JP2015154426A - Illumination light communication apparatus and illumination light communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an illumination light communication apparatus capable of transmitting a data signal without widening a frequency band while preventing a ratio of an ON-state time and an OFF-state time from being changed in accordance with contents of data.SOLUTION: An illumination light communication apparatus 1 is configured to perform transmission of a data signal together with illumination by means of illumination light of an illumination lamp 2. The illumination lamp 2 is capable of switching an ON state where illumination light is radiated and an OFF state where the illumination light is not radiated or is radiated with the less quantity of light than that in the ON state. For the data signal, a symbol Sy constituting the data signal is divided into one or more partition slots SP1 and a plurality of data slots SD1-SD4. The partition slot SP1 is provided in the head or the tail of the symbol Sy and includes one term to be the OFF state. Regarding the plurality of data slots SD1-SD4, one term to be the OFF state is included in any one data slot and the other data slots are brought into ON state in accordance with contents of data.

Description

  The present invention relates to an illumination light communication apparatus and an illumination light communication system for transmitting a data signal together with illumination by illumination light of an illumination lamp.

  In recent years, an illumination light communication device or an illumination light communication system that uses illumination light of an illumination lamp for data signal transmission along with the purpose of original illumination has been proposed. These have various characteristic applications by utilizing the fact that the transmission of the data signal is limited to the range where the illumination light reaches. For example, it is possible to transmit sound data with lighting in the exhibition spot area such as goods and arts and listen to explanations with earphones, etc., or transmit security data such as passwords along with lighting in the public wireless LAN area to illegally connect to the network. Intrusion can be prevented.

  Such an illumination light communication device or illumination light communication system turns on and off the illumination lamp for data signal transmission. If the ratio of the on-state time to the off-state time does not change, the human eye The lighting can be flicker-free. For this reason, it is desirable to transmit data signals after performing modulation processing so that their ratio does not change according to the contents of data. Here, the on state is a state in which the amount of light is larger than that in the off state, and the off state is a state in which the illumination lamp is turned off or the amount of light is less than the on state.

  As a modulation for that purpose, Patent Documents 1 to 3 and the like describe the inverted pulse position modulation (Inverted PPM). For example, in quaternary inversion pulse position modulation, as shown in FIG. 6, the time (for example, 0.1 millisecond to 0.4) of a symbol (indicated by Sy in FIG. 6) constituting a data signal to be transmitted. (Milliseconds) is divided into four slots (indicated by S1 to S4 in FIG. 6), and one slot among these slots S1 to S4 is put in an OFF state, and the other slots Is turned on so that 2-bit data, that is, four types of data “00”, “01”, “10”, and “11” are converted into four types of data signals.

  In addition, it is possible to perform binary inverted pulse position modulation by dividing a symbol into two slots and converting 1-bit data, that is, two types of data “0” and “1” into two types of data signals. . In addition, 8-level inversion pulse position modulation is possible in which a symbol is divided into 8 slots and 3-bit data, that is, 8 types of data “000” to “111” are converted into 8 types of data signals. . Similarly, inversion pulse position modulation of 16 values or more is also possible. In addition, as described in Patent Document 3, there may be a plurality of periods in which the slot is in the off state in one slot in the form of a pulse train (subcarrier).

  In such an illumination light communication device or illumination light communication system, a receiving device that has received illumination light from the illumination light communication device converts the illumination light into an electrical signal by a light receiver configured of a photodiode or a phototransistor. Then, the data is restored by performing a demodulation process corresponding to the modulation in the illumination light communication apparatus.

JP 2004-072365 A JP 2007-274466 A JP 2008-283446 A

  By the way, in such an illumination light communication apparatus or illumination light communication system, light other than the illumination light of the illumination light communication apparatus (for example, fluorescent light) is mixed, or the illumination light includes an undesired frequency component. Sometimes they become noise. The noise is often low frequency noise (eg, noise at a frequency such as 50 Hz or multiples of 60 Hz). In order to remove the influence of low-frequency noise, a high-pass filter is used before demodulation processing in the receiving apparatus.

