摘要
水声通信技术是当代海洋资源开发和国家安全保障的重要组成部分,也是我国海洋高技术急待研究开发的项目之一。随着现代海洋资源开发的迅猛发展和国家海洋安全的迫切需求,水声通信技术的研究越来越受到人们的重视。但是水声信道是一个十分复杂的时空频变随机多径信道,再加上高噪声、窄带宽、载波频率低、大起伏、传输时延大等特点,给水声通信带来极大的困难,其中强多径效应和大幅度起伏是造成水声通信性能较差的主要因素,它会导致信号幅度衰落和严重的码间干扰。
近年来实际应用的迫切需求,水声网络通信成为国际水声技术领域研究的热点课题。而在水声通信网络中,实现可靠、稳健的点对点物理通信是水声网络通信的前提。本论文选题正是在这样的研究背景下,结合国家863专项课题“分布式海洋水声通信技术研究”而提出的。
论文查阅了国内外大量水声通信相关文献资料,针对浅海水声信道的物理特性,基于射线理论建模,采用了Matlab对水声信道传输特性进行仿真研究。仿真结果表明,多途效应会造成接收信号的幅度衰落、频率扩展和码间干扰等,是影响水声通信有效和可靠性的主要原因,所以在水声通信中必须研究抗强多途径干扰的各种可能措施。由于扩频技术在抗码间干扰方面具有优良的特性,论文在分析了各种扩频技术之后,提出了采用跳频技术作为水声通信调制方式。根据水声信道声传输特点和跳频通信系统中同步信号快速、有效检测的重要性,论文设计了一种同步字头与频谱估计相结合捕获同步,互相关检测线性调频信号完成同步跟踪的同步方案。
由于高速信号处理技术(DSP)的快速发展,论文研究了基于DSP硬件的嵌入式水声跳频通信系统。在对水声信道进行较为深入分析的基础上,采用DSP设计并实现了跳频水声通信系统中的编解码与同步技术。通过实验室水池及厦门港海上测试,系统可在一定传输速率下、实现高可靠性传输,在浅海海域(2～12m),距离3km时,传输速率为200bit/s,误码率约为10~(-3)。
Underwater acoustic communication (UAC) Technology plays an important role in marine resource exploitation and national security etc. With the rapid development of marine resource exploitation and urgent demand of National Ocean security, UAC Technology has been paid more and more attention. However, underwater acoustic (UWA) channel is expressed as a complex channel which is randomly variable in time-space-frequency, coupled with its high noise, narrow bandwidth, low carrier frequency, large fluctuation, and transmission latency, which bring a great difficult to UAC. Strong multi-path effect and large amplitude fluctuation is the main factor that it will lead to signal fading and severe inter-symbol interference (ISI).
Urgent actual demand recently, underwater acoustic network becomes a research hotspot, in which a reliable and robust point-to-point communication is the precondition. This paper is just put forward in such circumstances, combined with the national 863 specific subject "Distribute UAC Technology research in ocean".
Consulted abundant domestic and foreign relevant references, according to physical characteristics of UWA channel, the paper uses Matlab to make a transmission characteristics simulation to UWA channel based on the ray theory. Through the simulation results, we can see that multi-path effect will cause receive signal fading, frequency spreading and ISI, which are main obstacles for reliable high-speed UAC, so all possible anti-strong multi-path interference measures must be studied. As spread spectrum (SS) technology in anti-ISI-interference has excellent properties, frequency-hopping (FH) technology is proposed as a concrete realization of the system through analysis of the various SS technology.
How to detect synchronized signal quickly, accurately and effectively is one of key techniques of FH communication in UWA channel. A synchronized scheme suitable for UWA channel is proposed in the paper, which uses Synchronized-head method combined with spectrum estimation to capture synchronization, and cross-correlation detection chirp signal to complete synchronization tracking.
According to rapid development of high speed digital signal processing (DSP) technology, this paper concentrates on DSP-based embedded acoustic FH communications system, which based on the UWA channel of analysis, focusing on decoding and synchronization technology. Through experiments both in the laboratory's pool and in Xiamen Harbor, this system can realize high reliable transmission in a certain transmission rate, 3km transmission distance is confined in the shallow sea (2～12m), with transfer rate up to 200 bit/s, and the bit error rate (BER) is about 10~(-3).
引文
[1]J.A.Catipovic.Performance limitation in underwater acoustic telemetry[J].IEEE J,Oceanic.Eng.
[2]许肖梅.浅海水声数据传输技术研究[D].厦门:厦门大学博士学位论文,2002.
[3]Daniel B.Kilfoyle,Arthur B.Baggeroer.The State of the Art in Underwater Acoustic Telemetry[J].IEEE Journal of Ocean Engineering,Vol.25,NO.1,January 2000,p4-27.
[4]Goalic,A,Trubuil,J,Lapierre,G,Labat,J.Real time low bit rate speech transmission through underwater acoustic channel[J].Oceans,2005,1:319-321.
[5]Ormondroyd,R.F.Dhanoa,J.S.Comparison of space-time block code and layered space-time MIMO systems for an underwater acoustic channel[J].Oceans-Europe,2005,1:255-260.
[6]Yeung L F,Bradbeer R S,Law E T M,Angus Wu,Bin Li,Gu Z G.Underwater Acoustic Mode M Using Multicarrier Modulation.OCEANS Proceedings,2003,3:1368-1375.
[7]Freitag,L.Stojanovic,M.Singh,S.Johnson,M.Analysis of channel effects on direct-sequence and frequency-hopped spread-spectrum acoustic communication[J].Oceanic Engineering,IEEE Journal,2001,26(4):586-593.
[8]Oe-Hyung Lee,Yoon-Jun Son,Ki-Man Kim.Underwater digital communication using acoustic channel estimation[J].Oceans '02 MTS/IEEE,2002,4:2453-2456.
[9]Yang,T.C.Differences between passive-phase conjugation and decision-feedback equalizer for underwater acoustic communications[J].Oceanic Engineering,IEEE Journal,2004,29(2):472-487.
[10]Rouseff,D.Jackson,D.R.Fox,W.L.J.Jones,C.D.Ritcey,J.A.Dowling,D.R.Underwater acoustic communication by passive-phase conjugation:theory and experimental results[J].Oceanic Engineering,2001,26(4):821-831.
[11]Rouseff,Daniel,Flynn,John A.Ritcey,James A.Fox,Warren L.J.Acoustic Communication Using Time-Reversal Signal Processing:Spatial and Frequency Diversity[J].High Frequency Ocean Acoustics Conference,AIP Conference Proceedings,2004,(728):83-89.
[12]G F Edelman,H C Song,S Kim,et al.Underwater acoustic communications using time reversal[J].IEEE Journal of Oceanic Engineering,2005,30(4):852-864.
[13]Akyildiz,I.F.Pompili,D.and Melodia,T.Underwater acoustic sensor networks:Research challenges[J].Elsevier's Journal of ad Hoc Networks,2005,3(3):257-279.
[14]Grund,M.Freitag,L.Preisig,J.Ball,K.The PLUSNet Underwater Communications System:Acoustic Telemetry for Undersea Surveillance[J].Oceans,2006:1-5.
[15]刘云涛,杨莘元,蔡惠智.一种提高高速水下通信性能的基带波形结构设计[J].声学学报,2005,30(5):435-441.
[16]孙小东,侯朝焕.一种差分解调OFDM跳频水声通信系统[J].电声技术,2007,31(10):71-74.
[17]殷敬伟,惠俊英,郭龙祥.点对点移动水声通信技术研究[J].物理学报,2008,57(03):1753-1758.
[18]刘林泉,梁国龙,吴波,周志强,李宏伟.一种低能耗的水声通信编码方案的研究[J].声学技术,2007,26(1):130-133.
[19]黄晓萍,桑恩方.一个水声扩频通信系统设计与实现[J].海洋工程,2007,25(1):127-132.
[20]何成兵,黄建国,张群飞,申晓红.M元线性调频远程水声通信新技术[J].西北工业大学学报,2005,23(6):777-780.
[21]李红娟,孙超.基于空时分组编码的水声MIMO通信系统仿真研究[J].系统仿真学报,2007,19(11):2539-2542.
[22]程恩.水声电子邮件传输研究[M].厦门:厦门大学通信工程系博士学位论文,2006.
[23]刘伯胜,雷家煜.水声学原理[M].哈尔滨:哈尔滨工程大学出版社,1993.
[24]许祥滨.抗多途径干扰的水声数字语音通信研究[D].厦门:厦门大学电子工程系博士学位论文,2003.
[25]汪德昭,尚尔昌等.水声学[M].北京:科学出版社,1981.
[26]R.Urick.Principles of Underwater sound,third edition,McGraw-Hill Book Company,1983.
[27]P.C.Etter.Underwater Acoustic Modeling:Principles,Techniques and Applications[M].Elsevier Applied Science London and New York,1991.
[28]R.Coates.An empirical formula for computing the Beckmann-Spizzichino surface reflection loss coefficient,IEEE Trans.Ultrason.Ferroelec.Frequency contr.,Vol.35,no.4,pp.522-523.
[29]Proakis J G.Digital Communication[M],third edition,1995.
[30]王峰,赵俊渭,鄢社锋.基于射线模型的水声信道的仿真软件设计[J].电声技术,2000年,第6期.
[31]郭长勇.浅海多途水声信道通信仿真研究[M].厦门:厦门大学海洋系硕士学位论文,2002.
[32]John G.Proakis,Coded modulation for digital communications over Rayleigh fading channels.IEEE J.Ocean.Eng.,1991,16(1):66-73.
[33]郑继禹,林基明.同步理论与技术[M].北京:电子工业出版社,2003.
[34]周求湛,胡封晔,张利平.弱信号检测与估计[M].北京:北京航空航天大学出版社,2007.
[35]樊养余等.基于高阶谱的舰船辐射噪声特征提取[J].声学学报,1999,24(6):611-616.
[36]王洪超.基于混沌预测的水声信号检测方法研究[M].西安:西北工业大学硕士学位论文,2007.
[37]彭启琮,管庆.DSP集成开发环境[M].北京:电子工业出版社,2004.
[38]曾一凡,李晖.扩频通信原理[M].北京:机械工业出版社,2005.
[39]牛富强,许肖梅.一种基于DSP的实时水声跳频通信系统研究[J].厦门大学报,2008,6.
[40]毛岱山.浅海声信道文本图象通信研究[M].厦门:厦门大学海洋系硕士学位论文,2006.
[41]LR Rabiner.Multirate Digital Signal Processing[M].Prentice-Hall PTR Upper Saddle River,NJ,USA,1996.
[42]Aiello M,Cataliotti A,Nucci.A Comparison of Spectrum Estimation Techniques for Periodic not Stationary Signals[C].IEEE Instrumentation and Measurement Technology Conference,2001:1130-1134.