In this work, a new multicast routing algorithm for wireless networks is presented. The algorithm, called SWIM (Source-initiated WIreless Multicast), is a depth-optimal multicast tree formation algorithm. SWIM is fully distributed and has an average computational complexity of O(N 2 ). SWIM forms a shared tree from the source(s) to destinations / yet, as a by-product, it creates a multicast mesh structure by maintaining alternative paths at every tree node. This makes SWIM suitable for both ad hoc networks and access networks with multiple gateways. An extension to the main algorithm is presented for the use in dynamic networks with mobility and/or dynamic destination group. Performance of SWIM is studied with simulations and is compared to other algorithms in the literature. Due to depth optimality, SWIM achieves a lower average and maximum delay than the compared algorithms. The throughput performance is found to be high. Working capability with rateless codes are also studied.

In the wake of major disasters, the failure of existing communications infrastructure and the subsequent lack of an effective communication solution results in increased risks, inefficiencies, damage and casualties. Currently available options such as satellite communication are expensive and have limited functionality. A robust communication solution should be affordable, easy to deploy, require little infrastructure, consume little power and facilitate Internet access. Researchers have long proposed the use of ad hoc wireless networks for such scenarios. However such networks have so far failed to create any impact, primarily because they are unable to handle network transience and have usability constraints such as static topologies and dependence on specific platforms. LifeNet is a WiFi-based ad hoc data communication solution designed for use in highly transient environments. After presenting the motivation, design principles and key insights from prior literature, the dissertation introduces a new routing metric called Reachability and a new routing protocol based on it, called Flexible Routing. Roughly speaking, reachability measures the end-to-end multi-path probability that a packet transmitted by a source reaches its final destination. Using experimental results, it is shown that even with high transience, the reachability metric - (1) accurately captures the effects of transience (2) provides a compact and eventually consistent global network view at individual nodes, (3) is easy to calculate and maintain and (4) captures availability. Flexible Routing trades throughput for availability and fault-tolerance and ensures successful packet delivery under varying degrees of transience. With the intent of deploying LifeNet on field we have been continuously interacting with field partners, one of which is Tata Institute of Social Sciences India. We have refined LifeNet iteratively refined base on their feedback. I conclude the thesis with lessons learned from our field trips so far and deployment plans for the near future.

