JP6658598B2 - Visible light communication system and visible light communication method - Google Patents

Description

  The present invention relates to a visible light communication system and a visible light communication method for performing data transmission using visible light.

  There is visible light communication as a method for transmitting information wirelessly. Visible light communication is a communication method in which data is superimposed on light of an LED (Light Emitting Diode) and information is transmitted. The receiving device detects the intensity of the LED light using a sensor that detects the intensity of the light, such as a PD (Photo Diode), and performs demodulation.

  For example, an LED illuminator installed on the ceiling is used as a transmitting device for visible light communication, data is superimposed on LED light to emit light, and based on the intensity of light obtained by receiving the light with a receiving device having a light receiving unit. Demodulated to obtain data. By transmitting data including certain position information of the LED illuminator using this visible light communication system, even if the position information cannot be obtained underground, such as GPS (Global Positioning System), the receiving device can use the LED lighting device. Position information transmitted from the device can be obtained.

  As a method for realizing visible light communication using illumination light, there is a method of transmitting information using a modulation method called pulse position modulation (PPM). The PPM is a method of transmitting information in correspondence with the position of a pulse having a fixed time width. In the case of M-PPM, the time width of one symbol is divided into M-divided slots, and the number of slots corresponding to the information to be transmitted is determined. Make a pulse at the position. For example, in the case of 4-PPM, four types of pulse patterns can be provided by setting any one of the four slots as a pulse, so that four types, that is, two bits of information are transmitted in one symbol. can do.

  At this time, the information can be superimposed on the illumination light by turning off the illumination when the pulse rises in the PPM signal and turning on the illumination when there is no pulse.

  However, in the visible light communication, when the number of transmitting devices is one, the receiving device can acquire data from the received visible light, but when the receiving devices simultaneously receive the light emitted from the plurality of transmitting devices, the respective It is difficult to separate the light from the transmitting device and acquire each data. For example, in a region where light from a plurality of transmitting devices reaches, even if there is data to be transmitted with only some information such as position information among data transmitted from each transmitting device, pulse position modulation is performed by each transmitting device. It is difficult to correctly separate the demodulated light and demodulate it.

  Therefore, by superimposing data for each illumination and exclusively dividing the emission time, that is, by multiplexing in a time-division manner, the receiving device receives light that is not affected by other illumination light. There has been a method of acquiring data from light received at each time (for example, see Patent Document 1).

JP-A-2012-202853 (pages 4 to 11, FIG. 4)

  However, the method of Patent Document 1 has a problem that the time required to transmit the same amount of information increases because the number of objects to be multiplexed in a time-division manner increases as the number of illuminations increases.

  SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and it is a visible light communication that enables a part of transmission data transmitted from a transmission device to be received in an area where light from a plurality of transmission devices reaches. The purpose is to provide a system.

In a visible light communication system according to the present invention, a visible light communication includes a transmitting device that emits visible light to transmit information, and a receiving device that receives the visible light from the transmitting device and receives the information. A first modulation unit configured to generate a first modulation signal by using a first modulation scheme in which the first information has a constant average amplitude level at a first center frequency. A second modulation is performed by performing primary modulation on the second information at a second center frequency lower than the first center frequency and performing secondary modulation using a second modulation scheme. a modulation unit, wherein the first modulation signal and the second modulated signal and adder for generating a sum to superimposed signals, the light emitting unit that emits light by controlling the intensity of the visible light based on the superimposition signal Wherein the receiving device emits light from the transmitting device. A light receiving unit that receives the light, and an average calculating unit that calculates an average for each predetermined period from a signal obtained by receiving the light, and the calculation result of the average calculating unit corresponds to the secondary modulation. A first demodulation unit for performing secondary demodulation and performing primary demodulation corresponding to the primary modulation to obtain the second information.

  According to the present invention, in a transmitting apparatus for transmitting transmission data including first information and second information, a second center lower than a first center frequency used when modulating the first information with respect to the second information. A second modulator for generating a second modulation signal using a signal obtained by performing primary modulation at a center frequency; and a visible light based on a superimposed signal obtained by adding the first modulation signal and the second modulation signal. By performing communication, it is possible to extract the second modulation signal component by calculating the average for each fixed period from the signal received by the receiving device, and demodulate the extracted second modulation signal component. There is an effect that the second information which is a part of the transmission data can be received even in a region where a plurality of lights reach.

