Drahtlose Kommunikationssysteme dringen in immer mehr Anwendungsbereiche vor. Für einige Anwendungsszenarien, wie etwa die Prozessautomatisierung in Fabriken und Industrieanlagen, ist die Zuverlässigkeit vieler drahtloser Kommunikationssysteme wie IEEE 802.11 (WLAN) oder Bluetooth aber noch unzureichend. Daher wurden für diese Anwendungsbereiche spezielle Kommunikationssysteme wie WirelessHART oder ISA 100.11a entwickelt. Diese basieren meist auf Time Division Multiple Access (TDMA) und erreichen durch exklusive Reservierungen deterministische Zuverlässigkeit, falls kein anderes Kommunikationssystem die genutzten Kanäle stört. Diese Arbeit behandelt geeignete Protokolle und Algorithmen, um die Zuverlässigkeit drahtloser Kommunikationssysteme zu verbessern. Im ersten Teil der Arbeit werden Verfahren für TDMA-basierte Kommunikationssysteme betrachtet. Basierend auf IEEE 802.15.4 werden mehrere Funktionalitäten für ProNet 4.0, einem an der Arbeitsgruppe Vernetzte Systeme der TU Kaiserslautern entwickelten Kommunikations-Stack für Industrie 4.0, entworfen und auf Imote 2 Sensorknoten implementiert. Zuverlässige Kommunikation bedarf Kenntnis von sowohl der Kommunikationstopologie, über die Knoten miteinander kommunizieren können, als auch der Interferenztopologie, die angibt, wie Knoten sich gegenseitig stören können. Dazu stellt die Arbeit mit dem Automatic Topology Discovery Protocol (ATDP) ein Verfahren zur automatischen Topologieerkennung vor. Anschließend wird QoS Multicast Routing betrachtet und mit dem QoS Multicast Routing Protocol (QMRP) ein Verfahren für partiell mobile Netzwerke entwickelt. Weiterhin wird mit ProMid eine Kommunikations-Middleware beschrieben, die ein hohes Abstraktionslevel aufweist und die darunter liegenden Schichten steuert. Die dienstorientierte Architektur nutzt eine verteilte Service Registry, wobei die Auswahl der Registry-Knoten anhand eines dafür entwickelten Clustering-Algorithmus erfolgt. Das Heterogeneous Network Clustering (HNC) genannte Verfahren berücksichtigt ein heterogenes Netzwerkmodell mit Knoten, die Clusterhead bzw. Gateway werden müssen, können bzw. nicht dürfen. Der zweite Teil der Arbeit behandelt Protokolle und Algorithmen für zuverlässige wettbewerbsbasierte Kommunikationssysteme. Die in diesem Kapitel vorgestellten Verfahren sind in einem auf WLAN basierenden Kommunikations-Stack implementiert und evaluiert worden. Zunächst wird ein Verfahren für die Topologieerkennung in WLAN-Netzwerken vorgestellt. Anschließend wird ein auf dem Token Bucket-Mechanismus basierendes Verfahren zur Verkehrskontrolle entwickelt. Daraus wird mit der Unusable Wasted Bandwidth Ratio eine Metrik abgeleitet, die es erlaubt, die Auslastung des Mediums abzuschätzen. Aufbauend auf dem Verfahren zur Verkehrskontrolle wird eine kooperative faire Bandbreitenskalierung für WLAN vorgestellt. Das Verfahren verteilt die Bandbreite fair unter den internen Knoten unter Berücksichtigung der Quality of Service (QoS) Anforderungen. Dabei reagiert es dynamisch auf Änderungen des externen Verkehrs und verhindert so Überlastsituationen. Letztlich wird ein Clustering-Protokoll vorgestellt, welches durch das Anwendungsszenario der Überwachung von Güterzügen motiviert ist und Linientopologien bildet sowie dynamisch repariert. Das auf Bluetooth LE aufbauende Verfahren dient dazu, Energie einzusparen, und wurde in einer Kooperation mit der Bosch Engineering GmbH entwickelt.

