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 visible light beam (F1) modulated 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, 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: A motor vehicle detection system comprising a light beam emission module and a light beam reception module

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

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

[0003] Conventionally, the light source that emits this light beam is controlled by a pulse-width modulated (PWM) electrical signal. The light source is thus periodically switched on and off by this PWM signal, so that the emitted light beam consists of successive light pulses occurring at a frequency high enough that they are indistinguishable to the human eye. The intensity of the emitted light beam is a function of the duty cycle of this PWM signal, making it possible to control it by adjusting this duty cycle and thus implement a photometric function.

[0004] Beyond performing one or more photometric functions, such as daytime running lights or low beams, various other functions can be implemented by this type of lighting module. For example, the light source of the lighting module can be controlled so that one of the pulses in the emitted light beam has a particularly high intensity. The lighting system can thus be equipped with a receiver module to receive the emitted light beam after reflection from an object near the vehicle. A vehicle's computer unit can then, after detecting the high-intensity pulse in the received light beam, determine the time of flight of the emitted light beam and thus estimate the distance between the vehicle and the object.

[0005] In this way, the light beam can retain its original function, namely to perform a photometric function, while allowing the light 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] However, this type of system based on the use of light pulses has a drawback. Indeed, the receiving module intended to receive the reflected light beam must include at least one photodetector to convert this light beam into an electrical signal, which can then be processed by the computing unit to detect a particular pulse.

[0007] However, under certain conditions, the signal-to-noise ratio of this photodetector can be significantly degraded due to stray light sources in the vehicle's environment, such as streetlights, headlights of oncoming or following vehicles, or even sunlight, and the nature of the objects in the environment, particularly their reflectivity. This degradation of the signal-to-noise ratio can then reduce the accuracy of the processing unit in estimating the distance to the target object, or even lead to false positives. Furthermore, if two vehicles equipped with the same system pass each other, a light pulse emitted by one of the lighting systems will be detected by the other, resulting in a false positive.

[0008] There is therefore a need for a lighting system of a motor vehicle, capable of emitting a light beam performing both a given photometric function and a telemetry function, and whose accuracy as well as signal-to-noise ratio are improved.

[0009] The present invention falls within this context and aims to meet this need.

[0010] To this end, the invention relates to a lighting system for a motor vehicle, including: a. an emission module comprising a light module capable of emitting a light beam whose spectrum has at least a 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 receiving module capable of receiving a light beam, in which the receiving module includes an elementary acquisition module comprising a photodetector capable of converting a light signal 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 for: i. generate a modulating data sequence from an initial pseudo-random binary sequence; and ii. transmit said modulating data sequence to the modulation unit for the emission of a light beam modulated by the emission module;

[0011] The invention is characterized in that, the computing unit being capable of receiving a data sequence demodulated by the demodulating unit from an electrical signal converted by the photodetector from a light beam received by the receiving module, the computing 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 modulated light beam emitted from the reception of said light beam received from the values ​​of the correlation function.

[0012] A pseudo-random binary sequence, or PRBS, is a data sequence composed of high values, namely "1s", and low values, namely "0s". This type of sequence exhibits particularly interesting properties. Indeed, its autocorrelation function is at its maximum for a zero time lag, that is, when the sequence is compared to itself, and has a value significantly lower than this maximum for all other time lags, that is, 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 generally generated using a linear feedback shift register, or LFSR (from the English "Linear Feedback Shift Register"), which produces a periodic recurrence sequence whose pattern is a pseudo-random binary sequence.

[0013] 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 emitting 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.

[0014] On the receiving chain side, the receiving module will receive a light beam composed of the modulated light beam and noise. The demodulation unit can then deduce a data sequence from the beam light received, for example by thresholding the electrical signals converted by the photodetector(s). Once this light beam is demodulated, the computing 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.

