224 research outputs found

    Maximizing Communication Concurrency via Link-Layer Packet Salvaging in Mobile Ad Hoc Networks

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    Carrier-sense medium access control (MAC) protocols such as the IEEE 802.11 distributed coordination function (DCF) avoid collisions by holding up pending packet transmission requests when a carrier signal is observed above a certain threshold. However, this often results in unnecessarily conservative communication, thus making it difficult to maximize the utilization of the spatial spectral resource. This paper shows that a higher aggregate throughput can be achieved by allowing more concurrent communications and adjusting the communication distance on the fly, which needs provisions for the following two areas. On the one hand, carrier sense-based MAC protocols do not allow aggressive communication attempts when they are within the carrier senseable area. On the other hand, the communication distance is generally neither short nor adjustable because multihop routing protocols strive for providing minimum hop paths. This paper proposes a new MAC algorithm, called multiple access with salvation army (MASA), which adopts less sensitive carrier sensing to promote more concurrent communications and adjusts the communication distance adaptively via packet salvaging at the MAC layer. Extensive simulation based on the ns-2 has shown MASA to outperform the DCF, particularly in terms of packet delay. We also discuss the implementation of MASA based on the DCF specification

    Network coded wireless architecture

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 183-197).Wireless mesh networks promise cheap Internet access, easy deployment, and extended range. In their current form, however, these networks suffer from both limited throughput and low reliability; hence they cannot meet the demands of applications such as file sharing, high definition video, and gaming. Motivated by these problems, we explore an alternative design that addresses these challenges. This dissertation presents a network coded architecture that significantly improves throughput and reliability. It makes a simple yet fundamental switch in network design: instead of routers just storing and forwarding received packets, they mix (or code) packets' content before forwarding. We show through practical systems how routers can exploit this new functionality to harness the intrinsic characteristics of the wireless medium to improve performance. We develop three systems; each reveals a different benefit of our network coded design. COPE observes that wireless broadcast naturally creates an overlap in packets received across routers, and develops a new network coding algorithm to exploit this overlap to deliver the same data in fewer transmissions, thereby improving throughput. ANC pushes network coding to the signal level, showing how to exploit strategic interference to correctly deliver data from concurrent senders, further increasing throughput. Finally, MIXIT presents a symbol-level network code that exploits wireless spatial diversity, forwarding correct symbols even if they are contained in corrupted packets to provide high throughput reliable transfers. The contributions of this dissertation are multifold. First, it builds a strong connection between the theory of network coding and wireless system design. Specifically, the systems presented in this dissertation were the first to show that network coding can be cleanly integrated into the wireless network stack to deliver practical and measurable gains. The work also presents novel algorithms that enrich the theory of network coding, extending it to operate over multiple unicast flows, analog signals, and soft-information.(cont.) Second, we present prototype implementations and testbed evaluations of our systems. Our results show that network coding delivers large performance gains ranging from a few percent to several-fold depending on the traffic mix and the topology. Finally, this work makes a clear departure from conventional network design. Research in wireless networks has largely proceeded in isolation, with the electrical engineers focusing on the physical and lower layers, while the computer scientists worked up from the network layer, with the packet being the only interface. This dissertation pokes a hole in this contract, disposing of artificial abstractions such as indivisible packets and point-to-point links in favor of a more natural abstraction that allows the network and the lower layers to collaborate on the common objectives of improving throughput and reliability using network coding as the building block. At the same time, the design maintains desirable properties such as being distributed, low-complexity, implementable, and integrable with the rest of the network stack.by Sachin Rajsekhar Katti.Ph.D

    Green Cellular Networks: A Survey, Some Research Issues and Challenges

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    Energy efficiency in cellular networks is a growing concern for cellular operators to not only maintain profitability, but also to reduce the overall environment effects. This emerging trend of achieving energy efficiency in cellular networks is motivating the standardization authorities and network operators to continuously explore future technologies in order to bring improvements in the entire network infrastructure. In this article, we present a brief survey of methods to improve the power efficiency of cellular networks, explore some research issues and challenges and suggest some techniques to enable an energy efficient or "green" cellular network. Since base stations consume a maximum portion of the total energy used in a cellular system, we will first provide a comprehensive survey on techniques to obtain energy savings in base stations. Next, we discuss how heterogeneous network deployment based on micro, pico and femto-cells can be used to achieve this goal. Since cognitive radio and cooperative relaying are undisputed future technologies in this regard, we propose a research vision to make these technologies more energy efficient. Lastly, we explore some broader perspectives in realizing a "green" cellular network technologyComment: 16 pages, 5 figures, 2 table

