Method and apparatus for identifying an absorptive radome lining

Abstract

The invention provides a method and a device for identifying an absorptive radome lining (4) on a device for emitting (3) electromagnetic radiation and receiving (5) a part of the radiation reflected at an object, wherein a radome (2) covers at least one antenna (1) of the device, wherein a mixer (8) mixes a frequency-modulated transmission signal (3) with a signal (5) received by the at least one antenna (1), performs an analog-to-digital conversion (9) on the mixing product of the mixer (8), transforms (10) the digitized signal into a two-dimensional spectrum (40), and in a first step (11), maps the two-dimensional spectrum by means of a transfer function (12), and in a second step (13), correlates the two-dimensional spectrum (40) mapped by means of the transfer function (12) with a correlation matrix (14) in order to perform pattern recognition.

Description

Field of the Invention

[0001] The present invention relates to a method and a device for identifying an absorptive radome lining on a device for emitting electromagnetic radiation and receiving a part of the radiation reflected at an object, wherein the radome covers at least one antenna of the device, and wherein a mixer mixes a frequency-modulated transmission signal with the signal received by at least one antenna, an analog-to-digital conversion is performed on the mixing product of the mixer, the digitized signal is transformed into a two-dimensional spectrum, and in a first step, the two-dimensional spectrum is mapped using a transfer function, and in a second step, the two-dimensional spectrum mapped using the transfer function is correlated with a correlation matrix for performing pattern recognition. Background Art

[0002] From DE 10 2009 001 231 A1, an FMCW radar positioning device is known, which has an antenna covered by a radome, a mixer for mixing a frequency-modulated transmission signal with the signal received by the antenna, a device for recording the mixing product of the mixer as a time-dependent signal, a device for calculating the spectrum of the time-dependent signal, and a device for detecting a reflective lining on the radome, wherein the device for detecting the reflective lining is configured to analyze the time-dependent signal and determine the reflection scale at the radome based on the amplitude of the signal. Summary of the Invention

[0003] Core and Advantages of the Invention

[0004] The core of the present invention is a method and a device for identifying an absorptive radome lining (Radombelag) of a device for emitting electromagnetic radiation and receiving a part of the radiation reflected by an object. Thereby, sensor blindness can be reliably identified, or a degradation of the range of action can be identified, and thus a quantitative statement can be made about a possible performance loss of an object detection system.

[0005] According to the invention, this is solved by the features of the independent claims. Advantageous refinements and configurations result from the dependent claims.

[0006] Absorptive radar sensor linings or absorptive radar sensor linings have the following disadvantages: Only a small part of the transmitted transmission power is reflected by the sensor lining, and thus the lining on the radome cannot be identified by a special reflection signal, but rather a part of the transmitted power is absorbed, i.e., energy is swallowed (verschlucken) by the lining, such that the identification of an absorptive radome lining or an absorptive radome lining cannot be normally recognized. It has been shown within the scope of the present invention how such a radome lining can still be identified by analyzing the internal noise signal.

[0007] Furthermore, it is advantageous to configure the corresponding device and the device according to the method features described according to the invention.

[0008] It is advantageously provided that the output signal of the high-frequency device of such a sensor is transformed into a two-dimensional spectrum after digitization. Advantageously, it can be provided that the two-dimensional spectrum is a velocity-distance spectrum (Geschwindigkeits-Abstands-Spektrum). The two-dimensional spectrum can either be a spectrum having continuous values once in the direction of the sensor distance and in a second dimension with respect to the relative velocity of the object; however, it is also possible that the two-dimensional spectrum has discrete values not only in the first dimension, i.e., the object distance, but also in the second dimension, i.e., the relative velocity of the object, and thus there is a discrete two-dimensional spectrum.

[0009] Furthermore, it is advantageous that the transfer function determines the noise level in the two-dimensional spectrum, in particular by using a significance level. The requirement for a suitable transfer function essentially lies in: using a continuous and monotonically increasing or decreasing function. It has been shown in practice that the spectral distribution of the received radar power can be described by a Chi 2 function. Therefore, it is advantageous to perform a Chi 2 test by means of a distribution function known from statistics. Here, the distribution function describes the probability distribution of the noise level in the two-dimensional spectrum. The significance level of the distribution function describes that all noise power values are below the selected level. Here, for example, the significance level can be selected such that the noise level is detected at 50%. According to an advantageous refinement of the invention, it may be advantageous to change the significance level of the distribution function in order to appropriately adjust the noise level.

