Basic study on acoustic communication using direct-sequence spread spectrum for underwater acoustic positioning

Supershort baseline (SSBL) underwater acoustic positioning is commonly utilized in estimating the positions of transponders, observation devices and submersibles. The new SSBL system in which a sea surface station and a sea bottom station communicate using the spectrum spread (SS) technique was studied with simulation. An M-sequence was adopted as pseudonoise (PN) code and PN code length was set for 15, 31, 63 and 127. Random noise and Doppler shift were considered as distortions. It became clear that the system becomes useless due to Doppler shift exponentially, and that under the condition with a large Doppler shift, the system is not available if the PN code length is longer than 31, that if the relative velocity between the transmitter and the receiver is less than 5 m/s, the system has the highest performance with a PN code length of 31 and that in case of a PN code length of 15 the system is stable under the same condition.