Nowadays,wireless connectivity is ubiquitous: humans use smartphones, smartwatches, laptops and other devices, while at the same time, the Internet of Things (IoT) is adding millions of connected objects. This large number of devices uses mainly the radio frequency (RF) spectrumfor communication. And a direct consequence of this exponential growth is the scarcity of free RF bands to cope with this demand.

To tackle this challenge, researchers have proposed using a different carrier: visible light. With Visible Light Communications (VLC), devices communicate with each other by modulating the intensity of their light-emitting diodes (LEDs) and demodulating it using light sensors. The key advantage of VLC is the utilization of the visible light spectrum, with free bands that do not interfere with traditional RF systems. Nonetheless, despite the efficiency of LED technology, luminaries still require several Watts to generate light. The need for this considerable amount of energy has triggered interest in a new research area: Passive VLC. The fundamental principle of Passive VLC is to exploit ambient light to create wireless links, thus reducing the energy required by transmitters to generate their own light.

Passive VLC is a promising area, but poses a daring challenge: modulate light without any control over the source. The research community has proposed using optical surfaces that block or reflect light dynamically as modulators, but these platforms provide limited data rates, ranging froma few tens of bps to a few kbps. Moreover, using the sun as the source of ambient light introduces another challenge: variations in position and intensity.

This dissertation aims to improve the performance of Passive VLC systems operating with sunlight, with a particular focus on increasing the data rate and resilience to the changing sun’s position.

Our first contribution is a short-range wireless link using a tiny screen as a transmitter and a camera as a receiver. The screen is a reflective surface, adapted to work with ambient light. The sunlight reaching the screen is modulated to transmit information to a smartphone’s camera, creating a stream of optical data. This screen-to-camera link using sunlight attains up to 10 kbps, ten times faster than previous similar systems, working from sunrise to sunset - independent of the sun’s position.

Inspired by the concept of Li-Fi, which combines illumination and VLC, our second contribution envisions the creation of a natural light bulb with wireless communication capabilities. Our design combines optical modulators, optical filters and sunlight collectors to track the sun’s position during the day and radiate modulated beams of sunlight in indoor scenarios. These beams of natural light provide illumination and communication and are the first to divide sunlight into two color channels to double the data rate.

Our third contribution proposes a novel link for robots to communicate using sunlight. We leverage a material used in solar technology, the Luminescent Solar Concentrator (LSC). An LSC surface absorbs light fromits top and emits it on its edges. We place LSCs on top of robots, together with liquid crystal cells (LCs), so sunlight arriving from the top can be modulated into data packets transmitted toward the edges. This novel communication systemallows task coordination between robots using sunlight.

Overall, this dissertation presents new Passive VLC systems focusing on applications that exploit the sun as the light source. Within this scenario, our focus has been to increase the data rate, with the first two contributions, and on making the systems resilient to the sun’s position, with all three contributions.@en

Embedded real-time systems, essential in industries like automotive, aviation, and medical devices, increasingly rely on multi-core platforms for efficient parallel processing to meet rising computational demands. However, they face significant challenges with energy consumption, particularly in energy-constrained environments where high energy usage affects system reliability and longevity. Consequently, researchers have focused on enhancing energy efficiency by dynamically adjusting the energy consumption profiles of system components to align with workload demands by leveraging energy management techniques such as dynamic voltage and frequency scaling (DVFS) while meeting timing requirements.

In this work, we consider the problem of energy-aware speed assignment for a hard real-time workload scheduled with an online global non-preemptive work-conserving job-level-fixed-priority scheduler on a multi-core platform with a discrete core-level DVFS model. Our solution determines a speed for each job in the workload to reduce the energy consumption of the system while ensuring the timing requirements of the workload. As we consider a non-preemptive execution model, the timing uncertainties in the workload can result in scheduling anomalies. Therefore, we use the schedule abstraction graph (SAG), a reachability-based response time analysis tool to explore all possible execution scenarios and identify any potential deadline violations.

The key idea of our work is to iteratively explore all execution scenarios using SAG with all jobs running at the most energy-efficient speeds while readjusting the speeds to resolve any potential deadline violation. To limit the speed readjustment search space, we present a novel approach for identifying connections between jobs scheduled on a multi-core platform, considering all possible speed combinations with the selected speed settings.

