JP2011205571A - Receiving apparatus and visible light communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiving apparatus and visible light communication system capable of optimizing reception processing in accordance with a received light wavelength, without performing multiplexing such as using a plurality of LEDs and without wasting, at a receiving side, light generated by a transmitting-side LED.SOLUTION: A receiving apparatus 30 for visible light communication has: a first photodetection sensor 31 including a first filter FLT31 passing light of an arbitrary wavelength band; a second photodetection sensor 32 including a second filter FLT32 passing light of a different band from the arbitrary wavelength band; and a signal processor 33 for receiving output signals from the first photodetection sensor 31 and the second photodetection sensor 32 and performing signal processing. The signal processor 33 performs signal processing using the one signal when any one of the signals from the first photodetection sensor 31 and the second photodetection sensor 32 can be received, and using a signal with higher reliability when both of the signals can be received.

Description

  The present invention relates to a receiving apparatus and a visible light communication system that can be employed for visible light communication using, for example, a light emitting element including a phosphor.

  In recent years, due to the improvement in luminance characteristics, light-emitting diodes (LEDs) have attracted attention as a light source for visible light communication as well as use of an illumination light source instead of a fluorescent lamp or an incandescent lamp.

In general, an LED used for visible light communication has both a transmission function and an illumination function.
For this reason, in visible light communication, the communicable range is limited to at least the illumination area.
This is a feature of visible light communication in which the communication range can be limited and it can be easily recognized visually.

By the way, since the LED used in visible light communication has both a transmission function and an illumination function, white light is required for a transmitter as an illumination device.
However, since there is no LED that emits white light alone, a technique of emitting white light by combining a phosphor with a violet LED or a blue LED is employed.
Hereinafter, this LED is referred to as a fluorescent LED.

In visible light communication, digital data is transmitted by turning on / off (turning on and off) LEDs at high speed.
However, the fluorescent LED has a limit in the control to turn on and off at high speed.
This is because a fluorescent LED has a certain delay until the phosphor absorbs and excites light energy emitted from the LED and emits visible light.
For this reason, even if a current is supplied to the fluorescent LED, a certain amount of time is required until the amount of visible light emitted is maximized.

Further, in the fluorescent LED, visible light emission is sustained to some extent even when the current to the LED is turned off and the light energy is cut off.
For this reason, even if the current supplied to the fluorescent LED is cut off, the amount of light becomes zero, and a certain amount of time is required until the light is turned off.

Due to such characteristics, in the visible light communication using the fluorescent LED, the limit of the communication speed is lower by one digit or more than in the case where the non-fluorescent LED is used.
In addition, there is a possibility that stable communication characteristics cannot be obtained, for example, the waveform of the reception signal corresponding to the transmission signal is deformed and the error rate in the demodulation processing on the reception side becomes high.
In short, in visible light communication using fluorescent LEDs, it is no exaggeration to say that the communication speed and stable communication operation depend on the material properties of the phosphor.

In order to overcome such a visible light communication problem, particularly the communication speed limit, for example, Patent Document 1 proposes a method of using a plurality of LEDs including a fluorescent LED.
The method according to this prior art document 1 arranges LEDs and photodiodes in an array and operates in parallel with each other to multiplex data transmission.

As another method, a technique disclosed in Patent Document 2 is known.
This is intended to increase the speed by arranging a filter that removes a wavelength component of 470 nm or more that affects the deformation of the waveform of the reception signal immediately before the reception side.

JP 2001-292107 A JP 2009-077344 A

With the method disclosed in Patent Document 1, it is possible to increase the communication speed by simply increasing the number of LEDs and increasing the multiplicity.
However, such a multiplexing method has the following problems.
In other words, an optical lens for associating a plurality of LEDs with a plurality of photodiodes and a focusing operation of the optical lens are indispensable, so that the positional relationship between the transmitting device and the receiving device is variable. Not suitable.
In addition, increasing the multiplicity increases the cost required for the photodiode, the light receiving circuit associated therewith, and the like.

  In addition, with the method of Patent Document 2 described above, light with a wavelength in question can be removed, but conversely, the amount of light that can be used for reception is greatly reduced, and as shown in FIG. Problems are obvious, such as a significant decrease and an increased error rate in the demodulation process on the receiving side.

