JP2011234204A - Optical communication system having light emission power control function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control light emission power of an LED for optical communication mounted on a terminal according to a battery consumption level and a communication distance.SOLUTION: A terminal includes a receiver 7 that receives an optical signal for visible light communication from a lighting device and a transmitter 8 that transmits an optical signal of visible light or an infrared light toward the lighting device side. The receiver 7 includes a signal intensity detector that detects the intensity of a reception signal from the lighting device. The terminal includes a battery voltage detector for detecting a voltage value of a battery 6. A signal processor 16 detects an output current of an infrared LED 24 using a current detection resistor 25 and compares the output current with the reception signal intensity of the visible light communication and the voltage of the battery. The signal processor 16 outputs a control signal to a driving circuit 23 based on the comparison result and the driving circuit 23 drives the infrared LED 24 by receiving the control signal. The infrared emission LED 24 is driven with an appropriate power value, considering both consumption status of the battery (a battery voltage) and a communication distance.

Description

  The present invention relates to an optical communication system that can control light emission power according to a communication distance and a battery voltage.

  Recently, a visible light communication system using LEDs has been proposed. As one of such visible light communication systems, between an LED used in a lighting device installed on a ceiling or the like and a portable communication terminal such as a headset or a PDA located within the irradiation range of the lighting device. There is something that communicates. In communication, both the uplink and the downlink may be performed by visible light communication. For example, the downlink may be performed by visible light communication and the uplink may be performed by infrared communication. In this case, a transmitter and a receiver for communication are provided in each of the luminaire and the terminal, an LED for illumination is used as the transmitter of the luminaire, and a light emitting element such as an infrared LED is used as the transmitter of the terminal. For the part, a photodetector such as a photodiode is used.

  In this system, in a luminaire, transmission is performed by superimposing a communication signal on a power line and oscillating a lighted LED in response to this signal. In a portable terminal, a light emitting element is provided by a battery installed in the terminal. Transmission is performed by driving. Therefore, if the terminal is continuously used, the light emission power on the terminal side decreases due to the discharge of the battery. In particular, since the terminal is carried by the user, the communication distance between the luminaire and the terminal changes, and the necessary communication distance cannot be ensured when the battery is consumed.

As means for solving this problem, for example, the inventions described in the following Patent Documents 1-4 are conventionally known.
In the invention of Patent Document 1, even when the distance between infrared communication devices changes during communication, the infrared light emission intensity is optimized according to the distance, and the power consumption of the infrared communication device is reduced.
The invention of Patent Document 2 stops only a function with high power consumption among a plurality of functions of a terminal and operates only a wireless unit with low power consumption.
The invention of Patent Document 3 generates and transmits an optical transmission signal while generating a power control signal based on the level detection signal transmitted from the fixed-side transceiver and performing output light power control of the laser diode.
In the invention of Patent Document 4, distance information is acquired from a distance sensor, and the transmitter is caused to emit light only when it exists within a predetermined communicable range.

JP 2002-374212 A JP 2002-208888 A JP 2008-244774 A JP 2008-028819 A

  In a visible light communication system, a plurality of terminals having different communication distances often communicate with one lighting fixture. In such a case, strong light that has arrived from a terminal near the luminaire may interfere with weak light emitted from a terminal that is away from the luminaire, which may cause a communication failure due to a so-called perspective problem. is there. In particular, this point becomes a big problem when transmitting from the terminal side to the luminaire. However, the inventions of Patent Documents 1 to 4 are all related to efficient use of light emission power to prevent battery consumption and light emission power control at the time of consumption. However, since power control is not performed when the battery is not consumed (when fully charged), no countermeasures are taken for the perspective problem.

  The present invention has been proposed in order to solve the above-described problems of the prior art, and the object thereof is to illuminate in consideration of both battery consumption (battery voltage value) and communication distance. An object of the present invention is to provide an optical communication system having a light emission power control function capable of stably performing communication between an apparatus and a terminal.

  In order to achieve the above object, an optical communication system having a light emission power control function according to the present invention includes a receiving unit that receives an optical signal for visible light communication from an illumination device, and a visible light or infrared ray on the illumination device side. A terminal equipped with a transmitter for transmitting an optical signal is provided with a signal intensity detector for detecting the intensity of a received signal from a lighting fixture, and a battery voltage detector for detecting a battery voltage value for driving the terminal. A signal processing unit that compares the received signal strength and the battery voltage with a reference value (a constant value or a reference value within a certain range) and controls the power supplied to the transmission unit provided in the terminal based on the comparison result. It is characterized by having.

