METHOD AND RADAR SENSOR FOR REDUCING THE INFLUENCE OF INTERFERENCE IN THE EVALUATION OF AT LEAST ONE RECEIVED SIGNAL

Description

[0001] The present invention relates to a radar sensor and a method for reducing the influence of interference during the evaluation of at least one received signal of a radar sensor, in particular a radar sensor installed in a vehicle, in which predetermined transmission signals are emitted and reflected partial signals are received in predetermined operating situations and the signals received for the predetermined operating situations are stored to determine an interference spectrum and the influence of interference is reduced by taking the interference spectrum into account during the signal evaluation. State of the art

[0002] From DE 10 2009 053 395 A1 a system and a method for monitoring target objects by means of a sensor arrangement is known, in which the generation, storage and verification of separate, user-definable test profiles is provided for the flexible evaluation of first target parameters for the various target objects determined via the sensor arrangement, without any intervention in safety-relevant system components being necessary.

[0003] A radar system is known from DE 698 34 710 T2. US 2009 / 121918 A1 relates to a radar device with simplified suppression of interference signal components. WO 2016 / 168334 A1 concerns noise reduction in radar devices. US 2015 / 097730 A1 relates to a radar sensor with a radome. US 2006 / 109170 A1 concerns power control in radar sensors. DE 10 2012 111933 A1 concerns the automatic detection and interpretation of traffic lights. Disclosure of the invention

[0004] The core of the present invention is to detect interference with the sensor due to its installation, particularly behind a vehicle body part, and to compensate for such interference signals during the reception of object signals. According to the invention, this is achieved by the features of the independent claims. Advantageous further developments and refinements are set out in the subclaims.

[0005] Advantageously, the method is performed separately for each receiving channel of the radar sensor. This feature allows a multi-channel radar sensor to be calibrated individually for each channel with respect to interference caused by multiple reflections, so that the overall result of the received signals has a lower interference level than if the calibration were performed jointly for all receiving channels.

[0006] It is also advantageous for the radar sensor to be located behind vehicle body panels. Modern motor vehicles prefer to position radar sensors installed at the front or rear so that they are concealed behind vehicle aprons, bumpers, or other body parts, so that the external appearance of the vehicle is not altered by the sensors. It is particularly advantageous for the vehicle body panels behind which the radar sensor is located to be body panels made of plastic. Plastic can be manufactured from material mixtures that allow the emitted and received radar radiation to pass through largely unchanged, so that the emitted and received electromagnetic signals are influenced and thus disrupted as little as possible by the body panels themselves.Additionally or alternatively, it may be advantageous for the body parts to be painted, in particular for the paint layers to be metallic paints, some of which contain metal particles. Such paint layers, especially those containing metal particles, sometimes exhibit a high reflectivity for electromagnetic radiation, so that painted vehicle parts, especially vehicle parts painted with metallic paints, can lead to interference with the sensor signals.

[0007] Furthermore, it is advantageous that the interference is generated by received signals caused by multiple reflections between the body part and the sensor radome. By arranging the radar sensors behind body parts, received signals from the radar sensor first pass through the body part and then through the radar sensor's radome. This can cause waves to travel back and forth between the radome surface and the inside of the vehicle body parts, resulting in multiple reflections that interfere with the received signals desired by the radar sensor and prevent reliable target detection.

