Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: A wide variety of design methodologies exist in literature and the methodologies employed may differ among companies and even among design teams. Therefore a software tool, called DiDeas II, is being developed for the early phases of mechanical engineering design. DiDeas II is customisable to accommodate various design methodologies. An approach for customisability which allows the user interface and data structure to be customised without changing the source code has been implemented in previous developments via an approach combining ontology and conceptual graphs. This approach is expanded in this thesis to allow for the implementation of various design methodologies through the use of tables for the display of information with inheritance of data among these tables. During groupwork, communication is both asynchronous and synchronous. DiDeas II has been developed in this thesis to facilitate and capture both asynchronous and synchronous communication between team members. Capturing such communications has the potential to provide insight into design decisions. The communication functionality was assessed in case studies in an academic environment. DiDeas II proved to be effective at recording “soft” information during design and placing the information into context for future reference. The degree to which DiDeas II could be customised to suit the design process at different companies was assessed through discussions with engineers in industry. These discussions showed that it was possible to customise DiDeas II according to the design processes followed by the participants. / AFRIKAANSE OPSOMMING: „n Wye verskeidenheid ontwerpsmetodologieë bestaan in die literatuur en die metodologieë wat gebruik word kan tussen maatskappye en selfs tussen ontwerpspanne verskil. Daarom word „n sagteware-hulpmiddel, genaamd DiDeas II, ontwikkel vir die vroeë fases van meganiese ingenieursontwerp. DiDeas II is pasbaar om voorsiening te maak vir verskeie ontwerpsmetodologieë. „n Benadering vir pasbaarheid wat toelaat dat die gebruikerskoppelvlak en datastruktuur aangepas kan word sonder om veranderings aan die bron-kode te maak, is geïmplementeer in vorige ontwikkelings deur „n benadering wat ontologie en konseptuele grafieke kombineer. Hierdie benadering is in hierdie tesis uitgebrei om voorsiening te maak vir die implementering van verskeie ontwerpsmetodologieë d.m.v. tabelle vir die vertoon van informasie, met data wat “oorgeërf” word tussen hierdie tabelle. Kommunikasie is beide asinkroon en sinkroon tydens groepwerk. DiDeas II is in hierdie tesis verder ontwikkel om beide asinkrone en sinkrone kommunikasie metodes te bemiddel en daarvan rekord te hou. Die rekordhouding van sulke kommunikasie het die potensiaal om insig te bied aangaande ontwerpbesluite. Die kommunikasie funksionaliteit is geassesseer in gevallestudies in „n akademiese omgewing. DiDeas II was effektief in die rekordhouding van “sagte” informasie tydens ontwerp, sowel as om sulke informasie binne konteks te plaas vir latere verwysing. Die mate waartoe DiDeas II aangepas kan word om voorsiening te maak vir die ontwerpsprosesse van verskillende maatskappye, is geassesseer deur gesprekke met ingenieurs in industrie. Hierdie gesprekke het getoon dat dit moontlik is om DiDeas II aan te pas volgens die ontwerpsprosesse wat die deelnemers gebruik.

