A comprehensive review on relay-assisted state estimation in networked systems: architectures, algorithms, and challenges

Abstract

Relay-assisted transmission has emerged as an effective means to enhance communication reliability and extend transmission range in networked systems. Integrating relay mechanisms into state estimation architectures can significantly enhance both accuracy and stability in remote and resource-constrained environments. This paper provides a comprehensive review of relay-assisted state estimation (RASE) for networked systems. First, the fundamental architectures of relay-assisted networks are formalised, and commonly used relay protocols are introduced including their mathematical models, engineering insights and multi-dimensional comparison. Then, the influence of relays on system performance is analysed and mainstream filtering algorithms in the relay-assisted context are compared, followed by a general workflow of RASE. Subsequently, state estimation algorithms developed for relay-assisted systems are systematically surveyed, covering nonlinear systems, complex dynamical networks, and several representative special system classes. Furthermore, the paper reviews RASE methods addressing key network-induced phenomena. They typically include fading channels, communication delays, and packet losses. Issues related to energy management and security are also discussed, such as energy harvesting, power scheduling, eavesdropping, and denial-of-service attacks. Finally, the paper summarises current research progress and highlights several open problems and promising directions for future investigation. The review aims to provide a structured reference and insights for researchers working on relay-assisted estimation in large-scale cyber-physical systems.