Our evaluations show that our solution can reduce the energy consumption of a system by 25.85%, on average with an average runtime overhead of 7.7 times higher than that of the schedulability analysis when running all jobs at the highest speed, for the speed range {0.74, 0.80, 0.87, 0.94, 1.00}. This demonstrates a considerable energy reduction potential with energy-aware speed assignment for static slack reclamation using a schedule abstraction graph.

In practical situations, computer vision technique is applied to solve various tasks, including image classification, object detection, image segmentation, and so on. The commonly used supervised learning training paradigm for the network models used to solve these tasks requires training data as well as the ground truth labels specifying the data samples' reference information for the task. However, getting labels for every task would be expensive or even almost impossible, such as medical images due to privacy reasons and expert annotations from medical professionals and facial recognition also because of privacy concerns. Many large-scale general datasets exist, like ILSVRC2012 for both image classification and object detection tasks and COCO also for objection tasks. , and the corresponding pre-trained models whose knowledge can be transferred to other fields. While deeper models typically have better performance and can learn better feature representation from the same tasks, increasing network models introduces difficulties in practical deployment, especially regarding resource limitation and response latency. We hope to explore the learning methods in knowledge distillation to help the smaller student network learn better features from the unlabeled training data and have better transfer performance on downstream tasks. With the remarkable success of contrastive learning, it has become one of the most promising methods of learning from unlabeled data. In this thesis, we proposed an unsupervised knowledge distillation method that applies a contrastive learning method to construct and extract relational knowledge from the feature representations of the intermediate layers as well as the final layer. The evaluation with the ILSVRC2012 dataset proves the effectiveness of the proposed method on feature learning as the method helped the ResNet-18 model achieve a 2% improvement in linear evaluation accuracy compared to the baseline model. Extensive experiments were conducted on eight transfer learning tasks, and the model trained by the proposed method outperformed its baseline model in all the eight classification tasks and also achieved better fine-tuning accuracy in the situation where only a small fraction of the ground truth label was available for fine-tuning.

The proliferation of video recording devices and facial recognition technology has led to significant privacy concerns, as surveillance systems can capture and identify individuals without their consent. Traditional facial obfuscation systems, which introduce pixel-level perturbations to images, aim to protect privacy by preventing unauthorized facial recognition. However, these systems are vulnerable to inversion attacks, where attackers can reverse the perturbations to restore original images, compromising privacy. This thesis addresses these vulnerabilities by proposing HyperObf, a novel approach utilizing HyperNet technology to generate unique obfuscation networks for each user. HyperObf ensures that each user’s images are distinctly protected, making it challenging for attackers to reverse-engineer the obfuscations. Our experiments demonstrate that inversion attacks can significantly degrade the protection offered by static obfuscation systems, with restored images achieving face recognition accuracy close to that of original images.
In contrast, HyperObf effectively mitigates these attacks, reducing the attack success rate to 30% compared to 60% for existing methods. Additionally, HyperObf can generate 100 personalized MaskNets in 0.2 seconds using high-performance computing resources. These findings highlight the potential of HyperObf to enhance privacy protection against unauthorized facial recognition and inversion attacks in the digital age.

Path finding is an important component in solving a wide array of engineering problems, ranging from video games to real-life applications such as automated warehouse management and autonomous vehicles.
Path finding algorithms are designed to solve complex problems, and in order to do so, assumptions are necessary to simplify the problems.
While these assumptions are important, using them makes the obtained algorithms less applicable to a real-life scenario, and as such, verifying how lifting some of them would affect the obtained results is worth pursuing.

Two main assumptions were identified and subsequently lifted.
First, classic multi-agent path finding algorithms use a centralized approach, where solutions are computed before execution.
This results in a long computation period followed by execution. Lifting this assumption results in a decentralized approach where agents solve conflicts on the go, while approaching their target.
The second assumption made by state of the art algorithms is that agents participating in a multi-agent path finding problem share a common goal: minimizing a global cost function.
This is not always applicable, as in a real-life scenario participating agents can have selfish goals.
This assumptions has been lifted by allowing agents to negotiate their paths by trading with the other participants to create better solutions for themselves.

