Method and device for transmitting and receiving at least one symbol carried by a light signal modulated by a control signal and defined by a pair of frequencies of the control signal

Abstract

The present invention relates to the transmission and reception of a light signal modulated by a PWM control signal in order to transmit at least one symbol, each symbol being represented by a pair of frequencies, the frequencies of the at least one pair of frequencies being determined so that when, during the modulation of the light signal, a first determined frequency is replaced by a second determined frequency, the higher frequency out of the first and second frequencies is at most equal to twice the lower frequency out of the first and second frequencies. Figure for the abstract: Figure 3

Description

Method and device for emitting at least one symbol carried by a light signal modulated by a control signal

[0001] The present invention relates to the transmission of symbols by modulation of light signals controlled by a pulse-width modulated control signal. Technological background

[0002] Light signal communication is a widely known technology. It is very often referred to as VLC (Visible Light Communication) or ILC (Infrared Light Communication).

[0003] VLC is a technology that uses electromagnetic waves in the visible light spectrum (frequency of 400 to 800 THz / wavelength of 780 to 375 nm) to transmit data. ILC is an alternative technology that uses electromagnetic waves in the infrared spectrum (frequencies of 3 THz to 384 THz / wavelength of 780 nm to 1 mm).

[0004] Unlike traditional wireless technologies such as Wi-Fi® or Bluetooth®, which use radio waves, VLC and ILC use light sources such as LEDs to transmit signals at up to 10 kbit / s over short distances.

[0005] Electronic devices can be configured to receive modulated light signals, such as those containing a photodiode. In certain situations, a mobile phone camera or a digital camera can also serve as a receiver for VLC-type modulated light signals. The image sensor in these devices consists of an array of photodiodes (pixels) that can provide either multiple channels (up to one pixel per channel) or spatial awareness of multiple light sources.

[0006] One of the main advantages of VLC and ILC is their enhanced security compared to wireless technologies, as light generally does not penetrate walls, significantly reducing the risk of unauthorized data interception. Furthermore, they can be used in environments where radio waves are prohibited, such as hospitals or airplanes.

[0007] VLC and ILC are also valued for their versatility. In addition to data transmission, they can be used for applications such as indoor positioning (localization inside buildings) and the provision of precise geolocation services.

[0008] However, VLC and ILC have some limitations. For example, VLC's efficiency is reduced in the presence of intense ambient light, which can affect data transmission quality. Furthermore, the range of VLC and ILC is limited compared to traditional wireless technologies.

[0009] Despite these limitations, VLC and ILC continue to attract increasing interest in various fields, including wireless communication, smart lighting, and navigation systems. With the ongoing development of LED technology and signal processing algorithms, VLC and ILC promise to play an increasingly important role in the modern communications landscape.

[0010] VLC and ILC are data communication methods that modulate a light signal using a control signal. This control signal is defined so that the modulated light signal flashes at a specific frequency. By varying the frequency, it is possible to transmit data in the form of symbols. This is known as modulation of the light signal by the control signal. The control signal is usually a PWM (Pulse Width Modulation) signal consisting of a series of pulses defining an alternation of high and low levels. Each high level corresponds to a high intensity level of the light signal (the "on" signal), and each low level corresponds to a low intensity level of the light signal (the "off" signal). The modulated light signal is then demodulated to recover the transmitted symbol(s).The modulation (and demodulation) is carried out according to a modulation rate which defines whether this modulation is carried out on part or all of the light power.

[0011] Modulating a light signal induces a flickering effect, which can be visible (when the light signal is in the visible spectrum) and therefore bothersome to the user. This flickering is regulated by standards such as IEEE 1789 (https: / / www.energy.gov / eere / ssl / articles / flicker-understanding-new-ieee-recommended-practice) or NF EN 12464-1. These standards recommend, in particular, using frequencies above 2 kHz for a modulation rate of 100% to avoid visible flickering. However, the inventor observed that flickering can be visible when the frequencies used are just above 2 kHz. To prevent this flickering from being visible, it is known to use frequencies well above 2 kHz, such as frequencies above 1 MHz.However, the use of this type of high frequency causes premature aging of lighting equipment because the high frequencies put a very high stress on this equipment, causing it to overheat.

[0012] One of the problems solved by the present invention is to modulate / demodulate a light signal (belonging to the visible or infrared spectrum) in such a way as to preserve lighting equipment which then operates in a nominal regime. Summary of the present invention

[0013] One object of the present invention is to solve at least one of the problems of the technological background described above.

[0014] According to a first aspect, the present invention relates to a method of emitting at least one symbol carried by a light signal modulated by a control signal, the control signal comprising a succession of time cycles, each time cycle being defined by an alternation of a high level corresponding to a high level of light intensity of the modulated light signal maintained for a first duration and a low level corresponding to a low level of light intensity of the light signal maintained for a second duration, a total duration of each time cycle being defined from a frequency, the method is characterized in that it comprises the following steps:- determination of at least one pair of frequencies, each pair of frequencies representing a symbol to be emitted;- the frequencies of said at least one determined frequency pair being determined such that, during the modulation of the light signal, a first determined frequency is replaced by a second determined frequency, the higher frequency, among said first and second frequencies, is at most equal to twice the lower frequency, among said first and second frequencies; - generation of the succession of time cycles, the total duration of at least one time cycle being defined from each frequency of each determined frequency pair; - modulation of the light signal by the generated control signal; and - emission of the modulated light signal.

[0015] According to a particular and non-limiting example of an embodiment, the highest frequency among the frequencies of said at least one determined pair of frequencies is at most equal to twice the lowest frequency among the frequencies of said at least one determined pair of frequencies.

[0016] According to a particular and non-limiting example of an embodiment, at least one of the time cycles of the succession of time cycles has a total duration defined from a starting frequency of the emission of said at least one symbol, the starting frequency of the emission of said at least one symbol being determined such that when, during the modulation of the light signal, the starting frequency of the emission of said at least one symbol is replaced by a frequency of one of said at least one determined pair of frequencies, the highest frequency, among the starting frequency of the emission of said at least one symbol and said frequency of said pair of frequencies, is at most equal to twice the lowest frequency, among the starting frequency of the emission of said at least one symbol and said frequency of said pair of frequencies.

[0017] According to a particular and non-limiting example of an embodiment, at least one of the time cycles of the succession of time cycles has a total duration defined from an end-of-emission frequency of said at least one symbol, the end-of-emission frequency of said at least one symbol being determined such that when, during the modulation of the light signal, a frequency of one of said at least one pair of frequencies determined by the end-of-emission frequency of said at least one symbol is replaced, the highest frequency, among the end-of-emission frequency of said at least one symbol and said frequency of said pair of frequencies, is at most equal to twice the lowest frequency, among the end-of-emission frequency of said at least one symbol and said frequency of said pair of frequencies.

[0018] According to a particular and non-limiting example of an embodiment, the highest frequency among the frequencies of said at least one determined pair of frequencies, the start frequency of transmission of said at least one symbol and the end frequency of transmission of said at least one symbol is at most equal to twice the lowest frequency among the frequencies of said at least one determined pair, the start frequency of transmission of said at least one symbol and the end frequency of transmission of said at least one symbol.

[0019] According to a particular and non-limiting example of an embodiment, at least one of the time cycles in the succession of time cycles has a defined duration starting from a determined cutoff frequency such that, during the modulation of the light signal, the cutoff frequency is replaced by a frequency of said at least one determined pair of frequencies or by the emission termination frequency of said at least one symbol, or during the replacement of a frequency of said at least one determined pair of frequencies or the emission start frequency of said at least one symbol by the cutoff frequency, the highest frequency among said frequency of said pair of frequencies, the emission start frequency of said at least one symbol, the emission termination frequency of said at least one symbol, and the cutoff frequency, is at most equal to twice the lowest frequency among said frequency of said pair of frequencies.the transmission start frequency of said at least one symbol, the transmission end frequency of said at least one symbol, and the cutoff frequency.

