Kliknij ten link, aby zobaczyć inne rodzaje publikacji na ten temat: Multi-access.
Rozprawy doktorskie na temat „Multi-access”
Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych
Sprawdź 50 najlepszych rozpraw doktorskich naukowych na temat „Multi-access”.
Przycisk „Dodaj do bibliografii” jest dostępny obok każdej pracy w bibliografii. Użyj go – a my automatycznie utworzymy odniesienie bibliograficzne do wybranej pracy w stylu cytowania, którego potrzebujesz: APA, MLA, Harvard, Chicago, Vancouver itp.
Możesz również pobrać pełny tekst publikacji naukowej w formacie „.pdf” i przeczytać adnotację do pracy online, jeśli odpowiednie parametry są dostępne w metadanych.
Przeglądaj rozprawy doktorskie z różnych dziedzin i twórz odpowiednie bibliografie.
1
Greaves, David J. "Multi-access metropolitan area networks." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303053.
Pełny tekst źródła
2
Shaw, David. "Development of a model for smart card based access control in multi-user, multi-resource, multi-level access systems." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 1999. https://ro.ecu.edu.au/theses/1229.
Pełny tekst źródłaStreszczenie:
The primary focus of this research is an examination of the issues involved in the granting of access in an environment characterised by multiple users, multiple resources and multiple levels of access permission. Increasing levels of complexity in automotive systems provides opportunities for improving the integration and efficiency of the services provided to the operator. The vehicle lease / hire environment provided a basis for evaluating conditional access to distributed, mobile assets where the principal medium for operating in this environment is the Smart Card. The application of Smart Cards to existing vehicle management systems requires control of access to motor vehicles, control of vehicle operating parameters and secure storage of operating information. The issues addressed include examination of the characteristics of the operating environment, development of a model and design, simulation and evaluation of a multiple application Smart Card. The functions provided by the card include identification and authentication, secure hash and encryption functions which may be applied, in general, to a wide range of access problems. Evaluation of the algorithms implemented indicate that the Smart Card design may be provably secure under single use conditions and conditionally secure under multiple use conditions. The simulation of the card design provided data to support further research and shows the design is practical and able to be implemented on current Smart Card types.
3
Choi, Byoung Jo. "Multi-carrier code division multiple access." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394098.
Pełny tekst źródła
4
Stirling-Gallacher, Richard. "Multi-carrier code division multiple access." Thesis, University of Edinburgh, 1997. http://hdl.handle.net/1842/13027.
Pełny tekst źródłaStreszczenie:
The topic of this thesis is the use of multi-carrier modulation with code division multiple access (CDMA). The motivation of this work is to establish if the combination of multi-carrier modulation with CDMA has a performance advantage over a conventional direct sequence CDMA (DS-CDMA) communication system. In this thesis three types of multi-carrier CDMA are identified and the main work is concentrated on one particular combination, which is referred to as one chip per carrier multi-carrier CDMA system. This system itself, however can be split into different variations and an examination of two of these is made. The first of these one chip per carrier multi-carrier CDMA systems utilises the same number of carriers as the spreading sequence length. The carriers overlap and adjacent chips of the spreading sequence modulate adjacent carriers. There is no guard interval and therefore intercarrier interference occurs. If the receiver is synchronised and has a perfect estimate of the channel, it is shown that this multi-carrier CDMA system has comparable performance to a DS-CDMA system of the same bandwidth. It is further shown that it is simple to compute the minimum mean square error criteria as the equaliser consists of <I>N</I> one tap equalisers, where <I>N</I> is the number of carriers. The second system utilises many overlapping low data rate orthogonal carriers. The orthogonality of the carriers is maintained due to cyclically extended guard interval and the number of carriers is much higher than the spreading sequence length. After spreading, the data streams are interleaved onto the carriers to maximise diversity. A practical form of maximum likelihood detection for 64 users is described. It is shown from simulation results that when the system is used in conjunction with ½ rate (constraint length 7) coding and equal gain combining the system can support 64 users at 6 dB <I>E<SUB>6</SUB>/N<SUB>6</SUB></I> for a bit error rate of 2 x 10<SUP>-3</SUP>. This compares with an equivalent DS-CDMA system which can only support 16 users for the same bit error rate and <I>E<SUB>6</SUB>/N<SUB>o</SUB></I>. These results assume perfect channel knowledge and synchronisation. It is further shown that to provide high spectral efficiency in a coded system a high rate convolutional coding scheme is needed. A combined decoder/canceller is also presented. Finally, techniques to achieve synchronisation and channel estimation algorithms are presented. These algorithms are considered in conjunction with the second system. In the framework of synchronisation, methods are presented for frequency and timing synchronisation. For channel estimation, simulation results are presented for a simple channel estimator.
5
Athamnah, Malek. "ENABLING MULTI-PARTY COLLABORATIVE DATA ACCESS." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/528695.
Pełny tekst źródłaStreszczenie:
Computer and Information Science<br>Ph.D.<br>Cloud computing has brought availability of services at unprecedented scales but data accessibility considerations become more complex due to involvement of multiple parties in providing the infrastructure. In this thesis, we discuss the problem of enabling cooperative data access in a multi-cloud environment where the data is owned and managed by multiple enterprises. We consider a multi-party collaboration scheme whereby a set of parties collectively decide accessibility to data from individual parties using different data models such as relational databases, and graph databases. In order to implement desired business services, parties need to share a selected portion of information with one another. We consider a model with a set of authorization rules over the joins of basic relations, and such rules are defined by these cooperating parties. The accessible information is constrained by these rules. Specifically, the following critical issues were examined: Combine rule enforcement and query planning and devise an algorithm which simultaneously checks for the enforceability of each rule and generation of minimum cost plan of its execution using a cost metric whenever the enforcement is possible; We also consider other forms of limiting the access to the shared data using safety properties and selection conditions. We proposed algorithms for both forms to remove any conflicts or violations between the limited accesses and model queries; Used graph databases with our authorization rules and query planning model to conduct similarity search between tuples, where we represent the relational database tuples as a graph with weighted edges, which enables queries involving "similarity" across the tuples. We proposed an algorithm to exploit the correlations between attributes to create virtual attributes that can be used to catch much of the data variance, and enhance the speed at which similarity search occurs; Proposed a framework for defining test functionalities their composition, and their access control. We discussed an algorithm to determine the realization of the given test via valid compositions of individual functionalities in a way to minimize the number of parties involved. The research significance resides in solving real-world issues that arise in using cloud services for enterprises After extensive evaluations, results revealed: collaborative data access model improves the security during cooperative data processes; systematic and efficient solving access rules conflict issues minimizes the possible data leakage; and, a systematic approach tackling control failure diagnosis helps reducing troubleshooting times and all that improve availability and resiliency. The study contributes to the knowledge, literature, and practice. This research opens up the space for further studies in various aspects of secure data cooperation in large-scale cyber and cyber-physical infrastructures.<br>Temple University--Theses
6
Wang, Kehao. "Multi-channel opportunistic access : a restless multi-armed bandit perspective." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00832569.
Pełny tekst źródłaStreszczenie:
In the thesis, we address the fundamental problem of opportunistic spectrum access in a multi-channel communication system. Specifically, we consider a communication system in which a user has access to multiple channels, but is limited to sensing and transmitting only on one at a given time. We explore how the smart user should exploit past observations and the knowledge of the stochastic properties of these channels to maximize its transmission rate by switching channels opportunistically. Formally, we provide a generic analysis on the opportunistic spectrum access problem by casting the problem into the restless multi-armed bandit (RMAB) problem, one of the most well-known generalizations of the classic multi-armed bandit (MAB) problem, which is of fundamental importance in stochastic decision theory. Despite the significant research efforts in the field, the RMAB problem in its generic form still remains open. Until today, very little result is reported on the structure of the optimal policy. Obtaining the optimal policy for a general RMAB problem is often intractable due to the exponential computation complexity. Hence, a natural alternative is to seek a simple myopic policy maximizing the short-term reward. Therefore, we develop three axioms characterizing a family of functions which we refer to as regular functions, which are generic and practically important. We then establish the optimality of the myopic policy when the reward function can be expressed as a regular function and the discount factor is bounded by a closed-form threshold determined by the reward function. We also illustrate how the derived results, generic in nature, are applied to analyze a class of RMAB problems arising from multi-channel opportunistic access. Next, we further investigate the more challenging problem where the user has to decide the number of channels to sense in each slot in order to maximize its utility (e.g., throughput). After showing the exponential complexity of the problem, we develop a heuristic v-step look-ahead strategy. In the developed strategy, the parameter v allows to achieve a desired tradeoff between social efficiency and computation complexity. We demonstrate the benefits of the proposed strategy via numerical experiments on several typical settings.
7
Garnes, Håvard Husevåg. "Access Control in Multi-Thousand-Machine Datacenters." Thesis, Norwegian University of Science and Technology, Department of Telematics, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9730.