The Selfish Localized Pathfinding (SLP) algorithm has been designed to lift these assumptions. It describes a decentralized algorithm that allows participating agents to negotiate their paths, which makes a good candidate for an application closer to real-life.

The SLP algorithm has been tested in order to evaluate its performance, both in terms of its ability to solve a set of test cases, and in terms of the cost incurred by the participating agents.
SLP performed well in varied domains.
SLP solved significantly more cases than Conflict Based Search, a centralized state of the art path finding algorithm.
This comes at the expense of an increase in the path lengths obtained by the algorithm.
This downside is offset by the significant decrease in the time required to solve problems, which can be divided in small clusters due to the decentralized approach of the algorithm.
On the whole, SLP can provide a good alternative to Conflict Based Search.

Human activity recognition plays an interesting and important role nowadays as there are a variety of use cases. It is utilized in health monitoring, in the development of human-computer interaction system and in security monitoring. However current methods involve usage of privacy sensitive data and impractical sensors for everyday usage. To tackle this problem, we aim to answer the research question "How to maximize the capabilities of in-mouth sensors for human activity recognition?". The main contributions of this paper are the classification of different gestures using an in-mouth device, implementation of a classifier directly onto a microcontroller and the evaluation whether the models can generalize to multiple people. To investigate this, we experimented with popular classical machine learning classifiers: Decision Tree, K-Nearest Neighbors, Support Vector Machine, Logistic Regression and Random Forest classifiers. The results shows that the F1-score of all classification problems are above 80% using the various classifiers along with different parameters.

This research investigates the detection of gestures using a torso-worn accelerometer sensor. Using the Conflab dataset, we focus on gestures during conversations in mingling scenarios. Due to significant variability in gesture styles among individuals, traditional methods face challenges in building personalized models. Our experiments demonstrate that Transductive Parameter Transfer (TPT), an adaptive transfer learning method, can more effectively model these individual differences in gesturing. To gain insights into individual expressiveness, we classify gestures into three classes: 'no gesture,' 'normal,' and 'large' gestures. TPT performed an average AUC score of 0.84 in binary classification and 0.77 in multiclass classification. These findings highlight the potential of using a single torso-worn accelerometer to understand social behavior in naturalistic settings.

Multiactivity analysis investigates one's coordination of actions within a social context, such as gestures and speech, usually using video recordings of the social activity, to further understand the rules of human behaviour. This paper focuses specifically on the coordination between speaking and drinking activities within a social setting, and explores the possibility of automatically identifying these events using audio captured from a drinking glass. As social interactions occur in vastly different contexts, this paper also investigates the effect that background noise might have on the accuracy of identifying these events. Different parameters and audio features were compared. Linear classification models LR and SVM with a linear kernel were able to achieve 100% accuracy for all sample lengths between 2 and 8 seconds using the first 20 PCA components from 60 audio features. The best performing feature in identifying speaking and drinking events was MFCCs, achieving an F₁ score of 99.4% on average across models with a training sample length of 3 seconds. Background noise had different effects on classification accuracy depending on the type, with music lowering the F₁ score to 74.3%, noisy room audio to 64.7%, and podcast audio simulating the presence of other speakers to 59.6% using MFCCs and a 3-second sample length

Various studies already exist about the lifecycle of software programs written in languages like Java, C and C++, but this is an under-reported area for the pure, functional programming language Haskell. This report explores steps in the development of Haskell programs, and particularly, of their bugs. By gaining more knowledge about a bug’s development and its different stages, possible patterns or trends can be found. Using these insights, developers could get a better understanding of the development process, and optimise it. The main question of the research is formulated as ‘What are the different stages of bugs in Haskell programs?’. We consider three different stages: bug introduction, bug detection and bug fixing. To gain more knowledge about these stages, different open-source Haskell repositories, and their bugs were analysed. We found the median time between the bug introduction and detection is 381 days. The median time between the bug detection and fixing turned out to be 3 days. Most bugs were detected and fixed at similar rates regardless of their complexity, except for bugs that were detected by the same developer who introduced the bug. In this case, the time it takes to detect the bug is 30% of the global median. These results motivate developers to check their code more extensively, as they detect bugs quicker than other developers would. It also motivates developers to work with shared code ownership, as having more developers familiar with the code should reduce bug-detection time. Moreover, this study shows that single-statement bugs, which needed a simple fix, occur 2.5 times more often in code when no test is written, which argues for developers to write more test code. Lastly, we recommend repository owners to be more strict with developers working structured and precisely so that they follow Git’s and the repository’s standards and write test code.

