Optical wireless communication method for underwater equipment

Abstract

The purpose of the present disclosure is to provide underwater equipment capable of performing control such that, in water, communication light for optical wireless communication is not affected by illumination light, and an image photographed by a camera using the illumination light is not affected by the communication light.　Underwater equipment according to the present invention comprises: an optical transmission / reception unit 13 that is movable in water and performs underwater optical communication with another communication device 20 by means of communication light; an imaging unit 11 that photographs the surroundings; an illumination unit 12 that irradiates an imaging target 30 of the imaging unit with illumination light; and a control unit 14 that performs time-division control such that a communication time by the communication light and a light emission time of the illumination light do not overlap.

Description

Optical wireless communication method for underwater devices

[0001] The present disclosure relates to an optical wireless communication system for spaces requiring illumination.

[0002] In recent years, while aerial drones have been under consideration for social implementation, development of underwater drones aimed at innovation in the underwater field is progressing (see, for example, Non-Patent Document 1). Aerial drones can be controlled wirelessly using radio waves and can also acquire location information using GPS, so their application to, for example, GPS-based delivery systems is progressing. However, the transmission characteristics of various physical media underwater are significantly limited compared to air, and the GPS signals required for control use radio waves, so they cannot reach underwater and location information cannot be acquired. Therefore, current underwater drones are controlled by an onboard operator viewing images from the underwater drone's camera via a cable called a tether.

[0003] Masaki Minami, "Current Status and Issues of Underwater Drone Systems," Measurement and Control 2020, Vol. 59, No. 7, pp. 492-496, Published 2020 / 07 / 17, Online ISSN 1883-8170, Print ISSN 0453-4662

[0004] Such tethered operations have the following issues: (a) multiple personnel are required for operation (pilot and cable operator); (b) there is a risk that the underwater drone itself will become tangled in the cable and become unable to navigate; (c) navigation in narrow spaces is difficult due to the risk of the cable becoming tangled in obstacles; and (d) the navigation range is limited to the length of the tether cable.

[0005] To overcome the aforementioned issues with underwater drones that require tether cables, it is necessary to establish a means of communication between the operator and the underwater drone. Possible communication methods include wireless communication using sound, light, radio waves, etc. Figure 1 summarizes the underwater characteristics and issues of each physical medium: sound, light, and radio waves.

[0006] Underwater communication using light (hereinafter referred to as optical wireless) is an attractive method when considering applications such as transmitting high-definition video from underwater industrial robots, etc. However, since the illumination light used for video capture underwater where sunlight does not reach and the visible light used for optical wireless communication interfere with each other, establishing a method to reduce the mutual influence of the two is a challenge.

[0007] In other words, in order to solve the above-mentioned problems, the present invention aims to provide underwater equipment that can be controlled so that optical wireless communication light is not affected by illumination light underwater, and so that images captured by a camera using illumination light are not affected by communication light.

[0008] In order to achieve the above object, the underwater device according to the present invention uses illumination light synchronized with the camera shutter and controls the illumination light and communication light to be emitted in a time-division manner.

[0009] Specifically, the underwater device of the present invention is an underwater device that can move underwater, and includes an optical transmitter / receiver unit that performs underwater optical communication with other communication devices using communication light, a photographing unit that photographs the surroundings, an illumination unit that illuminates the subject being photographed by the photographing unit with illumination light, and a control unit that performs time-sharing control so that the communication time using the communication light and the emission time of the illumination light do not overlap.

[0010] Since the illumination light and the communication light are emitted alternately, mutual interference between camera photography and optical wireless communication can be avoided. Therefore, the present invention can provide an underwater device that can be controlled underwater so that the optical wireless communication light is not affected by the illumination light, and so that images captured by a camera using the illumination light are not affected by the communication light.

[0011] The control unit of the underwater device according to the present invention preferably inserts a predetermined guard time between the communication time and the light emission time, thereby completely preventing the lights from overlapping each other.

[0012] The control unit of the underwater device of the present invention is characterized in that it notifies the other communication device of the transmission time via the optical transceiver unit based on the communication time and the light emission time, thereby making it possible to control the emission of communication light from the communication partner side as well.

[0013] The underwater communication system according to the present invention is an underwater communication system comprising the underwater device and the other communication device, wherein the other communication device comprises a communication control unit that determines whether or not the communication light from the underwater device is being received, and that transmits data to the underwater device by the communication light if the communication light is being received. By determining whether or not communication light is being received from the underwater device, the communication partner can stop emission of communication light that affects camera photography.

[0014] The above inventions can be combined as much as possible.

[0015] The present invention can provide underwater equipment that can be controlled underwater so that optical wireless communication light is not affected by illumination light, and so that images captured by a camera using illumination light are not affected by communication light.

