No description available.

No description available.

No description available.

No description available.

No

Yes / The reliability of delivering packets through multi-hop intermediate nodes is a significant issue in the mobile ad hoc networks (MANETs). The distributed mobile nodes establish connections to form the MANET, which may include selfish and misbehaving nodes. Recommendation based trust management has been proposed in the literature as a mechanism to filter out the misbehaving nodes while searching for a packet delivery route. However, building a trust model that relies on the recommendations from other nodes in the network is vulnerable to the possible dishonest behaviour, such as bad-mouthing, ballot-stuffing, and collusion, of the recommending nodes. . This paper investigates the problems of attacks posed by misbehaving nodes while propagating recommendations in the existing trust models. We propose a recommendation based trust model with a defence scheme that utilises clustering technique to dynamically filter attacks related to dishonest recommendations within certain time based on number of interactions, compatibility of information and node closeness. The model is empirically tested in several mobile and disconnected topologies in which nodes experience changes in their neighbourhoods and consequently face frequent route changes. The empirical analysis demonstrates robustness and accuracy of the trust model in a dynamic MANET environment.

Video communications play a vital role in present and future wireless ad hoc networks. One of the key requirements for a successful deployment of multimedia applications in multihop wireless networks is the ability to provide an acceptable video quality, even under a highly dynamic and perhaps unfriendly (or hostile) environment (e.g., in the presence of frequent node/link failure, interference, shadowing, fading, and so forth). Existing ad hoc routing protocols work well for data communications, but are not optimized for video, which is sensitive to latency and packet loss. Moreover, traditional end system based error control mechanisms alone cannot guarantee a sustainable video quality. Conventional QoS approaches typically optimize one or more network layer metrics, but they are usually agnostic to any kind of application layer performance. Consequently, new methodologies must be explored to improve the performance of video applications in multihop wireless networks. This dissertation directly addresses this important problem area by leveraging recent advances in video coding techniques along with novel cross-layer formulations and powerful optimization techniques. We follow an application centric cross-layer approach to address multimedia service provisioning over ad hoc networks. Our research efforts show that video communications over multihop wireless networks can substantially benefit from a cross-layer design principle by factoring in application layer video quality into routing algorithmic designs at the network layer. There are three components in this investigation, namely, (1) concurrent routing, (2) path selection and rate allocation, and (3) multipath routing for multiple description video. Each component addresses one or more unique challenges that hinder video communications in multihop wireless networks. Although we expect that a cross-layer approach will be more effective than a network centric (single-layer) approach in addressing application performance, it also brings in complex problems that cannot be effectively solved using traditional methods, and thus, calls for the design of customized algorithms. In concurrent routing, we focus on issues that arise while supporting multiple concurrent video communication sessions in an ad hoc network. These sessions compete for limited network resources (such as bandwidth) while interacting with each other. Such inter-session interactions couple the performance of an individual flow with that of other flows. Applying a video centric cross-layer design principle, we model the end-to-end video distortion as a function of network layer behavior, and formulate a network-wide optimal routing problem that minimizes the total video distortion. Results based on computational experiments performed using randomly generated network topologies establish the relative efficacy and robustness of the proposed genetic algorithm based solution approach. Specifically, we demonstrate that our approach outperforms other trajectory based metaheuristic approaches as well as with conventional network centric routing algorithms such as shortest path and disjoint shortest path routing. The joint path selection and rate allocation problem considers not only selecting the best set of paths for video communication, but also, computing the optimal video encoding rate and partitioning it among the chosen set of paths. The end-to-end video distortion is modeled as a function of network layer resources by capturing the tight coupling that exists between the optimal encoding rate for each video session, the selection of paths for video transmission, and the allocation of traffic among these selected paths. This problem is formulated as a nonlinear nonconvex programming problem, for which a tight linear programming relaxation is constructed via the Reformulation-Linearization Technique (RLT). This construct is embedded within a specialized branch-and-bound algorithm to achieve global optimality. Computational experience is reported for various problem instances, and the results validate the robustness of the proposed algorithmic procedure. The results exhibit the advantage of the solution approach over the popularly used max-min rate allocation scheme. The emergence of Multiple Description (MD) coding technique offers great potential for multipath routing of video in multihop wireless networks. In studying multipath routing for MD coding, we show that MD coded video, when used in combination with multipath routing in wireless networks, has tremendous advantages over traditional layered video coding techniques. We discuss how to implement an MD video codec and formulate a cross-layer optimization problem that can find a set of optimal paths, (one for each description) such that the overall video quality at the receiver is maximized. We further devise a specialized RLT-based branch-and-bound solution procedure for the ensuing 0-1 mixed integer nonconvex optimization problem. Convergence behavior of the proposed solution procedure is observed for various network topologies and the results further demonstrate the performance advantage of the proposed cross-layer approach over non-cross-layer approaches. The scope of this research is highly interdisciplinary. It intersects video communication, networking, optimization, and algorithm design. We expect that the theoretical and algorithmic results of this investigation will serve as important building blocks in developing a comprehensive methodology for addressing complex cross-layer problems in the area of wireless ad hoc networks. / Ph. D.