[0015] Given the autocorrelation properties of pseudo-random binary sequences, the correlation function thus estimated will be maximum for the time lag value corresponding to the time of flight of the modulated light beam emitted, reflected, and then received, even in the case of significant noise. Consequently, the processing unit can identify this time lag value associated with the maximum value of the correlation function with high accuracy and deduce the distance between the object on which the beam was reflected and the motor vehicle. Furthermore, given the cross-correlation properties, it appears unlikely that the reception of a modulated light beam emitted by an equivalent system from another motor vehicle would lead to the detection of a false positive.It is finally understood that the detection is performed not on a single pulse but on a complete data sequence, so that the signal-to-noise ratio of the system is improved.

[0016] Advantageously, the computing 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 lag, corresponds to the number of high values ​​in the sequence, while its value, for all other time lags, 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 maximum-length pseudo-random binary sequence, also called an MLS (Maximum Length Sequence) or M-sequence, this duty cycle is 50%.This duty cycle value thus increases the accuracy of peak detection, or maximum estimation, of the autocorrelation function, and therefore the accuracy of estimating the distance from the vehicle to the detected object.

[0017] In one embodiment of the invention, the modulation unit is capable of receiving a peak light power value from the processing unit, and the modulation unit is arranged to control the light module such that said modulated light beam is emitted only for high values ​​of said modulating data sequence received from the processing unit, and such that the modulated light beam is emitted according to said peak light power value. For example, the unit of The modulation unit is configured to generate a control signal, to modulate said control signal based on the received data sequence, and to control the emission of said modulated light beam by the light module based on the modulated control signal. If necessary, the modulation unit may be configured to control the light source of the light module, and in particular the power supply provided to this light source, to control the emission of the light beam. The control signal may, for example, be a pulse-width modulated control signal, the duty cycle of which is predefined according to a given setpoint, or a pulse-frequency modulated control signal, the frequency of which is predefined according to a given setpoint.It is thus understood that each pulse of the modulated light beam is emitted with said peak light power and that the average light power of the emitted modulated light beam, necessary for the realization of the photometric function, is thus defined by the peak light power, the duty cycle of the modulating data sequence and by the control signal.

[0018] Advantageously, the computing unit is capable of receiving a duty cycle instruction for the data sequence and is configured to generate an initial pseudo-random binary sequence, each data point 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. If necessary, the computing unit can be configured 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 increasing the peak power value associated with the high values, this decrease and 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 be modulated using the modulating sequence thus obtained and the modified pulse durations, so that each pulse of the modulated light beam is emitted for the pulse duration associated with the high value corresponding to that pulse and according to the peak light power value associated with that high value. It is understood that, given the decrease in the duty cycle of the modulating data sequence, the peak power can be increased without changing the average light power of the modulated light beam. This improves the signal-to-noise ratio of the system, since it will be easier for the demodulating unit to distinguish a pulse from the absence of a pulse in a received light beam, even in the case of significant noise.Note that the pulse duration can be reduced by adding low values ​​to the sequence. initial between high values ​​and / or by replacing high values ​​with low values ​​in the initial sequence.

[0019] In one embodiment, the pulse durations will all be decreased 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.

[0020] In an alternative or cumulative embodiment of the invention, the computing unit may be arranged to generate an initial pseudo-random binary sequence and to generate said modulating data sequence from a modification of the initial sequence according to a Manchester coding 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.

[0021] This operation thus makes it possible to obtain a modulating sequence that 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 exhibits a central peak, around its maximum, that is narrower than the central peak of the initial sequence, which further improves the signal-to-noise ratio of the system, insofar as the maximum of the correlation function can be discriminated by the computing unit with greater precision. On the other hand, it should be noted that this embodiment is particularly advantageous when the initial sequence is of the maximum size pseudo-random binary type.

