Wavelets for Orthogonal Time Frequency Space

Orthogonal Time Frequency Space (OTFS) has revolutionized wireless communication by introducing the concept of 2D modulation. Initially, OTFS was implemented using symplectic fast Fourier transform (SFFT)-based operations, and later, a lower complexity version using the ZAK transform was proposed. This research proposes a wavelet-based OTFS (W-OTFS) scheme. By leveraging the dual localization property of wavelets, the W-OTFS modulated signal is localized in both time and frequency domains, enhancing spectral efficiency and diversity while reducing inter-symbol interference (ISI), Doppler effects, and bit-error-rate (BER). Moreover, wavelets concentrate signal energy in critical regions of the time-frequency plane, significantly reducing the signal’s peak-to-average power ratio (PAPR). The sparse transformation matrix also reduces modulation-demodulation complexity. We further explore two applications of the proposed W-OTFS system in optical wireless communication (OWC) and reconfigurable intelligent surface (RIS)-assisted communication. We adopted a DC-biased optical W-OTFS (DCO W-OTFS) system. With all the advantages of the W-OTFS system, the proposed DCO W-OTFS scheme in OWC eliminates the need for maintaining Hermitian Symmetry, which typically causes half of the spectrum loss. Thus, the proposed DCO W-OTFS scheme effectively addresses a significant research problem in multi-carrier OWC. Additionally, the performance of the proposed W-OTFS system in RIS-assisted channels is explored. The diversity gain of W-OTFS, combined with the directive gain provided by RIS, significantly improves the system’s performance, particularly in environments abundant with non-line-of-sight (NLOS) paths. Consequently, RIS-assisted W-OTFS emerges as a promising candidate to meet the requirements of next-generation wireless communication.

• Supervision