Differential frequency hopping performance in doubly spread underwater acoustic communication channels

Abstract

Underwater acoustic communication requires waveforms that are robust to the signal distortions caused by the channel. Many waveforms used for this purpose require the transmission of training symbols that span the inter-symbol interference (ISI) to compensate for these channel effects. Differential frequency hopping (DFH) is a fast frequency hopping, digital signaling technology that requires minimal information at the transmitter to communicate in the underwater channel. The relationships between the parameters of Doppler spread‐inducing underwater environments and DFH bit‐error performance are characterized. Wind speed determines the nature of the effect that the water surface imposes on acoustic DFH waveforms with low wind speeds resulting in an essentially flat, low‐absorption sea surface. In this case, strong surface reflections and little frequency spreading make ISI the dominant effect on the received waveforms. At high wind speeds, air bubbles in the surface layer absorb almost all energy incident...