Interactive applications with automated feedback will largely influence the design of future networked infrastructures. In such applications, status information about an environment of interest is captured and forwarded to a compute node, which analyzes the information and generates a feedback message. Timely processing and forwarding must ensure the feedback information to be still applicable; thus, the quality-of-service parameter for such applications is the end-to-end latency over the entire loop. By modelling the communication of a feedback loop as a two-hop network, we address the problem of allocating network resources in order to minimize the delay violation probability (DVP), i.e. the probability of the end-to-end latency exceeding a target value. We investigate the influence of the network queue states along the network path on the performance of semi-static and dynamic scheduling policies. The former determine the schedule prior to the transmission of the packet, while the latter benefit from feedback on the queue states as time evolves and reallocate time slots depending on the queue’s evolution. The performance of the proposed policies is evaluated for variations in several system parameters and comparison baselines. Results show that the proposed semi-static policy achieves close-to-optimal DVP and the dynamic policy outperforms the state-of-the-art algorithms.

The evolution of the Internet of Things accelerated the development of Cyber-Physical Systems. Among them, Networked Control Systems (NCS) gained notable attention thanks to their application to industrial operations. Experimental NCS require expertise from control, computation, and communication disciplines. This requirement, together with the fragmentation of implementation platforms and experimental investigations, represents a challenge for the reproducibility and comparison of research results. In this paper, we tackle this problem by proposing a novel NCS benchmarking methodology that aids the reproducibility of NCS experiments. Relying on a novel approach to model the architectural elements and the delays of NCS, the methodology defines the experiment parameters and the relevant Key Performance Indicators (KPIs) that need to be observed during its execution. Furthermore, we detail the implementation of the first reproducible benchmarking platform for NCS. The proposed platform is open-source and designed to be easily reproducible and extensible by anyone. Finally, we replicate and evaluate the platform following the proposed NCS benchmarking methodology. The experimental results evaluate and compare the KPIs during the execution of the platform in different benchmarking scenarios, proving the validity of the proposed benchmarking methodology.

Cyber-Physical Systems (CPS) are widely spreading thanks to fast-paced technological breakthroughs of microcontrollers and communication networks. Among them, Networked Control Systems (NCS) gained notable attention thanks to their application in industrial operations. In NCS, the interconnection of a control logic with sensors and actuators used to steer a physical system occurs over a communication network. Despite large research interest on NCS, the reproducibility and comparison of experimental results are difficult to achieve. This is caused by the lack of well-established models and methodologies that combine the theoretical and practical aspects of NCS. We tackle this problem by proposing and demonstrating NCSbench: the first open-source reproducible benchmarking platform for NCS. NCSbench enables the benchmarking of research experiments using a networked two-wheeled inverted pendulum robot. For each benchmarking experiment, a set of values is measured and used to quantify the key performance indicators (KPIs) of the NCS. In our demonstration, we visualize in real-time the evolution of the benchmarking KPIs on a web-based Graphical User Interface.

In a so-called `Smart Factory', sensors, actuators, and a processing logic are interconnected via wireless communication. A popular class of industrial processes is Networked Control Systems (NCS), where the sensor, controller, and actuator of a control system are distributed over a network. Wireless brings several benefits to NCS but affects their performance. This aspect is particularly critical, as NCS pose stringent delay and reliability requirements to data packets in order to fulfil a desired Quality of Control (QoC). Industrial Wireless Sensor Networks (IWSN) is a candidate communication technology to haul NCS traffic. IWSN, however, suffer from packet loss caused by the harsh industrial environment. The characterization of the impact of delay and packet loss on the QoC of NCS is a challenging task, as it requires the analysis of mutually dependent random processes. We tackle this investigation deriving a delay-reliability model for IWSN based on the Loop Success Probability, a metric that associates the network performance to the QoC of the NCS. Initially, the effect of Loop Success Probability on QoC is evaluated, then, it is mathematically related to the end-to-end delays of IWSN packets. The model provides a connection between IWSN parameters and QoC and is used to define their operating regions. Via measurements of an IWSN testbed and a simulated NCS, we prove the validity of the proposed model.

