Industrial Wireless Sensor Networks (IWSNs) are found in many application domains that require low latency, robustness, and determinism. The IEEE 802.15.4 standard is not able to cope with the requirements of these applications. For this reason, the IEEE 802.15.4e amendment was introduced, which provides novel MAC-layer profiles that are optimized for a broad range of application domains, including process automation. This paper focuses on two of these profiles, i.e., the Deterministic and Synchronous Multi-channel Extension (DSME) and the Time Slotted Channel Hopping (TSCH). The aim of the paper is twofold. First, assessing their behavior in realistic process automation scenarios. Second, comparing their performance in terms of end-to-end delay, reliability and scalability. The ultimate aim of the work is identifying the limits of those protocols, thus paving the way to further work addressing suitable approaches to tackle them.

EtherCAT is a real-time Ethernet protocol for factory automation applications that enables periodic data exchange with cycle times of a few microseconds thanks to the capability to process frames “on-the-fly”. EtherCAT does not provide efficient mechanisms for enabling the transmission of asynchronous real-time data from slave nodes. This paper proposes an EDF-based Swapping Approach that allows slaves to send real-time asynchronous traffic over EtherCAT networks in an efficient way, while maintaining the interoperability with standard devices. The paper describes the EDF-based Swapping Approach and presents a comparative performance evaluation with both the EtherCAT standard and an approach in the literature that exploits CAN-Like arbitration.

This paper proposes a Lightweight version of the Precision Time Protocol, called L-PTP, for implementation on Powerline communication systems. The aim of this novel protocol is to reduce the number of messages exchanged to achieve synchronization, without penalizing its quality. L-PTP introduces several modifications to the original PTP and can be implemented on COTS devices. The paper focuses on the protocol and on the benefits of its combination with a virtual clock computation performed by a dynamic clock synchronization algorithm.

Performance evaluation via simulation requires to create models that are often difficult and are not able to faithfully reflect the operating conditions. This paper discusses an approach based on the integration of trace files into an OMNeT + + model. This approach allows to represent and evaluate complex systems by simple models. Moreover, in the case a simulation model of the communication system is not available, a trace file can efficiently substitute it. The results obtained with reference to a specific case study confirm the validity of the proposed approach and the advantages it offers over using just simulators.

Handoff is defined as the phase during which a mobile node has a temporary connection loss during the transfer from one wireless communication cell to another one. As in industrial applications wireless networks are often used to connect mobile devices such as, robot, trolleys, conveyors, to a control station, handoff introduces a temporary interruption of monitoring and control of the mobile device that can be disruptive. This paper proposes the Mobile Association Handoff Protocol (MAHP), which, if compared with the standard protocol, provides a notable reduction of the handoff latency.

This paper addresses the problem of supporting soft real-time traffic over IEEE 802.11 wireless local area networks in the presence of competing non-real-time traffic. The proposed solution is a wireless traffic smoother (WTS) which uses as inputs the throughput and the number of frame retransmissions at the MAC level. Combining these two inputs, the WTS is able to adapt the smoothing action to the current wireless network condition. The paper discusses the WTS, also highlighting the way it advances the current state of the art. Then, the WTS performance obtained from experiments performed on a real testbed, also in comparison to another approach recently proposed in the literature, is discussed.

The paper addresses the design of long distance wireless mesh networks (LDWMNs) and deals with implementing and managing wireless links in the wireless mesh backbone. The paper first examines the features of LDWMNs and some issues they impose. Then, the paper describes a solution based on the use of full duplex wireless links and discusses the way these links are implemented and managed to overcome the previously identified problems.

The Bluetooth (BT) standard, originally designed as a cable replacement technology for low-cost, effortless connection of electronic devices, is becoming quite an attractive option even in industrial communication, as it allows low-power, cheap and easy-to-build solutions to be obtained using the available BT modules and application profiles. The great recent interest in using Bluetooth in distributed process control systems (DPCSs) provides the motivation for this work, which has a twofold aim. Firstly, investigating scenarios and architectures enables full exploitation of BT capabilities in industrial communication. Secondly, exploring technological enhancements could improve the performance of the protocol even further

In modern process control systems, Ethernet is achieving a leading position, proposing itself as a network capable of supporting all communication needs at all levels in the Computer Integrated Manufacturing hierarchy. The main obstacle to using Ethernet at the Field level is the nondeterminism of the Ethernet MAC protocol, which cannot provide real-time traffic with bounded channel access times. This paper focuses on industrial applications featuring soft real-time constraints, such as periodic control or industrial multimedia, which do not require deterministic guarantees on deadline meeting. To cope with this class of applications, Ethernet should be able to guarantee the timely delivery of real-time packets in statistical terms. The paper presents fuzzy traffic smoothing, a technique to perform adaptive traffic smoothing over Ethernet networks at the Field level thus enabling them to provide a statistical bound on packet delivery time. Previous work showed that the fuzzy smoother outperforms other adaptive smoothers proposed in the literature. This paper addresses fuzzy smoother optimization through genetic algorithms. The proposed optimization is applied to tune the inference engine membership functions. The results obtained show the effectiveness of the approach.

