Stefano Vitturi

Hybrid wired/wireless networks for real-time communications

In this article, some considerations are presented about the way several well-known industrial networks (based on both fieldbus and industrial Ethernet solutions) can be practically extended with wireless subnetworks that rely on popular technologies, such as IEEE 802.11 and 802.15.4. This results in hybrid networks, which are able to combine the advantages of both wired and wireless solutions. In particular, advantages and drawbacks of several interconnection techniques are highlighted and, depending on the wired networks specifically taken into account, some hybrid configurations that are able to cope in a satisfactory way with the tight timing requirements often imposed by industrial control systems are suggested.

Experimental Characterization of Wireless Sensor Networks for Industrial Applications

The effects of interference in the setup of wireless sensor networks (WSNs) represent a critical issue, and as such, it needs to be carefully addressed. To this aim, helpful information can be achieved through measurements to be carried out in advance on suitable prototypes and testbeds. In this paper, the measurement of industrial WSN performance is dealt with. In particular, a suitable testbed enlisting IEEE 802.15.4 wireless sensor nodes is presented along with the results of some experiments carried out even in the presence of interference. The purpose is to show how to evaluate some specific parameters of a WSN employed for industrial applications to obtain useful information for its setup optimization in the presence of interference. The analysis will show that from the measurement of these parameters (number of failed pollings, polling round-trip time, experimental cycle time, and alarm latency), interference effects can effectively be recognized, and the network setup can be optimized.

Advances in automotive digital communications

In the past years, control systems of cars have moved from the analog to the digital domain, and these changes affected the communication subsystems too. The next step in this direction is achieving a higher degree of performance, dependability and integration, so as to meet the needs of tomorrows more and more demanding applications. In particular, x-by-wire systems are appearing as the challenge that will drive research efforts of the whole automotive industry for the next decade. This means that new technologies have to be developed for in-car networks, in order to provide the high performance required by the next generation of automotive systems. TTCAN, TTP/C, Byteflight, FlexRay and Bluetooth are some of the most promising emerging solutions that have already been defined and can be embedded right in new projects. In the automotive context, it is of paramount importance being able to evaluate the key features of each solution, as well as to verify whether or not they are able to meet the requirements of specific application fields. In this paper these technologies are discussed and their characteristics are compared, pointing out the main advantages and drawbacks.

Guest Editorial Special Section on Wireless Technologies in Factory and Industrial Automation—Part II

The three papers in this special section focus on wireless technologies in factory and industrial automation. The papers which appear in this second part cover everything from protocol design and evaluation to the design and assessment of system-level solutions for wireless sensor networks in industrial automation.

Performance analysis of Ethernet Powerlink networks for distributed control and automation systems

Industrial communication networks are a key element for developing advanced distributed control and automation systems. On the one hand, high performance and low costs are generally required to cope with more and more demanding application requirements, while, on the other hand, real-time capabilities are often needed in an increasing number of automation scenarios. Communication solutions based on Ethernet technologies are becoming popular in many industrial and factory environments and a number of soft/hard real-time competing products have been proposed in the last few years. This paper focuses on the Ethernet Powerlink standard, in general, and on some of its real-time characteristics, in particular. In fact, we present some basic results concerning both cyclic and acyclic real-time traffic in Ethernet Powerlink networks, obtained by extensive simulation, which can be used as a basic step for a better understanding of the real-time behavior of this protocol.

Analysis of master-slave protocols for real-time-industrial communications over IEEE802.11 WLANs

The recent performance improvements of wireless communication systems are making possible the use of such networks for industrial applications, which typically impose severe requirements in term of both real-time communications and dependability. Several independent studies have highlighted that the IEEE802.11 wireless LAN is one of the most suitable products for such applications. However, since such standard is only concerned with the lower layers of the communication stack, it is necessary to integrate it with appropriate protocols, typical of the industrial communications. In this direction, the protocols used by the traditional field buses could represent an interesting opportunity. In this paper we consider one of these protocols, based on a master-slave architecture, and analyze the possibility of implementing it on top of IEEE802.11. After a description of how the master-slave functions could be mapped onto the IEEE802.11 services, we develop a theoretical model of the proposed communication architecture which allows for the evaluation of some performance metrics

