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1
Widmer, Denise. "Hoi zäme - Ein Berufswahllehrmittel für Sonderschulen /". Zürich : Hochschule für Angewandte Psychologie, 2007. http://www.zhaw.ch/fileadmin/user_upload/psychologie/Downloads/Bibliothek/Arbeiten/D/d1964.pdf.
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2
Wong, Hoi-Ming [Verfasser]. "Upward planarization and layout / Hoi-Ming Wong". Dortmund : Universitätsbibliothek Technische Universität Dortmund, 2011. http://d-nb.info/1018124470/34.
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3
Chan, Ho-chung, e 陳浩忠. "Marine Life Centre at Hoi Ha Wan". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B3198437X.
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4
Chan, Ho-chung. "Marine Life Centre at Hoi Ha Wan". Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25952766.
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5
何偉廷 e Wai-ting Ho. "Diving Paradise-Scuba Diving Centre at Hoi Ha Wan". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31983881.
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6
Lai, Hoi-yan. "Beauty myth in Hong Kong : y Lai Hoi Yan". Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21375525.
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7
Ho, Wai-ting. "Diving Paradise-Scuba Diving Centre at Hoi Ha Wan". Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B2594745x.
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8
Fitzgerald, Emily. "‘Hoi, hoi!’ : An analysis of the portrayal of the female divers of Chejudo in the book Mom is a Haenyeo by Koh Hee Young". Thesis, Stockholms universitet, Avdelningen för koreanska, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-159448.
Testo completoAbstract (sommario):
Under senare år har the kvinnliga dykarna från Chejudo, Haenyŏ, presenterats i diverse media. Syftet med denna studie är att undersöka hur Haenyŏ framställs i en barnbok som i synnerhet har dem i fokus genom att analysera boken Mom is a Haenyeo. Metoden som tillämpades för denna studie var en kvalitativ metod där analysfrågor användes för att underlätta analysprocessen. Resultatet visar att Haenyŏ framställs på ett verklighetstroget och positivt sätt, men även att det fanns aspekter som var något romantiserade.In recent years the female divers of Chejudo, Haenyŏ, have been featured in various media. The purpose of this study is to examine how Haenyŏ are portrayed in a children’s book particularly focusing on them by analysing the book Mom is a Haenyeo. The method used for this study was a qualitative method using analysis questions to facilitate the process of analysis. The findings show that Haenyŏ are portrayed accurately and in a positive light, but also that there were aspects that were slightly romanticised.
9
Lo, Hoi Shan. "Effectiveness of a self-efficacy enhancing stroke self-management program on promoting recovery of community-dwelling stroke survivors". Thesis, Queensland University of Technology, 2016. https://eprints.qut.edu.au/99499/1/Hoi%20Shan_Lo_Thesis.pdf.
Testo completoAbstract (sommario):
This thesis reports a randomised controlled trial that evaluated the effectiveness of a new nurse-led self-efficacy enhancing stroke self-management program for Chinese community-dwelling stroke survivors. This new program underpinned by Bandura’s constructs of self-efficacy and outcome expectation, featured goal-setting, action-planning, and provided vicarious experiences by sharing with groups and video sessions about stroke survivors’ experience. The results provided significant evidence to inform clinicians’ and stakeholders’ decision-making in integrating the new program into current community support services for stroke survivors. It also highlighted nurses’ roles and contribution to stroke survivors’ recovery after discharge from hospital.
10
Phan, Thi Thanh Hoi [Verfasser]. "Testing levels of competencies in biological experimentation / Thi Thanh Hoi Phan". Kiel : Universitätsbibliothek Kiel, 2008. http://d-nb.info/1019552891/34.
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11
Winberg, Martin. "”Dina landsmän och översteprästerna har överlämnat dig åt mig” : Betydelsen av hoi Ioudaioi i Joh 18:1–19:22". Thesis, Umeå universitet, Institutionen för idé- och samhällsstudier, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-172593.
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12
Lam, King-yiu Katherine, e 林景瑤. "The colonization of an experimental artificial reef at Hoi Ha Wan Marine Park, Hong Kong". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31238749.
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13
Lam, King-yiu Katherine. "The colonization of an experimental artificial reef at Hoi Ha Wan Marine Park, Hong Kong /". Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20577114.
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14
Lau, Wai-lan Rossetti, e 劉惠蘭. "An education plan for secondary school projects in marine ecology at Hoi Ha Wan Marine Park". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1994. http://hub.hku.hk/bib/B31252904.
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15
Pham, Thi Bich Ngoc. "Driving Forces of Environmental Behaviour Changes on Cu Lao Cham Marine Protected Area, Hoi An, Vietnam". Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/24685.
Testo completoAbstract (sommario):
This thesis explores the factors underlying environmental behaviour change on Cu Lao Cham in Vietnam. It is widely recognised that residents have changed their environmental behaviour since the Cu Lao Cham Islands and surrounding marine areas became a Marine Protected Area (MPA) in 2005.
The research was conducted using a qualitative approach that examined the views and experiences of islanders, as well as the meaning of their behaviour. Interviews were conducted with local people, local leaders, local officials, MPA staff, researchers, NGO staff, international agencies and tourists.
Since the MPA was established, environmental behaviour changes developed under the influence of five different MPA projects. These were: restricted fishing zones, crab conservation, banning plastic bags, classification of solid waste and turtle recovery.
The study found that the people changed their behaviour from passive implementation of the regulations and guidance by the MPA to actively acquiring knowledge and changing attitudes and behaviour. New attitudes and behaviour were gradually internalised. People began by reluctantly following regulations initiated by the MPA and then internalised the behaviours as they recognised the value of the changes. This process opposes dominant models and theories of behaviour change which predict that attitude and intention need to change before behaviour.
The study argues that CLC people already had a strong sense of place and a desire to improve their livelihoods that motivated them to take actions towards protecting their place, once they recognised the benefits of MPA initiatives. During the course of implementing marine conservation, the people’s livelihoods were improved by the emerging tourism market which resulted from improved conservation. The main argument of this study is that environmental behaviour change can come from the lead of outsiders, combined with the insiders’ motivation, good governance and leadership.
16
Ngo, Thi Huong. "Le tourisme à base communautaire comme outil de développement local durable : le cas de Hoi An, Vietnam". Electronic Thesis or Diss., Université Côte d'Azur, 2024. http://www.theses.fr/2024COAZ0033.
