ELECTRONIC DEVICE ASSOCIATED WITH A PHOTOVOLTAIC MODULE TO OPTIMISE THE THROUGHPUT OF A BIDIRECTIONAL VLC TRANSMISSION

Abstract

The invention relates to a bidirectional wireless communication device which is based on the use of light, including emitting modules, each emitting amplitude- and/or phase-modulated light; and a receiving module made up of: a photodetector illuminated by said modulated light and generating a modulated electrical signal in response to said modulated light; and a processing module for processing the signal generated by said photodetector. The receiving module includes an electronic means positioned between the photodetector and the signal-processing module and capable of matching the impedance of the photodetector to maximise the signal-to-noise ratio of the electrical signal by minimising distortions of said electronic signal associated with incorrect impedance matching at the output of the photodetector, while maximising the level of the modulated electrical signal and the throughput of transmitted data.

Claims

1. A bidirectional wireless communication device based on the use of light, comprising: (a) one or more emission modules, each emission module including: a light source powered by a control means and emitting an amplitude- and/or phase-modulated light; a control means which generates an electrical signal derived from digital/analog conversion of source data to be transmitted; and (b) a reception module including: a photodetector illuminated by said modulated light and generating a modulated electrical signal in response to said modulated light; a processing module for the signal generated by said photodetector and capable of communicating with the control means via a return channel; said wireless communication device being characterized in that wherein the reception module further includes an electronic means connected between the photodetector and the signal processing module and capable of matching the impedance of the photodetector so as to maximize the signal-to-noise ratio of the modulated electrical signal by minimizing the distortions of said modulated electrical signal linked to a poor impedance matching at the output of the photodetector, while maximizing the level of the modulated electrical signal and the throughput of transmitted data.

2. The wireless communication device as claimed in claim 1, wherein said photodetector is a photovoltaic module capable of producing an electrical charge or power supply current.

3. The wireless communication device as claimed in claim 1, wherein said electronic means capable of matching the impedance of the photodetector comprises: physical components of variable values, such as capacitors, inductors and/or resistors; an electronic module for managing said physical components.

4. The wireless communication device as claimed in claim 1, wherein the electrical signal generated by said control module comprises a direct component and an alternating component.

5. The wireless communication device as claimed in claim 1, wehrein said modulated light is an incoherent or coherent light, emitted respectively by a light source such as a light-emitting diode or a laser diode.

6. The wireless communication device as claimed in claim 1, wherein said modulated light (1) is emitted by the light source in wavelength ranges corresponding to the visible, to the ultraviolet and/or to the infrared.

7. The wireless communication device as claimed in claim 1, wherein said source data (2) can be a reference signal or communication data.

8. The wireless communication device as claimed in claim 1, wherein said device comprises a plurality of emission modules which emit modulated lights with different modulation characteristics, the photodetector being incorporated in a mobile object which successively receives one or another of said modulated lights and having an electronic impedance matching means capable of maximizing the throughput of data transmitted by each of said emission modules.

9. A method for matching the impedance of the photodetector of the wireless communication device as claimed in claim 1, wherein the method comprises: (a) initializing the communication; (b) setting an initial impedance value using the electronic means, said value being a function of the nature of the photodetector; (c) setting a criterion representative of the quality of the electrical signal received which is acceptable for the communication, denoted an acceptable quality criterion; (d) adjusting the impedance of the photodetector by successive increments so as to maximize the criterion representative of the level of the electrical signal received, as long as the criterion representative of the quality of the electrical signal received is better than the acceptable quality criterion; and (e) transmitting the modulated light signal containing the communication data.

10. A method for matching the impedance of the photodetector of the wireless communication device as claimed in claim 1, wherein the method comprises: (a) initializing the communication; (b) setting an initial impedance value using the electronic means, said value being a function of the nature of the photodetector; (c) adjusting the impedance of the photodetector by successive increments so as to improve the criterion representative of the quality of the electrical signal received, said better criterion representative of the quality of the electrical signal received being denoted an optimized quality criterion with an impedance defined as a pre-optimized impedance; (d) adjusting the pre-optimized impedance of the photodetector by successive increments so as to maximize the criterion representative of the level of the electrical signal received, as long as the criterion representative of the quality of said electrical signal received is better than the optimized quality criterion; and (e) transmitting the modulated light signal containing the communication data.

