Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02842814 2015-09-22
DETERMINATION OF AN ITEM OF DISTANCE INFORMATION FOR A VEHICLE
The present invention relates to a method for a vehicle, in particular a
method for determining a
distance to an object in an environment of the vehicle, and also a
corresponding device.
In modern vehicles, for example, passenger automobiles or trucks, a variety of
so-called driver
assistance systems are used to assist a driver of the vehicle when driving the
vehicle. Such
driver assistance systems can contribute to avoiding accidents, for example,
and can relieve the
driver, whereby a comfort of the driver can be increased. For example, an
adaptive cruise
control system can automatically maintain a suitable distance to a leading
vehicle. Parking aids
can assist a driver when parking in and exiting a parking space. Further
assistance systems can
monitor a blind spot and carry out emergency braking or control interventions
depending on a
traffic situation, for example. To detect a current traffic situation in an
environment of the
vehicle, object detection systems are therefore necessary. Typical object
detection systems use
technologies, for example, radar, lidar, ultrasound, or automatic image
processing. Additional
costs may thus arise for corresponding sensors. In addition, such sensors are
to be housed at
suitable locations of the vehicle, whereby additional installation space is
required for these
sensors.
In this context, an illumination system having driver assistance capabilities
is disclosed in
WO 2008/154736 Al. For this purpose, vehicle lighting modules, for example,
front headlights,
taillights, brake lights, and interior lights, have additional detection
capabilities added, to
recognize the presence of obstructions, for example, automobiles, trucks,
pedestrians, and
other objects, or to measure the velocity of these obstructions. These
detection capabilities are
made available to driver assistance applications, for example, an adaptive
cruise control, a blind
spot monitor, and a precrash assistant. A light-emitting diode (LED) has the
capability of being
used as a light source for a light, on the one hand, and to be pulsed or
modulated as a source
for the detection system, on the other hand.
The object of the present invention is to provide an improved distance or
velocity measurement
for an object in an environment of the vehicle or for multiple objects in the
environment of the
vehicle.
- 1 -
According to the present invention, in one aspect there is provided a method
for a vehicle, the
method comprising: determining an operating state of the vehicle; selecting a
modulation
method as a function of the operating state of the vehicle, wherein the
modulation method
comprises at least one of: a frequency-modulated continuous wave method; a
random
frequency modulation method; a single-frequency modulation method; and a pulse
modulation
method; generating a modulated signal using the selected modulation
method;actuating a light
source of the vehicle using the modulated signal to emit light; receiving
light, which was emitted
by the light source and was reflected from an object in an environment of the
vehicle; generating
a reception signal as a function of the received light; generating a mixed
signal by mixing the
modulated signal with the reception signal; and determining a distance to the
object as a
function of the mixed signal.
According to the present invention, in another aspect there is provided a
device for carrying out
a method for determining an item of distance information for a vehicle, the
device comprising: a
light source, which is implemented to illuminate an object in an environment
of or inside the
vehicle; a sensor for receiving light of the light source reflected from the
object; and a
processing unit, which is coupled to the light source and the sensor; wherein
the device for
carrying out the method is implemented according to the method of the above
paragraph.
According to the present invention, in another aspect there is provided a
vehicle comprising: the
device defined in the above paragraph; an illumination unit for illuminating
an environment or an
interior of the vehicle, wherein the illumination unit comprises the light
source; and a driver
assistance system; wherein the device is coupled to the driver assistance
system and the
illumination unit.
According to the present invention, a method for a vehicle is provided, in
which a light source of
the vehicle is actuated using a modulated signal. Light which has been emitted
by the light
source and reflected from an object in an environment of the vehicle is
received and a reception
signal is generated as a function of the received light. The modulated signal,
using which the
light source of the vehicle was actuated, is correlated with the reception
signal and a
corresponding correlation signal is generated. A distance to the object is
determined as a
function of the correlation signal. For example, the modulated signal, using
which the light
source of the vehicle was actuated and therefore the light emitted by the
light source was
modulated, can be time-shifted and correlated with the reception signal. A
correlation maximum
results at the shifting time which is proportional to the distance of the
object. In other words, the
shifting time is proportional to a signal runtime from the light source to the
object and back to a
receiver of the vehicle. Since substantially noisy signals are analysed, which
can be influenced
CA 2842814 2017-07-24 2 -
by daylight, scattered light, or light from other vehicles, for example, the
level of the correlation
maximum is a measure of the signal strength, so that various objects can be
differentiated. A
resolution in the distance can be determined by a scanning frequency of the
reception signal.
Long signal sequences of the modulated signal can be used by the correlation.
A signal length
of the modulated signal is not restricted to the runtime of the signal for the
distance to be
measured. Furthermore, the analysis can be implemented digitally, for example,
and can
therefore be constructed cost-effectively.
The correlation signal can be generated, for example, by generating multiple
correlation
coefficients, to each of which a respective shifting time is assigned. Each
correlation coefficient
is formed by correlating the modulated signal, which is shifted by the
respective assigned
shifting time, with the reception signal. In other words, the reception signal
is correlated with
multiple differently time-shifted modulated signals and a corresponding
correlation coefficient is
thus formed for each shifting time. The distance to the object is determined
as a function of the
multiple correlation coefficients and the assigned shifting times. For this
purpose, the correlation
coefficients can be compared to a threshold value, for example, and if the
threshold value is
exceeded, it can be established that an object is present at a distance which
results from the
assigned shifting time.
The resolution in the distance to the object can be influenced by the scanning
frequency of the
reception signal. To achieve a high scanning rate, for example, a one-bit
conversion of the
reception signal can be carried out. For this purpose, the reception signal
can be generated
using a first signal value, for example, a 0 bit, if a level of the received
light falls below a specific
CA 2842814 2017-07-24 - 2a -
CA 02842814 2014-02-11
intensity, and a reception signal can be generated using a second signal
value, for example, a 1
bit, if the level of the received light reaches or exceeds the specific
intensity. Since the
significance of the correlation is in the time, no essential information is
lost by this coarse one-
bit conversion. The significance in the amplitude is unreliable in any case
because of the
amplitude modulation to be expected by way of the reflection on the object. A
correlator can be
constructed very simply and can process long signal sequences due to the
reception signal
reduced to one bit, whereby the correlation result can be improved. Since the
comparison
pattern for the reception signal is to be provided digitally upon the use of
the one-bit conversion,
it is advantageous to use a synthetic signal for the modulation of the light
source, which is then
generated with uniform quality as a function of the transmit clock. If the
receive clock is equal to
the transmit clock, clock errors, for example, as a result of temperature
drifts, can be avoided.
The above-described one-bit conversion can be carried out using an amplitude-
limited amplifier,
for example, which outputs the first signal value or the second signal value
as a function of the
received light.
The present invention provides a further method for a vehicle, in which a
light source of the
vehicle is actuated using a modulated signal and light, which was emitted by
the light source
and was reflected from an object in an environment of the vehicle, is
received. A reception
signal is generated as a function of the received light and a mixed signal is
generated by mixing
the modulated signal with the reception signal. A distance to the object in
the environment of the
vehicle is determined as a function of the mixed signal. The modulated signal
can be a signal,
the frequency of which changes chronologically, for example. By mixing the
modulated signal
with the reception signal, a mixed frequency is generated, which is
proportional to a distance of
an object, from which the light modulated using the modulated signal is
reflected. A location
resolution of multiple objects is a function of the resolution of the
frequency measurement and
therefore the measuring time. The method may be implemented in an integrated
circuit, for
example, by a corresponding analogue circuit, for example. A further advantage
of this method
is that both the distance to the object and the velocity of the object can be
measured by the
mixing of the modulated signal with the reception signal. The signals can be
mixed by
multiplying the modulated signal with the reception signal, for example.
The light source of the vehicle can comprise a light-emitting diode (LED) of,
for example, a
daytime running light, a low-beam headlight, a turn signal, a taillight, a
high-beam headlight, or a
reversing light of the vehicle. At typical response times of LEDs, in
particular of LEDs which
generate blue light, of 5-10 ns, modulation frequencies up to 100 MHz can be
used, for
example. By using light-emitting diodes of light sources which are available
on a vehicle in any
case, additional costs for corresponding light-emitting diodes for the
distance measurement and
a corresponding installation space can be saved. In addition, in particular
upon the use of light-
- 3 -
CA 02842814 2014-02-11
emitting diodes of a daytime running light, a low-beam headlight, or a high-
beam headlight of
the vehicle, high-performance light-emitting diodes can be used for the
distance measurement,
which allow a distance measurement over several hundred metres, for example.
According to a further embodiment, one of the following modulation methods is
used to
generate the modulated signal: a frequency-modulated continuous wave method, a
random
frequency modulation method, a single-frequency modulation method, or a pulse
modulation
method.
In the frequency-modulated continuous wave method, which is also referred to
as an FMCW
method (frequency modulated continuous wave) or chirp method, a modulation
frequency is
changed over a specific time from a starting frequency to an end frequency.