Testo completoAbstract (sommario):
La durabilité devient depuis ces dernières années une préoccupation importante. De nombreux pays ont commencé à aborder des problèmes environnementaux et sociaux à travers des politiques et des stratégies nationales, des nouveaux partenariats et de l'amélioration des pratiques touristiques durables dans l'ensemble du secteur touristique. Ces mesures visent à stimuler la croissance à long terme en maintenant un équilibre entre la protection de l'environnement, l'évolution des bénéfices économiques, l'établissement de la justice sociale, le maintien de l'intégralité culturelle et le passage du tourisme de masse à des solutions durables à long terme. Le tourisme à base communautaire (TBC) a été considéré comme l'un des outils efficaces pour le développement du tourisme durable, notamment dans les zones rurales, suburbaines et montagneuses. Bien qu'il existe de nombreuses recherches sur les avantages, le succès ou l'échec des projets de TBC, peu d'attention a été accordée à évaluer la durabilité du TBC et l'étude de ses liens avec les Objectifs de développement durable (ODD) des Nations Unies pour déterminer le TBC comme un outil qui soutient le développement durable. Cette recherche doctorale aborde cette lacune en menant une étude de cas dans les zones rurales de Hoi An.Afin de mieux comprendre le TBC et son rôle pour le développement durable local, la recherche a adopté une méthodologie mixte, comprenant des méthodes de collecte de données quantitatives et qualitatives ; des méthodes documentaires ont ainsi été utilisées. Les résultats de la recherche ont donc été enrichis et vérifiés les uns par les autres, ce qui a contribué à améliorer la fiabilité de la recherche dans son ensemble.La qualité du service et la durabilité du TBC à Hoi An ont été révélées à travers les perceptions des touristes et des habitants locaux. La thèse a ensuite prouvé le lien entre le TBC et les SDGs afin d'identifier le TBC comme un outil de soutien au développement durable.La thèse apporte des contributions théoriques et méthodologiques distinctes à la croissance documentaire sur le TBC et ses liens avec le développement local durable. L'étude atteint ses objectifs de (1) développer un modèle de chaîne de valeur du TBC englobant les principales parties prenante et leurs rôles au niveau local, (2) concevoir le TBC comme un outil pour le développement local durable, et (3) appliquer des solutions fournies pour développer un TBC durable à Hoi An. La thèse bénéficiera aux autorités locales et aux participants du TBC en apportant des preuves empiriques pour fonder des politiques et des stratégies qui facilitent les résultats de développement souhaités. Avec une forte concentration sur la durabilité et une compréhension détaillée des perspectives de la communauté locale, la thèse renforce la reconnaissance du TBC comme un outil de développement durable dans le monde entier. Cette thèse encourage l'implantation et le développement du TBC dans plusieurs communautés, particulièrement dans les pays émergents qui visent un développement durableIn recent years, sustainability has emerged as a critical concern. Many countries have started to address environmental and social problems through national policies and strategies, new partnerships, and promoting sustainable tourism practices across the tourism industry. These measures shall stimulate growth in the long term while maintaining a balance between environmental protection, promoting economic benefits, establishing social justice, maintaining cultural integrity, and shifting from mass tourism to long-term sustainable solutions. Community-based tourism (CBT) has been considered one of the efficient tools for sustainable tourism development, especially in rural areas, suburbs, and mountainous areas. Although there is much research on the benefits, success, or failure of CBT projects, not much attention has been paid to assessing the sustainability of CBT and examining its links to the United Nations Sustainable Development Goals (SDG) to establish CBT as a tool to support sustainable development. This doctoral research addressed this gap by conducting a case study in rural areas of Hoi An.To advance the understanding of CBT and its role in the sustainable development of the local, the research adopted a mixed methodology, including quantitative and qualitative data collection methods; documentary methods were also employed. Research findings have, therefore, been enriched and verified by each other and have helped improve the reliability of the research overall.The service quality and the sustainability of CBT in Hoi An were revealed through the perceptions of tourists and the locals, respectively. The thesis then showed the link between CBT and SGDs to identify CBT as a tool to support sustainable development.The thesis adds distinctive theoretical and methodological contributions to the growing literature on CBT and its links to sustainable local development. The study achieves its objectives of (1) developing the CBT value chain model encompassing key stakeholders and their roles at a local scale, (2) conceptualizing CBT as a tool for sustainable local development, and (3) providing solutions need to be applied to develop sustainable CBT in Hoi An. The thesis will benefit local authorities and CBT practitioners by providing empirical evidence to base policies and strategies that facilitate desired development outcomes. With a strong focus on sustainability and a detailed understanding of local community perspectives, the thesis reinforces the recognition of CBT as a tool for sustainable development worldwide. This thesis encourages implementing and developing CBT in more communities, especially developing countries that aim for sustainable development
17
Hui, Daniel Hoi [Verfasser]. "A Study of T. C. Chao’s Christology in the Social Context of China (1920-1949) / Daniel Hoi Hui". Bern : Peter Lang AG, Internationaler Verlag der Wissenschaften, 2017. http://d-nb.info/1138919403/34.
Testo completo
18
Gwynn, David M. "Hoi peri Eusebion : the polemic of Athanasius of Alkexandria (Bishop AD 328-373) and the early 'Arian controversy'". Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401521.
Testo completo
19
Collinson, Peter Ronald James. "The ecology of a peripheral, subtropical coral community in Hong Kong". Thesis, Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19667425.
Testo completo
20
李慶剛 e Hing-kong Edwin Lee. "Methods to assess fisheries enhancement by the deployment of artificial reefs (a case study at Hoi Ha Wan, Hong Kong)". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31254639.
Testo completo
21
Trinh, Thi Giao Chi [Verfasser]. "Flood-related health risk assessment: a case study in Hoi An City, Quang Nam province, Vietnam / Thi Giao Chi Trinh". Kassel : Kassel University Press, 2017. http://d-nb.info/1141708086/34.
Testo completo
22
Lee, Hing-kong Edwin. "Methods to assess fisheries enhancement by the deployment of artificial reefs (a case study at Hoi Ha Wan, Hong Kong) /". Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22264048.
Testo completo
23
Tsawe, Mluleki. "Inequalities in the use of maternal and reproductive health services in Sierra Leone". University of the Western Cape, 2019. http://hdl.handle.net/11394/6660.
Testo completoAbstract (sommario):
Philosophiae Doctor - PhDThis thesis extends the literature on the trends and magnitude of health inequalities in the area of maternal and reproductive health services in Sierra Leone, and particular across sub-Saharan Africa. It attempted to provide a good understanding of, not only the determinants of maternal and reproductive healthcare use, but also factors that enable health inequalities to exist in Sierra Leone. This is an appropriate topic in population health studies as it aims to address important questions on the research agenda in the context of sub-Saharan Africa, particularly in a country with poor health outcomes such as Sierra Leone. A proper understanding of not only the coverage rates of population health outcomes but also the extent of health inequalities as well as the factors that contribute to these inequalities is crucial for any government. The thesis applied various techniques in the analysis of DHS data (from 2008 and 2013 rounds) in an attempt to answer the research questions.
24
Ho, Carr Hoi Yi. "Toward better performing organic solar cells: impact of charge carrier transport and electronic interactions in bulk heterojunction blends /Ho Hoi Yi, Carr". HKBU Institutional Repository, 2017. https://repository.hkbu.edu.hk/etd_oa/359.
