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

Abstract

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.

Experimental demonstration on long-range time-reversal multiple-input/multiple-output underwater acoustic communication over tens of kbps in 12.5 km range

“…For MIMO communication, we utilize the ATR-DFE approach to decompose the signals from the intended transmitters. [15][16][17][18][19][20][21] In ATR, the estimated channel response is altered by an adaptive weight function calculated under the minimum-variance distortion-less response criteria to reduce the co-channel interference from other transmitters while the power from target transmitter is retained. 15,16) The ATR probe in the frequency domain w k ( f ) is given by:…”

“…In past studies, a single carrier system using a time-reversal based processing called adaptive time reversal (ATR) followed by a single channel DFE (ATR-DFE) have also been applied to SDM-MIMO UAC, [15][16][17][18][19][20][21] and their results give us some expectation to improve the communication rate. Specifically, the performance of the tank test for short range (about 20 m) using 5-channel 60 kHz centered transmitters show very high spectral efficiency of 16.7 bps Hz −1 at maximum throughput.…”

“…17) In addition, there is another experimental example of SDM-MIMO and mobile multi-user communication using 500 Hz sources for long-range transmission in deep sea area. 18,19) It is considered that the advantage of ATR-DFE for improving data rate and spectral efficiency is that spatial separation and removal of the effect of multipath by ATR and signal equalization by DFE are processed separately. As a result, by reducing the burden on the filter coefficient estimation for equalization, it is possible to reduce the training symbol length in signal design and improve the spectral efficiency of the signal configuration.…”

Suppression of effects of Doppler shifts of multipath signals in underwater acoustic communication

“…In this process, the signal-to-noise ratio (SNR) is improved by the effective usage of the energies of multipath signals [9]. Recently, applications for multiple-input/multiple-output (MIMO) and multiuser communication with time reversal have been studied [10][11][12][13][14].…”

Effective roughness on the sea surface for determining variability characteristics of reflected sound waves

“…In the field of acoustic communication, the multipath wave and Doppler effect caused by sound wave propagation in the sea are obstacles to realizing robust and high-rate acoustic communication. [1][2][3][4][5][6][7][8][9] The use of acoustic communication is increasing not only in deep-sea areas but also in shallow water areas such as harbors and coastal regions. 4) In order to improve communication performance in shallow water environments, it is necessary to clarify the variability characteristics of sea surface reflected waves quantitatively.…”