For example, the
modulation frequency is continuously changed from a low starting frequency to
a high end
frequency and the entire procedure is repeated upon reaching the end
frequency, i.e., after
reaching the end frequency, the modulation is continued with the starting
frequency. The
method can be coupled comparatively simply to a velocity measurement. In
addition, the
method is easily implementable by blanking out a synthetically generated
waveform, for
example. The light which is generated during this modulation method is well
visible due to the
continuous signal. The method is therefore suitable above all if an activated
light source, for
example, a daytime running light, can be modulated. The frequency-modulated
continuous
wave method can be analysed with the aid of the above-described frequency
mixing or with the
aid of the above-described correlation, for example.
In the random frequency modulation method, which is also referred to as the
REM method
(random frequency modulation) a modulation frequency is changed randomly or
pseudo-
randomly. This method is particularly advantageous if multiple light sources
illuminate a scene
simultaneously and measurement is to be performed using all of them
simultaneously. Each
light source has a random or pseudorandom signature, which can then be
differentiated. As in
the frequency-modulated continuous wave method, in the random frequency
modulation
method, the light source is continuously actuated, so that the light source is
visible. Therefore,
this method is also particularly suitable for a modulation of a daytime
running light of the vehicle.
In particular the above-described correlation method can be used to analyse
the random
frequency modulation method, i.e., to determine an item of distance
information with the aid of
the random frequency modulation method.
In the single-frequency modulation method, a constant modulation frequency is
used. Therefore,
the single-frequency modulation method can be implemented very simply.
However, because it
reacts very sensitively to interference due to, for example, fog, spray, dust,
or foreign light
- 4 -
CA 02842814 2014-02-11
sources, it can preferably be used where such interference cannot occur due to
the installation
location or for applications in which a temporary failure can be tolerated.
Therefore, the single-
frequency modulation method can be used in the interior of the vehicle or in
parking aids, for
example. The single-frequency modulation also presumes a permanently activated
light source
and is therefore particularly suitable for use in combination with a daytime
running light, for
example. An analysis of the single-frequency modulation to determine the
distance to an object
can be carried out with the aid of a phase measurement, for example, which can
be carried out
in the scope of the above-described correlation method, for example.
In the pulse modulation method, short pulses are generated, for example, in
the range of 10 to
100 ns. These pulses can optionally activate or deactivate the light source
for the pulse
duration. The measuring frequency can be in the range from 10 to 100 Hz, for
example, i.e., the
pulses will not be noticed by a human observer because of the low mean power.
This applies
both in the case of activated light sources, in which the light is deactivated
for the period of time
of the pulse, and for deactivated light sources, which are activated for the
pulse duration. In the
case of activated light sources, a "negative light pulse" therefore results,
and a "positive light
pulse" results in the case of deactivated light sources. An advantageous pulse
modulation
consists of a pulse sequence which has a high chronological significance via
uneven pulse
intervals. An analysis of the pulses of the pulse modulation method can be
carried out using the
above-described correlation method, for example, wherein a mathematical
description of the
pulse can also be used as a correlation pattern. Alternatively, the reception
signal can be
scanned over the measuring interval for the analysis of the pulse modulation
method. Multiple
such echograms can be recorded and added up as a distance histogram via an
oversannpling
method. Echo pulses are then recognized using a pulse analysis and a precise
distance is
ascertained using a focal point determination, for example. This method is
also suitable both for
positive and for negative light pulses.
According to a further embodiment, an operating state of the vehicle is
determined and one of
the modulation methods is selected, i.e., the frequency-modulated continuous
wave method, the
random frequency modulation method, the single-frequency modulation method, or
the pulse
modulation method. The modulated signal is generated using the selected
modulation method.
Therefore, an optimum modulation method for the current situation can be used.
The operating
state of the vehicle can comprise, for example, a velocity of the vehicle, an
activation state of
the light source, which indicates whether or not the light source is activated
to illuminate an
environment of the vehicle or to emit an optical signal, a travel direction of
the vehicle, a
previously provided item of position information, a weather condition in the
environment of the
vehicle, or a type of an assistance device of the vehicle, to which the
distance information is
provided. For example, the single-frequency modulation method can be used at
low velocities
- 5 -
CA 02842814 2014-02-11
during parking of the vehicle, while in contrast at higher velocities, the
frequency-modulated
continuous wave method or the random frequency modulation method is used. In
addition, for
example, it can be established whether the method is influenced by a source of
interference and
another modulation method can be selected as a function thereof. For example,
because of the
high precision, the frequency-modulated continuous wave method can be used
and, if a source
of interference is detected, it is possible to change over to the random
frequency modulation
method.
Furthermore, a device for determining an item of distance information for a
vehicle is provided
according to the present invention. The device comprises a light source for
illuminating an
object in an environment of or inside the vehicle, a sensor for receiving
light of the light source,
which was reflected from the object, and a processing unit, which is coupled
to the light source
and the sensor. The device is therefore suitable for carrying out one of the
above-described
methods or one of its embodiments and therefore also comprises the advantages
described in
conjunction with the method. In particular, the processing unit can be
designed to generate a
modulated signal and to activate the light source of the vehicle using the
modulated signal and
to generate a reception signal as a function of the light received using the
sensor. Furthermore,
the processing unit can be designed to generate a correlation signal by
correlating the
modulated signal with the received signal or a mixed signal by mixing the
modulated signal with
the received signal and to determine a distance to the object as a function of
the correlation
signal or the mixed signal, respectively.
Finally, according to the present invention, a vehicle is provided, which
comprises the above-
described device, an illumination unit for illuminating an environment or an
interior of the
vehicle, and a driver assistance system. The illumination unit comprises the
light source of the
above-described device for determining the distance information. The device is
coupled to the
driver assistance system and the illumination unit. The device can therefore
determine a
distance to an object with the aid of the illumination unit of the vehicle and
the sensor and can
provide this distance information in the driver assistance system_
The present invention will be described hereafter in detail with reference to
the drawing.
Figure 1 schematically shows a vehicle according to one embodiment of the
present invention
and an object in an environment of the vehicle.
Figure 2 shows steps of a method for determining a distance to an object
according to one
embodiment of the present invention.
- 6 -
CA 02842814 2014-02-11
Figure 3 shows steps of a method for determining a velocity of an object
according to one
embodiment of the present invention.
Figure 4 schematically shows a circuit of a light-emitting diode light source
according to one
embodiment of the present invention, which is designed to emit light for a
distance
measurement.
Figure 5 schematically shows the arrangement of components of the light-
emitting diode light
source of Figure 4 in a shared semiconductor housing.
Figure 6 shows steps of a method for determining a distance of an object
according to a further
embodiment of the present invention.
Figure 7 shows first detection regions of sensors of a device for determining
the position of an
object according to one embodiment of the present invention.
Figure 8 shows second detection regions of sensors of a device for determining
a position of an
object.
Figure 9 shows an overlap of the first and second detection regions of Figures
7 and 8, as are
detected by sensors of a device for determining a position of an object
according to one
embodiment of the present invention.
Figure 10 shows the second detection regions of Figure 8 with additional
fuzziness.
Figure 11 shows the overlap of the first and second detection regions of
Figure 9 with additional
fuzziness of the second detection regions.
Figure 12 shows transmitter segments, as are used by a light source of a
device according to
one embodiment of the present invention to detect a position of an object.
Figure 13 shows receiver segments, as are used by sensors of a device
according to one
embodiment of the present invention to determine a position of an object.
Figure 14 shows an overlap of the transmitter segments of Figure 12 and the
receiver segments
of Figure 13.
- 7 -
CA 02842814 2014-02-11
Figure 15 shows a near field view of transmitter segments which are generated
according to
one embodiment of the present invention by an offset arrangement of
transmission diodes.
Figure 16 shows a far field view of the transmitter segments of Figure 15.
Figure 17 shows method steps of a further method for determining items of
distance information
according to one embodiment of the present invention.
Figure 18 shows a scene with an object in an environment of a vehicle.
Figure 19 shows distance histograms of rows of the scene of Figure 18.
Figure 20 shows distance histograms of columns of the scene of Figure 18.
Figure 21 shows a vehicle according to one embodiment of the present
invention, which
simultaneously measures a distance to a leading vehicle and transmits data.
Figure 22 shows steps of a method according to one embodiment of the present
invention for
determining a distance to an object and for transmitting transmission data.
Figure 1 shows a vehicle 10 having a device for determining an item of
distance information.
The device comprises a light source 11, which is designed to illuminate an
object 17 in an
environment of the vehicle 10. The light source 11 can comprise, for example,
a daytime
running light, a low-beam headlight, a turn signal, a taillight, a high-beam
headlight, a fog light,
or a reversing light of the vehicle 10. The light source can furthermore
comprise one or more
light-emitting diodes, which generate light to illuminate the environment of
the vehicle 10 or a
signal light, for example, the light of a turn signal or a brake light. The
light source 11 can
additionally also comprise an illumination unit for illuminating an interior
of the vehicle 10, for
example, a dashboard illumination, or a passenger compartment illumination.