[0008] According to the invention, the predetermined operating situation is when the vehicle is stationary. When the vehicle is stationary, the vehicle's surroundings no longer move relative to the vehicle, so that stationary objects are also detected as stationary objects by the vehicle sensor. When driving, stationary objects also move relative to the sensor, so that distance values and relative speed values ​​are variable. When stationary, however, stationary objects can be detected as objects with a constant distance value and a relative speed equal to zero over many measuring cycles, and advantageous sensor calibration can be carried out using such stationary objects. Such an operating situation arises, for example, when the vehicle is stopped at red traffic lights, so that during such stationary periods while driving, interference caused by multiple reflections of the received signals can be regularly recalibrated.For example, it is possible to determine that a vehicle is stationary at a traffic light using data from a navigation database that stores the intersection at which traffic light regulations are in place. If the vehicle stops at such an intersection, it can be concluded that the vehicle is currently stopped at a red light. Additionally or alternatively, it is also possible for the vehicle to have a camera that is oriented at the front of the vehicle in the direction of travel and records the area in front of the vehicle. Such a front-of-vehicle camera can, for example, detect traffic lights and thus red light phases and thus start and abort a sensor calibration in time before the vehicle starts moving again after the traffic light changes to green.

[0009] Furthermore, it is advantageous for the predetermined transmission signals to be signals with a precisely predetermined signal shape and signal power. The transmission signals emitted during the predetermined operating situations should be transmitted with high accuracy in terms of signal shape and signal power, so that interference caused by multiple reflections can be detected as precisely as possible based on the received signals, thus enabling the most accurate calibration possible for driving operations.

[0010] Furthermore, it is advantageous that the method is carried out separately for each receiving channel of the radar sensor.

[0011] Furthermore, it is advantageous that the received signals of the predetermined transmitted signals are averaged over several signal cycles. This feature has the beneficial effect that frequently occurring disturbances are taken more into account in the calibration signal than rarely occurring disturbances that, for example, only appear once in several signal cycles. This allows a calibration signal to be generated that weights the frequency of the occurring disturbances according to their frequency and can thus optimally correspond to different driving situations.

[0012] Furthermore, it is advantageous that the averaged signals are added to the previous correction signal. If a new sensor calibration is performed while the vehicle is stationary, the previous correction signal does not have to be deleted and replaced with the new signal; instead, the newly determined calibration signal can be added to the existing calibration signal, possibly with appropriate weighting. This ensures that calibration signals that compensate for disturbances are not completely re-determined during a calibration process. This means that incorrect measurements during the calibration process have less dramatic effects on subsequent driving. This is because outliers are only included in the correction signal with a low weighting, and frequently occurring disturbances are taken into account with a high weighting.It is possible to determine an averaged signal for each respective receiving channel and to determine a correction signal separately for each receiving channel and, during a new calibration, to carry out the weighted addition of the new calibration signal separately for each receiving channel.

[0013] Furthermore, it is advantageous for the radar sensor to have multiple receiving channels, and for the interference spectrum to be recorded and / or stored separately and / or considered separately for each channel. This makes it possible to identify channel-specific interference and eliminate it from the received signals separately for each channel using the correction signal.

[0014] Furthermore, it is advantageous to provide a separate memory device or a separate area of a shared memory device for each of the multiple receiving channels, within which a separate interference spectrum is stored for each receiving channel. Thus, an interference spectrum can be stored for each receiving channel in a specially reserved memory, or, if a shared memory is used for all interference spectra of the multiple receiving channels, these different spectra can be stored in one memory device.

[0015] Furthermore, it is advantageous for the means for detecting the at least one predetermined operating situation to be used to supply a signal to the radar sensor. It can be provided that the signal supplied to the radar sensor is a signal representing the vehicle's standstill, for example, by evaluating a wheel speed sensor, a video image, or a speedometer signal. Furthermore, the predetermined operating situation can be detected by supplying the radar sensor with a signal representing the detection of a red traffic light applicable to the vehicle.For this purpose, it is advantageous to provide a camera in the front area of the vehicle that records the area in front of the vehicle in the direction of travel and can detect a red traffic light at the edge of the road or a red traffic light hanging above the lane, assign it to the vehicle's own lane, and thus recognize that the vehicle is stationary in front of a red traffic light and, if applicable, how long the vehicle will remain stationary. Once a predetermined operating situation has been detected, the transmission of predetermined transmission signals for sensor calibration is started, and the received signals, in particular those reflected by stationary or fixed objects, are evaluated, and a search is made for multiple reflections in the received signal, which are then evaluated to determine the correction signal.