[0020] According to a particular and non-limiting embodiment, if the frequencies of said at least one determined pair of frequencies, the start-up frequency of said at least one symbol and the end-up frequency of said at least one symbol belong to a set of frequencies whose highest frequency is less than or equal to four times the lowest frequency, the cutoff frequency is defined as a median value between the highest and lowest frequencies of the set of frequencies.

[0021] According to a particular and non-limiting embodiment, the control signal being a gate signal comprising a rising edge and a falling edge per time cycle, a replacement of a determined frequency by another determined frequency is triggered on the rising or falling edges of the time cycles.

[0022] According to a particular and non-limiting example of implementation, each time cycle whose total duration is defined by a frequency is repeated a defined number of times from a frequency of frequency change.

[0023] According to a particular and non-limiting example of implementation, the frequency of frequency change is at most equal to 100Hz.

[0024] According to a particular and non-limiting embodiment example, the frequency of frequency change varies according to lighting conditions of an environment in which the light signal is emitted.

[0025] According to a particular and non-limiting example of implementation, a duty cycle of each time cycle of the control signal is equal to the same value within a deviation around that value.

[0026] According to a second aspect, the present invention relates to a method for receiving at least one symbol carried by a light signal modulated by a control signal, the control signal being formed of a succession of time cycles, each time cycle being defined by an alternation of a high level of light intensity of the light signal maintained for a first duration and a low level of light intensity of the light signal maintained for a second duration, a total duration of each time cycle being defined from a frequency, the method is characterized in that it comprises the following steps:- reception and sampling of the light signal; and- demodulation of the light signal to obtain said at least one symbol, each symbol being represented by a pair of frequencies detected from a spectral analysis of samples of the received light signal;- the detected frequencies of said at least one pair of frequencies being such that when a first detected frequency is replaced by a second detected frequency during the demodulation of the light signal, the highest frequency, among said first and second detected frequencies, is at most equal to twice the lowest frequency, among said first and second detected frequencies.;

[0027] According to a particular and non-limiting example of an embodiment, the highest frequency among the detected frequencies of said at least one pair of frequencies is at most equal to twice the lowest frequency among the detected frequencies of said at least one pair of frequencies.

[0028] According to a particular and non-limiting example of an embodiment, the method further comprises a step of detecting a reception start frequency of said at least one symbol from a frequency spectrum of the light signal determined from a first set of samples of the received light signal, the detection of the reception start frequency of said at least one symbol preceding the detection of a first frequency of a first pair of frequencies representing a first symbol to be received.

[0029] According to a particular and non-limiting example of an embodiment, the method further comprises a step of detecting an end-of-reception frequency of said at least one symbol from a frequency spectrum of the light signal determined from a second set of samples of the received light signal, the detection of the end-of-reception frequency of said at least one symbol following the detection of a second frequency of a pair of frequencies representing a last symbol to be received.

[0030] According to a particular and non-limiting example of an embodiment, the detected frequencies of said at least one pair of frequencies, the reception start frequency of said at least one detected symbol and the reception end frequency of said at least one detected symbol belong to a set of frequencies whose highest frequency is at most equal to twice the lowest frequency of the set of frequencies.

[0031] According to a particular and non-limiting example of an embodiment, the method further comprises a step of detecting a cutoff frequency from a frequency spectrum determined from a fifth set of samples of the received light signal, the cutoff frequency being defined as a median value between the highest and lowest frequencies of the set of frequencies, the highest frequency of the set of frequencies being at most equal to four times the lowest frequency of the set of frequencies, the cutoff frequency being detected following the detection of each frequency of each pair of frequencies, the detection of the start frequency of reception of said at least one symbol and the detection of the end frequency of reception of said at least one symbol.

[0032] According to a particular and non-limiting embodiment example, the frequencies of the frequency set are less than 5kHz.

[0033] According to a particular and non-limiting example of embodiment, said at least one symbol is determined from a table defining an association between each symbol and a pair of frequencies.

[0034] According to a third aspect, the present invention relates to a light signal emitting device comprising a microcontroller configured for the implementation of the steps of the process according to the first aspect of the present invention.

[0035] According to a fourth aspect, the present invention relates to a light signal receiving device comprising a microcontroller configured for the implementation of the steps of the process according to the second aspect of the present invention.

[0036] According to a fifth aspect, the present invention relates to a computer program which includes instructions adapted for carrying out the steps of the process according to the first and / or the second aspect of the present invention, in particular when the computer program is executed by at least one processor.

[0037] Such a computer program can use any programming language, and be in the form of source code, object code, or an intermediate form between source code and object code, such as in a partially compiled form, or in any other desirable form.

[0038] According to a sixth aspect, the present invention relates to a computer-readable recording medium on which is recorded a computer program comprising instructions for carrying out the steps of the process according to the first and / or second aspect of the present invention.

[0039] On the one hand, the recording medium can be any entity or device capable of storing the program. For example, the medium can include a storage means, such as ROM, RAM, CD-ROM or microelectronic circuit-type ROM, or a magnetic recording means or a hard drive.

[0040] On the other hand, this recording medium can also be a transmissible medium such as an electrical or optical signal, such a signal being able to be transmitted via an electrical or optical cable, by conventional or radio frequency, by self-directing laser beam, or by other means. The computer program according to the present invention can, in particular, be downloaded from a network such as the Internet.

[0041] Alternatively, the recording medium may be an integrated circuit in which the computer program is incorporated, the integrated circuit being adapted to execute or to be used in the execution of the process in question. Brief description of the figures

[0042] Other features and advantages of the present invention will become apparent from the description of the specific and non-limiting embodiments of the present invention below, with reference to the attached Figures 1 to 22, in which:

[0043] illustrates a flowchart of the different stages of a process for emitting at least one symbol carried by a light signal modulated by a control signal, according to a particular embodiment of the present invention.

[0044] schematically illustrates an example of the time evolution of the control signal used to control the modulation of a light signal according to a particular and non-limiting embodiment of the present invention.

[0045] schematically illustrates an example of the time evolution of the control signal used to control the modulation of a light signal when a first frequency, replaced by a second frequency during the modulation of the light signal, is equal to twice the second frequency according to a particular and non-limiting embodiment of the present invention.

[0046] schematically illustrates an example of the time evolution of the control signal used to control the modulation of a light signal when a first frequency, replaced by a second frequency during the modulation of the light signal, is greater than a second frequency according to a particular and non-limiting embodiment of the present invention.

[0047] schematically illustrates an example of the time evolution of a control signal used to control the modulation of a light signal when the first frequency, replaced by a second frequency during the modulation of the light signal, is lower than the second frequency according to a particular and non-limiting embodiment of the present invention.

[0048] schematically illustrates step 120 of control signal generation according to a particular and non-limiting embodiment of the present invention.

[0049] schematically illustrates an example of the time evolution of the control signal used to control the modulation of the light signal according to a particular and non-limiting embodiment of the present invention.

[0050] illustrates a schematic example of the time evolution of the control signal used to control the modulation of a light signal according to a particular and non-limiting embodiment of the present invention.

[0051] illustrates a schematic example of the time evolution of the control signal used to control the modulation of a light signal according to a particular and non-limiting embodiment of the present invention.

[0052] illustrates a schematic example of the time evolution of the control signal used to control the modulation of a light signal according to a particular and non-limiting embodiment of the present invention.

[0053] illustrates a schematic example of the time evolution of the control signal used to control the modulation of a light signal according to a particular and non-limiting embodiment of the present invention.

[0054] illustrates examples of PWM signals with duty cycles ranging from 0% (zero light intensity level) to 100% (maximum light intensity level).

[0055] illustrates an example of a PWM signal with a constant duty cycle of 50%.

[0056] illustrates a flowchart of the different stages of a process for receiving at least one symbol carried by a light signal modulated by a control signal, according to a particular embodiment of the present invention.

[0057] illustrates a flowchart of the sub-steps of the 220 demodulation step of the light signal for the reception of at least one symbol, according to a particular embodiment of the present invention.

[0058] illustrates an example of steps 2210, 2220, 2240, 2250 and 2260 of step 220 of light signal demodulation, according to a particular embodiment of the present invention.

