JP5451670B2 - Visible light communication device - Google Patents

Description

  The present invention relates to a visible light communication device that performs communication using visible light irradiated to space, and in particular, performs high-speed visible light communication between an access point connected to a network and provided with a lamp and a portable information terminal. The present invention relates to a visible light communication device.

  Wireless communication using radio waves as a communication medium is used in many fields such as a cellular phone network, a wireless LAN, and short-range wireless communication.

  However, in wireless communication using radio waves as a medium, when transmission / reception is performed near a person, the transmission power cannot be increased in consideration of the influence of electromagnetic waves on the human body. In addition, the frequency band of radio waves used for wireless communication has already been allocated and used in many fields of use, and a wide frequency band cannot be freely used. Furthermore, there are restrictions such as restrictions on the use of radio waves in special environments such as hospitals.

  Therefore, in recent years, visible light communication using visible light as a communication medium has been developed, and a visible light communication system has been proposed in Patent Document 1 below.

  In this conventional visible light communication system, in order to perform visible light communication while using visible light as illumination light, information is transmitted and received using white light such as daylight color that does not feel uncomfortable as illumination light. For this reason, an LED (white light emitting diode) that emits white light is used as the light projecting element on the transmitting device side, and a light receiving element that receives white light and outputs a received light signal is also used on the light receiving device on the receiving device side. Is done.

JP 2007-266794 A JP 2009-260953 A

  However, an LED that emits white light usually generates light of a color complementary to the emission color of the light emitting diode in order to synthesize the white light, but the phosphor has a responsiveness. Because it is low, the frequency of the high-frequency signal superimposed on the white light can be kept low, and the light receiving element that receives the white light is difficult to operate at high speed when receiving visible light superimposed with the high-frequency signal, and the communication speed is suppressed. It was done.

  Therefore, the present inventors use a blue light photodiode that receives blue light with high sensitivity as the light receiving element of the receiver, and irradiates white light including blue light as visible light emitted from the lamp of the transmitter. In the above-mentioned Patent Document 2, a device that performs visible light communication between a transmitter (lamp) and a portable receiver has been proposed. Further, in an environment where radio waves cannot be used, a lamp fixed to a ceiling portion or the like is provided. It is configured as an access point for portable information terminals that can be connected to a wireless LAN, and bidirectional visible light communication is performed between the visible light communication device provided in the portable information terminal and the access point using white light for lighting of the lamp. There has been a need for a visible light communication device to perform.

  However, a visible light communication device that performs bidirectional visible light communication between a portable information terminal and an access point inevitably requires high-capacity data such as image data to be communicated at high speed. Communication speed is likely to be suppressed. In addition, users of portable information terminals that perform visible light communication with an access point having a lamp often perform the access operation with respect to the access point, so that the light is transmitted from the visible light transmitter of the portable information terminal. When the visible light to be emitted is the same white light as the visible light projected from the visible light transmitter on the lamp side, there is a problem that it is difficult for the user to recognize the access operation from the portable information terminal side.

  Also, if the uplink light from the portable information terminal side to the access point side is set to the same white light as the illumination light of the lamp, the access point lamp will illuminate the surrounding area with high-intensity white light. This white light may become disturbance light of the receiving device on the access point side, and is liable to cause a decrease in S / N ratio due to the disturbance light and a decrease in communication speed associated therewith.

  The present invention solves the above-described problems, and can perform high-speed communication using visible light between an access point (fixed station) provided with a lighting fixture and connected to a LAN and a portable information terminal. An object is to provide a visible light communication device.

In order to achieve the above object, a visible light communication device according to claim 1 of the present invention provides:
Light is emitted from an access point transmitter connected to a network to an access point equipped with a lamp from an access point transmitter that illuminates and projects illumination light superimposed with an information signal from a white LED of the lamp, and a terminal transmitter of a portable information terminal An access point receiving unit that receives visible light and extracts an information signal superimposed on the visible light; and
A terminal transmitter that projects visible light superimposed with an information signal on the portable information terminal from a projector, and illumination light projected from the lamp of the access point transmitter is received and superimposed on the illumination light. A visible light communication device that performs visible light communication between the access point and the portable information terminal,
The access point transmitter
A transmission data processing unit that rearranges transmission data so that each bit of a transmission data signal sent from the network and packetized is assigned to each subcarrier;
A modulation unit that digitally modulates each bit of the digital signal of transmission data sent from the transmission data processing unit for each subcarrier;
An S / P converter that converts the serial digital transmission signal modulated by the modulator into a data string of the number of subcarriers;
An inverse discrete Fourier transform unit for performing inverse fast Fourier transform on the digital transmission signal converted in parallel by the S / P conversion unit;
A D / A converter that converts the digital transmission signal obtained by inverse fast Fourier transform in the inverse discrete Fourier transform unit into an analog signal;
A synthesis unit that performs quadrature modulation and synthesis of the complex data converted into an analog signal by the D / A conversion unit using a cosine wave and a sine wave of the carrier frequency of the subcarrier;
An LED drive unit that drives the white LED of the lamp so as to amplify an analog high-frequency signal that is synthesized by the synthesis unit and modulated by a subcarrier and superimpose it on white light;
With
The access point receiver
A light receiver that receives blue light superimposed by an information signal emitted from a blue LED of a terminal transmission unit of the portable information terminal by a light receiving element;
A high-frequency amplifier that amplifies and outputs a high-frequency signal output from the light receiver in a low-noise state;
A demodulator that detects and demodulates the high-frequency received signal output from the high-frequency amplifier;
An IQ separation unit for separating the high-frequency reception signal output from the demodulation unit into an in-phase signal and a quadrature signal by multiplying a sine wave and a cosine wave;
An A / D converter that samples and converts the real part of the in-phase signal separated by the IQ separator and the imaginary part of the quadrature signal into a digital signal;
A complex value on the complex plane of each subcarrier is obtained from a complex value on the time axis that is a combination of the real part of the in-phase signal and the imaginary part of the quadrature signal output from the A / D converter. A discrete Fourier transform unit for performing a fast Fourier transform on
A P / S conversion unit that converts the parallel data of each subcarrier output from the discrete Fourier transform unit into serial data to be received data;
With
The terminal transmission unit, a transmission data processing unit that rearranges transmission data so that each bit of a transmission data signal is allocated to each subcarrier; and
A modulation unit that digitally modulates each bit of the digital signal of transmission data sent from the transmission data processing unit for each subcarrier;
An S / P converter that converts the serial digital transmission signal modulated by the modulator into a data string of the number of subcarriers;
An inverse discrete Fourier transform unit for performing inverse fast Fourier transform on the digital transmission signal converted in parallel by the S / P conversion unit;
A D / A converter that converts the digital transmission signal obtained by inverse fast Fourier transform in the inverse discrete Fourier transform unit into an analog signal;
A synthesis unit that performs quadrature modulation and synthesis of the complex data converted into an analog signal by the D / A conversion unit using a cosine wave and a sine wave of the carrier frequency of the subcarrier;
An LED drive unit that drives a blue LED so as to amplify an analog high-frequency signal synthesized by the synthesis unit and modulated by a subcarrier and superimpose it on blue light;
With
The terminal receiver is illuminated by a white LED of the access point transmitter of the access point and receives a white light superimposed with an information signal by a light receiving element;
A high-frequency amplifier that amplifies and outputs a high-frequency signal output from the light receiver in a low-noise state;
A demodulator that detects and demodulates the high-frequency received signal output from the high-frequency amplifier;
An IQ separation unit for separating the high-frequency reception signal output from the demodulation unit into an in-phase signal and a quadrature signal by multiplying a sine wave and a cosine wave;
An A / D converter that samples the real part of the in-phase signal separated by the IQ separator and the imaginary part of the quadrature signal and converts them into a digital signal;
A complex value on the complex plane of each subcarrier is obtained from a complex value on the time axis that is a combination of the real part of the in-phase signal and the imaginary part of the quadrature signal output from the A / D converter. A discrete Fourier transform unit for performing a fast Fourier transform on
A P / S conversion unit that converts the parallel data of each subcarrier output from the discrete Fourier transform unit into serial data to be received data;
With
The access point transmission unit projects white light from the white LED of the lamp as white light on which the information signal is superimposed as illumination light, while the terminal transmission unit of the portable information terminal transmits blue light from the blue LED on which the information signal is superimposed. The light is projected toward the access point.

