Semantics-Empowered Space-Air-Ground-Sea Integrated Network: New Paradigm, Frameworks, and Challenges
Siqi Meng, Shaohua Wu, Jiaming Zhang, Junlan Cheng, Haibo Zhou, Qinyu Zhang
TL;DR
This work addresses the inadequacy of Shannon-bit level approaches for the expansive, dynamic, and resource-constrained space-air-ground-sea integrated network (SAGSIN) envisioned for 6G. It introduces Perception-Communication-Computing-Actuation Integrated Paradigm (PCCAIP) to unify sensing, processing, and actuation for semantic communications, and divides semantic systems into significance-, meaning-, and effectiveness-oriented families. The paper surveys a broad range of semantic metrics, DL-based meaning extraction, and enhancement techniques (METs) plus task-oriented methods (EYTs) to achieve ultimate task effectiveness, including discussion of DeepJSCC, DL architectures, and edge/on-orbit computing. It also outlines future challenges such as unified semantic metrics, multi-modal semantic extraction, joint decision-execution design, and edge-intelligence-driven heterogeneous networks, highlighting potential 6G impact for robust, low-latency SAGSIN operations.
Abstract
In the coming sixth generation (6G) communication era, to provide seamless and ubiquitous connections, the space-air-ground-sea integrated network (SAGSIN) is envisioned to address the challenges of communication coverage in areas with difficult conditions, such as the forest, desert, and sea. Considering the fundamental limitations of the SAGSIN including large-scale scenarios, highly dynamic channels, and limited device capabilities, traditional communications based on Shannon information theory cannot satisfy the communication demands. Moreover, bit-level reconstruction is usually redundant for many human-to-machine or machine-to-machine applications in the SAGSIN. Therefore, it is imperative to consider high-level communications towards semantics exchange, called semantic communications. In this survey, according to the interpretations of the term "semantics", including "significance", "meaning", and "effectiveness-related information", we review state-of-the-art works on semantic communications from three perspectives, which are 1) significance representation and protection, 2) meaning similarity measurement and meaning enhancement, and 3) ultimate effectiveness and effectiveness yielding. Sequentially, three types of semantic communication systems can be correspondingly introduced, namely the significance-oriented, meaning-oriented, and effectiveness/task-oriented semantic communication systems. Implementation of the above three types of systems in the SAGSIN necessitates a new perception-communication-computing-actuation-integrated paradigm (PCCAIP), where all the available perception, computing, and actuation techniques jointly facilitates significance-oriented sampling & transmission, semantic extraction & reconstruction, and task decision. Finally, we point out some future challenges on semantic communications in the SAGSIN. ...