  However, the inversion pulse position modulated illumination light shown in Patent Documents 1 to 3 and the like has a wide frequency band and spreads in a low frequency direction. For example, in quaternary inversion pulse position modulation, as shown in FIG. 7, after the symbol Sy having the off-period in the first slot S1, it has the off-period in the fourth slot S4. The symbol Sy may come, and a low frequency component having a period almost twice as long as the time of the symbol Sy is generated. The illumination light spreads in the direction of the low frequency band. If the frequency band of the illumination light spreads in the low frequency direction, the difference in frequency from the low frequency noise described above is small and there is no room, so it is not easy to properly remove the influence of the low frequency noise with a high pass filter. Cases can also arise.

  The present invention has been made in view of the above-mentioned reasons, and the object thereof is data in which the ratio of the on-state time to the off-state time does not change according to the contents of the data and does not widen the frequency band. An illumination light communication apparatus and an illumination light communication system capable of transmitting a signal are provided.

  In order to achieve the above object, the illumination light communication apparatus according to claim 1 is an illumination light communication apparatus that transmits a data signal together with illumination by illumination light of the illumination lamp, and the illumination lamp includes the illumination light. Can be switched between an on-state that emits light and an off-state that emits less illumination light or emits less light than the on-state, and the data signal has one or more symbols constituting it. Is divided into a slot for data and a plurality of slots for data, and the slot for separation is provided at the beginning or end of the symbol, and includes one period in which the symbol is turned off. The plurality of data slots are characterized in that one of the data slots is in an OFF state according to the content of the data, and the other data slots are in the ON state. To do.

  The illumination light communication apparatus according to claim 2 is the illumination light communication apparatus according to claim 1, wherein the plurality of data slots are four or more.

  The illumination light communication apparatus according to claim 3 is the illumination light communication apparatus according to claim 1 or 2, wherein the number of the slot for separation is one.

  The illumination light communication apparatus according to claim 4 is the illumination light communication apparatus according to any one of claims 1 to 3, wherein the data signal is data converted by a modulation circuit. And

  The illumination light communication system according to claim 5 is the illumination light communication apparatus according to claim 4, a light receiver that converts the illumination light from the illumination light communication apparatus into an electrical signal, and a high-pass filter that removes low-frequency noise. A receiving device having a demodulation circuit that performs demodulation processing corresponding to the modulation circuit.

  According to the illumination light communication apparatus and the illumination light communication system of the present invention, the transmission of the data signal in which the ratio of the on-state time to the off-state time does not change according to the content of the data and the frequency band is not widened. Is possible.

It is a schematic diagram which shows the illumination light communication apparatus and illumination light communication system which concern on embodiment of this invention. It is a signal diagram which shows the structure of the data signal of an illumination light communication apparatus same as the above. It is a signal diagram which shows the example of the data signal of an illumination light communication apparatus same as the above. It is a schematic diagram which shows the structure of the experiment of an illumination light communication system same as the above. It is a wave form diagram which shows the experimental result of an illumination light communication system same as the above. It is a signal diagram which shows the structure of the data signal of the conventional illumination light communication apparatus. It is a signal diagram which shows the example of the data signal of the illumination light communication apparatus of FIG.

  Hereinafter, the form for implementing the illumination light communication apparatus and illumination light communication system which concern on this invention is demonstrated. As shown in FIG. 1, the illumination light communication apparatus 1 according to the embodiment of the present invention transmits a data signal together with illumination by illumination light of an illumination lamp 2.

  The illuminating lamp 2 can be switched between an on state in which illumination light is emitted and an off state in which illumination light is not emitted at high speed (for example, 0.01 milliseconds to 0.1 milliseconds or more). The off state may be a state that emits less light than the on state. The illumination lamp 2 is preferably an illumination lamp using a plurality of light emitting elements 2a (see FIG. 4) such as light emitting diodes (LEDs).

