JP2009290361A - Visible light communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve receiving performance of a visible light communication system for communication data and to improve the communication effective speed of the system. <P>SOLUTION: A luminaire includes a light source unit having LEDs of red, green and blue, and a transmission control unit which performs transmission control for a visible light signal, containing communication data and generated by modulating light emitted from a predetermined LED, to a reception terminal. The transmission control unit superposes a signal current corresponding to modulated information on a current supplied to the red LED based upon a duty ratio. In combination, illumination modes of the blue LED are changed in the start timing of the visible light signal. The change in illumination mode becomes a trigger signal indicating the start of visible light communication. Consequently, the start of the visible light communication is received independently of the visible light signal, so the receiving performance is improved. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a visible light communication system that performs communication between a lighting fixture and a signal receiving unit using visible light for illumination.

  2. Description of the Related Art Conventionally, as a visible light communication system as described above, a system in which a lighting fixture includes a light emitting diode (hereinafter referred to as an LED) and a control circuit that switches on and off the LED is known (patent) Reference 1). In this system, the control circuit switches on and off of the LED at high speed, and the signal reception unit transmits and receives communication data by decoding the blinking frequency by the switching. In this system, the brightness of the light emitted from the LED is constant during visible light communication and non-communication time by fixing the lighting time and extinguishing time of the LED at a predetermined ratio.

As another form of the above system, the luminaire is composed of LEDs of three colors, red, green and blue, and the control circuit modulates only the emitted light from the red LED, so that visible light containing communication data is contained. Some devices send signals (see Patent Document 2).
JP 2004-120101 A JP 2008-34988 A

  By the way, visible light communication is asynchronous wireless serial communication that does not use a clock signal for synchronization during communication. Visible light communication can be used as mobile communication when a receiving terminal serving as a signal receiving unit is possessed by a pedestrian or the like and a visible light signal is received by the receiving terminal while the pedestrian or the like is moving. is there. Therefore, in order to improve the performance of visible light communication, it is important to synchronize between the luminaire and the signal receiver.

  FIG. 8 shows the current waveform of the LED in the conventional system as described above. Here, modulation information for modulating the emitted light from the red LED is set according to predetermined communication data, and a signal current corresponding to this modulation information is superimposed on the current supplied to the red LED. As an encoding method for setting modulation information, a 4-value PPM method that represents 2-bit data with 4 pulses is used.

  Here, a start signal for informing the start timing of the signal is added to the visible light signal so that the lighting apparatus and the signal receiving unit can be synchronized. Specifically, the current supplied to the red LED is superimposed with a repetition signal composed of a high level and a low level for 8 pulses different from the signal current in the four-value PPM method. Thus, the start of visible light communication is notified only by the modulation pattern of red light emitted from the red LED.

  Therefore, in such a conventional system, when the S / N ratio is poor in the system, there is a high possibility that the signal receiving unit erroneously receives communication data. In addition, since the start signal as described above is added to the visible light signal transmitted from one LED, the effective communication speed of the system is reduced.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a visible light communication system capable of improving the reception performance of communication data and improving the effective communication speed of the system.

  In order to achieve the above object, a first aspect of the present invention is a visible light communication system that performs communication between a lighting fixture and a signal receiving unit using visible light for illumination, wherein the lighting fixture emits red light. A light source unit having a red light emitting diode, a green light emitting diode emitting green light, and a blue light emitting diode emitting blue light, a color temperature setting unit for setting the color temperature of light emitted from the light source unit, A lighting calculation unit that determines the duty ratio of the current supplied to the light emitting diodes of each color according to the color temperature set by the color temperature setting unit, and predetermined communication data is input, from a predetermined light emitting diode according to the communication data A communication setting unit for setting modulation information for modulating the emitted light, and a visible light signal obtained by modulating the emitted light from a predetermined light emitting diode, containing the communication data A transmission control unit that controls each of the units so as to be transmitted to the signal receiving unit, and the transmission control unit performs the lighting calculation only on one or two light emitting diodes of the light source unit. A modulation control unit for superimposing a signal current corresponding to modulation information in the communication setting unit on a current supplied to the light emitting diode based on a duty ratio by the unit, and lighting of at least one light emitting diode in the remaining light source units And a modulation trigger controller that switches the mode at the start timing of the visible light signal.

