Feedback Control Goes Wireless: Guaranteed Stability over Low-power Multi-hop Networks

Closing feedback loops fast and over long distances is key to emerging applications; for example, robot motion control and swarm coordination require update intervals of tens of milliseconds. Low-power wireless technology is preferred for its low cost, small form factor, and flexibility, especially if the devices support multi-hop communication. So far, however, feedback control over wireless multi-hop networks has only been shown for update intervals on the order of seconds. This paper presents a wireless embedded system that tames imperfections impairing control performance (e.g., jitter and message loss), and a control design that exploits the essential properties of this system to provably guarantee closed-loop stability for physical processes with linear time-invariant dynamics. Using experiments on a cyber-physical testbed with 20 wireless nodes and multiple cart-pole systems, we are the first to demonstrate and evaluate feedback control and coordination over wireless multi-hop networks for update intervals of 20 to 50 milliseconds.Comment: Accepted final version to appear in: 10th ACM/IEEE International Conference on Cyber-Physical Systems (with CPS-IoT Week 2019) (ICCPS '19), April 16--18, 2019, Montreal, QC, Canad

Constructive Interference in 802.15.4: A Tutorial

International audienceConstructive Interference (CI) can happen when multiple wireless devices send the same frame at the same time. If the time offset between the transmissions is less than 500 ns, a receiver will successfully decode the frame with high probability. CI can be useful for achieving low-latency communication or low-overhead flooding in a multi-hop low-power wireless network. The contribution of this article is threefold. First, we present the current state-of-the-art CI-based protocols. Second, we provide a detailed hands-on tutorial on how to implement CI-based protocols on TelosB motes, with well documented open-source code. Third, we discuss the issues and challenges of CI-based protocols, and list open issues and research directions. This article is targeted at the level of practicing engineers and advanced researchers and can serve both as a primer on CI technology and a reference to its implementation

