Parametric transmission of wide-band signals

The application of a parametric array to underwater (uw) communications has shown its value in different experimentations and in a 1750 meter transmission (near Nice) under the European MAST contract PARACOM. The attractive features of a parametric array are its wide bandwidth and its narrow beamwidth. Other advantages are the lightness and smallness of the array. Conversely parametric transduction requires great transmitting power. The experimental conditions are presented. Two parametric communications were conducted. The first one used FSK modulation with hopping which gives good protection against time spreading and is robust against synchronization problems. The error rate varied from 10/sup -5/ to error free and allowed very good image transmission. A second SSB communication is presented to compare voice transmission using parametric transduction with standard underwater telephony. Very good results much better than with standard uw telephone, were obtained and reveal the interest of such a parametric application. The results obtained with different types of modulations (FSK, BPSF, MSK and linear FM) are then presented and the transfer function of the array is analysed. An important result is that the received signals are very close transmitted. The transfer function behavior parametric array is quasi-linear and the great available bandwidth allows numerous applications in communication, detection, localization, target characterization.