Sixth-generation (6G) wireless communication systems, as stated in the European 6G flagship project Hexa-X, are anticipated to feature the integration of intelligence, communication, sensing, positioning, and computation. An important aspect of this integration is integrated sensing and communication (ISAC), in which the same waveform is used for both systems both sensing and communication, to address the challenge of spectrum scarcity. Recently, the orthogonal time frequency space (OTFS) waveform has been proposed to address OFDM's limitations due to the high Doppler spread in some future wireless communication systems. In this paper, we review existing OTFS waveforms for ISAC systems and provide some insights into future research. Firstly, we introduce the basic principles and a system model of OTFS and provide a foundational understanding of this innovative technology's core concepts and architecture. Subsequently, we present an overview of OTFS-based ISAC system frameworks. We provide a comprehensive review of recent research developments and the current state of the art in the field of OTFS-assisted ISAC systems to gain a thorough understanding of the current landscape and advancements. Furthermore, we perform a thorough comparison between OTFS-enabled ISAC operations and traditional OFDM, highlighting the distinctive advantages of OTFS, especially in high Doppler spread scenarios. Subsequently, we address the primary challenges facing OTFS-based ISAC systems, identifying potential limitations and drawbacks. Then, finally, we suggest future research directions, aiming to inspire further innovation in the 6G wireless communication landscape.

翻译：第六代（6G）无线通信系统——如欧洲6G旗舰项目Hexa-X所阐述——预计将融合智能、通信、感知、定位与计算功能。此融合过程中的重要环节是通感一体化（ISAC）技术，该技术采用同一波形实现感知与通信双重功能，以应对频谱资源短缺的挑战。近年来，针对未来无线通信系统中由高多普勒频移导致的正交频分复用（OFDM）局限性，学界提出了正交时频空间（OTFS）波形。本文系统梳理了面向ISAC系统的现有OTFS波形，并展望了未来研究方向。首先，我们阐述了OTFS的基本原理与系统模型，奠定对该创新技术核心概念与架构的基础认知。继而，我们概述了基于OTFS的ISAC系统框架，并全面综述了OTFS辅助型ISAC系统领域的最新研究进展与前沿动态。通过深入对比OTFS赋能ISAC操作与传统OFDM的差异，重点揭示了OTFS在高多普勒频移场景中的显著优势。随后，本文分析了OTFS-ISAC系统面临的主要挑战，识别其潜在局限性与不足。最后，我们提出未来研究方向，旨在为6G无线通信格局激发进一步的技术创新。