Pełny tekst źródłaStreszczenie:
<p>Large data centers are used for large-scale high-performance tasks that often includes processing and handling sensitive information. It is therefore important to have access control systems that are able to function in large-scale data centers. This thesis looks into existing solutions for the authentication step of access control in large data centers, and analyses how two authentication systems, Kerberos and PKI, will perform when employed on a larger scale, beyond what is normal in a large data center today. The emphasis in the analysis is on possible bottlenecks in the system, computational power spent on access control routines, procedures for administration and key distribution and availability of extension features needed in large scale data center scenarios. Our administration analysis will propose and present possible methods for initial key distribution to new machines in the data center, as well as methods for enrolling new users. We will also propose a method for automatic service instantiation in Kerberos and present a method for service instantiation in PKI. We will look at how the systems handle failed machines in the network, and look at how the systems handle breaches of trusted components. Our performance analysis will show that under given assumptions, both Kerberos and PKI will handle the average load in a hypothetical data center consisting of 100000 machines and 1000 users. We will also see that under an assumed peak load, Kerberos will be able to handle 10000 service requests in under 1 second, whereas the PKI solution would need at least 15 seconds to handle the same number of requests using recommended public key sizes. This means that some programs may need special configurations to work in a PKI system under high load.</p>
8
羅福隆 and Fook-loong Lo. "Performance of multi-channel random access networks." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31236029.
Pełny tekst źródła
9
Telatar, Ä°brahim Emre. "Multi-access communications with decision feedback decoding." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/13237.
Pełny tekst źródłaStreszczenie:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1992.<br>Includes bibliographical references (leaves 84-85) and index.<br>by Ä°brahim Emre Telatar.<br>Ph.D.
10
Yang, Xu. "Multi-channel Mobile Access to Web Services." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/30270.
Pełny tekst źródłaStreszczenie:
To support wireless-oriented services, a new generation of Web services called Mobile services (M-services) has emerged. M-services provide mobile users access to services through wireless networks. One of the important issues in M-service environment is how to discover and access M-services efficiently. In this dissertation, we propose time and power efficient access methods for M-services. We focus on methods for accessing broadcast based M-services from multiple wireless channels. We first discuss efficient access methods in data-oriented wireless broadcast systems. We then discuss how to extend current wireless broadcast systems to support simple M-services. We present a novel infrastructure that provides a multi-channel broadcast framework for mobile users to effectively discover and access composite M-services. Multi-channel algorithms are proposed for efficiently accessing composite
services. We define a few semantics that have impact on access efficiency in the proposed infrastructure. We discuss semantic access to composite services. Broadcast channel organizations suitable for discovering and accessing composite services are proposed. We also derive analytical models for these channel organizations. To provide practical study for the proposed infrastructure and access methods, a testbed is developed for simulating accessing M-services in a broadcast-based environment.
Extensive experiments have been conducted to study the proposed access methods and broadcast channel organizations. The experimental results are presented and discussed.<br>Ph. D.
11
Lo, Fook-loong. "Performance of multi-channel random access networks /." Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B18635568.
Pełny tekst źródła
12
Chebrolu, Kameswari. "Multi-access services in heterogeneous wireless networks /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2004. http://wwwlib.umi.com/cr/ucsd/fullcit?p3127621.
Pełny tekst źródła
13
Khadraoui, Younes. "Towards a seamless multi-technology access network." Thesis, Télécom Bretagne, 2016. http://www.theses.fr/2016TELB0411/document.
Pełny tekst źródłaStreszczenie:
Le trafic de données mobiles augmente de façon permanente. Afin d'éviter une saturation, les opérateurs doivent décharger le réseau cellulaire vers des réseaux d'accès alternatifs. WiFi se trouve être une bonne solution qui permet à l'opérateur de tirer parti de bandes de fréquence sans licence ainsi que du très grand nombre de points d'accès déjà déployés. Dans cette thèse, nous présentons tout d'abord un état de l'art des différentes solutions de couplage entre LTE et WiFi. Nous montrons que la plupart de ces solutions ne garantissent pas la continuité de session ou sont sujettes à une duplication des procédures de sécurité. Ceci a conduit à la proposition du Very Tight Coupling entre LTE et WiFi. Dans ce type d'architecture, les points d'accès WiFi sont connectés à une station de base LTE et les mécanismes de sécurité LTE sont réutilisées afin de permettre un accès rapide au réseau WiFi. Ceci permet également d'avoir une double connectivité et de garder le trafic de signalisation sur le réseau LTE, ce qui donne la possibilité d'avoir des procédures de sélection optimisées. Nous étudions comment le Very Tight Coupling peut être implémenté et comment les points d'accès WiFi intégrés dans les passerelles résidentielles peuvent être connectées aux stations de base LTE dans le cas d'un réseau fixe/cellulaire convergent. Nous évaluons ensuite par des outils mathématiques, les performances de différents schémas de couplage et calculons le taux de capacité pouvant être économisée. Ensuite, nous présentons une implémentation du Very Tight Coupling sur une plateforme utilisant une interface radio LTE réelle basée sur Open Air Interface. Nous effectuons plusieurs expérimentations afin de trouver la meilleure configuration du protocole de la couche liaison de données. Nous démontrons que le fait d'utiliser WiFi et LTE en parallèle n'augmente pas systématiquement le débit<br>The mobile data traffic has been continuously increasing. To avoid saturation of cellular network, operators need to use alternative access networks for offloading purpose. WiFi is a good solution as the operator can take advantage of its unlicensed spectrum as well as the large number of deployed WiFi access points.In this thesis, we first provide a state-of-the-art of the different coupling solutions between LTE and WiFi. We show that most solutions cannot guarantee session continuity or duplicate the security procedures. This leads to propose "Very Tight Coupling" between LTE and WiFi. In this architecture, WiFi access points are connected to the LTE base stations and the security mechanisms of LTE are reused to ensure fast access to WiFi. It allows dual connectivity and to keep control signalling in the LTE network, which gives the possibility to have optimized interface selection procedures.We study how very tight coupling can be implemented and how WiFi APs that integrated in customer residential gateways can be connected to LTE base stations in a converged fixed/cellular network. We then mathematically evaluate the performance of different deployment schemes and compute how much capacity can be saved on the LTE network. Furthermore, we implement the solution on a platform with a real LTE radio interface based on the Open Air Interface framework as a proof-of-concept. We perform several experiments to find the configuration of the link-layer protocols that gives the highest bit rate. In particular, we show that using WiFi and LTE simultaneously does not always increase the bit rate
14
Anastasopoulos, Achilles. "Cross model access in the multi-lingual, multi-model database management system." Thesis, Monterey, California. Naval Postgraduate School, 1997. http://hdl.handle.net/10945/8178.
Pełny tekst źródłaStreszczenie:
Approved for public release; distribution is unlimited<br>Relational, hierarchical, network, functional, and object oriented databases support its corresponding query language, SQL, DL/I, CODASYL-DML, DAPLEX, and OO-DML, respectively. However, each database type may be accessed only by its own language. The goal of M2DBMS is to provide a heterogeneous environment in which any supported database is accessible by any supported query language. This is known as cross model access capability. In this thesis, relational to object oriented database cross model access is successfully implemented for a test database. Data from the object oriented database EWIROODB is accessed and retrieved, using an SQL query from the relational database EWIROODB. One problem is that the two interfaces (object oriented and relational) create catalog files with different formation, which makes the cross model access impossible, initially. In this thesis the relational created catalog file is used, and the cross model access capability is achieved. The object oriented catalog file must be identical with the relational one. Therefore, work yet to be done is to write a program that automatically reformats the object oriented catalog file into an equivalent relational catalog file
15
Susani, Nahid. "On Open Platform for Multi-Access Edge Computing." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
Znajdź pełny tekst źródłaStreszczenie:
The Idea of moving the functions of centralized cloud computing to the edge devices of the network, brought several advantages such as low latency, higher spectral efficiency, supporting machine to machine communication. The idea of decoupling network function from infrastructure well applied for this revolution. Therefor, the concept of software defined network (SDN) and network function virtualization considered as emerging solutions for the future network. With applying NFV in the edge devices, computing services and also using network functions would be possible through using virtual machines provided by NFV. In the first chapter, there are introductions of cloud, Edge cloud computing and SDN/NFV due to the importance of these topics. Containerization of application is an another proposed concept as lightweight virtualization solution which besides NFV can be proper solution for delivering, implementing and running application in the edge network and using advantages. In fact, developer encapsulate applications inside of the containers and containerization will allows to delivery applications across different environments. In second chapter, centralized cloud and Edge Cloud had been explained and it had been moved to introducing kubernetes as Edge cloud orchestrator in third chapter. In this project, Kubernetes has been used as an open source platform for multi access edge computing which works as container cluster orchestrator. Forth chapter has been dedicated to Implementation and Evaluation of the work. Main targets of this real implementation will be extending platform of container cluster from single platform architecture to multi-platform architecture made by different physical infrastructure of AMD64 on Intel and ARM on Raspberry pi using docker containers. The second target of implementation is checking the feasibility of autoscalling number of pods based on CPU utilization of pods, across nodes with heterogeneous platform inside the same cluster.
16
Wuilbercq, Romain. "Multi-disciplinary modelling of future space-access vehicles." Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=24967.
