Method and device for demodulating data modulated by amplitude modulation of a light signal emitted by a light source of an emitting device

Abstract

Method and device for demodulating data modulated by amplitude modulation of a light signal emitted by a light source of an emitting device. This demodulation device acquires a digital image comprising an area illuminated by a light signal emitted by a source.It is configured to: - calculate (24) and store an average value per column of said digital image, in association with a column index, arranged between a first and a second edge index of the image; - determine (26) a maximum value of said average values, and calculate a threshold from said maximum value; - determine (28) a first column index corresponding to the first average value greater than or equal to said threshold from the first edge index, and a second column index corresponding to the first average value greater than or equal to said threshold from the second edge index; - demodulate (30, 32) binary data from the average values ​​between the first and second column indices. Figure for the abbreviation: Figure 2.

Description

Title of the invention: Method and device for demodulating data modulated by amplitude modulation of a light signal emitted by a light source of an emitting device

[0001] The invention relates to a method for demodulating data modulated by amplitude modulation of a light signal emitted by a light source of a transmitting device. It also relates to an associated demodulation device and an associated electronic apparatus.

[0002] The invention lies in the field of wireless communication technology using visible light, using a VLC (for "Visible Light Communication") system.

[0003] It applies in particular in the context of data communication using an encoder / transmitter implemented on industrial products having on the front a light indicator with light-emitting diodes (LEDs), e.g. a screen or one or more indicator lights, intended to provide information on a state of the product, the data being decodeable by a VLC receiver / decoder, integrated for example in a portable device, for example a mobile phone.

[0004] For example, the invention applies to products for monitoring and protecting electrical systems, but more generally applies to any type of product having a front-facing indicator light.

[0005] The use of wireless communication technology using visible light, also known as VLC, has developed recently and has found many applications.

[0006] A visible light communication (VLC) system comprises an encoder / transmitter device and a receiver / decoder device, positioned substantially opposite each other. The encoder / transmitter device comprises a light source, for example one or more light-emitting diode or LED lamps, and the receiver / decoder device comprises an image capture device, e.g. a CMOS camera.

[0007] The light source emits a light signal whose amplitude is modulated according to the data to be transmitted. The data is encoded into symbols by an encoding process, each symbol representing a bit to be modulated. The symbols are then encapsulated in formatted transmission packets to form a binary stream comprising a predetermined synchronization word (or synchronization sequence), followed by a formatted transmission packet containing a header, payload data, and an error-detection code. This binary stream is transformed An electrical signal controls the activation or deactivation of the light source at a frequency chosen so that the resulting flicker is imperceptible to the human eye. For example, when the light source is on (high state of the corresponding light signal), a binary '1' is transmitted, and when the light source is off (low state of the corresponding light signal), a binary '0' is transmitted. A different correspondence between high and low states and transmitted bits could be established without changing the principle of the method.

[0008] The receiver / decoder device applies digital image processing to the images acquired by the image capture device to perform demodulation of the modulated data, then decoding to obtain decoded data.

[0009] The acquired digital images comprise pixel matrices whose values ​​represent, in an area illuminated by the light source, the high or low state of the light source, or a transition between these states. Thus, an acquired digital image comprises an area with light and dark fringes, corresponding respectively to the high and low states of the light signal.

[0010] Known systems are particularly suitable for VLC communication with transmitters having powerful light sources and a large surface area.

[0011] In an application such as the one mentioned above, the products incorporating the aforementioned light indicators or screens are relatively small, and the light sources are also small, for example between 2 mm and 6 cm. When considering data transmission via VLC communication from such a product, for data reading by a portable electronic device, for example a smartphone, tablet, or laptop computer, the area of ​​the acquired image representing the light source occupies a variable surface area, decreasing with the distance between the image sensor and the product in question.

[0012] Figure 1 illustrates, by way of example, images of a 2.5 mm diameter LED light source captured at different distances, ranging from 2.5 mm to 5 cm. It can be observed that in the image captured at 2.5 mm, vertical fringes are visible, corresponding to the high and low states of the light source and the modulation values. As the distance between the image sensor and the light source increases, the corresponding area in the captured image decreases, becoming reduced to an almost point-like area against a dark, potentially noisy background. Thus, the amount of background noise increases with distance, while the light intensity of the corresponding area decreases with distance, which may introduce errors in the demodulation and decoding of the data.

[0013] There is therefore a need to improve the demodulation of data modulated by amplitude modulation of a light signal emitted by a light source.