[0016] Furthermore, it is advantageous for the radar sensor to be arranged behind a vehicle body part. In this case, it can be advantageous for the body part to be made of plastic, as this means that the electromagnetic radiation emitted and received by transmit and receive signals is hardly affected. The invention can be particularly advantageous if the radar sensor is used in a situation in which the body parts are painted, in particular painted using metallic paints that contain metal particles, as this makes the paint layers more reflective and the receive signal particularly prone to interference. By means of the method and the device according to the invention, such interference can be reduced or even avoided particularly efficiently.

[0017] Of particular importance is the implementation of the method according to the invention in the form of a control element provided for a control unit of an adaptive distance or speed control system of a motor vehicle. A program is stored on the control element that can be executed 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 implemented by a program stored on the control element, so that this control element provided with the program represents the invention in the same way as the method for which the program is suitable. In particular, an electrical storage medium can be used as the control element.

[0018] Further features, possible applications, and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, which are illustrated in the figures of the drawing. All described or illustrated features, individually or in any combination, constitute the subject matter of the invention, regardless of their summary in the patent claims or their reference back to them, as well as regardless of their wording or representation in the description or in the drawings. Short description of the drawings

[0019] In the following, exemplary embodiments of the invention are explained with reference to drawings. Figure 1 shows a schematic representation of a radar sensor installed behind a vehicle body part with resulting multiple reflections, Figure 2 shows a schematic representation of the effect of interference in the frequency spectrum, Figure 3 shows an embodiment of the receiving part of the device according to the invention and Figure 4 shows a schematic flow diagram for explaining the method according to the invention. Embodiments of the invention

[0020] In Figure 1A radar sensor 1 is shown schematically. The radar sensor 1 consists of a half-shell housing, which is closed at the front with a radome 4. The radome 4 can have a focus, for example in the form of a dielectric lens, or can be designed without a focus, so that the emitted and received electromagnetic radiation penetrates the radome 4 without changing the beam path. Furthermore, a body part 2 is shown in front of the radar sensor 1 with the radome 4, which is advantageously a plastic body part, often painted in the vehicle color with metal particles. By installing the radar sensor 1 behind the body part 2, the radar sensor 1 is not visible to the observer, so that any disturbance to the visual impression of the vehicle by sensors on the vehicle is not impaired. The radar sensor 1 has antennas inside it, in particular receiving antennas 3.The receiving antennas 3 can receive signals that were previously emitted by a transmitting antenna (not shown) and reflected by objects in the sensor detection range. Such received beams, which were reflected by objects within the sensor detection range, are represented by beams 5. This electromagnetic radiation, incident as received beams, penetrates the body part 2, which is made of a material that influences the beam path of the electromagnetic radiation as little as possible. Furthermore, the body part 2 is painted and, if necessary, provided with additional coatings so that the received beams 5 penetrate the body part 2 as completely as possible in the form of electromagnetic radiation, and as little radiation as possible is reflected away.After passing the body part 2, the electromagnetic radiation of the received beams 5 falls on the radome 4 of the radar sensor 1, with a first part of the received energy penetrating the radome 4 and being able to be picked up by the receiving antennas 3 as received signals. A second part of the received beams 5 is reflected by the radome surface and reflected back as reflected partial beams 6 at an angle of reflection towards the body part 2. This partial radiation 6 in turn strikes the inside of the body part 2 and can be reflected there again. In the worst case, this further reflection reflects almost all of the reflected partial beams 6 and the doubly reflected partial beams 7. These doubly reflected partial beams move almost parallel to the original received beams 5 and largely penetrate the radome 4, so that they are also received and evaluated by the receiving antennas 3.The receiving antennas 3 therefore receive the directly received received radiation 5, but also the doubly or even multiply reflected partial beams, which are received as echoes and represent an interference signal with respect to the intended received signal. These interference signals caused by multiple reflections should be avoided in order to ensure the most reliable operation of the radar sensor 1 and to be able to perform reliable object detection.

