Patent Publication Number: US-2021195720-A1

Title: System for communicating via signals of li-fi type

Description:
FIELD OF THE INVENTION 
     The present invention falls within the field of wireless communications. The invention preferably relates to a system for communicating data via Li-Fi signals coming from an infrared light source and/or a visible light source. The invention is in particular intended for an application in the aeronautical field, to equip an aircraft. 
     BACKGROUND OF THE INVENTION 
     Conventional aircraft cabins, in particular for mainline planes, are provided with pieces of equipment, such as screens, generally placed at the passenger seats, to offer each passenger limited access to media such as films. 
     To interconnect the various pieces of equipment present in the cabin, a large number of wirings must be installed throughout the cabin in areas that are sometimes not easily accessible, generally disposed under the floor or in the ceiling. 
     The weight of these wirings and the associated connections particularly affects the mass balance of the aircraft. 
     In addition, when an airline company has to redesign the cabin of the aircraft, all or part of these wirings must be replaced, resulting in significant maintenance times and downtime for the aircraft. 
     The replacement of these wired links by wireless links, in particular via the Wi-Fi (acronym for Wireless Fidelity) protocol, allowed to overcome the mentioned difficulties. 
     As a reminder, Wi-Fi allows to create a local wireless network, over a radius of several tens of metres, using radio waves from the electromagnetic spectrum. 
     Wireless connections of the Wi-Fi type have also allowed to cope with the growing need of passengers who also wish to take advantage of their electronic devices, such as phones, tablets and laptops. 
     However, this Wi-Fi communication protocol has many disadvantages, known elsewhere in their applications other than avionics:
         the use of Wi-Fi may cause interference with other apparatuses present on the aircraft;   the use of Wi-Fi moreover poses problems for the security of communications, the radio waves being able to pass through the walls; the signals can thus be intercepted and hacked,   the use of Wi-Fi also raises public health questions regarding the risks associated with prolonged exposure to such electromagnetic radiation.       

     OBJECT AND SUMMARY OF THE INVENTION 
     The present invention aims at overcoming the aforementioned disadvantages. 
     To this end, the present invention proposes a communication system by modulated optical signals of Li-Fi (acronym for Light Fidelity) signal type. 
     Li-Fi is a wireless communication technology based on the use of light in the visible range (wavelength comprised between 400 nm and 780 nm) or the infrared range (wavelength comprised between 780 nm and 2 μm) as information carrier. 
     The principle of Li-Fi is based on encoding and sending data via amplitude, frequency or phase modulation of a light source, according to a standardised protocol. 
     The communication system according to the invention allows the transmission of data to and from a plurality of defined privileged spaces. 
     The communication system is intended in particular for the aeronautical field, to equip an aircraft, but can also be intended for any other field, such as the railway field or else the automotive field, without this list being exhaustive, to equip any means of transport. 
     The communication system comprises:
         a plurality of first light sources, each first light source being adapted to emit, in the infrared, a modulated optical signal of the Li-Fi signal type, called first modulated optical signal,   a plurality of optical fibres,   a plurality of optical interfaces, one optical interface at an end of each optical fibre,
 
each optical fibre being adapted to guide a first modulated optical signal, coming from only one of said first light sources, in the direction of one of said optical interfaces adapted to broadcast said first modulated optical signal into a defined privileged space.
       