Pełny tekst źródłaStreszczenie:
Re-usable Single-Stage-To-Orbit (SSTO) vehicles represent a promising alternative to conventional expendable rocket launchers, since they will be capable of taking off from a conventional runway, delivering a payload to orbit and gliding back to their spaceport before preparing for re-launch. SSTOs are foreseen to reduce drastically the current costs of access to space and to increase the diversity of practical and economic space applications. The design of aircraft-like launchers is hampered by a myriad of design challenges, however. The coupling between the behaviour of their various systems challenges conventional aircraft design practices and requires that a detailed cross-disciplinary and systemic modelling approach be applied early on in their evolution toward a workable prototype. This dissertation focuses on the development of efficient algorithms and modelling strategies for the purpose of the multidisciplinary design and optimization of the next generation of fully reusable aircraft-like launch systems. The approach followed is to represent the vehicle as an interconnected system which can then be discretized into a series of constituent components. The resulting multidisciplinary design environment combines the use of a new reduced-order aerothermodynamic model, specifically conceived to provide a predictive accuracy suitable for preliminary design, with a series of tools that have been developed to model some of the critical components of SSTOs. This modelling environment can be used to predict the overall performance, mass and trajectory of the vehicle, to concurrently size the active and passive thermal shields, organize the internal configuration of the vehicle, and evaluate the performance of the propulsive device. A number of design applications and validations are provided to support the relevance of this approach to the modelling of the characteristics of the next generation of space-access vehicles.
17
SETTE, Ioram Schechtman. "Access control in IaaS multi-cloud heterogeneous environments." Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/22436.
Pełny tekst źródłaStreszczenie:
Submitted by Alice Araujo (alice.caraujo@ufpe.br) on 2017-11-30T16:45:19Z
No. of bitstreams: 2
license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5)
Ioram_Sette_PhD_Thesis.pdf: 10382850 bytes, checksum: a2a362f0971460d5758e3cf1ff71db96 (MD5)<br>Made available in DSpace on 2017-11-30T16:45:19Z (GMT). No. of bitstreams: 2
license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5)
Ioram_Sette_PhD_Thesis.pdf: 10382850 bytes, checksum: a2a362f0971460d5758e3cf1ff71db96 (MD5)
Previous issue date: 2016-08-11<br>CNPQ<br>Multiple Cloud Service Providers (CSPs) coexist nowadays offering their services competitively. To avoid vendor lock-in, users hire many services from an outsourced heterogeneous multi-cloud environment. This way, data and system security usually depend on isolated mechanism existing in each provider. Access Control (AC) mechanisms are responsible for the authentication, identification and authorisation
of users to resources. In the case of a multi-cloud environment, users often need to authenticate multiple times and also to define security policies for each CSP, which can possibly result in inconsistencies. The objective of this thesis is to provide a homogeneous access experience for users of heterogeneous multi-cloud services. Identity federations allow the Single Sign-On (SSO), i.e. users are identified and authenticated once by Identity Providers (IdPs) and gain access to trusted federated services. Nevertheless, authorisation federations or AC federations are not usual. Each cloud service uses to have its own AC mechanism, with their own policy definition languages. This work defines a solution that provides homogeneous authentication and authorisation to multiple heterogeneous Infrastructure as a Service (IaaS) platforms. This is possible through Identity Federations and Authorisation Policy Federations (APFs). In this solution, security policies are centrally stored in a “Disjunctive Normal Form (DNF)” and are semantically defined in terms of an Ontology. Therefore, cloud tenants can create APFs and bind their different accounts to them. Thus, global authorisation rules, defined and managed by the APF, can be enforced on all federated member accounts, providing a homogeneous access experience. A system prototype, composed of a central Policy Administration Point (PAP), called Federated Authorisation Policy Management Service (FAPManS), policy adaptors (translators) and a policy synchronization mechanism, was implemented for OpenStack and Amazon Web Services (AWS) cloud platforms. An ontology was also created based on their access control technologies. The “Level of Semantic Equivalence (LSE)” was defined as a metric that gives the percentage of policy rules that could be translated to the ontology terms. In the validation of this solution, authorization policies based on examples publicly provided by OpenStack and AWS were converted to ontology-based global rules and vice-versa with LSE above 80%.<br>Múltiplos provedores de computação em nuvem convivem hoje ofertando seus serviços de forma competitiva. Para evitar dependência (o chamado vendor lock-in), usuários utilizam muitos serviços em ambiente terceirizado e heterogêneo multi-nuvens. Desta forma, a segurança de dados e sistemas depende normalmente de mecanismos existentes isoladamente em cada um dos provedores. Mecanismos de controle de acesso são responsáveis pela autenticação, identificação e autorização dos usuários aos recursos. No caso de ambiente multi-nuvens, usuários geralmente precisam se autenticar diversas vezes e definir políticas de segurança para cada um dos serviços, que possivelmente podem apresentar inconsistências. O objetivo desta tese é proporcionar aos usuários de sistemas heterogêneos multi-nuvens uma experiência de acesso homogênea a estes serviços. Federações de identidade proporcionam o Single Sign-On (SSO), ou seja, os usuários são identificados e autenticados por provedores de identidade (IdPs) uma única vez e, através de protocolos como OpenID Connect, SAML ou ABFAB, recebem acesso a serviços federados com os quais possuem relação de confiança. No entanto, federações de autorização ou de políticas de controle de acesso não são comuns. Cada serviço de nuvem costuma ter seu próprio mecanismo de controle de acesso, com linguagens próprias de definição de políticas. Este trabalho define uma solução que provê autenticação e autorização homogêneas a usuários de múltiplos serviços de computação em nuvem heterogêneos no modelo de Infraestrutura como Serviço (IaaS). Isso é possível através de federações de identidade e de políticas de autorização. Nesta solução, políticas de segurança são armazenadas de forma centralizada no padrão “DNF” com semântica definida em uma Ontologia. Portanto, clientes de nuvens podem criar “Federações de Políticas de Autorização (APFs)” e associar suas contas em cada provedor a estas federações. Desta forma, regras de autorização globais, definidas e gerenciadas pela APF, passam a valer em todas as contas que fazem parte da federação, garantindo uma experiência homogênea de acesso. Um protótipo do sistema, composto de um Ponto de Administração de Políticas (PAP) centralizado e mecanismos de tradução e sincronismo de políticas, foi implementado para nuvens OpenStack e Amazon Web Services (AWS). Uma ontologia também foi definida baseada no controle de acesso destas tecnologias. A métrica “nível de equivalência semântica (LSE)” foi definida para calcular o percentual de regras de uma política que pode ser traduzido para termos de uma ontologia. Na validação da solução, políticas de autorização baseadas em exemplos fornecidos por OpenStack e AWS foram convertidos para regras globais, baseadas na ontologia, e vice-versa, com nível de equivalência semântica superior a 80%.
18
CHOWDHURY, KAUSHIK ROY. "MULTI-CHANNEL MEDIUM ACCESS PROTOCOLS FOR WIRELESS NETWORKS." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1142571415.
Pełny tekst źródła
19
Lim, Christopher. "Optimizing access radio in multi-radio mesh network /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?CSED%202009%20LIM.
Pełny tekst źródła
20
Forte, Manuela. "Access to broadcasting platforms in multi-sided markets." Thesis, IMT Alti Studi Lucca, 2010. http://e-theses.imtlucca.it/40/1/Forte_phdthesis.pdf.
Pełny tekst źródłaStreszczenie:
Chapter 1 gives a brief introduction to the dissertation.
Chapter 2 describes the functioning of the broadcasting market, with particular emphasis on the platforms involved, in order to prepare the reader for the analysis of platform competition strategies that follows. I discuss so-called “multi sided market theory”, and describe some examples of platforms. In this context I point out that the broadcasting sector involves both vertical integration, horizontal integration and multi-sided market platforms, and the theme of access to platforms is discussed with reference to all three types. In chapter 3 I stress that multi-sided platforms are pervaded by externalities. For this reason I deal with price allocation on the two sides of the market in order to demonstrate that price allocation by the platform is not neutral. Then I discuss the existence of price differences in one-sided and two-sided markets with both single homing and multihoming, and with exclusive and non-exclusive services. In chapter 4 under the leitmotiv of the evolution of pluralism of information, I review the main Italian Constitutional Court judgments on this topic and the ex ante regulation of the broadcasting sector in Italy, verifying whether the existing antitrust limits are still consistent with the current level of technology, considering the DVB-T broadcasting technique and the sale of frequencies on the secondary market.
In chapter 5 I describe the various relevant broadcasting markets in accordance with European Commission case decisions. I demonstrate that the activities of multi-sided broadcasting platforms are subject to Article 81 and 82 of the European Treaty, just like any other integrated platform, since in any case they can determine input or customer foreclosure. Furthermore I deal with the relationship between media broadcasting and the social value of sport with reference to the many antitrust cases in the broadcasting sector concerning the sale of sports event rights to media platforms, and I discus Italian Law 9/2008 which establishes the collective trading of such rights. Chapter 6 considers the issue of access to content by focusing on emerging multi-sided platforms. I compare them with the vertically integrated platforms and discuss the potential of multi-sided platforms to remove entry barriers to the sector by means of unbundling, which is made possible by the must-offer and must-carry obligations introduced into Italy by the most recent legislation.
