GB2500107A

GB2500107A - Method for discriminating between pulse echo signals and noise or interference in a driving assistance system

Info

Publication number: GB2500107A
Application number: GB1303536.5A
Authority: GB
Inventors: Michael Schumann
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2012-02-28
Filing date: 2013-02-27
Publication date: 2013-09-11
Anticipated expiration: 2033-02-27
Also published as: GB2500107B; FR2987452B1; FR2987452A1; DE102012202975B4; GB201303536D0; DE102012202975A1

Abstract

A method for environment recognition using at least one distance sensor that is capable of emitting a pulse 38, 38.1 with a defined transmission spectrum and receiving at least one signal in a measurement cycle Î T; the received signal is classified as an echo signal 40 or rejected as noise or interference 41 based on whether the received signal amplitude and phase lie within a plausible range. An interference signal may be detected as originating from an external source and its distance calculated and provided to a driving assistance system. The pulse transmitter is preferably ultrasonic but may be electromagnetic (radar, lidar or infra-red), and at least one parameter of the transmission spectrum may be varied in reaction to an interference signal. The method described may be carried out by a computer program or a driver assistance system in a vehicle.

Description

1

Description Title •

Method for environment recognition and driving assistance 5 system

Prior art

The invention relates to a method for environment 10 recognition using a distance sensor of a driving assistance system. The invention further relates to a driving assistance system for carrying out the method.

Driving assistance systems are additional devices in a 15 vehicle which assist the driver with the driving of the vehicle. Such driving assistance systems typically comprise different subsystems, such as driver information systems or predictive safety systems. For various of these subsystems, environment sensor systems are required which monitor the 20 environment of the vehicle in order, for'example, to detect objects which may constitute potential obstacles on the roadway. Typically, for environment recognition, distance sensors are used in a vehicle which, based-on a pulse echo method, measure the distance from objects in the 25 environment of the vehicle and the measured data of which serve as a basis for subsystems, such as the parking assistance, the blind spot monitoring or the lane monitoring.

30 In the pulse echo method, the propagation delay between transmitted pulse and received echo is measured, in order to be able to derive an unambiguous distance from the propagation delay, distance sensors work in an unambiguous

2 -

range. This means that the length of the measuring'cycles is determined by the maximum propagation delay of the transmit pulse to be expected. For example, in order to achieve a measuring distance of 5m, at a speed of sound of 5 343 m/s a measuring cycle of about 30 ms has to be observed. From KR 10 2001 0105677 A it is known to assign a detection time to an ultrasonic sensor. In the case of a signal which is detected after the detection time has elapsed, this is assumed to be interference. For 10 verification, a signal is transmitted by a second sensor.

During the distance measurement, noise is additionally superimposed on the measured data and reduces the measuring accuracy. In order to take account of only the measured •15 ■ values which lie above the noise level to be expected, threshold value characteristics are typically preset.

•• •• DE 10 2004 006 015 A1 describes such a method, in which the

• • •

• •

detection threshold is varied as a function of external

••••••

• •

conditions of the system.

• • •

• • • 90

• •• • ^ u

Besides the noise level, environmental influences may also interfere with the measurement. For example, air flows when

• « •

**** driving comparatively quickly may constitute interference

* * sources. Ultrasonic sensors of other vehicles which

25 themselves emit ultrasonic signals may also cause interference. In order to mask out this kind of interference,- the received echo signals are typically-filtered before they become the basis of the distance calculation. From DE 10 2009 002 870 A1 there is known a 30 method for recognising external interferers, in which ultrasonic pulses are emitted by a- plurality of transmitters simultaneously, in order to .verify echoes of the first ultrasonic pulse. .

3

Present-day driving assistance systems have high requirements in terms of the stability and the reliability of the sensor systems used and the environment data 5 obtained therefrom, since a driving assistance system can recognise situations and react accordingly, only' on the basis of the environment data. There is therefore a continuous interest in masking out interference as reliably ■ as possible, in order to be able to utilise the provided 10 environment data optimally for the assisted driving.

Disclosure of the invention

According to the invention, a method for environment recognition using at least one distance sensor is proposed, which comprises the following steps:

(a) emitting at least one pulse with a defined transmission spectrum;

(b) receiving at least one signal in a measuring cycle;

(c) classifying the received signal as an echo signal or as an interference signal, with a plausibility check being performed based on an amplitude and phase information of the received signal.

