Acoustic-assisted Underwater Visible Light Communication For Image Relay Transmission Using Fountain Codes

Underwater wireless sensor networks are widely used in underwater environment monitoring,underwater detection and other fields,and underwater wireless communication plays an important role as its key technology.Underwater acoustic communication is currently the most mature underwater wireless communication technology.It has the advantages of long communication range,large angle,and high reliability,but it has problems such as low transmission rate and high transmission delay.Underwater visible light communication has a higher bandwidth than underwater acoustic communication and can achieve higher transmission rate and lower transmission delay,the size and cost of the system are lower,and the energy consumption is smaller,but the communication range is much shorter due to the attenuation of visible light in underwater environment,and it requires line-of-sight propagation.Based on this background,this thesis first designs and implements an underwater acousticoptical cooperative communication system platform.Then,for the actual scenario of underwater image relay transmission,the advantages of underwater visible light communication and underwater acoustic communication are combined to realize acousticassisted visible light communication image relay transmission scheme using fountain codes.First,the design of the self-developed acoustic-optical cooperative communication system platform is introduced,including the overall architecture design of the system,underwater remote operated vehicle,visible light communication system,underwater acoustic communication system,and Qt GUI(Graphical User Interface)design.The nodes include underwater stationary nodes and underwater remote operated vehicle dynamic nodes.Then,based on the acoustic-optical cooperative communication system platform we developed,aiming at the reliable transmission of image in complex and changeable underwater environments,this thesis proposes an acoustic-assisted underwater visible light communication image relay transmission scheme with fountain codes.The scheme includes acoustic-assisted visible light communication link establishment protocol which is at the MAC layer,and pointto-point image transmission scheme that uses expanding window fountain codes with acoustic auxiliary feedback,as well as the relay forwarding protocol.First,at the application layer,the original image is progressively compressed and encoded based on wavelet transform to reduce the amount of transmitted data and make it have progressive transmission characteristics.Then,the visible light communication link is established through the acoustic handshake and optical handshake in the MAC layer protocol,and then concatenated channel coding scheme using expanding window fountain codes that can realize unequal error protection and RS codes is utilized to encode the progressive compression bit stream to adapt to the complex and changeable underwater environment and protect the image contour data with high priority.In order to reduce the decoding overhead caused by the unequal error protection feature of the expanding window fountain codes,it feeds back the decoding progress information of the expanding window fountain codes via underwater acoustic channel without establishing a fullduplex underwater visible light communication link.Finally,the self-developed acoustic-optical cooperative communication system platform is used to simulate and verify the proposed point-to-point image transmission scheme.The simulation and actual experimental comparison with other schemes can show that the point-topoint transmission scheme that uses extended window fountain codes with acoustic auxiliary feedback proposed in this thesis has large advantages in decoding overhead and throughput under the premise of ensuring the quality of image transmission.The actual experimental test also verifies the feasibility of the acoustic-assisted underwater visible light communication image relay transmission scheme proposed in this thesis has certain practical significance in underwater visible light communication.