Path-Specific Angle and Doppler Tracking in Dynamic Underwater Channels

We present a method for path-specific angle and Doppler tracking in the context of a single-input multiple-output single-carrier system for under-water acoustic communications. We address scenarios in which the multipath channel exhibits different Doppler distortions across different propagation paths. The proposed algorithm builds upon gradient-based beamforming methods to track the path angles and isolate the corresponding signal contributions. The isolated multi path signals are fed to a multi-channel fractionally-spaced decision-feedback equalizer (DFE), which couples a phase-locked loop (PLL) with a delay-locked loop (DLL) per beamformed path to perform adaptive resampling. The advantage of such an approach is not only in the ability to compensate for path-specific Doppler scaling, but also in reducing the overall equalizer complexity, which is now dictated by delay spreading on an individual path rather than the entire multipath spread. The performance is demonstrated through simulations of highly mobile scenarios with speeds on the order of 20 m/ s, showing excellent results in terms of data detection mean squared error (MSE).