[0059] illustrates an example of a frequency spectrum obtained from a discrete Fourier transform spectral analysis of a set of samples.

[0060] illustrates an example of updating the scores associated with the frequencies of the frequency set from three spectra determined from three consecutive sets of samples, according to a particular and non-limiting embodiment of the present invention.

[0061] illustrates an example of a base 64 table that groups 64 associations between symbols and pairs of frequencies, according to a particular and non-limiting embodiment of the present invention.

[0062] schematically illustrates a device 1 configured to emit and / or receive at least one symbol carried by a light signal modulated by a control signal, according to a particular and non-limiting embodiment of the present invention.

[0063] schematically illustrates an implementation of the device 2 for emitting light signals configured to emit at least one symbol carried by a light signal modulated by the control signal according to a particular and non-limiting example of the present invention.

[0064] schematically illustrates an implementation of the light signal reception device 3 configured to receive at least one symbol carried by a light signal modulated by the control signal 100 according to a particular and non-limiting example of the present invention. Description of examples of achievements

[0065] Methods and devices for emitting and receiving at least one symbol carried by a light signal modulated by a control signal will now be described in what follows with joint reference to figures 1 to 22. The same elements are identified with the same reference signs throughout the description that follows.

[0066] The terms "first(s)", "second(s)" (or "first(s)", "second(s)"), etc. are used in this document by arbitrary convention to allow identification and distinction of different elements (such as operations, means, frequency pairs, etc.) implemented in the embodiments described below.

[0067] Subsequently, a light signal is a signal that can belong to the visible spectrum or the infrared spectrum.

[0068] Infrared light (infrared spectrum) is classified into 3 groups:

[0069] -Near Infrared (NIR): This band covers wavelengths from 0.75 to 1.4 micrometers (750 to 1400 nanometers). Typical applications include remote sensing, fiber optic communication, and certain forms of medical imaging;

[0070] -Mid-infrared (MIR): Wavelengths in this band range from 1.4 to 3 micrometers (1400 to 3000 nanometers). MIR is used in various applications such as spectroscopy for chemical analysis and gas detection, as well as in certain heating technologies.

[0071] -Far Infrared (FIR): This band extends from 3 micrometers to approximately 1000 micrometers (3000 nanometers to 1 millimeter), although the precise classification may vary. FIR is primarily used for heating applications and certain types of remote sensing and thermal imaging.

[0072] For example, light signals may belong to the near-infrared frequency band, in the 750-950 nm range, with a peak at 850 nm.

[0073] The present invention relates to a method for emitting a light signal by a light signal emitting device and a method for receiving the light signal by a light signal receiving device. The light signal is modulated / demodulated to emit / receive at least one symbol between the light signal emitting / receiving devices. The modulation of the light signal is implemented by a modulation method controlled by a PWM-type control signal, and the demodulation is implemented by a demodulation method.

[0074] The modulation and demodulation methods according to the present invention make it possible to transmit a light signal between a light signal emitting device and a light signal receiving device without generating visible flickering (when these light signals belong to the visible spectrum) for a user and without causing premature aging of the emitting and receiving devices.

[0075] The modulation and demodulation processes according to the present invention make it possible to optimize the energy efficiency and lifespan of light signal emitting and receiving devices.

[0076] The modulation and demodulation methods according to the present invention use low frequencies (well below 1 MHz and close to 2 kHz) which optimize the efficiency of both the light signal transmitter and receiver devices, allowing lighting equipment to operate at its nominal capacity and thus preserving its lifespan. The transmission duration of the light signals modulated by these low frequencies improves the probability of correctly reading each frequency used for modulating the emitted light signals.

[0077] Laillustre un flowchart des différents étapes d’un processus d’émission d’at least un symbole porté par un signal lumière modulated par un signal control 100, selon une exemple d’incarnation particulier de la présent invention.

[0078] In step 110, a pair of frequencies (F 1, s F2 , s ) is determined for each symbol s y to be emitted. At least one pair of frequencies is determined, as many as there are symbols to be emitted.

[0079] The frequencies of said at least one pair of frequencies are constrained to be determined so that when, during the modulation of the light signal, a first determined frequency is replaced by a second determined frequency, the highest frequency, among said first and second frequencies, is at most equal to twice the lowest frequency, among said first and second frequencies.

[0080] This constraint on the frequencies of at least one determined frequency pair ensures that during a frequency change in the modulation of the light signal, the ratio of the lower of the two frequencies involved in this change to the higher of those two frequencies is at least 50%. For example, if a first frequency F1 is higher than a second frequency F2, then the ratio F2 / F1 is at least 50%. If the second frequency F2 is higher than the first frequency F1, then the ratio F1 / F2 is at least 50%.

[0081] For example, F1 = 2kHz and F2 = 3.5kHz to respect this constraint on frequencies.

[0082] Respecting the constraint on the frequencies of said at least one pair of frequencies avoids the appearance of a visible flickering effect of the modulated light signal (when this light signal belongs to the visible spectrum).

[0083] The first and second frequencies can be frequencies of the same frequency pair, that is, the first frequency can be frequency F 1,s y and the second frequency might be the frequency F 2,s of a frequency cut (F 1,s y F 2,s y But a first frequency can also be the frequency F 2,s y 1 of a pair of frequencies (F 1,s y 1 F 2,s y 1) representing a symbol s y 1 and the second frequency may be the frequency F 1,s y 2d'another pair of frequencies representing a symbol s y 2.

[0084] In step 120, the control signal 100 is generated. The generated control signal 100 comprises a succession of time cycles. The total duration of at least one time cycle is defined from each frequency of each determined frequency pair.

[0085] In step 130, the light signal is modulated by the generated control signal 100.

[0086] In step 140, the modulated light signal is emitted.

[0087] Laillust schematically illustrates an example of the time evolution of the control signal 100 used to control the modulation of the light signal according to a particular and non-limiting embodiment of the present invention.

[0088] The control signal 100 is of the PWM type. A PWM signal is a gate signal consisting of a succession of time cycles. Each time cycle is defined by an alternation of a high level, corresponding to a high intensity level of the light signal (the "on" light signal), maintained for a first duration 101, and a low level, corresponding to a low intensity level of the light signal (the "off" light signal), maintained for a second duration 102. A total duration 103 of each time cycle is defined from a frequency F i The total duration of a time cycle is equal to the inverse of a frequency.

[0089] The light signal is modulated by the control signal 100 (step 130). For this purpose, the light signal is at a high level of light intensity (“on”) when the control signal 100 is at a high level and at a low level of light intensity (“off”) when the control signal 100 is at a low level.

[0090] According to a particular and non-limiting embodiment of the present invention, the time cycle of duration 10³ can be repeated several times. The number of repetitions is defined by the inverse of a frequency change rate.

[0091] For example, the frequency change frequency is at least equal to 100Hz to ensure a frequency change speed of less than 10 ms and thus avoid the appearance of visible flickering of the light signal (when this light signal belongs to the visible spectrum).

[0092] The repetition of the time cycle increases the reliability of demodulation of the modulated light signal.

[0093] Furthermore, excessively slow frequency changes can impact the lighting level. Additionally, a change frequency below 100 Hz induces visible flickering of the modulated light signal (when this light signal belongs to the visible spectrum).

[0094] According to a particular and non-limiting embodiment of the present invention, the frequency of frequency change can vary depending on the lighting conditions of an environment in which the light signal is emitted.

[0095] For example, the lower the lighting conditions, e.g., the lighting conditions in the immediate environment of the light signal emitting device indicate low brightness, and the higher the number of repetitions, i.e., the lower the frequency of frequency changes.

[0096] For example, the frequency of frequency changes varies proportionally to the ambient brightness of the light signal emitting device.

[0097] For example, if the frequency change is 1 / 3, then the time cycle, with a total duration of 10³, is repeated three times. The light signal modulated by the control signal 100 flashes according to the frequency F. i for a duration of 104. Another frequency F j can then replace the frequency F i so that the light signal flashes according to the frequency F j The frequencies F i and F j can be equal or different.

