Achieving reliable and enhanced communication in vehicular ad hoc networks (VANETs)

A thesis submitted to the University of Bedfordshire in partial fulfilment of the requirement for the degree of Doctor of PhilosophyWith the envisioned age of Internet of Things (IoTs), different aspects of Intelligent Transportation System (ITS) will be linked so as to advance road transportation safety, ease congestion of road traffic, lessen air pollution, improve passenger transportation comfort and significantly reduce road accidents. In vehicular networks, regular exchange of current position, direction, speed, etc., enable mobile vehicle to foresee an imminent vehicle accident and notify the driver early enough in order to take appropriate action(s) or the vehicle on its own may take adequate preventive measures to avert the looming accident. Actualizing this concept requires use of shared media access protocol that is capable of guaranteeing reliable and timely broadcast of safety messages. This dissertation investigates the use of Network Coding (NC) techniques to enrich the content of each transmission and ensure improved high reliability of the broadcasted safety messages with less number of retransmissions. A Code Aided Retransmission-based Error Recovery (CARER) protocol is proposed. In order to avoid broadcast storm problem, a rebroadcasting vehicle selection metric η, is developed, which is used to select a vehicle that will rebroadcast the received encoded message. Although the proposed CARER protocol demonstrates an impressive performance, the level of incurred overhead is fairly high due to the use of complex rebroadcasting vehicle selection metric. To resolve this issue, a Random Network Coding (RNC) and vehicle clustering based vehicular communication scheme with low algorithmic complexity, named Reliable and Enhanced Cooperative Cross-layer MAC (RECMAC) scheme, is proposed. The use of this clustering technique enables RECMAC to subdivide the vehicular network into small manageable, coordinated clusters which further improve transmission reliability and minimise negative impact of network overhead. Similarly, a Cluster Head (CH) selection metric ℱ(\u1d457) is designed, which is used to determine and select the most suitably qualified candidate to become the CH of a particular cluster. Finally, in order to investigate the impact of available radio spectral resource, an in-depth study of the required amount of spectrum sufficient to support high transmission reliability and minimum latency requirements of critical road safety messages in vehicular networks was carried out. The performance of the proposed schemes was clearly shown with detailed theoretical analysis and was further validated with simulation experiments

Transport layer protocol design over flow-switched data networks

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 135-136).In this work, we explore transport layer protocol design for an optical flow-switched network. The objective of the protocol design is to guarantee the reliable delivery of data files over an all-optical end-to- end flow-switched network which is modeled as a burst-error channel. We observe that Transport Control Protocol (TCP) is not best suited for Optical Flow-Switching (OFS). Specifically, flow control and fair resource allocation through windowing in TCP are unnecessary in an OFS network. Moreover TCP has poor throughput and delay performance at high transfer rates due to window flow control and window closing with missing or dropped packets. In OFS, flows are scheduled and congestion control is performed by a scheduling algorithm. Thus, we focus on defining a more efficient transport protocol for optical flow-switched networks that is neither a modification of TCP nor derived from TCP. The main contribution of this work is to optimize the throughput and delay performance of OFS using file segmentation and reassembly, forward error-correction (FEC), and frame retransmission. We analyze the throughput and delay performance of four example transport layer protocols: the Simple Transport Protocol (STP), the Simple Transport Protocol with Interleaving (STPI), the Transport Protocol with Framing (TPF) and the Transport Protocol with Framing and Interleaving (TPFI). First, we show that a transport layer protocol without file segmentation and without interleaving and FEC (STP) results in poor throughput and delay performance and is not well suited for OFS. Instead, we found that interleaving across a large file (STPI) results in the best theoretical delay performance, though the large code lengths and interleaver sizes in this scheme will be hard to implement. Also, in the unlikely case that a file experiences an uncorrectable error, STPI requires extra network resources equal to that of an entire transaction for file retransmission and adds to the delay of the transaction significantly. For the above reason, we propose the segmentation of a file into large frames combined with FEC, interleaving, and retransmission of erroneous frames (TPFI) as the protocol of choice for an OFS network. In TPFI, interleaving combined with FEC and frame retransmission allows a file to be segmented into large frames (>100 Mbits). In addition, TPFI also allows for fewer processing and file segmentation and reassembly overhead compared with a transport layer protocol that does not include interleaving and FEC (TPF).by Henna Priscilla Huang.S.M