[0010] Furthermore, it is advantageous to detect reflective objects by means of pattern recognition in the two-dimensional spectrum mapped using the transfer function. The two-dimensional spectrum (which can in particular be a discrete two-dimensional spectrum) is mapped cell by cell using the transfer function, whereby the observed noise level in the spectrum can be determined and the noise can be reduced to the greatest possible extent without obscuring object detection.

[0011] Furthermore, it is advantageous that the pattern recognition in the two-dimensional spectrum searches for linear correlations. Thus, with a suitable selection of the modulation of the radar sensor, the detected objects in the two-dimensional spectrum can be represented by a descending straight line, i.e., a straight line with a negative slope. Therefore, it is advantageous that in a second step of the characteristic features, the pattern recognition searches for correlations with a descending linear pattern.

[0012] Furthermore, it is advantageous to determine the radome lining by determining the maximum cross-correlation from the values of the two-dimensional spectrum mapped using the transfer function together with the values of the correlation matrix. Particularly advantageously, pattern recognition is performed with the aid of the correlation matrix. For this purpose, different correlation matrices can be stored in the device, which correlation matrices, for example, have line segments with a descending form. Depending on the modulation selected, it is also possible to store other forms in the correlation matrix.

[0013] Furthermore, it is advantageous that the transfer function is variable and is changed according to the recognized object. Thus, it is advantageous if, in the two-dimensional spectrum, no object is recognized or only a few objects are recognized, to change the transfer function such that more noise is allowed, but thereby more object data can also be evaluated. If a radome lining with absorptive properties is formed on the radome surface, the received level drops, and this drop in the received level can be recognized by changing the significance level of the noise level, and the extent of the performance loss can be estimated. From this, the following possibility also results: to be able to switch off the radar sensor in good time if necessary before it no longer provides a reliable signal, but still to be able to operate the radar sensor for as long as the system degradation still permits.

[0014] Furthermore, it is advantageous to change the significance level of the distribution function at a predetermined interval. In the case of the value of the significance level at which the signal is drowned in the noise, the damping of the radome lining can be inferred.

[0015] In the case of an absorptive radome lining, it follows that only specific objects in the field of view of the sensor provide signal echoes. This results in only a few objects being present in the measurement from the field of view of the sensor, and the two-dimensional spectrum to be processed being only weakly occupied by the backscattered radar signals. Based on the physical properties of the object characteristics of the sensor measurement, such as distance and relative speed, for example, these form specific patterns in the two-dimensional spectrum. These patterns can be detected using different methods, such as pattern matching or contour recognition, and thus the recognition of the absorptive sensor lining can be improved.

[0016] By using the spectrum measured for the sensor function, the need for a separate measurement for radome lining recognition is eliminated. Thereby, running time is saved and the temperature balance of the sensor is improved. Since there are signals and noise in the two-dimensional spectrum, by using a spectrum that is only weakly occupied, the need for a relative measurement of the received level is eliminated.

[0017] For this reason, radar sensors and lidar sensors are particularly suitable as sensors, but in principle it is also conceivable to apply this to other sensor concepts. By applying different patterns, such as stationary, moving, and extended objects, object classification can be improved in addition by using the characteristics of the detected target in terms of its extension in the distance direction or relative velocity direction of the two-dimensional spectrum.

[0018] It is particularly important to implement the method according to the invention in the form of a control element, wherein the control element is provided for a control device for the adaptive distance or speed regulation of a motor vehicle. Here, a program is stored on the control element, which program is capable of running on a computing device, in particular on a microprocessor or signal processor, and is suitable for implementing the method according to the invention. In this case, the invention is thus implemented by a program stored on the control element, such that this control element equipped with the program depicts the invention in the same way as the method for which the program is suitable for execution. In particular, an electrical storage medium, such as a read-only memory, can be used as the control element. Other features, application possibilities, and advantages of the invention result from the following description of embodiments of the invention, which are shown in the figures of the drawings. Here, all features described or shown, either alone or in any combination, form the subject matter of the invention, regardless of their aggregation or their reference back in the claims, and regardless of their representation or presentation in the description or in the drawings.

