DE102014226030A1 - Method for operating a radar system and radar system - Google Patents

Abstract

The present invention discloses a method of operating a radar system having at least one radar sensor comprising emitting a radar signal having a plurality of ramps receiving the radar signal reflected from objects, calculating a two-dimensional spectrum for the received radar signal, determining a deviation of locality Maxima in the two-dimensional spectrum representing the objects from a shape expected for unaccelerated objects, and determining each acceleration of each of the objects based on the detected deviation. Furthermore, the present invention discloses a corresponding radar system.

Description

The present invention relates to a method of operating a radar system comprising at least one radar sensor. Furthermore, the present invention relates to a corresponding radar system.

State of the art

Also, when the present invention is described below in the context of vehicle radar systems, it is not limited thereto and may be used with any radar systems.

In modern vehicles, a variety of electronic systems are used, the z. B. can serve to assist a driver in driving the vehicle. Brake assistants, for example, can detect drivers driving ahead and brake and accelerate the vehicle accordingly, so that a predetermined minimum distance to the preceding road users is always maintained. Such brake assistants may also initiate emergency braking if they recognize that the distance to the preceding vehicle is too low.

Other driver assistance systems can also observe the area behind the vehicle and the driver, z. B. in a detected by a setting of the turn signal lane warning of an approaching vehicle, or z. B. the restraint systems of the vehicle, such. As belt tensioners, prepare when an imminent impact is detected.

In order to be able to provide such assistance systems in a vehicle, it is necessary to acquire data about the surroundings of the respective vehicle. In the above example of a brake assistant, it is z. For example, it may be necessary to detect the position of a preceding road user in order to be able to calculate the distance of the vehicle to the preceding road user.

To capture the vehicle environment different sensor types can be used. For example, radar sensors, ultrasonic sensors, cameras or the like can be used.

As radar sensors FMCW radar sensors are usually used in vehicles for detecting the vehicle environment, with which the distance of the vehicle to the preceding road user can be determined.

For example, the shows DE 10 2013 200 951 A1 such a radar sensor.

For a comprehensive environment detection is also desirable to be able to determine the acceleration of the preceding road user.

Disclosure of the invention

The present invention discloses a method with the features of claim 1 and a radar system with the features of claim 10.

Accordingly, it is provided:
A method of operating a radar system having at least one radar sensor, comprising emitting a radar signal having a plurality of ramps, receiving the radar signal reflected from objects, calculating a two-dimensional spectrum for the received radar signal, determining a deviation of the shape of local maxima in the radar two-dimensional spectrum representing the objects from a shape expected for unaccelerated objects, and determining each acceleration of each of the objects based on the detected deviation.

It is also provided:
A radar system comprising a radar sensor configured to emit a radar signal having a plurality of ramps and to receive the radar signal reflected from objects, and having a calculator which is configured to accelerate, based on the received radar signal, a method according to the invention To calculate objects.

Advantages of the invention

The finding underlying the present invention is that it is not possible in FMCW radar systems to detect the acceleration of an object directly. A detection of the acceleration of an object is z. B. only on the detection of two speeds of the object at different times and a subsequent difference or the like possible.

The idea underlying the present invention is now to take this knowledge into account and to provide a possibility in which, in a single measuring cycle, the acceleration of an object relative to the radar sensor or z. B. a vehicle in which the radar sensor is integrated, also called relative acceleration, can be detected.

For this purpose, the present invention provides that a radar signal is transmitted and the radar signal reflected by objects is received. This can be z. B. by a radar sensor of a radar system according to the invention.

For the received radar signal, a two-dimensional spectrum is then calculated. In particular, the two-dimensional spectrum can have a quadratic division into a multiplicity of frequency bins (k, l).

In order to determine the acceleration of objects relative to the radar sensor, the invention provides that in the two-dimensional spectrum the shape of the local maxima, which are caused by the objects, is evaluated. In particular, the deviation of the shape of the local maxima from a form expected for unaccelerated objects is evaluated, and the respective acceleration is determined based on the deviation. When using identical window functions in the evaluation of the radar signals, the form expected for unaccelerated objects forms a circle, for example.

As a result, the present invention makes it possible to detect the acceleration or the relative acceleration of objects in only one measurement cycle.

Advantageous embodiments and further developments emerge from the dependent claims and from the description with reference to the figures.