The device for
determining the distance information furthermore comprises an optical sensor
12 for receiving
light reflected from the object 17 and a processing unit 13, which is coupled
to the light source
11 and the sensor 12. For example, in the arrangement shown in Figure 1, if
the object 17 is
located at a distance 18 in the region in front of the vehicle 10, light 15
which was emitted by the
light source 11 is reflected from the object 17 and received as reflected
light 16 by the sensor
12. The mode of operation of the device for determining an item of distance
information will be
described hereafter with reference to Figure 2.
- 8 -
CA 02842814 2014-02-11
Figure 2 shows a method 20 for the vehicle 10 for determining the distance 18
between the
vehicle 10 and the object 17. In step 21, the light source 11 of the vehicle
10 is actuated using a
modulated signal. The modulated signal is generated by the processing unit 13.
The light 15
which was emitted by the light source 11 is reflected from the object 17 and
received as
reflected light 16 by the sensor 12 (step 22). In step 23, a reception signal
is generated as a
function of the received reflected light 16. The reception signal can comprise
an analogue or
digital electrical signal, for example. In step 24, the reception signal is
combined with the
modulated signal in the processing unit 13. For example, the modulated signal
and the
reception signal can be correlated or mixed, as described in detail hereafter.
The distance 18 to
the object 17 is determined in step 25 from a combination signal, for example,
a correlation
signal or a mixed signal. The distance to the object 17 thus determined can be
provided to a
driver assistance system 14 of the vehicle 10, for example. The driver
assistance system 14 can
comprise, for example, an adaptive cruise control system, a brake assistance
system, a parking
aid system, or a collision warning system. The object 17 can also be located
in the interior of the
vehicle 10 and can be illuminated by a corresponding illumination unit of the
vehicle in the
interior and the reflected light from the object can be received using a
corresponding sensor.
Distances to objects in the interior of the vehicle can thus be determined,
for example, to
recognize gestures of an operating system or, for example, in the event of an
accident, to detect
a current position of the head of an occupant in order to trigger appropriate
protective
mechanisms, for example, airbags.
In order that the above-described method can be used in the vehicle for
different driver
assistance systems, it can be necessary to use different transmission and
reception methods for
the different application cases. These methods can be selected depending on
the required
distance or application, for example. For this purpose, for example, an
operating state of the
vehicle 10 can be determined and a corresponding transmission and reception
method can be
selected as a function of the operating state of the vehicle, i.e., a
corresponding modulation
method for generating the modulated signal and a corresponding analysis method
(for example,
mixing or correlation) are selected as a function of the operating state. The
modulation method
can comprise, for example, a frequency-modulated continuous wave method, a
random
frequency modulation method, a single-frequency modulation method, or a pulse
modulation
method. These methods will be described in detail hereafter. The operating
state of the vehicle
can comprise, for example, a velocity of the vehicle, an activation state of a
light source of the
vehicle, which indicates whether or not the light source is activated to
illuminate an environment
of the vehicle or to emit an optical signal, a travel direction of the
vehicle, a previously
determined item of position information or distance information of an object
in the environment
of the vehicle, weather conditions in the environment of the vehicle, or
another type of an
assistance device of the vehicle, to which the distance information is
provided.
- 9 -
CA 02842814 2014-02-11
In the frequency-modulated continuous wave method, which is also referred to
as the FMCW
(frequency modulated continuous wave) method or as the chirp method, a
modulation frequency
is changed over a specific time from a starting frequency to an end frequency.
The modulation
frequency is preferably continuously changed from the starting frequency to
the end frequency.
The method can be used not only for distance measurement, as described
hereafter, but rather
also for a velocity measurement of the object 17. The generation of modulation
signals, in which
a modulation frequency is changed over a specific time continuously from a
starting frequency
to an end frequency, is known in the prior art and therefore the method can be
implemented
easily, for example, by blanking out a synthetically generated waveform. Using
the method, the
distance 18 to the object 17 can be continuously measured, whereby the method
is particularly
suitable for light sources 11 which are continuously activated. By way of the
continuous change
of the modulation frequency and therefore the transmission frequency of the
light source 11
from a starting frequency to an end frequency, a frequency ramp results. By
mixing the
transmission signal with the reception signal, which is received by the sensor
12, both the
distance 18 and the velocity of the object 17 can be directly measured. If
light-emitting diodes
(LED) are used as the light source 11, which have typical response times of 5-
10 ns, modulation
frequencies up to at most 100 MHz can be used, for example. The FMCW
modulation can
therefore use, for example, the transmission frequency of 10 MHz to 100 MHz
continuously over
a period of time of 0.5-400 ps, for example. The distance measurement can
optionally be
performed by means of frequency mixing or a correlation method if the
frequency-modulated
continuous wave method (FMCW) is used.
If the frequency-modulated continuous wave method is used, the transmission
signal and the
reception signal can be compared using a frequency mixer. An object at a
specific distance
generates a mixed frequency, which is proportional to the distance. The
location resolution of
multiple objects is a function of the resolution of the frequency measurement
and therefore the
measuring time. Such a frequency mixing method can be implemented as an
analogue circuit in
an integrated circuit, for example. For example, if a distance between 0 m and
40 m is to be
measured, the light requires approximately 3.3 ns/m x 40 m x 2 = 264 ns for
this distance there
and back along the arrows 15 and 16 of Figure 1. A useful signal length for
the FMCW signal of
approximately 500 ns results therefrom. A modulation down to 10 MHz for this
method is
therefore too low, so that a frequency deviation between 50 and 100 MHz is
preferably to be
used, which is changed linearly over 500 ns. At a distance 18 of 25 m, for
example, between the
vehicle 10 and the object 17, the reception signal is delayed by 165 ns in
relation to the
transmission signal. As described above, the transmission signal has a
frequency deviation of
50 MHz/500 ns = 100 kHz/ns due to the modulation. At a signal delay of the
reception signal of
165 ns, the reception signal has a frequency lower by 16.5 MHz than the
transmission signal.
-10-
CA 02842814 2014-02-11
By mixing the transmission signal with the reception signal, at the exemplary
distance of 25 m, a
frequency of 16.5 MHz is obtained. Expressed as a general rule, a frequency of
0.66 MHz per
metre of distance results due to the mixing.
In the case of distance measurement by means of the frequency-modulated
continuous wave
method, the transmission signal and the reception signal can also be
correlated with one
another, to determine the distance to the object 17 on the basis of a
correlation signal thus
generated. For this purpose, the modulated signal which was emitted is
correlated in a time-
shifted manner with the reception signal. A correlation maximum results at the
shifting time,
which is proportional to the distance 18 of the object 17. Since substantially
noisy signals are
analysed, the level of the correlation maximum is a measure of the signal
strength, so that
various objects 17 can be differentiated. The resolution in the distance can
be determined by
the scanning frequency of the reception signal, for example. To generate the
correlation signal,
multiple correlation coefficients can be generated. A respective shifting time
is assigned to each
correlation coefficient of the multiple correlation coefficients. Each
correlation coefficient is
formed by correlating the modulated signal, which is shifted by the respective
assigned shifting
time, with the reception signal. The distance to the object is determined as a
function of the
multiple correlation coefficients, for example, by determining an absolute or
local maximum, and
the assigned shifting times. It is advantageous to use a high significance of
the signal in the time
level by way of the continuously modulated FMCW signal, which contains many
frequencies
independent of one another. To achieve a high scanning rate of the reception
signal, for
example, a one-bit conversion can be advantageous. To generate the binary
reception signal,
the reception signal can be generated using a first signal value if a level of
the received light
falls below a specific intensity, and a reception signal can be generated
using a second signal
value if the level of the received light reaches or exceeds the specific
intensity. For this purpose,
for example, an amplitude-limited amplifier can be used, which generates a
reception signal
having unambiguous levels, for example, a binary sequence of zeros and ones,
as a function of
the received light. Since the significance is in the time, hardly any
information is lost by this
binary conversion, since the significance in the amplitude can be unreliable
as a result of the
amplitude modulation to be expected due to the object 17. Due to the reception
signal reduced
to binary signals, a corresponding correlator can be constructed comparatively
simply and can
be suitable for processing long sequences. This improves the correlation
result. If the reception
signal is provided in digital or binary form, it is advantageous that the
comparison pattern of the
modulated transmission signal is also digital. This can be achieved, for
example, by using a
synthesized digital signal to modulate the light source. This signal can be
generated with
uniform quality and only depending on a transmit cycle, for example. If the
received cycle is
equal to the transmit cycle, errors which occur, as a result of temperature
drifts, for example,
can be compensated for. Long signal sequences can be used due to the use of
the correlation
-11-
CA 02842814 2014-02-11
method. The usable frequency deviation is therefore not restricted to the
runtime of the signal
for the distance to be measured. As described above, the method can be
implemented solely
digitally and therefore can be constructed cost-effectively. For example, a
modulated signal
having a length of 50 ps ¨ 500 ps can be emitted and the frequency can be
increased from 10
MHz to 100 MHz over this time. Such a modulated signal may be generated via a
shift register
in which a synthetically generated signal is stored, for example. A clock
frequency with which
the transmission signal can be clocked out and the reception signal can be
clocked in
synchronously can be 1 GHz, for example, and is therefore implementable with
comparatively
low expenditure. The measuring time of 50 ps ¨ 500 ps is so rapid for most
applications of
driver assistance systems that multiplexing methods are also possible in the
case of
multichannel sensors. In addition, multiple measurements can be carried out
and averaged to
further improve the signal quality.