[0022] In yet another alternative or cumulative embodiment of the invention, the computing unit may be arranged to generate an initial pseudo-random binary sequence and to generate said modulating data sequence by inserting the data from the initial sequence into a null sequence larger than the initial sequence, each data element of the initial sequence being inserted into the null sequence at a position dependent on its position in the initial sequence. Similar to the previous embodiment, this operation thus makes it possible to obtain a modulating sequence that significantly 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, for a zero time lag, remains unchanged and corresponds to the number of high values ​​in the initial sequence, while its value, for all other time lags, is significantly reduced compared to the value of the autocorrelation function of the initial sequence. The maximum of the correlation function can therefore be discriminated by the computing unit with greater precision. On the other hand, given the decrease in the duty cycle of the... In 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.

[0023] For example, the null sequence may have a length equal to the square of the length of the initial sequence by being composed of a succession of null subsequences of a length equal to the length of the initial sequence. If necessary, 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 that 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.

[0024] One may indifferently use only one of these methods, or combine several of these methods, or even combine all of these methods, to generate the modulating sequence from the initial sequence, without going out of the scope of the present invention.

[0025] In one embodiment of the invention, the computing 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 time associated with said value. In other words, each value of the correlation function is thus associated with a time lag value of the modulating sequence used to estimate that value of the correlation function. The computing unit is thus arranged to identify the time lag value associated with the maximum value of the cross-correlation function.

[0026] Advantageously, the processing unit is configured to evaluate the cross-correlation of the demodulated data sequence and the delayed modulating data sequence using an AND logic gate if the duty cycle of the modulating data sequence is less than 25%. Indeed, it has been observed that the signal-to-noise ratio of the system is optimal for duty cycles around 50%, but degrades for lower duty cycles, particularly around 25%. This is because, at these duty cycles, the modulating sequence contains more low values ​​than high values. In the presence of noise, it is more complex to correlate low values ​​with each other than high values.Using an XNOR (exclusive NOR) logic gate, which verifies the synchronization of two signals for both low and high values, results in a degradation of the signal-to-noise ratio at low duty cycles. Conversely, at low duty cycles, using an AND (AND) logic gate, which verifies the synchronization of two signals only at high values, provides a higher signal-to-noise ratio than the XNOR gate. XOR logic. It is thus possible to decrease 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 modulated light beam emitted, while maintaining an optimal signal-to-noise ratio for the correlation operation.

[0027] Advantageously, the processing unit is configured to evaluate the cross-correlation of the demodulated data sequence and the delayed modulating data sequence by means of an XOR logic gate or an AND logic gate, the processing unit being configured to select one or the other of these gates depending on the duty cycle of the modulating data sequence. The processing unit can thus, depending on the use case, select the logic gate corresponding to the duty cycle used for that use case, for example, to adapt the system to degraded environmental conditions. For example, if the duty cycle is less than 25%, the processing unit can select the AND logic gate, and it can select the XOR logic gate otherwise.

[0028] 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 including 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.

[0029] The semiconductor could, for example, be gallium nitride, or GaN, capable of emitting blue light rays by electroluminescence in response to an electric current passing through it. The photoluminescent element could, 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 in response to the excitation produced by this light, of emitting yellow light rays. The photoluminescent element is arranged on the generator so that a portion of the blue light rays excites this element, causing it to emit yellow light rays by photoluminescence. The other portion of the blue light rays passes through this element. Thus, when electrically powered, the light source simultaneously emits blue and yellow light rays, the resulting light appearing white to the human eye.

[0030] The light source may thus be a laser-type source, a light-emitting diode, a vertical cavity laser diode emitting from the surface, also called VCSEL (from the English "Vertical-Cavity Surface-Emitting Laser") or a superluminescent diode or SLED (from the English "Superluminescent diode").

[0031] Advantageously, the light module may include an optical unit arranged to project the light rays emitted by the light source to form said light beam.

[0032] In one embodiment of the invention, the receiving module comprises a plurality of elementary acquisition modules, each comprising a photodetector capable of converting a light signal it receives into an electrical signal.

[0033] For example, the set of photodetectors can form a sensor, for example a single electronic component.

