An Extended Network Coding Opportunity Discovery Scheme in Wireless Networks

Network coding is known as a promising approach to improve wireless network performance. How to discover the coding opportunity in relay nodes is really important for it. There are more coding chances, there are more times it can improve network throughput by network coding operation. In this paper, an extended network coding opportunity discovery scheme (ExCODE) is proposed, which is realized by appending the current node ID and all its 1-hop neighbors' IDs to the packet. ExCODE enables the next hop relay node to know which nodes else have already overheard the packet, so it can discover the potential coding opportunities as much as possible. ExCODE expands the region of discovering coding chance to n-hops, and have more opportunities to execute network coding operation in each relay node. At last, we implement ExCODE over the AODV protocol, and efficiency of the proposed mechanism is demonstrated with NS2 simulations, compared to the existing coding opportunity discovery scheme.Comment: 15 pages and 7 figure

Opportunistic routing and network coding in multi-hop wireless mesh networks

The rapid advancements in communication and networking technologies boost the capacity of wireless networks. Multi-hop wireless networks are extremely exciting and rapidly developing areas and have been receiving an increasing amount of attention by researchers. Due to the limited transmission range of the nodes, end-to-end nodes may situate beyond direct radio transmission ranges. Intermediate nodes are required to forward data in order to enable the communication between nodes that are far apart. Routing in such networks is a critical issue. Opportunistic routing has been proposed to increase the network performance by utilizing the broadcast nature of wireless media. Unlike traditional routing, the forwarder in opportunistic routing broadcasts date packets before the selection of the next hop. Therefore, opportunistic routing can consider multiple downstream nodes as potential candidate nodes to forward data packets instead of using a dedicated next hop. Instead of simply forwarding received packets, network coding allows intermediate nodes to combine all received packets into one or more coded packets. It can further improve network throughput by increasing the transmission robustness and efficiency. In this dissertation, we will study the fundamental components, related issues and associated challenges about opportunistic routing and network coding in multi-hop wireless networks. Firstly, we focus on the performance analysis of opportunistic routing by the Discrete Time Markov Chain (DTMC). Our study demonstrates how to map packet transmissions in the network with state transitions in a Markov chain. We will consider pipelined data transfer and evaluate opportunistic routing in different wireless networks in terms of expected number of transmissions and time slots. Secondly, we will propose a regional forwarding schedule to optimize the coordination of opportunistic routing. In our coordination algorithm, the forwarding schedule is limited to the range of the transmitting node rather than among the entire set of forwarders. With such an algorithm, our proposal can increase the throughput by deeper pipelined transmissions. Thirdly, we will propose a mechanism to support TCP with opportunistic routing and network coding, which are rarely incorporated with TCP because the frequent occurrences of out-of-order arrivals in opportunistic routing and long decoding delay in network coding overpower TCP congestion control. Our solution completes the control feedback loop of TCP by creating a bridge between the sender and the receiver. The simulation result shows that our protocol significantly outperforms TCP/IP in terms of network throughput in different topologies of wireless networks

Contention techniques for opportunistic communication in wireless mesh networks

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

The 30/20 GHz flight experiment system, phase 2. Volume 2: Experiment system description

A detailed technical description of the 30/20 GHz flight experiment system is presented. The overall communication system is described with performance analyses, communication operations, and experiment plans. Hardware descriptions of the payload are given with the tradeoff studies that led to the final design. The spacecraft bus which carries the payload is discussed and its interface with the launch vehicle system is described. Finally, the hardwares and the operations of the terrestrial segment are presented

Architectures for the Future Networks and the Next Generation Internet: A Survey

Networking research funding agencies in the USA, Europe, Japan, and other countries are encouraging research on revolutionary networking architectures that may or may not be bound by the restrictions of the current TCP/IP based Internet. We present a comprehensive survey of such research projects and activities. The topics covered include various testbeds for experimentations for new architectures, new security mechanisms, content delivery mechanisms, management and control frameworks, service architectures, and routing mechanisms. Delay/Disruption tolerant networks, which allow communications even when complete end-to-end path is not available, are also discussed

Network coding: performance analysis and robust design in multi-hop wireless mesh networks

Network coding is an innovative idea to boost the capacity of wireless networks. However, there are not enough analytical studies on throughput and end-to-end delay of network coding in multi-hop wireless mesh network that incorporates the specifications of IEEE 802.11 Distributed Coordination Function. In this dissertation, we utilize queuing theory to propose an analytical framework for bidirectional unicast flows in multi-hop wireless mesh networks. We study the throughput and end-to-end delay of inter-flow network coding under the IEEE 802.11 standard with CSMA/CA random access and exponential back-o↵ time considering clock freezing and virtual carrier sensing, and formulate several parameters such as the probability of successful transmission in terms of bit error rate and collision probability, waiting time of packets at nodes, and retransmission mechanism. Our model uses a multi-class queuing network with stable queues, where coded packets have a non-preemptive higher priority over native packets, and forwarding of native packets is not delayed if no coding opportunities are available. The accuracy of our analytical model is verified using computer simulations. Furthermore, while inter-flow network coding is proposed to help wireless networks approach the maximum capacity, the majority of research conducted in this area is yet to fully utilize the broadcast nature of wireless networks, and to perform e↵ectively under poor channel quality. This vulnerability is mostly caused by assuming fixed route between the source and destination that every packet should travel through. This assumption not only limits coding opportunities, but can also cause bu↵er overflow at some specific intermediate nodes. Although some studies considered scattering of the flows dynamically in the network, they still face some limitations. This dissertation explains pros and cons of some prominent research in network coding and proposes a Flexible and Opportunistic Network Coding scheme (FlexONC) as a solution to such issues. Moreover, this research discovers that the conditions used in previous studies to combine packets of di↵erent flows are overly optimistic and would a↵ect the network performance adversarially. Therefore, we provide a more accurate set of rules for packet encoding. The experimental results show that FlexONC outperforms previous methods especially in networks with high bit error rates, by better utilizing redundant packets permeating the network, and benefiting from precise coding conditions