Low SNR communications using a double Wiener filter in an upwelling environment

Abstract

This paper presents a double Wiener filter approach for low SNR communications. Low power superim-posed training bitstreams are transmitted and recorded on a four-hydrophone pyramidal array. The method uses a minimum mean square error (MSE) Wiener filter for channel equalization. To explore temporal diversity, a fast Hadamard transform estimates the channel impulse responses for synchronization of the filtered bitstreams. Coherent averaging of time-aligned signals results in an error-corrected bitstream. A second Wiener filter is then applied over the averaged sequence to eliminate residual intersymbol interference. After removing the probe interference, the original message is recovered. To prove the concept, a small subset of data collected during the experiment BioCom’19 was used. The short-range experiment was performed in an upwelling shallow-water site, in Cabo Frio Island bay (Brazil), a challenging environment for communications due to the rapid ocean temperature stratification. Despite BER fluctuation, the proposed scheme proved robust, dealing with these short time scale signal fluctuations and high noise levels that hamper efforts to recover the message. The four channels were processed independently. Compared to a previous method based on a single Wiener, the double Wiener filter approach achieved better performance, providing an average MSE gain up to 2.8 dB.