Wireless Feedback Control with Variable Packet Length for Industrial IoT

TL;DR

This paper introduces an adaptive wireless control system for industrial applications that optimizes packet length to balance delay and reliability, improving control performance.

Contribution

It proposes a novel variable packet length scheme in WNCSs, formulating an optimal policy considering delay-reliability tradeoff based on system state.

Findings

Derived conditions for optimal packet length policies.

Showed improved control performance with adaptive packet lengths.

Analyzed the delay-reliability tradeoff in wireless control.

Abstract

The paper considers a wireless networked control system (WNCS), where a controller sends packets carrying control information to an actuator through a wireless channel to control a physical process for industrial-control applications. In most of the existing work on WNCSs, the packet length for transmission is fixed. However, from the channel-encoding theory, if a message is encoded into a longer codeword, its reliability is improved at the expense of longer delay. Both delay and reliability have great impact on the control performance. Such a fundamental delay-reliability tradeoff has rarely been considered in WNCSs. In this paper, we propose a novel WNCS, where the controller adaptively changes the packet length for control based on the current status of the physical process. We formulate a decision-making problem and find the optimal variable-length packet-transmission policy for minimizing the long-term average cost of the WNCSs. We derive a necessary and sufficient condition on the existence of the optimal policy in terms of the transmission reliabilities with different packet lengths and the control system parameter.