To Örebro University

Scheduling theory generally assumes that real-time systems are mostly composed of activities with hard real-time requirements. Many systems are built today by composing different applications or components in the same system, leading to a mixture of many different kinds of requirements with small parts of the system having hard real-time requirements and other larger parts with requirements for more flexible scheduling and for quality of service. Hard real-time scheduling techniques are extremely pessimistic for the latter part of the application, and consequently it is necessary to use techniques that let the system resources be fully utilized to achieve the highest possible quality. This paper presents a framework for a scheduling architecture that provides the ability to compose several applications or components into the system, and to flexibly schedule the available resources while guaranteeing hard real-time requirements. The framework (called FSF) is independent of the underlying implementation, and can run on different underlying scheduling strategies. It is based on establishing service contracts that represent the complex and flexible requirements of the applications, and which are managed by the underlying system to provide the required level of service.

Time triggered methods provide deterministic behaviour suitable for critical real-time systems. The), perform less favourably, however if the arrival times of some activities are not known in advance, in particular if overload situations have to be anticipated. In many systems, the criticality of only a subset of activities justify the cost associated with the time triggered methods.

In this paper we consider distributed systems where a subset of critical activities are handled in a time triggered fashion, via an offline schedule. At runtime, the arrival of aperiodic tasks may cause overload that demands to be handled in such a way that i) time triggered activities still meet all their original constraints, ii) execution of high-valued tasks are prioritised over tasks with lower value, iii) tasks can be quickly migrated to balance the overall system load.

We give a precise formulation of overload detection and value based task rejection in the presence of offline scheduled tasks, and present a heuristic algorithm to handle overload. To benefit from the distributed setting, the overload handling includes an algorithm that integrates migration of rejected tasks with resource reclaiming and an acceptance test of newly arrived tasks.

Simulation results underline the effectiveness of the presented approach.

Trends like Internet of Things (IoT), 5G and Cloud are pushing for device connectivity to the Internet, which affects industrial embedded systems with e.g., an increase in code base and functionality. Due to different application requirements, there are relative little reuse between embedded systems with different run-time context (from super loop to multi-threaded), and different types of communication (best effort and real time). In order to improve code reuse and changeability, we propose a flexible communication stack design, that can be configured for time sensitive communication with a real-time operating system (RTOS), or configured for best effort communication with either a super loop or an operating system (OS). Experiments demonstrate the flexibility and simplicity of the design with different configurations, e.g., super loop, single threaded, multi-threaded. Measurements show that the variations in performance related to run-time context scales as expected.

A trend in the industrial domain is that the networks are growing and becoming more complex, this is further accelerated by the digitalization trend. In order to address this, there is a need to improve the efficiency when moving between the R&D phases. For example, integrate innovative research findings into industrial systems, shorten time to market, improve product quality and reduce the number of issues. Despite a huge research effort on network simulators and emulators there are still some issues that needs to be addressed. This paper presents challenges that needs to be resolved, in order for the industry to adopt and benefit from using network simulators and emulators. The major challenges streamlining the workflow in and between the different R&D phases while preserving the real-time aspects in the entire industrial distributed control system.

Trends like the Cloud, Internet of Things and 5G are pushing for an increase in connectivity, but, introducing a new type of network in an industrial distributed control system is a big investment with high risks. Time to market with sufficient quality is crucial. However, when getting through the Research and Development (R&D) phases, a lot of time is spent on isolated activates, e.g., simulations, collecting requirements, design, coding, debugging, creating testbeds, and performing various tests. Therefore, there is a need to improve efficiency when moving between the R&D phases. For verification and validation of communication software, the most common network evaluation method in industry are real testbeds, mostly since a testbed can be very similar to the deployed system. Testbeds are, however, hard to debug and costly to maintain. Other network evaluation methods like simulators, have some strengths that testbeds are lacking, like repeatability, control over the network, and lower cost. However, code from simulators can seldom be reused, especially in industrial time-sensitive target systems, due to different abstraction levels, run-time behavior and system timing. This paper presents findings from a case study that targets improved efficiency, getting from research theories, to deployed devices in a homogeneous Industrial Wireless Sensor and Actuator Network (IWSAN). We propose a small subset of network simulators features which eases changeability, reuse, and debugging of communication software. The selected simulator features are evaluated with a proof of concept implementation that is customized to a research platform. The findings indicate improved efficiency when moving back and forth between activities in different R&D phases.