According to the invention, a driving assistance system for carrying out the above-described method is furthermore 30 proposed, which comprises the following components:

15

20

25

(i) at least one distance sensor for emitting at least one pulse with a defined transmission spectrum and/or for receiving at least one signal in a measuring cycle;

5 (ii) a component for classifying the received signal as an echo signal or as an interference signal by performing a plausibility check based on an.amplitude and phase information of the received signal.

10 In the context of the invention, the distance sensor may be part of the environment sensor system of a driving assistance system with different subsystems, for example a parking assistant, a blind spot, monitoring or an adaptive cruise control (ACC) system. In this regard,, the 15 environment sensor system of the driving assistance system serves for monitoring the vehicle environment, for which ultrasonic sensors, radar sensors, infrared sensors, LIDAR sensors or -optical sensors may be used. In particular, sensors which'determine the distance from objects in the 20 environment of the vehicle according to the principle of a pulse echo method are employed for the distance measurement. Preferably, ultrasonic sensors - are suitable as distance sensors. '

25 ' In general, the transmission spectrum of the distance sensor is determined by parameters, such as frequency, amplitude and phase. Thus, the transmission spectrum may comprise a signal with defined frequency, amplitude and signal shape, for example a square-wave pulse. Furthermore, 30 the transmission spectrum may be modulated in one parameter, for instance the-frequency. In particular, a transmission spectrum whose frequency varies over time (chirps) is suitable for distance sensors. A further

possibility is constituted by the superimposition of different signals with, for example, different frequencies or amplitudes in a transmission spectrum.

5 A measuring cycle in the context of the invention refers to a sequence of transmission and receiving intervals. In particular in the case of distance sensors which determine the- distance according to the principle of a pulse echo method, a measuring cycle comprises at least one 10 transmission interval, in which a transmit pulse with a transmission spectrum is emitted, and at least one receiving interval, in which echoes of the transmit pulse can be received. In this regard, the length of a measuring cycle is typically determined by the' maximum time to be 15 expected between emitting the pulse and receiving the associated echo.

In the context of the invention, the distance sensor can both emit a pulse and receive an echo. Although this design 20 is advantageous, it is in no way compulsory. Equally,

constructionally separate transmitters and receivers are also possible. In the case of constructionally separate units, at least two distance sensors are used to carry out the method according to the invention, one distance sensors 25 acting as "transmitter" when it emits a pulse, and one distance sensor acting as "receiver" when it receives a signal.

The method according to the invention can be carried out in 30 the context of a propagation delay measurement, the propagation delay measurement being performed with the aid of the distance sensor. In this regard, the distance sensor is firstly activated to emit pulses with a defined

transmission spectrum. The activation of the distance sensor can be effected in a driving assistance system, for example centrally, from a control device of the driving assistance .system or from an electronic device assigned to 5 the sensor, the transmission parameters, for instance the . frequency, the amplitude, the transmission duration or the modulation of a pulse or successive pulses, being variable and being adaptable to the particular situation, -for example to the speed of the vehicle or to the driving 10 manoeuvre to be performed. Subsequently, the emitted pulses are detected, on reflection on objects, as echoes by the distance sensor. From the propagation delay of a pulse,-i.e. the time between transmitting the pulse and receiving the echo, there then results the distance between the 15 object and the distance sensor, while taking account of the speed of the signal and optionally the vehicle speed.

Signals received by the distance sensor are typically supplied.to an electronic unit, such as the control device 20 of a driving assistance system or an electronic device assigned to the sensor, and are further processed there, in order to extract information, such as the propagation delay of the transmit pulse, from the received signal. Besides the propagation delay and the distance determination 25 resulting therefrom, it is also possible to analyse received.- signals' with regard to the amplitude and the phase information. The phase information is given here by the phase correlation between the received signal and the transmit pulse. With the aid of the amplitude_and the phase 30 information, the received signal is classified in the context of a plausibility check as an echo signal or as an interference signal.

