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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Adaptive Probabilistic Routing in Wireless Ad Hoc Networks

Hasan, Affaf, Liaqat, Ismail January 2013 (has links)
The goal of this thesis work is to analyze how design elements and wireless attributes affect opportunistic routing, and in this context develop a new protocol. The algorithm developed aims to improve opportunistic elements in comparison to a well-known opportunistic protocol Simple Opportunistic Adaptive Routing (SOAR).
2

Opportunistic Routing for Enhanced Source-location Privacy in Wireless Sensor Networks

Spachos, Petros 11 January 2011 (has links)
Wireless sensor networks (WSN) are an attractive solution for a plethora of communication applications, such as unattended event monitoring and tracking. One of the looming challenges that threaten the successful deployment of these sensor networks is source-location privacy, especially when they are used to monitor sensitive objects. In order to enhance source location privacy in sensor networks, we propose the use of an opportunistic routing scheme and we examine four different approaches. In opportunistic routing, each sensor transmits the packet over a dynamic path to the destination. Every packet from the source can therefore follow a different path toward the destination, making it difficult for an adversary to backtrack hop-by-hop to the origin of the sensor communication. Through theoretical analysis, we attempt to justify the use of opportunistic routing for the source-location problem. Moreover, simulations have been conducted in order to evaluate the performance of all the proposed schemes, in terms of source-location privacy.
3

Opportunistic Routing for Enhanced Source-location Privacy in Wireless Sensor Networks

Spachos, Petros 11 January 2011 (has links)
Wireless sensor networks (WSN) are an attractive solution for a plethora of communication applications, such as unattended event monitoring and tracking. One of the looming challenges that threaten the successful deployment of these sensor networks is source-location privacy, especially when they are used to monitor sensitive objects. In order to enhance source location privacy in sensor networks, we propose the use of an opportunistic routing scheme and we examine four different approaches. In opportunistic routing, each sensor transmits the packet over a dynamic path to the destination. Every packet from the source can therefore follow a different path toward the destination, making it difficult for an adversary to backtrack hop-by-hop to the origin of the sensor communication. Through theoretical analysis, we attempt to justify the use of opportunistic routing for the source-location problem. Moreover, simulations have been conducted in order to evaluate the performance of all the proposed schemes, in terms of source-location privacy.
4

Optimizing opportunistic communication in wireless networks

Han, Mi Kyung 17 November 2011 (has links)
Opportunistic communication leverages communication opportunities arising by chance to provide significant performance benefit and even enable communication where it would be impossible otherwise. The goal of this dissertation is to optimize opportunistic communication to achieve good performance in wireless networks. A key challenge in optimizing opportunistic communication arises from dynamic and incidental nature of communication. Complicated wireless interference patterns, high mobility, and frequent fluctuations in wireless medium make the optimization even harder. This dissertation proposes a series of optimization frameworks that systematically optimizes opportunistic communication to achieve good performance in wireless mesh networks and vehicular networks. We make the following three major contributions: First, we develop novel algorithms, techniques, and protocols that optimize opportunistic communication of wireless mesh network to achieve good, predictable user performance. Our framework systematically optimizes end-to-end performance (e.g., total throughput). It yields significant improvement over existing routing schemes. We also show that it is robust against inaccuracy introduced by dynamic network conditions. Second, we propose a novel overlay framework to exploit inter-flow network coding in opportunistic routing. In this framework, an overlay network performs inter-flow coding to effectively reduce traffic imposed on the underlay network, and an underlay network uses optimized opportunistic routing to provide efficient and reliable overlay links. We show that inter-flow coding together with opportunistic routing and rate-limiting brings significant performance benefit. Finally, we develop a novel optimization framework in vehicular networks to effectively leverage opportunistic contacts between vehicles and access points (APs). We develop a new mobility prediction algorithm and an optimization algorithm to determine an efficient replication scheme that exploit the synergy among Internet connectivity, local wireless connectivity, mesh network connectivity, and vehicular relay connectivity. Based on our framework, we develop a practical system that enables high-bandwidth content distribution and demonstrate the effectiveness of our approach using simulation, emulation, and testbed experiments. / text
5

Opportunistic routing in intermittently connected wireless mobile social networks

Khosravi, Arian 07 May 2012 (has links)
Consumer electronics such as cellular phones and portable computers with short-range communication capabilities have enabled the large-scale information dissemination through user mobility and contact, without the assistance of communication infrastructures. In such a new communication paradigm, one challenge is to determine when and how to forward a message to the destination, possibly through a series of third parties. This problem has attracted a lot of attention in the literature lately, with proposals ranging from epidemic to single or multi-copy spray and wait or focus strategies. However most existing work assumed independent or identically distributed mobility. Observing most human mobility and interaction are interest-driven in the real world, in this research, we evaluate the performance of these schemes with an interest-driven mobility model. We further propose to take the user interest into account when determining routing strategies to further improve the performance of these schemes for mobile social networks. Simulation results have demonstrated the efficacy of the interest-aware routing strategies. / Graduate
6

