Study On Underwater Acoustic Communication Based On MIMO Space-time Coding Scheme

MIMO(Multiple Input Multiple Output) technique which can greatly enhance the systemspectral efficiency and the system performance without increasing the time/frequencyresourse has drawn great attentions. STC(Space Time Coding) is always a hot research pointfor it make full use of the multiple independent transmission array of the MIMO channel toget spatial diversity gain and coding gain. Although the exsiting space-time code can obtainedmore ideal performance under the flat fading channel system when used in (UWA)underwater channel which is known as the multipath channel with the time/spatial/frequencycomponent is variable. Because of its complex transmission characteristics, the underwateracoustic space time coding system face the great challenges. In this article, the author focuson the different sound field environment of the system architecture. through thecomprehensive measure of space-time code transmission rate and decoding complexity andmaximize the diversity and multiplexing design indicators. Based on the domain extensionalgebra theory, the paper give a thorough and systematic research of the space time codingdesign, build a variety of transmission scheme which suitable for different applicaionscenarios and space time coding algorithm. The main research content of this article isfollowing as below:1: Based on the deep research of the underwater acoustic chanel characteristics and thesystem architecture of the space time coding, the article has constructed the different transmitMIMO communication system with the different sound field for the frist time.First of all, according to the characteristics of underwater acoustic channel and the differentdesign or requirement and influence of the sound field MIMO transmission array. Based onthe shallow sea and deep sea sound field characteristics,the paper respectively constructedHSTCDs-MIMO communication system framework and signal model. At the same time, theauthor constructed the limited feedback HSTCD-MIMO underwater acoustic communicationsystem framework and model.2: From the perspective of symmetrical open loop system in shallow sea field. The articlehas a deep analysis of the performance of space-time codes and low decoding complexity, andthen, the author gives two improved space-time code algorithm which has the higher code rateand more equilibrium of power distribution structure design.(1) For the common known orthogonal space-time code with high reliability design for alow decoding complexity always has very low code rate and the design structure is relatively fixed, aslo the peak power is higher. Based on tradeoff between diversity gain andmultiplexing rate design criterion, the article make full use of the extended orthogonal basismatrix theory and proposes a Euclid space isomorphism extension fields orthogonal matrixnamed as the design of HES-STBC algorithm. The given design of the code word matrixwhich relax the symmetric matrix of the traditional complex orthogonal space-time code(COD), maximize the limitation of the diversity gain and multiplexing system rate, at thesame time, the rate of the system performance is further improved.(2) Based on homomorphic extension theory and the quaternions theory, this paper putsforward to a kind of four order homomorphism orthogonal basis matrix Komwit space-timecoding algorithm. The proposed method extend the matix from low dimensional complexdomain matrix orthogonal projection to a even high-dimensional extended complex domainspace through the homomorphism of extension design basis matrix. In this paper, the codingmatrix hold the premise HES-STBC rate and system performance the code word matrixdesign more flexible. Meanwhile, the coding matrix not only meet the minimum NVDproperties of determinant criterion, but also it control the power of the system peak in a stablerange.The research results show that in shallow sea channel model, compared to the commoncode design and new design of space-time code with the freedom of code word, decodingcomplexity and coding gain and the system performance of code ber rate, the proposedHES-STBC greatly improves the code rate, and maximize the diversity and multiplexing gain.The Komwit-STBC space-time code in the promotion of code rate, at the same time, thedesign of code word is more flexible and solved the problem of the high PAPR of thetraditional QSTBC design.3: Based on the limit of the array number and aperture in deep-sea unmanned combatplatform(UUV) and from the perspective of asymmetric open loop system. The articlein-depth analysis of the asymmetric system under the rule of NVD-MDT optimization designand presents a fast decodable asymmetric space-time code construction algorithm.(1) Based on the deduction and analysis of the standard minimum determinant and thetightly bound of the coding gain. By showing that when the asymmetric MIMO system tomaximize the diversity and multiplexing gain, standard minimum determinant of the matrixpair error code word must satisfy the constraint conditions, and puts forward the asymmetricNVD-MDT space-time coding optimization design criteria in Nr=Nt n, n≥2MIMOsystem. (2) In the view of the4×2array, the article proposed a embedded type MDT space-timecode design Based on the4order Hamilton structure. At the same time, the paper presented aasymmetric center punched MDT space-time coding algorithm, and also, they introduced thesystem design of the imporved method.(3) In deep analysis of the characteristics of the space-time code to the6×3and6×2array. The article respectively proposed an imporved group-orthogonal MDT space-timeblock code and a punched-MDT space-time code based on punch the center of the basis matix.At last, the article gives the specific step of the design and the simulation result.The research results show that the proposed algorithm of asymmetric the space-time codehas the very high flexibility in the construction of the code word structure and coding rate andthe rate of dimension adjustable; Compared directly to the existing symmetric space-timecode for asymmetric systems, a novel proposed structure of space-time code with lowerdecoding complexity and smaller system design costs, meanwhile, the proposed method cansignificantly achieve better system performance.4: Based on the sparse characteristic of the shallow sea underwater acoustic channel, theauthor study on the limited feedback closed-loop system and present a limited feedbackdifferential precoding design scheme which based on cascade sparse quantitative of thechannel. On the other hand, the paper propose an imporved quantitative feedback adaptivetime space coding algorithm design.(1) In this paper, the anthor analyzes the sparse characteristics of shallow sea underwateracoustic channel. Based on the theroy of signal sparse representation and compress sensingand channel estimation. The article has proposed a quick search scheme which is based onsparse quantitative difference precoding design.(2) In the view of the traditional shallow sea limited feedback precoding cascade space-timecoding method, the author put forward to a kind of adaptive coding based on sparse shallowwater channel feedback design. This method could obtain the extra amount of array gain andable to achieve direct feedback system performance with the need of only6feedback bit.The Studies show that compared with the existing code scheme, through the use oflayered bidirectional search, the proposed sparse quantitative precoding scheme can obtain aeven faster speed of searching optimal code and better real-time performance and strongerresistance fading channel. According to the example and simulation results of the4×4and8×8array adaptive space-time code design, it verify the validity of the space-time code andthe value of application. Finally, the article has analyzed the design of high speed underwater acoustic space-timecoding scheme, summarizes the different transmission design scenarios of the space-timecode, given the design criteria when use in the actual engineering project and prospected thefuture research work.