  The illumination light communication device 1 includes a modulation circuit 3 that converts data sent to be transmitted by illumination light into a data signal. The data signal from the modulation circuit 3 is input to the illuminating lamp 2 and radiated as an optical signal. The modulation circuit 3 can also be provided outside the illumination light communication device 1.

  The symbol Sy constituting this data signal is divided into one delimiter slot SP1 and a plurality (specifically, four) data slots SD1 to SD4 as shown in FIG. The time of the delimiter slot SP1 and the time of each of the data slots SD1 to SD4 are equal to each other.

  The delimiter slot SP1 is provided at the beginning of the symbol Sy. The delimiter slot SP1 has only one period during which it is turned off. Specifically, as shown in FIG. 2, the OFF state may be continued for the entire period of time allocated to the slot for separation SP1. In the delimiter slot SP1, a plurality of off periods are not created in the form of a pulse train (subcarrier). This is because if the form of a pulse train (subcarrier) is used, the time of the separation slot SP1 (and hence the symbol time) becomes longer due to the limit of the response speed of the light receiving element 5a described later, and the transmission speed of the data signal becomes slower. It is easy.

  The delimiter slot SP1 may be provided at the end of the symbol Sy.

  In order to increase the amount of data transmitted per unit time, it is preferable to use the first slot or the last slot SP1. However, a plurality of slot slots SP1 may be provided at the beginning or end. In this case, one period is entered for each separation slot SP1 during the OFF state.

  The four data slots SD1 to SD4 have the same configuration as that of the four-value inversion pulse position modulation described in the background section. That is, similarly to the quaternary inverted pulse position modulation, 2 bits of data in one symbol Sy of the data signal, that is, 4 types of data “00”, “01”, “10”, “11” are 4 Converted to a different type of data signal. Of the four data slots SD1 to SD4, only one of the periods in which one of the data slots SD1 to SD4 is in an OFF state is entered according to the content of the data, and the other data slots are in an ON state. Specifically, as shown in FIG. 2, the OFF state may be continued for the entire period of time allocated to one of the data slots SD1 to SD4. In one of the data slots SD1 to SD4, a plurality of OFF periods in the form of pulse trains (subcarriers) are not created, similar to the separation slot SP1.

  As shown in FIG. 3, the data signal having such a delimiter slot SP1 is turned off in the fourth data slot SD4 next to the symbol Sy having a period in which the first data slot SD1 is turned off. Even if a symbol Sy having a period for entering a state comes, there is always a delimiter slot SP1 containing one period for the off state between the two symbols Sy and Sy. The frequency band is equal to or higher than the frequency of one symbol Sy as one cycle.

  As in the case of binary inverted pulse position modulation, the data slot converts 1-bit data, that is, two types of data “0” and “1” into two types of data signals in one symbol Sy of the data signal. It is also possible to convert it. Similarly to 8-level inverted pulse position modulation, 3-bit data, that is, 8 types of data “000” to “111” are converted into 8 types of data signals in one symbol Sy of the data signal. It is also possible to make it. Similarly, it is also possible to perform the same as inversion pulse position modulation of 16 values or more.

  Here, since the symbol Sy has the delimiter slot SP1 together with the data slot, the time ratio of the delimiter slot SP1 is relatively small in terms of the amount of data that can be transmitted per unit time. It is preferable. Therefore, the number of data slots is preferably 4 or more (modulation corresponding to inverted pulse position modulation of 4 values or more). However, since the number of data slots is too large, the time of the symbol Sy is lengthened and the frequency band is expanded in the low frequency direction, so that the frequency margin for low frequency noise is not reduced. When the number of data slots in one symbol Sy is large, it is possible to regularly add delimiter slots along the way.

  As shown in FIG. 1, the receiving device 4 that has received the illumination light from the illuminating lamp 2 constitutes the illumination light communication system, and receives the illumination light from a light receiving element 5a (see FIG. 4) such as a photodiode. The light receiver 5 is converted into an electric signal, and then the high-pass filter 6 removes the influence of low-frequency noise, and the data is restored through a demodulation circuit 7 that performs demodulation processing corresponding to the modulation circuit 3. The high pass filter 6 has a function of passing a frequency band equal to or higher than a set cutoff frequency, and includes a band pass filter and the like.

