Dissertations / Theses on the topic 'Broadcast dissemination'

Emergency Message (EM) dissemination in Vehicular Ad hoc Networks (VANETs) has attracted significant attention in Intelligent Transportation System (ITS) in recent years. Such dissemination mechanisms mostly rely on licensed Dedicated Short Range Communications (DSRC) systems such as IEEE 802.11p and IEEE PI609.1-4 standards. By timely broadcasting of emergency messages (EMs), drivers can avoid potentially dangerous accidents and experience a safer driving environment. As the result, a concern of the number of accidents is also reduced. Thus, an efficient broadcast protocol is required in this scenario. In this thesis, designs of robust broadcast protocols are considered for Emergency Message Dissemination in VANETs. It presents four innovative contributions. Firstly, a literature review as well as challenges and issues of the protocols designed for EM dissemination application are presented. Secondly, Priority-based Routing Protocol (PRP) and its reliability enhancement (PRP-RE) have been proposed as broadcast protocols for different types of EM disseminations, providing; 1) fully distributed broadcast protocol; 2) different Quality of Services (QoS) for different types of EMs: 3) maximum message dissemination distance per hop; and 4) high communication reliability. Thirdly, a more efficient and robust multi-hop broadcast protocol for time-critical EM disseminations is proposed as Trinary Partitioned Black-Burst based Broadcast Protocol (3P3B). A mini-DIPS in MAC sub-layer is introduced to give the time-critical EMs the highest priority access to the communication channel compared to other EMs. In addition, a trinary partitioning is designed to iteratively partition the communication area into small sectors, allowing only the furthest possible vehicle to perform EM forwarding. Therefore. 3P3B can increase dissemination speed and reduce contention period jitter. The performance evaluation results demonstrate that 3P3B outperforms benchmarks of the existing broadcast protocols in VANETs in terms of average message dissemination speed, message progress, communication delay, and packet delivery ratio. Finally, 3P3B-DTN is proposed based on an enhancement of 3P3B to deal with communications in a disruptive network with an introduction of EM store, carry, and forward to maximize packet delivery ratio while minimizing end-to-end delay. The performance evaluation results show that 3P3BDTN achieves higher packet delivery ratio than 3P3B even when the network is disrupted with a trade-off of higher end-to-end delay and overhead for those EMs, which would be lost otherwise.

Thesis (M.S. in Space Systems Operations) Naval Postgraduate School, September 1998.
"September 1998." Thesis advisor(s): Dan C. Boger, Carl R. Jones, John S. Osmundson. Includes bibliographical references (p. 191-194). Also available online.

Cette thèse s’articule autour de deux séries de travaux motivés par des expériences sur des fourmis. Bien qu’inspirés par labiologie, les modèles que nous développons utilisent une terminologie et une approche typique de l’informatique théorique.Le premier modèle s’inspire du transport collaboratif de nourriture au sein de l’espèce P. Longicornis. Certains aspectsfondamentaux du processus peuvent être décrits par un problème de recherche sur un graphe en présence d’un certain typed’indications bruitées à chaque noeud. Ces indications représentent de courtes traces de phéromones déposées devant l’objettransporté afin de faciliter la navigation. Dans cette thèse, nous donnons une analyse complète du problème lorsque le graphesous-jacent est un arbre, une hypothèse pertinente dans un cadre informatique. En particulier, notre modèle peut être vucomme une généralisation de la recherche binaire aux arbres, en présence de bruit. De manière surprenante, lescomportements des algorithmes optimaux dans ce cadre diffèrent suivant le type de garantie que l’on étudie : convergence enmoyenne ou avec grande probabilité.Le deuxième modèle présenté dans cette thèse a été conçu pour décrire la dissémination d’informations au sein de fourmis dudésert. Dans notre modèle, les échanges ont lieu uniformément au hasard, et sont sujets à du bruit. Nous prouvons une borneinférieure sur le nombre d’interactions requis en fonction de la taille du groupe. La borne, de même que les hypothèses dumodèle, semblent compatible avec les données expérimentales.Une conséquence théorique de ce résultat est une séparation dans ce cadre des variantes PUSH et PULL pour le problème du broadcast avec bruit. Nous étudions aussi une version du problème avec des garanties de convergence plus fortes. Dans cecas, le problème peut-être résolu efficacement, même si les échanges d’information au cours de chaque interaction sont très limités
This thesis is built around two series of works, each motivated by experiments on ants. We derive and analyse new models,that use computer science concepts and methodology, despite their biological roots and motivation.The first model studied in this thesis takes its inspiration in collaborative transport of food in the P. Longicornis species. Wefind that some key aspects of the process are well described by a graph search problem with noisy advice. The advicecorresponds to characteristic short scent marks laid in front of the load in order to facilitate its navigation. In this thesis, weprovide detailed analysis of the model on trees, which are relevant graph structures from a computer science standpoint. Inparticular our model may be viewed as a noisy extension of binary search to trees. Tight results in expectation and highprobability are derived with matching upper and lower bounds. Interestingly, there is a sharp phase transition phenomenon forthe expected runtime, but not when the algorithms are only required to succeed with high probability.The second model we work with was initially designed to capture information broadcast amongst desert ants. The model usesa stochastic meeting pattern and noise in the interactions, in a way that matches experimental data. Within this theoreticalmodel, we present in this document a strong lower bound on the number of interactions required before information can bespread reliably. Experimentally, we see that the time required for the recruitment process of even few ants increases sharplywith the group size, in accordance with our result. A theoretical consequence of the lower bound is a separation between theuniform noisy PUSH and PULL models of interaction. We also study a close variant of broadcast, without noise this time butunder more strict convergence requirements and show that in this case, the problem can be solved efficiently, even with verylimited exchange of information on each interaction