  In this case, it is also an aspect of the present invention that the signal processing unit uses the output current value of the transmission unit as the reference value.

  It is also an aspect of the present invention that the received signal strength and the battery voltage are compared based on a conversion table prepared in advance, and the smaller converted value is compared with the reference value.

  In the optical communication system having the light emission power control function of the present invention having the above-described configuration, the battery power consumption is reduced by reducing the light emission power when the battery is consumed so that short-distance communication is possible even with low power. Sometimes, the user ensures the communication state by bringing the terminal closer to the lighting device. On the other hand, when the communication distance approaches, the light emission power from the terminal is reduced so that communication failure does not occur. In particular, in the present invention, the emission power is not simply reduced by the communication distance, but by monitoring both the communication distance and the battery voltage, when the battery voltage is low, the emission power can be reduced even if the communication distance is close. Do not reduce. Thereby, when the battery voltage becomes low, when the terminal is brought close to the lighting device, the disadvantage that the emitted light power further decreases and communication becomes impossible is solved.

1 is a layout diagram showing Embodiment 1 of an optical communication system of the present invention. FIG. 3 is a block diagram illustrating a configuration of a terminal according to the first embodiment. FIG. 2 is a block diagram illustrating a configuration of a signal processing unit according to the first embodiment. 3 is a flowchart showing the operation of the terminal according to the first embodiment.

(1) Configuration of Embodiment 1 Hereinafter, the configuration of Embodiment 1 of the present invention will be described in detail with reference to FIGS.
In FIG. 1, the code | symbol 1 is an LED illuminating device, Comprising: As an example, it has several LED arrange | positioned by the fluorescent tube shape, and is being fixed to the ceiling other part of a building. The LED lighting device 1 is connected to a power source for lighting, a master unit for communication control, and another LED lighting device by a coaxial cable 2 that supplies power and signals. A master unit (not shown) controls light emission of each LED lighting device 1 and processes a signal received from a terminal through each LED lighting device 1, and the LED lighting device 1 is connected to the public network via this parent device. It is also connected to an external network.

  In the vicinity (communication range) of each LED lighting device 1, terminals such as a headset 5 and a PDA are arranged (carrying workers). The terminal is not necessarily limited to a headset or PDA, and any terminal that can perform visible light communication can be used. The terminal and each LED lighting device 1 exchange signals with the visible light communication system, but it is not always necessary to perform bidirectional visible light communication. In this embodiment, the downlink is visible light communication, and the uplink is Infrared communication. Therefore, in this embodiment, the LED lighting device 1 is provided with a receiving unit 4 such as a photodiode for receiving infrared rays. On the other hand, the headset 5 transmits infrared communication data to the lighting device 1 by a battery 6 serving as a driving power source, a visible light communication receiving unit 7 that receives visible light communication data from the lighting device 1, an infrared light emitting LED, and the like. An infrared communication transmitter 8 is provided.

  FIG. 2 shows a circuit configuration of the terminal of this embodiment having such a configuration. Since the terminal according to the present embodiment is the headset 5, the receiving circuit unit R that converts data received by visible light communication into sound information and the sound signal from the microphone provided in the terminal by infrared communication are used for the lighting device 1. And a transmission circuit unit S for sending to the side.

  The receiving circuit unit R receives visible light superimposed with communication data and converts it into an electrical signal, and outputs only the band necessary for reproduction as communication data from the output signal of the visible light receiving element 10. A band-pass filter 11 to be extracted, a limiter 12 that limits the amplitude of the signal that has passed through the band-pass filter 11 and outputs the signal as a signal having a constant width, and a demodulator 13 that demodulates the output signal from the limiter 12 to produce an analog audio signal; A power amplifier 14 that amplifies the output of the demodulator 13 and sends it to the speaker 15 is provided.

  The transmission circuit unit S includes a microphone 20 for voice input, a microphone amplifier 21 for amplifying the input voice signal, a modulator 22 for modulating an output signal from the microphone amplifier 21 to generate an AM or FM modulation signal, and this modulation. A drive circuit 23 for driving the infrared light emitting LED 24 according to the modulation signal from the device 22 is provided.

