FR3074383B1 - METHOD FOR RECEIVING A LIGHT SIGNAL MODULE VLC SIGNAL TYPE - Google Patents

Abstract

A method of receiving a VLC signal, comprising the steps of: - acquiring an image comprising fringes corresponding to high states and low states of the modulated light signal; converting the image into a signal of average intensities, the average intensity signal comprising components each representative of an average of luminous intensity of a row of the image; - assimilate the signal of average intensities to a time series, and implement a deseasonalization method on the time series, to obtain a curve recentered amplitude (26); - determining peak widths (27) of the amplitude recentering curve (26), by performing zero crossing detection of the amplitude recenter curve (27); reproducing a digital signal contained in the modulated light signal from the widths of the peaks (27).

Description

The invention relates to the field of methods for receiving modulated light signals of the VLC signal type (acronym for "Visible link: Light: Communication").

BACKGROUND OF THE INVENTION The transmission and reception of modulated light signals of the VLC signal type constitute a technology. Particularly promising for implementing an internal (or external) or external (or outdo) geolocation function of an electronic device.

· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·. ; museum, train station, airport-, shop, workspace, etc. The electronic device in question is for example a mobile phone, a tablet, a computer. portable, a: connected watch., etc.

The internal geolocation of the electronic apparatus uses a light emitting diode lamp (hereinafter referred to as an LED lamp) positioned in the room to emit modulated light signals to the electronic apparatus. The LED lamp thus performs both a lighting function of the room and the function of indoor geolocation.

The. Modulated light signals include an identifier of the LED lamp. The identifier contains position data of the LED lamp. The position data can directly contain the position of the LED lamp. Alternatively, the data, deposition can enable the electronic device to obtain the position of the LED lamp, which is stored for example in a server to which the electronic device accesses. Of course, it is possible to geo-localize an electronic apparatus using position data from a plurality of LED lamps.

Many technical challenges arise for designers of such systems using the transmission and reception of modulated light signals. one of these challenges concerns the reception of modulated light signals. Most of the existing electronic devices: mentioned earlier are not equipped with a modulated light signal reception device. It is therefore possible to provide the electronic device with additional reception equipment connected to a light port. device, for example to a female jack, or use a camera of the electronic device. In the latter case, the reception of the modulated light signals requires the processing of an image produced by the camera, which must be particularly perforated so that the reception of the modulated light signals is sufficiently effective.

OBJECT OF THE INVENTION The object of the invention is to improve the reception of modular light signals of the VLC signal type.

SUMMARY OF THE INVENTION

With a view to achieving this object, a method for receiving a modulated light signal of the VLC 'signal type, implemented in an electronic device comprising a camera comprising a camera, is proposed. CMOS sensor, the reception method comprising: the steps of. to acquire an image comprising fringes corresponding to high states and to low states of the modulated light signal; - convert the image; in a signal of average intensities, the signal, of average intensities comprising representative components, each of an average of luminous intensity; one row, one picture; - assimilate; signal of average intensities at a time series "and implement a deseasonalization method, on the time series, to obtain a curve .recentrée amplitude, - determine pi dev widths of the curve recentered amplitude, by performing a detection of: .passages by zero of the curve, recentered in amplitude; reproducing: a digital signal contained in the light signal modulated from the widths of the peaks, the reception method according to the invention significantly improves the reception of modulated light signals of the VLC signal type.

There is also provided an electronic apparatus comprising a camera comprising a CMOS sensor and a processing component in which is implemented the reception method just described. The invention will be better understood in the light of the following description of a particular implementation mode nonlimiting 1 invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made to the accompanying drawings, among which: FIG. 1 represents an LED lamp and a user equipped with a mobile telephone; FIG. 2 represents steps of a transmission method; FIG. 3 represents an identifier frame; FIG. 4 represents an identifier frame comprising a first coded signal; FIG. 5 represents a modulated identifier frame including a second coded signal; - Figure 6 shows an image produced by a camera of the mobile phone; - Figure 7 shows an object from Figure 6 and corresponding to an LED lamp; FIG. 8 shows the steps of a decoding phase of the method of receiving a modulated light signal of the VLC signal type according to FIG. The invention; FIG. 9 represents a curve of average intensity signal as a function of the rows; an image portion; - Figure 1.0 shows a curve refocused amplitude obtained from the curve · of: Figure 9; - the figure. 11 '.represents one; decoding table

