JPWO2020144858A1 - Optical communication device and optical communication method - Google Patents

Abstract

An optical transmitter (1) that emits transmitted light into water, a transmitted light monitor (6) that receives transmitted light emitted into water from the optical transmitter (1) as monitor light, and an optical transmitter (1). Calculated by the attenuation rate calculation unit (11) and the attenuation rate calculation unit (11) that calculate 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 water. 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 from the attenuated rate, and the signal-to-noise ratio is estimated based on the signal-to-noise ratio. The optical communication device is configured to include a characteristic control unit (18) that controls the characteristics of the transmitted light that affects the increase / decrease of the ratio.

Description

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 of the signal-to-noise ratio.

In the following Patent Document 1, the optical reception band control unit transmits an optical wireless section band change request to a communication partner optical wireless transmission device according to the signal level of the received signal detected by the signal level detection unit. The device is disclosed.
Further, the optical wireless transmission device disclosed in Patent Document 1 receives a band change request transmitted from the optical wireless transmission device of the communication partner, and generates a modulation clock generated by the clock generator according to the received band change request. I'm in control.

Japanese Unexamined Patent Publication No. 2003-218802

The optical wireless transmission device disclosed in Patent Document 1 is in a state where communication cannot be established with the optical wireless transmission device of the communication partner due to the poor environment of the optical wireless section. It is not possible to send and receive band change requests for the optical radio section to and from the wireless transmission device. When the optical wireless transmission device disclosed in Patent Document 1 cannot send and receive a band change request, it cannot change the band according to the signal level of the received signal.
Therefore, the optical radio 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 signal. It was.

The present invention has been made to solve the above problems, and even in a state where 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. It is an object of the present invention to obtain an optical communication device and an optical communication method capable of controlling the SNR of the received light when the signal is received as the received light.

The optical communication device according to the present invention includes an optical transmission unit that emits transmitted light into water, a transmission light monitor unit that receives transmission light emitted from the optical transmission unit into water as monitor light, and an optical transmission unit into water. An optical communication device of a communication partner from the attenuation rate calculation unit that 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 transmitted light emitted and the attenuation rate calculated by the attenuation rate calculation unit. Estimates the signal-to-noise ratio of the received light when the light signal emitted into the water is received as the received light, and controls 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. It is provided with a characteristic control unit.

According to the present invention, the signal pair of the received light when the characteristic control unit receives the optical signal emitted into the water from the optical communication device of the communication partner as the received light from the attenuation rate calculated by the attenuation rate calculation unit. The optical communication device was configured to estimate the signal-to-noise ratio 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. Therefore, the optical communication device according to the present invention receives an optical signal emitted into water from the communication partner's optical communication device as received light even when communication with the communication partner's optical communication device has not been established. The signal-to-noise ratio of the received light can be controlled.

It is a block diagram which shows the optical communication apparatus which concerns on Embodiment 1. FIG. It is a hardware configuration diagram which shows the hardware of the attenuation factor calculation unit 11, the demodulation unit 17, the table unit 19, the characteristic control processing unit 20, and the mobile body control unit 21 in the optical communication apparatus which concerns on Embodiment 1. FIG. It is a hardware block diagram of a computer when a part of an optical communication device is realized by software, firmware, etc. It is a flowchart which shows the optical communication method which is the processing procedure of an optical communication apparatus. It is explanatory drawing which shows the relationship between the turbidity in water and the attenuation rate At. Correspondence between the band B of the transmitted light, the attenuation factor At, the communication distance L between the optical communication device of its own and the optical communication device of the communication partner, and the SNR of the received light received by the optical signal receiving unit 12. It is explanatory drawing which shows. It is a flowchart which shows the processing procedure of the moving body control unit 21. It is a block diagram which shows the optical communication apparatus which concerns on Embodiment 2. It is a hardware configuration diagram which shows the hardware of the attenuation factor calculation unit 11, the demodulation unit 17, the characteristic control unit 18, the mobile body control unit 21, and the distance calculation unit 59 in the optical communication apparatus which concerns on Embodiment 2. FIG. It is a block diagram which shows the optical communication apparatus which concerns on Embodiment 3. It is a block diagram which shows the optical communication apparatus which concerns on Embodiment 4.

Hereinafter, in order to explain the present invention in more detail, a mode 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 the hardware of the attenuation factor calculation unit 11, the demodulation unit 17, the table unit 19, the characteristic control processing unit 20, and the mobile control unit 21 in the optical communication device according to the first embodiment. ..
In FIGS. 1 and 2, the optical transmission unit 1 includes a reference light source 2, a modulation signal generation unit 3, a modulator 4, and an optical antenna 5.
The optical transmission unit 1 emits the transmitted light into the water to transmit the transmitted light to each of the transmission light monitor unit 6 and the optical communication device of the communication partner.
The reference light source 2 outputs continuously oscillating light (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 modulation signal generation unit 3 changes the error correction code included in the modulation 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 modulated signal output from the modulated signal generation unit 3, and the generated modulated light is transmitted via an optical fiber. And output to the optical antenna 5. When the modulator 4 generates 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 only an example, and the modulator 4 may modulate the intensity of the CW light output from the reference light source 2, and further, the output of the reference light source 2 is directly modulated by an electric signal. May be.

The optical antenna 5 is realized, for example, by an optical telescope including 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. When the transmitted light is emitted into the water, the optical antenna 5 adjusts the beam spread angle of the transmitted light according to the control signal output from the characteristic control processing unit 20.

The transmission optical 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 light transmission unit 1 as monitor light.
The optical antenna 7 is realized, for example, by an optical telescope including a lens. The optical antenna 7 receives the transmitted light emitted into the water from the optical transmission unit 1 as monitor light, and outputs the received monitor light to the photodetector 8 via an 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 to a digital signal, and outputs the digital signal to the attenuation factor calculation unit 11.

