Hybrid Adaptive Biased Optical OTFS for RIS-Assisted OWC Systems

Adaptive biased optical orthogonal time frequency space (ABO-OTFS) faces challenges in achieving optimal spectral efficiency due to the presence of unused Doppler bins within the system. To address this, we propose two novel hybrid ABO-OTFS (HABO-OTFS) technologies for reconfigurable intelligent surface (RIS)-assisted optical wireless communication (OWe) systems. HABO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf>-OTFS integrates ABO-OTFS with pulse amplitude modulated discrete multitone (PAM-DMT), offering a straightforward implementation that enables the receiver to directly extract data without the need for complex demodulators. On the other hand, HABO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>-OTFS combines ABO-OTFS with various hybrid schemes in a layered approach, providing enhanced flexibility and more efficient utilization of spectral resources. Numerical results demonstrate that both HABO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf>-OTFS and HABO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>-OTFS significantly outperform the existing ABO-OTFS in terms of peak-to-average power ratio (PAPR), spectral efficiency, and power efficiency, underscoring their potential for superior performance in RIS-assisted OWC systems.