Real System Features and Implications in Underwater Acoustic Networks

As an emerging research area, underwater acoustic network (UAN) has attracted tremendous interests from both academia and industry in recent years. However, little work has been conducted to test algorithms and protocols in real sea experiments. Due to the complexity of acoustic environments and the uncertainties in acoustic systems, it is difficult for theoretical studies or simulations to evaluate UANs in the real world. Studying real system features of UANs has become crucial in the field. In this dissertation, I study the real system features revealed in sea tests and analyze their impact on underwater media access control (MAC), time synchronization and secret key generation protocols. The system features of UANs I identified include the long preamble of acoustic modems, heterogeneous packet delivery, communication range uncertainty, multi-hop interference, and delayed data transmission. Second, I analyze and evaluate representative MAC protocols in sea tests. Based on the field test results, I study the advantages, shortcomings and limitations of different MAC mechanisms and how they work in real systems. I also propose a practical MAC design for UANs. Third, I analyze the temporal and statistical features of message delivery delay in a lab environment and provide some guidelines on practical time synchronization protocol design and performance improvement. Fourth, I evaluate the performance of representative RSS based key generation approaches for underwater secure communications. Meanwhile, solutions to improve the performance in terms of key generation rate, randomness and key agreement probability are provided