Manchester .; 14, FIG. 1.2 represents a curve of a signal of average intensities in function of the rows of an image portion; - the figure. 1, 3 represents a curve .recentred in. Amplitude, obtained from the curve of the. Figure 12 through a deseasonalization method, using polynomial regression - Figure 14 shows a refocused amplitude curve, obtained by a seasonal adjustment method using a Hodrick-Prescott filter ciasique; FIG. 15 represents a curve recentered in amplitude, obtained thanks to the reception method according to the invention; FIG. 16 represents a first curve, a second curve and a third curve illustrating an error rate of reception of the identifier as a function of a distance, the first curve corresponding to the use of a deseasonalization method using a polynomial regression, the second curve corresponding to the use of a method of determination using a classical Hodrick-Prescott filter, the third curve corresponding to the use of a deseasonalization method used. In the reception method according to the invention, DETAILED DESCRIPTION OF THE INVENTION Firstly, a method for transmitting a modulated light signal of the VLC signal type is described. The emission process is set; implemented in a VLC signal transmitting device.

The VLC signal-emitting device comprises a light-emitting diode and a driving module for driving the light-emitting diode. The control module comprises a first processing component adapted to execute instructions of a program for implementing the various steps of the transmission method, and a driving component of the diode or driver, in English.

The first processing component here is a microcontroller, but could be a different component, for example a processor or an FPGA.

The driver is here a voltage driver.

With reference to FIG. 1, the VLC signal emitting device is integrated in an LED lamp 1. The LED lamp 1 is here positioned on the ceiling of a room of any building: museum, station, airport, shop, workspace, etc.

The LED lamp 1 uses the light-emitting diode to illuminate its environment. The LED lamp 1 thus fulfills a lighting function of the room.

The LED lamp 1 also performs an indoor geolocation function of an electronic apparatus provided with a VLC signal receiving device. The electronic device is in this case a mobile phone 2 which is provided with a user 3.

The indoor geolocation function works as follows. The VLC signal emitting device of the LED lamp 1 continuously transmits VLC signals transmitted comprising an identifier of the LED lamp 1. The identifier of the LED lamp 1 comprises position data of the LED lamp 1 in the room. The emission of emitted VLC signals consists in switching the light emitting diode so as to switch a light source produced by the light emitting diode to generate binary modulated light signals constituting. the signals. VLC issued ...

To 'Switch the diode. However, the control module selectively causes the light-emitting diode to supply a power supply current greater than a predetermined high current threshold or a lower power supply current than the light-emitting diode. a predefined low current threshold.

The supply current greater than the high predefined current threshold makes it possible to generate a high state of a transmitted VLC signal, ie a binary value equal to "1", while the supply current lower than the predefined low current threshold enables to generate a low state of the transmitted VLC signal, ie a binary value equal to "0".

When the mobile phone 2 receives the transmitted VLC signals, and thus the identifier of the LED lamp 1, the mobile phone 2 uses the position data of the LED lamp 1 to determine its own position in the room, and therefore the position of the user 3 in the room.

With reference to FIG. 2, the transmission method firstly comprises the step of generating a digital signal, of origin (step E1). The original digital signal contains, in particular first · data to be transmitted, in this case the identifier, of the.-, LED lamp 1. The identifier is composed of one. plurality of bits forming: one or more bytes. The duration of a high state or a low state of the identifier is: equal to T (period,) ...

The original digital template also gives a sum of: control (or checksum, in English.). The transmission method thus comprises the step of calculating a checksum on the identifier (step; Ë2). The calculation of the checksum consists here of making an addition, binary of the · dice of the identifier taken - two by two. A first intermediate sum composed of a plurality of bits is thus obtained. Then, each bit of the first intermediate sum is replaced by the opposite bit, to obtain a second intermediate sum. Finally, we take the last three bits of the second · intermediate sum! to obtain the sum of control! It illustrates by An example the obtaining of the sum of control. The identifier Id of the LED lamp 1 is: Id = Gbl010101Q.