The work in hand considers energy efficiency of data transmission in wireless networks with low data rate (=sensor networks). Often the network nodes are battery operated thus calling for node lifetimes of months or even years. Thus, energy efficiency becomes an important optimisation criteria when designing hardware as well as for the physical transmission, protocol design etc. In order to meet the tight energy constraints, it is necessary to optimise the system as a whole, not just single parameters. This work first shows a derived analysis model for calculating the energy consumption during data transmission. This model is based on a complex state diagram which is evaluated using Mason rules. Using this model the impact of individual parameters on the energy consumption can be computed. Herein the interference of other nodes is included as well. The individual parameters investigated include detection method, modulation scheme, error correction and channel access. The main conclusion is, that higher transmit power can yield decreased energy consumption if the time, which nodes spend in the energy intense active mode, is reduced. Ultra-Wideband-transmission (UWB) using short pulses (Impulse Radio-IR) is currently developing. The potential of this technology is a very simple power-efficient transmitter. Moreover, due to the short pulses, transmission time is short. These two facts promise an energy efficient operation in transmit mode. Nevertheless, performance of simple receivers is still quite low, especially in multi-path environments. Moreover there is the need of powerful synchronisation algorithms. Sensor networks usually possess multi-hop functionality. However, only in severe (block) fading channels multi-hop is more energy efficient than direct transmission. Supposed the transmit power is the same for all nodes, then the transmit power has to be dimensioned for the weakest link. Then, under certain conditions, cooperative relaying schemes can not capitalize the spatial diversity gain. - (This manuscript is also available - in the form of a book - from Dresden: Vogt (Verlag), ISBN:3-938860-02-2) / Die vorliegende Arbeit beschäftigt sich mit der Energieeffizienz der Datenübertragung in Funknetzwerken mit geringer Datenrate (=Sensornetzwerke). Die Netzknoten solcher Netzwerke sind zumeist batteriebetrieben und sollen Betriebsdauern von Monaten bis Jahren erreichen. Daher ist Energieeffizienz ein wichtiges Designmerkmal sowohl beim Hardwareentwurf als auch bei der physikalischen Übertragung, im Protokolldesign usw. Um den energetischen Beschränkungen gerecht zu werden, sollen nicht Einzelparameter optimiert werden, sondern das System insgesamt. In dieser Arbeit wird zunächst ein Analysemodell zur Berechnung des Energieverbrauchs bei der Datenübertragung entwickelt, welches diesen Forderungen gerecht wird. Dieses basiert auf einem komplexen Zustandsdiagramm, welches mit der Mason'schen Regel ausgewertet wird. Dieses Modell nutzend, kann der Einfluss von Einzelparametern auf den Energieverbrauch unter Berücksichtigung der Interferenzen anderer Netzknoten berechnet werden. Als Einzelparameter werden exemplarisch Detektionsverfahren, Modulation, Fehlerschutzkodierung und Kanalzugriff untersucht. Die Grunderkenntnis dieser Betrachtungenen ist, dass höhere Sendeleistungen zu geringerem Energieverbrauch führen, wenn dadurch die Zeit des Netzknotens im energieintensiven Aktiv-Mode verkürzt wird. Ultra-Wideband-Verfahren (UWB) mittels kurzen Pulsen (IR-UWB) befinden sich noch in einer frühen Entwickungsstufe. Das Potential liegt in einem sehr einfachen Senderaufbau, der sehr leistungseffiziente Sender ermöglicht. Aufgrund der kurzen Pulse ist zudem die Übertragungszeit sehr gering. Diese beiden Gegebenheiten lassen auf einen geringen Energieverbrauch hoffen. Allerdings ist die Leistungsfähigkeit von einfachen Empfängern insbesondere in Mehrwegekanälen sehr gering. Desweiteren gibt es noch intensiven Forschungsbedarf für leistungsfähige Synchronisationsalgorithmen. Sensornetzwerke verfügen im Allgemeinen über Multi-Hop-Funktionalität. Energetisch betrachtet, ist deren Einsatz aber nur in starken Blockschwundkanälen sinnvoll. Wird die Sendeleistung aller Netzknoten als konstant angenommen, muss die Sendeleistung auf die schwächste Verbindung dimensioniert werden. Bei kooperativen Vermittlungsverfahren kann dadurch unter bestimmten Bedingungen der räumliche Diversitätsgewinn nicht genutzt werden. - (Die Dissertation ist veröffentlicht im Verlag Vogt, Dresden, ISBN:3-938860-02-2)

Το ερευνητικό αντικείμενο και ο στόχος της διδακτορικής διατριβής είναι η πρόταση μιας ολοκληρωμένης λύσης για την υποστήριξη τηλεπικοινωνιακών εφαρμογών σε ασύρματα δίκτυα τα οποία δεν στηρίζονται σε σταθερές δικτυακές υποδομές. Ένα τέτοιο δίκτυο, το οποίο αναφέρεται στη διεθνή βιβλιογραφία ως Mobile Ad-hoc Network (MANET), είναι ένα αυτο-οργανώσιμο αυτο-σχηματιζόμενο ασύρματο δίκτυο με διαδρομές πολλαπλών τμημάτων (multi-hop), όπου η δομή του δικτύου αλλάζει δυναμικά λόγω της κινητικότητας των κόμβων ή αλλαγές στην τοπολογία. Η αρχιτεκτονική που προτείνεται για την ικανοποίηση των τιθέμενων απαιτήσεων στηρίζεται στην ανάπτυξη ενός ολοκληρωμένου επικοινωνιακού αρχιτεκτονικού πλαισίου για MANET δίκτυα το οποίο περιλαμβάνει μηχανισμούς μείωσης της κατανάλωσης ενέργειας που οφείλεται σε επικοινωνιακές λειτουργίες, την ανάπτυξη ενός εξειδικευμένου πρωτοκόλλου δρομολόγησης, τροποποιήσεις του πρωτοκόλλου TCP στο επίπεδο μεταφοράς και την υλοποίηση ενός νέου πρωτόκολλου διαχείρισης δικτύου. Η απόδοση της προτεινόμενης επικοινωνιακής διαστρωμάτωσης είναι υψηλή σε περιβάλλον με μεγάλη κινητικότητα των κόμβων και δυναμική αλλαγή της τοπολογίας ενώ παράλληλα η κατανάλωση ενέργειας των κόμβων παραμένει σχετικά χαμηλή. Οι αλγόριθμοι και τα πρωτοκόλλα που παρουσιάζονται σχεδιάστηκαν και υλοποιήθηκαν λαμβάνοντας υπόψη τους περιορισμούς και τις απαιτήσεις ενός ενσωματωμένου συστήματος, ενώ η απόδοση και αξιοπιστία τους τεκμηριώνονται θεωρητικά και με εξομοιώσεις. / The research objective of this thesis is a complete solution so as to support the implementation of telecommunication applications in wireless networks that operate without the presence of fixed infrastructure. Such a network, cited as Mobile Ad-hoc Network (MANET) in international literature, is a self-organized, auto-configured wireless network with multi-hop routing paths where its structure is modified dynamically due to node mobility and topological changes. In order to meet the above requirements a new communication framework for MANET networks is presented, which consists of the adaptation of communication-related energy reduction techniques, development of a specialized routing protocol at the network layer, modifications of the TCP protocol at the transport layer and the implementation of a novel network management protocol. The performance of the proposed protocol stack is satisfactory in dynamic network topologies with increased node mobility, whereas the node energy consumption remains in low levels. The presented algorithms and protocols are designed and implemented considering the constraints and requirements of an embedded system, while their performance and reliability is proved theoretically and by simulation results.

