【作者】 黄晓萍；

【导师】 桑恩方；

【作者基本信息】 哈尔滨工程大学 ， 信号与信息处理， 2007， 博士

【摘要】 随着水声通信的应用领域不断扩展,水声通信技术的研究成为现在水声技术的研究热点。水声信道的多径效应使信号产生严重衰落,是影响水声通信系统性能的主要因素。解决水声信道的多径干扰是水声通信研究的关键技术难题。目前抗多径干扰技术主要有:扩频技术、均衡技术、分集技术等。其中,扩频技术是一种十分有效的抗多径干扰技术。另外,扩频技术还具有很好的多址性能,因此也是构建水下通信网络的关键技术。然而,传统扩频码有一定的局限性:在扩频增益一定的情况下,可用的地址码数目有限;部分互相关时,其相关函数性能迅速下降。混沌序列对初始值和参数的极端敏感性,使其数目众多;同时,随着序列长度的增加,混沌序列的自相关和互相关函数的统计值可以接近于理想值;混沌序列具有伪随机特性。所以用混沌序列替代传统扩频码可以更大限度地发挥扩频通信技术的优势。本文以克服多径干扰、实现高可靠性、隐蔽性的水声通信为出发点,研究了混沌扩频技术以及在水声通信中应用的相关问题,并且通过仿真和试验验证了这种通信技术的良好性能和可行性。论文所作的工作主要有以下几个方面:1.对CDMA扩频通信的基本原理及关键技术作了研究。分析了异步DS-CDMA通信系统的性能,重点研究了伪码的捕获和跟踪以及多径分集接收技术。2.给出了混沌系统的概念,以及对混沌系统的刻画手段。列举了常见的一维混沌系统和高维混沌系统,基于Chebyshev映射和一种渐进理想的混沌映射,提出了一种新型的复合型混沌映射,并分析了其相关性能。3.以混沌序列在CDMA系统中的实际应用为出发点,对混沌序列的初值敏感性、奇偶互相关特性、自相关旁瓣均方根特性、互相关均方根特性、平衡性、游程性进行了分析,通过数值仿真,从统计理论的角度解释了一些混沌扩频序列优于m序列的主要原因以及有限长度效应对各项性能的影响,并总结了混沌扩频序列的优选原则。4.研究了混沌信号的同步和降噪两大技术。首先分析了基于Lorenz系统的驱动—响应同步法和主动—被动同步法的同步原理、误差模型和鲁棒性,并由计算机仿真验证并比较了这两种同步方法的性能。其次,研究了一类与帐篷映射拓扑同构的单峰映射和高维混沌信号的降噪方法,对高维混沌信号的局部投影降噪方法的邻域选择和特征空间的划分问题进行了改进,通过计算机仿真验证了方法的有效性。与传统的局部投影算法相比,改进后的算法更加有效地抑制了噪声。5.设计并实现了水声混沌扩频通信系统。对系统的性能和关键技术进行了理论分析、计算机仿真和部分试验数据处理。建立了水声混沌扩频通信系统的数学模型,推导了系统的平均信噪比,以及系统的近似误码率模型。对比分析了基于混沌扩频和m序列扩频的水声通信系统的抗噪声性能、抗多径干扰性能和抗多址干扰性能。关键技术包括:系统同步检测技术、信道估计技术、基于混沌序列的多普勒频偏补偿技术、抗多径干扰的混沌信号RAKE接收机技术。结合仿真和部分试验数据,分析了这些技术在实际的水声通信中的性能。提出了一种具有高鲁棒性的新型的同步信号结构——“双LFM信号加空闲信号”。提出了一种抗多普勒频偏方法。通过松花湖试验验证了系统的可行性和良好的通信性能。更多还原

【Abstract】 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.更多还原