The first sum · intermediate If is. such that: S, 1 = 0b 10 + 0bl0 + QblQ + 0bl0 = ®> Χϋΰ0.

By taking them; · Opposites, we get the. second intermediate sum S .g. ·:

Sa = 0b0111 ..

The checksum Os is therefore:

Cs = lll.

The transmission method then comprises the step of coding the original digital signal, that is to say the identifier and the checksum, using a first coding, to obtain a first coded signal (step E3). The first coding here is a Manchester coding. A bit equal to Q of the identifier and the checksum is encoded by a transition from a low state to a high state, while a bit equal to 1 is encoded by a transition from a high state to a high state. low state.

We note that the; Manchester coding is; a particular GO modulation K (for .Qn-Qff Keytiig) ... Any other ·. · encoding derived from an O.Q; K modulation could be used.

In this way, we obtain a coded identifier IdManci "and a coded checksum CsManch · The identically encoded IdManch; is :

IdMailcK = 10 01100110011001.

The CsManch coded checksum is: C SManeii3! 01010.

In the coded identifier and in the coded checksum, the maximum duration of a high state or of a; state is equal to T, and the maximum transition frequency Ftran between two transitions (from a high state to a low state or from a low state to a high state) is such that i

Ftran-2 / T ·

The transmission method then comprises the step of constructing an identifier frame; The construction of the xatit identifier train consists in designing bits. initially, the coded identifier and the Code Controlled Report (step E4). The frame: identifier is. a concatenated signal issued from; the concatenation of ·, start bits and the first coded signal.

The starting bits Bd are here such that:

^ Bd O1110010.

It should be noted that the starting bits comprise a succession of three consecutive "1s", ie three consecutive high states 3T, / 2. As a "such: inheritance is impossible in" 1 "', coded identifier, and in 1a. coded checksum, because of the use of Manchester coding, the three consecutive "1" make it possible to distinguish the start bits and thus the beginning of the identifier frame.

The identifier frame is therefore lé; .signal, emitted following: 011100101001100110011001101010.

The transmission process then comprises the step of; start transmitting the identifier frame (step E5-J.

At the time of, the broadcast. of the Identifier frame, the transmission method detects the low states of the identifier frame and, in particular, provides the first coded signal (step E6).

The identifier frame is coded using a second coding. The. second coding consists in modulating each state down. the identifier frame: to. a modulation frequency Fmoci (step E7). The modulation frequency Fmod is: higher: at the transition frequency, maximum Fi-ratr- The modulation frequency F & od is here. a multiple of the transit frequency i maximum Ftran. Here: frequency, modulation Fmoci is here such that:

Fmod = 2 Ftran = 4 / T.

With reference to FIG. 3, a second coded signal, which is a modulated identifier frame 5, is thus obtained from the identifier frame and thus from the first coded signal.

With reference to FIGS. 4 and 5, it can be seen that a low state 6 of duration T of an identifier frame 7 (unmodulated) containing the first coded signal Sel, is replaced by four transitions 8 of a low state. to a high state of the associated modulated identifier frame 10 containing the second coded signal Sep, and that a low state 12 of duration T / 2 is replaced by two transitions · 13 of a "baâ state towards a .. state, high die, frame: modulated identifier 1.0.

The modulation ceases when a transition from a low state to a high state is detected in the identifier frame and, in particular, in the first coded signal: (step ES). Then, .the detection of a low state of., The frame of identifier (not .modulated) resumes step E6.

The transmission process continues until the complete transmission of the modulated identifier frame (step E9), then resumes in step ES. The modulated identifier frame is thus reissued continuously.

In order to transmit the modulated identifier frame, it is thus necessary to supply the light emitting diode with a large average electrical power, greater than the electrical power that would be provided in the case where only a conventional Manchester coding (or other conventional coding) would be · use, ·

Indeed, the use of conventional Manchester encoding would result in: coded signals consisting of half-states, highs and half-marks; low states, and thus emitted VLC signals formed at half high and low states. The use of conventional Manchester encoding is therefore tantamount to supplying the electroluminescent diode with a feed stream; greater than the preset high current threshold during one. total time equal to one half of the time required to transmit ·: the VLC signals.,. and supplying the light emitting diode with a feed current lower than the predefined low current threshold for a total time equal to half the time required to transmit the VLC signals.

