  Online monitoring aims to evaluate or to predict, at runtime, whether or not
the behaviors of a system satisfy some desired specification. It plays a key
role in safety-critical cyber-physical systems. In this work, we propose a new
model-based approach for online monitoring for specifications described by
Signal Temporal Logic (STL) formulae. Specifically, we assume that the observed
state traces are generated by an underlying dynamic system whose model is
known. The main idea is to consider the dynamic of the system when evaluating
the satisfaction of the STL formulae. To this end, effective approaches for the
computation of feasible sets for STL formulae are provided. We show that, by
explicitly utilizing the model information of the dynamic system, the proposed
online monitoring algorithm can falsify or certify of the specification in
advance compared with existing algorithms, where no model information is used.
We also demonstrate the proposed monitoring algorithm by case studies.
