USE OF A RADAR SENSOR HAVING A WAVEGUIDE ANTENNA ARRAY FOR A METHOD FOR DETERMINING AN ESTIMATED EGO VELOCITY VALUE AND AN ESTIMATED ANGLE VALUE OF TARGETS

Abstract

Use of a radar sensor with a waveguide antenna array, having at least two groups of antenna units having a plurality of antenna elements, wherein antenna elements in each antenna unit are arranged next to one another in a first direction, wherein, in a first group, the antenna units are arranged offset with respect to one another in a second direction perpendicular to the first direction, and wherein, in a second group, the antenna units are arranged offset with respect to one another in the first direction, for a method for determining an estimated ego velocity value and an estimated angle value of targets. In the method, using the radar sensor, a distance between the radar sensor and the respective target is in each case measured, and a relative velocity of the respective target is in each case measured using the Doppler effect.

Claims

1-10. (canceled)

11. A method for determining an estimated ego velocity value and an estimated angle value of targets using a radar sensor with a waveguide antenna array, having at least two groups of antenna units having a plurality of antenna elements, wherein the antenna elements in each of the antenna units are arranged next to one another in a first direction, wherein, in a first group of the at least two groups of antenna units, the antenna units are arranged offset with respect to one another in a second direction perpendicular to the first direction, and wherein, in a second group of the at least two groups of antenna units, the antenna units are arranged offset with respect to one another in the first direction, the method comprising the following steps: measuring using the radar sensor, a distance between the radar sensor and each respective target; measuring, using the radar sensor, a relative velocity of each respective target using a Doppler effect; estimating a respective estimated angle value characterizing an angle between a direction of the radar sensor's ego velocity and each respective target; ascertaining an individual estimated ego velocity value of the radar sensor using the relative velocity and the estimated angle value for each target; classifying and subdividing the individual estimated ego velocity values in regard to stationary targets, the individual estimated ego velocity values of which lie within a predefinable range with respect to one another, and in regard to moving targets, the individual estimated ego velocity values of which lie outside the range; ascertaining a combined estimated ego velocity value from the individual estimated ego velocity values of the stationary targets; and ascertaining a corrected estimated angle value for each of the stationary targets using the combined estimated ego velocity value and the respective measured relative velocity.

12. The method according to claim 11, wherein, in the second group, the antenna units are additionally arranged offset with respect to one another in the second direction.

13. The method according to claim 11, wherein the at least two groups are alternately assigned to either the transmitting side or the receiving side.

14. The method according to claim 11, wherein the predefinable range is an error tolerance range ascertained from an error for the measurement of the relative velocity and from an error for the angle estimation.

15. The method according to claim 11, wherein an averaged velocity value for the stationary targets is determined as the combined estimated ego velocity value by weighted or unweighted averaging.

16. The method according to claim 11, wherein, for each moving target, the estimated angle value resulting from the angle estimation is adopted as the estimated angle value for the moving target.

17. The method according to claim 11, wherein an estimated velocity value for each moving target is ascertained from the relative velocity of the target measured using the Doppler effect.

18. The method according to claim 11, wherein an elevation angle is taken into account when ascertaining the individual estimated ego velocity value of the radar sensor using the relative velocity and the estimated angle value for each of the targets.

19. The method according to claim 11, wherein the radar sensor is a chirp sequence radar.

20. The method according to claim 11, wherein the ascertainment of the relative velocity is carried out using the Doppler effect using keystone processing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Embodiment examples of the present invention are shown in the figures and explained in more detail in the following description.

[0030] FIG. 1 shows an isometric illustration of a waveguide antenna of a radar sensor used for the method according to the present invention.

[0031] FIG. 2 shows a schematic illustration of a traffic situation, with a vehicle with the radar sensor and various targets and associated angles and relative velocities.

[0032] FIG. 3 shows a flowchart of an embodiment example of the method of the present invention.

[0033] FIG. 4A shows a diagram of the distribution of individual estimated ego velocity values of the radar sensor for different targets.

[0034] FIG. 4B shows a histogram for the distribution from FIG. 4A.

[0035] FIG. 5 shows a location diagram of a trajectory generated using one embodiment of the method according to the present invention and a trajectory generated using an odometry sensor