    Enhanced reliable and energy efficient pressure based data forwarding schemes for underwater wireless sensor networks

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    Data collection in Underwater Wireless Sensor Networks (UWSN) requires highly optimized communication approach in order to achieve efficient data packet delivery. This approach consists of different communication layers of which routing protocol is an important consideration. Several issues including packet entrapment due to void region, selection of forwarding node with insufficient link quality and packet collision in congested forwarding area have emanated. Therefore, three different research problems were formulated to address the issue of reliability and energy efficiency in data forwarding in UWSN. First, void handling for packet entrapment in the void region, which generate delays and communication overhead. Second, non-optimal node selection that causes forwarding delays and non-reliable packet delivery. Third, collision due to congestion, which leads to packet drop and unreliable packet delivery. Thus, enhanced reliable and energy-efficient pressure-based data forwarding schemes for UWSN were developed, which are the Communication Void Avoidance (CVA) to estimate neighbour nodes availability outside a void region in order to avoid voids and reduce delay; a Multi-metric Evaluation mechanism for next forwarder Node Selection (MENS) for optimal packet delivery; and a Congestion Avoidance and MITigation (CAMIT) in data forwarding for congestion and collision reduction in order to achieve reliable data forwarding. Several experiments were performed through simulations to access the performance of the proposed mechanisms and the results of each scheme were compared with related previously published protocols. The obtained results depict that the proposed schemes outperformed the existing schemes and significantly improved overall performance. CVA improved Packet Delivery Ratio by 12.8% to 18.7% and reduced End-to-end delay by 7.3% to 12.5% on average. MENS improved communication Data Rate by 13.2% to 15.1% and Energy Consumption improved by 10.6% to 15.3% on average. Lastly, CAMIT reduced Packet Drop ratio by 10.2% to 13% on average. The findings demonstrate the improved efficiency has been achieved by the CVA, MENS and CAMIT in terms of optimal node selection and reliability in packet forwarding in UWSN

