On the Mobile-to-Mobile Linear Time-Variant Shallow-Water Acoustic Channel Response

TL;DR

This paper characterizes the linear time-variant underwater acoustic channel response, revealing dependencies on absolute velocities and proposing methods to simulate dynamic channels from static models, especially for overspread channels.

Contribution

It introduces a novel analysis connecting static and dynamic channel impulse responses, highlighting the importance of absolute velocities in mobile-to-mobile underwater acoustic channels.

Findings

CIR depends on absolute velocities, not just relative velocity.

Connections enable dynamic channel simulation from static models.

Illustrations show different CIRs despite same relative velocity.

Abstract

We expose some concepts concerning the channel impulse response (CIR) of linear time-varying (LTV) channels to give a proper characterization of the mobile-to-mobile underwater channel. We find different connections between the linear time-invariant (LTI) CIR of the static channel and two definitions of LTV CIRs of the dynamic mobile-to-mobile channel. These connections are useful to design a dynamic channel simulator from the static channel models available in the literature. Such feature is particularly interesting for overspread channels, which are hard to characterize by a measuring campaign. Specifically, the shallow water acoustic (SWA) channel is potentially overspread due the signal low velocity of propagation which prompt long delay spread responses and great Doppler effect. Furthermore, from these connections between the LTI static CIRs and the LTV dynamic CIRS, we find that the SWA mobile-to-mobile CIR does not only depend on the relative velocity between transceivers, but also on the absolute velocity of each of them referred to the velocity of propagation. Nevertheless, publications about this topic do not consider it and formulate their equations in terms of the relative velocity between transceivers. We illustrate our find using two couples of examples where, even though the relative velocity between the mobiles is the same, their CIRs are not.