In one embodiment, calculating a two-dimensional spectrum comprises calculating a two-dimensional Fourier transform, in particular a two-dimensional fast Fourier transform. This allows a simple and fast calculation of the two-dimensional spectrum.

In one embodiment, determining the deviation comprises determining a direction of a major axis of an ellipse and a ratio of the major axis and a minor axis of the ellipse. This allows a simple geometric determination of the deviation of the shape.

In one embodiment, in determining each acceleration, the amount of acceleration of the corresponding object is determined based on the length of the major axis relative to the length of the minor axis of the respective ellipse. This can be determined in a very simple manner, the value or the amount of acceleration.

In one embodiment, in determining each acceleration, the sign of the acceleration is determined based on the direction of the main axis.

In one embodiment, a positive sign is determined for the acceleration when the component of the major axis is positive on the abscissa axis of the two-dimensional spectrum.

In one embodiment, a negative sign for the acceleration is determined when the component of the major axis is negative on the abscissa axis of the two-dimensional spectrum.

If only the direction of the main axis is used to determine the sign, this can be calculated very easily.

In one embodiment, in determining a deviation of the shape, linear amplitudes of the local maxima are calculated by means of a quadratic form of a Gaussian bell curve. By the quadratic form of the Gaussian bell curve, a basis for a numerical calculation of the accelerations can be provided.

In one embodiment, the method comprises estimating the parameters of the square shape, in particular by means of the least squares method. The method of least squares can z. B. be implemented efficiently in a control device or a computing device of a vehicle or a radar system.

In one embodiment, in determining each acceleration, a quadratic equation based on the quadratic form is solved. This allows a very simple calculation of the acceleration.

In one embodiment, the ramps of the radar signal are less than 200 microseconds in length.

The above embodiments and developments can, if appropriate, combine with each other as desired. Further possible refinements, developments and implementations of the invention also include combinations of features of the invention which have not been explicitly mentioned above or described below with regard to the exemplary embodiments. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

Brief description of the drawings

The present invention will be explained in more detail with reference to the exemplary embodiments indicated in the schematic figures of the drawings. It shows:

1 a flowchart of an embodiment of the method according to the invention;

2 a block diagram of an embodiment of the radar system according to the invention;

3 a spectrum for use in the method of the invention;

4 another spectrum for use in the method of the invention;

5 another spectrum for use in the method of the invention; and

6 another spectrum for use in the method according to the invention.

In all figures, the same or functionally identical elements and devices - unless otherwise stated - have been given the same reference numerals.

Embodiments of the invention

1 shows a flowchart of an embodiment of the method according to the invention.

The inventive method provides the transmission S1 of a radar signal 3 in front. The radar signal 3 is in particular as an FMCW radar signal 3 formed, which has a plurality of ramps in the frequency response, which z. B. may have a length of less than 200 microseconds. That of objects 4-1 . 4-2 reflected radar signal 3 is then received S2 and evaluated to speed up the objects 4-1 . 4-2 opposite the radar sensor 2 , also called relative acceleration, to be determined.

The evaluation consists of calculating S3 a two-dimensional spectrum 5-1 - 5-4 the received radar signals. In this case, the two-dimensional spectrum 5-1 - 5-4 in particular a division into a plurality of frequency bins k, l have. It represents the abscissa axis of the two-dimensional spectrum 5-1 - 5-4 the frequency within a ramp and the ordinate axis of the two-dimensional spectrum 5-1 - 5-4 represents the frequency across the ramps. Exemplary two-dimensional spectra 5-1 - 5-4 be in 3 - 6 explained in more detail. The two-dimensional spectrum 5-1 - 5-4 can z. B. by means of a Fourier transform or a fast Fourier transform are calculated.

Mathematically, the two-dimensional spectrum 5-1 - 5-4 in one embodiment, be defined as follows:

The values w _kl describe the two-dimensional form of local maxima 6-1 - 6-4 in the two-dimensional spectrum 5-1 - 5-4 which uses the window functions w ₁ (n), w ₂ (r) as well as the above equations of the movement of the objects 4-1 . 4-2 and the modulation parameters.

