A blind multichannel DFE receiver for precoded OQPSK signal transmission in shallow water

We apply a special modulation format derived from offset quadri-phase shift keying (OQPSK) to digital transmission and propose a novel practical multichannel receiver architecture for its demodulation. The receiver is based on the standard adaptive decision feed-back equalizer (DFE) which is extended so that both its multichannel feed-forward section and the feedback section operate fractionally spaced. We therefore introduce a new decision rule that exploits the structural properties of this signal type and allows the adaptive filters to be updated twice per symbol. This also enables the receiver to operate in a completely self-recovering, or 'blind' manner. To compensate for Doppler effects, explicit non-data-aided timing recovery and decision-directed carrier recovery is performed. To demonstrate the performance of the proposed system, the receiver is applied to experimental data for acoustic communication in shallow water where the information signal is both emitted by a fixed and a moving source.