Publish/subscribe communication paradigm is an interaction paradigm suitable for a variety of large scale dynamic applications, requiring selective events diffusion or data notification: news delivery, stock quoting, on-line games, dissemination of multimedia contents, services and resources discovery, remote control of critical infrastructures and management of large scale systems are examples of systems requiring such reactive communication paradigm. Content-based publish/subscribe is the most promising version of publish/subscribe system: in such systems, users subscribe to content-based conditions, and will be notified about the published events that satisfy their expressed conditions. Content-based style subscriptions are highly expressive and flexible, permitting the users to specify complex filtering criteria along multiple dimensions of the events content. In contrast to their flexibility and expressiveness, scalable content-based publish/subscribe systems are difficult to implement and the proposed solutions are not always mature. In other words, one of the most fundamental requirement in the area of content-based pub/sub systems is to design scalable and efficient event dissemination mechanisms maintaining the expressiveness in the subscription language and the flexibility in the structures defining the events. In addition, most of existing pub/sub systems assume that actors involved in the subscriptions management have global knowledge about active subscriptions. This assumption limits the scalability of the existing approaches when they are dealing with large scale and dynamical systems. In this thesis, we research for algorithms and techniques that permit to build content-based pub/sub systems over efficient data dissemination structures. The thesis consists on different kind of contributions. First of all, a global and systematic analysis of the functionalities of the event service has been produced, critically describing the current solutions, the strengths and the weaknesses of the existing approaches. In the second part, we propose innovative algorithms and architectures for pub/sub systems. We introduce novel approaches for content-based pub/sub systems, guaranteeing the expressiveness for any application domain and maintaining the scalability with respect to the number of participants and to the number subscriptions. The clustering functionality is designed to match application-level multicast techniques with content-based routing of events. We introduce clustering mechanisms (hierarchical and not hierarchical algorithms) in the event service to dynamically identify groups of users with similar preferences and to adapt these groups in the context of content-based publish/subscribe systems. One of the main feature of the proposed mechanism is the use of the system state knowledge sharing by system nodes, with the goal of limiting the system overhead in terms of computing, bandwidth and storage resources. Gossiping and probabilistic techniques represent a potential and open research field that has been analyzed and described within this work. In high dynamical large scale systems, the dynamic and unpredictable behavior of the nodes can cause problems to be resolved with approaches more adaptive and robust to the fast and frequent system changes. An innovative solution for pub/sub systems is proposed relying on an unstructured overlay network where a variant of subscriptions flooding-based algorithm is adopted to face with highly dynamical environments. Last contribution consists of examples of real applications that exploit the potentialities of the publish-subscribe paradigm model. We provide architectures based on the pub/sub models in the field of the infrastructures for monitoring critical systems and of the infrastructures for context-aware applications. Keywords: clustering, multicast dissemination, broadcast dissemination, collaborative p2p approaches, structured and unstructured overlay networks, distributed systems evaluation, architectures based on pub/sub models.

