Research On Transmission Optimization Of Underwater Acoustic Sensor Network Based On Fountain Codes

As an important technology in smart ocean project,underwater acoustic communication(UWAC)technology has experienced nearly half a century of development.There were a lot of researches about the network layer technology and methods of UWAC technology,and greatly improved the reliability and effectiveness of UWAC systems.Along with the development of UWAC technology,wireless network communication between sensor nodes has become possible,and gained extensive attention,making the engineering realization of underwater acoustic sensor network(UASN)possible.In UASN,reliable transmission is always one of the most important research topics in this field.This thesis was supported by National Natural Science Foundation of China project named “Research on multi-objective optimization of data transmission technology based on fountain codes in underwater acoustic network” and deeply analyzed the current development situation of the application of fountain codes in UASN at present.Research about the reliable UASN transmission problem was carried out from three aspects,i.e.,encoding and decoding algorithms for fountain code,encoding redundancy and transmitting power parameter optimization for fountain code,and fountain code-based UASN transmission protocol.First,due to the special characteristics of the UAC,this thesis focused on the perspective of enhancing the adaptability of the UASN to the underwater acoustic channel(UAC)environment.Employed the medium and short code length fountain codes(LT codes in this thesis)in the UASN to reduce the total number of encoding packets,thereby reducing the duration of one single communication,and making the fountain code-based UASN communication has better adaptability to the UAC environment.The main reasons of decoding failure of fountain codes are imperfect coverage of source data packets and short-cycle in encoding matrix.In order to improve the performance of LT codes with medium and short code length,this thesis studies from two aspects: reducing the presence of short-cycle in the encoding matrix and increasing the coverage rate of the source data packets.This thesis proposed a doping and non-uniformly selecting LT(DNS-LT)code encoding algorithm based on doping high degree encoding packets into encoding results and source data packet selection method that non-uniformly selecting among sets which were made up upon classification of source data packets.This encoding algorithm improved the coverage rate of the source data packets and reduced the probability that the generation of short-cycle in encoding matrix.There was no need for this doping and short-cycle eliminating encoding algorithm to optimizing degree distribution,and only need to improve the source data packets selection process.In addition,it has been observed that a lot of residual information in the stop set of iterative decoding algorithm can be utilized by the maximum likelihood decoding algorithm.Thus,a joint decoding algorithm that unified BP and OFG algorithms was proposed,which was named OFGBP joint decoding algorithm.Second,this thesis analyzed the UAC and the packet loss rate models according to the characteristics of the UAC environment,and then defined the communication efficiency and energy efficiency models.On this basis,the effects of encoding redundancy on communication efficiency and the impact of transmit power and encoding redundancy on energy consumption per single source data bit with optimal communication efficiency were analyzed.Then,the idea of energy consumption per single source data bit optimization based on the constraint of maximum communication efficiency was established.Two adaptive optimization strategies were proposed:(1)An adaptive encoding redundancy optimization strategy to optimize communication efficiency with fixed transmitting power called “NLMS-ARO”,(2)An encoding redundancy/transmitting power joint optimization based on the constraint of maximum communication efficiency strategy called “NLMS-JAPRO”.These two optimization strategies can be used in point-to-point communication between sensor nodes in UASN to optimize the communication efficiency and energy consumption per single source data bit.Finally,the advantages and challenges of fountain code-based multihop transmission in UASN were analyzed.The feasibility of designing fountain code-based multihop transmission protocol for UASN and the impact of encoding redundancy and transmitting power of each hop to the global performance were investigated.Subsequently,the Fountain code-based JAPRO multihop(JAPROMH)transmission protocol was proposed,and data processing flow on each kind of sensor node(source node,intermediate node,receiver sink node)was given.In order to reduce the processing complexity on the intermediate node,a partially decoding algorithm based on iteratively shortest path search simplification and a recoding algorithm were proposed.Simulation results show that the JAPROMH protocol,the partially decoding algorithm and the recoding algorithm can optimize the global communication efficiency and global energy consumption per single source data bit;reduce the end-to-end communication delay,the processing complexity on intermediate node,and the source data packets erasure rate;improve the end-to-end successfully delivery rate,and is beneficial to improve the global communication performance of the UASN.