JP2004297425A - Wireless optical communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless optical communication system which is stable and universal concerning the color temperature for illumination. <P>SOLUTION: The illumination is constituted of the wave length of not less than four visible colors, especially five colors in an illuminating device 102. LEDs 201-205 emit light in different wave length groups, and transmit data respectively. Thus, a higher transmission rate and the color temperature are realized as the finer illumination. Unstable color temperature unique to LED illumination is eliminated in the device 102, by receiving feedback of a value for correcting the color temperature from a terminal 110. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a device for spatial transmission, and more particularly to a wireless optical communication system for spatial transmission using LED light.
[0002]
[Prior art]
Since blue and violet colors have been added to the LEDs to increase the output, research and development have been conducted to realize illumination with LEDs with lower power consumption and longer life. There are roughly two methods for realizing indoor lighting with LEDs. One is to apply a fluorescent paint to a blue-violet or ultraviolet LED and to excite it with the light of the LED to obtain fluorescent light of a plurality of colors of visible light so that it looks white in total. The other is to emit light in combination with visible LEDs of a plurality of colors so that the LED looks totally white.
[0003]
The latter method has higher conversion efficiency from electric energy to light energy. However, since the light-emitting characteristics of each LED change depending on the light-emitting time, the ambient temperature, and the like, stable performance with respect to the total color (color temperature) cannot be obtained, and it is not regarded as a favorite in lighting applications.
[0004]
On the other hand, a wireless optical communication system that further performs data communication using the latter LED illumination has been proposed (for example, see Patent Document 1). In Patent Literature 1, a lighting device using an LED is modulated, and data is transmitted to a terminal installed indoors. Further, there is disclosed a system in which LED illumination is constituted by three primary colors, and a type of wavelength multiplex transmission in which each color is modulated with individual data. The receiving terminal separates the three colors of light and receives them with different light receiving means to obtain the original three data.
[0005]
[Patent Document 1]
JP-A-2002-290335
[0006]
[Problems to be solved by the invention]
In the conventional wireless optical communication system, there has been a problem that stable and free performance cannot be obtained for the color temperature as illumination.
SUMMARY OF THE INVENTION An object of the present invention is to provide a wireless optical communication system capable of obtaining stable and free performance with respect to color temperature as illumination. Another object of the present invention is to provide a wireless optical communication system having an improved wavelength multiplexing transmission function.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, there is provided a wireless device comprising at least one terminal and a lighting device for illuminating a room using a plurality of light emitting diodes and performing optical wireless communication with the terminal. In the optical communication system, the lighting device includes four or more groups having mutually different visible light emission center wavelengths, and a plurality of light emitting diodes that emit light that is data-modulated by different data independently for each of the groups. And a light emitting diode driving circuit for driving the plurality of light emitting diodes, wherein the terminal has one or more light receiving units, and the light receiving units transmit one of the four or more groups. And an optical filter for removing the other group, and light detecting means for extracting the data by detecting light transmitted through the optical filter. To provide a wireless optical communication system.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
(First Embodiment)
Hereinafter, a first embodiment of the wireless optical communication system of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing the configuration of the entire wireless optical communication system of the present invention.
In FIG. 1, an illuminating device 102 attached to a ceiling 101 uses an LED as a light source, and the LED in the illuminating device 102 uses LEDs of five kinds of wavelengths (λ1 to λ5) in a visible range. As described above, in the present invention, LEDs having different wavelengths of four or more colors in the visible region are used. The wavelengths are, for example, λ1 = 700 nm, λ2 = 612 nm, λ3 = 546 nm, λ4 = 480 nm, and λ5 = 430 nm.
[0009]
Each of the five wavelengths is modulated by different data, and the data is transmitted to each terminal 110 in the room.
Light of each wavelength is modulated by digital amplitude modulation (ASK), and the modulation rate is, for example, 50 Mbps, respectively. Data transmission of 250 Mbps in total is performed between the lighting device 102 and the terminal 110.
[0010]
The LED driver 103 drives an LED in the lighting device 102 according to externally input data.
The LED driver 103 includes a driver corresponding to each wavelength, and in some cases, each driver further includes a plurality of drive ICs. The number of LEDs connected to one driver IC is determined depending on the current driving capability of the driver IC and the required current amount of the LED. In the figure, the wires are collectively shown by one line.
[0011]
Although not shown, the transmission data is appropriately allocated to five wavelengths before being input to the LED driver 103.
Next, the configuration of the lighting device 102 will be described in more detail with reference to FIG.
FIG. 2 is a view of the lighting device 102 installed on the ceiling 101 with the lamp cover removed and viewed from below.
As shown in FIG. 2, for example, the LED cells 210 of the lighting device 102 are regularly arranged at equal intervals on a concentric circle centered on the center of the lighting device 102. At the innermost periphery, four LED cells 210 are arranged concentrically. Next, ten LED cells 210 are arranged concentrically outward. At the outermost periphery, 15 LED cells 210 are arranged concentrically.
