Resilient systems are crucial for modern interconnected applications, especially those with autonomous machine-to-machine communication. Standard network protocols can exhibit unacceptable recovery times for time-critical operations, and systems must withstand various disruptions beyond just connection failures.This paper addresses these vulnerabilities by proposing a robust communication architecture based on an adapted MQTT protocol employing duplicated packet transmission over parallel pathways. The approach, based on redundancy, employs a smart algorithm for selecting the best communication path to rely on. This strategy aims to ensure reliable data delivery and mitigate service interruptions, particularly for demanding industrial applications, while limiting resources and bandwidth consumption. The effectiveness of this architecture is validated through a real testbed implementation and online testing.

The extension of Time Sensitive Networking (TSN) to wireless domains is a key enabler for the realization of Industry 4.0 and 5.0 applications. Thanks to their characteristics in terms of latency and bandwidth, and the seamless integration with Ethernet TSN, 5G New Radio (NR) and 802.11 (WiFi) are the primary candidates for enabling wireless TSN applications. In the TSN context, precise time synchronization represents a funda-mental building block. In this paper, we focus on the assessment of the synchronization accuracy of IEEE 1588 (PTP) over 5G NR networks by considering different network configurations and traffic loads. The results provide preliminary insights into the performance of PTP over 5G NR and its suitability for TSN applications.

Critical infrastructure, utilities, and large enter-prises are increasingly complex. These sprawling systems, often geographically dispersed, rely on seamless coordination across vast networks. Typically, they use the internet and TCPIIP proto-cols for communication. However, ensuring system-level resilience requires exceptionally dependable network infrastructure. This paper proposes a solution built on a redundant version of the MQTT protocol, implemented directly at the network's endpoints. This approach ensures reliable communication even in the face of potential network issues. Additionally, the paper explores the potential for a future solution that analyzes multi-publisher/subscriber scenarios and, for this purpose, a prelimi-nary research on synchronizing communication among a larger number of devices within the network. The paper concludes by detailing the proposed solution, evaluating its effectiveness, and validating its practicality through experimentation.

The ever more used and widespread Time-Sensitive Networking (TSN) has changed real-time networks, enabling reliable communication for time-critical applications. At the same time Software-Defined Networking (SDN) has emerged as a solution to ensure proper quality of service for managing dynamic network configurations even in evolving topologies. This paper investigates the integration between TSN and SDN to enable dynamic network re-configuration and improve performance for time-critical applications. We present an experimental setup designed to evaluate this approach. The setup focuses on scenarios where an SDN controller can dynamically reroute critical data flows across different TSN network devices to avoid interference and maintain consistent Quality-of-Service (QoS).

The introduction of Time-Sensitive Networking (TSN) is revolutionizing real-time networks and time-critical applications. Recent advancements in this field extended the TSN capabilities to wireless technologies, giving rise to the concept of wireless TSN (WTSN). This paper focuses on the integration of wireless TSN with Software-Defined Networking (SDN) to enable dynamic network configuration and improve the performance of time-sensitive applications. We present a practical test environment that uses a hybrid network configuration consisting of wireless and wired TSN links. The primary objective is to evaluate the effectiveness of combining a TSN-capable network with an SDN controller. This setup enables dynamic configuration and routing within the system, allowing for prompt actions to address network issues, such as seamlessly re-routing data paths between the two links due to an increase in latency or packet loss. A measurement setup using OpenVSwitch in the wireless TSN domain is presented, along with the evaluation of time synchronization and dynamic route selection capabilities.

The introduction of the Industrial Internet of Things (IIoT) is dramatically changing the concept of manufacturing, ensuring better production flexibility, efficiency, safety and security. In this scenario, Functional Safety Networks are ever more deployed, being networks that allow to implement functional safety systems, integrated and cooperating with factory communication infrastructures that are ever more characterized by the deployment of wireless communication systems. Unfortunately, nowadays, the lack of safety protocols targeted for wireless networks represents a bottleneck in the novel smart factory development process. Thus, functional safety over wireless is becoming a hot research topic. In this paper, we address the adoption of Wi-Fi to implement functional safety networks by exploiting the black channel approach, which is at the basis of the most popular functional safety protocols designed for wired networks. In practice, with such an approach, the safety protocol is not aware of the underlying communication system. We focus on a specific protocol, namely FailSafe over EtherCAT (FSoE) and investigate its behavior over Wi-Fi. To this aim, we developed an experimental set-up and conducted several tests to adequately assess safety, reliability and timing performance. Specifically, we addressed the achievable Safety Integrated Level (SIL), the number of network re-initializations and the message delivery times. The analysis provided encouraging results and revealed different behaviors concerned with the use of different transport layer protocols (TCP and UDP) that suggest interesting future activities.

