WO2020144858A1 - Optical communication device and optical communication method - Google Patents

Abstract

An optical communication device is configured to comprise: a light transmission unit (1) that emits a transmission light into water; a transmission light monitor unit (6) that receives the transmission light emitted from the light transmission unit (1) into the water as a monitor light; an attenuation ratio calculation unit (11) that calculates an attenuation ratio of the light quantity of the monitor light received by the transmission light monitor unit (6) to the light quantity of the transmission light emitted from the light transmission unit (1) into the water; and a characteristic control unit (18) that estimates, from the attenuation ratio calculated by the attenuation ratio calculation unit (11), a signal-to-noise ratio of a received light when an optical signal emitted into the water from an optical communication device on the other end of communication is received as the received light, and that, on the basis of the signal-to-noise ratio, controls that characteristic of the transmission light which influences the increase or decrease of the signal-to-noise ratio.

Description

Optical communication device and optical communication method

The present invention relates to an optical communication device and an optical communication method for controlling the characteristics of transmitted light that affect the increase/decrease in signal-to-noise ratio.

In Patent Document 1 below, an optical wireless transmission in which an optical reception band control unit transmits a band change request of an optical wireless section to an optical wireless transmission device of a communication partner in accordance with a signal level of a light reception signal detected by a signal level detection unit. A device is disclosed.
Further, when the optical wireless transmission device disclosed in Patent Document 1 receives the band change request transmitted from the optical wireless transmission device of the communication partner, the optical wireless transmission device outputs the modulated clock generated by the clock generation unit according to the received band change request. Have control.

JP, 2003-218802, A

The optical wireless transmission device disclosed in Patent Document 1 has a poor environment in the optical wireless section, and therefore, when communication cannot be established with the optical wireless transmission device of the communication partner, It is not possible to transmit/receive a band change request in the optical wireless section to/from the wireless transmission device. The optical wireless transmission device disclosed in Patent Document 1 cannot change the band according to the signal level of the light reception signal when the band change request cannot be transmitted and received.
Therefore, the optical wireless transmission device disclosed in Patent Document 1 has a problem that a desired SNR may not be obtained as a signal-to-noise ratio (SNR: Signal-to-Noise Ratio) of a received light signal. It was

The present invention has been made to solve the above problems. Even when communication with the optical communication device of the communication partner has not been established, the light emitted into the water from the optical communication device of the communication partner. An object is to obtain an optical communication device and an optical communication method capable of controlling the SNR of received light when a signal is received as received light.

The optical communication device according to the present invention includes an optical transmitter that emits transmitted light into water, a transmitted light monitor that receives transmitted light emitted from the optical transmitter into the water as monitor light, and an optical transmitter from the optical transmitter into the water. The optical communication device of the communication partner based on the attenuation rate calculation unit that calculates the attenuation rate of the light intensity of the monitor light received by the transmission light monitor unit with respect to the light intensity of the emitted transmission light and the attenuation rate calculated by the attenuation rate calculation unit. Estimate the signal-to-noise ratio of the received light when the optical signal emitted from the water into the water is received, and control the characteristics of the transmitted light that affect the increase or decrease of the signal-to-noise ratio based on the signal-to-noise ratio And a characteristic control section for controlling the characteristics.

According to the present invention, the characteristic control unit, based on the attenuation rate calculated by the attenuation rate calculation unit, the signal pair of the received light when the optical signal emitted into the water from the optical communication device of the communication partner is received as the received light. The optical communication device is configured to estimate the noise ratio and control the characteristics of the transmitted light that influences the increase or decrease of the signal to noise ratio based on the signal to noise ratio. Therefore, the optical communication device according to the present invention receives the optical signal emitted into the water from the optical communication device of the communication partner as the received light even when the communication with the optical communication device of the communication partner is not established. In this case, the signal-to-noise ratio of the received light can be controlled.

1 is a configuration diagram showing an optical communication device according to a first embodiment. 3 is a hardware configuration diagram showing hardware of an attenuation rate calculation unit 11, a demodulation unit 17, a table unit 19, a characteristic control processing unit 20, and a mobile unit control unit 21 in the optical communication device according to the first embodiment. FIG. It is a hardware block diagram of a computer when a part of optical communication apparatus is implement|achieved by software or firmware. It is a flowchart which shows the optical communication method which is a processing procedure of an optical communication apparatus. It is explanatory drawing which shows the relationship between turbidity in water and attenuation rate At. Correspondence between the band B of the transmitted light, the attenuation factor At, the communication distance L between the own optical communication device and the optical communication device of the communication partner, and the SNR of the received light received by the optical signal receiving unit 12. FIG. 7 is a flowchart showing a processing procedure of the mobile control unit 21. 7 is a configuration diagram showing an optical communication device according to a second embodiment. FIG. FIG. 7 is a hardware configuration diagram showing hardware of an attenuation rate calculation unit 11, a demodulation unit 17, a characteristic control unit 18, a mobile unit control unit 21, and a distance calculation unit 59 in the optical communication device according to the second embodiment. FIG. 6 is a configuration diagram showing an optical communication device according to a third embodiment. FIG. 9 is a configuration diagram showing an optical communication device according to a fourth embodiment.

Hereinafter, in order to explain the present invention in more detail, modes for carrying out the present invention will be described with reference to the accompanying drawings.

Embodiment 1.
FIG. 1 is a configuration diagram showing an optical communication device according to the first embodiment.
FIG. 2 is a hardware configuration diagram showing hardware of the attenuation rate calculation unit 11, the demodulation unit 17, the table unit 19, the characteristic control processing unit 20, and the mobile unit control unit 21 in the optical communication device according to the first embodiment. ..
1 and 2, the optical transmitter 1 includes a reference light source 2, a modulation signal generator 3, a modulator 4 and an optical antenna 5.
The optical transmitter 1 emits the transmitted light into the water to transmit the transmitted light to the transmitted light monitor 6 and the optical communication device of the communication partner.
The reference light source 2 outputs continuous wave (CW:Continuous Wave) light to the modulator 4 via an optical fiber.

The modulation signal generation unit 3 generates a modulation signal including communication data to be communicated and an error correction code, and outputs the generated modulation signal to the modulator 4. The modulated signal generation unit 3 changes the error correction code included in the modulated signal according to the control signal output from the characteristic control processing unit 20.
The modulator 4 is connected to the reference light source 2 via an optical fiber.
The modulator 4 generates modulated light by modulating the phase of the CW light output from the reference light source 2 according to the modulation signal output from the modulation signal generation unit 3, and outputs the generated modulated light via an optical fiber. And outputs it to the optical antenna 5. When generating the modulated light, the modulator 4 changes the modulation speed of the modulated light according to the control signal output from the characteristic control processing unit 20. However, this is merely an example, and the modulator 4 may be a device that modulates the intensity of the CW light output from the reference light source 2, or a configuration in which the output of the reference light source 2 is directly modulated by an electric signal. May be

The optical antenna 5 is realized by, for example, an optical telescope having a lens. The optical antenna 5 is connected to the modulator 4 via an optical fiber. The optical antenna 5 emits the modulated light output from the modulator 4 into water as transmission light. The optical antenna 5 adjusts the beam divergence angle of the transmission light according to the control signal output from the characteristic control processing unit 20 when the transmission light is emitted into the water.

The transmission light monitor unit 6 includes an optical antenna 7, a photodetector 8, a current-voltage converter (hereinafter referred to as “IV converter”) 9, and an analog-digital converter (hereinafter referred to as “ADC”) 10. There is. The transmission light monitor unit 6 receives the transmission light emitted into the water from the optical transmission unit 1 as monitor light.
The optical antenna 7 is realized by, for example, an optical telescope including a lens. The optical antenna 7 receives the transmitted light emitted into the water from the optical transmitter 1 as monitor light, and outputs the received monitor light to the photodetector 8 via the optical fiber.

The photodetector 8 is connected to the optical antenna 7 via an optical fiber. The photodetector 8 converts the monitor light output from the optical antenna 7 into a current signal, and outputs the current signal to the IV converter 9.
The IV converter 9 converts the current signal output from the photodetector 8 into a voltage signal, and outputs the voltage signal to the ADC 10.
The ADC 10 converts the voltage signal output from the IV converter 9 from an analog signal into a digital signal, and outputs the digital signal to the attenuation rate calculation unit 11.

