received radar signals are recorded and mutually calculated (verrechnet) to obtain a synthetic aperture corresponding to the distance between x1 and x3, which is many times larger than the physical aperture of the radar sensor. This allows the positioning angle α3 of the object 12 to be measured with significantly higher angular resolution, at least at the end of the measurement cycle. Furthermore, by measuring the corresponding distance of the object 12 in a known manner using the radar sensor 14, the coordinate position (x0, y0) of the object 12 can be determined with high accuracy.

[0032] This measurement principle is applicable, for example, to mapping with high precision the outlines of objects in the immediate vicinity of vehicle 10, such as other vehicles parked on the side of the road and parking spaces between them. Similarly, the method can also be used to map objects in the more distant vicinity of a vehicle while it is in motion, or conversely, to precisely locate vehicle 10 itself based on measured positioning angles if the location of objects is known from a digital map.

[0033] Based on Figure 2 and Figure 3 Describe a possible analysis and processing method.

[0034] exist Figure 2 The diagram shows object 12 and the positioning angles α1, α2, and α3 for each of the three positions x1 to x3 of the vehicle. Furthermore, the velocity vector v of the vehicle 10 is shown for each position. It is assumed that this velocity vector is constant during the measurement period of the vehicle's movement from x1 to x3. Furthermore, in Figure 2 In the diagram, for each of the three positions, orthogonal projections of the velocity vector v onto the line of sight from the vehicle to object 12 are shown as p1, p2, and p3. The magnitudes of the projected vectors indicate the current relative velocity of object 12. When the object is still far from the vehicle in the x-axis direction, the relative velocity is almost equal to the vehicle's own velocity, but as the vehicle gets closer to object 12's position x0 on the x-axis, the relative velocity decreases. This relative velocity reaches a value of 0 at x0 and then becomes negative (as the object moves away).

[0035] exist Figure 3 In the diagram, the relative velocity, or the corresponding Doppler displacement D, is shown as a function of the position of vehicle 10 on the x-axis. The shape of the curve depends on the distance between the trajectories of object 12 and vehicle 10 in the y-axis direction. As the distance increases, the curve undergoes a central extension along the x-axis, with point x0 as the center of extension, as shown in... Figure 3 As indicated by the curve marked by the dashed line.

[0036] When radar sensor 14 operates in fast linear frequency modulation (FM), for each modulation ramp, a one-dimensional Fourier transform is performed over the duration of the modulation ramp to obtain the current distance between objects, a value that is not actually dependent on relative velocity. The two-dimensional fast Fourier transform of the signals obtained on successive modulation ramps provides a spectrum illustrating the relative velocity in the second dimension. If the integration time is chosen so short that the relative velocity is practically constant during that time, the current value of the relative velocity is obtained for each moment—and therefore for each position x of the vehicle along its trajectory—as represented by the projection vectors p1 to p3. Figure 3By comparing the curves shown, the position x0 of object 12 can be determined. Therefore, the positioning angle of the object can then be determined for each position of the vehicle on the x-axis.

[0037] If a longer integration time is chosen in the second dimension of the Fourier transform, the following spectrum is directly obtained: this spectrum is representative of the time variation of the relative velocity over the entire measurement period. Based on this spectrum, the position coordinates y0 of the object can be determined with particularly high accuracy for each moment, and thus the positioning angle can be determined.

[0038] exist Figure 4 The key components of the radar sensor 14 are shown in a block diagram. As is typical, the radar sensor has analog transmit and receive hardware 18, which is usually in the form of a high-frequency suitable circuit board. On this board are arranged multiple antenna patches, a local oscillator for generating a frequency-modulated transmit signal, and a mixer for mixing the received signal with the currently transmitted signal. The received signals, received in different receive channels (antenna patches) and down-mixed into the beat band, are transmitted as time signals to the digital computing unit 20 via an analog-to-digital converter.

[0039] The digitized time signal is transmitted via the first digital switch matrix 22, depending on the radar sensor's operating mode, either to the classical Doppler analysis processing unit 24 or the SAR analysis processing unit 26. In the Doppler analysis processing unit 24, the digitized complex amplitude of the received signal is recorded over the duration of a measurement period comprising multiple successive frequency ramps (linear frequency modulation). A two-dimensional spectrum is formed through a two-dimensional Fourier transform, indicating the spacing of the located objects in one dimension and the relative velocity in another. In this spectrum, each object is represented by peaks at the points of spacing and relative velocity. The signal from each individual antenna patch is analyzed in a dedicated receiving channel and converted into the corresponding spectrum. By comparing the complex amplitudes obtained for the same object (same peak) in different spectra, the object's positioning angle is determined with a certain accuracy through angle estimation. The positioning data thus obtained is then passed through the second digital switch matrix 28 to various downstream auxiliary functions, such as safety functions 30 (e.g., emergency braking, adaptive cruise control, etc.) and / or one or more comfort functions 32 (e.g., mapping, parking space search, etc.).