11. The method for matching the impedance of the photodetector of the wireless communication device as claimed in claim 9, wherein the initialization of the communication incomprises transmitting, via the emission module, a header signal associated with a reference signal known to the reception module.

12. The method for matching the impedance of the photodetector of the wireless communication device as claimed in claim 9, wherein the criterion representative of the quality of the signal transmitted is a characteristic of a Fourier transform, a bit error ratio, a frame error ratio or a packet error ratio of the signal transmitted.

13. The method for matching the impedance of the photodetector (11) of the wireless communication device as claimed in claim 9, wherein the criterion representative of the level of the signal transmitted is a signal-to-noise ratio, a peak-peak amplitude, a maximum amplitude or a minimum amplitude of the signal transmitted.

14. The method for matching the impedance of the photodetector (11) of the wireless communication device as claimed in claim 9, wherein the adjustment of the impedance of the photodetector by successive increments so as to reach a targeted criterion comprises: (a) choosing an incrementation pitch; (b) measuring the criteria representative of the quality or of the level of the electrical signal received obtained respectively for the reference signal, for the signal received with an impedance equal to the initial impedance plus the incrementation pitch and for the signal received with an impedance equal to the initial impedance minus the incrementation pitch; (c) comparing the criteria representative of the quality or of the level of the electrical signal received two-by-two, by setting an impedance value corresponding to the targeted criterion and by taking, for a new reference signal, the electrical signal received with said impedance value; (d) repeating the steps of measurement and of comparison of bit error ratios or of signal-to-noise ratios by an iterative method, until the targeted criterion is reached by the reference electrical signal.

Description

FIGURES

[0058] The invention will be better understood from its detailed description, in relation to the figures, in which:

[0059] FIG. 1 is a diagram of the bidirectional wireless communication device that is the subject of the invention;

[0060] FIGS. 2a, 2b and 2c are reproductions of the screen of an oscilloscope which displays the curves representative of the alternating component of the electrical signal emitted by the control module and the electrical signal generated by a photovoltaic module, for different impedance values;

[0061] FIG. 3 is a flow diagram of a method for matching the impedance of the photovoltaic module of the wireless communication device that is the subject of the invention;

[0062] FIG. 4 illustrates a particular embodiment of the device that is the subject of the invention, in which the reception module is incorporated in a mobile object which successively receives several modulated lights from different light sources.

DETAILED DESCRIPTION

[0063] Refer to FIG. 1, which is a diagram of the bidirectional wireless communication device that is the subject of the invention. This device comprises an emission module 10 and a reception module 20. The emission module 10 makes it possible to encode source digital data 2, for example from the internet, to transmit them in the form of an amplitude- and/or phase-modulated light 1. For this, the light source 9, such as a light-emitting diode, is powered by a control means 6 which generates an electrical signal generally comprising a direct component 7 and an alternating component 8. The direct component 7 is used to bias said light-emitting diode 9 in order to produce the lighting function, and the alternating component 8 is derived from the digital/analog conversion of the source data 2. The reception module 20 is composed of a photodetector such as a photovoltaic module 11 which transforms the modulated light 1 into a modulated electrical signal 14, an electronic means 13 for matching the impedance of the photovoltaic module 11, and a processing module 12 for the electrical signal 15. The processing module 12 for the electrical signal 15 is capable of communicating with the control means 6 of the emission module 10 via the return channel 17, and with the member for managing the electronic impedance matching means 13 via the channel 16. The role of the electronic means 13 is to match the impedance of the photovoltaic module 11 which acts on the quality and the level of the electrical signal 15 in order to maximize the throughput of the data transmitted 18.

[0064] FIGS. 2a, 2b and 2c are reproductions of the screen of an oscilloscope which displays the curves representative of the alternating component 8 of the electrical signal emitted by the control module 6 at a frequency of 1 kHz and of the electrical signal 15 generated by the photovoltaic module 11 for different impedance values adjusted via the electronic means 13.

