JP2015170962A - Transmitter, receiver, and underwater transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To implement transmission in which video data is hardly interrupted even when visible light is cut off in transmitting, under water, the video data by using the visible light.SOLUTION: When a transmission unit 34 in a transmitter 3A is transmitting video data while encoding it at a high rate, a reception unit 33, in the case of determining a reception interruption, identifies a GOP corresponding to the sequence number next to an already received sequence number received most recently. An encoder 32 encodes, at a low rate, video data from the head frame to the final frame of the identified GOP, and the transmission unit 34 transmits the video data. In the case of the reception interruption, the video data is not transmitted. The reception unit 33 restores an encoding rate to the former high rate, when reception recovery is determined, the video data encoded at the low rate from the head frame of the GOP starts to be transmitted from the transmission unit 34 and transmission of video data in the final frame is completed.

Description

  The present invention relates to a transmission device, a reception device, and an underwater transmission system that wirelessly transmit video data in water.

  Conventionally, as a technique for transmitting real-time images taken by a camera underwater, a technology is known in which a camera is installed in a waterproof housing and the output video from the camera is transmitted as an electrical signal to the outside via a cable. (See Patent Document 1). In this method, when a diver operates the camera, it is necessary to route the cable so that the operation is not hindered.

  However, it is difficult to route the cable underwater. For this reason, since the cable cannot be handled as intended by the diver, the camera operation may be affected.

  Therefore, in order to dramatically increase the degree of freedom in camera operation underwater, it has been desired to transmit video without using a cable.

  In general, when transmission in the frequency band of radio waves used outdoors is applied underwater, attenuation is increased and large-capacity transmission cannot be expected. Also, underwater, transmission by sound waves is possible, but since sound waves have a low frequency, large-capacity data such as images cannot be multiplexed. For this reason, a transmission technique using visible light has been proposed as a technique for wirelessly transmitting video data in water.

  Underwater, video transmission of about several tens of meters can be performed by electromagnetic waves within the visible light wavelength. On the other hand, since visible light has strong straightness, the light emitting element of the transmitting device and the light receiving element of the receiving device must always face each other. However, underwater, the position and orientation between the transmission device and the reception device often fluctuate, and this causes a misalignment. Therefore, a method for automatically detecting such a deviation in the direct relationship has been proposed (see Non-Patent Document 1).

JP 2009-204488 A

Mikio Maeda, “Research on Underwater Optical Transmission of Video Signals”, Radio Technology Association Report FORN, 2013.7, No.293, p.34-37

  In general, in a real environment such as in the sea, a direct relationship between a transmission device and a reception device cannot often be maintained constant due to fluctuations in water. In addition, since various suspended matters existing in water pass between the transmitting device and the receiving device, visible light communication is often completely interrupted. For this reason, the conventional transmission technology using visible light has a problem that the video taken by the camera is interrupted.

  Therefore, the present invention has been made to solve the above-described problems, and the purpose of the present invention is to transmit video data using visible light in water even when the visible light is blocked. An object of the present invention is to provide a transmission device, a reception device, and an underwater transmission system capable of realizing transmission in which data is hardly interrupted.

In order to achieve the above object, a transmission device according to claim 1 is a transmission device that transmits video data to a reception device using visible light in water, a buffer that stores the video data, and a buffer that is stored in the buffer. An encoder that encodes video data at a predetermined high rate or low rate and generates compressed data, and the compressed data generated by the encoder is divided into packets and stored as divided compressed data in the packet. A transmission unit that adds a sequence number corresponding to data to the packet, modulates the packet including the divided compressed data and the sequence number using a visible light carrier, and transmits a modulated signal; and the predetermined high rate Alternatively, an instruction for encoding at a low rate is output to the encoder and the sequence number is To the transmission unit, and from the reception device that has received the modulated signal, a reception unit that receives a sequence number included in the packet as a received sequence number. When a reception interruption is determined when the received sequence number is not received for a predetermined time in a state where the modulated signal of the packet including the divided compressed data encoded and divided at the high rate and the sequence number is transmitted, An instruction for encoding at a rate is output to the encoder, a sequence number corresponding to the divided compressed data encoded and divided at the low rate is output to the transmitter, and the transmitter is encoded at the low rate. The divided compressed data divided and the modulated signal of the packet including the sequence number are transmitted, When the reception recovery is determined when the received sequence number corresponding to the divided compressed data encoded and divided at the low rate is received, the divided compressed data in the video data of a predetermined size encoded at the low rate and the After the transmitter transmits a modulated signal of a packet including a sequence number, an instruction for encoding at a high rate is output to the encoder, and the sequence number corresponding to the divided compressed data to be encoded and divided at the high rate Is output to the transmission unit, and the transmission unit transmits the modulated signal of the packet including the divided compressed data encoded and divided at the high rate and the sequence number.

  The transmission apparatus according to claim 2 is the transmission apparatus according to claim 1, wherein the transmission unit further transmits the modulated signal of the packet including the divided compressed data and the sequence number, and then the same division is performed. The packet modulation signal including the compressed data and the sequence number is repeatedly transmitted continuously.

  According to a third aspect of the present invention, there is provided a transmission device for transmitting video data to a reception device using visible light in water, wherein the transmission device encodes the video data at a predetermined high rate to generate high-rate compressed data. An encoder, a second encoder that encodes the video data at a predetermined low rate to generate low-rate compressed data, a buffer that stores the low-rate compressed data generated by the second encoder, and a high rate Is input, the high-rate compressed data generated by the first encoder is divided for each packet, the divided high-rate compressed data is stored in the packet, and the divided high-rate compressed data is supported. A sequence number is added to the packet, and the packet including the divided high-rate compressed data and the sequence number is When modulated using a visible light carrier, transmits a modulated signal, or inputs a low rate instruction, the low rate compressed data stored in the buffer is divided for each packet, and the divided low rate compressed data And a sequence number corresponding to the divided low-rate compressed data is added to the packet, and the packet including the divided low-rate compressed data and the sequence number is modulated using a visible light carrier wave. A transmission unit that transmits a modulation signal, the high-rate or low-rate instruction and the sequence number are output to the transmission unit, and the sequence number included in the packet is received from the reception device that has received the modulation signal. A receiving unit that receives the received sequence number, and the receiving unit sends the divided high rate to the transmitting unit. When a reception interruption is determined when the received sequence number is not received for a predetermined time in a state where the modulated signal of the packet including the compressed data and the sequence number is transmitted, the low rate instruction and the divided low rate A sequence number corresponding to compressed data is output to the transmitter, and the transmitter transmits the divided low-rate compressed data and a modulated signal of a packet including the sequence number to correspond to the divided low-rate compressed data. When the reception recovery is determined when the received sequence number is received, the transmitter transmits the modulated signal of the packet including the divided low-rate compressed data and the sequence number in video data of a predetermined size, The sequence number corresponding to the high rate instruction and the divided high rate compressed data is preceded. Output to the transmitter, and cause the transmitter to transmit a modulated signal of a packet including the divided high-rate compressed data and the sequence number.

  Furthermore, the receiving device according to claim 4 is a receiving device that receives video data using visible light in water, wherein the receiving device receives a modulation signal transmitted from the transmitting device according to claim 1 or 3. Receiving the modulated signal, demodulating the modulated signal using the visible light carrier wave, generating a packet, extracting divided compressed data and a sequence number from the packet, and combining the divided compressed data; A receiving unit that generates compressed data, a sequence number extracted by the receiving unit is a received sequence number, a packet including the received sequence number is modulated using the visible light carrier, and a modulated signal is transmitted A transmission unit that stores the compressed data generated by the reception unit, and the compressed data from the buffer after a predetermined reproduction delay time. A decoder that reads out, decodes, and restores the original video data, and when the receiving unit generates the same compressed data in duplicate, deletes the duplicated compressed data from the buffer, and newly The generated compressed data is stored in the buffer.

  A receiving device according to claim 5 is the receiving device according to claim 4, instead of receiving the modulated signal transmitted from the transmitting device according to claim 1 or 3, according to claim 2 or claim 3. After receiving the modulated signal transmitted from the transmitting apparatus, the transmitting unit transmits the modulated signal of the packet including the received sequence number, and then repeats the modulated signal of the packet including the same received sequence number. It is characterized by transmitting continuously.

