Spread Spectrum Modulation with Grassmannian Constellations for Mobile Multiple Access Underwater Acoustic Channels

Area of Science:

• Underwater Acoustic Communications
• Mobile Communication Systems
• Signal Processing

Background:

• Autonomous Underwater Vehicles (AUVs) require reliable communication for fleet coordination.
• Existing underwater acoustic systems face challenges with phase rotation and spectrum efficiency.
• Grassmannian constellations offer robustness against phase rotation and potential spectrum efficiency gains.

Purpose of the Study:

• To evaluate Grassmannian constellations combined with a spread spectrum multiple access scheme for underwater acoustic mobile systems.
• To enable robust coordination of AUV fleets from surface or bottom control units.
• To assess the performance of a novel Multiuser Hyperbolic Frequency Modulation (MU-HFM) scheme.

Main Methods:

• Utilized Grassmannian modulation at the transmitter with non-coherent detection for phase rotation robustness.
• Implemented an orthogonal spread spectrum multiple access scheme: Multiuser Hyperbolic Frequency Modulation (MU-HFM).
• Employed a non-coherent array decoder at the receiver and evaluated performance over real underwater acoustic channel data.

Main Results:

• Demonstrated the feasibility of Grassmannian constellations for underwater acoustic mobile multiple access.
• Achieved spectrum efficiency gains compared to conventional differential modulation.
• Validated the proposed system's performance using sea-collected underwater acoustic channel responses.

Conclusions:

• Grassmannian constellations combined with MU-HFM provide an effective solution for underwater acoustic mobile communication.
• The non-coherent array decoder enhances system robustness in challenging underwater environments.
• This approach significantly improves spectrum efficiency for AUV coordination and other underwater applications.