A motor vehicle detection system comprising a light beam emission module and a light beam reception module

Abstract

The invention relates to a lighting system (1) for a motor vehicle, comprising an emission module (2) capable of emitting a modulated visible light beam (F1) from a modulating data sequence (Seq2); a reception module (3) capable of receiving a light beam (F2) and extracting a demodulated data sequence (Seq3); a processing unit (4) arranged to generate a modulating data sequence (Seq2) from an initial pseudo-random binary sequence (Seq1); for estimating values ​​of a correlation function (Fcorr) between said demodulated data sequence and said modulating data sequence using an AND logic gate (41); and for determining a time of flight (τ) separating the emission of said modulated light beam from the reception of said received light beam from the values ​​of the correlation function. Figure to be published with the abstract: Fig. 1

Description

Title of the invention: Motor vehicle detection system comprising a transmission module and a reception module for a light beam

[0001] The invention relates to the field of automotive lighting and functions for detecting an object by a motor vehicle and estimating the distance separating this object from the vehicle. More specifically, the invention relates to a lighting system for a motor vehicle capable of implementing telemetry functions by means of the light it emits, with improved precision.

[0002] It is known, in the automotive field, to use a pulsed light beam emitted by a light module of a lighting system of a motor vehicle to perform a given photometric function.

[0003] Conventionally, the light source enabling the emission of this light beam is controlled by a pulse width modulated electrical signal, or PWM (from the English "Pulse Width Modulation"). The light source is thus periodically activated and deactivated by this PWM signal, so that the emitted light beam is composed of light pulses succeeding one another with a frequency high enough that the human eye can no longer distinguish them. The intensity of the emitted light beam is a function of the duty cycle of this PWM signal, so that it is possible to control it by adjusting this duty cycle and therefore to perform a photometric function.

[0004] Beyond the realization of one or more photometric functions, such as a daytime running light or dipped-beam lighting, various functions can be implemented by this type of light module. For example, the light source of the light module can be controlled so that the pulses of the emitted light beam carry a data sequence. The lighting system can thus be equipped with a reception module in order to receive the emitted light beam, after reflection on an object in the vicinity of the vehicle. A computing unit of the motor vehicle can then, after detecting the data sequence in the received light beam, determine the time of flight of the emitted light beam and therefore evaluate the distance separating the vehicle from the object.

[0005] In this way, the light beam can retain its original function, namely performing a photometric function, while allowing the lighting system to implement a telemetry function, which can be particularly advantageous, for example, for driving assistance functions or in the context of autonomous or semi-autonomous driving.

[0006] In known systems, the detection of the data sequence in the received light beam is carried out by evaluating a cross-correlation of a data sequence contained in the emitted beam and a data sequence extracted from the received beam, this correlation being evaluated by means of logic gates of the EXCLUSIVE NOR type, also called XNOR. However, it has been found that the signal-to-noise ratio of the system is optimal for duty cycle values ​​around 50% but that it deteriorates for lower duty cycle values, in particular around 25%. Indeed, for these duty cycle values, the modulating sequence contains more low values ​​than high values. However, in the presence of noise, it is more complex to correlate low values ​​with each other than high values.The use of an EXCLUSIVE NOR logic gate, also called XNOR, which allows the synchronization of two signals to be checked for both low and high values, thus implies a degradation of the signal-to-noise ratio for low values ​​of the duty cycle.

[0007] There is thus a need for a lighting system for a motor vehicle, capable of emitting a light beam performing both a given photometric function and a telemetry function, and whose precision and signal-to-noise ratio are improved.

[0008] The present invention is placed in this context, and aims to meet this need.

[0009] For these purposes, the invention relates to a lighting system for a motor vehicle, comprising: a. an emission module comprising a light module capable of emitting a light beam whose spectrum has at least one portion in the visible spectrum and a modulation unit capable of receiving a data sequence, called modulating, and arranged to modulate said light beam emitted from the received data sequence; b. a reception module capable of receiving a light beam, in which the reception module comprises an elementary acquisition module comprising a photodetector capable of converting a light signal that it receives into an electrical signal and a demodulation unit connected to the photodetector and arranged to extract a data sequence, called demodulated, from an electrical signal converted by this photodetector; c. a computing unit arranged to generate a binary type modulating data sequence and to transmit said modulating data sequence to the modulation unit for the emission of a modulated light beam by the emission module;

[0010] The invention is characterized in that the calculation unit is capable of receiving a data sequence demodulated by the demodulation unit from a signal electrical converted by the photodetector from a light beam received by the reception module, the calculation unit is arranged to estimate values ​​of a correlation function between said demodulated data sequence and said modulating data sequence and to determine a time of flight separating the emission of said emitted modulated light beam from the reception of said received light beam from the values ​​of the correlation function and in that the calculation unit is arranged to estimate each value of the correlation function between said demodulated data sequence and said modulating data sequence by evaluating the cross-correlation of the demodulated data sequence and the modulating data sequence delayed by a given duration associated with said value;and in that the computing unit is arranged to evaluate the cross-correlation of the demodulated data sequence and the delayed modulating data sequence by means of an AND type logic gate if the duty cycle of the modulating data sequence is less than 25%. ;

[0011] According to the invention, each value of the correlation function is thus associated with a value of a time shift of the modulating sequence used to estimate this value of the correlation function. The calculation unit is thus arranged to identify the time shift value associated with the maximum value of the cross-correlation function. However, it has been found that for low values ​​of the duty cycle, in particular below 25%, the use of an AND type logic gate, also called AND, which makes it possible to verify the synchronization of two signals only for the high values, thus makes it possible to obtain a higher signal-to-noise ratio than the EXCLUSIVE NOR type logic gate.It is thus possible to reduce the duty cycle of the modulating sequence, for example by means of one of the methods listed above, so as to be able to increase the peak power of the pulses of the emitted modulated light beam, while maintaining an optimal signal-to-noise ratio for the correlation operation.

