Practical algorithms for distributed network control

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (pages 135-138).Optimal routing and scheduling algorithms have been studied for decades, however several practical issues prevent the adoption of these network control policies on the Internet. This thesis considers two distinct topics in distributed network control: (i) maximizing throughput in wireless networks using network coding, and (ii) deploying controllable nodes in legacy networks. Network coding is a relatively new technique that allows for an increase in throughput under certain topological and routing conditions. The first part of this thesis considers jointly optimal routing, scheduling, and network coding strategies to maximize throughput in wireless networks. We introduce a simple network coding strategy and fully characterize the region of arrival rates supported. We propose a centralized dynamic control policy for routing, scheduling, and our network coding strategy, and prove this policy to be throughput optimal subject to our coding constraint. We further propose a distributed control policy based on random access that optimizes for routing, scheduling, and pairwise coding, where pairwise coding captures most of the coding opportunities on random topologies. We prove this second policy to also be throughput optimal subject to the coding constraint. Finally, we reduce the gap between theory and practice by identifying and solving several problems that may occur in system implementations of these policies. Throughput optimal policies typically require every device in the network to make dynamic routing decisions. In the second part of this thesis, we propose an overlay routing architecture such that only a subset of devices (overlay nodes) need to make dynamic routing decisions, and yet maximum throughput can still be achieved. We begin by formulating an optimization problem that searches for the minimum overlay node placement that achieves maximum throughput. We devise an efficient placement algorithm which solves this problem optimally for networks not subject to interference constraints. Then we propose a heuristic control policy for use at overlay nodes, and show by simulation that this policy performs optimally in all studied scenarios.by Nathaniel Matthew Jones.Ph. D

A Study Of Genetic Representation Schemes For Scheduling Soft Real-Time Systems

This research presents a hybrid algorithm that combines List Scheduling (LS) with a Genetic Algorithm (GA) for constructing non-preemptive schedules for soft real-time parallel applications represented as directed acyclic graphs (DAGs). The execution time requirements of the applications\u27 tasks are assumed to be stochastic and are represented as probability distribution functions. The performance in terms of schedule lengths for three different genetic representation schemes are evaluated and compared for a number of different DAGs. The approaches presented in this research produce shorter schedules than HLFET, a popular LS approach for all of the sample problems. Of the three genetic representation schemes investigated, PosCT, the technique that allows the GA to learn which tasks to delay in order to allow other tasks to complete produced the shortest schedules for a majority of the sample DAGs

Autonomous optimization of UWB link access

We present a novel approach for interference management in low data rate IR-UWB networks that enables concurrent transmissions at full power while allows each source to independently adapt its pulse rate (transmitted pulses per second) to mitigate multi-user interference. The work is motivated by the fact that the distributed adaptation of IR-UWB pulse rate has not been sufficiently addressed in the literature before. Existing approaches rely on the presence of a central authority or assume a definite receiver technique. Our approach enables users to share the communication medium in an efficient way compatible with individual QoS requirements and it is independent of any particular modulation scheme or receiver technique

Cross-layer schemes for performance optimization in wireless networks

Wireless networks are undergoing rapid progress and inspiring numerous applications. As the application of wireless networks becomes broader, they are expected to not only provide ubiquitous connectivity, but also support end users with certain service guarantees. End-to-end delay is an important Quality of Service (QoS) metric in multihop wireless networks. This dissertation addresses how to minimize end-to-end delay through joint optimization of network layer routing and link layer scheduling. Two cross-layer schemes, a loosely coupled cross-layer scheme and a tightly coupled cross-layer scheme, are proposed. The two cross-layer schemes involve interference modeling in multihop wireless networks with omnidirectional antenna. In addition, based on the interference model, multicast schedules are optimized to minimize the total end-to-end delay. Throughput is another important QoS metric in wireless networks. This dissertation addresses how to leverage the spatial multiplexing function of MIMO links to improve wireless network throughput. Wireless interference modeling of a half-duplex MIMO node is presented. Based on the interference model, routing, spatial multiplexing, and scheduling are jointly considered in one optimization model. The throughput optimization problem is first addressed in constant bit rate networks and then in variable bit rate networks. In a variable data rate network, transmitters can use adaptive coding and modulation schemes to change their data rates so that the data rates are supported by the Signal to Noise and Interference Ratio (SINR). The problem of achieving maximum throughput in a millimeter-wave wireless personal area network is studied --Abstract, page iv

Routage et codage réseau inter-session dans les réseaux sociaux mobiles tolérant le délai

We consider Delay Tolerant Mobile Social Networks (DTMSN), made of wireless nodes with intermittent connections and clustered into social communities. This thesis deals with the analysis and design of information transfer strategies in DTMSN. It is mostly dedicated to investigate the use of Inter-Session Network Coding (ISNC) towards this goal. Network coding is a generalization of routing and ISNC is known as a difficult optimization problem in general, specifically because it can easily get detrimental, compared to no coding, if not designed carefully. The first part of this thesis addresses theoretically the optimization problem of the (non-ISNC) routing policy in DTMSNs. We generalize the existing results for homogeneous topologies. The second part of the thesis designs and models a parameterized pairwise ISNC control policy that encompasses both routing and coding controls with an energy constraint. In order to tackle heuristically the optimization problem, the third chapter presents an experimental study of pairwise ISNC to investigate when it can be beneficial or detrimental. We examine the impact on ISNC performance of a number of parameters, such as the constraint on the maximum number of copies per packet, the network load, the buffer size of the relay nodes and the buffer management policies. The fourth chapter addresses the design of decentralized coding criteria allowing to trigger online session mixing if ISNC may be beneficial. We test these coding criteria on both toy topologies and real-world traces, pointing out and explaining the limits of our approach.Nous considérons les Réseaux Sociaux Mobiles Tolérant le Délai (DTMSN), constitués de nœuds sans-fil avec une connectivité intermittente, et groupés en communautés sociales. Cette thèse traite de l’analyse et de la conception de stratégies de transfert de l’information dans les DTMSN. Elle est principalement dédiée à l’étude de codage réseau inter-session (ISNC) dans ce but. Le codage réseau est une généralisation du routage et ISNC est connu comme un problème d’optimisation difficile en général, spécifiquement parce qu’il peut vite devenir nuisible si non conçu avec soin. Le premier chapitre répond théoriquement au problème d’optimisation du routage (sans ISNC) dans les DTMSN. Nous généralisons les résultants existants pour les topologies homogènes. Le deuxième chapitre conçoit et modélise un contrôle de ISNC par paire, qui englobe conjointement le contrôle du routage et du codage, avec une contrainte d’énergie. Pour s’attaquer de façon heuristique à l’optimisation de ce contrôle, le troisième chapitre présente une étude expérimentale visant à identifier quand ISNC est bénéfique ou nuisible, en fonction du nombre maximum de copies par paquet, de la charge du réseau, de la taille de buffer des nœuds relais et de la gestion de buffer. Le quatrième chapitre présente la conception de critères décentralisés de codage, pour déclencher en ligne le mélange de sessions si ISNC peut être bénéfique. Nous testons ces critères sur des topologies simples et sur des traces réelles, en expliquant les limites de notre approche