With conventional Manchester encoding, the average electrical power supplied to the light emitting diode is therefore 50% of a maximum electrical power corresponding to a continuous emission of high states.

Here, by modulating the low states of the identifier frame 7, and thus of the first coded signal Sel, a modulated identifier frame 10 is obtained, and thus a second signal, coded Sda · * ·. of which: high states are more numerous and have a greater total duration. The time in which the light-emitting diode is powered by a feed current higher than the preset high-current threshold is larger, and the average electrical power supplied to the light-emitting diode is therefore increased. Electric power. average, supplied to the light emitting diode is here equal to 75% of the maximum electrical power,

The modulated identifier frame 10 is therefore associated with an average electrical power supplied to the high-energy LED of 75% of the maximum electrical power. By increasing the modulation frequency of the low states, the average electrical power supplied to the light-emitting diode, which can reach 95% of the maximum electrical power, is increased.

The second: coding is therefore intended to increase the average electrical power supplied to the rolifflinescent electric diode to generate the emitted VLC signals. The increase in the average electrical power makes it possible to increase the average luminous power produced by the light-emitting diode and therefore by the LED lamp 1. This improves the lighting of the room in which the LED lamp 1 is positioned.

Note that since the modulation frequency and the frequency band of the emitted VLC signals are known, a low pass filter can be used in the VLC signal receiving device of the mobile telephone 2 to filter the received VLC signals. thus recover the unmodulated identifier frame 7, simply coded in Manchester.

The method for receiving a modulated light signal of the VLC signal type according to the invention is now described. The reception method according to the invention is here implemented in the mobile telephone 2 and allows it to receive the transmitted VLC signals;

The mobile phone 2 includes a camera including a CMOS sensor (for compliments and M0t & X-Ox2de-Seïi�p & ndü'ùto.r). The receiving device of the mobile telephone 2 VLC signals comprises the mobile phone camera 2, which is therefore used to receive the received VLC signals. In addition to the camera, the device; reception includes a receiving module connected to the camera. The receiving module comprises a second processing component adapted to: executing instructions of a program for carrying out the different steps of the receiving method .... The second processing component is . right here. a processor, but could be a different component, for example a .mocontrol.or an FPGA.

We use here the drop-down shutter effect (or "foolling sim ple iron e £ e ec.t 2) CMOS sensor to .receive vlc signals received · ...

With reference to FIG. 6, the camera makes it possible to obtain images similar to the image 20. The image 20 comprises white fringes 21 and black fringes 22. Each white fringe 21 corresponds to a high state of a received VLC signal, while each black fringe 22 corresponds to a low state of the received VLC signal. We can thus find the moderated pattern of identification from Image 20.

The method of receiving a modulated light signal of the VLC signal type firstly comprises a preliminary step in which the camera is initialized. Initialization consists of setting parameters of the camera, including exposure time, ISO sensitivity and resolution.

The exposure time is the length of time that the CMOS sensor is exposed to light. A short exposure time produces relatively dark images because the amount of light to which the CMOS sensor is exposed is small. A long exposure time produces relatively bright images because the amount of light at which the CMOS sensor is exposed is important. In order to clearly distinguish the fringes 21 from the black fringes 22, and therefore the states of the low states of the VLC signals received, it is preferable to choose a short duration of exposure.

ISO sensitivity determines how sensitive the camera is to light. A high ISO sensitivity increases the sensitivity of the camera. By choosing a high ISO sensitivity, it improves the detection of changes in light intensity and therefore the contrast of the image 20. It is therefore possible to detect VLC signals emitted by increasing the distance between the LED lamp 1 and the telephone. 2. The ISO sensitivity of a conventional camera is typically between 100 and 800, but some recent mobile phones 2 are provided with a camera having an ISO sensitivity of 1600 or even mimics 320 0.