The modulated signal, with which the light source 11 is actuated, can
furthermore be generated
using a random frequency modulation method. A transmission frequency from a
frequency band
is randomly varied over a specific time. This method is also referred to as
random frequency
modulation (RFM). The above-described correlation method can be used in a
comparable
manner to determine the distance to the object 17. The random frequency
modulation method
offers a very high level of interference resistance, for example, with respect
to scattered light
and other measuring methods. In addition, multiple measuring channels can be
measured
simultaneously, since corresponding crosstalk from other measuring channels is
suppressed by
the correlation analysis. The modulation frequencies and the time length of
the transmission
signal can be selected to be comparable to those of the frequency-modulated
continuous wave
method. The random frequency modulation method can therefore be used in
particular if
multiple light sources illuminate a scene or a room simultaneously and
measurement is to be
performed using all of them simultaneously. For example, using the random
frequency
modulation method, measurements can be carried out simultaneously using all
headlights of the
vehicle 10. Each light source receives a separate significant signature, which
can then be
differentiated by the correlation method. In addition, data which are coded
into the modulation
signal can simultaneously be transmitted to other vehicles or receivers on the
roadside. For a
continuous distance measurement, a continuous actuation of the light source 11
is necessary,
so that this method is particularly suitable for light sources which are
continuously activated, for
example, a daytime running light or a headlight when travelling at night. The
above-described
frequency-modulated continuous wave method and the above-described random
frequency
modulation method can also be used in combination. For example, the frequency-
modulated
continuous wave method can first be used because of the better signal quality.
If sources of
interference are detected, for example, light sources of other vehicles, it is
possible to switch
over to the random frequency modulation method. It is also possible to switch
over at least
- 12-
CA 02842814 2014-02-11
temporarily to the random frequency modulation method if a data transmission
is necessary.
The light source 11 and the sensor 12 can be used equally for the frequency-
modulated
continuous wave method and for the random frequency modulation method.
Furthermore, a single-frequency modulation method can be used to generate the
modulated
signal to actuate the light source 11 in the method for determining the
distance to the object 17.
The single-frequency modulation method uses a constant modulation frequency
and is therefore
particularly simple to implement. However, it can be interfered with
comparatively easily by mist,
spray, dust, or foreign light sources, and therefore can be used in particular
in applications
where such interference cannot occur due to the installation location, for
example, or if a
temporary failure can be tolerated, for example, in the case of a distance
measurement in the
interior or in the case of parking aids, in which excessively close measuring
does not have
negative consequences and the required intervals are low due to the low
velocity of the vehicle
or spray development is insignificant. For a continuous distance measurement,
a permanently
active light source is also necessary in the single-frequency method, so that
the single-
frequency method can preferably be used in conjunction with a daytime running
light or a low-
beam headlight of the vehicle, for example. A distance determination, i.e., an
analysis of the
single-frequency modulation method, can be reduced to a phase measurement, for
example,
which determines a phase difference between the modulated signal and the
reception signal.
For example, the phase measurement can be performed digitally via an AND
linkage by a
comparison of the reception signal to the modulated signal. Suitable typical
modulation
frequencies are in the range from 5-20 MHz, for example. In this range,
uniqueness of the
phase analysis based on the foundation of the single-frequency modulation can
be ensured.
Finally, a pulse modulation method can be used to generate the modulated
signal for actuating
the light source 11. Using the pulse modulation method, measurements can also
be performed
in particular if the light source 11 is deactivated. The short light pulses of
the pulse modulation
method can be formed such that they are not visible or are hardly visible to
the observer. If a
light source is activated, the pulse modulation method can also be used, by
forming the light
source for the pulse duration, or, in other words, by generating "negative"
light pulses. The
pulse modulation method therefore suggests itself in particular where
measurement is to be
performed at a low measuring frequency of 10 to 100 Hz, for example, and the
light for the
measurement is not to be recognizable. Light sources, for example, a low-beam
headlight, a
turn signal light, a taillight, a brake light, or a reversing light, which are
not activated at the
measuring time, can be activated using short pulses having a length of 10 to
100 ns, for
example, which are not noticed by a human observer because of the low average
power. In the
case of activated light sources, the light can be deactivated for a short
period of time of 10 to
100 ns, for example, whereby a negative light pulse results, which can also be
detected by the
- 13-
CA 02842814 2014-02-11
sensor 12. The determination of the distance 18 to the object 17 can be
performed using the
above-described correlation method, for example, if the pulse modulation
method is used. In
particular, a pulse modulation can be used, which consists of a pulse
sequence, which has a
high chronological significance via uneven pulse intervals. The reception
signal, which is
generated as a function of the received light, can in turn be correlated with
the modulated signal
or alternatively a mathematical description of the pulse can also be used as a
correlation pattern
for the pulse modulation. The reception signal can be scanned over the
measuring interval.
Multiple such echograms can be recorded and added up as a distance histogram
via an
oversampling method. Echo pulses can then be recognized using a pulse analysis
and a
precise distance 18 can be ascertained using a focal point determination, for
example. The
method is suitable both for positive and for negative pulses.
As already mentioned above in conjunction with the frequency-modulated
continuous wave
method, in addition to the distance 18 to the object 17, a velocity of the
object 17 can also be
determined. This will be described hereafter in detail with reference to
Figure 3. Figure 3 shows
a method 30 for determining a velocity of the object 17. In step 31, the light
source 11 of the
vehicle 10 is actuated using a frequency-modulated signal. In step 32, the
reflected light 16 is
received, which was emitted by the light source 11 and was reflected from the
object 17 in the
environment of the vehicle 11. In step 33, a reception signal is generated as
a function of the
received light 16. In step 34, a differential frequency between a frequency of
the frequency-
modulated signal, using which the light source 11 was actuated, and a
frequency of the
reception signal is determined by mixing the two signals. An item of velocity
information of the
object 17 is determined in step 35 on the basis of the mixed signal, i.e., as
a function of the
differential frequency. The frequency-modulated signal can be generated in
particular according
to the above-described frequency-modulated continuous wave method, in which
the modulation
frequency of the frequency-modulated signal is changed over a specific time
from a starting
frequency to an end frequency. As described above, an item of distance
information to the
object 17 can also be determined as a function of the reception signal and the
frequency of the
frequency-modulated signal, for example, by mixing the signals or correlating
the signals. The
frequency of the frequency-modulated signal is preferably in a range from 10
to 200 MHz.
The method will be described in detail hereafter as an example on the basis of
a modulation
with the aid of a frequency-modulated continuous wave method (FMCW). In the
case of FMCW
modulation, a continuous frequency deviation of, for example, 10 MHz to 100
MHz is modulated
in 40 microseconds. Due to a distance of 200 metres between the vehicle 10 and
the object 17,
a shift by 1.32 ps or 2.97 MHz results. A further mixed frequency results due
to a relative
velocity of v according to the Doppler formula:
- 14-
CA 02842814 2014-02-11
/ c
.1 = = fo
+ v
wherein f is the modulation frequency, to is the frequency of the reception
signal, and c is the
velocity of light. In the following table, the Doppler frequency shift for
various velocities of the
object is shown.
Modulation frequency
Doppler frequency
______________________________________ 20 MHz 40 MHz 60 MHz
80 MHz 100 MHz
20 km/h ' 0.37 Hz 0.74 Hz 1.11 Hz 1.48 Hz 1.85 Hz
40 km/h 0.74 Hz 1.48 Hz 2.22 Hz 2.96 Hz 3.70 Hz
60 km/h 1.11 Hz 2.22 Hz 3.33 Hz 4.44 Hz 5.56 Hz
80 km/h 1.48 Hz 2.96 Hz 4.44 Hz 5.93 Hz 7.41 Hz
100 km/h 1.85 Hz 3.70 Hz 5.56 Hz 7.41 Hz 9.26 Hz
120 km/h 2.22 Hz 4.44 Hz 6.67 Hz 8.89 Hz 11.11 Hz
.3
0 140 km/h 2.59 Hz 5.19 Hz 7.78 Hz
10.37 Hz 12.96 Hz
160 km/h 2.96 Hz 5.93 Hz 8.89 Hz 11_85 Hz 14.81 Hz
180 km/h 3.33 Hz 6.67 Hz 10.00 Hz 13.33 Hz 16.67 Hz
200 km/h 3.70 Hz 7.41 Hz 11.11 Hz 14.81 Hz 18.52 Hz
220 km/h 4.07 Hz 8.15 Hz 12.22 Hz 16.30 Hz 20.37 Hz
240 km/h 4.44 Hz 8.89 Hz 13.33 Hz 17.78 Hz 22.22 Hz
260 km/h 4.81 Hz 9.63 Hz 14.44 Hz 19.26 Hz 24.07 Hz
The table shows that the Doppler frequency is dependent on the modulation
frequency. A higher
modulation frequency also results in a higher Doppler frequency. The FMCW
modulation can
therefore be changed, for example, such that in 20 ps, for example, the
frequency of 10 MHz is
modulated to 100 MHz and then the frequency of 100 MHz is maintained for a
further 20 ps.