7

In one implementation of the method according to the invention, both for the amplitude and for the phase information of the received signal, a plausibility range is set. The plausibility range here is dependent, similar to 5 the.length of a measuring cycle, on the values to be expected for the amplitude and for the phase information of an echo signal. This is determined in particular by the parameters of the transmitted pulse. Thus, for example, for a given amplitude and frequency modulation of the transmit 10 pulse, a characteristic is calculated which correlates the ' amplitude of an echo signal to be expected with the distance or with the propagation delay. From this there results, for each measured propagation delay or the •distance resulting therefrom and for each.measured 15 amplitude of the received signal, a physically plausible range which .takes account of the .measuring inaccuracies. Here, the amplitude of the received signal is dependent on the reflectivity of the reflecting objects and because of this may vary greatly.

20

The plausibility range for the amplitude therefore preferably comprises, a threshold value .as upper limit. In particular, the plausibility range for the amplitude comprises amplitudes which lie below a threshold value of 5 25 to 10% above the valve to be expected for the amplitude at a given distance. Interference signals with amplitudes which lie below this threshold value are classified by performing a plausibility check with the phase information. In addition to the threshold value, it is possible to 30 consider as lower limit a minimum value for the amplitude which depends on the determinability of the phase information. This value is determined by the error in determining the phase information, which increases for

8

decreasing amplitudes. The phase information thus becomes less accurate and can no longer be readily utilised, for instance by means of additional filters, for performing a plausibility check.

5

Similarly, a physically plausible range can be set for the phase information. Thus, for each measured propagation delay.or the distance resulting therefrom, there results a phase correlation to be expected of an echo signal with 10 respect to the transmit pulse. For each measured phase correlation of the received signal with respect to the transmit pulse, a physically plausible range can be set which takes account of measuring inaccuracies with respect to the value to be expected. In this regard, phase 15 information of 1 corresponds to a -received signal having a maximum correlation with the transmitted signal. For example, the plausibility range for the phase information may lie between plausibility coefficients of 0.2 and 1,

with a lower limit lying at 0.2 to 0.4 and an upper limit 20 lying at 0.9 to 1 of the value to be expected for the phase information at a given propagation delay. The,, plausibility • range for the phase information may lie, for example, between a phase correlation coefficient of 0.4 to 1.

25 In one implementation of the method according to the

' invention, • in the context' of the.plausibility check it is determined whether the amplitude and the' phase information of the received signal lie within or outside the respective plausibility range. Furthermore, the plausibility check 30 with regard to the phase information can be performed under the condition that the amplitude- of the signal exceeds a minimum value. Additionally or alternatively, received signals, with amplitudes lying below the minimum value can .

9

be filtered by, for example, identifying them by means of a matched filter and optionally suppressing them.

In a further implementation of the method according to the 5 ' invention, the plausibility, range for the phase information can vary as a function of the amplitude, where, for example,- a linear relationship between the. plausibility range for the phase information and the amplitude can be assumed. If the phase information, for example, lies in the. 10. lower range of the associated plausibility range and the amplitude lies in the upper range of the associated plausibility range, it can be inferred from this that an interference signal is present. This is because the greater the amplitude is, the more accurate the phase information 15 and thus the correlation between received and transmitted signal can be determined. ■ The error in determining the phase information for large amplitudes close' to the threshold value thus allows a smaller plausibility range in the phase information. Conversely, the determination of the. 20. phase information is less accurate, the smaller the amplitude, i.e. the closer the amplitude lies to the minimum value for the amplitude, and/the phase information is thus plausible over a larger range.

25 If the distance sensor receives signals, the amplitude and phase information of which lies within the respective plausibility range, the received signal constitutes an echo of the transmit pulse. The result of this is that the received signal can be identified as an echo signal and 30 thus as object detection.

Conversely, the distance sensor can also receive signals, , the amplitude and phase information of which do not lie in

• • • < • •

• • * * • ♦

» * I

10

the respective plausibility range, and are identified as interference. Such signals can come, for example, from an external interferer, such as another distance sensor, compressed-air guns, background noises, such as key rattling, or electromagnetic interferers, such as induction loops, and there is no correlation between the transmit pulse and the received signal. Consequently, classifying • such signals as echo signals would result in an incorrect distance measurement.