    Contention techniques for opportunistic communication in wireless mesh networks

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    Auf dem Gebiet der drahtlosen Kommunikation und insbesondere auf den tieferen Netzwerkschichten sind gewaltige Fortschritte zu verzeichnen. Innovative Konzepte und Technologien auf der physikalischen Schicht (PHY) gehen dabei zeitnah in zelluläre Netze ein. Drahtlose Maschennetzwerke (WMNs) können mit diesem Innovationstempo nicht mithalten. Die Mehrnutzer-Kommunikation ist ein Grundpfeiler vieler angewandter PHY Technologien, die sich in WMNs nur ungenügend auf die etablierte Schichtenarchitektur abbilden lässt. Insbesondere ist das Problem des Scheduling in WMNs inhärent komplex. Erstaunlicherweise ist der Mehrfachzugriff mit Trägerprüfung (CSMA) in WMNs asymptotisch optimal obwohl das Verfahren eine geringe Durchführungskomplexität aufweist. Daher stellt sich die Frage, in welcher Weise das dem CSMA zugrunde liegende Konzept des konkurrierenden Wettbewerbs (engl. Contention) für die Integration innovativer PHY Technologien verwendet werden kann. Opportunistische Kommunikation ist eine Technik, die die inhärenten Besonderheiten des drahtlosen Kanals ausnutzt. In der vorliegenden Dissertation werden CSMA-basierte Protokolle für die opportunistische Kommunikation in WMNs entwickelt und evaluiert. Es werden dabei opportunistisches Routing (OR) im zustandslosen Kanal und opportunistisches Scheduling (OS) im zustandsbehafteten Kanal betrachtet. Ziel ist es, den Durchsatz von elastischen Paketflüssen gerecht zu maximieren. Es werden Modelle für Überlastkontrolle, Routing und konkurrenzbasierte opportunistische Kommunikation vorgestellt. Am Beispiel von IEEE 802.11 wird illustriert, wie der schichtübergreifende Entwurf in einem Netzwerksimulator prototypisch implementiert werden kann. Auf Grundlage der Evaluationsresultate kann der Schluss gezogen werden, dass die opportunistische Kommunikation konkurrenzbasiert realisierbar ist. Darüber hinaus steigern die vorgestellten Protokolle den Durchsatz im Vergleich zu etablierten Lösungen wie etwa DCF, DSR, ExOR, RBAR und ETT.In the field of wireless communication, a tremendous progress can be observed especially at the lower layers. Innovative physical layer (PHY) concepts and technologies can be rapidly assimilated in cellular networks. Wireless mesh networks (WMNs), on the other hand, cannot keep up with the speed of innovation at the PHY due to their flat and decentralized architecture. Many innovative PHY technologies rely on multi-user communication, so that the established abstraction of the network stack does not work well for WMNs. The scheduling problem in WMNs is inherent complex. Surprisingly, carrier sense multiple access (CSMA) in WMNs is asymptotically utility-optimal even though it has a low computational complexity and does not involve message exchange. Hence, the question arises whether CSMA and the underlying concept of contention allows for the assimilation of advanced PHY technologies into WMNs. In this thesis, we design and evaluate contention protocols based on CSMA for opportunistic communication in WMNs. Opportunistic communication is a technique that relies on multi-user diversity in order to exploit the inherent characteristics of the wireless channel. In particular, we consider opportunistic routing (OR) and opportunistic scheduling (OS) in memoryless and slow fading channels, respectively. We present models for congestion control, routing and contention-based opportunistic communication in WMNs in order to maximize both throughput and fairness of elastic unicast traffic flows. At the instance of IEEE 802.11, we illustrate how the cross-layer algorithms can be implemented within a network simulator prototype. Our evaluation results lead to the conclusion that contention-based opportunistic communication is feasible. Furthermore, the proposed protocols increase both throughput and fairness in comparison to state-of-the-art approaches like DCF, DSR, ExOR, RBAR and ETT

    Rede multi-tecnologia para recolha de dados ambientais através de comunicações oportunistas

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    mestrado em Engenharia Eletrónica e TelecomunicaçõesO conceito de Smart City surge da combinação do paradigma de Internet of Things (IoT) sobre contextos urbanos aliado à exploração de soluções de Tecnologias de Informação e Comunicação (TIC). O típico cenário de Smart City tem de lidar com desafios, tais como as elevadas quantidades de sensores e geradores de dados, dos quais alguns são colocados em dispositivos de grande mobilidade, visando a recolha e geração de todo o tipo de informações e levando ao aumento do número de dispositivos comunicantes. Esta dissertação foca o desenvolvimento e implementação de uma plataforma heterogénea de sonorização ambiental com o objectivo de servir de infraestrutura para aplicações no âmbito das Smart Cities. Esta pretende tirar proveito da utilização de múltiplas tecnologias de comunicação, nomeadamente tecnologias de longo e curto alcance. Para al em disto, visto que a plataforma visa ambientes urbanos, esta tira proveito de uma rede oportunista e tolerante a atrasos, Delay Tolerant Network (DTN), através de entidades m oveis que circulam pela cidade, nomeadamente bicicletas. Assim sendo, esta dissertação propõe: (1) o desenho e desenvolvimento da rede e dos seus constituintes; (2) uma extensão a um protocolo de controlo de acesso ao meio, Medium Access Control (MAC), para a tecnologia LoRa com o objectivo de o dotar compatível para ambientes de gateways múltiplas; (3) novas estratégias de encaminhamento para a rede tolerante a atrasos, tendo em consideração a topologia e as características apresentadas por esta. As avaliações realizadas permitiram concluir que o protocolo MAC para LoRa em ambientes de gateways múltiplas proposto contribui para um aumento da escalabilidade da rede, bem como para uma melhoria do seu desempenho. Relativamente às estratégias de encaminhamento propostas para a DTN, os testes realizados permitiram avaliar o impacto que cada estratégia tem sobre o comportamento da rede, nomeadamente a taxa de entrega dos pacotes de dados, a sobrecarga da rede, o número de pacotes transmitidos, entre outros. Com estes resultados foi possível perceber as in- suficiências que as funcionalidades propostas têm sobre a solução geral, e identificar as caraterísticas necessárias de uma solução escalável para a recolha de dados massivos num ambiente de IoT.The Smart City concept is the combination of the Internet of Things (IoT) paradigm under an urban context with the exploitation of Information and Communication Technologies (ICT) solutions. The typical Smart City scenario has to deal with an extensive amount of sensors and data generators, some of them placed in high mobile devices, deployed to collect and generate all type of information which will increase the number of communicating machines. This dissertation focuses on the development and implementation of a heterogeneous environmental sensing platform to serve as an infrastructure for Smart City applications. It aims to take advantage of the use of multiple communication technologies, namely long and short range. Being within an urban environment, the platform bene ts from an opportunistic and Delay Tolerant Network (DTN) through mobile entities that travel over the city, such as bicycles. Therefore, this dissertation proposes: (1) the design and development of the network and its elements; (2) an extension to a LoRa Medium Access Control (MAC) protocol in order to endow it with capabilities to operate in multi-gateway environments; and lastly, (3) new forwarding strategies for the opportunistic network that takes into consideration the network topology. The performed evaluations showed that the proposed multi-gateway LoRa MAC protocol contributes to increase the LoRa network scalability, as well as its performance. The performed tests to the proposed DTN forwarding strategies evaluate the impact of each strategy on the network behavior, namely the delivery ratio, network overhead, number of transmitted packets, among others. As a result, it is possible to perceive which are the in- uences introduced by the proposed functionalities on the overall solution, and identify the characteristics of a scalable solution to collect massive data in an IoT environment