Design and Real-World Evaluation of Dependable Wireless Cyber-Physical Systems

The ongoing effort for an efficient, sustainable, and automated interaction between humans, machines, and our environment will make cyber-physical systems (CPS) an integral part of the industry and our daily lives. At their core, CPS integrate computing elements, communication networks, and physical processes that are monitored and controlled through sensors and actuators. New and innovative applications become possible by extending or replacing static and expensive cable-based communication infrastructures with wireless technology. The flexibility of wireless CPS is a key enabler for many envisioned scenarios, such as intelligent factories, smart farming, personalized healthcare systems, autonomous search and rescue, and smart cities. High dependability, efficiency, and adaptivity requirements complement the demand for wireless and low-cost solutions in such applications. For instance, industrial and medical systems should work reliably and predictably with performance guarantees, even if parts of the system fail. Because emerging CPS will feature mobile and battery-driven devices that can execute various tasks, the systems must also quickly adapt to frequently changing conditions. Moreover, as applications become ever more sophisticated, featuring compact embedded devices that are deployed densely and at scale, efficient designs are indispensable to achieve desired operational lifetimes and satisfy high bandwidth demands. Meeting these partly conflicting requirements, however, is challenging due to imperfections of wireless communication and resource constraints along several dimensions, for example, computing, memory, and power constraints of the devices. More precisely, frequent and correlated message losses paired with very limited bandwidth and varying delays for the message exchange significantly complicate the control design. In addition, since communication ranges are limited, messages must be relayed over multiple hops to cover larger distances, such as an entire factory. Although the resulting mesh networks are more robust against interference, efficient communication is a major challenge as wireless imperfections get amplified, and significant coordination effort is needed, especially if the networks are dynamic. CPS combine various research disciplines, which are often investigated in isolation, ignoring their complex interaction. However, to address this interaction and build trust in the proposed solutions, evaluating CPS using real physical systems and wireless networks paired with formal guarantees of a system’s end-to-end behavior is necessary. Existing works that take this step can only satisfy a few of the abovementioned requirements. Most notably, multi-hop communication has only been used to control slow physical processes while providing no guarantees. One of the reasons is that the current communication protocols are not suited for dynamic multi-hop networks. This thesis closes the gap between existing works and the diverse needs of emerging wireless CPS. The contributions address different research directions and are split into two parts. In the first part, we specifically address the shortcomings of existing communication protocols and make the following contributions to provide a solid networking foundation: • We present Mixer, a communication primitive for the reliable many-to-all message exchange in dynamic wireless multi-hop networks. Mixer runs on resource-constrained low-power embedded devices and combines synchronous transmissions and network coding for a highly scalable and topology-agnostic message exchange. As a result, it supports mobile nodes and can serve any possible traffic patterns, for example, to efficiently realize distributed control, as required by emerging CPS applications. • We present Butler, a lightweight and distributed synchronization mechanism with formally guaranteed correctness properties to improve the dependability of synchronous transmissions-based protocols. These protocols require precise time synchronization provided by a specific node. Upon failure of this node, the entire network cannot communicate. Butler removes this single point of failure by quickly synchronizing all nodes in the network without affecting the protocols’ performance. In the second part, we focus on the challenges of integrating communication and various control concepts using classical time-triggered and modern event-based approaches. Based on the design, implementation, and evaluation of the proposed solutions using real systems and networks, we make the following contributions, which in many ways push the boundaries of previous approaches: • We are the first to demonstrate and evaluate fast feedback control over low-power wireless multi-hop networks. Essential for this achievement is a novel co-design and integration of communication and control. Our wireless embedded platform tames the imperfections impairing control, for example, message loss and varying delays, and considers the resulting key properties in the control design. Furthermore, the careful orchestration of control and communication tasks enables real-time operation and makes our system amenable to an end-to-end analysis. Due to this, we can provably guarantee closed-loop stability for physical processes with linear time-invariant dynamics. • We propose control-guided communication, a novel co-design for distributed self-triggered control over wireless multi-hop networks. Self-triggered control can save energy by transmitting data only when needed. However, there are no solutions that bring those savings to multi-hop networks and that can reallocate freed-up resources, for example, to other agents. Our control system informs the communication system of its transmission demands ahead of time so that communication resources can be allocated accordingly. Thus, we can transfer the energy savings from the control to the communication side and achieve an end-to-end benefit. • We present a novel co-design of distributed control and wireless communication that resolves overload situations in which the communication demand exceeds the available bandwidth. As systems scale up, featuring more agents and higher bandwidth demands, the available bandwidth will be quickly exceeded, resulting in overload. While event-triggered control and self-triggered control approaches reduce the communication demand on average, they cannot prevent that potentially all agents want to communicate simultaneously. We address this limitation by dynamically allocating the available bandwidth to the agents with the highest need. Thus, we can formally prove that our co-design guarantees closed-loop stability for physical systems with stochastic linear time-invariant dynamics.:Abstract Acknowledgements List of Abbreviations List of Figures List of Tables 1 Introduction 1.1 Motivation 1.2 Application Requirements 1.3 Challenges 1.4 State of the Art 1.5 Contributions and Road Map 2 Mixer: Efficient Many-to-All Broadcast in Dynamic Wireless Mesh Networks 2.1 Introduction 2.2 Overview 2.3 Design 2.4 Implementation 2.5 Evaluation 2.6 Discussion 2.7 Related Work 3 Butler: Increasing the Availability of Low-Power Wireless Communication Protocols 3.1 Introduction 3.2 Motivation and Background 3.3 Design 3.4 Analysis 3.5 Implementation 3.6 Evaluation 3.7 Related Work 4 Feedback Control Goes Wireless: Guaranteed Stability over Low-Power Multi-Hop Networks 4.1 Introduction 4.2 Related Work 4.3 Problem Setting and Approach 4.4 Wireless Embedded System Design 4.5 Control Design and Analysis 4.6 Experimental Evaluation 4.A Control Details 5 Control-Guided Communication: Efficient Resource Arbitration and Allocation in Multi-Hop Wireless Control Systems 5.1 Introduction 5.2 Problem Setting 5.3 Co-Design Approach 5.4 Wireless Communication System Design 5.5 Self-Triggered Control Design 5.6 Experimental Evaluation 6 Scaling Beyond Bandwidth Limitations: Wireless Control With Stability Guarantees Under Overload 6.1 Introduction 6.2 Problem and Related Work 6.3 Overview of Co-Design Approach 6.4 Predictive Triggering and Control System 6.5 Adaptive Communication System 6.6 Integration and Stability Analysis 6.7 Testbed Experiments 6.A Proof of Theorem 4 6.B Usage of the Network Bandwidth for Control 7 Conclusion and Outlook 7.1 Contributions 7.2 Future Directions Bibliography List of Publication