In a further implementation of the method according to the invention, interference signals in particular for the distance determination are rejected.•Alternatively, the amplitude ahd/or the phase information.of the received 15 interference signal can be further processed. Thus, for example, from the amplitude and/or the phase information of the received interference signal, an external interferer can be recognised and a distance of the distance sensor ' from the external interferer, in particular an ultrasonic 20 sensor of another vehicle, can be estimated. From the distance of the external interferer, it is also possible to extract further information, comprising, for example, the movement, the speed, the acceleration and information regarding the position of an external interferer. 25 Additionally or alternatively, at least one parameter of the transmission spectrum, for instance the frequency or its modulation, can be varied in reaction to an interference signal which can be assigned, for example, to an external interferer, in order to reduce the influence of 30 the external interferer on the distance sensor.

The information that an external interferer has been detected and/or its distance can be furthermore•provided to

11

a higher-order system, in particular a driving assistance system. Thus, this information can be utilised for further subsystems, in particular those based on tracking algorithms, for instance the parking assistance, the blind 5 spot monitoring or the lane monitoring.

The driving assistance system according to the invention is preferably designed for carrying out the method described above. In this regard, the individual components constitute 10 functional components or routines which are, for example, executed in the context of a computer program on an electronic unit, such as programmable computer device. The computer device may,. for example, be a control device (ECU) for implementing a driving assistance system or a subsystem 15 thereof in a vehicle.

The distance sensor of the driving assistance system may, for example, be configured as an ultrasonic sensor, radar sensor, infrared sensor, LIDAR sensor or optical sensor, 20 which can act a receiver and/or transmitter. Preferably, the distance sensor is an ultrasonic sensor.

The ECU can communicate with the distance sensor via control signals. Thus, control signals can be generated 25 which trigger the distance sensor to emit pulses with a defined transmission spectrum. Conversely, the distance sensor can also pass on received signals to the ECU for signal processing. Thus, in the context of the signal processing in the.ECU, the classification of the received 30 signal as an echo signal or as an interference signal can be carried out. For this purpose, a plausibility check is performed which is based on an amplitude and phase information of the received signal. Alternatively, the

12

signal processing, in particular the generation of a control signal and the plausibility check, can be carried out in an electronic device assigned to the sensor, the results of which can be optionally communicated' to the ECU.

'5

-According, to the invention, a computer program for carrying out a.method described herein when the computer program is executed on a programmable computer device is furthermore proposed. The computer program can be stored on a machine-10 readable storage medium, for instance on a permanent or rewritable storage medium or in assignment to a computer device, or on a removable CD-Rom, DVD or a USB stick. Additionally or alternatively, the computer program can be provided on a computer device such as a server for 15 downloading, for example via a data network, such as the Internet or a communications connection,.such as for instance a telephone line or a wireless connection.

Advantages of the invention

20. -

The invention enables a more reliable environment recognition using a distance sensor, and in particular through the simultaneous inclusion of the amplitude and the phase information of the received signal in a plausibility 25 check, interference signals can be reliably distinguished from echo signals. As a result, high-quality, data .are available, allowing a reliable object recognition and distance measurement. Thus, the measured data of the distance sensor can be utilised to provide the maximum 30 information content to subsequent systems. In particular, the plausibility check makes- it possible to distinguish external interferers, such as distance sensors of other vehicles, from actual obstacles.

13

On detection of an external interferer, the measured values can be utilised to determine further information. Thus, external interferers can be detected even before entering the detection range of the distance sensor and taken into account early by the driving assistance system.

Furthermore, interference by the external interferers in one's own system can be minimised by changing the frequencies in the transmission spectrum of the distance sensor. The invention thus assists not only one's own driving assistance system but also external systems and can contribute to a general improvement of the environment detection.

Driving assistance systems frequently utilise distance sensors for environment recognition. With the improved processing of the measured data, the environment recognition of the driving assistance system is thus also improved. This is reflected immediately in the responsiveness and the reliability of the driving assistance system. In particular,, the information that there is an external interferer with an estimated distance can be utilised to adapt the reaction of the driving assistance system accordingly. For example, interventions of the driving assistance system in active system components of the vehicle, such as the brake system or the drive system, which interventions are to be performed owing to Incorrect distance values, can be prevented.

