本研究主要將三種陣列信號處理之方法，應用於多重輸入多重輸出水下通訊之聲束聚焦及水下串音通訊，分別為聲音對比控制法、時間反轉法與適應性時間反轉法。聲音對比控制法為聲束聚焦技術，可用於增加或減少特定區域的聲音勢能密度，亦即聲音亮暗區，並達到避免監聽及改善通訊品質之目的。時間反轉法已廣泛的應用在克服水下聲音通道多重路徑的影響。然而，更發展出適應時間反轉法來提升水下聲音通訊的串音問題。
水下聲束聚焦方面，本研究利用計算聲線法推估聲音通道之脈衝響應函數，經過聲音對比控制法之處理，可推估其權重函數增加或減少特定區域的聲音勢能密度，為評估此法之可行性模擬環境為一150米之等聲速之海水層與海床，而陣列設置參數影響這些方法的效果。因此，根據模擬之結果，討論陣列麥克風之數量、聲源發射頻率、控制區域與陣列水平距離及控制區域幾何關係對此方法之影響，以便應用於後續水下通訊之相關研究。水下串音通訊方面，本研究採用拖航水槽做為水下通訊測試平台，做為時間反轉法與適應性時反法之性能評估。此平台實際上對聲波通訊的好處在於更容易探討陣列設置參數的影響，如訊雜比，單一通道與多通道，聲源陣列之間距等，這些參數對水下串音通訊品質所造成的影響。實驗採用兩個發射聲源分別發射10kHz及16kHz為中心頻率的調變波，接收陣列由四個水下麥克風組成且距離發射陣列30米。
根據數值分析結果發現聲音對比控制法之聲束聚焦於淺海模擬環境，有效地提升指定接收區域聲場之能量。另一方面，根據實驗結果發現時間反轉法與適應性時間反轉法的效果隨著接收陣列的數量而增加。整體而言，適應性時間反轉法的訊雜比與錯誤率之效能皆優於時間反轉法，陣列設置參數如聲源陣列之間距影響此法之效果。聲音對比控制法未來將可應用頻率鍵移調變技術於提升水下通訊品質，時間反轉法與適應性時間反轉法亦可應用於提升多重輸入多重輸出水下通訊之傳輸速率。

This study implementing three kinds of array signal processing that apply on sound focusing and crosstalk for multiple-input-multiple-output underwater communication applications. Those are the acoustic contrast control, time reversal mirror and adaptive time reversal mirror. Acoustic contrast control is a sound focusing technique. This technique can the establishment of two zones: a bright zone around the user and a dark zone for other regions to improve underwater communication applications. Then, time reversal mirror has been widely applied to mitigate the inter-symbol interference in underwater channels. Meanwhile, an adaptive time reversal mirror is introduced to improve the crosstalk quality between receivers in underwater acoustic communication.
For underwater sound focusing, numerical analysis for acoustic contrast control was simulated by using ray method for Green’s function calculation between the source point and the field point in a shallow water channel. It provides the optimal sound contrast for increasing or decreasing the potential sound energy of a specific area. To verify the proposed method, a150-mdepth shallow-water channel was simulated. However, array configuration affects the performance of those mechanisms. Therefore, effects of the parameters, which comprised the number of control sources, transmission frequency, control distances between sources, and control zone of a geometric location, were simulated. For underwater crosstalk communication, to explore the effectiveness of time reversal mirror and adaptive time reversal mirror, this study explored both mechanisms in an experiment using a towing tank as a testing platform. The advantage of this process is its simplicity in examining the effects of the array configuration of this crosstalk mechanism. The experiment using dual sources transmit 10 and 16 kHz modulated signal and four hydrophones as receiver array over a 30m communication range. Results of array configuration parameters are discussed i.e. the effects of signal to noise ratio in a single and multi-channel, number of receivers, spacing between sources and noise energy threshold.
The simulation results show that acoustic contrast control is an effective approach for sound focusing in shallow water that can increase the potential sound energy of a specific area. On the other hand, the experimental data demonstrate both time reversal mirror and adaptive time reversal mirror have better performance when the number of receivers increases. Overall, the performance of adaptive time reversal mirror is better than time reversal mirror in terms of BER and SNR. Then, the array configuration such as number of receivers and spacing between sources affects the performance of SNR and BER. In the future, acoustic contrast control can be applied to enhance underwater communications by using frequency-shift keying modulation. Time reversal mirror and adaptive time reversal mirror can be applied as the alternative way to increase the data rate at short ranges for multiple-input-multiple-output communication applications.

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