As redes metropolitanas comunitárias desempenham um papel de relevância crescente na sociedade actual, onde a informação e o conhecimento são factores chave nos processos produtivos e de inovação, essenciais ao desenvolvimento económico e social. Entendemos por redes metropolitanas comunitárias as infra estruturas de comunicação que abrangendo uma área geográfica de alguns quilómetros quadrados, cobrindo toda ou parte de uma cidade ou região, são detidas e operadas por determinadas comunidades ou entidades em sua representação, tendo em vista a prestação de serviços de interesse geral a essas mesmas comunidades.Para possibilitar a existência de serviços on line de ensino (eLearning), de investigação (eScience), de saúde (eHealth) e de governação (eGovernment), bem como o funcionamento de comunidades virtuais e o desenvolvimento de serviços emergentes, as infra estruturas de comunicação de elevada capacidade, disponibilidade e desempenho são essenciais. As administrações locais são cada vez mais chamadas a intervir, quer pela opinião da própria comunidade, quer por recomendações de instituições supranacionais como a União Europeia, no sentido de criarem e operarem redes metropolitanas que aliem as características supracitadas ao baixo custo das comunicações. Têm surgido nos últimos anos várias iniciativas de criação de infra estruturas metropolitanas de fibra óptica tanto na Europa como no Canadá, Austrália e Estados Unidos.Neste trabalho analisam se e descrevem se as opções tecnológicas mais relevantes para utilização no âmbito da implantação de redes metropolitanas, abordando as suas características e vantagens e desvantagens sob variados pontos de vista, com o objectivo de apresentar uma proposta para a criação de uma infra estrutura de comunicações de elevada capacidade na cidade do Porto.Chegámos a uma solução concreta, incluindo não só as componentes passiva e activa da rede, como também uma visão sobre a forma como os diferentes serviços poderão ser oferecidos e um modelo de operação adequado ao cenário concreto da cidade. A solução apresentada baseia se na oferta de serviços do tipo VPLS (Virtual Private LAN Services), e é suportada por uma infra estrutura de comutação IP com MPLS (Multiprotocol Label Switching).Este trabalho, bem como as conclusões que apresentamos, podem dar um contributo relevante para apoiar as decisões a tomar ao nível do sub projecto Infra estrutura Física, do projecto Porto Digital, que faz parte do Projecto Nacional das Cidades e Regiões Digitais, e que a Universidade do Porto coordena. / Community operated Metropolitan Area Networks play an increasingly important role in today's society; information and knowledge are key elements of the production and innovation processes, as part of economic and social development.We define community operated metropolitan area networks as those communication infrastructures which span a geographical area of a few square kilometres and extend over all or part of a town or region. Owned and operated by a specific community or an entity that represents it, they aim to offer a set of services of common interest to those communities.In order to enable online services such as eLearning, eSience, eHealth and eGovernment, as well as to promote the establishment of virtual communities and the development of emerging services, communication infrastructures which provide high capacity, availability and performance are essential.Local governments are increasingly encouraged to intervene, both by public opinion and supranational entities such as the European Union. They are expected to deploy and operate metropolitan area networks with the abovementioned characteristics, providing citizens with low-cost communication facilities. Several such fibre optic infrastructures have been implemented in the last few years, not only in Europe but also in Canada, Australia and the United States.This essay analyzes and describes the most relevant technological options concerning the deployment of metropolitan networks; It focuses on their characteristics, advantages and disadvantages in order to present a proposition for the creation of a high-capacity communication infrastructure in the city of Porto.An actual solution has been reached, comprising not only the passive and active components of the network, but also a general approach to the way the different services may be provided, as well as an operational model fitting the specific requirements of the city. This solution is based on the Virtual Private LAN Services Model, implemented over a Multiprotocol Label Switching enabled IP backbone.This work, as well as its conclusions, may be a relevant contribution to the decision making process concerning the subproject "Infra-estrutura Física" (physical infrastructure) coordinated by the University of Porto and which is part of the project "Porto Digital", included in the national initiative "Cidades e Regiões Digitais".

Multiprocessor architectures

Thesis--PlanB (M.S.)--University of Wisconsin--Stout, 2001. / Includes bibliographical references.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3694. Adviser: Mark A. Hasegawa-Johnson. Includes bibliographical references (leaves 167-173) Available on microfilm from Pro Quest Information and Learning.