[0012]
Each LED cell 210 has LEDs 201 to 205 of five colors arranged as shown in FIG. The LEDs 201 to 205 are arranged as close as possible. This suppresses the phenomenon that the shadow formed when the light from the lighting device 102 shines on the indoor object is rainbow-colored.
[0013]
These LED cells 210 are supplied with a drive current corresponding to each wavelength from the LED driver 103 shown in FIG.
When the LED driver 103 is installed in the immediate vicinity of each of the LEDs 201 to 205, digital data to be transmitted is supplied to the LED driver 103 provided for each LED cell 210. When a plurality of LEDs of the same wavelength are driven by one LED driver 103, a driving current is supplied from the LED driver 103 provided for each wavelength to the LED of the same wavelength.
[0014]
The drive current supplied to the LED or the digital signal supplied to the LED cell 210 in accordance with the transmitted digital data is desirably connected to the LED of the same wavelength by an equal-length wiring. This example will be described with reference to FIG.
[0015]
FIG. 3 shows an example in which equal-length wiring is provided to the LED 204 having the wavelength λ4 in each LED cell 210.
A wiring 301 indicated by a two-dot chain line supplies a drive current to the fifteen LED cells 210 arranged on the outermost concentric circle. A wiring 302 indicated by a dashed line supplies a drive current to ten LED cells 210 arranged on the second concentric circle from the inside. A wiring 303 shown by a solid line supplies a drive current to the four LED cells 210 arranged on the innermost concentric circle.
[0016]
The wirings 301, 302, and 303 shown in FIG. 3 have the same wiring distance from the center of the lighting device 102 to the LED 204. Equal length wiring is also performed for each of the other four wavelengths.
[0017]
By performing equal-length wiring in this way, LEDs having the same wavelength are modulated at substantially the same timing. As a result, a signal reaching the terminal 110 under illumination of the lighting device 102 (a total signal obtained by adding the light emitted from each LED cell 210) due to a difference in the modulation timing of the LED having the same wavelength has a distorted waveform. Can be prevented.
[0018]
Next, the configuration of the terminal 110 that receives the data light transmitted from the lighting device 102 will be described with reference to the drawings.
FIG. 4 is a diagram illustrating an example of a configuration of an optical receiver provided in terminal 110.
FIG. 4A shows an optical receiver 400 that receives all the wavelengths (λ1 to λ5) output from the illumination device 102 in FIG. 1, and FIG. 4B shows light of a type that receives only some of the wavelengths. Receiver 450. Thus, the optical receiver does not necessarily need to be configured to be able to receive all wavelengths (λ1 to λ5).
[0019]
The optical receiver 400 includes light receiving units 401, 402, 403, 404, and 405 corresponding to all wavelengths of λ1 to λ5. The optical receiver 450 includes light receiving units 451, 452, and 453 corresponding to a total of three wavelengths of λ1, λ2, and λ3.
[0020]
Since the operation of each light receiving unit is the same in any of the optical receivers, the operation of the light receiving unit will be described with reference to FIG.
In FIG. 4A, light output from the illumination device 102 enters the optical receiver 400.
The light receiving unit 401 is provided with a filter 421 that transmits light of λ1 at a light incident portion of the light receiver 411, removes other wavelengths output by the LED of the illumination device 102, and passes only light of the wavelength λ1. As a result, the light receiver 411 receives only the data superimposed on the light having the wavelength λ1. Similarly, the light receiving units 402 to 405 of the other wavelengths λ2 to λ5 use the filters 422 to 425 and receive only the data superimposed on the light of the wavelengths λ2, λ3, λ4, and λ5.
[0021]
The light receiving units 401 to 405 output the received data to a block that performs the following processing (data format conversion and the like) as appropriate.
As described above, the LED lighting is constituted by LEDs of four or more colors.
As described in the conventional example, if there are LEDs of three primary colors, white light can be synthesized, and further, light of any color can be synthesized by adjusting the power of each light. However, it is desirable that the number of colors be larger because of the following points.
[0022]
(A) Even if LEDs corresponding to the three primary colors are prepared, it is difficult to accurately prepare LEDs having wavelengths corresponding to the three primary colors due to variations in the LED manufacturing process and the like. As a result, the colors that can be combined are limited. If the number of colors is large, even if each wavelength is somewhat inaccurate, the limitation on the synthesized color due to the inaccuracy of the wavelength is greatly relaxed.
[0023]
(B) Large-capacity communication is desired. The modulation speed of a single LED is at most several hundred Mbps, and the modulation speed of a high-brightness LED for illumination is further reduced. Therefore, the larger the number of wavelengths, the larger the capacity.
