Blind adaptive equalization of underwater acoustic channels using second-order statistics

In this paper, a completely unsupervised receiver concept based on nondata-aided timing recovery, blind multichannel equalization and carrier phase recovery is proposed. The core of the receiver is an adaptive multichannel equalizer, which uses linear predictions of the observations. To employ this powerful second-order cyclostationary method, which has been proposed only recently, the influence of a carrier frequency offset, e. g. due to Doppler, is discussed. It is shown that such an offset results in a spinning estimate of the transmitted symbol sequence at the output of the equalizer. To compensate for this rotation, a decision-directed phase-locked loop is proposed. The receiver is then tested with measured shallow water data gathered during the ROBLINKS 1999 sea trial. The obtained results demonstrate that completely blind processing of the received signals is possible.