  In this study, we investigate a context-aware status updating system
consisting of multiple sensor-estimator pairs. A centralized monitor pulls
status updates from multiple sensors that are monitoring several
safety-critical situations (e.g., carbon monoxide density in forest fire
detection, machine safety in industrial automation, and road safety). Based on
the received sensor updates, multiple estimators determine the current
safety-critical situations. Due to transmission errors and limited
communication resources, the sensor updates may not be timely, resulting in the
possibility of misunderstanding the current situation. In particular, if a
dangerous situation is misinterpreted as safe, the safety risk is high. In this
paper, we introduce a novel framework that quantifies the penalty due to the
unawareness of a potentially dangerous situation. This situation-unaware
penalty function depends on two key factors: the Age of Information (AoI) and
the observed signal value. For optimal estimators, we provide an
information-theoretic bound of the penalty function that evaluates the
fundamental performance limit of the system. To minimize the penalty, we study
a pull-based multi-sensor, multi-channel transmission scheduling problem. Our
analysis reveals that for optimal estimators, it is always beneficial to keep
the channels busy. Due to communication resource constraints, the scheduling
problem can be modelled as a Restless Multi-armed Bandit (RMAB) problem. By
utilizing relaxation and Lagrangian decomposition of the RMAB, we provide a
low-complexity scheduling algorithm which is asymptotically optimal. Our
results hold for both reliable and unreliable channels. Numerical evidence
shows that our scheduling policy can achieve up to 100 times performance gain
over periodic updating and up to 10 times over randomized policy.