[0016] FIG. 1 is a table explaining the characteristics and problems of various wireless communications. FIG. 2 is a diagram explaining an underwater communication system according to the present invention. FIG. 3 is a diagram explaining time-division control of illumination light and communication light performed by a control unit of an underwater device according to the present invention. FIG. 4 is a diagram explaining the operation of a communication partner of an underwater communication system according to the present invention. FIG. 5 is a diagram explaining time-division control of illumination light and communication light performed by a control unit of an underwater device according to the present invention. FIG. 6 is a diagram explaining the relationship between the exposure time of an imaging unit and the light-emitting time of an illumination unit of an underwater system according to the present invention. FIG. 7 is a diagram explaining the relationship between the exposure time of an imaging unit and the light-emitting time of an illumination unit of an underwater system according to the present invention. FIG. 8 is a diagram explaining the relationship between the exposure time of an imaging unit and the light-emitting time of an illumination unit of an underwater system according to the present invention.

[0017] The following description of the preferred embodiments of the present invention will be given with reference to the accompanying drawings. The preferred embodiments described below are examples of the present invention, and the present invention is not limited to the preferred embodiments. In this specification and the drawings, components having the same reference numerals are intended to represent the same components.

[0018] 2 is a diagram illustrating the underwater communication system of this embodiment. The underwater communication system includes an underwater device 10 and another communication device 20. The underwater device 10 is, for example, an underwater drone. The communication device 20 is, for example, a ship, a submarine, or another underwater drone that communicates with the underwater device 10.

[0019] The underwater device 10 includes an optical transmitter / receiver 13 that performs underwater optical communication with another communication device 20 using communication light, an image capturing unit 11 that captures images of the surroundings, and an illumination unit 12 that illuminates an object 30 to be captured by the image capturing unit with illumination light. The communication device 20 also includes an optical transmitter / receiver 23 that performs underwater optical communication with the underwater device 10.

[0020] The underwater device 10 further includes a control unit 14 that performs time-division control so that the communication time using the communication light and the emission time of the illumination light do not overlap. Fig. 3 is a diagram illustrating the time-division control of the illumination light and the communication light performed by the control unit 14. The control unit 14 causes the illumination unit 12 to output illumination light in synchronization with the exposure of the photographing unit 11. The control unit 14 then controls the illumination unit 12 and the optical transceiver 13 to emit the illumination light and the communication light in a time-division manner.

[0021] Specifically, as shown in FIG. 3 , the emission of each light is controlled so that the emission time t1 of the illumination light and the emission time t2 of the communication light do not overlap. Here, the emission time t1 of the communication light refers not only to the physical emission but also to the communication time using the communication light. That is, when on-off keying is performed, the off state is the emission time t2 of the communication light even though no light is being output. Furthermore, because there is a possibility that reflected light of the communication light from the optical transmitter / receiver 13 may enter the photographing unit 11, and there is a possibility that communication light from the optical transmitter / receiver 23 or its reflected light may enter the photographing unit 11, the emission time of both the optical transmitter / receiver 13 and the optical transmitter / receiver 23 is included in the emission time t2 of the communication light.

[0022] Here, it is preferable that the control unit 14 inserts a predetermined guard time tg between the communication time and the light emission time. The guard time tg can further reduce the influence of the illumination light on the optical transceivers 13 and 23 and the influence of the communication light on the image capture unit 11. In addition, it is possible to reduce the power consumption of the illumination light, and extend the operating time of the battery-powered underwater device 10.

[0023] As shown in Figure 4, the control unit 14 controls the emission start time and duration of the optical transceiver unit 13, the emission start time and duration of the illumination unit 12, and the exposure time of the photographing unit 11 based on the clock of the clock generating source 15 within the underwater drone, in order to control the emission of illumination light and communication light in a time-division manner.

[0024] Meanwhile, there are two control methods for the light emission time of the optical transceiver 23 of the communication device 20: (Method 1) The control unit 14 notifies the other communication device 20 of the transmission time of the other communication device 20 via the optical transceiver 13 based on the communication time and the light emission time. That is, in this method, the control unit 14 acquires information in advance regarding the light emission start time and duration of the optical transceiver 13, the light emission time of the illumination unit 12, and the exposure time of the imaging unit 11, and notifies the communication device 20 of this information, thereby controlling the light emission start time and duration of the optical transceiver 23, i.e., the communication time of the optical transceiver 23.

[0025] (Method 2) FIG. 5 is a flowchart illustrating the operation of the communication control unit 24 in this method. The communication control unit 24 determines whether communication light is being received from the underwater device 10 (step S01). If communication light is being received ("Yes" in step S01), the communication control unit 24 causes the optical transceiver 23 to transmit data to the underwater device 10 via communication light (step S02). After completing data transmission, or if communication light is being received ("No" in step S01), the communication control unit 24 waits until the next communication light is received from the underwater device 10 (step S03). That is, in this method, the communication control unit 24 detects communication light from the optical transceiver 13 and controls the optical transceiver 23 so that only the light emission time of the detected communication light is used as the light emission time (communication time). Here, the control unit 14 may cause the optical transceiver 13 to emit an idle signal to indicate to the communication device 20 the time during which communication is possible, even if no data is being transmitted from the underwater drone 10.