Situations in which the environment sensor system of the driving.assistance system provides the relevant data for assisting the driver occur frequently and a driving assistance system designed according to the invention can

10

14

thus contribute to improved assistance. The increased system availability additionally increases the utility value and the acceptance of corresponding driving assistance systems. Moreover, the proposed method for environment detection can be implemented, without •additional hardware components, by a software update,.thus enabling cost-effective and simple realisation.

Brief description of the drawings

Further aspects and advantages of the invention will now be described with reference to' the appended drawings, in which: .

15 Figure 1 shows a vehicle equipped with a driving assistance system according to the invention, in an exemplary- driving situation,

Figure 2 schematically shows a signal profile for a 20 complete measuring cycle for distance measurement,

Figure 3 shows characteristic curves 'With exemplary measuring points for discrimination between 25' actual objects and interference signals,

Figure 4 shows an exemplary representation of the plausibility ranges for the amplitude and the. phase information at a given distance,

30

Figure 5 shows a working method of the driving assistance system from Figure 1, in the form of a flow diagram.

15

• • • • • ♦ • • • •

Embodiments of the invention

In Figure 1 there is schematically indicated a driving 5 situation with several vehicles 1.0, 12, 14 situated in the immediate vicinity of one another. In this case, the vehicles 10,' 12 are moving directly behind one another in a first direction 16. A further vehicle 14 is travelling on the opposite lane, in a direction 18 opposite the first 10 direction 16, past the vehicles 10, 12. Furthermore, the vehicles 10, 12, 14 are each eguipped with a driving assistance system 11, 13, 15. The driving assistance system 11, 13, 15 comprises an ultrasound-based system for monitoring the environment having several ultrasonic 15 sensors 20, 22, 24, 26, 28, 30, 32, 34, 36 (abbreviated

20...36), which are installed at the front, at the rear and at the sides on the vehicles 10, 12, 14. Each ultrasound-based system is controlled by a central ECU 37, 38, 39 which communicates with the ultrasonic sensors 20...36.

20 Besides the ultrasound-based system for monitoring the environment, the driving assistance system 11, 13, 15 may comprise further environment sensor systems, not shown in Figure 1.

25 As vehicles 10, 12, 14 are travelling past or in situations . with a high traffic volume, for example in a traffic jam or at a red light, the vehicles 10, 12, 14 may be situated in the immediate vicinity of one another, at least, for a short time. The respective driving assistance systems 11, 13, 15

30 can therefore detect further vehicles 10, 12, 14, situated in front of, behind or beside them, as objects using the ultrasonic sensors 20...36 installed on the vehicle. .

16

Furthermore, the ultrasonic sensors 20...36 of the vehicles 10, 12, 14 may interfere with one another. Thus, for example in the situation shown in Figure 1, the ultrasonic sensors 26 fitted at the rear on the vehicle 12 may 5 interfere with the ultrasonic sensors 22 fitted at the front on the vehicle 10. Such interference comprises, for example, the reception of incorrect ultrasonic signals by an ultrasonic sensor, for example 22, which have, been emitted by another ultrasonic sensor, for example 26, and 10 have no connection with the emitted pulse of the ultrasonic sensor 22. These interference signals result in the detection of "ghost objects" and may cause incorrect behaviour of the driving assistance system 11.

15 In order to- avoid such situations, the driving assistance system 11, 13, 15 according to the invention performs a plausibility check, by means of which actual echoes 40 can be distinguished from interference signals 41. The amplitude 4 6.2, 48.2, 50.2 and the phase information of the 20 received signals 40, 41 are utilised for this, an actual echo signal 4 0 being assumed when the amplitude 4 6 and phase information lie in a predetermined plausibility range 44. Otherwise, an interference signal 41 is inferred, which is rejected or further processed in^the ECU 21, 27, 33.

25

The phase information in this case describes- the phase matching which determines how well the receive signal matches the transmit signal if the two were graphically 'laid on top of one another. Mathematically, this is 30 described by the correlation function of transmit and receive signal. For example: if a signal were transmitted at 50 kHz and the receive signal had 60 kHz, then there would be a poor correlation and a correlation coefficient

17

less than 1, because the wave crests and troughs diverge. If-the receive signal likewise had 50 kHz and the wave crests and troughs coincided, this corresponds to a high correlation between the signals and the correlation 5 coefficient would be 1. The phase information therefore typically corresponds to the correlation coefficient between the transmit and receive signal.