[0034] Advantageously, the photodetector of the elementary acquisition module(s) is an avalanche photodiode. This type of photodetector is also known as a SPAD, from the English "Single-Photon Avalanche Diode". A set of avalanche photodiodes can thus form a silicon photomultiplier or SiPM (from the English "Silicon PhotoMultiplier"). This type of photodetector makes it possible to detect the impact of a single photon with a high gain, for example on the order of 10⁶, and therefore to compensate for the degradation of the signal-to-noise ratio due to external conditions.

[0035] According to one embodiment of the invention, the receiving module may include an optical unit arranged in front of the elementary acquisition module.

[0036] 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.

[0037] Preferably, the emitting module is arranged so that the light beam participates, wholly or partially, in the performance of a predetermined regulatory photometric function. For example, it could be a daytime running light (DRL), which has the advantage of being emitted over a wide field with low intensity.

[0038] The invention also relates to a method for detecting an obstacle located in the environment of a motor vehicle and estimating the distance separating this object from the vehicle, the method being implemented by a light system, in particular by a light system according to the invention.

[0039] Advantageously, the process comprises the following steps: a. Generation, by a computing unit of the light system, of a modulating data sequence from an initial pseudo-random binary type sequence; b. Modulation, by a modulation unit of the lighting system, of a light beam emitted by a light module of the lighting system; c. Reception and conversion, by an elementary acquisition module of the light system, of a light beam into an electrical signal; d. Demodulation, by a demodulation unit of the light system, of the electrical signal to extract a demodulated data sequence; e. Estimation of values, by the computing unit, of a correlation function between said demodulated data sequence and said modulating data sequence; and f. Determination of a time of flight separating the emission of said modulated light beam emitted from the reception of said light beam received from the values ​​of the correlation function.

[0040] The present invention is now described by means of purely illustrative and in no way limiting examples of the scope of the invention, and from the accompanying drawings, in which the various figures represent:

[0041] [Fig.1] represents, schematically and partially, a view of a system of a motor vehicle according to an example of an embodiment of the invention;

[0042] [Fig.2] represents, schematically and partially, a telemetry method implemented by the system of [Fig.1];

[0043] [Fig.3] represents, schematically and partially, a first example of generation of a modulating data sequence by the system's computing unit of [Fig.1];

[0044] [Fig.4] represents, schematically and partially, a second example of generation of a modulating data sequence by the system's computing unit of [Fig.1];

[0045] [Fig.5] represents, schematically and partially, a third example of generation of a modulating data sequence by the system's computing unit of [Fig.1];

[0046] [Fig.6] represents, schematically and partially, an example of an embodiment of the calculation unit of the system of [Fig.1].

[0047] In the following description, identical elements, by structure or by function, appearing on different figures retain, unless otherwise specified, the same references.

[0048] A system 1 of a motor vehicle is shown in [Fig.1] according to an example of an embodiment of the invention.

[0049] The system 1 comprises an emission module 2 arranged to emit a light beam Fl and a reception module 3 intended to receive a light beam F2.

[0050] 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 within the motor vehicle, without departing from the scope of the present invention.

[0051] The emission module 2 comprises a light module 21 and a modulation unit 22.

[0052] The light module 2 is arranged so that the light beam Fl it emits has an electromagnetic spectrum, at least a portion of which lies in the visible spectrum. In the example described, the spectrum has an intensity peak PI, or line, in the blue at 450 nm. It should be noted that the spectrum may have other intensity peaks in the visible and / or infrared ranges.

[0053] In order to emit this light beam Fl, 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 FL. 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 a combination of several of these optical elements.

[0054] The light source 23 comprises, for example, a semiconductor generator (not shown), for example gallium nitride or GaN, capable of emitting, by electroluminescence and in response to an electric current passing through it, blue light beams 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 excitation by this light, of emitting yellow light beams.