In recent years, Factory Automation is evolving towards the so-called Industry 4.0, and the creation of a smart factory ecosystem comprising of ubiquitously interconnected objects, namely the Industrial Internet of Things (IIoT), is gaining much research interest. This paradigm aims at developing new smart technological equipment and protocols, thus providing interconnection among "factory objects" anywhere and at any time. In this context, people and machines have to safely cooperate and a high level of protection needs to be guaranteed for both operators and the surrounding environment. For this reason, safety systems, aiming at decreasing risks and failure probabilities, are nowadays of uttermost importance. Several Functional Safety communication protocols have been developed during these years pointing to increase data integrity and guarantee protection in a safety system. Popular examples are Fail Safe over EtherCAT (FSoE), ProfiSAFE, and OPC-UA Safety. These protocols, al-though conceived for wired networks, can be in principle adopted also by wireless communication, as they are developed by using a black channel approach. Nevertheless, the implementation of these protocols over different wireless networks is challenging as they might not ensure the required Safety Integrated Level (SIL). This paper, moving from the aforementioned observations and the need for wireless solutions in the IIoT context, focuses on proposing a possible implementation of FSOE over Wi-Fi, running UDP at the transport layer. In particular, by using suitable experimental outcomes, an OMNeT++ simulator has been calibrated, thus enabling the possibility to analyze the proposed protocol in wide industrial systems.

The papers in this special section focus on industrial cyber-physical systems (CPS), with an emphasis on computing and communications applications. CPS systems are defined by integrating computation and communication facilities on the one hand and the monitoring and control of physical processes on the other hand. Industrial cyber–physical systems (ICPS) refer to the science and art of designing and using cyber–physical systems for industrial and process control applications, for example in smart factories, smart energy grids, smart transportation systems, smart cities, and several other areas. Many of these applications are time- and mission-critical and hence often require low latency and high reliability. In parallel, there has been a strong growth in integrating intelligence, often in the form of machine/deep learning, into applications, which also leads to vastly increasing computational requirements. These innovations then will be integrated into complex systems, which need to be properly engineered to become safe, reliable, trustworthy, and secure while at the same time being cost-efficient.

Modern industrial manufacturing plants, especially those using coordinated electrical drives with strict timing requirements, make extensive use of real-time communication networks. These systems, typically, are based on various topologies, include diverse protocols, and connect devices from different manufacturers, which may make them difficult to study, plan and optimize. As a solution, the adoption of digital twins allows to simulate such systems under various operating conditions in a low-cost and zero-risk environment. In this paper we address the digital twin of a networked electrical drive system, focusing on the real-time communication network used to connect the drives. In particular, we describe the simulation model of Profinet IO RT Class 1, implemented as an extension of the INET library of OMNeT++. Moreover, we present the outcomes of the tests carried out on a prototype simulated network and compare them with those of the equivalent real one.

Wireless technologies play a key role in the Industrial Internet of Things (IIoT) scenario, for the development of increasingly flexible and interconnected factory systems. Wi-Fi remains particularly attracting due to its pervasiveness and high achievable data rates. Furthermore, its Rate Adaptation (RA) capabilities make it suitable to the harsh industrial environments, provided that specifically designed RA algorithms are deployed. To this aim, this paper proposes to exploit Reinforcement Learning (RL) techniques to design an industry-specific RA algorithm. The RL is spreading in many fields since it allows to design intelligent systems by means of a stochastic discrete-time system based approach. In this work we propose to enhance the Robust Rate Adaptation Algorithm (RRAA) by means of a RL approach. The preliminary assessment of the designed RA algorithm is carried out through meaningful OMNeT++ simulations, that allow to recognize the beneficial impact of the introduction of RL with respect to several industry-specific performance indicators.

