Optimal DCO-OFDM signal shaping with double-sided clipping in visible light communications

Area of Science:

• Optical Communications
• Signal Processing
• Wireless Technologies

Background:

• Visible light communication (VLC) systems utilize direct-current-biased optical orthogonal frequency-division multiplexing (DCO-OFDM) for high-speed data transmission.
• Light-emitting diodes (LEDs) in VLC have limited dynamic range, necessitating unipolar intensity modulation (IM) and leading to unavoidable double-sided signal clipping.
• Clipping distortion in DCO-OFDM systems reduces transmission efficiency and necessitates optimized signal shaping techniques.

Purpose of the Study:

• To investigate and optimize signal shaping design for DCO-OFDM systems subject to double-sided clipping in both flat and dispersive channels.
• To derive optimal bias and power allocation strategies that minimize clipping distortion and maximize data transmission rates.
• To establish a theoretical understanding of the relationship between double-sided and single-sided clipping impacts on signal shaping.

Main Methods:

• Derivation of optimal bias for flat and dispersive channels, analyzed through effective signal-to-noise ratio (SNR) and information theory.
• Analytical characterization of optimal power for flat channels.
• Development of an algorithm for optimal power allocation in dispersive channels, inspired by flat channel solutions.
• Investigation of the impact of top clipping by establishing a connection to downside-clipping only scenarios.

Main Results:

• Optimal bias values were derived for both flat and dispersive channels, offering theoretical and practical advantages.
• Optimal power allocation strategies were analytically determined for flat channels and algorithmically proposed for dispersive channels.
• A novel understanding of the interplay between double-sided clipping and single-sided clipping was established, clarifying the role of top clipping.
• Simulations confirmed the superior performance of the proposed signal shaping techniques over existing methods.

Conclusions:

• The proposed signal shaping design effectively reduces clipping distortion in DCO-OFDM VLC systems.
• Optimized bias and power allocation strategies lead to improved transmission rates and system performance.
• The study provides a comprehensive framework for understanding and mitigating clipping effects in VLC OFDM systems.