Research On Low Redundancy Data Transmission Strategy Of Digital Fountain Codes

Underwater acoustic sensor networks (UASNs) could collect, process and transfer information within a specific area, making it a promising tool in implementing underwater applications like ocean marine data collection, disaster warning and underwater military reconnaissance. However, underwater acoustic communication suffers characteristics of narrow band, long time-delay, limited energy and complex noise, presenting a great challenge for onshore transmission strategies to be directly applied to UASNs. Data transmission based on digital fountain codes (DFC) is not sensitive to the transport order of information sequence,and can make full use of the mutual information between network nodes to improve the efficiency of transmission, thus receives extensive attention. Based on the project funded by the National Natural Science Foundation, to solve the problem of large redundancy,information transparency and equal error protection property of transmission strategies based on DFC, this thesis researches on low redundancy transmission algorithm and unequal error protection (UEP) algorithm of DFC, and on this basis explore low redundancy data transmission scheme suitable for UASNs. The main content includes:1) Based on the study of the basic theory of DFC, the existing low redundancy fountain code algorithms and UEP fountain code algorithms are further studied. Then the research analyzes the major factors that may influence the performance of data transmission based on DFC and the problems in applying the existing strategies to UASNs.2) On the basis of arithmetic coding algorithm, the low redundancy LT code is designed to improve the efficiency and security of data transmission. Simulations are performed under VS2010 software, and the results show that the advanced algrithem performs better in term of physical layer transmission efficiency and data anti-interception capability.3) Weighted expanding window fountain code suitable for UASNs is designed by integrating existing UEP fountain codes, and the asymptotic property of the proposed algorithm is theoretically analysed and simulated using AND-OR Tree Analysis. Then the performance improvement of the modified strategy in terms of symbol loss rate and decoding successful rate are verified by computer simulations.4) On the basis of further optimizing the transmission strategy by introducing correlation chain feedback, low redundancy data transmission scheme based on DFC is proposed utilizing the aforementioned modified strategies. In order to demonstrate that the proposed scheme is suitable for UASNs, performance indicators like end to end delay, network throughput, average transmission redundancy and the number of retransmission are tested by the UASN model established on OPNET modeler.