[0012] Advantageously, the calculation unit is arranged to evaluate the cross-correlation of the demodulated data sequence and the delayed modulating data sequence by means of an EXCLUSIVE NOR logic gate or by means of an AND logic gate, the calculation unit being arranged to select one or the other of these gates as a function of the duty cycle of the modulating data sequence. The calculation unit can thus, depending on the use case, select the logic gate corresponding to the duty cycle used for this use case, for example to adapt the system to degraded environmental conditions. For example, if the duty cycle is less than 25%, the calculation unit can select the AND logic gate, and it can select the EXCLUSIVE NOR logic gate, otherwise.

[0013] In one embodiment of the invention, the computing unit is arranged to generating an initial pseudo-random binary sequence and generating said modulating data sequence from said initial sequence.

[0014] A pseudo-random binary sequence, or PRBS (from the English "Pseudo Random Binary Sequence"), is a data sequence composed of high values, namely "1s", and low values, namely "0s". This type of sequence has particularly interesting properties. Indeed, its autocorrelation function is maximum for a zero time shift, that is to say when the sequence is compared to itself, and has a value significantly lower than this maximum for all other time shifts, that is to say when the sequence is compared to time-shifted versions of itself. Furthermore, the cross-correlation function between two pseudo-random binary sequences is significantly lower than the maximum of the autocorrelation functions of these sequences.Finally, this type of sequence is usually generated using a linear feedback shift register, or LFSR, which produces a periodic recurring sequence whose pattern is a pseudo-random binary sequence.

[0015] It is thus understood that the invention proposes to use such a type of pseudo-random binary sequence to obtain a sequence modulating the light beam emitted by the light module of the emission module, which natively performs a photometric function. The resulting light beam could for example be a pulsed beam, each pulse corresponding to one or more consecutive high values ​​of the modulating sequence and the interval separating two consecutive pulses corresponding to one or more consecutive low values ​​of the modulating sequence. Due to the cyclic nature of this sequence, the modulated light beam emitted will periodically contain this sequence while continuously performing the photometric function.

[0016] On the reception chain side, the reception module will receive a light beam composed of a part of the modulated light beam and noise. The demodulation unit can then deduce a data sequence from the received light beam, for example by thresholding the electrical signals converted by the photodetector(s). Once this light beam is demodulated, the calculation unit can then estimate the values ​​of a correlation function between the demodulated data sequence and the modulating data sequence, each value of the correlation function is associated with a value of a time shift of the modulating sequence, or of the demodulated sequence, used to estimate this value of the correlation function.

[0017] Taking into account the autocorrelation properties of pseudorandom binary sequences, the correlation function thus estimated will be maximum for the time shift value corresponding to the time of flight of the modulated light beam. emitted, reflected and then received, even in the event of significant noise. Consequently, the computing unit can identify this time shift value associated with the maximum value of the correlation function with significant precision and deduce the distance separating the object on which the beam was reflected and the motor vehicle. Furthermore, given the properties of cross-correlation, it thus appears unlikely that the reception of a modulated light beam emitted by an equivalent system of another motor vehicle would lead to the detection of a false positive. Finally, it is understood that the detection is carried out not on a single pulse but on a complete data sequence, so that the signal-to-noise ratio of the system is improved.

[0018] Advantageously, the calculation unit is arranged to generate an initial pseudo-random binary sequence of maximum size and to generate said modulating data sequence from said initial sequence. For a pseudo-random binary sequence, the maximum of the autocorrelation function, i.e. for a zero time shift, corresponds to the number of high values ​​in the sequence, while its value, for all other time shifts, corresponds to this number of high values ​​multiplied by the duty cycle of the sequence, i.e. the ratio between the number of high values ​​and the total length of the sequence. For a pseudo-random binary sequence of maximum size, also called MLS (from the English “Maximum Length Sequence”) or M-sequence, this duty cycle is 50%.This duty cycle value thus makes it possible to increase the accuracy of peak detection, or estimation of the maximum, of the autocorrelation function, and therefore the accuracy of estimation of the distance from the vehicle to the detected object.

[0019] In one embodiment of the invention, the modulation unit is capable of receiving a peak light power value from the calculation unit and the modulation unit is arranged to control the light module so that said modulated light beam is emitted only for high values ​​of said modulating data sequence received from the calculation unit and so that the modulated light beam is emitted according to said peak light power value. For example, the modulation unit is arranged to generate a control signal, to modulate said control signal from the received data sequence and to control the emission of said modulated light beam by the light module from the modulated control signal. Where appropriate, the modulation unit may be arranged to control the light source of the light module, and in particular a power supply supplied to this light source, to control the emission of the light beam.The control signal could, for example, be a pulse width modulated control signal, the duty cycle of which is predefined according to a given instruction, or a pulse frequency modulated control signal, the frequency of which is predefined according to a given instruction. It is thus understood that each pulse of the beam. modulated light is emitted with said peak light power and that the average light power of the emitted modulated light beam, necessary to carry out the photometric function, is thus defined by the peak light power, the duty cycle of the modulating data sequence and by the control signal.