In this paper we consider an Industrial Internet of Things (IIoT) system, based on the production of 3D-printed artifacts that are equipped with embedded sensors to monitor some environmental variables such as temperature, humidity, etc. These sensors allow to gather information during the production phase of the artifacts, as well as while they are deployed in their final locations, so that diverse operations (e.g. tuning of the production parameters, predictive maintenance, environmental monitoring) can be undertaken. Monitoring is implemented via LoRaWAN, a Low Power Wide Area Network (LPWAN) that allows to acquire data from the sensors embedded in the artifacts. After a description of the IIoT system, we provide the description of some experimental tests we carried out in this challenging context, aimed at investigating both the reliability of the transmission and the battery life time. The outcomes of such experiments indicate the actual feasibility of the proposed technique.

In this article, we investigate an innovative solution, to implement high sampling frequency industrial control by means of networked embedded systems connected via WiFi. The basic idea relies on a co-design approach for the control application, which is then able to adapt its sampling period, as well as to tune the Wi-Fi parameters, according to the feedback coming from the network. To this end, we implemented a cross-layer architecture acting at both application and data-link layers, which features a robust frame-delay state estimator, a time-efficient communication policy, and a specific tuning of the critical protocol parameters. Suitable hardware-in-the-loop experiments have been carried out exploiting two different embedded systems available off-the-shelf. The preliminary results, obtained from an extensive experimental campaign, are encouraging since they show that the proposed architecture enables industrial control applications requiring a sampling rate up to 1000 Hz, even in presence of communication impairments.

People affected by the Parkinson's disease are often subject to episodes of Freezing of Gait (FoG) near specific areas within their environment. In order to prevent such episodes, this paper presents a low-cost indoor localization system specifically designed to identify these critical areas. The final aim is to exploit the output of this system within a wearable device, to generate a rhythmic stimuli able to prevent the FoG when the person enters a risky area. The proposed localization system is based on a classification engine, which uses a fingerprinting phase for the initial training. It is then dynamically adjusted by exploiting a probabilistic graph model of the environment.

With the rise of Industry 4.0 and of the Industrial Internet, the computing and communication infrastructures achieved an essential role within process and factory automation, and cyberphysical systems in general. In this scenario, the OPC UA standard is currently becoming a widespread opportunity to enable interoperability among heterogeneous industrial systems. Nonetheless, OPC UA is characterized by a complex protocol architecture, that may impair the scalability of applications and may represent a bottleneck for its effective implementation in resource-constrained devices, such as low-cost industrial embedded systems. Several different OPC UA implementations are available, which in some significant cases are released under an open source license. In this context, the aim of this paper is to provide an assessment of the performance provided by some of these different OPC UA implementations, focusing specifically on potential development and resource bottlenecks. The analysis is carried out through an extensive experimental campaign explicitly targeting general purpose low-cost embedded systems. The final goal is to provide a comprehensive performance comparisons to allow devising some useful practical guidelines.

Wireless networks are ever more deployed in industrial automation systems in various types of applications. A significant example in this context is represented by the transmission of safety data that, traditionally, was accomplished by wired systems. In this paper we propose an implementation of the Fail Safe over EtherCAT (FSoE) protocol on the top of IEEE 802.11 WLAN. The paper, after a general introduction of FSoE, focuses on the implementation of such protocol on commercial devices running UDP at the transport layer and connected via the IEEE 802.11 Wireless LAN. Then the paper presents some experimental setups and the tests that have been carried out on them. The obtained results are encouraging, since they show that good safety performance can be achieved even in the presence of wireless transmission media.

Networked embedded systems for industrial control based on wireless support provide several advantages over wired counterparts, but often reveal unsuitable for the most demanding industrial control applications, such as advanced manufacturing and cooperative robotics. Data exchange over IEEE 802.11 networks may theoretically represent an appropriate solution for time-critical applications, provided that unreliability and non- determinism issues are properly handled. In this respect, this paper hence proposes an original solution, based on a cross- layer approach, to allow the realization of high-speed industrial control-over-Wi-Fi networked embedded systems. The proposal implements a novel robust frame-delay state estimator, a time efficient communication policy, and a specific tuning of critical protocol parameters. Suitable hardware-in-the-loop experiments have been carried out implemented exploiting two different embedded systems. Preliminary results show that the proposed architecture enables industrial control applications requiring a sampling rate of up to 1 kHz, even in presence of non negligible communication errors.