[0040] In the SAR analysis and processing unit 26, the digitized received signal is also recorded within a defined measurement period and subjected to a two-dimensional Fast Fourier Transform. The resulting spectrum provides the object spacing for each located object in one dimension. However, in another dimension, the spectrum is not analyzed and processed with respect to relative velocity, but rather with respect to the distance between objects. Figure 3 The dependence of relative velocity on positioning angle, as described herein, assumes that the object being located is stationary (this can be verified based on characteristic variations in object spacing) and that vehicle 10 moves along a linear trajectory at a constant and known speed during the duration of the measurement period. Depending on available computing power, this analysis processing can be performed in parallel for multiple receiving channels or for only a single receiving channel. As a result of the analysis processing in SAR analysis processing unit 26, object spacing data and high-resolution angle data are again obtained, or equivalently, the position coordinates (x, y) of each object are obtained; however, relative velocity data is typically not available, or at least not relative velocity data with high temporal resolution. This data is also delivered to safety function 30 and / or comfort function 32 via digital switch matrix 28.

[0041] In the example shown, the computing unit 20 further includes a fusion stage 34, in which the positioning data obtained by the analysis and processing units 24 and 26 are optionally fused together, weighted according to the quality of the data obtained through different analysis and processing methods. The fused result is also further transmitted to the safety function 30 and the comfort function 32 via a second digital switch matrix.

[0042] The analysis and processing units 24 and 26 further determine the optimal operating parameters for the corresponding analysis and processing algorithm for the transmitting and receiving hardware 18, and provide the corresponding control signal 36 to the hardware so that the operating parameters are matched to the corresponding measurement mode.

[0043] The radar sensor 10 also has a mode selection level 38, which can be integrated into the computing unit 20; however, it is shown as a separate block here for clarity. This mode selection level 38 receives request signals from safety functions 30 and comfort functions 32, assigns these request signals higher or lower priority based on traffic conditions (or driver instructions), and determines the current operating mode of the radar sensor based on these priorities. For example, if one of the safety functions 30 identifies a critical traffic situation indicating an impending collision, the data required for the emergency braking function (i.e., particularly high-resolution spacing and speed data) receives the highest priority, and the computing unit operates in a mode in which the primary or only Doppler analysis processing unit 24 is activated.

[0044] Figure 5Show the timeline for running based on Figure 4 The method for the radar sensor 10, in which the Doppler analysis processing unit 24 and the SAR analysis processing unit 26 operate in a time-division multiplexing manner. The time-division multiplexing period comprises a certain number N of successive measurement periods, which are... Figure 5 The data are numbered consecutively from 0 to N. Measurement periods 0 to N-1 are Doppler measurement periods, each with a duration Tcd during which the received signal is recorded. Each Doppler measurement period is separated by a processing time Tpd, during which the data recorded during the previous measurement period is analyzed and processed in the Doppler analysis and processing unit 24.

[0045] After the final Doppler measurement period N-1, and again after a processing time of length Tpd, is period N, which is the SAR measurement period, and in the example shown, this period has a longer duration Tcs than the Doppler measurement period. Then, after the SAR measurement period N, and after a processing time Tps for analyzing and processing the measurement data by the SAR analysis and processing unit 26, is the first Doppler measurement period "0" of the next multiplexing period.

[0046] If mode selection level 38 determines that comfort functions require higher priority—for example, because the driver of vehicle 10 is searching for a parking space—the multiplexing scheme is altered by reducing the number of Doppler measurement cycles per multiplexing cycle, thereby increasing the relative number of SAR measurement cycles. In extreme cases, Doppler measurement cycles can be completely stopped for the duration of the parking space search.

Claims

1. A method for using a radar sensor (14) in a motor vehicle (10), wherein, in SAR measurement mode, an object, including a stationary object (12), is located with high angular resolution according to the synthetic aperture principle, characterized in that, The same radar sensor (14) operates in staggered or simultaneous time in the SAR measurement mode and the Doppler measurement mode, wherein, in the Doppler measurement mode, the relative velocity of objects, including moving objects, is measured at a greater time resolution than in the SAR measurement mode. In the method, Depending on traffic conditions, the system switches between the SAR measurement mode and the Doppler measurement mode. The measurement cycle sequences in the Doppler measurement mode and the SAR measurement mode are interleaved according to a multiplexing scheme. The relative frequencies of the measurement cycles in the Doppler measurement mode and the SAR measurement mode vary according to traffic conditions. Measurement results obtained under different measurement modes are integrated, wherein, corresponding to the quality that the measurement results can achieve under the corresponding measurement mode, the results obtained under different measurement modes that involve the same measurement parameter are weighted.

2. The method according to claim 1, wherein the operating parameters of the analog transmitting and receiving hardware (18) of the radar sensor (14) are dynamically matched to the respective measurement modes to be applied.

3. The method according to claim 1 or 2, wherein the request signals for the safety and comfort functions of the motor vehicle are given a higher or lower priority according to the traffic conditions, and the measurement mode of the radar sensor is determined based on the priority.

4. A radar sensor for performing the method according to any one of the preceding claims, the radar sensor having analog transmitting and receiving hardware (18) and a digital computing unit (20), characterized in that, The transmitting and receiving hardware (18) and the computing unit (20) are configured to operate the radar sensor (14) in the SAR measurement mode and the SAR measurement mode in a time-staggered or simultaneous manner.

5. The radar sensor according to claim 4, wherein the radar sensor has a positioning angle range (16) extending over at least 90°.

6. A motor vehicle having a radar sensor (14) according to claim 5, wherein the radar sensor (14) is mounted in a vehicle (10) such that the positioning angle range (16) of the radar sensor covers at least the forward direction of the vehicle and a region on at least one side of the vehicle, on the side of the vehicle.

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