A Unifying View of OTFS and Its Many Variants

TL;DR

This paper unifies OTFS and its variants, clarifying their relationships, features, and detection schemes, demonstrating their advantages in high-mobility environments with numerical comparisons and insights for future research.

Contribution

It provides a comprehensive overview of OTFS and related modulations, establishing their connections, and offering a unified detection framework and performance analysis.

Findings

OTFS can be viewed as a precoded FBMC using ISFFT.

OTFS and variants outperform OFDM in high-mobility scenarios.

Various detection schemes have different efficacies in high-mobility channels.

Abstract

High mobility environment leads to severe Doppler effects and poses serious challenges to the conventional physical layer based on the widely popular orthogonal frequency division multiplexing (OFDM). The recent emergence of orthogonal time frequency space (OTFS) modulation, along with its many related variants, presents a promising solution to overcome such channel Doppler effects. This paper aims to clearly establish the relationships among the various manifestations of OTFS. Among these related modulations, we identify their connections, common features, and distinctions. Building on existing works, this work provides a general overview of various OTFS-related detection schemes and performance comparisons. We first provide an overview of OFDM and filter bank multi-carrier (FBMC) by demonstrating OTFS as a precoded FBMC through the introduction of inverse symplectic finite Fourier transform (ISFFT). We explore the relationship between OTFS and related modulation schemes with similar characteristics. We provide an effective channel model for high-mobility channels and offer a unified detection representation. We provide numerical comparisons of power spectrum density (PSD) and bit error rate (BER) to underscore the benefit of these modulation schemes in high-mobility scenarios. We also evaluate various detection schemes, revealing insights into their efficacies. We discuss opportunities and challenges for OTFS in high mobility, setting the stage for future research and development in this field.