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Performance assessment of single and multiple antenna relays for the uplink OFDM systems

Lima, H.; Moço, A.; Silva, A.; Gameiro, A.
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
56.26%
The aim of this paper is to propose and assess the performance of cooperative schemes designed for the uplink OFDM based systems with mobile relays with an antenna array. We consider the use of an antenna array at the base station and a single antenna at the user terminal. We compare the situations at which the relay is equipped with one or two antennas. We assume that some of the user terminals deployed in a certain area could act as relaying-able terminals for the communication of other users. Two types of relay assisted protocols are considered: equalize-and-forward and decode-and-forward. The performance of the proposed relay-assisted schemes is evaluated under realistic scenarios, considering typical pedestrian scenarios based on WiMAX specifications. The proposed schemes are also compared against the OFDM based non-cooperative systems. Numerical results show that the availability of antenna arrays at the relays significantly improves the cooperative systems performance, which outperform the non-cooperative ones in all studied scenarios; CODIV - FP7/ICT/2007/215477; PHOTON FPDC - EEA-TEL/72890/2006

Multiple antenna relay-assisted schemes for the uplink OFDM based systems

Moço, A.; Lima, H.; Silva, A.; Gameiro, A.
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
46.2%
The aim of this paper is to propose and assess the performance of multiple antenna half-duplex relay-assisted cooperative schemes designed for the uplink OFDM based systems. We consider the use of an antenna array at the relay and base station and a single antenna at the mobile terminals. Two types of relay protocols are considered: equalize-and-forward and decode-and-forward. The performance of the proposed multiple antenna relay-assisted schemes is evaluated under realistic scenarios, considering typical pedestrian scenarios based on WiMAX specifications. The proposed schemes are also compared against the OFDM based non-cooperative systems. The goal is to identify the scenarios in which cooperating may be beneficial. Numerical results show that multiple antenna relay-assisted schemes outperform the non-cooperative ones in most of the studied scenarios.; CODIV - FP7/ICT/2007/215477; PHOTON FPDC/EEA-TEL/72890/2006

Distributed space-frequency block coding for a 2-antenna relay in downlink OFDM systems

Teodoro, Sara; Silva, Adão; Gil, João M.; Gameiro, Atílio
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
56.21%
In this paper we evaluate the coded and uncoded performance of a 2-antenna terminal relaying schem, for downlink OFDM based systems, using efficient space-frequency block coding protocols. We consider that the relay and the base station are equipped with 2 antennas and the user terminal has a single antenna. Two types of relay protocols are accounted for: Equalize-and-Forward and Decode-and-Forward. Signals expressions are derived and the bit error rates obtained for a pratical and preeminent scenario, with LTE parameters and using convolutional channel coding. The performance of the proposed relay-assited scheme is evaluated under realistic scenarios, considering typical pedestrian scenarios based on LTE specifications. Results are compared to those of other relay-assisted design approaches that have been recently proposed for the case of 1-antenna relay and the non-cooperative systems. For this comparison, we implement three propagation scenarios, with different SNR transmission conditions among links. Simulation results show that the availability of a bi-antenna array at the relay significantly improves the cooperative system performance, but improvements are highly dependent on the scenarios and relay protocol as well as of the cooperative second-hop quality.; CODIV - FP7-ICT/2007-215477; AGILE - PTDC/EEA-TEL/71417/2006; FCT

Channel estimation schemes for OFDM relay-assisted systems

Neves, Darlene; Ribeiro, Carlos; Silva, Adão; Gameiro, Atílio
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
56.13%
The aim of this paper is to adapt and evaluate the performance of two classical pilot-aided channel estimation schemes designed for OFDM systems: least square and minimum mean square error, in a relay-assisted scenario. We consider the Amplify-and-Forward, which is the simplest relay protocol for cooperative systems. Also, we consider the use of a single antenna at all the terminals: base station, user terminal and relay node. In our scenario, it is assumed that some of the user terminals deployed in a certain area could act as relaying-able terminals for the communications of other users. In this communication we show that the classical channel estimation techniques designed for conventional wireless communications can be extended for relay-assisted based systems under some modifications. © 2009 IEEE.; European CODIV project (ref. FP7-ICT-2007-215477); Portuguese Foundation for Science and Technology (FCT)

