Co-design Approaches to Dependable Networked Control Systems

Chapter 3

QoC-aware Dynamic Network QoS Adaptation 1

3.1. Overview

When engineers are designing complex networked control systems (NCS), the main efforts are generally put towards dealing with the negative influences arising from the network and its interactions with the global system performance. Theories and methods are hence developed to adapt the control to network-induced delays, packet losses, jitter or even asynchronous sampling. These methods encompass the estimation or observation of the quality of service (QoS), and it is assumed that these parameters are non-controllable. However, it might be possible, in a particular situation, to improve the performances offered by the network rather than modifying the control parameters, and even degrading the global system performance. In this situation, a set of techniques able to adjust the QoS offered by a network are proposed in order to enhance the QoC. They aim at providing a certain level of performance to a network data flow, while achieving an efficient and balanced utilization of network resources as defined by [ZAM 08]. The field of the QoS control includes applications related to the call admission method, scheduling policy, r o uting protocol, flow control strategies, and various other resource allocation problems. In the NCS framework, the hot issue is to adapt the network according to the evolution of the QoC parameter and not just the network’s behavior. This means that application constraints coming from one or even ...