METHOD FOR ELEVATION ANGLE ESTIMATION BASED ON AN ULTRASOUND SENSOR

Abstract

A method for determining the elevation angle and/or azimuth angle of a signal received by an ultrasound sensor includes: providing an ultrasound sensor with a frequency-dependent radiation pattern; transmitting a first ultrasound wave at a first frequency; transmitting a second ultrasound wave at a second frequency different from the first frequency; receiving reflections of the first and second waves, the reflections being caused by an object; and determining the elevation angle of the first and second reflected waves based on amplitudes of the reflections of the first and second waves. Determining the elevation angle (and/or azimuth angle includes calculating a ratio between the amplitudes of received reflections of the first and second waves and mapping a calculated ratio to an elevation angle and/or azimuth angle. The mapping is based on a predetermined ratio curve or ratio dataset which associates a certain amplitude ratio to an elevation angle and/or azimuth angle.

Claims

1. A method for determining the elevation angle and/or azimuth angle of a signal received by an ultrasound sensor, the method comprising: providing an ultrasound sensor with a frequency-dependent radiation pattern; transmitting at least a first ultrasound wave at a first frequency; transmitting at least a second ultrasound wave at a second frequency different from the first frequency; receiving reflections of the first and second ultrasound waves, the reflections being caused by a certain object; determining the elevation angle and/or azimuth angle of the first and second reflected ultrasound waves based on amplitudes of the reflections of the first and second ultrasound waves; wherein determining the elevation angle and/or azimuth angle is performed by calculating a ratio between the amplitudes of the reflections of the first and second ultrasound waves and mapping the calculated ratio to an elevation angle and/or azimuth angle, wherein the mapping is performed based on a predetermined ratio curve or ratio dataset which associates a certain amplitude ratio to an elevation angle and/or azimuth angle.

2. The method according to claim 1, wherein the radiation pattern of the ultrasound sensor narrows with increasing frequency.

3. The method according to claim 1, wherein determining the elevation angle comprises removing ambiguities of the radiation pattern in a vertical direction.

4. The method according to claim 3, wherein the ambiguities of the radiation pattern in the vertical direction are removed by using at least one ultrasound sensor providing an asymmetric radiation pattern in the vertical direction.

5. The method according to claim 3, wherein the ambiguities of the radiation pattern in the vertical direction are removed by using received reflections of at least one further ultrasound sensor.

6. The method according to claim 3, wherein ambiguities of the radiation pattern in the vertical direction are removed assuming that a detected object is arranged in a lower half-space.

7. The method according to claim 3, wherein ambiguities of the radiation pattern in the vertical direction are removed by using at least one further sensor using a technology different to ultrasound.

8. The method according to claim 1, wherein the azimuth angle of the object is determined based on at least one further ultrasound sensor located at a different position.

9. The method according to claim 1, wherein transmitting the first and second ultrasound waves is performed by providing a frequency-modulated transmit pulse to the ultrasound sensor.

10. The method according to claim 9, wherein the frequency-modulated transmit pulse comprises a linearly or non-linearly varied frequency over time.

11. The method according to claim 9, wherein the frequency-modulated transmit pulse comprises a frequency varying in steps over time.

12. The method according to claim 1, further comprising providing multiple transmit pulses having different center frequencies to the ultrasound sensor.

13. A driving assistance system comprising at least one ultrasound sensor having a frequency-dependent radiation pattern and a control entity for controlling a provision of ultrasound signals to the ultrasound sensor, the control entity being configured to: initiate transmission of at least a first ultrasound wave at a first frequency; initiate transmission of at least a second ultrasound wave at a second frequency different from the first frequency; receive information regarding reflections of the first and second ultrasound waves, the reflections being caused by a certain object; determine the elevation angle and/or azimuth angle of the first and second reflected ultrasound waves based on the amplitudes of the reflections of the first and second ultrasound waves; determine the elevation angle and/or azimuth angle by calculating a ratio between the amplitudes of received reflections of first and second ultrasound waves and mapping the calculated ratio to an elevation angle and/or azimuth angle, wherein the mapping is performed based on a predetermined ratio curve or ratio dataset which associates a certain amplitude ratio to an elevation angle and/or azimuth angle.

14. A vehicle comprising a driving assistance system, the driving assistance system configured to perform a method according to claim 1.