No description available.

Road accidents represent a serious social problem and are one of the leading causes of human death and disability on a global scale. To reduce the risk and severity of a road accident, a variety of new safety applications can be realized through wireless communications among vehicles driving nearby each other, or among vehicles and especially deployed road side units (RSUs), a technology known as a vehicular ad hoc network (VANET). Most of the VANET-enabled safety applications are based on broadcasting of safety messages by vehicles or RSUs, either periodically or in case of an unexpected event, such as a hard brake or dangerous road condition detection. Each broadcast safety message should be successfully delivered to the surrounding vehicles and RSUs without any excess delay, which is one of the main functions of a medium access control (MAC) protocol proposed for VANETs. This thesis presents VeMAC, a new multichannel time division multiple access (TDMA) protocol specifically designed to support the high priority safety applications in a VANET scenario. The ability of the VeMAC protocol to deliver periodic and event-driven safety messages in VANETs is demonstrated by a detailed delivery delay analysis, including queueing and service delays, for both types of safety messages. As well, computer simulations are conducted by using MATLAB, the network simulator ns-2, and the microscopic vehicle traffic simulator VISSIM, in order to evaluate the performance of the VeMAC protocol, in comparison with the IEEE 802.11p standard and the ADHOC MAC protocol (another TDMA protocol proposed for ad hoc networks). A real city scenario is simulated and different performance metrics are evaluated, including the network goodput, protocol overhead, channel utilization, protocol fairness, probability of a transmission collision, and safety message delivery delay. It is shown that the VeMAC protocol considerably outperforms the existing MAC schemes, which have significant limitations in supporting VANET safety applications. In addition to enhancing road safety, in-vehicle Internet access is one of the main applications of VANETs, which aims at providing the vehicle passengers with a low-cost access to the Internet via on-road gateways. This thesis presents a new strategy for deploying Internet gateways on the roads, in order to minimize the total cost of gateway deployment, while ensuring that a vehicle can connect to an Internet gateway (using multihop communications) with a probability greater than a specified threshold. This cost minimization problem is formulated by using binary integer programming, and applied for optimal gateway placement in a real city scenario. To the best of our knowledge, no previous strategy for gateway deployment has considered the probability of multihop connectivity among the vehicles and the deployed gateways. In order to allow a vehicle to discover the existence of an Internet gateway and to communicate with the gateway via multihops, a novel data packet routing scheme is proposed based on the VeMAC protocol. The performance of this cross-layer design is evaluated for a multichannel VANET in a highway scenario, mainly in terms of the end-to-end packet delivery delay. The packet queueing at each relay vehicle is considered in the end-to-end delay analysis, and numerical results are presented to study the effect of various parameters, such as the vehicle density and the packet arrival rate, on the performance metrics. The proposed VeMAC protocol is a promising candidate for MAC in VANETs, which can realize many advanced safety applications to enhance the public safety standards and improve the safety level of drivers/passengers and pedestrians on roads. On the other hand, the proposed gateway placement strategy and packet routing scheme represent a strong step toward providing reliable and ubiquitous in-vehicle Internet connectivity.

