Time-reversed communication over Doppler-spread underwater channels

This paper analyzes the impact of Doppler shifts induced by source motion on the focusing performance of a time-reversal array. These arrays have recently attracted research interest due to their ability to project signals with low intersymbol interference at specific locations in the ocean, with no knowledge of environmental parameters. Although time reversal relies on bidirectional exchange of signals in a static environment, it is shown that source motion does not destroy the multipath compensation property; It simply causes amplitude modulation and rotation of the constellation. Wavefront segmentation techniques are proposed to obtain multiple simultaneous signals at the focus where Doppler distortion of each constellation is essentially reduced to a uniform phase rotation.