15. A driving assistance system comprising at least one ultrasound sensor having a frequency-dependent radiation pattern, the driving assistance system being configured to: initiate transmission of at least a first ultrasound wave at a first frequency; initiate transmission of at least a second ultrasound wave at a second frequency different from the first frequency; receive information regarding reflections of the first and second ultrasound waves, the reflections being caused by a certain object; determine the elevation angle and/or azimuth angle of the first and second reflected ultrasound waves based on the amplitudes of the reflections of the first and second ultrasound waves; determine the elevation angle and/or azimuth angle by calculating a ratio between the amplitudes of received reflections of first and second ultrasound waves and mapping the calculated ratio to an elevation angle and/or azimuth angle, wherein the mapping is performed based on a predetermined ratio curve or ratio dataset which associates a certain amplitude ratio to an elevation angle and/or azimuth angle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

[0037] FIG. 1 shows a schematic illustration of a parking situation in which a vehicle is parking into a parking space;

[0038] FIG. 2 schematically illustrates the radiation pattern of an ultrasound sensor included in a bumper in the parking situation of FIG. 1;

[0039] FIG. 3 illustrates the gain of an ultrasound sensor dependent on elevation angle for two different ultrasound frequencies;

[0040] FIG. 4 illustrates the ratio of gain of an ultrasound sensor dependent on elevation angle according to FIG. 3;

[0041] FIG. 5 illustrates the 2D-radiation pattern of an ultrasound sensor dependent on azimuth and elevation angles for two different ultrasound frequencies;

[0042] FIG. 6 illustrates a linearly frequency-modulated first ultrasound signal and a stepped frequency-modulated second ultrasound signal; and

[0043] FIG. 7 shows a schematic block diagram illustrating the steps of a method for determining the elevation angle of a signal received by an ultrasound sensor.

DETAILED DESCRIPTION

[0044] The present invention will now be described more fully with reference to the accompanying drawings, in which example embodiments are shown. The embodiments in the figures may relate to preferred embodiments, while all elements and features described in connection with embodiments may be used, as far as appropriate, in combination with any other embodiment and feature as discussed herein, in particular related to any other embodiment discussed further above. However, this invention should not be construed as limited to the embodiments set forth herein. Throughout the following description similar reference numerals have been used to denote similar elements, parts, items or features, when applicable.

[0045] The features of the present invention disclosed in the specification, the claims, examples and/or the figures may both separately and in any combination thereof be material for realizing the invention in various forms thereof.

[0046] FIG. 1 shows a schematic top view on a parking situation in which a vehicle 1 is parking into a parking space being bordered by a curb 3.

[0047] The vehicle 1 comprises a driving assistance system having multiple ultrasound sensors 2 being placed at different positions at the vehicle 1.

[0048] The curb 3 may comprise a certain height and can be detected by said driving assistance system, specifically by one or more ultrasound sensors 2 of the driving assistance system.

[0049] FIG. 2 shows a side-view of the parking situation. On the left side, a bumper 1.1 of the vehicle 1 is shown which may comprise one or more ultrasound sensors 2. The ultrasound sensor 2 may have a radiation pattern 2.1 comprising a lower radiation pattern portion which covers a lower half-space LHS and an upper radiation pattern portion which covers an upper half-space UHS. The dashed line indicates a horizontal plane dividing the radiation pattern 2.1 in said lower radiation pattern portion and said upper radiation pattern portion. A curb 3 may be located in said lower half-space LHS.

[0050] FIG. 3 shows the radiation pattern 2.1 of an ultrasound sensor 2 in vertical direction, i.e. the angle values refer to elevation angle, at different frequency values. The solid line indicates the radiation pattern 2.1 at a first frequency and the dashed line indicates the radiation pattern 2.1 at a second frequency, said first and second frequencies being different and said first frequency being higher than the second frequency. As shown, the radiation pattern 2.1 of the ultrasound sensor 2 narrows with increasing frequency.

[0051] Therefore, by providing ultrasound waves to the ultrasound sensor 2 at at least two different frequencies and evaluating the amplitudes of the reflected waves having different frequencies, the elevation angle α of an object (in the present example the curb 3) causing said reflections can be determined. More specifically, the elevation angle α can be determined by comparing the amplitudes of the reflected waves. Due to the frequency dependency of the radiation pattern leading to different shapes of radiation pattern and therefore an elevation dependency of the radiation pattern, the elevation angle α of the object can be determined.

[0052] The step of comparing the amplitudes of the reflected waves comprises calculating a ratio of the amplitudes of the reflected waves and mapping said ratio to an elevation value, wherein said mapping is performed based on a predetermined ratio curve or ratio dataset which associates a certain amplitude ratio to an elevation angle and/or azimuth angle.

[0053] FIG. 4 shows a graph illustrating the quotient of amplitudes of reflected waves having different frequency and being received from different elevation angles. By means of said graph, a ratio value of a first reflected wave having a first frequency and a second reflected wave having a second frequency can be associated to an elevation angle.

