METHOD AND MOTOR VEHICLE RADAR SYSTEM FOR TRACKING AN OBJECT

Abstract

Methods for tracking an object (104), comprising: Transferring a source signal (122) into a volume containing the object (104); Receiving a reflected signal (124) from the volume in response to the source signal (122), wherein the reflected signal (124) includes a reflection (124o) of the source signal (122) from the object (104); Determining a range (r) for the object (104) from the reflected signal (124); Estimating a ground signal (124g) in a specific area (r); Estimating the amount of the ground signal (124g) in the reflected signal (124), wherein the estimation of the amount of the ground signal (124g) in the reflected signal (124) comprises forming a ratio that compares the ground signal (124g) in the specified area (r) with a total reflected signal in the specified area (r); and Selecting the object (104) to track based on estimating the amount of ground signal (124g) in the reflection (124o) from the object (104), characterized by the fact that forming the ratio includes: Correlate the ground signal (124g) in the specified area (r) with the reflected signal (124) in the specified area (r) of the object (104) to obtain a correlation value; Determining overall performance in a specific area (r); and Calculating the ratio of the correlation value in the specific area (r) to the overall performance in the specific area (r).

Description

INTRODUCTION

[0001] The invention relates to a method for tracking an object and a motor vehicle radar system for tracking an object. The subject matter of the disclosure relates to radar systems, and in particular to a system and method for mitigating the effects of ground reflections in radar signals.

[0002] Vehicle tracking systems include one or more radar systems capable of determining parameters such as the ranges of various objects relative to the vehicle and the speeds of the objects relative to the vehicle. The tracking system can use these parameters to alert the driver to the objects or to operate the vehicle's autonomous driving system to perform maneuvers that avoid interference with the objects. A radar system includes a transceiver that transmits a source signal, generally a radio frequency signal, into a volume of space containing the objects, and a receiver that receives reflected signals (reflections of the source signal) from the objects. Due to the location of the radar system on the vehicle, a significant portion of the source signal is reflected off the ground and can obscure reflections from the objects, thereby compromising the reliability of the tracking system.Accordingly, it is desirable to provide a method for determining the effect of ground signals in a reflection signal received at a radar system.

[0003] The document DE 10 2009 032 124 A1 discloses a method according to the preamble of claim 1 and a motor vehicle radar system according to the preamble of claim 4. The documents DE 10 2013 209 530 A1, DE 102 07 437 A1 and DE 698 29 777 T2 disclose related methods and systems.

[0004] It is an object of the invention to improve driving safety.

[0005] This object is achieved according to the invention by the features of the independent claims. Advantageous further developments are defined in the subclaims. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Features, advantages and details appear only as examples in the following detailed description of the embodiments, which detailed description refers to the drawings, where: Fig. 1 shows a vehicle with an autonomous drive system suitable for improving the driving safety of the vehicle; Fig. Figure 2 shows a side view of the vehicle and the radar transducer mounted on the front bumper of the vehicle; Fig. Figure 3 is a schematic diagram illustrating a method for determining the amount of ground signal in a reflected signal; Fig. 4 shows spectra for a reflected signal and for a calibration ground signal in one embodiment; and Fig. Figure 5 shows a flowchart illustrating the method disclosed herein for tracking an object in an environment including a ground signal. DETAILED DESCRIPTION

[0007] The following description is merely exemplary in nature and is not intended to limit the present disclosure in its applications or uses. It should be noted that throughout the drawings, the same reference characters refer to the same or corresponding parts and features.

[0008] According to an exemplary embodiment of the disclosure, Fig. 1 shows a vehicle 100 with an autonomous driving system 102 suitable for improving the driving safety of the vehicle 100. In one embodiment, the autonomous driving system 102 can be used to provide a signal to a driver of the vehicle 100 to alert the driver to one or more objects in the vicinity of the vehicle 100. In another embodiment, the autonomous driving system 102 can cause the vehicle 100 to react to one or more objects without waiting for a driver response or alerting the driver.

[0009] The autonomous driving system 102 includes a radar system 108, a control unit 116, and a collision avoidance system 112. The radar system 108 operates one or more radar transducers at various locations on the vehicle 100, such as the transducer 110 at a front of the vehicle 100, e.g., on a front bumper. Other exemplary transducer locations may include, for example, a rear of the vehicle 100, such as on a rear bumper, or a side of the vehicle, such as a side mirror. The transducer 110 includes a transmitter and receiver. The transmitter of the transducer 110 transmits a source signal 122 into a volume in front of the vehicle 100 in which the object 104 is located. The object 104 may include an exemplary object of interest to the driver of a vehicle 100, such as a tree, a vehicle, a pedestrian, a light pole, etc. The object 104 may be stationary or in motion.The source signal 122 travels into the volume over a selected angular range. The reflection of the source signal 122 from elements in the volume is received at the receiver as a reflected signal 124. The reflected signal 124 may include various reflection signals. The object 104 reflects the source signal 122 in the form of a reflection 124o. Some of the reflected signals 214 are due to the reflection of the source signal 122 from the ground, also referred to herein as a ground signal 124g. Thus, in any region of the object 104, a portion of the reflected signal 124 is due to a reflection 124o from the object 104, and a portion of the reflected signal 124 is a ground signal 124g.