Sensors are used to monitor and control the physical environment. A Wireless Sen- sor Network (WSN) is composed of a large number of sensor nodes that are densely deployed either inside the phenomenon or very close to it [18][5]. Sensor nodes measure various parameters of the environment and transmit data collected to one or more sinks, using hop-by-hop communication. Once a sink receives sensed data, it processes and forwards it to the users. Sensors are usually battery powered and it is hard to recharge them. It will take a limited time before they deplete their energy and become unfunctional. Optimizing energy consumption to prolong network lifetime is an important issue in wireless sensor networks. In mobile sensor networks, sensors can self-propel via springs [14], wheels [20], or they can be attached to transporters, such as robots [20] and vehicles [36]. In static sensor networks with uniform deployment (uniform density), sensors closest to the sink will die first, which will cause uneven energy consumption and limitation of network life- time. In the dissertation, the nonuniform density is studied and analyzed so that the energy consumption within the monitored area is balanced and the network lifetime is prolonged. Several mechanisms are proposed to relocate the sensors after the initial deployment to achieve the desired density while minimizing the total moving cost. Using mobile relays for data gathering is another energy efficient approach. Mobile sensors can be used as ferries, which carry data to the sink for static sensors so that expensive multi-hop communication and long distance communication are reduced. In this thesis, we propose a mobile relay based routing protocol that considers both energy efficiency and data delivery delay. It can be applied to both event-based reporting and periodical report applications. / Another mechanism used to prolong network lifetime is sensor scheduling. One of the major components that consume energy is the radio. One method to conserve energy is to put sensors to sleep mode when they are not actively participating in sensing or data relaying. This dissertation studies sensor scheduling mechanisms for composite event detection. It chooses a set of active sensors to perform sensing and data relaying, and all other sensors go to sleep to save energy. After some time, another set of active sensors is chosen. Thus sensors work alternatively to prolong network lifetime. / by Yinying Yang. / Vita. / Thesis (Ph.D.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Future wireless networks will be required to support multimedia traffic in addition to traditional best-effort network services. Supporting multimedia traffic on wired networks presents a large number of design problems, particularly for networks that run connectionless data transport protocols such as the TCP/IP protocol suite. These problems are magnified for wireless links, as the quality of such links varies widely and uncontrollably. This dissertation presents new tools developed for the design and realization of wireless networks including, for the first time, analytical channel models for predicting the efficacy of error control codes, interleaving schemes, and signalling protocols, and several novel algorithms for matching and adapting system parameters (such as error control and frame length) to time-varying channels and Quality of Service (QoS) requirements.

Wireless communication is witnessing tremendous growth with the proliferation of various standards covering wide, local, and personal area networks, which operate at different frequency bands. Future wireless terminals will not only need to support multiple standards, but also need to be multi-functional to keep pace with the demands of the consumers. For such an implementation, the local oscillator (LO) turns out to be the bottleneck, which must exhibit frequency agility by generating a very wide range of carrier frequencies in order to access all the specified communication standards. This dissertation presents various design techniques to realize compact low-cost low-power and broadband oscillators in silicon-based technologies. The two most suitable techniques for broadband signal generation: (1) Use of widely tunable active inductor, and (2) Use of switched resonator have been thoroughly evaluated. A fully reconfigurable active inductor with a widely tunable feedback resistor has been proposed. Using the proposed tunable active inductor in a VCO generates frequency tuning ranges higher than 100%, and helps achieve the highest PFTN Figure-of-Merit among Si-based active inductor VCOs reported in literature till date. The large-signal non-linearity of the active inductor has been utilized to develop the first reported broadband harmonic active inductor-based VCO. The degradation of phase noise due to active inductors is partially solved by a noise optimization guideline for active inductors. Utilizing the low saturation voltage of HBT technologies and high-Q short line inductors seems to be very useful to reduce power consumption of cross-coupled VCOs while achieving low phase noise performance simultaneously.

In this thesis, we investigate cooperation by applying OFDM signals to cooperative relay networks. We consider the single path relay network and the multiple path relay network. Using the amplify-and-forward relay algorithm, we derive the input-output relations and mutual informations of both networks. Using a power constraint at each relay, we consider two relay power allocation schemes. The first is constant gain allocation, where the amplifying gain used in the amplify-and-forward algorithm is constant for all subcarriers. The second is equal power allocation, where each subcarrier transmits the same power. The former scheme does not require CSI (channel state information), while the latter one does. We simulate the mutual informations using the two relay power allocation schemes. Results indicate that equal power allocation gives a slightly higher mutual information for the single path relay network. For the multiple path network, the mutual information is practically the same for both schemes. Using the decode-and-forward relay algorithm, we derive the input-output relations for both networks. The transmitter and each relay are assumed to have uniform power distributions in this case. We simulate the BER (bit error rate) and WER (word error rate) performance for the two networks using both the amplify-and-forward and decode-and-forward relay algorithms. For the single path relay network, amplify-and-forward gives very poor performance, because as we increase the distance between the transmitter and receiver (and thus, add more relays), more noise and channel distortion enter the system. Decode-and-forward gives significantly better performance because noise and channel distortion are eliminated at each relay. For the multiple path relay network, decode-and-forward again gives better performance than amplify-and-forward. However, the performance gains are small compared to the single path relay network case. Therefore, amplify-and-forward may be a more attractive choice due to its lower complexity.