The adoption of real-time wireless technologies within the ever-growing field of networked industrial control systems is continuously gaining popularity. Widespread sensing and actuation devices based on high-throughput wireless standards allow for an increased system mobility and lower configuration and maintenance costs. The IEEE 802.11 standard, especially in its most recent amendments, pushes performance to a very high level, theoretically approaching those of the most common real-time Ethernet networks. Its nondeterministic communication behavior, however, makes 802.11 unsuitable for mission- and safety-critical applications with high-reliability requirements, at least in its standard form. In this paper, we present several major solutions that tackled this issue to achieve real-time and reliability guarantees in wireless networked control systems, capitalizing on the strong efforts devoted to the adoption of IEEE 802.11 physical layer (PHY) technologies. We first provide a deep analysis of the 802.11 protocols in order to propose guidelines toward smart parameter selection at the data-link layer (DLL). In addition, the design of effective rate selection algorithms is considered as a way of increasing both the timeliness and reliability of data delivery. A further systematic solution is represented by real-time (RT)-WiFi, a new time-division multiple-access (TDMA)-based highly configurable DLL protocol that enables high-speed hard real-time data exchange over 802.11 networks. An important goal of this paper is also to provide a thorough comparison among different discussed solutions, in order to put in evidence their advantages and disadvantages, possibly in relation with systems based on different underlying PHYs. We will finally highlight the open challenges and future directions in this active research field.

The demand for fast and reliable wireless connectivity in industrial applications is always increasing. Several new technologies have been proposed in recent years to improve the performance of wireless networks, including full-duplex wireless, which allows a terminal to simultaneously transmit and receive in the same frequency band. This paper explores the potential impact of this technology in real-time industrial networks, showing that it can be useful to increase the reliability of latency-constrained applications.

In this paper we address the safety strategies for networked electrical drive systems, in the context of industrial automation. Specifically, it is considered the handling of errors and faults that may occur during the execution of safety related functions, on a set of electrical drives. Such devices, which operate in a coordinated way, are connected via an industrial communication network and use a safety industrial protocol. In this respect, a novel approach that exploits a distributed consensus algorithm to identify and possibly recover the aforementioned errors is devised and discussed in comparison with a traditional safe shut-down strategy. The theoretical performance figures and the effectiveness of the proposed approach are evaluated in a real industrial case study considering two different widespread network topologies.

In the last decade, several localization systems have been proposed, some of them achieving an accuracy in the order of decimeters. Nonetheless, a broad range of these methods may reveal unattractive for low-cost and resource-bounded mobile application scenarios. Indeed, significant constraints stem from costs and availability of the required technological infrastructure for the target environment. In addition, resources necessary to train and run the localization algorithm may pose stringent requirements in terms of time, power and computational. In the aforementioned context, this paper presents an effective radio-based positioning algorithm able to localize the user by exploiting a graph-based representation of the environment. The graph is created by analyzing the received signal level and the movement directions of a mobile device with respect to a set of real and virtual landmarks. The comparison with a commercial localization system proves the effectiveness and accuracy of the proposed approach.

Low‐Power Wide‐Area Networks (LPWANs) have recently emerged as appealing communication systems in the context of the Internet of Things (IoT). Particularly, they proved effective in typical IoT applications such as environmental monitoring and smart metering. Such networks, however, have a great potential also in the industrial scenario and, hence, in the context of the Industrial Internet of Things (IIoT), which represents a dramatically growing field of application. In this paper we focus on a specific LPWAN, namely, LoRaWAN, and provide an assessment of its performance for typical IIoT employments such as those represented by indoor industrial monitoring applications. In detail, after a general description of LoRaWAN, we discuss how to set some of its parameters in order to achieve the best performance in the considered industrial scenario. Subsequently we present the outcomes of a performance assessment, based on realistic simulations, aimed at evaluating the behavior of LoRaWAN for industrial monitoring applications. Moreover, the paper proposes a comparison with the IEEE 802.15.4 network protocol, which is often adopted in similar application contexts. The obtained results confirm that LoRaWAN can be considered as a strongly viable opportunity, since it is able to provide high reliability and timeliness, while ensuring very low energy consumption.

