JP5044502B2 - Visible light communication system - Google Patents

Description

  The present invention particularly relates to a visible light communication technique using LED illumination light.

  In recent years, development of visible light communication technology for transmitting and receiving data using LED illumination light using a light emitting diode element (hereinafter referred to as LED) has been promoted (see, for example, Patent Document 1). LED lighting is attracting attention as an alternative to fluorescent lighting in buildings, airports, and homes.

Visible light communication has the advantage that the confidentiality of communication data is high and there is almost no adverse effect on the human body compared to wireless communication using radio waves, in addition to the advantage that LED lighting equipment as lighting equipment can also be used for communication. It has. That is, since visible light communication can limit a communication area to the range which visible light reaches, it is excellent in the security of communication data.
JP 2007-78224 A

  Visible light communication has various features compared to wireless communication using radio waves. Visible light communication transmits encoded data by switching the LED on and off at a high cycle. On the other hand, in the visible light communication, it is necessary to maintain the illumination function even during data communication. Therefore, in order to suppress the flickering phenomenon of the illumination, it is required to keep the distribution (duty ratio) of the lighting time and the extinguishing time of the LED as constant as possible. In addition, when the duty ratio is very uneven, when the transmission data is demodulated on the visible light receiving side, a situation may arise in which the synchronization clock necessary for the demodulation processing cannot be recovered.

  Conventionally, a method for ensuring the uniformity of the duty ratio has been proposed, but there is not necessarily an effective method. In particular, on the visible light transmission side, a specific bit sequence (for example, a continuous logic 0 bit sequence) appears periodically due to the code conversion method when transmitting data is modulated, and the duty ratio is periodically biased. The flickering phenomenon of lighting may become remarkable.

  Accordingly, an object of the present invention is to achieve a practically excellent visible light communication by making the duty ratio uniform during visible light transmission and suppressing the flickering phenomenon of illumination during visible light communication.

Visible light communication system according to an aspect of the present invention, a light emitting element that emits illumination light, a visible light transmission apparatus comprising driving means for driving the light emitting element outputs a pulse signal, the visible light transmission apparatus A visible light communication device including a light receiving device including a light receiving element that receives illumination light emitted from the light source and converts the illumination light into an electrical signal, wherein the visible light transmission device turns on and off the light emitting element. Based on the duty ratio, the bit string of the transmission data to be transmitted superimposed on the illumination light to the visible light receiver is an inappropriate bit string in which the bit number of logic 0 or logic 1 exceeds the reference value and continues. A data detection means for detecting the detection result of the data detection means, and means for generating modulation data for modulating the transmission data to control the on / off time of the pulse signal. Modulation means including means for changing the modulation data so that an appropriate duty ratio can be set, and instruction information for instructing the visible light receiving device to change the modulation data by the modulation means. The visible light receiving device is configured to demodulate and receive the instruction information superimposed on the illumination light, and to demodulate from the modulation data superimposed on the illumination light. A visible light communication system comprising: demodulating means for demodulating the transmission data by using demodulating information, and demodulating by changing the demodulating information according to the instruction information .

  ADVANTAGE OF THE INVENTION According to this invention, the duty ratio at the time of visible light transmission can be equalize | homogenized, the flicker phenomenon of the illumination at the time of visible light communication can be suppressed, and practically excellent visible light communication can be implement | achieved.

  Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment]
FIG. 1 is a diagram illustrating a main part of a visible light communication system according to the present embodiment.

  As shown in FIG. 1, the visible light communication system is broadly divided into a visible light transmitting device 1 that transmits transmission data superimposed on the LED illumination light 200, and the LED illumination light 200 is received and the transmission data is demodulated and received. The visible light receiving device 2 is configured.

  The visible light transmission device 1 includes a transmission buffer 10, a data monitoring unit 11, a light emission control unit 12, and a light emission unit 15. The visible light transmission device 1 is, for example, an LED lighting facility installed in a building, and is connected to a network (for example, a local area network: LAN) 3.

  The transmission buffer 10 stores transmission data (digital signal) 100 transmitted from, for example, a server (not shown) via the network 3. The data monitoring unit 11 monitors the bit string of the transmission data 100 stored in the transmission buffer 10 and detects a bit string in which the duty ratio of turning on / off the LED element is inappropriate as will be described later. Here, the duty ratio is the ratio between the lighting time and the extinguishing time of the LED element, in other words, the ratio between the on time and the off time of the pulse signal (drive pulse current) for driving the LED element. In order to suppress the flicker phenomenon of LED lighting, it is desirable to make the duty ratio uniform. In other words, an inappropriate duty ratio is a non-uniform duty ratio.