[0098] Laillustrate schematically an example of time evolution of the control signal 100 used to control the modulation of a light signal when a first frequency F1, replaced by a second frequency F2 during the modulation of the light signal, is equal to twice the second frequency F2 according to a particular and non-limiting embodiment of the present invention.

[0099] The control signal 100 is described here with a frequency change frequency of 1 / 3, that is to say that a first time cycle of duration 1031 defined from the first frequency F1 is repeated three times (total duration 1041) and a second time cycle of duration 1032 defined from the second frequency F2 is repeated three times (duration 1042).

[0100] According to this example, the first frequency F1 is equal to twice the second frequency F2, i.e. F1=2*F2, and the duration 1032 is equal to twice the duration 1031. The duration 1042 is equal to twice the duration 1041. The ratio F2 / F1 = 50%, which verifies the constraint on the frequencies F1 and F2 that prevents a visible flicker of the light signal (when this light signal belongs to the visible spectrum).

[0101] Laillustrate schematically an example of time evolution of the control signal 100 used to control the modulation of a light signal when a first frequency F1, replaced by a second frequency F2 during the modulation of the light signal, is greater than a second frequency F2 according to a particular and non-limiting embodiment of the present invention.

[0102] The control signal 100 is described here with a frequency change frequency of 1 / 3, i.e. a first time cycle of duration 1031 defined from the first frequency F1 is repeated three times (total duration 1041) and a second time cycle of duration 1032 defined from the second frequency F2 is repeated three times (duration 1042).

[0103] According to this example, for the constraint on frequencies F1 and F2 to be verified, the first frequency F1 must be less than twice the second frequency F2, i.e. F1 < 2 * F2, and the duration 1032 is then less than twice the duration 1031. The duration 1042 is less than twice the duration 1041. The ratio F2 / F1 > 50%, which verifies the constraint on frequencies F1 and F2, preventing visible flickering of the light signal (when this light signal belongs to the visible spectrum).

[0104] The illustration schematically shows an example of the time evolution of a control signal used to control the modulation of a light signal when the first frequency F1, replaced by a second frequency F2 during the modulation of the light signal, is lower than the second frequency F2 according to a particular and non-limiting embodiment of the present invention.

[0105] The control signal 100 is described here with a frequency change frequency of 1 / 3, that is to say that a first time cycle of duration 1031 defined from the first frequency F1 is repeated three times (total duration 1041) and a second time cycle of duration 1032 defined from the second frequency F2 is repeated three times (duration 1042).

[0106] According to this example, for the constraint on frequencies F1 and F2 to be verified, the second frequency F2 of the frequency pair must be less than twice the first frequency F1, i.e. F2 < 2 * F1, and the duration 1031 is then less than twice the duration 1032. The duration 1041 is less than twice the duration 1042. The ratio F1 / F2 > 50%, which verifies the constraint on frequencies F1 and F2, preventing visible flickering of the light signal (when this light signal belongs to the visible spectrum).

[0107] The diagram schematically illustrates step 120 of the generation of the control signal 100 according to a particular and non-limiting embodiment example of the present invention.

[0108] The control signal 100 comprises a succession of time cycles.

[0109] Step 120 is an iterative step which includes sub-steps 1210-1230.

[0110] In substep 1210, one of said at least one pair of frequencies (F1s y , F2 s y ) determined in step 110 is considered.

[0111] In substep 1220, at least one first time cycle s1 followed by at least one second time cycle s2 are added to the sequence of time cycles of the control signal 100. Each first time cycle s1 has a total duration (1031) defined from the first frequency F1 s y of the frequency pair (F1 s y , F2 s y ) considered. Each second time cycle s2 has a total duration of 1032 defined from the second frequency F2 s y of the frequency pair (F1 s y , F2 s y ) considered. Step 1220 ends when each pair of frequencies (F 1s y , F 2s y ) determined was considered (substep 1230).

[0112] The number of first time cycles s1 is defined from the frequency of frequency change and the number of second time cycles s2 is defined from the frequency of frequency change.

[0113] Laillust schematically illustrates an example of the time evolution of the control signal 100 used to control the modulation of the light signal according to a particular and non-limiting embodiment of the present invention.

[0114] According to this example, a pair of frequencies is determined to emit a symbol with a frequency change frequency equal to 1 / 3. The succession of time cycles of the control signal 100 then comprises three first time cycles s1 followed by three second time cycles s2.

[0115] According to a particular and non-limiting example of substep 1220, illustrated in the figure, at least one third time cycle s3 may be added to the succession of time cycles of the control signal 100. Said at least one third time cycle s3 precedes said at least one first time cycle s1 of the succession of time cycles of the control signal 100.

[0116] According to the example above, if a symbol s y is emitted with a change frequency equal to 1 / 3, the succession of time cycles of the control signal 100 comprises 3 third time cycles s 3suivis de 3 premiers cycles temporels s1dont la durée totale (1031) est déterminée à partir de la fréquence F1sydu couple de fréquence (F1sy, F2sy) représentant le symbole syà émettre (ou le premier symbole si plusieurs symboles sont à émettre), suivis de 3 deuxièmes cycles temporels s2dont la durée totale (1032) est déterminée à partir de la fréquence F2sydu couple de fréquence (F1sy, F2sy).

[0117] Each third time cycle s3a has a total duration of 1033 defined from a starting frequency F s emission of at least one symbol. The starting frequency F s is determined so that during a replacement, during the modulation of the light signal (step 130), of the starting frequency F sby a frequency of a determined pair of frequencies, the highest frequency, among said frequency of said pair of frequencies and the starting frequency F s , is at most equal to twice the lowest frequency, among said frequency of said determined frequency pair and the starting frequency F s The number of the third time cycle s3 is defined from the frequency of frequency change.

[0118] According to this last particular and non-limiting example of substep 1220, at least one of the time cycles in the succession of time cycles can have a total duration defined from the starting frequency F s .

[0119] The time sequence of frequencies used for modulating the light signal is then given by [F s ][F 1s y ][F 2s y ].

[0120] According to a particular and non-limiting embodiment of substep 1220, illustrated in Figure 1, at least one fourth time cycle s4 may be added to the sequence of time cycles of the control signal 100. Said at least one fourth time cycle s4 follows the last of said at least one second time cycle s2 of the sequence of time cycles of the control signal 100, the total duration of which 1032 is a function of the second frequency F 2s of the frequency couple (F 1s , F 2s ) representing the last symbol issued.

[0121] According to the example above, if a symbol s y is emitted with a change frequency equal to 1 / 3, the succession of time cycles of the control signal 100 comprises the first 3 time cycles s1 whose total duration (1031) is determined from the frequency F 1s y of the frequency pair (F 1s y , F 2s y ) representing the symbol s yto be emitted, followed by 3 second time cycles s2 whose total duration (1032) is determined from the frequency F 2s1 of the frequency couple (F 1s1 , F 2s1 ) followed by 3 temporal cycles s4.

[0122] Each fourth time cycle s4a has a total duration of 1034 defined from an end frequency F e of emission of at least one symbol. The end frequency F e The emission frequency of at least one symbol is determined so that, during the modulation of the light signal (step 130), a frequency of a pair of frequencies is replaced by the end frequency F e , the highest frequency, among said frequency of said frequency pair and the end frequency F e , is at most equal to twice the lowest frequency, among said frequency of said frequency pair and the end frequency F eThe fourth time cycle number s4 is defined from the frequency of frequency change.

[0123] According to this last particular and non-limiting example of substep 1220, at least one of the time cycles in the succession of time cycles can have a total duration defined from the end frequency F e .

[0124] The time sequence of frequencies used for modulating the light signal is then given by [F 1s y ][F 2s y ] [F e ].

[0125] Laillustre un example de schematicement un example de temps évolution du signal de contrôle 100 utile pour contrôle de modulation du signal lumière selon une example d’incarnation particulier et non limite de la présent invention.