FIG. 3 is a diagram illustrating an example of an installation state of the visible light communication system according to the first embodiment; FIG. 1 is a diagram schematically illustrating a visible light communication system according to a first embodiment; FIG. 3 is a diagram illustrating an example of a first modulation scheme according to the first embodiment. FIG. 3 is a diagram schematically illustrating a second modulation unit according to the first embodiment. FIG. 3 is a diagram illustrating a modulation example of the secondary modulation unit 1022 according to the first embodiment. FIG. 4 is a diagram illustrating a synthesis example of an adding unit 103 according to the first embodiment. FIG. 3 is a diagram schematically illustrating a signal separation unit 203 according to the first embodiment. FIG. 3 is a diagram illustrating a separation example of a signal separation unit 203 according to the first embodiment. FIG. 3 is a diagram schematically illustrating a first demodulation unit 205 according to the first embodiment. FIG. 9 is a diagram schematically illustrating a transmission device 11 according to a second embodiment. FIG. 9 is a diagram schematically illustrating a second modulation unit 112 according to the second embodiment. FIG. 17 is a diagram illustrating an output example of a selection unit 1125 according to the second embodiment. FIG. 13 is a diagram schematically illustrating a receiving device 21 according to a third embodiment. FIG. 14 is a diagram schematically illustrating a first demodulation unit 215 according to the third embodiment.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating an example of an installation state of the visible light communication system according to the present embodiment. In the visible light communication system according to the present embodiment, a plurality of transmission devices 10 are provided on the ceiling. FIG. 1 shows that N transmission devices 10 are provided.

  In FIG. 1, a region where light emitted by the transmitting device 10 provided adjacently, for example, the first transmitting device 10-1 reaches, and a region where light emitted by the second transmitting device 10-2 reaches are overlapped. It indicates that you are doing. Also, a situation where the receiving device 20 is receiving light in the overlapping area is shown.

  Next, the visible light communication system will be described. FIG. 2 is a diagram schematically illustrating the visible light communication system according to the present embodiment.

  The transmission device 10 includes a first modulation section 101, a second modulation section 102, an addition section 103, a D / A conversion section 104, and a light emitting section 105. First information (also referred to as large-capacity information) and second information (also referred to as high-reliability information) are input as transmission data, and the light emitting unit 105 emits illumination light on which the transmission data is superimposed.

  The receiving device 20 includes a light receiving unit 201, an A / D conversion unit 202, a signal separation unit 203, a large capacity information demodulation unit (second demodulation unit) 204, and a highly reliable information demodulation unit (first demodulation unit) 205. . The light emitted from the transmitting device 10 is received by the light receiving unit 201 and demodulated to acquire transmission data S204 and S205.

  Next, the transmitting device 10 will be described. The transmission device 10 inputs the first information and the second information as transmission data. The first information is normal information, and the second information includes more important information, such as position information, that the receiving device 20 wants to acquire than the first information. Here, when the second information is position information, an illumination identification ID, or the like, it is desirable that the second information be different between transmission devices provided at positions where irradiation areas of the output illumination light overlap. . The second information is desirably unique for each transmission device. However, the second information may be the same information between transmission devices provided at positions where irradiation areas of output illumination light do not overlap.

  First modulation section 101 receives the first information and performs first modulation. The first modulation uses a modulation method such as PPM in which the average amplitude is constant. By employing a modulation method in which the average amplitude is constant, the light output from the light emitting unit described below does not generate visible flicker, and can function as illumination.

  FIG. 3 shows an example of a 4-PPM modulation method as an example of a first modulation method according to the first embodiment. In this case, first modulation section 101 converts the first information into a 2-bit data string in 4 slots and performs 4-PPM modulation. Here, the time of one slot is denoted by ts1. Since one slot time ts1 is one symbol for four slots, the center frequency (first center frequency) in the first modulation is ４ts1 [Hz].

  As shown in FIG. 3, in the 4-PPM modulation system, when the input data is 00, the first slot out of the four slots is at the low level (0), and the second to fourth slots are at the high level (1). Modulated. Similarly, when the input data is 01, the second slot of the four slots is modulated to the low level (0), and the first, third, and fourth slots are modulated to the high level (1). When the input data is 10, the third slot of the four slots is modulated to the low level (0) and the first, second, and fourth slots are modulated to the high level (1). When the input data is 11, the fourth slot of the four slots is modulated to a low level (0), and the first to third slots are modulated to a high level (1).