Network programming is one of the most important applications in Wireless Sensor Networks as It provides an efficient way to update program Images running on sensor nodes without physical access to them. Securing these updates, however, remains a challenging and important issue, given the open deployment environment of sensor nodes. Though several security schemes have been proposed to impose the authenticity and Integrity protection on network programming applications, they are either energy Inefficient as they tend to use digital signature or lacks the data confidentiality. In addition, due to the absence of secure memory management in the current sensor hardware, the attacker could inject malicious code into the program flash by exploiting buffer overflow In the memory despite the secure code dissemination. The contribution of this thesis Is to provide two software-based security protocols and one hardware-based remote attestation protocol for network programming application. Our first protocol deploys multiple one-way key chains for a multi-hop sensor network. The scheme Is shown to be lower In computational, power consumption and communication costs yet still able to secure multi??hop propagation of program images. Our second protocol utilizes an Iterative hash structure to the data packets in network programming application, ensuring the data confidentiality and authenticity. In addition, we Integrated confidentiality and DoS-attack-resistance in a multi??hop code dissemination protocol. Our final solution is a hardware-based remote attestation protocol for verification of running codes on sensor nodes. An additional piece of tamper-proof hardware, Trusted Platform Module (TPM), is imposed into the sensor nodes. It secures the sensitive information (e.g., the session key) from attackers and monitors any platform environment changes with the Internal registers. With these features of TPM, the code Injection attack could be detected and removed when the contaminated nodes are challenged in our remote attestation protocol. We implement the first two software-based protocols with Deluge as the reference network programming protocol in TinyOS, evaluate them with the extensive simulation using TOSSIM and validate the simulation results with experiments using Tmote. We implement the remote attestation protocol on Fleck, a sensor platform developed by CSIRO that Integrates an Atmel TPM chip.

In Intelligent Transportation Systems (ITS), disseminating warning messages in a timely and efficient way through wireless short-range communications can save many lives and reduce traffic congestion. A geographical broadcast protocol provides data delivery to specified geographical areas, using multi-hop communications if needed. Among the main challenges for such protocols are forwarder selection and the reduction of the number of hops required to reach and cover the destination area.  In this thesis we propose an efficient geographical broadcast protocol called Preferred and Contention Based Forwarding (PCBF) and evaluate it through simulations. PCBF uses a combination of contention-based forwarding and selecting preferred forwarders also found in other protocols like Emergency Message Dissemination for Vehicular Environments (EMDV). Since the preferred forwarder is allowed to immediately forward the packet (evading contention among other potential forwarders), this approach reduces end-to-end delays. Notable extensions of PCBF compared to EMDV are the use of direct negative acknowledgements in case of unnecessary rebroadcasts and the use of forwarders outside the target region.  Our simulation results show that the PCBF protocol outperforms selected other protocols in terms of end-to-end delay, re-broadcast overhead and reliability in both sparse and dense networks.

Such large quantities of data and information are already being "trafficked" over networks, that the term information commerce has been coined. To facilitate information commerce, various infrastructures have been used, ranging from the Internet to local area networks. However, traditional information access strategies, termed pull-based strategies, tend to work poorly in most frameworks due to the notion of communication asymmetry [IVB97]. An alternative paradigm of disseminating information to a large number of clients is through the use of broadcasts. This dissertation addresses two major issues of interest in the broadcast scenario: (1) determining what to broadcast, and how the clients retrieve from the broadcasts, and, (2) how to provide secure access control to broadcast data. In this dissertation, we explore the general domain of data organization and access in broadcasts. Specifically, we design solutions that enable clients to retrieve their data of interest efficiently, as well as with a minimum of energy expenditure, particularly in a wireless context, and, we facilitate clients' subscription to the broadcast data by providing a secure access control layer.

Gli algoritmi di gossip sono utilizzati per la disseminazione di messaggi in una rete peer-to-peer. La tesi tratta lo sviluppo, l'implementazione e l'analisi di quattro nuovi algoritmi di gossip "a due fasi". Gli algoritmi sono stati sviluppati e testati con il simulatore LUNES per poi essere analizzati in vari confronti con gli algoritmi classici dell'ambito, ovvero Fixed Probability e Conditional Broadcast. Le prove sono state effettuate su varie tipologie di grafi, ovvero Random, Scale-free, Small-world e K-Regular.