The master/slave time division duplex approach implemented in the Bluetooth MAC sublayer simplifies management of the physical communication channel, but suffers from some limitations which prevent efficient bandwidth exploitation and may affect the overall throughput and message delays. These limitation have up to now prevented Bluetooth being extensively and successfully used in areas which differ from the traditional target applications this protocol has been developed for. We address these limitations and propose alternative slave/slave operating modes which enable Bluetooth to support new kinds of applications, such as the ones typical of distributed process control systems.

In large-size plants, complex communication infrastructures, comprising numerous links and routers, are often needed in order to support the flow of information required for distributed process management. The aim of this paper is addressing congestion control mechanisms to be implemented inside routers in order to avoid, or at least limit, congestion and buffer overflow in a multi-hop network. The paper presents two congestion control mechanisms which exploit the features of the IPv6 protocol and experimental results obtained through measurements in a real scenario.

Task-level or job-level isolation is commonly used in real-time systems to prevent a job that overruns from affecting jobs belonging to other tasks (task-level isolation) or to the same task (job-level isolation). Although such an isolation provides the desired protection and simplifies analysis, it often results in degraded performance (in terms of deadline meeting) because it limits the exploitation of residual processor time resulting from jobs that underruns. We propose a new overrun handling method called randomized dropping that relaxes the isolation to make effective use of such residual processor time. We apply the proposed randomized dropping to the EDF scheduling and give an analysis technique to compute the probability of deadline meeting. Experimental results show that the proposed overrun handling method outperforms previous approaches based task-level or job-level isolation.

This paper describes a stochastic analysis method for general periodic real-time systems. The proposed method accurately computes the response time distribution of each task in the system, thus making it possible to determine the deadline miss probability of individual tasks, even for systems with maximum utilization factor greater than one. The method uniformly covers both fixed-priority scheduling (such as rate monotonic) as well as dynamic-priority scheduling (such as earliest deadline first) and can handle arbitrary relative deadlines and execution time distributions. The accuracy of the method is proven by comparing the results from the analysis with those obtained from simulations, as well as other methodologies in the literature.

In modern process control systems the different activities are organised by structuring plant as a hierarchy of functional levels. In order to take into account the different requirements of the traffic exchanged at the various levels in the hierarchy, communication architectures are also organised as levels of networks using different communication protocols according to their specific operating conditions. The heterogeneous nature of these networks, however, causes problems of incompatibility and complicates the exchange of information between different levels. For this reason, manufacturers and users are currently showing great interest in harmonising the communication infrastructure at the plant level, and Ethernet technology seems to be the most natural candidate for a number of practical and economic reasons. The paper addresses some issues about the use of Ethernet as a single network technology in a process control system, especially focusing on how to improve timeliness in the delivery of real-time data over a shared Ethernet network used at the field level. Two suitable approaches are presented and evaluated using simulation. One of them is priority-based, while the second is based on adaptive traffic smoothing.

The aim of this paper is to discuss the problems relating to communication in distributed process control, highlighting the limits of traditional centralized communication systems based on point-to-point connections. The paper shows the real advantages that can be obtained by using a distributed common-bus communication system in time-critical process control applications, highlighting its impact on the architecture of control systems from the point of view of both hardware and software. Particular reference is made to the International Electrotechnical Commission/Instrument Society of America (IEC/ISA) communication system which is close to becoming an international standard. In particular, the solution based on the use of the distributed common-bus communication protocol is applied to the control of an orange-picking robot, which had previously been implemented in a traditional way using point-to-point communications. The choice of a case study referring to a robot control system seems an appropriate benchmark for the real potential of the fieldbus because the processes involved in a robot control system have highly critical time constraints which may stress the fieldbus communication system. The paper presents a qualitative analysis of the advantages that can be obtained by introducing the fieldbus into the orange picking robot control system. The analysis gives a detailed illustration of the hardware and software modification needed to replace the traditional point-to-point control systems of the orange picking robot with the fieldbus. Then an evaluation of the performance of fieldbus system is provided. The evaluation is made by modeling and simulating the distributed communication system with transition timed Petri nets (TTPNs). The results obtained in the study as a whole confirm the authors' conviction that, by careful analysis, it is possible and advantageous even in difficult cases to replace classical centralized point-to-point control systems with distributed systems based on use of the fieldbus.

