| With the sustaining development of Underwater Acoustic (UWA) communications'application domain, the research of UWA communications techniques has become today's hotspot. The signal's fading which is caused by UWA channel multipath propagation is the main factors influencing the performance of UWA communications systems. At present, the main anti-multipath interference technologies are spread-spectrum technology, equalization, diversity technology and so on. Because of spread-spectrum techniques' ability of resisting multipath interference and multi-access, it is the key technique which is used to transmit datas in underwater wireless acoustic communications networks.However, there are some limitations of traditional spread spectrum sequence: if spreading gain is certain, the number of available sequences is limited; performance of cross-correlation function rapidly declined when partial cross-sorrelation was done. Chaotic sequence has the extreme sensitivity of the initial values and parameters, so that we can get large number of them. Meanwhile, with the length's increase, chaotic sequences' autocorrelation and cross-correlation function can be closer to the ideal value statistically. Chaotic sequence is pseudo-random sequence. Therefore, it can better maximize the advantages of spread spectrum communication technology to replace the traditional spread-spectrum sequence with chaotic sequence.In this thesis, in order to realize UWA communication with performances of anti-multipath interference, high reliability, concealment, technologies on chaotic spread spectrum and their application in UWA communication were studied. Through computer simulations and trials, the good performance and the feasibility of such communication technologies were verified. The main contents of this thesis are as follows:1. A detailed presentation and mathematical description were made about CDMA communication's fundmental principles and key technologies. Performances of asynchronous DS-CDMA system were analysed. Focuses were the acquisition and tracking of PN sequence and multi-path diversity reception technology.2. The concept of chaotic system and means to describe it were given. Common low-dimensional chaotic system and high-dimensional chaotic system were introduced, a new compound chaotic map was proposed. Each of them is given its corresponding maps or chaotic equations. Related properties of them were analysed.3. Methods were introduced to analyse performances of chaotic spread-spectrum sequence from the requirement of spread-spectrum sequence in DS-CDMA systems. Chaotic sequence's construction way and its initial sensitivity were studied. The performances of correlation function, balance and trip characteristics of chaotic sequence were analysed and compared with m-sequence. Statistic variance was analysed at the same time. The principle of chaotic sequence's optimization choice was given.4. Two key technologys were studied. They were synchronization and noise reduction of chaotic signals. Firstly, synchronization principle, error model and robust performance of drive-response synchronization method and active-passive synchronization method were studied based on the Lorenz system. This two methods's performances were validated and compared by computer simulations. Secondly, the noise reduction method for single peak chaotic maps and high-dimensional chaotic signal were studied. Local-projection noise-reduction arithmetic for high-dimensional chaotic signal was modified. Two aspects were improved. They were neighborhood's choice and division between signal space and noise space. This improved arithmetic was validated by computer simulation. Compared with traditional LP algorithm, the improved one reduces noise more effectively.5. An UWA chaotic spread-spectrum communication system was designed and realized. Theoretic analysis, simulations and partial lake-data processing were done about system's performances and key technologies. A mathematical model of UWA chaotic DS-CDMA system was established. System's average signal-to-noise and approximate bit-error-rate model were given. Compared with m-sequence, performances of anti-noise, anti-multipath and anti-multiaccess of UWA chaotic DS-CDMA system were analysed theoretically. Computer simulations about them were also done.Key technologies of UWA chaotic DS-CDMA system were system synchronization, channel estimation, Doppler frequency compensation and chaotic signal's RAKE receiver to anti multi-path. These technologies' performances in actual UWA communication were studied by simulation and patial lake-data. A novel synchronization signal structure was proposed with high robust. It was composed by two linear frequency-modulating signals and vacancy signal. This system's feasibility and good communication performances were validated by Songhua lake-trial.
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