Distributed scheduling algorithms for LoRa-based wide area cyber-physical systems

Low Power Wide Area Networks (LPWAN) are a class of wireless communication protocols that work over long distances, consume low power and support low datarates. LPWANs have been designed for monitoring applications, with sparse communication from nodes to servers and sparser from servers to nodes. Inspite of their initial design, LPWANs have the potential to target applications with higher and stricter requirements like those of Cyber-Physical Systems (CPS). Due to their long-range capabilities, LPWANs can specifically target CPS applications distributed over a wide-area, which is referred to as Wide-Area CPS (WA-CPS). Augmenting WA-CPSs with wireless communication would allow for more flexible, low-cost and easily maintainable deployment. However, wireless communications come with problems like reduced reliability and unpredictable latencies, making them harder to use for CPSs. With this intention, this thesis explores the use of LPWANs, specifically LoRa, to meet the communication and control requirements of WA-CPSs. The thesis focuses on using LoRa due to its high resilience to noise, several communication parameters to choose from and a freely modifiable communication stack and servers making it ideal for research and deployment. However, LoRaWAN suffers from low reliability due to its ALOHA channel access method. The thesis posits that "Distributed algorithms would increase the protocol's reliability allowing it to meet the requirements of WA-CPSs". Three different application scenarios are explored in this thesis that leverage unexplored aspects of LoRa to meet their requirements. The application scenarios are delay-tolerant vehicular networks, multi-stakeholder WA-CPS deployments and water distribution networks. The systems use novel algorithms to facilitate communication between the nodes and gateways to ensure a highly reliable system. The results outperform state-of-art techniques to prove that LoRa is currently under-utilised and can be used for CPS applications.Open Acces

RIOT-ROS2: Low-Cost Robots in IoT Controlled via Information-Centric Networking

International audienceIn the future, IoT devices will be part of the robotics ecosystem, and the border between IoT and robotics will blur. Already today, we observe converging trends between low-end IoT devices and minibots (i.e. tiny, cheap robots) concerning their hardware, and open source software. Micro-drones are an example of this trend. In this paper, we explore the potential of programming minibots with the open source robotics software framework ROS2, running on top of the IoT operating system RIOT; we call the fruitful association of both elements RIOT-ROS2. In this article, the emphasis is particularly on the networking layer: using an information-centric networking (ICN) paradigm, we design and implement the communication primitives for RIOT-ROS2. We further evaluate the performance of our design on prototype minibots based on cheap, off-the-shelf hardware elements. We show that RIOT-ROS2 fits on low-end robotics hardware such as a System-on-Chip costing under $2, based on an ARM Cortex-M0+ microcontroller. Our experiments also show that the latency incurred with our information-centric approach is acceptable for minibot control, even on a low-throughput IEEE 802.15.4 radio

Kommunikation und Bildverarbeitung in der Automation

In diesem Open-Access-Tagungsband sind die besten Beiträge des 9. Jahreskolloquiums "Kommunikation in der Automation" (KommA 2018) und des 6. Jahreskolloquiums "Bildverarbeitung in der Automation" (BVAu 2018) enthalten. Die Kolloquien fanden am 20. und 21. November 2018 in der SmartFactoryOWL, einer gemeinsamen Einrichtung des Fraunhofer IOSB-INA und der Technischen Hochschule Ostwestfalen-Lippe statt. Die vorgestellten neuesten Forschungsergebnisse auf den Gebieten der industriellen Kommunikationstechnik und Bildverarbeitung erweitern den aktuellen Stand der Forschung und Technik. Die in den Beiträgen enthaltenen anschaulichen Beispiele aus dem Bereich der Automation setzen die Ergebnisse in den direkten Anwendungsbezug