[0024]
(C) In the case of performing wireless optical communication using LED illumination as a light source, since communication is based on diffused light (light that spreads in all directions from the light source), waveform tailing due to multipath occurs (details will be described later). Depending on the structure of the room or the like, the modulation speed may be limited to a modulation speed lower than the modulation speed of the LED alone due to the tailing. If the number of colors (the number of multiplexed wavelengths) is large, a certain transmission rate can be guaranteed in total even if the modulation speed of each color is suppressed low and the limitation due to the tailing is relaxed.
[0025]
With such a configuration, it is possible to guarantee a variable width of the color as illumination, and it is possible to realize a high transmission rate.
Next, the bit rate limitation by multipath will be described with reference to FIGS.
First, a phenomenon in which a waveform has a tail due to indoor multipath will be described with reference to FIG.
As shown in FIG. 5, when the terminal 110 is on the side of a reflector, for example, the wall 501, the terminal 110 has light 502 that directly reaches from the lighting device 102 and light 503 that once reaches the wall 501 and then reaches the wall 501. .
[0026]
Even if the lighting device 102 is wired with the same length as shown in FIG. 3, the light emitted from each LED may reach the terminal 110 with a slight shift due to the positional relationship between the terminal 110 and the lighting device 102. become.
[0027]
For this reason, even if the waveform emitted from each LED of the illumination device 102 is a perfect rectangular wave as shown in FIG. 6A, the rising of the waveform reaching the terminal 110 is shown in FIG. 6B. As a result, the waveform becomes slightly dull.
[0028]
For the falling portion, in addition to the rounding of the waveform generated for the same reason, the light once reflected by the wall 501 arrives with a delay, so that the trailing portion is added to the waveform.
Depending on the amount of reflection from wall 501, this tailing severely limits the bit rate.
For example, one time slot time of a 20 Mbps data signal is 50 ns, which is 15 m in terms of the optical path length of light propagating in the air. This is 1.5 m at 200 Mbps.
[0029]
Assuming that the average of the optical path length difference between the light that directly reaches the terminal 110 from the lighting device 102 and the light that arrives after being reflected by the wall 501 is about 50 cm, at 20 Mbps it is about 1/30 of one time slot, so the waveform is rounded. Hardly occurs. However, at 200 Mbps, this becomes 1/3, and a clear waveform rounding is observed.
[0030]
Since the power of the light source is very large in the wireless optical communication by the illumination device 102, the bit rate limitation due to insufficient power, which has been a problem in the conventional diffusion type wireless optical communication, hardly causes a problem. However, the bit rate is effectively limited by the tailing due to multipath. Of course, there is no problem if the size of the multipath is sufficiently small. However, since the size of the multipath depends on the material of the object causing reflection, it is practically uncontrollable.
[0031]
On the other hand, since the illuminating device 102 is a diffusion type light source, there is a correlation between the optical path length difference generated by the multipath and the magnitude of the light passing through the path, and the light in the path increases as the optical path length difference increases. Become smaller.
[0032]
Therefore, it is necessary to limit the bit rate to such a degree that the waveform is not seriously affected even if there is a multipath from a material having a high reflectance such as a mirror in the line design.
The above is the details of the bit rate limitation by the multipath.
In the present application, unlike a conventional example, a plurality of wavelengths are individually received by a plurality of receiving units provided in an optical receiver without being separated. That is, it is assumed that an optical filter for extracting only each wavelength is attached to the incident surface of each receiving unit, and each optical receiving unit is spatially arranged. The light from the LED lighting is diffused light, and light having substantially the same content arrives at a place several mm to several cm away, so that it is effectively used. It is much cheaper, simpler, and less lossy than using a conventional dichroic filter for separating light from one entrance port in cascade.
[0033]
In the wireless optical communication system of the present invention, the bit rate does not need to be the same for each wavelength. If emphasis is placed on the function as illumination, the magnitude of the power for each wavelength always occurs. At this time, for a wavelength having a large power, a higher bit rate may be set. By setting a higher bit rate at a wavelength with a large power, data can be transmitted efficiently with illumination close to natural light.
[0034]
The number of wavelengths is preferably as large as possible for reasons (a), (b) and (c) above. However, the emission spectrum of the LED has a certain width, and there is a limit to packing in a limited region of the visible region with a small number of overlapping portions (of course, if the number of overlapping portions increases, crosstalk between wavelengths may occur. Waveform distortion may occur due to severe demands on the center wavelength and wavelength bandwidth of the wavelength filter of the optical receiving unit, resulting in deterioration of the yield, and necessity of receiving the signal at the end of the emission spectrum. There is).
[0035]
Further, the shape of the emission spectrum of the LED is slightly different depending on the specific structure and composition of the LED even when the center wavelength is the same. It is desirable to pack with. The emission spectrum width of the LED is, for example, about 650 nm at the center wavelength, and is about 80 nm (full width 20 dB down from the peak). The emission spectrum width tends to decrease as the center wavelength decreases, but considering that the visible region is only about 400 nm from 400 nm to 800 nm, it can be said that about five colors can be packed with a margin.