The attenuation rate calculation unit 11 is realized by, for example, the attenuation rate calculation circuit 31. The attenuation rate calculation unit 11 calculates the attenuation rate of the light amount of the monitor light received by the transmission light monitor unit 6 with respect to the light amount of the transmission light emitted from the optical transmission unit 1 into the water. The attenuation rate calculation unit 11 outputs the calculated attenuation rate to each of the characteristic control processing unit 20 and the moving body control unit 21.
The amount of monitor light received by the transmitted light monitor unit 6 is directly proportional to the digital signal output from the ADC 10.
In the optical communication device shown in FIG. 1, it is assumed that the light amount of the transmitted light emitted from the optical transmitter 1 into the water is stored in the internal memory of the attenuation rate calculator 11 as an existing value. However, this is only an example, and the measured value of the light amount of the transmission light emitted from the optical antenna 5 may be given to the attenuation rate calculation unit 11 from the outside.

The optical signal receiver 12 includes an optical antenna 13, a photodetector 14, an IV converter 15, and an ADC 16.
When an optical signal including communication data is emitted into water from an optical communication device of a communication partner, the optical signal receiving unit 12 receives the optical signal emitted into water as received light.
The optical antenna 13 is realized by, for example, an optical telescope including a lens. The optical antenna 13 receives an optical signal emitted into the water from the optical communication device of the communication partner as received light, and outputs the received received light to the photodetector 14 via the optical fiber.

The photodetector 14 is connected to the optical antenna 13 via an optical fiber. The photodetector 14 converts the received light output from the optical antenna 13 into a current signal, and outputs the current signal to the IV converter 15.
The IV converter 15 converts the current signal output from the photodetector 14 into a voltage signal, and outputs the voltage signal to the ADC 16.
The ADC 16 converts the voltage signal output from the IV converter 15 from an analog signal into a digital signal, and outputs the digital signal to the demodulation unit 17.

The demodulation unit 17 is realized by, for example, the demodulation circuit 32. The demodulation unit 17 demodulates the communication data included in the optical signal received by the optical signal reception unit 12.

The characteristic control unit 18 includes a table unit 19 and a characteristic control processing unit 20.
The characteristic control unit 18 receives the received light when the optical signal receiving unit 12 receives the optical signal emitted into the water from the optical communication device of the communication partner as the received light based on the attenuation rate calculated by the attenuation rate calculating unit 11. The signal-to-noise ratio (SNR: Signal-to-Noise Ratio) is estimated.
The characteristic control unit 18 controls, based on the SNR, the characteristic of the transmission light that affects the increase/decrease of the SNR.
The table unit 19 is realized by the storage circuit 33, for example. The table unit 19 stores the correspondence relationship among the band of the transmitted light, the attenuation rate, the communication distance, and the SNR of the received light received by the optical signal receiving unit 12.

The characteristic control processing unit 20 is realized by, for example, the characteristic control processing circuit 34. The characteristic control processing unit 20 refers to the correspondence relationship stored in the table unit 19 and determines the SNR of the reception light from the attenuation rate calculated by the attenuation rate calculation unit 11, the band of the transmission light, and the required value of the communication distance. To estimate. The required value of the communication distance is the communication distance requested by the user, and the communication distance is the communication distance between the own optical communication device and the optical communication device of the communication partner. The required value of the communication distance may be externally provided to the characteristic control processing unit 20 or may be stored in the internal memory of the characteristic control processing unit 20.
The characteristic control processing unit 20 compares the estimated SNR of the received light with the SNR threshold value. The SNR threshold value may be given to the characteristic control processing unit 20 from the outside, or may be stored in the internal memory of the characteristic control processing unit 20.
If the estimated SNR of the received light is smaller than the threshold value, the characteristic control processing unit 20 outputs a control signal to the modulator 4 to decrease the modulation speed so that the SNR of the received light becomes large.
Alternatively, if the estimated SNR of the received light is smaller than the threshold, the characteristic control processing unit 20 sends a control signal indicating that the beam divergence angle of the transmitted light is narrowed so that the SNR of the received light becomes large. Output to.
Alternatively, if the estimated SNR of the received light is smaller than the threshold value, the characteristic control processing unit 20 outputs to the modulation signal generation unit 3 a control signal indicating that the ratio of error correction codes in the modulation signal should be increased.

The moving body control unit 21 is realized by, for example, the moving body control circuit 35. The moving body control unit 21 obtains a communicable distance between its own optical communication device and the optical communication device of the communication partner based on the attenuation rate calculated by the attenuation rate calculation unit 11. If the communicable distance is shorter than the required value of the communication distance, the mobile body control unit 21 controls the mobile body (not shown) equipped with its own optical communication device to operate its own optical communication device. Bring it closer to the optical communication device of the other party. The required value of the communication distance may be given to the characteristic control processing unit 20 from the outside, or may be stored in the internal memory of the mobile unit control unit 21.
The moving body may be any one that can move in water with the optical communication device mounted, and corresponds to a submarine or an underwater drone.

In FIG. 1, each of the attenuation rate calculation unit 11, the demodulation unit 17, the table unit 19, the characteristic control processing unit 20, and the moving body control unit 21, which are some of the constituent elements of the optical communication device, are as shown in FIG. It is supposed to be realized by dedicated hardware. That is, it is assumed that a part of the optical communication device is realized by the attenuation rate calculation circuit 31, the demodulation circuit 32, the storage circuit 33, the characteristic control processing circuit 34, and the moving body control circuit 35.

Here, the memory circuit 33 is, for example, a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable Read Only Memory), or an EEPROM (Electrically Reversible Memory). It corresponds to a volatile semiconductor memory, a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, or a DVD (Digital Versatile Disc).
Further, each of the attenuation rate calculation circuit 31, the demodulation circuit 32, the characteristic control processing circuit 34, and the moving body control circuit 35 is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application). A specific integrated circuit (FPC), a field-programmable gate array (FPGA), or a combination thereof is applicable.

Some components of the optical communication device are not limited to those realized by dedicated hardware. For example, at least one of the attenuation rate calculation unit 11, the demodulation unit 17, the table unit 19, the characteristic control processing unit 20, and the mobile unit control unit 21 is realized by software, firmware, or a combination of software and firmware. It may be one.
Software or firmware is stored in the memory of the computer as a program. The computer means hardware that executes a program, and corresponds to, for example, a CPU (Central Processing Unit), a central processing unit, a processing unit, an arithmetic unit, a microprocessor, a microcomputer, a processor, or a DSP (Digital Signal Processor). To do.

FIG. 3 is a hardware configuration diagram of a computer when a part of the optical communication device is realized by software or firmware.
When a part of the optical communication device is realized by software, firmware or the like, the table unit 19 is configured on the memory 41 of the computer. A program for causing a computer to execute the processing procedures of the attenuation rate calculation unit 11, the demodulation unit 17, the characteristic control processing unit 20, and the moving body control unit 21 is stored in the memory 41. Then, the processor 42 of the computer executes the program stored in the memory 41.
FIG. 4 is a flowchart showing an optical communication method which is a processing procedure of the optical communication device.

2 shows an example in which some of the constituent elements of the optical communication device are realized by dedicated hardware, and in FIG. 3, an example in which a part of the optical communication device is realized by software or firmware. Is shown. However, this is merely an example, and some of the constituent elements of the optical communication device may be realized by dedicated hardware and the remaining constituent elements may be realized by software or firmware.

Next, the operation of the optical communication device shown in FIG. 1 will be described.
The items relating to the characteristics of the transmitted light that affect the increase/decrease in the SNR of the received light received by the optical signal receiving unit 12 include the modulation speed V of the modulated light generated by the modulator 4 and the transmitted light output from the optical antenna 5. The beam divergence angle θ and the error correction code included in the modulation signal generated by the modulation signal generation unit 3 are considered.
In the optical communication device shown in FIG. 1, the characteristic control unit 18 controls at least one of the modulation speed V of the modulated light, the beam divergence angle θ of the transmitted light, and the error correction code as the characteristics of the transmitted light.
Here, for convenience of description, it is assumed that the communicable distance L _p is equal to or larger than the required value of the communication distance L. The communicable distance L _p is the longest distance between the own optical communication device and the optical communication device of the communication partner, which has an SNR of 0 [dB] or more. Even if the communicable distance L _p is equal to or larger than the required value of the communication distance L, the desired SNR is not always obtained, so the characteristic control unit 18 controls the characteristic of the transmitted light.