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0036] FIG. 1 shows a waveguide antenna 100 of a radar sensor S not shown in detail here. The waveguide antenna 100 has a waveguide antenna array consisting of multiple antenna elements 101. A plurality of antenna elements 101, in this example twelve each, are arranged in a column in a first direction R1 and together form an antenna unit 102 (in FIG. 1, an antenna unit is marked with a frame as an example). In this example, the first direction R1 corresponds to the vertical direction in a global reference system. The antenna elements 101 of an antenna unit 102 together transmit and receive radar signals. In FIG. 1, the phase centers 103 are marked for each antenna unit 102. The antenna units 102 of the waveguide antenna array are subdivided into two groups 104, 105. In this example, the first group 104 comprises eight antenna units 102, each of which has twelve antenna elements 101 arranged in columns in the first direction R1. In the first group 104, the antenna units 102 are arranged offset with respect to one another in the second direction R2. In this example, the second direction R2 corresponds to one of the horizontals in a global reference system and in this example, as shown in FIG. 2, runs in the direction of the ego velocity v.sub.ego of a vehicle F that has the radar sensor S. In general, the second direction R2 can also be at an angle to the ego velocity v.sub.ego of the vehicle F. As a result, only the antenna lobe is swiveled. The second direction R2 is associated with the azimuth angles .sub.1, .sub.2, .sub.3 and the first group 104 of antenna units 102 is used to measure the azimuth angles .sub.1, .sub.2, .sub.3. In this example, the second group 105 comprises three antenna units 102, which in turn each have twelve antenna elements 101 arranged in columns in the first direction R1. In the second group 105, the antenna units 102 are arranged offset with respect to one another in both the first direction R1 and the second direction R2. The second group 105 of the antenna units 102 serves to measure the elevation angles .sub.i and to measure the azimuth angles .sub.1, .sub.2, .sub.3. In the state shown here, the first group 104 of the antenna units 102 is assigned to the receiving side RX and the second group 105 of the antenna units 102 is assigned to the transmitting side TX. The radar signals received by the first group 104 are processed by means of digital beamforming. However, the assignment can also be changed so that the first group 104 is assigned to the transmitting side TX and the second group 105 is assigned to the receiving side RX. The waveguide antenna 100 is thus designed for MIMO. In other embodiment examples not shown, in the second group 105, the antenna units 102 may be arranged offset with respect to one another only in the first direction R1. This simplifies two-dimensional digital beamforming. The radar sensor S with the described waveguide antenna 100 or the described waveguide antenna array is used for the method described below.

[0037] FIG. 2 shows a schematic illustration of a traffic situation, with a vehicle F carrying a radar sensor S with a waveguide antenna 100 described above, and multiple other vehicles designated as targets Z1 to Z3. Typically, there are other targets in the vicinity that are not shown here, such as buildings, the infrastructure of the road, i.e. traffic signs, guard rails, and the like, or the road itself. The vehicle F and thus also the radar sensor S move along a straight line with an ego velocity v.sub.ego. From the radar sensor S, the azimuth angle .sub.1, .sub.2, .sub.3 between the direction of the ego velocity v.sub.ego and the direction of the respective target Z1, Z2, Z3 is displayed for each target Z1, Z2, Z3 shown. In addition, the relative velocity v.sub.rel,1, v.sub.rel,2, V.sub.rel,3 Of each target Z1, Z2, Z3 in relation to the radar sensor S is shown. If one of the targets, for example target Z1, is a stationary target, i.e. it is not moving, the associated relative velocity v.sub.rel,1 is given as a projection of the ego velocity v.sub.ego of the radar sensor S onto the associated azimuth angle .sub.1. The projections are shown in FIG. 1 for all three targets Z1, Z2, Z3. For a moving target, for example target Z2, which is moving at an unknown velocity, the velocity of target Z2 is part of the relative velocity v.sub.rel,2 and the measured relative velocity v.sub.rel,2 deviates from the projection.

[0038] FIG. 3 shows a flowchart of an embodiment example of the method according to the present invention. A plurality of targets, generally referred to here as i, are examined. Measurements 1 are taken while the vehicle F and the radar sensor S are moving. The measurements 1 are carried out using frequency-modulated continuous wave radar modulation (FMCW), in which chirp signals with rapidly increasing linear frequency ramps of the same slope are emitted at predetermined time intervals. The reflected signals are recorded and processed as received signals. Mixing the instantaneous transmitted signal with the received signal produces a low-frequency beat signal the frequency of which is proportional to the distance to the target i. Measurements 1 are carried out in such a way that the Doppler effect or the Doppler shift in the beat frequency is negligible or is taken into account in the evaluation.

[0039] Keystone processing 2 is then carried out. This involves estimating the Doppler shift or Doppler frequency by determining the temporal development of the phase of the complex measurement signals across the frequency ramps and compensating the corresponding linear change in distance (migration) for each estimated value. As a result, relative velocities {circumflex over (v)}.sub.rel,i are ascertained for each target i. The distance is then estimated using conventional Fourier processing 3, in particular a Fast Fourier Transform (FFT) from the time domain to the frequency domain. The generated two-dimensional spectra (distance and relative velocity) of the individual transmit-receive channel combinations are non-coherently averaged 4. For this purpose, the magnitude of each of these spectra is formed and these magnitudes or their magnitude squares are then summed. Detection with a constant false alarm rate (CFAR) 5 is used to recognize the targets in the measurements.