[0019] A computer program or computer program product having program code is also advantageous, which program code can be stored on a machine-readable carrier or storage medium, such as a semiconductor memory, a hard disk memory, or an optical memory, and is in particular used for executing, implementing, and / or controlling the steps of a method according to one of the above-described embodiments when the program product or program is implemented on a computer, a programmable control device, or a similar device. Description of the Drawings

[0020] Embodiments of the invention are subsequently explained with reference to the drawings.

[0021] Figure 1 A schematic block diagram of a device according to the invention is shown,

[0022] Figure 2 A special configuration of the transfer function is shown in the form of a distribution function,

[0023] Figure 3 An exemplary correlation matrix for a descending straight line is shown, and

[0024] Figure 4 A two-dimensional velocity-distance spectrum for explaining the method according to the invention is shown. Detailed Description of the Invention

[0025] In Figure 1An exemplary block diagram of a device according to the invention for emitting electromagnetic radiation and receiving a portion of the radiation reflected at an object is shown. Antenna 1 can be seen, which is operated as a monostatic antenna in the example shown, i.e., as an antenna that can both transmit and receive. Alternatively, it is also possible to implement the invention in a bistatic system by respectively providing separate antennas for transmitting and receiving electromagnetic radiation.

[0026] Oscillator 7 is operated here to provide a signal at the carrier frequency of the device. For this purpose, it is possible to supply the signal of oscillator control device 6 to oscillator 7. This oscillator control device 6 can, for example, keep the generated frequency constant, but depending on which modulation mode should be transmitted, the frequency can also be linearly increased, decreased, or regulated in steps (constant regulated) in a predefined pattern. The transmission signal generated by means of oscillator 7 is guided to mixer 8, which also serves as a transmit and receive switching device and forwards the transmission signal to antenna 1.

[0027] Antenna 1 radiates electromagnetic transmission signal 3, which penetrates radome 2 during normal operation and has the task of detecting objects in the sensor environment. After it (this) has passed through radome 2 again, the object in the sensor environment reflects the emitted radiation 3 back to the transmitter and is received as received radiation 5 by transmit and receive antenna 1. The received signal received by antenna 1 is supplied to mixer 8 by mixing the received signal with the transmission signal and demodulating it. Mixer 8 generates an intermediate frequency signal, which is output to the downstream analog-to-digital converter 9.

[0028] After digitizing the intermediate frequency signal in the analog-to-digital converter, the signal is subjected to a device for Fourier transform, in particular a discrete and two-dimensional Fourier transform, and then device 10 outputs a spectrum or a two-dimensional spectrum, which is further processed.

[0029] Radome 2 can, for example, be a covering of the device according to the invention, which protects the components from weather and mechanical influences. In addition, it is also conceivable that radome 2 is constructed in a lenticular shape and thus also additionally has focusing characteristics for the emitted and received electromagnetic radiation.

[0030] If the vehicle gets dirty during driving operation, or the vehicle is operated in the rain or in the snow, it is possible that the absorptive layer 4 or the absorbent layer 4 adheres to the sensor radome 2. The absorptive layer 4 or the absorbent layer 4 not only absorbs the emitted transmitted radiation but also absorbs the received radiation to be received and converts it into loss heat within the layer. Since almost no reflected signal is generated by the absorptive layer 4, it is very difficult to identify the absorptive layer 4 on the radome surface 2, such that the sensor may become blind (erblinden) during continued operation without this being noticed. This means that even if there is an object in the environment and the sensor's mode of operation is as set, the sensor no longer receives the received signal from which the object is inferred. In order to still be able to identify the absorptive radome lining 4, the two-dimensional velocity-distance spectrum output by the device 10 is further evaluated.

[0031] For this purpose, this is carried out in a first step in the device 11, namely the mapping device (Mapping). This means that each value of the two-dimensional spectrum is fed as an input value to the transfer function 12, and the output value of the transfer function 12 is assigned to the input value. Here, the transfer function 12 can be any arbitrary continuous, especially climbing (steige) and monotonically increasing or decreasing function. The distribution function known from statistics, also denoted as CDF (= Cumulative Distribution Function), has proven to be particularly suitable.