[0020] Advantageously, the calculation unit is able to receive a duty cycle instruction of the data sequence and the calculation unit is arranged to generate an initial sequence of pseudo-random binary type, each data item of said initial sequence being associated with the same predetermined pulse duration and the high values ​​of the initial sequence being associated with the same predetermined peak power value. Where appropriate, the calculation unit can be arranged to generate said modulating data sequence from the initial sequence by decreasing only the pulse durations associated with the high values ​​of said initial sequence and by increasing the peak power value associated with the high values, this decrease and this increase being carried out according to a factor determined from the duty cycle instruction and the duty cycle of the initial sequence.Preferably, the control signal generated by the modulation unit will thus be modulated using the modulating sequence thus obtained and the pulse durations thus modified, so that each pulse of the modulated light beam is emitted during the pulse duration associated with the high value corresponding to this pulse and according to said peak light power value associated with this high value. It is thus understood that, taking into account the reduction in the duty cycle of the modulating data sequence, the peak power can be increased without the average light power of the modulated light beam changing. This improves the signal-to-noise ratio of the system, since it will be simpler for the demodulation unit to distinguish a pulse from an absence of a pulse in a received light beam, including in the event of significant noise.Note that the reduction of the pulse duration can be achieved by adding low values ​​in the initial sequence between the high values ​​and / or by replacing high values ​​with low values ​​in the initial sequence.

[0021] In an exemplary embodiment, the pulse durations will all be reduced by a factor corresponding to the ratio between the duty cycle of the initial sequence and the duty cycle setpoint and the peak powers will all be increased by a factor corresponding to the multiplication of this ratio by the initial peak power.

[0022] In an alternative or cumulative embodiment of the invention, the calculation unit may be arranged to generate an initial pseudo-random binary type sequence and to generate said modulating data sequence from a modification of the initial sequence according to a Manchester coding type algorithm. For example, in the initial sequence, each low value may be replaced by one or more successive low values ​​followed by a high value and each high value by a high value followed by one or more successive low values.

[0023] This operation thus makes it possible to obtain a modulating sequence which significantly improves the correlation properties of the initial sequence and whose duty cycle is reduced. On the one hand, the correlation function of the modulating sequence thus obtained then has a central peak, around its maximum, narrowed with respect to the central peak of the initial sequence, which makes it possible to further improve the signal-to-noise ratio of the system, insofar as the maximum of the correlation function can be discriminated by the calculation unit with greater precision. On the other hand, it will be noted that this embodiment is particularly advantageous when the initial sequence is of the pseudo-random binary type of maximum size.

[0024] In yet another alternative or cumulative embodiment of the invention, the calculation unit may be arranged to generate an initial sequence of pseudo-random binary type and to generate said modulating data sequence by inserting the data of the initial sequence into a null sequence of size greater than the initial sequence, each data item of the initial sequence being inserted into the null sequence at a position dependent on its position in the initial sequence. In a similar manner to the previous mode, this operation thus makes it possible to obtain a modulating sequence which substantially improves the correlation properties of the initial sequence and whose duty cycle is reduced.Indeed, the maximum of the autocorrelation function of the sequence thus obtained, that is to say for a zero time shift, remains unchanged and corresponds to the number of high values ​​in the initial sequence, while its value, for all other time shifts, is significantly reduced with respect to the value of the autocorrelation function of the initial sequence. The maximum of the correlation function can thus be discriminated by the calculation unit with greater precision. On the other hand, taking into account the reduction in the duty cycle of the data sequence, the peak power of the pulses of the emitted modulated light beam can then be increased, in a manner equivalent to the previous mode.

[0025] For example, the null sequence may be of length equal to the square of the length of the initial sequence by being composed of a succession of null subsequences of length equal to the length of the initial sequence. Where appropriate, each data item of the initial sequence may be inserted into the null subsequence whose position in the null sequence corresponds to the position of this data item in the initial sequence, this data item being inserted into this subsequence at a position corresponding to its position in the initial sequence.

[0026] It is possible to use just one of these methods, or to combine several of these methods, or even to combine all of these methods, to generate the modulating sequence from the initial sequence, without departing from the scope of the present invention.

[0027] In one embodiment of the invention, the light module is capable of emitting a light beam whose spectrum has a peak at a wavelength in the visible range, in particular between 400 nm and 500 nm. Advantageously, the light module comprises a light source comprising a semiconductor generator capable of emitting an elementary light beam, in particular whose spectrum has a peak at a wavelength in the visible range, and a photoluminescent element capable of converting said elementary light beam to obtain said light beam.

[0028] The semiconductor may, for example, be a gallium nitride, or GaN, capable of emitting, by electroluminescence and in response to an electric current passing through it, rays of blue light. The photoluminescent element may, for example, be in the form of a resin comprising a cerium-doped yttrium aluminum garnet, or CE:YAG, capable of absorbing blue light and, by photoluminescence and in response to the excitation produced by this light, of emitting rays of yellow light. The photoluminescent element is arranged on the generator so that a portion of the blue light rays excites this element so that it emits, by photoluminescence, rays of yellow light. The other portion of the blue light rays passes through this element. Thus, the light source simultaneously emits, when it is electrically powered, rays of blue and yellow light, the light thus formed appearing white to the human eye.

