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Dynamic Spectrum Sharing in Cognitive Radio and Device-to-Device SystemsJanuary 2017 (has links)
abstract: Cognitive radio (CR) and device-to-device (D2D) systems are two promising dynamic spectrum access schemes in wireless communication systems to provide improved quality-of-service, and efficient spectrum utilization. This dissertation shows that both CR and D2D systems benefit from properly designed cooperation scheme.
In underlay CR systems, where secondary users (SUs) transmit simultaneously with primary users (PUs), reliable communication is by all means guaranteed for PUs, which likely deteriorates SUs’ performance. To overcome this issue, cooperation exclusively among SUs is achieved through multi-user diversity (MUD), where each SU is subject to an instantaneous interference constraint at the primary receiver. Therefore, the active number of SUs satisfying this constraint is random. Under different user distributions with the same mean number of SUs, the stochastic ordering of SU performance metrics including bit error rate (BER), outage probability, and ergodic capacity are made possible even without observing closed form expressions. Furthermore, a cooperation is assumed between primary and secondary networks, where those SUs exceeding the interference constraint facilitate PU’s transmission by relaying its signal. A fundamental performance trade-off between primary and secondary networks is observed, and it is illustrated that the proposed scheme outperforms non-cooperative underlay CR systems in the sense of system overall BER and sum achievable rate.
Similar to conventional cellular networks, CR systems suffer from an overloaded receiver having to manage signals from a large number of users. To address this issue, D2D communications has been proposed, where direct transmission links are established between users in close proximity to offload the system traffic. Several new cooperative spectrum access policies are proposed allowing coexistence of multiple D2D pairs in order to improve the spectral efficiency. Despite the additional interference, it is shown that both the cellular user’s (CU) and the individual D2D user's achievable rates can be improved simultaneously when the number of D2D pairs is below a certain threshold, resulting in a significant multiplexing gain in the sense of D2D sum rate. This threshold is quantified for different policies using second order approximations for the average achievable rates for both the CU and the individual D2D user. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017
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Dissémination de contenus populaires et tolérants au délai dans les réseaux cellulaires / Dissemination of popular and delay-tolerant content in cellular networksBelouanas, Salah-Eddine 13 October 2017 (has links)
Les ressources cellulaires sont précieuses et doivent être préservées dès que possible. Dans cette thèse, nous abordons le problème de la dissémination de contenus dans un réseau cellulaire surchargé. La première partie présente SCoD (Scheduled Content Delivery), une stratégie de dissémination purement cellulaire qui exploite la mobilité des utilisateurs ainsi que leur tolérance aux délais afin d’effectuer des transmissions différées. SCoD attend que les utilisateurs se rassemblent autour d’un minimum de points d’accès afin que le nombre total de transmissions soit réduit. Pour déclencher des transmissions, SCoD repose sur différentes fonctions de décision qui déclenchent aux instants opportuns une transmission en multicast. La deuxième partie de cette thèse traite également le problème d’économie de ressources cellulaires, mais en l’attaquant sous un autre angle. Nous exploitons des communications D2D que nous associons au multicast pour réduire la charge sur l’infrastructure. Nous analysons les avantages des communications opportunistes dans le contexte d’un service de diffusion de contenus basé sur les abonnements des utilisateurs. Nous présentons nos résultats pour deux cas de figure. Tout d’abord, nous illustrons le bénéfice des communications D2D dans le cadre d’un processus de diffusion, où le coût d’une transmission opportuniste est négligeable par rapport à celui d’une transmission cellulaire. Nous considérons ensuite le cas où les utilisateurs doivent être indemnisés pour leur participation au processus de diffusion, et où il y a donc un compromis à trouver. Nous fournissons des lignes directrices dans ce sens et nous montrons la variation d’un tel compromis en fonction de plusieurs paramètres du réseau. / Cellular resources are valuable and must be saved whenever possible. In this thesis, we address the problem of content dissemination within an overloaded cellular network. Firstly, we propose SCoD (Scheduled Content Delivery), a purely cellular dissemination strategy that exploits the mobility of users and their delay tolerance in order to postpone transmissions. SCoD waits for users to gather around a minimum number of access points so that the total number of transmissions is reduced. To trigger transmissions, SCoD relies on different decision functions which launch, if necessary, a multicast transmission. The second part of this thesis deals with the same problem of saving cellular resources, but from another angle. We use D2D (Device-to-Device) communications with multicast to mitigate the traffic load on the infrastructure. We study the benefits of opportunistic communications in the context of a content distribution service based on user subscriptions. We present our results in two ways. First, we illustrate the benefits of D2D communications in a content dissemination process where the cost of opportunistic transmission is negligible compared to that of cellular transmission. Then, we consider the case where users must be compensated for their participation in the dissemination process. Therefore, there is a tradeoff to be found, we thus provide guidelines in this direction and show the variation of such a tradeoff as a function of several network parameters.