This paper presents the use of Hopfield-type neural networks for process scheduling in the area of factory automation, where bus-based communication systems, called FieldBuses, are widely used to connect sensors and actuators to the control systems. We show how it overcomes the problem of the computational complexity of the algorithmic solution. The neural model proposed allows several processes to be scheduled simultaneously; the time required is polynomial with respect to the number of processes being scheduled. This feature allows real-time process scheduling and makes it possible for the scheduling table to adapt to changes in process control features. The paper presents the neural model for process scheduling and assesses its computational complexity, pointing out the drastic reduction in the time needed to generate a schedule as compared with the algorithmic scheduling solution. Finally, the authors propose an on-line scheduling strategy based on the neural model which can achieve real-time adaptation of the scheduling table to changes in the manufacturing environment.

The paper deals with the problem of scheduling the transmission of periodic processes in a distributed FieldBus system, defining the conditions guaranteeing correct transmission. The scheduling of periodic processes fixes the transmission times for each process in a table, whose length is equal to the Least Common Multiple (LCM) of all the periods. This involves great memorization problems when some periods are relatively prime. The authors identify the theoretical conditions which allow the length of the scheduling table to be drastically reduced, but still guarantee correct transmission. On the basis of the theoretical conditions given, the authors present a pre-run-time scheduling algorithm which determines a transmission sequence for each producing process within the desired scheduling interval. An online scheduling algorithm is also proposed to schedule new transmission requests which are made while the system is functioning. The reduction in the schedule length may increase the number of transmissions, thus reducing the effective bandwidth and increasing the communication overload. In order to make as complete an analysis as possible of the scheduling solution, the authors also present an analysis of both the computational complexity of the algorithms proposed and the communication overload introduced.>

The authors deal with the problem of the information exchange between processes in extended fieldbus systems. As is known, although most of the traffic in these systems is within a single bus, there is always a certain amount transiting from one fieldbus to another, often covering a certain distance. There is therefore the problem of finding ways to interconnect the various fieldbuses in such a way as to meet the time constraints imposed by the applications. The paper proposes and then assesses a way of interconnecting even a large number of fieldbuses, introducing delays which are compatible with process control requirements.>

In this paper, the authors adopt a neural approach to deal with the problem of routing in a packet switching network. The aim is to define a routing strategy which will combine the advantages of both the centralized and the distributed approaches. The neural approach presented is based on the idea of inserting a neural network (N/N) into each node in the computer network which will be responsible for computing the route between its node and the immediately adjacent one. Two distributed routing solutions are presented in the paper based on an optimizing network and a mapping network. The routing obtainable and the implementation resources needed for the two approaches are evaluated. Finally, the performance offered by the neural strategies proposed is compared with that offered by classical distributed and centralized routing solutions. As a parameter of merit, the effect of overloading caused by the additional traffic present in each solution is used.

The work presented is a case study of the application on the FieldBus protocol to motor cars. The problem of the management of traffic made up of the various actuation and control signals present in a car is addressed, and criteria for allocation of the available bandwidth and assessing the behavior of the FieldBus in various traffic conditions are discussed. The results obtained show that, in the particular case considered, the FieldBus proved to be perfectly capable of meeting the communication requirements of car control systems.>

An expert system implemented for studying chronic venous insufficiency is described. This disease is actually classified into three possible stadia, but studies performed on several patients showed that a further stadium exists. The system has been used for statistical evaluations of patient symptoms to detect those characterizing this stadium. An architecture for the expert system is proposed, with emphasis on the implementation of the knowledge base.>

The Language for temporal ordering specification (LOTOS) is a formal description technique whose development is under way within ISO, the International Organization for standardization, mainly for application to open systems interconnection (OSI) standards. The paper presents a LOTOS specification of the PROWAY interface for process control applicatioins, defined by IEC, the International Electrotechnical Commision. LOTOS is shown to be tailored for the specification of asynchronous systems. In particular, it proves suitable for the specification both of the services which define an interface and of the protocols which implement it. The paper shows how LOTOS supports formal reasoning aimed at establishing consistency between service and protocol specifications. Two examples of such a verification are developed that are related to the PROWAY interface. Finally, advantages and limitations of this approach are outlined.