[0029] The light source may thus be a laser type source, a light-emitting diode, a vertical cavity surface-emitting laser diode, also called VCSEL (from the English “Vertical-Cavity Surface-Emitting Laser”) or even a superluminescent diode or SLED (from the English “Superluminescent diode”).

[0030] Advantageously, the light module may comprise an optical unit arranged to project the light rays emitted by the light source to form said light beam.

[0031] In one embodiment of the invention, the reception module comprises a plurality of elementary acquisition modules each comprising a photodetector capable of converting a light signal that it receives into an electrical signal.

[0032] For example, the set of photodetectors can form a sensor, for example a single electronic component.

[0033] Advantageously, the photodetector of the or each elementary acquisition module is an avalanche photodiode. This type of photodetector is also known as SPAD, from the English “Single-Photon Avalanche Diode”. The set of avalanche photodiodes can thus form a silicon photomultiplier or SiPM (from the English “Silicon PhotoMultiplier”). This type of photodetector allows the detection of the incidence of a single photon with a significant gain, for example of the order of 106, and therefore to compensate for the degradation of the signal-to-noise ratio due to external conditions

[0034] According to an exemplary embodiment of the invention, the reception module may comprise an optical unit arranged in front of the elementary acquisition module.

[0035] In one embodiment of the invention, the transmission module is arranged in a front headlight of the motor vehicle. Advantageously, the reception module and the transmission module are arranged in a front headlight of the motor vehicle.

[0036] Preferably, the emission module is arranged so that the light beam participates, totally or partially, in the realization of a predetermined regulatory photometric function. It could for example be a daytime running light or DRL (from the English “Daytime Running Lamp”), which has the advantage of being emitted in a wide field with a low intensity.

[0037] The invention also relates to a method for detecting an obstacle located in the environment of a motor vehicle and for estimating the distance separating this object from the vehicle, the method being implemented by a lighting system, in particular by a lighting system according to the invention.

[0038] The present invention is now described with the aid of examples which are purely illustrative and in no way limitative of the scope of the invention, and from the appended drawings, drawings in which the various figures represent:

[0039] [Fig-1] represents, schematically and partially, a view of a system of a motor vehicle according to an exemplary embodiment of the invention;

[0040] [Fig.2] represents, schematically and partially, a telemetry method implemented by the system of [Fig.l];

[0041] [Fig.3] represents, schematically and partially, a first example of generation of a modulating data sequence by the calculation unit of the system of [Fig.l];

[0042] [Fig.4] represents, schematically and partially, a second example of generation of a modulating data sequence by the calculation unit of the system of [Fig.l];

[0043] [Fig.5] represents, schematically and partially, a third example of generation of a modulating data sequence by the calculation unit of the system of [Fig.l];

[0044] [Fig.6] represents, schematically and partially, an example of embodiment of the calculation unit of the system of [Fig.l].

[0045] In the following description, elements that are identical, by structure or by function, appearing in different figures retain, unless otherwise specified, the same references.

[0046] [Fig.l] shows a system 1 of a motor vehicle according to an exemplary embodiment of the invention.

[0047] The system 1 comprises an emission module 2 arranged to emit a light beam F1 and a reception module 3 intended to receive a light beam F2.

[0048] In the example described, the transmission module 2 and the reception module 3 are arranged in the same front headlight of the motor vehicle. It may be provided that the modules 2 and 3 are arranged in different locations of the motor vehicle, without departing from the scope of the present invention.

[0049] The emission module 2 comprises a light module 21 and a modulation unit 22.

[0050] The light module 2 is arranged so that the light beam F1, which it emits, has an electromagnetic spectrum of which at least a portion is located in the visible spectrum. In the example described, the spectrum has an intensity peak P1, or line, in the blue at 450 nm. It will be noted that it is possible for the spectrum S to have other intensity peaks, in the visible and / or in the infrared.

[0051] In order to emit this light beam F1, the light module 21 comprises a light source 23 capable of emitting light rays and an optical unit 24 arranged to project these light rays to form the light beam F1. In the invention, the optical unit 24 may indifferently comprise one or more reflectors, one or more lenses, one or more diaphragms or one or more collimators or even a combination of several of these optical elements.

[0052] The light source 23 comprises, for example, a semiconductor generator (not shown), for example a gallium nitride or GaN, capable of emitting, by electroluminescence and in response to an electric current passing through it, rays of blue light with an emission peak at 450 nm. The light source also comprises a photoluminescent element, in the form of a resin comprising a cerium-doped yttrium aluminum garnet, or CE:YAG, capable of absorbing blue light and, by photoluminescence and in response to the excitation produced by this light, of emitting rays of yellow light.

[0053] The photoluminescent element is arranged on the generator so that a portion of the blue light rays excites this element so that it emits, by photoluminescence, yellow light rays. The other portion of the blue light rays passes through this element. Thus, the light source 23 simultaneously emits, when electrically powered, blue and yellow light rays, the light thus formed appearing white to the human eye.

[0054] To the extent that the light beam Fl is composed, partially or totally, of white light, it is possible to use this light beam Fl to participate, partially or totally, in the realization of a photometric function, in particular regulatory, predetermined. In this case, the optical unit 24 is arranged to shape this light beam Fl so that its photometric distribution satisfies the requirements of said function. For example, it may be provided that the light beam Fl participates in the realization of a function of the daytime running light type, or DRL.