  Further, the underwater transmission system according to claim 6 is an underwater transmission system configured to include a transmission device that transmits video data using visible light in water and a reception device that receives video data from the transmission device. A first buffer that stores the video data; an encoder that encodes the video data stored in the first buffer at a predetermined high rate or low rate to generate compressed data; and A packet including the divided compressed data and the sequence number, wherein the compressed data generated by the above is divided into packets, stored as divided compressed data in the packet, and a sequence number corresponding to the divided compressed data is added to the packet. A first transmission unit that modulates a visible light carrier wave and transmits a modulated signal; and the predetermined height A sequence included in the packet from the receiving apparatus that has received the modulated signal and outputs the sequence number to the first transmitting unit. A first reception unit that receives a number as a received sequence number, and the first reception unit encodes the high-rate divided compressed data and the sequence into the first transmission unit In the state where the modulated signal of the packet including the number is transmitted, when the reception interruption is determined when the received sequence number is not received for a predetermined time, an instruction for encoding at a low rate is output to the encoder, and A sequence number corresponding to the divided compressed data encoded and divided at a low rate is output to the first transmitter. The first transmission unit transmits the divided compressed data encoded and divided at the low rate and the modulated signal of the packet including the sequence number, and corresponds to the divided compressed data encoded and divided at the low rate. If reception recovery is determined when the received sequence number is received, the first transmission unit transmits the divided compressed data and the modulation signal of the packet including the sequence number in the video data of a predetermined size encoded at the low rate. Outputs to the encoder an instruction for encoding at a high rate, and outputs a sequence number corresponding to the divided compressed data encoded and divided at the high rate to the first transmitter, In the first transmission unit, the divided compressed data encoded and divided at the high rate, and the A modulated signal of a packet including a sequence number is transmitted, and the receiving device receives the modulated signal, generates a packet by demodulating the modulated signal using the visible light carrier wave, and divides and compresses from the packet A second receiving unit that extracts data and a sequence number, generates compressed data by combining the divided compressed data, a sequence number extracted by the second receiving unit is a received sequence number, and the received A second transmitter that modulates a packet including a sequence number using the visible light carrier and transmits a modulated signal; and a second buffer that stores compressed data generated by the second receiver. A decoder that sequentially reads out and decodes the compressed data from the second buffer after a predetermined reproduction delay time and restores the original video data. When the second receiving unit generates the same compressed data in duplicate, the second compressed data is deleted from the second buffer and the newly generated compressed data is stored in the second buffer. It is characterized by.

  As described above, according to the present invention, when video data is transmitted underwater with visible light, it is possible to realize transmission in which video data is hardly interrupted even when visible light is blocked.

1 is a diagram illustrating a schematic configuration of an underwater transmission system including a transmission device and a reception device according to an embodiment of the present invention. It is a block diagram which shows the structure of the transmitter and receiver by 1st Embodiment (Example 1) of this invention. It is a figure explaining the relationship between GOP (Group Of Pictures), a frame, and a packet in video data. 6 is a flowchart illustrating processing of the transmission device according to the first embodiment. 6 is a flowchart illustrating reception interruption determination processing according to the first embodiment. It is a figure explaining the process of the transmitter by Example 1. FIG. It is a figure which shows the change of the transmission rate accompanying the rate switch at the time of reception interruption. 6 is a flowchart illustrating processing of a reception unit in the transmission apparatus according to the first embodiment. 6 is a flowchart illustrating processing of a transmission unit in the transmission apparatus according to the first embodiment. 6 is a flowchart illustrating processing of the receiving device according to the first embodiment. It is a flowchart which shows the determination process of reception interruption by the 2nd Embodiment (Example 2) of this invention. 10 is a flowchart illustrating processing of a transmission unit in the transmission apparatus according to the second embodiment. 10 is a flowchart illustrating processing of a receiving device according to the second embodiment. It is a block diagram which shows the structure of the transmitter and receiver by 3rd Embodiment (Example 3) of this invention. 10 is a flowchart illustrating processing of a transmission device according to a third embodiment. 14 is a flowchart illustrating processing of a transmission unit in the transmission apparatus according to the third embodiment.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
[Underwater transmission system]
First, an underwater transmission system including a transmission device and a reception device according to an embodiment of the present invention will be described. FIG. 1 is a diagram illustrating a schematic configuration of an underwater transmission system. The underwater transmission system 1 includes a camera 2, a transmission device 3, and a reception device 4, and transmits an image captured by the camera 2 in water (for example, in the sea) to the reception device 4 via the transmission device 3. The video is displayed in real time on a video monitor 5 provided underwater. The camera 2, the transmission device 3, and the reception device 4 are provided so as to be movable in water. The video monitor 5 is provided outside and underwater.

  The camera 2 and the transmission device 3 are connected by a wired cable 6, and the transmission device 3 and the reception device 4 are connected by underwater radio in which visible light communication is performed. The receiving device 4 and the video monitor 5 are connected by a wired cable 7.

  The transmission device 3 inputs a baseband video signal of an image captured by the camera 2 underwater from the camera 2, encodes and compresses the video data of the baseband video signal, and generates compressed data. Then, the transmission device 3 modulates the compressed data using the visible light carrier wave (modulates the compressed data to the visible light), and transmits the modulated signal to the reception device 4 through the visible light underwater radio.

  It is assumed that the video data is encoded at a high rate or a low rate, and a high rate rate value and a low rate rate value are set in advance. At the start of transmission, high-quality video data encoded at a high rate is transmitted.

  The receiving device 4 receives the modulated signal from the transmitting device 3, demodulates the modulated signal (visible light demodulation) using a visible light carrier wave, generates compressed data, and stores the compressed data in a buffer. Then, the receiving device 4 reads the compressed data from the buffer after a predetermined reproduction delay time, decodes (decodes) the data, and restores the original baseband video signal to the video data. Then, the reception device 4 outputs the baseband video signal to the video monitor 5.

  Thereby, since the video image | photographed with the camera 2 in water is displayed on the video monitor 5 in real time, the operator who is watching the video monitor 5 can observe the video in water in real time.

  In the embodiment of the present invention, when the transmission apparatus 3 determines that the visible light communication with the reception apparatus 4 has been disconnected while encoding and transmitting the video data at a high rate, the transmission apparatus 3 increases the encoding rate. Switch from low to low rate. Then, the transmission device 3 stores the video data encoded at a low rate, and transmits the stored video data at the upper limit rate of the transmission band when the visible light communication is restored. In this case, the transmission device 3 identifies the GOP that was being transmitted, transmits video data encoded at a low rate from the first frame, and when transmission of the video data of the last frame is completed, Return to the high rate.

  In the embodiment of the present invention, when receiving the video data from the transmission device 3, the reception device 4 transmits the sequence number to the transmission device 3 in order to make the transmission device 3 determine whether or not the visible light communication is disconnected. 3 to send. Then, when the video data is received from the first frame of the GOP, the receiving device 4 deletes the duplicate video data.

  In this way, the compressed data encoded at a low rate in the transmission device 3 is stored in the memory when the visible light communication is disconnected, and at the upper limit rate of the transmission band when the visible light communication is restored. 4 is transmitted at high speed. In this case, the video data already stored in the buffer is read and reproduced in the receiving device 4 while the visible light communication is disconnected. When the visible light communication is restored, the video data encoded at a low rate is transmitted at a high speed and stored in the buffer, so that when the video data is read from the buffer within a predetermined reproduction delay time, The video data is not interrupted, and real-time video observation is realized.

[Example 1]
First, the first embodiment (Example 1) of the present invention will be described. In the first embodiment, if it is determined that communication is interrupted while transmitting video data encoded at a high rate on the transmission side, the encoding rate is switched to a low rate, and if recovery of communication is determined, encoding is performed at a low rate. The transmitted video data is transmitted, and after the transmission from the start frame to the last frame of the GOP that was being transmitted is completed, the encoding rate is returned to the high rate, and the video data encoded at the high rate is transmitted.

  FIG. 2 is a block diagram illustrating configurations of the transmission device 3 and the reception device 4 according to the first embodiment. The underwater transmission system 1 according to the first embodiment includes a transmission device 3A and a reception device 4. When transmitting video data using visible light, an analog modulation technique can be used. Here, the underwater transmission system 1 can digitally modulate an Ethernet (registered trademark) packet and can perform two-way communication. Is assumed. The same applies to Examples 2 and 3 below.

(Configuration of Transmitting Device 3A / Example 1)
First, the configuration of the transmission device 3A according to the first embodiment will be described in detail. The transmission device 3A includes a buffer 31, an encoder 32, a reception unit 33, and a transmission unit 34. The buffer 31 is provided in the preceding stage of the encoder 32, and the encoding rate of the encoder 32 is obtained when the visible light communication is disconnected. Is configured to switch from a high rate to a low rate.

  The buffer 31 stores the video data of the baseband video signal from the camera 2 for each frame, and immediately outputs the stored video data to the encoder 32. The buffer 31 holds the stored video data for a predetermined time, and deletes the video data after a predetermined time has elapsed. Further, when the frame number is input from the receiving unit 33, the buffer 31 outputs the video data of the frame number to the encoder 32.

  The encoder 32 receives a high-rate or low-rate rate switching instruction from the receiving unit 33, inputs video data from the buffer 31, encodes video data at the rate of the rate switching instruction, and generates compressed data. The compressed data is output to the transmission unit 34.

  The receiving unit 33 receives a packet including a received sequence number, which will be described later, from the receiving device 4, and determines that the reception is disconnected when the packet is not received for a predetermined period of time. In this case, it is determined that the packet transmitted from the transmission device 3A to the reception device 4 has not arrived at the reception device 4, and it is determined that the visible light communication between the transmission device 3A and the reception device 4 has been disconnected. Is done. This is because transmission and reception are disconnected at the same time when bidirectional visible light communication is performed.