  The second modulator 102 receives the second information and performs the second modulation. FIG. 4 is a diagram schematically illustrating the second modulation unit 102. Second modulation section 102 receives the second information and performs primary modulation in primary modulation section 1021. The primary modulation uses, for example, PPM modulation. In this case, modulation is performed at a symbol time that is a second center frequency lower than the center frequency used in the first modulation scheme. That is, when the primary modulation performed by the second modulation unit 102 is 4-PPM modulation, a slot time ts2 having a longer time than the slot time ts1 in the first modulation is used.

  The secondary modulation section 1022 performs secondary modulation on the signal S1021 primary-modulated by the primary modulation section 1021 using the second modulation scheme, and generates a second modulated signal S102. As an example of the secondary modulation (second modulation method), there is spread spectrum using a unique code. In this case, the spread spectrum is performed on the signal S1021 using the unique code as a spread code. As the unique code, a spread code using a pseudo random noise (PN) pattern sequence is used. Further, as the unique code, a pattern sequence that is different between the transmission devices provided at the position where the irradiation area of the output illumination light overlaps is used. Although the unique code is desirably unique for each transmitting device, the same unique code may be used between transmitting devices provided at positions where the irradiation areas of the output illumination light do not overlap.

  FIG. 5 is a diagram illustrating a modulation example of the secondary modulation unit 1022. Here, a case is shown where the output S1021 "1011" of the primary modulation section 1021 in which the 2-bit string "01" of the second information is primary-modulated by 4-PPM modulation is spread. The unique code is repeated for each slot of the primary modulation section 1021, using a chip length tc equal to or shorter than the slot time of the primary modulation section 1021. FIG. 5 shows that the unique code uses a 5-chip pattern sequence represented by “10110”.

  The center frequency of second modulation signal S102 generated by secondary modulation section 1022 is lower than the center frequency of first modulation signal S101 from first modulation section 101 and higher than the frequency that can be perceived by human eyes. Shall be. At the same time, a modulation method that makes the average amplitude of the second modulation signal S102 constant is used. That is, the chip length tc used in the secondary modulator 1022 is set to be longer than one slot time ts1 of the PPM modulation used in the first modulator 101.

  As described above, by using a modulation method that makes the center frequency of the first modulation signal S101 and the center frequency of the second modulation signal S102 higher than the frequency that can be perceived by a human, and at the same time, uses a modulation method that has a constant average signal amplitude. The light output from 10 will not produce visible flicker. As a result, the transmission device 10 can function as lighting.

  The adder 103 adds and synthesizes the first modulation signal S101 from the first modulator 101 and the second modulation signal S102 from the second modulator 102. FIG. 6 is an example diagram showing a digital signal S103 that is an addition result obtained by adding and combining the first modulation signal S101 and the second modulation signal S102. As shown in FIG. 6, the chip length tc used in the secondary modulator 1022 is set longer than one slot time ts1 of the PPM modulation used in the first modulator.

  The D / A converter 104 converts the digital signal resulting from the addition from the adder 103 into an analog signal.

  The light emitting unit 105 emits visible light having a luminous intensity based on the analog signal generated by the D / A conversion unit 104. For example, it generates visible light having a luminous intensity proportional to the analog waveform received from the D / A converter 104. As an example, visible light having a luminous intensity inversely proportional to the analog waveform received from the D / A converter 104 may be generated.

Further, the light emitting unit 105 is not limited to one light source for one transmission device. For example, it is needless to say that a plurality of LEDs may be provided as in the case of a fluorescent lamp type LED lighting, and light may be emitted based on an analog signal generated by the common D / A converter 104. Absent. The light sources of a plurality of lighting devices may be collectively used as the light emitting unit 105 of one transmission device.

  Further, FIG. 1 shows a situation in which N transmitting devices 10 are provided as respective lighting devices, but a plurality of transmitting devices may be provided in the same lighting device. For example, in the case of a lighting device including a plurality of LEDs, a part of the plurality of LEDs is used by the light emitting unit 105 included in the transmitting device 10-1, and the other LEDs are included in the light emitting unit 105 included in the transmitting device 10-2. May be used.