Testo completoAbstract (sommario):
Organic photovoltaic (OPV) is an exciting energy harvesting technique. Although its power conversion efficiency (PCE) now exceeds 10% in a research laboratory, the processing window of an OPV cell is still narrow. A fundamental understanding of the OPV materials is desired. This thesis presents the charge carrier transport properties and electronic interactions in the bulk heterojunction (BHJ) active layer of OPV cells. They were found to be well correlated with OPV device performances. Space-charge-limited current (SCLC) measurements and admittance spectroscopy (AS) were employed to study the charge transports, while photothermal deflection spectroscopy (PDS) was used to probe the trap densities inside the materials. Beneficial effects of a common solvent additive, 1,8-diiodooctance (DIO), on PTB7:PC71BM OPV cells have been investigated. With DIO present in the casting solution, the resulting BHJ films have much enhanced electron mobilities, whereas the impact on the hole mobility is negligible. The origin of increased electron mobility is the reduced average electron hopping distance for those films prepared with DIO solvent additive. A balance of hole-electron mobility by tuning the DIO concentration was demonstrated to be the way to optimize the OPV device performance. In light of carrier transport measurement results, a "polymer-rich" strategy with preserved device performance was demonstrated. After understanding the importance of balanced hole-electron mobility, the impact of donor-acceptor weight ratio on the performance of PTB7 : PC71BM based OPV cells was explored. Early stage electronic donor-acceptor interactions were revealed using ultra-low dosages of fullerenes. Before electron transport pathways percolate, the unconnected fullerene domains act as traps and hinder electron transport. From PDS, the trap density observed inside BHJ films was found to be anti-correlated with the fill factor of OPV devices. The origin of low FFs is mainly due to electron traps and localized states from fullerenes. Based on the observations, it is proposed that PC71BM tends to intercalate with PTB7 backbone instead of forming self-aggregates before the electron pathway percolation. Apart from investigating the fundamentals in OPV devices, a solution to improve its processing window was proposed in this thesis. Thermally stable polymer : fullerene OPV cells were fabricated by employing fluorenone-based solid additives. A charge transfer interaction between the additives and donor moiety of polymer formed a locked network which freezes the BHJ morphology under thermal stress. The most promising result retains 90% of the origin efficiency, upon thermal aging at 100 °C for more than 20 hours in PTB7:PC71BM solar cells. Besides fullerene-based OPV, all-polymer photovoltaic solar cells (all-PSCs) were also investigated. Two new difluorobenzene-naphthalene diimide based polymer electron acceptors, one random (P1) and one regioregular (P2) structure, were compared. P2 exhibited a much better molecular packing, a higher electron mobility and more balanced hole-electron mobilities in its composite film with polymer donor, PTB7-Th. An optimized PTB7-Th:P2 device can achieve a respectably high PCE over 5% for all-PSC devices. These all-PSCs should open a new avenue for next generation OPVs.
25
Yu, Hoi Fung Verfasser], Jochen [Akademischer Betreuer] [Greiner e Elisa [Akademischer Betreuer] Resconi. "Constraints on the Prompt Emission Mechanism of Gamma-Ray Bursts using Time-Resolved Spectroscopy / Hoi Fung Yu. Betreuer: Jochen Greiner. Gutachter: Jochen Greiner ; Elisa Resconi". München : Universitätsbibliothek der TU München, 2016. http://d-nb.info/1085018466/34.
Testo completo
26
Sin, Fung-siu Iris. "Offshore sedimentary environments in Mirs Bay, Hong Kong /". Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21021181.
Testo completo
27
Chen, Quanjun Computer Science & Engineering Faculty of Engineering UNSW. "Analysis and application of hop count in multi-hop wireless ad-hoc networks". Awarded By:University of New South Wales. Computer Science & Engineering, 2009. http://handle.unsw.edu.au/1959.4/44769.
Testo completoAbstract (sommario):
Hop count, i.e., the number of wireless hops a packet has to go through to reach the destination, is a fundamental metric in multi-hop wireless ad-hoc networks. Network performance, such as throughput, end-to-end delay, energy consumption, and so on, depends critically on hop count. Previous work on modeling hop count is limited in making unrealistic simplifying assumptions either at the physical or network, or both layers of the communication protocol stack. A key contribution of this thesis is to present an analytical model to derive the probability distribution of hop count under realistic assumptions at both physical and network layers. Specifically, the model considers a log-normal shadowing radio propagation capable of accommodating the random signal fading observed in most wireless communication environments, and the widely used geographic routing at the network layer. Validation of the model is achieved by a comprehensive set of simulation experiments including a trace driven simulation of a real-word vehicular ad-hoc network. The model reveals that the presence of randomness in radio propagation reduces the required number of hops to reach a given destination significantly. To demonstrate the utility of the proposed hop count model, the thesis proposes three new applications which address some of the key challenges in multi-hop wireless networks. The first application derives the per-node packet forwarding load in multi-hop wireless sensor networks and reveals that the nodes in the vicinity of the base station has a significantly less forwarding load than previously thought under simplifying radio propagation and routing assumptions. The second application demonstrates that using hop count as a measure of distance traveled by a data packet, geocasting can be achieved in multi-hop wireless networks in situations when some of the network nodes do not have access to reliable location information. Finally, the proposed hop count model is used to evaluate the performance of the third application which demonstrates that the overhead of geographic routing can be reduced significantly by embracing a position update philosophy which adapts to the mobility and communication patterns of the underlying ad-hoc network.
28
Pandey, Manoj Kumar. "A Hop-by-Hop Architecture for Multicast Transport in Ad Hoc Wireless Networks". Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd3119.pdf.
Testo completo
29
Wang, Zhenyu. "Channel modelling for urban multi-hop/ad hoc networks". Thesis, University of Bristol, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435742.
Testo completo
30
Di, Felice Marco <1980>. "Cross-layer optimizations in multi-hop ad hoc networks". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/915/1/Tesi_Di_Felice_Marco.pdf.
Testo completoAbstract (sommario):
Unlike traditional wireless networks, characterized by the presence of last-mile, static and
reliable infrastructures, Mobile ad Hoc Networks (MANETs) are dynamically formed by
collections of mobile and static terminals that exchange data by enabling each other's
communication. Supporting multi-hop communication in a MANET is a challenging
research area because it requires cooperation between different protocol layers (MAC,
routing, transport). In particular, MAC and routing protocols could be considered
mutually cooperative protocol layers. When a route is established, the exposed and
hidden terminal problems at MAC layer may decrease the end-to-end performance
proportionally with the length of each route. Conversely, the contention at MAC layer
may cause a routing protocol to respond by initiating new routes queries and routing table
updates.
Multi-hop communication may also benefit the presence of pseudo-centralized virtual
infrastructures obtained by grouping nodes into clusters. Clustering structures may
facilitate the spatial reuse of resources by increasing the system capacity: at the same
time, the clustering hierarchy may be used to coordinate transmissions events inside the
network and to support intra-cluster routing schemes. Again, MAC and clustering
protocols could be considered mutually cooperative protocol layers: the clustering
scheme could support MAC layer coordination among nodes, by shifting the distributed
MAC paradigm towards a pseudo-centralized MAC paradigm. On the other hand, the
system benefits of the clustering scheme could be emphasized by the pseudo-centralized
MAC layer with the support for differentiated access priorities and controlled contention.
In this thesis, we propose cross-layer solutions involving joint design of MAC, clustering
and routing protocols in MANETs.
As main contribution, we study and analyze the integration of MAC and clustering
schemes to support multi-hop communication in large-scale ad hoc networks. A novel
clustering protocol, named Availability Clustering (AC), is defined under general nodes'
heterogeneity assumptions in terms of connectivity, available energy and relative
mobility. On this basis, we design and analyze a distributed and adaptive MAC protocol,
named Differentiated Distributed Coordination Function (DDCF), whose focus is to
implement adaptive access differentiation based on the node roles, which have been
assigned by the upper-layer's clustering scheme. We extensively simulate the proposed
clustering scheme by showing its effectiveness in dominating the network dynamics,
under some stressing mobility models and different mobility rates. Based on these results,
we propose a possible application of the cross-layer MAC+Clustering scheme to support
the fast propagation of alert messages in a vehicular environment.
