【作者】 黄晶晶；

【导师】 胡晓毅；

【作者基本信息】 厦门大学 ， 通信与信息系统， 2009， 硕士

【摘要】 海洋水声信道是一种极其复杂多变的时-空-频变信道。信道带宽窄、多径干扰强、传输损耗大是水声通信中实现高速可靠传输的主要障碍。正交频分复用技术(OFDM)是一种多载波调制技术,有较高的频带利用率和传输速率,在不使用复杂的信道均衡技术的条件下可以较好地克服由多径效应带来的码间串扰(ISI)。但是,OFDM对同步误差非常敏感,当存在同步误差必然会引入子载波间干扰(ICI)或ISI,这将影响信道估计的准确度,进而影响OFDM的系统性能。OFDM系统要在接收端获得信道信息,实现实时而准确的相干解调,信道估计是必不可少的。本文针对这些问题研究了OFDM水声通信系统中的联合同步和信道估计技术,并进行了仿真和试验,结果表明系统有效,方法可行。全文的主要工作概括如下:一、论文在分析水声信道的特性和OFDM系统的基本原理的基础上,介绍了OFDM水声通信系统的基本实现结构和系统参数的选择。二、对OFDM系统中的信道估计技术进行研究。着重对基于频域导频的信道估计算法进行归纳和总结,在讨论传统导频分布格式优缺点的基础上,给出了基于块状导频直接判决和梳状导频联合跟踪的改进算法。最后,我们还介绍了基于CAZAC序列相关运算的信道估计算法。三、在分析同步误差对信道估计性能影响的基础上,研究了基于最大似然准则和基于判决的联合同步和信道估计技术。通过仿真,对比分析了算法在AWGN信道和多径衰落信道下的同步、信道估计性能。最后通过实验室水池和海洋试验进一步验证了联合估计算法在实际系统中的性能。结果表明,本文介绍的联合估计算法在水声通信中是行之有效的。更多还原

【Abstract】 Ocean channel is such a complex environment that it varies with time, frequency and space. Narrow available bandwidth, great transmission loss and severe multipath effect are the main barriers to the implementation of high speed reliable communication in an underwater acoustic (UWA) channel. Orthogonal Frequency Division Multiplexing (OFDM) is a technology of multicarrier modulation which has high utilization of the frequency spectrum and raises the transmission rate. It combats the inter-symbol interference (ISI) caused by multipath effect without complex channel equalization. However, OFDM is very sensitive to synchronization errors which may introduce much ICI and ISI that greatly degrade the performance of channel estimation and the BER performance of OFDM system. In order to realize real-time and accurate coherent demodulation, we must estimate the channel. This paper investigates combined synchronization and channel estimation technology for OFDM underwater communication system, and carries out simulation and experiment. The results show the feasibility of the scheme.The main contents are summarized as follows:1. Based on analysis on the characteristics of underwater acoustic channel andbasic principle of OFDM system, the parameter selection and basic structure of OFDM system are produced.2. Channel estimation technology for OFDM underwater communication system is studied. This thesis emphasizes on induction and summarization on OFDM channel estimation algorithm which is based on frequency pilot. We not only discuss the advantages and disadvantages of traditional pilot distribution formats, but also improve the algorithm based on decision directed of block-type pilot and tracking of comb-type pilot. Finally, we introduce the channel estimation algorithm based on CAZAC sequence correlation.3. We analyze how synchronization error effects on channel estimation. Thekey research is on combined synchronization and channel estimation technology based on maximum likelihood criterion and detected-directed. According to simulation and comparison, we analyze the synchronization and channel estimation performance under both AWGN channel and multipath fading channel. At last, we verify the performance of combined synchronization and channel estimation algorithm in practical system by pool and sea testing. The results show the feasibility of the scheme in underwater acoustic communication.更多还原