  Next, each component of the receiving device 20 will be described. The light receiving unit 201 receives visible light. An example of a sensor that receives the intensity of visible light is a PD.

  The A / D conversion unit 202 converts an analog waveform indicating the intensity of visible light received by the light receiving unit 201 into a digital signal waveform.

  The signal separation unit 203 separates the digital signal waveform converted by the A / D conversion unit 202 into a first received signal component and a second received signal component.

  FIG. 7 is a diagram schematically illustrating the signal separation unit 203. The signal separation unit 203 includes an average calculation unit 2031 that receives the digital signal waveform converted by the A / D conversion unit 202 as an input, an offset removal unit 2032 that receives the result of the average calculation unit 2031 as an input, and an A / D conversion unit. And a subtraction unit 2033 to which the digital signal waveform converted in 202 and the result of the offset removal unit 2032 are input.

  The average calculation unit 2031 divides the digital signal waveform S202 converted by the A / D conversion unit 202 into blocks at predetermined time intervals, and calculates an average value of each block. The interval between blocks is higher than the center frequency of the first modulation signal S101 and lower than the center frequency of the second modulation signal S102. For example, blocks are divided by the chip length tc used in the secondary modulation unit 1022.

  The offset removing unit 2032 removes an offset component resulting from the average calculating unit 2031. For example, the minimum value of the average result S2031 is regarded as the DC component, and the offset removal result S2032 is calculated by subtracting the minimum value of the average result S2031 from the average result S2031.

  The subtractor 2033 subtracts the offset removal result S2032 from the digital signal waveform S202 converted by the A / D converter 202.

  FIG. 8 is a diagram illustrating a separation example of the signal separation unit 203. Here, a digital signal waveform S202 shown in FIG. 8 shows a signal obtained by receiving visible light emitted by one transmission device 10. As illustrated in FIG. 8, the signal S2032 obtained by removing the offset of the signal S2031 obtained by averaging the digital signal waveform S202 becomes the signal component of the second modulated signal S102 in the transmission device 10. On the other hand, the result S2033 generated by the subtraction unit 2033 is a signal component of the first modulated signal S101 in the transmission device 10.

  FIG. 9 is a diagram schematically illustrating the first demodulation unit 205 (high-reliability information demodulation unit). The first demodulation unit 205 receives the offset removal result S2032. The first demodulation unit 205 has a secondary demodulation unit 2051 and a primary demodulation unit 2052 for each unique code. FIG. 9 shows that a secondary demodulation unit 2051 and a primary demodulation unit 2052 are provided for each of N types of unique codes from 1 to N. For example, if there are three types of unique codes used in the transmission device, the transmission device has N types of secondary demodulation units 2051 and primary demodulation units 2052 including at least three types of unique codes used in the transmission device.

  The secondary demodulation unit 2051 performs secondary demodulation on the offset removal result S2032 using the input unique code. The secondary demodulation is a demodulation method corresponding to the secondary modulation method applied in the secondary modulation section 1022 of the transmission device 10, and for example, the secondary modulation of the transmission device is performed by spectrum spreading using a unique code as a spreading code. If so, spectrum despreading using the unique code as a spread code is performed. At this time, when spectrum despreading is performed using the same unique code as the unique code used in transmitting apparatus 10, a signal having one value in a unique code unit (ts2 unit in FIG. 5) can be obtained.

  On the other hand, when spectrum despreading is performed using a unique code different from the unique code used in transmitting apparatus 10, there is a change in the signal value in a unique code unit (ts2 unit in FIG. 5). It can be determined that the code is different from the unique code used for spread spectrum in the transmitting device.

  Primary demodulation section 2052 performs primary demodulation on the result from secondary demodulation section 2051 corresponding to the primary modulation scheme used in primary modulation section 1021 of transmitting apparatus 10. If the primary modulation used in primary modulation section 1021 is 4-PPM for one slot time ts2, demodulation is performed at 4-PPM for one slot time ts2.

  If the primary demodulation unit 2052 determines that the input result from the secondary demodulation unit 2051 has one value per unique code unit, the primary demodulation unit 2052 outputs the primary demodulation result. If it cannot be determined that the result from 2051 has one value in a unique code unit, it outputs no primary demodulation result or outputs information indicating that there is a spectrum despreading error.

  The first demodulation unit 205 outputs, from each of the primary demodulation units 2052, a result S205 of the primary demodulation in which spectrum despreading has been correctly performed.