  The reception unit 33 determines reception recovery when receiving a packet including a received sequence number, which will be described later, from the reception device 4 after reception interruption. In this case, the packet transmitted from the transmission device 3A to the reception device 4 is also determined to have arrived at the reception device 4, and it is determined that the visible light communication between the transmission device 3A and the reception device 4 has been recovered. The

  When the encoding rate is switched from a high rate to a low rate, the receiving unit 33 outputs the frame number of video data to be encoded and transmitted at a low rate to the buffer 31. Thereby, the video data of the frame number is output from the buffer 31 to the encoder 32, and the video data of the frame number is encoded by the encoder 32 at a low rate.

  The receiver 33 outputs a high rate or low rate rate switching instruction to the encoder 32. As a result, the encoder 32 encodes the video data at the rate of the rate switching instruction.

  In the embodiment of the present invention, when the reception unit 33 determines reception interruption, the reception unit 33 outputs a low-rate rate switching instruction to the encoder 32 and stores the GOP of the video data being transmitted in the buffer 31. In order to sequentially output video data from the first frame to the last frame of the GOP from the buffer 31, the frame numbers are sequentially output to the buffer 31. Further, the receiving unit 33 outputs a sequence number to the transmitting unit 34 in order to sequentially transmit packets of video data encoded at a low rate from the first frame to the last frame of the GOP.

  When receiving unit 33 determines reception recovery, transmission of video data packets encoded at a low rate is completed up to the last frame of the GOP, and then outputs a high-rate rate switching instruction to encoder 32. The buffer 31 receives the frame number of the final frame from the receiving unit 33 and outputs the video data of the final frame, and then sequentially outputs the video data from the first frame of the next GOP. The encoder 32 encodes video data from the first frame of the GOP at a high rate. Further, the receiving unit 33 sequentially outputs the sequence number to the transmitting unit 34 in order to sequentially transmit video data packets encoded at a high rate from the first frame of the GOP.

  The transmitter 34 receives the compressed data from the encoder 32 and also receives the sequence number from the receiver 33, and divides the compressed data into packets. Then, the transmission unit 34 stores the divided compressed data (divided compressed data) in the packet and generates a packet by sequentially adding a sequence number, and modulates the visible light using a visible light carrier, The modulated signal is transmitted to the receiving device 4 by underwater radio of visible light.

  In this case, for a packet generated by the transmission unit 34 (a packet including a sequence number and divided compressed data), the receiving unit 33 sets the sequence number, the divided compressed data, and the GOP to which the frame of the divided compressed data belongs. Perform the association. Thereby, the receiving unit 33 can recognize which divided compressed data, which frame corresponds to which received compressed sequence number received from the receiving device 4, and which GOP.

  FIG. 3 is a diagram for explaining the relationship between GOPs, frames, and packets in video data. As shown in FIG. 3, the GOP is composed of a plurality of frames. The compressed data of each frame is divided and transmitted together with the sequence number by a plurality of packets storing the divided compressed data.

(Processing of Transmitter 3A / Example 1)
Next, the processing of the transmission device 3A shown in FIG. 2 will be described in detail. FIG. 4 is a flowchart showing the processing of the transmission device 3A, FIG. 6 is a diagram for explaining the processing of the transmission device 3A, and FIG. 7 is a diagram showing the change in the transmission rate accompanying rate switching when reception is interrupted. It is.

  Referring to FIG. 4, first, transmitting apparatus 3A encodes video data at a high rate to generate compressed data (hereinafter referred to as high-rate compressed data) at the start of transmission (step S401). A packet including the compressed data and the sequence number is transmitted (step S402). As a result, video data encoded at a high rate is transmitted.

  The transmission device 3A receives the packet including the received sequence number from the reception device 4, and determines whether or not the reception is interrupted (step S403). If it is determined in step S403 that the reception is not interrupted (step S403: N), the transmission device 3A performs the high rate encoding process in step S401 and the packet transmission process in step S402. As a result, transmission of video data encoded at a high rate continues unless reception is interrupted.

  In FIG. 6, the first GOP includes frames 1-1 (frame number 1-1) to frames 1-N (frame number 1-N frames), and the second GOP starts from frame 2-1. An example in which the frame 2-N is configured and the third GOP is configured from the frame 3-1 to the frame 3-N is illustrated. In this example, video data encoded at a high rate is transmitted in packets from frame 1-1 to frame 2-n, and reception interruption is determined in packets in the middle of frame 2-n. The

  In FIG. 7, the horizontal axis indicates time, and the vertical axis indicates the transmission rate of packets transmitted from the transmission device 3A. It is assumed that the transmission band for visible light communication has a sufficient margin for the encoding rate. As shown in FIG. 7, when video data encoded at a high rate is being transmitted, real-time transmission according to the encoding rate is realized.

  Returning to FIG. 4, on the other hand, if the transmitting apparatus 3A determines in step S403 that the reception is interrupted (step S403: Y), the transmitting apparatus 3A proceeds to step S404 and transmits the video data encoded at a low rate. .

  FIG. 5 is a flowchart showing the reception interruption determination process according to the first embodiment, and shows the process of step S403 shown in FIG. The receiving unit 33 of the transmitting device 3A confirms whether or not a packet including the received sequence number has been received from the receiving device 4 at a predetermined timing (step S501). The predetermined timing is, for example, the timing at which the receiving unit 33 outputs the sequence number to the transmitting unit 34, or the timing of a predetermined cycle.

  If reception of the packet cannot be confirmed in step S501 (step S501: N), the reception unit 33 waits for a predetermined time (step S502), and receives a packet including the received sequence number from the reception device 4 again. It is confirmed whether or not it has been done (step S503).

  If the reception unit 33 cannot confirm the reception of the packet in step S503 (step S503: N), the reception unit 33 determines that the packet has not been received for a certain period of time (step S504). In this case, it is determined that the packet transmitted from the transmission device 3A to the reception device 4 has not arrived at the reception device 4, and it is determined that the visible light communication between the transmission device 3A and the reception device 4 has been disconnected. The

  On the other hand, if the reception unit 33 confirms reception of the packet in step S501 or step S503 (step S501: Y, step S503: Y), the reception unit 33 ends the process and repeats the process of FIG.

  Returning to FIG. 4, when the transmitting apparatus 3A determines that the reception is interrupted in step S403 (step S403: Y), the GOP corresponding to the sequence number next to the received sequence number included in the last received packet is returned. The video data from the first frame to the last frame of the GOP is encoded at a low rate (step S404). Then, the transmission device 3A transmits a packet including compressed data encoded at a low rate (hereinafter referred to as low-rate compressed data) and a sequence number (step S405). Since the visible light communication between the transmission device 3A and the reception device 4 is disconnected, the packet does not arrive at the reception device 4, and the transmission device 3A includes the received sequence number that is the sequence number. The packet cannot be received.

  In this case, the first video data in the first frame of the GOP is not transmitted. However, by repeating the processing of step S404, step S405 and step S406 described later, the first video data in the first frame is sequentially encoded at a low rate. Therefore, low-rate compressed data is generated corresponding to all the video data from the first frame to the last frame of the GOP and stored in the memory.

  Similar to the process of step S403, the transmission device 3A receives the packet including the received sequence number from the reception device 4, and determines whether or not the reception is cut off (step S406). If it is determined in step S406 that the reception is interrupted (step S406: Y), the transmitting apparatus 3A proceeds to step S404, and performs the low-rate encoding process in step S404 and the packet transmission process in step S405.

  In step S405, the transmitting apparatus 3A transmits the already transmitted packet to which the same sequence number is added (the same packet to which the first low-rate compressed data in the first frame of the GOP is stored and the sequence number is added). Since the transmission device 3A can determine that the packet transmission from the transmission device 3A is also disconnected until the packet including the new received sequence number (the same sequence number) is received from the reception device 4, the transmission device 3A As long as there is a packet, the packet with the same sequence number is continuously transmitted.

  In the example of FIG. 6, when reception interruption is determined in a packet in the middle of the frame 2-n, the GOP of the video data being transmitted is specified as the second GOP, and the first frame 2-1 Packet transmission is repeated. Also, as shown in FIG. 7, when it is determined that reception has been interrupted, transmission is not performed as long as it continues.

  If the transmitting device 3A receives the received sequence number from the receiving device 4 in step S406 and determines that the reception is not interrupted (step S406: N), the transmitting device 3A determines that reception has been recovered (visible light communication has been recovered). Then, the transmitting apparatus 3A completes transmission of the low-rate compressed data up to the final frame and determines whether or not reception has been confirmed (step S407), that is, the received sequence number received from the receiving apparatus 4 is the final frame. It is determined whether it is a sequence number corresponding to the last low-rate compressed data (sequence number added to the last packet of the last frame).

  In step S407, the transmission apparatus 3A has not completed transmission until the final frame and has not confirmed reception until the final frame (the received sequence number received from the reception apparatus 4 corresponds to the last low-rate compressed data of the final frame). When it is determined that it is not a sequence number (step S407: N), the process proceeds to step S404, and the transmission of the low-rate compressed data is continued.