In Figure 2 there is plotted a signal profile of the oscillation amplitude, A, against time, t, for a complete measuring cycle AT, which amplitude is measured by an ultrasonic sensor 20...36. The measuring cycle AT begins with a transmit pulse 38.1 and lasts until a further transmit pulse 38.2. Firstly, the ultrasonic sensor 20...36 receives a digital transmit pulse or a transmit command from the ECU 21, 27, 33 of- the driving assistance System

11, 13, 15.- As a result, the ultrasonic sensor 20... 36 is excited to oscillate with, for example, square-wave pulses. The ultrasonic sensor 20...36 emits an•ultrasonic pulse for a certain time, with no reception being possible during the decay time ATi. After the time interval ATj., the ultrasonic sensor is ready to receive for the time interval AT2. The sound reflected by objects, for example another vehicle 10,

12, 14, causes the membrane, which has settled again, of the ultrasonic sensor 20...36 to oscillate again, resulting in the echo signals 40.

The oscillations are converted by the ultrasonic sensor 20...36 into an electrical signal and further processed by 30 the sensor electronics. The acquired environment data are finally provided to the ECU 21, 27, 33 and utilised for controlling further components of the driving assistance system 11, 13, 15,- for example for issuing warnings to the

10

15

20

• • * • • •

• *

25

driver. Furthermore, from the instants at which the echo signals 40 were detected and the initially emitted pulse 38, there results the propagation delay or, taking account of the speed of sound, the distance between the ultrasonic 5 sensor 20...36 and the detected object.

Besides the echo signals 40, however, signals 41 may also occur during a measuring cycle AT. Over the course of the measuring cycle AT, the signal 41 has a higher amplitude 10 than the echo signals 40, despite the distance damping of the echo amplitude which is to be expected. Such signals 41 may come, in particular, from active external interferers, such as ultrasonic sensors 20...36 of other vehicles 10, 12, 14. Recognition and suppression of such signals can be 15 carried out firstly on the basis of the amplitude values

46.2, 48.2, 50.2. A more reliable way, however, consists in taking account also of the phase information of the received signal 40, 41 in the plausibility check, since the •;•••• phase information of the received signal 40, 41 can provide

20 further information'about its origin. In this case,

• • •

*** * advantageously the effects are combined, so that the amplitude 46.2, 48.2, 50.2. of the signal 40, 41 decreases

I .with the distance, and for signals 40, 41 with large

• •• •

• amplitudes 46.2, 48..2, 50.2 the phase information can be

• . •

25 determined more accurately.

With the aid of the plausibility check, it is thus possible to distinguish between echo signals 40 and interference signals 41. Figure 3 shows, by way of.example, 30 characteristics 42 of an ultrasonic sensor 20...36 with measuring points 4 6.2, 48.2, 50.2, with the aid of which the plausibility check according to the invention is described in more detail.

19

Figure 3 shows characteristics 42 which link the amplitude 46.2, 48.2, 50.2 of received signals 40, 41 with the propagation delay or equivalently the distance d of a 5 detected-object. In this-case, a maximum amplitude 48.2 to be expected results from the distance damping of the amplitude 46.2, 48.2, 50.2 for each measured propagation delay between transmitted pulse 30 and received pulse 40. These values correspond to the characteristic 42.2. Owing 10 to measuring inaccuracies and deviations from the assumed model for the distance "damping, furthermore a plausibility range 44 is set which takes account of deviations from the values 42.1 to be expected. This plausibility range 44 is given by the threshold values of the characteristics 42.1 15 and lies, for example, between ± 5 to 10% of the amplitude to be expected.

During the operation of the ultrasonic sensor 20...36, different signals 40,.41 are received and firstly evaluated 20 with the aid of the characteristics 42, as shown in Figure 3. If a signal having a distance 48.1 and an amplitude 48.2 is received, this point 48 lies within the plausibility range 44 for the amplitude and indicates an echo signal 41. Received signals 40, 41 having an amplitude below the 25 threshold value, and thus below.the characteristic 42.1, may be plausible owing to the reflectivity of objects and the- atmospheric damping due to the absorption in air, and therefore likewise lie in the plausibility range 44.

