Energy-efficient networking in wireless ad hoc networks (Doctoral thesis)

Παπανίκος, Νικόλαος

Wireless multi-hop ad hoc networks are self-organizing networks that can be spontaneously deployed without any need of fixed infrastructure. In order to enable communication, network nodes share their resources to store and forward other nodes' data packets. However, the current hardware technology significantly limits the battery power network nodes run on. As a result, designing energy-efficient networking algorithms is of paramount importance for the viability of this type of networks. In the present thesis, we study networking algorithms that rely on packet redundancy to provide fair communication. This approach can significantly increase the number of transmissions and have a severe impact on the energy efficiency. Our main goal is to devise novel algorithms that efficiently handle packet redundancy in order to reduce the related energy costs without compromising the overall performance. We focus on two well-known fields; broadcasting in mobile ad hoc networks (MANETs) and routing in opportunistic networks (OppNets). In the first part, we examine energy-efficient broadcasting in MANETs. The latest trend in this field combines traditional broadcast schemes with network coding. Besides enhancing the energy efficiency through the reduction of transmissions, this synergy also increases the resilience to loss and improves security. Initially, we focus on XOR-based broadcasting and reveal cases where the well-established approach suffers performance breakdowns. We attribute this behavior to an essential component of the underlying broadcast algorithm that is inherently incompatible with network coding. To tackle the problem, we introduce a novel coding-friendly broadcast algorithm. Furthermore, for the first time, we use XOR coding as a mechanism not only for enhancing energy efficiency but also for reducing the end-to-end-delay. Through extensive simulations, we demonstrate the effectiveness of the proposed algorithm on improving the energy efficiency, delivery delay and utilization of network resources. Then, we focus on RLNC-based broadcasting and introduce an analytical model that captures the performance of coding-based broadcast schemes. We observe that the traditional approach to combine RLNC and probabilistic forwarding significantly impacts the performance of RLNC. To this end, we design a novel RLNC-based broadcast algorithm that for the first time applies RLNC over CDS-based broadcasting. The proposed algorithm provides a more systematic pruning of redundant transmissions without compromising RLNC's efficiency. We also investigate generation management that is a key issue in RLNC and introduce a new distributed scheme that is suitable for mobile environments. Finally, through extensive simulations, we show that the proposed algorithm outperforms XOR-based as well as RLNC-based schemes even when global knowledge is used for managing packet generations. In the second part of the thesis, we investigate energy-efficient routing in OppNets. The prominent routing strategy in coping with intermittent connectivity of this type of networks is packet replication. Although this strategy maximizes the delivery efficiency, it can lead to the creation of an excessive number of replicas thus exhausting the limited energy resources of the network nodes. We introduce a simple yet efficient method which allows nodes to share information about the replication process in order to avoid unnecessary replication. The proposed approach comes at negligible cost and significantly increases the energy efficiency without sacrificing delivery rate. At the same time, our solution is generic in the sense that it can be implemented regardless of the utility metric used for making replication decisions. Additionally, we provide a lightweight extension based on Bloom filters that further improves the energy efficiency. In contrast to state-of-the-art, the proposed extension allows non-carrier nodes to play a more active role in the replication process and deny receiving redundant packet replicas. We validate the performance gains of our solutions through analysis as well as extensive simulations. Finally, we examine some interesting topics that lie within the context of efficient routing in OppNets. These involve the implementation of an event-driven simulator for OppNets, the development of a paradigm for constructing large scale synthetic trace from real ones and the design of a congestion control algorithm that provides an effective trade-off between fairness and performance.
Institution and School/Department of submitter: Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Μηχανικών Η/Υ & Πληροφορικής
Subject classification: Networking
Keywords: Δίκτυα Η/Υ,Ασύρματα αδόμητα δίκτυα,Οπορτουνιστικά δίκτυα,Δρομολόγηση,Ευρεία εκπομπή,Κωδικοποίηση δικτύου,Αλγόριθμοι δικτύωσης,Πρωτόκολλα δρομολόγησης,Εξοικονόμηση ενέργειας,Διακοπτόμενη συνδεσιμότητα,Δρομολόγηση πολλαπλών αντιτύπων,Networking,Wireless ad hoc networks,Mobile ad hoc networks,Opportunistic networks,Routing,Broadcasting,Energy efficiency,Network coding,XOR coding,Random linear network coding,RLNC,Multi-copy routing,Replication-based routing
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