얕은 수심을 갖는 수중 음향 채널의 수직 공간 코히어런스 분석

Abstract

Spatial coherence is important for spatial signal processing which is used to overcome signal fading in time-varying frequency selective channel like the underwater acoustic channel. As discussed in [1], the spatial coherence determines the diversity combining gain as well as the beamforming gain obtainable by use of multiple receivers and suggests which scheme is better between diversity combining and beamforming for communication in the channel considered. In shallow water, the spatial coherence is affected much by the signals scattered from the sea surface [2] and accordingly it is expected to show different characteristics over different frequencies as well as different transmitter-receiver ranges due to the variation of the surface scattered signals. In this work, the results of an experiment to measure the vertical spatial coherence in waters 20 m deep are analyzed. The measurements were conducted over various carrier frequencies from 20 to 40 kHz at transmitter-receiver ranges from 0.1 to 1 km. The channel impulse responses are estimated from the received signals and averaged to obtain the power delay profiles for analyzing the signal propagation structure. The power angular profiles also are obtained by the wideband conventional beamforming and they are compared with the spatial coherences obtained with the same data.