  The light emission control unit 12 controls driving of LED (light emitting diode) elements included in the light emitting unit 15 to turn on / off the LED illumination light 200. The light emission control part 12 implement | achieves the visible light communication function which carries out drive control of the LED element according to the modulation data which modulated (encoded) the transmission data mentioned later with the illumination function by light emission of the LED illumination light 200. FIG.

The light emission control unit 12 includes an LED driver 13 that drives and controls the LED elements included in the light emission unit 15, and a modulation table (D / A modulation table or D / A encoding table) for modulating (encoding) transmission data. 14 As shown in FIG. 2A, the modulation table 14 is
It includes modulation tables (1 to n) of a plurality of types of modulation (encoding) systems. The light emission control unit 12 converts the transmission data into modulation data of a different modulation (encoding) method by selecting each modulation table (1 to n). The LED driver 13 outputs a pulse signal (analog signal) 110 corresponding to the duty ratio of the on / off time corresponding to each modulation data, and drives and controls the LED element of the light emitting unit 15.

  On the other hand, the visible light receiving device 2 includes a reception buffer 20, a demodulation unit 21, a light receiving unit 23, and a data processing unit 24. The visible light receiving device 2 is, for example, a portable terminal that receives various types of information (transmission data) through visible light communication with the visible light transmitting device 1.

  The reception buffer 20 stores the data 220 demodulated by the demodulation unit 21 as reception data (that is, transmission data 100). The light receiving unit 23 includes a light receiving element (for example, a photodiode element) that receives the LED illumination light 200 emitted from the light emitting unit 15 of the visible light transmitting device 1 and converts it into an electrical signal (analog signal).

  The demodulator 21 converts the analog signal output from the light receiver 23 into a digital signal, and further demodulates the data 220 (that is, the transmission data 100) using the demodulation table 22. As shown in FIG. 2B, the demodulation table 22 includes a plurality of types of demodulation (decoding) schemes corresponding to the modulation tables (1 to n) of the plurality of types of modulation (encoding) schemes of the visible light transmitting apparatus 1. Demodulation tables (1 to n). Therefore, the demodulator 21 converts the analog signal 210 modulated by any one of the modulation tables (1 to n) used in the visible light transmission apparatus 1 and digitally outputs one of the corresponding demodulation tables (1 to n). The signal data 220 is demodulated.

  The data processing unit 24 is a microprocessor (CPU) that takes out the data 220 (transmission data 100) stored in the reception buffer 20 and executes data processing by a designated application program. Specifically, the data processing unit 24 executes processing for displaying information (transmission data 100) transmitted from the visible light transmitting device 1 on the display of the mobile terminal.

(Operation of visible light communication system)
Hereinafter, the operation of the visible light communication system of this embodiment will be described with reference to the flowcharts of FIGS. 3 and 4.

  First, as shown in FIG. 4, the visible light transmitter 1 according to the present embodiment transmits (distributes) the modulation table 14 to the visible light receiver 2 by visible light communication using the LED illumination light 200 at regular intervals. (Step S1). The visible light receiving device 2 generates a demodulation table 22 corresponding to the modulation table 14 demodulated and received, and sets it in the demodulator 21 (steps S11 and S12).

  In this case, the visible light transmitting apparatus 1 modulates and transmits transmission data (modulation table 14) to which identification information for identifying the modulation table 14 is added using a basic modulation table (for example, the modulation table 1). To do. In the visible light receiving device 2, the demodulator 21 demodulates using the demodulation table (demodulation table 1) corresponding to the basic modulation table (modulation table 1).

  Next, in the visible light transmission apparatus 1, the transmission buffer 10 stores transmission data (digital signal) 100 transmitted via the network 3. The data monitoring unit 11 monitors the bit string of the transmission data 100 stored in the transmission buffer 10 and detects a bit string with an inappropriate duty ratio (step S2). Specifically, the data monitoring unit 11 determines, for example, whether or not the bit number of logic 0 is a continuous bit string exceeding the reference value.

