Research Of Key Techniques Of The Integrated Network Of Underwater Acoustic Communications

Underwater acoustic communications have very important utilizations for national defense and national economic construction. The key techniques are foundationally researched in key technologies concerned with integrated network of underwater acoustic communications, using the theories of blind signal process, OFDM technology, CDMA technology, and the network communication theory and technology. The main research contents and achievements are as follows:(1) The hierarchy structure of integrated network of underwater acoustic communications are proposed. The whole underwater acoustic communication networks (UACN) are consisted of main node, some sub-node and many of terminals, they can provide multi-service by harmonized operating and organic relating each other. The conceptions of main link, vice link and sub-link are proposed. The management mechanism which main node manage whole UACN, sub-node manage terminals in its covering region is described.(2) The characters of ocean acoustic channel are analyzed, the conclusion that ocean acoustic channel is a spatio-temporal varying random channel is obtained. The channel of underwater acoustic channel can be decomposed into three components in that the first is stably multi-path channel, the second is slowly varying multi-path channel, and the third is random channel. The first and second channels can be measured by using copy relative method and pulse relative, but the random channel cannot be obtained by measure. It is necessary that use blind process and blind equalization for ocean acoustic channel in order to enhance reliability of information transmission.(3) The techniques about blind identification and blind equalization of underwater acoustic channel, and blind identification of OFDM system are studied. The mathematic model of blind identification for channel based on subspace is established, and the decomposition of subspace is also studied. The algorithms of blind identification for channel are constructed under the linear restriction condition and two-order type restriction condition, and method of blind identification for channel is induced using few vectors of noise space under two-order type restriction condition.The algorithm of blind identification for OFDM is induced using adequately characters of redundancies information of cycle prefix of OFDM signal. It can be blind identified for OFDM system by constructing a simply Toepltz matrix without over-sample and without changing structure of OFDM signal, the computing quantitative is reduced.(4) MC-CDMA underwater acoustic transmission link is studied. The basic principle of multi-user underwater acoustic transmission system is proposed combining with spread frequency technology and OFDM. The issues of frequency deviation estimation and timing estimation are study using maximum likelihood method with one OFDM block, and the quickly estimation algorithm is proposed.It is indicated that MC-CDMA has better performance of anti-noise in multi-users transmission; furthermore, has low BER performance under lower SNR by simulation experiment, it is also indicated that a few cycle prefix of OFDM signal can ensure precision of timing estimation and frequency estimation.(5) The basic methods of underwater acoustic multi-user detection techniques are discussed. The algorithm of MMSE multi-user detection is improved with considering of channel and its relativity, and that the optimum solution of MMSE for multi-user detection can be guaranteed to converge in searching space by addition new linear constraint condition.(6) The hierarchy structure of integrated network of underwater acoustic communication is detailedly studied. The definitions and functions about the node, terminal, basic communication manners, and physical channels are detailedly described, the principle and regulation about accessing time slot of public physical channel. The material formats of communication protocol of data link layer are defined, the model of correspondence mechanism of negotiation-request-acknowledge-information transmission is detailedly mathematically analyzed, and the formulas about utilization ratio of time slot and loss ratio of information transmission are developed.The structures and management mechanism of static and dynamic router management of multi-access transfer layer is detailedly defined and described. The link, bandwidth, authentication, PN code, and operation status management are also detailedly defined and described in management layer. Finally, the serve layer of terminal is defined and described.