Chapter 7 contains my conclusions.
21
Zandegran, Antony Jeyasehar Ansel. "Multi-operator, Multi-Radio Performance Monitoring and Context-Aware access Provision Test-bed." Thesis, KTH, Kommunikationssystem, CoS, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-141707.
Pełny tekst źródła
22
Rondinini, Giorgia. "Role-Based Access Control in ambienti cloud multi-region." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
Znajdź pełny tekst źródłaStreszczenie:
Negli ultimi anni si è assistito a un incremento dell'uso del cloud, con cambiamenti nel tipo di servizi distribuiti tramite esso e nel tipo di infrastruttura utilizzata per supportare tali servizi. Il comprensibile desiderio di migliorare i servizi offerti, diminuendo però i costi di gestione e manutenzione, sta portando infatti all'utilizzo di infrastrutture cloud eterogenee, spesso distribuite su più aree geografiche. Tale eterogeneità delle infrastrutture rende complicato garantire la sicurezza dei sistemi, in un mondo in cui gli attacchi informatici sono sempre più diffusi ed è sempre più importante impedire ai non autorizzati di accedere a dati e funzioni protette.
Lo scopo di questa tesi è creare un sistema di controllo degli accessi basato sui ruoli, o RBAC, atto a operare in modo distribuito in un ambiente cloud multi-region. Nei primi capitoli della tesi è descritto l'ambito in cui si è svolta la progettazione del sistema, ovvero il cloud computing e la sua sicurezza. Nel Capitolo 4 si trova una descrizione generale del sistema di gestione degli accessi creato. Successivamente sono stati spiegati gli strumenti utilizzati per la realizzazione del sistema e come esso sia stato creato. Negli ultimi capitoli sono poi riportati i test effettuati per valutare il sistema creato e i loro risultati.
23
Hussain, Tassadaq. "A novel access pattern-based multi-core memory architecture." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/284910.
Pełny tekst źródłaStreszczenie:
Increasingly High-Performance Computing (HPC) applications run on heterogeneous multi-core platforms. The basic reason of the growing popularity of these architectures is their low power consumption, and high throughput oriented nature. However, this throughput imposes a requirement on the data to be supplied in a high throughput manner for the multi-core system.
This results in the necessity of an efficient management of on-chip and off-chip memory data transfers, which is a significant challenge. Complex regular and irregular memory data transfer patterns are becoming widely dominant for a range of application domains including the scientific, image and signal processing. Data accesses can be arranged in independent patterns that an efficient memory management can exploit.
The software based approaches using general purpose caches and on-chip memories are beneficial to some extent. However, the task of efficient data management for the throughput oriented devices could be improved by providing hardware mechanisms that exploit the knowledge of access patterns in memory management and scheduling of accesses for a heterogeneous multi-core architecture.
The focus of this thesis is to present architectural explorations for a novel access pattern-based multi-core memory architecture. In general, the thesis covers four main aspects of memory system in this research.
These aspects can be categorized as: i) Uni-core Memory System for Regular Data Pattern. ii) Multi-core Memory System for Regular Data Pattern. iii) Uni-core Memory System for Irregular Data Pattern. and iv) Multi-core Memory System for Irregular Data Pattern.<br>Les aplicacions de computació d'alt rendiment (HPC) s'executen cada vegada més en plataformes heterogènies de múltiples nuclis. El motiu bàsic de la creixent popularitat d'aquestes arquitectures és el seu baix consum i la seva natura orientada a alt throughput. No obstant, aquest thoughput imposa el requeriment de que les dades es proporcionin al sistema també amb alt throughput. Això resulta en la necessitat de gestionar eficientment les trasferències de memòria (dins i fora del chip), un repte significatiu. Els patrons de transferències de memòria regulars però complexos així com els irregulars són cada vegada més dominants per a diversos dominis d'aplicacions, incloent el científic i el processat d'imagte i senyals. Aquests accessos a dades poden ser organitzats en patrons independents que un gestor de memòria eficient pot explotar. Els mètodes basats en programari emprant memòries cau de propòsit general i memòries al chip són beneficioses fins a cert punt. No obstant, la tasca de gestionar eficientment les transferències de dades per a dispositius orientats a throughput pot ser millorada oferint mecanismes hardware que explotin el coneixement dels patrons d'accés de les aplicacions, així com la planificació dels accessos a una arquitectura de múltiples nuclis. Aquesta tesis està enfocada a explorar una arquitectura de memòria novedosa per a processadors de múltiples nuclis, basada en els patrons d'accés. En general, la recerca de la tesis cobreix quatres aspectes principals del sistema de memòria. Aquests aspectes són: i) sistema de memòria per a un únic nucli amb patrons regulars, ii) sistema de memòria per a múltiples nuclis amb patrons regulars, iii) sistema de memòria per a un únic nucli amb patrons irregulars, iv) sistema de memòria per a múltiples nuclis amb patrons irregulars.
24
Kwak, Hyunsun. "Study on Access Protocols for Multi-hop Wireless LAN." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147594.
Pełny tekst źródła
25
Ye, Qianyun. "2.4-GHz Wireless Network Based Multi-Tag Access System." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-188491.
Pełny tekst źródłaStreszczenie:
Machine-to-Machine technology has been intensively researched recently which is believed to take the role of leading ICT industry development. Wireless Sensor Networks provide solution to integrate numerous numbers of machines who require features include low power, low cost, and flexible, which can be fulfilled by applying Zigbee technique. This thesis devotes an effort into Wireless Sensor Network development that a Multi- Tag System operating on 2.4-GHz wireless network is developed. A theoretical study about ZigBee protocol and its bottom layers IEEE 802.15.4 standard is provided to lay a foundation of the design work. The thesis also includes a practical usage of low cost TI CC2530 Systom-on-Chip, together with the illustration of software development inside the chip. The design work provides GUI Platform for users to register themselves into the network and central monitoring platform to track all users within the area. Both GUI platforms are developed based on VB IDE. The Multi-Tag Access System is suitable for attendee control functionality in big-scale conference, events, and lecture, which is also a prototype expecting more functionality to be added in the future.
26
Muayyadi, Ali. "Wavelet-based multi-carrier code division multiple access systems." Thesis, University of Plymouth, 2003. http://hdl.handle.net/10026.1/527.
Pełny tekst źródła
27
Jun, Sang-Woo. "Scalable multi-access flash store for Big Data analytics." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87947.
Pełny tekst źródłaStreszczenie:
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 47-49).<br>For many "Big Data" applications, the limiting factor in performance is often the transportation of large amount of data from hard disks to where it can be processed, i.e. DRAM. In this work we examine an architecture for a scalable distributed flash store which aims to overcome this limitation in two ways. First, the architecture provides a high-performance, high-capacity, scalable random-access storage. It achieves high-throughput by sharing large numbers of flash chips across a low-latency, chip-to-chip backplane network managed by the flash controllers. The additional latency for remote data access via this network is negligible as compared to flash access time. Second, it permits some computation near the data via a FPGA-based programmable flash controller. The controller is located in the datapath between the storage and the host, and provides hardware acceleration for applications without any additional latency. We have constructed a small-scale prototype whose network bandwidth scales directly with the number of nodes, and where average latency for user software to access flash store is less than 70[mu]s, including 3.5[mu]s of network overhead.<br>by Sang-Woo Jun.<br>S.M.
28
美霖, 何., and Meilin He. "Multi-rate coding schemes for gaussian multiple access channel." Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB13071670/?lang=0, 2018. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB13071670/?lang=0.
Pełny tekst źródłaStreszczenie:
本研究で提案するマルチレート符号化法は、各ユーザが同じ通信路符号器を持つものの、符号器のパラメータ(Repeat Accumulate符号の繰り返し回数)と符号器に直列に連接する拡散列の長さを変化させることで、異なるレートの情報伝送を実現する、という方法である。通信路にガウス雑音が加算される場合、任意に低い誤り率の高信頼通信を可能にし、合計伝送レートを最大にする最適な通信路符号のパラメータと拡散長を理論解析で求める。<br>In this dissertation, the same encoder is employed for each user, and different rate transmissions is realized by adjusting the parameter of the encoder. We analyze the decoding performances of our coding schemes, and obtain the optimal coding parameters, which gives the maximum sum rates and approach the theoretical limits of the channel. The proposed coding schemes support multimedia services, and avoid employing multiple channel encoders to implement the multi-rate transmission.<br>博士(工学)<br>Doctor of Philosophy in Engineering<br>同志社大学<br>Doshisha University
29
Mursia, Placido. "Multi-antenna methods for scalable beyond-5G access networks." Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS532.