  According to a second aspect of the present invention, in the first aspect of the invention, the modulation light emitting diode on which the signal current corresponding to the modulation information is superimposed by the modulation control unit is a red light emitting diode, and the modulation trigger control unit The triggering light emitting diode whose lighting mode is switched by is a blue light emitting diode.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the modulation control unit is configured to transmit the visible light signal during visible light communication and during non-communication when the visible light signal is not transmitted. The magnitude of the current supplied to the light emitting diode for modulation is controlled during visible light communication so that the light output of the light emitting diode for modulation becomes equal.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects of the present invention, the signal receiving unit is configured to turn on the trigger light emitting diode at the start timing of the visible light signal. The modulation period of the visible light signal is acquired.

  According to the first aspect of the present invention, since the lighting mode of the light emitting diode different from the light emitting diode on which the signal current corresponding to the modulation information is superimposed is switched at the start timing of the visible light signal, the change in the lighting mode is visible. This trigger signal indicates the start of optical communication. Therefore, the signal receiving unit can receive the trigger signal as a signal independent of the visible light signal, and can reliably recognize the start of visible light communication, thereby improving data reception performance. In addition, since it is not necessary to add a start signal for notifying the start timing of the signal to the visible light signal, the effective communication speed of the system is improved.

  According to the invention of claim 2, since the light emitting diode for modulation is a red light emitting diode, a highly versatile red photodiode is used as a light receiving element for receiving a visible light signal from the light emitting diode in the signal receiving unit. This system can be configured at low cost. In addition, since the wavelength range of red light is far from general illumination light, even if other fluorescent lamps are lit in the installation space of the luminaire of this system, the data reception performance in the signal reception unit is degraded. There is nothing to do. Also, since blue light has less influence on the brightness of white light than red light and green light, the red light, green light and blue light of the light emitting diodes of each color are combined to emit white light from the light source unit. In this case, since the triggering light emitting diode is a blue light emitting diode, the influence of white light on the color temperature due to switching of the lighting mode of the light emitting diode can be reduced.

  According to the invention of claim 3, when the white light is emitted from the light source unit by combining the red light, the green light and the blue light of the light emitting diodes of the respective colors, the light from the light source unit during the visible light communication and the non-communication time The color change of white light can be reduced.

  According to the invention of claim 4, since it becomes easy to achieve synchronization between the lighting fixture and the signal receiving unit, the data receiving performance in the signal receiving unit is improved. Further, since the signal receiving unit can acquire the modulation period before receiving the visible light signal, the communication speed can be automatically set when the system can select a plurality of data communication speeds.

(First embodiment)
A visible light communication system according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an electrical block configuration of a visible light communication system 1 according to the present embodiment. A visible light communication system (hereinafter referred to as this system) 1 performs communication using visible light for illumination, and is output from a lighting fixture 2 that outputs illumination light including communication data, and the lighting fixture 2. It is comprised with the receiving terminal 3 as a signal receiving part which receives communication data with the illumination light.

  First, the structure of the lighting fixture 2 of this system 1 is explained in full detail. The luminaire 2 includes a light source unit 21 composed of a plurality of light emitting diodes (hereinafter referred to as LEDs), a plurality of driver circuits 22 for lighting the light source unit 21, and lighting for controlling the color temperature of light emitted from the light source unit 21. And a control unit 23. The light source unit 21 includes a red LED 21a that emits red light, a green LED 21b that emits green light, and a blue LED 21c that emits blue light. Each driver circuit 22 is provided for each color LED, and a PWM system or a current mirror system circuit is used as the circuit. The lighting control unit 23 sets the color temperature of the light emitted from the light source unit 21 and the current supplied to each color LED according to the color temperature set by the color temperature setting unit 23a. A lighting calculation unit 23b for determining a duty ratio. The lighting control unit 23 is configured by a microcomputer or the like.

  In addition, the luminaire 2 is supplied with a data source 24 for storing communication data to be transmitted to the receiving terminal 3 and communication data stored in the data source 24, and radiates light from a predetermined LED corresponding to the communication data. A communication setting unit 25 for setting modulation information for modulation, and transmission control for performing control so that a visible light signal containing communication data and modulated from radiation emitted from a predetermined LED is transmitted to the receiving terminal 3 Part 26. Examples of the data source 24 include storage devices such as a ROM and a flash memory. Further, the data source 24 may be a personal computer connected to the lighting fixture 2 via a network, a dip switch for switching and setting communication data, or the like. In the communication setting unit 25, for example, a quaternary PPM method is used as an encoding method when setting modulation information for modulating the emitted light.