  When an inappropriate bit string is not detected by the data monitoring unit 11, the light emission control unit 12 uses the basic modulation table (1) included in the modulation table 14 to transmit data 100 stored in the transmission buffer 10. Is modulated (NO in step S3). Here, as shown in FIGS. 3A and 3B, the light emission control unit 12 uses, for example, a 4B / 5B encoding method, for example, 4 bits (4B) using the basic modulation table (1). The transmission data 100 is converted into 5-bit (5B) modulation data (encoded data).

  As shown in FIG. 3C, the LED driver 13 of the light emission control unit 12 outputs a pulse signal (control signal) 110 corresponding to the modulation data to the light emission unit 15 to drive the LED element (step S6). Thereby, the LED illumination light 200 on which the transmission data 100 is superimposed is emitted from the light emitting unit 15 (step S7). At this time, as shown in FIG. 3C, the duty ratio corresponds to the ratio of the on (ON) time and the off (OFF) time of the pulse signal 110, and corresponds to the ratio of the lighting time and the extinguishing time of the LED element. .

  In the visible light receiving device 2, when the light receiving unit 23 receives the LED illumination light 200 emitted from the light emitting unit 15, the light receiving unit 23 converts the light into an electric signal (analog signal) 210 and outputs it to the demodulating unit 21 (YES in step S 15). S16). The demodulator 21 converts the analog signal 210 into a digital signal, and further uses the demodulation table (1) corresponding to the basic modulation table (1) to demodulate the transmission data 100, which is the decoded data 220 (step). S17).

  The reception buffer 20 stores the data 220 demodulated by the demodulator 21 as reception data (that is, transmission data 100) (step S18). The data processing unit 24 takes out the transmission data 100 stored in the reception buffer 20 and executes data processing by a designated application program, for example, processing for displaying on the display of the portable terminal.

  With respect to the basic operation as described above, an operation when the data monitoring unit 11 detects a bit string having an inappropriate duty ratio from the transmission data 100 stored in the transmission buffer 10 will be described.

  That is, for example, when the data monitoring unit 11 detects a bit string in which the number of logical 0 bits exceeds the reference value and continues, the data monitoring unit 11 switches the modulation table (YES in step S3). The light emission control unit 12 switches the modulation table 14 to a modulation table (for example, the table 2) for modulating the modulation data into a bit string that provides an appropriate duty ratio (step S4). At this time, the light emission control unit 12 transmits a switching command indicating that the modulation table has been switched to the visible light receiving device 2 via the light emitting unit 15 (step S5).

  The light emission control unit 12 modulates the transmission data 100 stored in the transmission buffer 10 using the switched modulation table (2). The LED driver 13 of the light emission control unit 12 outputs a pulse signal (control signal) corresponding to the modulation data to the light emission unit 15 to drive the LED element (step S6). Thereby, the LED illumination light 200 on which the transmission data 100 is superimposed is emitted from the light emitting unit 15 (step S7). At this time, the ratio between the turn-on time and the turn-off time of the LED element becomes a uniform duty ratio even if an inappropriate bit string is included in the transmission data 100 by switching the modulation table.

  In the visible light receiving device 2, when the light receiving unit 23 receives the LED illumination light 200 emitted from the light emitting unit 15, the light receiving unit 23 converts the light into an electric signal (analog signal) 210 and outputs it to the demodulating unit 21 (YES in step S 15). S16). Here, the visible light receiving device 2 receives the switching command transmitted from the visible light transmitting device 1 (YES in step S13). Thereby, the demodulator 21 switches from the demodulation table (1) corresponding to the basic modulation table (1) to the demodulation table (2) corresponding to the switched modulation table (2) (step S14).

  The demodulator 21 converts the analog signal 210 into a digital signal, and further demodulates the transmission data 100, which is the decoded data 220, using the switched demodulation table (2) (step S17). The reception buffer 20 stores the data 220 demodulated by the demodulator 21 as reception data (that is, transmission data 100) (step S18). The data processing unit 24 takes out the transmission data 100 stored in the reception buffer 20 and executes data processing by a designated application program, for example, processing for displaying on the display of the portable terminal.

  As described above, according to the present embodiment, the visible light transmission device 1 monitors the bit string of the transmission data 100, and thus the bit string in which the duty ratio corresponding to the distribution of the lighting time and the lighting time of the LED element becomes non-uniform. Switch the modulation table. As a result, the LED element can be driven and controlled with a pulse signal with a uniform duty ratio, and the LED illumination light 200 with a uniform distribution of lighting time and extinguishing time can be emitted. That is, it is possible to suppress the occurrence of the flickering phenomenon in the LED illumination light 200, and to realize a stable LED illumination without the flickering phenomenon together with the visible light communication function that transmits the transmission data 100 superimposed on the visible light.

