Towards Standardizing OTFS: A Candidate Waveform for Next-Generation Wireless Networks

TL;DR

This work advocates OTFS modulation in the delay-Doppler domain as a promising 6G waveform to meet stringent mobility, reliability, and sensing KPIs while maintaining backward compatibility with OFDM-based systems. It outlines practical implementation paths on existing OFDM infrastructure (SFFT-based downlink and DZT-based uplink), develops a complexity-efficient MU-MIMO-OTFS precoding framework, and highlights the DD-ISAC advantages enabled by the DD-domain channel representation. Through performance evaluation, the paper demonstrates competitive sum spectral efficiency and high-resolution sensing capabilities, with an explicit discussion of interference patterns and latency considerations. It also provides a forward-looking agenda on standardization, theoretical DD sensing foundations, latency-coded DD communications, and the development of DD radiomaps to support robust, scalable 6G networks.

Abstract

The standardization of the sixth-generation (6G) has recently commenced to address the rapidly growing demands for enhanced wireless network services. Nevertheless, existing wireless systems, particularly at the physical layer waveform level, remain inadequate for achieving the ambitious key performance indicators (KPIs) envisioned for 6G. Specifically, orthogonal frequency division multiplexing (OFDM), the widely adopted waveform in fifth-generation new radio (5G-NR) networks, suffers from inherent limitations in satisfying these stringent requirements. In practice, OFDM can experience severe inter-carrier interference (ICI), resulting in a pronounced data rate error floor caused by high Doppler shifts. Additionally, the repetitive usage of cyclic prefixes (CPs), intended to combat multipath delays, results in significant spectral inefficiency. These fundamental drawbacks pose critical obstacles to fulfilling 6G performance objectives. Orthogonal time frequency space (OTFS) modulation has recently emerged as a promising waveform candidate, addressing the aforementioned challenges by exploiting the unique characteristics of the delay-Doppler (DD) domain channel. Unlike OFDM, OTFS is inherently resilient to channel distortions induced by delay and Doppler effects, while remaining sensitive to time and frequency shifts. Such intrinsic properties are instrumental in enabling OTFS, with joint communication and sensing capabilities, to embrace, rather than combat, dynamic channel conditions. Motivated by these compelling advantages, this article investigates the feasibility and practical implementation of OTFS modulation leveraging the current OFDM-based wireless systems.

Figures (6)

• Figure 1: 5G-NR (inner circle) versus 6G (outer circle) capabilities ITU2023.
• Figure 2: WSSUS regions and channel responses in different domains.
• Figure 3: OTFS transceivers for both downlink (upper-figure) and uplink (lower-figure) built upon an OFDM-based architecture.
• Figure 4: The block diagram and interference pattern of the considered THP-based downlink MU-MIMO-OTFS transmissions.
• Figure 5: Interference pattern comparison between MU-MIMO-OTFS and MU-MIMO-OFDM.