  The present invention is a receiving device that can optimize reception processing according to the light receiving wavelength without using the plurality of LEDs to multiplex and without causing the receiving side to waste light emitted from the transmitting side LED. And providing a visible light communication system.

  A receiving apparatus according to a first aspect of the present invention includes a first light receiving sensor including a filter that transmits light in an arbitrary wavelength band, and a filter that transmits light in a band different from the arbitrary wavelength band. A second light receiving sensor; and a signal processing unit that performs signal processing in response to an output signal of the first light receiving sensor and / or the second light receiving sensor, and the signal processing unit includes the first light receiving sensor. When only one of the sensor and the second light receiving sensor can be received, the one signal is used. When both signals are received, the signal having higher reliability is used. Perform signal processing.

  Preferably, the signal processing unit has a longer wavelength for the light transmitted by the filter included in the second light receiving sensor than the light transmitted by the filter included in the first light receiving sensor. When the signals of both the first light receiving sensor and the second light receiving sensor are received, signal processing is performed using the signal of the first light receiving sensor.

  A visible light communication system according to a second aspect of the present invention includes a visible light communication light source and a receiving device that receives light from the visible light communication light source, and the visible light communication light source includes a light emitting diode. (LED), a phosphor that receives light emitted from the LED and emits light having a longer wavelength than the LED bare chip, and a light emission control unit that controls blinking of the LED, and the receiving device includes: A first light receiving sensor including a filter that transmits light in a wavelength band including light, and a second light receiving sensor including a filter that transmits light in a band including light of the phosphor in a band different from the wavelength band. A sensor, and a signal processing unit that performs signal processing in response to an output signal of the first light receiving sensor and / or the second light receiving sensor, wherein the signal processing unit includes the first light receiving sensor and the second light receiving sensor. Light receiving sensor The one of the signal when only is able to receive Re or the other signal, if both signals are successfully received and performs signal processing using the signal of the first light-receiving sensor.

  Preferably, the reception device further includes a transmission unit, and the visible light communication light source further includes a transmission signal reception unit of the transmission unit, and the transmission unit includes the first signal processing unit in the first signal processing unit. When the signal of the light receiving sensor is received, a communication enable signal indicating that reception by the first light receiving sensor is possible is transmitted, and when the receiving unit receives the communication enable signal, the receiving unit Control to increase the communication speed of visible light communication.

  According to the present invention, it is possible to optimize the reception process according to the light reception wavelength without performing multiplexing such as using a plurality of LEDs and without causing the reception side to waste light emitted from the transmission side LED. .

It is a figure which shows the example of the emission spectrum of blue LED and yellow fluorescent substance. It is a figure which shows the structural example of the visible light communication system which concerns on embodiment of this invention. It is a figure which shows the structural example of the light source for visible light communications of the visible light communication system which concerns on this embodiment, and a receiver. It is a figure which shows the light wave which a 1st photodiode and a 2nd photodiode receive through the 1st and 2nd filter. It is a flowchart which shows the fundamental operation | movement by the side of the receiver of the visible light communication system which concerns on this embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a diagram illustrating a configuration example of a visible light communication system according to the embodiment of the present invention.
FIG. 3 is a diagram illustrating a configuration example of the visible light communication light source and the reception device of the visible light communication system according to the present embodiment.

  The visible light communication system 10 according to the present embodiment includes a visible light communication light source 20 and a receiving device 30 that receives light from the visible light communication light source 20.

As shown in FIG. 3, the visible light communication light source 20 includes a single or a plurality of light emitting diodes (LEDs) 21, a phosphor 22 that receives light emitted from the LEDs 21 and emits light having a longer wavelength than the LED bare chip, and an LED 21. And a light emission control unit 23 that controls blinking of the light.
In addition, the visible light communication light source 20 includes a reception unit 24 that receives a transmission signal SND including a high-speed communication enable signal transmitted from the reception device 30 and outputs an instruction corresponding to the reception signal to the light emission control unit 23. .
When receiving the communicable signal, the receiving unit 24 controls the light emission control unit 23 to increase the communication speed of visible light communication.