A Review on Cooperative Question-Answering Systems

Melo, Dora; Pimenta Rodrigues, Irene; Beires Nogueira, Vitor
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
46.12%
The Question-Answering (QA) systems fall in the study area of Information Retrieval (IR) and Natural Language Processing (NLP). Given a set of documents, a QA system tries to obtain the correct answer to the questions posed in Natural Language (NL). Normally, the QA systems comprise three main components: question classification, information retrieval and answer extraction. Question classification plays a major role in QA systems since it classifies questions according to the type in their entities. The techniques of information retrieval are used to obtain and to extract relevant answers in the knowledge domain. Finally, the answer extraction component is an emerging topic in the QA systems. This module basically classifies and validates the candidate answers. In this paper we present an overview of the QA systems, focusing on mature work that is related to cooperative systems and that has got as knowledge domain the Semantic Web (SW). Moreover, we also present our proposal of a cooperative QA for the SW.

Group decision making in a prototype engineering system : the Federal Open Market Committee; Exploration of group decision making in engineering systems : data, models, and lateral alignment

Lawson, Christopher M. (Christopher Michael)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 156 p.
ENG
Relevância na Pesquisa
46.07%
All ES evolve as the result of stakeholder decisions and decision processes that affect their design and operation. These decision making problems often involve many stakeholders, each of whom have a say in the outcome. This has been termed a lateral alignment problem, as opposed to a unitary decision making problem. Lateral alignment focuses on group decision making where stakeholders are nominally organizationally independent, interact to maximize their own goals and simultaneously a common goal, and who are able to influence decision outcomes to varying degrees through power and influence. Previous work in the relevant literatures has focused on two variants used to assess and model group decision making. Type 0 Group Decision problems involve anonymous voting, where stakeholders do not interact. Type 1 Group Decision problems involve non-cooperative interaction where stakeholders try to maximize their self-interest through negotiation. We define the lateral alignment problem as a Type 2 Group Decision problem, which involve elements of both non-cooperative and cooperative behavior. Type 2 Group Decisions have not been fully treated in the existing literatures. In this thesis, we evaluate a prototype Type 2 Group Decisions: the Federal Open Market Committee (FOMC) from 1970-1994 as a test case. One major advantage of studying the FOMC is the availability of data and relevant analytical published work. Our original empirical findings include: 1. Information ambiguity is the major factor that impacts coalition dynamics...

Cooperative Partial Detection for MIMO Relay Networks

Amiri, Kiarash
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
46.16%
Cooperative communication has recently re-emerged as a possible paradigm shift to realize the promises of the ever increasing wireless communication market; how- ever, there have been few, if any, studies to translate theoretical results into feasi- ble schemes with their particular practical challenges. The multiple-input multiple- output (MIMO) technique is another method that has been recently employed in different standards and protocols, often as an optional scenario, to further improve the reliability and data rate of different wireless communication applications. In this work, we look into possible methods and algorithms for combining these two tech- niques to take advantage of the benefits of both. In this thesis, we will consider methods that consider the limitations of practical solutions, which, to the best of our knowledge, are the first time to be considered in this context. We will present complexity reduction techniques for MIMO systems in cooperative systems. Furthermore, we will present architectures for flexible and configurable MIMO detectors. These architectures could support a range of data rates, modulation orders and numbers of antennas, and therefore, are crucial in the different nodes of cooperative systems. The breadth-first search employed in our realization presents a large opportunity to exploit the parallelism of the FPGA in order to achieve high data rates. Algorithmic modifications to address potential sequential bottlenecks in the traditional bread-first search-based SD are highlighted in the thesis. We will present a novel Cooperative Partial Detection (CPD) approach in MIMO relay channels...

