NEXUS (Networked Exchange of Unified Systems) for Data Exchange in a Federated Smart City Digital Twin: A Case Study on Twin Cities

The integration of digital twin (DT) technology into urban planning represents a significant step toward sustainable, resilient, and intelligent cities. However, unifying multiple DTs across a smart city into a city-level federated digital twin (FDT) requires robust interoperability and the ability to manage vast, heterogeneous data streams. In this paper, we propose NEXUS (Networked Exchange of Unified Systems) - a system architecture for a data exchange platform designed to federate the DTs of twin cities (Birmingham, UK and Ulsan, South Korea) within a unified FDT ecosystem. The goal is to provide a structured framework for integrating and managing diverse urban data streams in real time, thereby contributing to the development of a cohesive smart city FDT. Within the unified NEXUS platform, a range of city DTs can align their actions with broader federation goals to achieve systemwide coherence while preserving the autonomy of each city's digital twin. After reviewing existing system architectures for data exchange in FDTs, we present a hybrid architecture that combines the structured layering of traditional DT architectures with the flexibility and scalability of a microservices-based composable design. This hybrid architecture is well-suited for large-scale, cloudbased deployments, facilitating agile development and integration of new services in complex urban cyber-infrastructure. We demonstrate how the proposed federated data exchange model advances the twin cities' transition toward smarter city operations in both the UK and South Korea.