Ph.D
Group : Parallel Systems

Patterns of Mobility and Clock Synchronization in Wireless Networks

Starts on 01/10/2018
Advisor : LAMBERT, Alain
[NOWAK Thomas]

Funding : Bourse pour étudiant étranger
Affiliation : Université Paris-Saclay
Laboratory : LRI - ParSys

Defended on 08/11/2021, committee :

Research activities :

Abstract :
Mobility in conventional ad-hoc networks is a challenge due to the constant invalidation of end-to-end paths. We deal with mobile ad-hoc networks where humans are the main carriers of mobile devices. A good understanding of human mobility patterns aids the design of a realistic mobility model as a tool for evaluating network protocols. Conventional models for evaluating network protocols in early ad-hoc networks (e.g., random walks, random waypoints, random directions) fail to properly capture human mobility. In fact, recent studies have shown that human mobility is influenced by personal habits, social relationships, environmental features, and locations preferences. Therefore, a realistic model should be able to include these features. In this regard, we develop a heuristic to characterize human mobility based on spatial, temporal, and connectivity features using real traces. Consequently, we uncover temporal dynamic movement clusters associated with individual users. We also study the distribution of the travel distance, pause time, angle of movement, contact duration, and inter-contact duration. Motivated by our findings, we proposed a new synthetic mobility model that mimics realistic features of human mobility. We validate the model by comparing its synthetic traces against real mobility measurements. Moreover, in a smart-campus environment, networks support applications for environmental monitoring and indoor/outdoor positioning, sometimes with a large deployment of sensors. Considering the limitation of sensors such as battery limitation, dynamicity, and low computing clock rate, sensor clocks need to have a common time to perform information fusion algorithms, implement energy management protocols, or real-time processing for safety applications. Given this, we proposed a pulse-coupled distributed clock synchronization algorithm for wireless sensor networks to reduce the clock skew due to the ambient conditions, mobility, or manufacturing defects. In our algorithm, sensors measure time differences by only exchanging zero-bit pulse instead of packets. Therefore our algorithm is lightweight and robust to the failure of the sensors in the network. The proposed algorithm is compared to previous works under static and mobile settings, and the results show that it can reduce the clock skew, especially in a dynamic environment with high uncertainty in clock drift and unexpected topological changes like vehicular networks.

CAUSAL LEARNING FOR DIAGNOSTIC SUPPORT


CAUSAL UNCERTAINTY QUANTIFICATION UNDER PARTIAL KNOWLEDGE AND LOW DATA REGIMES


MICRO VISUALIZATIONS: DESIGN AND ANALYSIS OF VISUALIZATIONS FOR SMALL DISPLAY SPACES
The topic of this habilitation is the study of very small data visualizations, micro visualizations, in display contexts that can only dedicate minimal rendering space for data representations. For several years, together with my collaborators, I have been studying human perception, interaction, and analysis with micro visualizations in multiple contexts. In this document I bring together three of my research streams related to micro visualizations: data glyphs, where my joint research focused on studying the perception of small-multiple micro visualizations, word-scale visualizations, where my joint research focused on small visualizations embedded in text-documents, and small mobile data visualizations for smartwatches or fitness trackers. I consider these types of small visualizations together under the umbrella term ``micro visualizations.'' Micro visualizations are useful in multiple visualization contexts and I have been working towards a better understanding of the complexities involved in designing and using micro visualizations. Here, I define the term micro visualization, summarize my own and other past research and design guidelines and outline several design spaces for different types of micro visualizations based on some of the work I was involved in since my PhD.