[0055] In addition to this photometric function, the light beam Fl allows the system 1 to perform functions of detecting and evaluating the position of an object O on the road, as will be described in connection with [Fig.2] which represents a telemetry method implemented by the system 1.

[0056] For these purposes, the system 1 comprises a calculation unit 4.

[0057] In a first step E1, the calculation unit 4 generates an initial data sequence Seql. The initial sequence Seql is, in the example described, a binary type sequence, composed of “0” and “1”, pseudo random and of maximum size, also called M-sequence.

[0058] It may be provided that this sequence Seql is stored in a memory of the calculation unit 4 (not shown), the calculation unit 4 then generating this sequence periodically. Alternatively, it may be provided that the calculation unit is equipped with a linear feedback shift register, the initial state, the number of stages and the logic gates of which have been defined so that the sequence of bits generated by the register is periodic and the pattern of which is the sequence Seql. Whatever the embodiment envisaged, the calculation unit 4 thus generates the sequence Seql periodically and continuously.

[0059] In a second step E2, the calculation unit 4 generates a data sequence Seq2, called modulating, from the initial sequence Seq1, while retaining at least the same autocorrelation and cross-correlation properties of the initial sequence Seq1. Different methods for generating this modulating sequence will be described later. It will be possible to use just one of these methods or to combine several of these methods, or even all of these methods, in any order. Alternatively, it will be possible to provide that the modulating sequence Seq2 is identical to the initial sequence Seq1.

[0060] It may in particular be provided, depending on the generation method used, that the modulating sequence Seq2 is generated continuously from each bit of the initial sequence Seq1 which is generated, that each initial sequence Seq1 generated is stored in a buffer memory in order to be able to generate the modulating sequence Seq2, or even that the modulating sequence Seq2 is stored in the memory of the calculation unit 4, which thus directly generates this sequence Seq2 without generating the initial sequence Seq1.

[0061] Concomitantly, the calculation unit 4 defines a peak power value Pp as well as a pulse duration Tp, and transmits the data sequence Seq2, the power peak Pp and pulse duration Tp at modulation unit 22.

[0062] In a third step E3, the modulation unit 22 modulates the light beam Fl emitted by the light module 21, from this data sequence Seq2, for example by controlling the electrical power supplied to the light source 23.

[0063] In the example described, the modulation unit 22 comprises a generator of a pulse frequency modulated control signal. This control signal makes it possible to control a switching power supply (not shown) of the light source 23. Conventionally, the frequency setpoint of this control signal, set by the modulation unit 22, thus makes it possible to control the average electrical power supplied to the light source 23, and therefore to control the light intensity of the light beam F1, so as to satisfy the requirements of the photometric function that it performs.

[0064] Thus, the modulation unit 22 converts the data sequence Seq2 into a modulating signal and modulates the initial control signal using this modulating signal. In other words, the light beam Fl thus emitted under the control of the modulated signal Sseq is composed of a train of light pulses. The pulses follow one another with a sufficiently high variable frequency, for example greater than 10 MHz, in particular between 50 MHz and 100 MHz, so that the human eye can no longer distinguish them. Furthermore, the amplitude, width and / or position of each pulse with respect to the period allows the light beam Fl to transport the data sequence to the reception module 3.

[0065] It will be noted that in the example described, each light pulse corresponds to a bit of value “1” of the modulating sequence Seq2, the width of the pulse corresponding to the pulse duration Tp and its light power corresponding to the peak power Pp. The average power Pm of a portion of the light beam Fl containing the sequence Seq2 is thus defined by the number of bits of value “1” of this sequence Seq2 with respect to the total number of bits of this sequence Seq2, by the pulse duration Tp and by the peak power Pp:

[0066] [Math.l] Pm = Pp.Tp.DCs where Pm is the average power of the beam Fl, Pp is the peak power, Tp is the pulse duration and DCS is the duty cycle of the modulating sequence Seq2, defined as the ratio between the number of bits with value “1” in this sequence Seq2 and the total number of bits in this sequence Seq2.

[0067] The average power Pm of the light beam Fl being generally constrained by the regulatory requirements governing the photometric function that the beam Fl must perform, the calculation unit 4 can thus generate the values ​​of the peak power Pp and the pulse duration Tp as a function of the duty cycle DCS of the modulating sequence Seq2 and of a photometric function setpoint, for example expressed as an average power setpoint or a frequency setpoint of the modulated signal Sseq.

[0068] It will be noted that other types of modulation may be used indifferently within the framework of the present invention, and in particular pulse code modulation (or PCM for “Puise Code Modulation”), pulse amplitude modulation (or PAM for “Puise Amplitude Modulation”), pulse width modulation (or PWM for “Puise Width Modulation”) or even pulse position modulation (or PPM for “Puise Position Modulation”).

[0069] The light beam Fl is thus emitted until it reaches an object O, located in the environment of the vehicle, which reflects it in the direction of the reception module 3. The light beam F2 received by the reception module is thus composed of a part of the light beam Fl reflected by the object O and of noise, for example generated by sources of stray light such as urban lighting, automobile lighting, or even the sun.

[0070] The reception module 3 comprises an optical unit 31, downstream of which a plurality of elementary acquisition modules 32 are provided. The reception module 3 also comprises a demodulation unit 33.

[0071] Each of the elementary acquisition modules 32 comprises a photodetector. The light beam F2 received by the reception module 3 is thus concentrated by the optical unit 31 onto one or more of the photodetectors.