The possibility of extending real-time Ethernet networks employed in industrial applications with wireless links can lead to several benefits in terms of cost reduction and easier deployment. However, delays and jitter introduced by both the wireless medium and the interconnection systems may degrade the network performance significantly. This paper describes the advantages introduced by the IEEE 802.11n WLAN amendment in this scenario and considers, as an example of application, its use for the wireless extension of an Ethernet Powerlink network. Different configurations are compared through experimental measurements, showing that an adequate setting of the IEEE 802.11 MAC parameters, as well as the use of a suitable rate adaptation technique, allow to achieve effective performance. Particularly, a bounded polling time can be obtained, which represents a fundamental aspect for real-time communications.

Recently, different communities in computer science, telecommunication, and control systems have devoted a huge effort towards the design of energy efficient solutions for data transmission and network management. This paper collocates along this research line and presents a novel energy efficient strategy conceived for Ethernet networks. The proposed strategy, which exploits the opportunities offered by the IEEE 802.3az amendment to the Ethernet standard (known as energy efficient Ethernet) is based on the possibility of predicting the future traffic from the analysis of the current data flow. In agreement with the results of such a dynamic prediction, Ethernet links can be forced into a low power consumption state for variable intervals. Theoretical bounds are derived to detail how the performance figures depend on the parameters of the designed strategy and scale with respect to traffic load. Furthermore, simulation results carried out with both real and synthetic traffic traces are presented to prove the effectiveness of the strategy, which leads to considerable energy savings at the cost of only a limited bounded delay in data delivery.

The multirate support feature has been introduced by the IEEE 802.11 standard to improve the system performance, and has been widely exploited by means of rate adaptation (RA) strategies within general purpose wireless LANs. These strategies revealed ineffective for real-time industrial communications, and alternative solutions, better tailored for such a specific field of application, were investigated. The preliminary outcomes of the analyses carried out were promising, even if they clearly indicated that further efforts were necessary. In this direction, this paper first proposes rate selection for industrial networks (RSIN), an innovative RA algorithm specifically conceived for the real-time industrial scenario with the goal of minimizing the transmission error probability, while taking into account the deadline imposed to packet delivery. Then, it describes the practical implementation of RSIN on commercial devices, along with that of other formerly introduced RA techniques. Finally, the paper presents a thorough performance analysis, carried out to investigate the behavior of the addressed RA schemes. Such an assessment was performed via both experimental campaigns and simulations. The obtained results, on one hand, confirm the effectiveness of the RA techniques purposely designed for real-time industrial communication. On the other hand, they clearly indicate that RSIN outperforms all the other strategies.

IEEE 802.11 wireless LANs introduced the Multi-Rate Support as an effective tool for performance tuning. This feature is implemented by means of specific Rate Adaptation (RA) algorithms, that in general have been designed with the goal of throughput maximization, targeting at general purpose communication networks. Unfortunately, industrial real-time communication systems are characterized by very different performance requirements, and hence dedicated, more tailored, RA algorithms have to be devised. The proposed algorithm called Rate Selection for Industrial Networks (RSIN) is a significant step in this direction, being designed from its beginning as an optimization problem, in which the knowledge of the signal-to-noise-ratio is exploited to cope with the industrial traffic requirements. A preliminary assessment has indicated that the performance figures of RSIN are promising. In this paper, we aim at providing a complete characterization of such algorithm, assessing the impact of possible uncertainties in the estimation of the channel status and evaluating the scalability of the proposed strategy from one link to a network. The outcomes of these analyses revealed that RSIN is able to enhance timeliness and reliability of a wireless network in a robust and scalable way, making it suitable for adoption in industrial contexts.