[0014] To this end, the invention proposes a method for demodulating data modulated by amplitude modulation of a light signal emitted by a light source of a transmitting device, the method comprising the acquisition of a digital image having an area illuminated by said light signal, said area having fringes corresponding to high and low states of the light signal. This method further comprises the steps of:

[0015] -calculation of an average value per column of said digital image, and storage of the average values ​​per column in association with a column index, arranged between a first edge index corresponding to a first edge of said image and a second edge index corresponding to a second edge of said image;

[0016] -determination of a maximum value of said average values, and calculation of a threshold from said maximum value,

[0017] - determination of a first column index corresponding to the first value average greater than or equal to said threshold starting from the first edge index, and a second column index corresponding to the first average value greater than or equal to said threshold starting from the second edge index;

[0018] - extraction of a subset of average values ​​between the first column index and the second column index;

[0019] -demodulation of binary data from said subset of average values.

[0020] Advantageously, the proposed method allows for dynamic adaptation, without prior knowledge, to extract and process an image area corresponding to the light source. Thus, advantageously, this improves demodulation and decoding while allowing for some flexibility in positioning the image sensor of the receiving device relative to the light source.

[0021] The method for demodulating data modulated by amplitude modulation of a light signal according to the invention may have one or more of the characteristics below, taken independently or according to all acceptable combinations.

[0022] The threshold is a percentage of said maximum value, preferably between 30% and 50%.

[0023] The threshold is equal to 40% of said maximum value.

[0024] In the memorization step, the average values ​​per column are stored in a table or in a list ordered according to the column indices.

[0025] The binary data demodulation step includes calculating a threshold curve using a segmentation method.

[0026] According to another aspect, the invention relates to a device for demodulating data modulated by amplitude modulation of a light signal. Amplitude dilation of a light signal emitted by a light source of a transmitting device, the demodulation device being configured to acquire a digital image comprising an area illuminated by said light signal, said area having fringes corresponding to high and low states of the light signal. This device further comprises modules configured to:

[0027] -calculate an average value per column of said digital image, and store average values ​​per column in association with a column index, arranged between a first edge index corresponding to a first edge of said image and a second edge index corresponding to a second edge of said image;

[0028] -determine a maximum value of said average values, and calculate a threshold from said maximum value,

[0029] - determine a first column index corresponding to the first value an average greater than or equal to said threshold starting from the first edge index, and a second column index corresponding to the first average value greater than or equal to said threshold starting from the second edge index;

[0030] -extract a subset of average values ​​between the first column index and the second column index;

[0031] -demodulate binary data from said subset of average values.

[0032] In one embodiment, the threshold is a percentage of said maximum value, preferably between 30% and 50%.

[0033] According to another aspect, the invention relates to an electronic device comprising an image sensor and a demodulation device as briefly described above.

[0034] According to a particular characteristic, the electronic device is a mobile phone or an electronic tablet.

[0035] Other features and advantages of the invention will become apparent from the description given below, by way of example and not limitation, with reference to the accompanying figures, among which:

[0036] [Fig-1] [Fig.1], already described, illustrates a plurality of images from the same source light captured at increasing distances;

[0037] [Fig.2] [Fig.2] is a schematic representation of a transmitter and a receiver of a VLC communication system;

[0038] [Fig.3] [Fig.3] is a synoptic diagram of the main steps in a demonstration process Dulation according to the invention;

[0039] [Fig.4] [Fig.4] illustrates examples of one-dimensional signals corresponding to average values ​​per column of a digital image acquired by a receiver.

[0040] Fig. 2 illustrates a VLC communication system 2, comprising a transmitter device 4 in unidirectional communication with a receiver device 6.

[0041] The transmitting device 4, also simply called the transmitter, is configured to encode, modulate and transmit digital data D using amplitude modulation of a light signal emitted by a light source 8, for example consisting of one or more lamps, adapted to emit waves of wavelength in the visible spectrum, the wavelength being between 380nm and 780nm.

[0042] The transmitter 4 includes a coding module 10 and a modulation module 12, which controls the amplitude of a light signal emitted by the light source 8.

[0043] The encoding module 10 implements, for example, an encoding that transforms bits into code words, also called symbols. In the VLC 2 system, the encoding module 10 implements Manchester encoding and formatting into transmission packets formatted according to a chosen protocol.

[0044] Manchester encoding, according to the IEEE 802.3 standard, consists of encoding a "1" as "01" and a "0" as "10".

[0045] The symbols are then encapsulated in formatted transmission packets, to form a binary train comprising a predetermined synchronization word, followed by a formatted transmission packet comprising a header, useful data and an error-detecting code.