     Each optical fibre is also adapted to transport a modulated optical signal of the Li-Fi signal type coming from the associated defined privileged space, called second modulated optical signal, in the direction of a device for acquiring said second modulated optical signal. 
     The second modulated optical signal is emitted by a light source located in a piece of equipment disposed in the privileged space. Preferably, said light source emits in the infrared. 
     Such a communication system allows the creation of a delimited privileged space, and allows a connection to a network given to a user located only in this privileged space. Any attempt to connect to this network outside of the privileged space is made impossible, thanks to the use of Li-Fi technology. 
     Such a communication system advantageously allows a connection, which is simultaneous or not, of all the pieces of equipment (mobile phone, tablet, fixed screen, laptop, etc.) disposed in a privileged space, to a given network. 
     Such a communication system, combining Li-Fi technology and optical fibre for its ability to distribute data, allows to overcome the problems of installation complexity and wiring weight, but also constraints related to data security, electromagnetic pollution encountered with Wi-Fi and its health problems. 
     The use of infrared light, invisible to the human eye, for the distribution of data, via Li-Fi technology, within the privileged space allows to provide a user located in this privileged space, with a connection, regardless of the lighting illuminating the privileged space. 
     Such a communication system according to the invention advantageously allows to broadcast distinct data into each privileged space. It allows to address to a user identified in a privileged space, specific data adapted to said user. 
     According to particular implementations, the communication system according to the invention further meets the following features, implemented separately or in each of their technically operative combinations. 
     In preferred embodiments of the invention, to reduce power consumption as well as cost, each first light source is a light-emitting diode. 
     In other embodiments of the invention, each first light source is a laser. 
     In particular embodiments of the invention, the communication system comprises a single second light source adapted to emit an optical signal in the visible spectrum, called visible optical signal. This second light source allows to illuminate several privileged spaces. Each optical fibre is adapted to transport optical signals coming from only one of said first light sources and from the second light source, in the direction of one of said optical interfaces. 
     In such an embodiment, the distribution of the visible light and data, in a privileged space, takes place on a single medium, the optical fibre. This arrangement facilitates installation and further reduces the weight of the wiring. 
     The use of two separate light sources, one emitting in the visible range to illuminate the privileged space, the other to distribute the data, allows to provide a user located in the privileged space with access to internet data and/or entertainment when the light is off in said privileged space. 
     In particular exemplary embodiments of the invention, the second light source is adapted to emit an optical signal of white light. 
     In preferred embodiments, the communication system comprises a plurality of second light sources, each second light source being adapted to emit an optical signal in the visible spectrum, called visible optical signal. Each second light source is intended for lighting a single privileged space. Each optical fibre is adapted to guide the first optical signal coming from one of said first light sources and the visible optical signal coming from only one of said second light sources, in the direction of one of said optical interfaces. 
     According to preferred embodiments, each second light source is adapted to emit a modulated visible optical signal. The communication system further comprises a plurality of switching devices, one switching device per privileged space. Each switching device being adapted:
         when a privileged space is illuminated by a second light source, to deactivate the first light source,   when a privileged space is not illuminated by a second light source, to activate the first light source.       