[0010] The radar system 108 controls the operation of the transducer 110 and receives radar measurement data of the object 104. The radar measurement data may include an intensity, frequency, etc., of the source signal 122 and an intensity, frequency, etc., of the reflected signal 124. The radar system 108 provides the radar measurement data to the control unit 116.

[0011] The control unit 116 may include one or more processors 114 for determining a location and / or velocity (i.e., Doppler frequency) of the object 104 from the radar measurement data. In addition, the control unit 116 may perform the methods described herein for mitigating the impact of the ground signal 124g in the reflected signal 124. Depending on the relative strength of the ground signal in the reflected signal 124, the processor 114 may determine that the reflected signal 124 is either indistinguishable from a ground signal 124g or that the reflected signal 124 represents an object 104 that the control unit 116 wishes to track. If the reflected signal 124 is determined to represent an object 104 for tracking, the control unit 116 may provide the position and / or velocity of the object 104 to the collision avoidance system 112.

[0012] The collision avoidance system 112 receives inputs (e.g., speed, braking rate, acceleration) of the vehicle 100 from internal components and other sensors of the vehicle 100 and uses this information, along with the determined position and / or speed of the object 104, to determine a path to avoid impacting the object 104. The collision avoidance system 112 may alert a driver if the object 104 poses a hazardous situation to the vehicle 100. Alternatively, the collision avoidance system 112 may maneuver the vehicle 100 along the determined path by making one or more changes to the speed of the vehicle 100, changing the direction of travel of the vehicle, etc. In this way, the collision avoidance system 112 provides the ability for the vehicle 100 to safely travel through its environment without interacting with the object 104.

[0013] Fig. Figure 2 shows a side view of the vehicle 100 and the radar transducer 110 mounted on the front bumper of the vehicle. The transducer 110 is located at a selected height h above the ground and detects the object 104 within the range r from the transducer 110. Based on the height h of the transducer 110 and the range r to the object 104, an elevation angle α for the object 104 can be determined. Reflected signals received within the range r from an elevation or height below the elevation angle α are reflections from the ground. Reflected signals received within the range r from an elevation or height above the elevation angle α can be considered reflections from the object 104.

[0014] The method disclosed herein compares a signal reflection from the object in a selected area of ​​the object with a ground signal in the selected area to determine whether a received reflected signal represents an object for tracking. The ground signal is provided during a calibration stage by storing a calibration ground signal in a memory of the control unit 116 and accessing the calibration ground signal at an appropriate time. To obtain a calibration ground signal, the transducer 110 is placed in an open environment devoid of objects. The transducer 110 is placed at a height h corresponding to the height at which the transducer 110 is disposed on the vehicle 100. In such an open environment, the signals received at the transducer 110 are solely due to reflection from the ground, i.e., a calibration ground signal.The calibration ground signal is stored in a memory. In one embodiment, the calibration ground signal is stored as a frequency spectrum in k-space, for example, by performing a Fast Fourier Transform (FFT) on the received calibration ground signal. The memory can store additional ground signals for a variety of transducer frequencies, transducer heights, etc.

[0015] Fig. 3 shows a schematic diagram 300 illustrating a method for determining the amount of ground signal in a reflected signal. The method may be performed by a processor, such as processor 114 of control unit 116. Diagram 300 includes a detector 302 that receives radar reflection signals and a storage device 304. Detector 302 receives a reflected signal from a volume proximate vehicle 100 by transmitting a source signal into the volume and receiving a reflected signal in response. For illustration, the volume includes a single object. Therefore, the plurality of reflections come from both the object and the ground. The reflected signal is used to determine a region of the object. In various methods, a Fast Fourier Transform (FFT) is performed on the reflected signal to obtain a frequency spectrum in k-space.

[0016] Fig. 4 shows spectra for a reflected signal and for a calibration ground signal in one embodiment. K-space 402 displays a spectrum 406 for the reflected signal. Spectrum 406 includes a frequency peak 408. Some of spectra 406 may be due to ground signals. The position of frequency peak 408 corresponds to the range of object 104. K-space 404 displays a spectrum 410 of the calibration ground signal obtained during calibration. Each k-space 402 and 404 includes multiple frequency-domain bins. The size of the frequency-domain bin is the same for each of k-spaces 402 and 404 because the same frequency is used in calibration as in tracking. The range bin of k-space 402 that includes frequency peak 408 is identified and provided to storage device 304, which stores k-space 404.In k-space 404, the portion 412 of the spectrum 410 within the identified range bin is selected for further calculations. The portion 412 of the spectrum 410 within the identified range bin provides a ground signal intensity in the selected area of ​​the object 104.