  Specifically, as shown in FIGS. 7A to 7C, when there is specific data of a bit string in which the duty ratio is non-uniform in the transmission data 100, by switching the modulation table, By adjusting the light emission timing of the LED element, the duty ratio of the LED illumination light can be made uniform.

  On the other hand, the visible light receiving device 2 that receives the LED illumination light 200 and demodulates the transmission data 100 receives the switching command indicating the switching of the modulation table from the visible light transmitting device 1, so that the switched modulation table is displayed. The transmission data can be demodulated by switching to the corresponding demodulation table. Therefore, the visible light receiver 2 can reliably demodulate the transmitted transmission data 100.

  Therefore, if it is the visible light communication system of this embodiment, it becomes possible to implement | achieve practically excellent visible light communication which has the data communication function by visible light communication, and the stable LED illumination function without a flicker phenomenon. .

  In the present embodiment, the configuration in which the visible light transmitter 1 transmits the modulation table 14 to the visible light receiver 2 during the initial operation has been described. However, the present invention is not limited to this, and the visible light transmitter 1 and the visible light receiver are not limited thereto. Each of the devices 2 may have a configuration in which a modulation table and a demodulation table are set in advance. The visible light transmitter 1 can maintain the correspondence between modulation and demodulation with the visible light receiver 2 by transmitting a switching command.

[Second Embodiment]
Hereinafter, the visible light communication system according to the second embodiment will be described. In addition, since the principal part of the visible light communication system of this embodiment is the same as that shown in FIG. 1, description is abbreviate | omitted.

  In this embodiment, in the visible light receiving device 2, the demodulation table 22 of the demodulation unit 21 has a function as an encryption key for the purpose of improving the confidentiality of visible light communication.

  Specifically, for example, in a specific LED illumination area, the visible light transmission device 1 distributes to the visible light reception device 2 a demodulation table 22 that can be arbitrarily updated by a specific conversion table update command. The visible light receiver 2 demodulates the visible light transmission data modulated by the modulation table 14 corresponding to the demodulation table 22 from the visible light transmitter 1.

  As described above, according to the present embodiment, in a specific LED illumination area, when the visible light receiving device 2 receives and sets the demodulation table 22 having a function as an encryption key, visible light transmission is performed. The visible light transmission data transmitted from the device 1 can be demodulated. On the other hand, in a specific LED illumination area, the visible light receiving device 2 that has not received and set the demodulation table 22 having the function as an encryption key cannot demodulate the visible light transmission data transmitted from the visible light transmitting device 1. . Therefore, in a specific LED illumination area, the visibility of visible light communication can be realized by providing the visible light communication with an encryption / decryption function.

[Third Embodiment]
Hereinafter, a visible light communication system according to the third embodiment will be described. In addition, since the principal part of the visible light communication system of this embodiment is the same as that shown in FIG. 1, description is abbreviate | omitted.

  In this embodiment, in the visible light transmitting apparatus 1, the data monitoring unit 11 monitors whether or not constant transmission data is always input from the network 3 to the transmission buffer 10. When the data monitoring unit 11 detects a state in which transmission data is not input to the transmission buffer 10 for a certain period, the light emission control is performed on the predetermined data for the detected non-input period after a certain transmission data is transmitted by the light emission control unit 12. Transmitted by the unit 12. Specifically, after transmitting certain transmission data, the light emission control unit 12 transmits, for example, only during a non-input period in which inverted data of the transmission data is detected.

  As described above, according to the present embodiment, depending on the transmission state of transmission data, the LED illumination light 200 emitted from the light emitting unit 15 has a biased lighting ratio that becomes too bright or too dark. Can be avoided. That is, when a state in which constant transmission data is not always input to the transmission buffer 10 occurs, the LED illumination light 200 has a biased lighting ratio, and there is a high possibility that the flickering phenomenon of illumination becomes remarkable.

  Therefore, in the present embodiment, after transmitting certain transmission data, for example, by transmitting inverted data of the transmission data only during a non-input period, the lighting ratio of the LED illumination light 200 can be made uniform. Of course, when the visible light receiving device 2 transmits the inverted data of the transmission data after the certain transmission data is transmitted from the visible light transmitting device 1, the inverted data is received as the received data. Is not processed.

