Efficient Multihop Wireless Communications in VANETs

Oggigiorno, una quota rilevante dei veicoli presenti sul mercato è dotata di notevoli capacità computazionali, sensoriali e cognitive. Questi veicoli ``intelligenti'' otterrebbero un beneficio ancora maggiore da queste potenzialità, attraverso l'impiego delle cosiddette comunicazioni inter-veicolari (Inter-Vehicular Communications, IVCs), un insieme di protocolli, standard e tecnologie in grado di dotare i veicoli di capacità comunicative. In particolare, grazie alle tecnologie IVCs, i veicoli possono creare reti decentralizzate, ed auto-organizzate, comunemente note come Vehicular Ad-hoc NETworks (VANETs). Quest'ultime possono essere formate, sia fra veicoli, determinando la realizzazione di comunicazioni inter-veicolari pure (Vehicle-to-Vehicle communications, V2V), oppure coinvolgendo anche nodi fissi (ad esempio, posti ai lati delle strade), determinando la realizzazione di comunicazioni da veicolo verso infrastruttura (Vehicle-to-Infrastructure, V2I), o da infrastruttura verso veicolo (Infrastructure-to-Vehicle I2V). In questa tesi presenteremo una famiglia di protocolli di instradamento a passi multipli, adatti per un largo spettro di applicazioni nell'ambito delle VANET, quali la prevenzione di incidenti stradali, o applicazioni di raccolta dati, in scenari di tipo V2V, V2I, o I2V. Il primo protocollo che viene proposto è un nuovo schema di broadcasting probabilistico per reti lineari a passi multipli, noto come Irresponsible Forwarding (IF), secondo il quale ogni veicolo decide probabilisticamente se effettuare la ritrasmissione (broadcast) di un messaggio ricevuto. La probabilità di ritrasmissione è determinata sulla base della propria distanza dalla sorgente e della densità spaziale dei propri vicini. I vantaggi principali del protocollo IF rispetto alle soluzioni presenti in letteratura, sono costituiti dalla sua natura intrinsecamente distribuita, dalla bassa latenza, e dall'assenza di overhead, in quanto esso non prevede l'utilizzo di pacchetti ausiliari di supporto Successivamente, presenteremo un secondo protocollo di instradamento probabilistico, noto come Silencing Irresponsible Forwarding (SIF), che riprendendo le idee alla base di IF, permette di ottenere una maggiore efficienza (e.g., un minore numero di ritrasmissioni), senza penalizzarne l'affidabilità, e mantenendo valori di latenza comparabili ad IF. In seguito, verrà inoltre proposto un protocollo di clustering decentralizzato, noto come Cluster-Head Election IF (CHE-IF). Quest'ultimo si propone di sfruttare lo spontaneo processo di formazione di cluster effimeri di nodi nelle reti veicolari, in maniera distribuita ed efficiente. Per ottenere questo risultato, CHE-IF utilizza l'idea alla base di IF, ma introducendo dei pacchetti di controllo aggiuntivi, espressamente dedicati alla realizzazione di cluster di nodi. Infine, le prestazioni di tutti i protocolli proposti verranno testate mediante simulazioni numeriche in realistici scenari veicolari, quali autostrade e strade urbane, assumendo di utilizzare interfacce radio compatibili con lo standard IEEE 802.11p.Nowadays, most of the vehicles available on the market are provided by sensorial, computational, and cognitive skills. Vehicles can achieve a higher awareness level, by exploiting these potentialities through Inter-Vehicular Communications (IVCs), a set of technologies that gives networking capabilities to the vehicles. Leveraging on the IVC technology, vehicles can create decentralized and self-organized vehicular networks, commonly denoted as Vehicular Ad-hoc NETworks (VANETs). These networks can be formed between vehicles, leading to Vehicle-to-Vehicle communications (V2V), or they can also involve some fixed network nodes (e.g., access points or road side unit) leading to the so-called Vehicle-to-Infrastructure (V2I) and Infrastructure-to-Vehicle (I2V) communications. In this thesis we present a family of multihop broadcast forwarding protocols suitable for a wide range of VANETs applications, ranging from accident-preventing, to data collection applications, in V2V, V2I, or I2V scenarios. The first proposed protocol is a new probabilistic-based broadcasting scheme for multi-hop linear networks, denoted as Irresponsible Forwarding (IF), where each vehicle probabilistically rebroadcasts a received data packet on the basis of (i) its distance from the source and (ii) the spatial density of its neighbors. The main advantages of the IF protocol with respect to solutions present in the literature, are its inherently distributed nature, the low-latency, and the absence of overhead, since auxiliary supporting packets are not needed. On the basis of the IF concept, we will present an improved probabilistic forwarding protocol, denoted as Silencing Irresponsible Forwarding (SIF) protocol, able to guarantee a greater efficiency (e.g., a smaller number of retransmissions), without penalizing the reliability, and maintaining a comparable latency. Furthermore, we will propose a novel decentralized clustering protocol, denoted as Cluster-Head Election IF (CHE-IF), whose goal is which of exploiting the spontaneous formation of ephemeral clusters of vehicles in VANETs, in a distributed and efficient manner. This result is achieved by enhancing IF with some additional control messages, aimed at the creation of cluster of nodes. Finally, the performance of the proposed protocols will be tested through numerical simulations in realistic vehicular environments, such as highways and urban roads, by using radio interfaces compliant with the IEEE 802.11p standard