30 Received signals 40, 41, having for example a distance 46.1 and an amplitude 46.2, lie with the point 4 6 outside the plausibility range 44 and are unphysical. Such signals are ■ - therefore implausible and can be identified as interference

20

signals without checking the phase information. The plausibility check with regard to the phase information is thus performed when the amplitude of the received signal 40, 41 at a given distance is below a threshold value 42.1.

5 Additionally, the phase information can be determined only inaccurately for smaller amplitudes 50 ..2 .' Therefore, it is furthermore conceivable to perform the plausibility check with regard to the phase information, when the amplitude of the received signal 40, 41 exceeds a minimum val.ue 50.2.

10

If the amplitude of the received signal 40, 41 lies in the plausibility range 44 and if additionally the phase correlation extracted from the received signal 40, 41 with respect to the transmitted pulse 38 is inconsistent with 15 the phase correlation to be expected, then, for example, the signal corresponding to point 48 is classified as an interference signal 41 from an external interferer, for instance an ultrasonic sensor 20...36 of another vehicle 10, 12, 14. The information that an ultrasonic sensor

20 20...36 of another vehicle has been detected as an external interferer and optionally its distance can furthermore be provided to the higher-order driving assistance- system 11, 13, 15.

25 Figure 4 shows the plausibility check with regard to the amplitude 4 8.2, 50.2 and the phase information of the received signal 4.0, 41 with the aid of an exemplary representation of the plausibility ranges 44, 84 for the amplitude and the phase information at a given distance. .

30 Thus, the plausibility range 86 is firstly set by the respective plausibility ranges of the amplitude 44 and the phase information 84.' For the amplitude, this results from the maximum physically possible threshold value 42.1 and

21

optionally from the minimum value 50.2 starting from which a checking of the phase information is useful. The plausibility range 84 for the phase information likewise results from the physically possible limits 72, 70 between 5 which the phase information can lie. "A typical range 8 4 for the phase information lies, for example, between 0.4 and 1.

From the respective plausibility ranges 44, 84 for the amplitude and the phase information, there results a two-10 dimensional range 86 comprising plausible values. In order to refine the plausibility check further, a further discrimination is performed in the range 8 6, the plausibility range 84 for the phase information being matched to the respective amplitude, since at amplitudes 15 below the minimum amplitude value 50.2, the phase information can only be determined inaccurately. Therefore, in the range 79 a greater plausibility range 8 4 is assumed and optionally further filters are used to discriminate signals from noise. Towards greater amplitude values, the 20 determination of the phase information becomes more accurate and the plausibility range 84 can be continuously reduced with increasing amplitudes.

From this there results the division, shown by way of 25 example in Figure 4, of the range 86, into an implausible range 82 and a plausible range 88. Finally, the plausibility check in the context of the method according ' to the invention can be refined to such an extent that only values which fall within the range 88 at a given distance ■ 30 are identified as echo signals, and signals which lie outside this range 86 are identified as interference . signals. Thus, high-quality data are provided, which allow reliable object recognition and distance measurement.

22

Additionally, the data of detected external interferers are utilised to determine further information. For instance, external interferers can be detected even before entering the detection range of the distance sensor and be taken 5 into account early by the driving assistance system.

Furthermore,- interference by the external interferer in one's own system can be minimised by changing the frequencies in the transmission spectrum of the- distance sensor.

10

In Figure 5 there is illustrated a flow diagram 60 which explains the interplay between the components of the driving assistance system 11, 13, 1'5 according to the invention. In a step 62, pulses are emitted by the distance 15 sensor with a defined transmission spectrum, for instance a frequency-modulated transmission spectrum. With this, the measuring cycle AT begins.' In step 64, the distance sensor is. ready to receive and receives signals until the end of the measuring cycle AT.

