在地球上，有超過70%的表面被海水所覆蓋，近年來許多科學家與學者紛紛將眼光投向大海中蘊藏的各種可能性，因此水下的無線傳輸技術開始被廣泛的討論及研究，各種應用也隨之而生。在水下感測網路中，由於無線電波與光波的特性並不適合在以水為媒介的環境中進行長距離的傳輸，取而代之的則是聲波，然而聲波在水中具有高傳播延遲與高位元錯誤率等特性，對於需要即時性與資料正確性的應用來說，是迫切需要解決的重大問題，且由於水下環境的種種特性，針對無電線波所設計之繞徑協定，將無法直接應用在水下聲波感測網路中。本論文主要探討水下雜訊與聲速變化對於位元錯誤率與傳播延遲之影響，並利用其特性設計一適用於水下感測網路之繞徑協定。透過分析水下雜訊在不同深度之變化，估測一路徑上每一步之預期傳輸次數，並結合聲速變化得出該路徑之傳輸時間，進而評估兩者對路徑選擇之影響，並以此為根據設計一繞徑協定。最後透過實驗模擬，發現本論文所提出之繞徑協定，在傳輸時間與封包抵達率上皆有較好之表現。

In underwater acoustic networks, a transmission is done by means of acoustic wave. However, acoustic transmissions suffer long propagation delay and high bit error rate, especially for real time applications. Since speed of sound and underwater noises are varied with water depth, therefore, this thesis takes sound speed and underwater noises into account and proposes a channel-aware depth-adaptive routing protocol, named CDRP, for underwater acoustic sensor networks to relief propagation delay and transmission error rate. In CDRP, the source constructs a virtual ideal path to the sink while it has data to send. According to its one-hop neighbor information, the source then chooses one or several proper forwarders to relay the data. Likewise, the forwarders select next forwarders in the same way until the data is sent to the sink. To our best knowledge, CDRP is the first routing protocol considering the effects of underwater noise and sound speed with depth variation. The simulation results show that CDRP has better performance in end-to-end delay and packet delivery ratio.

Contents
1 Introduction 1
1.1 Motivation 3
1.2 Organization 4
2 Preliminaries 5
2.1 Noise in Underwater 6
2.2 Speed of Sound in Underwater 7
2.3 Routing Schemes in Underwater 10
3 Path Analysis 13
3.1 Numerical Analysis 14
3.2 End-to-End Transmission Time Estimation of Straight Path 19
3.3 End-to-End Transmission Time Estimation of Upward Path 20
3.4 End-to-End Transmission Time Estimation of Downward Path 21
3.5 Analysis Result 22
4 Channel-Aware Depth-Adaptive Routing Protocol(CDRP) 24
4.1 Ideal Virtual Path 25
4.2 Transmission Mode 26
4.3 Relay Selection 27
5 Performance Evaluations 31
5.1 Packet Delivery Ratio 32
5.2 End to End Delay 37
6 Conclusions 42
6.1 Contributions 42
6.2 Future Work 43
Bibliography 44
Appendix 48

List of Figures
Figure 1.1 A common scenario of UASNs. 2
Figure 2.1 Noise power in terms of frequencies in different wind speed. 8
Figure 2.2 Sound speed in terms of underwater depth. 10
Figure 3.1 Attenuation of acoustic waves with different frequencies in terms
of different distance. 16
Figure 3.2 Attenuation of PN in terms of water depth. 17
Figure 3.3 Upward, straight, and downward paths in the network. 19
Figure 3.4 Straight path. 20
Figure 3.5 Straight path. 21
Figure 3.6 Straight path. 22
Figure 4.1 Structure of ideal path table. 26
Figure 4.2 The schematic of the transmission mode switching. 27
Figure 4.3 The schematic of the symbols used in Eq. (4.1). 29
Figure 5.1 Comparisons of the packet delivery ratio in terms of the width of the network while the source node is located at the depth of 3 km. 33
Figure 5.2 Comparisons of the packet delivery ratio in terms of the width of the network while the source node is located at the depth of 5 km. 34
Figure 5.3 Comparisons of the packet delivery ratio in terms of the width of the network while the source node is located at the depth of 7 km. 35
Figure 5.4 Comparisons of the packet delivery ratio in terms of the wind speed and the width of the network while the source node is located at the depth of 3 km. 36
Figure 5.5 Comparisons of the packet delivery ratio in terms of the wind speed and the width of the network while the source node is located at the depth of 3 km. 37
Figure 5.6 Comparisons of the packet delivery ratio in terms of the wind speed and the width of the network while the source node is located at the depth of 7 km. 38
Figure 5.7 Comparisons of the packet delivery ratio in terms of the wind speed and the width of the network while the source node is located at the depth of 7 km. 39
Figure 5.8 Comparisons of the packet delivery ratio in terms of PSTinc and PSTdec and the width of the network while the source node is located at the depth of 3 km. 39
Figure 5.9 Comparisons of the packet delivery ratio in terms of the wind speed and the width of the network while the source node is located at the depth of 7 km. 40
Figure 5.10 Comparisons of the end-to-end delay in terms of the width of the network while the source node is located at the depth of 3 km. 40
Figure 5.11 Comparisons of the end-to-end delay in terms of the width of thenetwork while the source node is located at the depth of 5 km. 41
Figure 5.12 Comparisons of the end-to-end delay in terms of the width of thenetwork while the source node is located at the depth of 7 km. 41

List of Tables
Table 1.1 The differences between UASNs and WSNs. 2
Table 3.1 Symbol descriptions. 19
Table 5.1 System parameters in the simulations. 32

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