The attenuation factor calculation unit 11 is realized by, for example, the attenuation factor 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 light 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 light of the monitor light received by the transmission 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 amount of transmitted light emitted from the optical transmission unit 1 into the water is stored in the internal memory of the attenuation factor calculation unit 11 as an existing value. However, this is only an example, and the measured value of the amount of transmitted light emitted from the optical antenna 5 may be given to the attenuation factor calculation unit 11 from the outside.

The optical signal receiving unit 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 a communication partner's optical communication device, the optical signal receiving unit 12 receives the optical signal emitted into the water as received light.
The optical antenna 13 is realized, for example, by an optical telescope including a lens. The optical antenna 13 receives an optical signal emitted into water from an optical communication device of a communication partner as received light, and outputs the received received light to a photodetector 14 via an 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 to 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 receiving 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 from the attenuation rate calculated by the attenuation rate calculating unit 11. Signal-to-noise ratio (SNR: Signal-to-Noise Radio) is estimated.
The characteristic control unit 18 controls the characteristics of the transmitted light that affect the increase / decrease of the SNR based on the SNR.
The table unit 19 is realized by, for example, a storage circuit 33. The table unit 19 stores the correspondence between the band of the transmitted light, the attenuation factor, 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 obtains the SNR of the received light from the required values of the attenuation rate, the band of the transmitted light, and the communication distance calculated by the attenuation factor calculation unit 11. 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 optical communication device of the user and the optical communication device of the communication partner. 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 characteristic control processing unit 20.
The characteristic control processing unit 20 compares the estimated SNR of the received light with the threshold value of the SNR. The threshold value of SNR 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 indicating that the modulation speed is lowered so that the SNR of the received light becomes large.
Alternatively, the characteristic control processing unit 20 sends a control signal indicating that the beam spread angle of the transmitted light is narrowed so that the SNR of the received light becomes large if the estimated SNR of the received light is smaller than the threshold value. Output to.
Alternatively, the characteristic control processing unit 20 outputs a control signal indicating 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 value to the modulated signal generation unit 3.

The mobile control unit 21 is realized by, for example, the mobile control circuit 35. The moving body control unit 21 obtains a distance at which communication is possible between its own optical communication device and the communication partner's optical communication device 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 a mobile body (not shown) equipped with its own optical communication device to control its own optical communication device. Try to get closer to the optical communication device of the communication partner. 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 control unit 21.
The moving body may be any one that can move underwater with the optical communication device mounted, and corresponds to a submarine, an underwater drone, or the like.

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

Here, the storage circuit 33 is, for example, a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable Read Online Memory), an EPROM (Electrically Memory), etc. A volatile semiconductor memory, a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, or a DVD (Digital Versaille Disc) is applicable.
Further, each of the attenuation factor calculation circuit 31, demodulation circuit 32, characteristic control processing circuit 34, and mobile control circuit 35 is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, or an ASIC (Application). Special Integrated Circuit), FPGA (Field-Programmable Gate Array), 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 factor calculation unit 11, the demodulation unit 17, the table unit 19, the characteristic control processing unit 20, or the mobile control unit 21 is realized by software, firmware, or a combination of software and firmware. It may be one.
The software or firmware is stored as a program in the memory of the computer. A computer means hardware for executing a program, and corresponds to, for example, a CPU (Central Processing Unit), a central processing unit, a processing unit, a computing device, 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, firmware, or the like.
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 the computer to execute the processing procedures of the attenuation factor calculation unit 11, the demodulation unit 17, the characteristic control processing unit 20, and the mobile 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.

Further, FIG. 2 shows an example in which each of a part of the components of the optical communication device is realized by dedicated hardware, and FIG. 3 shows an example in which a part of the optical communication device is realized by software, firmware, or the like. Is shown. However, this is only an example, and some components in the optical communication device may be realized by dedicated hardware, and the remaining components may be realized by software, firmware, or the like.

Next, the operation of the optical communication device shown in FIG. 1 will be described.
As items related to the characteristics of the transmitted light that affect the increase / decrease of the SNR of the received light received by the optical signal receiving unit 12, 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 spreading angle θ and the error correction code included in the modulated signal generated by the modulated signal generation unit 3 can be considered.
In the optical communication device shown in FIG. 1, the characteristic control unit 18 controls at least one or more of the modulation speed V of the modulated light, the beam spread angle θ of the transmitted light, and the error correction code as the characteristics of the transmitted light.
Here, for convenience of explanation, it is assumed that the distance L _{p at} which communication is possible is equal to or greater than the required value of the communication distance L. The communicable distance L _p is the longest distance between the optical communication device of oneself 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 greater than the required value of the communication distance L, the desired SNR is not always obtained, so the characteristic control unit 18 controls the characteristics of the transmitted light.

The reference light source 2 outputs 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 generates modulated light by modulating the phase of the CW light output from the reference light source 2 according to the modulated signal output from the modulated signal generation unit 3. The modulator 4 outputs the generated modulated light to the optical antenna 5 via an optical fiber.
When the optical antenna 5 receives 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 transmitting unit 1 as monitor light (step ST1 in FIG. 4). The optical antenna 7 outputs the received monitor light to the photodetector 8 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 to a digital signal D, and outputs the digital signal D to the attenuation factor calculation unit 11.

When the attenuation factor calculation unit 11 receives the digital signal D from the ADC 10, the attenuation factor calculation unit 11 calculates the light amount _Pr ⁰ of the monitor light received by the transmission light monitor unit 6 from the digital signal D as shown in the following equation (1). ..
_Pr ⁰ = c ₁ × D (1)
In equation (1), c ₁ is a constant of proportionality.
When the attenuation rate calculation unit 11 calculates the light amount _Pr ⁰ of the monitor light, as shown in the following equation (2), the light amount of the monitor light with respect to _{the light amount P t} ^{0 of the transmitted light emitted from the optical antenna 5 into the water.} _{The attenuation rate At of Pr} ⁰ is calculated (step ST2 in FIG. 4).