Pełny tekst źródłaStreszczenie:
L’augmentation exponentielle des équipements d’utilisateurs sans fil (UEs) et des services des réseaux associés aux déploiements actuels de cinquième génération (5G) pose plusieurs défis de conception sans précédent qui doivent être résolus avec l’avènement des futurs réseaux au-delà de la 5G. Plus précisément, la demande croissante de débits de données élevés ainsi que la nécessité de desservir un grand nombre d’appareils hétérogènes, allant des téléphones mobiles classiques aux objets connectés formant l’internet des objets (IoT), motivent l’étude de nouveaux schémas de traitement et de transmission du signal. À cet égard, les sorties multiples massives à entrées multiples (massive MIMO) sont une technologie d’accès bien établie, qui permet de desservir plusieurs dizaines d’UEs en utilisant lesmêmes ressources temps-fréquence au moyen de techniques de formation de faisceau hautement directionnelles. Cependant, le massive MIMO présente des problèmes d’évolutivité dans les scénarios accès massif où la population UE est composée d’un grand nombre de périphériques hétérogènes. En effet, si la disponibilité d’un grand nombre d’antennes dans les émetteurs-récepteurs massive MIMO apporte des gains de performances substantiels, elle augmente également considérablement la surcharge et la complexité du système. Plus précisément, la dimensionnalité élevée des canaux nécessite l’allocation de ressources temps-fréquence considérables pour acquérir les informations d’état de canal (CSI) et se traduit par de grandes opérations matricielles pour construire des précodeurs/décodeurs. De plus, dans le contexte de communications de multidiffusion comme, par exemple, la mise en cache périphérique sans fil ou la diffusion de messages critiques pour la mission, les techniques d’antennes multiples conventionnelles présentent des taux de disparition lorsque le nombre d’UEs augmente même dans le régime d’antenne massif. Enfin, le grand nombre de chaînes de radiofréquences (RF) associées aux émetteurs-récepteurs massive MIMO, qui sont utilisés pour contrer les pertes de propagation dans des environnements difficiles tels que, par exemple, à des fréquences d’ondes millimétriques (mmWave), se heurte au budget de puissance limité des appareils IoT. Dans cette thèse, nous proposons de nouvelles méthodes à antennes multiples évolutives pour l’amélioration des performances dans les scénarios d’intérêt susmentionnés. Plus précisément, nous décrivons le rôle fondamental joué par le CSI statistique qui peut être mis à profit pour réduire à la fois la complexité et la surcharge pour l’acquisition de CSI et pour la suppression des interférences multi-utilisateurs. En effet, lorsque les UEs sont équipés au moins de duex antennes, leurs propriétés de sélectivité spatiale peuvent être exploitées pour imposer une orthogonalité statistique parmi les transmissions interférentes. De plus, nous exploitons les communications de périphérique à périphérique (D2D) pour surmonter le goulot d’étranglement fondamental de la multidiffusion conventionnelle. En particulier, nous exploitons les capacités de précodage d’un émetteur multi-antennes pour sélectionner soigneusement les UEs dans des conditions de canal favorables, qui à leur tour agissent comme des relais opportunistes et retransmettent le message via les liaisons D2D. Enfin, dans le cadre des communications mmWave, nous explorons les avantages des surfaces intelligentes reconfigurables (RISs) récemment proposées, qui sont un catalyseur clé de l’innovation grâce à leur structure intrinsèquement passive qui permet de contrôler l’environnement de propagation et de contrer efficacement les pertes de propagation. En particulier, nous utilisons la formation de faisceaux passive au niveau du RIS, c’est-à-dire sans aucune dépense d’énergie significative, ainsi que la formation de faisceaux active conventionnelle au niveau de l’émetteur pour augmenter considérablement les performances du réseau<br>The exponential increase of wireless user equipments (UEs) and network services associated with current 5G deployments poses several unprecedented design challenges that need to be addressed with the advent of future beyond-5G networks and novel signal processing and transmission schemes. In this regard, massive MIMO is a well-established access technology, which allows to serve many tens of UEs using the same time-frequency resources. However, massive MIMO exhibits scalability issues in massive access scenarios where the UE population is composed of a large number of heterogeneous devices. In this thesis, we propose novel scalable multiple antenna methods for performance enhancement in several scenarios of interest. Specifically, we describe the fundamental role played by statistical channel state information (CSI) that can be leveraged for reduction of both complexity and overhead for CSI acquisition, and for multiuser interference suppression. Moreover, we exploit device-to-device communications to overcome the fundamental bottleneck of conventional multicasting. Lastly, in the context of millimiter wave communications, we explore the benefits of the recently proposed reconfigurable intelligent surfaces (RISs). Thanks to their inherently passive structure, RISs allow to control the propagation environment and effectively counteract propagation losses and substantially increase the network performance
30
Farhat, Soha. "Access Selection and Pricing in Multi-operator Wireless Networks." Thesis, Rennes 1, 2016. http://www.theses.fr/2016REN1S029/document.
Pełny tekst źródłaStreszczenie:
Notre travail se situe dans le contexte de partage de réseau mobile actif, ou un nombre d'opérateurs partagent leur accès radio, afin de former un système multi-technologie multi-opérateur. Le but de notre étude est de montrer les avantages de la coopération entre les opérateurs, principalement en ce qui concerne les revenus. De plus, nous cherchons des stratégies pour surpasser les conséquences négatives du partage des ressources, surtout celles touchant la performance des réseaux des opérateurs coopérants. Nous avons montré que les bénéfices de la coopération dépendent fortement du choix de partenaires, la tarification de service ( cout de transfert) entre les partenaires, et combien un opérateur partage de ses ressources. Notre travail consiste, en premier temps, à proposer un algorithme de sélection d'accès applicable dans un réseau multi-opérateurs. Cet algorithme devrait garantir la satisfaction en QoS de l'utilisateur et celle en profit de son opérateur d'accès à l'Internet. Ainsi, un algorithme adoptant une décision hybride, NP-BPA (Nearest Performance and Best Profit Algorithm), est proposé. En deuxième temps, nous étudions la tarification de service entre les opérateurs partenaires, précisément le coût de transfert d'un utilisateur. Ce dernier paye juste le prix du service que son opérateur d'accès à l'Internet détermine, il est inconscient du transfert. Les modèles de tarification proposés relient le coût de transfert d'un opérateur au prix adopté pour le service des clients. Le premier modèle, ACAG (As Client As Guest), suggère que le coût de transfert d'un opérateur soit égal à son prix de service. Le deuxième modèle, MIWC (Maximum Income When Cooperating), suggère que les coûts de transfert des opérateurs coopérants soient identiques, et égaux au prix de service le plus élevé des partenaires. Et, le troisième modèle, MCWC (Minimum Cost When Cooperating), suggère que les coûts de transfert des opérateurs coopérants soient identiques et égaux au plus petit prix de service des partenaires. La décision du meilleur modèle à adopter lors de la coopération, intervient une interaction entre les différents partenaires. Nous avons modélisé cette interaction à l'aide de la théorie de jeux. Nous avons exploité un jeu Stackelberg à deux niveaux, TPA (Transaction Pricing and Access Selection), où les opérateurs de service agissent comme Leaders et les opérateurs d'accès à l'Internet des utilisateurs à transférer agissent comme Followers. Finalement, nous avons considéré le mode d'accès hybride pour la coopération. Ce mode d'accès est proposé comme solution surtout pour les opérateurs partageant la plus grande capacité. La performance du réseau de ces opérateurs est relativement affaiblie suite à la coopération. Nous avons vérifié que le pourcentage de blocage diminue quand l'opérateur, ayant une capacité élevée, réduit le pourcentage de ressources partagées. Pour un même pourcentage de partage, le profit d'un opérateur diffère avec le modèle de tarification adopté. Ainsi, une bonne décision doit être prise, concernant le pourcentage de partage et le modèle de tarification, tout en tenant compte de l'effet de cette décision sur les autres partenaires du système. C'est pourquoi que nous avons proposé un nouvel jeu séquentiel à deux niveaux, afin de modéliser l'interaction entre les opérateurs, pour le partage de ressources et la tarification du coût de transfert<br>We consider a roaming-based infrastructure sharing system, where multiple operators share their radio access in a multi-operator environment. Indeed, when the home operator of a user is unable to satisfy its constraints, because of lack of resources or QoS, a transaction event is triggered. It consists in transferring the considered user to another operator in order to access the service. Moreover, when there are more than two operators sharing their access, the user transfer process includes an access selection decision in order to choose the best operator for service. Furthermore, when a user is transferred, its home operator must pay some transaction cost as cooperation fees for the new service operator. This transaction is seamless to the user. Therefore, the inter-operators sharing agreement set for cooperation must include three important issues: the selection decision algorithm, the transaction cost pricing scenario, and the percentage of resources shared by each operator. In the first part, we introduce our selection decision algorithm in a multi-operator environment, NP-BPA (Nearest Performance and Best Profit Algorithm). It is based on a multi-criteria cost function which groups the different parameters that enable a satisfying selection decision, for the operators and users. In the second part, we study the transaction cost. We find rational that an operator sets its transaction cost as a function of its service price. We consider a sharing system of three partners, interacting to decide the best transaction cost. Taking into account that the service of a guest user may affect the probability of acceptance of a client, an operator looks for preserving the expected revenue from its client. Therefore, we propose the first pricing scenario, ACAG (As Client As Guest) that aims to set the transaction cost of an operator equal to its service price. However, every operator seeks to maximize its revenue; therefore it is expected to set a higher transaction cost. How much higher? This must respect the sharing agreement between different partners and the service prices they adopt. To be optimistic, we propose a second pricing scenario MIWC (Max In When Cooperating). With this scenario all partners agree to have a transaction cost equal to the highest service price announced in the system. But, this scenario may cause losses in some cases where an operator setting a low service price performs a lot of transactions. To be fair, we propose a third pricing scenario MCWC (Min Cost When Cooperating). With this scenario all partners agree to have a transaction cost equal to the lowest service price announced in the system. In order to decide the best pricing scenario to adopt in the sharing system, a two stage Stackelberg game, TPA (Transaction Pricing and Access Selection) game, is formulated. In this game, the operators are the players; the service operators are the leaders and the home operator of a transferred user is a follower. In the third part, we consider a three operator sharing system with hybrid access mode. In this system partners decide to share a restricted amount of their capacity. We show how the sharing factor affects the blocking rates and affect the global profits. Further, the achieved profit does not depend only on the sharing factor, but also on the adopted pricing scenario. Therefore an economic framework based on game theoretical analysis is proposed. It models the interaction between the sharing system operators for resource sharing and pricing, in addition to the access selection. A sequential game is formulated, where the players are the operators. In the first stage, the sharing partners decide the proportion of resources they will share and the transaction pricing scenario in order to maximize their own profits. In the second stage, the home operator of a transferred user selects the suitable service operator. A bi-level optimization problem is solved and equilibrium is found
31
Bhuchhada, Jay Kumar. "Multi-Access Edge Computing Assisted Mobile Ad-hoc Cloud." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39572.