  In the present embodiment, in addition to the receiving circuit unit R and the transmitting circuit unit S, a signal processing unit 16 that outputs a control signal to the driving unit 23 of the infrared light emitting LED 24 is provided in the terminal. The signal processing unit 16 acquires the received signal strength (RSSI) of the visible light communication signal received from the limiter 12 by the visible light receiving element 10, the voltage value of the battery 6 that is the power source of the terminal, The LED output current value obtained through the current detection resistor 25 connected between the LEDs 24 is acquired. Based on the received signal strength, the battery voltage value, and the LED output current value, the signal processing unit 16 outputs an LED current control output (control voltage value), and outputs it from the drive circuit 23 to the LED 24 based on the current control output. Increase or decrease the drive current.

  An example of the signal processing unit 16 is shown in FIG. The signal processing unit 16 includes a reception signal strength detection unit 30 connected to the limiter 12 of the reception circuit unit R and a battery voltage detection unit 31 connected to the battery 6. Outputs of the received signal strength detection unit 30 and the battery voltage detection unit 31 are connected to a comparison unit 32. The comparison unit 32 converts the input data from the detection units 30 and 31 into a reference value that can be compared. 33 is connected. That is, input data from each of the detection units 30 and 31 is read as a voltage value, shaped by a filter (not shown), and then sent to the comparison unit 32.

  In the conversion table 33, for example, for the received signal strength, the filter output voltage value is converted into a reference value A having a maximum value of 0.1 and a minimum value of 1.0, and returned to the comparison unit 32. As for the battery voltage, the filter output voltage value is converted into a reference value B having a maximum value of 1.0 and a minimum value of 0.3, and is returned to the comparison unit 32.

  That is, in the conversion table 33, for the received signal strength, for example, when the reference value A is set in the range of 0.1 to 1.0, the minimum value 0 of the reference value A is obtained when the received signal strength is the highest. .1 is set as the filter output voltage value, and when the received signal strength is the lowest, the maximum value 1.0 of the reference value A is set as the filter output voltage value and returned to the comparison unit 32. For the battery voltage, for example, when the reference value B is set in the range of 0.3 to 1.0, the maximum value 1.0 of the reference value B is set as the filter output voltage value when the battery is fully charged. When the battery is exhausted, the minimum value 0.3 of the reference value B is set as the filter output voltage value and returned to the comparison unit 32.

  Thus, in the present invention, when the communication distance is short, that is, when the received signal strength is high, the emission power of the infrared LED is reduced by reducing the reference value A to solve the perspective problem during communication. Further, when the battery power is consumed, the communication power can be continued even with a short communication distance by reducing the emission power of the infrared LED. Therefore, the higher the read battery voltage is, the higher the reference value B is. Has increased. Accordingly, the increase / decrease in the filter output voltage of the received signal strength and the filter output voltage of the battery voltage are reversed from the increase / decrease in the reference values A and B based on these filter output voltages.

  The comparison unit 32 compares the reference values A and B, and outputs the target value C to the control determination unit 34 with the smaller one as the target value C. An LED current detection unit 35 is connected to the control determination unit 34, and the target value C and an LED current filter output value shaped by a filter (not shown) are input from the LED current detection unit 35. The initial value α of the LED current is also stored in the control determination unit 34. By comparing the target value C with the LED current filter output value and the initial value α of the LED current in the comparison unit 32, it is determined whether or not the LED current during driving is increased or decreased. A control output signal is output from the control command output unit 36 to the drive circuit 23 as a control output signal.

(2) Operation of Embodiment 1 The operation of Embodiment 1 will be described with reference to the flowchart of FIG.
In the system of the first embodiment, when communication is started between the lighting device 1 and the headset 5 which is a terminal by downlink visible light communication and uplink infrared communication, on the terminal side, as shown in FIG. The visible light communication signal received by the visible light receiving element 10 is converted into an audio signal by the receiving circuit unit R and output from the speaker 15, and the audio signal from the microphone 20 is output from the drive circuit 23 by the transmitting circuit unit S. The infrared light emitting LED 24 is caused to emit light by converting the LED driving signal.

  In this case, in order to control the light emission power of the infrared light emitting LED 24 from the drive circuit 23 according to the distance between the lighting device 1 and the terminal and the consumption level of the battery 6 of the terminal, the LED current control as shown in the flowchart of FIG. Start (step 1). First, the control determination unit 34 in FIG. 3 stores the LED current initial value α at the start time (step 2). Next, the received signal strength detection unit 30 reads the received signal strength RSSI from the limiter 12 (step 3), performs predetermined filtering (step 4), and outputs it to the comparison unit 32. The comparison unit 32 converts the RSSI voltage filter output into a reference value A by referring to the conversion table 33 (step 5).