  The result S205 obtained from the first demodulation unit 205 is the result of the primary demodulation obtained from the unique code used on the transmitting device 10 side, and acquires the second information (highly reliable information) on the transmitting device 10 side. be able to.

  For example, when the receiving device 20 receives light at a position where the irradiation areas of the transmitting device 10-1 and the transmitting device 10-2 in FIG. 1 overlap, the second code using the unique code used for the transmitting device 10-1 is used. The result from the secondary demodulation unit 2051-1 and the result from the secondary demodulation unit 2051-2 using the unique code used in the transmission device 10-2 can correctly perform spectrum despreading and use the respective second information. Can be obtained.

  On the other hand, the second demodulation unit 204 receives the result S2033 generated by the subtraction unit 2033 and demodulates using the demodulation method based on the first modulation method used by the transmission device 10. If the primary modulation used in the first modulation section 101 is 4-PPM for one slot time ts1, demodulation is performed at 4-PPM for one slot time ts1. Accordingly, when the receiving device 20 receives light at a position where the irradiation areas from the transmitting device 10 do not overlap, the first information (large-capacity information) on the transmitting device 10 side can be acquired. When the receiving device 20 receives light at a position where the irradiation areas from the transmitting device 10 overlap, when there is a large difference between the light amount from one transmitting device 10 and the light amount from the other transmitting device 10 In some cases, it may be possible to acquire the first information (large-capacity information) from the transmission device 10 on the side where the light amount is large.

  In the visible light communication system configured as described above, the second information (highly reliable information), which is a part of the transmission data, is received even when the receiving device 20 receives light at a position where the irradiation areas overlap. It has the effect that it can be done. Further, since transmission is not performed in a time-division manner by the number of overlapping transmission devices as in Patent Document 1, there is no problem that the time required to transmit the same amount of information is lengthened by the number of overlapping transmission devices. .

  Furthermore, since the first information and the second information are respectively modulated and multiplexed, the first information is transmitted more than the data sequence obtained by time-division multiplexing the first information and the second information. This has the effect of reducing the time required to perform the operation.

  In addition, the second received signal component related to the second information can be extracted from the received signal obtained by receiving the light by a small operation of calculating the average value, and the second received signal component extracted from the obtained received signal can be extracted. , The first received signal component can be extracted simply by subtracting

  The unique code used in each transmitting device 10 is the same as the unique code of the transmitting device 10 on the receiving device 20 side by adopting not only different unique codes but also unique codes having an orthogonal relationship. Can be obtained as a signal that is easy to identify. This is because even if the component of the second modulation signal generated by spectrum conversion using another unique code is mixed in the received light, the component of the second modulation signal is subjected to spectrum despreading. Since the signal level takes a low (almost “0”) value, the value of the spectrum despreading result by the component of the second modulated signal generated by performing spectrum conversion using the same unique code clearly appears. Because it is easy.

  In addition, even when the irradiation areas of the plurality of transmission devices 10 overlap, when the same second information is transmitted from the plurality of transmission devices 10, even if the same unique code is used, the reception device 20 It is possible to demodulate the second information.

  As the visible light communication system, the second modulation unit 102 of the transmission device 10 performs the secondary modulation to obtain the second modulation signal S102. However, the secondary modulation unit 1021 performs the secondary modulation without performing the secondary modulation. As the output result of the second modulated signal S102, the receiving apparatus 20 may perform the primary demodulation without performing the secondary demodulation to acquire the second information. Such a configuration of the visible light communication system is realized by designing the chip length tc to be equal to the second center frequency. In this case, of the light output from the transmission device 10 provided at the position where the irradiation area overlaps, the second information of the transmission device 10 having a high light intensity received by the light receiving unit 201 of the reception device 20 is transmitted. It is possible to receive. The signal S2032 removed by the offset removing unit 2032 in the receiving device 20 is greatly affected by the signal level of the second modulated signal S102 from the transmitting device 10 having a high light intensity received by the light receiving unit 201 of the receiving device 20. This is because

Embodiment 2 FIG.
The visible light communication system according to the second embodiment further controls the amount of light from the light emitting unit on the transmitting device side based on the luminous intensity information. The luminous intensity information is information for controlling the luminous intensity, which is the intensity of the visible light transmitted by the transmitting device 11.