Finally, it is advantageous to choose a resolution close to or equal to 640 × 480 to decode the VLC signals received in a relatively short time.

Once the camera has been initialized, an image is processed to decode the received VLC signals.

It is possible that several sources of light emission, that is to say here several LED lamps 1, emit in the room VLC signals emitted: simultaneously. In this case, if the camera has a sufficient field of view or the distance between the camera and each LED lamp 1 is relatively large, the image 20 may contain white fringes 21 and representative black fringes 22 emitted VLC signals produced by several LED lamps 1>

In this case, the receptor method detects all the LED lamps 1 present in the image 20. Then, the receiving method successively decodes the received VLC signals from each LED lamp 1, starting with the LED lamp 1 closest to the center of the image 20 and ending with the farthest LED lamp 1 The reception method thus comprises a step of: thresholding the image: 20. The thresholding step consists in keeping, in the image 20, only the pixels presenting the image. a light intensity greater than a predetermined light intensity threshold. A plurality of preliminary shapes are thus obtained.

Then, morphological operations are implemented in the image 20. The morphological operations include opening morphological operations and morphological closure operations. In this way, spaces of small size and deprived of pixels are filled inside the preliminary forms, and small and isolated sets of pixels are eliminated in the vicinity of the preliminary shapes.

With reference to FIG. 7, there is thus obtained in the image 20 a plurality of object1 similar to the object, 2.3. Each object 23 of image 20 corresponds to a lamp. : â LED 1 ...,

Then, a related component labeling algorithm is applied to each object in the image.

A centroxde of each object, 23 is then determined. A Euclidean distance between the centroid of each object 23 and the center of the image 20 is calculated.

Thus, a table of objects 23 is obtained. In the object table 23, the objects 23 are classified according to their distance from the center of the image 20, in an order of increasing distance.

Once all the LED lamps 1 have been identified and all the corresponding objects 23 have been; stored in the table, a first image portion corresponding to the object 23 'located in the first position in the object table 23 is first extracted from the image 20.

The first portion of the image corresponds therefore to the LED lamp 1.. more, close due back of the image, 2.0. the first image portion is. defined, so that. '.the lamp · to. LED 1. is located in the center of the. First picture portion. decoding phase is · applied on the. first portion of .image: · /, .to decode the received VLÇ signal produced by · the lamp: to: led l. The decode phase is performed by a programmed decoder. , the receiving device of the mobile phone 2., decoding phase is then repeated for each object 2.3 of the object table, and therefore for each LED lamp 1. Each LED lamp 1 is located in the center of a associated image portion. One portion of image is of course an image. If only one LED lamp 1 is in the room and only one object 23 is detected in: image 20, it is possible either to perform the decoding phase on the entire Image 20, or to extract a image portion of the image 20 centered on the object 23.

With reference to FIG. 8, the phase of decoding Pha comprises first and foremost a conversion step (step E20). The image portion is a two-dimensional signal. The conversion: .consisted to convert the. image portion in a signal, to a · dimension .., The decoder worked: in fact mainly with signals to. a dimension. For this, the average of the intensity intensities of the pixels of each row of. the image portion is calculated.,

We note here, for each portion of amage, it is possible to sample the columns forming the portion of the image: to reduce, the number of columns on which the conversion is carried out. By performing a consistent sampling, at. select one column all: M columns, and Oh considering that the total number of columns of a portion of image is equal to n, the processing is carried out on a number j of columns, j being equal to the whole part of the report n / M. We. thus considerably reduces the size of the image portion, and thus significantly reduces the calculation time.

There is thus obtained a signal of average intensities, representative of the received VLC signal, comprising: components each equal to an average of the light intensities of the rows of the image portion.

With reference to FIG. 9, the curve 24 of the average intensity signal is formed by a succession of peaks 25. The peaks 25 comprise peaks of maximum local intensity. and. peaks of minimum local intensity .. Each peak of maximum local intensity: corresponds to a high state due, signal. VLC received, and each peak of local minimum intensity corresponds to. a • low state of the received VLC signal. Fear to obtain the number of bits corresponding to a high state or a low state. It is advisable to evaluate a width of each peak 25.

