The Effect of Directional Ambient Noise on an Underwater Acoustic Link in Shallow Environments

To evaluate the performance of underwater acoustic communication systems, it is typically assumed that the noise at the receiver is uncorrelated spatially and temporally. This assumption underestimates the impact of acoustic ocean ambient noise on the performance of communication systems. In this article, the impact of ocean ambient noise on a coherent acoustic communication system is analyzed. The communication performance is assessed in narrowband conditions at a center frequency of ${\text{2.048}\;\text{kHz}}$ using the noise measurements from two different experiments—DalComm1 and the shallow water Canada Basin acoustic propagation experiment (SW CANAPE). DalComm1 focuses on characterizing the acoustic channel over ranges of 1–10 km on the Nova Scotian littoral, while the spatio-temporal variability of noise propagation in shallow and deep water environments was characterized during the CANAPE experiments. The ambient noise coherence and directionality in both environments were also measured. Two distinct noise modeling methodologies are presented to represent realistic synthetic ambient noise with defined directionality. Further, the synthetic noise is validated against measured ambient noise. The impact of ambient noise characteristics on an optimum space-time filter is characterized. A frame structure with an optimum training duration is also defined for the adaptive filter. It is observed that the bit-error rate of the space-time filter depends on optimizing the training and payload duration in the received signal.