  On the other hand, in step S407, the transmitting apparatus 3A has completed transmission up to the final frame and has received reception confirmation (the received sequence number received from the receiving apparatus 4 is a sequence number corresponding to the last low-rate compressed data of the final frame). If it is determined (Yes in step S407), the process proceeds to step S401, and a high rate encoding process in step S401 and a packet transmission process in step S402 are performed. In this case, in step S401 and step S402, the transmission apparatus 3A performs high-rate encoding processing and packet transmission from the GOP next to the GOP encoded and transmitted at the low rate. As a result, after the transmission of 1 GOP low-rate compressed data is completed, the transmission of high-rate compressed data is resumed.

  In the example of FIG. 6, when reception is restored, video data encoded at a low rate is transmitted in the packets from the first frame 2-1 to the last frame 2-N of the second GOP. For the packets after the first frame 3-1 of the third GOP, video data encoded at a high rate is transmitted.

  Also, as shown in FIG. 7, when reception is restored (when reception interruption time elapses), video data encoded at a low rate is transmitted. Since the video data encoded at a low rate is not transmitted during the reception interruption time but is stored in the memory waiting for the start of transmission, it is immediately read out from the memory when reception is restored, and the transmission bandwidth is reduced. Sent at the maximum rate. In other words, transmission of video data encoded at a low rate is a smaller amount and higher speed transmission than transmission of video data encoded at a high rate.

  In FIG. 7, for example, when the upper limit rate of the transmission band (Ethernet (registered trademark) wire rate) is 50 Mbps and video data encoded at a high rate of 10 Mbps is transmitted (in this state, the encoding rate is set to the encoding rate). The video data is transmitted at the corresponding 10 Mbps transmission rate.) It is assumed that the reception interruption is determined, the encoding rate is switched to a low rate of 1 Mbps, and the reception interruption time is 2 seconds. When reception is restored, video data (compressed data encoded at a low rate) corresponding to 2 seconds (2 Mbits) of reception interruption time is transmitted at a transmission rate of 50 Mbps for 0.04 seconds. Thereafter, the encoding rate is again switched to a high rate of 10 Mbps. In the receiving apparatus 4 described later, when the reproduction delay time at the start of decoding is 2.04 seconds or more, the video data is decoded without interruption.

  In the receiving device 4, the reproduction delay time is assumed to be a reception interruption time when reception interruption occurs in consideration of the underwater environment, the situation of the opposite relationship with the movement of the transmission device 3A and the reception device 4, and the like. To be preset.

(Processing of Receiving Unit 33 in Transmitting Device 3A / Example 1)
Next, the processing of the reception unit 33 in the transmission device 3A illustrated in FIG. 2 will be described in detail. FIG. 8 is a flowchart showing the processing of the receiving unit 33. First, in order to instruct high-rate encoding transmission, the receiving unit 33 outputs a high-rate rate switching instruction to the encoder 32 and also outputs a sequence number to the transmitting unit 34 (step S801). Accordingly, the encoder 32 encodes the video data input from the buffer 31 at a high rate, and the transmission unit 34 transmits a packet including the high rate compressed data and the sequence number.

  The reception unit 33 receives a packet including a received sequence number, which is a sequence number included in the packet transmitted by the transmission unit 34, from the reception device 4 in the same manner as the processing in step S403 in FIG. 4 and the processing in FIG. It is determined whether or not (step S802). If the reception unit 33 determines in step S802 that the packet including the received sequence number has been received (step S802: Y), that is, if it is determined that the reception is not interrupted, the reception unit 33 proceeds to step S801 and proceeds to the next high rate. In order to transmit the packet storing the compressed data with the next sequence number added, the high-rate encoding transmission instruction is continued. Thereby, unless reception is interrupted, a packet of video data encoded at a high rate is transmitted.

  If it is determined in step S802 that the packet including the received sequence number has not been received (step S802: N), that is, if the reception unit 33 determines that the reception has been interrupted, the receiving unit 33 has received the last received sequence. The GOP corresponding to the sequence number next to the number is specified (step S803).

  The receiving unit 33 outputs a low-rate rate switching instruction to the encoder 32 in order to instruct low-rate encoding transmission, and stores the frame numbers from the first frame to the last frame of the GOP specified in step S803 in the buffer 31. The sequence number is sequentially output, and the sequence number for transmitting the low-rate compressed data is output to the transmission unit 34 (step S804). Thereby, the encoder 32 encodes the video data from the first frame to the last frame input from the buffer 31 at a low rate, and the transmission unit 34 transmits a packet including the low-rate compressed data and the sequence number. This packet does not arrive at the receiving device 4 because the visible light communication between the transmitting device 3A and the receiving device 4 is disconnected.

  Similarly to the processing in step S802, the reception unit 33 includes a sequence number included in the packet transmitted by the transmission unit 34 (the packet storing the first low-rate compressed data in the first frame of the GOP specified in step S803). It is determined whether or not a packet including the received sequence number is received from the receiving device 4 (step S805). If it is determined in step S805 that the packet including the received sequence number has not been received (step S802: N), that is, if the reception unit 33 determines that the reception has been interrupted, the reception unit 33 proceeds to step S804. Continue rate encoding transmission instructions. As a result, unless reception is recovered, low-rate compressed data is generated, and the same packet (the already transmitted packet with the same sequence number added (the first low-rate compressed data in the first frame of the GOP identified in step S803) The transmission of the same packet with the stored sequence number added is continued.

  If the reception unit 33 determines in step S805 that the packet including the received sequence number has been received from the reception device 4 (step S805: Y), the reception unit 33 determines that reception has been recovered (visible light communication has been recovered). Then, the low-rate compressed data is continuously transmitted at high speed by the transmission unit 34, and the reception unit 33 determines that the received sequence number determined in step S805 is the last received sequence number of the last frame (the last frame of the last frame). It is determined whether or not the sequence number is added to the packet (step S806).

  If the reception unit 33 determines in step S806 that the received sequence number is not the last received sequence number of the last frame (step S806: N), the reception unit 33 proceeds to step S804 and continues the low-rate encoding transmission instruction. .

  On the other hand, if the receiving unit 33 determines in step S806 that the received sequence number is the last received sequence number of the last frame (step S806: Y), transmission of the low-rate compressed data is completed up to the last frame. Then, it is determined that the reception has been confirmed, and the process proceeds to step S801 to restart the instruction for high-rate encoding transmission.

  In this case, the reception unit 33 outputs a high rate rate switching instruction to the encoder 32 and also outputs a sequence number to the transmission unit 34 in step S801. Further, since the output of the video data of the last frame is completed, the buffer 31 sequentially outputs the video data from the first frame to the encoder 32 for the next GOP. As a result, the encoder 32 encodes the video data from the first frame of the next GOP at a high rate, and the transmitter 34 transmits a packet including the high-rate compressed data and the sequence number from the first frame of the next GOP. .

(Processing of Transmission Unit 34 in Transmission Device 3A / Example 1)
Next, processing of the transmission unit 34 in the transmission device 3A illustrated in FIG. 2 will be described in detail. FIG. 9 is a flowchart showing processing of the transmission unit 34. First, the transmission unit 34 inputs compressed data from the encoder 32 (step S901). Then, the transmission unit 34 divides the compressed data into a predetermined size and stores it in the memory.

  The transmission unit 34 inputs a sequence number from the reception unit 33 (step S902). When the transmission target compressed data is stored in the memory and the transmission target sequence number is also input, the transmission unit 34 reads the compressed data divided from the memory, stores the compressed data in the packet, and A packet is generated by adding a sequence number in order (step S903), the visible light is modulated using a visible light carrier wave, and the modulated signal is transmitted to the receiving device 4 by underwater wireless visible light (step S903). S904). Then, the process of FIG. 9 is repeated. Note that if the compressed data to be transmitted is not stored in the memory or the sequence number to be transmitted is not input, the transmitting unit 34 does not perform processing.

  Here, as illustrated in FIG. 7, the transmission unit 34 performs real-time transmission corresponding to high-rate encoding while transmitting packets of high-rate compressed data. The transmission unit 34 transmits the low-rate compressed data packet as described above while the reception unit 33 determines that the reception is interrupted. However, the packet does not arrive at the reception device 4 and the packet Continue sending. When the reception is recovered, the transmission unit 34 arrives at the low-rate compressed data packet at the reception device 4 and, while performing this transmission, realizes small-volume transmission and high-speed transmission at the upper limit rate of the transmission band.

  As described above, according to the transmission device 3A of the first embodiment, in the state where the video data is encoded and transmitted at a high rate, the reception interruption is interrupted by not receiving the received sequence number from the reception device 4 for a certain period of time. When the determination is made, the GOP corresponding to the sequence number next to the last received sequence number is identified, the encoding rate is switched from the high rate to the low rate, and the video data of the last frame from the first frame of the identified GOP is converted to the low rate. Encoded with and sent. In this case, the video data is not transmitted because the reception is interrupted. When the transmission device 3 receives the received sequence number from the reception device 4 and determines reception recovery, the transmission device 3 transmits video data encoded at a low rate from the first frame to the last frame of the GOP, and the video of the last frame is transmitted. When data transmission is completed (when the last received sequence number of the last frame is received), the encoding rate is returned to the original high rate, and video data is encoded and transmitted from the first frame of the next GOP at a high rate. I made it.

