Dynamic Scheduling for Delay-Critical Packets in a Networked Control System Using WirelessHART

In future industrial scenarios, Wireless Sensor Net-works (WSN) are envisioned to support the traffic of Net-worked Control Systems (NCS). WirelessHART is a prevalentWSN protocol that uses the Time Slotted Channel Hopping(TSCH) medium access to cope with the delay and reliabilityrequirements of NCS in the harsh industrial environment. InTSCH, time slots and frequencies can be scheduled by a networkcoordinator to provide Quality of Service (QoS). In contrast toprevious works that consider the end-to-end delay requirement ofa flow of packets, we focus on a finite sequence of time-criticalpackets. These packets may belong to a time-critical messagewhose latency could significantly impact the NCS. Given an end-to-end delay deadline, our objective is to minimize the DelayViolation Probability (DVP) for a finite sequence of packets bydynamically scheduling the time slots in each frame. This is achallenging task as DVP depends on the instantaneous state ofthe network and requires its transient analysis. In this work,we model the wireless NCS as a two-queues WirelessHARTnetwork and propose the first transient analysis of DVP fora finite sequence of time-critical packets. Noting that DVPcannot be directly used for dynamic resource allocation, wepropose a heuristic algorithm by relating DVP with the network’sthroughput. The proposed heuristic maximizes the expectedthroughput, is computed by solving a finite-horizon MarkovDecision Process (MDP) and can be implemented at the networkcoordinator. Using simulation we demonstrate that the MDP-based heuristic achieves lower DVP compared to the classicalMaxWeight and Weighted-Fair Queuing.QC 20210315</p