  FIG. 2 shows the configuration of the 4-value PPM system. By using this method, as shown in the figure, 2-bit data is represented by four pulse waveforms, and the light output of the light source unit 21 can be made constant regardless of the contents of the communication data.

  The transmission control unit 26 applies a signal current corresponding to the modulation information in the communication setting unit 25 to the current supplied to the LED based on the duty ratio of the lighting calculation unit 23b for only one LED of the light source unit 21. A superimposing modulation control unit 26a and a modulation trigger control unit 26b for switching the lighting mode of at least one LED in the remaining light source unit 21 at the start timing of the visible light signal are provided. The transmission control unit 26 is configured by a microcomputer or the like. In the present embodiment, the modulation LED on which the signal current corresponding to the modulation information is superimposed by the modulation control unit 26a is the red LED 21a, and the trigger LED whose lighting mode is switched by the modulation trigger control unit 26b is the blue LED 21c. is there. The modulation control unit 26a is configured to control the current supplied to the LED 21a during visible light communication so that the light output of the red LED 21a is equal between visible light communication that transmits a visible light signal and non-communication that does not transmit a visible light signal. Control the size. The modulation trigger control unit 26b switches the lighting mode of the blue LED 21c from the “lighting state” to the “lighting state” at the start timing of the visible light signal.

FIG. 3 shows current waveforms of the LEDs 21a, 21b, and 21c of the respective colors. The red LED 21a, the blue LED 21c, and the green LED 21b are supplied with current based on the duty ratio determined by the lighting calculation unit 23b. The current values I _R , I _G , and I _B of the currents that flow through the red LED 21a, blue LED 21c, and green LED 21b are set so that the white light emitted from the light source unit 21 has the color temperature set in the color temperature setting unit 23a. It is set in advance. Here, the time per one cycle of blinking of the LEDs 21a, 21b, and 21c of each color is set so that humans do not feel flickering of light, and specifically, a boundary between whether the light appears to flicker or feels continuous light. It is set below the reciprocal of the critical fusion frequency which is the frequency. This critical fusion frequency is about 30 to 40 Hz.

In addition, a signal current corresponding to the modulation information in the communication setting unit 25 is superimposed on the current flowing through the red LED 21a, and the modulation waveform portion has a configuration in which communication data is encoded by the above four-value PPM method. Yes. Here, at the beginning part of the modulated waveform portion, the current value of the blue LED21c is composed of 0 and _{I B,} thereby, the lighting aspect of blue LED21c, "off state at the start timing of the visible light signal from the red LED21a To "lit state".

  Next, returning to FIG. 1, the receiving terminal 3 of the system 1 will be described in detail. The receiving terminal 3 is composed of a PDA (Personal Digital Assistant) or a mobile phone that can receive data by visible light, and can use various applications such as navigation, still image display, and moving image display based on the received communication data. is there. The receiving terminal 3 receives the red light transmission filter 31 that transmits only the light from the red LED 21a, the blue light transmission filter 32 that transmits only the light from the blue LED 21c, and the light transmitted through the red light transmission filter 31. A red light receiving unit 33 that performs photoelectric conversion and a blue light receiving unit that receives light transmitted from the blue light transmission filter 32 and performs photoelectric conversion are provided. The red light receiving unit 33 and the blue light receiving unit 34 are configured by photodiodes or phototransistors. Further, the red light receiving unit 33 and the blue light receiving unit 34 may be color sensors in which the above-described filters are integrated with photodiodes and can independently receive light from each color LED.

  The receiving terminal 3 also includes a signal processing unit 35 that amplifies and filters the electrical signal photoelectrically converted by the red light receiving unit 33, and a demodulation control unit that demodulates the processing signal from the signal processing unit 35 and acquires communication data. 36, a display 37 that displays video corresponding to the communication data acquired by the demodulation control unit 36, and a speaker 38 that outputs audio corresponding to the communication data. The signal processing unit 35 includes, for example, an operational amplifier and a bandpass filter, and acquires a processing signal binarized by amplification and filtering processing. The demodulation control unit 36 is constituted by a microcomputer or the like, demodulates the processing signal binarized by the signal processing unit 35, and transmits digitally converted communication data to the display 37 and the speaker 38. At this time, the demodulation control unit 36 performs error processing or the like as necessary.

