【作者】 徐小卡；

【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， 2009， 博士

【摘要】 传统的单载波相干水声通信采用自适应判决反馈均衡的结构和相位跟踪的方法,随着通信速率的提高,符号持续时间变短,信道的时延扩展导致均衡器的复杂度升高,阻碍了其在高速水声通信中的进一步应用。正交频分复用(OFDM)技术是首先在无线电视频广播和通信中发展起来的新技术。由于其具有频谱利用率高、抗多径和脉冲噪声能力强、在高效带宽利用率情况下的高速传输能力以及简单的实现方法,使其成为近年来高速水声通信中的研究重点和热点之一高速水声通信面临最困难的问题就是有限的带宽、强多途和信道结构的快速时变,再加上海洋环境的高噪声背景,使水声信道成为迄今为止最困难的无线通信信道。正因为如此,高速高可靠性的水声通信,尤其是浅海水声通信成为世界性的难题。本论文主要针对浅海水声通信中OFDM的关键技术与应用进行了研究,所做的工作主要有：1.编码OFDM (COFDM)技术研究。研究了Turbo码的在水声OFDM系统中的应用,并与目前普遍使用的卷积码和RS码进行了性能比较,最后对近年来因Turbo研究而重新认识到性能优越的低密度奇偶校验码(LDPC)码进行了初步探讨,并通过仿真、信道水池和湖上试验进行了验证。2.OFDM水声移动通信系统中多普勒估计与补偿。设计了两种基于循环前缀OFDM (CP-OFDM)系统的多普勒估计与补偿算法,分别是基于块多普勒估计和基于单频信号测频的方法,并且在国内首次进行了较为规范的基于OFDM的移动水声通信的外场试验,试验验证了所设计的两种算法的有效性,并且分析了两种算法各自的优缺点及未来的发展。3.分析比较了不同种类的信道估计与补偿技术并指出如何选择信道估计与补偿算法。针对基于辅助导频的信道估计(PSAM)的导频结构、导频位置信道估计和内插滤波器结合水声信道进行了仿真比较,并对不同导频间隔进行了性能分析。针对OFDM的不同保护间隔(CP-OFDM, ZP-OFDM)进行了性能比较,并结合运算量给出了选择保护间隔的依据。结合浅海水声信道的稀疏特性,提出了一种基于DFT和最小二乘(LS)相结合的信道估计与补偿技术,并且通过仿真和试验验证了改进的算法性能。4.OFDM水声通信中的空间分集技术。分析了分集技术的3种基本的分集合并方式——最大比合并、等增益合并和选择性合并,并结合OFDM具体技术分别分析了不同分集技术在OFDM系统中的应用和运算量比较,最后对前DFT最大比合并(Pre-DFT-MRC)、后DFT最大比合并(Post-DFT-MRC)、后DFT等增益合并(Post-DFT-EQU)、后DFT选择性合并(Post-DFT-SC)进行了仿真和信道水池试验。通过运算量、仿真结果和试验结果进行比较,给出了空间分集算法的选择依据。更多还原

【Abstract】 In traditional single-carrier coherent underwater acoustic communication, adaptive decision feedback equalizer coupled with phase tracking methods is adopted. As the communication rate is increasing, symbol duration is becoming shorter, and equalizer is more complex with channel delay spread, the application of traditional methods is hampered in high-speed underwater acoustic communication.Orthogonal frequency division multiplexing (OFDM) has been successfully used in broadband wireless communication over radio channel. Because the performances such as high spectrum efficiency, strong anti-multipath and impulse noise ability, high-speed transmission capacity under efficient bandwidth utilization, and simple implementation, OFDM becomes one of the research priorities and hotspots in high-speed underwater acoustic communication.The most difficult problems in realizing high-speed underwater acoustic communication are limited bandwidth, strong multi-path and rapid time-varying in channel structure. Considering the high noise background in the marine environment, so far the underwater acoustic channel has become the most difficult wireless communication channel. Therefore, how to realize high-speed and reliable underwater acoustic communication, especially in shallow water, is a worldwide problem.In this thesis, key technologies and applications of OFDM are researched mainly for the shallow underwater acoustic communication. The works done as follows:1. Coded OFDM (COFDM). Application of Turbo code is studied in underwater acoustic OFDM system, and the performances of Turbo code are compared with the popular convolutional code and Reed-Solomon (RS) code. Then LDPC code, of which the excellent performances are re-recognized through studying the Turbo code, is explored primarily and validated by simulating and experimenting in the pool and lake test.2.Doppler estimation and compensation in mobile OFDM underwater acoustic communication system. Two algorithms based on CP-OFDM are designed which are block Doppler estimation and frequency measurement method based on single-frequency signal. Also the experiment about mobile underwater acoustic communication on OFDM is done, the two algorithms are validated, and the advantages and disadvantages as well as the development are analyzed.3.Channel estimation and compensation. Analysis and Comparison of the different types of channel estimation and compensation techniques are made out, the principles of how to choose the estimation and compensation methods are pointed out. For different guard intervals (CP-OFDM, ZP-OFDM), capabilities are compared, principles of choosing guard intervals are given. Finally, considering the sparse features in shallow acoustic channel, a channel estimation and compensation method based on the combination of DFT and LS is given, and the improved algorithm performances are validated through simulation and experiments.4. Spatial diversity in OFDM underwater acoustic communication. Three kinds of diversity combining methods are analyzed, which are the Maximum Ratio Combining (MRC), Equal Gain Combining (EGC) and Selection Combining (SC). Different spatial diversity techniques combined OFDM are analyzed in computational complexity and error-rate performance. At last, Pre-DFT-MRC, Post-DFT-MRC, Post-DFT-EQU, Post-DFT-SC are simulated and experimented in pool test. Through the comparison of computational complexity, simulation and experiment results, the principles of choosing spatial diversity algorithms are given.更多还原