Functionality for various services of scheduling algorithms is typically provided as extensions to a basic paradigm, intertwined in the kernel architecture. Thus, scheduling services come in packages around single paradigms, fixed to a certain methodology and kernel architecture. Temporal constraints of applications are addressed by a combination of scheduler and system architecture. Consequently, changing system architecture results in a complete rescheduling of all tasks, calling for a new cycle of analysis and testing from scratch, although a schedule meeting all temporal constraints already existed.

We propose a component based architecture for schedule reuse. Instead of tying temporal constraints, scheduler, and system architecture together, we provide methods which allow for the reuse of existing schedules on various system architectures. In particular, we show how a schedule developed for table driven, dynamic or static priority paradigm can be reused in the other schemes.

We address an architecture to disentangle actual scheduling from dispatching and other kernel routines with a small interface, suited for a variety of scheduling schemes as components.

The invention is a method for communication between a wireless device node in a wireless sensor network (WSN) and control apparatus or control processes of an industrial control system (ICS). The wireless network includes a plurality of device nodes and at least one gateway (GW). The method comprises receiving at a gateway an aggregated data packet (ADP) for a final address in the ICS. The gateway processes the data packet, detects that it is an aggregated data packet and reconstructs the original data packets contained therein. The gateway then sends each of the original data packets as standard data packets to the intended final address in the ICS. In other aspects of the invention a method, system and a computer program for carrying out the method are described.

With the growing interest in adoption of wireless technologies in industrial automation and the continuous search for new revenue streams new players are entering the arena in order to make their business grow further. One of the emerging wireless technologies aiming to support industrial automation applications is 5G, targeting anything from extreme throughput (> 10 Gbit/s) to extreme low latency (≤ 1 ms) to ultra high reliability (≥ 99.999%). In this article we intend to discuss the potential and challenges of adopting 5G in real industrial environments and give a more balanced picture compared to previous articles mainly written by telecom researchers and vendors as a way to promote their technology. Specifically, this article will discuss and provide some real industrial requirements, describe the main technical features of 5G and try to assess what applications it will support that are not by already supported by existing technologies. In the end, the success of 5G will depend on appealing business models and scalability, i.e., whether or not the same equipment can be deployed worldwide without any changes and spectrum rules, and the migration paths beyond 5G for reasonable business risks.

Communication blackout is one of the most serious pitfalls of Wireless Sensor Networks (WSN) in industrial automation context. The industrial radio channel exhibits pronounced effects of multipath fading and wireless LAN (WLAN) interference that can potentially lead to temporary communication failures, as well as complete isolation of network devices. The current IWSN standards adopt known countermeasures to cope with the harshness of the radio channel, but they lack solutions specifically oriented to detect blackouts and self-recover the communication fulfilling hard deadline constraints. In this work we focus on the problem of blackout detection with specific interest for the WirelessHART standard, introducing a Blackout Detection Service (BDS) expressly addressed to multi-hop periodic communication with sensors and actuators. The BDS monitors end-to-end acknowledgement messages and builds specific metrics to promptly identify communication outages, enabling three criticality classes. The algorithm is tested in the ns-2 network simulator and results show that the proposed system is able to detect blackout events with reaction delays of the order of 4-5 times the refresh rate of nodes and to discriminate between small and temporary network issues and serious blackout scenarios, opening the field for recovery strategies.