Multidisciplinary optimizations (MDOs) encompass optimization problems that combine different disciplines into a single optimization with the aim of converging towards a design that simultaneously fulfills multiple criteria. For example, considering both fluid and structural disciplines to obtain a shape that is not only aerodynamically efficient, but also respects structural constraints. Combined with CAD-based parametrizations, the optimization produces an improved, manufacturable shape. For turbomachinery applications, this method has been successfully applied using gradient-free optimization methods such as genetic algorithms, surrogate modeling, and others. While such algorithms can be easily applied without access to the source code, the number of iterations to converge is dependent on the number of design parameters. This results in high computational costs and limited design spaces. A competitive alternative is offered by gradient-based optimization algorithms combined with adjoint methods, where the computational complexity of the gradient calculation is no longer dependent on the number of design parameters, but rather on the number of outputs. Such methods have been extensively used in single-disciplinary aerodynamic optimizations using adjoint fluid solvers and CAD parametrizations. However, CAD-based MDOs leveraging adjoint methods are just beginning to emerge. This thesis contributes to this field of research by setting up a CAD-based adjoint MDO framework for turbomachinery design using both fluid and structural disciplines. To achieve this, the von Kármán Institute’s existing CAD-based optimization framework cado is augmented by the development of a FEM-based structural solver which has been differentiated using the algorithmic differentiation tool CoDiPack of TU Kaiserslautern. While most of the code could be differentiated in a black-box fashion, special treatment is required for the iterative linear and eigenvalue solvers to ensure accuracy and reduce memory consumption. As a result, the solver has the capability of computing both stress and vibration gradients at a cost independent on the number of design parameters. For the presented application case of a radial turbine optimization, the full gradient calculation has a computational cost of approximately 3.14 times the cost of a primal run and the peak memory usage of approximately 2.76 times that of a primal run. The FEM code leverages object-oriented design such that the same base structure can be reused for different purposes with minimal re-differentiation. This is demonstrated by considering a composite material test case where the gradients could be easily calculated with respect to an extended design space that includes material properties. Additionally, the structural solver is reused within a CAD-based mesh deformation, which propagates the structural FEM mesh gradients through to the CAD parameters. This closes the link between the CAD shape and FEM mesh. Finally, the MDO framework is applied by optimizing the aerodynamic efficiency of a radial turbine while respecting structural constraints.

Scaling up conventional processor architectures cannot translate the ever-increasing number of transistors into comparable application performance. Although the trend is to shift from single-core to multi-core architectures, utilizing these multiple cores is not a trivial task for many applications due to thread synchronization and weak memory consistency issues. This is especially true for applications in real-time embedded systems since timing analysis becomes more complicated due to contention on shared resources. One inherent reason for the limited use of instruction-level parallelism (ILP) by conventional processors is the use of registers. Therefore, some recent processors bypass register usage by directly communicating values from producer processing units to consumer processing units. In widely used superscalar processors, this direct instruction communication is organized by hardware at runtime, adversely affecting its scalability. The exposed datapath architectures provide a scalable alternative by allowing compilers to move values directly from output ports to the input ports of processing units. Though exposed datapath architectures have already been studied in great detail, they still use registers for executing programs, thus limiting the amount of ILP they can exploit. This limitation stems from a drawback in their execution paradigm, code generator, or both. This thesis considers a novel exposed datapath architecture named Synchronous Control Asynchronous Dataflow (SCAD) that follows a hybrid control-flow dataflow execution paradigm. The SCAD architecture employs first-in-first-out (FIFO) buffers at the output and input ports of processing units. It is programmed by move instructions that transport values from the head of output buffers to the tail of input buffers. Thus, direct instruction communication is facilitated by the architecture. The processing unit triggers the execution of an operation when operand values are available at the heads of its input buffers. We propose a code generation technique for SCAD processors inspired by classical queue machines that completely eliminates the use of registers. On this basis, we first generate optimal code by using satisfiability (SAT) solvers after establishing that optimal code generation is hard. Heuristics based on a novel buffer interference analysis are then developed to compile larger programs. The experimental results demonstrate the efficacy of the execution paradigm of SCAD using our queue-oriented code generation technique.