Graphic Design is one part of the producer services sector of the modern metropolitan region. It is a sector that has experienced considerable development in terms of number of firms through demand created by the expansion of advertising and multi media. To date research has established that producer services, particularly finance related ones, agglomerate in the central city to take advantage of the agglomeration economies available in large metropolitan areas. This thesis argues that one of the key factors for the agglomeration of graphic design is the need for face-to-face communication with clients and other firms. There has been some work undertaken looking at the location of non-finance producer services, such as design, although these have been presented as snapshots at a point in time.This thesis extends this understanding through an analysis of agglomerations of graphic design firms over a twenty year time horizon. Using details of firm location in Melbourne every five years from 1981 to 2001 the thesis uses a geospatial analytical technique to identify agglomerations and explores the change in the size, location and density of agglomerations of firms. This research shows that the initial agglomeration of 1981 was still present by 2001 and had been joined by a number of new agglomerations ringing the Melbourne CBD while at the same time there has also been a dispersal of firms to the middle suburbs. In order to provide some insight in to the agglomeration of graphic design firms this research also examines the geography of two industries allied to graphic design: advertising and printing. This research shows that graphic designers and advertising agencies tend to locate in similar parts of inner Melbourne which may be due to the need for face-to-face contact between fims in these two industries. (For complete abstract open document)

Vision based technology such as motion detection has long been limited to the domain of powerful processor intensive systems such as desktop PCs and specialist hardware solutions. With the advent of much faster mobile phone processors and memory, a plethora of feature rich software and hardware is being deployed onto the mobile platform, most notably onto high powered devices called smart phones. Interaction interfaces such as touchscreens allow for improved usability but obscure the phone’s screen. Since the majority of smart phones are equipped with cameras, it has become feasible to combine their powerful processors, large memory capacity and the camera to support new ways of interacting with the phone which do not obscure the screen. However, it is not clear whether or not these processor intensive visual interactions can in fact be run at an acceptable speed on current mobile handsets or whether they will offer the user a better experience than the current number pad and direction keys present on the majority of mobile phones. A vision based finger interaction technique is proposed which uses the back of device camera to track the user’s finger. This allows the user to interact with the mobile phone with mouse based movements, gestures and steering based interactions. A simple colour thresholding algorithm was implemented in Java, Python and C++. Various benchmarks and tests conducted on a Nokia N95 smart phone revealed that on current hardware and with current programming environments only native C++ yields results plausible for real time interactions (a key requirement for vision based interactions). It is also shown that different lighting levels and background environments affects the accuracy of the system with background and finger contrast playing a large role. Finally a user study was conducted to ascertain the overall user’s satisfaction between keypad interactions and the finger interaction techniques concluding that the new finger interaction technique is well suited to steering based interactions and in time, mouse style movements. Simple navigation is better suited to the directional keypad.

This work describes the process of the design of a flight software for a space-qualified device, outlines the development and testing of the SW, and provides a description of the final product. The flight software described in this work has been developed for the project Demise Observation Capsule (DOC). DOC is a device planned to be attached to an upper stage of a launch vehicle and observe its demise during atmospheric re-entry at the end of its mission. Due to constraint on communication time during the mission and the need to maximize the amount of transferred data, a custom communication protocol has been developed. / Demise Observation Capsule

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 Publications

Digital communication through communication platforms has increased and changed significantly during the last decade and recently not least because of the corona pandemic, which has shifted many face-to-face activities to the internet (Obringer R. , et al., 2021). This paper firstly contains a quantitative survey study that investigates human behaviour and their experience on digital communication platforms with a focus on media transfer of photos and videos. Afterwards, the data sizes of various media after transfers through diverse communication platforms are explored in an experiment. This is followed by the development of a prototype in which sustainable design is implemented and aim to nudge the user to more sustainable-friendly digital behaviour relating data transfers of media and the settings of a communication platform. Finally, the prototype undergoes usability testing through which the user experience and positive environmental impact is evaluated. The findings reveal that the implementation of sustainability-focused nudges, features and design within a communication platform can lead users to more sustainable decisions in one or more areas of the platform and thus improve its environmental footprint.