[0036]
On the other hand, when viewed from the viewpoint of dimming (color temperature), for example, a fluorescent lamp or the like has an emission line having a wavelength close to the three primary colors and an emission line with a weak power in between the emission lines. Color is realized. Also, relatively high-end inkjet printers use five (+) black inks for natural coloring. A combination of three colors and one color between each color is a combination that facilitates dimming (a color control algorithm is easy). For this reason, about five colors are appropriate for fine control of the color temperature.
[0037]
As described above, by setting the number of wavelengths (colors) of the diodes in the visible region of LED lighting to five colors, it is possible to reduce the overlap of emission spectra, reduce crosstalk between wavelengths, and achieve fine dimming. Become.
[0038]
(Second embodiment)
Hereinafter, a second embodiment of the wireless optical communication system of the present invention will be described in detail with reference to the drawings. In the second embodiment, it is possible to transmit a signal from the terminal to the lighting device.
[0039]
FIG. 7 is a diagram showing the configuration of the entire wireless optical communication system of the present invention.
In FIG. 7, each terminal 710 includes an upstream optical transmitter having an infrared wavelength λ6 (for example, 850 nm). In response to this, the lighting device 702 includes an upstream optical receiver corresponding to λ6. The bit rate of the upstream signal is, for example, 1 Mbps.
[0040]
The light source used in the upstream optical transmitter provided in each terminal 710 is, for example, an LED. However, since the upstream signal light does not require a function as illumination, a semiconductor laser having an output within a range that satisfies eye safety standards is used. (LD).
[0041]
Further, since it is not necessary to illuminate the whole room unlike the lighting device 702, even if the light source for the upstream signal of the terminal 710 is a diffused light, the light source of the lighting device 702 is directed to an optical receiver by narrowing the spread angle to some extent. A beam that emits light may be used.
[0042]
However, in the latter case, a beam tracking function is required.
In addition, the uplink signal usually does not require as much bandwidth as the downlink signal, and therefore may have a lower bit rate than the downlink signal.
Since the light from the LED lighting is diffused light, if a receiving unit is provided on the lighting device side, there is a possibility that the light of the own device may be sneak around and received. Therefore, it is desirable to realize uplink communication with light having a wavelength not used by the lighting device. Light of a visible wavelength that is not used in the lighting device may be used, but when monochromatic light is sent from the terminal to the lighting device in the visible range, the lighting device is illuminated with that color, The color balance of the lighting is lost. Therefore, the uplink from the terminal to the lighting device is desirably one of infrared light and ultraviolet light, and among them, communication using infrared light in which the semiconductor light emitting and receiving element is developed is desirable.
[0043]
It is not necessary that all of the three terminals 710 have an optical transmitter for uplink signals. In this example, for example, two of the three terminals 710 have optical transmitters for uplink signals.
Next, the configuration of the lighting device 702 that receives data light using infrared rays transmitted from the terminal 710 will be described in more detail with reference to FIG.
FIG. 8 is a view of the lighting device 702 installed on the ceiling 101 with the lamp cover removed and viewed from below. Note that the same components as those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted.
[0044]
The LED cells 210 of the lighting device 702 are arranged, for example, in the same manner as in FIG.
In the lighting device 702, an optical receiver 800 for an upstream signal for receiving the infrared ray of the wavelength λ6 transmitted from the terminal 710 is provided at the center of the lighting device 702. The structure of the upstream optical receiver 800 is the same as that of the light receiving unit 401 shown in FIG. 4 except that the optical filter 421 provided on the light receiving surface side of the light receiver 411 is designed to transmit only infrared light of wavelength λ6. I have. Thereby, the lighting device 702 can receive the infrared ray of the wavelength λ6 transmitted from the terminal 710.
[0045]
Next, the configuration of the terminal 710 will be described with reference to the drawings.
FIG. 9 is a diagram illustrating an example of a configuration of the terminal 710. Note that the same components as those in FIG. 4A are denoted by the same reference numerals, and description thereof is omitted.
In FIG. 9, in addition to the optical receiver 400, an optical transmitter for uplink signal 901 is provided in the terminal 710. The upstream signal light transmitter 901 transmits data to the lighting device 702 using infrared light having the wavelength λ6.
[0046]
In the example of FIG. 7, two terminals 710 have an upstream signal transmitter 901. When the plurality of terminals 710 output an optical signal to the illumination device 702 using the infrared ray having the same wavelength λ6, some kind of access control is necessary. For example, it is preferable to avoid collision of signals with TDMA or the like as much as possible. In this case, a narrow-band line using infrared light may be shared with a control signal line (control line). In this case, since a control signal such as access permission is exchanged via infrared light of wavelength λ6, it is necessary to provide an optical transmitter of wavelength λ6 also on the lighting device 702 side. At this time, it is necessary to carefully dispose the λ6 light between the optical receiving unit having the wavelength λ6 and the optical transmitter having the wavelength λ6 so that no wraparound of the light may occur. Similarly, it is necessary to install an optical receiver having the wavelength λ6 on the terminal 710 side. Of course, any one of the wavelengths λ1 to λ5, which is visible light, may be used for the downstream control signal.