  Note that the portable information terminal is a concept including a mobile terminal, a movable computer terminal such as a notebook computer, and the like.

  According to the visible light communication device of the present invention, a lamp fixed on a ceiling or the like is used as an access point of a portable information terminal connectable to a wireless LAN, and visible light is used between the portable information terminal and the access point. Large-capacity bidirectional high-speed communication can be performed. Also, in such visible light communication, a user using a portable information terminal can transmit blue light from a terminal transmission unit of the portable information terminal to an access point that illuminates and projects white light from a lamp as illumination light. Since the light is projected, the blue light projected from the terminal transmitter is easily visually recognized, and the user is performing an uplink by performing visible light communication from the portable information terminal to the access point. Can be easily recognized.

  Also, since the uplink light projection from the portable information terminal side to the access point side becomes blue light unlike white light for lighting of the lamp, an optical filter that transmits only blue light in front of the light receiver If this is arranged, disturbance light such as white light from the lamp can be effectively removed, and a decrease in S / N ratio due to the disturbance light and a decrease in communication speed associated therewith can be avoided.

  Also, when the uplink light projection from the mobile terminal side to the access point side is blue light, a blue light photodiode having a high light receiving sensitivity in the wavelength region of blue light is placed on the receiver of the access point receiver. Such a blue light photodiode has a very high light receiving sensitivity and a high frequency signal response speed, and can receive a large amount of information superimposed on visible light at high speed.

  Here, in the light receivers of the access point receiver and the terminal receiver, a resistor and a coil are connected in series between the anode of the light receiving element and the ground, and the photocurrent is converted into a high frequency voltage signal. A voltage conversion circuit can be connected. According to the present invention, the impedance on the output side of the light receiving element can be increased to efficiently extract the high frequency component of the photocurrent.

  In addition, a buffer amplifier that converts high input impedance to low output impedance is connected between the current / voltage conversion circuit connected to the output side of the receiver of the access point receiver and the terminal receiver and the high frequency amplifier, It is desirable that the buffer amplifier has a source follower circuit.

  According to the present invention, the input impedance of the buffer amplifier can be increased to efficiently extract a high-frequency voltage signal, and the output side impedance of the buffer amplifier provided with the source follower circuit can be decreased, thereby The wide-band high-frequency signal that is output can be input to the next-stage high-frequency amplifier with good frequency characteristics, and the wide-band high-frequency signal can be amplified well.

  In addition, in the light receivers of the access point receiver and the terminal receiver, a reflective condensing type light receiving element having a structure in which the light receiving element is disposed on the front surface of the concave mirror and facing the reflecting surface thereof is arranged alone or in an array. It is possible to use a reflective condensing type light receiver arranged in parallel. According to the present invention, the access point receiving unit and the terminal receiving unit receive the visible light projected from the terminal transmitting unit or the access point transmitting unit well with high-speed response, and the access point and the portable information terminal. High-capacity high-speed communication using visible light can be performed.

  In addition, a band correction amplifier is connected to the output side of the combining unit of the access point transmission unit and the terminal transmission unit, and the band correction amplifier uses the inverse distortion characteristic as a transmission signal in advance with respect to the nonlinear distortion of the frequency characteristic of the LED. In addition, it is desirable to configure to correct. According to the present invention, even when an LED, which tends to be distorted in frequency characteristics, is used for visible light projection, such that the emission level decreases as the frequency increases, distortion occurs in the spectrum distribution of the OFDM transmission signal. Therefore, the transmission signal can be superimposed on the visible light of the LED and transmitted at a high speed, whereby the OFDM signal can be normally demodulated on the receiving side.

  In addition, a band correction amplifier that performs band correction amplification of an analog high-frequency signal synthesized by the synthesis unit and modulated by subcarriers, and an output side of the band correction amplifier in the LED drive unit of the access point transmission unit and terminal transmission unit A transmission signal amplifier to be connected can be provided, an impedance matching circuit can be connected between the transmission signal amplifier and the LED driving unit, and the output side of the transmission signal amplifier can be connected to the LED driving unit with a low impedance. According to the present invention, the amplifier substrate including the transmission signal amplifier and the LED substrate on which the heat generating LED is mounted can be separately arranged and connected between them by the coaxial cable. The influence can be minimized, and an access point transmission unit can be shared and easily connected to an access point having a type of lamp having a different number of white LEDs.

  According to the visible light communication device of the present invention, a large-capacity high-speed communication by visible light can be performed between an access point connected to a network and provided with a lamp and a portable information terminal. In the uplink to the access point, it is possible to easily recognize the access operation by visually recognizing the blue light emitted from the terminal transmitter with respect to the white illumination light.

It is a schematic block diagram of the visible light communication apparatus which shows embodiment of this invention. It is the top view seen from the lower surface of the access point provided with the lamp. It is a block diagram of the configuration of an access point. It is a structure block diagram by the side of a portable information terminal. It is a circuit diagram of the LED drive part of an access point transmission part. It is a circuit diagram of the terminal receiving part by the side of a portable information terminal.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the visible light communication device performs high-speed bidirectional visible light communication between an access point (fixed station) 1 connected to a network such as a LAN and provided with a lamp 3 and a portable information terminal 5. Configured to do.
[access point]
An access point 1 that constitutes a fixed station of a visible light communication apparatus is installed above, for example, an underground shopping center or a room interior of a building, is configured to include a lamp 3, and irradiates illumination light from the lamp 3 to the room or the like. As shown in FIG. 2, the lamp 3 includes a large number of white LEDs 30 that radiate visible light (white light) in an annular shape in a circular base, and the white LEDs 30 are driven by an LED of the access point transmitter 2 described later. The unit 9 superimposes an OFDM-modulated high-frequency information signal on the white light, and irradiates the visible light as illumination and information communication.
[Configuration of access point transmitter]
As shown in FIG. 3, the access point transmission unit 2 receives packet data transmitted through a network such as a LAN, and receives an input data processing unit 10 that recombines the data for OFDM modulation, and is transmitted from the input data processing unit 10. Each bit of the transmitted data signal is digitally modulated with respect to each subcarrier, the digitally modulated serial data string is converted into parallel, and then the parallel data is converted into time series data by inverse fast Fourier transform. After the data is converted to an analog signal, an OFDM modulator 20 that synthesizes and modulates the transmission data signal for OFDM, and a high-frequency signal of the transmission data that is sent from the OFDM modulator 20 and is OFDM-modulated are input. A white LED (white) that irradiates white light for illumination and outputs it to the LED driver 36 An LED driving unit 9 for applying to the optical diode) 30 so as to superimpose the high frequency transmission signal, and includes a.

  As shown in FIG. 2, the white LED 30 has a large number of high-intensity white LEDs arranged in an annular shape within the circular base of the lighting lamp 3, and the information signal such as an image signal sent through the LAN is sent to the lamp 3. An information signal is transmitted to the terminal receiving unit 7 of the portable information terminal 5 that is superimposed on the white light (illumination light) emitted from the white LED 30 and arranged within the reach of the illumination light. White light is a concept including so-called daytime light and white light.