Implementation and Characterization of a Multi-hop 6TiSCH Network for Experimental Feedback Control of an Inverted Pendulum

International audience6TiSCH is a technology being standardized at the IETF which brings determinism to low-power wireless communication. In a 6TiSCH network, all communication is orchestrated by a communication schedule. This paper explores the applicability of this new technology to control systems. In particular, we apply it to the inverted pendulum, a canonical control system in which a cart moves along a track to keep a pendulum –which naturally falls over – upright. This paper presents the first characterization and implementation of a closed-loop wirelessfeedback control network using completely standards-compliant IEEE802.15.4 TSCH technology. First, we implement a control loop in OpenWSN and experimentally evaluate the performance of the network by varying the radio duty cycle, number of hops, and introducing controlled external interference. We show that 100% reliability can be achieved while maintaining latencies well below the critical delay of the system. Second, we use the network on an inverted pendulum system and show that angular deviations from the upright position do not exceed 3 degrees, even in a multi-hop setup. Finally, we discuss the results in detail, and advocate for a co-design of the controller and the networking system

The Adoption of Emerging Technologies in Canada and their Impact on Innovation Performance

RÉSUMÉ: Bien que de nombreuses études aient exploré le rôle de l’adoption de la technologie sur l’innovation et le rendement des entreprises, toutes se sont concentrées sur quelques technologies et sur une catégorie en particulier. Les avantages de leur adoption ont été démontrés par de nombreux chercheurs et comprennent notamment l’augmentation de la productivité, une meilleure qualité des produits, la réduction des coûts, une meilleure adaptation aux besoins des clients, etc. Dans cette thèse, nous examinons une liste exhaustive de technologies appartenant à 4 catégories principales: la chaîne d’approvisionnement, l’intelligence d’affaires ainsi que la fabrication de pointe, qui est normalement divisée en deux sous-catégories, la conception et la fabrication. Notre recherche explore ces technologies sous différents angles pour comprendre leur effet sur la propension à innover. Nous utilisons trois approches différentes pour analyser l’impact de ces technologies. Tout d’abord, nous examinons le nombre de technologies adoptées combinées à des pratiques d’innovation ouverte qui auraient un effet sur la propension à innover. Pour estimer ces facteurs, nous utilisons une simple régression logistique. Parce que nous nous intéressons aux obstacles qui empêchent l’adoption, nous utilisons un modèle variable instrumental où nous considérons l’adoption des technologies comme endogènes. Les variables qui peuvent influer sur l’adoption de la technologie comprennent : les dépenses en immobilisations (CAPEX), les mesures de nombre adoptées pour contrer les obstacles ainsi que le recrutement d’employés liés à l’adoption de la technologie. La deuxième approche que nous utilisons est une analyse de panier de marché (MBA) utilisant l’algorithme apriori contenu dans une librairie R. Un MBA nous permet de trouver des complémentarités entre les technologies car les résultats montrent les faisceaux de technologies qui sont les plus populaires parmi les entreprises. En utilisant chaque famille de technologies, nous pouvons trouver ceux qui sont achetés ensemble le plus souvent. Enfin, en utilisant une autre libraire R (cspade), nous utilisons une autre approche qui ajoute une notion séquentielle à l’adoption. Non seulement nous pouvons trouver quelles technologies sont adoptées dans les mêmes faisceaux, mais nous pouvons également comprendre lesquelles sont adoptées en premier. L’enquête que nous utilisons fournit des informations sur le moment où une technologie a été adoptée (pour 3 ans, moins de 3 ans ou prévue dans les 3 prochaines années). Ces 3 timestamps sont essentiels pour comprendre que les entreprises adoptent les bons outils menant à des technologies émergentes telles que l’IdO et l’IA dans un proche avenir. Nos résultats montrent que le nombre de technologies adoptées a un impact significatif et positif sur la propension à innover, ce qui est vrai pour toutes les familles de technologies. En outre, les pratiques d’innovation ouverte telles que les alliances stratégiques et la collaboration avec les fournisseurs ont un impact positif sur la propension à innover, ce qui est similaire à ce qui a été trouvé dans des recherches antérieures. Le nombre de technologies adoptées a une incidence sur le nombre de mesures d’atténuation adoptées, un CAPEX plus élevé et sur le recrutement de nouveaux employés relatifs à l’adoption. Les trois