In MSFMCW, multiple source frequency modulated continuous wave, based radar procedures are _slow N identical LFMCW ramps 20-1 - 20-n sent out. These ramps 20-1 - 20-n are called "fast ramps". The center frequencies of the fast ramps also form an LFMCW ramp over time 21 , This is called a "slow ramp". This connection is in 7 shown. The ramp lift of a fast ramp 20-1 - 20-n For _almost a ramp duration, F is _{almost fast} and N _almost samples per fast ramp 20-1 - 20-n , The hub of the slow ramp 21 is denoted by F _slow and the _{ramp duration} is T _slow = N _slow T _r2r at N _slow fast ramps 20-1 - 20-n with time difference (ramp-to-ramp) T _r2r ≥ T _almost in a slow ramp 21 ,

For evaluation, the deviations of the forms of local maxima 6-1 - 6-4 in the two-dimensional spectrum 5-1 - 5-4 from a form expected for unaccelerated objects, e.g. B. a circular shape, determines S4, and the acceleration of the respective maximum 6-1 - 6-4 corresponding object 4-1 . 4-2 determined based on the respective deviation, S5.

At the same time determination of forms of local maxima can 6-1 - 6-4 in one embodiment, for. B. be performed numerically.

To describe the forms of the local maxima 6-1 - 6-4 z. B. in linear amplitudes, a Gaussian bell curve can be used. The power distribution in dB, z. B. after normalization to the power at the position of the respective maximum 6-1 - 6-4 , is thus described by a quadratic form:

k . l describes the (interpolated) position of the respective maximum 6-1 - 6-4 , σ _k , σ _l are the standard deviations in the two dimensions and ρ is the correlation coefficient.

und die dazugehörigen Leistungswerte in einem Vektor beschrieben:

From the power values of the nine around the respective maximum 6-1 - 6-4 lying bins in the two-dimensional spectrum 5-1 - 5-4 (ie k = k ₀ -1, k ₀ , k ₀ + 1 and l = l ₀ -1, l ₀ , l ₀ + 1) can be the parameters of the quadratic form or the inverse covariance matrix C ^-1 z. For example, using the least-squares method. These are the nine relative bin positions (k - k , l - l ) united in a 9 × 2 matrix:

and the corresponding performance values are described in a vector:

The parameters of the inverse covariance matrix C ^-1 can then be determined as follows

M ⁺ denotes the pseudoinverse of the matrix M.

From the estimated parameters α ^, β ^, γ ^ For example, in one embodiment, the acceleration may be determined directly. The parameters depend on this α ^, β ^, γ ^ from the speed and acceleration of each object 2-1 . 2-2 from.

In another embodiment, an estimate of the covariance matrix C i is first obtained by inverting the estimated inverse covariance matrix

The element C ^ ₁₂ contains the covariance c ^ _kl between (k, l), which depends on the modulation parameters, the window functions as well as the speed and the acceleration. A quadratic shape is used to model the dependence on velocity and acceleration:

In one embodiment, coefficients that are so small that they can be neglected are deleted to simplify the formula. This can in one embodiment, for. B. apply to the coefficients c ₂ and c ₃ , which are usually smaller than 10 ^-17 . Thus, the above equation simplifies to: c ^ _kl ≈ c ₁ + c ₄ · v ² + c ₅ · a ² + c ₆ · v · a

The velocity v can be assumed to be known since it is directly from the (interpolated) position of the respective maximum 6-1 - 6-4 can be determined. Thus, the above equation yields a quadratic equation for the unknown acceleration a. Since it is a quadratic equation, one obtains as possible estimates:

For an embodiment in which c ₅ = 0, there is only one estimated value:

In general, one of the two estimates a ^ _1,2 amount implausibly large values, whereby the correct value can be easily recognized.

Alternatively, in one embodiment, the decision as to which of the two estimates is correct may be made by solving the linear equation for a ^.

The coefficients c ₁ ,..., C ₆ can be determined in different ways. In one embodiment, the coefficients c ₁ ,..., C _{6 can} be determined numerically. Alternatively, the coefficients c _1, ..., c are determined experimentally ₆ or determined by simulations.

In one embodiment, the coefficients c ₁ ,..., C _{6 can} be determined numerically such that one of the equations for c ^ _kl For a variety of speeds and accelerations is best met. This can be z. B. be solved as a numerical optimization problem.

In one embodiment, the coefficients c ₁ , ..., c ₆ for each type of radar sensor 2 with which the present method is to be used, and for which respective modulation parameters are determined.