  The data processing unit 13 of the input data processing unit 10 includes a CPU, a memory, a register, and the like, and inputs packet data for transmission sent from the LAN through the Ethernet interface 11 (Ethernet is a registered trademark). A transmission data signal from the LAN can be input through a LAN cable, but since a commercial power source is connected to the access point 1 provided with the lamp 3, transmission data from the LAN is transmitted through power line communication using the commercial power line. A signal can also be input.

  The input data processing unit 10 temporarily stores the bucket data in the data buffer 12, and the data processing unit 13 uses the data memory 14 to reassemble the packet data for OFDM, and from the input / output unit 15. It is configured to output to the OFDM modulator 20.

  The OFDM modulator 20 includes a digital modulation unit 21 that digitally modulates each bit of a transmission data signal for each subcarrier. On the output side of the digital modulation unit 21, a digitally modulated serial data string, that is, each bit of data is provided. Is connected to each subcarrier, and an S / P conversion unit 22 for converting into parallel is connected.

  The digital modulation unit 21 digitally modulates the transmission data signal for OFDM transmitted from the input data processing unit 10 using a modulation method such as 64QAM, 16QAM, or PSK, and the S / P conversion unit 22 performs digital modulation. When N (for example, 1024) subcarriers are used so that each bit of the data string is allocated to each subcarrier, each bit of the data string is converted into N parallel data, and the parallel data is inversely discrete. It is comprised so that it may output to the Fourier-transform part 23.

  The inverse discrete Fourier transform unit 23 performs inverse Fourier transform on the digitized and digitally modulated N symbol data sequences at high speed, and the calculation result is converted into time domain complex data consisting of real numbers and imaginary numbers as a D / A conversion unit 25. , 26.

  The access point transmitter 2 transmits an information signal by superimposing the high-frequency signal on the visible light emitted from the white LED 30 using, for example, a high-frequency frequency band of 4 MHz to 34 MHz. Since there is nonlinear distortion in this frequency region, the band correction amplifier 31 is connected to the output side of the OFDM modulator 20 so as to correct the distortion of the frequency characteristics of the white LED 30 in advance.

  The real and imaginary complex data output from the inverse discrete Fourier transform unit 23 and subjected to the inverse Fourier transform are respectively sent to the D / A conversion units 25 and 26 and converted into analog signals. The complex data converted into analog signals by the conversion units 25 and 26 is sent to the synthesis unit 27. In the synthesizer 27, the pair of complex data is orthogonally modulated using a cosine wave and a sine wave of a carrier frequency of, for example, 4 MHz to 34 MHz of the subcarrier, and OFDM-modulated from the synthesizer 27, and the high frequency of 4 MHz to 34 MHz A transmission signal is output.

  As described above, the OFDM modulator 20 digitally modulates each bit of the transmission data signal transmitted from the input data processing unit 10 for each subcarrier by the digital modulation unit 21, and converts the digitally modulated serial data string into S / P. After conversion into parallel by the conversion unit 22, the parallel data is converted into time-series data by inverse fast Fourier transform at the inverse discrete Fourier transform unit 23.

  Then, the real number and imaginary number of the complex data output from the inverse discrete Fourier transform unit 23 are sent to the D / A conversion units 25 and 26 and converted into analog signals by the D / A conversion units 25 and 26. The complex data converted into the analog signal is sent to the synthesizing unit 27, and the pair of complex data is synthesized by the synthesizing unit 27 by orthogonal modulation using the cosine wave and sine wave of the carrier frequency of the subcarrier. The transmission signal subjected to OFDM modulation is output from the combining unit 27 of the OFDM modulator 20 to the band correction amplifier 31.

  The band correction amplifier 31 amplifies the high frequency transmission signal so as to apply band equalization correction to the OFDM modulated high frequency transmission signal, and thereby, a high frequency signal having a very wide frequency band such as 4 MHz to 34 MHz is obtained. This circuit corrects the white LED 30 according to the frequency characteristics. The frequency characteristics of the white LED 30 are usually nonlinear characteristics such that the lower the frequency, the higher the emission level, and the higher the frequency, the lower the emission level. For this reason, when an OFDM-modulated transmission signal is amplified and applied to the white LED 30 as it is, distortion occurs in the spectral distribution of the transmission signal, and large-capacity information cannot be transmitted and received at high speed. For this reason, the band correction amplifier 31 is configured to amplify the high-frequency transmission signal while performing band correction by adding the inverse characteristic of the frequency characteristic of the white LED 30 to the signal.

  As a result, when transmitting a signal using a high-frequency wide band such as 4 MHz to 34 MHz, the white LED 30 having a frequency characteristic in which the emission level increases as the frequency decreases and decreases as the frequency increases. Even when used for light, the transmission signal is superimposed on the visible light of the LED without distortion in the spectral distribution of the OFDM transmission signal so that a large amount of information can be transmitted at high speed. It has become.

  A transmission signal amplifier 32 for amplifying the transmission signal to a level that can be superimposed on the white LED 30 is connected to the output side of the band correction amplifier 31. As shown in FIG. 5, the transmission signal amplifier 32 includes a high-frequency amplifier 38 that amplifies a high-frequency signal to a level that can be superimposed on the white LED 30 as a main part, and an unbalance / balance conversion circuit on the input side of the high-frequency amplifier 38. 37 is connected. The unbalance / balance conversion circuit 37 is configured using a transformer or the like, and converts the input unbalanced transmission signal into a balance and outputs it to the high frequency amplifier 38 in order to widen the dynamic range of the high frequency amplifier 38.

  As shown in FIG. 5, an impedance matching circuit 33 is connected to the output side of the high frequency amplifier 38, and the output side of the high impedance high frequency amplifier 38 is converted to a low impedance (for example, 50Ω) by an impedance matching transformer. The LED drive unit 9 having the white LED 30 is connected to the output side of the transmission signal amplifier 32. However, the LED drive unit 9 having the white LED 30 needs to be provided with a radiation fin, and is separated from the transmission signal amplifier 32. In order to replace and use the LED driver 9 having different brightness and different number of white LEDs 30 as an access point transmitter 2, a low impedance coaxial cable 35 is used. It is assumed to be connected. For this reason, the impedance matching circuit 33 using the transformer TR1 for impedance matching is connected to the output side of the transmission signal amplifier 32.

Further, as shown in FIGS. 4 and 5, the LED drive unit 9 is connected to the output side of the impedance matching circuit 33 via the coaxial cable 35. The LED drive unit 9 performs impedance conversion through the impedance matching circuit 34 so as to match the high-frequency transmission signal (transmission signal having the subcarrier carrier frequency of the OFDM signal) input through the coaxial cable 35 with the input impedance of the white LED 30. A high frequency transmission signal is applied to the cathode of the white LED 30. On the other hand, the white LED 30 is used both for illumination of the lamp 3 and for visible light communication, and is configured by connecting a number of high-intensity white LEDs in series and arranging them in an annular shape so as to obtain the required illuminance. As shown in FIG. 5, a DC power supply circuit is connected to the anode side of the white LED 30.
[Configuration of access point receiver]
As shown in FIG. 3, the access point receiving unit 4 receives blue light, which is projected from a blue LED 39 of a terminal transmission unit 6 of the portable information terminal 5 described later, on which an information signal is superimposed, by a reflection / condensing type light receiving element. A photoreceiver 41 that receives the photocurrent output from the photoreceiver 41, a buffer amplifier 42 that removes the DC component, buffers and amplifies the AC voltage signal, and outputs it to the next-stage high-frequency amplifier 43, and a buffer amplifier A high frequency amplifier 43 that receives the high frequency voltage signal output from 42, amplifies and outputs the signal in a low noise state, a demodulation unit 44 that detects and demodulates the high frequency reception signal output from the high frequency amplifier 43, and outputs from the demodulation unit 44 The high-frequency received signal is quadrature-modulated using a cosine wave and a sine wave, and separated into an in-phase signal and a quadrature signal, and the real part of the in-phase signal separated by the IQ separation unit 45 is quadrature Trust The A / D converters 46 and 47 that sample and convert the imaginary part of the signal into digital signals, and the real part of the in-phase signal and the imaginary part of the quadrature signal output from the A / D converters 46 and 47 are combined. The discrete Fourier transform unit 48 that performs fast Fourier transform so as to obtain the complex value on the complex plane of each subcarrier from the complex value on the time axis, and the parallel of each subcarrier output from the discrete Fourier transform unit 48 And a P / S conversion unit 49 that converts the data into serial data to be received data.