[Fourth Embodiment]
FIG. 5 is a block diagram for explaining a configuration of a visible light communication system according to the fourth embodiment. In the visible light communication system of the present embodiment, the configuration other than the voltage controller 16 is the same as that shown in FIG.

  In the present embodiment, the light emission control unit 12 includes a voltage controller 16 for controlling the drive voltage of the LED driver 13. The voltage controller 16 controls the drive voltage of the LED driver 13 in accordance with an instruction from the data monitoring unit 11.

  Specifically, the data monitoring unit 11 monitors the bit string of the transmission data 100 stored in the transmission buffer 10, and there is a bit string in which the duty ratio corresponding to the distribution of the lighting time and the lighting time of the LED elements becomes uneven. In this case, the voltage controller 16 is instructed to keep the LED illumination light quantity constant. The voltage controller 16 controls the drive voltage of the LED driver 13 in accordance with an instruction from the data monitoring unit 11 to keep the illumination light amount of the LED elements included in the light emitting unit 15 constant.

  As described above, according to the present embodiment, when there is an inappropriate bit string in which the bit string of transmission data has a non-uniform duty ratio, the drive voltage of the LED driver 13 is controlled to reduce the illumination light amount of the LED element. By keeping it constant, it is possible to avoid the flickering phenomenon of illumination due to non-uniformity of the lighting ratio of the LED illumination. As a result, the number of tables of the modulation table 14 and the demodulation table 22 can be reduced, and control for switching the tables of the modulation table 14 and the demodulation table 22 is possible only when the lighting ratio of the LED illumination is large. It becomes.

  In addition, by controlling the amount of LED illumination light that cannot be recognized by the voltage controller 16 according to the present embodiment, for example, the LED illumination can be turned on with a weak illuminance without turning off the LED illumination. In addition, the LED lighting can be turned on with strong illuminance at the time of lighting. Thereby, the flickering phenomenon of illumination can be suppressed by controlling the intensity of LED illumination.

[Fifth Embodiment]
FIG. 6 is a block diagram for explaining a configuration of a visible light communication system according to the fifth embodiment. The visible light communication system of this embodiment has a configuration including a transmission buffer 17 including a plurality of transmission buffers (1 to n), a reception buffer 25 including a plurality of reception buffers (1 to n), and a data restoration unit 26. . In the visible light communication system of the present embodiment, the modulation table 14 and the demodulation table 22 are not provided. Other configurations are the same as those shown in FIG.

  In the visible light communication system according to the present embodiment, in the visible light transmission device 1, the data monitoring unit 11 monitors a bit string of transmission data stored in each transmission buffer (1 to n) of the transmission buffer 17. When the data monitoring unit 11 continuously transmits the transmission data stored in each transmission buffer (1 to n), the lighting duty ratio of the LED illumination light 200 does not become uneven in the light emitting unit 15. The transmission order of each transmission data transmitted from each transmission buffer (1 to n) is changed. The light emission control unit 12 modulates each transmission data in the transmission order instructed by the data monitoring unit 11 and transmits the data by superimposing it on the LED illumination light 200 from the light emitting unit 15.

  On the other hand, in the visible light receiver 2, the demodulator 21 demodulates each transmission data as received data from the electrical signal from the light receiver 23 that has received the LED illumination light 200 from the visible light transmitter 1. The data restoring unit 26 stores the demodulated reception data in the reception buffer 25 by rearranging the demodulated reception data based on the transmission order of the transmission data instructed to be changed by the data monitoring unit 11. Here, in the visible light transmitter 1, the data monitoring unit 11 transmits a change instruction to the visible light receiver 2 via the light emitting unit 15. The data restoration unit 26 recognizes the transmission order of each transmission data based on the change instruction. The visible light receiving device 2 demodulates the transmission data stored in each transmission buffer (1 to n) of the visible light transmitting device 1 by the data restoration unit 26 and stores it in each corresponding reception buffer (1 to n). To do.