  FIG. 10 is a diagram schematically illustrating the transmission device 11 according to the present embodiment. The transmission device 11 includes a first modulation unit 101, a second modulation unit 112, an addition unit 103, a D / A conversion unit 104, and a light emitting unit 105, and has a luminous intensity in addition to the first information and the second information. Enter information. The transmitting device 11 in the visible light communication system according to the present embodiment is different from the transmitting device 10 according to the first embodiment in the second modulator 112, and other components having the same reference numerals have the same configurations and operations as described above. The description is omitted because it is the same.

  FIG. 11 is a diagram schematically illustrating the second modulation unit 112 according to the second embodiment. The second modulator 112 includes a light intensity adjustment signal generator 1123, a second secondary modulator 1124, and a selector 1125 in addition to the primary modulator 1021 and the secondary modulator 1022.

  The primary modulation section 1021 and the secondary modulation section 1022 are the same as those in the first embodiment, and a description thereof will be omitted.

  The light intensity adjustment signal generation unit 1123 outputs a signal having an amplitude level proportional to the light intensity information. For example, luminous intensity information of 16 levels is represented by 4 bits. Since the light emitting unit 105 does not emit light at the Low level, the value of the light intensity adjustment signal is set to a smaller value as the setting of the visible light represented by the light intensity information is lower.

  The second secondary modulation section 1124 performs spectrum spreading on the light intensity adjustment signal S1123 from the light intensity adjustment signal generation section 1123 using the unique code M. The unique code M at this time is different from the unique code used in the secondary modulation section 1022, and uses a unique code having an orthogonal relationship.

  The selection unit 1125 receives the output S1022 from the secondary modulation unit 1022 and the output S1124 from the second secondary modulation unit 1124, and alternately selects and outputs them. The selection unit 1125 switches the output faster than can be recognized by human eyes. The output of the selection unit 1125 is converted into an analog signal by the D / A conversion unit 104 at the subsequent stage, and the light emission unit 105 emits light.

  As described above, S1022, which is a result of spectrum spreading based on the second information, and S1124, which is a result of spectrum spreading based on luminous intensity information, are caused to emit light by alternately switching signals. If the setting is low, the intensity of the emitted light is low, and if the setting is high, the intensity of the light is high.

  In addition, by performing the switching in the selection unit 1125 at a speed higher than that which can be recognized by the human eyes, it is possible to suppress flicker of light from appearing to human eyes due to the difference between the average amplitude levels of the outputs from the respective spread spectrum units. be able to.

  Also, S1022, which is the result of spectrum spreading based on the second information, can be emitted at a constant light intensity without decreasing the luminous intensity, so that the receiving intensity of the light does not decrease on the receiving device 112 side. , Not affected by brightness adjustment.

  Further, the second secondary modulation section 1124 uses a unique code having an orthogonal relationship, which is different from the unique code used in the secondary modulation section 1022, so that the receiving apparatus 112 demodulates the second information on the second side. The influence of the secondary modulation section 1124 is eliminated.

Embodiment 3 FIG.
The receiving device of the visible light communication system according to the third embodiment demodulates the first information based on the SN information obtained from the first demodulation unit that demodulates the second information.

  Here, the unique code used in the transmission device of the visible light communication system according to the present embodiment uses a unique code that is different between the transmission devices provided at positions where the irradiation areas of the output illumination light overlap and that are orthogonal to each other. .

FIG. 13 is a diagram schematically illustrating the receiving device 21 according to the present embodiment. The receiving device 21 includes a light receiving unit 201, an A / D conversion unit 202, a signal separation unit 203, a large-capacity information demodulation unit (second demodulation unit) 214, and a highly reliable information demodulation unit (first demodulation unit) 215. . The receiving device 21 in the visible light communication system according to the present embodiment is different from the receiving device 20 according to the first embodiment in that the second demodulation unit 214 and the first demodulation unit 215 are different, and other components having the same reference numerals. Has the same configuration and operation as those described above, and a description thereof will not be repeated.

  FIG. 14 is a diagram schematically illustrating the first demodulation unit 215. The first demodulation unit 215 receives the offset removal result S2032. The first demodulation unit 215 has a secondary demodulation unit 2051 and a primary demodulation unit 2052 for each unique code. FIG. 14 shows that a secondary demodulation unit 2051 and a primary demodulation unit 2052 are provided for each of 1 to N types of unique codes. For example, if there are three types of unique codes used in the transmission device, the transmission device has N types of secondary demodulation units 2051 and primary demodulation units 2052 including at least three types of unique codes used in the transmission device. The first demodulation unit 215 further includes an SN ratio calculation unit 2154.

