Signal processing in underwater acoustic communication system for manned deep submersible "Jiaolong"

For the first time in the world, underwater acoustic transmission of images, human voice, data and texts between 7000 m depth underwater and ocean surface was accomplished by underwater acoustic communication system of manned deep submersible "Jiaolong". In this paper, signal processing in underwater acoustic communication system for manned deep submersible "Jiaolong" is introduced. (1) Four communication methods are integrated to meet different needs: 1) Coherent underwater acoustic communication, with a variable transmission rate from 5 kbps to 15 kbps, to transmit images. 2) Non-coherent underwater acoustic communication, with a transmission rate 300 bps, to transmit texts, instructions, and sensor data. 3) Spread spectrum underwater acoustic communication, with a transmission rate 16 bps, to transmit instructions. 4) Underwater voice communication, using single sideband modulation to transmit human voice. (2) Signal processing method in coherent communication mainly consists of concatenation of decision feedback equalizer and Turbo decoder, and wavelet based image compression with fixed length coding. In the equalizer, Doppler compensation, multichannel combining and equalizer coefficients updating are all using fast self-optimized adaptive algorithm. (3) A linear hydrophone array is lowered from the mother ship to certain depth, and spatial diversity combining technology is adopted. (4) Diving trial of "Jiaolong" was carried out in Pacific Ocean. The communication distance can cover nearly all ocean depth. An optical/acoustic image can be transmitted in 7 or 14 seconds.