Inom en nära framtid kommer så kallade digitala underhållningssystem att bli mer och mer populära i hemmen. En stor fördel med dessa system är att apparaterna, t.ex. TVn, DVDn, digital boxen, och datorn, kommer att kunna kopplas ihop trådlöst, vilket gör det möjligt att slippa sladdar mellan dem.Detta innebär också att flera apparater (TVn, PCn, eller mobiltelefonen) kommer att ha möjlighet att spela upp en DVD film som sitter i DVD spelaren, oavsett vart i huset apparaterna finns. Det blir till och med möjligt att flytta de mobila apparaterna medans filmen spelas upp, t.ex. kan man gå runt i huset samtidigt som man tittar på filmen på en liten handdator eller mobiltelefon. Detta är inte möjligt idag eftersom man kopplar en sladd direkt mellan DVD spelaren och TVn.

De digitala underhållningssytemen måste klara av att hantera både ljud (musik) och bild (film) på ett sätt som är tillfredställande för den som använder systemet, d.v.s, kvaliteten på ljudet som spelas upp eller bilden som visas måste vara minst lika bra som den är idag.

Detta kommer att ställa höga krav på apparaterna, som måste hålla de kvalitetskrav som ljud (musik) och bildströmmar (film) har. Tack vare flexibiliteten, d.v.s, möjligheten att ha mobila apparater, i dessa system, och kraven på systemen, uppstår nya problem som inte funnits innan. T.ex. så har inte handdatorer eller mobiltelefoner den tekniska möjligheten att spela upp en DVD film med samma kvalitet som på en TV. Ett annat problem är den varierande kapaciteten i det trådlösa nätverket som knyter samman alla apparater. På grund av att nätverket är väldigt känsligt för störningar (t.ex. från mikrovågsugnar) så varierar kapaciteten för nätverket hela tiden, något som inte är fallet när man har ett nätverk med sladdar. Detta leder till problem med den trådlösa överföringen mellan olika apparater. Eftersom en DVD film kräver en hel del kapacitet från nätverket, och man inte kan vara säker på vad som finns tillgängligt så vet man inte om överföringen av filmen kommer att gå bra.

I vår forskning presenterar vi två olika sätt att hantera problemen med olika apparaters tekniska begränsningar och det trådlösa nätverkets varierande kapacitet. För att hantera problemet med olika apparater och dess varierande tekniska möjligheter så har vi tagit fram metoder som möjliggör för oss att anpassa uppgifterna (t.ex. spela musik eller film) som utförs på apparaten beroende på den tekniska kapaciteten de har. Vi föreslår även en metod där vi mäter hur mycket kapacitet som det finns tillgängligt i det trådlösa nätverket. Eftersom kapaciteten på nätverket varierar repeterar vi mätningen med jämna mellanrum så att vi hela tiden har en aktuell bild av vad som finns tillgängligt. Vi använder sedan den informationen för att anpassa det som skall överföras (musik eller film) för att hela tiden göra det bästa möjliga av situationen.

The Internet of Things (IoT) is captivating the society because of its potential to rapidly transform businesses and people’s lives. It is widely believed that IoT will also transform the industrial automation business in terms of improved productivity, less cost, flexibility, and increased revenues. Hence, there are some challenges that needs to be addressed when IoT is introduced to the industrial automation domain. This paperaims to present realistic requirements and highlights identified challenges such as security, interoperability, deterministic and low latency communication, and how the required availability (uptime) can be kept. Moreover, the paper also point out the need of standardization and sustainable business models. The conclusion is that introducing IoT devices and connecting them directly to cloud services is not straightforward for process automation.

Industrial wireless sensor and actuator networks are gaining momentum and have started to target new and more demanding application scenarios extending pure monitoring scenarios. In this paper we discuss the needs for simple and more accurate TDMA timing synchronization to enable the future applications. We present a novel TDMA timing synchronization protocol which is simple to implement, as well as a performance evaluation using of-the-shelf hardware indicating measured worst case synchronization errors less than 10 microseconds at five hops from the synchronization master. The paper shows that it is possible to realize synchronization on average around 1 microsecond with little effort and negligible computational or network overhead.