式（３）において、Ｌは、通信距離の要求値である。通信距離Ｌの要求値は、外部から減衰率算出部１１に与えられるものであってもよいし、減衰率算出部１１の内部メモリに格納されているものであってもよい。図１に示す光通信装置では、通信距離Ｌの要求値が、外部から減衰率算出部１１に与えられる旨の記載を省略している。Here, the damping factor calculation unit 11 calculates the damping factor At according to the equation (2). However, this is only an example, and the attenuation factor calculation unit 11 sets the attenuation rate At as, for example, the attenuation amount of the amount _{of light Pr} ^{0 per distance of 1 [m] as shown in the following equation (3).} It may be calculated.

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

The attenuation rate calculation unit 11 outputs the calculated attenuation rate At to each of the characteristic control processing unit 20 and the moving body control unit 21.
Assuming that the distance between the optical communication device of oneself and the optical communication device of the communication partner is constant, the attenuation factor 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 factor At increases as the turbidity of water increases, and the amount of light _Pr 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 between the transmission light band B, the attenuation factor At, the communication distance L, and the SNR of the received light.
FIG. 6 is an explanatory diagram showing the correspondence between the band B of the transmitted light, the attenuation factor 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 Pr} ^{0 per distance of 1 [m] is described.}

When the characteristic control processing unit 20 receives the attenuation rate At from the attenuation rate calculation unit 11, the characteristic control processing unit 20 refers to the correspondence relationship shown in FIG. 6 stored in the table unit 19, and the attenuation rate calculated by the attenuation rate calculation unit 11. The SNR of the received light received by the optical signal receiving unit 12 is estimated from the required values of At, the band B of the transmitted light, and the communication distance L (step ST3 in FIG. 4).
In the characteristic control processing unit 20, for example, the transmission light band B is 500 [MHz], _{the attenuation amount of the light amount Pr} ⁰ per distance of 1 [m] is 5 [dB / m], and the required value of the communication distance L is set. If it is 15 [m], it is estimated that the SNR of the received light is 10 [dB].
In the characteristic control processing unit 20, for example, the transmission light band B is 50 [MHz], _{the attenuation amount of the light amount Pr} ⁰ per distance of 1 [m] is 2 [dB / m], and the required value of the communication distance L is set. 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 threshold value Th _{SNR of the SNR} (step ST4 in FIG. 4). The threshold value of SNR, Th _SNR, is a value larger than 0 [dB].
If the estimated SNR of the received light _{is smaller than the threshold value Th SNR} (in the case of 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 indicated control signal ct ₁ is output to the modulator 4 (step ST5 in FIG. 4).
If the estimated SNR of the received light _{is equal to or higher than the threshold value Th SNR} (step ST4 in FIG. 4: NO), the _{characteristic control processing unit 20 sends a control signal ct 1} indicating that the modulation speed V is lowered 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 modulated signal output from the modulated signal generation unit 3.
_{When the modulator 4 generates the modulated light, if it receives the control signal ct 1} indicating that the modulation speed V is lowered from the characteristic control processing unit 20 (in the case of step ST6: YES in FIG. 4), the modulator 4 is generated last time. A 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 ct 1} indicating that the modulation speed V is to be lowered from the characteristic control processing unit 20 (step ST6: NO in FIG. 4), the previously generated modulation 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 an optical fiber.
When the optical antenna 5 receives 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 a characteristic of the transmitted light that affects the increase / decrease of the SNR. The characteristic control processing unit 20 may control the beam spread angle θ of the transmitted light as a characteristic of the transmitted light that affects the increase / decrease of the SNR.
When the characteristic control processing unit 20 controls the beam spreading angle θ of the transmitted light, if the estimated SNR of the received light _{is smaller than the threshold Th SNR} , the beam spreading angle of the transmitted light is increased so that the SNR of the received light becomes large. _{A control signal ct 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 higher than the threshold value Th SNR , the characteristic control processing unit 20 does not output the control signal ct 2} indicating that the beam spreading angle θ of the transmitted light is narrowed to the optical antenna 5.

_{If the optical antenna 5 receives the control signal ct 2} indicating that the beam spreading angle θ of the transmitted light is narrowed from the characteristic control processing unit 20, the transmitted light having a narrower beam spreading angle θ than the transmitted light emitted last time. Is emitted into the water.
_{If the optical antenna 5 does not receive the control signal ct 2} indicating that the beam spreading angle θ of the transmitted light is narrowed from the characteristic control processing unit 20, the transmitted light having the same beam spreading angle θ as the previously emitted transmitted light is underwater. It emits to.
The optical antenna 5 includes an optical fiber that emits transmitted light and a lens for adjusting the beam spread angle θ of the transmitted light emitted from the optical fiber, and the output end of the transmitted light and the lens. By changing the distance between them, the beam spread angle θ of the transmitted light can be adjusted.