Pełny tekst źródłaStreszczenie:
Mobile Ad-hoc Cloud offers users the capability to offload intensive tasks on a cloud composed of voluntary mobile devices. Due to the availability of these devices in the proximity, intensive tasks can be processed locally. In addition, the literature referred to in the text, distinguishes a specific class of application to be well addressed when processed at the user level. However, due to lack of commitment, mobility, and unpredictability of the mobile devices, providing a rich ad-hoc cloud service is challenging. Furthermore, the resource availability of these devices impacts the service offered to the requester.
As a result, this thesis aims to address the challenges mentioned above. With the support of Multi-Access Edge Computing, a mobile ad-hoc Infrastructure as a Service composition framework is proposed. An ad-hoc application server is designed to operate over the MEC platform to compose and manage the mobile ad-hoc cloud. The server uses the information provided by the MEC services to compose volunteer resources for a given request. As well, a heuristic approach for a multi-dimensional bin packing technique is considered, while extending the Euclidean distance for sub-tasks selection. In addition, to address the lack of resource availability, an architecture for MAC using SDN is proposed. The logically centralized controller works with the application server to migrate requests seamlessly from one region to another. Inspired by the benefits of the MEC, a mobility mechanism is introduced to address the movement of the participants. Finally, based on the evaluation, it was observed that the proposed MAC framework not only provided better use of resources but also provided a consisted and scalable service.
32
Furuskär, Anders. "Radio resource sharing and bearer service allocation for multi-bearer service, multi-access wireless networks." Doctoral thesis, KTH, Signals, Sensors and Systems, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3502.
Pełny tekst źródłaStreszczenie:
<p>Two expected characteristics of future wireless networks aresupport for multiple bearer services, which in turn enablemultiple end-user services, and the parallel use of multipleradio access technologies. This dissertation discusses radioresource management principles to improve capacity for suchmulti-bearer service, multi-access networks.</p><p>More specifically, it is first focused on how to mostefficiently share the radio resource between bearer servicegroups within one access technology. A general principle forsharing resources in interference limited systems is proposed,and its expected performance estimated. The proposedinterference balancing principle maximizes capacity byadjusting the power budgets per bearer service group so thatthe maximum tolerable interference levels are equal for allbearer services. To verify its validity, the interferencebalancing principle is applied to the 3rd generation cellularsystems GSM/EDGE and WCDMA in a set of multi-bearer servicecase studies. It is seen that interference balancing maystraightforwardly be introduced in these systems, and thatsignificant capacity gains over non-balanced scenarios can beachieved.</p><p>Secondly, how to best share traffic load between thedifferent sub-systems in a multi-access scenario isinvestigated. The capability to handle bearer services, andthereby also end-user services, typically differs betweensub-systems. The overall multi-access system capacity istherefore affected by the allocation of bearer services on tosub-systems. Based on this, a simple principle for findingfavorable, under certain constraints near-optimum, sub-systembearer service allocations is derived. It is seen that for agiven service mix combined capacities beyond the sum of thesub-system capacities may be achieved by using the favorablebearer service allocations. Significant capacity gains are alsoseen in a case study in which the bearer service allocationprinciple is applied to a combined GSM/EDGE and WCDMAmulti-access system. The bearer service type may be said toreflect an expected radio resource cost for supporting a userin each sub-system. By taking into account the actual radioresource cost, which may differ from the expected cost, whenassigning users to subsystems, further capacity gains areachievable.</p>
33
Abedi, Saied. "Genetic multi-user detection for code division multiple access systems." Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/843016/.
Pełny tekst źródłaStreszczenie:
The origins of spread spectrum are in navigation and military systems. Techniques originally developed to reduce the effects of the intentional jamming also proved suitable for communications through dispersive channels in cellular applications. In 1949 the first time hoping spread spectrum multiple access system has been introduced by John Pierce. A direct-sequence spread spectrum system has been proposed by De Rosa-Rogoff later in 1950. He has also introduced the concept of processing gain. However the commercialisation of cellular direct-sequence code division multiple access (DS-CDMA) systems became possible only during the 1980's and 1990's. In 2000 and beyond we will be witness to the standardisation and commercialisation of wide band CDMA system with a bandwidth of 5 MHz or more. While CDMA presents a number of advantages for cellular mobile communications, it has its own drawbacks. Good air interface designs provide efficient solutions for the terrestrial cellular system. We first take a look at the problem of narrow-band and partial band interference suppression in a CDMA system. By using Poor's model for partial-band interference, some interference suppression techniques are analysed. Then the concept of hybrid genetic prediction is introduced which outperforms the nonlinear techniques in terms of SNR improvements. The performance of a CDMA system can be degraded by Multiple Access Interference (MAI) due to the presence of many users in the same bandwidth. After analysing the structure and performance of existing multi user detection techniques, a low complexity bit level detector is proposed to reduce MAI in synchronous CDMA (S-CDMA) system for an AWGN channel. It is shown how it is possible to reach almost the single user bound by combining detection theory and the fundamentals laws of evolution found in nature. Nonlinear mappings are added to the proposed detector to increase detector's performance by reducing the misleading effect of noise on the detection process. Then for Asynchronous CDMA (A-CDMA), a novel packet level genetic detector is proposed. The near-far resistance feature of the proposed detector is studied. The effect of different parameters of genetic engine i.e. chromosome length, gene's value or mutation and crossover probabilities on its performance are characterised. Different initialisation methods are introduced. For high bit rate CDMA system in multimedia applications in a dispersive CDMA channel, Inter Symbol Interference (ISI) becomes another highly important factor that degrades system performance. It is shown how it is possible to use a signal sub-space based detector as a core detector for a hybrid genetic Multi user detector.
34
Backa, John Andrew. "Network access to multi-level secure databases from desktop clients." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq23778.pdf.
Pełny tekst źródła
35
Hultell, Johan. "Access selection in multi-system architectures : cooperative and competitive contexts." Licentiate thesis, Stockholm : Kommunikationssystem, Kungl. Tekniska högskolan (KTH), 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4286.
Pełny tekst źródła
36
Koudouridis, Georgios. "Study of Multi-Radio Transmission Diversity in Heterogeneous Access Networks." Licentiate thesis, KTH, Kommunikationsnät, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-122723.