[0017] Returning to Fig. 3, the ground signal in the selected area is correlated with the reflection signal of the object in the selected area using a correlation function 306. In particular, a correlation function 306 is calculated that includes the portion 412 of the spectrum 410 and the portion of the spectrum 406 within the identified frequency bin. This correlation function 306 provides a correlation value 'a' in the area of ​​the object 104. The reflected signal in the area of ​​the object is then used to generate a total power 'b' for the area of ​​the object. The total power for the area may include a power for the identified frequency bin in k-space 402. A ratio a / b is formed from the correlation value in the area and the total power in the area. The ratio a / b is a measured value for a set of ground signals in the reflection in the area of ​​the object.The ratio a / b is compared to a selected noise threshold ε to select a course of action regarding the reflected signal. If the ratio a / b is greater than the selected noise threshold, the received signal is considered to be due in large part to a ground signal. Such signals are of little interest for tracking. Thus, if a / b>=ε, the processor 114 may select to ignore the signal. However, if a / b<ε, the processor 114 may determine that the signal corresponds to the object 104. The processor 114 may then select to perform or initiate a tracking operation on the object 104.

[0018] After tracking the object 104, parameters of the object, such as range, Doppler frequency, relative speed, etc., can be provided to the collision avoidance system 112 so that the vehicle 110 can maneuver safely with respect to it. In various embodiments, the decision process (i.e., comparing the ratio a / b to the noise threshold ε) allows both the processor 114 and the collision avoidance system 112 to ignore ground signals, thereby freeing up resources that would otherwise be used to track less interesting ground signals.

[0019] Fig.5 shows a flowchart 500 illustrating the method disclosed herein for tracking an object in an environment containing a ground signal. In box 502, a reflected signal is obtained from a volume of space containing the object. In box 504, a range of the object is determined from the reflected signal. In box 506, a calibration ground signal corresponding to the range of the object is obtained. In box 508, the calibration ground signal in the range of the object is correlated with the reflectance obtained from the object to obtain a correlation value in the range of the object. In box 510, a total power in the range of the object is determined. In box 512, a ratio of the correlation value in the range to the total power in the range is formed. In box 514, the ratio is compared to a selected noise threshold.If the ratio in box 516 is greater than or equal to the noise threshold, the signal is ignored as a pure ground signal. If the ratio is less than the noise threshold, the signal is assumed to represent the object in box 518, and the object is tracked.

Claims

[1] A method for tracking an object (104), comprising: Transmitting a source signal (122) into a volume containing the object (104); Receiving a reflected signal (124) from the volume in response to the source signal (122), the reflected signal (124) including a reflection (124o) of the source signal (122) from the object (104); Determining a range (r) for the object (104) from the reflected signal (124); Estimating a ground signal (124g) in the specified area (r); Estimating an amount of the ground signal (124g) in the reflected signal (124), wherein estimating the amount of the ground signal (124g) in the reflected signal (124) comprises forming a ratio comparing the ground signal (124g) in the determined area (r) with a total reflected signal in the determined area (r); and Selecting the object (104) to track based on estimating the amount of ground signal (124g) in the reflection (124o) from the object (104), characterized by that forming the relationship includes: Correlating the ground signal (124g) in the specific area (r) with the reflected signal (124) in the specific area (r) of the object (104) to obtain a correlation value; Determining a total power in the specified range (r); and Forming the ratio of the correlation value in the given area (r) to the total power in the given area (r). [2] The method of claim 1, further comprising at least one of the following: (i) ignoring the reflection (124o) of the object (104) if the ratio is greater than a selected noise threshold; and (ii) tracking the object (104) if the ratio is less than a selected noise threshold. [3] The method of claim 1, wherein the ground signal (124g) is a calibration ground signal obtained by transmitting the source signal (122) into a calibration volume providing only ground reflections, the ground signal (122g) being estimated by selecting the calibration ground signal for the area of ​​the object (104). [4] A motor vehicle radar system (108) for tracking an object (104), comprising: a transmitter for transmitting a source signal (122) into a volume containing the object (104); a receiver for receiving a reflected signal (124) from the volume in response to the source signal (122), the reflected signal (124) including a reflection (124o) of the source signal (122) from the object (104); and a processor (114) configured to: Determining an area (r) for the object (104) from the reflected signal (124), Estimating a ground signal (124g) for the specific area (r) of the object (104), Estimating an amount of the ground signal (124g) in the reflection (124o) from the object (104), comprising forming a ratio between the ground signal (124g) in the specific area (r) to a total reflected signal in the specific area (r), and Selecting the object (104) to track the object (104) based on estimating the amount of ground signal (124g) in the reflection (124o) from the object (104), characterized by that forming the relationship includes: Correlating the ground signal (24g) in the specific area (r) with the reflected signal (124) in the specific area (r) of the object (104) to obtain a correlation value; Determining a total power in the specified range (r); and Forming the ratio of the correlation value in the given area (r) to the total power in the given area (r). [5] The automotive radar system (108) of claim 4, wherein the processor (114) is further configured to at least one of the following: (i) disregard the signal as noise if the ratio is greater than a selected noise threshold; and (ii) track the object (104) if the ratio is less than a selected noise threshold. [6] The automotive radar system (108) of claim 4, wherein the ground signal (124g) is a calibration ground signal obtained by transmitting the source signal (122) into a calibration volume containing only ground reflections (124g), the processor (114) estimating the ground signal (124g) by selecting the calibration ground signal at the region of the object (104).

Images