Mobility-based Candidate Selection and Coordination in Opportunistic Routing for Mobile Ad-Hoc Networks

Tahooni, Mohammad January 2014 (has links)
Opportunistic Routing (OR) is an effective and enhanced routing scheme for wireless multihop environment. OR is an approach that selects a certain number of best forwarders (candidates) at each hop by taking the advantage of the broadcast nature of the wireless medium to reach the destination. When a set of candidates receive the packet, they coordinate with each other to figure out which one has to forward the packet toward the destination. Most of the research in this area has been done in mesh networks where nodes do not have mobility. In this survey, we propose a new OR protocol for mobile ad hoc scenarios called as Enhanced Mobility-based Opportunistic Routing (EMOR) protocol. To deal with the node mobility, we have proposed a new metric which considers the following: geographical position of the candidates; the link delivery probability to reach them; the number of neighboring nodes of candidates; and the predicted position of nodes using the motion vector of the nodes. We have compared EMOR with five other well-known routing protocols in terms of delivery ratio, end-to-end delay, and expected number of transmissions from source to the destination. Our simulation results show that proposed protocol improves delivery ratio and number of expected transmission in terms of different type of mobility models.
7

Opportunistic Routing in Multihop Wireless Networks: Capacity, Energy Efficiency, and Security

Zeng, Kai 24 July 2008 (has links)
"Opportunistic routing (OR) takes advantages of the spatial diversity and broadcast nature of wireless networks to combat the time-varying links by involving multiple neighboring nodes (forwarding candidates) for each packet relay. This dissertation studies the properties, energy efficiency, capacity, throughput, protocol design and security issues about OR in multihop wireless networks. Firstly, we study geographic opportunistic routing (GOR), a variant of OR which makes use of nodes' location information. We identify and prove three important properties of GOR. The first one is on prioritizing the forwarding candidates according to their geographic advancements to the destination. The second one is on choosing the forwarding candidates based on their advancements and link qualities in order to maximize the expected packet advancement (EPA) with different number of forwarding candidates. The third one is on the concavity of the maximum EPA in respect to the number of forwarding candidates. We further propose a local metric, EPA per unit energy consumption, to tradeoff the routing performance and energy efficiency for GOR. Leveraging the proved properties of GOR, we propose two efficient algorithms to select and prioritize forwarding candidates to maximize the local metric. Secondly, capacity is a fundamental issue in multihop wireless networks. We propose a framework to compute the end-to-end throughput bound or capacity of OR in single/multirate systems given OR strategies (candidate selection and prioritization). Taking into account wireless interference and unique properties of OR, we propose a new method of constructing transmission conflict graphs, and we introduce the concept of concurrent transmission sets to allow the proper formulation of the maximum end-to-end throughput problem as a maximum-flow linear programming problem subject to the transmission conflict constraints. We also propose two OR metrics: expected medium time (EMT) and expected advancement rate (EAR), and the corresponding distributed and local rate and candidate set selection schemes, the Least Medium Time OR (LMTOR) and the Multirate Geographic OR (MGOR). We further extend our framework to compute the capacity of OR in multi-radio multi-channel systems with dynamic OR strategies. We study the necessary and sufficient conditions for the schedulability of a traffic demand vector associated with a transmitter to its forwarding candidates in a concurrent transmission set. We further propose an LP approach and a heuristic algorithm to obtain an opportunistic forwarding strategy scheduling that satisfies a traffic demand vector. Our methodology can be used to calculate the end-to-end throughput bound of OR in multi-radio/channel/rate multihop wireless networks, as well as to study the OR behaviors (such as candidate selection and prioritization) under different network configurations. Thirdly, protocol design of OR in a contention-based medium access environment is an important and challenging issue. In order to avoid duplication, we should ensure only the "best" receiver of each packet to forward it in an efficient way. We investigate the existing candidate coordination schemes and propose a "fast slotted acknowledgment" (FSA) to further improve the performance of OR by using a single ACK to coordinate the forwarding candidates with the help of the channel sensing technique. Furthermore, we study the throughput of GOR in multi-rate and single-rate systems. We introduce a framework to analyze the one-hop throughput of GOR, and provide a deeper insight on the trade-off between the benefit (packet advancement, bandwidth, and transmission reliability) and cost (medium time delay) associated with the node collaboration. We propose a local metric named expected one-hop throughput (EOT) to balance the benefit and cost. Finally, packet reception ratio (PRR) has been widely used as an indicator of the link quality in multihop wireless networks. Many routing protocols including OR in wireless networks depend on the PRR information to make routing decision. Providing accurate link quality measurement (LQM) is essential to ensure the right operation of these routing protocols. However, the existing LQM mechanisms are subject to malicious attacks, thus can not guarantee to provide correct link quality information. We analyze the security vulnerabilities in the existing link quality measurement (LQM) mechanisms and propose an efficient broadcast-based secure LQM (SLQM) mechanism, which prevents the malicious attackers from reporting a higher PRR than the actual one. We analyze the security strength and the cost of the proposed mechanism. "
8