[0047]
As described above, in addition to the downlink communication from the LED lighting to the terminal, by performing the uplink communication from the terminal to the LED lighting with infrared light, it is possible to transmit the uplink data from the terminal 710 side. Become.
[0048]
Also, in this example, infrared light is used as an uplink from the terminal to the lighting device, but it is not always necessary to use light, and wireless may be used as the uplink.
(Third embodiment)
Hereinafter, a third embodiment of the wireless optical communication system of the present invention will be described in detail with reference to the drawings. In the third embodiment, the color temperature of the illuminating light by the lighting device is controlled by using the terminal having the light receiving unit corresponding to all the wavelengths of the downstream visible light among the terminals having the upstream optical transmitter. It is possible to do.
[0049]
FIG. 10 is a diagram showing a configuration of a lighting device and a terminal corresponding to such a function. The same components as those in FIGS. 7 and 9 are denoted by the same reference numerals, and description thereof will be omitted.
In FIG. 10, a terminal 1010 includes light receiving units 401 to 405 that receive wavelengths λ1 to λ5 of visible light output from a lighting device 702.
The light receiver 411 provided in the light receiving units 401 to 405 outputs the value of the optical power detected for each wavelength to the power monitor 1011.
The power monitor 1011 outputs the value of the optical power detected by the light receiving units 401 to 405 to the upstream signal optical transmitter 901.
The upstream signal optical transmitter 901 outputs the value of the optical power input from the power monitor 1011 to the lighting device 702 using infrared light having the wavelength λ6.
The lighting device 702 outputs the power information received by the upstream light receiver 800 shown in FIG. 8 to the color temperature control unit 1050. The color temperature control unit 1050 estimates (calculates) the spectrum shape, that is, the color temperature from the power information input from the terminal 1010, and outputs a color temperature correction value for correcting the deviation from the desired color temperature to the LED driver. Output to 103. The LED driver 103 adjusts the power ratio of each wavelength so that the light output from the lighting device 702 has a desired color temperature. As a result, the color temperature of the entire light output from the lighting device 702 is maintained at a desired color temperature.
[0050]
Note that the processing for estimating (calculating) the color temperature does not necessarily need to be performed on the lighting device 702 side. For example, the terminal 1010 holds information about a desired color temperature by being notified in advance from the lighting device 702 or the like. Then, the terminal 1010 estimates a color temperature from the power value obtained by the power monitor 1011, and obtains a wavelength to be corrected and its correction value from the held desired color temperature. The terminal 1010 may output the obtained correction value to the lighting device 702 by using an up system using the infrared ray λ6.
[0051]
The simplest way of detecting the optical power in each of the light receiving units 401 to 405 is to measure the DC photocurrent value of the photodiode.
However, as a result of, for example, sunlight at sunset, light from other than the illumination device 702 enters the light receiving units 401 to 405 of the terminal 710 to increase the DC photocurrent, and the spectrum of the sunlight or the like increases in the illumination device. It is envisioned that the spectrum will differ from the spectrum corresponding to the desired color temperature of 702.
[0052]
In such a case, if the total color temperature including sunlight is the desired target color temperature as the final target, the measurement of the DC photocurrent value described above may be used.
However, normally, since the color temperature of the lighting device 702 alone is controlled, a change in the measured value due to sunlight at dusk or the like is not preferable. Therefore, if possible, the amplitude of the data component superimposed on the wavelengths λ1 to λ5 should be detected instead of the DC photocurrent value. In some cases, the amplitude of the data component may be different depending on the wavelength. In this case, if the amplitude of the modulated signal at the time of the modulated signal in the lighting device 702 is known, it is detected on the terminal 1010 side. Then, by knowing how much the amplitude differs, the spectral shape can be estimated and the color temperature can be estimated.
[0053]
As a result, the color temperature of the lighting device alone can always be controlled without being affected by sunlight at sunset or the like.
As described above, in the third embodiment, the power of the light of each wavelength is detected by the optical receiver having the light receiving unit that receives all of the visible light of a plurality of wavelengths emitted from the lighting device. The color temperature of the illumination can be estimated by detecting the ratio of these optical powers. Therefore, the light power or information obtained by processing the light power and calculating the ratio and color temperature is sent to the lighting device through the uplink. The lighting device controls the desired color temperature by using the information. As a result, information on the color temperature is fed back, so that the color temperature of the illumination can be stabilized.
[0054]
(Fourth embodiment)
A photodiode is usually used as a light receiving element for optical communication. The conversion efficiency and the dark current of the photodiode vary depending on the temperature, albeit slightly.