The reference light source 2 outputs the CW light to the modulator 4 via an optical fiber.
The modulation signal generation unit 3 generates a modulation signal including communication data to be communicated and an error correction code, and outputs the generated modulation signal to the modulator 4.

The modulator 4 modulates the phase of the CW light output from the reference light source 2 in accordance with the modulation signal output from the modulation signal generation unit 3 to generate modulated light. The modulator 4 outputs the generated modulated light to the optical antenna 5 via the optical fiber.
Upon receiving the modulated light from the modulator 4, the optical antenna 5 emits the modulated light as transmission light into the water.

The optical antenna 7 receives the transmitted light emitted into the water from the optical transmitter 1 as monitor light (step ST1 in FIG. 4). The optical antenna 7 outputs the received monitor light to the photodetector 8 via the optical fiber.
The photodetector 8 converts the monitor light output from the optical antenna 7 into a current signal, and outputs the current signal to the IV converter 9.
The IV converter 9 converts the current signal output from the photodetector 8 into a voltage signal, and outputs the voltage signal to the ADC 10.
The ADC 10 converts the voltage signal output from the IV converter 9 from an analog signal into a digital signal D, and outputs the digital signal D to the attenuation rate calculation unit 11.

When the attenuation rate calculator 11 receives the digital signal D from the ADC 10, the attenuation rate calculator 11 calculates the light quantity P _r ⁰ of the monitor light received by the transmission light monitor 6 from the digital signal D as shown in the following equation (1). ..
P _r ⁰ =c ₁ ×D (1)
In Expression (1), c ₁ is a proportional constant.
Attenuation rate calculating unit 11, calculating the amount P _r ⁰ of the monitor light, the following equation as shown in (2), the amount of light from the optical antenna 5 of the monitor light to the light quantity P _t ⁰ of the transmitted light emitted in water The attenuation rate At of P _r ⁰ is calculated (step ST2 in FIG. 4).

Here, the attenuation rate calculation unit 11 calculates the attenuation rate At according to the equation (2). However, this is merely an example, and the attenuation rate calculation unit 11 calculates the attenuation rate At as the attenuation rate At, for example, as shown in the following expression (3), the attenuation amount of the light amount P _r ⁰ per 1 [m] distance. It may be calculated.

In Expression (3), L is a required value of communication distance. The required value of the communication distance L may be given to the attenuation rate calculation unit 11 from the outside, or may be stored in the internal memory of the attenuation rate calculation unit 11. In the optical communication device shown in FIG. 1, description that the required value of the communication distance L is externally given to the attenuation rate calculation unit 11 is omitted.

The damping rate calculation unit 11 outputs the calculated damping rate At to each of the characteristic control processing unit 20 and the moving body control unit 21.
Assuming that the distance between the own optical communication device and the optical communication device of the communication partner is constant, the attenuation rate At is directly proportional to the turbidity in water as shown in FIG. Turbidity is an index showing the turbidity of water. Therefore, the attenuation rate At increases as the turbidity of water increases, and the light amount P _r ⁰ of the monitor light increases.
FIG. 5 is an explanatory diagram showing the relationship between the turbidity in water and the attenuation rate At.

As shown in FIG. 6, the table unit 19 stores the correspondence relationship among the band B of the transmitted light, the attenuation rate At, the communication distance L, and the SNR of the received light.
FIG. 6 is an explanatory diagram showing a correspondence relationship between the band B of the transmitted light, the attenuation rate At, the communication distance L, and the SNR of the received light received by the optical signal receiving unit 12.
However, in FIG. 6, as the attenuation rate At, the attenuation amount of the light amount P _r ⁰ per distance of 1 [m] is described.

When the characteristic control processing unit 20 receives the attenuation rate At from the attenuation rate calculating unit 11, the characteristic control processing unit 20 refers to the correspondence relationship shown in FIG. 6 stored in the table unit 19 and calculates the attenuation rate calculated by the attenuation rate calculating unit 11. The SNR of the received light received by the optical signal receiving unit 12 is estimated from At, the required bandwidth B of the transmitted light, and the required value of the communication distance L (step ST3 in FIG. 4).
The characteristic control processing unit 20 determines, for example, that the band B of the transmitted light is 500 [MHz], the attenuation amount of the light amount P _r ⁰ per distance of 1 [m] is 5 [dB/m], and the required value of the communication distance L is If it is 15 [m], it is estimated that the SNR of the received light is 10 [dB].
The characteristic control processing unit 20 determines, for example, that the attenuation B of the light amount P _r ⁰ per distance of 1 [m] is 50 [MHz] and the required value of the communication distance L is 50 [MHz]. If it is 30 [m], it is estimated that the SNR of the received light is 44 [dB].

The characteristic control processing unit 20 compares the estimated SNR of the received light with the SNR threshold Th _SNR (step ST4 in FIG. 4). The threshold Th _SNR of _SNR is a value larger than 0 [dB].
If the estimated SNR of the received light is smaller than the threshold Th _SNR (step ST4: YES in FIG. 4), the characteristic control processing unit 20 lowers the modulation speed V so that the SNR of the received light becomes large. The control signal cnt ₁ shown is output to the modulator 4 (step ST5 in FIG. 4).
If the estimated SNR of the received light is equal to or greater than the threshold Th _SNR (step ST4: NO in FIG. 4), the characteristic control processing unit 20 sends the control signal cnt ₁ indicating that the modulation speed V is reduced to the modulator 4. Do not output.

As described above, the modulator 4 generates the modulated light by modulating the phase of the CW light output from the reference light source 2 according to the modulation signal output from the modulation signal generation unit 3.
When the modulator 4 receives the control signal cnt ₁ indicating that the modulation speed V should be decreased from the characteristic control processing unit 20 when generating the modulated light (step ST6 of FIG. 4: YES), the modulator 4 generated the light previously. Modulated light having a modulation speed V lower than that of the modulated light is generated (step ST7 in FIG. 4).
If the modulator 4 does not receive the control signal cnt ₁ indicating that the modulation speed V should be reduced from the characteristic control processing unit 20 (step ST6 in FIG. 4, NO), the previously generated modulated light and the modulation speed V are The same modulated light is generated (step ST8 in FIG. 4).

The modulator 4 outputs the generated modulated light to the optical antenna 5 via the optical fiber.
Upon receiving the modulated light from the modulator 4, the optical antenna 5 emits the modulated light as transmission light into the water (step ST9 in FIG. 4).

In the flowchart shown in FIG. 4, the characteristic control processing unit 20 controls the modulation speed V of the modulated light as the characteristic of the transmitted light that affects the increase/decrease in SNR. The characteristic control processing unit 20 may control the beam divergence angle θ of the transmitted light as the characteristic of the transmitted light that affects the increase/decrease in SNR.
When controlling the beam divergence angle θ of the transmitted light, the characteristic control processing unit 20 increases the beam divergence angle of the transmitted light so that the SNR of the received light becomes large if the estimated SNR of the received light is smaller than the threshold Th _SNR. A control signal cnt ₂ indicating that θ is narrowed is output to the optical antenna 5.
If the estimated SNR of the received light is equal to or more than the threshold Th _SNR , the characteristic control processing unit 20 does not output the control signal cnt ₂ indicating that the beam divergence angle θ of the transmitted light is narrowed to the optical antenna 5.

If the optical antenna 5 receives a control signal cnt ₂ indicating that the beam divergence angle θ of the transmitted light is narrowed from the characteristic control processing unit 20, the transmitted light whose beam divergence angle θ is narrower than that of the previously emitted transmitted light. Is emitted into the water.
If the optical antenna 5 does not receive the control signal cnt ₂ indicating that the beam divergence angle θ of the transmitted light is narrowed from the characteristic control processing unit 20, the transmitted light having the same beam divergent angle θ as the previously emitted transmitted light is transmitted to the underwater. Emit to.
The optical antenna 5 includes an optical fiber that emits the transmitted light and a lens that adjusts the beam divergence angle θ of the transmitted light that is emitted from the optical fiber. The beam divergence angle θ of the transmitted light can be adjusted by changing the distance between them.