     Thus, when the privileged space is lighted, the data communication and the lighting is carried out by the same second light source. When the privileged space is not lighted, the data communication is carried out only by the first light source. 
     In preferred embodiments, each second light source is a combination of at least two light-emitting diodes, or lasers, each adapted to emit a different colour temperature to create mood light in the privileged space. 
     According to preferred embodiments, the plurality of first light sources, the plurality of second light sources and the plurality of acquisition devices are arranged in a data transmission/reception unit. 
     According to preferred embodiments, the plurality of first light sources and the plurality of acquisition devices are arranged in a data transmission/reception unit, and the plurality of second light sources are arranged outside said data transmission/reception unit. 
     According to particular embodiments of the invention, the communication system comprising a device for controlling the turning on/off of the optical signal in the visible spectrum in a privileged space. 
     The invention also relates to an aircraft comprising a communication system as defined above in one of its embodiments. 
     Such a communication system arranged in an aircraft allows the creation of a privileged space allowing a connection of a passenger to the internal and/or external network of the aircraft only in his privileged space, for example a physical location linked to the seat for the passenger. Any connection external to the aircraft on the aircraft network is made impossible, thanks to the use of Li-Fi technology. 
     Such a communication system arranged in an aircraft advantageously allows to distribute data internal and/or external to the aircraft to one or more multiple pieces of equipment (mobile phone, tablet, fixed screen, laptop, etc.) disposed in the same privileged space. 
     Such a communication system, combining Li-Fi technology and optical fibre for its ability to distribute data, allows to overcome the current problems of installation complexity and the weight of wiring in the aircraft but also the constraints related to data security, electromagnetic pollution encountered with Wi-Fi. 
     Such a communication system arranged in an aircraft advantageously allows to broadcast distinct data into each privileged space. It allows to address to a user (passenger, cabin crew members) identified in a privileged area specific data adapted to said user. For example, it may be considered to inform an identified passenger about his next connection, any delays . . . . It may also be considered to prohibit the broadcasting of entertainment data to cabin crew members. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood upon reading the following description given with reference to the appended drawings: 
         FIG. 1  illustrates a schematic representation of an aircraft cabin incorporating a first configuration of a communication system; 
         FIG. 2  illustrates an example of a data transmission/reception unit of the communication system of  FIG. 1 ; 
         FIG. 3  illustrates a schematic representation of an aircraft cabin incorporating a variant of the first configuration of the communication system; 
         FIG. 4  illustrates a schematic representation of an aircraft cabin incorporating a second configuration of a communication system; 
         FIG. 5  illustrates an example of a data transmission/reception unit of the communication system of  FIG. 4 ; 
         FIG. 6  illustrates another example of a data transmission/reception unit of the communication system of  FIG. 4 ; 
         FIG. 7  illustrates a schematic representation of an aircraft cabin incorporating a variant of the second configuration of the communication system; and 
         FIG. 8  illustrates an example of a data transmission/reception unit of the communication system of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION 
     The present invention relates to a data communication system. 
     The communication system can, in general, equip any means of transport, in particular those in the aeronautical, railway or automotive fields, without this being restrictive of the invention. 
     The invention is described in the particular context of one of its preferred fields of application wherein the communication system is disposed in a civilian airliner. However, nothing excludes having the communication system in any other type of aircraft, whether it is civilian or military. Thus, it may be possible for example to have the communication system in a helicopter. 
       FIG. 1  schematically illustrates the interior of an aircraft cabin  20  wherein a communication system  10  according to a first configuration of the invention is deployed. The cabin  20  conventionally comprises a plurality of seats  21 , in particular for accommodating passengers, corridors  22  for the passage of passengers and cabin crew members, and galley spaces  23 . 
     In the remainder of the description, the acronym CCM will be used to designate the cabin crew members. 
     In the example of  FIG. 1 , three passenger seats  21 , a galley space  23  and a corridor  22  are shown. 
     The communication system  10  according to the invention is adapted to communicate with pieces of equipment  70  either boarded by passengers, such as for example a tablet, a telephone or else a laptop, or present on board the aircraft, such as screens integrated into the seats  21  of the aircraft. 
     The communication system  10  according to the invention advantageously allows passengers and members of the CCM to have access to entertainment data or Internet data, regardless of the piece of equipment  70  used, in defined privileged spaces  25 . 
     Privileged space  25  means a unique and personal connection space allowing a passenger or a member of the CCM to receive and/or send data internal and/or external to the aircraft in a secure and personalised manner in a defined physical location. 
     In a particular exemplary embodiment, a privileged space  25  may correspond to a space delimited by a seat  21 , for a passenger. Thus, each passenger, when seated in his seat  21 , benefits from a unique and personal connection space to receive and transmit data confidentially. Other privileged spaces may allow to cover parts of the corridor  22  or a galley space  23 , mainly for the CCM. 
     The communication system  10  preferably comprises, as illustrated in  FIG. 1 :
         a unit  30  for transmitting/receiving data,   a plurality of optical fibres  40 , at the output of the data transmission/reception unit  30 ,   a plurality of optical interfaces  50 , one optical interface  50  at the end of each optical fibre  40 .       

     The data transmission/reception unit  30  comprises, as illustrated in  FIG. 2 , a control unit  31  adapted to convert a digital signal, carrying the data information to be transmitted, into a modulated optical signal. The modulated optical signal is of the Li-Fi type. 
     This digital signal comes, for example, from the central processing units of on-board multimedia systems (IFE), of cabin systems. 
     The data transmission/reception unit  30  further comprises a plurality of first light sources  33 . 
     Each first light source  33  receives an instruction from the control unit  31  and is controlled to emit a modulated optical signal, called first modulated optical signal. It is quite clear that the first modulated optical signal is of the Li-Fi type. 
     In a non-limiting exemplary embodiment, this modulation of the optical signal is obtained by controlling the intensity of the first light source  33  in a variable manner at very high frequency. 
     Each first light source  33  is advantageously adapted to emit in the infrared range. 
     In a preferred embodiment, each first light source  33  is a light-emitting diode (LED). 
     In another exemplary embodiment, each first light source  33  is a laser. 
     The set of first light sources  33  preferably forms a first emission module  32 . 
     The data transmission/reception unit  30  further comprises a plurality of optical modules  34 . 
     An optical module  34  is adapted to couple a first modulated optical signal coming from a first light source  33  into an optical fibre  40 . 
     It is understood here that there are as many optical fibres  40  and optical modules  34  as there are first light sources  33 . 
     An optical fibre  40  is adapted to transport a first optical signal coming from a first light source  33  to an optical interface  50 . 
     An optical interface  50 , due to its geometric features, allows to confine a first modulated optical signal, emitted by a first light source  33 , in a restricted broadcasting cone defining the volume of a privileged space  25 . 
     The number of first light sources  33 , by extension the number of associated optical modules  34 , optical fibres  40  and optical interfaces  50 , advantageously corresponds to the number of privileged spaces  25  that are desired on board the aircraft. 
     In the non-limiting exemplary embodiment illustrated in  FIG. 1 , the communication system  10  is intended to transmit data to and from five privileged spaces  25 . This communication system  10  comprises:
         a unit  30  for transmitting/receiving data comprising five first light sources (not shown),   five optical fibres  40  at the output of the data transmission/reception unit  30 , each optical fibre  40  being connected to a first light source  33 ,   five optical interfaces  50 , one optical interface  50  at the output of each optical fibre  40 ; three optical interfaces  50  each disposed at a passenger seat  21 , one optical interface  50  disposed at the corridor  22  and one optical interface  50  disposed at the galley space  23 . Each optical interface  50  broadcasts a first modulated optical signal into a privileged space  25 .       