The Doppler frequency can then be measured at 100 MHz, for example. The
Doppler frequency
can be directly determined by mixing the transmission frequency with the
reception frequency,
for example. For practical reasons, however, the Doppler frequency can
alternatively be
determined by mixing the reception signal with a further signal, which has a
frequency deviating
by a predetermined value from the frequency of the frequency-modulated
transmission signal.
For example, the reception signal can be compared to or mixed with a signal
which has a
frequency lower by 100 kHz than the frequency-modulated transmission signal.
Therefore, in
the example shown in the table, frequencies between 100,000 and 100,024 Hz are
obtained for
the Doppler frequency for velocities between 0 and 260 km/h. These
significantly higher
frequencies can be measured more easily and can arise within the measuring
duration of 20 ps,
for example.
-15-
CA 02842814 2014-02-11
As described above, the light source 11 of the vehicle 10 is to be modulated
in a frequency
range of 10 MHz to 100 MHz, for example. In particular, light-emitting diode
light sources are
suitable for this purpose, which use semiconductor light-emitting diodes to
generate the light 15.
In particular light-emitting diodes which generate ultraviolet or blue light
have such a large
modulation bandwidth. For the colour conversion into white light or light
components of other
colours, for example, red or green light, these light-emitting diodes can
additionally have
phosphor coatings, which convert ultraviolet light or blue light into light of
other colours. The
high-frequency light for the distance measurement or velocity measurement is
in particular the
blue light of the light-emitting diodes. The currents through the light-
emitting diodes are in the
range of several amperes to achieve corresponding light ranges. To achieve
efficient
modulation, a corresponding actuation of the light-emitting diode must be
designed accordingly.
Figure 4 shows a light-emitting diode light source 40, which is also referred
to as a modulation
circuit and which has a corresponding layout. The light-emitting diode light
source 40 comprises
a light-emitting diode 41, a switch element 42, and an energy storage element
43. The light-
emitting diode 41 can preferably comprise a light-emitting diode which
generates blue light or at
least has a blue light component, as described above. The switch element 42
can comprise a
transistor, for example, in particular a field-effect transistor. The energy
storage element can
comprise a capacitor, for example. The switch element 42 is actuated by a
modulated signal 44.
A power supply comprises a ground terminal (GND) 45 and a power supply
terminal (Vcc) 46.
When the switch element 42 switches through as a result of an activation by
the modulated
signal 44, a current flows from the supply voltage terminal 46 through the
light-emitting diode 41
to the ground terminal 45 and, in addition, a further current of a charge
stored in the energy
storage element 43 flows from a first terminal 47 through the switch element
42 and the light-
emitting diode 41 to a second terminal 48 of the energy storage element 43. As
a result of the
high switching frequencies, a construction having the shortest possible lines,
in particular
between the elements 41, 42, and 43, is to be sought, so that the inductance
of the lines is as
low as possible and therefore losses, susceptibility to interference, and in
particular interfering
radiation are as low as possible. In the blocked state of the switch element
42, the energy
storage element 43 is charged by the supply voltage 46 and the ground terminal
45. In the
switched-through state of the switch element 42, the energy storage element
provides a very
large current through the light-emitting diode 41 for a short period of time.
Therefore, in
particular the connections between the energy storage element 43, the switch
element 42, and
the light-emitting diode 41 are to be kept as short as possible. If the lines
in the circuit light-
emitting diode 41, switch 42, and energy store 43 become excessively long,
they represent an
inductor, which "opposes" any current change. A very high voltage is thus
necessary to be able
to generate a modulation, which represents a rapid current change. A few
millimetres of line
length can already have a substantial influence. The energy which is stored in
the lines during
- 16-
CA 02842814 2014-02-11
the modulation is partially absorbed in the lines and converted into heat and
another part is
emitted as interfering radiation. For example, to generate 10 W of light using
the light-emitting
diode 41, a current of approximately 10 A through the light-emitting diode 41
is necessary. If the
light pulse is to be 50 ns long, for example, nearly 200 V are necessary in a
wired construction
in which the light-emitting diode 41, the switch element 42, and the capacitor
43 are arranged as
separate elements on a printed circuit. Accordingly, an energy demand of 200 V
x 10 A x 50 ns
= 0.1 mJ is necessary. With a construction in SMD technology, for example, 60
V and 10 A are
necessary, i.e., an energy demand of 30 pJ. With an optimized construction,
which will be
shown hereafter in conjunction with Figure 5, however, only 8 V and 10 A are
necessary, i.e., an
energy demand of 4 pJ. In all cases, approximately 40 W are absorbed in the
light-emitting
diode 41. The efficiency is thus 50% in the optimized construction,
approximately 6% in the
construction using SMD technology, and the efficiency is only 2% in the wired
construction on a
printed circuit.
Figure 5 shows the optimized construction of the light-emitting diode light
source 40. The light-
emitting diode light source 40 comprises the light-emitting diode 41, the
switch element 42, and
the energy storage element 43. The switch element 42 is coupled in a series
circuit to the light-
emitting diode 41. The energy storage element 43 is coupled in parallel to the
series circuit of
light-emitting diode 41 and switch element 42. When the switch element 42
switches through, a
current path is switched through the light-emitting diode 41, which extends
from a first terminal
47 of the energy storage element 43 via a first line section 50 to the switch
element 42 and
extends from there via a second line section 51 to the light-emitting diode
41. The current path
extends to the second terminal 48 of the energy storage element 43 via a third
line section 52.
As shown in Figure 5, the elements 41, 42, and 43 are arranged in a shared
housing 54. In
other words, the semiconductor elements 41 and 42 and the capacitor 43 are
housed without a
separate housing in the shared housing 54. The lengths of the connections 50
to 52 can thus be
designed to be correspondingly short. For example, the entire current path
which connects the
energy storage element 43, the light-emitting diode 41, and the switch element
42, can have a
length of less than 12 mm. The length of the current path is preferably
shorter than 9 mm. Each
of the connections 50, 51, and 52 can be 1 to 3 mm, for example. The
connections 50 to 52 can
form, together with the terminals 44 to 46, a so-called lead frame, which
provides the external
terminals 44 to 46 of the light-emitting diode light source 40, on the one
hand, and provides the
connections 50 to 52 for coupling the elements 41 to 43, on the other hand. As
a result of the
short connection lengths of the connections 50 to 52, a high efficiency of the
light-emitting diode
light source 40 can be achieved. Multiple light-emitting diode light sources
can be implemented
in the housing 54, by correspondingly arranging multiple light-emitting diodes
41, switch
elements 42, and energy stores 43 on a shared lead frame in the shared housing
54. The light-
emitting diode 41 can generate light having a wavelength of less than 760 nm,
preferably less
-17-
CA 02842814 2014-02-11
than 500 nm, i.e., blue light in particular. In addition, a phosphor coating
can be provided in the
housing 54, which converts ultraviolet light or blue light, which is generated
by the light-emitting
diode 41, into light of other colours. The light-emitting diode light source
40 or multiple of the
light-emitting diode light sources 40 can be used in an illumination unit 11
of the vehicle 10, for
example, to illuminate an environment of the vehicle 10 or to generate a light
signal, for
example, a turn signal or a brake light.
In the above-described methods and devices, existing illumination units of the
vehicle, for
example, headlights of a low-beam headlight, fog lights, turn signals, brake
lights, or reversing
headlights are used to generate a modulated light signal, which is reflected
from an object in the
environment of the vehicle and is received by a sensor on the vehicle. A
distance or a velocity of
the object can be determined from the reception signal of the sensor and the
knowledge about
the modulated signal, using which the illumination unit of the vehicle was
actuated. Since the
primary function of the illumination unit is to illuminate an environment of
the vehicle or to emit a
light signal, for example, a turning signal or a braking signal, a method 60
is described
hereafter, which simultaneously ensures a determination of an item of distance
information. For
this purpose, firstly an operating state of the vehicle is detected in step
61. The operating state
of the vehicle can be a setpoint state for the illumination unit of the
vehicle, for example, which
indicates whether the illumination unit is to be activated or deactivated. The
detection of the
operating state can furthermore comprise a determination of an ambient
brightness in an
environment or within the vehicle or a determination of a distance measuring
range, for which
the distance information is to be determined. In step 62, a modulated
transmission signal is
generated as a function of the operating state thus determined. For example, a
first modulated
transmission signal can be generated if the setpoint state for the
illumination unit indicates that
the illumination unit is to be activated. Furthermore, a second modulated
transmission signal
can be generated, which is converted to the first modulated transmission
signal, if the setpoint
state indicates that the illumination unit is to be deactivated. Thus, for
example, in the case of
deactivated illumination unit, a modulated transmission signal can be
generated, which
comprises short light pulses, the energy of which is not sufficient to be seen
by an observer.