[0032] After mapping the transfer function 12 to the two-dimensional spectrum, in a second step the two-dimensional spectrum is fed to a correlator in such a way that a cross-correlation is performed with one or more stored correlation matrices. The one correlation matrix or the multiple correlation matrices exemplarily have the form of possible object detections in the two-dimensional spectrum. By cross-correlating with the one correlation matrix or the multiple correlation matrices, the desired form in the two-dimensional spectrum can be identified, and thus the object detection in the two-dimensional spectrum can be identified. These identified objects can be output as the output signal 15 for further evaluation, for example for determining the distance and relative speed of the detected object.

[0033] In Figure 2The transfer function 12 is shown, which can be implemented exemplarily as a distribution function CDF. The received level of the two-dimensional spectrum after performing a 2D Fourier transform is plotted on the abscissa 20 of the shown graph. A scale between 0 and 1 is shown on the ordinate 21, which represents the probability value between 0 and 1. The distribution function 12 is located in the graph such that the distribution function has a significance level 23. For example, the significance level can be selected such that the significance level corresponds to the value 0.5 on the ordinate 21. The significance level 23 has a noise level 22 as the assigned input value of the abscissa 20. By shifting the distribution function 12 to the left or right (which is indicated by the arrow 24), the variability of the significance level is shown and can be adjusted such that the noise level 22 can be adjusted accordingly.

[0034] In Figure 4 a, a two-dimensional velocity-distance spectrum is shown, which shows the axis k on the abscissa 41, on which the distance values are shown, or in the case of a discrete Fourier transform, the so-called distance bins. In Figure 4 a, the second dimension of the spectrum, i.e., the velocity values, is shown on the ordinate 42, which in the case of a discrete Fourier transform again represents the so-called velocity bins. As the two-dimensional output spectrum 40 output after the Fourier transform of the device 10 according to Figure 1 is plotted within the boundaries of the shown graph. The spectrum contains intensity values 43, 44, which are caused on the one hand by noise as shown, for example, by the object 43, but also by object detection as shown by the object signal 44. In the case of correspondingly high noise or correspondingly weak object signals, it is not easy to distinguish the object signal and the noise from each other. Even in the case of sensor performance degradation caused by the absorptive radome lining 4 on the radome 2, the object detection 44 and the noise 43 in the two-dimensional output spectrum 40 become blurred with each other.

[0035] By applying the distribution function 12 according to Figure 2 to the Figure 4 a spectrum shown in, it is possible to adjust the noise level 22 accordingly by appropriately selecting the significance level 23. Thereby, most of the noise detection 43 is eliminated, and the object detection 44 becomes correspondingly more visible. This is shown in Figure 4 b, in such a way that the probability mapping noise spectrum 45 is again plotted in the two-dimensional spectrum of the distance bins 41 and the velocity bins 42 on the axes k and l. The output signal of the device 11 according to Figure 1 is fed to the correlator 13, which correlates the two-dimensional spectrum according to Figure 4 b with one or more correlation matrices according to Figure 3 .

[0036] For this purpose, an exemplary correlation matrix is shown in Figure 3 The correlation matrix shown in Figure 3 consists of columns 0 to x in the horizontal extent and rows 0 to y in the vertical extent. This grid structure of cells (Zellen) can now be occupied in the individual cells, as indicated, for example, by cell 32, or can remain unoccupied, as shown by exemplary cell 31. Here, the occupied cell 32 can have the value 1, while the unoccupied cells can have the value 0. Since Figure 4 the two-dimensional spectrum of b is a discrete two-dimensional spectrum, Figure 3 the correlation matrix 30 in Figure 3 must likewise have discrete values. The cells of the correlation matrix 30 in Figure 1 are occupied by cell 32 such that it has, for example, a descending straight line, i.e., a line with a negative constant slope. In the correlator 13 according to Figure 1 the spectrum of b is correlated with the aid of the correlation matrix 3 by correlating the individual segments of different sizes and different positions in the two-dimensional spectrum 45. If the correlation value increases, the cell under investigation has a high similarity to the sought-after form that the occupied cell 32 of the correlation matrix 30 has. By analyzing the maximum value, it is now possible to detect the form stored in the correlation matrix 30 within the two-dimensional spectrum. In the present example, this results in Figure 4 the object detection 44 in b representing a descending straight line having a high correlation value with the correlation matrix 30 of Figure 4 and thus detecting the descending straight line 47 according to Figure 3 c. When analyzing Figure 4 the noise detection 43 in b, no or only very low correlation values can be determined, such that these noise detections are not recognized as straight lines. Figure 4 b, no or only very low correlation values can be determined, such that these noise detections are not recognized as straight lines.