[0126] According to this example, the succession of time cycles of the control signal 100 comprises the first, second, third, and fourth time cycles described above. The control signal 100 is described here with a frequency change frequency of 1 / 3, i.e., each time cycle is repeated three times. The time sequence of frequencies used for modulating the light signal is then given by [F s ] [F 1s y ][F 2s y ] [F e ].

[0127] According to a particular and non-limiting embodiment of the present invention, the highest frequency among the frequencies of said at least one determined pair of frequencies is at most equal to twice the lowest frequency among the frequencies of said at least one determined pair of frequencies.

[0128] This example of implementation ensures that the constraint on frequencies is verified regardless of changes between the frequencies of said at least one determined frequency pair during the modulation of the light signal.

[0129] According to a particular and non-limiting embodiment of the present invention, the highest frequency among the frequencies of said at least one determined pair of frequencies and the starting frequency F s is at most equal to twice the lowest frequency among the frequencies of said at least one determined pair of frequencies and the starting frequency F s .

[0130] This example implementation ensures that the frequency constraint is satisfied regardless of changes between the frequencies of at least one determined frequency pair and between the frequencies of at least one determined frequency pair and the starting frequency F s .

[0131] According to a particular and non-limiting embodiment of the present invention, the highest frequency among the frequencies of said at least one determined couple and the end frequency F e is at most equal to twice the lowest frequency among the frequencies of said at least one determined pair and the end frequency F e .

[0132] This example implementation ensures that the frequency constraint is satisfied regardless of changes between the frequencies of said at least one determined frequency pair and between said at least one determined frequency pair and the end frequency F e during the modulation of the light signal.

[0133] According to a particular and non-limiting embodiment of the present invention, the highest frequency among the frequencies of said at least one determined couple, the starting frequency F s and the end frequency Fe is at most equal to twice the lowest frequency among the frequencies of said at least one determined pair, the starting frequency F s and the end frequency F e .

[0134] This example implementation ensures that the frequency constraint is satisfied regardless of changes between the frequencies of at least one determined frequency pair and between the frequencies of at least one determined frequency pair, the starting frequency F s and the end frequency F e during the modulation of the light signal.

[0135] According to a particular and non-limiting embodiment of substep 1220, at least one fifth time cycle s5 is added to the sequence of time cycles of the control signal 100 following the last of each series of at least one time cycle in the sequence of time cycles whose duration is determined from a specified frequency. The number of fifth time cycles s5 is defined from the frequency of frequency change.

[0136] If the succession of time cycles of the control signal 100 also includes at least a third time cycle s 3, the succession of time cycles of the control signal 100 may further include at least a fifth time cycle s5, said at least a fifth time cycle s5 being following the last of said at least a third time cycle s3.

[0137] If the succession of time cycles of the control signal 100 also includes at least a fourth time cycle s 4, the control signal 100 may further include at least one fifth time cycle s5, said at least one fifth time cycle s5 being following the last of said at least one fourth time cycle s4.

[0138] Laillust schematically illustrates an example of the time evolution of the control signal 100 used to control the modulation of a light signal according to a particular and non-limiting embodiment of the present invention.

[0139] According to the example above, a symbol s y emitted with a change frequency of 1, the succession of time cycles of the control signal 100 comprises a third time cycle s3 (last time cycle of a series of 1 third time cycles s3) followed by a fifth time cycle s5 followed by a first time cycle s 1(dernier cycle temporel d’une série de 1 premier cycle temporel s1) suivi d’un cinquième cycle temporel s5suivi d’un deuxième cycle temporel s2(dernier cycle temporel d’une série de 1 deuxième cycle temporel s2) suivi d’un cinquième cycle temporel s5suivi d’un quatrième cycle temporel s4(dernier cycle temporel d’une série de 1 quatrième cycle temporel s4) suivie d’un cinquième cycle temporel s5.

[0140] Each fifth time cycle s5a has a total duration of 1035 defined from a cutoff frequency F c The cutoff frequency F c is determined so that during a replacement, during the modulation of the light signal (step 130), of the cutoff frequency F c by a frequency of a determined pair of frequencies or by the end frequency F e or during a replacement of a frequency of a determined pair of frequencies or the starting frequency F s by the cutoff frequency F c , the highest frequency, among said frequency of said pair of frequencies, the starting frequency F s , the end frequency F e and the cutoff frequency F c , is at most equal to twice the lowest frequency, among said frequency of said frequency pair, the starting frequency F s , the end frequency F e and the cutoff frequency F c .

[0141] According to this last particular and non-limiting example of substep 1220, at least one of the time cycles in the succession of time cycles can have a total duration defined from the cutoff frequency F c .

[0142] According to the example above, the time sequence of frequencies used for modulating the light signal is then given by [F s ] [F c ] [F 1s y ] [F c ] [F 2s y ] [F c ][F e ][F c ].

[0143] According to a particular embodiment and limiting my statement of the present invention, if the frequencies of said at least a determined pair of frequencies, the starting frequency F s and the end frequency F ebelong to a set F of frequencies whose highest frequency is less than or equal to four times the lowest frequency, the cutoff frequency is defined as a median value between the highest and lowest frequencies of the set F of frequencies.

[0144] The use of the cutoff frequency F c is advantageous because it allows increasing the difference between the lowest and highest frequencies among the frequencies of said at least one determined range of frequencies, the starting frequency F s and the end frequency F e .

[0145] Indeed, to prevent a visible flicker from appearing (when the light signal belongs to the visible spectrum) during a frequency replacement during the modulation of the light signal, at least a fifth time cycle s5 is added in the succession of time cycles of the control signal 100 between each series of time cycles s1, s2, s3, s4.

[0146] Thus, the replacement of a first frequency of a determined frequency pair during the modulation of the light signal (belonging to the visible spectrum) by the cutoff frequency F c then the replacement of the cutoff frequency F cBy using a second frequency within the frequency pair, the frequency constraint is checked and a visible flicker of the light signal is avoided, which would occur if the first frequency were replaced by the second frequency without passing through the cutoff frequency. The same applies to any other frequency change, particularly that of the start frequency F. s of emission of said at least one symbol by a frequency of a pair of frequencies or that of a frequency of a pair of frequencies by the end frequency F e .

[0147] The light intensity of a PWM-modulated light signal varies according to a duty cycle defined by the ratio of the duration of a high level of the PWM signal to the duration of a low level of the PWM signal.

[0148] The illustration shows examples of PWM signals with a period of pPWM and duty cycles (DC) ranging from 0% (light intensity level read) to 100% (maximum light intensity level). The dotted line on the illustration represents a resulting light intensity level.

[0149] According to a particular and non-limiting embodiment of the present invention, the duty cycle can be at most equal to 85%.

[0150] This particular embodiment prevents the equipment from being subjected to excessive stress and the risk of overheating. For example, if the highest frequency in the set F of frequencies is 5 kHz, the duration of each time cycle will not exceed 30 ms, thus preventing the light signal emitter and receiver devices implementing the present invention from overheating.

[0151] According to a particular and non-limiting embodiment of the present invention, the duty cycle can be at least equal to 15%.

[0152] This example is advantageous because it guarantees that the light signal receiving device receives enough light to demodulate that light signal.

[0153] According to a particular and non-limiting embodiment of the present invention, the duty cycle of each time cycle of the control signal 100 can be equal to the same value within a deviation around this value, i.e. that this duty cycle is quasi-constant.

[0154] Figure 1 illustrates an example of a PWM signal with a constant duty cycle of 50% for frequencies of 3 kHz and 4 kHz. The PWM signal is a gate signal comprising rising and falling edges. In Figure 1, the rising edges are marked by dots.

[0155] Maintaining a constant duty cycle avoids effects of variation in light intensity, and therefore visible flickering (when the light signal belongs to the visible spectrum).

[0156] According to a particular and non-limiting embodiment of the present invention, the frequency change can be triggered synchronously with a rising or falling edge of the control signal 100.

[0157] This example makes it possible to keep the duty cycle constant and to avoid the appearance of visible flickering of the modulated light signal (when this light signal belongs to the visible spectrum).

