  Communication Based Train Control (CBTC) system is the state-of-the-art train
control system. In a CBTC system, to guarantee the safety of train operation,
trains communicate with each other intensively and adjust their control modes
autonomously by computing critical control parameters, e.g. velocity range,
according to the information they get. As the correctness of the control
parameters generated are critical to the safety of the system, a method to
verify these parameters is a strong desire in the area of train control system.
In this paper, we present our ideas of how to model and verify the control
parameter calculations in a CBTC system efficiently. - As the behavior of the
system is highly nondeterministic, it is difficult to build and verify the
complete behavior space model of the system online in advance. Thus, we propose
to model the system according to the ongoing behavior model induced by the
control parameters. - As the parameters are generated online and updated very
quickly, the verification result will be meaningless if it is given beyond the
time bound, since by that time the model will be changed already. Thus, we
propose a method to verify the existence of certain dangerous scenarios in the
model online quickly. To demonstrate the feasibility of these proposed
approaches, we present the composed linear hybrid automata with readable shared
variables as a modeling language to model the control parameters calculation
and give a path-oriented reachability analysis technique for the scenario-based
verification of this model. We demonstrate the model built for the CBTC system,
and show the performance of our technique in fast online verification. Last but
not least, as CBTC system is a typical CPS system, we also give a short
discussion of the potential directions for CPS verification in this paper.
