Industrial control over wireless networks

Abstract

Traditionally, industrial control systems have relied on hardwired information flows among sensor, actuator and control nodes over rather simple network architectures. Over the last decades, distributed control systems have seen a transition to communication buses, such as fieldbus and Ethernet. At present, there is a major interest in taking a further step in this evolution by incorporating wireless connectivity with a concrete perspective of achieving increased efficiency, flexibility, mobility and easier installation. As a matter of fact, wireless technology is already present in several manufacturing and process industries. Wireless links have already been installed for long-range (100–1000 m) monitoring applications, wireless LANs have been used for applications with non-stringent communication requirements (e.g. logistics) and wireless communication has been even used for instrumentation setups (e.g. temperature and pressure measurements). Distributed estimation and control under communication constraints; Communication and network design for distributed control; Control-communication co-design; Software architectures for distributed control; Applications of wireless communication for distributed control. We open the issue with a paper by Manfredi that addresses the critical problem of reliable management for monitoring and control in industrial environments. An analysis of the various aspects of this problem is offered, while reviewing the efforts in the field. The contributions of the paper lay in the following areas: (i) investigation of the interactions between contention resolution and congestion control mechanisms in wireless industrial sensor networks with the use of simulation to quantify the impact of network parameters on performance metrics (e.g. packet loss); (ii) a reliable sink resource allocation strategy based on log-utility fairness criteria (iii) the analysis, design and validation of a reliable distributed sink control with a sufficient condition for wireless network stability in the presence of multiple sinks and heterogeneous sensors and (iv) analysis and controller performance evaluation by a Matlab/Simulink-based simulator. The paper by Rabi et al. investigates the problem of state estimation, where sensor measurements are sent over a medium shared using a contention-based access mechanism. State estimation is a key component of modern automation systems and contention-based medium access is supported in most standards. The estimator performance depends on the dynamics of the individual systems and the nominal sampling interval. More interestingly, it also depends on the distribution of transmission delays and loss rates of sensor packets which, in turn, depend on the applied medium access control scheme and the number of contending nodes. This paper presents analytical expressions for estimation error variance under varying sampling interval, and develops novel formulas for the statistics of packet latencies and losses that arise when nodes contend for medium access. Combining these results, the paper studies optimal sampling interval selection and establishes scaling limits of estimation performance with respect to the number of contending nodes. A basic aspect in the analysis and the design of systems of cooperative agents is related to the effect of the agent information exchange on the coordination performance. A coordination task widely treated in the literature is the so-called average consensus. This is the problem of driving states of a set of dynamic systems to a common state that corresponds to the average of the initial states. The paper by Carli et al. proposes a quantized strategy that reaches the initial average asymptotically. The strategy adapts coding/decoding strategies that were proposed for centralized control and communication problems to the distributed consensus problem. In particular, by resorting to both analytical techniques and simulations, the convergence properties of