In the flowchart shown in FIG. 4, the characteristic control processing unit 20 controls the modulation speed V of the modulated light as the characteristic of the transmitted light that affects the increase/decrease in SNR. The characteristic control processing unit 20 may control the error correction code included in the modulated signal as the characteristic of the transmission light that affects the increase/decrease in SNR.
When controlling the error correction code included in the modulated signal, the characteristic control processing unit 20 indicates, for example, that the ratio of the error correction code in the modulated signal is increased if the estimated SNR of the received light is smaller than the threshold Th _SNR. The signal cnt ₃ is output to the modulation signal generation unit 3.
If the estimated SNR of the received light is equal to or higher than the threshold Th _SNR , the characteristic control processing unit 20 does not output the control signal cnt ₃ indicating that the ratio of the error correction code in the modulated signal is increased to the modulated signal generation unit 3.

As described above, the modulation signal generation unit 3 generates the modulation signal including the communication data to be communicated and the error correction code, and outputs the generated modulation signal to the modulator 4.
When the modulation signal generation unit 3 receives the control signal cnt ₃ indicating that the ratio of the error correction code in the modulation signal is increased from the characteristic control processing unit 20 when generating the modulation signal, the modulation signal generation unit 3 includes the previously generated modulation signal. A modulated signal containing a larger number of error correction codes than the error correction code is generated. When the modulation signal generation unit 3 uses a parity bit as the error correction code, for example, the ratio of the error correction code in the modulation signal can be increased by increasing the number of parity bits.
If the modulation signal generation unit 3 does not receive the control signal cnt ₃ indicating that the ratio of the error correction code in the modulation signal is increased from the characteristic control processing unit 20, it is the same as the error correction code included in the modulation signal generated last time. Generate a modulated signal containing a number of error correction codes.

Here, if the estimated SNR of the received light is smaller than the threshold Th _SNR , the characteristic control processing unit 20 outputs the control signal cnt ₃ indicating that the ratio of the error correction code in the modulation signal is increased to the modulation signal generation unit 3. doing. However, this is merely an example, and the characteristic control processing unit 20 outputs to the modulation signal generation unit 3 the control signal cnt ₃ indicating that the error correction code having the error correction capability higher than the previous time is included in the modulation signal. May be.
If the modulation signal generation unit 3 receives from the characteristic control processing unit 20 a control signal cnt ₃ indicating that an error correction code having an error correction capability higher than that of the previous time is included in the modulation signal, the modulation signal generation unit 3 includes the previously generated modulation signal. A modulated signal including an error correction code having a higher error correction capability than that of the error correction code is generated.

In the optical communication device shown in FIG. 1, the characteristic control processing unit 20 determines the modulation speed V of the modulated light, the beam divergence angle θ of the transmitted light, or the error included in the modulated signal as the characteristics of the transmitted light that affects the increase or decrease of the SNR. The correction code is controlled.
The characteristic control processing unit 20 controls the increase or decrease of the SNR by controlling at least one of the modulation speed V of the modulated light, the beam divergence angle θ of the transmitted light, and the error correction code included in the modulated signal. You can
Which of the modulation speed V of the modulated light, the beam divergence angle θ of the transmitted light, and the error correction code to be included in the modulated signal to be controlled may be set in the characteristic control processing unit 20, or may be externally controlled. The processing unit 20 may be instructed.

The relationship between the SNR of the received light and the modulation speed V of the modulated light and the beam divergence angle θ of the transmitted light is as follows. When the modulation speed V or the beam divergence angle θ changes, the SNR of the received light changes. You can see that it changes.

In equations (4) to (8), c ₃ and c ₄ are proportional constants, P _r ^E is the received power of the received light, and P _shot ^E is the noise power of the received light.
Further, S _det is the sensitivity of the photodetector 8, R _L is the resistance value of the amplifier incorporated in the photodetector 8, e is the charge amount of electrons, and Are is the surface area of the lens included in the optical antenna 7. Is.
The photodetector 8 has a built-in amplifier. For example, the amplifier amplifies the monitor light output from the optical antenna 7 and converts the amplified monitor light into a current signal.

In the description so far, it is assumed that the communicable distance L _p is equal to or larger than the required value of the communication distance L.
However, in practice, the communication distance L _p may be shorter than the required value of the communication distance L. When the communicable distance L _p is shorter than the required value of the communication distance L, the optical communication device of its own and the optical communication device of the communication partner cannot perform optical signal communication.
The mobile unit control unit 21 is equipped with its own optical communication device in order to enable optical signal communication when the communicable distance L _p is shorter than the required value of the communication distance L. A mobile unit (not shown) is controlled to bring its own optical communication device closer to the communication partner optical communication device.

FIG. 7 is a flowchart showing a processing procedure of the mobile unit control unit 21.
Hereinafter, the operation of the mobile control unit 21 will be described with reference to FIG. 7.
Upon receiving the attenuation rate At from the attenuation rate calculation section 11, the mobile unit control section 21 communicates the distance L _p between its own optical communication apparatus and the optical communication apparatus of the communication partner based on the attenuation rate At. Is calculated (step ST21 in FIG. 7).
The mobile control unit 21 can obtain the distance L _{p at} which the optical communication device of its own and the optical communication device of the communication partner can communicate by referring to the correspondence relationship shown in FIG. 6, for example.

Specifically, the mobile control unit 21 has, for example, a band B of transmission light of 500 [MHz] and an attenuation amount of the light amount P _r ⁰ per distance of 1 [m] of 5 [dB/m]. If so, the communication-enabled distance L _p is specified to be 16 [m].
If the band B of the transmitted light is 500 [MHz] and the attenuation amount of the light amount P _r ⁰ per distance of 1 [m] is 2 [dB/m], the moving body control unit 21 performs communication. The possible distance L _p is specified to be 40 [m].

The mobile control unit 21 compares the communication distance L _p with the communication distance L (step ST22 in FIG. 7).
If the communicable distance L _p is shorter than the communication distance L (step ST22: YES in FIG. 7), the mobile unit control unit 21 mounts its own optical communication device on a mobile unit (not shown). Is controlled to bring its own optical communication device closer to the optical communication device of the communication partner (step ST23 in FIG. 7). In the optical communication device shown in FIG. 1, the azimuth α from the optical communication device of itself to the optical communication device of the communication partner in the mobile unit control unit 21 is an existing value.
When the optical communication device of its own approaches the optical communication device of the communication partner and the communicable distance L _p becomes equal to or more than the communication distance L, the optical communication device of its own and the optical communication device of the communication partner are optically connected. Signal communication may be implemented.
If the communicable distance L _p is equal to or longer than the communication distance L (step ST22: NO in FIG. 7), the mobile body control unit 21 mounts its own optical communication device on a mobile body (not shown). Do not control.

Here, the mobile unit control unit 21 brings its own optical communication device close to the optical communication device of the communication partner so that the communicable distance L _{p is set} to the communication distance L or more and optical signal communication can be performed. I have to. However, this is merely an example, and the mobile unit control unit 21 can perform communication of an optical signal by changing the band B of the transmitted light so that the communicable distance L _p becomes equal to or longer than the communication distance L. You may do it.
For example, when the band B of the transmitted light is 500 [MHz] and the attenuation amount of the light amount P _r ⁰ per distance of 1 [m] is 5 [dB/m], the moving body control unit 21 determines that the transmitted light is When the band B of is changed to 50 [MHz], the communicable distance L _p is extended from 16 [m] to 17 [m].
For example, when the band B of the transmitted light is 500 [MHz] and the attenuation amount of the light amount P _r ⁰ per distance of 1 [m] is 2 [dB/m], the moving body control unit 21 determines that the transmitted light is When the band B of is changed to 50 [MHz], the communicable distance L _p is extended from 40 [m] to 43 [m].
If communication is possible distance L _p Nobile, communication coverage distance L _p may become more communication distance L.