    In-Network Processing For Mission-Criticalwireless Networked Sensing And Control: A Real-Time, Efficiency, And Resiliency Perspective

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    As wireless cyber-physical systems (WCPS) are increasingly being deployed in mission-critical applications, it becomes imperative that we consider application QoS requirements in in-network processing (INP). In this dissertation, we explore the potentials of two INP methods, packet packing and network coding, on improving network performance while satisfying application QoS requirements. We find that not only can these two techniques increase the energy efficiency, reliability, and throughput of WCPS while satisfying QoS requirements of applications in a relatively static environment, but also they can provide low cost proactive protection against transient node failures in a more dynamic wireless environment. We first study the problem of jointly optimizing packet packing and the timeliness of data delivery. We identify the conditions under which the problem is strong NP-hard, and we find that the problem complexity heavily depends on aggregation constraints instead of network and traffic properties. For cases when the problem is NP-hard, we show that there is no polynomial-time approximation scheme (PTAS); for cases when the problem can be solved in polynomial time, we design polynomial time, offline algorithms for finding the optimal packet packing schemes. We design a distributed, online protocol tPack that schedules packet transmissions to maximize the local utility of packet packing at each node. We evaluate the properties of tPack in NetEye testbed. We find that jointly optimizing data delivery timeliness and packet packing and considering real-world aggregation constraints significantly improve network performance. We then work on the problem of minimizing the transmission cost of network coding based routing in sensor networks. We propose the first mathematical framework so far as we know on how to theoretically compute the expected transmission cost of NC-based routing in terms of expected number of transmission. Based on this framework, we design a polynomial-time greedy algorithm for forwarder set selection and prove its optimality on transmission cost minimization. We designed EENCR, an energy-efficient NC-based routing protocol that implement our forwarder set selection algorithm to minimize the overall transmission cost. Through comparative study on EENCR and other state-of-the-art routing protocols, we show that EENCR significantly outperforms CTP, MORE and CodeOR in delivery reliability, delivery cost and network goodput. Furthermore, we study the 1+1 proactive protection problem using network coding. We show that even under a simplified setting, finding two node-disjoint routing braids with minimal total cost is NP-hard. We then design a heuristic algorithm to construct two node-disjoint braids with a transmission cost upper bounded by two shortest node-disjoint paths. And we design ProNCP, a proactive NC-based protection protocol using similar design philosophy as in EENCR. We evaluate the performance of ProNCP under various transient network failure scenarios. Experiment results show that ProNCP is resilient to various network failure scenarios and provides a state performance in terms of reliability, delivery cost and goodput. Our findings in this dissertation explore the challenges, benefits and solutions in designing real-time, efficient, resilient and QoS-guaranteed wireless cyber-physical systems, and our solutions shed lights for future research on related topics
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