variables ont un effet significatif et positif. Nous trouvons également des ensembles de technologies qui sont compatibles avec ce que nous avions prédit sur la base de notre examen technique exhaustif. Par exemple, des outils comme WMS (Warehouse Management System), Demand Forecasting (DF) et Customer Relation Management (CRM) constituent le faisceau le plus populaire lié aux technologies de la chaîne d’approvisionnement. Ce résultat a été prédit parce qu’il y a trois outils qui sont essentiels au processus de la chaîne d’approvisionnement qui permettent aux entreprises d’être efficaces lorsqu’elles prévoient la demande et gèrent les besoins des clients. Dans la catégorie Business Intelligence (BI), le groupe le plus populaire comprenait Software-as-a-service (SaaS) et Infrastructure-as-a-service (IaaS) avec plus de 27% des entreprises qui les adoptent. SaaS est particulièrement important pour les petites entreprises qui ne veulent pas construire une infrastructure pour gérer leurs besoins en technologies de l’information (TI). Dans les technologies de fabrication de pointe, ERP et MRPI ont été les groupes les plus populaires avec un taux d’adoption de 15%, tandis que les robots et le contrôle numérique informatique (CNC) ont été adoptés par 7% des entreprises. Malgré des taux d’adoption plus faibles dans le domaine de la fabrication, lorsque nous avons examiné les entreprises qui avaient l’intention d’adopter, nous avons remarqué que les technologies d’impression 3D étaient parmi les plus populaires. Nous voyons un résultat similaire lorsque nous examinons les technologies BI avec un logiciel de données massives (BDS), qui est une condition préalable pour rendre la mise en oeuvre de l’IA possible à l’avenir. Bien qu’en 2014 l’adoption du BDS ait été faible, nous constatons une augmentation constante lorsque nous analysons les entreprises qui prévoient l’adopter. En ajoutant une composante temporelle aux règles d’associations, il y avait entre 12% et 14% qu’une entreprise adopte un logiciel de données massives dans un temps futur. En combinant BDS et RTM en une seule technologie, le taux d’adoption d’une de ces deux technologies augmente à 40%. Une histoire similaire s’est dressée pour l’utilisation des imprimantes 3D. Lorsqu’elles sont considérées individuellement, le taux d’adoption futur est autour de 16%. Lorsqu’on considère au moins une des trois types d’imprimantes (3DP, 3DM ou 3DO), le taux d’adoption augmente à 33%, suggérant qu’une compagnie sur trois à l’intention d’adopter cette technologie dans le futur. Notre étude a des implications théoriques et pratiques. Premièrement, nous avons démontré que l’adoption de technologies de pointe peut avoir un effet endogène sur la propension à innover. Cet effet s’explique par le nombre de mesures d’atténuation adoptées pour contrer les obstacles à l’adoption, le CAPEX pour n’en nommer que quelques-uns. Nous avons également trouvé des faisceaux populaires de technologies qui sont adoptées ensemble. D’un point de vue théorique, c’est la première fois qu’une analyse du panier de marché (MBA) est utilisée pour comprendre le comportement des entreprises adoptant des technologies de pointe qui jouent un rôle dans l’amélioration des performances en matière d’innovation. D’un point de vue pratique, nous avons constaté que si les entreprises préfèrent acheter des technologies « à la carte », il existe encore des modèles émergents qui pourraient se traduire par des pratiques exemplaires pour les entreprises à la recherche de technologies qui peuvent le mieux servir leur coeur de métier.----------ABSTRACT: While many studies have explored technology the role of technology adoption on innovation and firm performance, there were all focussed on a few technologies and on one category in particular. The benefits of adopting them have been demonstrated by many scholars and include productivity increase, better product quality, cost reduction, better adaptation to customers’ needs, etc. This thesis explores an exhaustive list of technologies from four main categories: supply chain, business intelligence and analytics as well as advanced manufacturing, which is normally divided into two subcategories, design and fabrication. This research explores these technologies from various angles to understand their effect on the propensity to innovate. Three different approaches are used to analyze the impact of these technologies. First, the number of technologies adopted combined with open innovation practices that are thought to have an effect on the propensity to innovate are explored. To estimate these factors, a simple logistic regression is used. Because there is an interest in the obstacles that prevent adoption, an instrumental variable model is used, where the adoption of technologies is considered as endogenous. Variables that can affect technology