However, we can see on your figure 9. .que: the amplitude of. curve 24 is not; centered on a value of amp, you die ·· Constant. This is because, since the LED lamp 1 is located in the center of there, the image carrier, the light intensity is more important in the center of the portion of the image. image .gu7 at the ends of the .portion image.

Thus, prior to the evaluation of the width of the peaks 25, the amplitude of the curve 21 of the intensity signal; averages is recentered, on · "A virtual null value, to obtain a curve, recentered, in amplitude 26 of a signal centered in amplitude, visible in FIG. thus defined with respect to the same reference of light intensity, corresponding to the virtual zero value 28, and the width of each peak 27 corresponds to the width of the peak 27 at the level of this null value: virtual; ,

To do this, we assimilate the signal of average intensities to a time series, and we use a method of deseasonalization of time series. A trend of the time series ·, is then determined, then c.est. The trend is subtracted from the signal of average intensities to obtain a signal of average intensities refocused.

The series of seasonal deseasonalization method used here. a filter of. Modtick Prescott.

Suppose, then, that the signal of average intensities is a temporal elect constituted of vail, yt, and. that each value yt is equal to the sum ··, a trend component gt and a cyclical component; ct, so that · ·: yt = gt + Ct, with t = 1, T,

The determination; cyclic components and allows the amplitude-centered curve to be produced 26. The use of the Hodriok-Prescott filter has the objective of "calculating the cyclic components" and starting from the values and solving the problem. de · minimization following

The minimization problem uses a smoothing parameter λ.

The smoothing parameter λ "penalizes" the variability of the trend component gt. The higher the value of the smoothing parameter λ, the lower the variability of the trend component gt, and the more the trend component is smoothed. On the contrary, the lower the value of the smoothing parameter λ, the greater the variability of the trend component gt. When the value of the smoothing parameter λ is close to zero, the trend component gt becomes equivalent to the value yt.

The minimization problem that has just been mentioned can also be written as follows:

where yT is a vector whose components are y'f: f · §γ is a vector whose components · are the gt., Iÿ is the identical identity and F is the following ... pentadiogonal matrix .:

So we have

.And so :

we. it is is. a vector whose components are the. ct *

Val has smoothing parameter: λ depends on the periodicity; yt data ..

Here, as the LED lamp 1 is located in the center of the image portion, the intensity of the medium intensity signal is relatively strong in the middle of the time series, and relatively low at the beginning and at the end of the series. time. These differences in intensity tend to affect the efficiency of the Hodrick-Prescott filter.

To solve c & problem, different smoothing parameter values are used.

Considering that the time series yt has an equal size year, the smoothing parameter is the following smoothing vector:

The smoothing parameter is thus a smoothing vector comprising a plurality of components.

The plurality of components comprises central components, located in the center of the smoothing vector, and extrema components located at the ends of the smoothing device.

The Components: central: · have taledis superior to those of the extremal components.

A value of a central component is greater than 10,000, and a value of an extreme-male component is less than, ΙΟΌΌ.

The values of the extremal components are here equal to 800 and to 500. The values of the central components are here equal to 1100, 1600 and 14CQ0.

Thus, the smoothing is relatively weak at the beginning and the end of the time series, because the low luminous intensity of the received VLC signal results in a small amplitude of the signal of average intensities, which requires a weak smoothing. On the contrary, the smoothing is relatively strong in the middle of the time series because the strong light intensity

the signal ¥ LC received results in a large amplitude of the signal of average intensities, which requires a strong smoothing.

The amplitude-centered curve 26 of the amplitude-centered signal is thus obtained (step E21 of FIG. 8).

It is then necessary to determine the bits constituting the VLC signal received from the amplitude-centered curve 26 and, in particular, the number of bits of each sequence of high and low states. The width of each peak 27 corresponds to a number of bits equal to 1 (for a maximum local intensity peak) or 0 (for a peak of minimal local intensity).

For this purpose, the width of each peak 27 of the amplitude-recentered curve 26 is measured by carrying out detection of the zero crossings (or zero-crossing detection, in English) of. 1a. Recenter curve, amplitude 26 (step E22).

