  Age of Information is a newly introduced metric, getting vivid attention for
measuring the freshness of information in real-time networks. This parameter
has evolved to guarantee the reception of timely information from the latest
status update, received by a user from any real-time application. In this
paper, we study a centralized, closed-loop, networked controlled industrial
wireless sensor-actuator network for cyber-physical production systems. Here,
we jointly address the problem of transmission scheduling of sensor updates and
the restoration of an information flow-line after any real-time update having
hard-deadline drops from it, resulting a break in the loop. Unlike existing
real-time scheduling policies that only ensure timely updates, this work aims
to accomplish both the time-sensitivity and data freshness in new and
regenerative real-time updates in terms of the age of information. Here, the
coexistence of both cyber and physical units and their individual requirements
for providing the quality of service to the system, as a whole, seems to be one
of the major challenges to handle. In this work, minimization of staleness of
the time-critical updates to extract maximum utilization out of its information
content and its effects on other network performances are thoroughly
investigated. A greedy scheduling policy called Deadline-aware highest latency
first has been used to solve this problem; its performance optimality is proved
analytically. Finally, our claim is validated by comparing the results obtained
by our algorithm with those of other popular scheduling policies through
extensive simulations.