Emotion recognition in Virtual Reality(VR) has the potential to offer numerous benefits across various sectors such as mental healthcare, education, marketing, entertainment, etc. Although emotion recognition itself is a mature field, the sub-field of VR-based emotion recognition is still in its early stages of development. It was found that a limiting factor in the progress of this field is a lack of sufficient data for research and development of advanced deep learning models. Also, the equipment currently used to measure emotion-related signals is expensive and impractical for general usage. This thesis aims to support the progress in this field by creating a VR-based emotion recognition dataset using VR equipment only. This addresses the problem of insufficient data available for research and development, and also reduces the reliance on expensive and impractical equipment for emotion recognition.

To create a good quality dataset, several important things had to be addressed. First of all, the stimuli to evoke the emotions had to be carefully selected to ensure that genuine emotional responses were evoked and recorded in the dataset. Then, an efficient data collection system had to be created to ensure that the data collection process ran effectively, smoothly and consistently. Then, a proper labeling process had to be designed to annotate the data as accurately as possible. Finally, the compiled dataset was validated by showing that the chosen stimuli were effective in evoking the intended emotions. This was verified through the analysis of pupil response data, which is one of the recorded data modalities.

This thesis project explores how V2X communication between electric vehicles (EV) and charging stations can be used to reduce en-route charging times. This is done using standardized V2X messages for EV charging, as well as proposing an extension to these messages to include data on the intentions of other vehicles. As individual vehicles can have significant effects on the total waiting time at EV charging stations, knowing the intentions of other vehicles will allow drivers to better avoid congested charging stations and achieve a lower total journey time. The performance of the system is evaluated using state-of-the-art traffic and communications simulators showing that using V2X can reduce journey times by 70%. Aside from demonstrating the performance using simulation the system has also been implemented on a real life test vehicle using functional V2X hardware to show that the system is viable for implementation.

Saxophone is a musical instrument that tends to be out of tune. I have invented an automatic tuning saxophone mouthpiece that can help saxophonists play in tune by correcting their notes' frequencies in real time during performances using a stepper motor.

Computer Architects often walk the tightrope between performance, power and area while designing modern day processors. This daunting task is made even more challenging by short Time-to-Market requirements set by the clients. In light of these challenges, architectural simulators provide a much needed tool for the architects to gauge the impact of their innovations rather quickly. Arguably, use of such simulators is essential in avoiding a product recall due to the processor failing to deliver on performance/power requirements for the intended application. The thesis is in-line with the objective of identifying and addressing the bottlenecks in the RISC-V simulation ecosystem and contribute in the development of RISC-V infrastructure.
The intended objective of an architectural simulator is to capture the trend of the real hardware (i.e., performance improvement due to micro-architectural changes in real hardware should be eloquently captured by the simulator). A good simulator shall have high throughput (less simulation time) and should be easily re-configurable. The re-configurability of the simulator can be as fine as micro-architectural changes or as large as a new ISA being simulated. These attributes of speed and re-configurability come at the cost of accuracy. A high error in performance statistics of the simulator fails to engender confidence among the prospective users. Hence, validating performance of simulators against hardware is essential.
The thesis introduces the need for a full system architectural simulator for RISC-V processors followed by a brief, yet crisp review of the past attempts at making such simulators. The review is from the perspective of existing methodologies for performance validation of the simulators. The work also proposes a new methodology for validating system simulators. Although, the proposed methodology is generic and can be extended to other ISAs (such as ARM, x86, etc.), the target hardware chosen are RISC-V ISA based systems that span both commercially, IP protected processor as well as open-source processors widely adopted by the RISC-V community.
The error in validated simulator is reduced to 22.9% and 18.9% for selected SPEC2017 benchmarks applications, by calibrating the CPU model. The methodology also streamlines CPU performance validation of the simulators.