La convergencia de las telecomunicaciones, la informática, la tecnología inalámbrica y los sistemas de transporte, va a facilitar que nuestras carreteras y autopistas nos sirvan tanto como plataforma de transporte, como de comunicaciones. Estos cambios van a revolucionar completamente cómo y cuándo vamos a acceder a determinados servicios, comunicarnos, viajar, entretenernos, y navegar, en un futuro muy cercano. Las redes vehiculares ad hoc (vehicular ad hoc networks VANETs) son redes de comunicación inalámbricas que no requieren de ningún tipo de infraestructura, y que permiten la comunicación y conducción cooperativa entre los vehículos en la carretera. Los vehículos actúan como nodos de comunicación y transmisores, formando redes dinámicas junto a otros vehículos cercanos en entornos urbanos y autopistas. Las características especiales de las redes vehiculares favorecen el desarrollo de servicios y aplicaciones atractivas y desafiantes. En esta tesis nos centramos en las aplicaciones relacionadas con la seguridad. Específicamente, desarrollamos y evaluamos un novedoso protocol que mejora la seguridad en las carreteras. Nuestra propuesta combina el uso de información de la localización de los vehículos y las características del mapa del escenario, para mejorar la diseminación de los mensajes de alerta. En las aplicaciones de seguridad para redes vehiculares, nuestra propuesta permite reducir el problema de las tormentas de difusión, mientras que se mantiene una alta efectividad en la diseminación de los mensajes hacia los vehículos cercanos. Debido a que desplegar y evaluar redes VANET supone un gran coste y una tarea dura, la metodología basada en la simulación se muestra como una metodología alternativa a la implementación real. A diferencia de otros trabajos previos, con el fin de evaluar nuestra propuesta en un entorno realista, en nuestras simulaciones tenemos muy en cuenta tanto la movilidad de los vehículos, como la transmisión de radio en entornos urbanos, especialmente cuando los edificios interfieren en la propagación de la señal de radio. Con este propósito, desarrollamos herramientas para la simulación de VANETs más precisas y realistas, mejorando tanto la modelización de la propagación de radio, como la movilidad de los vehículos, obteniendo una solución que permite integrar mapas reales en el entorno de simulación. Finalmente, evaluamos las prestaciones de nuestro protocolo propuesto haciendo uso de nuestra plataforma de simulación mejorada, evidenciando la importancia del uso de un entorno de simulación adecuado para conseguir resultados más realistas y poder obtener conclusiones más significativas.
Martínez Domínguez, FJ. (2010). Improving Vehicular ad hoc Network Protocols to Support Safety Applications in Realistic Scenarios [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/9195
Palancia

