【作者】 张国平；

【导师】 张浩；

【作者基本信息】 中国海洋大学 ， 计算机应用技术， 2013， 博士

【摘要】 近些年，电磁前兆场在洛伦兹介质和徳拜介质等色散介质中的传播分析和实验证明了布里渊前兆场的脉冲峰值代数衰减特性，这一研究成果激起了雷达探测、微波成像、超宽带通信等多个领域研究者的极大兴趣，形成了一个新的研究热点。但在水下通信领域尚无更深入的研究，因此本文从水下通信的角度对布里渊前兆场在淡水和海水中的传播特性进行了分析，探讨了水下短距离脉冲通信的可行性。在电磁场的稳态部分到达前出现的电磁振荡称为电磁前兆场，电磁前兆场包括高频谱能量主导的索末菲前兆场和低频谱能量主导的布里渊前兆场，其中布里渊前兆场因在色散介质中的幅度衰减速度小而备受关注。淡水和海水都属于色散介质，电磁波在色散介质中传播会受到相位色散和频率色散的相互作用，在传播几个吸收深度后，其传播过程逐渐演变为一个局部具有相对固定频率和衰减速度的且以恒定速度传播的余波行为。布里渊前兆场的传播受到介质的色散特性和初始信号能量频谱分布的影响，因此深入研究介质色散特性以及不同信号的频谱对布里渊前兆场的传播影响，对于选择或设计水下通信的脉冲信号，实现短距离、高带宽水下无线通信具有重要的意义。介质的色散特性是影响布里渊前兆传播的主要因素，而色散特性主要受介电常数的影响。淡水和海水的介电常数既有形式简单的理论模型，也有依据测量数据拟合出来的实际模型。本文在不同介电常数模型分析的基础上，以形式简单的理论模型完成了电磁场传播的近似表示和传播动态描述；给出了不同介质模型的鞍点动态、复相位函数以及电磁场传播的近似公式；验证了淡水和海水不同介质模型的鞍点动态、复相位函数动态以及布里渊前兆传播动态；分析了不同介电常数模型对布里渊前兆传播的影响。初始信号的频谱能量分布是影响布里渊前兆传播的另一个主要因素，因此必须要选择或设计适合水下通信的信号。信号在传播过程中的幅度衰减和时域宽度特性是衡量信号是否适合水下通信的标准。本文分别选取单脉冲超宽带信号、载波调制信号和双布里渊脉冲信号等三类八种信号，分析了不同信号在淡水和海水中不同相对传播距离上的传播动态；得到了不同输入信号幅度衰减和时域宽度特性；确定了双梯形脉冲作为水下脉冲通信的候选信号。在水下通信的自然环境中，既要考虑水体盐度和温度差异对水下通信的影响，又要确定脉冲的操作频率和时间间隔，它们决定通信范围和信道带宽的主要因素。本文在完成水体盐度、温度和脉冲频率对脉冲传播影响分析的基础上，重点分析了淡水50米范围内和海水1米范围内的双梯形脉冲的传播情况；综合考虑实际传播范围内的脉冲幅度和相对传播距离上的脉冲传播特性，给出了不同通信范围内可能达到的最大通信带宽，得出了在淡水5米范围内和海水0.1米范围内可以达到100MHz通信带宽的重要结论。本文作为水下脉冲通信的基础研究工作，详细地分析了淡水和海水的介质特性、布里渊前兆场的传播动态和不同信号的传播特性，选择了水下脉冲通信候选信号，预测了不同通信范围内的信道带宽，这些工作对水下通信的后续实验和信道建模具有一定的借鉴意义。更多还原

【Abstract】 In recent years, the analysis and experiments of electromagnetic precursors fieldpropagation in Lorentz and Debye dispersive medium have proved Brillouinprecursors’ peak amplitude algebraic attenuation property. This research has arousedgreat interest of researchers in the fields of radar remote sensing, microwave imaging,ultra-wideband communications, and has became a new research focus. However,underwater communications has not been studied deeply, so Brillouin precursor fieldpropagation characteristics in freshwater and seawater were analyzed from the pointof view of the underwater communication, and the feasibility of underwater shortdistance pulse communication was discussed.The electromagnetic oscillations before the arrival of the steady-state portion ofthe electromagnetic field are called electromagnetic precursor field, which includesthe Sommerfeld precursor with high spectral energy and the Brillouin precursor withlow spectral energy. Brillouin precursor has been more concerned for itslow-attenuation in the dispersive medium. Freshwater and seawater are dispersivemedia. The electromagnetic wave propagating in a dispersive medium is interacted byphase dispersion and frequency dispersion, after spreading several absorption depthdistances, which will gradually evolves into a local mature dispersion regime with arelatively fixed frequency and decay rate at a constant speed. Brillouin precursor fieldpropagation is affected by the dispersion characteristics of the dielectric and the initialsignal energy spectrum distribution. Therefore, the depth study of the propagationeffects of the dielectric dispersion characteristics and the spectrum of the differentsignals on Brillouin precursor field has great significance for the selection or designof the underwater communication pulse signal, and then achieve the underwatercommunication in short distance with high bandwidth. The main factor that affects the Brillouin precursor propagation is the dispersioncharacteristics of the dielectric, which is mainly influenced by permittivity. Thedielectric constant models of freshwater and seawater have both the simple theoreticalmodel and the practical model using measurement data fitting. On the base of thedifference analysis between the dielectric constant models, approximaterepresentation and dynamic description of the electromagnetic field propagation havebeen completed in the form of a simple theoretical model; The approximate formulasof saddle point dynamics, complex phase function, as well as electromagnetic fieldpropagation are given with different dielectric constantmodels for freshwater andseawater; Saddle point dynamics, complex phase function, and Brillouin precursorpropagation dynamics are verified in freshwater and seawater with different dielectricmodel; Influence of different the dielectric constant model on Brillouin precursorpropagation are analyzed.The spectral energy distribution of the initial signal is another main factor toaffect the Brillouin precursor propagation, so the suitable signal form for underwatercommunication must be selected or designed. The amplitude attenuationcharacteristics and temporal width spreading characteristics of signal are standards tomeasure whether a signal is suitable for underwater communication. In the analysisprocess, three types of eight kinds of signals of single pulse ultra-wideband signals,carrier modulation signals and double Brillouin pulse signals are selected to analyzepropagation dynamics with relative propagation distance in freshwater and seawater,and to get the amplitude attenuation factor and the temporal width spreading factor ofthe propagation process, and the double trapezoidal pulse is selected as the candidateunderwater pulse communication signal.In underwater communication natural environment, it is necessary to considerthe influences of water salinity and temperature on the underwater communications,and the determination of the operating frequency and pulse intervals which determinethe communication range and bandwidth of the channel. On the basis of the analyzingof the influence of water salinity, temperature and pulse frequency of the pulse propagation, the study is focused on the double trapezoidal pulse propagation within50meters in freshwater and within1meter in seawater; the maximum possiblecommunication bandwidth within different communication range is predicted bycomprehensive consideration of the pulse amplitude with the actual propagationdistance and the pulse propagation characteristics with relative propagation distance,and then the important conclusion that the communication bandwidth can reach100MHz within5meters in freshwater and within0.1meter range in seawater isderived.As the basic research in underwater pulse communication, the details of thedielectric characteristics of freshwater and seawater, the Brillouin precursor fieldpropagation dynamics and the propagation characteristics of signals are analyzed, thecandidate pulse signal underwater communication is selected, and the communicationrange and channel bandwidth are predicted, which provide a reference for nextexperiments and underwater communication channel modeling.更多还原