Experimental study on multiple-input/multiple-output communication with time reversal in deep ocean

Multiple-input/multiple-output (MIMO) communication using adaptive time reversal is examined by comparing orthogonal frequency division multiplexing (OFDM) with simulated MIMO test signals by synthesizing experimental data in deep ocean. The experiment was carried out in a 1,100-m-depth area at a range of 10 km with a bandwidth of 500 ± 50 Hz. Although time variance is not included in analysis of OFDM, it is impossible to increase the numbers of MIMO channels with OFDM. On the other hand, with adaptive time reversal, it is possible to achieve 8 × 20 and 6 × 20 MIMO communication with binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK), respectively, in spite of time variance and input signal-to-noise ratio (SNR) degradation due to synthesized signals. Thus, it is demonstrated that adaptive time reversal shows a much better performance than OFDM in MIMO underwater acoustic communication.