In the wireless optical communication system of the present embodiment, wavelength multiplexing with a very wide width is performed. In such a case, photodiodes having the same composition cannot receive all wavelengths (efficiently). If photodiodes of different compositions or photodiodes of the same composition have significantly different light receiving wavelengths, the light receiving characteristics do not show the same temperature characteristics.
[0055]
In the fourth embodiment, when calculating the ratio of the optical power detected by each light receiving unit, the characteristic correction is performed in consideration of the different temperature characteristics of the photodiodes used in each light receiving unit. Thereby, the calculation result of the color temperature is made constant regardless of the temperature.
[0056]
Hereinafter, a fourth embodiment of the wireless optical communication system of the present invention will be described in detail with reference to the drawings.
FIG. 11 is a diagram showing the overall configuration of the wireless optical communication system of the present invention. In FIG. 11, the same components as those in FIG. 10 are denoted by the same reference numerals, and description thereof will be omitted. As shown in FIG. 11, a temperature detecting unit 1101 is provided near the light receiving units 401 to 405 of the optical receiver 400. The temperature detecting unit 1101 outputs a temperature near the light receiving units 401 to 405 to the power monitor 1011.
[0057]
The power monitor 1011 is different from the third embodiment in the following points. In the power monitor 1011, the temperature characteristics of the photodiode used in each light receiver 411 are registered in advance. For this registration, any memory such as a ROM or any other device that can register characteristics may be used.
[0058]
The power monitor 1011 compares the value of the optical power measured by the light receiver 411 in each of the light receiving units 401 to 405 with the temperature characteristic registered in advance and the temperature detected by the temperature detecting unit 1101. Correct so that the value is correct.
[0059]
As a result, it is possible to reduce the estimation error of the color temperature due to the season and the temperature.
(First example of color temperature control method)
When controlling the color temperature in the above-described embodiment for controlling the color temperature, it is necessary to control the average output light power of the LED provided for each wavelength in some form.
As a first method of changing the average light power of each wavelength LED by controlling the color temperature of the lighting device, the data mark rate (the ratio of bit “1” to all bits) is changed. The configuration of the lighting device 702 side in this example is the same as that of FIGS. 10 and 11, but a digital signal processing unit that can change the mark rate in response to a control signal from the color temperature control unit 1050 is provided in the LED driver 103. Have been.
[0060]
By using this method, the following three effects can be obtained.
Since the change of the mark ratio can be performed by the signal processing of the digital unit, the hardware can be easily mounted.
-It is not necessary to change the modulation amplitude of data.
In the above-described embodiment, it is necessary to perform high-speed and large-current modulation on the LED driver 103 that drives the illumination LED. However, the LED driver 103 capable of such an operation can operate fine characteristics and operate with stability. It is difficult to achieve both. However, if a method based on the control of the mark ratio is used, there is no need to control the amplitude, so that it is not necessary to add a detailed operation to the LED driver 103.
[0061]
FIG. 12 shows the operation when the optical power is changed by controlling the mark ratio.
The digital data to be transmitted is converted into digital data having a predetermined mark rate by a digital signal processing unit (not shown) in the LED driver 103 in advance.
FIGS. 12A and 12B are diagrams showing the light emission power of the LED when the mark ratio is about 0.5 and 0.3, respectively. The average optical power is 40% smaller in FIG. 12B than in FIG.
[0062]
By controlling the average light power by changing the mark ratio in this manner, color temperature control can be performed.
(Second example of color temperature control method)
As a second method of changing the average light power of the LED of each wavelength to control the color temperature of the lighting device, the DC offset of the LED modulation signal may be changed.
When the LED on the lighting device side is driven in a state of a poor extinction ratio, the output average light power of the LED can be controlled by adjusting the DC offset corresponding to “0” of the modulation signal. As described above, it is difficult to realize a high-current and high-speed signal amplitude drive unit so that it can be operated finely. If the extinction ratio is deliberately degraded by operating the current applied to the LED in such a manner that only a part of it is turned on / off instead of turning it on / off in response to the information, it corresponds to the DC offset. There is a circuit for adding a DC current and a modulation current corresponding to a modulation signal, and the DC current and the modulation current can be independently controlled before the addition circuit. That is, in order to control the average optical power, only the DC current needs to be controlled. This facilitates control of the average output power.
[0063]
Hereinafter, the configuration on the lighting device 702 side when changing the DC offset of the LED modulation signal will be described with reference to the drawings.
FIG. 13 is a diagram showing a configuration of the lighting device 702 side. 13 that are the same as those in FIG. 10 have the same reference numerals and description thereof will be omitted.
In FIG. 13, digital data to be transmitted is supplied to the LED driver 103 via the input terminal 1300.
In the LED driver 103, the signal amplitude drive unit 1301 converts digital data input from the input terminal 1300 into data of a current for driving the LED and outputs the data to the current adder 1302.