Each peak of maximum local intensity corresponds, according to its width, to one of the following sequences: 1, 11, 111.

Each peak of local intensity: minimum: corresponds, according to its width, to one of the sequences. following: 0, 00.

A received digital signal representative of the received VLC signal is thus obtained.

Then, once the sequences of high states and. Low states have been decoded. The receiving method includes the step of detecting the start bits (step 23). As a reminder, the start bits contain the sequence:

Qlll / OOIG,

A sliding window is applied to the received digital signal to detect the start bits.

Then, once the start bits have been identified, the bits of the coded identifier and the coded control sum can be recovered.

The bits of the received digital signal, which follow the start bits, undergo for this a Manchester decoding (step E24). For this, 22 bits are here taken into account from the end of the start bits. the Manchester decoding is carried out using the table of FIG. 11. If no error is identified during the Manchester decoding, an eleven-bit sequence is obtained in which the first eight bits correspond to the (uncoded) identifier of the LED lamp 1 and the last three bits correspond to the checksum (uncoded). Manchester decoding makes it possible to detect an error if the received digital signal contains sequences of two consecutive "1s", or two consecutive "0s" (with the exception, .bleh, Sut of the starting bits;) ·, because decoding, corresponding to the table is performed for pairs of two bits. However, even if no error is detected by Manchester decoding, it is possible that the received digital signal contains an error.

The. For example, the following .Manchester digital signal can be output: 01-01-1.0-01-1..Q-1Q- "1.0" -01.,. which corresponds to the following uncoded numeric sign: 00101110.

If the coded digital signal received is: 10-01-10-01-10-10-10-01> what corresponds to. unencrypted digital signal · next receipt: 1010: 1110 ,. no error will be detected at the time of Manchester decoding, while the received uncoded digital signal is different from the uncoded digital signal transmitted. The use of the checksum avoids this type of error.

The computation of the checksum consists again in performing a binary addition of the bits of the identifier taken in pairs. A first intermediate sum composed of a plurality of bits is thus obtained. Then, we replace each bit of the first intermediate sum by the opposite bit, to obtain a second intermediate sum. · Finally we take the last three · bits of .Là. second interim sum to get the ... checksum. We checked, if the checksum. Obtained in the received digital signal corresponds to that of the digital signal emitted (step E25).

If the sum of the control corresponds, the reception method includes the step of providing to the second component of: processing of the mobile telephone the identifier of the lamp. LED 1, bridge that the .gem.o-calification of the mobile phone 2 pui.ése. to be realized ·. Otherwise, a message; error is generated by the second processing component (step: E26).

Of course, all, steps of the decoding phase ·. Fhjd. Then, for each object 23 of the 'object table' 23 (and therefore for each lamp at LË'D 1), they are realized in an order corresponding to the. position of objects; 23 in the table with 'objects:, 23.

Figs. 12 to .1.6 allow us to perform perf: Odffiân: c: es ·. : · process, reception,.

FIG. 12 represents a 3: 0 · curve of a signal of average intensities, FIG. 13 represents a re-centered curve in amplitude 3.1 obtained using. a deseasonalization method using a polynomial regressive. Figure 14 shown; a curve '· recentered in amplitude 32 · Achieved: thanks to a: method of seasonal adjustment Using a filter .; of Hdr.ie: k '-: Pr'e'S'C0t: t classical. FIG. 1.5 shows a: Regraced curve in amplitude · 33 obtained by the reception method described here.

It will be noted that the amplitude-recentered curve 31 and the recentered amplitude curve 32 are not centered on the "zero" virtual value between the rows 280. at 350, contrary to the recentered curve · ên amplitude 33, which is perfectly centered on the 'null' value: virtual: 35.

Figure 16 shows a first curve 36, a second curve 37 and a third curve 38.