[0072] The photodetectors are identical and are each formed by an avalanche photodiode of a silicon photomultiplier. These photodiodes are distributed in a matrix manner. It will be noted that the dimensions of the photodetectors are of the order of a micrometer. The assembly thus forms a sensor whose spatial reception resolution is of the order of 1°, or even 0.1°, and whose detection capabilities, due to the use of avalanche photodiodes, are particularly high, even in the case of degraded acquisition conditions.

[0073] In a step E4, each of the photodetectors converts the portion of the light beam F2 that it receives into an electrical signal Sel that it transmits to the demodulation unit 33, which can then extract from it a data sequence Seq3, called demodulated, in a step E5.

[0074] In the example described, the demodulation unit 33 can for example, in step E5, count, from the electrical signal Sel, the number of photons received by an elementary acquisition module 32 during a time interval corresponding to a pulse duration Tp, then determine by thresholding with respect to a value determined from the peak power Pp whether this quantity of photons corresponds or not to a pulse of the light beam Fl, and therefore to a bit of value “1” or to a bit with a value of “0”.

[0075] The demodulated binary sequence Seq3 is thus transmitted to the calculation unit 4, which estimates, in a step E6, values ​​of a correlation function Fcorr between the modulating sequence Seq2 and the demodulated sequence Seq3.

[0076] In step E6, the calculation unit 4 thus evaluates, for a plurality of time shift values, the value of the cross-correlation, by means of a cyclic convolution product, between the demodulated sequence Seq3 and the modulating sequence Seq2 delayed according to each of the time shift values.

[0077] Taking into account the autocorrelation and cross-correlation properties of pseudo-random binary type sequences, the correlation function Fcorr will thus be maximum for a time shift value corresponding to the time of flight of the light beam Fl, separating the instant when it is emitted by the emission module 2 and the instant when it is received by the reception module 3, the modulating sequence Seq2 delayed by this value thus corresponding substantially to the demodulated sequence Seq3, apart from the noise.

[0078] In a step E7, the calculation unit 4 identifies this maximum value of the correlation function Fcorr and estimates the value r of this flight time of the light beam Fl between the object O and the vehicle, associated with this maximum value.

[0079] In a step E8, the calculation unit 4 estimates the distance d separating the object O from the vehicle.

[0080] [Fig.3] shows a first method for generating the modulating sequence Seq2 from the initial sequence Seql.

[0081] In the example described, each bit with value “1” of the initial sequence Seql should correspond to a pulse in the light beam Fl of duration Tp and power Pp. However, in the event of significant noise, it is possible that the demodulation unit 33, during the thresholding operation, mistakenly considers that it is in the presence of a pulse of the light beam Fl and assigns a value of “1” to the bit. A solution to overcome these false positives would be to increase the peak power Pp so as to improve the signal-to-noise ratio. However, this operation would lead to an increase in the average power Pm of the light beam Fl which would make it incompatible with the regulatory requirements of the photometric function that this beam Fl must perform.

[0082] In order to address this problem, the method of [Fig. 3] proposes, in response to a duty cycle instruction received by the calculation unit 4, to duplicate each bit of the initial sequence Seq1, then to replace certain bits of value “1” with bits of value “0” so that the duty cycle of the new sequence Seq2 corresponds substantially to the instruction received by the calculation unit. In the example described, a percentage, defined from the instruction received and the duty cycle of the initial sequence, of bits of value “1” at each end of sub-sequence of bits of value “1” is thus deleted. This operation substantially preserves the autocorrelation properties and cross-correlation of the initial sequence Seql.

[0083] It can thus be seen that this operation amounts to reducing the pulse durations Tp' of the pulses of the light beam Fl, according to the following equation:

[0084] [Math.2] •TT f DO 2 , where Tp is the initial pulse duration, T'p is the new pulse duration, DCi is the duty cycle of the initial sequence Seql and DC2 is the duty cycle of the modulating sequence Seq2.

[0085] It will be noted that, in the case where the initial sequence Seql is generated by the calculation unit 4, it will be possible to directly provide a register of larger size making it possible to generate the intermediate sequence corresponding to the duplication of the bits of the initial sequence Seql.

[0086] In return, in order to maintain a constant average power Pm, the calculation unit 4 can then increase the peak power value P'P, according to the following equation:

[0087] [Math.3] P' — p 1 p-DCÎ^p , where Pp is the initial peak power, P'p is the new peak power, DCi is the duty cycle of the initial sequence Seql and DC2 is the duty cycle of the modulating sequence Seq2.

[0088] This improves the signal-to-noise ratio of the system, since it will be simpler for the demodulation unit 33 to distinguish a pulse from an absence of a pulse in a received light beam F2, even in the event of significant noise.

[0089] [Fig.4] shows a second method for generating the modulating sequence Seq2 from the initial sequence Seql.

[0090] As shown in [Fig.4], the autocorrelation function Fcorr of a pseudo-random binary sequence is given by the following equation:

[0091] [Math.4] / \ [ m v if v = 0 (modN) Fcorrtv = . \ / [ -, Otherwise , where Fcorr(v) is the autocorrelation function of the sequence for a time shift v, mi is the number of bits with value “1” in the sequence and N is the total number of bits in the sequence.

[0092] In other words, this function Fcorr classically has a shape with a plateau from which a peak extends. However, in the presence of noise, the values ​​of the autocorrelation function Fcorr, both at the peak and at the plateau, can deviate from these values, more or less strongly depending on the signal-to-noise ratio. in other words, points around the peak may have a value higher or lower than the expected value of the peak, so that there is an uncertainty on a set of points around the peak in determining whether it is the peak or not, and that this uncertainty disappears at a given distance from the peak, of the order of the initial pulse duration.