Vehicular networking is envisioned to be a key technology area for significant growth in the coming years. Although the expectations for this emerging technology are set very high, many practical aspects remain still unsolved for a vast deployment of vehicular networks. This dissertation addresses the enabling physical layer techniques to meet the challenges in vehicular networks operating in mobile wireless environments. Considering the infrastructure-less nature of vehicular networks, we envision cooperative diversity well positioned to meet the demanding requirements of vehicular networks with their underlying distributed structure. Cooperative diversity has been proposed as a powerful means to enhance the performance of high-rate communications over wireless fading channels. It realizes spatial diversity advantages in a distributed manner where a node uses others antennas to relay its message creating a virtual antenna array. Although cooperative diversity has garnered much attention recently, it has not yet been fully explored in the context of vehicular networks considering the unique characteristics of vehicular networks, this dissertation provides an error performance analysis study of cooperative transmission schemes for various deployment and traffic scenarios. In the first part of this dissertation, we investigate the performance of a cooperative vehicle-to-vehicle (V2V) system with amplify-and-forward relaying for typical traffic scenarios under city/urban settings and a highway area. We derive pairwise error probability (PEP) expressions and demonstrate the achievable diversity gains. The effect of imperfect channel state information (CSI) is also studied through an asymptotical PEP analysis. We present Monte-Carlo simulations to confirm the analytical derivations and present the error rate performance of the vehicular scheme with perfect and imperfect-CSI. In the second part, we consider road-to-vehicle (R2V) communications in which roadside access points use cooperating vehicles as relaying terminals. Under the assumption of decode-and-forward relaying, we derive PEP expressions for single-relay and multi-relay scenarios. In the third part, we consider a cooperative multi-hop V2V system in which direct transmission is not possible and investigate its performance through the PEP derivation and diversity gain analysis. Monte-Carlo simulations are further provided to con firm the analytical derivations and provide insight into the error rate performance improvement.

Made available in DSpace on 2016-06-02T19:05:42Z (GMT). No. of bitstreams: 1 3072.pdf: 1703350 bytes, checksum: 5213111edf7f7c40880a68e93c0462c0 (MD5) Previous issue date: 2010-02-18 / Universidade Federal de Sao Carlos / Mobile computing devices often present high processing power and include several wireless network interfaces. 4G networks promise to provide a unified IP based infrastructure with QoS and security support for the communications using such devices. Transmission delays, and network disruptions, however, are often common when considering the current transmissions of mobile users. This work presents a software communications architecture which is tolerant to transmission delays and intermittent connectivity by exploring a hop-by-hop forwarding mode in DTNs. The proposed architecture is organized as a set of functional layers, which allow the use of different forwarding policies and network technologies. By providing the forwarding of objects, named bundles, an unlimited number of high level communication applications can be implemented on top of the architecture. Security aspects concerning the proper identification of users and transmission bundles, as well as the confidentiality and authentication of the received information are considered in the project of the developed architecture. Log keeping of the bundle forwarding activities performed by the architecture, including the interactions among users and the data passing operations, may be further investigated for use in different context aware forwarding and social organization algorithms. A partial implementation of the developed architecture was made and the results demonstrate the viability of its operation. / Dispositivos computacionais móveis comumente apresentam elevada capacidade de processamento e disponibilidade de múltiplas interfaces de comunicação em rede. Sob o ponto de vista da transmissão de dados, redes 4G deverão prover uma infraestrutura unificada baseada no uso do protocolo IP, com suporte a segurança e QoS para esses dispositivos. Atrasos de propagação, rupturas e perdas de conectividade, contudo, ainda são comuns quando se considera a mobilidade dos usuários. Este trabalho apresenta uma arquitetura de comunicação tolerante a atrasos e conectividade intermitente, que explora o modo de encaminhamento ponto a ponto para prover transmissões em redes DTNs. A arquitetura é organizada em camadas, possibilitando o uso de diferentes políticas de encaminhamento e de diferentes tecnologias de transmissão. Ao prover o encaminhamento de objetos de transmissão, chamados bundles, um número ilimitado de serviços de comunicação em alto nível pode ser implementado sobre a arquitetura desenvolvida. Questões de segurança na identificação dos usuários e dos bundles transmitidos, bem como a confidencialidade e a autenticação das informações são considerados no projeto da arquitetura desenvolvida. O registro de operações realizadas durante os encaminhamentos, incluindo contatos entre usuários e eventos de transmissão, pode ainda servir para alimentar uma base de dados a ser explorada por diferentes algoritmos relacionados a organizações sociais e políticas de encaminhamento cientes de contexto. Uma implementação parcial das funcionalidades previstas pela arquitetura foi realizada e os resultados obtidos mostram a viabilidade de sua operação.