  Next, the operation of the visible light communication system 1 configured as described above will be described. First, operation | movement of the lighting fixture 2 is demonstrated. Here, it is assumed that the color temperature of the light emitted from the light source unit 21 is set in the color temperature setting unit 23a. For example, when white light is emitted from the light source unit 21, the color temperature is set to 5000 Kelvin, and the set color temperature is set to a pulse lighting with the current value of the current supplied to each color LED 21a, 21b, 21c being constant. In the experiment, the duty ratio of the red LED 21a is about 61%, the duty ratio of the green LED 21b is about 80%, and the duty ratio of the blue LED 21c is about 15% in the experiment. In addition, it is assumed that modulation information for modulating the emitted light from the red LED 21a corresponding to the communication data stored in the data source 24 is set in the communication setting unit 25.

  The lighting calculation unit 23b determines the duty ratio of the current supplied to the LEDs 21a, 21b, and 21c of each color according to the color temperature set in the color temperature setting unit 23a. Each duty ratio determined by the lighting operation unit 23 b is set in each driver circuit 22. The modulation control unit 26a superimposes a signal current corresponding to the modulation information in the communication setting unit 25 on the current supplied to the red LED 21a based on the duty ratio by the lighting calculation unit 23b. Thereby, the visible light signal which modulated the radiation light from red LED21a containing communication data is sent out. At this time, the packet length of the communication data is limited to the lighting time of one cycle of blinking in the red LED 21a based on the duty ratio by the lighting calculation unit 23b. In addition, the modulation trigger control unit 26b switches the lighting mode of the blue LED 21c from the “light-off state” to the “light-on state” at the start timing of the visible light signal.

  Next, the operation of the receiving terminal 3 will be described. The red light receiving unit 33 receives light transmitted through the red light transmitting filter 31 and performs photoelectric conversion, and the blue light receiving unit 34 receives light transmitted from the blue light transmitting filter 32 and performs photoelectric conversion. The signal processing unit 35 amplifies and filters the electrical signal photoelectrically converted by the red light receiving unit 33 to obtain a binarized processing signal. The demodulation control unit 36 demodulates the processing signal from the signal processing unit 35 and acquires communication data. At this time, the demodulation control unit 36 determines the start of visible light communication based on a level change from “Low” to “High” of the signal output from the blue light receiving unit 34. The demodulation control unit 36 operates various applications such as navigation, still image display, and moving image display, and transmits the digitally converted communication data to the display 37 and the speaker 38.

  As described above, according to the visible light communication system 1 according to the present embodiment, the lighting mode of the blue LED 21c different from the red LED 21a on which the signal current according to the modulation information is superimposed is switched at the start timing of the visible light signal. This change in lighting mode becomes a trigger signal indicating the start of visible light communication. Therefore, the receiving terminal 3 can receive the trigger signal as a signal independent of the visible light signal and can reliably recognize the start of visible light communication, so that the data reception performance is improved. In addition, since it is not necessary to add a start signal for notifying the start timing of the signal to the visible light signal, the effective communication speed of the system 1 is improved.

  Further, since the modulation LED is a red LED 21a, a highly versatile red photodiode can be used as a light receiving element for receiving a visible light signal from the LED 21a in the receiving terminal 3, and the system 1 can be made inexpensive. Can be configured. In addition, since the wavelength range of red light is far from general illumination light, even if other fluorescent lamps or the like are lit in the installation space of the luminaire 2 of the system 1, the data reception performance in the reception terminal 3. Will not drop. Also, since blue light has less influence on the luminance of white light than red light and green light, the red light, green light, and blue light of the LEDs 21a, 21b, 21c of the respective colors are combined to generate white light from the light source unit 21. When light is emitted, the trigger LED is the blue LED 21c, so that the influence of white light on the color temperature due to switching of the lighting mode of the LED 21c can be reduced.