Vice versa, if the illumination unit is to be activated, a modulated
transmission signal can be
generated which deactivates the illumination unit for short pulses, which are
so short that they
are not noticed by an observer and therefore the illumination unit appears to
be continuously
activated. In step 63, the illumination unit 11 of the vehicle 10 is actuated
using the generated
transmission signal. In step 64, reflected light 16 is received, which was
emitted as light 15 by
the illumination device 11 and was reflected from the object 17. In step 65, a
reception signal is
generated as a function of the received light 16. In step 66, the reception
signal is combined
with the transmission signal and in step 67, the distance of the object 17 is
determined from the
combination.
- 18-
CA 02842814 2014-02-11
The amount of light which cannot be seen by an observer is dependent, inter
alia, on the overall
brightness of the environment of the vehicle and a contrast in the
transmission plane. During the
day, substantially larger amounts of light can be emitted by the illumination
unit, which are not
noticed by an observer, than at night. A signal-to-noise ratio is typically
significantly worse
during the day due to the interfering light of the sun, so that during the day
higher transmission
powers are necessary than at night. During the day, for example, powers of up
to 2 mJ can be
emitted, which are not noticed by an observer. In the method, an average power
of the
modulated signal can therefore be set as a function of the operating state, in
particular an
ambient brightness. Furthermore, the transmission power can be set as a
function of a distance
measuring range, for which the distance measuring information is to be
determined. This is
dependent on the requirement of an application, for example, which uses the
distance
information. A driver assistance system for adaptive cruise control or a
collision avoidance
system can require a greater distance measuring range than a parking system.
The modulated transmission signal can comprise a pulse-modulated signal, for
example. The
pulse-modulated signal can have a pulse duration in the range of 1 to 500 ns,
preferably 10 to
100 ns. A frequency at which the pulses of the pulse-modulated signal are
repeated can be in
the range of 1 to 1000 Hz, preferably 10 to 100 Hz.
The illumination unit of the vehicle can comprise the above-described light-
emitting diode light
source or multiple light-emitting diodes, for example. In the case of white
light-emitting diodes,
the primary blue light component can be used as a modulation carrier. It is
modulated at high
frequency with the modulated transmission signal and remains in the spectrum
of the white
light-emitting diode. The phosphor of the light-emitting diode cannot follow
the rapid modulation,
since it is generally sluggish. A white, uniformly illuminating light thus
results for human
perception, while its blue component has the desired modulation.
A further illumination unit of the vehicle can be actuated as a function of
the operating state of
the vehicle and the modulated transmission signal. For example, the vehicle 10
travels on a
highway and a driver assistance system, for example, an adaptive cruise
control, is activated.
The headlights of the vehicle are deactivated. Therefore, a modulated
transmission signal is
generated, which comprises short-term light pulses. An item of distance
information to an object
in front of the vehicle can thus be provided for the adaptive cruise control
system. An activation
of the driving lights of the vehicle is therefore not necessary, i.e., all of
the energy for all light-
emitting diode lights of the headlights of the vehicle does not have to be
provided, which can be
advantageous in particular for an electric vehicle. In particular the adaptive
cruise control
system requires a long measuring range. If, as described above, the headlights
are deactivated
-19-
CA 02842814 2014-02-11
during the day, the high-beam headlights can be used with high energy to emit
measuring
pulses, which have a long range. In contrast, if the vehicle travels in
darkness, the high-beam
headlights are modulated by briefly reducing the brightness, to allow the long
measuring range.
If there is an oncoming vehicle in darkness, operation of the high-beam
headlights is no longer
possible, in order not to dazzle the driver of the oncoming vehicle. In this
case, light-emitting
diodes of the low-beam headlights can be modulated by briefly reducing the
brightness, to
determine an item of distance information. Simultaneously, light-emitting
diodes of the high-
beam headlights can be modulated using short pulses, to determine an item of
distance
information, without dazzling the oncoming traffic. In other words, several
LEDs are briefly
activated (in this case LEDs of the deactivated high-beam headlights) and
other light-emitting
diodes are briefly deactivated (in this case light-emitting diodes of the low-
beam headlights). A
long measuring range can thus be made possible, without the light-emitting
diodes for the high-
beam headlights dazzling or annoying the oncoming vehicle.
In the above-described methods and devices, a distance of the object 17 or a
velocity of the
object 17 was determined while using an illumination unit 11 provided on the
vehicle 10 in any
case, e.g., a low-beam headlight, a daytime running light, or a high-beam
headlight of the
vehicle 10. It will be described hereafter how an item of position
information, i.e., in addition an
item of direction information of the object 17 in relation to the vehicle 10
can additionally be
determined while using the above-described method.
According to one embodiment, the sensor 12 of the vehicle 10 comprises at
least two first
sensors for receiving light, which was generated by the light source 11 of the
vehicle and was
reflected from a scene, which comprises the object 17, in the environment of
the vehicle. A
respective first detection region of the scene is assigned to each of the at
least two sensors.
The first detection regions are arranged in a row in a first direction. Figure
7 shows 15 first
detection regions, which are assigned to 15 first sensors. The 15 first
detection regions are
arranged in a horizontal direction. Two of the 15 first detection regions are
identified with the
reference signs 71 and 72. The sensor 12 furthermore comprises at least two
second sensors
for receiving light reflected from the scene, wherein a respective second
detection region of the
scene is assigned to each of the at least two second sensors. The second
detection regions are
arranged in a second direction in a row. The second direction is different
from the first direction.
In Figure 8, two second detection regions 81 and 82 are shown, which are
arranged in a vertical
direction in a row. In addition, further detection regions are shown in Figure
8, which are also
arranged in pairs in the vertical direction in a row, for example, the two
third detection regions
83 and 84. The processing unit 13 is designed to determine a position of the
object 17 in the
environment of the vehicle 10 as a function of signals of the first and second
sensors. One of
the first detection regions, for example, the region 71, partially overlaps
one of the second
- 20 -
CA 02842814 2014-02-11
detection regions, for example, the region 81. The one of the first detection
regions, i.e., the
region 71, can additionally partially overlap a further one of the second
detection regions, for
example, the region 82, as shown in Figure 9. The third detection regions 83,
84, which are
monitored by corresponding third sensors, can be arranged in such a manner
that one of the
first detection regions, for example, the detection region 71, partially
overlaps one of the second
detection regions, for example, the region 81, a further one of the second
detection regions, for
example, the region 82, one of the third detection regions, for example, the
region 83, and a
further one of the third detection regions, for example, the region 84.
The position determination of the object 17 with the aid of the overlapping
detection regions, as
were described above, will be described in detail hereafter. In comparison
thereto, it is to be
noted here, that in the case of non-overlapping detection regions, using five
detection regions,
for example, only five different position regions can be differentiated for
the object 17. By way of
the overlap of the detection regions, as shown in Figure 9, however, eight,
different position
regions for the object 17 can be differentiated using the detection regions 71
and 81-84. If only
the sensor which is assigned to one of the detection regions 81-84 detects the
object 17, the
object 17 is located in a region which is assigned to the corresponding sensor
and which the
region which is assigned to the sensor 71 does not overlap. Therefore, four
different regions can
already be differentiated for the object 17. If the object 17 is detected in
one of the regions 81-
84 and additionally in the region 71, the object 17 must be located in one of
the four overlapping
regions, which result due to the overlap of the region 81 with the region 71,
the region 82 with
the region 71, the region 83 with the region 71, or the region 84 with the
region 71. Four further
position regions can thus be differentiated for the object 17. If the sensors
are arranged in such
a manner that the detection regions shown in Figures 7 and 8 can be monitored
separately, by
way of the overlap shown in Figure 9, a total of 56 different regions, in
which the object 17 can
be detected separately, can be implemented using the required 15 first sensors
for the regions
of Figure 7 and the 16 sensors for the regions of Figure 8.
The second detection regions can additionally in turn be overlapping in the
vertical direction and
can additionally be overlapping in the horizontal direction with further
detection regions, for
example, the third overlapping regions 83, 84. This can be achieved, for
example, by a so-called
"fuzziness" of the assigned sensors. Figure 10 shows the above-described
overlap of the
second, third, and further detection regions. In combination with the first
detection regions of
Figure 7, a variety of different regions can therefore be provided for the
position determination of
the object 17, as shown in Figure 11. By overlapping the first detection
regions with one
another, the resolution of the position determination of the object 17 can be
increased further,
which is not shown in Figure 11 for reasons of comprehensibility, however.
Furthermore,
Figures 9 and 11 show that in particular in the centre, i.e., in the region in
which the horizontally
- 21 -
CA 02842814 2014-02-11
arranged detection regions and the vertically arranged detection regions
overlap, a particularly
high resolution of the position determination of the object 17 can be
achieved. This can be
advantageously used for many driver assistance systems of a vehicle, since in
particular in the
straight-ahead direction of the vehicle, a high resolution is advantageous,
while a lower
resolution can generally be tolerated in the edge region.
