Low probability of detection underwater acoustic communications using direct-sequence spread spectrum

Area of Science:

• Underwater acoustic communications
• Signal processing
• Spread spectrum technology

Background:

• Direct-sequence spread spectrum (DSSS) is crucial for underwater acoustic (UWA) communication.
• Source or receiver motion introduces significant phase changes, challenging traditional phase-detection receivers.
• High processing gain is desired for low signal-to-noise ratio (SNR) operation and reduced probability of detection.

Purpose of the Study:

• To develop a robust receiver algorithm for DSSS UWA communications with moving nodes.
• To address the challenges posed by phase fluctuations due to motion.
• To enable secure, low-SNR communication by minimizing the probability of detection.

Main Methods:

• Proposed a pair of energy detectors insensitive to phase fluctuations.
• Utilized detector outputs to determine relationships between adjacent symbols.
• Focused on long code sequences for high processing gain.
• Calculated probability of detection (P(D)) in a shallow water environment.

Main Results:

• Achieved good performance with signal-to-noise ratio (SNR) as low as -10 dB using at-sea data.
• Demonstrated the effectiveness of energy detectors in handling phase variations.
• Showcased the trade-off between processing gain, data rate, and SNR.

Conclusions:

• The proposed energy detector-based method offers a viable solution for DSSS UWA communications in dynamic environments.
• The approach enables reliable communication at very low SNRs, enhancing covert operations.
• The findings are applicable to scenarios requiring high processing gain for secure, long-range underwater data transmission.