[0055] The photoluminescent element is arranged on the generator such that a portion of the blue light rays excites this element, causing it to emit yellow light rays by photoluminescence. The remaining portion of the blue light rays passes through this element. Thus, the light source 23 simultaneously emits blue and yellow light rays when electrically powered, the resulting light appearing white to the human eye.

[0056] Insofar as the light beam Fl is composed, partially or entirely, of white light, it is possible to use this light beam Fl to participate, partially or entirely, in the performance of a predetermined photometric function, particularly a regulatory one. In this case, the optical unit 24 is arranged to shape this light beam Fl so that its photometric distribution meets the requirements of said function. For example, it may be provided that the light beam Fl participates in the performance of a daytime running light, or DRL, function.

[0057] In addition to this photometric function, the light beam Fl enables the system 1 to perform functions of detection and evaluation of the position of an object O on the road, as will be described in relation to [Fig.2] which represents a telemetry process implemented by the system 1.

[0058] For these purposes, system 1 includes a computing unit 4.

[0059] In a first step El, the computing 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 an M-sequence.

[0060] This Seql sequence can be stored in a memory of the arithmetic unit 4 (not shown), with the arithmetic unit 4 then generating this sequence periodically. Alternatively, the arithmetic unit can be equipped with a linear feedback shift register, the initial state, number of stages, and logic gates of which have been defined such that the bit sequence generated by the register is periodic and its pattern is the Seql sequence. In any of the embodiments considered, the arithmetic unit 4 thus generates the Seql sequence periodically and continuously.

[0061] In a second step E2, the computing unit 4 generates a modulating data sequence Seq2 from the initial sequence Seql, preserving at least the same autocorrelation and cross-correlation properties as the initial sequence Seql. Various methods for generating this modulating sequence will be described later. One may use only one of these methods or combine several of them, or even all of them, in any order. Alternatively, the modulating sequence Seq2 may be identical to the initial sequence Seql.

[0062] Depending on the generation method used, it may be provided that the modulating sequence Seq2 is generated continuously from each bit of the initial sequence Seql which is generated, that each initial sequence Seql generated is stored in a buffer memory in order to generate the modulating sequence Seq2, or even that the modulating sequence Seq2 is stored in the memory of the computing unit 4, which thus directly generates this sequence Seq2 without generating the initial sequence Seql.

[0063] Simultaneously, the calculation unit 4 defines a peak power value Pp and a pulse duration Tp, and transmits the data sequence Seq2, the peak power Pp and the pulse duration Tp to the modulation unit 22.

[0064] 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 power supply provided to the light source 23.

[0065] In the example described, the modulation unit 22 includes a generator of a pulse frequency modulated control signal. This control signal allows control of a switched-mode power supply (not shown) of the light source 23. Conventionally, the frequency setpoint of this control signal, fixed by the modulation unit 22, thus allows control of the average electrical power supplied to the light source 23, and therefore control of the luminous intensity of the light beam Fl, so as to satisfy the requirements of the photometric function it performs.

[0066] 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 at 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 carry the data sequence to the receiving module 3.

[0067] It should be noted that, in the example described, each light pulse corresponds to a bit with a value of "1" in the modulating sequence Seq2, the pulse width corresponds to the pulse duration Tp, and its light power corresponds 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 with a value of "1" in this sequence Seq2 relative to the total number of bits in this sequence Seq2, by the pulse duration Tp, and by the peak power Pp:

[0068] [Math.l] P m = Pp.Tp.DC s 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 a value of '1' in this Seq2 sequence and the total number of bits in this Seq2 sequence.

[0069] Since the average power Pm of the light beam Fl is 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 DCS duty cycle of the modulating sequence Seq2 and a photometric function setpoint, for example expressed as an average power setpoint or a frequency setpoint of the modulated signal Sseq.

[0070] It should be noted that other types of modulation can be used interchangeably within the framework of the present invention, and in particular pulse code modulation (or PCM from the English "Puse Code Modulation"), pulse amplitude modulation (or PAM from the English "Puse Amplitude Modulation"), pulse width modulation (or PWM from the English "Puse Width Modulation") or pulse position modulation (or PPM from the English "Puse Position Modulation").

