수열 길이와 변조 신호 변수가 M수열을 이용한 시불변 통신 채널 측정에 미치는 영향 연구

Abstract

Underwater acoustic channel is characterized by time-varying multi-path environment. Such environment causes difficulty in acoustic communications. In order to design an effective communication system in a given environment, the acoustic channel must be identified. Among various probe signals M-sequence is widely used for channel measurement because of its impulse-like autocorrelation. However, the importance of M-sequence parameters has been ignored. Thus, this paper tries to investigate the effect of M-sequence parameters - code length, roll-off factor, filter delay, symbol time - on the measurement of underwater acoustic channel. As a basic step noise-free time-invariant ideal channel is assumed and zero-crossing impulse width, half-power impulse width, sidelobe peak value, and background level are examined. Two path condition is also used as a simulated channel to find out the effect on multi-path delays and their peak values. As a result we found that assuming no background noise large roll-off factor and 1-symbol filter delay are optimal parameters to identify multi-path delays and their peak values for the ideal channel.