  Secondary demodulation section 2051 is the same as secondary demodulation section 2051 in the first embodiment, and a description thereof will be omitted.

  The SN ratio calculation unit 2154 sets the maximum amplitude level to the signal (S) for the output signal from the secondary demodulation unit 2051 having the largest maximum amplitude level among the output signals from the respective secondary demodulation units 2051, and The sum of the maximum amplitude levels in the signal from the secondary demodulation unit 2051 is used as noise (N) to calculate a signal-to-noise ratio (SN ratio). If the obtained S / N ratio is equal to or higher than a preset threshold, an enable signal S2153 indicating execution of demodulation is output, and if lower than the threshold, an enable signal S2153 indicating execution of demodulation is output.

  The second demodulation unit 214 receives the result S2033 generated by the subtraction unit 2033 and the enable signal S2153 from the SN ratio calculation unit 2154, and if the enable signal S2153 indicates the execution of demodulation, the second demodulation unit 214 uses the second signal. Demodulation is performed using a demodulation method based on the first modulation method. On the other hand, when the enable signal S2153 indicates that demodulation is not performed, demodulation is not performed.

  As described above, when the SN ratio of the output signal from the secondary demodulation section 2051 having the largest maximum amplitude level is high, it is considered that the first information (large-capacity information) can be demodulated, and the demodulation result is determined. It is possible to obtain. Here, it is desirable that the threshold value is set based on an S / N ratio in which normal reception is possible in advance when demodulating the first modulation.

  Therefore, since the receiving device 21 does not output the first information that is likely to include an error, there is an effect that the reliability of the first information output from the receiving device increases.

  In addition, since unnecessary demodulation processing can be eliminated, there is an effect that the amount of calculation can be reduced.

10, 11 Transmitting device 101 First modulation unit 102 Second modulation unit 1021 Primary modulation unit 1022 Secondary modulation unit 103 Addition unit 104 D / A conversion unit 105 Light emitting unit 1123 Light intensity adjustment signal generation unit 1124 Second secondary Modulation section 1125 Selection section 20, 21 Receiving device 201 Light reception section 202 A / D conversion section 203 Signal separation section 2031 Average calculation section 2032 Offset removal section 2033 Subtraction section 203 Addition section 204 Second demodulation section 205 First demodulation section 2051 Secondary demodulation unit 2052 Primary demodulation unit 2153 SN ratio calculation unit

Claims (12)

