Experimental Results of Short Range Wideband Acoustic Communication Using QPSK and 8PSK

In JAMSTEC, the acoustic communication is investigated, especially in deep water environment. Then, short-range (up to 500 m) high speed (around 64 kbps) acoustic communication system for deep sea environment is investigated in our group. To obtaining an real sea data of acoustic transmission, an experiment was carried out at the depth of 1,000 m in February 2007. A transmitter was moored at near sea bottom and a receiver was suspended from a surface ship by wire rope. The distance between the transmitter and the receiver was 250 - 550 m. Carrier frequency of a transducer is 80 kHz, and its bandwidth is 40 kHz. Two omni-directional hydrophones were used for receiving the acoustic signal. After recovering the receiver, the demodulation was processed by software as a post processing. Quadrature phase shift keying (QPSK) and 8PSK were used as its modulation method. The data of several transmission speed (16 k symbol per second (sps), 20 ksps, 25 ksps and 40 ksps) were obtained. The two channel decision feedback equalizer (DFE) was applied for the demodulation algorithm. A phase compensation unit was included in the multi channel DFE. In this experiment, when the signal to noise ratio (SNR) was higher than 12 dB, error free communication was carried out in case of QPSK. And also when the SNR was higher than 20 dB, error free communication was carried out in case of 8PSK. Furthermore, it is proved that 80 kbps of transmission rate was achieved at up to 510 m using QPSK, and 120 kbps of transmission rate was achieved at up to 300 m using 8PSK.