  Thus, after the reception recovery is determined, the video data encoded at the low rate is transmitted within the upper limit of the transmission band in a smaller amount and at a higher speed than the video data encoded at the high rate.

  When the receiving device 4 receives video data encoded at a low rate within a predetermined reproduction delay time, the image quality of the video displayed on the video monitor 5 deteriorates, but the displayed video is not interrupted. That is, when video data is transmitted underwater with visible light, even if the visible light is interrupted, the video data can be continuously transmitted without interruption. Accordingly, since the video data is difficult to be interrupted, for example, even when a command is issued from the receiving device 4 to the transmitting device 3A by voice or the transmitting device 3A is remotely controlled, the work can be performed smoothly. It becomes.

(Configuration of Receiving Device 4 / Example 1)
Next, the configuration of the receiving device 4 according to the first embodiment will be described in detail. With reference to FIG. 2, the reception device 4 includes a reception unit 41, a transmission unit 42, a buffer 43, and a decoder 44.

  The receiving unit 41 receives the modulated signal from the transmitting device 3, demodulates the modulated signal with visible light, generates a packet, and extracts the divided compressed data and the sequence number from the packet. Then, the receiving unit 41 combines the divided compressed data to generate compressed data, stores the compressed data in the buffer 43 for each frame, and outputs the sequence number to the transmitting unit 42 as the received sequence number.

  In the embodiment of the present invention, when receiving the compressed data from the first frame of the GOP, the receiving unit 41 deletes the duplicated compressed data. Specifically, when the reception unit 41 generates low-rate compressed data in a certain GOP and high-rate compressed data of the same GOP is stored in the buffer 43, the receiving unit 41 deletes the high-rate compressed data from the buffer 43. The new low rate compressed data is stored in the buffer 43.

  As a result, when the reception unit 41 receives high-rate compressed data and the reception is cut off in the middle of the GOP and then receives low-rate compressed data from the first frame of the same GOP, the receiving unit 41 is in the middle of the GOP. The high-rate compressed data received up to is deleted.

  Note that the receiving unit 41 has previously received information from the transmission apparatus 3A and obtained information on association between the sequence number, the divided compressed data, and the GOP to which the frame of the divided compressed data belongs. Assume that the stored correspondence table is held.

  The transmission unit 42 receives the received sequence number from the reception unit 41, stores the received sequence number, generates a packet, modulates the packet with visible light, and transmits the modulated signal with an underwater radio of visible light. Send to.

  The buffer 43 stores the compressed data, and the stored compressed data is read by the decoder 44 at a predetermined timing.

  The decoder 44 sequentially reads out and decodes (decodes) the compressed data from the buffer 43 after a predetermined reproduction delay time, and restores the original baseband video signal to the video data. Then, the decoder 44 outputs the baseband video signal to the video monitor 5.

  Here, when the high-rate compressed data is read from the buffer 43, the decoder 44 decodes the high-rate compressed data at a rate corresponding to the high rate. When the decoder 44 reads low-rate compressed data from the buffer 43, the decoder 44 decodes the low-rate compressed data at a rate corresponding to the low rate.

(Processing of receiving apparatus 4 / Example 1)
Next, the processing of the receiving device 4 shown in FIG. 2 will be described in detail. FIG. 10 is a flowchart showing processing of the receiving device 4. First, the reception device 4 receives a packet from the transmission device 3A (step S1001), and extracts divided compressed data and a sequence number from the packet (step S1002).

  The receiving device 4 transmits the sequence number extracted in step S1002 as a received sequence number to the transmitting device 3A (step S1003), combines the divided compressed data extracted in step S1002, and generates compressed data. Data is stored in the buffer 43 for each frame, decoded after a predetermined reproduction delay time, and output to the video monitor 5 (step S1004).

  The receiving device 4 refers to the correspondence table in which the correspondence information between the sequence number, the divided compressed data, and the GOP is stored, and based on the sequence number extracted in step S1002, the division extracted in step S1002 It is determined whether or not the compressed data is the first divided compressed data of the first frame of the GOP (step S1005).

  When the receiving device 4 determines in step S1005 that the extracted divided compressed data is the first divided compressed data of the first frame of the GOP (step S1005: Y), the receiving device 4 refers to the correspondence table and has already stored the same data. The compressed data in the GOP is deleted from the buffer 43 (step S1006). Then, if the receiving apparatus 4 determines in step S1005 that the divided compressed data is not the first divided compressed data of the first frame of the GOP (step S1005: N), or proceeds from step S1006, and repeats the process of FIG.

  As described above, according to the receiving device 4 of the first embodiment, the received video is received in order to receive the video data and the sequence number from the transmitting device 3A and cause the transmitting device 3A to determine whether or not the communication is disconnected. The sequence number corresponding to the data is transmitted to the transmitting apparatus 3A as the received sequence number. Further, the received video data is stored in the buffer 43, and after a predetermined reproduction delay time, the video data is read from the buffer 43 and decoded, and when the video is displayed on the video monitor 5, the video data received from the transmitter 3A is displayed. Of these, when video data is received redundantly from the first frame of the GOP (when video data encoded at a low rate is received), duplicate video data already received and stored (video encoded at a high rate) Data) is deleted from the buffer 43.

  As a result, while the communication is disconnected, the video data already stored in the buffer 43 (video data encoded at a high rate) is read and decoded, and the video is displayed on the video monitor 5. When communication is restored, video data encoded at a low rate is transmitted in a small amount and at a high speed and stored in the buffer 43. In this case, if the video data is read from the buffer 43 and decoded within the predetermined reproduction delay time, the image quality of the video displayed on the video monitor 5 deteriorates, but the displayed video is not interrupted. That is, when video data is transmitted underwater with visible light, even if the visible light is interrupted, the video data can be continuously transmitted without interruption. Accordingly, since the video data is difficult to be interrupted, for example, even when a command is issued from the receiving device 4 to the transmitting device 3A by voice or the transmitting device 3A is remotely controlled, the work can be performed smoothly. It becomes.

[Example 2]
Next, a second embodiment (Example 2) of the present invention will be described. The second embodiment is an extension of the first embodiment, and is characterized in that transmission is continuously repeated between the transmission side and the reception side. As a result, transmission at the upper limit rate of the transmission band becomes possible, so that it is possible to easily determine whether or not reception is interrupted.

  The configuration of the second embodiment is the same as the configuration of the first embodiment shown in FIG. 2, and the processing of the transmitting device 3A and the receiving device 4 in the second embodiment is basically the same as that of the first embodiment. The receiving unit 33 and the transmitting unit 34 of the transmitting device 3A in the second embodiment and a part of the receiving unit 41 and the transmitting unit 42 of the receiving device 4 perform processing different from the first embodiment.

(Receiving unit 33 of transmitting apparatus 3A / Example 2)
Specifically, the receiving unit 33 of the transmission device 3A according to the second embodiment performs processing of step S802 and step S805 (reception interruption determination processing different from that of the first embodiment in the processing illustrated in FIG. 8, illustrated in FIG. Step S403 and the process of FIG. 5) are performed.

  FIG. 11 is a flowchart illustrating a reception interruption determination process according to the second embodiment, and corresponds to the process according to the first embodiment illustrated in FIG. The receiving unit 33 of the transmitting device 3A checks whether or not a packet including the received sequence number has been received from the receiving device 4 (step S1101).

  If the reception unit 33 cannot confirm the reception of the packet in step S1101 (step S1101: N), the reception unit 33 determines a reception interruption (step S1102). In this case, it is determined that the packet transmitted from the transmission device 3A to the reception device 4 has not arrived at the reception device 4, and it is determined that the visible light communication between the transmission device 3A and the reception device 4 has been disconnected. The

  On the other hand, when the reception unit 33 confirms reception of the packet in step S1101 (step S1101: Y), the reception unit 33 ends the process and repeats the process of FIG.

  As a result, the receiving unit 33 can immediately determine the reception interruption without waiting for a certain time when the packet including the received sequence number has not been received.

(Transmitter 34 of Transmitter 3A / Example 2)
Further, as described above, the transmission unit 34 of the transmission device 3A in the second embodiment performs processing different from that in the first embodiment illustrated in FIG. 9 (step S402 and step different from the first embodiment in the processing illustrated in FIG. 4). Packet transmission processing in step S405).

  FIG. 12 is a flowchart illustrating the processing of the transmission unit 34 according to the second embodiment. The transmission unit 34 performs the same processing as Step S901 and Step S902 of the first embodiment illustrated in FIG. 9 (Step S1201, Step S1202), and whether or not new compressed data has been input from the encoder 32 in Step S1201. Is determined (step S1203).

  If it is determined in step S1203 that new compressed data has already been input (step S1203: Y), the transmission unit 34 performs the same processing as steps S903 and S904 of the first embodiment illustrated in FIG. 9 (step S1203). S1204, step S1205).

  On the other hand, if it is determined in step S1203 that new compressed data has not been input (step S1203: N), the transmission unit 34 determines whether the packet transmission has reached the upper limit rate of the transmission band of visible light communication. (Step S1206).