Much like wearable devices today, ingestible devices have emerged as a promising platform for continuous health monitoring, and potentially even intervention. Recent research has demonstrated the feasibility of ingestible devices with a retention mechanism, enabling them to remain in the stomach for weeks. Equipping these devices with sensors capable of measuring complex biomarkers, would open up an entirely new era of continuous health monitoring.

This research focuses on the design of a gas sensor array for a retentive ingestible device, targeting the measurement of volatile organic compounds in the gastrointestinal tract. The research specifically addresses the outpatient treatment of alcoholism, in collaboration with the emergency medicine department at Brigham and Women's Hospital, Harvard Medical School. Current treatment relies on manual registration of drinking behavior, and the incorporation of an ingestible device that is able to continuously monitor drinking behavior enables more accurate behavioral assessment, and more targeted support and treatment.

Given the novelty of this approach, a sensor array capable of assessing ethanol concentrations in the air was gradually subjected to more complex tasks. Furthermore, a key aspect of the research was the design of an artificial gastric environment, that replicates the conditions and challenges that the sensor array would encounter within the human body. This experimental environment played a crucial role by providing a realistic testing platform without the need for a fully functional ingestible device, which can be incredibly challenging and resource-intensive to manufacture.

To ensure functionality in humid conditions, the sensors are encapsulated using parylene C and polycaprolactone (PCL) - biocompatible materials commonly used in the design of biomedical devices. The impact of these encapsulation methods on the sensors is thoroughly assessed, to determine their viability for in-vivo applications.

The findings of this study reveal that employing a convolutional neural network can enable the accurate measurement of ethanol in air, using off-the-shelf air quality sensors and algorithms with low computational complexity. It is worth highlighting that the neural network is capable of performing inference directly on the ingestible device. Furthermore, initial results show that a combination of parylene C and PCL, achieved through dip-coating in a PCL-dichloromethane solvent, yields a sensor capable of reliably distinguishing ethanol percentages from 4 to 11 volume percentages, while continually submerged in a self-designed artificial gastric environment.

Overall, this research contributes to the advancement of ingestible sensors and their potential for continuous health monitoring, with a use case in alcoholism treatment. The outcomes show the potential to produce a sensor array encapsulated in biocompatible materials, with a data-driven sensor fusion algorithm that is deployable on-device, which brings us closer to practical in-vivo applications. Additionally, the design and utilization of an artificial gastric environment establishes a solid foundation for future studies and the data generation that is vital for this technology.

High Performance Computing (HPC) facilities play a crucial role in acceler- ating Electronic Design Automation (EDA) procedures at NXP Semiconduct- ors. The increasing number of job requests and workloads has led to a surge in memory demand, which is a costly resource. To address this, we leverage memory swap space on disk as a more affordable extension of main memory. By employing a job submit-time parameter called memory reservation, we can increase the cluster jobs’ parallelism, and control the memory swap space usage. The primary goal of this thesis is to find the optimal cost and performance by optimizing the memory reservation parameter. To achieve this goal, we created an effective parameter optimizer that employs a one-way search method to determine the best memory reservation, focusing on scenarios with a large homogeneous job set running on an overloaded system. Our contributions include improving the memory utilization efficiency in HPC by utilizing swap space. Previous work used Machine Learning models to predict maximum memory usage and reduce over-reservation; and our work further reduces memory usage per job. The results demonstrate that the parameter optimizer effectively minimizes the cost and performance at the same time, leading to up to 43% cost saving for a job among our test cases.