[0026] If the optical transceiver 13 and the optical transceiver 23 are capable of full-duplex communication using wavelength multiplexing or the like, they can emit light (communicate) simultaneously as shown in Fig. 6(A) using both the above-mentioned methods 1 and 2. Also, if the optical transceiver 13 and the optical transceiver 23 are capable of half-duplex communication, they can emit light (communicate) alternately as shown in Fig. 6(B) using the above-mentioned method 1 or the following method 3. (Method 3) A certain period of time after the optical transceiver 13 finishes emitting light is considered to be the communication available time for the optical transceiver 23.

[0027] The relationship between the exposure time of the image capture unit and the light emission time of the illumination unit will be described below. (Relationship 1) FIG. 7 is a diagram illustrating Relationship 1. The control unit 14 controls the exposure time Exp of the image capture unit 11 so that it is other than the communication light emission time L2. In other words, the exposure time Exp and the illumination light emission time L1 do not necessarily need to coincide. If the illumination light emission timing and the exposure timing cannot be controlled accurately, it is sufficient to control the exposure time Exp so that it is other than the communication light emission time L2, as shown in FIG. 7. FIG. 7(A): Case where the exposure time Exp is longer than the illumination light emission time L1. FIG. 7(B): Case where the illumination light emission time L1 is longer than the exposure time Exp. FIG. 7(C): ​​Case where the illumination light emission time is later than the exposure time. FIG. 7(D): Case where the exposure time is later than the illumination light emission time.

[0028] (Relationship 2) Fig. 8 is a diagram illustrating Relationship 2. When the exposure of the photographing unit 11 is a rolling shutter, the control unit 14 determines the time (T2 ｋ ~T3 ｋ The control unit 14 adjusts the exposure time Exp so that the start time of the illumination light emission L1 is T2 ｋ After that, the end time of the illumination light emission L1 is T3 ｋ and the start time of communication light emission L2 is T4 ｋ After that, the end time of communication light emission L2 is T1 ｋ＋１ The control unit 14 controls the photographing unit 11, the illumination unit 12, and the light transmitting / receiving unit 13 so that the exposure time of all the lines is earlier than the predetermined time. By performing control as shown in FIG.

[0029] (Relationship 3) FIG. 9 is a diagram illustrating Relationship 3. Relationship 3 is a relationship when the exposure of the photographing unit 11 is a rolling shutter, and further, communication light from either or both of the optical transceiver 13 and the optical transceiver 23 does not affect the photographing unit 11 during the exposure Exp. In this relationship, the control unit 14 stops the communication light emission (communication light emission L2-2 in FIG. 9) of the optical transceiver (optical transceiver 23 in FIG. 9) that outputs communication light that does not affect the photographing unit 11 after the end time of illumination light emission L1 (time T3 in FIG. 9).ｋ 9 ) and before the start time of the next illumination light emission L1 (time T2 ｋ＋１ 9, the control unit 14 controls the communication so as to end the communication before the time when the communication is possible.

[0030] (Relationship 4) Fig. 10 is a diagram illustrating Relationship 4. Relationship 4 is a relationship when the exposure of the imaging unit 11 is a rolling shutter and the exposure Exp time of each line is short. For example, the exposure start time T2 of line n is short. ｋ is the exposure end time T3 of line 1 ｋ In this case, the control unit 14 sets the start time of the illumination light emission L1 to the exposure start time T1 of the first line 1 to be exposed. ｋ Before the end of illumination light emission L1, the exposure end time T4 of line n is the last exposure. ｋ 10, the control unit 14 controls the exposure time Exp of all lines to be constant even if the exposure time Exp is short.

[0031] 10: Underwater device (underwater drone) 11: Photography unit 12: Lighting unit 13: Optical transmitter / receiver unit 14: Control unit 15: Clock generator 20: Communication device 23: Optical transmitter / receiver unit 24: Communication control unit

Claims

1. An underwater device that can move underwater, comprising: an optical transmitter / receiver unit that performs underwater optical communication with other communication devices using communication light; a photographing unit that photographs the surroundings; an illumination unit that illuminates the subject being photographed by the photographing unit with illumination light; and a control unit that performs time-sharing control so that the communication time using the communication light and the emission time of the illumination light do not overlap.

2. The underwater device according to claim 1, characterized in that the control unit inserts a predetermined guard time between the communication time and the light emission time.

3. The underwater device according to claim 1, characterized in that the control unit notifies the other communication device of the transmission time via the optical transceiver unit based on the communication time and the light emission time.

4. An underwater communication system comprising an underwater device according to any one of claims 1 to 3 and the other communication device, wherein the other communication device is provided with a communication control unit that determines whether or not the communication light from the underwater device is being received, and if the communication light is being received, transmits data to the underwater device via the communication light.

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