Generalized Predictive Control in a Wireless Networked Control System

The NCS (networked control system) is different from the conventional control systems which is the integration of the automation and control over communication network. When an NCS operates over the communication network, one of the major challenges is the network-induced delay in data transfer among the controllers, actuators, and sensors. This delay degrades system performance and causes system unstablility. This paper proposes a GPC (generalized predictive control) with the Kalman state estimator to compensate for the network-induced delay and packet loss. The GPC is implemented in WiNCS (Wireless NCS) based on IEEE 802.11 standard. An analytical NCS model and NS2 (network simulator version 2) are developed to simulate and evaluate the performance under the effect of various delays and packet loss rates. The result shows that the proposed GPC is adaptive and robust to the uncertainties in a time-delay system. The WiNCS is evaluated with latency and throughput measurements in various environments. The experiment setup conforming to the IEEE 802.11 standard achieves an average latency of 1.3？ms and a data throughput of 3.000？kB/s up to a distance of 70？m. The results demonstrate the feasibility of real-time closed-loop control with the proposed concept. 1. Introduction In recent years, there has been an increasing interest in implementing networked transmission protocols (e.g., wire/wireless local area networks) in automation and control system. Cost effectiveness and flexibility are achieved using communication protocol in the feedback control. The NCS closes the feedback control loops through a real-time network. The control signals to the actuators and the feedback signals from sensors are in the form of information packages [1, 2]. Interconnecting the sensors, actuators, and controllers via networks can eliminate wiring, reduce installation costs, and enable remote monitoring and tuning. Additional components and modules can be added without additional circuitry to the existing layout. The controllers effectively share the data via the information technology allowing easy data fusion and integration to the controller for an intelligent decision or optimal operation in a large and complex process [3, 4]. The potential applications of NCS include industrial automation, military, hazardous environment exploration, or robots application. Three methods on scheduling packets were proposed to improve NCS performance and stability as static scheduler, try-once-discard (TOD) scheduler with continuous priority level, and TOD with discrete priority level [5,