20

In step 66, the received 'signals 40, 41 are.analysed and classified as an echo signal 40 or as an interference signal 41. In doing so, based on the amplitude 46.2, 48.2, 50.2 and the phase information of the -received- signals 40, 25 41, a plausibility check is performed and it is checked whether the amplitude 46.2, 48.2, 50.2 and the phase information of the lie within the respective plausibility range 44. Thus, in a particularly advantageous manner, use Is made of the fact that the amplitude 46.2, 48.2, 50.2 of 30 the signal 40, 41 decreases with the distance, and for signals 40, 41' with large amplitudes the phase information can be determined relatively accurately. The check with regard to amplitude 4 6.2, 48.2, 50.2 and phase information

23

thus constitutes a reliable way of recognising and suppressing external interferers in the receiving spectrum of an ultrasonic sensor 20...36.

The invention is not .limited to the exemplary embodiments described here and the aspects highlighted therein. Rather, a multiplicity of modifications lying within the scope of practice of a person skilled in the art are possible within the scope specified" by the "appended claims.

Claims

Glaims

1. Method for environment recognition (60) using at least one distance sensor (20...36) comprising the following * 5 steps:

(a) emitting (62) at least one pulse (38, 38.2, 38.1) with a defined transmission spectrum;

10 (b) receiving (64) at least one signal (40, 41) in a measuring cycle (AT);

(c) classifying (66) the received signal (40, 41) a~s an echo signal (40) or as an interference signal (41), with a 15 plausibility check being performed based on an amplitude (46.2, 48.2, 50.2) and phase information of the received signal (40, 41) .

2. Method according to Claim 1, characterised in that a 20 propagation delay measurement is performed with the aid of the distance sensor (20...36).

3. Method according to one of Claims 1 and 2,

characterised in that, for the amplitude (46.2, 48.2, '50.2)

25 and the phas.e information of the received signal (40, 41), in each case a plausibility range (44, 84) is set, and in the plausibility check it is determined whether the - amplitude (46.2, 48.2, 50.2) and the phase information of the received signal (40, 41),lie within or outside the 30 respective plausibility range (44, 84).

4. Method according to Claim 3, characterised in that the plausibility range for the amplitude comprises amplitudes

25

which lie below a threshold value of 5 to 10% above the value to be expected for the "amplitude at a given distance.

5. Method according to one of Claims 3 and 4,

5 characterised in that the plausibility range for the phase information lies between phase correlation coefficients of 0.2 and 1.

6. Method according to one of Claims 3 ,to 5,

.10 characterised in that the plausibility range for the phase information varies as a function of the.amplitude.

7. Method according to one of Claims 3 to 6,

characterised in that a received signal (40, 41), the

15 amplitude (46.2, 48.2, 50.2) and phase information of which lie within the respective plausibility range (44), is classified as an echo signal (40), and a received signal (40, 41), the amplitude (46.2, 48.2, 50.2) or phase information of which lie outside the respective 20 plausibility range (44), is identified as an interference signal (41).

8. Method according to one of Claims 1 to 7,

characterised in that the received .interference signal (41) is rejected.

9. Method according to one of Claims 1 to 8,

characterised in that at least one parameter of the transmission spectrum is varied in reaction to an

30 interference signal (41).

10. Method according to one of Claims 1 to 9, characterised in that the amplitude (46-. 2, 48.2, 50.2)

26

and/or the phase information of the received interference signal (41) are further processed.

t • • • • t

Ma •

• •••

10

15

11. Method according to Claim 10, characterised in that, from the amplitude (46.2, 48.2, 5.0.2) and/or the phase information of the received interference signal (41), an external interferer is recognised and a distance of the-distance sensor (20...36) from the external interferer is estimated.

12. Method according to Claim 11, characterised in that the information that an external interferer. has been detected and/or its distance are provided to a higher-order system (11, 13, 15).

13. .Computer program for carrying out the method according to one of Claims 1 to 12 when the computer program is executed on a programmable computer•device.

20

14. Driving assistance system (11, 13, 15) for carrying out the method according to one of Claims 1 to 12 having the following components:

(i) ■ at least one distance sensor (20...36) for emitting 25 . at least one pulse. (38, 38.2, 38.1) with a defined transmission spectrum and/or for receiving at least one-signal (40,.41) in a measuring cycle (AT);

(ii) a component (21, 27, 33) for classifying the received 30 signal (40, 41) as an echo signal (40).or as an interference signal (41), with a plausibility check being . performed based on an amplitude (4 6.2, 48.2, 50.2) and phase information of the received signal (40, 41).