In the flowchart shown in FIG. 4, the characteristic control processing unit 20 controls the modulation speed V of the modulated light as a characteristic of the transmitted light that affects the increase / decrease of the SNR. The characteristic control processing unit 20 may control the error correction code included in the modulated signal as a characteristic of the transmitted light that affects the increase / decrease of the SNR.
When the characteristic control processing unit 20 controls the error correction code to be included in the modulated signal, if the estimated SNR of the received light _{is smaller than the threshold Th SNR} , for example, the control indicating that the ratio of the error correction code in the modulated signal is increased. The signal ct 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 ct 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 a 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 generates the modulation signal, if the characteristic control processing unit 20 receives the control signal ct 3} indicating that the ratio of the error correction code in the modulation signal is increased, the modulation signal generation unit 3 includes the previously generated modulation signal. Generates a modulated signal containing more error-correcting codes than the error-correcting codes. When the modulation signal generation unit 3 uses, for example, a parity bit as an error correction code, the proportion of the error correction code in the modulation signal can be increased by increasing the number of bits of the parity bit.
The modulation signal generation unit 3 is the same as the error correction code included in the previously generated modulation signal unless the _{control signal ct 3} indicating that the ratio of the error correction code in the modulation signal is increased is received from the characteristic control processing unit 20. 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 a control signal ct 3} indicating that the ratio of the error correction code in the modulated signal is increased to the modulated signal generation unit 3. doing. However, this is only an example, and the characteristic control processing unit 20 outputs a control signal ct ₃ indicating that an error correction code having a higher error correction capability than the previous time is included in the modulation signal to the modulation signal generation unit 3. You may.
_{If the modulation signal generation unit 3 receives from the characteristic control processing unit 20 a control signal ct 3} indicating that an error correction code having a higher error correction capability than the previous time is included in the modulation signal, the modulation signal generation unit 3 includes the modulation signal generated last time. Generates a modulated signal containing an error correction code having a higher error correction capability than the error correction code.

In the optical communication device shown in FIG. 1, the characteristic control processing unit 20 includes the modulation speed V of the modulated light, the beam spread angle θ of the transmitted light, or an error included in the modulated signal as the characteristics of the transmitted light that affect the increase / decrease of the SNR. The correction code is controlled.
The characteristic control processing unit 20 controls an increase / decrease in SNR by controlling one or more of the modulation speed V of the modulated light, the beam spreading angle θ of the transmitted light, and the error correction code included in the modulated signal. Can be done.
Which of the modulation speed V of the modulated light, the beam spreading angle θ of the transmitted light, and the error correction code included in the modulated signal is controlled may be set in the characteristic control processing unit 20, or the characteristic control may be performed from the outside. It may be instructed by the processing unit 20.

式（４）〜（８）において、ｃ_３，ｃ_４は、比例定数、Ｐ_ｒ ^Ｅは、受信光の受信電力、Ｐ_ｓｈｏｔ ^Ｅは、受信光の雑音電力である。
また、Ｓ_ｄｅｔは、光検出器８の感度、Ｒ_Ｌは、光検出器８に内蔵されているアンプの抵抗値、ｅは、電子の電荷量、Ａｒｅは、光アンテナ７が備えるレンズの表面積である。
なお、光検出器８は、アンプを内蔵しており、例えば、アンプが、光アンテナ７から出力されたモニタ光を増幅し、増幅後のモニタ光を電流信号に変換する。The relationship between the SNR of the received light, the modulation speed V of the modulated light, and the beam spreading angle θ of the transmitted light is as follows. When the modulation speed V or the beam spreading angle θ changes, the SNR of the received light changes. You can see that it changes.

In the formula _{(4) ~ (8),} c 3, c 4 are proportional _{constants, P} ^{r E} is the received power of the received _{optical, P shot} ^E is the noise power of the received light.
Further, S _det is the sensitivity of the photodetector 8, _RL is the resistance value of the amplifier built in the photodetector 8, e is the amount of charge 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 distance L _{p at} which communication is possible is equal to or greater than the required value of the communication distance L.
However, in reality, the distance L _{p at} which communication is possible 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 communicate the optical signal.
The mobile control unit 21 is equipped with its own optical communication device in order to enable communication of optical signals when the communication _{range L p is shorter than the required value of the communication distance L.} By controlling a mobile body (not shown), one's own optical communication device is brought closer to the optical communication device of the communication partner.

FIG. 7 is a flowchart showing a processing procedure of the mobile control unit 21.
Hereinafter, the operation of the moving body control unit 21 will be described with reference to FIG. 7.
Mobile Control unit 21 receives the attenuation factor At the attenuation rate calculating unit 11, based on the attenuation factor At, distance communication is possible between the optical communication device of the communication partner with its own optical communication device L _p (Step ST21 in FIG. 7).
Mobile Control unit 21 is, for example, by referring to the correspondence relationship shown in FIG. 6, it is possible to obtain a distance L _p communication is possible between the optical communication apparatus and communication own optical communication apparatus partner.

Specifically, in the mobile control unit 21, for example, the band B of the transmitted light is 500 [MHz], and _{the attenuation amount of the light amount Pr} ⁰ per distance of 1 [m] is 5 [dB / m]. If so, it is specified that the communicationable distance L _p is 16 [m].
For example, if the band B of the transmitted light is 500 [MHz] and _{the attenuation amount of the light amount Pr} ⁰ per distance of 1 [m] is 2 [dB / m], the mobile body control unit 21 can communicate. It is specified that the possible distance L _p is 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 communication distance L p} is shorter than the communication distance L (in the case of step ST22: YES in FIG. 7), the mobile body control unit 21 is equipped with its own optical communication device and is not shown. 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, in the mobile control unit 21, the direction α from the optical communication device of its own to the optical communication device of the communication partner is an existing value.
When one's own optical communication device approaches the optical communication device of the communication partner and the communication distance L _p becomes equal to or more than the communication distance L, the own optical communication device and the communication partner's optical communication device become optical. Signal communication can be carried out.
_{If the communication distance L p} is equal to or greater than the communication distance L (step ST22: NO in FIG. 7), the mobile body control unit 21 is equipped with its own optical communication device and is not shown. Does not control.