     The optical fibres  40  are preferably deployed in an upper part of the aircraft, as illustrated in  FIG. 1 . 
     The optical interfaces  50  are preferably disposed in a ceiling  24  of the aircraft, for example above each seat  21 , near the individual aerators. 
     The data transmission/reception unit  30  is in turn preferably delocalised, for example in a part of the aircraft gathering all or part of the electronic and electrical pieces of equipment necessary for the operation of the aircraft. 
     In a preferred exemplary embodiment of an optical fibre, the optical fibre  40  is a glass optical fibre. Such an optical fibre allows to transport an optical signal, with limited attenuation. 
     In other non-limiting exemplary optical fibre embodiments, said optical fibre may be a plastic fibre or a plastic-coated glass fibre, such as a PCF fibre (acronym for “Polymer Cladded Fiber”), a PCS fibre (acronym for “Plastic Cladded Silica”), an HCS fibre (acronym for “Hard-Clad Silica”) or else an HPCF fibre (acronym for “Hard Polymer Cladded Fibre”). 
     The optical interface  50  is advantageously a passive optical interface, that is to say an optical interface not supplied with electricity. 
     In an exemplary embodiment of an optical interface, the optical interface  50  comprises a lens or a lens system. 
     In an embodiment of an optical interface, the optical interface  50  is a lens. 
     In an embodiment, the optical interface  50  is installed, for example on the ceiling, with at least one degree of rotation, so that the passenger and/or the cabin crew members can orient it, and consequently orient the positioning of the privileged space, according to his wishes, within the limit of not covering the closest privileged space. 
     The transmission/reception unit  30  can easily be assimilated to an access point called Li-Fi access point, configured to generate and transmit Li-Fi type signals. The optical fibres  40  and the optical interfaces  50  are optical elements advantageously intended for, respectively, transporting these Li-Fi type signals and broadcasting them into privileged spaces. 
     In order to carry out the internet and/or entertainment data communication from the data transmission/reception unit  30  to a piece of equipment  70  in a privileged space, said piece of equipment should preferably comprise a module for acquiring the first modulated optical signal (not shown). Said acquisition module is adapted to detect the variations in intensity of the first modulated optical signal emitted by the first light source  33 , and broadcasted by the optical interface  50 . The acquisition module of the equipment  70  converts the data of variations in intensity of the optical signal into a digital signal. This digital signal is then processed and translated into information that can be used by said piece of equipment. 
     In an exemplary embodiment, the acquisition module of the piece of equipment is a photodiode. 
     To establish two-way data communication between the communication system and a piece of equipment  70  in a privileged space, and to reciprocally allow data to be transmitted from said piece of equipment, the communication system  10  comprises a device  35  for acquiring a modulated optical signal, preferably placed in the control unit  31 . 
     Thus, to allow data communication in a bidirectional manner per privileged space, the control unit  31 , in the downward communication direction, is adapted to convert a digital signal into a modulated optical signal and, in the upward communication direction, is adapted to convert a modulated optical signal into a digital signal. 
     “In the downward communication direction” means that the communication system  10  operates by transmitting data to a piece of equipment  70 . 
     “In the upward communication direction” means that the communication system  10  operates by receiving data from a piece of equipment  70 . 
     In an exemplary embodiment of an acquisition device, the acquisition device of the communication system  10  is a photodiode  35 . 
     Preferably, the communication system  10  comprises as many acquisition devices  35  as there are first light sources  33 . 
     Thus, for each privileged space  25  that is desired in the aircraft, a first light source  33 , an acquisition device  35 , an optical fibre  40  and an optical interface  50  are associated. 
     Each acquisition device  35  is adapted to detect variations in the intensity of a modulated optical signal, called second modulated optical signal, emitted by a piece of equipment  70 , located in the privileged space  25 , provided with a light source (not shown). It is quite clear that the second modulated optical signal is of the Li-Fi type. Preferably, the light source of the piece of equipment  70  emits in the infrared range. 
     In a non-limiting exemplary embodiment of this light source, said light source of the piece of equipment  70  is a light-emitting diode or a laser. 
     The light source of the piece of equipment  70  is adapted to emit the second modulated optical signal according to the information to be communicated to the data transmission/reception unit  30 . 
     The first light source  33  of the data transmission/reception unit  30  and the light source of the piece of equipment  70  preferentially emit at a different wavelength in the infrared range. 
     The second modulated optical signal coming from the piece of equipment  70  passes through an optical interface  50 , is transported by an optical fibre  40  to the data transmission/reception unit  30 , and then directed, via an optical module  34 , to an acquisition device  35  of the communication system  10 . 
     Each optical fibre  40  advantageously allows the transport of a modulated optical signal in the direction of downward communication (first modulated optical signal) and in that of the upward communication (second modulated optical signal). 