[0021] The reception situation as per Figure 1 shown, after evaluation of the receiving beams 5 leads to frequency spectra, as shown for example in Figure 2a and 2b are shown. Thus, in Figure 2aThe frequency f is plotted on the abscissa and the intensity A is plotted on the ordinate. If the received signal 5 is received without multiple reflections 6, 7 occurring, an intermediate frequency signal 8 is produced at the center frequency f 0 , which can be evaluated and analyzed without interference. In the case that multiple reflections 6, 7 occur and superimpose the received signal 5, an intermediate frequency signal is produced as in Figure 2b Here, too, the frequency f was shown on the abscissa and the amplitude A of the intermediate frequency signal was shown on the ordinate. Figure 2b is again, just like in Figure 2a, an exemplary intermediate frequency signal 8 is shown, which again has a center frequency f 0. The multiple reflections 6, 7 result in an interference spectrum 9 which has a lower amplitude A than the undisturbed intermediate frequency signal 8 and has a center frequency fr. Since the center frequency fr of the interference spectrum 9 is only slightly spaced from the center frequency f 0 of the intermediate frequency spectrum 8, both spectra overlap in wide frequency ranges, so that the interference spectrum 9 or the multiple reflections cannot be filtered out of the received signal. If previously known signals are transmitted as transmission signals during certain operating states, in particular when the vehicle is stationary, the shape and intensity of the disturbed intermediate frequency spectrum 8 are known.If the interference influences 9 overlap during this measurement, the current interference spectrum can be determined and stored by calculating the difference during the predetermined operating situations. By subtracting the interference signal from the disturbed reception spectrum 8, as shown in . Figure 2b As shown, interference due to multiple reflections 6, 7 can be largely eliminated and thus a more reliable and accurate determination of the object data from the received signal can be achieved.

[0022] In Figure 3 A schematic embodiment of the device according to the invention is shown. On the left, the body part 2 is shown, which covers the radar sensor 1. Behind the body part 2, the radar sensor 1 is arranged with a radome 4, which is designed with or without focusing. The housing of the radar sensor 1, like the radome 4, is in Figure 3not shown for reasons of clarity. The radar sensor 1 shown as an example has four receive channels that process and evaluate received signals in parallel. A receive module 11 is shown, which can be a high-frequency module of the radar sensor 1, for example. This high-frequency module 11 has three receive antennas that receive the receive beams 5 and are also superimposed by multiple reflections 6, 7 of the receive beams. These interfered receive signals are forwarded by the receive antennas 3 to a receive filter 12, with a separate receive filter 12 being provided for each receive channel. This receive filter 12 can, for example, be a bandpass filter that filters out unwanted frequency components from the receive spectrum. However, this receive filter 12 is not able to filter out the largely superimposed interference signal 9 from the receive signal 8.The filtered received signal is output in each receive channel by the receive filter 12 to an analog / digital converter 13, with a separate analog / digital converter 13 being provided for each receive channel. In an alternative embodiment, a very powerful analog / digital converter 13 can also sample all channels by sequentially sampling the receive channels. In a preferred embodiment, the analog / digital converters 13 convert the filtered received signals into digital signals for each channel in parallel and simultaneously. In the downstream subtraction device 14, which is again implemented separately for each receive channel, an interference signal 16 is supplied from an evaluation and calculation device 15.This supply of the calculated and previously determined interference signal r 1 , r 2 , r 3 , r 4 occurs via an output line 16 for the interference spectrum rx from the evaluation and calculation device 15, where the interference spectra r 1 , r 2 , r 3 , r 4 for each receive channel are stored in a memory device. By subtracting the respective interference spectrum rx in the subtraction device 14, a recently determined interference spectrum, which results from the multiple reflections 6, 7, is subtracted from the current receive signal, so that a receive signal that is as interference-free as possible is output from the subtraction device 14 to the evaluation and calculation device 15.In the evaluation and calculation device 15, the received signals are evaluated with regard to detected objects and, for example, lists of detected objects in the vehicle's surroundings are generated, which are used for further vehicle functions, such as emergency braking functions or adaptive distance and cruise control functions. If the vehicle stops, for example, because it is stopping at a red light, this is detected by the speed sensor v, which can be a wheel speed sensor, for example, and a speed signal 10 is output to the evaluation and calculation device 15. This ensures that the evaluation of the received signals is interrupted in the evaluation and calculation device 15 and standardized transmission signals are emitted by the transmitting antennas (not shown).The received signals 5 received during this predetermined operating situation are received by the receiving antennas 3 and fed to the subtraction devices 14 via the receiving filters 12 and analog / digital converters 13. For example, during these predetermined operating situations, the output of the interference spectra rx via the output lines 16 can be interrupted. Thus, during the predetermined operating situations, the evaluation and calculation device 15 receives received signals that originate from predetermined transmitted signals and in which the interference spectra 9 are present due to multiple reflections.In the evaluation and calculation device 15, an interference spectrum rx can then be determined and stored for each reception channel and, when the vehicle is started up again, can be fed to the subtraction device 14 as a new interference spectrum rx via the output line 16, so that the reception signals received during driving can be compensated by updated interference spectra.