[0093] Therefore, the identification of the maximum of this autocorrelation function makes it possible to identify this peak with limited precision, of the order of 2.TP, where Tp is the initial pulse duration, which may be insufficient with regard to the precision requirements of the telemetry system.

[0094] In order to increase the precision, the method of [Fig.3] proposes to modify the initial sequence Seql using Manchester coding, where each bit of value "1" is replaced by a sequence of one bit of value "1" followed by one or more bits of value "0" and where each bit of value "0" is replaced by a sequence of one or more bits of value "0" followed by one bit of value "1". This operation substantially preserves the autocorrelation and cross-correlation properties of the initial sequence Seql.

[0095] In the example of [Fig.3], each bit of value “1” is replaced by a sequence of a bit of value “1” followed by a bit of value “0” and where each bit of value “0” is replaced by a sequence of a bit of value “0” followed by a bit of value “1”.

[0096] This modification thus makes it possible to modify the shape of the autocorrelation function Fcorr, so that the uncertainty range on the position of the maximum is reduced to 4 / 3.TP, where Tp is the initial pulse duration. This improves the accuracy of the system.

[0097] [Fig.5] shows a third method of generating the modulating sequence Seq2 from the initial sequence Seql.

[0098] In this third method, the calculation unit 4 generates a null sequence, i.e. containing only bits of value “0”, and modifies this sequence by means of the initial sequence Seql to obtain the sequence Seq2.

[0099] In the example described, the null sequence generated by the calculation unit 4 is of size NN, where N is the total number of bits of the initial sequence Seql, and is thus composed of N sub-sequences each composed of N bits of value “0”.

[0100] The calculation unit 4 then inserts each bit of the initial sequence Seql into one of the sub-sequences whose position in the null sequence corresponds to the position of this bit in the initial sequence, this bit being inserted into this sub-sequence at a position corresponding to its position in the initial sequence Seql.

[0101] Thus, in the example described, a bit bi of position i in the initial sequence Seql is thus inserted into the ith subsequence, in position i of this subsequence. This operation substantially preserves the autocorrelation and cross-correlation properties of the initial sequence Seql. In other words, the sequence Seq2 can be given by the following equation:

[0102] [Math.5] b , [b» if j=(iV)N+i 7 l 0, otherwise , where b'j is the bit in position j of the sequence Seq2, bi is the bit in position i of the sequence Seq2 and N is the total number of bits in the sequence Seql.

[0103] It is thus understood that the cyclic ratio DC2 of the sequence Seq2 is reduced with respect to the cyclic ratio DCi of the initial sequence Seql, by a ratio N.

[0104] From then on, the plateau of the correlation function Fcorr, initially positioned at mi / 2, where mi is the number of bits of value "1" of the initial sequence Seql, is positioned, for Seq2 at mi / 4, which therefore makes it possible to further improve the accuracy of the telemetry. In addition, this reduction in the duty cycle, in a manner equivalent to the method of [Fig.3], thus makes it possible to increase the peak power Pp of the pulses of the light beam Fl.

[0105] In [Fig.6], a partial embodiment of the calculation unit 4 implementing the convolution operation for estimating the values ​​of the correlation function between the modulating sequence Seq2 and the demodulated sequence Seq3 has been described.

[0106] The calculation unit 4 comprises, on the one hand, a sub-unit 41 evaluating the cross-correlation of the demodulated sequence Seq3 and the delayed modulating sequence Seq2 by means of an AND type logic gate. It comprises, on the other hand, a sub-unit 42 evaluating the cross-correlation of the demodulated sequence Seq3 and the delayed modulating sequence Seq2 by means of an EXCLUSIVE NOR type logic gate.

[0107] The outputs of these sub-units 41 and 42 are connected to the inputs of a multiplexer 43, receiving on its control input, an instruction determined by the calculation unit 4 as a function of the duty cycle DC2 of the modulating sequence Seq2.

[0108] Finally, the output of the multiplexer 43 is connected to a sub-unit 44 determining, from the values ​​of the correlation function transmitted to it, the maximum value, the time of flight of the light beam Fl and the distance d from the object O.

[0109] The multiplexer 43 thus propagates on its output, and towards the sub-unit 44, the correlation function determined by the sub-unit 41 or by the sub-unit 42 as a function of the value of this duty cycle DC2. More precisely, in the example described, if the duty cycle becomes less than 25%, the calculation unit 4 generates an instruction for selecting the output of the sub-unit 41 and if the duty cycle becomes greater than 25%, the calculation unit 4 generates an instruction for selecting the output of the sub-unit 42.

[0110] It is thus possible, for the control unit, to select the AND or EXCLUSIVE NOR logic gate so as to obtain a signal-to-noise ratio, during the correlation operation, which is optimal with regard to the duty cycle DC2 of the modulating sequence Seq2.

[0111] It will be noted that the calculation unit 4 may, depending on the vehicle's traffic conditions for example, select the sub-unit 41 or the sub-unit 42 according to the duty cycle used for the generation of the modulating sequence Seq2, so as to maintain an optimal correlation duty cycle.