The detection regions of Figures 7-11 are perpendicular to the measuring
direction, i.e.,
perpendicular to the arrow 16 of Figure 1.
A further possibility for determining an item of position information of the
object 17 in relation to
the vehicle 10 will be described in conjunction with Figures 12-14.
The illumination unit 11 of the vehicle 10 has at least one first light source
and one second light
source. The first and second light sources are activatable independently of
one another. The
first light source is designed to illuminate a first illumination region of a
scene in an environment
of or inside the vehicle 10. The second light source is designed to illuminate
a second
illumination region of the scene. The first illumination region is different
from the second
illumination region. In Figure 12, multiple illumination regions 121-127 are
shown. For example,
the first illumination region can be the region 121 and the second
illumination region can be the
region 122. The sensor 12 comprises at least one first sensor and one second
sensor for
receiving light reflected from the scene. A first detection region of the
scene is assigned to the
first sensor and a second detection region of the scene is assigned to the
second sensor. The
first detection region is different from the second detection region. Six
detection regions 131-136
are shown in Figure 13. For example, the first detection region can be the
region 131 and the
second detection region can be the region 132. The processing unit 13
activates the first and
second light source and optionally further light sources to generate the
illumination regions 123-
127 and determines a position of the object 17 in the environment of the
vehicle 10 as a function
of signals of the first and second sensors and optionally further sensors,
which are assigned to
the detection regions 133-136, and as a function of the activation of the
light sources. The
regions 121-127 and 131-136 are in the plane of the arrows 15 and 16 of Figure
1, for example.
The detection regions can be arranged aligned with the illumination regions,
for example, i.e.,
the detection region 131 substantially corresponds to the illumination region
121, the detection
region 132 substantially corresponds to the illumination region 122, etc. Each
of the detection
regions can have a predetermined angle range, for example, 100, or, as shown
in Figures 12
and 13, 20 . The segments thus formed can be scanned successively in a so-
called time
multiplexing method. Since distance measurements can be carried out within a
segment within
a very short time, for example, within 50 ps using the above-described
distance measuring
- 22 -
CA 02842814 2014-02-11
methods, in particular using the frequency-modulated continuous wave method or
random
frequency modulation method, the entire angle range which is covered by the
segments can be
scanned in a very short time. For example, if an angle range of 1200 is to be
scanned in 100
segments, the entire angle range can be scanned in 600 ps at a measuring time
of 50 ps per
segment. The entire angle range of 120 can be scanned in 6 ms even at a
longer measuring
time of 500 ps. Typical applications of driver assistance systems require
measuring times in the
range of 30 ms ¨ 50 ms, so that sufficiently rapid scanning is possible. The
resolution of the
scanning can be improved by not equipping every angle segment with a
corresponding
transmitter and receiver, but rather by using segments which respectively
overlap by half. Figure
14 shows such an overlap of the illumination regions 121-127 with the
detection regions 131-
136. Both the illumination regions and the detection regions respectively
comprise an angle
range of 20 . Due to the offset overlap of the illumination regions 121-127
with the detection
regions 131-136, twelve 10 segments result, which can be scanned using seven
light sources
and six sensors. The segments can be arranged adjacent to one another, since a
time
multiplexing method is used and therefore crosstalk from one segment to an
adjacent segment
is not relevant. Only one pair composed of transmitter and receiver is always
operated at one
point in time, so that it can be established unambiguously in which segment a
signal occurs. In
other words, the first detection region 131 overlaps a subregion of the first
illumination region
121 and a subregion of the second illumination region 122. The second
detection region 132
comprises a further subregion of the second illumination region 122. The
second detection
region 132 is separate from the first illumination region 121.
In addition, an item of information for a visual range estimation can be
obtained from the
arrangement of illumination regions and detection regions described above in
conjunction with
Figures 12-14, if detection regions which are not assigned to an illumination
region at all are
simultaneously also analysed. For example, for a distance measurement, the
light source for the
illumination region 121 and the sensor for the detection region 131 are
operated. A measuring
segment results in the overlap region between the illumination region 121 and
the measuring
region 131. Simultaneously or also in a time multiplexing method, a sensor is
queried, which is
assigned to the detection region 136. If this sensor also reports a distance
signal as a result of
the light output for the illumination region 121, this can only arise from
secondary scattered light.
If signals occur here in the case of very remote illumination regions and
detection regions, this is
because of very thick fog, for example. If the segments are closer together,
for example, if the
detection region 133 delivers a distance signal, measurable secondary
scattering thus already
occurs at lower particle densities. By analysing regions at different
distances, the fog can be
evaluated in a very well graduated manner. A current visual range can be
estimated therefrom.
- 23 -
CA 02842814 2014-02-11
For the segmented illumination of the environment of the vehicle 10, multiple
light sources are
necessary, as described above. For this purpose, for example, multiple light-
emitting diodes of a
low-beam headlight or in particular of a daytime running light, which has a
linear structure, can
be used, for example. In order to achieve a uniform appearance in particular
in the case of a
linear daytime running light, for example, light-emitting diodes arranged
spaced apart in the
daytime running light can be interconnected in groups and illuminate a
respective illumination
region. Interposed light-emitting diodes can illuminate further illumination
regions. In other
words, for example, the first light source, which is used to generate the
illumination region 121,
can comprise at least one first light-emitting diode and one second light-
emitting diode. A
second light source, which illuminates the illumination region 122, can also
comprise at least
one light-emitting diode or multiple light-emitting diodes. The first and the
second light-emitting
diodes of the first light source and the light-emitting diode of the second
light source are
arranged in a row, wherein the light-emitting diode of the second light source
is arranged
between the first and second light-emitting diodes of the first light source.
Since the brightness
of the light-emitting diodes can vary during the distance measurement, due to
this offset
arrangement, these brightness differences cannot be perceived by an observer.
Alternatively,
however, an interesting design effect can thus also be provided, if the
brightness differences are
visible to an observer.
Figure 15 shows a near field of illumination regions as a result of an offset
arrangement of light-
emitting diodes. A strip light 151 comprises 21 light-emitting diodes. The
strip light 151 can be a
strip light of a daytime running light, for example, and can have a length of
42 cm, for example.
Seven illumination regions or segments having an angle of respectively 200 are
illuminated
using the strip light 151. Each segment is generated by respectively three
light-emitting diodes
at a distance of 14 cm. Figure 15 shows the segments which can be illuminated
by the
individual light-emitting diodes. The far field of the segments generated by
the light-emitting
diodes of the strip light 151 is shown in Figure 16. The illumination regions
121-127, which
approximately comprise 20 , are clearly recognizable here.
Various assistance systems of a vehicle can require an item of information of
the environment of
the vehicle, which provides a high resolution of an image of a scene in front
of the vehicle from
the viewpoint of the vehicle, wherein each region or pixel of the item of
image information is
assigned a corresponding distance value to an object in this region. This item
of image
information can be necessary to be able to detect obstructions above or below
a specific region,
for example, such as obstructions located on the roadway, such as barriers,
which cannot be
driven over. Figure 17 shows a method 170 for determining such items of
distance information.
In step 171, the scene in the environment of the vehicle is illuminated. The
method 170 is
usable not only outside the vehicle, but rather also inside the vehicle, to be
able to recognize
- 24 -
CA 02842814 2014-02-11
gestures of a driver, for example. The light reflected from the scene is
received using the sensor
12 of the vehicle 10. In step 172, multiple first distance histograms are
determined as a function
of the received light. A respective first strip-shaped region of the scene is
assigned to a
respective first distance histogram of the multiple first distance histograms.
The first distance
histogram comprises a strength of reflections in a distance range due to
objects in the assigned
first strip-shaped region. In step 173, multiple second distance histograms
are determined as a
function of the received light. A respective second strip-shaped region of the
scene is assigned
to a respective second distance histogram of the multiple second distance
histograms. The
second distance histogram comprises a strength of reflections in a distance
range due to
objects in the assigned second strip-shaped region. In step 174, a distance is
determined as a
function of the multiple first distance histograms and the multiple second
distance histograms for
a region of the scene. The region of the scene comprises an intersection
region of one of the
first strip-shaped regions with one of the second strip-shaped regions. The
first strip-shaped
regions are preferably parallel to one another along the longitudinal
direction thereof and the
second strip-shaped regions are preferably parallel to one another along the
longitudinal
direction thereof. The longitudinal direction of the first strip-shaped
regions is preferably
perpendicular to the longitudinal direction of the second strip-shaped
regions. The first strip-
shaped regions can comprise rows of the scene in front of the vehicle or
inside the vehicle and
the second strip-shaped regions can comprise columns of the scene. To
determine the multiple
first distance histograms and the multiple second distance histograms, the
sensor 12 can
comprise a receiver matrix, in which rows and columns can optionally be
interconnected, so that
a reception signal arises either from the sum of all elements in one column or
from the sum of
all elements of one row. All rows and columns can be individually measured.
The distance
measurements can be carried out using one of the above-described methods, for
example, by
modulating the light source of the vehicle appropriately and correlating or
mixing the reception
signal from one of the rows or columns with the transmission signal for the
illumination unit 11.