Synchronization in Cooperative Communication Systems

Nasir, Ali Arshad
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Thesis (PhD); Doctor of Philosophy (PhD)
EN_AU
Relevância na Pesquisa
46.2%
Cooperative communication is an attractive solution to combat fading in wireless communication systems. Achieving synchronization is a fundamental requirement in such systems. In cooperative networks, multiple single antenna relay terminals receive and cooperatively transmit the source information to the destination. The multiple distributed nodes, each with its own local oscillator, give rise to multiple timing offsets (MTOs) and multiple carrier frequency offsets (MCFOs). Particularly, the received signal at the destination is the superposition of the relays' transmitted signals that are attenuated differently, are no longer aligned with each other in time, and experience phase rotations at different rates due to different channels, MTOs, and MCFOs, respectively. The loss of synchronization due to the presence of MTOs and MCFOs sets up the recovery of the source signal at the destination to be a very challenging task. This thesis seeks to develop estimation and compensation algorithms that can achieve synchronization and enable cooperative communication for both decode-and-forward (DF) and amplify-and-forward (AF) relaying networks in the presence of multiple impairments, i.e., unknown channel gains, MTOs, and MCFOs. In the first part of the thesis...

Distributed Space-Time Block Codes in Wireless Cooperative Networks

YI, ZHIHANG
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 915514 bytes; application/pdf
EN; EN
Relevância na Pesquisa
45.97%
In cooperative networks, relays cooperate and form a distributed multi-antenna system to provide spatial diversity. In order to achieve high bandwidth efficiency, distributed space-time block codes (DSTBCs) are proposed and have been studied extensively. Among all DSTBCs, this thesis focuses on the codes which are single-symbol maximum likelihood (ML) decodable and can achieve the full diversity order. This thesis presents four works on single-symbol ML decodable DSTBCs. The first work proposes the row-monomial distributed orthogonal space-time block codes (DOSTBCs). We find an upper bound of the data-rate of the row-monomial DOSTBC and construct the codes achieving this upper bound. In the second work, we first study the general DOSTBCs and derive an upper bound of the data-rate of the DOSTBC. Secondly, we propose the row-monomial DOSTBCs with channel phase information (DOSTBCs-CPI) and derive an upper bound of the data-rate of those codes. Furthermore, we find the actual row-monomial DOSTBCs-CPI which achieve the upper bound of the data-rate. In the third and fourth works of this thesis, we focus on error performance analysis of single-symbol ML decodable DSTBCs. Specifically, we study the distributed Alamouti's code in dissimilar cooperative networks. In the third work...

MULTI-USER MULTI-ANTENNA COOPERATIVE CELLULAR SYSTEMS

Zheng, YI
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
46.22%
To meet the very high data rate requirements for wireless Internet and multimedia services, cooperative systems with multiple antennas have been proposed for future generation wireless systems. In this thesis, we focus on multiple antennas at the source, relay and destination. We study both downlink and uplink cooperative systems with single antenna relays. For downlink systems, the optimal precoder to minimize the sum transmit power subject to quality of service (QoS) constraints with fixed relay weights is derived. We also study the optimization of relay weights with a fixed precoder. An iterative algorithm is developed to jointly optimize the precoder and relay weights. The performance of the downlink system with imperfect CSI as well as multiple receive antennas is also studied. For the uplink system, we similarly derive the optimum receiver as in the downlink with fixed relay weights. The optimization of relay weights for a fixed receiver is then studied. An iterative algorithm is developed to jointly optimize the receiver and relay weights in the uplink. Systems with imperfect channel estimation are also considered. The study of cooperative MIMO systems is then extended to a multi-cell scenario. In particular, two scenarios are studied. In the first...

Analogues of the Smale and Hirsch Theorems for Cooperative Boolean and Other Discrete Systems

Just, Winfried; Enciso, German A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.1%
Discrete dynamical systems defined on the state space {0,1,...,p-1}^n have been used in multiple applications, most recently for the modeling of gene and protein networks. In this paper we study to what extent well-known theorems by Smale and Hirsch, which form part of the theory of (continuous) monotone dynamical systems, generalize or fail to do so in the discrete case. We show that that arbitrary m-dimensional systems cannot necessarily be embedded into n-dimensional cooperative systems for n=m+1, as in the Smale theorem for the continuous case, but we show that this is possible for n=m+2 as long as p is sufficiently large. We also prove that a natural discrete analogue of strong cooperativity implies nontrivial bounds on the lengths of periodic orbits and imposes a condition akin to Lyapunov stability on all attractors. Finally, we explore several natural candidates for definitions of irreducibility of a discrete system. While some of these notions imply the strong cooperativity of a given cooperative system and impose even tighter bounds on the lengths of periodic orbits than strong cooperativity alone, other plausible definitions allow the existence of exponentially long periodic orbits.; Comment: 22 pages New version with dedication to Avner Friedman