When the communicable distance L _p becomes equal to or longer than the communication distance L, the transmission light monitor unit 6, the attenuation rate calculation unit 11, the characteristic control unit 18, and the optical transmission unit 1 repeat the processing shown in steps ST1 to ST9 of FIG. carry out.

The optical antenna 13 receives the optical signal emitted from the optical communication device of the communication partner when the optical communication device of the communication partner emits the optical signal into the water when the communicable distance L _p is the communication distance L or more. Receive as light. The optical antenna 13 outputs the received light received to the photodetector 14 via an optical fiber.
Upon receiving the received light from the optical antenna 13, the photodetector 14 converts the received light into a current signal and outputs the current signal to the IV converter 15.
Upon receiving the current signal from the photodetector 14, the IV converter 15 converts the current signal into a voltage signal and outputs the voltage signal to the ADC 16.
When the band of the optical signal radiated from the optical communication device of the communication partner is notified from the optical communication device of the communication partner, the characteristic control processing unit 20 sends the band parameter indicating the band of the optical signal to the IV converter 15. Output.
When the band of the optical signal emitted from the optical communication device of the communication partner changes, the SNR of the received light received by the optical antenna 13 changes. If the IV converter 15 receives the band parameter from the characteristic control processing unit 20, the IV converter 15 is based on the band of the optical signal indicated by the band parameter so that the change of the SNR becomes small even if the band of the received light changes. , Adjust the magnitude of the voltage signal.

Upon receiving the voltage signal from the IV converter 15, the ADC 16 converts the voltage signal from an analog signal into a digital signal and outputs the digital signal to the demodulation unit 17.
Upon receiving the digital signal from the optical signal receiving unit 12, the demodulating unit 17 demodulates the communication data included in the optical signal received by the optical antenna 13 from the digital signal.

In the first embodiment described above, reception when the characteristic control unit 18 receives the optical signal emitted into the water from the optical communication device of the communication partner as the received light based on the attenuation rate calculated by the attenuation rate calculation unit 11 The optical communication device shown in FIG. 1 is configured so as to estimate the SNR of light and control the characteristics of the transmitted light that affects the increase or decrease of the SNR based on the SNR. Therefore, the optical communication device shown in FIG. 1 receives the optical signal emitted into the water from the optical communication device of the communication partner as the received light even when the communication with the optical communication device of the communication partner is not established. The SNR of the received light at that time can be controlled.

In the optical communication device shown in FIG. 1, when the SNR of the received light is equal to or higher than the threshold Th _SNR , the characteristic control processing unit 20 prevents the modulator 4 from outputting the control signal cnt ₁ indicating that the modulation speed V is reduced. ing. Alternatively, if the SNR of the received light is equal to or higher than the threshold Th _SNR , the characteristic control processing unit 20 does not output the control signal cnt ₂ indicating that the beam divergence angle θ of the transmitted light is narrowed to the optical antenna 5. .. Alternatively, when the SNR of the received light is equal to or higher than the threshold Th _SNR , the characteristic control processing unit 20 does not output the control signal cnt ₃ indicating that the ratio of the error correction code in the modulated signal is increased to the modulated signal generation unit 3. ing.
However, this is only an example, SNR of the received light, the threshold value _Th threshold for large SNR limit than _{SNR Th SNR-up (Th SNR} <Th SNR-up) is greater than _{(SNR> Th SNR- up} ), the characteristic control processing unit 20 may output the control signal cnt ₁ indicating that the modulation speed V is increased to the modulator 4.
When the modulator 4 receives the control signal cnt ₁ indicating that the modulation speed V is increased from the characteristic control processing unit 20, the modulator 4 generates a modulated light having a higher modulation speed V than the previously generated modulated light.
If the SNR of the received light is equal to or higher than the threshold Th _SNR and the SNR of the received light is equal to or lower than the upper threshold Th _SNR-up (Th _SNR ≤ SNR ≤ Th _SNR-up ), the characteristic control processing unit 20 The control signal cnt ₁ is not output to the modulator 4.
Note that the threshold Th _SNR-up for the upper limit of the SNR may be externally provided to the characteristic control processing unit 20 or may be stored in the internal memory of the mobile unit control unit 21. Good.

If the SNR of the received light is larger than the threshold S Th- _NR-up for the upper limit of the SNR (SNR>Th _SNR-up ), the characteristic control processing unit 20 indicates that the beam divergence angle θ of the transmitted light is widened. The control signal cnt ₂ shown may be output to the optical antenna 5.
If the optical antenna 5 receives a control signal cnt ₂ indicating that the beam divergence angle θ of the transmission light is to be widened from the characteristic control processing unit 20, the transmission light having a wider beam divergence angle θ than the previously emitted transmission light. Is emitted into the water.
If the SNR of the received light is equal to or higher than the threshold Th _SNR and the SNR of the received light is equal to or lower than the upper threshold Th _SNR-up (Th _SNR ≤ SNR ≤ Th _SNR-up ), the characteristic control processing unit 20 The control signal cnt ₂ is not output to the optical antenna 5.

Further, if the SNR of the received light is larger than the upper threshold Th _{SNR-up of the SNR} (SNR>Th _SNR-up ), the characteristic control processing unit 20 indicates that the ratio of the error correction code in the modulated signal is reduced. The control signal cnt ₃ shown is output to the modulation signal generation unit 3.
If the modulation signal generation unit 3 receives the control signal cnt ₃ indicating that the ratio of the error correction code in the modulation signal is reduced from the characteristic control processing unit 20, the modulation signal generation unit 3 outputs the control signal cnt ₃ more than the error correction code included in the previously generated modulation signal. , Generates a modulated signal containing a small number of error correction codes.
If the SNR of the received light is equal to or higher than the threshold Th _SNR and the SNR of the received light is equal to or lower than the upper threshold Th _SNR-up (Th _SNR ≤ SNR ≤ Th _SNR-up ), the characteristic control processing unit 20 The control signal cnt ₃ is not output to the modulation signal generation unit 3.

In the optical communication device shown in FIG. 1, the characteristic control processing unit 20 fixes a threshold Th _SNR to be compared with the SNR of received light.
However, this is merely an example, and the characteristic control processing unit 20 may change the threshold Th _SNR according to the band B of the transmitted light, for example. Characteristic control processing unit 20, for example, than the threshold _{Th SNR} during lower bandwidth B of the transmitted light, to lower the threshold value _{Th SNR} when high bandwidth B of the transmitted light.

In the optical communication device shown in FIG. 1, if the communicable distance L _p is greater than or equal to the communication distance L, the mobile body control unit 21 does not control the mobile body equipped with its own optical communication device. ing.
However, this is merely an example, and if the distance L _{p at} which communication is possible is larger than the upper limit threshold Th _L-up (L<Th _L-up ) that is larger than the communication distance L, then (L _p >Th _{L). -Up} ), the mobile unit control unit 21 may control the mobile unit to move its own optical communication device away from the optical communication device of the communication partner.
If the communicable distance L _p is greater than or equal to the communication distance L and the communicable distance L _p is less than or equal to the upper limit threshold Th _L-up (L≦L _p ≦Th _L-up ), move The body control unit 21 does not control the moving body.

Embodiment 2.
In the optical communication device shown in FIG. 1, the moving body control unit 21 is given a request value for the communication distance L from the outside.
In the second embodiment, an optical communication device including a distance calculation unit 59 that calculates a distance L from its own optical communication device to an optical communication device of a communication partner and outputs the calculated distance L to the mobile unit control unit 21 will be described. To do.

FIG. 8 is a configuration diagram showing an optical communication device according to the second embodiment.
FIG. 9 is a hardware configuration diagram showing the hardware of the attenuation rate calculation unit 11, the demodulation unit 17, the characteristic control unit 18, the moving body control unit 21, and the distance calculation unit 59 in the optical communication device according to the second embodiment. ..
8 and 9, the same reference numerals as those in FIGS. 1 and 2 indicate the same or corresponding portions, and thus the description thereof will be omitted.