[0065] FIGS. 2a and 2b present two cases where the impedance matching is not optimized. The electrical signal 15a is distorted and its amplitude is too weak for the signal processing module 12 to be able to detect it (FIG. 2a). The quality and the level of the signal are not therefore acceptable for the communication to take place. The electrical signal 15b is not distorted, but its amplitude is too weak for the signal processing module 12 to be able to detect it (FIG. 2b). In this case, it is the level of the signal which limits the communication. FIG. 2c presents an optimized impedance matching, with an electrical signal 15c whose quality and level are good. This last configuration makes it possible to maximize the throughput of data transmitted 18.

[0066] FIG. 3 is a flow diagram of a method for matching the impedance of the photovoltaic module of the wireless communication device that is the subject of the invention. To make it easier to understand the description of FIG. 3, the bit error ratio or the packet error ratio, that is thus sought to be minimized in this example, is taken for quality criterion (CQ) of the signal received. Also taken for level criterion (CN) is the signal-to-noise ratio. Said impedance matching method comprises the following steps:

[0067] 1. initialization of the communication;

[0068] 2. initialization of the system by: [0069] a. choosing the initial value of the impedance IM of the photovoltaic module defined by the impedance matching software as a function notably of the nature of the photodetector and of the type of modulation; [0070] b. defining an acceptable quality criterion CQ_Acc as a function of the parameters of the communication such as the throughput, the type of modulation or the illumination; [0071] c. measuring a signal level criterion CN_Ref for the reference signal received with an initial impedance IM; [0072] d. choosing the incrementation pitch P, whose value can be real or imaginary;

[0073] 3. impedance matching algorithm comprising the following steps: [0074] a. initialization of the impedance matching; [0075] i. initialization of the value IM_1 equal to the value IM+P; [0076] measurement of CN_1 (corresponding to the value of IM_1) [0077] measurement of CQ_1 (corresponding to the value of IM_1) [0078] ii. initialization of the value IM_2 equal to the value IM-P; [0079] measurement of CN_2 (corresponding to the value of IM_2) [0080] measurement of CQ_2 (corresponding to the value of IM_2) [0081] b. impedance matching: [0082] i. if CQ_Acc>min(CQ_1, CQ_2) [0083] if CN_1>CN_ref and CQ_1<CQ_Acc [0084] initialization* of the value IM_3=IM_1+P [0085] measurements of the values CN_3 and CQ_3 [0086] if CN_1<CN_3 and CQ_3<CQ_Acc then IM_1=IM_3 and CN_1=CN_3 and the process resumes at the step of initialization* of the value IM_3=IM_1+P [0087] if CN_1>CN_3 and CQ_3<CQ_Acc then the impedance is optimized and has the value IM_1 [0088] if CQ_3>CQ_Acc [0089] then the impedance is optimized and has the value IM_1 [0090] if CN_2>CN_Ref and CQ_2<CQ_Acc [0091] initialization** of the value IM_3=IM_2+P [0092] measurements of the value CN_3 and CQ_3 [0093] if CN_2<CN_3 and CQ_3<CQ_Acc then IM_2=IM_3 and CN_2=CN_3 and the process resumes at the step of initialization** of the value IM_3=IM_2+P [0094] if CN_2>CN_3 and CQ_3<CQ_Acc then the impedance is optimized and has the value IM_2 [0095] if CQ_3>CQ_Acc [0096] then the impedance is optimized and has the value IM_2 [0097] else the optimized impedance has the value IM [0098] ii. if CQ_Acc<min(CQ_1, CQ_2) [0099] the impedance is optimized and the value of this impedance is equal to IM

[0100] FIG. 4 illustrates a particular embodiment of the device that is the subject of the invention, in which the reception module 20 is incorporated in a mobile object which successively receives during its movements, several modulated lights (1a, 1b, 1c) derived from different emission modules (10a, 10b, 10c) and whose frequency and/or phase modulations can be different. That illustrates the capacity of the reception module 20, by virtue of the impedance matching function of the photovoltaic module 11, to universally decode source data transmitted by different emission modules (10a, 10b, 10c).

ADVANTAGES OF THE INVENTION

[0101] Ultimately, the invention meets the aims set well by making it possible to improve the quality and the level of the signal received by a photodetector, which makes it possible to increase the data transmission throughputs and/or to be able to successively decode information transmitted by different emission modules.