In recent years, along with the expansion of offshore activities such as offshore wind farm development, subsea resource exploitation, and port and harbor construction, and with the increasing sophistication of underwater platforms such as remotely operated vehicles (ROVs) and unmanned underwater vehicles (UUVs), the demand for underwater acoustic communication is increasing as a stable means of communication underwater. In particular, to support seabed warfare (SBW) and establish kill chains, detection reports and targeting information must be shared among underwater platforms in a timely and reliable manner, making underwater acoustic communication prediction technology, which enables a priori assessment of communication coverage and performance, increasingly important.

NEC Corporation has developed sonar prediction that visualizes sonar detection performance / coverage based on underwater acoustic propagation simulation for defense sonar applications, and has accumulated expertise in assessing detection coverage while taking into account the effects of the marine environment on acoustic propagation, including sound　speed profile, bathymetry, and sea-surface and bottom boundary conditions. In this presentation, we introduce our ongoing development of underwater acoustic communication prediction technology for visualizing communication coverage by leveraging the expertise and techniques developed through sonar prediction.

Predicting underwater acoustic communication performance requires more than merely estimating received level alone or merely determining whether an acoustic arrival/path exists; it is necessary to appropriately model multipath propagation caused by surface and bottom reflections, which is especially pronounced in shallow waters, as well as its temporal variation. Sea-surface-motion-induced variations in path-length differences, phase reversal at the sea surface, and multipath interference and fading have a major impact on communication quality, so evaluation of communication coverage that neglects these factors lacks reliability. In addition, because the modeling of multipaths considering temporal variation requires a large number of statistical trials, computational efficiency is therefore a key challenge.

In the proposed approach, to predict communication performance under time-varying sea-surface conditions, the travel time and propagation parameters of each acoustic path are computed using ray tracing, and a channel impulse response (CIR) is generated, thereby capturing the time-varying multipath structure due to surface and bottom reflections. Furthermore, we describe efforts to reduce the computational cost associated with the statistical trials required to account for the effects of sea surface motion. In addition, the same framework can also synthesize received waveforms by convolving the CIR with the transmitted signal.

This presentation reports on our ongoing work on a method for predicting communication coverage that accounts for time-varying sea-surface conditions, as well as on waveform synthesis enabled by the same processing framework. The application of communication prediction technology that accurately identifies communication coverage is directly linked to the selection of optimal modulation type, operating frequencies and bandwidths, the selection of appropriate operating ranges and depths, mission engineering, the formulation of operational plans, and the design of underwater acoustic communication systems, and this technology is expected to provide actionable guidance for these activities.