Pełny tekst źródłaStreszczenie:
With the advent of multi-radio access (MRA), an integration of differentradio access technologies (RATs) into a heterogeneous radio access network(RAN) becomes feasible. Such integration allows a user to be at any instantof time served by one or multiple radio accesses (RAs) concurrently, where anRA constitutes an independent radio resource, such as a carrier or a channel,implemented by a single RAT. It also allows a user´s service demands to bemapped onto the aggregated network resources in a transparent and efficientway. An approach for the realization of such multi-radio integrated environmentsis through a unifying generic link layer (GLL) that provides joint radiolink processing and enables communication between nodes and devices acrossdifferent radio accesses.Based on the requirements on multi-access, an architecture that supportsMRA is suggested and the functions of GLL that aims at integrating andutilising multiple RATs are defined. We explore the potential for performanceimprovements through novel extensions of the transmission diversityparadigm which builds on GLL functions that enable multi-radio access selection.Multi-radio transmission diversity (MRTD) is defined as the dynamicselection of radio access for the transmission of a user´s data and it can bethought of as consisting of a packet scheduler operating across multiple radiointerfaces. Different MRTD schemes may be envisaged through combinationsof access re-selection rate, transmission parallelism and transmission redundancy.The re-selection rate refers to the rate at which radio access selectionis performed. It may range from multiple IP packets to one single MACframe. Switched MRTD corresponds to an access selection scheme where auser transmits via one RA at a time, while parallel MRTD corresponds to ascheme where simultaneous transmissions over multiple RAs are scheduled.Finally, redundancy refers to the transmission of copies of the same data overmultiple RAs to increase the possibility of correct reception.The benefits of MRTD are investigated by simulation studies on two multiradiocase scenarios, based on generic RATs and on specific RATs respectively.In the RAT generic scenario, switched MRTD has been evaluated for networktopologies of collocated and non-collocated RAs consisting of macroand pico-cells. In the case of collocated RAs, spectral efficiency is increasedby exploiting diversity in multi-path fading while in non-collocated RAs, thespectral efficiency increase is due to diversity exploitation in both shadowingand multi-path fading. Simulation results show that switched MRTD is mostadvantageous when the RAs provide comparable throughputs. Furthermore,when combined with multi-radio ARQ, MRTD significantly reduces packetloss and packet transmission delays. This is also shown in the specific radioaccesssimulation scenario where a delay sensitive voice service is studied. Inaddition, switched MRTD provides comparable gains to parallel MRTD interms of average packet transmission delay and packet loss, while using lessradio resources. In all cases, it is concluded that maximum performance isconditioned on the reporting delays of the channel quality indicator (CQI).Reporting delays of CQI that are half the channel coherence time render sucha complex MRTD mechanism less effective.<br><p>QC 20130531</p>
37
Beainy, Charif. "On modeling and interference cancellation in some multi-access channels." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29529.
Pełny tekst źródłaStreszczenie:
The effects of interference and channel noise make reliable communication a challenging problem. Most existing multiuser communication systems still perform far below their theoretical limits, partly because the implementation of optimal multiuser receivers has exponential complexity. This thesis studies aspects of transmission over the multi-access (MAC) channel in case of K equal power users. It is motivated by wireless communication systems with perfect power control and optical transmission in local area networks.<br>Limits on CDMA transmission are obtained using multi-access channel models and capacity calculations. Using these insights, a technique is proposed to increase throughput over MAC channels by exploiting controlled amount of user asynchronism. Consequently, a trellis based multiuser detector is proposed as a means to exploit the MAC channel capacity. Simulation results indicate that the proposed iterative detector has polynomial implementation complexity; achieves close to optimal performance in uncoded CDMA environments with strong interference, and outperforms the upper-bound of perfectly synchronized and noiseless BPSK based TDMA.
38
Bourret, Jason C. "Response restriction and contingent access to responding in multi-response environments." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0012800.
Pełny tekst źródła
39
Zhang, Jian. "Equilibrium design for multi-channel random access networks with selfish users." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-32646.
Pełny tekst źródłaStreszczenie:
Recently, there has been increasing research in the inefficency in spectrum utilization, which is mainly caused by fixed spectrum allocation policies. There are some proposed approaches to solve this inefficiency, like Dynamic Spectrum Access (DSA), which allows users to share spectrum resources. Implementing DSA in a distributed way can avoid problems with system complexity that can arise in centralized DSA systems; however, it can create incentives for the users to behave selfishly. Selfish behavior reduces the sfficiency of the DSA system, and it causes the system to end up in one of many possible operating points, which makes the performance analysis difficult. In this work, we study a multichannel random access system with selfish users and we propose two mechanisms in which the access point charges users for transmissioon. We analyze the performance of these mechanisms using Game Theory. Results show that by charging users for transmission, we can reduce the possible operating points of the system to a single one. Of the two proposed mechanisms, the per-channel cost mechanism performs rather well, bringing the system sum utility close to that of scheduling systems.
40
Yanikömeroglu, Halim. "Multi-antenna systems and interconnection strategies for CDMA wireless access networks." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0007/NQ41536.pdf.
Pełny tekst źródła
41
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.
Pełny tekst źródła
42
Piao, Guihua. "Radio resource management for integrated services in multi-radio access networks." Kassel Kassel Univ. Press, 2006. http://www.uni-kassel.de/hrz/db4/extern/dbupress/publik/abstract.php?978-3-89958-269-7.
Pełny tekst źródła
43
Piao, Guihua. "Radio resource management for integrated services in multi-radio access networks." Kassel Kassel Univ. Press, 2007. http://d-nb.info/986595012/34.
Pełny tekst źródła
44
Skelton, Benjamin C. "Reduced complexity asynchronous multi-user receivers for spread spectrum multiple access." Thesis, University of Canterbury. Electrical and Electronic Engineering, 2000. http://hdl.handle.net/10092/5743.
Pełny tekst źródłaStreszczenie:
One of the major problems facing the implementation of multi-user detectors in a mobile radio multiple access environment is the complexity of the receiver structure. This thesis addresses this problem and develops three related receiver structures based on the maximum likelihood multi-user detector. They allow a degradation in performance to be traded for a reduction in the complexity of the receiver. The first family of reduced complexity receivers is derived considering a serial partitioning of the maximum likelihood trellis. A receiver with two degrees of freedom is developed by the application of reduced state sequence estimation (RSSE) techniques to the first receiver. A maximum-ratio combining-like detector with self-noise cancellation is derived for the multi-path fading channel. All three receiver structures allow for significant reductions in complexity with respect to the maximum likelihood detector with only modest performance reductions.
45
Farhoudi, Mohammad Hassan. "Multi-plane routing practical applications in future all-IP access networks." Thesis, King's College London (University of London), 2018. https://kclpure.kcl.ac.uk/portal/en/theses/multiplane-routing-practical-applications-in-future-allip-access-networks(be4b52e5-c43f-4b23-8a58-8ccd8c5b8eff).html.
Pełny tekst źródłaStreszczenie:
The Internet has proven to be a major contributor to the world and has had a significant impact on many aspects of our lives over the past decades. It continues to have the potential to impact societies, businesses and governments in different ways. Despite the clear significance of Internet as a key enabler of a big technological revolution, there are rising challenges associated with the exponential growth of the Internet. In addition, accelerated in part by the massive increase in devices and the capabilities of those devices, Internet traffic is increasingly becoming more dynamic and demanding. Meanwhile, users expect a quality delivery facilitated by service providers across the mobile networks from core to access. Internet Protocol (IP) as the underlying foundation for the next-generation networks is becoming increasingly relevant considering the ubiquitous installed IP infrastructure. Correspondingly, different suggestions are being explored about the facilitation of next-generation access networks via IP mechanisms, with a growing trend towards a flat IP structure and novel topological set-ups in the backhaul. With the expected surge in global IP traffic, service providers would need to adapt accordingly to operate disruption and loss free networks supported with the developing IP infrastructure. This calls for a consistent routing optimization strategy to minimize loss in data transmission. Hence, a resilient, efficient and easily implementable routing paradigm that employs suitable Traffic Engineering (TE) techniques aligned with the developing nature of future access networks must be applied. It becomes imperative that the routing considerations for IP access networks converge with the ones found in conventional intra-domain routing. Multi-Plane Routing (MPR) is a routing optimization approach that consolidates various aspects in an all-IP access network infrastructure and consists of both offline and online TE approaches. MPR integrates the recent multi-topology approach that leverages multiple alternative paths (for each Ingress-Egress pair) through a network that divides the physical network topology into several logical routing planes facilitating path diversity. In this thesis, MPR is extended from a practical prospective in line with the architectural evolution of access networks and the introduction of new traffic types and applications. The offline and online TE strategies of MPR have been modified to suit the flattened network architecture. Correspondingly, a MPR-based TE approach is proposed considering two different scenarios to reflect the evolution in the architectural design of access network structures under a realistic traffic scenario. It becomes evident that for ranges of topologies, MPR’s utilization of the whole topology in building path diversity in networks, allows for significant improvement of networks’ capacity, performance and support for meshing. Moreover, with the rise of different traffic types of various nature, Quality of Service (QoS) is increasingly becoming important. Tactile Internet is considered in this thesis in addition to other traffic applications. To this end, a novel routing technique which accommodates for the strict requirements of this new traffic type in access networks architectures will be proposed. Validation of the proposed techniques through simulations have been performed and presented, illustrating the effectiveness of the proposed methods.
46
Band, Ian W. "Multi-user receiver structures for direct sequence code division multiple access." Thesis, University of Edinburgh, 1998. http://hdl.handle.net/1842/10722.