  Further, when the white light is emitted from the light source unit 21 by combining the red light, the green light, and the blue light of the LEDs 21a, 21b, and 21c of each color, the white color from the light source unit 21 during visible light communication and during non-communication The color change of light can be reduced.

(Second Embodiment)
A visible light communication system according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 4 shows an electrical block configuration of the visible light communication system 1 according to the present embodiment, and FIG. 5 shows current waveforms of LEDs 21a, 21b, and 21c of the respective colors. This embodiment is different from the first embodiment in that the lighting device 2 multiplex-transmits communication data by using a red LED 21a and a green LED 21b as LEDs for modulation.

  The communication setting unit 25 of the system 1 divides communication data input from the data source 24 into two data corresponding to the red LED 21a and the green LED 21b according to a predetermined rule set in advance. Corresponding modulation information is set. Examples of the predetermined rule include a method of assigning numbers to divided data and assigning odd numbers to red LEDs 21a and even numbers to green LEDs 21b. In addition to the red LED 21a, the modulation control unit 26a of the system 1 superimposes a signal current corresponding to the modulation information in the communication setting unit 25 on the current supplied to the green LED 21b based on the duty ratio by the lighting calculation unit 23b. Here, since green light has a great influence on the luminance of white light, visible light is emitted when white light is emitted from the light source unit 21 by combining the red light, green light, and blue light of the LEDs 21a, 21b, and 21c of each color. The lighting level at the time of non-communication is set to approximately 3/4 of the maximum value of the lighting level at the time of visible light communication so that the light output of the light source unit 21 becomes equal during communication and during non-communication. Further, the time per blinking cycle of the LEDs 21a, 21b, and 21c of the respective colors is set to be equal to or less than the reciprocal number of the critical fusion frequency as in the first embodiment. The modulation trigger control unit 26b switches the lighting mode of the blue LED 21c at the start timing of the visible light signal, as in the first embodiment.

  The reception terminal 3 of the system 1 includes a red light transmission filter 31, a blue light transmission filter 32, a red light reception unit 33, and a blue light reception unit 34, and a green light transmission filter that transmits only light from the green LED 21b. 39 and a green light receiving unit 40 that receives light transmitted through the green light transmission filter 39 and performs photoelectric conversion. The signal processing unit 35 amplifies and filters the electrical signal photoelectrically converted by the green light receiving unit 40 in addition to the electrical signal photoelectrically converted by the red light receiving unit 33, and receives the red light receiving unit 33 and the green light receiving unit. Two types of processing signals corresponding to the unit 40 are acquired. The demodulation control unit 36 demodulates the two types of processing signals from the signal processing unit 35 and synthesizes the two digitally converted communication data.

  Thereby, it becomes possible to perform data communication efficiently between the lighting fixture 2 and the receiving terminal 3, and the effective communication speed of this system 1 improves.

(Third embodiment)
A visible light communication system according to the third embodiment of the present invention will be described with reference to FIG. 6 and FIG. FIG. 6 shows current waveforms of the LEDs 21a, 21b and 21c of the respective colors in the visible light communication system 1 according to the present embodiment. This embodiment is different from the first embodiment in that the communication data stored in the data source 24 is divided into a plurality of packets, and the visible light signal of the red LED 21a spans a plurality of blinking periods by the duty control of the LED. Is different. The modulation trigger control unit 26b switches the lighting mode of the blue LED 21c from the “light-off state” to the “light-on state” at the start timing of the visible light signal corresponding to the start portion of the head packet, and starts the start portion of the packet other than the head packet. At the start timing of the visible light signal corresponding to, the lighting mode of the blue LED 21c is not switched. The demodulation control unit 36 of the receiving terminal 3 acquires communication data divided into a plurality of packets based on the electric signal photoelectrically converted by the blue light receiving unit 34. Thereby, it is possible to send communication data in which a visible light signal extends over a plurality of blinking periods by duty control.

(Fourth embodiment)
A visible light communication system according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 7 shows current waveforms of the LEDs 21a, 21b and 21c of the respective colors in the visible light communication system 1 according to the present embodiment. In the present embodiment, the modulation trigger controller 26b superimposes a pulsed signal current having the same period as the modulation period s of the visible light signal from the red LED 21a on the current drive current supplied to the blue LED 21c. I have to. The receiving terminal 3 acquires the modulation period of the visible light signal by the lighting mode of the blue LED 21c at the start timing of the visible light signal as described above. Thereby, since the receiving terminal 3 is easy to synchronize with a visible light signal, the data reception performance in the receiving terminal 3 improves. In addition, since the receiving terminal 3 can acquire the modulation period before receiving the visible light signal, the communication speed can be automatically set when the system 1 can select a plurality of data communication speeds. Become.