[0158] Laillustre un flowchart des différents étapes d’un processus de recevoir d’at least un symbole porté par un signal lumière modulated par le signal de contrôle 100, selon une exemple d’incarnation particulier de la présent invention.

[0159] The light intensity of the light signal is modulated by a control signal 100 consisting of a succession of time cycles. Each time cycle is defined by an alternation between a high level, corresponding to a high level of light intensity of the light signal (the "on" signal), maintained for a first duration, and a low level, corresponding to a low level of light intensity of the light signal (the "off" signal), maintained for a second duration. The total duration of each time cycle is defined from a frequency within a set F of frequencies. For example, the modulation of the light signal is controlled by the control signal 100 generated by the process of...

[0160] In step 210, the light signal is received and sampled according to a sampling frequency.

[0161] For example, the received light signal is sampled at a frequency of 44kHz.

[0162] In a step 220, the light signal is demodulated to obtain said at least one symbol, each symbol being represented by a pair of frequencies detected from a spectral analysis of samples of the received light signal.

[0163] The detected frequencies of said at least one pair of frequencies comply with the constraint on the frequencies described above, that is to say that when a first detected frequency is replaced by a second detected frequency during the demodulation of the light signal, the highest frequency, among said first and second detected frequencies, is at most equal to twice the lowest frequency, among said first and second detected frequencies.

[0164] According to a particular and non-limiting embodiment of the present invention, the highest frequency among the detected frequencies of said at least one pair of frequencies is at most equal to twice the lowest frequency among the detected frequencies of said at least one pair of frequencies.

[0165] Laillustre un flowchart des sous-steps demodulation step 220 de signal lumière pour le réception du moins un symbole, selon une exemple d'incarnation particulier de la présent invention.

[0166] Step 220 is an iterative step. At each iteration, a symbol s y is obtained by executing substeps 2210-2260.

[0167] In sub-step 2210, a first frequency F1 ,s y is detected from a frequency spectrum of the light signal determined from a set E1d'samples of the received light signal.

[0168] In sub-step 2220, a second frequency F2 ,s y is detected from a frequency spectrum of the light signal determined from a set E2d'samples of the received light signal.

[0169] In substep 2230, the symbol s y is determined from the frequency pair (F 1,s y , F 2,s y ) detected.

[0170] The first frequency F 1,s y and the second frequency F 2,s y detected from the frequency pair (F 1,s y , F 2,s y ) comply with the frequency constraint described above.

[0171] According to a particular and non-limiting embodiment of the present invention, in substep 2240, a starting frequency F sof reception of said at least one symbol can be detected from a frequency spectrum of the light signal determined from a set E3 of samples of the received light signal, the detection of the starting frequency F s preceding the detection of a first frequency of a first pair of frequencies representing a first symbol to be received.

[0172] Detection of the starting frequency F s indicates the start of the demodulation process of the received light signal for the reception of at least one symbol.

[0173] According to a particular and non-limiting embodiment of the present invention, in a substep 2250, a termination frequency F e The reception of said symbol, at least one symbol, can be detected from a frequency spectrum of the light signal determined from a set E4 of samples of the received light signal, the detection of the end frequency F efollowing the detection of a second frequency of a pair of frequencies representing a final symbol to be received.

[0174] The detection of the end frequency F e indicates that the last symbol to be received has been received.

[0175] According to a particular and non-limiting embodiment of the present invention, the detected frequencies of said at least one pair of frequencies, the starting frequency F s detected and the end frequency F e detected can belong to a set F of frequencies whose highest frequency is at most equal to twice the lowest frequency of the set F of frequencies.

[0176] For example, the frequency set F includes frequencies ranging from 2kHz to 4kHz.

[0177] According to a particular and non-limiting embodiment of the present invention, in a substep 2260, a cutoff frequency F ccan be detected from a frequency spectrum determined from a set E5 of samples of the received light signal, the cutoff frequency F c can be defined as a median value between the highest and lowest frequencies of the set F of frequencies, the highest frequency of the set F of frequencies being at most equal to four times the lowest frequency of the set F of frequencies, the cutoff frequency F c being detected following the detection of each frequency of each pair of frequencies.

[0178] According to one variant, the cutoff frequency F c can also be detected following the detection of the starting frequency F s .

[0179] According to one variant, the cutoff frequency F c can also be detected following the detection of the end frequency F e .

[0180] The use of the cutoff frequency F c is advantageous because it allows increasing the amplitude of the entire frequency range F compared to the previous implementation example which does not use a cutoff frequency F c .

[0181] For example, the frequency set F includes frequencies that can range from 2kHz to 8kHz.

[0182] Furthermore, the use of the cutoff frequency F c This allows the received light signal to be demodulated without needing to know a parameter of the modulation process, because the cessation of score updates, described later, is determined by the time interval between the detection of two consecutive cutoff frequencies. This time interval can vary depending on, for example, the lighting conditions in the environment of the light signal emitter.

[0183] According to a particular and non-limiting embodiment of the present invention, the frequencies of the set F of frequencies are less than 5kHz.

[0184] For example, the frequency set F includes frequencies ranging from 2kHz to 5kHz and the median frequency F c is equal to 3.5kHz.

[0185] According to a particular and non-limiting embodiment of the present invention, the detection of a frequency (step 2210, 2220, 2240, 2250 and 2260) from a frequency spectrum of the light signal determined from a set of samples may include steps 2270 and 2280.

[0186] Laillustre an example of steps 2210, 2220, 2240, 2250 and 2260 of step 220 of light signal demodulation, according to a particular embodiment of the present invention.

[0187] Steps 2210, 2220, 2240, 2250 and 2260 each detect a frequency F r (first frequency F1,s , second frequency F2 ,s , starting frequency F s , end frequency F e , cutoff frequency F c ) from a set of samples E i (i=1 to 5).

[0188] In step 2270, SCi scores associated with the frequencies of the frequency set F are evaluated from the amplitudes of the corresponding frequencies of the frequency spectrum determined from the sample set E i .

[0189] According to a particular and non-limiting embodiment of the present invention, step 2270 comprises substeps 2271 to 2273.

[0190] In substep 2271, a frequency spectrum SPi of the light signal is determined from continuously received samples of the light signal. This means that spectral analysis is performed over a sliding time window so that the frequency spectrum is updated as new samples of the light signal become available. Thus, the first set E1(i=1) of available samples is formed (for example, the first 128 samples), and a frequency spectrum of the light signal is determined. At least one new sample becomes available, and the second set of samples E2(i=2) is formed from this at least one new sample and, possibly, from at least one sample from the first set E1. At least one new sample becomes available, and the third set E3(i=3) of samples is formed from this at least one new sample and, possibly, from at least one sample from the second set E2, and so on.

[0191] For example, each sample set comprises 128 samples (N=128).

[0192] According to a particular and non-limiting embodiment of the present invention, a frequency spectrum of the light signal is determined by applying a discrete Fourier transform to samples of a set of samples of the received light signal.

[0193] To do this, N samples x(n) (n=0,…, N-1) of the received light signal are defined on the sliding time window of duration T=N*Te with Fe=1 / Te. N points S(k) of the frequency spectrum are then determined on this time window of duration T by applying the discrete Fourier transform, each of these points S(k) corresponding to a particular frequency and amplitude of a frequency component of the frequency spectrum:

[0194]

[0195] Laillustre an example of a frequency spectrum SPi determined by discrete Fourier transform of a set of samples E i The frequency spectrum is represented in a two-dimensional space where the x-axis represents the frequencies composing this frequency spectrum and the y-axis represents the amplitudes corresponding to these frequencies. In the example, the frequency spectrum SP1 is determined from N=11 samples.

[0196] In substep 2272, the SCi scores associated with the frequencies of the F set of frequencies are initialized, for example to 0.

[0197] In substep 2273, the SCi score of each frequency in the frequency set F is updated from the frequency amplitudes of at least one SPi frequency spectrum determined from at least one sample set E i .

[0198] This illustrates an example of updating the SCi scores associated with the frequencies of the set F of frequencies from three SPi spectra determined from three sets E i of consecutive samples according to a particular and non-limiting embodiment of the present invention.