[0071] The light beam Fl is thus emitted until it reaches an object O, located in the environment of the vehicle, which reflects it towards the receiving module 3. The light beam F2 received by the receiving module is thus composed of a part of the light beam Fl reflected by the object O and noise, for example generated by sources of parasitic light such as urban lighting, car lighting, or even the sun.

[0072] The receiving module 3 includes an optical unit 31, downstream of which are provided a plurality of elementary acquisition modules 32. The receiving module 3 also includes a demodulation unit 33.

[0073] Each of the elementary acquisition modules 32 includes a photodetector. The light beam F2 received by the receiving module 3 is thus concentrated by the optical unit 31 onto one or more of the photodetectors.

[0074] The photodetectors are identical and each consists of an avalanche photodiode in a silicon photomultiplier. These photodiodes are arranged in a matrix. It should be noted that the dimensions of the photodetectors are on the order of a micrometer. The assembly thus forms a sensor with a spatial reception resolution on the order of 1°, or even 0.1°, and whose detection capabilities, due to the use of avalanche photodiodes, are particularly high, even under degraded acquisition conditions.

[0075] In a step E4, each of the photodetectors converts the portion of the light beam F2 that it receives into an electrical signal Sel which it transmits to the demodulation unit 33, which can then extract a data sequence Seq3, called demodulated, in a step E5.

[0076] 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 regard 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 with a value of "1" or to a bit with a value of "0".

[0077] The demodulated binary sequence Seq3 is thus transmitted to the computing unit 4, which estimates, in a step E6, values ​​of a correlation function Fcorr between the modulating sequence Seq2 and the demodulated sequence Seq3.

[0078] In step E6, the computing 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.

[0079] Given the autocorrelation and cross-correlation properties of pseudo-random binary sequences, the correlation function Fcorr will thus be maximum for a time offset value corresponding to the time of flight of the light beam Fl, separating the instant when it is emitted by the transmitting module 2 and the instant when it is received by the receiving module 3, the modulating sequence Seq2 delayed by this value thus corresponding substantially to the demodulated sequence Seq3, up to noise.

[0080] In a step E7, the computing unit 4 identifies this maximum value of the correlation function Fcorr and estimates the value r of this time of flight of the light beam Fl between the object O and the vehicle, associated with this maximum value.

[0081] In a step E8, the calculation unit 4 estimates the distance d separating the object O from the vehicle.

[0082] A first method for generating the modulating sequence Seq2 from the initial sequence Seql has been represented in [Fig.3].

[0083] In the described example, each bit with a value of "1" in the initial sequence Seql should correspond to a pulse in the light beam Fl of duration Tp and power Pp. However, in the case of significant noise, it is possible that the demodulation unit 33, during the thresholding operation, may mistakenly interpret a pulse in the light beam Fl as being present and assign the bit a value of "1". One solution to overcome these false positives would be to increase the peak power Pp in order 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.

[0084] To address this problem, the method in [Fig. 3] proposes, in response to a duty cycle instruction received by the processing unit 4, to duplicate each bit of the initial sequence Seql, and then to replace certain bits with a value of "1" with bits with a value of "0" so that the duty cycle of the new sequence Seq2 corresponds approximately to the instruction received by the processing unit. In the example described, a percentage, defined from the received instruction and the duty cycle of the initial sequence, of bits with a value of "1" at each end of a subsequence of bits with a value of "1" is thus removed. This operation essentially preserves the autocorrelation and cross-correlation properties of the initial Seql sequence.

[0085] 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:

[0086] [Math.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.

[0087] It should 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 allowing the generation of the intermediate sequence corresponding to the duplication of the bits of the initial sequence Seql.

[0088] Conversely, 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:

[0089] [Math.3] *P~ DC2 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.

