수중통신에서 채널 추정기법에 관한 연구

Abstract

In recent years, underwater acoustic communication have received much attention as their applications, have begun to shift from military toward commercial. The growing interest in underwater acoustic communications come as a response to the rapidly growing needs for wireless underwater communications, brought in part by the broadening of applications, such as military and commercial ones. Commercial applications which have received much attention lately are pollution monitoring in environmental systems, remote control in off-shore oil industry, and collection of scientific data recorded at benthic station without the need for retrieving the instruments. Many developing applications include of commercial and military are now calling for real-time communication with submarines and autonomous underwater vehicles, not only in point-to-point links, but also in network configurations.

This research has aimed toward bringing together many of the well established principles of wireless radio communications and re-considering them for application in underwater acoustic channels. However, the adverse effects of underwater propagation has on the digital acoustic signals often require development of specialized communication techniques. Many solutions have been offered, and the extensive research of the past years has established underwater acoustic communications as a new field of applied engineering.

In this thesis, a new method of channel estimation for underwater acoustic communication is considered. Signal transmitted in the underwater has multiple interactions with the sea surface, the bottom, and volume. Multipath propagation in underwater acoustic communication causes distortion to high-speed digital signals. The proposed method reduces distortion of received signal by multipath propagation. The proposed method is similar to the passive phase conjugation technique. However, the difference is that the probe signal is used for underwater communication channel estimation. The underwater channel impulse responses are estimated by eigenvalue decomposition algorithm. The channel vectors are in the null space of the covariance matrix of the received signal at receiver array. The received data signals are convolved with the time-reversed channel impulse responses. The results of this processing reduce distortion of received signal. The performances of the proposed method are evaluated in various environments.