This licentiate thesis work investigates two medium access control (MAC) methods, when used in traffic safety applications over vehicular ad hoc networks (VANETs). The MAC methods are carrier sense multiple access (CSMA), as specified by the leading standard for VANETs IEEE 802.11p, and self-organizing time-division multiple access (STDMA) as used by the leading standard for transponders on ships. All vehicles in traffic safety applications periodically broadcast cooperative awareness messages (CAMs). The CAM based data traffic implies requirements on a predictable, fair and scalable medium access mechanism. The investigated performance measures are channel access delay, number of consecutive packet drops and the distance between concurrently transmitting nodes. Performance is evaluated by computer simulations of a highway scenario in which all vehicles broadcast CAMs with different update rates and packet lengths. The obtained results show that nodes in a CSMA system can experience unbounded channel access delays and further that there is a significant difference between the best case and worst case channel access delay that a node could experience. In addition, with CSMA there is a very high probability that several concurrently transmitting nodes are located close to each other. This occurs when nodes start their listening periods at the same time or when nodes choose the same backoff value, which results in nodes starting to transmit at the same time instant. The CSMA algorithm is therefore both unpredictable and unfair besides the fact that it scales badly for broadcasted CAMs. STDMA, on the other hand, will always grant channel access for all packets before a predetermined time, regardless of the number of competing nodes. Therefore, the STDMA algorithm is predictable and fair. STDMA, using parameter settings that have been adapted to the vehicular environment, is shown to outperform CSMA when considering the performance measure distance between concurrently transmitting nodes. In CSMA the distance between concurrent transmissions is random, whereas STDMA uses the side information from the CAMs to properly schedule concurrent transmissions in space. The price paid for the superior performance of STDMA is the required network synchronization through a global navigation satellite system, e.g., GPS. That aside since STDMA was shown to be scalable, predictable and fair; it is an excellent candidate for use in VANETs when complex communication requirements from traffic safety applications should be met.

Orientador: Michel Daoud Yacoub / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-10T09:17:00Z (GMT). No. of bitstreams: 1 Medeiros_AlvaroAugustoMachadode_D.pdf: 910419 bytes, checksum: 8fee720ee964b6908659ff1ab27c754e (MD5) Previous issue date: 2007 / Resumo: As redes ad hoc são redes sem um controle centralizado, cujos nós se comunicam através de um canal sem fio diretamente ou através de múltiplos saltos. Uma questão complexa referente a redes ad hoc é o cálculo da capacidade. Estimar quantas transmissões a rede permite, garantindo qualidade de serviço aos usuarios é uma tarefa difícil em virtude de duas características da rede: o canal sem fio e as transmissões em múltiplos saltos. Este trabalho propõe um novo método para cálculo da capacidade através da probabilidade de outage que considera ambos os aspectos. Este método apresenta vantagens como fácil implantação, baixo esforço computacional e resultados praticamente indistinguíveis daqueles obtidos atraves de simulação. O metodo pode ser aplicado aos mais variados ambientes de propagação e qualquer topologia de rede. Modelos de interferência mais realistas, bem como a questão do roteamento são também abordados ao longo do trabalho / Abstract: Ad hoc networks are networks that operate without centralized control, whose nodes communicate through wireless links in a single or multihop way. A complex issue about ad hoc networks is the capacity estimation. The computation of how many transmissions the network can support ensuring a quality of service for its users is a difficult task due to two central aspects: the wireless medium and the multihop nature of transmissions. An analytical method to calculate the capacity through the computation of the outage probability considering both aspects is proposed in this work. This method presents advantages such as simple implementation, low computational efforts and practically indistinguishable results from those obtained through simulation. This method can be applied to many propagation environments and to any network topology. More realistic interference models and the routing issue are also described along this work / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica