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1 学校编码 :10384 分类号密级学号 : UDC 硕士学位论文时变信道下的时间反转扩频水声通信研究 Research on Time Reversal Spread Spectrum Underwater Acoustic Communication in Time-varying Channels 周跃海指导教师姓名 : 童峰教授专业名称 : 海洋物理论文提交日期 : 年 0 5 月论文答辩时间 : 年 0 6 月学位授予日期 : 年 04 月答辩委员会主席 : 评阅人 : 2013 年 05 月

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4 DSP TMS320DSP6713 I

5 Abstract Abstract With the rapid development of marine exploitation, marine environment monitoring, marine national defense and security, the requirement of transmitting information through underwater channel is increasing in recent years, so underwater acoustic communication has drawn significant attention. However, the complexity, time-varying and uncertainty of underwater acoustic channel character lead to Doppler shifting, multi-path, time and frequency selective fading, which bring considerable challenges to R&D of high performance underwater acoustic communication system. With the development of underwater acoustic signal processing, especially the fresh development of time reversal and digital hardware processing platform, robust point to point communication and underwater acoustic network become possible. Time reversal becomes a research focus in underwater acoustic communication in recent years, because time reversal technology can concentrate multipath and improve output signal-to-noise ratio (OSNR) without knowing channel character in advance. Direct sequence spread spectrum has been exploited widely in underwater acoustic because of its advantage of anti-multipath, anti-jamming and spreading gain. Considering the performance degradation of time reversal method under time-varying channel, by combining time reversal and spread spectrum we proposed a novel scheme for time reversal spread spectrum UWA communication in the presence of time variation. The proposed scheme utilizes previously decided bits to generate spread spectrum sequences as the training signal to update the channel estimation, and adopts the output of the channel estimator for time reversal processing to facilitate multipath and noise robust demodulation. The mechanism of the proposed method not only enables the multi-path focusing, but also omits the employment of the probe. In addition, the proposed scheme is robust to low SNR and convenient for implementation. Furthermore, we compare the performance of channel estimation time reversal under different SNR. The main contributions of this paper are as follows: 1 We proposed a scheme based on time reversal and spread spectrum under time-varying channel, by employing decided information to estimate channel II

6 Abstract character, and utilizing the channel response for time reversal. The proposed time reversal communication scheme is suitable for low SNR condition due to its inherent spread spectrum feature. 2 This paper compared the performance between different updating frequency of channel estimation based time reversal method and classic probe updating based time reversal method, analyzed the performance of channel estimation based time reversal method under different SNR. 3 Based on above investigation, hardware implementation of the proposed time reversal DS scheme was carried out based on DSP platform, by which the effectiveness of the proposed scheme was validated with lake trial. Keyword time-varying channel time reversal direct sequence spread spectrum channel estimation III

7 Abstract Modem DBPSK IV

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9 Contents contents Abstract(in Chinese) Abstract Chapter 1 Preface Introduction Developing status of underwater acoustic communication Developing status of underwater acoustic Modem Developments and advances in Time Reversal Communication Main Content of this dissertation Chapter 2 Underwater acoustic channel and its characteristics Underwater acoustic channel Characteristics of underwater acoustic channel Sound speed in the ocean Transmission loss Multipath spread Undulating effect and Doppler spread Oceanic noise Time-varying characteristics of underwater acoustic channel Chapter 3 Time Reversal and Direct Sequence Spread Spectrum Principle of time reversal Active time reversal Passive time reversal Principle of direct sequence spread spectrum Theoretical basis of spread spectrum technology Principle of DBPSK Chapter 4 Time Reversal and spread spectrum communication under time-varying channel Time reversal under time-varying channel The scheme of time reversal spread spectrum system Scheme of time reversal spread spectrum based on probe updating VI

10 Contents Scheme of time reversal spread spectrum based on channel estimation Adaptive channel estimation algorithm Chapter 5 Passive time reversal spread spectrum implementation base on DSP design Hardware design TMS320C MAX274 filtering circuit AD603 circuit Software implementation Main process of system Receive and demodulation signal Chapter 6 Experimental results and analysis Experiment Environmental character of trial area Signal modulation and demodulation Lake trial Experiment Experimental design Experimental results Chapter 7 Summary 59 References 60 VII

11 1.1 71% 60 50% 70% [1] [2] - - [3] - - [4] 1

12 RAKE [5] [6] Modem [7] Modem - - AquaNodes 12 Seaweb MAST (Marine Science and Technology program) ROBLINKS (Long Range Shallow water Robust Acoustic communication Links) SWAN (Shallow Water Acoustic communication Network) 2

13 1.2 [8] [9] 21 DSP [10]

14 1.3 Modem Modem Modem 1.1 LinkQuest UWM Modem Fig.1.1 UWM series Modem of LinkQuest Corporation 1.1 LinkQuest UWM Modem UWM Modem UWM1000 UWM2000 UWM2200 UWM3000 UWM4000 UWM10000 Modem LinkQuest UWM Modem AUV AUV LinkQuest UWM Modem [11] 1.2 Woods Hole Modem [12] Modem TI TMS320C5416 DSP Modem bps Modem FSK PSK FH-FSK PSK 4

15 1.1 UWM Modem Table 1.1 the parameters of UWM Modem 1.2 Wools Hole Modem Fig.1.2 Micro underwater acoustic Modem of Wools Hole 1.3 Benthos Modem Fig.1.3 Underwater acoustic Modem of Benthos coroporation 5

16 1.3 Benthos Modem 12-48VDC Modem 9-14kHz 16-21kHz RS S2C L220 Modem Fig.1.4 Underwater acoustic Modem of L S2C L 220 [13] Chips S2C S2C L200 Modem 210kHz-290kHz 10 72kbps 10-7 DC12V 1.5W 3W 1.5 MQ Modem Fig.1.5 Modem of Institute of Acoustics Chinese Academy of Sciences 1.5 MQ [14] MQ MQ Modem 6

17 Degree papers are in the Xiamen University Electronic Theses and Dissertations Database. Full texts are available in the following ways: 1. If your library is a CALIS member libraries, please log on and submit requests online, or consult the interlibrary loan department in your library. 2. For users of non-calis member libraries, please mail to etd@xmu.edu.cn for delivery details.

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