     Each optical module  34 , besides the fact of coupling the first modulated optical signal coming from a first light source  33  on an optical fibre  40 , is advantageously adapted to separate the wavelengths specific to each modulated optical signal to/from the optical fibre  50  (that is to say the wavelength of the first infrared modulated optical signal, in the downward communication direction, and the wavelength of the second infrared modulated optical signal, in the upward communication direction). 
     In a variant of this first configuration of the communication system  10 , illustrated in  FIG. 3 , said system may comprise several data transmission/reception units  30 . 
     Such a variant can be considered, for example for an aircraft comprising a number of seats  21  for the passengers and a number of areas to be covered for the CCM which are relatively large, such as a long-haul aircraft. 
     The number of data transmission/reception units  30  may vary depending on the number of seats  21 , the number of areas to be covered for the CCM, the number of optical fibres  40  at the output, or else the throughput performance that the user (passenger or CCM member) needs. 
     In the non-limiting example of  FIG. 3 , the communication system  10  is intended to transmit data to and from five privileged spaces  25 . It comprises two data transmission/reception units  30 , a first data transmission/reception unit  30  to serve three privileged spaces (three passenger seats), a second data transmission/reception unit  30  to serve two privileged spaces (a galley space  23  and part of the corridor  22 ). The first data transmission/reception unit  30  comprises three first light sources  33 . Each first light source  33  is connected, via an optical fibre  40 , to an optical interface  50  disposed at a passenger seat  21 . The second data transmission/reception unit  30  comprises two first light sources  33 . One first light source  33  is connected, via an optical fibre  40 , to an optical interface  50  disposed at part of the corridor  22 . Another first light source  33  is connected, via an optical fibre  40 , to an optical interface  50  disposed at the galley space  23 . 
     In a second configuration of the communication system  10 , illustrated in  FIGS. 4 and 5 , said communication system  10  is adapted, in addition to the transmission/reception of data, to transmit visible light in the privileged spaces  25 . 
     For this second configuration, the data transmission/reception unit  30  comprises a plurality of second light sources  36 . 
     Each second light source  36  is adapted to emit an optical signal in the visible range, preferably a white light optical signal. This optical signal will be referred to hereinafter as visible optical signal. 
     Each second light source  36  is, for example, a light-emitting diode, a laser, a combination of light-emitting diodes or a combination of lasers. 
     In a preferred embodiment, a second light source is a combination of at least two visible light-emitting diodes (or a combination of lasers), each emitting a different colour temperature to create mood light to the privileged space  25  associated with this second light source. 
     The data transmission/reception unit  30  preferably comprises as many second light sources  36  as there are first light sources  33 . Each second light source  36  is configured to emit an optical signal visible in a single privileged space  25 . 
     The set of second light sources preferably forms a second emission module  37 . 
     In an exemplary embodiment, illustrated in  FIG. 5 , the second transmission module  37  is disposed in the data transmission/reception unit  30 . 
     In this second configuration, each optical module  34  is adapted to couple the first modulated optical signal coming from a first light source  33  and the visible optical signal coming from a second light source  36  in a single optical fibre  40 . 
     Each optical module  34  is also adapted to combine and/or separate the wavelengths specific to each optical signal to/from the optical fibre  40  (that is to say the wavelength of the visible optical signal, the wavelength of the first infrared modulated optical signal, in the downward direction, and the wavelength of the second infrared modulated optical signal, in the upward direction). 
     In an exemplary embodiment, the optical module  34  comprises a multiplexer and a demultiplexer. 
     Each optical fibre  40  is also adapted to transport both the visible optical signal and the first and second infrared modulated optical signals. 
     In an embodiment, the communication system  10  comprises a device  60  for controlling the turning on/off of the optical signal visible in a privileged space  25 , accessible to the passenger, to allow him to turn on or off the visible light, without impacting data communication. 
     In an exemplary embodiment, the control device  60  is a push button disposed near the optical interface  50 . 
     The communication system  10 , in this second configuration, thus allows to advantageously separate the light distribution from the data distribution function. 
     Thus, the communication system  10  advantageously allows to distribute data, even when the visible light is turned off. 
     In one variant embodiment (not shown) of the second configuration of the communication system, the data transmission/reception unit  30  comprises a second light source  36  of sufficient power to emit an optical signal visible for several privileged spaces  25 , or even a single second light source  36  of sufficient power to emit an optical signal visible in all the privileged spaces  25  served by the data transmission/reception unit  30 . 
     In another variant embodiment of the second configuration of the communication system, as illustrated in  FIGS. 7 and 8 , the second transmission module  37  is disposed outside the data transmission/reception unit  30 . Such an arrangement advantageously allows to physically separate the various functions of the communication system:
         the data transmission/reception unit  30  allows the distribution of data to the privileged space,   the second emission module  37  allows the generation of lighting in the privileged space.       