The acoustic communication unit 50 includes a position coordinate acquisition unit 51, a modulation signal generation unit 52, a sound source 53, a modulator 54, a sound emitting unit 55, and a sound signal receiving unit 56.
The position coordinate acquisition unit 51 is realized by, for example, a GPS receiver that receives a GPS signal transmitted from a GPS (Global Positioning System) satellite. The position coordinate acquisition unit 51 acquires the position coordinates of the moving body equipped with its own optical communication device, and outputs the position information indicating the position coordinates to the modulation signal generation unit 52 and the distance calculation unit 59.

The modulation signal generation unit 52 generates a modulation signal including the position information output from the position coordinate acquisition unit 51, and outputs the generated modulation signal to the modulator 54.
The sound source 53 is a device that generates sound, and outputs the generated sound to the modulator 54.
The modulator 54 generates a modulated sound by modulating the phase of the sound output from the sound source 53 according to the modulated signal output from the modulated signal generation unit 52, and outputs the generated modulated sound to the sound emitting unit 55. ..
The sound emitting unit 55 is realized by, for example, a speaker. The sound emitting unit 55 transmits the sound signal to the optical communication device of the communication partner by emitting the modulated sound output from the modulator 54 into the water as a sound signal.

The sound signal reception unit 56 includes a sound pickup unit 57 and a demodulation unit 58. The sound signal receiving unit 56 receives a sound signal transmitted from the optical communication device of the communication partner. The sound signal transmitted from the optical communication device of the communication partner includes position information indicating the position coordinates of the optical communication device of the communication partner.
The sound pickup unit 57 is realized by, for example, a microphone. The sound pickup unit 57 receives the sound signal transmitted from the optical communication device of the communication partner, and outputs the received sound signal to the demodulation unit 58.
The demodulation unit 58 demodulates the position information included in the sound signal output from the sound pickup unit 57, and outputs the demodulated position information to the distance calculation unit 59.

The distance calculation unit 59 is realized by the distance calculation circuit 36 shown in FIG. 9, for example. The distance calculation unit 59 uses the position coordinates indicated by the position information output from the position coordinate acquisition unit 51 and the position coordinates indicated by the position information output from the demodulation unit 58, from its own optical communication device to the optical communication of the communication partner. The distance L to the device is calculated. In addition, the distance calculation unit 59 uses the position coordinates indicated by the position information output from the position coordinate acquisition unit 51 and the position coordinates indicated by the position information output from the demodulation unit 58, from its own optical communication device to the communication partner. The direction α to the optical communication device is calculated. The distance calculation unit 59 outputs the calculated distance L to each of the characteristic control processing unit 20 and the moving body control unit 21, and outputs the calculated azimuth α to the moving body control unit 21.

In FIG. 8, each of the attenuation rate calculation unit 11, the demodulation unit 17, the table unit 19, the characteristic control processing unit 20, the moving body control unit 21, and the distance calculation unit 59, which are some of the constituent elements of the optical communication device, are illustrated. It is assumed that it is realized by dedicated hardware as shown in FIG. That is, it is assumed that a part of the optical communication device is realized by the attenuation rate calculation circuit 31, the demodulation circuit 32, the storage circuit 33, the characteristic control processing circuit 34, the moving body control circuit 35, and the distance calculation circuit 36. ..

Each of the attenuation rate calculation circuit 31, the demodulation circuit 32, the characteristic control processing circuit 34, the moving body control circuit 35, and the distance calculation circuit 36 is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, An ASIC, an FPGA, or a combination thereof is applicable.

Some components of the optical communication device are not limited to those realized by dedicated hardware. For example, any one or more of the attenuation rate calculation unit 11, the demodulation unit 17, the table unit 19, the characteristic control processing unit 20, the moving body control unit 21, or the distance calculation unit 59 may be software, firmware, or software and firmware. It may be realized by a combination of.
When a part of the optical communication device is realized by software or firmware, the table unit 19 is configured on the memory 41 of the computer shown in FIG. A program for causing a computer to execute the processing procedures of the attenuation rate calculation unit 11, the demodulation unit 17, the characteristic control processing unit 20, the moving body control unit 21, and the distance calculation unit 59 is stored in the memory 41 shown in FIG. Then, the processor 42 of the computer executes the program stored in the memory 41.

Next, the operation of the optical communication device shown in FIG. 8 will be described.
However, since the components other than the acoustic communication unit 50, the distance calculation unit 59, and the mobile body control unit 21 are the same as those of the optical communication device shown in FIG. 1, here, the acoustic communication unit 50, the distance calculation unit 59, and the mobile body control unit. Only the operation 21 will be described.

The position coordinate acquisition unit 51 acquires the position coordinates (x ₁ , y ₁ , z ₁ ) of the moving body equipped with its own optical communication device.
When the position coordinate acquisition unit 51 acquires the position coordinates (x ₁ , y ₁ , z ₁ ) of the moving body, the modulation signal generation unit 52 outputs position information indicating the acquired position coordinates (x ₁ , y ₁ , z ₁ ). And the distance calculation unit 59.
Upon receiving the position information from the position coordinate acquisition unit 51, the modulation signal generation unit 52 generates a modulation signal including the position information and outputs the generated modulation signal to the modulator 54.

The sound source 53 generates a sound and outputs the generated sound to the modulator 54.
The modulator 54 generates a modulated sound by modulating the phase of the sound output from the sound source 53 according to the modulated signal output from the modulated signal generation unit 52, and outputs the generated modulated sound to the sound emitting unit 55. ..
The sound emitting unit 55 transmits the sound signal to the optical communication device of the communication partner by emitting the modulated sound output from the modulator 54 into the water as a sound signal.

The optical communication device of the communication partner emits a sound signal including position information indicating position coordinates (x ₂ , y ₂ , z ₂ ) into the water, and includes, for example, a large amount of data or confidentiality data. The existing optical signal is emitted into the water.
The optical signal is suitable for transmitting a large amount of data, etc., but when the turbidity of water is large, the attenuation is large.
The sound signal is not suitable for transmitting a large amount of data or the like as compared with the optical signal. However, compared to optical signals, sound signals can be transmitted and received even when the turbidity of water is large and the attenuation is small, even if the distance between own optical communication device and the optical communication device of the communication partner is long. You can
The sound pickup unit 57 receives the sound signal transmitted from the optical communication device of the communication partner, and outputs the received sound signal to the demodulation unit 58.
Upon receiving the sound signal from the sound pickup unit 57, the demodulation unit 58 demodulates the position information included in the sound signal, and outputs the demodulated position information to the distance calculation unit 59.

The distance calculation unit 59 calculates the position coordinates (x ₁ , y ₁ , z ₁ ) indicated by the position information output from the position coordinate acquisition unit 51 and the position coordinates (x ₂ , indicated by the position information output from the demodulation unit 58. From y ₂ ,z ₂ ), the communication distance L, which is the distance from the own optical communication device to the communication partner optical communication device, is calculated as shown in the following equation (9).

In addition, the distance calculation unit 59 uses the position coordinates (x ₁ , y ₁ , z ₁ ) and the position coordinates (x ₂ , y ₂ , z ₂ ) to transmit from its own optical communication device to the communication partner optical communication device. The azimuth α is calculated. The calculation process of the azimuth α is a known technique, and thus detailed description thereof is omitted.
The distance calculation unit 59 outputs the calculated distance L to each of the characteristic control processing unit 20 and the moving body control unit 21, and outputs the calculated azimuth α to the moving body control unit 21.
In the moving body control unit 21, if the azimuth α from the own optical communication device to the communication partner optical communication device is an existing value, the distance calculation unit 59 needs to output the azimuth α to the moving body control unit 21. There is no.

Upon receiving the attenuation rate At from the attenuation rate calculation section 11, the mobile unit control section 21 determines whether the optical communication apparatus of its own and the optical communication apparatus of the communication partner are based on the attenuation rate At, as in the first embodiment. Then, a distance L _p at which communication is possible is obtained.
Upon receiving the communication distance L from the distance calculation unit 59, the mobile body control unit 21 compares the communication distance L _p with the communication distance L.
If the distance L _{p at} which communication is possible is shorter than the communication distance L, the mobile unit control unit 21 controls the mobile unit equipped with its own optical communication device, as in the first embodiment. The optical communication device of 1 is brought closer to the optical communication device of the communication partner.
However, since the moving body control unit 21 receives the azimuth α from the distance calculation unit 59, it controls the moving body so that the moving body moves in the direction α.
If the communicable distance L _p is equal to or longer than the communication distance L, the moving body control unit 21 does not control the moving body as in the first embodiment.