  The light receiver 41 of the access point receiving unit 4 includes a light receiving element that receives visible light that is projected from the blue LED 39 of the terminal transmission unit 6 of the portable information terminal 5 and that superimposes an information signal. A blue light photodiode having high light receiving sensitivity in the wavelength region of blue light is used. Further, the light receiving device 41 is a reflective condensing type light receiving device having a structure in which a plurality of light receiving element members, each having a photodiode disposed at the substantially focal position of the concave mirror, are arranged in an array. . Thereby, the light receiver 41 has a very high light receiving sensitivity and a high-frequency signal response speed, and can receive a large amount of information superimposed on visible light at high speed.

  As shown in FIG. 6, in the light receiver 41 of the access point receiver 4, a resistor R and coils L1 and L2 are connected in series between the anode of the light receiving element and the ground so that the photocurrent is converted into a high-frequency voltage signal. A current / voltage conversion circuit 42a for conversion is connected. The resistance value of the resistor R of the current / voltage conversion circuit 42a is such that the amplifier does not saturate even when the visible light received by the light receiver 41 has high illuminance, and the amplifier can effectively amplify the signal even at low illuminance. Set to In addition, two coils L1 and L2 are connected to the resistor R through a series connection, so that the output impedance of the light receiver 41 can be increased and the high-frequency component of the photocurrent can be efficiently extracted. Yes.

  Further, in the access point receiver 4, a buffer amplifier 42 provided with a source follower circuit is connected between the current / voltage conversion circuit 42a and the high frequency amplifier 43 as shown in FIG. As shown in FIG. 6, the buffer amplifier 42 uses an FET, and two capacitors C1 and C2 are connected in parallel on the gate input side thereof, so that a high-frequency voltage is generated from the photocurrent output from the light receiver 41. Only the components are taken out efficiently. Further, the buffer amplifier 42 receives a high-frequency voltage signal with a high input impedance, and outputs a low-impedance output to the next-stage high-frequency amplifier 43 with a wide-band frequency characteristic through the source follower circuit. The high frequency signal can be amplified with good frequency characteristics. As shown in FIG. 6, the output side of the high frequency amplifier 43 is connected to the demodulator 44 shown in FIG. 3 through capacitors C3 and C4, a resistor R2, and a connector CN1.

  The demodulator 44 detects and demodulates the high-frequency received signal (digitally modulated signal) amplified and output from the high-frequency amplifier 43, and outputs the demodulated high-frequency signal to the IQ separator 45. The IQ separation unit 45 connected to the output side of the demodulation unit 44 inputs the high-frequency reception signal output from the demodulation unit 44, and performs quadrature modulation using a cosine wave and a sine wave to obtain a baseband signal. The phase signal and the quadrature signal are separated and output to the A / D converters 46 and 47, respectively.

  The A / D converters 46 and 47 each input the real part of the in-phase signal separated by the IQ separator 45 and the imaginary part of the quadrature signal, sample and convert them into a digital signal, and the discrete Fourier transform part 48. Output to. The discrete Fourier transform unit 48 inputs the complex-value digital signals on the time axis, which are output from the A / D conversion units 46 and 47, and combines the real part of the in-phase signal and the imaginary part of the quadrature signal. A fast Fourier transform is performed so as to obtain a complex value on the complex plane of each subcarrier from the digital signal, and the digital signal is returned to the data of each subcarrier.

The P / S conversion unit 49 connected to the output side of the discrete Fourier transform unit 48 inputs the parallel data of each subcarrier output from the discrete Fourier transform unit 48, converts these parallel data into serial data, and The received data is output to the input / output unit 15 of the input data processing unit 10. As a result, the information signal received by the access point receiver 4 is demodulated and output to the LAN through the Ethernet interface 11 by the operation of the data processor 13.
[Personal digital assistant]
As shown in FIG. 1, the portable information terminal 5 is provided with a terminal transmission unit 6 and a terminal reception unit 7 that perform bidirectional visible light communication with the access point 1. The portable information terminal 5 is basically composed of a mobile terminal, a computer terminal such as a movable notebook personal computer, etc., and a CPU that functions as a computer, a ROM of a fixed memory, a RAM that constitutes a work area of the CPU , A storage device for storing basic software such as an OS and various application software, an input means for a user to input an operation, a display for displaying an image, and the like.
[Configuration of terminal transmitter]
The terminal transmission unit 6 of the portable information terminal 5 is basically configured in the same manner as the configuration of the access point transmission unit 2, and as shown in FIG. 4, the transmission data is input and the data for OFDM modulation is input. Recombination, the transmission / reception data processing unit 16 that processes the reception data input from the terminal reception unit 7, and each bit of the transmission data signal sent from the transmission / reception data processing unit 16 is digitally modulated for each subcarrier, After converting the data string to parallel, the parallel data is converted into time series data by inverse fast Fourier transform, and the time series data is converted into an analog signal and then synthesized to modulate the transmission data signal for OFDM. An OFDM modulator 20 and a high frequency signal of transmission data sent from the OFDM modulator 20 and modulated by OFDM are input, and the high frequency signal is increased. And output to the LED driver 36, and includes an LED driving unit 9 to the blue LED (blue light emitting diode) 39 is applied so as to superimpose the high frequency transmission signal for irradiating blue light.

  As shown in FIG. 1, the blue LED 39 is attached to a part of the case of the portable information terminal 5 and emits blue light toward the access point 1. The blue light emitted from the blue LED 39 is a visible light having a spectrum having a very high peak at a wavelength of about 460 nm, but has a peak at a wavelength of about 500 nm, for example, from blue-violet having a peak at a wavelength of about 405 nm. It is a concept that includes visible light in the blue-green spectral range.

  The data processing unit 13 of the transmission / reception data processing unit 16 includes a CPU, a memory, a register, and the like, and can also be configured to serve as a CPU of the computer terminal of the portable information terminal 5. The data processing unit 13 operates so that transmission data to be transmitted is reassembled for OFDM using the data memory 14 and output from the input / output unit 15 to the OFDM modulator 20.

  The OFDM modulator 20 includes a digital modulation unit 21 that digitally modulates each bit of a transmission data signal for each subcarrier. On the output side of the digital modulation unit 21, a digitally modulated serial data string, that is, each bit of data is provided. Is connected to each subcarrier, and an S / P conversion unit 22 for converting into parallel is connected.