  In such an illumination light communication device 1 or illumination light communication system, the illumination light of the illumination light communication device 1 does not flicker in human eyes because the ratio of the on-state time to the off-state time does not change. It can be lighting. Further, since this illumination light has a frequency band that is equal to or higher than a frequency with one symbol as one cycle, the frequency is low with respect to low-frequency noise such as light other than mixed illumination light (for example, fluorescent light). This makes it easy to properly remove the influence of low frequency noise by the high-pass filter 6 in the receiver 4.

  An experiment conducted by the present inventor will be described. In the illumination light communication system of this experiment, as shown in FIG. 4, the illumination lamp 2 has a plurality of light emitting elements 2a of white light emitting diodes and an illumination lamp control circuit 2b for controlling the light emitting elements 2a. The data signal shown in FIG. 3 was input to the illumination lamp 2. One symbol time was set to 0.2 milliseconds (one slot time was set to 0.04 milliseconds). The receiving device 4 has a simple configuration as follows. That is, the light receiver 5 has a resistor 5b connected to a light receiving element 5a of a photodiode, and the high-pass filter 6 includes a capacitor 6a, a resistor 6b, and an amplifier 6c that amplifies the voltage at the connection point. A connection point between the light receiving element 5 a and the resistor 5 b in the light receiver 5 is connected to one end of the capacitor 6 a of the high pass filter 6. The high-pass filter 6 has a cut-off frequency of 4 kHz, and its output signal is output from the output terminal of the amplifier 6c.

  FIG. 5 is a photograph of the oscilloscope screen showing the waveform of the data signal input to the illuminating lamp 2 in the upper stage and the waveform of the output signal of the high pass filter 6 in the lower stage. The ground level is shown at the left end. From FIG. 5, it can be seen that the waveform of the output signal of the high-pass filter 6 follows the data signal input to the illuminating lamp 2 in a positive and negative manner with respect to the ground level. As described above, since the data signal can be transmitted even if the cutoff frequency is set high in the receiving device 4, it is easy to appropriately remove the influence of the low frequency noise.

  The illumination light communication apparatus and the illumination light communication system according to the embodiments of the present invention have been described above, but the present invention is not limited to those described in the embodiments, and is within the scope of the matters described in the claims. Various design changes are possible.

DESCRIPTION OF SYMBOLS 1 Illumination light communication apparatus 2 Illumination lamp 3 Modulation circuit 4 Receiving device 5 Light receiver 5a Light receiving element 6 High pass filter 7 Demodulation circuit Sy symbol SP1 Separation slot SD1-SD4 Data slot

Claims (5)

An illumination light communication device that transmits a data signal together with illumination by illumination light of an illumination lamp,
The illuminating lamp is switchable between an on state that emits the illumination light and an off state that does not emit the illumination light or emits less light than the on state.
The data signal is formed by dividing a symbol constituting the data signal into one or a plurality of separation slots and a plurality of data slots,
The delimiter slot is provided at the beginning or end of the symbol, and includes one period in which the symbol is turned off.
The plurality of data slots includes one period in which one of the data slots is turned off according to the content of data, and the other data slots are turned on. Communication device. In the illumination light communication apparatus according to claim 1,
4. The illumination light communication apparatus according to claim 1, wherein the plurality of data slots are four or more. In the illumination light communication apparatus according to claim 1 or 2,
The illumination light communication apparatus according to claim 1, wherein the separation slot is one. The illumination light communication apparatus according to any one of claims 1 to 3,
2. The illumination light communication apparatus according to claim 1, wherein the data signal is data converted by a modulation circuit. The illumination light communication apparatus according to claim 4;
A receiver having a light receiver that converts the illumination light from the illumination light communication device into an electrical signal, a high-pass filter that removes low-frequency noise, and a demodulation circuit that performs demodulation processing corresponding to the modulation circuit;
An illumination light communication system comprising: