運用被動相位共軛等化理論於淺海環境之通訊成效分析

Analysis of Long Range Communication Performance based on Passive Phase Conjugation in Shallow Water

邱永盛(Yung-Sheng Chiu)

指導教授 ： 陳琪芳

國立臺灣大學/工學院/工程科學及海洋工程學研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.01496

摘要

無資料

關鍵字

被動相位共軛法 ； 水下通訊 ； 符間干擾 ； 南海 ； 非線性內波

並列摘要

Underwater acoustic communication in a shallow water waveguide has had a great growing in the past 15 years for commercial and other applications. The traditional techniques of wireless communication which were well developed in air are adopted for the underwater acoustic communication system. However, the results could not bring about satisfying communication performance on the ground of serious intersymbol interference (ISI) which is induced by time-varying multipath effect in horizontal underwater waveguide. For using adaptive equalizers and phase-lock loop etc., the UWA communication would possibly be achieved better but with unacceptable computational complexity. Time-Reversal Mirror (TRM) and Passive-Phase Conjugation (PPC) are new equalization techniques proposed and developed in the aspect of acoustic propagation physics in order to overcome the difficulty as mentioned above. They are different from the traditional techniques in the aspect of signal processing.
PPC and TRM, based on acoustic mode orthogonality as well as mode closure relation, could produce time-domain focusing for a distorted signal by using a densely-sampling vertical receiving array or source-receiver array which entirely cover water column. PPC is the passive version of TRM, which is the result of cross-correlation of impulse response and the impulse response immediately after, can be utilized as the self-channel equalizer to enhance the communication performance. However, it is not necessary and doable to utilize PPC in UWA communication system with a perfectly-covering receiver array. The equalization performance revealed that it depended on the specification of the receiving array such as the aperture, the deployed depth, and the number of hydrophones used of an array. On the other hand, some research shows that the performance of PPC equalizer could be good on the circumstances that only few receivers are used. Nevertheless, the explanations and the further investigations for the good performance are not yet addressed. Thus, this dissertation studied the performance of the PPC equalizer based on a prior knowledge of acoustic field. The objective is to quantify, predict and explore the robustness and performance of the PPC equalizer with using arbitrary vertical line array (VLA).
To achieve the objective, analytical derivation is performed in this dissertation, and the derivation shows that the performance of PPC equalizer would depend upon acoustic mode field. According to this relation between acoustic mode field and equalization output, two assumptions are made here. One is that the performance of PPC equalizer with single-channel processing would be better if there are more acoustic modes interfering with each other at that depth. And the other assumption is that the output of multi-channel equalization would be better if the mode composition at each channel differs more. Experimental data collected in the Asian Seas International Acoustics Experiment (ASIAEX) and simulation results are used to examine and manifest these assumptions. The acoustic mode fields under different ocean circumstances are obtained based on pseudo-inverse method. Moreover, the data is then processed with quadrature-demodulation receiver as well as PPC equalizer to present the communication performances on the ground of various mode fields. The analyses not only manifest the two assumptions but also give an idea about the communication performance and it’s variation in the shallow waters.
The contribution of this dissertation is to find out the relationship between the acoustic mode field and the performance of PPC equalizer, and then provide an idea of optimum combination of least receivers with the a priori knowledge of acoustic field.

並列關鍵字

Passive-Phase Conjugation ； Underwater Communication ； Intersymbol Interference ； South China Sea ； Nonlinear Internal Wave

參考文獻

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