[0046] For example, when Manchester encoding is used, the synchronization word is the pattern '1111' because, by definition, this pattern is not part of Manchester encoding. In other words, no series of symbols in Manchester encoding forms a sequence of four '1's.

[0047] The size of the packets varies, depending on the intended application. It is indicated in the packet header.

[0048] The error detection code is for example a cyclic redundancy check code such as CRC8 or CRC 16.

[0049] The modulation module 12 implements an "on-off" or OOK modulation (from the English "On-Off Keying"). In this type of modulation, the light signal emitted by the light source is in a high state (i.e., light source on) to transmit a binary '1' or in a low state (i.e., light source off) to transmit a '0', with a frequency high enough to prevent the flicker from being visible to the human eye.

[0050] In one embodiment, the coding module 10 and the modulation module 12 are implemented by a computing processor 15. For example, the processor implemented by the transmitting device 4.

[0051] Alternatively, each of the coding modules 10 and modulation modules 12 is a dedicated module implemented as a programmable logic component such as an FPGA (Field Programmable Gate Array) or as a dedicated integrated circuit, such as an ASIC (Application Specified Integrated Circuit).

[0052] For example, the emitting device 4 is integrated into an industrial product and the light source 8 comprises one or more LED lamps, forming a light indicator initially intended to signal the operating status of the industrial product. The light source is preferably integrated so as to illuminate a portion of a face of the industrial product, visible to a user when the industrial product is in the operating position; for example, when the industrial product is fixed to a support, the illuminated portion is located on the front face of the product.

[0053] The modulation of the emitted light signal is indiscernible to the naked eye. Advantageously, modulating the light signal to transmit additional digital data does not disrupt the initial function of the light indicator of the industrial product.

[0054] For example, the digital data D includes additional information relating to the industrial product, such as a unique product identifier, an IP (Internet Protocol) address or a URL (Uniform Resource Locator or web address), a key or code, the status of the registers, a BLE (Bluetooth Low Energy) pairing password, or dynamic keys for Zigbee commissioning. More generally, the digital data D includes information on wireless communication commissioning or pairing, measurements taken by the product, and the product's status. This makes it easier, for example, to install and commission or to maintain a product by a user. It also makes it possible to improve the cybersecurity of a product.

[0055] The modulated light signal is emitted by the light source 8.

[0056] The receiving device 6, also simply called receiver, includes an image sensor 20, for example an optical camera with CMOS sensors (for "Complementary metal-oxide-semiconductor"), adapted to capture light signals in the form of a digital image, a digital image being composed of one or more pixel matrices, each pixel of a pixel matrix having an associated numerical value.

[0057] Depending on the calibration parameters of the image sensor 20, in particular the sensitivity (expressed in ISO or gain in dB), the exposure time, and the image (or frame) acquisition time, the acquired digital images contain values ​​representative of the high or low state, or of a transition between these states, in an image area illuminated by the light source. Thus, an acquired digital image contains an area with light and dark fringes, corresponding respectively to the high and low states of the light signal.

[0058] The acquired digital image is transmitted to a demodulation device 22, and the result of the demodulation device 22 is transmitted to a decoding module 23 to obtain as output a set of decoded digital data D*.

[0059] In the absence of loss or error, the decoded digital data D* are identical to the digital data D.

[0060] In one embodiment, the demodulation device 22 and the decoding module 23 are implemented by a computing processor 25.

[0061] Alternatively, each of the demodulation devices 22 and decoding devices 23 is a dedicated module implemented as a programmable logic component such as an FPGA (Field Programmable Gate Array) or as a dedicated integrated circuit, such as an ASIC (Application Specified Integrated Circuit).

[0062] In one embodiment, the receiving device 6 is a portable electronic device, such as a mobile phone or smartphone, an electronic tablet, a laptop computer, or any other portable electronic device equipped with a camera and an electronic computing device.

[0063] When the receiving device 6 is placed by a user so that the image sensor 20 of the receiving device is placed substantially opposite the light source 8, at a distance from the light source 8 chosen by the user and for example between 0cm (i.e., right next to it) and 6cm, and the receiving device 6 is put into a VLC reception mode, the image or images captured include, in an area illuminated by the light signal emitted by the light source, vertically arranged fringes representing the high or low states of the emitted signal.

[0064] Thus, a wireless data transmission is carried out between the transmitter 4 and the receiver 6, using VLC communication.

[0065] The demodulation device 22 is an electronic computing device implementing the demodulation process of data modulated by amplitude modulation of a light signal emitted by the light source 8 of the emitting device 4.