[0064]
On the other hand, power information is received by the upstream optical receiver 800 shown in FIG. 8, and this power information is output to the bias current supply means 1303.
The bias current supply unit 1303 calculates the color temperature, and outputs a bias current of the LED of each wavelength to the current adder 1302 to obtain a desired color temperature.
The current adder 1302 adds the current input from the signal amplitude drive unit 1301 and the bias current input from the bias current supply unit 1303, and outputs the result to the LEDs 201 to 205.
[0065]
The LEDs 201 to 205 are driven by the currents input from the current adder 1302 and emit light.
This operation will be described with reference to FIG.
FIG. 14 shows how the DC offset of the modulation signal is changed according to the required average optical power.
In FIG. 14B, the magnitude of the DC offset is reduced, and in FIG. 14B, the average optical power is reduced by about 40% compared to FIG. 14A.
In FIG. 14, the mark rate of the current for the data output from the signal amplitude drive unit 1301 is １ ／.
As can be seen from FIG. 14, the sum of the DC offset and the average optical power included in the data section is the total average optical power.
If the current-output light power characteristic of the LED is not linear, the DC current value applied to the LED and the DC offset of the output light power are not proportional, so that the correction or the correction to obtain the desired output light power is performed. Feedback is needed.
[0066]
In the example described above, the current for the DC offset (the bias current) output from the bias current supply unit 1303 and the unit for supplying the current for the data output from the signal amplitude drive unit 1301 are different. Therefore, when changing the DC offset, only the current from the bias current supply means 1303 needs to be changed. In this method, the color temperature of the entire illuminating light from the illumination device 702 can be maintained at a predetermined color temperature by individually changing only the current output from the bias current supply unit 1303. The required signal amplitude drive section 1301 does not need to be changed, and the configuration can be simplified.
[0067]
In this color temperature control method, the description will be made assuming that illumination is performed using five visible light wavelengths λ1 to λ5. However, the number is not necessarily limited to five, and may be four or more.
[0068]
(Fifth embodiment)
In the fifth embodiment, it is assumed that the communication function of the lighting device is used even in the daytime, and the mode in which both the lighting function and the communication function function and the mode in which only the communication functions are separately provided. Features.
[0069]
In the present embodiment, the method described above (second method of controlling color temperature) is used.
The lighting device of the present application provides an indoor wireless communication environment. Indoor wireless communication is likely to be performed even during daylight hours. When an LED is used with a poor extinction ratio, the DC offset is used for indoor lighting. Therefore, when room lighting is not required, the DC offset is removed, and the LED is driven only by the current corresponding to the modulation signal. By doing so, when sunlight is inserted and indoor lighting is not required or a small amount of light is sufficient, electric power only for lighting is not used, so that power can be saved.
[0070]
Hereinafter, the configuration on the lighting device 702 side when changing the DC offset of the LED modulation signal will be described with reference to the drawings.
FIG. 15 is a diagram showing a configuration of the lighting device 702 side. Note that the same components as those in FIG. 13 are denoted by the same reference numerals and description thereof is omitted.
In FIG. 15, a lighting ON / OFF control unit 1501 is newly provided. The lighting ON / OFF control unit 1501 is supplied with a control signal indicating whether to turn on or off the lighting in accordance with an operation of a switch or the like by a user. The illumination ON / OFF control unit 1501 controls ON / OFF of the bias current supply unit 1303 according to the control signal. When the lighting is turned on, it is turned on, and when the lighting is turned off, it is turned off.
[0071]
The bias current supply unit 1303 functions when it is turned on by the lighting ON / OFF control unit 1501 to supply a DC current to the current adder 1302, and when it is turned off, stops its function and turns off the current adder 1302. Do not supply DC current to
[0072]
Next, the operation at this time will be described with reference to FIG.
FIG. 16A shows a mode in which both the illumination function and the communication function are functioning, which has a large DC offset, and this portion mainly fulfills the function of illumination.
FIG. 16B shows a mode in which only the communication function is functioning, in which the light is shining only with the brightness corresponding to the average power of the data component.
FIG. 16A shows a state where the light is shining brightly, while FIG. 16B shows a state where the light is dimly lit.
By supporting the communication-only mode in this way, it is not necessary to keep the lights on in a room brightly lit by sunlight in the daytime, and energy can be saved.
Note that, in each of the embodiments described above, only the main parts related to the configuration of the present application are shown, and other elements (for example, an access control unit, Power supply etc.) are omitted.
[0073]
Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements in an implementation stage without departing from the scope of the invention. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Further, components of different embodiments may be appropriately combined.
[0074]
【The invention's effect】
As described above, according to the present invention, wireless optical communication is performed using an illumination device including four or more visible LEDs, so that a stable and flexible performance can be achieved with respect to a higher transmission rate and color temperature as illumination. The resulting wireless optical communication system can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining an overall configuration of a first embodiment according to a wireless optical communication system of the present invention.