The Multirate Support feature has been introduced by the IEEE 802.11 standard to improve system performance. It has been widely exploited within general purpose Wireless LANs by means of Rate Adaptation (RA) strategies, that unfortunately revealed ineffective for the case of real-time industrial communications. This paper presents the innovative Rate Selection for Industrial Networks (RSIN) algorithm, specifically conceived for the real-time industrial scenario with the goal of minimizing the transmission error probability, while taking into account the deadlines imposed to packet delivery.

In the last years, IEEE 802.11 Wireless LANs (WLANs) have proved their effectiveness for a wide range of real-time industrial communication applications. Nonetheless, the introduction of the important IEEE 802.11n amendment, which is commonly implemented in commercial devices, has not been adequately addressed in this operational framework yet. IEEE 802.11n encompasses several enhancements at both physical (PHY) and medium access control (MAC) layers that may bring considerable improvements to the performance of WLANs deployed in real-time industrial communication systems. To this regard, in this paper, we present a thorough investigation of the most important IEEE 802.11n features, addressing in particular, specific performance indicators such as timeliness and reliability, which are crucial for industrial communication systems. To this aim, after an accurate theoretical analysis, we implemented a suitable experimental setup and carried out several measurement sessions to obtain an exhaustive performance assessment. The outcomes of these experiments, on one hand, revealed that the adoption of IEEE 802.11n can actually provide significant improvements to the performance of the IEEE 802.11 WLAN in the industrial communication scenario. On the other hand, the assessment allowed to select, among the various options of IEEE 802.11n, the parameter settings which may ensure the best behavior in this specific (and demanding) field of application.

The IEEE 802.11 standard, since its earliest versions, provides the multi-rate support feature typically exploited by Rate Adaptation (RA) techniques to dynamically select the most suitable transmission rate, based on an estimation of the channel status. With the release of the IEEE 802.11n amendment, several enhancements have been introduced to the standard, notably the support for MIMO architectures, whose benefits can be effectively combined with multi-rate support. In an industrial communication scenario, the RA algorithms commonly available for general purpose applications revealed ineffective. This led to the definition of purposely designed algorithms, with the aim of improving the real-time behavior of IEEE 802.11 networks. In this paper we take into consideration these techniques, as well as some general purpose RA strategies, and analyze their implementation on an IEEE 802.11n communication system deployed in an industrial scenario. Furthermore, we propose an effective parameters tuning for the considered RA algorithms, as well as some enhancements conceived to enforce their timeliness. An exhaustive assessment, carried out via numerical simulations, shows that the improved techniques allow to achieve excellent performance.

IEEE 802.11 systems are drawing an ever increasing interest for wireless industrial communication, also thanks to the interesting features provided by the most recent and advanced amendments to this standard, such as IEEE 802.11n. Due to the intrinsic unreliability of the wireless medium, the current research efforts aim at improving both timeliness and reliability of such a protocol in view of its adoption for real-time applications. A significant issue in this context is represented by the reduction of the randomness that affects packet delivery times. An important benefit in this direction can be obtained by the deactivation of the standard legacy carrier sensing and backoff procedures. In this paper we show, through a simulative assessment, that a fine control of such features leads to improved real-time performance.

In the last years, IEEE 802.11 Wireless LANs (WLANs) have proved their effectiveness for a wide range of real-time industrial communication applications. Nonetheless, the enhancements at the PHY and MAC layers introduced by the IEEE 802.11n amendment have not yet been adequately addressed in the context of industrial communication. In this paper we investigate the impact of some IEEE 802.11n new features on some important performance figures for industrial applications, such as timeliness and reliability.

To increase the energy efficiency of Ethernet networks, in 2010, the IEEE published the IEEE 802.3az amendment, known as Energy Efficient Ethernet (EEE). The amendment introduces a new operational mode, defined as Low Power Idle (LPI), that allows to considerably reduce the power consumption of inactive Ethernet links. In this paper, we address the application of EEE to Real-Time Ethernet (RTE) networks, the popular communication systems typically employed in factory automation, characterized by tight timing requirements. We start with a description of the EEE basics and, subsequently, focus on the introduction of EEE in the industrial communication scenario. Then, we specifically address the implementation of effective EEE strategies for some popular RTE networks. The analysis is carried out on configurations commonly deployed at low levels of factory automation systems. The obtained results show that considerable power savings can be achieved with very limited impact on network performance.