[0023] In Figure 4: shows a schematic flow diagram to illustrate the method according to the invention. The method starts in step 20, for example when the radar sensor is put into operation or when the vehicle is put into operation by switching on the ignition. After the method has started in step 20, the current driving speed v is read in in the following step 21. The driving speed can come, for example, from a speed sensor on a vehicle wheel or from a satellite navigation system or from a radar sensor that measures the relative speed to stationary objects. In the following step 22, a check is carried out to determine whether the current speed v = 0. If v = 0, the vehicle is currently stationary. If v ≠ 0, the vehicle is moving and has a relative speed greater than or less than zero with respect to the detected stationary objects, depending on the direction in which positive or negative signals are transmitted.negative relative velocities are defined. In this case, step 22 branches to "No," and the process continues in step 21 with the vehicle speed v being read in again. During this time, transmission signals are emitted by the radar sensor and reflected partial waves are received. Based on the detected objects, an emergency braking function, adaptive cruise control, or another driver assistance function is executed. If it is determined in step 22 that the vehicle is currently stationary, i.e., v = 0, step 22 branches to "Yes" and continues in step 23 by transmitting standardized transmission signals. These standardized transmission signals are transmission signals whose modulation form and transmission intensity have been very precisely defined.In the following step 24, received signals of the standardized transmission signals are received, whereby these received signals also have multipath reflections 6, 7, which lead to interference spectra 9 that are superimposed with the useful spectra 8. In step 25, these received signals of the standardized transmission signals are stored and optionally added up over several cycles. After step 25, it is possible for the standardized transmission signals to be transmitted again, provided the vehicle is still stationary, which is why the flow diagram jumps back to step 23 after step 25 according to the dashed line 26. For example, it can be provided that this loop is repeated n times, so that, for example, n = 20 or n = 50 standardized transmission signal cycles are run through.By adding together these received signals of the standardized transmitted signals, interference that, for example, only occurred in a few cycles of the n repetitions can be averaged out by means of lower weighting, and interference patterns that occur regularly are taken into account by means of greater weighting in the interference signal 9 to be determined. After completion of the optionally provided n repetitions, the method continues in step 27 by updating the current interference spectrum 9 based on the current reflection situation and using these new interference spectra r 1 , r 2 , r 3 , r 4 , which were determined separately for each received channel, to compensate for the interference in the received signals.After step 27, the method continues in step 21 by transmitting transmission signals and applying the updated new interference spectrum 9 from the received signals in the evaluation by subtraction in order to compensate for multiple reflections in the received signal.

