Scheduling Status Update for Optimizing Age of Information in the Context of Industrial Cyber-Physical System

Age of Information has been emerged as an interesting metric in real-time wireless networks that captures the freshness of information in the underlying applications. This topic is motivated by the problem in which the users of a network care about timely information defined as the age of the most recent status update a user has received. In the proposed work, we have studied this concept in the context of an industrial wireless sensor-actuator network for cyber-physical production systems. Such a network with ever-changing dynamics requires continuous updates of the system states and ongoing tasks by exchanging the time-critical, event-driven, and/or time-driven information to maintain the stability of the system, failing which may lead to shut down of the plant and other fatal consequences. Different real-time transmission scheduling algorithms manage how the channel resources are allocated each time depending on the packet arrivals to minimize the age of the information. However, unlike other real-time networks like broadcasting and sensor networks, etc. in cyber-physical systems, cyber and physical devices have different requirements to improve their quality of performance. Balancing between the performance criteria of both cyber and physical units seems to be a great challenge. In this work, the minimization of staleness of the real-time updates by minimizing the age of information and their effect on network performance have been studied extensively for this purpose. Two greedy scheduling policies have been proposed: one for the total age minimization and another one for stale age and jitter minimization. Their performances and complexities are compared with other existing scheduling algorithms. Moreover, the optimality of each of our proposed algorithms are proved analytically and claims are validated via simulation results too. Eventually, these results come to a conclusion that minimum age does not always guarantee the maximum freshness of information and satisfactory system performance at the same time.