Here, the mobile control unit 21 brings its own optical communication device closer to the optical communication device of the communication partner so that the communication distance L _p can be set to the communication distance L or more and the optical signal can be communicated. I have to. However, this is only an example, and the mobile control unit 21 can perform optical signal communication by, for example, changing the band B of the transmitted light so that the communicable distance L _{p is set} to the communication distance L or more. You may do so.
For example, when the band B of the transmitted light is 500 [MHz] and _{the attenuation amount of the light amount Pr} ⁰ per distance of 1 [m] is 5 [dB / m], the moving body control unit 21 sends the transmitted light. When the band B of is changed to 50 [MHz], the communicationable distance _Lp 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 Pr} ⁰ per distance of 1 [m] is 2 [dB / m], the moving body control unit 21 sends the transmitted light. When the band B of is changed to 50 [MHz], the communicationable distance _Lp is extended from 40 [m] to 43 [m].
If the communicable distance L _p is extended, the communicable distance L _p may be greater than or equal to the communication distance L.

When the communication distance L _p becomes the communication distance L or more, the transmission optical monitor unit 6, the attenuation factor calculation unit 11, the characteristic control unit 18, and the optical transmission unit 1 repeat the processes shown in steps ST1 to ST9 of FIG. carry out.

When the communication partner's optical communication device emits an optical signal into the water when the communication _{distance L p} is equal to or greater than the communication distance L, the optical antenna 13 receives the optical signal emitted from the communication partner's optical communication device. Receive as light. The optical antenna 13 outputs the received received light to the photodetector 14 via an optical fiber.
When the photodetector 14 receives 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 known from the optical communication device of the communication partner, the characteristic control processing unit 20 sets the band parameter indicating the band of the optical signal to the IV converter 15. Output.
When the band of the optical signal radiated 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 in 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 to a digital signal and outputs the digital signal to the demodulation unit 17.
When the demodulation unit 17 receives a digital signal from the optical signal reception unit 12, the demodulation unit 17 demodulates the communication data included in the optical signal received by the optical antenna 13 from the digital signal.

In the above-described first embodiment, the characteristic control unit 18 receives an optical signal emitted into water from the optical communication device of the communication partner from the attenuation rate calculated by the attenuation rate calculation unit 11 as received light. The optical communication device shown in FIG. 1 was configured so as to estimate the SNR of light and control the characteristics of transmitted light that affect the increase / decrease of SNR based on the SNR. Therefore, the optical communication device shown in FIG. 1 receives an optical signal emitted into water from the communication partner's optical communication device as received light even when communication with the communication partner's optical communication device has not been established. The SNR of the received light can be controlled.

In the optical communication device shown in FIG. 1, if the SNR of the received light is _{equal to or higher than the threshold value Th SNR , the characteristic control processing unit 20 does not output the control signal ct 1} indicating that the modulation speed V is lowered to the modulator 4. ing. Alternatively, if the SNR of the received light _{is equal to or higher than the threshold value Th SNR , the characteristic control processing unit 20 does not output the control signal ct 2} indicating that the beam spreading angle θ of the transmitted light is narrowed to the optical antenna 5. .. 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 ct 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 a control signal ct 1} indicating that the modulation speed V is increased to the modulator 4.
_{If the modulator 4 receives the control signal ct 1} indicating that the modulation speed V is increased from the characteristic control processing unit 20, the modulator 4 generates the modulation light having a modulation speed V higher than that of the modulation light generated last time.
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 threshold Th SNR-up for the upper limit (Th SNR} ≤ SNR ≤ Th _SNR-up ), the characteristic control processing unit 20 The control signal ct ₁ is not output to the modulator 4.
_{The threshold value Th SNR-up} for the upper limit of the SNR may be given to the characteristic control processing unit 20 from the outside, or may be stored in the internal memory of the mobile control unit 21. Good.

Further, if the SNR of the received light _{is larger than the threshold value Th SNR-up} for the upper limit of the SNR (SNR> Th _SNR-up ), the characteristic control processing unit 20 widens the beam spreading angle θ of the transmitted light. The control signal ct ₂ shown may be output to the optical antenna 5.
_{If the optical antenna 5 receives the control signal ct 2} indicating that the beam spreading angle θ of the transmitted light is widened from the characteristic control processing unit 20, the transmitted light having a wider beam spreading angle θ than the transmitted light emitted last time. 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 threshold Th SNR-up for the upper limit (Th SNR} ≤ SNR ≤ Th _SNR-up ), the characteristic control processing unit 20 The control signal ct ₂ is not output to the optical antenna 5.

Further, if the SNR of the received light _{is larger than the threshold value Th SNR-up} for the upper limit of the SNR (SNR> Th _SNR-up ), the characteristic control processing unit 20 reduces the ratio of the error correction code in the modulated signal. The indicated control signal ct ₃ is output to the modulation signal generation unit 3.
_{If the modulation signal generation unit 3 receives the control signal ct 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 is more than the error correction code included in the previously generated modulation signal. , Generates a modulated signal with few 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 threshold Th SNR-up for the upper limit (Th SNR} ≤ SNR ≤ Th _SNR-up ), the characteristic control processing unit 20 The control signal ct 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 the threshold value Th SNR} to be compared with the SNR of the received light.
However, this is only an example, and for example, the characteristic control processing unit 20 may change the _{threshold value Th SNR according to the band B of the transmitted light.} 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 communication distance L p} is equal to or greater than 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 communicationable distance L _p is larger than the upper limit threshold Th _L-up (L <Th _L-up ) larger than the communication distance L (L _p > Th _{L). -Up} ), the mobile body control unit 21 may control the mobile body to keep its optical communication device away from the optical communication device of the communication partner.
If the communicable distance L _p is equal to or greater than the communication distance L and the communicable distance L _p is equal to or less than the upper limit threshold Th _{L-up (L ≤ L p} ≤ Th _L-up ), the mobile is moved. The body control unit 21 does not control the moving body.

