Intersymbol interference in underwater acoustic communications using time-reversal signal processing.

Area of Science:

• Underwater Acoustics
• Signal Processing
• Ocean Engineering

Background:

• Underwater acoustic communication faces challenges from signal time spread.
• Time-reversal processing offers pulse compression for communication applications.
• Passive time-reversal processing uses receive-only arrays for matched filtering.

Purpose of the Study:

• To develop a physics-based model for uncompensated intersymbol interference (ISI) in passive time-reversal equalizers.
• To analyze the performance limitations of passive time-reversal processing in underwater acoustic communication.

Main Methods:

• Developed a physics-based model utilizing a normal-mode expansion of the acoustic field.
• Approximated the matched-filtering integral and interpreted results using the waveguide invariant.
• Calculated formal statistical averages of the soft demodulation output after array combining and sampling.

Main Results:

• The model quantifies uncompensated intersymbol interference (ISI) in passive time-reversal equalizers.
• Performance scaling is shown to depend on signal bandwidth, number and position of array elements, and matched filter length.
• Predicted performance scaling shows good agreement with field experiment observations.

Conclusions:

• Passive time-reversal processing alone is insufficient for perfect pulse compression due to uncompensated ISI.
• The developed model accurately predicts the performance limitations and scaling behavior of these systems.
• Understanding ISI is crucial for optimizing underwater acoustic communication systems employing time-reversal techniques.