Attractors in coherent systems of differential equations

Angeli, David; Hirsch, Morris W.; Sontag, Eduardo D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/10/2007
Relevância na Pesquisa
46%
Attractors of cooperative dynamical systems are particularly simple; for example, a nontrivial periodic orbit cannot be an attractor. This paper provides characterizations of attractors for the wider class of coherent systems, defined by the property that no directed feedback loops are negative. Several new results for cooperative systems are obtained in the process.

On a Smale Theorem and Nonhomogeneous Equilibria in Cooperative Systems

Enciso, German A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/06/2007
Relevância na Pesquisa
56.12%
A standard result by Smale states that n dimensional strongly cooperative dynamical systems can have arbitrary dynamics when restricted to unordered invariant hyperspaces. In this paper this result is extended to the case when all solutions of the strongly cooperative system are bounded and converge towards one of only two equilibria outside of the hyperplane. An application is given in the context of strongly cooperative systems of reaction diffusion equations. It is shown that such a system can have a continuum of spatially inhomogeneous steady states, even when all solutions of the underlying reaction system converge to one of only three equilibria.; Comment: 12 pages

A simple proof of monotonicity for linear cooperative systems of ODEs

Mierczyński, Janusz
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/04/2013
Relevância na Pesquisa
46.04%
We present a simple proof of monotonicity for cooperative systems of linear ordinary differential equations, without having recourse to approximation by strongly cooperative systems.; Comment: 3 pages; contains a simple proof of a known fact; comments are welcome

A cooperative system which does not satisfy the limit set dichotomy

Sontag, Eduardo D.; Wang, Yuan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/05/2005
Relevância na Pesquisa
46.07%
The fundamental property of strongly monotone systems, and strongly cooperative systems in particular, is the limit set dichotomy due to Hirsch: if x(0) < y(0), then either omega(x) < omega(y), or omega(x) = omega(y) and both sets consist of equilibria. We provide here a counterexample showing that this property need not hold for (non-strongly) cooperative systems.

Floquet bundles for tridiagonal competitive-cooperative systems with Applications

Fang, Chun; Gyllenberg, Mats; Wang, Yi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/05/2012
Relevância na Pesquisa
46.04%
For a general time-dependent linear competitive-cooperative tridiagonal system of differential equations, we obtain canonical Floquet invariant bundles which are exponentially separated in the framework of skew-product flows. Such Floquet bundles naturally reduce to the standard Floquet space when the system is assumed to be time-periodic. The obtained Floquet theory is applied to study the dynamics on the hyperbolic omega-limit sets for the nonlinear competitive-cooperative tridiagonal systems in time-recurrent structures including almost periodicity and almost automorphy.; Comment: 30pages

Spreading speeds and traveling waves for non-cooperative integro-difference systems

Wang, Haiyan; Castillo-Chavez, Carlos
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.15%
The development of macroscopic descriptions for the joint dynamics and behavior of large heterogeneous ensembles subject to ecological forces like dispersal remains a central challenge for mathematicians and biological scientists alike. Over the past century, specific attention has been directed to the role played by dispersal in shaping plant communities, or on the dynamics of marine open-ocean and intertidal systems, or on biological invasions, or on the spread of disease, to name a few. Mathematicians and theoreticians, starting with the efforts of researchers that include Aronson, Fisher, Kolmogorov, Levin, Okubo, Skellam, Slobodkin, Weinberger and many others, set the foundation of a fertile area of research at the interface of ecology, mathematics, population biology and evolutionary biology. Integrodifference systems, the subject of this manuscript, arise naturally in the study of the spatial dispersal of organisms whose local population dynamics are prescribed by models with discrete generations. The brunt of the mathematical research has focused on the the study of existence traveling wave solutions and characterizations of the spreading speed particularly, in the context of cooperative systems. In this paper, we characterize the spreading speed for a large class of non cooperative systems...