2 shows a block diagram of an embodiment of the radar system according to the invention 1 ,

The radar system 1 has a radar sensor 2 on which a radar signal 3 sending out. Here is the radar signal 3 in one embodiment as an FMCW radar signal 3 formed, which has a plurality of successive ramps. In particular, in one embodiment, the ramps may have a duration of less than 200 microseconds.

In 2 are two objects 4-1 . 4-2 representing the radar signal 3 reflect. The radar sensor 2 takes the reflected radar signal 3 on. Become the objects 4-1 . 4-2 accelerated with an acceleration, which depends on the acceleration of the radar sensor 2 or z. B. a vehicle in which the radar sensor 2 is arranged, deviates, exists between the respective object 4-1 . 4-2 and the radar sensor 2 a relative acceleration, which with the help of the radar system 1 and the method of the invention can be determined.

The radar sensor transmits signals representing the received radar signal 3 to a computing device 11 which made these based on the under 1 described method the respective acceleration 7 the objects 4-1 . 4-2 calculated.

3 shows an exemplary two-dimensional spectrum 5-1 a radar signal 3 for explaining the method according to the invention.

The spectrum 5-1 is a two-dimensional spectrum 5-1 in which a maximum 6-1 is present, the decaying signal values are concentric to the maximum 6-1 arranged circles shown.

The 4 - 6 also show two-dimensional spectra 5-2 - 5-4 , which are each in the same place as the two-dimensional spectrum 5-1 of the 3 a maximum 6-2 - 6-4 exhibit. The two-dimensional spectra 5-1 - 5-4 are divided into bins, especially in so-called frequency bins. The ordinate axis shows the I frequency bins and the abscissa axis the k frequency bins.

The spectrum of 3 shows a maximum 6-1 which is an object 4-1 . 4-2 indicates, whose relative speed and relative acceleration are 0.

4 shows another exemplary two-dimensional spectrum 5-2 a radar signal 3 for explaining the method according to the invention.

In contrast to 3 shows the two-dimensional spectrum 5-2 of the 4 a maximum 6-2 for an object 4-1 . 4-2 whose relative acceleration is 0, but whose relative speed is greater than 0. It can be seen that although the shape of the maximum is still circular, the circle is now larger.

In 4 It can be seen that a relative speed greater than 0 is the shape of the local maximum 6-2 opposite to the shape of the local maximum 6-1 not changed but just changed its size.

Below a local maximum 6-1 - 6-4 is not a single value in this context. Rather, it is under a local maximum 6-1 - 6-1 in this context, to understand the entire range around a respective maximum value.

5 shows another exemplary two-dimensional spectrum 5-3 a radar signal 3 for explaining the method according to the invention.

The two-dimensional spectrum 5-3 of the 5 represents an object 4-1 . 4-2 , which has a relative speed greater than 0 and a relative acceleration greater than 0 with respect to the radar sensor 2 or the vehicle in which the radar system 1 is arranged.

The object 4-1 . 4-2 thus moves away from the radar sensor 2 with increasing speed.

In the two-dimensional spectrum 5-3 it can be seen that the shape of the maximum 6-3 is no longer circular. Rather, the shape of the maximum 6-3 distorted to an ellipse whose main axis 9-1 on both the ordinate axis and the abscissa axis in a positive direction. In the diagram of 5 shows the main axis 9-1 So right above. Consequently, the minor axis shows 10-1 the ellipse to the top left.

The greater the relative acceleration of the in the two-dimensional spectrum 5-3 The larger the ratio of the main axis is, the larger it becomes 9-1 and minor axis 10-1 the ellipse. The ellipse is thus further stretched with increasing relative acceleration.

6 shows another exemplary two-dimensional spectrum 5-4 a radar signal 3 for explaining the method according to the invention.

The two-dimensional spectrum 5-4 also represents an object 4-1 . 4-2 , which has a relative speed greater than 0 and a relative acceleration not equal to 0. In contrast to 5 has the in 6 represented object 4-1 . 4-2 but a relative acceleration which is less than 0.

That by the maximum 6-4 represented object 4-1 . 4-2 thus moves away with decreasing speed from the radar sensor 2 ,

In 6 it can be seen that a negative relative acceleration of the object 4-1 . 4-2 This causes the sign of the component of the main axis 9-2 the ellipse on the abscissa axis changes sign. The main axis 9-2 shows in 6 So left above and the minor axis 10-2 points to the bottom left.