  The receiving device 30 includes a first light receiving sensor 31, a second light receiving sensor 32, a signal processing unit 33, and a transmitting unit 34.

  The first light receiving sensor 31 receives the first filter FLT 31 that transmits light in the wavelength band including the light of the LED 21 of the light source 20, and the light that has passed through the first filter FLT 31, and receives the electrical signal as a signal processing unit 33. A first photodiode PD31 that outputs to the first photodiode PD31.

  The second light receiving sensor 32 transmits the second filter FLT32 that transmits light in a band including the light of the phosphor 22 in a band different from the wavelength band transmitted by the first filter FLT31, and the second filter FLT32. A second photodiode PD32 that receives the received light and outputs an electrical signal to the signal processing unit 33.

The signal processing unit 33 receives the output signals from the first light receiving sensor 31 and the second light receiving sensor 32 and performs signal processing.
Specifically, when only one of the first light receiving sensor 31 and the second light receiving sensor 32 can be received, the signal processing unit 33 determines that both signals are received. If reception is possible, signal processing is performed using a highly reliable signal from the first light receiving sensor 31.

When the signal processing unit 33 is able to receive the signal from the first light receiving sensor 31, the transmitting unit 34 transmits a communicable signal indicating that the signal can be received by the first light receiving sensor 31 to the receiving unit 24 of the light source 20. Send to.
The communication between the transmission unit 34 and the reception unit 24 can be performed by wireless communication, or can be performed by wired communication.

As described above, in the visible light communication system 10 according to this embodiment, one “fluorescent LED” is arranged in the light source 20 on the transmission side.
The first filter FLT 31 in the receiving device 30 has a high-pass filter (HPF) characteristic.
The second filter FLT 32 has a low pass filter (LPF) characteristic.
Here, for example, when the cutoff wavelength of the first filter FLT31 is 470 nm and the cutoff wavelength of the second filter FLT32 is 500 nm, the first photodiode PD31 and the second photodiode PD32 receive through each filter. FIG. 4 shows the light wave.

FIG. 4 shows an actual measurement of the spectrum of commercially available white LED illumination. Since the frequency is one peak around 450 nm and one peak gently between 520 and 600 nm, the blue light emitting LED and the yellow phosphor are You can see that it is a combination.
When a high-pass filter is applied to a fluorescent LED having such characteristics at 470 nm, the first photodiode PD31 receives light at a shaded portion indicated by A in FIG.
Similarly, the second photodiode PD32 that uses a low-pass filter at 500 nm receives light in the shaded portion indicated by B in FIG.

As shown in this example, generally, in the fluorescent LED, the amount of light emitted from the phosphor is larger than the amount of light emitted from the LED 21.
Further, the phosphor 22 has a feature that it can emit only light having a longer wavelength than the light wave used for excitation. Even with the same amount of light, longer wavelength light is more likely to propagate through the air.
Accordingly, it can be seen that in the visible light communication system 10, the second photodiode PD32 is in a state where communication can be started first.

  FIG. 5 is a flowchart showing a basic operation on the receiving device side of the visible light communication system according to the present embodiment.

The receiving apparatus 30 is normally in a standby state for a communication start signal (ST1).
For the above-described reason, only the second photodiode PD32 on the second light receiving sensor 32 side is set in a standby state, and the first photodiode PD31 of the first light receiving sensor 31 is optional.
When a communication start signal is received, such as recognizing SOF by the second photodiode PD32 of the second light receiving sensor 32, reception is started by the second photodiode PD32 (ST2, ST3). The first photodiode PD31 of one light receiving sensor 31 is shifted to a standby state.
When the first photodiode PD31 of the first light receiving sensor 31 is ready for reception, reception starts with the first photodiode PD31 as the main (ST4).
At this time, the reception of the second photodiode PD32 is not interrupted, but is continuously received (ST5 and ST6).
When the first photodiode PD31 of the first light receiving sensor 31 can start reception, reception is performed with the first photodiode PD31 as the main (ST7 to ST9).
It is known that the light wave emitted from the phosphor 22 is weak depending on the phosphor 22, but the waveform is generally distorted by a phenomenon such as phosphorescence or delayed fluorescence.
Therefore, the light wave received by the second photodiode PD32 of the second light receiving sensor 32 has an advantage that it can be received from a long distance because it has a long wavelength and a large amount of light. However, the rate of occurrence of reception errors may increase.
When reception is started by the first photodiode PD31 of the first light receiving sensor 31, this problem can be reduced by shifting main communication to the first photodiode PD31.