Pełny tekst źródłaStreszczenie:
This thesis reports on an investigation of various system architectures and receiver structures for cellular communications systems which discriminate users by direct sequence code division multiple access (DS-CDMA). Attention is focussed on the downlink of such a spread spectrum system and the influence of a number of design parameters is considered. The objective of the thesis is to investigate signal processing techniques which may be employed either at the receiver, or throughout the system to improve the overall capacity. The principles of spread spectrum communication are first outlined, including a discussion of the relative merits of spreading sequence sets, and a description of various signal processing techniques which are to be applied to the multi-user environment. The measure of system performance is introduced, and the conventional DS-CDMA system is analysed theoretically and through simulation to provide a reference performance level. Adaptive algorithms, which iteratively approximate the minimum mean square error (Wiener) receiver filter, are then investigated, both in stationary additive white Gaussian noise (AWGN) and in a more realistic radio channel. The inter-dependence of the system chip-rate, maximum Doppler offset induced by the motion of the receiver and the tuning parameters of the adaptive algorithm are demonstrated. Aspects of forward error correction (FEC) coding are then investigated, with convolutional coding on the data used both as an alternative to and as a supplement of direct sequence spreading. The most efficient use of the available expansion in bandwidth is shown to be dependent on a balance between FEC coding power and the capacity of the spreading sequence set chosen. Methods of combining multiple access interference cancellation techniques with convolutional coding and Viterbi decoding are considered. New structures are proposed which incorporate FEC decoding at the intermediate stage of the canceller, and the performance of these receivers is analysed theoretically. Simulations confirm that significant capacity improvements may be achieved, at tolerable increases in computational complexity and processing delay.
47
Wan, Zhiwen. "Cooperative and Adaptive Medium Access Control in Multi-hop Wireless Networks." FIU Digital Commons, 2008. http://digitalcommons.fiu.edu/etd/272.
Pełny tekst źródłaStreszczenie:
Due to low cost and easy deployment, multi-hop wireless networks become a very attractive communication paradigm. However, IEEE 802.11 medium access control (MAC) protocol widely used in wireless LANs was not designed for multi-hop wireless networks. Although it can support some kinds of ad hoc network architecture, it does not function efficiently in those wireless networks with multi-hop connectivity. Therefore, our research is focused on studying the medium access control in multi-hop wireless networks. The objective is to design practical MAC layer protocols for supporting multihop wireless networks. Particularly, we try to prolong the network lifetime without degrading performances with small battery-powered devices and improve the system throughput with poor quality channels. In this dissertation, we design two MAC protocols. The first one is aimed at minimizing energy-consumption without deteriorating communication activities, which provides energy efficiency, latency guarantee, adaptability and scalability in one type of multi-hop wireless networks (i.e. wireless sensor network). Methodologically, inspired by the phase transition phenomena in distributed networks, we define the wake-up probability, which maintained by each node. By using this probability, we can control the number of wireless connectivity within a local area. More specifically, we can adaptively adjust the wake-up probability based on the local network conditions to reduce energy consumption without increasing transmission latency. The second one is a cooperative MAC layer protocol for multi-hop wireless networks, which leverages multi-rate capability by cooperative transmission among multiple neighboring nodes. Moreover, for bidirectional traffic, the network throughput can be further increased by using the network coding technique. It is a very helpful complement for current rate-adaptive MAC protocols under the poor channel conditions of direct link. Finally, we give an analytical model to analyze impacts of cooperative node on the system throughput.
48
Abuhaija, Belal Saleh. "A simulation framework for service continuity over multi access wireless networks." Thesis, University of South Wales, 2010. https://pure.southwales.ac.uk/en/studentthesis/a-simulation-framework-for-service-continuity-over-multi-access-wireless-networks(5b370ae0-47b2-43b7-b0f2-91b1fd5fd3b8).html.
Pełny tekst źródłaStreszczenie:
Mobile communication systems have continued to evolve by the release of new standards for HSPA and the release of new standards for LTE in release 8 and release 9. The new releases aim at providing higher data rates to accommodate the envisioned services of 3GPP in voice, data, image transmission, video, multimedia service and broadband services. Catering for a wide variety of services to satisfy the demands imposed on mobile networks by the user diversity and demanding applications, the air interface has been identified as the major bottleneck in the mobile networks. Network planning engineers and operators are deploying the new air interfaces in the same cell sites, which gives rise to several internetworking issues among the different air interfaces from radio resources management to service call continuity issues due to user's mobility and changing point of attachment. Deployment of different air interfaces coupled with traffic diversity requests further complicates the managements of the mobile networks. One of The main objectives of this research is to propose and evaluate solutions that address the internetworking of the different radio air interfaces in proposing a call admission control algorithm that can utilize different air interfaces capabilities and to determine which traffic types are better suited to be serviced by an interface. The proposed algorithm will consider the availability of the interface, the load of the network and the user equipment capabilities. Another main objective of this research is to propose and evaluate solutions that address changing the point of attachment of the users due to mobility in the form of handover algorithm. The proposed algorithm will consider the coverage of the node, direction and speed of the user, the network load, the air interface availability and the user equipment capabilities. Another main objective of this research is to design and implement a simulation system which includes all 3GPP standardized technologies. The simulation tool was designed as a discrete event simulation (DBS) system which includes all the standardized air interface technologies and services. The simulation tool was designed using Visual C# to take advantage of the object oriented capabilities of the Windows environment and libraries. The simulation tool was essential in evaluating the proposed algorithms in the first two objectives.
49
Hoblos, Jalaa. "Access Disparity Modeling and Fairness Provisioning in Multi-Hop Wireless Networks." Kent State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=kent1365703079.
Pełny tekst źródła
50
Djahel, Soufiene. "Secure routing and medium access protocols in wireless multi-hop networks." Thesis, Lille 1, 2010. http://www.theses.fr/2010LIL10094/document.
Pełny tekst źródłaStreszczenie:
Récemment, les comportements malveillants dans les réseaux sans fil multi-sauts ont attiré l’attention de la communauté scientifique. La prolifération rapide du nombre de dispositifs sans fil ainsi que la diversification des applications basées sur ces réseaux ont grandement contribué à l’amélioration de la qualité de vie ainsi que la modernisation de la société. Cependant, la nécessité de sécuri ser ces réseaux et de garantir la robustesse de leurs services est devenue une préoccupation majeure. En effet, les caractéristiques spécifiques de ces réseaux, telles que l’absence d’infrastructure et l’absence d’une entité centrale de confiance, font que les réponses à leurs problèmes de sécurité sont tout à fait différentes de celles des réseaux filaires. De plus, le manque de confiance entre les nœuds rend ces problèmes encore plus critiques. L’objectif de cette thèse vise à contribuer au renforcement de la sécurité dans les réseaux sans fil multi-sauts. Elle se focalise sur l’étude des comportements malveillants au niveau des couches MAC et réseau. Nous nous intéressons au développement de nouvelles solutions pour faire face à l’attaque du trou noir ”Black hole” dans le contexte du protocole OLSR, ainsi qu’analyser le comportement des nœuds cupides ”Greedy” au niveau de la couche MAC, dans toutes ses versions.Une attaque de trou noir peut être menée suivant deux scénarios. Le premier scénario consiste à lancer l’attaque, exclusivement, au niveau de la couche réseau. Le second scénario consiste en une attaque multi-couches. Dans le cadre de cette thèse, nous analysons l’impact de ces deux types d’attaques et proposons des contre-mesures appropriées. Au niveau de la couche MAC, nous étudions particulièrement le comportement cupide adaptatif dans le cadre des réseaux sans fil maillés et nous proposons une solution originale baptisée, FLSAC, afin de prévenir ce type de menace. Dans le cadre des réseaux mobiles ad hoc (MANETs), nous définissons un nouveau modèle de comportement des nœuds cupides. Nous développons aussi un nouvel algorithme de backoff, dont l’avantage principal est d’assurer une détection rapide des nœuds cupides non conformes aux spécifications du protocole IEEE802.11. Cet algorithme offre un mécanisme de réaction qui incite un nœud cupide à se comporter correctement en lui donnant la chance de se repentir après détection<br>While the rapid proliferation of mobile devices along with the tremendous growth of various applications using wireless multi-hop networks have significantly facilitate our human life, securing and ensuring high quality services of these networks are still a primary concern. In particular, anomalous protocol operation in wireless multi-hop networks has recently received considerable attention in the research community. These relevant security issues are fundamentally different from those of wireline networks due to the special characteristics of wireless multi-hop networks, such as the limited energy resources and the lack of centralized control. These issues are extremely hard to cope with due to the absence of trust relationships between the nodes.To enhance security in wireless multi-hop networks, this dissertation addresses both MAC and routing layers misbehaviors issues, with main focuses on thwarting black hole attack in proactive routing protocols like OLSR, and greedy behavior in IEEE 802.11 MAC protocol. Our contributions are briefly summarized as follows. As for black hole attack, we analyze two types of attack scenarios: one is launched at routing layer, and the other is cross layer. We then provide comprehensive analysis on the consequences of this attack and propose effective countermeasures. As for MAC layer misbehavior, we particularly study the adaptive greedy behavior in the context of Wireless Mesh Networks (WMNs) and propose FLSAC (Fuzzy Logic based scheme to Struggle against Adaptive Cheaters) to cope with it. A new characterization of the greedy behavior in Mobile Ad Hoc Networks (MANETs) is also introduced. Finally, we design a new backoff scheme to quickly detect the greedy nodes that do not comply with IEEE 802.11 MAC protocol, together with a reaction scheme that encourages the greedy nodes to become honest rather than punishing them