[0037] Therefore, Figure 4 the two-dimensional spectrum shown in c represents the result of the correlator 13, which is output, for example, as the output signal 15 and exemplarily has a descending straight line 47, which can be assigned to a particular combination consisting of the distance d and the relative velocity v. In the case of a degradation of the sensor performance due to an absorptive radome lining, the received power drops strongly, such that object detection can hardly be detected in the noise. By, for example, shifting the distribution function 12 in the direction 24 to Figure 2The significance level 23 in [it] is shifted, which can reduce the evaluated noise level to such an extent that object detection 44 can be reliably identified, thereby forming a sensor that operates reliably even under adverse conditions. By shifting the distribution function 12 in one of the directions 24 to shift the Figure 2 the significance level 23 in [it] is shifted. It is possible to determine how strongly the radome lining 4 damps by determining to what extent the distribution function 12 or the noise level 22 must be shifted on the axis of the reception level 20.

Claims

1. A method for identifying an absorptive radome lining (4) on a device for transmitting electromagnetic radiation and receiving a portion of the radiation reflected at an object, wherein the electromagnetic radiation is radar radiation, wherein a radome (2) covers at least one antenna (1) of the device, wherein a mixer (8) mixes a frequency-modulated transmission signal (3) with a signal (5) received by the at least one antenna (1), wherein an analog-to-digital conversion (9) is performed on the mixed product of the mixer (8), wherein the device identifies the absorptive radome lining (4), transforms (10) the digitized signal into a two-dimensional spectrum (40), characterized in that, in a first step (11), the two-dimensional spectrum is mapped using a transfer function (12), and in a second step (13), the two-dimensional spectrum (40) mapped using the transfer function (12) is correlated with a correlation matrix (14) for performing pattern recognition.

2. The method according to claim 1, wherein The two-dimensional spectrum (40) is a velocity-distance spectrum.

3. The method according to claim 1 or 2, characterized in that, The transfer function (12) determines the noise level in the two-dimensional spectrum (40).

4. The method according to claim 3, wherein The transfer function (12) determines the noise level in the two-dimensional spectrum (40) by using a significance level (22).

5. The method according to claim 3, characterized in that A reflective object (47) is detected by using pattern recognition (13) in the two-dimensional spectrum mapped using the transfer function (12).

6. The method according to claim 5, characterized in that, The pattern recognition in the two-dimensional spectrum searches for linear correlations.

7. The method according to claim 6, characterized in that, The radome lining (4) is determined by determining the maximum of the cross-correlation from the values of the two-dimensional spectrum (40) mapped using the transfer function (12) together with the values of the correlation matrix (14).

8. The method according to any one of the preceding claims 1 to 2, characterized in that The transfer function (12) is variable (24) and is changed according to the identified object (47).

9. The method according to any one of the preceding claims 1 to 2, characterized in that, The transfer function (12) is a distribution function.

10. The method according to any one of the preceding claims 1 to 2, characterized in that The transfer function (12) is implemented as a distribution function, wherein the significance level (22) of the distribution function (12) is changed at a predetermined interval, and the damping of the radome lining (4) is inferred from the values of the significance level (22) at which the signal (44) is drowned in noise (43).

11. A computer program product, which is configured to execute, implement, and / or control the method according to any one of claims 1 to 10.

12. A machine-readable storage medium, on which the computer program product according to claim 11 is stored.

13. A device for transmitting electromagnetic radiation and receiving a portion of the radiation reflected at an object, the device: has at least one antenna (1), which is covered by a radome (2); has a mixer (8) for mixing a frequency-modulated transmission signal (3) with a signal (5) received by the at least one antenna (1); means for performing analog-to-digital conversion on the mixed product of the mixer (8), wherein the portion of the radiation is radar radiation, wherein the device identifies the absorptive radome lining (4), characterized in that means for calculating a two-dimensional spectrum (40) of the digitized signal, means for providing a transfer function (12), and Apparatus for pattern recognition (13, 14) in a two-dimensional spectrum (40) using the provided transfer function (12).

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