In today’s computer networks we see an ongoing trend towards wireless communication technologies, such as Wireless LAN, Bluetooth, ZigBee and cellular networks. As the electromagnetic spectrum usable for wireless communication is finite and largely allocated for exclusive use by respective license holders, there are only few frequency bands left for general, i.e. unlicensed, use. Subsequently, it becomes apparent, that there will be an overload situation in the unlicensed bands, up to a point where no communication is possible anymore. On the other hand, it has been observed that licensed frequency bands often go unused, at least at some places or over time. Mitola combined both observations and found the term Cognitive Radio Networks [Mit00], denoting a solution for spectrum scarcity. In this concept, so called Secondary Users are allowed to also use licensed bands (attributed to a Primary User) as long as it is vacant. In such networks, all obligations reside with Secondary Users, especially, they must avoid any interference with the Primary User. They must therefore reliably sense the presence of Primary Users and must decide which available spectrum to use. These two functionalities are called Spectrum Sensing and Spectrum Mobility and describe 2 out of 4 core functionalities of Cognitive Radio Networks and are considered in this thesis. Regarding Spectrum Sensing, we present our own approach for energy detection in this thesis. Energy detection essentially works by comparing measured energy levels to a threshold. The inherent problem is on how to find such thresholds. Based on existing work we found in literature, we improve techniques and assert the effectiveness of our additions by conducting real world experiments. Regarding Spectrum Mobility, we concentrate on the point, where the Primary User shows up. At this point, nodes must not use the current channel anymore, i.e. they also have no possibility to agree on another channel to switch to. We solve this problem by employing channel switching, i.e. we change channels proactively, following a schedule shared by all nodes of the network. The main contribution of this thesis is on how to synthesize those schedules to guarantee robust operation under changing conditions. For integration, we considered three dimensions of robustness (of time, of space and of channel) and, based on our algorithms and findings, defined a network protocol, which addresses perturbation within those dimensions. In an evaluation, we showed that the protocol is actually able to maintain robust operation, even if there are large drops in channel quality.

In the avionics domain, “ultra-reliability” refers to the practice of ensuring quantifiably negligible residual failure rates in the presence of transient and permanent hardware faults. If autonomous Cyber- Physical Systems (CPS) in other domains, e.g., autonomous vehicles, drones, and industrial automation systems, are to permeate our everyday life in the not so distant future, then they also need to become ultra-reliable. However, the rigorous reliability engineering and analysis practices used in the avionics domain are expensive and time consuming, and cannot be transferred to most other CPS domains. The increasing adoption of faster and cheaper, but less reliable, Commercial Off-The-Shelf (COTS) hardware is also an impediment in this regard. Motivated by the goal of ultra-reliable CPS, this dissertation shows how to soundly analyze the reliability of COTS-based implementations of actively replicated Networked Control Systems (NCSs)—which are key building blocks of modern CPS—in the presence of transient hard- ware faults. When an NCS is deployed over field buses such as the Controller Area Network (CAN), transient faults are known to cause host crashes, network retransmissions, and incorrect computations. In addition, when an NCS is deployed over point-to-point networks such as Ethernet, even Byzantine errors (i.e., inconsistent broadcast transmissions) are possible. The analyses proposed in this dissertation account for NCS failures due to each of these error categories, and consider NCS failures in both time and value domains. The analyses are also provably free of reliability anomalies. Such anomalies are problematic because they can result in unsound failure rate estimates, which might lead us to believe that a system is safer than it actually is. Specifically, this dissertation makes four main contributions. (1) To reduce the failure rate of NCSs in the presence of Byzantine errors, we present a hard real-time design of a Byzantine Fault Tolerance (BFT) protocol for Ethernet-based systems. (2) We then propose a quantitative reliability analysis of the presented design in the presence of transient faults. (3) Next, we propose a similar analysis to upper-bound the failure probability of an actively replicated CAN-based NCS. (4) Finally, to upper-bound the long-term failure rate of the NCS more accurately, we propose analyses that take into account the temporal robustness properties of an NCS expressed as weakly-hard constraints. By design, our analyses can be applied in the context of full-system analyses. For instance, to certify a system consisting of multiple actively replicated NCSs deployed over a BFT atomic broadcast layer, the upper bounds on the failure rates of each NCS and the atomic broadcast layer can be composed using the sum-of-failure-rates model.