The IEEE 802.3az amendment to the Ethernet standard, referred to as energy-efficient Ethernet (EEE), encompasses the new low power Idle operational mode that allows to strongly decrease the energy consumption of inactive links. The introduction of EEE in real-time industrial communications represents an interesting topic currently addressed by the scientific community, as well as by some standardization bodies. The outcomes of these activities are promising, since effective EEE strategies can be devised, and are able to cope with the very tight timing requirements of industrial communication. Unfortunately, the proposed analyses do not address implementation issues that, conversely, represent a crucial aspect in this scenario. Hence, in this paper, we specifically focus on practical issues concerned with the adoption of EEE strategies by real-time Ethernet (RTE) networks. At first, we address the use of commercially available network components and describe a measurement setup that can be adopted to achieve the adequate characterization of such components. Furthermore, we show that, in an RTE perspective, link activations/deactivations should be independently managed by suitably designed EEE strategies at the application level. Consequently, we defined a set of network services that have to be made available in the device drivers. Hence, we consider a generic RTE network and discuss methods for the practical implementation of those EEE strategies. A performance assessment carried out via theoretical models as well as numerical simulations shows that EEE strategies can be effectively implemented with considerable power savings at the expense of only minimal performance degradation.

The flexibility and reconfigurability requirements of factories and manufacturing plants of the future can be partially met by adopting technologies and solutions already available for testing and experimentation. Openness and adherence to international standards are becoming increasingly important in modern distributed production and automation systems, especially when they have to cope with ever-increasing product differentiations and short product lifecycles. However, the increased flexibility and openness should not come to detriment of the system real-time characteristics. This paper deals with a pilot mechatronic architecture for agile transport systems, which has been specifically developed to enable the study of the aforementioned aspects in the framework of the “Factory of the Future” Italian flagship project. In particular, the paper focuses on possible bottlenecks and pitfalls at the operating system and communication levels, and provides preliminary indications on how to address or mitigate them by means of solutions already available on the market.

Industrial communication systems, like the very popular real-time Ethernet networks, are ever more used to carry multimedia traffic, i.e. that generated by applications employing complex sensors such as, for example, video cameras. Ethernet networks, however, revealed to be quite inefficient in terms of energy saving since the power consumption of a link between any two devices does not decrease significantly during the (statistically long) idle periods, i.e. the intervals of time in which the link is not crossed by traffic. In this paper we present a novel traffic shaping technique that aims at saving energy when the multimedia industrial traffic has self similar characteristics. In particular, the proposed method combines the statistical properties of the traffic, with the opportunities offered by the recent amendment to the Ethernet standard, called Energy Efficient Ethernet (EEE), to design a strategy based on the analysis of current traffic levels and the prediction of the incoming data flow. Simulation results are presented to prove the effectiveness of the strategy which leads to considerable energy savings at the expense of only a limited bounded delay in frame delivery.

This paper investigates an original system for wireless control and monitoring of an agricultural machine. The system is implemented by means of an IEEE 802.11-based soft realtime communication architecture which enables the connection of the machine with off-the-shelf mobile devices, like widespread tablet PCs, that could hence replace traditional ad-hoc developed operator panels. The harsh surrounding environment, however, introduces severe requirements. Hence, focusing on the wireless communication behavior, the paper yields a thorough performance analysis derived by extensive experimental campaigns. By investigating the outcomes of these measurement sessions, the paper assesses some causes of performance degradation, and provides viable and easy to implement solutions to improve the overall system behavior.

The IEEE 802.3az amendment, known as Energy Efficient Ethernet (EEE), has been conceived to reduce the overall power consumption of Ethernet networks, defining a new operational mode, namely Low Power Idle, that allows the partners of a network link to timely enter a state characterized by a limited consumption. In this paper we focus on the application of EEE concepts to industrial real-time Ethernet networks. We firstly describe the behavior of EEE-enabled links when subjected to typical industrial traffic, providing an assessment of both actual power savings and delays that might affect frames delivery. Subsequently, we carry out a simulation analysis for a specific network, Ethernet POWERLINK, aimed at verifying its real behavior when EEE is adopted. The results show that considerable power savings may be achieved without influencing network performance.