The receiver matrix can have 300 rows and 700 columns, for example, i.e., a
total of 1000 rows
and columns. At a measuring time per row or column of 50 us, for example,
these 1000
measurements can be performed in 50 ms. Only one distance-resolved echogram is
available
per row or column, respectively, a so-called distance histogram. This can be
processed using a
method similarly as in a computer tomograph to form a pixel-resolved image. To
reduce the
processing expenditure, a specific region of interest can be selected using
the same method.
The corresponding reception elements of the receiver matrix are interconnected
for this region
and only this region is observed and analysed.
It is possible to change over dynamically between different regions to be
analysed and thus to
adapt to various driving situations.
- 25 -
CA 02842814 2014-02-11
The above-described method will be described hereafter with reference to
Figures 18 to 20 on
the basis of an example. Figure 18 shows a scene in an environment of the
vehicle. A vehicle
182 is located on a roadway 181. The scene is subdivided in the form of a
matrix into a plurality
of regions. In the example shown in Figure 18, the scene is subdivided into 14
rows and 19
columns, so that a total number of 266 regions results. This small number of
rows and columns
was selected for reasons of comprehensibility in Figures 18 to 20. Practical
implementations
can have at least 100 rows and at least 200 columns, for example, preferably
300 rows and 700
columns. The sensor 12 accordingly preferably comprises a sensor matrix having
a
corresponding row and column resolution. The illumination unit 11 of the
vehicle 10 illuminates
the scene shown in Figure 18, preferably using a light-emitting diode light
source, and an
analysis is performed using one of the above-described modulation methods, for
example, the
frequency-modulated continuous wave method, the random frequency modulation
method, the
single-frequency modulation method, or the pulse modulation method. By
interconnecting the
receiver matrix in rows or columns, distance-resolved echograms are generated
for the rows
and columns.
Figure 19 shows corresponding distance-resolved echograms for the 14 rows of
the scene of
Figure 18. The echogram for the fifth row from the bottom of the scene of
Figure 18 is to be
described hereafter in detail as an example. The echogram for this fifth row
is identified in
Figure 19 with the reference sign 191. As is apparent from Figure 19, the
echogram has an
elevated signal level in the range from 60 to 110 metres. Vice versa,
essentially no signal level
is present in the range from 10 to 60 metres and in the range from 110 to 150
metres. This
means that at least one object is located in the range from 60 to 110 m in the
fifth column.
However, multiple objects can be present in this region. It is not apparent
from the echogram of
Figure 19 where the object is located in the horizontal direction, i.e., in
which column region the
object is located.
Figure 20 shows corresponding echograms for the 19 columns of the scenes of
Figure 18.
Reference is made as an example in this context to the column 6 from the left
of Figure 18,
which is identified in Figure 20 with the reference sign 201. The echogram 201
of the sixth
column shows that one object or multiple objects is/are located in the range
of 60 to 110 metres
distance. The echogram of the columns again contains no information about the
distribution of
the objects within the column.
A corresponding item of distance information to objects in the scene can be
determined from the
entirety of the echograms for each of the 266 individual regions of the scene
of Figure 18. An
item of region-specific information can be obtained with the aid of a two-
dimensional Fourier
transform, for example, from the distance-resolved echograms of the rows and
columns.
- 26 -
CA 02842814 2014-02-11
The distance-resolved echograms in Figures 19 and 20 are dimensionless and can
indicate a
relative size, for example, which indicates what percentage of the surface
region in the form of
rows and columns has a respective distance to the vehicle.
Both with pulse modulation and with the random frequency modulation method
(REM), it is
possible to encode an item of information in the emitted signal 15, which can
be decoded by a
receiver. This information can be used, for example, for communication between
vehicles, so-
called car-to-car communication, or for communication between the vehicle 10
and an
infrastructure object, for example, a traffic signal or a traffic control
system. Figure 22 shows a
method 220, using which items of digital information can be transmitted
simultaneously with a
distance measurement. Figure 21 shows the vehicle 10 and a further vehicle 210
and an
infrastructure object 211. Using the method 220 described in Figure 22, a
distance between the
vehicles 10 and 210 can be measured and an item of information, in particular
an item of digital
information, can be transmitted to the vehicle 210 or the infrastructure
object 211
simultaneously.
In step 221, a modulated signal is generated as a function of transmission
data, which are to be
transmitted by the vehicle 10. In step 222, the light source 11 of the vehicle
10 is actuated using
the modulated signal. In step 223, light 16, which was emitted as light 15 by
the light source 11
and was reflected from the vehicle 210 or another object in the environment of
the vehicle 10, is
received. In step 224, a reception signal is generated as a function of the
received light. The
reception signal can comprise an analogue electrical signal or a digital
signal, for example. In
step 225, the reception signal is combined with the modulated signal, for
example, with the aid
of the above-described correlation method, and in step 226, the distance
between the vehicle
10 and the vehicle 210 is determined from a combination signal of this
combination. The
modulation method for generating the modulated signal can comprise in
particular a random
frequency modulation method or a pulse modulation method. In the frequency
modulation
method, a modulation frequency is changed as a function of the transmission
data. In the pulse
modulation method, a pulse interval or a pulse length is changed as a function
of the
transmission data. The modulated signal can additionally be generated as a
function of random
data.
The data which are to be transmitted from the vehicle 10 are therefore
transmitted in the
modulation of the transmission signal. For example, as shown in Figure 21, a
bit sequence 213
can be transmitted with the aid of the modulated transmission signal from the
vehicle 10 both to
the vehicle 210 travelling ahead and to the infrastructure object 211, as
shown by the light
propagation arrows 15 and 212. Receivers in the vehicle 210 or in the
infrastructure object 211,
- 27-
CA 02842814 2014-02-11
respectively, can receive and demodulate the modulated transmission signal and
thus reclaim
and process the transmission data 213. The encoding of the transmission data
213 in the
modulated transmission signal will be described hereafter in detail as an
example for a pulse
modulation method and a random frequency modulation method (RFM).
In the pulse modulation method, light pulses are transmitted at a pulse
repetition rate. This is
typically long in comparison to the pulse length of the light pulses. Since it
is unfavourable for
the distance measurement if the pulse repetition rate is constant, the
interval between the
pulses can be varied in a certain range to avoid beat states, for example. To
transmit data, for
example, this variation of the interval between the pulses can be subdivided
into a static
component and a systematic component. For example, pulses having a length of
50 ns and a
pulse repetition rate of 25 kHz, i.e., 40 ps, can be used. To measure a
distance in the range of
up to 250 m, for example, the pulse interval should not fall below 250 m x 6.6
ns/m x 2 = 3.3 ps.
It is therefore possible to vary the pulse interval between 3.3 ps and 76 ps.
In a system having a
runtime distance measurement and a base timing of 25 ns, 2936 possible
variations result. Of
these, 512 can be used, for example, to transmit 9 bits. Of these, for
example, 6 bits can
comprise the transmission data to be transmitted and the remaining 3 bits can
be randomly
varied. The interval between the pulses therefore varies by 12.8 ps from 33.6
to 46.6 ps.
Therefore, 6 bits of transmission data can be transmitted every 40 ps, whereby
a net data rate
of 150 kb per second is achieved.
In random frequency modulation (RFM), for example, frequencies can be varied
from 10 MHz to
100 MHz within 40 ps. In a random frequency modulation method without data
transmission,
multiple frequencies are statically selected randomly from this frequency
band, which are then
modulated successively and thus result in a frequency train which is
significant for the
measurement. For the transmission of the transmission data, the frequency
selection is no
longer carried out randomly, but rather comprises at least one systematic
component. For
example, frequencies can be synthesized in frequency steps of 10 kHz from the
band from 10 to
100 MHz. Therefore, 9000 different frequencies are possible. Of these, for
example, 512 can
again be used as significant frequencies, so that a frequency interval of
approximately 175 kHz
results for each item of information. A typical frequency modulation receiver
can differentiate
frequencies by 50 kHz without problems, so that the transmitted items of
information can easily
be decoded if a frequency interval of 50 kHz or more is maintained. For the
random variation to
reduce interfering influences, 125 kHz or 62.5 kHz still remains.
- 28 -
CA 02842814 2014-02-11
List of reference numerals
vehicle
11 light source
5 12 optical sensor
13 processing unit
14 driver assistance system
light
16 reflected light
10 17 object
18 distance
method
21-25 step
method
15 31-35 step
light-emitting diode light source
41 light-emitting diode
42 switch element
43 energy storage element
20 44 modulated signal
ground terminal
46 power supply terminal
47 first terminal
48 second terminal
25 50-52 connections
54 housing
60 method
61-67 step
71, 72 detection region
30 81-84 detection region
121-127 illumination region
131-136 detection region
151 strip light
170 method
35 171-174 step
181 roadway
182 vehicle
191 echogram
- 29 -
CA 02842814 2014-02-11
201 echogram
210 vehicle
211 infrastructure object
212 light propagation arrow
213 transmission data
220 method
221-226 step
- 30 -