A transmitting device that emits visible light to transmit information, and a visible light communication system including a receiving device that receives the visible light from the transmitting device and receives the information,
The transmission device,
A first modulation unit configured to generate a first modulation signal by using a first modulation scheme in which the first information has a constant average amplitude level at a first center frequency;
A second modulation for performing a first modulation on the second information at a second center frequency lower than the first center frequency and performing a second modulation using a second modulation method to generate a second modulation signal; Department and
An adder that adds the first modulation signal and the second modulation signal to generate a superimposed signal;
A light-emitting unit that emits light by controlling the intensity of the visible light based on the superimposed signal,
The receiving device,
A light receiving unit that receives light emitted from the transmitting device,
An average calculation unit that calculates an average for each fixed period from a signal obtained by the light receiving unit receiving light,
A first demodulation unit that performs secondary demodulation corresponding to the secondary modulation and performs primary demodulation corresponding to the primary modulation to obtain the second information with respect to the calculation result of the average calculation unit. Characteristic visible light communication system. The receiving device,
An offset removing unit that removes a DC component from a calculation result of the average calculating unit;
A subtraction unit that subtracts the result of the offset removal unit from the signal obtained by receiving the light,
2. The apparatus according to claim 1, further comprising: a second demodulation unit configured to acquire the first information by using a first demodulation method corresponding to the first modulation method with respect to a result of the subtraction unit. Visible light communication system. The second modulation scheme is spread spectrum using a unique code,
The first demodulation unit includes:
2. The visible demodulation according to claim 1, wherein the primary demodulation is performed by holding at least the eigencode used by the transmission device, performing spectrum despreading using the eigencode based on a calculation result of the average calculation unit, and performing the primary demodulation. Optical communication system. A plurality of the unique codes are provided in the different transmission devices,
In the receiving device,
The first demodulation unit holds the unique code used by the provided transmission device, and obtains the spectrum despread using the unique code from the calculation result of the average calculation unit. 4. The visible light communication system according to claim 3, wherein the primary demodulation is performed on a result of the spectrum despreading. 5. The visible light communication system according to claim 3, wherein a chip length of the unique code is longer than a cycle of the first center frequency and equal to or shorter than a cycle of the second center frequency. 6. . The transmitting device further inputs light intensity information,
The second modulation unit includes:
A primary modulation unit that performs primary modulation on the second information at the second center frequency;
A first spread spectrum unit for performing spread spectrum on the output of the primary modulation unit using the unique code;
A light intensity adjustment signal generation unit that generates a light intensity adjustment signal based on the light intensity information,
A second spread spectrum unit for performing spread spectrum on the light intensity adjustment signal using a second unique code having a orthogonal relationship with the unique code;
6. A signal obtained by alternately selecting a result of the first spread spectrum unit and a result of the second spread spectrum unit in time, as the second modulated signal. The visible light communication system according to any one of the above items. The receiving device,
An offset removing unit that removes a DC component from a calculation result of the average calculating unit;
A subtraction unit that subtracts the result of the offset removal unit from the signal obtained by receiving the light,
4. The apparatus according to claim 3, further comprising: a second demodulation unit configured to acquire the first information using a first demodulation method corresponding to the first modulation method with respect to a result of the subtraction unit. 5. Item 7. The visible light communication system according to any one of items 6. The second demodulation unit includes:
It further comprises an SN ratio calculating unit that calculates an SN ratio based on each spectrum despread result obtained by performing spectrum despreading using the respective unique code from the calculation result of the average calculating unit. The visible light communication system according to claim 7, wherein The second demodulation unit includes:
9. The visible light communication system according to claim 8, wherein when the SN ratio is higher than a predetermined threshold, execution of the first demodulation unit is controlled. A first modulation unit configured to generate a first modulation signal by using a first modulation scheme in which the first information has a constant average amplitude level at a first center frequency;
A second modulation for performing a first modulation on the second information at a second center frequency lower than the first center frequency and performing a second modulation using a second modulation method to generate a second modulation signal; Department and
An adder that adds the first modulation signal and the second modulation signal to generate a superimposed signal;
A light-emitting unit that emits light by controlling the intensity of visible light based on the superimposed signal. A first modulation signal is generated by using a first modulation scheme in which the first information has a constant average amplitude level at a first center frequency, and the second information is converted to a second information lower than the first center frequency. A primary modulation is performed at a center frequency of 2 and a secondary modulation is performed using a second modulation method to generate a second modulation signal. The first modulation signal and the second modulation signal are added and superimposed. A light receiving unit that generates a signal and receives the emitted light by controlling the intensity of visible light based on the superimposed signal,
An average calculation unit that calculates an average for each fixed period from a signal obtained by the light receiving unit receiving light,
A first demodulation unit that performs secondary demodulation corresponding to the secondary modulation and performs primary demodulation corresponding to the primary modulation to obtain the second information with respect to the calculation result of the average calculation unit. Characteristic receiving device. A transmitting device that emits visible light to transmit information, and a visible light communication method of a visible light communication system including a receiving device that receives the visible light from the transmitting device and receives the information,
The transmission device,
A first modulation step of generating a first modulation signal using a first modulation scheme in which the first information has a constant average amplitude level at a first center frequency;
A second modulation for performing a first modulation on the second information at a second center frequency lower than the first center frequency and performing a second modulation using a second modulation method to generate a second modulation signal; Steps and
An adding step of adding the first modulation signal and the second modulation signal to generate a superimposed signal;
A light emission step of emitting light by controlling the intensity of the visible light based on the superimposed signal,
The receiving device,
A light receiving step of receiving light emitted from the transmitting device,
An average calculation step of calculating an average for each fixed period from the signal obtained by receiving the light,
A first demodulation step of performing a secondary demodulation corresponding to the secondary modulation and performing a primary demodulation corresponding to the primary modulation to obtain the second information with respect to the calculation result of the average calculation step. Characteristic visible light communication method.

Images