A journey toward modeling and resolving doppler in underwater acoustic communications

Underwater acoustic (UWA) communications is the only reliable method for long-distance communications underwater, and is widely used in commercial, scientific, and military scenarios. However, the UWA channel is most challenging due to its double dispersion property in both long time delay and large Doppler spread, resulting in severe multipath spread and time variation. Among these, Doppler spread is one of the most critical challenges, and researchers have proposed various models in order to resolve Doppler spread in UWA channels. In this article, an overview of Doppler modeling and resolving is provided, divided into four stages: the quasi-static model of the mid-1980s, the uniform Doppler shift model in the 1990s, the basis expansion model and uniform path speed models of the late 1990s, and the recently developed non-uniform path speed model. Furthermore, the UWA channel sparsity property utilized by each of those models will also be discussed.