[0040] Furthermore, an angle estimation 6 is carried out in which estimated azimuth angle values {circumflex over ()}.sub.i are ascertained for the targets. The estimated azimuth angle value {circumflex over ()}.sub.i represents the azimuth angle between a measurement axis of the radar sensor S and the target i and thus also reflects the installation situation of the radar sensor S. Since the installation situation is known, the estimated azimuth angle value {circumflex over ()}.sub.i can be converted into an estimated value for the azimuth angle .sub.i between the direction of the ego velocity v.sub.ego and the direction of the target i by coordinate transformation. In the case shown in FIG. 2, the measuring axis is perpendicular to the direction of the ego velocity v.sub.ego. This results in the following correlation: {circumflex over ()}.sub.i=90.sub.i. Digital beamforming is used for the angle estimation 6. Simultaneous measurements are taken across the multiple antenna units 102 on the waveguide antenna array and a phase difference is calculated, from which the estimated azimuth angle value {circumflex over ()}.sub.i can then be ascertained. The influence of the ego velocity v.sub.ego of the radar sensor S is negligible for this type of angle estimation, so that the estimated azimuth angle values {circumflex over ()}.sub.i are ascertained independently of the ego velocity v.sub.ego of the radar sensor S. The angle estimation 6 also includes ascertainment of an elevation angle .sub.i between the plane in which the vehicle is moving and the height at which the target i is detected.

[0041] For each target i, the relative velocity {circumflex over (v)}.sub.rel,i, the estimated azimuth angle value {circumflex over ()}.sub.i and, if applicable, the elevation angle .sub.i are thus known. An individual estimated ego velocity value v.sub.ego,i is thus calculated 7 separately for each target i according to formula 2:

[00002]$\begin{array}{cc}{\hat{v}}_{\mathrm{ego},i}=\frac{{\hat{v}}_{\mathrm{rel},i}}{\sin {\hat{}}_i.Math.\cos {}_i}& \left(\mathrm{Formula}2\right)\end{array}$

[0042] FIG. 4A shows a diagram of the individual estimated ego velocity values {circumflex over (v)}.sub.ego,i calculated in this way for some targets i. FIG. 4B shows a histogram in which the ascertained number n is plotted for a plurality of different individual estimated ego velocity values {circumflex over (v)}.sub.ego,i. In both figures it can be seen that the individual estimated ego velocity values {circumflex over (v)}.sub.ego,i accumulate in an area B. In a typical traffic situation, there are significantly more stationary targets than moving targets with the same relative velocity radial to the radar sensor S.

[0043] With reference to FIG. 3, a clustering 8 is performed in which the individual estimated ego velocity values {circumflex over (v)}.sub.ego,i that are within the range B are assigned to stationary targets and the individual estimated ego velocity values {circumflex over (v)}.sub.ego,i that are outside the range B are assigned to moving targets. Thus the moving targets are identified (MTImoving target Indication) and separated from the stationary targets. Range B is defined by the errors in measurement 1 and angle estimation 6 and represents an error tolerance range.

[0044] The individual estimated ego velocity values {circumflex over (v)}.sub.ego,i associated with the stationary targets, i.e., located within the range B, are averaged 9 to obtain a combined estimated ego velocity value {circumflex over (v)}.sub.ego,komb. Different types of averaging can be performed, for example a classical averaging, such as an arithmetic mean, a weighted averaging, for example with weights depending on the signal-to-noise ratio, a determination of the maximum in the histogram, a formation of a median, etc. Since the combined estimated ego velocity value {circumflex over (v)}.sub.ego,comb was calculated, in principle, without the moving targets, it can be regarded as an estimated value {circumflex over (v)}.sub.ego for the actual ego velocity {circumflex over (v)}.sub.ego of the radar sensor S. This achieves autofocus. For each stationary target, an angle calculation 10 is also performed from the relative velocity {circumflex over (v)}.sub.rel,i for the stationary target ascertained by the keystone processing 2 with the aid of the Doppler effect and the calculated individual estimated ego velocity value {circumflex over (v)}.sub.ego,i for the stationary target using formula 3:

[00003]$\begin{array}{cc}{\hat{}}_{\mathrm{corr},i}=\arcsin \left(\frac{{\hat{v}}_{\mathrm{rel},i}}{{\hat{v}}_{\mathrm{ego}}\cos {}_i}\right)& \left(\mathrm{Formula}3\right)\end{array}$

[0045] Consequently, a corrected estimated angle value {circumflex over ()}.sub.corr,i is calculated, which can be considered as the actual azimuth angle of the target with respect to the radar sensor S.

[0046] For the moving targets, however, the angle calculation 10 described above would lead to an incorrect angle estimation, as the velocity component of the moving target is unknown and therefore cannot be taken into account. Consequently, for a moving target, the estimated azimuth angle value {circumflex over ()}.sub.i ascertained during the angle estimation 6 is adopted 11. Although this does not improve the angle estimation, it does avoid incorrect angle estimation. Finally, a radial estimated velocity value of the moving target can be calculated 12 by subtracting from the relative velocity {circumflex over (v)}.sub.rel,i ascertained by the keystone processing 2 with the aid of the Doppler shift the combined estimated ego velocity value {circumflex over (v)}.sub.ego,comb ascertained for the stationary targets by averaging 9 weighted by the cosine of the azimuth of this target.

[0047] FIG. 5 shows a comparison between an odometry trajectory T.sub.o, which was ascertained conventionally using an odometry sensor, and a trajectory T.sub.v, which was generated using an embodiment of the method according to the present invention. It can be seen that the two trajectories match very well and thus the autofocus using the method according to the present invention provides precise results.