[0199] According to the example, the set F of frequencies comprises three frequencies F1, F C and F2. At a), the SC1 score associated with the frequency F1 is updated from the amplitude a1 of the first of the three frequency spectra, the SC score c of the cutoff frequency F c is updated from the amplitude a cThe SC2 score for frequency F2 is updated from the amplitude a2 of the first of the three frequency spectra. In lab), the SC1 score associated with frequency F1 is updated from the amplitude corresponding to frequency F1 of the second of the three frequency spectra. c of the cutoff frequency F c is updated from the amplitude a c corresponding to the cutoff frequency F c The second of the three frequency spectra and the SC2 score of frequency F2 is updated from the amplitude a2 corresponding to frequency F2 of the second of the three frequency spectra. At lac), the SC1 score associated with frequency F1 is updated from the amplitude corresponding to frequency F1 of the third of the three frequency spectra, the SC score c of the cutoff frequency F c is updated from the amplitude a ccorresponding to the cutoff frequency F c of the third of the three frequency spectra and the SC2 score of the frequency F2 is updated from the amplitude a2 corresponding to the frequency F2 of the third of the three frequency spectra.

[0200] As an example, an SCi score associated with a frequency from the F set of frequencies is updated from a frequency spectrum by adding the amplitude of that frequency from the frequency spectrum.

[0201] According to a particular and non-limiting example of the present invention, the updating of scores stops when a variation between two frequencies detected from two consecutive frequency spectra is greater than a threshold.

[0202] This example implementation allows the updating of scores to be stopped without the demodulator knowing the modulation parameters of the light signal such as the frequency of frequency change.

[0203] As an example, the threshold value may vary depending on the lighting conditions of an environment in which the light signal is received.

[0204] For example, the lower the lighting conditions, e.g., the lighting conditions in the immediate environment of the light signal demodulator indicate low brightness, and the lower the threshold value will be.

[0205] For example, the threshold value may vary proportionally to the ambient brightness of the light signal receiver.

[0206] In substep 2280, after the scores have been updated, the frequency F r is detected among the frequencies of the set F of frequencies from the SCi scores associated with the frequencies of the set F of frequencies.

[0207] For example, the frequency associated with the highest score is the F frequency. r détectée.

[0208] According to a particular and non-limiting embodiment of the present invention, a symbol is represented by a pair of frequencies (F1 ,s , F2 ,s ) and the association between a symbol and a pair of frequencies is stored in a reference frequency table.

[0209] Laillum illustrates an example of a base-64 table that groups 64 associations between symbols and frequency pairs, according to a particular and non-limiting embodiment of the present invention. In this example, the symbols A, B, etc., are represented by frequency pairs expressed in binary form, in which each frequency is identified by three bits. For example, the symbol 'E' is associated with the binary word 000100, where 000 identifies the first frequency of the frequency pair and 100 identifies the second frequency of the frequency pair.

[0210] Laillust schematically illustrates a device 1 configured to emit and / or receive at least one symbol carried by a light signal modulated by a control signal, according to a particular and non-limiting embodiment of the present invention.

[0211] Device 1 is, for example, configured to carry out the operations described opposite the steps of at least one of the processes described opposite Figures 1, 6, and 14-16. Examples of such a device 1 include, but are not limited to, electronic equipment used, for example, for lighting an enclosed environment. The elements of device 1, individually or in combination, may be integrated into a single integrated circuit, into several integrated circuits, and / or into discrete components. Device 1 may be implemented as electronic circuits or software (or computer) modules, or a combination of electronic circuits and software modules.

[0212] Device 1 comprises one (or more) microprocessor(s) 10 configured to execute instructions for carrying out the steps of at least one of the processes described opposite Figures 1, 6, 14-16. The microprocessor 10 may include integrated memory, an input / output interface, and various circuits known to those skilled in the art. Device 1 may further comprise at least one memory 11, for example, volatile and / or non-volatile memory, and / or include a memory storage device that may comprise volatile and / or non-volatile memory, such as EEPROM, ROM, PROM, RAM, DRAM, SRAM, flash, magnetic disk, or optical disk.

[0213] The computer code comprising the instructions corresponding to the steps of at least one of the processes described opposite figures 1, 6, 14-16 which it is necessary to load and execute by the microprocessor 10 is for example stored on memory 11.

[0214] According to various specific and non-limiting embodiment examples, device 1 can be configured to be coupled in communication with other similar devices or systems and / or with external devices such as, for example, remote servers equipped with means of communication.

[0215] According to a particular and non-limiting embodiment, device 1 may include a block 12 of interface elements for communicating with these external devices. The interface elements of block 12 may include one or more of the following interfaces: - radio frequency (RF) interface, for example of the Wi-Fi® type (according to IEEE 802.11), for example in the 2.4 or 5 GHz frequency bands, or of the Bluetooth® type (according to IEEE 802.15).1), in the 2.4 GHz frequency band, or Sigfox type using UBN (Ultra Narrow Band) radio technology, or LoRa in the 868 MHz frequency band, LTE (Long-Term Evolution), LTE-Advanced; USB interface (Universal Serial Bus); HDMI interface (High Definition Multimedia Interface); LIN interface (Local Interconnect Network).

[0216] According to a particular and non-limiting embodiment, device 1 can provide output signals to one or more external devices, such as a display screen 15, touch or non-touch, one or more speakers 16 and / or other peripherals 17 via output interfaces 18, 19, 20 respectively. According to a variant, one or more of the external devices is integrated into device 1.

[0217] The diagram schematically illustrates an implementation of the device 2 for emitting light signals configured to emit at least one symbol carried by a light signal modulated by the control signal 100 according to a particular and non-limiting example of the present invention.

[0218] Device 2 includes a driver 180 (driver in English) which provides electrical power to the other electrical elements of device 1. For example, driver 180 converts an alternating voltage of 110-220v into a direct voltage of 7-50V.

[0219] Device 2 also includes a pilot signal generator 181 and a light signal generator 182 driven by the pilot signal at the output of generator 181.

[0220] For example, the light signal generator 182 is a light-emitting diode driven by the pilot signal at the output of the generator 181.

[0221] The generator 181 includes a microcontroller 183 configured to generate the control signal 100 according to the process described opposite 1a and 6 and a DC voltage modulation means 184 driven by the control signal 100 to provide the signal which drives the voltage across the terminals of the light signal generator 182. For example the DC voltage modulation means 184 is a MOSFET type transistor.

[0222] For example, the MOSFET transistor is suitable to support frequencies of at least 100KHz.

[0223] According to one variant, the generator 181 may include a voltage converter 185 which adapts the output voltage of the driver 180 to the supply voltage of the microcontroller 183.

[0224] According to this device 2, the DC voltage modulation means 184 is controlled by the control signal 100 generated at the output of the microcontroller 183. The signal at the output of the DC voltage modulation means 184 controls the power supply of the light signal generator 182 to reproduce the variations in light intensity of the control signal 100. A symbol can then be transmitted by the light signal thus modulated which is produced by the light signal generator 182.

[0225] For example, the elements of the light signal generator 182 can be grouped on the same printed circuit board (PCB for Printed Circuit Board).

[0226] The diagram schematically illustrates an implementation of the light signal reception device 3 configured to receive at least one symbol carried by a light signal modulated by the control signal 100 according to a particular and non-limiting example of the present invention.

[0227] Device 3 is configured to identify blinking frequencies of a continuous light signal (when this light signal belongs to the visible spectrum), i.e., as samples of this light signal become available.

[0228] For example, blinking frequencies can range from 2kHz to 5kHz.

[0229] Device 3 is also configured to minimize its electrical energy consumption.

[0230] Device 3 includes a light signal reader 191 such as a single-crystal photosensitive unit.

[0231] Device 3 further includes a filter 192 and an amplifier 193 associated with a means for varying the amplification level 194. The amplifier 193 amplifies the filtered signal according to the light intensity of the signal, using an amplification level adjusted by the means 194. The amplifier thus amplifies the filtered light signal to its maximum (before saturation) to optimize demodulation performance. Device 1 is then configured to demodulate a light signal under varying lighting conditions ranging from 10 lux to 10,000 lux.

