Blind Fractionally Spaced Channel Equalization for Shallow Water PPM Digital Communications Links

Area of Science:

• Underwater acoustic digital communications
• Signal processing for wireless communication

Background:

• Underwater acoustic channels suffer from inter-symbol interference (ISI) due to signal distortion.
• Shallow water environments present significant challenges with short coherence times and large delay spreads from multipath effects.
• Effective channel equalization is vital for reliable underwater acoustic communication links.

Purpose of the Study:

• To analyze the performance of acoustic digital links using pulse position modulation (PPM) in severe multipath scenarios.
• To explore the exploitation of spectral redundancy in PPM signals with fractional sampling.
• To develop and evaluate a novel blind equalization scheme for these challenging conditions.

Main Methods:

• Performance analysis of acoustic digital links with pulse position modulation.
• Utilizing fractional sampling at the receiver to exploit signal spectral redundancy.
• Devising a novel blind equalization scheme based on a modified Bussgang approach with M-memory nonlinearity, where M is the PPM order.

Main Results:

• Demonstrated the feasibility of the proposed blind equalization technique.
• Assessed the performance quality of the equalization scheme in severe multipath scenarios.
• Confirmed that spectral redundancy in PPM signals can be effectively leveraged with fractional sampling.

Conclusions:

• The novel blind equalization scheme is effective for underwater acoustic digital communications in multipath environments.
• Fractional sampling combined with PPM offers a promising approach for improving link reliability.
• The developed technique shows potential for extension to more complex communication scenarios.