  The digital modulation unit 21 digitally modulates the transmission data signal for OFDM sent from the transmission / reception data processing unit 16 by a modulation scheme such as 64QAM, 16QAM, PSK, and the S / P conversion unit 22 is digitally modulated. When N (for example, 1024) subcarriers are used so that each bit of the data string is allocated to each subcarrier, each bit of the data string is converted into N parallel data, and the parallel data is inversely discrete. It is comprised so that it may output to the Fourier-transform part 23.

  The inverse discrete Fourier transform unit 23 performs inverse Fourier transform on the digitized and digitally modulated N symbol data sequences at high speed, and the calculation result is converted into time domain complex data consisting of real numbers and imaginary numbers as a D / A conversion unit 25. , 26.

  In the terminal transmission unit 6, for example, using a high frequency band of 4 MHz to 34 MHz, the high frequency signal is superimposed on the visible light emitted from the blue LED 39 and the information signal is transmitted. Since there is nonlinear distortion in this frequency region, the band correction amplifier 31 is connected to the output side of the OFDM modulator 20 so as to correct the distortion of the frequency characteristic of the blue LED 39 in advance.

  The real and imaginary complex data output from the inverse discrete Fourier transform unit 23 and subjected to the inverse Fourier transform are respectively sent to the D / A conversion units 25 and 26 and converted into analog signals. The complex data converted into analog signals by the conversion units 25 and 26 is sent to the synthesis unit 27. In the synthesizer 27, the pair of complex data is orthogonally modulated using a cosine wave and a sine wave of a carrier frequency of, for example, 4 MHz to 34 MHz of the subcarrier, and OFDM-modulated from the synthesizer 27, and the high frequency of 4 MHz to 34 MHz A transmission signal is output.

  As described above, the OFDM modulator 20 digitally modulates each bit of the transmission data signal transmitted from the transmission / reception data processing unit 16 for each subcarrier by the digital modulation unit 21, and converts the digitally modulated serial data string into S / P. After conversion into parallel by the conversion unit 22, the parallel data is converted into time-series data by inverse fast Fourier transform at the inverse discrete Fourier transform unit 23.

  Then, the real number and imaginary number of the complex data output from the inverse discrete Fourier transform unit 23 are sent to the D / A conversion units 25 and 26 and converted into analog signals by the D / A conversion units 25 and 26. The complex data converted into the analog signal is sent to the synthesizing unit 27, and the pair of complex data is synthesized by the synthesizing unit 27 by orthogonal modulation using the cosine wave and sine wave of the carrier frequency of the subcarrier. The transmission signal subjected to OFDM modulation is output from the combining unit 27 of the OFDM modulator 20 to the band correction amplifier 31.

  The band correction amplifier 31 amplifies the high frequency transmission signal so as to apply band equalization correction to the OFDM modulated high frequency transmission signal, and thereby, a high frequency signal having a very wide frequency band such as 4 MHz to 34 MHz is obtained. This is a circuit for correcting according to the frequency characteristics of the blue LED 39. The frequency characteristics of the blue LED 39 are usually nonlinear characteristics such that the lower the frequency, the higher the emission level, and the higher the frequency, the lower the emission level. For this reason, if an OFDM-modulated transmission signal is amplified as it is and applied to the blue LED 39, the spectral distribution of the transmission signal is distorted, and large-capacity information cannot be transmitted and received at high speed. For this reason, the band correction amplifier 31 is configured to amplify the high-frequency transmission signal while performing band correction by adding the inverse characteristic of the frequency characteristic of the blue LED 39 to the signal.

  Thus, for example, when transmitting a signal using a high-frequency wide band, such as 4 MHz to 34 MHz, the blue LED 39 having a frequency characteristic in which the light emission level is higher as the frequency is lower and the light emission level is lower as the frequency is higher is projected. Even when used for light, the transmission signal is superimposed on the visible light of the LED without distortion in the spectral distribution of the OFDM transmission signal so that a large amount of information can be transmitted at high speed. It has become.

  A transmission signal amplifier 32 for amplifying the transmission signal to a level that can be superimposed on the blue LED 39 is connected to the output side of the band correction amplifier 31. As shown in FIG. 5, the transmission signal amplifier 32 includes a high frequency amplifier 38 that amplifies a high frequency signal to a level that can be superimposed on the blue LED 39 as a main part. 37 is connected. The unbalance / balance conversion circuit 37 is configured using a transformer or the like, and converts the input unbalanced transmission signal into a balance and outputs it to the high frequency amplifier 38 in order to widen the dynamic range of the high frequency amplifier 38.

  As shown in FIG. 5, an impedance matching circuit 33 is connected to the output side of the high-frequency amplifier 38, and the output side of the high-impedance high-frequency amplifier 38 is converted to a low impedance (for example, 50Ω) by an impedance matching transformer. The output of the transmission signal amplifier 32 is connected to the LED driver 9 of the blue LED 39 via the coaxial cable 35.

Further, as shown in FIGS. 4 and 5, the LED drive unit 9 is connected to the output side of the impedance matching circuit 33 via the coaxial cable 35. The LED drive unit 9 performs impedance conversion through the impedance matching circuit 34 so as to match the high-frequency transmission signal (transmission signal having the subcarrier carrier frequency of the OFDM signal) input through the coaxial cable 35 with the input impedance of the blue LED 39. A high frequency transmission signal is applied to the cathode of the blue LED 39. When the LED drive unit 9 is directly connected to the output side of the high frequency amplifier 38, the impedance matching circuits 33 and 34 and the coaxial cable 35 can be omitted.
[Configuration of terminal receiver]
The terminal receiving unit 7 is basically configured in the same manner as the access point receiving unit 4, and as shown in FIG. 4, visible light emitted from the white LED 30 of the access point transmitting unit 2 and superimposed with an information signal is A photoreceiver 41 that receives light by a reflection-condensing light-receiving element and a photocurrent output from the photoreceiver 41 are input, the DC component is removed, and the AC voltage signal is buffered and amplified to the next-stage high-frequency amplifier 43. A buffer amplifier 42 to be output, a high frequency amplifier 43 to which the high frequency voltage signal output from the buffer amplifier 42 is input, amplified and output in a low noise state, and a demodulation to detect and demodulate the high frequency received signal output from the high frequency amplifier 43 44, an IQ separation unit 45 that performs quadrature modulation on the high-frequency reception signal output from the demodulation unit 44 using a cosine wave and a sine wave, and separates the in-phase signal and the quadrature signal, and an IQ separation unit 4 The A / D converters 46 and 47 that sample the real part of the in-phase signal and the imaginary part of the quadrature signal that are separated in step S4 and convert them into digital signals, and the A / D converters 46 and 47 output the same part. A discrete Fourier transform unit 48 that performs fast Fourier transform so as to obtain a complex value on a complex plane of each subcarrier from a complex value on a time axis obtained by combining a real part of a phase signal and an imaginary part of an orthogonal signal; And a P / S converter 49 that converts the parallel data of each subcarrier output from the Fourier transform unit 48 into serial data to be received data.

  The light receiver 41 of the terminal receiving unit 7 is configured to include a light receiving element that receives visible light emitted from the white LED 30 of the lamp 3 of the access point 1 and superimposed with an information signal. The light receiving device 41 is a reflective condensing type light receiving device having a structure in which a plurality of light receiving element members formed by arranging photodiodes facing the concave surface at a substantially focal position of the concave mirror are arranged in an array. Thereby, the light receiver 41 has a very high light receiving sensitivity and a high-frequency signal response speed, and can receive a large amount of information superimposed on visible light at high speed.