At the same time, we investigate the integration of MAC and routing protocols in large
scale multi-hop ad-hoc networks. A novel multipath routing scheme is proposed, by
extending the AOMDV protocol with a novel load-balancing approach to concurrently
distribute the traffic among the multiple paths. We also study the composition effect of a
IEEE 802.11-based enhanced MAC forwarding mechanism called Fast Forward (FF),
used to reduce the effects of self-contention among frames at the MAC layer. The
protocol framework is modelled and extensively simulated for a large set of metrics and
scenarios.
For both the schemes, the simulation results reveal the benefits of the cross-layer
MAC+routing and MAC+clustering approaches over single-layer solutions.
31
Di, Felice Marco <1980>. "Cross-layer optimizations in multi-hop ad hoc networks". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/915/.
Testo completoAbstract (sommario):
Unlike traditional wireless networks, characterized by the presence of last-mile, static and
reliable infrastructures, Mobile ad Hoc Networks (MANETs) are dynamically formed by
collections of mobile and static terminals that exchange data by enabling each other's
communication. Supporting multi-hop communication in a MANET is a challenging
research area because it requires cooperation between different protocol layers (MAC,
routing, transport). In particular, MAC and routing protocols could be considered
mutually cooperative protocol layers. When a route is established, the exposed and
hidden terminal problems at MAC layer may decrease the end-to-end performance
proportionally with the length of each route. Conversely, the contention at MAC layer
may cause a routing protocol to respond by initiating new routes queries and routing table
updates.
Multi-hop communication may also benefit the presence of pseudo-centralized virtual
infrastructures obtained by grouping nodes into clusters. Clustering structures may
facilitate the spatial reuse of resources by increasing the system capacity: at the same
time, the clustering hierarchy may be used to coordinate transmissions events inside the
network and to support intra-cluster routing schemes. Again, MAC and clustering
protocols could be considered mutually cooperative protocol layers: the clustering
scheme could support MAC layer coordination among nodes, by shifting the distributed
MAC paradigm towards a pseudo-centralized MAC paradigm. On the other hand, the
system benefits of the clustering scheme could be emphasized by the pseudo-centralized
MAC layer with the support for differentiated access priorities and controlled contention.
In this thesis, we propose cross-layer solutions involving joint design of MAC, clustering
and routing protocols in MANETs.
As main contribution, we study and analyze the integration of MAC and clustering
schemes to support multi-hop communication in large-scale ad hoc networks. A novel
clustering protocol, named Availability Clustering (AC), is defined under general nodes'
heterogeneity assumptions in terms of connectivity, available energy and relative
mobility. On this basis, we design and analyze a distributed and adaptive MAC protocol,
named Differentiated Distributed Coordination Function (DDCF), whose focus is to
implement adaptive access differentiation based on the node roles, which have been
assigned by the upper-layer's clustering scheme. We extensively simulate the proposed
clustering scheme by showing its effectiveness in dominating the network dynamics,
under some stressing mobility models and different mobility rates. Based on these results,
we propose a possible application of the cross-layer MAC+Clustering scheme to support
the fast propagation of alert messages in a vehicular environment.
At the same time, we investigate the integration of MAC and routing protocols in large
scale multi-hop ad-hoc networks. A novel multipath routing scheme is proposed, by
extending the AOMDV protocol with a novel load-balancing approach to concurrently
distribute the traffic among the multiple paths. We also study the composition effect of a
IEEE 802.11-based enhanced MAC forwarding mechanism called Fast Forward (FF),
used to reduce the effects of self-contention among frames at the MAC layer. The
protocol framework is modelled and extensively simulated for a large set of metrics and
scenarios.
For both the schemes, the simulation results reveal the benefits of the cross-layer
MAC+routing and MAC+clustering approaches over single-layer solutions.
32
Al, Mojamed Mohammad. "A one hop overlay system for mobile ad hoc networks". Thesis, University of Stirling, 2016. http://hdl.handle.net/1893/24320.
Testo completoAbstract (sommario):
Peer-to-Peer (P2P) overlays were initially proposed for use with wired networks. However, the very rapid proliferation of wireless communication technology has prompted a need for adoption of P2P systems in mobile networks too. There are many common characteristics between P2P overlay networks and Mobile Ad-hoc Networks (MANET). Self-organization, decentralization, a dynamic nature and changing topology are the most commonly shared features. Furthermore, when used together, the two approaches complement each other. P2P overlays provide data storage/retrieval functionality and MANET provides wireless connectivity between clients without depending on any pre-existing infrastructure. P2P overlay networks can be deployed over MANET to address content discovery issues. However, previous research has shown that deploying P2P systems straight over MANET does not exhibit satisfactory performance. Bandwidth limitation, limited resources and node mobility are some of the key constraints. This thesis proposes a novel approach, OneHopOverlay4MANET, to exploit the synergies between MANET and P2P overlays through cross-layering. It combines Distributed Hash Table (DHT) based structured P2P overlays with MANET underlay routing protocols to achieve one logical hop between any pair of overlay nodes. OneHopOverlay4MANET constructs a cross-layer channel to permit direct exchange of routing information between the Application layer, where the overlay operates, and the MANET underlay layer. Consequently, underlay routing information can be shared and used by the overlay. Thus, OneHopOverlay4MANET reduces the typical management traffic when deploying traditional P2P systems over MANET. Moreover, as a result of building one hop overlay, OneHopOverlay4MANET can eliminate the mismatching issue between overlay and underlay and hence resolve key lookups in a short time, enhancing the performance of the overlay. v In this thesis, we present OneHopOverlay4MANET and evaluate its performance when combined with different underlay routing protocols. OneHopOverlay4MANET has been combined with two proactive underlays (OLSR and BATMAN) and with three reactive underlay routing protocols (DSR, AODV and DYMO). In addition, the performance of the proposed system over OLSR has been compared to two recent structured P2P over MANET systems (MA-SP2P and E-SP2P) that adopted OLSR as the routing protocol. The results show that better performance can be achieved using OneHopOverlay4MANET.
33
Westin, Ola. "TCP Performance in Wireless Mobile Multi-hop Ad Hoc Networks". Thesis, KTH, Mikroelektronik och Informationsteknik, IMIT, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-93070.
Testo completoAbstract (sommario):
There are many issues that limit the performance of wireless mobile multi-hop ad hoc networks (MANETs). One of them is that TCP is not well adapted to networks where routes can change or disappear often. In this paper the behaviour of a standard TCP implementation is studied in situations typical for MANETs and compared to the behaviour of a partial implementation of a ATCP, a TCP modification that is intended to increase performance in MANETs. Simulations with simple scenarios show that TCP easily creates a full network load which causes send failures and decreased throughput performance. In some cases the partial ATCP implementation increases throughput but more often it causes an increased amount of duplicate retransmissions. In these scenarios it is unlikely that even a complete ATCP implementation would increase throughput performance. A few modifications to ATCP and TCP are analysed. Especially a limit of the congestion window size shows a large throughput increase. The results are inconclusive, the simulations are too simple to show if the results are applicable in more complex scenarios. It is not clear if ATCP actually is useful in a MANET.Många faktorer begränsar prestandan i trådlösa mobila multi-hopp ad hoc-nätverk (MANET:er). En av dem är att TCP inte är anpassat till nätverk där rutter ofta kan förändras eller försvinna. I den här rapporten studeras hur en vanlig TCP-implementation uppför sig i typiska MANET-situationer. Detta beteende jämförs mot en partiell implementation av ATCP, en TCPmodifiering som är tänkt att öka prestanda i MANET:er. Simuleringar med enkla scenarier visar att TCP lätt genererar en full nätverkslast vilket orsakar misslyckade sändningar och en minskad genomströmningsprestanda. I vissa fall ökar den partiella ATCP-implementationen genomströmningen, men oftare ger den en ökad mängd onödiga omsändningar. I dessa scenarier är det inte troligt att ens en komplett ATCP-implementation skulle öka genomströmningsprestanda. Några mindre förändringar av ATCP och TCP analyseras. Särskilt ger en begränsning av stockningsfönstret en stor ökning av genomströmningen. Resultaten är ofullständiga. Simuleringarna är för enkla för att kunna visa om om resultaten är tillämpliga i mer komplexa scenarier. Det är inte klarlagt ifall ATCP verkligen är användbart i ett MANET.