adoption include capital expenditures (CAPEX), the number measures adopted to counter obstacles as well as the recruitment of employees pertaining to technology adoption. The second approach used is a market basket (MBA) analysis using the apriori library in R. A MBA allows to find complementarities between technologies because results show the bundles of technologies that are the most popular amongst firms. Using each family of technologies, it is possible to find the ones that are purchased together most often. Finally, using an additional R library (cspade), another approach that adds a sequential notion to the adoption is adopted. Not only it becomes possible to find which technologies are adopted within the same bundles, but understanding which ones are adopted first can also be studied. The survey provides information on when a technology has been adopted (for three years, less than three years or planned in the next three years). These three timestamps are crucial to understand companies are adopting the right tools leading to emerging technologies such as IoT and AI in the near future. The results show that the number of adopted technologies has a significant and positive impact on the propensity to innovate and this is true across all families of technologies. Furthermore, open innovation practices such as strategic alliances and collaboration with suppliers have positive impact on the propensity to innovate, which is what is similar to what was found in previous research. The number of adopted technologies is impacted by the number of mitigating measures adopted, a higher CAPEX and by the recruitment of new employees pertaining to the adoption. All three variables have a significant and positive effect. It should be noted that bundles of technologies that are consistent with what was predicted based on the exhaustive technical review were also found. For instance, tools like Warehouse Management System (WMS), Demand Forecasting (DF) and Customer Relation Management (CRM) form the most popular bundle related to supply chain technologies. This result was predicted because these three tools are core to the supply chain process that allows firms to be efficient when forecasting demand and managing customers’ needs. In the Business Intelligence (BI) category, the most popular bundle included software-as-a-service (SaaS) and Infrastructure-as-a-service (IaaS) with over 27% of firms adopting them. SaaS is particularly important for small companies that don’t want to build an infrastructure to manage their Information Technology (IT) needs. In the advanced manufacturing technologies, ERP and MRPII were the most popular bundles with 15% adoption rate while robots and Computer Numerical Control (CNC) were adopted by 7% of firms. Despite lower adoption rates in the manufacturing sphere, analyzing firms that planned to adopt suggested that 3D printing technologies were amongst the most popular. A similar result was observed for BI technologies with Big Data Software (BDS), which is a prerequisite to make AI implementation possible in the future. While in 2014, BDS adoption was low, there was a consistent increase in the adoption rate within the firms planning to adopt it. By adding the temporal dimension to the previous association rules, there were important elements that were discovered. The apparent increase in planned BDS adoption translated in a low probability of adoption (confidence between 12% and 14%) when taking time into consideration. However, assuming that BDS and RTM are the same technology, the probability of adopting either one of these technologies increases to about 40%. The same results were observed with 3D technologies, where 3DM and 3DP each had around 16% chance of being adopted in the future. Combining all 3D printing technologies as a single technology, this number increases to 33%, suggesting that 1 out 3 of firms planned to adopt additive manufacturing technologies sometime in the future. This study has some theoretical and practical implications. First, it was demonstrated that advanced technology adoption can have an endogenous effect on the propensity to innovate. This effect can be explained by the number of mitigating measures adopted to counter the obstacles to adoption, the CAPEX to name a few. Popular bundles of technologies that are adopted together were also observed. From a theoretical standpoint, it is the first time that a market basket analysis (MBA) is used to understand the behaviour of firms adopting advanced technologies that play a role in improving innovation performance. From a practical standpoint, it should be noted that while companies prefer to purchase technologies “à la carte”, there are still some emerging patterns that could translate into best practices for firms looking at which technologies are best suited to their core business