  As shown in FIG. 6, in the light receiver 41 of the terminal receiving unit 7, a resistor R and coils L1 and L2 are connected in series with the anode of the light receiving element between the ground and the photocurrent is converted into a high frequency voltage signal. The current / voltage conversion circuit 42a is connected. The resistance value of the resistor R of the current / voltage conversion circuit 42a is such that the amplifier does not saturate even when the visible light received by the light receiver 41 has high illuminance, and the amplifier can effectively amplify the signal even at low illuminance. Set to In addition, two coils L1 and L2 are connected to the resistor R through a series connection, so that the output impedance of the light receiver 41 can be increased and the high-frequency component of the photocurrent can be efficiently extracted. Yes.

  Furthermore, in the terminal receiver 7, a buffer amplifier 42 provided with a source follower circuit is connected between the current / voltage conversion circuit 42a and the high frequency amplifier 43 as shown in FIG. As shown in FIG. 6, the buffer amplifier 42 uses an FET, and two capacitors C1 and C2 are connected in parallel on the gate input side thereof, so that a high-frequency voltage is generated from the photocurrent output from the light receiver 41. Only the components are taken out efficiently. Further, the buffer amplifier 42 receives a high-frequency voltage signal with a high input impedance, and outputs a low-impedance output to the next-stage high-frequency amplifier 43 with a wide-band frequency characteristic through the source follower circuit. The high frequency signal can be amplified with good frequency characteristics. As shown in FIG. 6, the output side of the high frequency amplifier 43 is connected to the demodulator 44 shown in FIG. 4 through capacitors C3 and C4, a resistor R2, and a connector CN1.

  The demodulator 44 detects and demodulates the high-frequency received signal (digitally modulated signal) amplified and output from the high-frequency amplifier 43, and outputs the demodulated high-frequency signal to the IQ separator 45. The IQ separation unit 45 connected to the output side of the demodulation unit 44 inputs the high-frequency reception signal output from the demodulation unit 44, and performs quadrature modulation using a cosine wave and a sine wave to obtain a baseband signal. The phase signal and the quadrature signal are separated and output to the A / D converters 46 and 47, respectively.

  The A / D converters 46 and 47 each input the real part of the in-phase signal separated by the IQ separator 45 and the imaginary part of the quadrature signal, sample and convert them into a digital signal, and the discrete Fourier transform part 48. Output to. The discrete Fourier transform unit 48 inputs the complex-value digital signals on the time axis, which are output from the A / D conversion units 46 and 47, and combines the real part of the in-phase signal and the imaginary part of the quadrature signal. A fast Fourier transform is performed so as to obtain a complex value on the complex plane of each subcarrier from the digital signal, and the digital signal is returned to the data of each subcarrier.

The P / S conversion unit 49 connected to the output side of the discrete Fourier transform unit 48 inputs the parallel data of each subcarrier output from the discrete Fourier transform unit 48, converts these parallel data into serial data, and The received data is output to the input / output unit 15 of the transmission / reception data processing unit 16. As a result, the information signal received by the terminal receiving unit 7 is demodulated, captured by the operation of the data processing unit 13, stored in the data memory 14, and then, according to the operation of the portable information terminal 5, Information is displayed on the display, and in the case of audio information, audio is output from a speaker (not shown).
[Operation of visible light communication device]
Next, the operation of the visible light communication apparatus having the above configuration will be described. When the lamp 3 of the access point 1 illuminates the room or the like, the LED driver 36 operates when the power is turned on, and the white LED 30 emits white light as illumination light to illuminate the room or the like.

  When the access point transmission unit 2 is activated and a transmission signal such as an image signal or an audio signal is sent to the input data processing unit 10 through the LAN, the data processing unit 13 in FIG. The packet data is input, and the data memory 14 is used to reassemble the packet data for OFDM, and the data is output from the input / output unit 15 to the OFDM modulator 20.

  When the digital modulation unit 21 of the OFDM modulator 20 receives the transmission data signal for OFDM sent from the input data processing unit 10, the digital modulation unit 21 digitally converts each bit of the transmission data signal for each subcarrier by a modulation scheme such as 64QAM. The modulated serial data signal is sent to the S / P converter 22.

  When the digitally modulated serial data is input, the S / P converter 22 uses N (for example, 1024) subcarriers so that each bit of the data sequence is assigned to each subcarrier. Each bit is converted into N pieces of parallel data, and the parallel data is output to the inverse discrete Fourier transform unit 23.

  Next, the inverse discrete Fourier transform unit 23 performs inverse discrete Fourier transform at high speed on the parallel symbol data sequence that is digitally modulated and configured to assign each bit of the data sequence to each subcarrier, and the calculation result is The data is output to the D / A converters 25 and 26 as time domain complex data consisting of real and imaginary numbers.

  The real and imaginary complex data subjected to the inverse discrete Fourier transform are respectively sent to the D / A converters 25 and 26 and converted into analog signals, and then converted into analog signals by the D / A converters 25 and 26, respectively. The converted complex data is sent to the synthesis unit 27. In the synthesizer 27, the pair of complex data is orthogonally modulated and synthesized using a cosine wave and a sine wave of a carrier frequency of, for example, 4 MHz to 34 MHz of the subcarrier, and OFDM modulated from the synthesizer 27 by 4 MHz to 34 MHz. The high-frequency transmission signal is output to the band correction amplifier 31.

  The band correction amplifier 31 amplifies the high frequency transmission signal so as to apply band equalization correction to the OFDM modulated high frequency transmission signal, and thereby, a high frequency signal having a very wide frequency band such as 4 MHz to 34 MHz is obtained. Correction is made according to the frequency characteristics of the white LED 30 of FIG. That is, the frequency characteristics of the white LED 30 are usually nonlinear characteristics such that the lower the frequency, the higher the emission level, and the higher the frequency, the lower the emission level. Therefore, the nonlinear characteristics of the white LED 30 are corrected. Therefore, the band correction amplifier 31 amplifies the high-frequency transmission signal while performing band correction by adding the inverse characteristic of the frequency characteristic of the white LED 30 to the signal.

  As a result, when transmitting a signal in a high-frequency wide band such as 4 MHz to 34 MHz, the white LED 30 having a frequency characteristic in which the emission level is higher as the frequency is lower and the emission level is lower as the frequency is higher is for visible light projection. Even if it is used, the transmission signal can be superimposed on the visible light of the LED without causing distortion in the spectrum distribution of the transmission signal of the OFDM system, and a large amount of information can be transmitted at high speed.

  In the next transmission signal amplifier 32, the band-corrected high-frequency transmission signal is converted into a balanced transmission signal by the unbalance / balance conversion circuit 37 to widen the dynamic range of the next-stage high-frequency amplifier 38. . The next high frequency amplifier 38 amplifies the high frequency transmission signal to a level that can be superimposed on the white light of the white LED 30. The amplified transmission signal is input to the LED driver 36 through the impedance matching circuits 33 and 34. The LED driver 36 superimposes the OFDM-modulated high-frequency transmission signal and superimposes the high-frequency transmission signal in a state where the white LED 30 is driven to emit light. Visible light is emitted from the white LED 30 in FIG. 3 for visible light communication and illumination.

  When the user of the portable information terminal 5 wants to access the access point 1 and capture data, the user places the portable information terminal 5 within the white light irradiation range of the white LED 30 of the lamp 3 and activates the terminal receiving unit 7. . When the terminal receiving unit 7 operates, the light receiver 41 of the terminal receiving unit 7 in FIG. 4 receives white light and outputs a photocurrent, and the photocurrent is removed from the DC component, and an AC voltage signal (high frequency received signal) is generated. Input to the buffer amplifier 42, and the buffer amplifier 42 outputs the received signal input at a high input impedance to the high frequency amplifier 43 at the next stage as a low output impedance. The high-frequency amplifier 43 efficiently amplifies a fine high-frequency voltage signal input with a low input impedance in a low noise state and outputs it to the demodulator 44.