34
Murray, David. "Cross layer performance improvements in Multi-hop Ad-hoc networks". Thesis, Murray, David (2011) Cross layer performance improvements in Multi-hop Ad-hoc networks. PhD thesis, Murdoch University, 2011. https://researchrepository.murdoch.edu.au/id/eprint/5805/.
Testo completoAbstract (sommario):
The multi hop architecture can provide greater range, spatial efficiency and throughput with lower power consumption than a traditional point coordinated design. In addition, the self-configuring, self-healing characteristics of this architecture enable previously infeasible network scenarios and applications. These benefits have motivated a significant volume of research. Unfortunately, the ISO networking model was not designed for multi hop ad hoc networks and subsequently, some cross layer interactions are necessary to provide adequate performance. This thesis develops and evaluates solutions to multiple performance problems. It makes contributions in the areas of routing, multi-hop contention and acknowledgement efficiency. The results are captured using a real world testbed. The first study evaluates three popular mesh routing protocols. The second contribution creates a novel channel selection mechanism that operates with multiple radios to overcome multi hop performance degradations. The final study shows the extent of the 802.11 acknowledgement overhead. A novel distributed proxy is created to eliminate this overhead in multi hop ad hoc networks.
35
Koo, Jeong-Hoi. "Using Magneto-Rheological Dampers in Semiactive Tuned Vibration Absorbers to Control Structural Vibrations". Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/29023.
Testo completoAbstract (sommario):
Since their invention in the early 1900s, Tuned Vibration Absorbers (TVAs) have shown to be effective in suppressing vibrations of machines and structures. A vibration absorber is a vibratory subsystem attached to a primary system. It normally consists of a mass, a spring, and a damper. Mounted to the primary system, a TVA counteracts the motions of the primary system, "absorbing" the primary structure's vibrations. A conventional passive TVA, however, is only effective when it is tuned properly, hence, the name "tuned" vibration absorber. In many practical applications, inevitable off-tuning (or mistuning) of a TVA occurs because of the system's operating conditions or parameter changes over time. For example, the mass in a building floor could change by moving furnishings, people gathering, etc., which can "off-tune" TVAs. When TVAs are off-tuned, their effectiveness is sharply reduced. Moreover, the off-tuned TVAs can excessively amplify the vibration levels of the primary structures; therefore, not only rendering the TVA useless but also possibly causing damage to the structures. Off-tuning is one of the major problems of conventional passive TVAs.
This study proposes a novel semiactive TVA, which strives to combine the best features of passive and active TVA systems. The semiactive TVA in this study includes a Magneto-Rheological (MR) damper that is used as a controllable damping element, for providing the real-time adjustability that is needed for improving the TVA performance.
This study is conducted in two phases. The first phase provides a numerical investigation on a two-degree-of-freedom (2-DOF) numerical model in which the primary structure is coupled with a TVA. The numerical investigation considers four semiactive control methods for the MR TVAs, in addition to an equivalent passive TVA. These numerical models are optimally tuned using numerical optimization techniques to compare each TVA system. These tuned systems then serve as the basis for numerical parametric studies for further evaluation of their dynamic performance. The parametric study covers the effects of damping, as well as system parameter variations (off-tuning). The results indicates that semiactive TVAs are more effective in reducing the maximum vibrations of the primary structure and are more robust when subjected to off-tuning. Additionally, the numerical study identifies the "On-off Displacement-Based Groundhook control (on-off DBG)" as the most suitable control method for the semiactive TVA among control methods considered in this study.
For the second phase of this study, an experimental study is performed on a test setup, which represents a 2-DOF structure model coupled with an MR TVA. Using this setup, a series of tests are conducted in the same manner as the numerical study to evaluate the performance of the semiactive TVA. The primary purposes of the experiment are to further evaluate the most promising semiactive control methods and to serve as a "proof-of-concept" of the effectiveness of this MR TVA for floor vibration applications. The results indicate that the semiactive TVA with displacement-based groundhook control outperforms the equivalent passive TVA in reducing the maximum vibrations of the primary structure. This confirms the numerical result that identifies on-off DBG control method as the "best" control method for the MR TVA among four semiactive control schemes considered. The experimental robustness study is also conducted, focusing on the dynamic performance of both the passive and the semiactive TVAs when the mass of the primary system changes (mass off-tuning). The mass of the primary system varied from -23 % to +23 % of its nominal value by adding and removing external masses. The experimental results show that the semiactive TVA is more robust to changes in the primary mass than the passive TVA.
These results justify the benefits of the use of semiactive MR TVAs in structures, such as building floor systems. The off-tuning analysis further suggests that, in practice, semiactive TVAs should be tuned slightly less than their optimum in order to compensate for any added masses to the structure. Additionally, the lessons learned from the experimental study have paved the way for implementing the semiactive MR TVA on a test floor, which is currently in progress under a separate study.Ph. D.
36
Xu, Lei. "Potential single-occupancy vehicle demand for the Katy Freeway and Northwest Freeway high-occupancy vehicle lanes". Texas A&M University, 2005. http://hdl.handle.net/1969.1/4358.
Testo completoAbstract (sommario):
Since the 1960âÂÂs, high-occupancy vehicle (HOV) lanes have been successfully used as a
travel demand management technique. In recent years, there has been a growing interest
in the use of high-occupancy toll (HOT) lanes as an alternative to HOV lanes to help
manage the increasing demand for travel. HOT lanes combine pricing and vehicle
occupancy restrictions to optimize the demand for HOV lanes. As two of the four HOT
lanes in the world, the HOT lane facilities in Houston, Texas received relatively low
patronage after operating for over 6 years on the Katy Freeway and over 4 years on the
Northwest Freeway. There existed an opportunity to increase the usage of these HOT
lanes by allowing single-occupancy vehicle (SOV) travelers to use the lanes, for an
appropriate toll. The potential SOV demand for HOV lane use during the off-peak
periods from the Katy Freeway and Northwest Freeway general-purpose lane (GPL)
travelers was estimated in this study by using the data collected from a 2003 survey of
travelers on the Katy and Northwest Freeway GPLs who were not enrolled in
QuickRide. Based on survey results, more travelers would choose to drive on the HOT lanes
as SOV travelers during the off-peak periods when the facilities provided higher travel
time savings and charged lower tolls. Two important factors influencing travelersâ use
of the HOV lanes were their value of travel time savings (VTTS) and penalty for
changing travel schedule (VPCS). It was found that respondents had VTTS
approximately 43 percent of their hourly wage rate and VPCS approximately 3 percent
of their hourly wage rate. Combining this information with current travel time savings
and available capacity on the HOV lanes, it was found that approximately 2000 SOV
travelers per day would pay an average toll of $2.25 to use the HOV lanes during the
off-peak periods.
