ABSTRACT
In seismology, a profile of the earth's crust is synthesized from the set of delays experienced by a probing signal. Determining differences in arrival times or time delay between the paths of a transmission channel is of primary interest in many applications where spatial resolution of signal arrival paths is not feasible. In communication, multipath impedes the extraction of information; specification of the time delay enhances the possibility of echo removal. For a priori unknown signals, autocorrelation and cepstrum techniques have been applied to the extraction of time delay. This chapter introduces the general multipath problem in operator form and constructs a functional model of the channel where, besides the additive effect of noise, sinusoidal interference and signal distortion are taken into account. Attention is directed at two factors in a basic two-path ocean channel that would affect the processing schemes unfavorably: noise and sinusoidal interference.
