Multiuser Communication with Adaptive Time Reversal Under Doppler Effect

In underwater acoustic communication, the effect of transmitter movement is very large owing to the low acoustic propagation speed, and the frequency shifts due to Doppler effect have different values depending on the propagation angle of each multipath. These problems are critical to orthogonal frequency division multiplexing (OFDM) which is a widely used, representative method. In the meantime, by passive time reversal (PTR), different frequency shifts are converged to one frequency shift by wave focusing in signal processing. In this study, it is confirmed that this advantageous characteristic is not lost in multiuser communication using adaptive PTR, which is an enhanced version of time reversal for spatial division multiplexing (SDM). At-sea experiments for multiuser communication with two transmitters, one of which was a moving transmitter, were carried out. As a result, it was demonstrated that adaptive PTR enables multiuser communication independently of the velocity of the moving transmitter even under multiuser interference.