Embodiment 2.
In the optical communication device shown in FIG. 1, the mobile control unit 21 is given a required value of the communication distance L from the outside.
In the second embodiment, the optical communication device including the distance calculation unit 59 that calculates the distance L from the optical communication device of its own to the optical communication device of the communication partner and outputs the calculated distance L to the mobile 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 factor calculation unit 11, the demodulation unit 17, the characteristic control unit 18, the mobile control unit 21, and the distance calculation unit 59 in the optical communication device according to the second embodiment. ..
In FIGS. 8 and 9, the same reference numerals as those in FIGS. 1 and 2 indicate the same or corresponding parts, 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 emission unit 55, and a sound signal reception 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 each of 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 receiving unit 56 includes a sound collecting unit 57 and a demodulating unit 58. The sound signal receiving unit 56 receives the 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 collecting unit 57 is realized by, for example, a microphone. The sound collecting 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 collection unit 57, and outputs the demodulated position information to the distance calculation unit 59.

The distance calculation unit 59 is realized by, for example, the distance calculation circuit 36 shown in FIG. 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 to perform optical communication of the communication partner from its own optical communication device. The distance L to the device is calculated. Further, 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 to communicate with each other from its own optical communication device. Calculate the direction α to the optical communication device. 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 direction α to the moving body control unit 21.

In FIG. 8, each of the attenuation factor calculation unit 11, the demodulation unit 17, the table unit 19, the characteristic control processing unit 20, the mobile control unit 21, and the distance calculation unit 59, which are some components of the optical communication device, is shown in FIG. It is assumed that it will be realized by dedicated hardware as shown in 9. That is, it is assumed that a part of the optical communication device is realized by the attenuation factor 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 factor calculation circuit 31, demodulation circuit 32, characteristic control processing circuit 34, mobile control circuit 35, and distance calculation circuit 36 is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, and the like. ASIC, FPGA, or a combination of these 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 damping factor calculation unit 11, the demodulation unit 17, the table unit 19, the characteristic control processing unit 20, the mobile control unit 21, or the distance calculation unit 59 may be software, firmware, or software and firmware. It may be realized by the combination of.
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 shown in FIG. A program for causing the computer to execute the processing procedures of the attenuation factor 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 same as the optical communication device shown in FIG. 1 except for the acoustic communication unit 50, the distance calculation unit 59, and the mobile control unit 21, the acoustic communication unit 50, the distance calculation unit 59, and the mobile control unit 21 are described here. Only the operation of 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 position coordinate acquisition unit 51 generates the modulation signal generation unit 52 for the position information indicating the acquired position coordinates (x ₁ , y ₁ , z _1). And output to each of the distance calculation unit 59.
When the modulation signal generation unit 52 receives 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 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.

Optical communication device of the communication partner, to emit a sound signal containing position information indicating a position coordinate _{(x 2, y 2, z} 2) in water, for example, include data or confidentiality of mass data The existing optical signal is emitted into the water.
The optical signal is suitable for transmitting a large amount of data or the like, but when the water becomes turbid, the attenuation becomes large.
The sound signal is not suitable for transmitting a large amount of data or the like as compared with the optical signal. However, sound signals are less attenuated than optical signals even when the water is turbid, so they can be transmitted and received even if the distance between one's own optical communication device and the other party's optical communication device is long. Can be done.
The sound collecting 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.
When the demodulation unit 58 receives the sound signal from the sound collection 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.

また、距離算出部５９は、位置座標（ｘ_１，ｙ_１，ｚ_１）と位置座標（ｘ_２，ｙ_２，ｚ_２）とから、自らの光通信装置から通信相手の光通信装置への方位αを算出する。方位αの算出処理自体は、公知の技術であるため詳細な説明を省略する。
距離算出部５９は、算出した距離Ｌを特性制御処理部２０及び移動体制御部２１のそれぞれに出力し、算出した方位αを移動体制御部２１に出力する。
なお、移動体制御部２１において、自らの光通信装置から通信相手の光通信装置への方位αが既値であれば、距離算出部５９は、方位αを移動体制御部２１に出力する必要がない。 _{The distance calculation unit 59 includes 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. since y _{2, z 2)} and, as shown in the following equation (9), calculates the communication distance L is a distance from its optical communications device to the optical communication apparatus of the communication partner.

Further, the distance calculation unit 59 transfers from its own optical communication device to the communication partner's optical communication device from _{the position coordinates (x 1} , y ₁ , z ₁ ) and the position coordinates (x ₂ , y ₂ , z _2). Calculate the azimuth α. Since the calculation process of the direction α itself is a known technique, detailed description thereof will be 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 direction α to the moving body control unit 21.
If the mobile control unit 21 has an already-valued direction α from its own optical communication device to the communication partner's optical communication device, the distance calculation unit 59 needs to output the direction α to the mobile control unit 21. There is no.

Upon receiving the attenuation factor At from the attenuation factor calculation unit 11, the moving body control unit 21 receives the attenuation factor At from the optical communication device of the communication partner with the optical communication device of itself based on the attenuation factor At, as in the first embodiment. _{Find the} distance L p that can be communicated with.
When the mobile body control unit 21 receives 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 communication distance L p} is shorter than the communication distance L, the mobile body control unit 21 controls the mobile body equipped with its own optical communication device and itself, as in the first embodiment. Bring the optical communication device of the above close to the optical communication device of the communication partner.
However, since the moving body control unit 21 receives the direction α from the distance calculation unit 59, the moving body control unit 21 controls the moving body so that the moving body moves in the direction of the direction α.
_{As long as the communication distance L p} is equal to or greater than the communication distance L, the mobile body control unit 21 does not control the mobile body as in the first embodiment.

In the optical communication device shown in FIG. 8 _{, if the communication distance L p} is equal to or greater than 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 communicationable 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 control unit. The 21 may control the mobile body to move its own optical communication device away from the communication partner's optical communication device.
If the communicable distance L _p is equal to or greater than the communication distance L and the communicable distance L _p is equal to or less than the upper limit threshold Th _{L-up (L ≤ L p} ≤ Th _L-up ), the mobile is moved. The body control unit 21 does not control the moving body.