  In addition, this invention is not restricted to the structure of the said various embodiment, A various deformation | transformation is possible in the range which does not change the meaning of invention. For example, the modulation trigger control unit 26b may switch the lighting state of the blue LED 21c from the “lighting state” to the “lighting state” at the start timing of the visible light signal.

1 is a block diagram of a visible light communication system according to a first embodiment of the present invention. Explanatory drawing of the encoding by the 4-value PPM system in a communication setting part. (A) is a figure which shows the current waveform of each LED of the said visible light communication system, (b) is a figure which shows a modulation waveform part in the current waveform of red LED. The block diagram of the visible light communication system which concerns on the 2nd Embodiment of this invention. (A) is a figure which shows the current waveform of each LED of the said visible light communication system, (b) is a figure which shows a modulation waveform part in the current waveform of red LED, (c) is a modulation waveform part in the current waveform of green LED. FIG. (A) is a figure which shows the current waveform of each LED of the visible light communication system which concerns on the 3rd Embodiment of this invention, (b) is a figure which shows a modulation waveform part in the current waveform of red LED. (A) is a figure which shows the current waveform of each LED of the visible light communication system which concerns on the 4th Embodiment of this invention, (b) is a figure which shows a modulation waveform part in the current waveform of red LED, (c) is blue The figure which shows a modulation waveform part in the current waveform of LED. The figure which shows the current waveform of each LED of the conventional visible light communication system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Visible light communication system 2 Lighting fixture 3 Receiving terminal (signal receiving part)
21 Light Source 21a Red LED (Red Light Emitting Diode)
21b Green LED (Green Light-Emitting Diode 21c Blue LED (Blue Light-Emitting Diode)
23a color temperature setting unit 23b lighting calculation unit 25 communication setting unit 26 transmission control unit 26a modulation control unit 26b modulation trigger control unit

Claims (4)

In a visible light communication system that performs communication between a lighting fixture and a signal receiver using visible light for illumination,
The lighting fixture is:
A light source unit having a red light emitting diode that emits red light, a green light emitting diode that emits green light, and a blue light emitting diode that emits blue light;
A color temperature setting unit for setting a color temperature of light emitted from the light source unit;
A lighting operation unit that determines a duty ratio of current supplied to the light emitting diodes of the respective colors according to the color temperature set by the color temperature setting unit;
Predetermined communication data is input, a communication setting unit for setting modulation information for modulating the emitted light from a predetermined light emitting diode according to the communication data;
A transmission control unit that controls each of the above-described units so that a visible light signal that includes the communication data and that modulates the emitted light from a predetermined light-emitting diode is transmitted to the signal reception unit;
The transmission control unit
For only one or two light emitting diodes in the light source unit, a signal current corresponding to the modulation information in the communication setting unit is superimposed on the current supplied to the light emitting diode based on the duty ratio by the lighting calculation unit. A modulation control unit,
A visible light communication system, comprising: a modulation trigger control unit that switches a lighting mode of at least one light-emitting diode in the remaining light source units at a start timing of the visible light signal. The light emitting diode for modulation on which the signal current according to the modulation information is superimposed by the modulation control unit is a red light emitting diode,
2. The visible light communication system according to claim 1, wherein the light emitting diode for trigger whose lighting mode is switched by the modulation trigger control unit is a blue light emitting diode.   The modulation control unit is configured to transmit the visible light signal during visible light communication so that the light output of the modulation light emitting diode is equal between the visible light communication when the visible light signal is transmitted and the non-communication time when the visible light signal is not transmitted. The visible light communication system according to claim 1 or 2, wherein a magnitude of a current supplied to the light emitting diode for modulation is controlled.   4. The signal receiving unit according to claim 1, wherein the signal receiving unit acquires a modulation cycle of the visible light signal according to a lighting mode of a triggering light emitting diode at a start timing of the visible light signal. The visible light communication system according to item.

Images