[0232] Device 3 further includes a microcontroller 195 configured to demodulate the filtered and amplified light signal according to a process described opposite Figures 14-16 and obtain the symbol represented by the light signal.

[0233] Of course, the present invention is not limited to the embodiments described above but extends to a method for transmitting or receiving at least one symbol carried by a light signal modulated by a control signal, which would include secondary steps without falling outside the scope of the present invention. The same would apply to a device configured for implementing such a method.

Claims

Method of emitting at least one symbol carried by a light signal modulated by a control signal, the control signal comprising a succession of time cycles, each time cycle being defined by an alternation of a high level corresponding to a high level of light intensity of the modulated light signal maintained for a first duration and a low level corresponding to a low level of light intensity of the light signal maintained for a second duration, a total duration of each time cycle being defined from a frequency, the method is characterized in that it comprises the following steps:- determination (110) of at least one pair of frequencies, each pair of frequencies representing a symbol to be emitted;- the frequencies of said at least one determined frequency pair being determined such that, during the modulation of the light signal, a first determined frequency is replaced by a second determined frequency, the higher frequency, among said first and second frequencies, is at most equal to twice the lower frequency, among said first and second frequencies; - generation (120) of the succession of time cycles, the total duration of at least one time cycle being defined from each frequency of each determined frequency pair; - modulation (130) of the light signal by the generated control signal; and - emission (140) of the modulated light signal. A method according to claim 1, wherein the highest frequency among the frequencies of said at least one determined pair of frequencies is at most equal to twice the lowest frequency among the frequencies of said at least one determined pair of frequencies. A method according to claim 1 or 2, wherein at least one of the time cycles in the succession of time cycles has a total duration defined from a starting frequency of emission of said at least one symbol, the starting frequency of emission of said at least one symbol being determined such that when, during modulation of the light signal, the starting frequency of emission of said at least one symbol is replaced by a frequency of one of said at least one determined pair of frequencies, the highest frequency, among the starting frequency of emission of said at least one symbol and said frequency of said pair of frequencies, is at most equal to twice the lowest frequency, among the starting frequency of emission of said at least one symbol and said frequency of said pair of frequencies. A method according to claim 3, wherein at least one of the time cycles of the succession of time cycles has a total duration defined from an end-of-emission frequency of said at least one symbol, the end-of-emission frequency of said at least one symbol being determined such that during a replacement, during the modulation of the light signal, of a frequency of one of said at least one pair of frequencies determined by the end-of-emission frequency of said at least one symbol, the highest frequency, among the end-of-emission frequency of said at least one symbol and said frequency of said pair of frequencies, is at most equal to twice the lowest frequency, among the end-of-emission frequency of said at least one symbol and said frequency of said pair of frequencies. A method according to claim 4, wherein the highest frequency among the frequencies of said at least one determined pair of frequencies, the emission start frequency of said at least one symbol and the emission end frequency of said at least one symbol is at most equal to twice the lowest frequency among the frequencies of said at least one determined pair, the emission start frequency of said at least one symbol and the emission end frequency of said at least one symbol. A method according to claim 4, wherein at least one of the time cycles in the succession of time cycles has a defined duration starting from a determined cutoff frequency such that, during the modulation of the light signal, the cutoff frequency is replaced by a frequency of said at least one determined pair of frequencies or by the emission termination frequency of said at least one symbol, or during the replacement of a frequency of said at least one determined pair of frequencies or the emission start frequency of said at least one symbol by the cutoff frequency, the highest frequency among said frequency of said pair of frequencies, the emission start frequency of said at least one symbol, the emission termination frequency of said at least one symbol, and the cutoff frequency, is at most equal to twice the lowest frequency among said frequency of said pair of frequencies.the transmission start frequency of said at least one symbol, the transmission end frequency of said at least one symbol, and the cutoff frequency. A method according to claim 6, wherein if the frequencies of said at least one determined pair of frequencies, the start-up frequency of said at least one symbol and the end-up frequency of said at least one symbol belong to a set of frequencies whose highest frequency is less than or equal to four times the lowest frequency, the cutoff frequency is defined as a median value between the highest and lowest frequencies of the set of frequencies. A method according to any one of the preceding claims, wherein the control signal being a gate signal comprising a rising edge and a falling edge per time cycle, a replacement of one determined frequency by another determined frequency is triggered on the rising or falling edges of the time cycles. A method according to any one of the preceding claims, wherein each time cycle whose total duration is defined by a frequency is repeated a defined number of times from a frequency of frequency change. Method according to claim 9, wherein the frequency of frequency change is at most equal to 100Hz. A method according to claim 9, wherein the frequency of frequency change varies according to lighting conditions of an environment in which the light signal is emitted. A method according to any one of claims 1 to 11, wherein a duty cycle of each time cycle of the control signal is equal to the same value within a deviation around that value. A method for receiving at least one symbol carried by a light signal modulated by a control signal, the control signal being formed of a succession of time cycles, each time cycle being defined by an alternation of a high level of light intensity of the light signal maintained for a first duration and a low level of light intensity of the light signal maintained for a second duration, a total duration of each time cycle being defined from a frequency, the method is characterized in that it comprises the following steps: - reception and sampling of the light signal; and - demodulation of the light signal to obtain said at least one symbol, each symbol being represented by a pair of frequencies detected from a spectral analysis of samples of the received light signal;- the detected frequencies of said at least one pair of frequencies being such that when a first detected frequency is replaced by a second detected frequency during the demodulation of the light signal, the highest frequency, among said first and second detected frequencies, is at most equal to twice the lowest frequency, among said first and second detected frequencies.; A method according to claim 13, wherein the highest frequency among the detected frequencies of said at least one pair of frequencies is at most equal to twice the lowest frequency among the detected frequencies of said at least one pair of frequencies. Method according to claim 13 or 14, further comprising a step (2240) of detecting a reception start frequency of said at least one symbol from a frequency spectrum of the light signal determined from a first set of samples of the received light signal, the detection of the reception start frequency of said at least one symbol preceding the detection of a first frequency of a first pair of frequencies representing a first symbol to be received. Method according to claim 15, further comprising a step (2250) of detecting an end-of-reception frequency of said at least one symbol from a frequency spectrum of the light signal determined from a second set of samples of the received light signal, the detection of the end-of-reception frequency of said at least one symbol following the detection of a second frequency of a pair of frequencies representing a last symbol to be received. A method according to claim 16, wherein the detected frequencies of said at least one pair of frequencies, the reception start frequency of said at least one detected symbol, and the reception end frequency of said at least one detected symbol belong to a set of frequencies whose highest frequency is at most equal to twice the lowest frequency of the set of frequencies. A method according to claim 17, further comprising a step (2260) of detecting a cutoff frequency from a frequency spectrum determined from a fifth set of samples of the received light signal, the cutoff frequency being defined as a median value between the highest and lowest frequencies of the set of frequencies, the highest frequency of the set of frequencies being at most equal to four times the lowest frequency of the set of frequencies, the cutoff frequency being detected following the detection of each frequency of each pair of frequencies, the detection of the reception start frequency of said at least one symbol and the detection of the reception end frequency of said at least one symbol. A method according to any one of claims 17 or 18, wherein the frequencies of the frequency set are less than 5kHz. A method according to any one of the claims, wherein said at least one symbol is determined from a table defining an association between each symbol and a pair of frequencies. Light signal emitting device comprising a microcontroller configured for the implementation of the process steps according to any one of claims 1-12, 19-20. Light signal receiving device comprising a microprocessor configured for carrying out the steps of the process according to any one of claims 13 to 20. Computer program that includes instructions adapted for carrying out the steps of the process according to any one of claims 1 to 20 when the computer program is executed by at least one processor. Computer-readable recording medium on which is recorded a computer program comprising instructions for carrying out the steps of the process according to any one of claims 1 to 20.

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