Real-time Ethernet networks for motion control

Communication networks have been traditionally employed in motion control applications, especially within factory automation systems. While in the past they were merely used to exchange non time critical data (e.g. parameters and configuration data) nowadays they allow for much more powerful performance. In particular, the recently introduced Real-time Ethernet (RTE) networks, have been explicitly designed in order to cope with very tight timing constraints in terms of both determinism and real-time. In this paper we focus on two popular RTE networks, namely Ethernet POWERLINK and EtherCAT, and provide an example of their employment for a coordinated motion control application. In particular, we consider the tracking of a circular trajectory by the coordinated motion of two independent axes where the velocity set-points are transmitted to the electrical drives implementing the axis control by means of the RTE networks. After providing some essential features of the two networks, we describe the configurations adopted for the coordinated motion control application. Then we check the effectiveness of the solution proposed by means of numerical simulations which take into consideration possible error scenarios deriving from the adoption of the communication networks such as transmission errors, communication delays and cable breaks.

On the Rate Adaptation Techniques of IEEE 802.11 Networks for Industrial Applications

The performance of the IEEE 802.11 WLAN are influenced by the wireless channel characteristics that reflect on the signal-to-noise ratio (SNR), particularly in industrial communication systems, that often operate in harsh environments. In order to cope with SNR reductions, the IEEE 802.11 WLAN specification suggests to adapt (reduce) the transmission rate, since the modulation techniques employed at the lower rates are more robust. However, the standard does not define any rate adaptation (RA) technique, leaving the actual implementation to the device manufacturers choice. In this paper we focus on RA techniques for industrial communication systems that are typically subjected to tight reliability and timing requirements. In detail, we compare the performance figures of a general purpose widespread technique, namely the automatic rate fallback (ARF), with those of the RA techniques actually implemented on two commercially available IEEE 802.11 devices via a set of practical experiments. The obtained results show that these techniques are characterized by a relevant number of packet retransmissions that may introduce a considerable randomness on the service time, possibly leading to performance degradation. Consequently, we propose two new techniques and evaluate their behavior by means of numerical simulations carried out for typical industrial traffic profiles. The outcomes are encouraging since the proposed RA techniques show in most cases better performance than ARF.

Performance analysis of PROFINET networks

Nowadays, Ethernet networks may be profitably employed also at the lowest levels of factory automation systems. Indeed, suitable application layer protocols for Ethernet have been recently developed in order to cope with the critical requirements imposed by the industrial applications. In this paper we focus on the protocols used by PROFINET, an emerging standard for industrial communications based on Ethernet, which is now available in two different versions, named CBA and IO. After a description of the protocols, we show the results of some tests aimed at evaluating the performances of such a network. In particular, we concentrate the attention on the times necessary to transfer limited amounts of data among stations. With regard to PROFINET CBA, the outcomes of an experimental set-up comprising several components, show, for the transfer times, highly variable values, dependent on the network load. Conversely, for PROFINET IO, the results of a set of numerical simulations we performed, allow to expect constant transfer times of some milliseconds, or even less, provided that an accurate time synchronization between stations is maintained.

Analysis of Ethernet Powerlink Wireless Extensions Based on the IEEE 802.11 WLAN

The industrial communication scenario is experiencing the introduction of wireless networks at all levels of factory automation systems. The benefits deriving from such an innovation are manifold, even if wireless systems cannot be thought as a complete replacement of wired networks. Rather, they will be even more used in the near future to realize hybrid (wired/wireless) configurations. In particular, it is envisaged that wireless networks may be employed to implement extensions of (possibly already installed) wired systems. In this paper we consider wireless extensions of Ethernet Powerlink, a very popular Real-Time Ethernet network, implemented by means of the IEEE 802.11 WLAN. Specifically, we focus on a widespread network configuration and address two types of extensions based on, respectively, bridge and gateway devices. In the second part of the paper we provide an analysis of the hybrid networks aimed at evaluating the most relevant performance indexes. Since the reliability of wireless networks may represent a critical aspect, the analysis is carried out taking into account the presence of interference as well as fading in the wireless segment. The results we show, obtained from a theoretical analysis and validated by numerical simulations, allow to get some useful insights on the overall performance of the hybrid networks.