Dans le cadre des systèmes de transport intelligents (STI), les véhicules peuvent avoir beaucoup de capteurs (caméras, lidars, radars, etc.) et d’applications (évitement des collisions, surveillance du trafic, etc.) générant des données. Ils représentent alors une source d’information importante. Les applications locales peuvent augmenter considérablement leur efficacité en partageant une telle information au sein du réseau. La précision des données, la confiance et la pertinence peuvent être vérifiées lors de la réception de données provenant d’autres nœuds. Par conséquent, nous croyons qu’une question importante à répondre dans ce contexte est: “Comment partager efficacement les données dans un tel environnement?” Le partage de données est une tâche complexe dans les réseaux dynamiques. De nombreuses problèmes telles que les connexions intermittentes, la variation de la densité du réseau et la congestion du médium de communication se posent. Une approche habituelle pour gérer ces problèmes est basée sur des processus périodiques. En effet, un message envoyé plusieurs fois peut atteindre sa destination même avec des connexions intermittentes et des réseaux à faible densité. Néanmoins, dans les réseaux à haute densité, ils peuvent entraîner une congestion du médium de communication. Dans cette thèse, nous abordons le problème du partage de données dans des réseaux dynamiques en nous appuyant sur des horizons de pertinence. Un horizon est défini comme une zone dans laquelle une information devrait être reçue. Nous commençons par nous concentrer sur le partage de données au sein des voisins directs (à 1 saut de distance). Ensuite, nous proposons une solution pour construire une carte des voisins, centrée sur le nœud ego, dans un horizon à n sauts. Enfin, nous relâchons la définition de l’horizon pour la définir de façon dynamique, où différents éléments de données peuvent atteindre des distances différentes (sauts). En ce qui concerne la solution pour les horizons à 1 saut, notre technique adaptative prend en compte la dynamique des nœuds et la charge du réseau. Afin d’assurer une diffusion efficace des données dans différents scénarios, la fréquence d’envoi des messages est définie en fonction des mouvements des véhicules et d’une estimation du taux de perte du réseau. Après, nous nous concentrons sur la carte des voisins jusqu’à n sauts de distance. Comme la communication avec des nœuds éloignés apporte des problèmes supplémentaires (actions de transfert, retards plus importants, informations périmées), une évaluation de confiance des nœuds identifiés et une estimation de fiabilité du chemin vers chaque voisin sont ajoutées à la carte. Au lieu d’exécuter des processus de diffusion séparés, notre troisième contribution porte sur une stratégie de coopération dont l’objectif principal est de diffuser des données tout en satisfaisant la plupart des nœuds. À cette fin, une trame unique est transmise de nœud en nœud. Sa charge utile est mise à jour localement afin qu’elle contienne les éléments de données les plus pertinents en fonction de certains critères (par exemple, urgence, pertinence). Une telle stratégie définit ainsi un horizon centré sur les données. Nous validons nos propositions au moyen d’émulations de réseaux réalistes. De toutes nos études et des résultats obtenus, nous pouvons affirmer que notre approche apporte des perspectives intéressantes pour le partage de données dans des réseaux dynamiques comme les VANET
In the context of Intelligent Transportation Systems - ITS, vehicles may have a lot of sensors (e.g. cameras, lidars, radars) and applications (collision avoidance, traffic monitoring, etc.) generating data. They represent then an important source of information. Local applications can significantly increase their effectiveness by sharing such an information within the network. Data accuracy, confidence and pertinence can be verified when receiving data from other nodes. Therefore, we believe that an important question to answer in this context is: “How to efficiently share data within such an environment?” Data sharing is a complex task in dynamic networks. Many concerns like intermittent connections, network density variation and communication spectrum congestion arise. A usual approach to handle these problems is based on periodic processes. Indeed, a message sent many times can reach its destination even with intermittent connections and low density networks. Nevertheless, within high density networks, they may lead to communication spectrum scarcity. In this thesis we address the problem of data sharing in dynamic networks by relying in so-called horizons of pertinence. A horizon is defined as an area within which an information is expected to be received. We start focusing on data sharing within direct neighbors (at 1-hop of distance). Then we propose a solution to construct a map of neighbors, centered in the ego-node, within a horizon of n-hops. Finally, we relax the horizon definition to a dynamic defined one where different data items may reach different distances (hops). Regarding the solution for 1-hop horizons, our adaptive technique takes into account nodes’ dynamics and network load. In order to ensure an effective data dissemination in different scenarios, the sending messages frequency is defined according to vehicles movements and an estimation of the network loss rate. Following, we focus on the map of neighbors up to n-hops of distance. As communicationwith distant nodes brings additional concerns (forwarding actions, larger delays, out-of-date information), a trust evaluation of identified nodes and a reliability estimation of the multi-hop path to each neighbor is added to the map. Instead of running separated disseminating processes, our third contribution deals with a cooperative strategy with the main goal of disseminating data while satisfying most of the nodes. For this purpose a unique frame is forwarded from node to node. Its payload is locally updated so that it contains the most relevant data items according to some criteria (e.g. urgency, relevance). Such a strategy defines thus a data-centered horizon. We validate our proposals by means of realistic network emulations. From all our studies and achieved results we can state that our approach brings interesting insights for data sharing in dynamic networks like VANETs