Quality-aware Content Adaptation in Digital Video Streaming

User-generated video has attracted a lot of attention due to the success of Video Sharing Sites such as YouTube and Online Social Networks. Recently, a shift towards live consumption of these videos is observable. The content is captured and instantly shared over the Internet using smart mobile devices such as smartphones. Large-scale platforms arise such as YouTube.Live, YouNow or Facebook.Live which enable the smartphones of users to livestream to the public. These platforms achieve the distribution of tens of thousands of low resolution videos to remote viewers in parallel. Nonetheless, the providers are not capable to guarantee an efficient collection and distribution of high-quality video streams. As a result, the user experience is often degraded, and the needed infrastructure installments are huge. Efficient methods are required to cope with the increasing demand for these video streams; and an understanding is needed how to capture, process and distribute the videos to guarantee a high-quality experience for viewers. This thesis addresses the quality awareness of user-generated videos by leveraging the concept of content adaptation. Two types of content adaptation, the adaptive video streaming and the video composition, are discussed in this thesis. Then, a novel approach for the given scenario of a live upload from mobile devices, the processing of video streams and their distribution is presented. This thesis demonstrates that content adaptation applied to each step of this scenario, ranging from the upload to the consumption, can significantly improve the quality for the viewer. At the same time, if content adaptation is planned wisely, the data traffic can be reduced while keeping the quality for the viewers high. The first contribution of this thesis is a better understanding of the perceived quality in user-generated video and its influencing factors. Subjective studies are performed to understand what affects the human perception, leading to the first of their kind quality models. Developed quality models are used for the second contribution of this work: novel quality assessment algorithms. A unique attribute of these algorithms is the usage of multiple features from different sensors. Whereas classical video quality assessment algorithms focus on the visual information, the proposed algorithms reduce the runtime by an order of magnitude when using data from other sensors in video capturing devices. Still, the scalability for quality assessment is limited by executing algorithms on a single server. This is solved with the proposed placement and selection component. It allows the distribution of quality assessment tasks to mobile devices and thus increases the scalability of existing approaches by up to 33.71% when using the resources of only 15 mobile devices. These three contributions are required to provide a real-time understanding of the perceived quality of the video streams produced on mobile devices. The upload of video streams is the fourth contribution of this work. It relies on content and mechanism adaptation. The thesis introduces the first prototypically evaluated adaptive video upload protocol (LiViU) which transcodes multiple video representations in real-time and copes with changing network conditions. In addition, a mechanism adaptation is integrated into LiViU to react to changing application scenarios such as streaming high-quality videos to remote viewers or distributing video with a minimal delay to close-by recipients. A second type of content adaptation is discussed in the fifth contribution of this work. An automatic video composition application is presented which enables live composition from multiple user-generated video streams. The proposed application is the first of its kind, allowing the in-time composition of high-quality video streams by inspecting the quality of individual video streams, recording locations and cinematographic rules. As a last contribution, the content-aware adaptive distribution of video streams to mobile devices is introduced by the Video Adaptation Service (VAS). The VAS analyzes the video content streamed to understand which adaptations are most beneficial for a viewer. It maximizes the perceived quality for each video stream individually and at the same time tries to produce as little data traffic as possible - achieving data traffic reduction of more than 80%

Distributed Real-time Systems - Deterministic Protocols for Wireless Networks and Model-Driven Development with SDL

