Analysis and Modeling of Time-Varying Multipath Amplitude in High-Speed Mobile Underwater Acoustic Channels

In underwater acoustic communication (UAC), channels are typically assumed to be stationary or slowly time-varying during short communication events, with a single statistical distribution generally sufficient to describe path amplitude variation. However, our UAC channel measurements in high-speed mobile scenarios reveal the limitations of traditional single-state fading models and wide-sense stationary assumptions. The measured time-varying impulse responses (TVIR) demonstrate that rapid changes in propagation distance and environment lead to three non-stationary time-varying characteristics: line-of-sight (LOS) propagation loss related to relative movement distance, shadowing-induced average level fluctuations, and rapid oscillations due to scattering paths superposition. To characterize these dynamic properties and enable realistic time-varying multipath simulation, we propose a multiscale amplitude fading model based on finite state Markov chains (FSMCs). To validate the effectiveness of the proposed amplitude simulation model, comparative analyses are conducted with classical wireless mobile channel fading models, including Rician, lognormal, and Nakagami-m distributions. Evaluation metrics involved time-domain envelope and autocorrelation functions. The results indicate that our model effectively captures the dynamic trends of UAC channels in high-speed mobile scenarios.