The second embodiment is received by the sound signal receiving unit 56 and the sound signal receiving unit 56 that receive a sound signal including position information indicating the position of the optical communication device of the communication partner from the optical communication device of the communication partner. The mobile control unit 21 is capable of communicating with a distance calculation unit 59 that calculates the distance L from the optical communication device of its own to the optical communication device of the communication partner 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 moving body equipped with its own optical communication device is controlled to use its own optical communication device as the communication partner's optical communication device. The optical communication device shown in FIG. 8 was configured so as to be close to each other. Therefore, the optical communication device shown in FIG. 8 can control the SNR of the received light as in the first embodiment even if the distance L from its own optical communication device to the communication partner's optical communication device changes. 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 optical communication device of the communication partner.
In the third embodiment, an optical communication device including a sound signal transmission / reception 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 parts, 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 transmission / reception unit 61 emits the sound signal into the water and receives the reflected signal of the sound signal reflected by the optical communication device of the communication partner.
In the optical communication device shown in FIG. 10, it is sufficient that the sound signal transmission / reception unit 61 can transmit / receive sound signals, and the sound source 53 directly emits sound without the sound signal transmission / reception unit 61 including the modulator 54. It may be output to the sound section 55.
On the other hand, when the sound signal transmission / reception unit 61 includes the modulator 54, the modulation signal generation unit 52 may be included in the sound signal transmission / reception unit 61.

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

Next, the operation of the optical communication device shown in FIG. 10 will be described.
However, since the parts other than the sound signal transmission / reception unit 61 and the distance calculation unit 62 are the same as the optical communication devices shown in FIGS. 1 and 8, only the operations of the sound signal transmission / reception unit 61 and the distance calculation 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 calculates the distance between the generated modulated sound and the sound emitting unit 55. Output to each of the units 62.
The sound emitting unit 55 emits the modulated sound output from the modulator 54 as a sound signal toward the optical communication device of the communication partner into the water.

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 collecting unit 57 receives the sound signal reflected by the optical communication device as a reflected signal, and outputs the received reflected signal to the distance calculation unit 62.

式（１０）において、εは、音速である。
音速εは、水中の温度によって変化するため、距離算出部６２が、水中の温度を取得し、取得した温度に従って音速εを補正するようにしてもよい。
距離算出部６２は、取音部５７が音信号を出射する方向に基づいて、自らの光通信装置から通信相手の光通信装置への方位αを求めるようにしてもよい。距離算出部６２は、方位αを求めた場合、方位αも移動体制御部２１に出力する。
なお、移動体制御部２１において、自らの光通信装置から通信相手の光通信装置への方位αが既値であれば、距離算出部６２は、方位αを移動体制御部２１に出力する必要がない。The distance calculation unit 62 measures the time T from when the modulated sound is output from the modulator 54 to the sound emitting unit 55 until the sound collecting unit 57 receives the reflected signal of the sound signal. Immediately after the modulated sound is output from the modulator 54 to the sound emitting unit 55, the sound emitting unit 55 outputs the modulated sound as a sound signal, and the output time of the modulated sound by the modulator 54 and the sound emitting unit The output time of the sound signal by 55 is approximately the same time.
When the time T is measured, the distance calculation unit 62 calculates and calculates the distance L from its own optical communication device to the communication partner's optical communication device from the measured time T, as shown in the following equation (10). The distance L is output to each of the characteristic control processing unit 20 and the moving body control unit 21.

In equation (10), ε is the speed of sound.
Since the sound velocity ε changes depending on the temperature in water, the distance calculation unit 62 may acquire the temperature in water and correct the sound velocity ε according to the acquired temperature.
The distance calculation unit 62 may obtain the direction α from its own optical communication device to the communication partner optical communication device based on the direction in which the sound collection unit 57 emits a sound signal. When the distance calculation unit 62 obtains the direction α, the distance calculation unit 62 also outputs the direction α to the moving body control unit 21.
If the mobile control unit 21 has an already-valued direction α from its own optical communication device to the communication partner's optical communication device, the distance calculation unit 62 needs to output the direction α to the mobile control unit 21. There is no.

In the third embodiment, the sound signal transmission / reception 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. The distance L from the optical communication device of oneself to the optical communication device of the communication partner is calculated from the time from the output of the sound signal from the sound signal transmission / reception unit 61 to the reception of the reflected signal by the sound signal transmission / reception unit 61. _{If the distance L p} that the moving body control unit 21 can communicate with is shorter than the distance L calculated by the distance calculation unit 62, the moving body control unit 21 is equipped with its own optical communication device. The optical communication device shown in FIG. 10 is configured so as to control the body and bring its own optical communication device closer to the optical communication device of the communication partner. Therefore, the optical communication device shown in FIG. 10 can control the SNR of the received light as in the first embodiment even if the distance L from its own optical communication device to the communication partner's optical communication device changes. it can.

Embodiment 4.
The optical communication device shown in FIG. 1 includes an optical antenna 7 and an optical antenna 13 as optical antennas of the receiving system.
In the fourth embodiment, an optical communication device including only the optical antenna 71 as the optical antenna of the 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. 1 indicate the same or corresponding parts, and thus the description thereof will be omitted.
The optical antenna 71 also serves as an optical antenna 7 included in the transmission optical monitor unit 6 shown in FIG. 1 and an optical antenna 13 included in the optical signal receiving unit 12 shown in FIG. The optical antenna 71 receives the transmitted light emitted into the water from the optical transmission unit 1 as monitor light, and outputs the received monitor light to the wavelength separation unit 72 via an optical fiber. Further, the optical antenna 71 receives an optical signal emitted into water from the optical communication device of the communication partner as received light, and outputs the received received light to the wavelength separation unit 72 via an optical fiber.