[0090] This improves the signal-to-noise ratio of the system, since it will be easier for the demodulation unit 33 to distinguish a pulse from the absence of a pulse in a received light beam F2, even in the case of significant noise.

[0091] A second method for generating the modulating sequence Seq2 from the initial sequence Seql has been represented in [Fig.4].

[0092] As shown in [Fig.4], the autocorrelation function Fcorr of a pseudo-random binary sequence is given by the following equation:

[0093] [Math.4] Fcorr v = • nip if v = 0 (mod N) half » —, smon , where Fcorr(v) is the autocorrelation function of the sequence for a time shift v, mi is the number of bits with the value '1' in the sequence and N is the total number of bits in the sequence.

[0094] In other words, this function Fcorr classically exhibits a shape with a plateau from which a peak extends. However, in the presence of noise, the values ​​of the function Autocorrelation values ​​(Fcorr), both at the peak and plateau levels, can deviate from these values, more or less significantly depending on the signal-to-noise ratio. In other words, points around the peak may have a value higher or lower than the expected peak value, so there is uncertainty about a set of points around the peak in determining whether or not it is the peak, and this uncertainty disappears at a given distance from the peak, on the order of the initial pulse duration.

[0095] Therefore, identifying the maximum of this autocorrelation function allows us to identify this peak with limited precision, on the order of 2TP, where Tp is the initial pulse duration, which may be insufficient with regard to the precision requirements of the telemetry system.

[0096] To increase accuracy, the method in [Fig. 3] proposes modifying the initial Seql sequence using Manchester encoding, where each bit with a value of "1" is replaced by a sequence of one bit with a value of "1" followed by one or more bits with a value of "0", and where each bit with a value of "0" is replaced by a sequence of one or more bits with a value of "0" followed by a bit with a value of "1". This operation substantially preserves the autocorrelation and cross-correlation properties of the initial Seql sequence.

[0097] In the example of [Fig.3], each bit with a value of "1" is replaced by a sequence of a bit with a value of "1" followed by a bit with a value of "0" and where each bit with a value of "0" is replaced by a sequence of a bit with a value of "0" followed by a bit with a value of "1".

[0098] This modification thus makes it possible to change 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.

[0099] A third method of generating the modulating sequence Seq2 from the initial sequence Seql has been represented in [Fig.5].

[0100] In this third method, the computing unit 4 generates a null sequence, that is to say containing only bits of value "0", and modifies this sequence by means of the initial sequence Seql to obtain the sequence Seq2.

[0101] In the example described, the null sequence generated by the computing 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".

[0102] The calculation unit 4 then inserts each bit of the initial sequence Seql into one of the subsequences whose position in the null sequence corresponds to the position of that bit in the initial sequence, that bit being inserted into this subsequence at a position corresponding to its position in the initial sequence Seql.

[0103] Thus, in the example described, a bit bi at position i in the initial sequence Seql is inserted into the i-th subsequence, at position i of that 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:

[0104] [Math.5] b ir if j = (i-1) JV + i J 1 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.

[0105] It is thus understood that the duty cycle DC2 of the Seq2 sequence is reduced with respect to the duty cycle DCi of the initial Seql sequence, by a ratio N.

[0106] Therefore, the plateau of the correlation function Fcorr, initially positioned at mi / 2, where mi is the number of bits with the value "1" in the initial sequence Seql, is positioned, for Seq2, at mi / 4, which further improves the accuracy of the telemetry. In addition, this reduction in the duty cycle, equivalent to the method in [Fig. 3], thus increases the peak power Pp of the pulses of the light beam Fl.

[0107] In [Fig.6], we have described an example of a partial realization of the computing unit 4 implementing the convolution operation for estimating the values ​​of the correlation function between the modulating sequence Seq2 and the demodulated sequence Seq3.