As described above, according to the present embodiment, the visible light communication system 10 includes the visible light communication light source 20 and the receiving device 30 that receives light from the visible light communication light source 20.
The visible light communication light source 20 includes an LED 21, a phosphor 22 that receives light emitted from the LED 21 and emits light having a longer wavelength than the LED bare chip, and a light emission control unit 23 that controls blinking of the LED 21.
The receiving device 30 includes a first light receiving sensor 31 including a first filter FLT 31 that transmits light in a wavelength band including the light of the LED 21, and light in a band including the light of the phosphor 22 in a band different from the wavelength band. A second light receiving sensor 32 having a second filter FLT 32 that transmits the light, and a signal processing unit 33 that receives the output signals of the first light receiving sensor 31 and the second light receiving sensor 32 and performs signal processing. .
The signal processing unit 33 can receive both signals when only one of the first light receiving sensor 31 and the second light receiving sensor 32 is received. In this case, signal processing is performed using the signal of the first light receiving sensor 31.
Therefore, according to the present embodiment, the following effects can be obtained.

  That is, according to the present embodiment, it is possible to realize visible light communication with high reliability at high speed by using it preferentially, and when it is difficult to receive the light of the LED, it is possible to communicate by using the light of the phosphor The distance, the light propagation condition, etc. can be widely maintained.

  DESCRIPTION OF SYMBOLS 10 ... Visible light communication system, 20 ... Light source for visible light communication, 21 ... LED, 22 ... Phosphor, 23 ... Light emission control part, 24 ... Reception part, 30 ...・ Receiving device, 31... First light receiving sensor, 32... Second light receiving sensor, 33... Signal processing section, 34... Transmitting section, FLT 31. .. second filter, PD31... First photodiode, PD32... Second photodiode.

Claims (4)

A first light receiving sensor including a filter that transmits light of an arbitrary wavelength band;
A second light receiving sensor including a filter that transmits light in a band different from the arbitrary wavelength band;
A signal processing unit that performs signal processing in response to an output signal of the first light receiving sensor and / or the second light receiving sensor,
The signal processing unit
When only one of the first light receiving sensor and the second light receiving sensor is received, the one signal is received. When both signals are received, the one having higher reliability is received. A receiver for visible light communication that performs signal processing using the signal. The signal processing unit
The light transmitted through the filter provided in the second light receiving sensor has a longer wavelength than the light transmitted through the filter provided in the first light receiving sensor, and the first light receiving sensor and the second light are transmitted in the signal processing unit. When both signals of the light receiving sensor are received,
The visible light communication receiving device according to claim 1, wherein signal processing is performed using a signal of the first light receiving sensor. A light source for visible light communication;
A receiver for receiving light from the visible light communication light source,
The visible light communication light source is:
A light emitting diode (LED);
A phosphor that emits light of a longer wavelength than the LED bare chip upon receiving the light emission of the LED;
A light emission control unit for controlling blinking of the LED,
The receiving device is:
A first light receiving sensor including a filter that transmits light in a wavelength band including the light of the LED;
A second light receiving sensor comprising a filter that transmits light in a band including the light of the phosphor in a band different from the wavelength band;
A signal processing unit that performs signal processing in response to an output signal of the first light receiving sensor and / or the second light receiving sensor,
The signal processing unit
When only one of the first light receiving sensor and the second light receiving sensor is received, the one light receiving sensor is received. When both signals are received, the first light receiving sensor is received. Visible light communication system that performs signal processing using the signal. In the receiving device,
A transmission unit, the visible light communication light source further includes a transmission signal reception unit of the transmission unit,
The transmitter is
When the signal of the first light receiving sensor can be received in the signal processing unit, a communicable signal indicating that the signal can be received by the first light receiving sensor is transmitted.
The receiver is
The visible light communication system according to claim 3, wherein when the communication enable signal is received, the light emission control unit performs control to increase a communication speed of visible light communication.

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