Experimental research on adaptive multichannel equalization for underwater communications

An experiment was conducted in Trondheim harbor, Norway on 30^th June 2010 to test coherent underwater acoustic communication using an adaptive multichannel equalization scheme. Signals of different phase shift keying modulation were transmitted at distances of 2 km and 4 km. The acoustic source suspended by the NTNU research vessel R/V Gunnerus transmitted each signal every 152.548 s for about 45 minutes in a depth fluctuated acoustic channel. In the direction of communication, the water depth changes from 10 m to 380 m. At the receiver, a cross receiving array of 10 hydrophones was used in a water depth of 10 m. Based on passive phase conjugation, the equalization scheme jointly updates the tap weights along with multichannel carrier-phase tracking by digital phase locked loops. The results using independent carrier-phase tracking and common carrier-phase tracking were analyzed and compared. Presented results demonstrate that the equalization scheme along with the common carrier-phase tracking is feasible for a multichannel receiver located at the shallow water.