  The demodulator 44 detects and demodulates the high frequency received signal output from the high frequency amplifier 43, and outputs the demodulated high frequency received signal to the next IQ separator 45. The IQ separation unit 45 performs quadrature modulation on the input high-frequency reception signal using a cosine wave and a sine wave, and separates the signal into an in-phase signal and a quadrature signal. Next, the real part of the in-phase signal and the imaginary part of the quadrature signal separated by the IQ separation unit 45 are output to the A / D conversion units 46 and 47, respectively. After being sampled and converted into a digital signal, it is input to the discrete Fourier transform unit 48.

  The discrete Fourier transform unit 48 performs fast Fourier transform so as to obtain the complex value on the complex plane of each subcarrier from the complex value on the time axis that combines the real part of the in-phase signal and the imaginary part of the quadrature signal. The parallel data of each subcarrier output from the discrete Fourier transform unit 48 is converted into serial data by the P / S conversion unit 49 and input to the input / output unit 15 of the transmission / reception data processing unit 16 as reception data. The data processing unit 13 of the transmission / reception data processing unit 16 shown in FIG. 4 stores the input received data in the data memory 14, and information on characters and images based on the received data according to the operation of the portable information terminal 5 by the user. Appears on the display.

  On the other hand, when transmitting data by uplinking the portable information terminal 5 to the access point 1, when the terminal transmission unit 6 of the portable information terminal 5 is activated, the transmission / reception data processing unit 16 of the terminal transmission unit 6 of FIG. The transmission data is recombined for OFDM, and the data is output from the input / output unit 15 to the OFDM modulator 20.

  When the digital modulation unit 21 of the OFDM modulator 20 receives the transmission data signal for OFDM sent from the input data processing unit 10, the digital modulation unit 21 digitally converts each bit of the transmission data signal for each subcarrier by a modulation scheme such as 64QAM. The modulated serial data signal is sent to the S / P converter 22.

  When the digitally modulated serial data is input, the S / P converter 22 uses N (for example, 1024) subcarriers so that each bit of the data sequence is assigned to each subcarrier. Each bit is converted into N pieces of parallel data, and the parallel data is output to the inverse discrete Fourier transform unit 23.

  Next, the inverse discrete Fourier transform unit 23 performs inverse discrete Fourier transform at high speed on the parallel symbol data sequence that is digitally modulated and configured to assign each bit of the data sequence to each subcarrier, and the calculation result is The data is output to the D / A converters 25 and 26 as time domain complex data consisting of real and imaginary numbers.

  The real and imaginary complex data subjected to the inverse discrete Fourier transform are respectively sent to the D / A converters 25 and 26 and converted into analog signals, and then converted into analog signals by the D / A converters 25 and 26, respectively. The converted complex data is sent to the synthesis unit 27. In the synthesizer 27, the pair of complex data is orthogonally modulated and synthesized using a cosine wave and a sine wave of a carrier frequency of, for example, 4 MHz to 34 MHz of the subcarrier, and OFDM modulated from the synthesizer 27 by 4 MHz to 34 MHz. The high-frequency transmission signal is output to the band correction amplifier 31.

  The band correction amplifier 31 amplifies the high frequency transmission signal so as to apply band equalization correction to the OFDM modulated high frequency transmission signal, and thereby, a high frequency signal having a very wide frequency band such as 4 MHz to 34 MHz is obtained. Correction is made according to the frequency characteristics of the blue LED 39. That is, the frequency characteristics of the blue LED 39 are usually nonlinear characteristics such that the lower the frequency, the higher the emission level, and the higher the frequency, the lower the emission level. Therefore, the nonlinear characteristic of the blue LED 39 is corrected. Therefore, the band correction amplifier 31 adds the inverse characteristic of the frequency characteristic of the blue LED 39 to the signal, and amplifies the high-frequency transmission signal while performing band correction.

  In the next transmission signal amplifier 32, the band-corrected high-frequency transmission signal is converted into a balanced transmission signal by the unbalance / balance conversion circuit 37 to widen the dynamic range of the next-stage high-frequency amplifier 38. . The next high frequency amplifier 38 amplifies the high frequency transmission signal to a level that can be superimposed on the blue light of the blue LED 39. The amplified transmission signal is input to the LED driver 36 through the impedance matching circuits 33 and 34. The LED driver 36 in FIG. 4 drives the blue LED 39 to emit light, and superimposes the OFDM-modulated high-frequency transmission signal on the blue light. Blue light is superimposed on the high-frequency transmission signal from the LED 39 and irradiated toward the access point 1. That is, at the time of uplink from the portable information terminal 5 to the access point 1, blue light different from the white light of the lamp 3 is projected and visible light communication is performed.

  Therefore, the user who uses the portable information terminal 5 projects blue light from the terminal transmission unit 6 to the access point 1 that illuminates and projects white light from the lamp 3 as illumination light. Therefore, the blue light projected from the terminal transmitter 6 can be easily visually recognized. As a result, the user can easily recognize the uplink state by performing visible light communication from the portable information terminal 5 to the access point 1.

  Also, since the uplink light projection from the portable information terminal 5 side to the access point 1 side becomes blue light unlike the white light for illumination of the lamp 3, only the blue light is applied to the front surface of the light receiver 41. By disposing an optical filter that transmits light, disturbance light such as white light from the lamp 3 can be effectively removed, and a decrease in S / N ratio due to the disturbance light and a decrease in communication speed associated therewith can be avoided. .

  On the other hand, when the light receiver 41 of the access point receiver 4 of the access point 1 receives the blue light emitted from the blue LED 39 of the terminal transmitter 6, the light receiver 41 of FIG. 3 outputs a photocurrent, and the photocurrent is The DC component is removed and an AC voltage signal (high frequency received signal) is input to the buffer amplifier 42. The buffer amplifier 42 outputs the received signal input with a high input impedance to the next stage high frequency amplifier 43 as a low output impedance. The high-frequency amplifier 43 efficiently amplifies a fine high-frequency voltage signal input with a low input impedance in a low noise state and outputs it to the demodulator 44.

  The demodulator 44 detects and demodulates the high frequency received signal output from the high frequency amplifier 43, and outputs the demodulated high frequency received signal to the next IQ separator 45. The IQ separation unit 45 performs quadrature modulation on the input high-frequency reception signal using a cosine wave and a sine wave, and separates the signal into an in-phase signal and a quadrature signal. Next, the real part of the in-phase signal and the imaginary part of the quadrature signal separated by the IQ separation unit 45 are output to the A / D conversion units 46 and 47, respectively. After being sampled and converted into a digital signal, it is input to the discrete Fourier transform unit 48.

  The discrete Fourier transform unit 48 performs fast Fourier transform so as to obtain the complex value on the complex plane of each subcarrier from the complex value on the time axis that combines the real part of the in-phase signal and the imaginary part of the quadrature signal. The parallel data of each subcarrier output from the discrete Fourier transform unit 48 is converted into serial data by the P / S conversion unit 49 and input to the input / output unit 15 of the input data processing unit 10 as reception data. The data processing unit 13 of the input data processing unit 10 operates so that the input received data is recombined into packet data using the data buffer 12 and is output to the LAN through the Ethernet interface 11.

In this way, a large-capacity high-speed communication of the OFDM system using visible light can be performed between the access point 1 connected to the network and provided with the lamp 3 and the portable information terminal 5. In the uplink to the access point 1, it is possible to easily recognize the blue light emitted from the terminal transmission unit 6 with respect to the white illumination light and easily recognize the access operation.