In the optical communication device shown in FIG. 8, if the communicable distance L _p is greater than or equal to the communication distance L, the mobile body control unit 21 does not control the mobile body equipped with its own optical communication device. ing.
However, this is only an example, and if the communicable distance L _p is larger than the upper limit threshold Th _L-up larger than the communication distance L (L _p >Th _L-up ), the mobile unit control unit. The control unit 21 may control the mobile unit to move its own optical communication device away from the communication partner optical communication device.
If the communicable distance L _p is greater than or equal to the communication distance L and the communicable distance L _p is less than or equal to the upper limit threshold Th _L-up (L≦L _p ≦Th _L-up ), move The body control unit 21 does not control the moving body.

In the above-described second embodiment, the sound signal receiving unit 56 that receives a sound signal including position information indicating the position of the communication partner optical communication device from the communication partner optical communication device, and the sound signal receiving unit 56 receive the sound signal. The mobile body control unit 21 can communicate with the distance calculation unit 59 that calculates the distance L from the own optical communication device to the communication partner optical communication device from the position information included in the sound signal. If the distance L _p is shorter than the distance L calculated by the distance calculation unit 59, the mobile body equipped with its own optical communication device is controlled so that its own optical communication device becomes the communication partner optical communication device. The optical communication device shown in FIG. Therefore, the optical communication device shown in FIG. 8 can control the SNR of the received light even if the distance L from the own optical communication device to the communication partner optical communication device changes, as in the first embodiment. it can.

Embodiment 3.
In the optical communication device shown in FIG. 8, the sound signal receiving unit 56 receives a sound signal including position information indicating the position of the communication partner optical communication device.
In the third embodiment, an optical communication device including a sound signal transmitting/receiving unit 61 that emits a sound signal into water and receives a reflected signal of the sound signal reflected by the optical communication device of the communication partner will be described.

FIG. 10 is a configuration diagram showing an optical communication device according to the third embodiment.
In FIG. 10, the same reference numerals as those in FIGS. 1 and 8 indicate the same or corresponding portions, and thus the description thereof will be omitted.
The sound signal transmitting/receiving unit 61 includes a sound source 53, a modulator 54, a sound emitting unit 55, and a sound collecting unit 57. The sound signal transmitting/receiving unit 61 emits the sound signal into the water and receives the reflection signal of the sound signal reflected by the optical communication device of the communication partner.
In the optical communication device shown in FIG. 10, the sound signal transmitting/receiving unit 61 needs only to be able to transmit/receive a sound signal. The sound signal transmitting/receiving unit 61 does not include the modulator 54, and the sound source 53 directly emits sound. You may make it output to the sound part 55.
On the other hand, when the sound signal transmitting/receiving unit 61 includes the modulator 54, the modulation signal generating unit 52 may be included in the sound signal transmitting/receiving unit 61.

The distance calculation unit 62 is realized by the distance calculation circuit 36 shown in FIG. 9, for example. The distance calculation unit 62 measures the time T from the output of the modulated sound from the modulator 54 to the sound emitting unit 55 until the sound pickup unit 57 receives the reflected signal of the sound signal. The distance calculation unit 62 calculates the distance L from the optical communication device of its own to the optical communication device of the communication partner from the measured time T, and the calculated distance L is calculated by the characteristic control processing unit 20 and the mobile unit control unit 21, respectively. Output to.

Next, the operation of the optical communication device shown in FIG. 10 will be described.
However, except for the sound signal transmitting/receiving unit 61 and the distance calculating unit 62, the operation is the same as that of the optical communication device shown in FIGS. 1 and 8, and therefore, only the operations of the sound signal transmitting/receiving unit 61 and the distance calculating unit 62 will be described here. ..
The modulator 54 generates a modulated sound by modulating the phase of the sound output from the sound source 53 according to the modulated signal output from the modulated signal generation unit 52, and the generated modulated sound is generated by the sound emitting unit 55 and the distance calculation. Output to each of the units 62.
The sound emitting unit 55 emits the modulated sound output from the modulator 54 into the water as a sound signal toward the optical communication device of the communication partner.

The sound signal emitted from the sound emitting unit 55 is reflected by the optical communication device of the communication partner, and the sound signal reflected by the optical communication device returns to its own optical communication device as a reflected signal.
The sound pickup unit 57 receives the sound signal reflected by the optical communication device as a reflection signal, and outputs the received reflection signal to the distance calculation unit 62.

The distance calculation unit 62 measures the time T from the output of the modulated sound from the modulator 54 to the sound emitting unit 55 until the sound pickup unit 57 receives the reflected signal of the sound signal. When the modulated sound is output from the modulator 54 to the sound emitting unit 55, the sound emitting unit 55 immediately outputs the modulated sound as a sound signal. The output time of the modulated sound by the modulator 54 and the sound emitting unit 55 The output time of the sound signal by 55 is almost the same time.
When the distance calculation unit 62 measures the time T, the distance calculation unit 62 calculates the distance L from the own optical communication device to the optical communication device of the communication partner from the measured time T, as shown in the following formula (10). The distance L is output to each of the characteristic control processing unit 20 and the moving body control unit 21.

In Expression (10), ε is the speed of sound.
Since the sound speed ε changes depending on the temperature in water, the distance calculation unit 62 may acquire the temperature in water and correct the sound speed ε according to the acquired temperature.
The distance calculation unit 62 may obtain the azimuth α from the optical communication device of its own to the optical communication device of the communication partner based on the direction in which the sound pickup unit 57 emits the sound signal. When calculating the azimuth α, the distance calculation unit 62 also outputs the azimuth α to the moving body control unit 21.
In the mobile unit control unit 21, if the azimuth α from the own optical communication device to the communication partner optical communication device is an existing value, the distance calculation unit 62 needs to output the azimuth α to the mobile unit control unit 21. There is no.

In the third embodiment described above, the sound signal transmitting/receiving unit 61 that emits a sound signal into the water from the optical communication device of the communication partner and receives the reflected signal of the sound signal reflected by the optical communication device of the communication partner, From the time from the sound signal transmitting/receiving unit 61 emitting the sound signal to the reception of the reflected signal by the sound signal transmitting/receiving unit 61, the distance L from the own optical communication device to the optical communication device of the communication partner is calculated. If the distance L _{p at} which the mobile body control unit 21 can communicate is shorter than the distance L calculated by the distance calculation unit 62, the mobile unit control unit 21 includes a distance calculation unit 62. The optical communication device shown in FIG. 10 is configured so that the user's body is controlled to bring its own optical communication device closer to the communication partner optical communication device. Therefore, the optical communication device shown in FIG. 10 can control the SNR of the received light even if the distance L from the own optical communication device to the communication partner optical communication device changes, as in the first embodiment. it can.

Fourth Embodiment
The optical communication device shown in FIG. 1 includes an optical antenna 7 and an optical antenna 13 as an optical antenna of a receiving system.
In the fourth embodiment, an optical communication device including only an optical antenna 71 as an optical antenna of a receiving system will be described.

FIG. 11 is a configuration diagram showing an optical communication device according to the fourth embodiment. In FIG. 11, the same reference numerals as those in FIG.
The optical antenna 71 also serves as the optical antenna 7 included in the transmission light monitor unit 6 illustrated in FIG. 1 and the optical antenna 13 included in the optical signal receiving unit 12 illustrated in FIG. The optical antenna 71 receives the transmitted light emitted into the water from the optical transmitter 1 as monitor light, and outputs the received monitor light to the wavelength demultiplexer 72 via an optical fiber. Further, the optical antenna 71 receives an optical signal emitted into the water from the optical communication device of the communication partner as received light, and outputs the received received light to the wavelength demultiplexing unit 72 via the optical fiber.