37
Zhang, Xin. "Network Formation and Routing for Multi-hop Wireless Ad-Hoc Networks". Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11470.
Testo completoAbstract (sommario):
An energy-aware on-demand Bluetooth scatternet formation and routing protocol taking into
account network architecture and traffic pattern is proposed. The scatternet formation protocol is able to cope with multiple sources initiating
traffic simultaneously as well as prolong network lifetime. A modified Inquiry scheme using extended ID packet is introduced for fast device discovery and power efficient propagation of route request messages with low delay. A mechanism employing POLL packets in Page processes is proposed to transfer scatternet formation and route reply information without extra overhead. In addition, the energy aware forwarding nodes selection scheme is based on local information and results in more uniform network resource utilization and improved network lifetime. Simulation results show that this protocol can provide scatternet formation
with reasonable delay and with good load balance which results in prolonged network lifetime for Bluetooth-based wireless sensor networks.
In this research, a metric-based scatternet formation algorithm for the Bluetooth-based sensor motes is presented. It optimizes the Bluetooth network formation from the hop distance
and link quality perspectives. In addition, a smart repair mechanism is proposed to deal with link/node failure and recover the network connectivity promptly with low overhead. The experiments with the Intel Mote platform demonstrate the effectiveness of the optimizations.
This research also investigates the scalability of ad hoc routing protocols in very large-scale wireless ad hoc networks. A comprehensive
simulation study is conducted of the performance of an on-demand routing protocol on a very large-scale, with as many as 50,000 nodes in the network. The scalability analysis is addressed based on various network sizes, node density, traffic load, and mobility. The reasons for packet loss are analyzed and categorized at each network layer. Based on the observations, we observe the effect of the parameter selection and try to exhaust the scalability boundary
of the on-demand routing protocol for wireless ad hoc networks.
38
Rajendran, Venkatesh. "Medium access control protocols for multi-hop wireless ad hoc networks /". Diss., Digital Dissertations Database. Restricted to UC campuses, 2006. http://uclibs.org/PID/11984.
Testo completo
39
Antic, Filip S. "Capactiy of single-hop communication links in wireless ad hoc networks". Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/33100.
Testo completoAbstract (sommario):
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (leaves 67-68).
This thesis defines the capacity of single-hop communication links in wireless ad hoc networks as the transferable data rate over that link determined by the Shannon limit and by the fixed modulation scheme and bit error rate. The resulting capacity formulas are derived under the assumption of r-3.8 path loss and uniform, but random, distribution of users. Rank of the link R is defined and included in the capacity formulas. After defining link capacity, the improvement of capacity is studied when different network components are implemented. These include successive interference cancellation (SIC), and multiple antenna arrays at the transmitting and the receiving end of the link. These strategies are then compared in terms of the dB improvement of capacity that they provide. Network parameter NP is defined in order to characterize spatial reuse in the network, and optimal network parameter is determined for maximizing link capacity in the process of dividing the network single frequency channel into equally sized subchannels.
by Filip S. Antic.
M.Eng.
40
Zhao, Xiwei. "Foundational Forensic Techniques for Cellular and Ad Hoc Multi-hop Networks". FIU Digital Commons, 2008. http://digitalcommons.fiu.edu/etd/23.
Testo completoAbstract (sommario):
The Internet has become an integral part of our nation's critical socio-economic infrastructure. With its heightened use and growing complexity however, organizations are at greater risk of cyber crimes. To aid in the investigation of crimes committed on or via the Internet, a network forensics analysis tool pulls together needed digital evidence. It provides a platform for performing deep network analysis by capturing, recording and analyzing network events to find out the source of a security attack or other information security incidents. Existing network forensics work has been mostly focused on the Internet and fixed networks. But the exponential growth and use of wireless technologies, coupled with their unprecedented characteristics, necessitates the development of new network forensic analysis tools. This dissertation fostered the emergence of a new research field in cellular and ad-hoc network forensics. It was one of the first works to identify this problem and offer fundamental techniques and tools that laid the groundwork for future research. In particular, it introduced novel methods to record network incidents and report logged incidents. For recording incidents, location is considered essential to documenting network incidents. However, in network topology spaces, location cannot be measured due to absence of a 'distance metric'. Therefore, a novel solution was proposed to label locations of nodes within network topology spaces, and then to authenticate the identity of nodes in ad hoc environments. For reporting logged incidents, a novel technique based on Distributed Hash Tables (DHT) was adopted. Although the direct use of DHTs for reporting logged incidents would result in an uncontrollably recursive traffic, a new mechanism was introduced that overcome this recursive process. These logging and reporting techniques aided forensics over cellular and ad-hoc networks, which in turn increased their ability to track and trace attacks to their source. These techniques were a starting point for further research and development that would result in equipping future ad hoc networks with forensic components to complement existing security mechanisms.
41
Qin, Xiaoqi. "On Throughput Maximization in a Multi-hop MIMO Ad Hoc Network". Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/23160.
Testo completoAbstract (sommario):
In recent years, there has been a growing research interest in throughput optimization problems in a multi-hop wireless network. MIMO (multiple-input multiple-output), as an advanced physical layer technology, has been employed in multi-hop wireless networks to increase throughput with a given bandwidth or transmit power. It exploits the use of multiple antennas at the transmitter and receiver to increase spectral efficiency by leveraging its spatial multiplexing (SM) and interference cancellation (IC) capabilities. Instead of carrying complex manipulations on matrices, degree-of-freedom(DoF) based MIMO models, which require only simple computations, are widely used in networking research to exploit MIMO\'s SM and IC capabilities.In this thesis, we employ a new DoF model, which can ensure feasible solution and achieve
a higher DoF region than previous DoF-based models. Based on this model, we study the DoF scheduling for a multi-hop MIMO network. Specifically, we aim to maximize the minimum rate among all sessions in the network. Some researches have been done based on this model to solve throughput optimization problems with the assumption that the route of each session is given priori. Although the fixed routing decreases the size of the problem, it also limits the performance of the network to a great extent.
The goal of this thesis is to employ this new model to solve the throughput maximization
problem by jointly considering flow routing, scheduling, and DoF allocation for SM and IC. We
formulate it as a mixed integer linear program (MILP), which cannot be solved efficiently by
commercial softwares even for moderate sized networks. Thus, we develop an efficient polynomial time algorithm by customizing the sequential fixing framework. Through simulation results, we show that this algorithm can efficiently provide near-optimal solutions for networks with different sizes.
Master of Science
42
Rieser, Eva. "The role of HOIL-1, HOIP and SHARPIN in immune signalling". Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/17941.
