From Data Mirror to Smart Copilot: A Survey on NextG Semantic Communication for Propelling Digital Twin World Into Cognitive Stage

The revolution of information technologies is blur-ring the boundary between physical and virtual worlds, with digital twin (DT) at the forefront of this transformation. Mean-while, DT is evolving from offering simple data mirrors to smart copilots, capable of understanding user’s intents and proactively providing profound insights. This ushers in the pivotal cognitive stage of the DT, where humans or embodied artificial intelligence agents (EAIs) can obtain cognitive perceptions within the DT world. Among various issues, in the cognitive stage, establishing strong interactions between the physical and DT worlds is critical. This paper thus explores the Next-Generation Semantic Communication (NextG-SemCom), well-suited for this issue, to fully enable the DT world with human-like cognitive capabilities. NextG-SemCom is envisioned as a cognitive-native paradigm that leverages Large AI Models (LAMs) as its core engine to perform intent understanding, contextual planning, and intent-oriented generative extraction. NextG-SemCom establishes a closed cognitive loop that shifts communication from data-driven to cognitive-driven, thereby not only reducing the traffic overhead, but also achieving cognitive comprehension of the transmitted information. This paper provides the first survey of the NextG-SemCom driven DT world, focusing on the advancement, trend and vision. We start by tracing the evolution of the DT from the initial virtual mapping stage to the current cognitive stage, and detail the distinguishing features of NextG-SemCom. We then present a holistic framework of cognitive interactions in the DT world, analyzing its core components, including the NextG-SemCom codec and network management, along with its design requirements and challenges. Furthermore, we discuss potential applications across a spectrum of human-human, human-EAI, and EAI-EAI interactive scenarios. Finally, we outline future research directions to provide a roadmap and inspire further studies in this promising field.