FIG. 2 illustrates a structure of a lighting device.
FIG. 3 is a diagram illustrating equal-length wiring of a lighting device.
FIG. 4 is a diagram illustrating a configuration of a terminal.
FIG. 5 is a view for explaining waveform skirting by multipath.
FIG. 6 is a view for explaining waveform tailing by multipath.
FIG. 7 is a diagram for explaining the overall configuration of a second embodiment according to the wireless optical communication system of the present invention.
FIG. 8 illustrates a structure of a lighting device.
FIG. 9 is a diagram illustrating a configuration of a terminal.
FIG. 10 is a diagram illustrating a configuration of a terminal according to a third embodiment of the wireless optical communication system of the present invention.
FIG. 11 is a diagram illustrating a configuration of a terminal according to a fourth embodiment of the wireless optical communication system of the present invention.
FIG. 12 is a diagram for explaining an operation when the optical power is changed by controlling the mark ratio.
FIG. 13 illustrates a structure of a lighting device.
FIG. 14 is a diagram for explaining the operation of the method for changing the optical power.
FIG. 15 illustrates a structure of a lighting device.
FIG. 16 is a diagram for explaining an LED drive current at the time of lighting ON / OFF control.
[Explanation of symbols]
101: ceiling, 102, 702: lighting device, 103: LED driver, 110, 710, 1010: terminal, 201 to 205: LED, 210: LED cell, 301, 302, 303: wiring, 400, 450: optical receiver , 401, 402, 403, 404, 405, 451, 452, 453: light receiving unit, 411: light receiver, 421 to 421, filter, 501: wall, 502, 503: light, 800: light receiver for upstream signal, Reference numeral 901: an optical transmitter for an upstream signal; 1011, a power monitor; 1050, a color temperature controller; 1101, a temperature detecting means; 1301, an input terminal; 1302, a current adder; 1303, a bias current supplying means; Unit, 1501 ... Lighting ON / OFF control unit.

Claims (11)

In a wireless optical communication system comprising at least one terminal and a lighting device that illuminates a room using a plurality of light emitting diodes and performs optical wireless communication with the terminal,
The lighting device,
A plurality of light-emitting diodes, each comprising four or more groups having emission center wavelengths in the visible region different from each other, and emitting light modulated by data independently of each of the groups,
A light emitting diode drive circuit for driving the plurality of light emitting diodes,
The terminal is
Having one or more optical receiving units,
An optical filter that transmits one of the four or more groups and removes the other group; and a light detection unit that extracts the data by detecting light transmitted through the optical filter. A wireless optical communication system comprising: The wireless optical communication system according to claim 1, wherein the number of the groups is five. Further, the terminal is:
An upstream data input terminal to which upstream data to be transmitted to the lighting device is input;
Transmitting means for transmitting the uplink data input from the uplink data input terminal to the lighting device,
The lighting device,
3. The wireless optical communication system according to claim 1, further comprising a receiving unit that receives the uplink data transmitted from the transmitting unit. The wireless optical communication system according to claim 3, wherein the lighting device and the terminal use infrared light for transmitting and receiving uplink data. Further, at least one of said terminals comprises:
Having optical receiving units corresponding to all of the four or more groups,
Transmitting a signal corresponding to the optical power detected by each of the optical receiving units as the uplink data by the transmitting unit,
The lighting device,
And a color temperature correction means for correcting a color temperature of the entire lighting device by changing a drive current of the light emitting diode drive circuit in accordance with the signal received by the reception means. 5. The wireless optical communication system according to 3 or 4. Further, the terminal is:
Temperature measuring means for measuring the temperature near the receiving unit,
Correction means for correcting, in accordance with the temperature measured by the temperature characteristic means, a signal corresponding to the light power in a direction in which the color temperature of the lighting device as a whole is more correctly corrected. The wireless optical communication system according to claim 5, wherein The lighting device,
7. The wireless optical communication system according to claim 5, wherein a color temperature of light emitted by the entire lighting device is corrected by controlling a mark ratio of a modulation signal for driving the light emitting diode. The lighting device,
7. The wireless optical communication system according to claim 5, wherein a color temperature of light emitted by the entire lighting device is corrected by controlling a DC offset amount of a modulation signal for driving the light emitting diode. 9. The wireless optical communication system according to claim 8, wherein the DC offset amount of the light emitting diode is made substantially zero according to a user operation. The lighting device,
The wireless optical communication system according to any one of claims 1 to 9, wherein wires of equal length are provided between the light emitting diode drive circuit and the light emitting diodes having the same light emission center wavelength. When performing wireless optical wireless communication using a plurality of emission center wavelengths between the lighting device and the terminal,
11. The wireless optical communication system according to claim 1, wherein the lighting device transmits faster bit rate data to the terminal with light having a light emission center wavelength having higher light power. 12. .

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