In a networked system, the communication system is indispensable but often the weakest link w.r.t. performance and reliability. This, particularly, holds for wireless communication systems, where the error- and interference-prone medium and the character of network topologies implicate special challenges. However, there are many scenarios of wireless networks, in which a certain quality-of-service has to be provided despite these conditions. In this regard, distributed real-time systems, whose realization by wireless multi-hop networks becomes increasingly popular, are a particular challenge. For such systems, it is of crucial importance that communication protocols are deterministic and come with the required amount of efficiency and predictability, while additionally considering scarce hardware resources that are a major limiting factor of wireless sensor nodes. This, in turn, does not only place demands on the behavior of a protocol but also on its implementation, which has to comply with timing and resource constraints. The first part of this thesis presents a deterministic protocol for wireless multi-hop networks with time-critical behavior. The protocol is referred to as Arbitrating and Cooperative Transfer Protocol (ACTP), and is an instance of a binary countdown protocol. It enables the reliable transfer of bit sequences of adjustable length and deterministically resolves contest among nodes based on a flexible priority assignment, with constant delays, and within configurable arbitration radii. The protocol's key requirement is the collision-resistant encoding of bits, which is achieved by the incorporation of black bursts. Besides revisiting black bursts and proposing measures to optimize their detection, robustness, and implementation on wireless sensor nodes, the first part of this thesis presents the mode of operation and time behavior of ACTP. In addition, possible applications of ACTP are illustrated, presenting solutions to well-known problems of distributed systems like leader election and data dissemination. Furthermore, results of experimental evaluations with customary wireless transceivers are outlined to provide evidence of the protocol's implementability and benefits. In the second part of this thesis, the focus is shifted from concrete deterministic protocols to their model-driven development with the Specification and Description Language (SDL). Though SDL is well-established in the domain of telecommunication and distributed systems, the predictability of its implementations is often insufficient as previous projects have shown. To increase this predictability and to improve SDL's applicability to time-critical systems, real-time tasks, an approved concept in the design of real-time systems, are transferred to SDL and extended to cover node-spanning system tasks. In this regard, a priority-based execution and suspension model is introduced in SDL, which enables task-specific priority assignments in the SDL specification that are orthogonal to the static structure of SDL systems and control transition execution orders on design as well as on implementation level. Both the formal incorporation of real-time tasks into SDL and their implementation in a novel scheduling strategy are discussed in this context. By means of evaluations on wireless sensor nodes, evidence is provided that these extensions reduce worst-case execution times substantially, and improve the predictability of SDL implementations and the language's applicability to real-time systems

Mobile Ad-Hoc Networks

Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of-the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: quality-of-service and video communication, routing protocol and cross-layer design. A few interesting problems about security and delay-tolerant networks are also discussed. This book is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks

Recent Advances in Cellular D2D Communications

Device-to-device (D2D) communications have attracted a great deal of attention from researchers in recent years. It is a promising technique for offloading local traffic from cellular base stations by allowing local devices, in physical proximity, to communicate directly with each other. Furthermore, through relaying, D2D is also a promising approach to enhancing service coverage at cell edges or in black spots. However, there are many challenges to realizing the full benefits of D2D. For one, minimizing the interference between legacy cellular and D2D users operating in underlay mode is still an active research issue. With the 5th generation (5G) communication systems expected to be the main data carrier for the Internet-of-Things (IoT) paradigm, the potential role of D2D and its scalability to support massive IoT devices and their machine-centric (as opposed to human-centric) communications need to be investigated. New challenges have also arisen from new enabling technologies for D2D communications, such as non-orthogonal multiple access (NOMA) and blockchain technologies, which call for new solutions to be proposed. This edited book presents a collection of ten chapters, including one review and nine original research works on addressing many of the aforementioned challenges and beyond

Proceedings of the Third Edition of the Annual Conference on Wireless On-demand Network Systems and Services (WONS 2006)

Ce fichier regroupe en un seul documents l'ensemble des articles accéptés pour la conférences WONS2006/http://citi.insa-lyon.fr/wons2006/index.htmlThis year, 56 papers were submitted. From the Open Call submissions we accepted 16 papers as full papers (up to 12 pages) and 8 papers as short papers (up to 6 pages). All the accepted papers will be presented orally in the Workshop sessions. More precisely, the selected papers have been organized in 7 session: Channel access and scheduling, Energy-aware Protocols, QoS in Mobile Ad-Hoc networks, Multihop Performance Issues, Wireless Internet, Applications and finally Security Issues. The papers (and authors) come from all parts of the world, confirming the international stature of this Workshop. The majority of the contributions are from Europe (France, Germany, Greece, Italy, Netherlands, Norway, Switzerland, UK). However, a significant number is from Australia, Brazil, Canada, Iran, Korea and USA. The proceedings also include two invited papers. We take this opportunity to thank all the authors who submitted their papers to WONS 2006. You helped make this event again a success

Research on Teaching and Learning In Biology, Chemistry and Physics In ESERA 2013 Conference

This paper provides an overview of the topics in educational research that were published in the ESERA 2013 conference proceedings. The aim of the research was to identify what aspects of the teacher-student-content interaction were investigated frequently and what have been studied rarely. We used the categorization system developed by Kinnunen, Lampiselkä, Malmi and Meisalo (2016) and altogether 184 articles were analyzed. The analysis focused on secondary and tertiary level biology, chemistry, physics, and science education. The results showed that most of the studies focus on either the teacher’s pedagogical actions or on the student - content relationship. All other aspects were studied considerably less. For example, the teachers’ thoughts about the students’ perceptions and attitudes towards the goals and the content, and the teachers’ conceptions of the students’ actions towards achieving the goals were studied only rarely. Discussion about the scope and the coverage of the research in science education in Europe is needed.Peer reviewe