[0112] The foregoing description clearly explains how the invention makes it possible to achieve the objectives it has set itself, namely to provide a system of a motor vehicle capable of performing telemetry functions from visible light and whose signal-to-noise ratio and measurement accuracy are improved. These objectives are achieved in particular by modulating the light beam emitted from a modulating data sequence generated from a pseudo-random binary sequence.

[0113] In any event, the invention cannot be limited to the embodiments specifically described in this document, and extends in particular to any equivalent means and to any technically effective combination of these means. In particular, it may be possible to use other types of light source than that described, such as a laser diode, a VCSEL or a SLED. It may also be possible to provide other photometric functions than that described, and in particular dipped beam type lighting functions or position light type signaling functions. It may also be possible to provide other methods of generating a modulating sequence than those described.

Claims

Claims

1. Lighting system (1) of a motor vehicle, comprising: a. an emission module (2) comprising a light module (21) capable of emitting a light beam (Fl) whose spectrum has at least one portion in the visible spectrum and a modulation unit (22) capable of receiving a data sequence, called modulating, and arranged to modulate said light beam emitted from the received data sequence; b. a reception module (3) capable of receiving a light beam (F2), in which the reception module comprises an elementary acquisition module (32) comprising a photodetector capable of converting a light signal that it receives into an electrical signal and a demodulation unit (33) connected to the photodetector and arranged to extract a data sequence, called demodulated, from an electrical signal converted by this photodetector; c. a calculation unit (4) arranged to generate a binary type modulating data sequence (Seq2) and to transmit said modulating data sequence to the modulation unit (22) for the emission of a modulated light beam (Fl) by the emission module; characterized in that, the calculation unit (4) being able to receive a demodulated data sequence (Seq3) by the demodulation unit from an electrical signal (Sel) converted by the photodetector from a light beam (F2) received by the reception module (3), the calculation unit (4) is arranged to estimate values of a correlation function (Fcorr) between said demodulated data sequence (Seq3) and said modulating data sequence (Seql) and to determine a time of flight (r) separating the emission of said emitted modulated light beam from the reception of said received light beam from the values of the correlation function, in that the calculation unit (4) is arranged to estimate each value of the correlation function (Fcorr) between said demodulated data sequence (Seq3) and said modulating data sequence (Seq2) by evaluating the cross-correlation of the demodulated data sequence and the modulating data sequence delayed by a given duration associated with said value; and in that the calculation unit (4) is arranged to evaluate the cross-correlation of the demodulated data sequence and the delayed modulating data sequence by means of an AND type logic gate (41) if the duty cycle (DC2) of the modulating data sequence is less than 25%.

2. Lighting system (1) according to the preceding claim, wherein the calculation unit (4) is arranged to evaluate the cross-correlation of the demodulated data sequence (Seq3) and the delayed modulating data sequence (Seq2) by means of a logic gate (42) of the EXCLUSIVE NOR type or by means of a logic gate (41) of the AND type, the calculation unit being arranged to select one or the other of these gates as a function of the duty cycle (DC2) of the modulating data sequence.

3. Lighting system (1) according to one of the preceding claims, in which the calculation unit (4) is arranged to generate an initial pseudo-random binary type sequence (Seql) and to generate said modulating data sequence (Seq2) from said initial sequence.

4. Lighting system (1) according to the preceding claim, in which the calculation unit (4) is arranged to generate an initial pseudo-random binary type sequence of maximum size (Seql) and to generate said modulating data sequence (Seq2) from said initial sequence.

5. Lighting system (1) according to one of the preceding claims, wherein the modulation unit (22) is capable of receiving a peak light power value (Pp) from the calculation unit (4) and in that the modulation unit is arranged to control the light module (21) so that said modulated light beam (Fl) is emitted only for high values of said modulating data sequence (Seq2) received from the calculation unit and so that the modulated light beam is emitted according to said peak light power value.

6. Lighting system (1) according to the preceding claim, in which the calculation unit (4) is capable of receiving a duty cycle instruction (DC2) of the data sequence, in which the calculation unit is arranged to generate an initial pseudo-random binary type sequence (Seql), each data item of said initial sequence being associated with the same predetermined pulse duration (Tp) and the high values of the initial sequence being associated with the same predetermined peak power value (Pp), characterized in that the calculation unit is arranged to generate said modulating data sequence (Seq2) from the initial sequence by decreasing only the pulse durations (Tp') associated with the high values of said initial sequence and by increasing the peak power value (P'P) associated with the high values, this decrease and this increase being carried out according to a factor determined from the duty cycle setpoint and the duty cycle (DCi) of the initial sequence.

7. Lighting system (1) according to one of the preceding claims, characterized in that the calculation unit (4) is arranged to generate an initial pseudo-random binary type sequence (Seql) and to generate said modulating data sequence (Seq2) from a modification of the initial sequence according to a Manchester coding type algorithm.

8. Lighting system (1) according to one of the preceding claims, characterized in that the calculation unit (4) is arranged to generate an initial pseudo-random binary type sequence (Seql) and to generate said modulating data sequence (Seq2) by inserting the data of the initial sequence into a null sequence of size greater than the initial sequence, each data of the initial sequence being inserted into the null sequence at a position dependent on its position in the initial sequence.

9. Lighting system (1) according to one of the preceding claims, characterized in that the emission module (2) is arranged in a front headlight of the motor vehicle.

10. Lighting system (1) according to the preceding claim, in which the emission module (2) is arranged so that the light beam (Fl) participates, totally or partially, in the realization of a predetermined regulatory photometric function.

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