This thesis has studied an oversight in the scientific literature on Wi-Fi 6 modelling and attempts to quantify the prevalence and effect of this omission.
This effect was dubbed the ”backoff reset” and roughly means that a device connected to a Wi-Fi 6 network that recently received the green-light to send from the access point and, as such, has successfully sent a message, should reset the remaining time it will wait to send its next message.
The problem statement was then based on this effect and read as follows:
”What is the effect on performance metrics of resetting a station’s backoff stage and counter after an UL-OFDMA transmission?”
To allow readers new to the Wi-Fi space to be able to follow along, a brief introduction was given to some of the core concepts of Wi-Fi 6 and a preliminary literature survey was performed to find out how often the backoff reset is omitted.
From this census, it was found that only five out of fifteen papers likely included the backoff reset in their results.
To analyze the effects of the backoff reset on network performance, a series of experiments were performed in a simulator.
In these experiments, the system with a backoff reset, named the ”reset” system,
was pitched against a system without the reset, called the ”continue” system, while varying various network parameters.
From these results, the following conclusion is drawn: ”The ”reset” system outperforms the ”continue” system in certain situations on (a combination of) latency and collision probability, but is generally strictly worse on all five key metrics in a typical, flexible Wi-Fi deployment, where data rates and the amount of
connected devices can change rapidly. We thus accept the research hypothesis.” Finally, an overview of the situations in which the ”reset” system can outperform the ”continue” system was given and the limitations of this study were discussed, after which future work was proposed.

The agricultural industry is undergoing a transformative shift towards efficiency and large-scale production. Manual labor is unable to meet the increasing demand, leading to the development of automation techniques. During production, objects are adjusted and moved along a line to maintain productivity. This work investigates the feasibility of developing a system that detects and determines the position and rotation of a small clipping object in a cluttered environment. To achieve this feasibility, a neural network has been trained on a custom dataset with images containing 6-D pose annotations of a clip that do not require manual annotations. The designed system also executes a validation step with a second set of sensors in the form of a stereo camera. The entire methodology has been evaluated on a test setup. The small and round properties of the clip cause a rotational error that does not fall in positional and rotational requirements set by a mechanical grabber on a robotic arm. Higher positional precision of annotation data and depth information from the stereo camera is necessary to make this methodology feasible.

Modern vehicles have multiple different buses to communicate between components, like CAN (FD) and FlexRay. ZF builds ”innovation vehicles” with new components to showcase and test them. These components are connected to the automotive buses. ZF uses a web-based Human Machine Interface (HMI) to control and view the state of these parts. This HMI is needed because some systems are not visible or controllable in regular operation. A gateway is required to connect the HMI and the buses. ZF currently uses a CAN to WebSocket gateway that does not support other buses. There is no readily available hardware with the required buses and interfaces. A WebSocket interface is required, as the HMI is running in a browser, limiting the possible protocols.
Therefore, the challenge for this thesis is how to (re)design this HMI system for future innovation vehicles with buses besides CAN. Each vehicle can have a different number and types of buses, so the system must be able to cope with this. The HMI system is not the only part in the network, so it also must be efficient to not interfere with other systems, like network cameras. This redesign was done by analysing the types of buses, the hardware that could be used, and the software components needed for this flexible system. The software components were mapped onto the available hardware to make the architecture as flexible and efficient as possible. Two mappings are proposed, one using a Software Gateway, a custom application with support for different hardware interface drivers, capable of running on Windows, Linux and in containers. The other mapping uses WebSockify, where WebSocket messages are converted to TCP/UDP messages.
These two mappings were combined into a single architecture to combine the features and possibilities of both systems. Then a Minimum Viable Product (MVP) was made to test the envisioned architecture, showing excellent results compared to the current solution while adding more flexibility and other features. Using this new HMI system, the HMI developers can interface with more types of networks, build HMIs that connect to multiple different vehicles and make distributed HMI systems.

Programmers spend significantly more time trying to comprehend existing code than writing new code. They gain an understanding of the code by navigating the code base in an IDE, by reading documentation online, and by browsing code repositories on websites such as GitHub. To create rich experiences for programming languages across those various media is a large effort for developers of programming languages. This effort might be worthwhile for popular languages, but for new or experimental languages the required effort is often too large. Solutions to reduce this effort of implementing an IDE exist,such as LSP, but to reduce the effort in other places outside IDEs, we introduce the Codex metadata format, which separates language-specific generation of code metadata from its language-agnostic presentation. To demonstrate this approach by implementing four language-specific metadata generators (based on LSP, CTAGS, TextMate and Elaine) and two language-agnostic presentations (PDF documents and a code viewer websites) of code and metadata. To demonstrate different kinds of code metadata, we implemented four code exploration services: syntax colouring, code navigation, structure outline, and diagnostic messages. We show that with the Codex metadata format, we can decouple the metadata generators from the presentations.