Queue-Aware Distributive Resource Control for Delay-Sensitive Two-Hop MIMO Cooperative Systems

Wang, Rui; Lau, Vincent K. N.; Cui, Ying
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/10/2010
Relevância na Pesquisa
46.04%
In this paper, we consider a queue-aware distributive resource control algorithm for two-hop MIMO cooperative systems. We shall illustrate that relay buffering is an effective way to reduce the intrinsic half-duplex penalty in cooperative systems. The complex interactions of the queues at the source node and the relays are modeled as an average-cost infinite horizon Markov Decision Process (MDP). The traditional approach solving this MDP problem involves centralized control with huge complexity. To obtain a distributive and low complexity solution, we introduce a linear structure which approximates the value function of the associated Bellman equation by the sum of per-node value functions. We derive a distributive two-stage two-winner auction-based control policy which is a function of the local CSI and local QSI only. Furthermore, to estimate the best fit approximation parameter, we propose a distributive online stochastic learning algorithm using stochastic approximation theory. Finally, we establish technical conditions for almost-sure convergence and show that under heavy traffic, the proposed low complexity distributive control is global optimal.; Comment: 30 pages, 7 figures

Os sistemas cooperativistas brasileiro e alemão: aspectos comparativos; Brazilian and german cooperativism systems: comparative aspects

Wstphal, Vera Herweg
Fonte: Universidade de São Paulo. Faculdade de Economia, Administração e Contabilidade de RP Publicador: Universidade de São Paulo. Faculdade de Economia, Administração e Contabilidade de RP
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; ; ; ; Formato: application/pdf
Publicado em 01/12/2008 POR
Relevância na Pesquisa
46.09%
Este trabalho objetiva apresentar diferenças na constituição histórica dos sistemas cooperativistas, bem como comparar a legislação cooperativista, a organização interna e a organização dos sistemas cooperativistas alemão e brasileiro, destacando semelhanças e diferenças entre os mesmos. O estudo foi realizado por meio de pesquisa bibliográfica e análise de conteúdo de fontes documentais. Na Alemanha o cooperativismo surgiu pela organização de setores empobrecidos da população, enquanto auxílio mútuo para melhorar sua condição social e econômica. Atualmente, cerca de 95% do setor primário e 35% do setor financeiro organizam-se de forma cooperativada. No setor secundário o cooperativismo não tem fixação significativa. Já as cooperativas habitacionais e de consumo são expressivas e nos últimos anos, observa-se um crescimento de cooperativas na área de prestação de serviços. No Brasil, as primeiras cooperativas surgiram como forma de auxílio mútuo, mas é pós-1960 que há um crescimento massivo de cooperativas. Elas foram fomentadas pelo Estado, sobretudo na agricultura, consolidando o agronegócio. Nos últimos anos a quantidade de cooperativas ascende em setores como saúde, educação e serviços. Enquanto na Alemanha as cooperativas privilegiam a dimensão econômica e são organizadas de forma autônoma...

An Efficient Δ-Causal Distributed Algorithm for Synchronous Cooperative Systems in Unreliable Networks

Pomares Hernández,Saúl E.; López Domínguez,Eduardo; Rodríguez Gómez,Gustavo
Fonte: Centro de Investigación en computación, IPN Publicador: Centro de Investigación en computación, IPN
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2010 EN
Relevância na Pesquisa
66.16%
In cooperative systems causal ordering delivery has been used to resolve problems of coherency of type producer-consumer. Causal order delivery is important for distributed systems since it allows an asynchronous execution to participants. When time delivery constraints are considered, ensuring causal delivery becomes more complex, as is the case for synchronous cooperative systems, such as Telemedicine and Teleimmersion. In these systems, the messages (units of data of continuous and discrete media) have an associated lifetime that determines the period of useful time in which the messages must be delivered. On the other hand, generally in these systems there is no time for retransmit them when messages are lost. Causal order with time constraints has previously been addressed, and it is called Δ-causal order. In this paper, we present an efficient Δ-causal distributed algorithm for unreliable networks that is characterized by the use of a forward error correction (FEC) scheme and a distributed method to calculate the message lifetime based on relative time points (i.e. no global time is used). We show the efficiency of our Δ-causal algorithm in terms of the control information attached per message.