The first curve 36, the second curve 37 and the third curve 38 illustrate a rate of error of reception of the identifier of the lamp at E: 1 by the mobile telephone 2, This is a function of the distance between the mobile telephone 2 and the LED lamp 1. Here: first curve 36 corresponds to the use of a seasonal adjustment method using a polynomial regression. second curve 37 corresponds to the use of a deseasonalization method using a Hodrick-Prescott olasic filter.The third · curve: ·· 3 · 8 corresponds to the use of a ·· method: ··, seasonal adjustment used in the method of reception described here.

The content of the equation is equal to 0.0093% for curve 36, to: for curve 37, and to. 0.0030% for curve 38 ·. The reception method just described is therefore very efficient, in particular when the distance between the LED lamp 1 and the mobile phone 2 is important. The invention is not limited to the particular embodiment that has just been described, but, quite the contrary, covers any variant entering the frame; of the invention as defined by the claims.

It has been described here that the second; In order to increase the average electrical power supplied to the light-emitting diode, coding is intended to encode the first coded signal in order to achieve a frequency modulation on the low states of the first coded signal. This type of second encoding is particularly. advantageous: in the case where the driver of the. diode · is · a voltage driver. C: e ··· fifteenth coding ·, is also .particulièrement advantageous in the case where. a drive is positioned at the input of the driver, whether the driver is a voltage driver or a driver of: current.

In the case where the driver is a: current driver, and where a drive is not positioned at the input of the driver, it is partly advantageous to choose, another type of second. , coding. The second coding then consists in modifying a duty cycle of the first coded signal (obtained following Manchester coding). For example, a duration of the high states of the first coded signal will be increased. This increases the duration of the current pulsations which drive the diode, and thus the average electrical power supplied to the light-emitting diode and thus the average luminous power produced by the light-emitting diode are increased.

Although the implementation of the invention has here been described in an indoor geolocation function, the invention can of course be implemented in a different application, for example in an external geolocation function.

Claims (9)

1. A method for receiving a modulated light signal of the VLC signal type, implemented in an electronic device (2) comprising a camera comprising a CMOS sensor, the reception method comprising the steps of: acquiring an image: (20) comprising fringes (21, 22) corresponding to high states and low states of the modulated light signal; converting the image into a signal of average intensities, the average intensity signal comprising components each representative of an average luminous intensity of a row of the image - assimilating the signal of average intensities to a time series, and implement a seasonal adjustment method on the time series * to obtain an amplitude-centered curve (26); - determining peak widths (27) of the amplitude recentering curve (26), by performing zero crossing detection of the amplitude recenter curve (27); reproducing a digital signal contained in the modulated light signal from the widths of the peaks (27). 2. The reception method according to claim 1, wherein the deseasonalization method implements a Hodri ck-Prescott filter. 3> Reception method: according to claim 2, wherein the implementation of the Hodrick-Prescott filter uses a smoothing parameter, the parameter of. smoothing being a smoothing vector comprising a plurality of components ... 4. The method of reception, according to claim 3, the plurality of components comprising central components and extenal components, the central components; having values higher than those of the extremal components. 5. The reception method according to claim 4, wherein a value of a central component is greater than 10000, and wherein a value of an extremal component is less than 1000. 6. Reception method according to claim 1, for receiving modulated light signals generated by separate light emitting sources, the reception method further comprises a step, to implement morphological operations on the image (2: 0) to distinguish objects (23) each corresponding to a.; source; light emission. 7. · Reception method according to claim 6,. further comprising a step of applying an algorithm d. labeling in. · components .; related to each object; (23). 8. The method of receiving, according to claim 6, further comprising the steps of determining a centroid of each object; : (2: 3), and calculate a Euclidean distance. ·· between the eentrorde. of·. .. each object (23) and the center · of the image (: .2-.0). 9. A reception method according to claim 6, further comprising the step of extracting from the image; (2 (0) image portions comprising: each object. (.23) / each object) (2,3) being positioned at the center of the (corresponding image portion: 10. The method of receiving according to one of the preceding claims, the modulated light signal having position data used to geo-locate the electronic device. 11. An electronic apparatus comprising a camera comprising a CMOS sensor, and a processing component in which the reception method according to one of the preceding claims is implemented. 12. Electronic device according to claim 11, the electronic device being a mobile phone (2) or a tablet or a laptop or a connected watch.