Claims

1. Method for reducing the influence of interference in the evaluation of at least one reception signal (5) of a radar sensor (1) installed in a vehicle, wherein predetermined transmission signals are emitted in predetermined operating situations and partial signals (5) reflected twice or multiple times are received, and the signals (5) received for the predetermined operating situations are stored for the purpose of determining an interference spectrum (r1, r2, r3, r4) and the influence of interference (7, 9) is reduced by taking into account the interference spectrum (r1, r2, r3, r4) during the signal evaluation, characterized in that the predetermined operating situations are the standstill of the vehicle in front of traffic lights, wherein, if the predetermined operating situation is detected, the emission of the predetermined transmission signals for sensor calibration is started and the reception signals which are then received and are reflected at stationary or fixed objects are evaluated and a search is made for multiple reflections in the reception signal, which are evaluated in order to determine a correction signal.

2. Method according to Claim 1, characterized in that the method is carried out separately for each reception channel of the radar sensor (1).

3. Method according to Claim 1 or 2, characterized in that the radar sensor (1) is arranged behind painted body parts (2) which are produced from plastic.

4. Method according to Claim 3, characterized in that the interference (7, 9) is reception signals (5) which arise as a result of multiple reflections (6, 7) between the body part (2) and the sensor radome (4).

5. Method according to one of the preceding claims, characterized in that the predetermined transmission signals are signals having an exactly predetermined signal shape and signal power.

6. Method according to one of the preceding claims, characterized in that the method is carried out separately for each reception channel of the radar sensor (1).

7. Method according to one of the preceding claims, characterized in that the reception signals (5) of the predetermined transmission signals are averaged over a plurality of signal cycles (26).

8. Method according to Claim 7, characterized in that the averaged signals are added to the previous correction signal.

9. Radar sensor (1), having devices for reducing the influence of interference (r1, r2, r3, r4) in the evaluation of at least one reception signal (5) of the radar sensor (1) installed in a vehicle, wherein means (10, 21, 22) are provided and are used to detect at least one predetermined operating situation, transmission devices are provided and emit predetermined transmission signals when the presence of at least one of the predetermined operating situations is detected, and reception devices (3, 11, 12, 13, 14) are provided and receive partial signals (5) reflected twice or multiple times, and means (15) are provided, in which at least one interference spectrum (r1, r2, r3, r4) is stored and in which the signals received for the predetermined operating situations are stored for the purpose of determining the interference spectrum (r1, r2, r3, r4), and at least one calculation means (15) is provided and reduces the influence of the interference (r1, r2, r3, r4) by taking into account the at least one interference spectrum (r1, r2, r3, r4), characterized in that the means (10) for detecting the at least one predetermined operating situation is the supply of a signal to the radar sensor (1), - which represents the standstill of the vehicle (v=0), or - which is the detection of a red traffic light applicable to the vehicle, which is generated in the vehicle by means of a video camera oriented in the direction of travel and starts - the emission of the predetermined transmission signals (23) and - the averaging (24, 25, 26) of the reception signals (5), wherein, if the predetermined operating situation is detected, the emission of the predetermined transmission signals for sensor calibration is started and the reception signals which are then received and are reflected at stationary or fixed objects are evaluated and a search is made for multiple reflections in the reception signal, which are evaluated in order to determine a correction signal.

10. Radar sensor (1) according to Claim 9, characterized in that in that the radar sensor (1) has a plurality of reception channels (3) and the interference spectrum (r1, r2, r3, r4) is detected separately and / or stored separately and / or taken into account separately for each channel.

11. Radar sensor (1) according to Claim 10, characterized in that a separate storage device or a separate region of a common storage device is provided for each of the plurality of reception channels (3), in which a separate interference spectrum (r1, r2, r3, r4) is stored for each reception channel.

12. Radar sensor (1) according to one of Claims 9 to 11, characterized in that the radar sensor (1) is arranged behind painted body parts (2) made of plastic.