DESCRIPTION OF SYMBOLS 1 Access point 2 Access point transmission part 3 Lamp 4 Access point reception part 5 Portable information terminal 6 Terminal transmission part 7 Terminal reception part 9 LED drive part 10 Input data processing part 11 Ethernet interface 12 Data buffer 13 Data processing part 14 Data memory 15 Input / output unit 16 Transmission / reception data processing unit 20 OFDM modulator 21 Digital modulation unit 22 S / P conversion unit 23 Inverse discrete Fourier transform unit 25 D / A conversion unit 27 Synthesis unit 30 White LED
31 Band Correction Amplifier 32 Transmission Signal Amplifier 33 Impedance Matching Circuit 34 Impedance Matching Circuit 35 Coaxial Cable 36 LED Driver 37 Unbalance / Balance Conversion Circuit 38 High Frequency Amplifier 39 Blue LED
DESCRIPTION OF SYMBOLS 41 Photoreceiver 42 Buffer amplifier 42a Current / voltage conversion circuit 43 High frequency amplifier 44 Demodulation part 45 IQ separation part 46 A / D conversion part 48 Discrete Fourier transform part 49 P / S conversion part

Claims (6)

An access point transmitting unit that illuminates and projects illumination light superimposed on an information signal from an LED of the lamp to an access point that is connected to a network and has a lamp, and a visible light projected from a projector of the terminal transmitter of the portable information terminal An access point receiving unit that receives light and extracts an information signal superimposed on the visible light; and
A terminal transmitter that projects visible light superimposed with an information signal on the portable information terminal from a projector, and illumination light projected from the lamp of the access point transmitter is received and superimposed on the illumination light. A visible light communication device that performs visible light communication between the access point and the portable information terminal,
The access point transmission unit
A transmission data processing unit that rearranges transmission data so that each bit of a transmission data signal sent from the network and packetized is assigned to each subcarrier;
A modulation unit that digitally modulates each bit of the digital signal of transmission data sent from the transmission data processing unit for each subcarrier;
An S / P converter that converts the serial digital transmission signal modulated by the modulator into a data string of the number of subcarriers;
An inverse discrete Fourier transform unit for performing inverse fast Fourier transform on the digital transmission signal converted in parallel by the S / P conversion unit;
A D / A converter that converts the digital transmission signal obtained by inverse fast Fourier transform in the inverse discrete Fourier transform unit into an analog signal;
A synthesis unit that performs quadrature modulation and synthesis of the complex data converted into an analog signal by the D / A conversion unit using a cosine wave and a sine wave of the carrier frequency of the subcarrier;
An LED drive unit that drives the LED of the lamp so as to amplify an analog high-frequency signal synthesized by the synthesis unit and modulated by a subcarrier and superimpose it on white light;
With
The access point receiver
A light receiver that receives blue light superimposed by an information signal emitted from a blue LED of a terminal transmission unit of the portable information terminal by a light receiving element;
A high-frequency amplifier that amplifies and outputs a high-frequency signal output from the light receiver in a low-noise state;
A demodulator that detects and demodulates the high-frequency received signal output from the high-frequency amplifier;
An IQ separation unit for separating the high-frequency reception signal output from the demodulation unit into an in-phase signal and a quadrature signal by multiplying a sine wave and a cosine wave;
An A / D converter that samples and converts the real part of the in-phase signal separated by the IQ separator and the imaginary part of the quadrature signal into a digital signal;
A complex value on the complex plane of each subcarrier is obtained from a complex value on the time axis that is a combination of the real part of the in-phase signal and the imaginary part of the quadrature signal output from the A / D converter. A discrete Fourier transform unit for performing a fast Fourier transform on
A P / S conversion unit that converts the parallel data of each subcarrier output from the discrete Fourier transform unit into serial data to be received data;
With
The terminal transmission unit, a transmission data processing unit that rearranges transmission data so that each bit of a transmission data signal is allocated to each subcarrier; and
A modulation unit that digitally modulates each bit of the digital signal of transmission data sent from the transmission data processing unit for each subcarrier;
An S / P converter that converts the serial digital transmission signal modulated by the modulator into a data string of the number of subcarriers;
An inverse discrete Fourier transform unit for performing inverse fast Fourier transform on the digital transmission signal converted in parallel by the S / P conversion unit;
A D / A converter that converts the digital transmission signal obtained by inverse fast Fourier transform in the inverse discrete Fourier transform unit into an analog signal;
A synthesis unit that performs quadrature modulation and synthesis of the complex data converted into an analog signal by the D / A conversion unit using a cosine wave and a sine wave of the carrier frequency of the subcarrier;
An LED drive unit that drives a blue LED so as to amplify an analog high-frequency signal synthesized by the synthesis unit and modulated by a subcarrier and superimpose it on blue light;
With
The terminal receiver is illuminated by a white LED of the access point transmitter of the access point and receives a white light superimposed with an information signal by a light receiving element;
A high-frequency amplifier that amplifies and outputs a high-frequency signal output from the light receiver in a low-noise state;
A demodulator that detects and demodulates the high-frequency received signal output from the high-frequency amplifier;
An IQ separation unit for separating the high-frequency reception signal output from the demodulation unit into an in-phase signal and a quadrature signal by multiplying a sine wave and a cosine wave;
An A / D converter that samples the real part of the in-phase signal separated by the IQ separator and the imaginary part of the quadrature signal and converts them into a digital signal;
A complex value on the complex plane of each subcarrier is obtained from a complex value on the time axis that is a combination of the real part of the in-phase signal and the imaginary part of the quadrature signal output from the A / D converter. A discrete Fourier transform unit for performing a fast Fourier transform on
A P / S conversion unit that converts the parallel data of each subcarrier output from the discrete Fourier transform unit into serial data to be received data;
With
The access point transmission unit projects white light from the white LED of the lamp as white light on which the information signal is superimposed as illumination light, while the terminal transmission unit of the portable information terminal transmits blue light from the blue LED on which the information signal is superimposed. A visible light communication device that projects light toward an access point.   A current / voltage converter that converts a photocurrent into a high-frequency voltage signal by connecting a resistor and a coil in series with the anode of the light receiving element to the light receiver of the access point receiver and the terminal receiver. The visible light communication apparatus according to claim 1, wherein a circuit is connected.   The buffer amplifier which converts a high input impedance into a low output impedance is connected between the current / voltage conversion circuit and the high frequency amplifier, and the buffer amplifier has a source follower circuit. 2. The visible light communication device according to 2.   As the light receiver of the access point receiver and the light receiver of the terminal receiver, a reflective condensing type light receiving element having a structure in which a light receiving element is disposed on the front surface of a concave mirror and facing the reflecting surface thereof is arranged alone or in an array form 4. The visible light communication device according to claim 1, wherein a reflection condensing type light receiver arranged in parallel is used.   A band correction amplifier is connected to the output side of the combining unit of the access point transmission unit and the terminal transmission unit, and the band correction amplifier is used for nonlinear distortion of frequency characteristics of the LEDs of the access point transmission unit and the terminal transmission unit. On the other hand, the visible light communication apparatus according to claim 1, wherein the visible light communication apparatus is configured to correct an inverse characteristic of distortion in advance by adding to a transmission signal.   The LED driving unit of the access point transmission unit and the terminal transmission unit includes a band correction amplifier that performs band correction amplification of an analog high-frequency signal synthesized by the synthesis unit and modulated by a subcarrier, and an output side of the band correction amplifier 5. The visible light communication device according to claim 1, further comprising a transmission signal amplifier connected to the LED driver, wherein an impedance matching circuit is connected between the LED of the LED driving unit and the transmission signal amplifier.

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