In future industrial scenarios, Wireless Sensor Networks (WSN) are envisioned to support the traffic of Networked Control Systems (NCS). WirelessHART is a prevalent WSN protocol that uses the Time Slotted Channel Hopping (TSCH) medium access to cope with the delay and reliability requirements of NCS in the harsh industrial environment. In TSCH, time slots and frequencies can be scheduled by a network coordinator to provide Quality of Service (QoS). In contrast to previous works that consider the end-to-end delay requirement of a flow of packets, we focus on a finite sequence of time-critical packets. These packets may belong to a time-critical message whose latency could significantly impact the NCS. Given an end-to-end delay deadline, our objective is to minimize the Delay Violation Probability (DVP) for a finite sequence of packets by dynamically scheduling the time slots in each frame. This is a challenging task as DVP depends on the instantaneous state of the network and requires its transient analysis. In this work, we model the wireless NCS as a two-queue lossy wireless network and propose the first transient analysis of DVP for a finite sequence of time-critical packets. Noting that DVP cannot be directly used for dynamic resource allocation, we propose a heuristic algorithm by relating DVP with the network's throughput. The proposed heuristic maximizes the expected throughput, is computed by solving a finite-horizon Markov Decision Process (MDP), and can be implemented at the network coordinator. Using simulation we demonstrate that the MDP-based heuristic achieves lower DVP compared to the classical MaxWeight and Weighted-Fair Queuing.

Wireless Avionics Intra-Communications (WAIC) is an emerging standard to migrate regulatory and safety-related applications from wired networks to wireless means in next generation aircraft. Removing most of the cables from the fuselage will benefit to the overall efficiency of aircraft. On the other hand, it is a difficult task to achieve the Quality of Service (QoS) performance of wired networks by wireless technologies. Also, the Radio Altimeter (RA) interference in the same spectrum is another obstacle to overcome. Current Long Term Evolution (LTE) and emerging Fifth Generation (5G) technologies advertise promising specifications that can meet the requirements of WAIC networks. Therefore, the goal of this study is to evaluate the feasibility of supporting high data rate WAIC applications with LTE/5G by means of analytical and experimental studies. Measurements conducted in unoccupied mockup cabin and outside environment show that at least one cellular technology can meet the requirements of high data rate WAIC classes in the absence of RA interference. In coupling scenarios, robustness strategies should be considered to improve the network resilience. Finally, a network architecture based on the experimental results is presented to show an example usage scenario of a high data rate WAIC network.

Industrial control systems are foreseen to operate over hybrid wired/wireless networks. While the controller will be deployed in the wired network, sensors and actuators will be deployed in a wireless sensor network (WSN). To support QoS for control systems, an end-to-end delay bound and a target reliability must be provided in both wireless and wired domains. However, for industrial WSNs, guaranteeing reliability is a challenging task because of low-power communications and the harsh wireless environment. In this work, we present the first QoS framework for arbitrary hybrid wired/wireless networks, which guarantees that the delay bound and the target reliability of each application are provided. As part of this framework, we propose the first reliability-based scheduler for WSN able to achieve a target reliability in the presence of dynamic interference. Simulations of the proposed scheduler prove its suitability in different interference scenarios and motivate further work.

Guaranteeing reliability in highly interfered environments is a challenging requirement of current and future wireless applications. A promising state-of-the-art solution for low-power wireless technologies, e.g., wireless sensor networks (WSNs), is frequency hopping aided with black- and white-listing of channels. Both methods, although increase reliability, sacrifice frequency resources. Extensive measurements of channels' packet drop probabilities show that interfered channels are not fully blocked. Motivated by this discovery, we propose the whitening - a methodology for reliable hopping sequence design without resource sacrifice. We model the efficiency of interfered ISM band channels, and study the gains and trade-offs of applying whitening in different scenarios. Application reliability is achieved by granting re-transmissions within a time deadline. Simulations and measurements, performed on the exemplary use case of Time Slotted Channel Hopping WSNs, show that the proposed methods outperform state-of-the-art solutions in the presence of interference in terms of reliability.