The wavelength separation unit 72 is connected to the optical antenna 71 via an optical fiber, and is connected to the photodetector 8 via an optical fiber. Further, the wavelength separation unit 72 is connected to the photodetector 14 via an optical fiber. The wavelength separation unit 72 outputs the monitor light output from the optical antenna 71 to the photodetector 8 via the optical fiber, and outputs the received light output from the optical antenna 71 to the photodetector via the optical fiber. Output 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, since the optical communication device is the same as that shown in FIG. 1 except for the optical antenna 71 and the wavelength separation unit 72, only the operations of the optical antenna 71 and the wavelength separation unit 72 will be described here.
When the transmitted light is emitted from the optical transmission unit 1 into the water, the optical antenna 71 receives the transmitted light as monitor light and outputs the received monitor light to the wavelength separation unit 72 via an optical fiber.
Further, when the optical signal is emitted into the water from the optical communication device of the communication partner, the optical antenna 71 receives the optical signal as the received light, and the received received light is transmitted to the wavelength separation 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 separation 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.
In the optical communication device shown in FIG. 11, the number of optical antennas in the receiving system can be reduced as compared with the optical communication device shown in FIG.

In the present invention, within the scope of the invention, it is possible to freely combine each embodiment, modify any component of each embodiment, or omit any component in each embodiment. ..

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

1 Optical transmitter, 2 Reference light source, 3 Modulated signal generator, 4 Modulator, 5 Optical antenna, 6 Transmitted optical monitor, 7 Optical antenna, 8 Optical detector, 9 IV converter, 10 ADC, 11 Attenuation rate calculation Unit, 12 optical signal receiver, 13 optical antenna, 14 optical detector, 15 IV converter, 16 ADC, 17 demodulator, 18 characteristic control unit, 19 table unit, 20 characteristic control processing unit, 21 mobile control unit, 31 Attenuation rate calculation circuit, 32 Demodulation circuit, 33 Storage circuit, 34 Characteristic control processing circuit, 35 Mobile 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 acquisition unit, 58 demodulation unit, 59 distance calculation unit, 61 sound signal transmission / reception unit, 62 distance calculation unit, 71 optical antenna , 72 Wave separator.

Claims (13)

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, and a transmission light monitor unit.
An attenuation factor calculation unit that 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 transmitted light emitted from the light transmission unit into the water.
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-to-noise ratio is estimated. An optical communication device including a characteristic control unit that controls the characteristics of the transmitted light that influences an increase or decrease in the signal-to-noise ratio based on the noise ratio. The optical communication device according to claim 1, wherein the characteristic control unit controls the characteristics of the transmitted light so that the signal-to-noise ratio becomes equal to or higher than a threshold value. The optical transmitter generates modulated light according to the modulated 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 the modulation speed of the modulated light as a characteristic of the transmitted light based on the signal-to-noise ratio. The light according to claim 1, wherein the characteristic control unit controls a beam spread angle of the transmitted light emitted from the optical transmission unit as a characteristic of the transmitted light based on the signal-to-noise ratio. Communication device. The optical transmitter generates modulated light according to the modulated 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 transmitted light based on the signal-to-noise ratio. Based on the attenuation rate calculated by the attenuation rate calculation unit, the distance at which communication is possible between the optical communication device of oneself and the optical communication device of the communication partner is obtained, and the distance at which the communication is possible is the self. 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 moving body equipped with the optical communication device of the company is controlled to use the optical communication device of the communication partner with the light of the communication partner. The optical communication device according to claim 1, further comprising a mobile control unit that is close to the communication device. 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 optical communication device of the communication partner.
A distance calculation unit that calculates the distance from its own optical communication device to the optical communication device of the communication partner from the position information included in the sound signal received by the sound signal reception 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 device and the optical communication device of the communication partner is obtained, and the communication possible distance is the said. If the distance is shorter than the distance calculated by the distance calculation unit, the moving body on which the own optical communication device is mounted is controlled 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 a unit. A sound signal transmission / reception unit 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.
The distance from the optical communication device of oneself to the optical communication device of the communication partner is calculated from the time from the output of the sound signal from the sound signal transmission / reception unit to the reception of the reflected signal by the sound signal transmission / reception unit. Distance calculation unit and
Based on the attenuation rate calculated by the attenuation rate calculation unit, the distance at which communication is possible between the own optical communication device and the optical communication device of the communication partner is obtained, and the communication possible distance is the said. If the distance is shorter than the distance calculated by the distance calculation unit, the moving body on which the own optical communication device is mounted is controlled 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 a unit. The optical communication device according to claim 1, wherein the optical transmission unit generates modulated light by modulating the phase of continuously oscillating light according to a modulated signal, and emits the modulated light as transmission light into water. The optical communication device according to claim 1, wherein the optical transmission unit generates modulated light by modulating the intensity of continuously oscillating light according to a modulated signal, and emits the modulated light as transmission light into water. When an optical signal containing communication data is emitted into water from the optical communication device of the communication partner, an optical signal receiving unit that receives the optical signal emitted into the water, and an optical signal receiving unit.
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 reception unit. One optical antenna also serves as an optical antenna included in the transmission optical monitor unit and an optical antenna included in the optical signal reception unit.
The optical communication device according to claim 11, wherein the one optical antenna receives each of the transmitted light and the optical signal. 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 unit as the monitor light,
The attenuation factor 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 transmitted light emitted from the light transmission unit into the water.
The characteristic control unit estimates the signal-to-noise ratio of the received light when the light 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 unit. An optical communication method that controls the characteristics of the transmitted light that affect the increase / decrease of the signal-to-noise ratio based on the signal-to-noise ratio.

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