[0066] In one embodiment, the demodulation device 22 comprises:

[0067] -a module 24 configured to calculate an average value per column of said digital image, and to store average values ​​per column in association with a column index, arranged between a first edge index corresponding to a first edge of said image and a second edge index corresponding to a second edge of said image;

[0068] - a module 26 configured to determine a maximum value of said average values, and to calculate a threshold from said maximum value,

[0069] - a module 28 configured to determine a first column index cor corresponding to the first average value greater than or equal to said threshold starting from the first edge index, and a second column index corresponding to the first average value greater than or equal to said threshold starting from the second edge index;

[0070] -a module 30 configured to extract a subset of average values ​​between the first column index and the second column index;

[0071] -a module 32 configured to demodulate binary data from said subset of average values.

[0072] Preferably, modules 24, 26, 28, 30, and 32 are implemented as software instructions forming a computer program which, when executed by a processing unit 25, performs the modulated data demodulation process as described below. This software code is stored in an electronic memory of the receiving device 6.

[0073] When the process is implemented in the form of one or more software programs, that is, in the form of a computer program, also called a computer program product, it is further capable of being stored on a computer-readable medium (not shown). A computer-readable medium is, for example, a medium capable of storing electronic instructions and being connected to a bus of a computer system. For example, a readable medium is an optical disc, a magneto-optical disc, ROM, RAM, any type of non-volatile memory (e.g., FLASH or NVRAM), or a magnetic card. A computer program comprising software instructions is then stored on the readable medium.

[0074] Alternatively, each of the modules 24, 26, 28, 30, 32 is a dedicated module implemented as a programmable logic component such as an FPGA (Field Programmable Gate Array) or as a dedicated integrated circuit, such as an ASIC (Application Specified Integrated Circuit).

[0075] Fig. 3 is a synoptic diagram of the main steps of an embodiment of a method for demodulating data modulated by amplitude modulation of a light signal emitted by a light source of an emitting device.

[0076] The method includes a step 40 of acquiring a digital image, comprising an area illuminated by the light source, the area comprising fringes corresponding to high and low states of the light signal, and fringes corresponding to a transition between these states.

[0077] The acquired digital image is a grayscale image, corresponding to the luminance of the light signal. It is formed of a pixel matrix, each pixel having a value representing an associated grayscale level. For example, each pixel takes a value coded on 8 or 16 bits.

[0078] For example, when luminance is coded on 256 levels of grey, the light fringes correspond to a high state of the light signal, and the dark fringes correspond to a low state of the light signal, and the grey fringes correspond to the transitions between these states.

[0079] The method then includes a step 42 of calculating an average value by column of the digital image, and storage of average values ​​calculated in association with a column index.

[0080] For example, the calculated average values ​​are stored in an array or in an ordered list of values, the list being ordered according to the column indices. The calculated average values ​​form a one-dimensional SI signal (or 1D signal) representative of the columns of the digital image.

[0081] The SI signal thus formed is illustrated in graph G1 of [Fig.4], which represents column index values ​​on the abscissa and calculated average values ​​on the ordinate.

[0082] For a digital image with N columns, the column indices are integer indices between a first edge index, for example i=0, corresponding to a first edge of the acquired digital image, and a second edge index, for example i=Nl, corresponding to a second edge of the acquired digital image. In other words, the first edge is a first vertical edge of the digital image, and the second edge is the second vertical edge, parallel to the first edge.

[0083] The process then includes a step 44 of determining the maximum value Vmax of the calculated and stored average values, and a step 46 of calculating a threshold Th from the maximum value Vmax.

[0084] Preferably, the threshold Th is equal to a percentage of Vmax, for example 40% of V max*

[0085] More generally, the threshold Th is equal to a percentage P% of Vmax between 30% and 50%.

[0086] The threshold Th is also stored.

[0087] The process then includes a step 48 of determining a first column index, cb corresponding to the first average value greater than or equal to the threshold Th starting from the first edge index and traversing the column indices in the ascending direction, and of determining a second column index, c2, corresponding to the first average value greater than or equal to the threshold Th starting from the second edge index and traversing the column indices in the descending direction.

[0088] In other words, the second index corresponds to the last average value greater than or equal to the threshold Th of the stored 1D signal, by traversing the indices in the ascending direction.

[0089] Thus, all the values ​​of the samples of the signal S1 (signal of average values) between 0 (first edge index) and crl and all the values ​​of the signal SI between c2+l and Nl (second edge index) are below the threshold Th.

[0090] A subset of average values, forming a subsignal S2, is then extracted in the extraction step 50, the subsignal S2 being formed from the average values ​​comprising between the first column index Ci and the second column index c2.