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Protocol design and performance evaluation for wireless ad hoc networksTong, Fei 10 November 2016 (has links)
Benefiting from the constant and significant advancement of wireless communication technologies and networking protocols, Wireless Ad hoc NETwork (WANET) has played a more and more important role in modern communication networks without relying much on existing infrastructures. The past decades have seen numerous applications adopting ad hoc networks for service provisioning. For example, Wireless Sensor Network (WSN) can be widely deployed for environment monitoring and object tracking by utilizing low-cost, low-power and multi-function sensor nodes. To realize such applications, the design and evaluation of communication protocols are of significant importance. Meanwhile, the network performance analysis based on mathematical models is also in great need of development and improvement.
This dissertation investigates the above topics from three important and fundamental aspects, including data collection protocol design, protocol modeling and analysis, and physical interference modeling and analysis. The contributions of this dissertation are four-fold.
First, this dissertation investigates the synchronization issue in the duty-cycled, pipelined-scheduling data collection of a WSN, based on which a pipelined data collection protocol, called PDC, is proposed. PDC takes into account both the pipelined data collection and the underlying schedule synchronization over duty-cycled radios practically and comprehensively. It integrates all its components in a natural and seamless way to simplify the protocol implementation and to achieve a high energy efficiency and low packet delivery latency. Based on PDC, an Adaptive Data Collection (ADC) protocol is further proposed to achieve dynamic duty-cycling and free addressing, which can improve network heterogeneity, load adaptivity, and energy efficiency. Both PDC and ADC have been implemented in a pioneer open-source operating system for the Internet of Things, and evaluated through a testbed built based on two hardware platforms, as well as through emulations.
Second, Linear Sensor Network (LSN) has attracted increasing attention due to the vast requirements on the monitoring and surveillance of a structure or area with a linear topology. Being aware that, for LSN, there is few work on the network modeling and analysis based on a duty-cycled MAC protocol, this dissertation proposes a framework for modeling and analyzing a class of duty-cycled, multi-hop data collection protocols for LSNs. With the model, the dissertation thoroughly investigates the PDC performance in an LSN, considering both saturated and unsaturated scenarios, with and without retransmission. Extensive OPNET simulations have been carried out to validate the accuracy of the model.
Third, in the design and modeling of PDC above, the transmission and interference ranges are defined for successful communications between a pair of nodes. It does not consider the cumulative interference from the transmitters which are out of the contention range of a receiver. Since most performance metrics in wireless networks, such as outage probability, link capacity, etc., are nonlinear functions of the distances among communicating, relaying, and interfering nodes, a physical interference model based on distance is definitely needed in quantifying these metrics. Such quantifications eventually involve the Nodal Distance Distribution (NDD) intrinsically depending on network coverage and nodal spatial distribution. By extending a tool in integral geometry and using decomposition and recursion, this dissertation proposes a systematic and algorithmic approach to obtaining the NDD between two nodes which are uniformly distributed at random in an arbitrarily-shaped network.
Fourth, with the proposed approach to NDDs, the dissertation presents a physical interference model framework to analyze the cumulative interference and link outage probability for an LSN running the PDC protocol. The framework is further applied to analyze 2D networks, i.e., ad hoc Device-to-Device (D2D) communications underlaying cellular networks, where the cumulative interference and link outage probabilities for both cellular and D2D communications are thoroughly investigated. / Graduate / 0984 / 0544 / tong1987fei@163.com
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Contemporary electromagnetic spectrum reuse techniques: tv white spaces and D2D communications / TÃcnicas contemporÃneas de reuso do espectro electromagnÃtico: tv de espaÃos branco e comunicaÃÃes D2DCarlos Filipe Moreira e Silva 15 December 2015 (has links)
CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Over the last years, the wireless broadband access has achieved a tremendous success.
With that, the telecommunications industry has faced very important changes in terms
of technology, heterogeneity, kind of applications, and massive usage (virtual data tsunami)
derived from the introduction of smartphones and tablets; or even in terms of market structure
and its main players/actors. Nonetheless, it is well-known that the electromagnetic spectrum is
a scarce resource, being already fully occupied (or at least reserved for certain applications). Tra-
ditional spectrum markets (where big monopolies dominate) and static spectrum management
originated a paradoxal situation: the spectrum is occupied without actually being used!
In one hand, with the global transition from analog to digital Television (TV), part of the
spectrum previously licensed for TV is freed and geographically interleaved, originating the
consequent Television White Spaces (TVWS); on the other hand, the direct communications
between devices, commonly referred as Device-to-Device (D2D) communications, are attracting
crescent attention by the scientific community and industry in order to overcome the scarcity
problem and satisfy the increasing demand for extra capacity. As such, this thesis is divided in
two main parts: (a) Spectrum market for TVWS: where a SWOT analysis for the use of TVWS
is performed giving some highlights in the directions/actions that shall be followed so that its
adoption becomes effective; and a tecno-economic evaluation study is done considering as a
use-case a typical European city, showing the potential money savings that operators may reach
if they adopt by the use of TVWS in a flexible market manner; (b) D2D communications: where
a neighbor discovery technique for D2D communications is proposed in the single-cell scenario
and further extended for the multi-cell case; and an interference mitigation algorithm based
on the intelligent selection of Downlink (DL) or Uplink (UL) band for D2D communications
underlaying cellular networks.
