Experiments on Acoustic Communication with Quadrature Amplitude Modulation in Multipath Environment

An experiment on high-speed underwater acoustic data communication was carried out at real sea as a time-variant multipath channel. Demodulation was processed by a multichannel decision feedback equalizer (DFE) demodulator with adaptive filtering. The modulation method used was 16-quadrature amplitude modulation (16-QAM), transmitting rate was 32 k bit per second (bps), carrier frequency was 20 kHz, and bandwidth was 8 kHz (16–24 kHz). Good demodulation results were obtained at a sea trial despite the presence of high-level multipaths. At real sea, we proved that high-speed (32 kbps) acoustic communication can be realized even in a multipath fading channel with 16-QAM. Therefore, it is expected that the flexibility of the design of underwater equipment will be improved, because the influence of a circumferential structure can be neglected.