Combatting loss in wireless networks

Rozner, Eric John 27 January 2012 (has links)
The wireless medium is lossy due to many reasons, such as signal attenuation, multi-path propagation, and collisions. Wireless losses degrade network throughput, reliability, and latency. The goal of this dissertation is to combat wireless losses by developing effective techniques and protocols across different network layers. First, a novel opportunistic routing protocol is developed to overcome wireless losses at the network layer. Opportunistic routing protocols exploit receiver diversity to route traffic in the face of loss. A distinctive feature of the protocol is the performance derived from its optimization can be achieved in real IEEE 802.11 networks. At its heart lies a simple yet realistic model of the network that captures wireless interference, losses, traffic, and MAC-induced dependencies. Then a model-driven optimization algorithm is designed to accurately optimize the end-to-end performance, and techniques are developed to map the resulting optimization solutions to practical routing configurations. Its effectiveness is demonstrated using simulation and testbed experiments. Second, an efficient retransmission scheme (ER) is developed at the link layer for wireless networks. Instead of retransmitting lost packets in their original forms, ER codes packets lost at different destinations and uses a single retransmission to potentially recover multiple packet losses. A simple and practical protocol is developed to realize the idea, and it is evaluated using simulation and testbed experiments to demonstrate its effectiveness. Third, detailed measurement traces are collected to understand wireless losses in dynamic and mobile environments. Existing wireless drivers are modified to enable the logging and analysis of network activity under varying end-host configurations. The results indicate that mobile clients can suffer from consecutive packet losses, or burst errors. The burst errors are then analyzed in more detail to gain further insights into the problem. With these insights, recommendations for future research directions to mitigate loss in mobile environments are presented. / text
9

Development of an energy and geographic aware opportunistic network coding scheme / Mario Johann Engelbrecht

Engelbrecht, Mario Johann January 2012 (has links)
The evolution of communication networks has led us to an era where you cannot only perform surgery halfway across the world, but do so while being in the comfort of your own home. By eliminating the need for wires, wireless networks revolutionised communication networks by enabling nodes to communicate while being in a mobile state. The concept opened many doors to new applications and possibilities. Network Coding is a technique that optimises the throughput of a network by coding packets. Geo-Routing is a routing method that operates by using the geographical distances between nodes as the routing metric. Opportunistic Routing is a routing method that exploits the broadcast characteristics of wireless networks. In this thesis, we developed a routing scheme that incorporates Network Coding, Geo- Routing and energy aware conditions. It accomplishes this task by using one of the key phases constituting Opportunistic Routing. The developed routing scheme was implemented in OMNeT++. Various simulation experiments were conducted in OMNeT++ pertaining to the implemented scheme. The results indicate significant increase in performance metrics such as throughput and survivability. / Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013
10

Development of an energy and geographic aware opportunistic network coding scheme / Mario Johann Engelbrecht

Engelbrecht, Mario Johann January 2012 (has links)
The evolution of communication networks has led us to an era where you cannot only perform surgery halfway across the world, but do so while being in the comfort of your own home. By eliminating the need for wires, wireless networks revolutionised communication networks by enabling nodes to communicate while being in a mobile state. The concept opened many doors to new applications and possibilities. Network Coding is a technique that optimises the throughput of a network by coding packets. Geo-Routing is a routing method that operates by using the geographical distances between nodes as the routing metric. Opportunistic Routing is a routing method that exploits the broadcast characteristics of wireless networks. In this thesis, we developed a routing scheme that incorporates Network Coding, Geo- Routing and energy aware conditions. It accomplishes this task by using one of the key phases constituting Opportunistic Routing. The developed routing scheme was implemented in OMNeT++. Various simulation experiments were conducted in OMNeT++ pertaining to the implemented scheme. The results indicate significant increase in performance metrics such as throughput and survivability. / Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013

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