Wireless sensor networks are becoming more and more adopted into industrial plants and Wireless HART is the first wireless sensor network standard to emerge, which specifically is designed to support the specific requirements posed by the industry. Automation industry requires wireless sensor network devices to have a very long lifetime, often up to 5 - 10 years without a battery change. This puts requirements on how the wireless sensor network technology should be designed to minimize energy consumption while still fulfilling the application requirements. Packet aggregation is an essential technique in mission critical wireless sensor networks for achieving effective transmission and hence better power conservation.

In this article we propose a flexible packet aggregation scheme for Wireless HART which reduces energy consumption of each device. The proposed scheme only requires a minor change to the Wireless HART standard but still preserves the end-to-end security and retains backward compatibility with non aggregating devices. We show by calculations that our proposed packet aggregation solution reduces energy consumption for a network by up to 50%, which will result in a significant increase in lifetime of Wireless HART devices.

Testing in realistic environments is often overlooked in the early development of new technology. This paper describes a test to evaluate the whole chain from an accelerometer mounted on a motor to a sensor node sending wireless data to an access point. A pilot gives a great opportunity to get input from end-users (which could be very useful at the initial stages of a project), and provide potential contacts for next pilots.

The goal of the pilot was to get a better understanding of the targeted environment and possible interference It may also lead to the discovery of issues not yet thought of, issues important for the resulting design of the end product.

Wireless communication has gained more interest in industrial automation due to flexibility, mobility, and cost reduction. Wireless systems, in general, require additional and different engineering and maintenance tasks, for example cryptographic key management. This is an important aspect that needs to be addressed before wireless systems can be deployed and maintained efficiently in the industry. In this paper, we take an holistic approach that addresses safety and security regardless of the underlying media. In our proposed framework we introduce security modules which can be retrofitted to provide end-to-end integrity and authentication measures by utilizing the black channel concept. With the proposed approach, we can extend and provide end-to-end security as well as functional safety using existing automation equipment and standards, such as Profisafe, Profinet IO, and WirelessHART. Furthermore, we improve the WirelessHART standard with periodic and deterministic downlink transmissions to enable efficient usage of wireless actuators, as well as improving the performance of functional safety protocols.

In this paper we describe a method to integrate WirelessHART networks in Distributed Control Systems (DCS)using PROFINET IO. By modeling the WirelessHART network in the Generic Station Description file, that describes a PROFINET IO device, the WirelessHART related configuration can be distributed from the central engineering stations. In this way, both process controller configuration and WirelessHART network configuration is engineered and maintained from a central location. Thus the end-user do not need any additional tool-specific training, as the existing tools are used to engineer the WirelessHART networks. We base the method of integration on the keywords simple deployment and maintenance, and flexible topology. A proof-of-concept implementation of the proposed method shows that it is possible to download WirelessHART configuration both to the WirelessHART network managers, as well as the WirelessHART sensors. By integrating WirelessHART in this way, maintenance is greatly simplified as the actual configuration will be downloaded automatically by the DCS when faulty field devices are replaced.

Wireless sensor and actuator networks bring many benefits to industrial automation systems. However, unreliable wireless and multihop communications among sensors and actuators cause challenges in designing such systems. Wireless HART is the first standard for wireless real-time industrial applications. However, current Wireless HART standard does not provide services for efficient usage of actuators, which are an essential part of automation. In this paper we focus on Wireless HART and propose a periodic and deterministic downlink transmission functionality which enables efficient usage of actuators and control applications. Furthermore, we define new HART commands extending the interface, without affecting available services, to support the integration of actuators. This can be achieved with minor changes in the current standard.