Technologies of information transmission and processing

Сборник содержит статьи, тематика которых посвящена научно-теоретическим разработкам в области сетей телекоммуникаций, информационной безопасности, технологий передачи и обработки информации. Предназначен для научных сотрудников в области инфокоммуникаций, преподавателей, аспирантов, магистрантов и студентов технических вузов

Re-feedback: freedom with accountability for causing congestion in a connectionless internetwork

This dissertation concerns adding resource accountability to a simplex internetwork such as the Internet, with only necessary but sufficient constraint on freedom. That is, both freedom for applications to evolve new innovative behaviours while still responding responsibly to congestion; and freedom for network providers to structure their pricing in any way, including flat pricing. The big idea on which the research is built is a novel feedback arrangement termed ‘re-feedback’. A general form is defined, as well as a specific proposal (re-ECN) to alter the Internet protocol so that self-contained datagrams carry a metric of expected downstream congestion. Congestion is chosen because of its central economic role as the marginal cost of network usage. The aim is to ensure Internet resource allocation can be controlled either by local policies or by market selection (or indeed local lack of any control). The current Internet architecture is designed to only reveal path congestion to end-points, not networks. The collective actions of self-interested consumers and providers should drive Internet resource allocations towards maximisation of total social welfare. But without visibility of a cost-metric, network operators are violating the architecture to improve their customer’s experience. The resulting fight against the architecture is destroying the Internet’s simplicity and ability to evolve. Although accountability with freedom is the goal, the focus is the congestion metric, and whether an incentive system is possible that assures its integrity as it is passed between parties around the system, despite proposed attacks motivated by self-interest and malice. This dissertation defines the protocol and canonical examples of accountability mechanisms. Designs are all derived from carefully motivated principles. The resulting system is evaluated by analysis and simulation against the constraints and principles originally set. The mechanisms are proven to be agnostic to specific transport behaviours, but they could not be made flow-ID-oblivious

Transporte de informação directamente sobre sistemas de comunicação ópticos

Mestrado em Engenharia ElectrónicaNum futuro próximo, a informação transmitida entre vários utilizadores, seja áudio, vídeo ou dados, poderá ser transportada directamente sobre redes ópticas. Neste sentido, têm sido estudadas e analisadas várias tecnologias emergentes de redes ópticas, que culminaram com o aparecimento de soluções que permitem a integração de redes IP (Internet Protocol) sobre redes ópticas. Tendo em vista este cenário, o objectivo deste trabalho foi o estudo dos mecanismos de transporte de informação sobre sistemas de comunicação ópticos. Foi dada especial relevância a tecnologias ópticas multicanal utilizadas actualmente, o Wavelength Division Multiplexing (WDM) e o Multiprotocol Label Switching (MPLS). Uma vez que uma das formas usuais de avaliar o impacto da camada física nos sistemas de comunicação é através das taxa de erro binários, foi efectuada a caracterização da camada física em termos de taxas de erros binários e da probabilidade de erros na transmissão de pacotes de informação. Este estudo englobou várias fases, nomeadamente a caracterização do meio de transmissão, a fibra (através da taxa de erros binários e do factor Q), e a análise do impacto dos erros binários nas camadas de ligação de dados, de rede e de transporte, traduzida na probabilidade de erros em sequências de bits. Foi também abordado o impacto dos esquemas de detecção e/ou de correcção de erros utilizados nas várias camadas protocolares. Finalmente, foi analisado e caracterizado o comportamento da rede em função das características físicas do canal de transmissão.In a near future, information (audio, video and data) may be transmitted between several users directly over optical networks. Several emerging technologies on optical networks, which allow the IP (Internet Protocol) integration in the optical domain, have already been widely studied and analyzed. Keeping in mind this scenario, the goal of this work was the study of the information transport mechanisms over optical communication systems. Special attention was given to technologies currently used, the Wavelength Division Multiplexing (WDM) and the Multiprotocol Label Switching (MPLS). The Bit Error Rate (BER) is used as a measure of the negative effects of all physical impairments on the fibre, being usually a comprehensive criterion for the evaluation of the signal transmission quality. This way, the physical layer characterization was made in terms of BER and/or packet error rate (PER). This study concerned several stages: the fibre characterization in terms of BER and Q-factor, the study of the impact of the binary errors in the network behaviour, and the study and analysis of the error detection and correction schemes used in the several layers. Finally, the network behaviour was analysed and characterized as a function of the channel physical characteristics and constraints