  On the other hand, before or after reading the RSSI voltage, the battery voltage detection unit 31 reads the voltage value of the battery 6 (step 6), performs predetermined filtering (step 7), and outputs it to the comparison unit 32. The comparison unit 32 converts the RSSI voltage filter output into a reference value B by referring to the conversion table 33 (step 8). Next, the comparison unit 32 compares the two reference values A and B (step 9), and sets the smaller value as the target value C (steps 10 and 11).

  Before and after the determination of the target value C, the LED current detection unit 35 reads the current LED current (step 12) and performs predetermined filtering (step 13). A value obtained by dividing C and the filtered LED current filter output by the target value C is compared with the LED current initial value α stored in advance (step 14). When the comparison result is smaller than the initial value α, that is, when the communication distance is long or the remaining battery power is large, the current control output from the control command output unit 35 is increased by a predetermined ΔV, thereby The LED current for driving the infrared light emitting LED 34 is increased (step 15). On the other hand, when the comparison result is larger than the initial value α, that is, when the communication distance is short or the battery is exhausted, the current control output from the control command output unit 35 is decreased by a predetermined ΔV. Thus, the LED current for driving the infrared light emitting LED 34 is decreased (step 16).

(3) Effects of Example 1 According to Example 1 having the above-described configuration, when the communication distance is short and the received signal strength is high, the terminal is turned into the lighting device by reducing the emission power of the infrared LED. It is possible to prevent communication failure that occurs when approaching. In addition, when the battery power is exhausted, the user can continue the communication even with low power by bringing the terminal closer to the lighting device while the emission power of the infrared LED is reduced. As a result, communication can be performed for a relatively long time even when the battery is exhausted, and there is no inconvenience that the communication is suddenly disconnected when the battery is exhausted.

(4) Other Embodiments The present invention is not limited to the first embodiment, and the following configuration is also included in the present invention.
(a) The reference values A and B when the filter output voltage of the received signal strength and the filter output voltage of the battery voltage are compared are not limited to the values as in the above embodiment, It can be appropriately changed according to the degree, battery capacity, and the like.
(b) As the current control output for driving the infrared LED, in addition to the circuit in which the LED current increases as the current control output voltage increases as in the previous embodiment, the LED current decreases as the current control output voltage increases. It is also possible to employ a circuit that In that case, the reference value of each comparison unit and the comparison expression of the control determination unit may be changed.
(c) Although the infrared rays were used as the uplink in the above embodiment, the uplink can also be set to visible light communication by using a visible light (white) LED as a transmission unit of the terminal.
(d) The flow chart of FIG. 4 reads in the order of communication signal strength, battery voltage, and LED current. However, it is not always necessary to read and compare each data in this way. Depending on the method, the order of reading and comparison can be changed.

DESCRIPTION OF SYMBOLS 1 ... LED lighting apparatus 2 ... Coaxial cable 3 ... LED
4 ... Infrared communication receiver 5 ... Headset 6 ... Battery 7 ... Visible light communication receiver 8 ... Infrared communication transmitter 10 ... Visible light receiving element 11 ... Band pass filter 12 ... Limiter 13 ... Demodulator 14 ... Power amplifier 15 ... Speaker 16 ... Signal processing unit 20 ... Microphone 21 ... Microphone amplifier 22 ... Modulator 23 ... Infrared light emitting LED drive circuit 24 ... Infrared light emitting LED
25 ... Current detection resistor 30 ... Received signal strength detection unit 31 ... Battery voltage detection unit 32 ... Comparison unit 33 ... Conversion table 34 ... Control determination unit 35 ... LED current detection unit 36 ... Control command output unit S ... Transmission circuit unit R ... Receiver circuit

Claims (3)

To a terminal equipped with a receiving unit that receives an optical signal for visible light communication from an illuminating device and a transmitting unit that transmits an optical signal of visible light or infrared light to the illuminating device side,
A signal strength detection unit for detecting the strength of the received signal from the lighting fixture;
A battery voltage detector for detecting a battery voltage value for driving the terminal;
A signal processing unit that compares the detected received signal strength and battery voltage with a reference value, and controls power supplied to a transmission unit provided in the terminal based on the comparison result;
An optical communication system having a light emission power control function.   2. The optical communication system having a light emission power control function according to claim 1, wherein the signal processing unit uses an output current value of the transmission unit as the reference value.   The signal processing unit converts the received signal strength and the battery voltage into reference values prepared in a conversion table prepared in advance, compares the received signal strength and the reference value of the battery voltage, and compares the reference values. The optical communication system having a light emission power control function according to claim 1 or 2, wherein a smaller value is compared with the reference value.

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