|Abstract: ||近十年來，水下聲波通訊是重點的研究項目，其應用範圍包括海洋 環境資料收集、海岸資源探勘、污染監控及軍事監測等。在水下感測網路 中，監測點的儀器與海上工作站均配置聲訊收發器，可以彼此通訊。水下 通道的主要障礙包括可用頻寬極為有限、都卜勒與時間延遲擴展大及多路 徑衰減嚴重。這些因素會嚴重影響資料傳輸率與通訊可靠度，因此需要先 進的訊號處理技術來克服這些不利的通道因素。 本計畫的目標在於研究先進的多載波調變的正交分頻多工(OFDM) 水下通訊技術及以嵌入式發展平台來設計及實現聲波數據機，並配合中央 氣象局媽祖計畫(MACHO)規劃的宜蘭頭城海域海域進行水下通訊實驗， 以建立自主性的水下通訊能力。在聲波接收機方面，必須考量多路徑衰減 所引起的符元間干擾和非同步所引起的載波間干擾的消除方法，包括符元 時間、都卜勒相移、載波頻率偏差的估計和矯正，以降低誤碼率。此外， 水下通道的脈衝響應函數具有時變性而且無法預知，因此上述的同步與解 調後的通道估測與符元偵測必須考量適應性的訊號處理方式，以隨時因應 水下通道環境的變化。本計畫為子計畫(四)，期程為兩年期，從事聲波數 據機的理論研究與嵌入式發展平台的軟體設計、電腦模擬驗證，及使用總 計畫提供的聲源發射器與接收聲納陣列於宜蘭頭城海域進行水下通訊實 驗，以驗證聲波數據機系統在海洋環境中的實現程度。此外，期間規劃與 子計畫(五)合作進行宜蘭頭城海域的實測，以獲得水下聲傳通道的估測模 型，做為電腦模擬驗證之用途。|
During the past decade, underwater sensor networks with wireless acoustic communication is the main research topic. Its applications include environmental data collection, offshore exploration, pollution monitoring, and military surveillance, etc. In underwater sensor networks, sensor nodes and surface stations are equipped with acoustic modems to communicate with each other. Major obstacles posed by an underwater acoustic channel are rather small available bandwidth, large Doppler and delay spreads and severe multipath fading. These factors can severely limit data transmission rate and degrade reliability, thus advanced communication techniques are needed to combat these channel impairments. The project is aimed at investigating advanced underwater communication technologies, such as orthogonal frequency division multiplexing (OFDM) multicarrier modulation, designing and implementing acoustic modem , and conducting wireless underwater acoustic communication experiments near the Tou-Chen harbor as planned in the MACHO project of the central weather bureau for establishing our underwater communication capability. For acoustic receiver, schemes to reduce intersymbol interference caused by multipath fading as well as the intercarrier interference induced by synchronization loss should be considered , including symbol timing , Doppler phase shift, and carrier frequency offset estimation and compensation, to reduce bit error rate. In addition, because the impulse response of the underwater acoustic channel is time-variant and unknown, the aforementioned synchronization, channel estimation and data symbol detection require adaptive processing in order to cope with the variations of the underwater channel. The project is intended to be completed within two years. We intend to research the acoustic modem theory based on OFDM transmission, design its software using the embedded development system, perform computer simulations and conduct underwater communication experiments near the Tou-Chen harbor, using the acoustic transducer and receiving sonar array system provided by the main project , to investigate the communication feasibility of the developed acoustic modem in the practical ocean environment. In addition, we will cooperate with the other team ( subproject 5) to conduct the experiments related to the impulse response measurements of the same ocean field to obtain the underwater acoustic model to be used in computer simulations.