碩士 / 國立臺灣科技大學 / 資訊工程系 / 98 / Underwater synchronization is special issue for sensor networks. The problem is much more challengeable than the conventional synchronization problem on the ground. On the one hand, this is because underwater sensors cannot receive signals from GPS satellites directly. On the other hand, since electromagnetic signals decay extremely fast in water, traditional wireless message exchange using electromagnetic signals is not suitable for underwater environment.
This thesis investigates Doppler Effect experienced by an underwater mobile sensor when receiving ultrasonic signals from a fixed buoy on the surface of the water. Since the speed of ultrasonic signals is much slower than that of electromagnetic signals, ultrasonic signals can result in more obvious Doppler Effect. Furthermore, propagation delay of the slow speed ultrasonic signals cannot be ignored anymore in underwater environment. Thus, distance estimation between buoy node and sensor node becomes a critical factor in order to determine propagation delay for time synchronization. Two methods are proposed to estimate this distance, namely Underwater Distance Estimation-Nonlinear Regression (UDE-NR) and Underwater Distance Estimation-Simple Approximation (UDE-SA). UDE-NR estimates the sensor’s speed, depth under the surface, and horizontal distance from the buoy node by fitting the parameters to the non-linear objective frequency function. To reduce the complexity of the calculation, UDE-SA estimates the sensor’s speed and horizontal distance from the buoy based on the received signal and determines the depth of the sensor by linear regression to a simplified objective function. Propagation delay of the signal is then estimated and used to achieve time synchronization among sensors.
| Identifer | oai:union.ndltd.org:TW/098NTUS5392047 |
| Date | January 2010 |
| Creators | Chun-Hsien Lee, 李俊賢 |
| Contributors | Tai-Lin Chin, 金台齡 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 46 |
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