[0054] As shown in FIGS. 3 to 5, the radiation pattern 2.1 may be symmetric or essentially symmetric with respect to a centre elevation angle. In the present example, the centre elevation angle may be, for example, 0° or essentially 0°, i.e. the radiation pattern 2.1 may be symmetric with respect to a horizontal plane. According to other embodiments, the ultrasound sensors installed in the vehicle 1 may be pitched slightly upwards. Thus, for example, the centre elevation angle may be in the range between 1° to 10°, especially in the range between 1° to 4°. Said symmetry of radiation pattern 2.1 may lead to an ambiguity in determining elevation angle, i.e. a certain amplitude ratio of the reflected waves can be associated with at least two elevation angles. A first, positive elevation angle may be arranged in the upper half-space UHS and a second, negative elevation angle may be arranged in the lower half-space LHS.

[0055] Said ambiguity of elevation angle can be resolved in different ways:

[0056] According to a first embodiment, a further sensor, specifically an ultrasound sensor having a radiation pattern being non-symmetric with respect to the horizontal symmetry plane of the other sensors can be used. Based on a measured amplitude derived from said further sensor, the ambiguity can be remedied.

[0057] According to another embodiment, the ambiguity can be remedied by assuming that the detected object is always arranged in the lower half-space LHS because in the vast majority of cases, said assumption leads to a correct detection result.

[0058] According to yet another embodiment, the ambiguity can be remedied by using a further information source, e.g. a further ultrasound sensor with an inclined radiation pattern (i.e. the beam maximum of radiation pattern is not arranged in the first sensor's horizontal plane). A further example may be a sensor using technology different to ultrasound, e.g. a camera, radar sensor, LIDAR sensor etc.

[0059] Also information obtained by said one or more ultrasound sensors at different positions of the vehicle 1 can be used to remove ambiguities. In other words, multiple information gathered at different vehicle positions along the trajectory are exploited to remove ambiguities.

[0060] As shown in FIG. 5, the radiation pattern of an ultrasound sensor may have a 2D-shape, i.e. a certain beam shape in view of azimuth and elevation. Therefore also ambiguity of detection results occurs in the horizontal direction, i.e. in azimuth. In order to resolve azimuth ambiguity, information of a further sensor located at a different location (e.g. at a different position on the bumper) can be used. A preferred technique for remedying azimuth ambiguity may be trilateration.

[0061] As mentioned before, determination of elevation angle exploits the frequency dependency of radiation pattern of an ultrasound sensor 2, i.e. the 2D-shape of radiation beam is dependent on the frequency of the ultrasound wave. Said ultrasound waves having at least two different frequencies can be generated as follows:

[0062] According to a first embodiment, two or more transmit pulses having different centre frequencies can be used.

[0063] According to a second embodiment, a frequency-modulated transmit pulse can be used. Said frequency-modulated transmit pulse may be, for example, a linear frequency-modulated signal (also called “chirp signal”).

[0064] According to a third embodiment, a single frequency-modulated transmit pulse can be used where the frequency follows a step function.

[0065] FIG. 6 shows a linear frequency-modulated signal and a stepped frequency-modulated signal. The frequency of linear frequency-modulated signal changes linearly over time, whereas the frequency of stepped frequency-modulated signal changes stepwise over time.

[0066] FIG. 7 shows a block diagram illustrating method steps of a method for determining the elevation angle α of a signal received by an ultrasound sensor 2.

[0067] First, an ultrasound sensor 2 with a frequency-dependent radiation pattern is provided (S10).

[0068] Said ultrasound sensor 2 transmits at least a first ultrasound wave at a first frequency (S11) and at least a second ultrasound wave at a second frequency different to the first frequency (S12).

[0069] After transmitting said ultrasound waves, reflections of the first and second ultrasound waves are received, said reflections being caused by a certain object (S13).

[0070] After receiving said reflections, the elevation angle α of the first and second reflected ultrasound waves is determined based on the amplitudes of the reflections of the first and second ultrasound waves (S14), wherein determining the elevation angle α is performed by calculating a ratio between the amplitudes of received reflections of first and second ultrasound waves and mapping the calculated ratio to an elevation angle α, and wherein said mapping is performed based on a predetermined ratio curve or ratio dataset which associates a certain amplitude ratio to an elevation angle.

[0071] It should be noted that the description and drawings merely illustrate the principles of the proposed invention. Those skilled in the art will be able to implement various arrangements that, although not explicitly described or shown herein, embody the principles of the invention.

LIST OF REFERENCE NUMERALS

[0072] 1 vehicle [0073] 1.1 bumper [0074] 2 ultrasound sensor [0075] 2.1 radiation pattern [0076] 3 curb [0077] LHS lower half-space [0078] UHS upper half-space