Testo completoAbstract (sommario):
Members of the tumour necrosis factor receptor (TNFR) superfamily, the interleukin-1 Receptor (IL-1R), the Toll-like Receptor (TLR) and the NOD-like receptor (NLRs) families play crucial roles in the initiation of innate immune responses. Even though the stimulation of these different receptors is triggered by upstream signalling components which are largely receptor-specific, their signalling cascades generally converge in the activation of both mitogen-activated protein kinases (MAPKs) and the inhibitor of nuclear factor– B (I B) kinases (IKKs). The activation of MAPKs and IKKs are crucial events in the signalling cascades of TNFR-, IL-1R-, TLR- and NLR family members and result in the activation of distinct transcription factors such as AP-1 and NF- B, respectively. In order to gain a more comprehensive picture of the signalling components associated with TNFR1 our group developed a modified tandem affinity purification (moTAP) strategy. This led to the identification of three novel components of the native TNFR1 signalling complex (TNFRSC): HOIL-1, HOIP and SHARPIN. Together, they form the “linear ubiquitin chain assembly complex” (LUBAC), a tripartite E3 ligase complex which generates linear ubiquitin chains. LUBAC activity is required for efficient TNF-mediated activation of NF- B and JNK by linearly ubiquitinating NEMO and RIP1 in the TNF-RSC. Mutation of the SHARPIN-encoding gene in mice results in chronic proliferative dermatitis (cpdm). The cpdm phenotype is characterised by inflammatory skin lesions and defective lymphoid organogenesis. In this thesis it is shown that mouse embryonic fibroblasts (MEFs) and primary keratinocytes generated from cpdm mice showed impaired activation of the MAPK- and NF- B signalling pathways following stimulation by various TNF and IL-1 family members as well as by different TLR ligands. These alterations were also apparent in bone marrow-derived macrophages isolated from cpdm mice. Thereby, lack of SHARPIN exerted an inhibitory effect on gene-activatory signal transduction by these immune stimuli. Similar defects in NF- B and MAPK signalling were also observed with a ligand for the NLR family member NOD2. Cells generated from mice conditionally deficient for the other LUBAC components exhibited similar alterations in diverse innate immune signalling pathways. These results imply that SHARPIN and HOIL-1 cannot substitute each other but instead cooperate with HOIP to generate linear ubiquitin chains in the signalling pathways that are activated by diverse immune receptors. In summary, the results of this thesis identify LUBAC and the linear ubiquitin chains it generates as previously unrecognised components of various signalling pathways which are central to the induction of immunity and regulation of inflammation.
43
Viswanath, Kumar. "Adaptive integrated approach to group communications in multi-hop ad-hoc networks /". Diss., Digital Dissertations Database. Restricted to UC campuses, 2005. http://uclibs.org/PID/11984.
Testo completo
44
Oehlsen, Golaleh [Verfasser]. "Stochastic Geometric Distances in Multi-Hop Wireless Ad Hoc Networks / Golaleh Oehlsen". München : Verlag Dr. Hut, 2012. http://d-nb.info/1020299436/34.
Testo completo
45
Lu, Yu Ming. "Routing strategies for capacity enhancement in multi-hop wireless ad hoc networks". Thesis, University of York, 2007. http://etheses.whiterose.ac.uk/11080/.
Testo completoAbstract (sommario):
This thesis examines a Distributed Interference Impact Probing (DIIP) strategy for Wireless Ad hoc Networks (WANETs), using a novel cross-layer Minimum Impact Routing (MIR) protocol. Perfonnance is judged in tenns of interference reduction ratio, efficiency, and system and user capacity, which are calculated based on the measurement of Disturbed Nodes (DN). A large number of routing algorithms have been proposed with distinctive features aimed to overcome WANET's fundamental challenges, such as routing over a dynamic topology, scheduling broadcast signals using dynamic Media Access Control (MAC), and constraints on network scalability. However, the scalability problem ofWANET cannot simply adapt the frequency reuse mechanism designed for traditional stationary cellular networks due to the relay burden, and there is no single comprehensive algorithm proposed for it. DIIP enhances system and user capacity using a cross layer routing algorithm, MIR, using feedback from DIIP to balance transmit power in order to control hop length, which consequently changes the number of relays along the path. This maximizes the number of simultaneous transmitting nodes, and minimizes the interference impact, i.e. measured in tenns of 'disturbed nodes'. The perfonnance of MIR is examined compared with simple shortest-path routing. A WANET simulation model is configured to simulate both routing algorithms under multiple scenarios. The analysis has shown that once the transmitting range of a node changes, the total number of disturbed nodes along a path changes accordingly, hence the system and user capacity varies with interference impact variation. By carefully selecting a suitable link length, the neighbouring node density can be adjusted to reduce the total number of DN, and thereby allowing a higher spatial reuse ratio. In this case the system capacity can increase significantly as the number of nodes increases. In contrast, if the link length is chosen regardless ofthe negative impact of interference, capacity decreases. In addition, MIR diverts traffic from congested areas, such as the central part of a network or bottleneck points.
46
Van, Der Werf Steven Martijn. "Architecture and performance of multi-hop wireless ad-hoc routing protocol (MultiWARP)". Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/1989.
Testo completoAbstract (sommario):
In recent years, a great deal of attention has been given to wireless connectivity solutions that are capable of establishing wireless ad-hoc networks between mobile nodes. Whilst most of these networks are formed using a combination of fixed and mobile infrastructure, completely infrastructure-less networks are thought to become more commonplace in the future. Moreover, this type of network structure seeks to utilise multi-hop connectivity between mobile nodes rather than the traditional single-hop connectivity established between fixed access points.The initial configuration phase and subsequent maintenance phase of a multi-hop wireless ad-hoc network requires the use of appropriate routing functions to exist between the mobile nodes. Therefore, it is essential that a routing protocol capable of determining correct and optimal routing path information in the presence of node mobility and the mobile radio environment be sought. Furthermore, it is beneficial to utilise the limited wireless bandwidth efficiently, such that a routing protocol should be designed specifically in the context of a multi-hop wireless ad-hoc network topology. This can be achieved through employing a non-hierarchical approach and using neighbouring nodes to act as intermediate relay nodes.The proposed routing protocol, called the Multi-hop Wireless Ad-hoc Routing Protocol (MultiWARP), is comprised of both a proactive and reactive routing component, thus forming a hybrid protocol which is able to exploit the benefits of each component. It is shown that manipulating these two components within the context of an awareness region, which divides the network into 2 regions, the routing overhead can be minimised. For the proactive component, the necessary network topology information that must be transmitted between neighbouring nodes is encoded within a routing update (RUPDT) packet. In this study, three alternative RUPDT encoding schemes have been formulated to encode the network topology in an efficient manner to reduce the RUPDT packet size.For the reactive component, a novel covercasting mechanism is designed that minimises the number of route request (RREQ) transmissions required to determine the routing path by utilising existing routing table information. Supplementary techniques are then utilised, such as snooping, route repair, and route optimisation to further optimise performance and minimise the route discovery delay (latency). This same covercasting mechanism is then utilised to efficiently transmit periodic RUPDT packets between neighbouring nodes to maintain routing table validity at each node, without having to resort to flooding which causes the “broadcast storm problem”. In addition, several route selection algorithms are considered which distribute traffic data between the intermediate relay nodes comprising the ad-hoc network.The performance and computational complexity of the proposed hybrid routing protocol is shown by means of computer simulations and theoretical analysis. Various traffic scenarios and topologies are presented to obtain the routing protocol performance metric results, and these are compared with other protocols found in the literature. For a multi-hop wireless ad-hoc network, it is shown that the proposed hybrid routing protocol, MultiWARP, is able to achieve higher average system performance in terms of improved throughput and stability performance when compared to other wireless ad-hoc routing protocols, such as DSR.
47
Mahdi, Rafid, e Pontus Tobiasson. "An experimental verification of single-frequency networks in multi-hop ad hoc networks". Thesis, Mittuniversitetet, Avdelningen för informations- och kommunikationssystem, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-27968.
