USAM: A Unified Safety-Age metric for Timeliness in Heterogeneous IoT Systems
2026-03-27 • Information Theory
Information Theory
AI summaryⓘ
The authors point out that existing ways to measure how fresh information is in IoT systems don’t consider strict timing rules needed for safety. To fix this, they created a new metric called USAM that combines freshness, meeting deadlines, and guaranteed response times into one measure. They studied IoT devices that don’t send data very often and found that in such cases, device readiness is more important than traffic load for meeting timing requirements. Their results show that USAM better reflects when a system can safely handle mixed traffic compared to older freshness metrics. This helps design safer communication systems for large IoT deployments.
Internet of Things (IoT)Age of Informationcyber-physical systemsdeadline reliabilityresponse-time feasibilitymachine-type communicationsqueueing delaysreceiver duty cyclefunctional safety
Authors
Mikael Gidlund
Abstract
Massive Internet-of-Things (IoT) deployments must simultaneously support monitoring, control, and safety-critical communication over shared wireless infrastructure. Classical timeliness metrics, such as Age of Information and its variants, quantify the freshness of received updates but do not account for deterministic safety timing requirements that arise in cyber-physical systems. Consequently, freshness-oriented metrics may indicate satisfactory performance even when worst-case timing guarantees required by functional safety standards are violated. This paper introduces the Unified Safety--Age Metric (USAM), a safety-aware timeliness metric that integrates information freshness, deadline reliability, and deterministic response-time feasibility into a single architecture-aware performance measure. We consider heterogeneous IoT traffic served by a gateway with intermittent receiver readiness and analyze system behavior in the ultra-sparse regime typical of massive machine-type communications. The analysis shows that, as device activity decreases, queueing delays become negligible and system timeliness becomes dominated by infrastructure readiness and deterministic response-time constraints. In this regime, feasibility is determined primarily by the receiver duty cycle rather than by average traffic load. Numerical results illustrate the safety-blindness of classical freshness metrics and demonstrate that USAM explicitly captures the feasibility boundary imposed by heterogeneous traffic requirements. The proposed framework provides a foundation for analyzing safety-aware communication architectures in large-scale IoT systems.