A summary of the principal conclusions is as follows: (a) The TVWS defenders shall
focus on the promotion of a real-time secondary spectrum market, where through the correct
implementation of policies for protection ratios in the spectrum broker and geo-location
database, incumbents are protected against interference; (b) It became evident that an operator
would recover its investment around one year earlier if it chooses to deploy the network
following a flexible spectrum market approach with an additional TVWS carrier, instead of
the traditional market; (c) With the proposed neighbor discovery technique the time to detect
all neighbors per Mobile Station (MS) is significantly reduced, letting more time for the actual
data transmission; and the power of MS consumed during the discovery process is also reduced
because the main processing is done at the Base Station (BS), while the MS needs to ensure that
D2D communication is possible just before the session establishment; (d) Despite being a simple
concept, band selection improves the gains of cellular communications and limits the gains
of D2D communications, regardless the position within the cell where D2D communications
happen, providing a trade-off between system performance and interference mitigation. / Nos Ãltimos anos, o acesso de banda larga atingiu um grande sucesso. Com isso, a indÃstria
das telecomunicaÃÃes passou por importantes transformaÃÃes em termos de tecnologia,
heterogeneidade, tipo de aplicaÃÃes e uso massivo (tsunami virtual de dados) em consequÃncia
da introduÃÃo dos smartphones e tablets; ou atà mesmo na estrutura de mercado e os seus
principais jogadores/atores. PorÃm, à sabido que o espectro electromagnÃtico à um recurso
limitado, estando jà ocupado (ou pelo menos reservado para alguma aplicaÃÃo). O mercado
tradicional de espectro (onde os grandes monopÃlios dominam) e o seu gerenciamento estÃtico
contribuÃram para essa situaÃÃo paradoxal: o espectro està ocupado mas nÃo està sendo usado!
Por um lado, com a transiÃÃo mundial da TelevisÃo (TV) analÃgica para a digital, parte do
espectro anteriormente licenciado para a TV Ã libertado e geograficamente multiplexado para
evitar a interferÃncia entre sinais de torres vizinhas, dando origem a ÂespaÃos em branco na
frequÃncia da TV ou Television White Spaces (TVWS); por outro lado, as comunicaÃÃes diretas
entre usuÃrios, designadas por comunicaÃÃes diretas Dispositivo-a-Dispositivo (D2D), estÃ
gerando um crescente interesse da comunidade cientÃfica e indÃstria, com vista a ultrapassar
o problema da escassez de espectro e satisfazer a crescente demanda por capacidade extra.
Assim, a tese està dividida em duas partes principais: (a) Mercado de espectro eletromagnÃtico
para TVWS: onde à feita uma anÃlise SWOT para o uso dos TVWS, dando direÃÃes/aÃÃes a
serem seguidas para que o seu uso se torne efetivo; e um estudo tecno-econÃmico considerando
como cenÃrio uma tÃpica cidade Europeia, onde se mostram as possÃveis poupanÃas monetÃrias
que os operadores conseguem obter ao optarem pelo uso dos TVWS num mercado flexÃvel;
(b) ComunicaÃÃes D2D: onde uma tÃcnica de descoberta de vizinhos para comunicaÃÃes D2D Ã
proposta, primeiro para uma Ãnica cÃlula e mais tarde estendida para o cenÃrio multi-celular; e
um algoritmo de mitigaÃÃo de interferÃncia baseado na seleÃÃo inteligente da banda Ascendente
(DL) ou Descendente (UL) a ser reusada pelas comunicaÃÃes D2D que acontecem na rede celular.
Um sumÃrio das principais conclusÃes à o seguinte: (a) Os defensores dos TVWS devem-se
focar na promoÃÃo do mercado secundÃrio de espectro electromagnÃtico, onde atravÃs da
correta implementaÃÃo de politicas de proteÃÃo contra a interferÃncia no broker de espectro e
na base de dados, os usuÃrios primÃrio sÃo protegidos contra a interferÃncia; (b) Um operador
consegue recuperar o seu investimento aproximadamente um ano antes se ele optar pelo
desenvolvimento da rede seguindo um mercado secundÃrio de espectro com a banda adicional
de TVWS, em vez do mercado tradicional; (c) Com a tÃcnica proposta de descoberta de vizinhos,
o tempo de descoberta por usuÃrio à significativamente reduzido; e a potÃncia consumida
nesse processo à tambÃm ela reduzida porque o maior processamento à feito na EstaÃÃo RÃdio
Base (BS), enquanto que o usuÃrio sà precisa de se certificar que a comunicaÃÃo direta Ã
possÃvel; (d) A seleÃÃo de banda, embora seja um conceito simples, melhora os ganhos das
comunicaÃÃes celulares e limita os das comunicaÃÃes D2D, providenciando um compromisso
entre a performance do sistema e a mitigaÃÃo de interferÃncia.
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