[0091] The sub-signal S2 is represented in the graph G2 of [Fig.4].

[0092] Advantageously, the sub-signal S2 corresponds to the area actually illuminated by the light source.

[0093] Advantageously, the method allows the size of the sub-signal S2 to be dynamically adapted without prior knowledge of the size (e.g., the diameter) of the light source and the distance between the image sensor and the light source. Thus, the potentially noisy, spurious values ​​corresponding to the (unlit) image background are automatically eliminated.

[0094] The process then includes a demodulation of binary data from the subset of average values ​​extracted in step 50.

[0095] In one embodiment, the demodulation is carried out in two steps, respectively a step 52 of calculating a thresholding curve by a segmentation method, and a step 54 of extracting binary data by applying the thresholding curve to each column of the digital image.

[0096] In one embodiment, the segmentation method for calculating the thresholding curve is a polynomial curve fitting.

[0097] The calculated thresholding curve Cth is illustrated on graph G2 of [Fig.4].

[0098] For each column index, if the average value is above the decimal point corresponding to the threshold curve, a binary value equal to 1 is extracted, and if the average value is below the point on the threshold curve, a binary value equal to 0 is extracted.

[0099] The invention has been described above in the context of a vertical orientation of the fringes observed in the digital image. This orientation is related to the direction of observation of the captured digital image. It is clear that it is easy for a person skilled in the art to transpose the described method for an application to digital images with horizontal fringes.

[0100] Advantageously, the method allows binary data to be extracted from an illuminated area of ​​the digital image by dynamic adaptation, and therefore the potentially noisy background image is not used in the demodulation step. The accuracy of the demodulation is thus increased.

[0101] Advantageously, modulating the light signal to transmit additional digital data does not disrupt the original function of the industrial product's indicator light. Thus, it is possible to integrate the proposed functionality without requiring significant structural modifications to existing products, thereby limiting costs.

Claims

Demands

1. A method for demodulating data modulated by amplitude modulation of a light signal emitted by a light source (8) of an emitting device, the method comprising an acquisition (40) of a digital image comprising an area illuminated by said light signal, said area comprising fringes corresponding to high and low states of the light signal, the method being characterized in that it further comprises steps of: -calculating (42) an average value per column of said digital image, and storing the average values ​​per column in association with a column index, arranged between a first edge index corresponding to a first edge of said image and a second edge index corresponding to a second edge of said image;-determination (44) of a maximum value (Vmax) of said average values, and calculation (46) of a threshold from said maximum value, -determination (48) of a first column index (c1) corresponding to the first average value greater than or equal to said threshold starting from the first edge index, and of a second column index (c2) corresponding to the first average value greater than or equal to said threshold starting from the second edge index; -extraction (50) of a subset of average values ​​between the first column index and the second column index; -demodulation (52, 54) of binary data from said subset of average values.

2. A method according to claim 1, wherein said threshold is a percentage of said maximum value, preferably between 30% and 50%.

3. Method according to claim 2, wherein said threshold is equal to 40% of said maximum value.

4. A method according to any one of claims 1 to 3, wherein in the storage step (42), the average values ​​per column are stored in a table or in a list ordered according to the column indices.

5. A method according to any one of claims 1 to 4, wherein the binary data demodulation step includes calculating a threshold curve by a segmentation method.

6. Device for demodulating data modulated by modulation amplitude of a light signal emitted by a light source of an emitting device, the demodulation device being configured to acquire a digital image comprising an area illuminated by said light signal, said area comprising fringes corresponding to high and low states of the light signal, the device being characterized in that it further comprises modules configured to: -calculate (24) an average value per column of said digital image, and store average values ​​per column in association with a column index, arranged between a first edge index corresponding to a first edge of said image and a second edge index corresponding to a second edge of said image;-determine (26) a maximum value of said average values, and calculate a threshold from said maximum value, -determine (28) a first column index corresponding to the first average value greater than or equal to said threshold starting from the first edge index, and a second column index corresponding to the first average value greater than or equal to said threshold starting from the second edge index; -extract (30) a subset of average values ​​between the first column index and the second column index; -demodulate (32) binary data from said subset of average values.

7. Demodulation device according to claim 6, wherein said threshold is a percentage of said maximum value, preferably between 30% and 50%.

8. Electronic device comprising an image sensor and a device for demodulating data modulated by amplitude modulation of a light signal according to claims 6 and 7.

9. Electronic device according to claim 8, said electronic device being a mobile phone or electronic tablet with at least one integrated CMOS image capture device.

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