This thesis investigates distributed medium access control (MAC) protocols custom tailored to both impulse-based ultra wideband (I-UWB) radios and to large ad hoc and sensor networks. I-UWB is an attractive radio technology for large ad hoc and sensor networks due to its robustness to multipath fading effects, sub-centimeter ranging ability, and low-cost, low-power hardware. Current medium access control (MAC) protocols for I-UWB target small wireless personal area networks (WPANs) and cellular networks, but they are not suitable for large, multihop ad hoc and sensor networks. Therefore, this paper proposes a new type of MAC protocol that enables ad hoc and sensor networks to realize the benefits of I-UWB radios. First, we propose a method to overcome the challenges of quickly, reliably, and efficiently sensing medium activity in an ultra wideband network. This provides a base MAC protocol similar to carrier sense multiple access (CSMA) in narrowband systems. Next, we propose to exploit the unique signaling of I-UWB to improve performance over the base MAC protocol without the associated overhead of similar improvements in narrowband systems. I-UWB enables a distributed multichannel MAC protocol, which improves throughput. I-UWB also facilitates a busy signal MAC protocol, which reduces wasted energy from corrupt packets. Finally, because the I-UWB Physical Layer and MAC Layer affect the network and application layers, we propose a cross-layer adaptive system that optimizes performance. Physical Layer simulations show that both the base protocol and the improvements are practical for an I-UWB radio. Networks level simulations characterize the performance of the proposed MAC protocols and compare them to existing MAC protocols. / Ph. D.

This dissertation focuses on an efficient cooperative communication method for wireless ad hoc networks. Typically, performance enhancement via cooperative communications can be achieved at the cost of other system resources such as additional bandwidth, transmit power, or more complex synchronization methods between cooperating signals. However, the proposed ooperative transmission scheme in this research utilizes system resources more efficiently by reducing the redundant and wasteful cooperating signals typically required, while maintaining the desired performance improvement. There are four main results in this dissertation. First, an efficient cooperative retransmission scheme is introduced to increase bandwidth efficiency by reducing wasteful cooperating signals. The proposed cooperative transmission method does not require any additional information for cooperation. Furthermore, we ensure good quality for the cooperating signals through a simple yet effective selection procedure. Multiple cooperating nodes can be involved in the cooperation without prior planning via distributed beamforming. The proposed cooperative retransmission scheme outperforms traditional retransmission by the source as well as other cooperative methods in terms of delay and packet error rate (PER). Secondly, the outage probabilities of the cooperative retransmission scheme are analyzed for both the perfect synchronization case and when offset estimation is performed for distributed beamforming. The performance with offset estimation is close to the perfect synchronization case, especially for short data packets. A low-rate feedback channel is introduced to adjust the phase shift due to channel variation and the residual frequency offset. It is shown that substantial gain can be achieved with a low-rate feedback channel, even for long data packets. Third, the throughput efficiency and average packet delay of the proposed cooperative retransmission scheme are analyzed using a two-state Markov model for both a simple automatic repeat request (ARQ) and a hybrid ARQ technique. The benefits of the cooperative ARQ approach are also verified in a multihop network with random configurations when there are concurrent packet transmissions. The average transmit power for the cooperating signals is also investigated in the proposed cooperative transmission scheme with various power control approaches. Finally, cooperative multiple input multiple output (MIMO) systems are examined, mainly focusing on power allocation methods to increase overall channel capacity. An efficient and simple power allocation method at the cooperating node is proposed which can be used for an arbitrary number of antennas without any additional information. / Ph. D.

A wireless Mobile Ad Hoc Network (MANET) comprises of a number of mobile nodes that uses multi-hop routing to provide network connectivity. MANETs require self-organizing capabilities as there are no centralized points (base stations, access points etc), and each mobile node functions as router and/or hosts. The wireless topology in MANET can change rapidly with mobility of nodes in unpredictable ways or remain static for long periods of time. MANETs have applications in neighborhood area networks (NANs), impromptu communication among groups of people, disaster management and dynamic military systems. As progress in MANET continues, there is an increase in demand with regard to supporting content-rich video streaming in such networks. This is due to the fact that real-time video is far more substantive than simple data communication. This work involves implementing a Genetic Algorithm (GA) based multipath routing methodologies in a proactive routing protocol (Optimized Link State Routing Protocol) to send/forward/receive multimedia streams on experimental testbed. We study the problem of multipath video routing in wireless ad hoc networks by following an application-centric cross-layer approach. A full implementation of GA-based routing and real-time video conferencing application (server and client) written in C++ is presented. The robustness of our routing scheme was tested through experiments using five computer nodes. The performance of the routing protocol for video, as well as issues such as applicability and scalability in practice are addressed. / Master of Science