博士
國立臺灣大學
電機工程學研究所
91
The advance in wireless communication enables users to access information systems anytime, anywhere, via various mobile devices such as notebooks, tablet PCs, personal digital assistants (PDAs) and GPRS-enabled cellular phones. Service providers are establishing a number of mobile services including weather forecasting, stock information dissemination, location-dependent query, route guidance and so on. To provide such services, researchers have encountered and are endeavoring to overcome challenges in related research areas, including mobile data management, wireless network infrastructure, location-dependent data management, and pervasive computing, to name a few. A mobile computing environment is in essence a distributed system. However, a computing environment is more challenging than a traditional distributed system due to the following characteristics: resource limited mobile devices, low network bandwidth, heterogeneity on mobile devices and user mobility. In recent years, data broadcast becomes a promising technique in a mobile computing environment. However, most prior works are under the premise that each user requests only one data item at a time and the requests for all data items are independent. However, in many real applications, some data items are semantically related and there exists dependency among the requests of these data items. Broadcast program generation algorithms assuming independent requests might not be able to effectively optimize the performance of the broadcast programs. This is the very problem we shall address in this dissertation. In addition to broadcast mode, channels can operate in on-demand mode in which a client explicitly sends data requests to retrieve the data items of interest. The major advantage of data broadcast is its scalability since the performance of the system does not depend on the number of clients listening to the broadcast channels. However, the performance degrades as the number of data items being broadcast increases. It has been shown that the combined use of the broadcast and on-demand channels can utilize bandwidth more efficiently. Hence, we also explore the problem of data and channel allocation to partition a given number of communication channels into broadcasting ones and on-demand ones. To address the problems resulting from the heterogeneity of various mobile devices, a proxy capable of transcoding (referred to as a transcoding proxy) is placed between a client and an information server to coordinate the mismatch between what the server provides and what the client prefers. Since proxy-based approaches are transparent to the content providers and users, this kind of approaches is able to simplify the design of servers and clients. However, most research works in transcoding proxies in mobile computing environments are under the traditional client-server architecture and do not employ the data broadcast technique. Hence, the transcoding proxies are not scalable and the network bandwidth is not well utilized. In addition, most prior studies do not consider the issue of quality of service (abbreviated as QoS) which is crucial in a mobile computing environment. In view of this, we design a scalable and QoS-aware transcoding proxy by utilizing the on-demand broadcasting technique to provide scalable and QoS-aware services.

博士
國立臺灣大學
電機工程學研究所
91
The needs of various classes of modern data and information applications, especially those targeted at mobile computing, demand the support of adaptive data broadcasting, and the support in turn demands a new kind of data dissemination framework. For proper implementation, the service model of adaptive data broadcasting must provide the methodologies of dynamic traffic awareness and dynamic broadcast content adaptation. At the same time, these methodologies must be implemented as a distributed data dissemination platform, having the guarantees of efficiency, reliability, robustness, and scalability. We advocate that the design and development of adaptive data broadcasting schemes should be backward compatible, rather than replacing the conventional paradigm, in accordance with the principles of information dissemination and dynamic data management. To this end, in this dissertation, we formulate the fundamentals of adaptive data broadcasting, relate them to the traditional data broadcast scheme, and devise several promising mechanisms. Note that prior researches in the data broadcast realm are mainly based on the traditional data management model, where data items are independent, persistent, and static. In fact, however, many modern information broadcast applications enable the generation and spread of dynamic data. To fulfil the requirements for the dissemination of dynamic data and information broadcast services on broadcast channels, we address the impacts of dynamic traffic awareness and dynamic broadcast content adaptation. Accordingly, we propose in this dissertation four promising mechanisms for this purpose:\ particularly, (1) Dynamic Broadcast Traffic Awareness, (2) Adaptive Multi-Channel Data Dissemination, (3) Adaptive Information Dissemination with Loan-Based Feedback Control, and (4) On Scheduling Sequential Objects with Periodicity for Dynamic Information Dissemination. Considering the nature of dynamic traffic changes, Chapter 2 devises an innovative traffic awareness mechanism, by exploiting the significant potential of client impatience, to estimate the dynamic access frequency distribution. In comparison with the probing and the feedback techniques, the proposed \textit{selective deferment and reflection} (SDR) technique is light-weight and of low complexity. Extensive simulations show that in the case of an increasing/decreasing workload, the real access frequency distribution is bounded by two specific estimated distributions. This fact in turn suggests us to devise a trigonometric tuning method to further enhance the estimation. Consequently, the dynamic traffic awareness mechanism is able to generate an access frequency distribution very close to the real one, showing the feasibility and reliability for adaptive data broadcasting. Chapter 3 proposes an \textit{adaptive multi-channel data dissemination} (AMD) mechanism, which supports the \textit{multi-channel traffic awareness} (MCTA) and the \textit{deterministic balance search} (DBS), in order to pursuit the fairness and robustness for a hybrid data delivery in multi-channel data dissemination environments. In light of the SDR technique, MCTA\ is able to periodically estimate the dynamic access frequencies of all items in the push channels. With the MCTA estimation, furthermore, DBS employs a heuristic search for the global balance, where the push access time and the pull response time are minimized. The experimental results show that the estimated access frequency distribution by MCTA has high accuracy. In addition, DBS\ is robust against the slight accuracy difference caused by MCTA, and notedly attains a global balance very close to the optimum. In order to support the dissemination of static and dynamic information services simultaneously, the work in Chapter 4 devises the \textit{% group-based information dissemination} (GID) mechanism with the \textit{% loan-based slot allocation and feedback control} (LSAFC) technique. The GID mechanism not only supports dynamic information dissemination, but also is backward compatible with the conventional data broadcast scheme. Both of the client-oriented and the server-oriented traffic factors are involved in the GID\ mechanism. Further, we design the LSAFC technique to sustain dynamic traffic changes. Accordingly, the integration of the GID\ mechanism and the LSAFC\ technique is able to perform the adaptations of broadcast slot allocation, group association, group popularity and classification, and broadcast program. Performance study shows that the GID mechanism is very scalable and attains a substantial reduction of dynamic message traffic. In addition, the LSAFC technique is able to functionally complement the GID mechanism, therefore making the GID mechanism more efficient and robust. With regard to data association, dependency, and dynamics, Chapter 5 studies the problem of scheduling dynamic time-sequential data objects in a generalized clients-providers-servers system. According to the principle of periodicity, the scheduling optimization is transformed as the procedure of finding a solution in solving the algebraic problem. In light of the derived upper and lower bounds of mean service access time, a deterministic selection algorithm is developed for the optimal approximation. Several gain measure functions are designed to incrementally enhance the deterministic object selection in response to dynamic data traffic. The broadcast sequence is guaranteed corresponding to the object production order so as to make sure of the correctness of information in the broadcast schedule. Performance evaluation shows the presented deterministic strategy performs prominently in the approximation of schedule optimization. Hence, the mean service access time is minimized to the extent of being close to the theoretical optimum.