  If the transmission unit 34 determines in step S1206 that the packet transmission has not reached the upper limit rate of the transmission band of visible light communication (step S1206: N), the packet of the same GOP currently transmitted (transmitted packet) ) Are repeatedly transmitted (step S1207). Thereby, the packet is transmitted at the upper limit rate of the transmission band.

  When the packet transmission has reached the upper limit rate of the transmission band of visible light communication in step S1205 and step S1206 (step S1206: Y), the transmission unit 34 shifts from step S1207 and repeats the process shown in FIG.

(Receiving unit 41 and transmitting unit 42 of receiving apparatus 4 / Example 2)
As described above, the receiving unit 41 and the transmitting unit 42 of the receiving device 4 in the second embodiment perform processing different from that in the first embodiment.

  FIG. 13 is a flowchart illustrating processing of the receiving device 4 according to the second embodiment. The receiving unit 41 of the receiving device 4 performs the same processing as steps S1001 and S1002 of the first embodiment illustrated in FIG. 10 (steps S1301 and S1302).

  The transmission unit 42 continuously and repeatedly transmits a packet including the received sequence number to the transmission device 3A using the sequence number extracted by the reception unit 41 in step S1302 as the received sequence number (step S1303). As a result, the same packet including the latest received sequence number is always transmitted, and the packet transmitted from the receiver 4 is transmitted at the upper limit rate of the transmission band as well as the packet transmitted from the transmitter 3A.

  The receiving unit 41 determines whether or not the sequence number extracted in step S1302 is a new sequence number different from the previously received sequence number (step S1304). If the reception unit 41 determines in step S1304 that the sequence number is new (step S1304: Y), the reception unit 41 combines the divided compressed data extracted in step S1302 to generate compressed data. Then, the decoder 44 reads and decodes the compressed data from the buffer 43 after a predetermined reproduction delay time, and outputs the decoded data to the video monitor 5 (step S1305).

  On the other hand, if the reception unit 41 determines in step S1304 that the sequence number is not a new sequence (step S1304: N), the reception unit 41 deletes the divided compressed data extracted in step S1302 (step S1306).

  Based on the sequence number extracted in step S1302, the receiving unit 41 proceeds from step S1305 and refers to the correspondence table in which the correspondence information between the sequence number, the divided compressed data, and the GOP is stored. It is determined whether or not the divided compressed data extracted in step S1302 is the first divided compressed data of the first frame of the GOP (step S1307).

  If the receiving unit 41 determines in step S1307 that the extracted divided compressed data is the first divided compressed data of the first frame of the GOP (step S1307: Y), the reception unit 41 refers to the correspondence table and has already stored the same data. The compressed data in the GOP is deleted from the buffer 43 (step S1308). Then, when it is determined in step S1306 or step S1307 that the divided compressed data is not the first divided compressed data of the first frame of the GOP (step S1307: N), or the process proceeds from step S1308, and the process of FIG. 13 is repeated.

  As described above, according to the transmission device 3A of the second embodiment, in addition to performing the same processing as the transmission device 3A of the first embodiment, when transmitting the video data encoded at a high rate, the transmission unit 34 If new video data has not been input and packet transmission has not reached the upper limit rate of the visible light communication transmission band, the packet of the same GOP currently being transmitted (transmitted packet) is continuously repeated. Transmitted at the upper limit rate of the transmission band.

  Thereby, the receiving device 4 can receive a packet at the upper limit rate of the transmission band and can transmit a packet including the received sequence number at the upper limit rate of the transmission band. For example, even when a short communication interruption of about several packets occurs, when the reception device 4 receives a packet including a sequence number at the time of communication interruption after the communication recovery, the transmission device 3A is an example There is no need to switch the rate as in 1, and the receiving device 4 can continue to receive the video data, and the video is not interrupted.

  Further, the reception unit 33 of the transmission device 3A determines the reception interruption without waiting for a fixed time when the reception sequence number to be transmitted at the upper limit rate of the transmission band is not received from the reception device 4. As a result, reception interruption can be immediately determined. In other words, the processing configuration for determining the reception interruption can be simplified as compared with the first embodiment in which the reception interruption is determined by waiting for a certain time and the example in which the reception interruption information is directly acquired from the reception side, for example. In addition, it is possible to speed up the determination of reception interruption.

  Further, according to the transmission device 3A of the second embodiment, the same effects as those of the first embodiment are obtained. That is, when video data is transmitted underwater with visible light, even if the visible light is interrupted, the video data can be continuously transmitted without interruption.

  Furthermore, according to the receiving device 4 of the second embodiment, in addition to performing the same processing as the receiving device 4 of the first embodiment, the transmitting unit 42 transmits the sequence number received by the receiving unit 41 as the received sequence number. It was made to always transmit to apparatus 3A continuously. Thus, since the received sequence number is transmitted to the transmission device 3A at the upper limit rate of the transmission band, the transmission device 3A can immediately determine whether or not the reception has been interrupted without waiting for a certain period of time.

  Further, according to the receiving device 4 of the second embodiment, the same effects as those of the first embodiment are obtained. That is, when video data is transmitted underwater with visible light, even if the visible light is interrupted, the video data can be continuously transmitted without interruption.

Example 3
Next, a third embodiment (Example 3) of the present invention will be described. The third embodiment is a modification of the first embodiment. On the transmission side, when the video data encoded at the high rate is transmitted and the video data encoded at the low rate is stored in the buffer, the communication is interrupted. If it is determined, the video data is read from the buffer to switch to transmission of video data encoded at a low rate, and if communication recovery is determined, transmission of video data encoded at a low rate is transmitted from the GOP start frame to the final frame. After completing the above, it returns to transmission of video data encoded at a high rate. Accordingly, since it is only necessary to provide a buffer that stores only video data (compressed data) encoded at a low rate, the buffer capacity can be reduced as compared with the case of providing a buffer that stores a baseband video signal.

  FIG. 14 is a block diagram illustrating configurations of the transmission device 3 and the reception device 4 according to the third embodiment. The underwater transmission system 1 according to the third embodiment includes a transmission device 3B and a reception device 4. Comparing the configuration of the first embodiment illustrated in FIG. 2 with the configuration of the third embodiment illustrated in FIG. 14, both the first and third embodiments are the same in that the same receiving device 4 is provided. Is different in that a transmission device 3B different from the transmission device 3A of the first embodiment is provided.

(Configuration of Transmitter 3B / Example 3)
First, the configuration of the transmission device 3B according to the third embodiment will be described in detail. The transmission device 3B includes encoders 51 and 52, a buffer 53, a reception unit 54, and a transmission unit 55. The buffer 53 is provided at the subsequent stage of the encoder 52, and high-speed compression is performed when visible light communication is disconnected. It is configured to switch from data transmission to low-rate compressed data transmission.

  The encoder 51 is a high-rate encoder, which inputs a baseband video signal from the camera 2 and encodes the video data of the baseband video signal at a predetermined rate (high rate) to generate high-rate compressed data. The high rate compressed data is output to the transmission unit 55.

  The encoder 52 is a low-rate encoder, which receives a baseband video signal from the camera 2 and outputs video data of the baseband video signal at a predetermined rate (low rate, lower than the high rate in the encoder 51). The low rate compressed data is generated by encoding, and the low rate compressed data is stored in the buffer 53.

  The buffer 53 receives the low-rate compressed data from the encoder 52 and stores the low-rate compressed data for each frame. The buffer 53 holds the stored low-rate compressed data for a predetermined time, and deletes the low-rate compressed data after a predetermined time has elapsed. Further, when the frame number is input from the receiving unit 54, the buffer 53 outputs the low-rate compressed data of the frame number to the transmitting unit 55.

  The receiving unit 54 performs the same processing as the receiving unit 33 illustrated in FIG. When the reception unit 54 determines that the reception has been interrupted, the reception unit 54 outputs a low-rate rate switching instruction to the transmission unit 55, and for the GOP of the video data that is being transmitted, In order to sequentially output the rate compressed data from the buffer 53, the frame numbers are sequentially output to the buffer 53. In addition, the receiving unit 54 outputs a sequence number to the transmitting unit 55 in order to sequentially transmit low-rate compressed data packets from the first frame to the last frame of the GOP.

  When the reception unit 54 determines the reception recovery, after the transmission of the low-rate compressed data packet is completed up to the last frame of the GOP, the reception unit 54 outputs a high-rate rate switching instruction to the transmission unit 55 and the high-rate compressed data. Is output to the transmission unit 55. As a result, the transmission unit 55 sequentially transmits the high-rate compressed data input from the encoder 51 and the high-rate compressed data from the first frame of the next GOP.

  The transmission unit 55 receives the high rate compressed data from the encoder 51, the low rate compressed data from the buffer 53, and the sequence number and the rate switching instruction from the reception unit 54. The transmission unit 55 divides the high-rate compressed data for each packet when a high-rate rate switching instruction is input, and divides the low-rate compressed data for each packet when a low-rate rate switching instruction is input.