7 shows a diagram of a radar signal, as in a method according to the invention or a radar system according to the invention 1 can be used.

The diagram shows the frequency over the ordinate axis and the time over the abscissa axis. It can be seen that the radar signal a variety 20-1 - 20-n a high slope, so-called. Fast ramps, whose center frequencies form a ramp of low slope, so-called. Slow ramps.

N _slow is the number of fast ramps 20-1 - 20-n , The center frequencies of the fast ramps also ramp up over time 21 , represented by a dotted line. This is called a "slow ramp". The ramp lift of a fast ramp 20-1 - 20-n For _almost a ramp duration, F is _{almost fast} and N _almost samples per fast ramp 20-1 - 20-n , The hub of the slow ramp 21 is denoted by F _slow and the _{ramp duration} is T _slow = N _slow T _r2r at N _slow fast ramps 20-1 - 20-n with time difference (ramp-to-ramp) T _r2r ≥ T _almost in a slow ramp 21 ,

Although the present invention has been described above with reference to preferred embodiments, it is not limited thereto, but modifiable in a variety of ways. In particular, the invention can be varied or modified in many ways without deviating from the gist of the invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102013200951 A1 [0008]

Claims (10)

Method for operating a radar system ( 1 ), which at least one radar sensor ( 2 ), comprising: emitting (S1) a radar signal ( 3 ) having a plurality of ramps; Receiving (S2) of objects ( 4-1 . 4-2 ) reflected radar signal ( 3 ); Calculating (S3) a two-dimensional spectrum ( 5-1 - 5-4 ) for the received radar signal ( 3 ); Determining (S4) a deviation of the shape of local maxima ( 6-1 - 6-4 ) in the two-dimensional spectrum ( 5-1 - 5-4 ), which the objects ( 4-1 . 4-2 ) from a form expected for unaccelerated objects; and determining (S5) each acceleration ( 7 ) each of the objects ( 4-1 . 4-2 ) based on the detected deviation. The method of claim 1, wherein calculating a two-dimensional spectrum ( 5-1 - 5-4 ) comprises calculating a two-dimensional Fourier transform, in particular a two-dimensional fast Fourier transform. The method of claim 1, wherein determining the deviation comprises determining a direction of a major axis. 9-1 . 9-2 ) of an ellipse and a ratio of the main axis ( 9-1 . 9-2 ) and a minor axis ( 10-1 . 10-2 ) of the ellipse. Method according to claim 3, wherein when determining in each case an acceleration ( 7 ) the amount of acceleration ( 7 ) of the corresponding object ( 4-1 . 4-2 ) based on the length of the main axis ( 9-1 . 9-2 ) in relation to the length of the minor axis ( 10-1 . 10-2 ) of the respective ellipse is determined. Method according to one of claims 3 and 4, wherein when determining in each case an acceleration ( 7 ) the sign of the acceleration ( 7 ) based on the direction of the main axis ( 9-1 . 9-2 ) is determined. Method according to claim 5, wherein a positive sign for acceleration ( 7 ) is determined when the component of the main axis ( 9-1 . 9-2 ) on the abscissa axis of the two-dimensional spectrum ( 5-1 - 5-4 ) is positive; and / or where a negative sign for the acceleration ( 7 ) is determined when the component of the main axis ( 9-1 . 9-2 ) on the abscissa axis of the two-dimensional spectrum ( 5-1 - 5-4 ) is negative. Method according to one of the preceding claims, wherein, in determining a deviation of the shape, linear amplitudes of the local maxima ( 6-1 - 6-4 ) can be calculated by means of a quadratic form of a Gaussian bell curve. The method of claim 7, comprising: Estimating the parameters of the quadratic form, in particular by means of the method of least squares. Method according to claim 8, wherein when determining in each case an acceleration ( 7 ) solves a quadratic form based quadratic equation. Radar system ( 1 ), with a radar sensor ( 2 ), which is designed to generate a radar signal ( 3 ), which has a plurality of ramps and that of objects ( 4-1 . 4-2 ) reflected radar signal ( 3 ) to recieve; with a computing device, which is formed, with a method according to one of the preceding claims, based on the received radar signal ( 3 ) an acceleration ( 7 ) of the objects ( 4-1 . 4-2 ) to calculate.

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