The multi-rate support is a feature made available by the IEEE 802.11 Wireless LAN to dynamically adapt its transmission rate to the underlying wireless channel state. This feature, which makes use of suitable rate adaptation (RA) techniques, allows to reach the best transmission success probability, even in the presence of noisy channels. The most popular RA technique, available for general purpose applications, is the Automatic Rate Fallback (ARF). In this paper we focus on the performance of two alternative RA techniques, namely Static retransmission rate ARF (SARF) and Fast rate reduction ARF (FARF), specifically conceived for the industrial communication scenario. In particular, we take into consideration a prototype network, typical of low levels of factory automation systems, and evaluate the behavior of these techniques by means of meaningful performance indicators obtained through numerical simulations. We also propose a comparison with results obtained, for the same network, when fixed transmission rates are used. Simulations have been carried out using both channel and devices models that reflect experimental outcomes. The analysis reveals that both SARF and FARF perform effectively since they are able to ensure short cycle times along with limited randomness.

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.

The problem of enhancing reliability while providing real-time guarantees in industrial communication over wireless networks has been widely addressed by the scientific literature. Several analyses have been carried out that consider this problem in a real-time scheduling framework, modeling both real-time transmission flows and possible retransmissions as a set of periodic tasks. These analyses, however, approach the schedulability problem from a high level point of view, where lower communication layers are modeled as if they were a unique stack that introduces a certain error probability and do not take into account their actual behavior. In this paper, we present an accurate evaluation of the transmission times of the packets belonging to the flows in case of an IEEE 802.11g WLAN is employed at the lower layers. Moreover, we address the negative influence of the wireless network non-deterministic behavior, mainly caused by both backoff procedures and MAC-layer retransmissions, on the feasibility of a flow set providing some possible solutions.

In industrial communication systems, the unavailability of models of real components, in particular of their behavior in the presence of non-ideal channels, often leads to consistent differences between theoretical/simulative analysis and experimental results. In this paper we consider a hybrid (Ethernet/IEEE 802.11) network employing access points from different vendors and measure a specific performance index, namely the service time, for various transmission rates focusing on the effects of both internal component behaviors and channel conditions. The obtained results show how, in case of small payload packets transmitted on noisy channels, the choice of a fixed low transmission rate guarantees better service times. Indeed, decreasing the transmission rate on the wireless segment below 54 Mb/s reveals effective, since it limits the occurrence of packet errors and the consequent retransmissions reducing the service time variability to the intrinsic randomness of the employed devices.

In this paper, we consider retransmission strategies for centralized cyclic polling-based systems over wireless channels subject to external interference. The considered strategies differ in the time when retransmissions for one particular node are carried out, and in the number of retransmissions that can be carried out for one node. We show experimentally and by simulation that two related strategies introduced in this paper, called the queueing-based strategies, significantly outperform the traditional strategy (in which all admissible trials towards one node are carried out subsequently) in terms of the average number of nodes that cannot be successfully served in a cycle. These performance gains are achieved without increasing the average total transmission effort.

In this paper we consider retransmission strategies for centralized cyclic polling-based systems over wireless channels subject to external interference. The considered strategies differ in the time when retransmissions for one particular node are carried out, and in the number of retransmissions that can be carried out for one node. We show experimentally and by simulation that two related strategies introduced in this paper, called the queueing-based strategies, significantly outperform the traditional strategy in which all admissible trials towards one node are carried out subsequently in terms of the average number of nodes that cannot be successfully served in a cycle. These performance gains are achieved without increasing the average total transmission effort.

In the modern wireless applications of factory automation, interference phenomena among near operating wireless networks can be the cause of severe performance degradation. To avoid this possibility and prevent deleterious system failures, simulations may offer a real and reliable solution. In this paper a new simulator is presented, allowing cross-layer analysis of interference phenomena arising among IEEE 802.15.4 wireless sensor networks (WSNs) and IEEE 802.11 wireless local area networks. The purpose is to provide an accurate tool able to forecast possible interference effects on a WSN and by which optimize the setup of some suitable network parameters such as the position of wireless nodes.