[0108] The processing unit 4 comprises, on the one hand, a subunit 41 evaluating the cross-correlation of the demodulated sequence Seq3 and the delayed modulating sequence Seq2 by means of an AND logic gate. It comprises, on the other hand, a subunit 42 evaluating the cross-correlation of the demodulated sequence Seq3 and the delayed modulating sequence Seq2 by means of an XOR logic gate.

[0109] The outputs of these subunits 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.

[0110] Finally, the output of the multiplexer 43 is connected to a subunit 44 which determines, 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 of the object O.

[0111] The multiplexer 43 thus propagates on its output, and to the subunit 44, the correlation function determined by the subunit 41 or by the subunit 42 depending on the value of this duty cycle DC2. More precisely, in the example described, if the duty cycle becomes less than 25%, the arithmetic unit 4 generates an instruction of output selection of subunit 41 and if the duty cycle becomes greater than 25%, the arithmetic unit 4 generates an instruction to select the output of subunit 42.

[0112] It is thus possible for the control unit to select the AND or XOR logic gate so as to obtain a signal-to-noise ratio, during the correlation operation, optimal with regard to the duty cycle DC2 of the modulating sequence Seq2.

[0113] It should be noted that the calculation unit 4 will be able, depending on the vehicle's traffic conditions for example, to select subunit 41 or subunit 42 according to the duty cycle used for the generation of the modulating sequence Seq2, so as to maintain an optimal correlation duty cycle.

[0114] The preceding description clearly explains how the invention achieves its stated objectives, namely to provide a motor vehicle system 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 emitted light beam from a modulating data sequence generated from a pseudo-random binary sequence.

[0115] In any event, the invention is not limited to the embodiments specifically described in this document, and extends in particular to all equivalent means and to any technically feasible combination of these means. In particular, it may be envisaged that other types of light source than that described may be used, such as a laser diode, a VCSEL, or an SLED. It may also be envisaged that other photometric functions than that described may be performed, and in particular, dipped beam lighting functions or position light signaling functions. It may also be envisaged that other methods of generating a modulating sequence than those described may be used.

Claims

1. Demands 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 a 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 receiving module (3) capable of receiving a light beam (F2), in which the receiving module comprises an elementary acquisition module (32) including a photodetector capable of converting a light signal which 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 computing unit (4) arranged for: i. generate a modulating data sequence (Seq2) from an initial pseudo-random binary sequence (Seql); and ii. 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 processing unit (4) being capable of receiving a data sequence (Seq3) demodulated by the demodulation unit from an electrical signal (Sel) converted by the photodetector from a light beam (F2) received by the receiving module (3), the processing unit (4) is arranged to estimate values ​​of a correlation function (Fcorr) between said demodulated data sequence (Seq3) and said modulating data sequence (Seq2) and to determine a time of flight (r) separating the emission of said modulated light beam emitted from the reception of said light beam received from the values ​​of the correlation function and in that 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.

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

3. A light system (1) according to any one of the preceding claims, wherein the modulation unit (22) is capable of receiving a peak light power value (Pp) from the computing unit (4) and wherein 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 computing unit and so that the modulated light beam is emitted according to said peak light power value.

4. A lighting system (1) according to the preceding claim, wherein the processing unit (4) is capable of receiving a duty cycle (DC2) command from the data sequence, wherein the processing unit is arranged to generate an initial sequence (Seql) of the pseudo-random binary type, each data point 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 processing 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 increasing the peak power value (P'P) associated with the high values,This decrease and increase are achieved according to a factor determined from the duty cycle setpoint and the duty cycle (DCi) of the initial sequence.

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

6. Light system (1) according to any one of the preceding claims, characterized in that the computing unit (4) is arranged to generate an initial sequence (Seql) of pseudo-random binary type 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.

7. Light system (1) according to any one of the preceding claims, wherein the computing 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.

8. A light system (1) according to the preceding claim, wherein the computing 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 an XOR logic gate (42) or by means of an AND logic gate (41), the computing unit being arranged to select either of these gates according to the duty cycle (DC2) of the modulating data sequence.

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

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