碩士
淡江大學
資訊工程學系資訊網路與通訊碩士班
102
Effectively broadcasting emergency messages in vehicular ad hoc networks (VANETs) is an important issue in VANETs. This paper proposes a Dynamic Partition Assisted Broadcast (DPAB) protocol to effectively broadcast emergency messages in VANETs. Adjusting the power level of control messages to estimate the network density and dynamically partition a transmission range into segments are the major techniques in DPAB. To do so can not only find the best vehicle in the furthest possible segment to relay the emergency messages in the network, but also can reduce the interference among vehicles to save the network resource and increase the packet delivery ratio. Based on the mathematical analyses and network simulations, the proposed protocol, DPAB, has a significant performance against the related work in one hop delay and packet delivery ratio.

碩士
淡江大學
資訊工程學系資訊網路與通訊碩士班
100
Recently, wireless communications have been used in the daily life with the growth of the wireless networks, such as vehicular ad hoc networks. The rapid development of transport increases the congestion and traffic accident. Therefore, many countries develop the intelligent transportation system and subsystem, dedicated short range communication technology to apply on the vehicular ad hoc networks for the communications among vehicles in the high mobile environments. The main purpose of the vehicular ad hoc networks is to provide the emergency message dissemination and normal data transmissions. In order to keeps drivers far away the traffic accident, the broadcast of immediate emergent notifications in vehicular ad hoc networks has become one of the hot research issues. Therefore, this thesis proposes a reliable emergent notifications broadcast protocol using directional antennas in vehicular ad hoc networks. The proposed protocol assigns the forwarding vehicle based on the neighboring vehicular information. Therefore, the protocol not only provides a broadcast of the reliable emergent notifications, but also shorts the wasted time used for the assignment of the forwarding vehicle and the collection of neighboring vehicular information.

In mobile and wireless networks, data broadcasting for popular data items enables the efficient utilization of the limited wireless bandwidth. However, efficient data scheduling schemes are needed to fully exploit the benefits of data broadcasting. Towards this goal, several broadcast scheduling policies have been proposed. These existing schemes have mostly focused on either minimizing response time, or drop rate, when requests are associated with hard deadlines. The inherent inaccuracy of hard deadlines in a dynamic mobile environment motivated us to use Service Level Agreements (SLAs) where a user specifies the utility of data as a function of its arrival time. Moreover, SLAs provide the mobile user with an already familiar quality of service specification from wired environments. Hence, in this dissertation, we propose SAAB, an SLA-aware adaptive data broadcast scheduling policy for maximizing the system utility under SLA-based performance measures. To achieve this goal, SAAB considers both the characteristics of disseminated data objects as well as the SLAs associated with them. Additionally, SAAB automatically adjusts to the system workload conditions which enables it to constantly outperform existing broadcast scheduling policies.