  The transmission unit 55 stores the divided high-rate compressed data or low-rate compressed data in the packet, and sequentially adds sequence numbers to the packet. Then, the transmission unit 55 generates a packet, modulates the packet with visible light using a visible light carrier wave, and transmits the modulated signal to the receiving device 4 through underwater wireless light.

  In this case, for a packet generated by the transmission unit 55 (a packet including a sequence number and divided compressed data), the receiving unit 54 sets the sequence number, the divided compressed data, and the GOP to which the frame of the divided compressed data belongs. Perform the association. As a result, the receiving unit 54 can recognize which divided compressed data, which frame corresponds to which received compressed sequence number received from the receiving device 4, and which GOP.

(Processing of Transmitter 3B / Example 3)
Next, the processing of the transmission device 3B illustrated in FIG. 14 will be described in detail. FIG. 15 is a flowchart showing processing of the transmission device 3B. First, the encoder 51 of the transmission device 3B encodes the video data of the baseband video signal input from the camera 2 at a high rate (step S1501), and the transmission unit 55 starts the high-rate compressed data and sequence number at the start of transmission. Is transmitted (step S1502). As a result, video data encoded at a high rate is transmitted.

  Simultaneously with the processing of step S1501 and step S1502, the encoder 52 encodes the video data of the baseband video signal input from the camera 2 at a low rate (step S1503), and stores the low-rate compressed data in the buffer 53. (Step S1504).

  The receiving unit 54 receives the packet including the received sequence number from the receiving device 4 and determines whether or not the reception is interrupted in the same processing as shown in FIG. 5 (step S1505). If the reception unit 54 determines in step S1505 that the reception is not interrupted (step S1505: N), the high rate encoding process in step S1501, the packet transmission process in step S1502, the low rate encoding process in step S1503, and the step S1504. Low-rate compressed data storage processing is performed. As a result, video data encoded at a low rate is always stored, and transmission of video data encoded at a high rate continues unless reception is interrupted.

  On the other hand, if the reception unit 54 determines in step S1505 that the reception has been interrupted (step S1505: Y), the reception unit 54 proceeds to step S1506 and transmits the video data encoded at a low rate.

  If the reception unit 54 determines in step S1505 that the reception has been interrupted (step S1505: Y), it identifies the GOP corresponding to the sequence number next to the received sequence number included in the last received packet, and the GOP The frame number for outputting the low-rate compressed data from the first frame to the last frame is sequentially output to the buffer 53. When the frame number is input from the receiving unit 54, the buffer 53 starts from the first frame of the GOP. Low-rate compressed data up to the final frame is sequentially output to the transmission unit 55 (step S1506).

  The transmission unit 55 transmits a packet including low-rate compressed data and a sequence number (step S1507). Since the visible light communication between the transmission device 3B and the reception device 4 is disconnected, the packet does not arrive at the reception device 4, and the transmission device 3B receives the packet including the received sequence number. I can't.

  Here, although not explicitly shown in the flowchart of FIG. 15, in the low-rate compressed data output process in step S1506 and the packet transmission process in step S1507, the low-rate encoding process in step S1503 and the low-rate compressed data storage process in step S1504 Is always done.

  Similarly to the processing in step S1505, the reception unit 54 receives the packet including the received sequence number from the reception device 4, and determines whether or not the reception is interrupted (step S1508). If the reception unit 54 determines in step S1508 that the reception is interrupted (step S1508: Y), the reception unit 54 proceeds to step S1506, and low-rate compressed data output processing in step S1506 and packet transmission processing in step S1507 are performed.

  In this case, in step S1507, the transmission unit 55 transmits the already transmitted packet to which the same sequence number is added (the same packet to which the first low-rate compressed data in the first frame of the GOP being transmitted is stored and the sequence number is added). Send. Since the transmission unit 55 can determine that the packet transmission from the transmission device 3B is also disconnected until the reception unit 54 receives the packet including the new received sequence number from the reception device 4, as long as the reception is disconnected. Continue to transmit packets with the same sequence number.

  If the reception unit 54 receives the received sequence number from the reception device 4 in step S1508 and determines that the reception is not interrupted (step S1508: N), the reception unit 54 determines that reception has been recovered (visible light communication has been recovered). Then, the receiving unit 54 completes transmission of the low-rate compressed data up to the final frame and determines whether or not reception has been confirmed (step S1509), that is, the received sequence number received from the receiving device 4 is the final frame. It is determined whether it is the sequence number corresponding to the last low-rate compressed data (sequence number added to the packet to which the last low-rate compressed data of the last frame is transmitted).

  In step S1509, the reception unit 54 has not completed transmission until the final frame and has not confirmed reception until the final frame (the received sequence number received from the reception device 4 corresponds to the last low-rate compressed data of the final frame). When it is determined that it is not a sequence number (step S1509: N), the low-rate compressed data output process at step S1506 and the packet transmission process at step S1507 are continued.

  On the other hand, in step S1509, the receiving unit 54 completes transmission up to the final frame and has confirmed reception (the received sequence number received from the receiving device 4 is a sequence number corresponding to the last low-rate compressed data of the final frame). If it is determined (Yes) (step S1509: Y), the process proceeds to step S1501 and step S1503. In this case, in step S1502, the transmission unit 55 transmits a high-rate compressed data packet from the GOP next to the GOP that transmitted the low-rate compressed data packet. Thereby, after the transmission of the video data of the GOP encoded at the low rate is completed, the transmission of the video data encoded at the high rate is resumed.

(Processing of Transmitter 55 in Transmitting Device 3B / Example 3)
Next, processing of the transmission unit 55 in the transmission device 3B illustrated in FIG. 14 will be described in detail. FIG. 16 is a flowchart showing the processing of the transmission unit 55. First, the transmission unit 55 inputs high rate compressed data from the encoder 51 (step S1601). Then, the transmission unit 55 divides the high-rate compressed data into a predetermined size and stores it in the memory.

  The transmission unit 55 inputs a sequence number and a rate switching instruction from the reception unit 54 (step S1602). Then, the transmission unit 55 determines whether the rate switching instruction indicates a high rate or a low rate (step S1603).

  If the transmission unit 55 determines in step S1603 that the rate switching instruction indicates a high rate (step S1603: rate switching instruction = high rate), the high-rate compressed data to be transmitted is stored in the memory, When the sequence number to be transmitted is input, the high-rate compressed data divided from the memory is read, the high-rate compressed data is stored, and a packet is generated by sequentially adding the sequence number (step S1604). The packet is subjected to visible light modulation using a visible light carrier wave, and the modulated signal is transmitted to the receiving device 4 by underwater wireless visible light (step S1607). Then, the process of FIG. 16 is repeated. Note that if the high-rate compressed data to be transmitted is not stored in the memory or the sequence number to be transmitted is not input, the transmission unit 55 does not perform processing.

  On the other hand, when the transmission unit 55 determines in step S1603 that the rate switching instruction indicates a low rate (step S1603: rate switching instruction = low rate), the transmission unit 55 receives the low-rate compressed data. The low rate compressed data is read out from the buffer 53 (step S1605). The transmission unit 55 divides the low-rate compressed data into a predetermined size and stores it in the memory.

  When the transmission target low-rate compressed data is stored in the memory and the transmission target sequence number is input, the transmission unit 55 reads the low-rate compressed data divided from the memory and stores the low-rate compressed data. At the same time, a packet is generated by sequentially adding a sequence number (step S1606), the visible light is modulated using a visible light carrier wave, and the modulated signal is transmitted to the receiving device 4 by underwater wireless light. (Step S1607). Then, the process of FIG. 16 is repeated. If the low-rate compressed data to be transmitted is not stored in the memory or the sequence number to be transmitted is not input, the transmitting unit 55 does not perform processing.

  As described above, according to the transmission device 3B of the third embodiment, video data is encoded at a high rate, high-rate compressed data is transmitted, video data is encoded at a low rate, and low-rate compressed data is stored in the buffer 53. When the reception interruption is determined by not receiving the received sequence number from the receiving device 4 for a certain period of time, the GOP corresponding to the sequence number next to the last received sequence number is specified and specified. Low-rate compressed data from the first frame to the last frame of the GOP is read from the buffer 53 and transmitted. In this case, the video data is not transmitted because the reception is interrupted. When the transmission device 3B receives the received sequence number from the reception device 4 and determines reception recovery, the transmission device 3B transmits low-rate compressed data from the first frame to the last frame of the GOP, and the low-rate compressed data of the last frame Is completed (when the last received sequence number of the last frame is received), the transmission is returned to the transmission of the high-rate compressed data, and the high-rate compressed data is transmitted from the first frame of the next GOP.

  Thereby, there exists an effect similar to Example 1. That is, when video data is transmitted underwater with visible light, even if the visible light is interrupted, the video data can be continuously transmitted without interruption.

  In addition, the transmission device 3B includes two high-rate encoders 51 and two low-rate encoders 52, and includes a buffer 53 only in the subsequent stage of the low-rate encoder 52. The high-rate compressed data is directly output from the high-rate encoder 51 to the transmission unit 55, and the low-rate compressed data is output from the low-rate encoder 52 and temporarily stored in the buffer 53, and the low-rate compressed data Is transmitted from the buffer 53 to the transmission unit 55.

  Thereby, since only the low-rate compressed data is stored in the buffer 53, the required buffer capacity can be reduced compared to the first and second embodiments in which the baseband video signal is stored in the buffer 31.

  Further, the receiving device 4 of the third embodiment has the same configuration as that of the first embodiment, and therefore has the same effect as that of the first embodiment.

  The present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the technical idea thereof. For example, in the third embodiment, the first embodiment is modified, but the second embodiment may be modified. In this case, a modification of the third embodiment is that when transmitting high-rate compressed data on the transmission side, the transmission unit 55 does not input new high-rate compressed data, and packet transmission is the upper limit of the transmission band. If the rate has not been reached, a packet of the same GOP currently being transmitted (transmitted packet) is repeatedly transmitted continuously. Then, unless new high-rate compressed data is input, the transmission unit 55 repeatedly transmits packets of the same GOP at the upper limit rate of the transmission band. On the other hand, when new high-rate compressed data is input, the transmission unit 55 stops the process of repeatedly transmitting the same GOP packet repeatedly, and transmits the input high-rate compressed data packet.

DESCRIPTION OF SYMBOLS 1 Underwater transmission system 2 Camera 3 Transmitter 4 Receiver 5 Video monitor 6, 7 Cable 31, 43, 53 Buffer 32, 51, 52 Encoder 33, 41, 54 Receiver 34, 42, 55 Transmitter 44 Decoder

Claims (6)

In a transmitter that transmits video data to a receiver using visible light in water,
A buffer for storing the video data;
An encoder that encodes video data stored in the buffer at a predetermined high rate or low rate to generate compressed data;
The compressed data generated by the encoder is divided into packets and stored as divided compressed data in the packet, and a sequence number corresponding to the divided compressed data is added to the packet, and the divided compressed data and the sequence number are A transmitter that modulates a packet including the carrier wave of visible light and transmits a modulated signal;
An instruction for encoding at the predetermined high rate or low rate is output to the encoder, the sequence number is output to the transmitter, and the sequence included in the packet is received from the receiving device that has received the modulated signal. A receiving unit for receiving a number as a received sequence number,
The receiver is
In the state where the transmission unit transmits the modulated signal of the packet including the divided compressed data encoded and divided at the high rate and the sequence number, the reception is disconnected when the received sequence number is not received for a predetermined time. When the determination is made, an instruction for encoding at a low rate is output to the encoder, and a sequence number corresponding to the divided compressed data that is encoded and divided at the low rate is output to the transmission unit. Transmitting a modulated signal of a packet including divided compressed data encoded and divided at a low rate and the sequence number;
When receiving recovery is determined when the received sequence number corresponding to the divided compressed data encoded and divided at the low rate is received, the divided compressed data in the video data of a predetermined size encoded at the low rate and the After the transmitter transmits a modulated signal of a packet including a sequence number, an instruction for encoding at a high rate is output to the encoder, and the sequence number corresponding to the divided compressed data to be encoded and divided at the high rate Is transmitted to the transmission unit, and the transmission unit transmits the modulated signal of the packet including the divided compressed data encoded and divided at the high rate and the sequence number. The transmission apparatus according to claim 1,
The transmitter is
After the modulated signal of the packet including the divided compressed data and the sequence number is transmitted, the modulated signal of the packet including the same divided compressed data and the sequence number is repeatedly transmitted continuously. Transmitter device. In a transmitter that transmits video data to a receiver using visible light in water,
A first encoder that encodes the video data at a predetermined high rate to generate high rate compressed data;
A second encoder that encodes the video data at a predetermined low rate to generate low rate compressed data;
A buffer for storing low-rate compressed data generated by the second encoder;
When a high-rate instruction is input, the high-rate compressed data generated by the first encoder is divided for each packet, the divided high-rate compressed data is stored in the packet, and the divided high-rate compressed data is converted into the divided high-rate compressed data. A corresponding sequence number is added to the packet, the divided high-rate compressed data and the packet including the sequence number are modulated using a visible light carrier, and a modulated signal is transmitted.
Alternatively, when a low rate instruction is input, the low rate compressed data stored in the buffer is divided for each packet, the divided low rate compressed data is stored in the packet, and the divided low rate compressed data is supported. A transmission unit that adds a sequence number to the packet, modulates the divided low-rate compressed data and the packet including the sequence number using a visible light carrier, and transmits a modulated signal;
A receiving unit that outputs the high-rate or low-rate instruction and the sequence number to the transmitting unit, and receives the sequence number included in the packet as a received sequence number from the receiving device that has received the modulated signal; With
The receiver is
When the transmission unit transmits the modulated signal of the packet including the divided high-rate compressed data and the sequence number, and the reception sequence number is not received for a predetermined time, it is determined that the reception interruption has occurred. A rate instruction and a sequence number corresponding to the divided low-rate compressed data are output to the transmission unit, and the transmission unit transmits a modulated signal of a packet including the divided low-rate compressed data and the sequence number. ,
When receiving recovery is determined when the received sequence number corresponding to the divided low-rate compressed data is received, the divided low-rate compressed data and the modulation signal of the packet including the sequence number in video data of a predetermined size are obtained. After the transmission unit transmits, the high rate instruction and a sequence number corresponding to the divided high rate compressed data are output to the transmission unit, and the divided high rate compressed data and the sequence are output to the transmission unit. A transmission apparatus that transmits a modulated signal of a packet including a number. A receiving apparatus for receiving video data using visible light in water, wherein the receiving apparatus receives a modulated signal transmitted from the transmitting apparatus according to claim 1 or 3.
The modulated signal is received, the modulated signal is demodulated using the visible light carrier wave, a packet is generated, the divided compressed data and the sequence number are extracted from the packet, and the divided compressed data is combined and compressed. A receiver for generating data;
The sequence number extracted by the receiving unit is a received sequence number, a packet including the received sequence number is modulated using the visible light carrier, and a transmitting unit that transmits a modulated signal;
A buffer for storing compressed data generated by the receiving unit;
A decoder that sequentially reads and decodes the compressed data from the buffer after a predetermined reproduction delay time, and restores the original video data;
The receiver is
When the same compressed data is generated in duplicate, the received compressed data is deleted from the buffer, and the newly generated compressed data is stored in the buffer. The receiving device according to claim 4,
Instead of receiving the modulated signal transmitted from the transmitter of claim 1 or claim 3, the modulated signal transmitted from the transmitter of claim 2 or claim 3 is received,
The transmitter is
After transmitting the modulated signal of the packet including the received sequence number, the transmitter further repeatedly transmits the modulated signal of the packet including the same received sequence number. In an underwater transmission system configured to include a transmission device that transmits video data using visible light in water and a reception device that receives video data from the transmission device,
The transmitter is
A first buffer for storing the video data;
An encoder that encodes video data stored in the first buffer at a predetermined high rate or low rate to generate compressed data;
The compressed data generated by the encoder is divided into packets and stored as divided compressed data in the packet, and a sequence number corresponding to the divided compressed data is added to the packet, and the divided compressed data and the sequence number are A first transmitter that modulates a packet including the carrier using visible light and transmits a modulated signal;
An instruction for encoding at the predetermined high rate or low rate is output to the encoder, the sequence number is output to the first transmitter, and the packet is received from the receiving device that has received the modulated signal. A first receiving unit that receives the included sequence number as a received sequence number,
The first receiving unit includes:
When the first transmission unit is not receiving the received sequence number for a predetermined time in a state where the modulated signal of the packet including the divided compressed data encoded and divided at the high rate and the sequence number is transmitted. When the reception interruption is determined, an instruction for encoding at a low rate is output to the encoder, and a sequence number corresponding to the divided compressed data encoded and divided at the low rate is output to the first transmitter. Causing the first transmitter to transmit a modulated signal of a packet including the divided compressed data encoded and divided at the low rate and the sequence number;
When receiving recovery is determined when the received sequence number corresponding to the divided compressed data encoded and divided at the low rate is received, the divided compressed data in the video data of a predetermined size encoded at the low rate and the After the first transmitter transmits a modulated signal of a packet including a sequence number, it outputs an instruction for encoding at a high rate to the encoder, and also supports divided compressed data that is encoded and divided at the high rate A sequence number to be output to the first transmission unit, and the first transmission unit to transmit the divided compressed data encoded and divided at the high rate and the modulated signal of the packet including the sequence number,
The receiving device is:
The modulated signal is received, the modulated signal is demodulated using the visible light carrier wave, a packet is generated, the divided compressed data and the sequence number are extracted from the packet, and the divided compressed data is combined and compressed. A second receiver for generating data;
A second transmission unit that uses the sequence number extracted by the second reception unit as a received sequence number, modulates a packet including the received sequence number using the visible light carrier, and transmits a modulated signal When,
A second buffer for storing compressed data generated by the second receiving unit;
A decoder for sequentially reading out and decoding the compressed data from the second buffer after a predetermined reproduction delay time, and restoring the original video data;
The second receiver is
When the same compressed data is generated in duplicate, the duplicated compressed data is deleted from the second buffer, and the newly generated compressed data is stored in the second buffer. Transmission system.

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