Testo completoAbstract (sommario):
A multi-hop ad hoc network requires no infrastructure, like base stations or routers to function. This means that it can quickly be deployed and in movement, making it ideal for scenarios like natural disasters or battlefield communication. A single-frequency network (SFN) is the idea that transmitters can cooperate to send the same signals simultaneously over the same frequency channel, such that the signals are amplified. It was previously proposed that SFNs could be created in multi-hop ad hoc networks. According to simulations, this could improve the energy consumption, signal reachability, and data transfer rate. As this has only been simulated, the purpose of this project is to experimentally verify that SFN is attainable in a multi-hop ad hoc network, and to assess what the difficulties are of an actual implementation. The method involved synchronizing the transmission of two devices operating under the 802.11a standard. A multi-hop ad hoc network was created by changing the settings of the network interface cards. The devices used were mainly laptops and transmissions were monitored in Wireshark. The laptops were forced to send on one frequency channel to make interference possible, and identical packets were sent. Experiments were made to assess whether SFN was attained. The packet loss rate and distance were used to evaluate the results. The results suggest that a synchronized transmission off by less than 2 μs was attained. However, the error of these measurements were neither known nor approximable. This meant it was hard to know when a SFN was formed. The results indicate that SFN was attained, as the packet loss rate decreased significantly when employed. The effectiveness of SFN was hard to assess because the results were not comparable with the simulation values. The difficulty of an actual implementation is deemed to be the synchronization of transmissions.
48
Suthaputchakun, Chakkaphong. "Multi-hop broadcast protocols for emergency message dissemination in vehicular ad hoc networks". Thesis, University of Surrey, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608349.
Testo completoAbstract (sommario):
Emergency Message (EM) dissemination in Vehicular Ad hoc Networks (VANETs) has attracted significant attention in Intelligent Transportation System (ITS) in recent years. Such dissemination mechanisms mostly rely on licensed Dedicated Short Range Communications (DSRC) systems such as IEEE 802.11p and IEEE PI609.1-4 standards. By timely broadcasting of emergency messages (EMs), drivers can avoid potentially dangerous accidents and experience a safer driving environment. As the result, a concern of the number of accidents is also reduced. Thus, an efficient broadcast protocol is required in this scenario. In this thesis, designs of robust broadcast protocols are considered for Emergency Message Dissemination in VANETs. It presents four innovative contributions. Firstly, a literature review as well as challenges and issues of the protocols designed for EM dissemination application are presented. Secondly, Priority-based Routing Protocol (PRP) and its reliability enhancement (PRP-RE) have been proposed as broadcast protocols for different types of EM disseminations, providing; 1) fully distributed broadcast protocol; 2) different Quality of Services (QoS) for different types of EMs: 3) maximum message dissemination distance per hop; and 4) high communication reliability. Thirdly, a more efficient and robust multi-hop broadcast protocol for time-critical EM disseminations is proposed as Trinary Partitioned Black-Burst based Broadcast Protocol (3P3B). A mini-DIPS in MAC sub-layer is introduced to give the time-critical EMs the highest priority access to the communication channel compared to other EMs. In addition, a trinary partitioning is designed to iteratively partition the communication area into small sectors, allowing only the furthest possible vehicle to perform EM forwarding. Therefore. 3P3B can increase dissemination speed and reduce contention period jitter. The performance evaluation results demonstrate that 3P3B outperforms benchmarks of the existing broadcast protocols in VANETs in terms of average message dissemination speed, message progress, communication delay, and packet delivery ratio. Finally, 3P3B-DTN is proposed based on an enhancement of 3P3B to deal with communications in a disruptive network with an introduction of EM store, carry, and forward to maximize packet delivery ratio while minimizing end-to-end delay. The performance evaluation results show that 3P3BDTN achieves higher packet delivery ratio than 3P3B even when the network is disrupted with a trade-off of higher end-to-end delay and overhead for those EMs, which would be lost otherwise.
49
Seddik, Alaa. "TCP performance study and enhancements within wireless multi-hop ad hoc network environments". Thesis, Evry-Val d'Essonne, 2009. http://www.theses.fr/2009EVRY0006/document.
Testo completoAbstract (sommario):
Les réseaux ad hoc diffèrent des réseaux filaires par la multitude de perturbation auxquels ils sont sujets. Alors qu’une rupture de lien est un événement plutôt rare sur des réseaux filaires, et généralement imputable à l’état physique du matériel intermédiaire, cet événement est courant avec les communications radio. Ceci est lié à la qualité du signal reçu de l’autre extrémité ou à la configuration de l’environnement. Les perturbations causées par l’environnement ne mènent pas seulement à une rupture d’un lien, elles peuvent avoir un impact sur la réception des données. La volatilité des liens est typique dans les réseaux sans fil alors pour les réseaux filaires ce problème est inexistant. TCP, qui est prévu pour assurer la transmission fiable des données, n’a été conçu qu’en tenant compte des contraintes des réseaux filaires. Ainsi, certains événements dans la transmission de données sans fil peuvent être mal interprétés et engendrer une mauvaise réaction de TCP. Pour améliorer la performance de TCP dans les réseaux ad hoc, l’objectif de cette thèse est double. Dans un premier temps, une étude complète des performances de TCP dans les réseaux ad hoc est dressée. Celle-ci concerne à la fois les débits atteignables et aussi la consommation d’énergie induite par l’utilisation de ce protocole de transport dans un réseau ad hoc. Cette étude permet d’identifier les points d’amélioration de TCP pour qu’il soit utilisable dans les réseaux ad hoc. Dans un second temps, nous proposons une nouvelle variante de TCP, appelée TCP-WELCOME, dont l’objectif est de traiter de façon adéquate les différents types de perte de paquets sur un réseau ad hoc et optimiser la performance de TCPWireless ad hoc networks are different from wired networks by the multitude of data packet loss situations they are subjected to. This is due to the characteristics of wireless channel that might obstruct the proper reception of data packet at the destination end. In some case, these vulnerabilities of wireless channel can result in a complete link failure. Although link failure is of low probability in wired networks, it is rather common in wireless networks. The volatility of communication channel is a typical problem with wireless links, which is not the case with wired cables. TCP is a transport protocol that aims at ensuring high reliability and guarantying reception of data packets. However, TCP was designed for wired networks to address congestion, which is the main cause for data packet loss in wired networks. Therefore, other types of data packet loss encountered in wireless networks are prone to misinterpretation by TCP, which will lead to TCP performance degradation within the network. To overcome the performance limitation of TCP when used within ad hoc networks, the aim of this thesis is twofold. First, a complete performance study of TCP over ad hoc networks is achieved. This evaluation concerns two performance metrics: the achievable throughput and the energy consumption of TCP within ad hoc networks. This study allows identifying the potential room of improvement to enhance TCP efficiency in ad hoc networks. Second, we propose a new TCP variant, TCP-WELCOME that optimizes the performance of TCP in ad hoc networks through its ability to distinguish among, and efficiently deal with, different data packet loss situations, within ad hoc networks
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Seddik, Alaa Agoulmine Nazim. "TCP performance study and enhancements within wireless multi-hop ad hoc network environments". S. l. : S. n, 2009. http://www.biblio.univ-evry.fr/theses/2009/2009EVRY0006.pdf.
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