The wavelength separation section 72 is connected to the optical antenna 71 via an optical fiber, and is connected to the photodetector 8 via an optical fiber. The wavelength separation unit 72 is also connected to the photodetector 14 via an optical fiber. The wavelength demultiplexing unit 72 outputs the monitor light output from the optical antenna 71 to the photodetector 8 via the optical fiber, and the received light output from the optical antenna 71 via the optical fiber to the photodetector. It outputs to 14.
In the optical communication device shown in FIG. 11, the wavelength of the monitor light output from the optical antenna 71 and the wavelength of the received light output from the optical antenna 71 are different from each other.

Next, the operation of the optical communication device shown in FIG. 11 will be described.
However, except for the optical antenna 71 and the wavelength demultiplexing unit 72, the optical communication device is the same as the optical communication device shown in FIG.
When the transmission light is emitted into the water from the optical transmission unit 1, the optical antenna 71 receives the transmission light as monitor light, and outputs the received monitor light to the wavelength separation unit 72 via the optical fiber.
Further, the optical antenna 71 receives an optical signal as received light when the optical signal is emitted into the water from the optical communication device of the communication partner, and receives the received light to the wavelength demultiplexing unit 72 via the optical fiber. Output.

The wavelength separation unit 72 wavelength-separates the monitor light output from the optical antenna 71 and the received light output from the optical antenna 71.
The wavelength demultiplexing unit 72 outputs the monitor light after wavelength separation to the photodetector 8 via the optical fiber, and outputs the received light after wavelength separation to the photodetector 14 via the optical fiber. To do.
The optical communication device shown in FIG. 11 can reduce the number of optical antennas in the receiving system more than the optical communication device shown in FIG.

It should be noted that, within the scope of the invention, the invention of the present application is capable of freely combining the respective embodiments, modifying any constituent element of each embodiment, or omitting any constituent element in each embodiment. ..

The present invention is suitable for an optical communication device and an optical communication method for controlling the characteristics of transmitted light that affect the increase/decrease in signal-to-noise ratio.

1 optical transmitter, 2 reference light source, 3 modulated signal generator, 4 modulator, 5 optical antenna, 6 transmitted light monitor, 7 optical antenna, 8 optical detector, 9 IV converter, 10 ADC, 11 attenuation rate calculation Section, 12 optical signal receiving section, 13 optical antenna, 14 photodetector, 15 IV converter, 16 ADC, 17 demodulation section, 18 characteristic control section, 19 table section, 20 characteristic control processing section, 21 moving body control section, 31 attenuation rate calculation circuit, 32 demodulation circuit, 33 storage circuit, 34 characteristic control processing circuit, 35 moving body control circuit, 36 distance calculation circuit, 41 memory, 42 processor, 50 acoustic communication unit, 51 position coordinate acquisition unit, 52 modulation Signal generation unit, 53 sound source, 54 modulator, 55 sound emission unit, 56 sound signal reception unit, 57 sound pickup unit, 58 demodulation unit, 59 distance calculation unit, 61 sound signal transmission/reception unit, 62 distance calculation unit, 71 optical antenna , 72 Wavelength separation unit.

Claims (13)

1. An optical transmitter that emits transmitted light into the water,
   A transmission light monitor unit that receives the transmission light emitted into the water from the light transmission unit as monitor light,
   An attenuation rate calculation unit that calculates an attenuation rate of the light amount of the monitor light received by the transmission light monitor unit with respect to the light amount of the transmission light emitted into the water from the light transmission unit,
   From the attenuation rate calculated by the attenuation rate calculation unit, the signal-to-noise ratio of the received light when the optical signal emitted into the water from the optical communication device of the communication partner is received as the received light is estimated, and the signal pair An optical communication device, comprising: a characteristic control unit that controls a characteristic of the transmitted light that affects an increase or decrease in the signal-to-noise ratio based on a noise ratio.
2. The optical communication device according to claim 1, wherein the characteristic control unit controls the characteristic of the transmitted light so that the signal-to-noise ratio becomes equal to or higher than a threshold value.
3. The optical transmitter generates modulated light according to a modulation signal, and emits the modulated light as transmission light into water,
   The optical communication device according to claim 1, wherein the characteristic control unit controls a modulation speed of the modulated light as a characteristic of the transmission light based on the signal-to-noise ratio.
4. The light according to claim 1, wherein the characteristic control unit controls a beam divergence angle of the transmission light emitted from the optical transmission unit as a characteristic of the transmission light based on the signal-to-noise ratio. Communication device.
5. The optical transmitter generates modulated light according to a modulation signal, and emits the modulated light as transmission light into water,
   The optical communication device according to claim 1, wherein the characteristic control unit controls an error correction code included in the modulated signal as a characteristic of the transmission light based on the signal-to-noise ratio.
6. Based on the attenuation rate calculated by the attenuation rate calculation unit, the distance at which communication is possible between the own optical communication apparatus and the optical communication apparatus of the communication partner is obtained, and the communication possible distance is the If it is shorter than the distance from the optical communication device of the communication partner to the optical communication device of the communication partner, the mobile body equipped with the optical communication device of its own is controlled, and the optical communication device of the own is set to the optical communication device of the communication partner. The optical communication device according to claim 1, further comprising a mobile unit control unit that is close to the communication device.
7. From the optical communication device of the communication partner, a sound signal receiving unit that receives a sound signal including position information indicating the position of the optical communication device of the communication partner,
   From the position information included in the sound signal received by the sound signal receiving unit, a distance calculating unit that calculates the distance from the optical communication device of its own to the optical communication device of the communication partner,
   Based on the attenuation rate calculated by the attenuation rate calculation unit, the distance at which communication is possible between the own optical communication apparatus and the optical communication apparatus of the communication partner is obtained, and the distance at which the communication is possible is the If the distance is shorter than the distance calculated by the distance calculation unit, the moving body control that controls the moving body equipped with the own optical communication device to bring the own optical communication device closer to the optical communication device of the communication partner. The optical communication device according to claim 1, further comprising:
8. A sound signal transmitting/receiving unit that emits a sound signal into water and receives a reflection signal of the sound signal reflected by the optical communication device of the communication partner,
   From the time from the sound signal transmitting/receiving unit emitting the sound signal to the reception of the reflected signal by the sound signal transmitting/receiving unit, the distance from the own optical communication device to the optical communication device of the communication partner is calculated. A distance calculation unit,
   Based on the attenuation rate calculated by the attenuation rate calculation unit, the distance at which communication is possible between the own optical communication apparatus and the optical communication apparatus of the communication partner is obtained, and the distance at which the communication is possible is the If the distance is shorter than the distance calculated by the distance calculation unit, the moving body control that controls the moving body equipped with the own optical communication device to bring the own optical communication device closer to the optical communication device of the communication partner. The optical communication device according to claim 1, further comprising:
9. The optical communication device according to claim 1, wherein the optical transmitter generates modulated light by modulating the phase of continuous wave light according to a modulation signal, and emits the modulated light into water as transmission light.
10. The optical communication device according to claim 1, wherein the optical transmission unit generates modulated light by modulating the intensity of continuous wave light according to a modulation signal and emits the modulated light as transmission light into water.
11. When an optical signal including communication data is emitted into the water from the optical communication device of the communication partner, an optical signal receiving unit that receives the optical signal emitted into the water,
    The optical communication device according to claim 1, further comprising a demodulation unit that demodulates communication data included in the optical signal received by the optical signal receiving unit.
12. One optical antenna serves both as an optical antenna included in the transmitted light monitor section and an optical antenna included in the optical signal receiving section,
    The optical communication device according to claim 11, wherein the one optical antenna receives each of the transmitted light and the optical signal.
13. The optical transmitter emits the transmitted light into the water,
    The transmitted light monitor unit receives the transmitted light emitted into the water from the optical transmitter as monitor light,
    The attenuation rate calculation unit calculates the attenuation rate of the light amount of the monitor light received by the transmission light monitor unit with respect to the light amount of the transmission light emitted into the water from the optical transmission unit,
    The characteristic control section estimates the signal-to-noise ratio of the received light when the optical signal emitted into the water from the optical communication device of the communication partner is received as the received light from the attenuation rate calculated by the attenuation rate calculation section. And an optical communication method for controlling the characteristics of the transmitted light that influences the increase or decrease of the signal-to-noise ratio based on the signal-to-noise ratio.

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