     In another variant embodiment of the second configuration of the communication system, as illustrated in  FIG. 6 , the communication system is configured to allow data communication via visible or infrared light. In this variant, the second light sources  36  are therefore adapted to emit a modulated optical signal to transmit the data. It is quite clear that the modulated optical signal is of the Li-Fi type. 
     In this variant, the communication system further comprises a plurality of switching devices  38 . 
     Preferably, the plurality of switching devices  38  are disposed in the data transmission/reception unit  30 , between, on the one hand, the control unit  31 , and on the other hand, the first light sources  33  and the second light sources  36 . 
     It will be understood that there are as many switching devices  38  as there are first light sources  33  and second light sources  36 . 
     A switching device  38  is preferably configured:
         when an associated privileged space is lighted by a second light source, to deactivate the first light source so that data communication is carried out only by the second light source,   when an associated privileged space is not lighted by a second light source, to activate the first light source so that data communication is carried out only by the first light source.       

     In other words, when a second light source is inactive (i.e. the privileged space is not lighted), the first light source  33  receives an instruction from the control unit and is controlled to emit a first infrared modulated optical signal containing the data to be transmitted. When a second light source is active (i.e. the privileged space is lighted), the first light source  33  does not receive any instruction from the control unit. The second light source receives an instruction from the control unit and is controlled to emit a modulated visible optical signal containing the data to be transmitted. 
     Such a variant advantageously allows to reduce the power consumption of the communication system  10  for transmitting the data using only, either:
         a second light source  36 , when the privileged space  25  is lighted by said second light source; the functions of light and data distribution are combined;   a first light source  32 , when the privileged space  25  is not lighted; the function of light distribution is separated from that of data distribution; the data are distributed even when the light is turned off.       

     Although the invention has been described in the case of a two-way data communication between the communication system and a single piece of equipment in a privileged space, it is clear that the communication system of the invention can establish a two-way communication with several pieces of equipment located in the same privileged space, simultaneously or not, provided that each piece of equipment comprises a light source and an acquisition module as described above.