  As described above, according to the present embodiment, when transmission data stored in each transmission buffer (1 to n) is continuously transmitted, the light emitting unit 15 emits light by rearranging the transmission order of the transmission data. It is possible to avoid a situation in which the duty ratio of the LED illumination light 200 is not uniform. Therefore, the flickering phenomenon of LED illumination in visible light communication can be suppressed.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The block diagram which shows the structure of the visible light communication system regarding the 1st Embodiment of this invention. The figure for demonstrating the structure of the modulation table and demodulation table regarding this embodiment. The figure for demonstrating the basic modulation operation | movement with the visible light transmitter regarding this embodiment. The flowchart for demonstrating operation | movement of the visible light communication system regarding this embodiment. The block diagram which shows the structure of the visible light communication system regarding 4th Embodiment. The block diagram which shows the structure of the visible light communication system regarding 5th Embodiment. The figure for demonstrating the effect of 1st Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Visible light transmitter, 2 ... Visible light receiver, 3 ... Network,
DESCRIPTION OF SYMBOLS 10 ... Transmission buffer, 11 ... Data monitoring part, 12 ... Light emission control part, 13 ... LED driver,
14 ... modulation table, 15 ... light emitting unit, 16 ... voltage controller, 17 ... transmission buffer,
20 ... reception buffer, 21 ... demodulation unit, 22 ... demodulation table, 23 ... light receiving unit,
24 ... Data processing unit, 25 ... Reception buffer, 26 ... Data restoration unit,
100: Transmission data, 200: LED illumination light.

Claims (10)

A light emitting element for emitting illumination light, a visible light transmission apparatus comprising driving means for driving the light emitting element outputs a pulse signal,
A visible light communication system comprising a visible light receiving device including a light receiving element that receives illumination light emitted from the visible light transmitting device and converts the illumination light into an electrical signal,
The visible light transmitter is
Based on the duty ratio of turning on and off the light emitting element, the bit string of the transmission data to be transmitted to the visible light receiving device while being superimposed on the illumination light has a logical 0 or logical 1 bit number exceeding a reference value. Data detecting means for detecting a continuous bit string as an inappropriate bit string;
A means for generating modulation data for controlling the on / off time of the pulse signal by modulating the transmission data, and changing the modulation data so that an appropriate duty ratio can be set according to the detection result of the data detection means Modulation means including means to:
Instruction means for instructing the visible light receiving device to change the modulation data by the modulation means, and transmitting the control information by controlling the driving means;
The visible light receiving device is:
Means for demodulating and receiving the instruction information superimposed on the illumination light;
Visible light communication system comprising: demodulating means for demodulating the transmission data by using demodulation information from the modulation data superimposed on the illumination light, and changing and demodulating the demodulation information according to the instruction information . The modulating means includes
Modulation table information including a plurality of types of encoding conversion tables for modulating the transmission data;
Initially, using a specified encoding conversion table, the bit string of the transmission data is encoded to generate modulation data,
The visible light communication system according to claim 1, wherein the modulation data is changed by switching an encoding conversion table so that an appropriate duty ratio can be set according to a detection result of the data detection unit . The visible light transmitter is
3. The visible light communication system according to claim 1 , further comprising a unit that controls the driving unit to transmit the demodulation information to the visible light receiving device . The visible light transmitter is
The visible light communication system according to claim 2 , further comprising means for controlling the driving means to transmit the modulation table information as information for generating the demodulation information to the visible light receiving apparatus. The notification means includes
5. The visible light communication system according to claim 3, wherein after transmitting the demodulation information, the instruction information is transmitted when the modulation data is changed by the modulation unit . 6. The modulating means includes
The visible light communication system according to claim 1, wherein the modulation data is changed so that a lighting time of the light emitting element becomes constant according to a detection result of the data detection unit . The demodulating means includes
A plurality of types of demodulation tables corresponding to the plurality of types of encoding conversion tables, as the demodulation information;
The visible light communication system according to claim 2, wherein the demodulation table is switched according to the instruction information . The demodulation means includes
In a specific illumination area, a plurality of types of demodulation tables corresponding to the plurality of types of encoding conversion tables are received as the demodulation information from the visible light transmitting device,
The visible light communication system according to claim 2, wherein a demodulation table is updated in accordance with an update command from the visible light transmission device . The visible light transmitter is
Transmission buffer means for inputting and storing the transmission data transmitted from the outside;
The transmission buffer means is monitored, a period during which the transmission data is not input is detected, and after the transmission means transmits a certain transmission data, the driving means is controlled only during the period to transmit the inverted data of the transmission data. Data monitoring means
The visible light communication system according to claim 1, further comprising: The visible light transmitter is
A voltage controller for controlling the drive voltage of the drive means;
The voltage controller is configured to control a driving voltage of the driving unit to keep the illuminance of the light emitting element constant when the inappropriate bit string is detected by the data detecting unit. Item 12. The visible light communication system according to Item 1 .

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