<p> Space-time convolutional code (STCC) is a technique that combines transmit diversity and coding to improve reliability in wireless fading channels. In this proposal, we demonstrate a systematic design of multi-level quadrature amplitude modulation (M-QAM) STCCs utilizing quadrature phase shift keying (QPSK) STCC as component codes for any number of transmit antennas. Morever, a low complexity decoding algorithm is introduced, where the decoding complexity increases linearly by the number of transmit antennas. The approach is based on utilizing a group interference cancellation technique also known as combined array processing (CAP) technique. </p><p> Finally, our research topic will explore: with the current approach, a scalable STTC with better performance as compared to space- time block code (STBC) combined with multiple trellis coded modulation (MTCM) also known as STBC-MTCM; the design of low complexity decoder for STTC; the combination of our approach with multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM).</p>

Ever evolving wireless communication standards, reduced time-to-market and a need for flexibility and interoperability of multiple wireless communication technologies on a single device are the driving factors behind implementation of wireless standards on Software Defined Radios (SDR) platforms. The concept behind SDR is to implement as much functionality on software as possible. SDR provide greater interoperability and programmability compared with traditional hardwired implementation at the cost of higher power consumption and market cost. SDR is the driving technology for the next generation of co-operative and cognitive radios. For implementing an SDR, the existing wireless communication algorithms needs to be modified and an appropriate hardware platform needs to be selected. The IEEE 802.15.4 LR-WPAN standard requires low cost and low-power consuming devices. The data rate requirements are also low (such as 250 kbps). Traditionally, the devices compliant with the standard are hardwired system-on-chip implementation which provides benefit in terms of power and cost. Recently, there has been significant effort on modeling the IEEE 802.15.4 SDR systems which provide greater interoperability and programmability of the devices. In this study, Transport Triggered Architecture (TTA) based Application Specific Processor is selected for SDR implementation of the IEEE 802.15.4 2.4 GHz physical layer for studying the performance of such system in terms of Bit-Error-Rate, CPU cycle count, and processor chip area. As part of this work, different SDR frameworks like GNU Radio, Matlab-Simulink etc. were evaluated for their feasibility of providing an agile platform for the development. These existing frameworks need an operating system for their execution and are not suitable for stand-alone systems such as a TTA based processor. The work also includes the study of different receiver algorithms and design choices for the transceiver implementation. Based on existing literature and Matlab modeling, Asynchronous Zero-Crossing Detector (AZCD) based non-coherent receiver algorithm is selected for the implementation. The algorithm provides the required BER performance with very less complex computation and is suited for low power and low chip area implementations. The transmitter and receiver are implemented on single-core TTA processors which provide the required performance in terms of BER and data throughput. The processors designed need a very low silicon area and clock frequency for their realization.

Since the integration of data services into cellular communications, cellular operators are struggling to harness the overwhelming data traffic on their networks. Underlay Device-to-Device (D2D) communication is a new and promising paradigm which allows proximate mobile users to have direct communication over the cellular spectrum that may be reused by other cellular users in the same cell. This new paradigm is proposed to assist the cellular operators to deal with the booming demand of mobile users. Recent studies have shown that underlay D2D communication significantly increases the cellular network capacity, and enables cellular operators to support rich multimedia services. However, reusing cellular resources for both D2D and cellular communication introduces interference issues. In such systems, interference management is of utmost importance because improper interference coordination may lead to a self-destructive network. Power control and beamforming appears to be viable techniques for interference management which can also be used to enhance the energy efficiency of the system. Network coordinated sum power optimization schemes for D2D communications underlaying uplink and downlink cellular spectrum is considered in this thesis. In particular, the system optimization target is to minimize the sum transmission power while guaranteeing the user specific rate constraints. Novel algorithms are proposed to solve the power minimization problem optimally. For the uplink, the problem is solved using joint transmit power control and receive beamforming algorithm. The downlink problem is reformulated as a second-order cone program (SOCP), and thus, it can be solved efficiently via standard SOCP solvers. Moreover, a decentralized algorithm is proposed that reduces the amount of control information exchange in comparison to the centralized approach. The performance of the proposed algorithms is compared with the conventional cellular scheme. Simulation results demonstrate that the proposed underlay D2D communication approach is capable of achieving significant performance gains over the conventional cellular scheme. Results also illustrate that the power consumption of the system is highly affected by the location of the interfering cellular user and whether the resources are shared in uplink or downlink. Therefore, four different resource sharing areas are defined for D2D communications. These areas specify the type of resources (i.e., downlink and uplink) suitable for D2D communication.

In the uplink channel of the 3GPP long term evolution (LTE) and LTE-Advanced (LTE-A) systems, signal carrier frequency-division multiplexing access (SC-FDMA) transmission scheme is employed instead of orthogonal frequency-division multiplexing (OFDM) to reduce the peak-to-average power ratio (PAPR). However, compared to OFDM, SC-FDMA has lower channel throughput, since it suffers from inter-symbol interference (ISI). Multi-rate equalizer (MRE) is a novel low complexity and non-linear equalizer which can increase the channel throughput. The basic idea of the MRE is that it first decomposes the single ISI channel into two parallel sub-channels by employing multi-rate signal processing and successive interference cancellation (SIC). Then, this decomposition procedure can be executed recursively to further increase the number of sub-channels. The ISI decreases as the number of sub-channels increases. Meanwhile, since the MRE does not require pre-coding, it does not increase PAPR. The practical implementation of the MRE is not straightforward. An algorithm, which can recursively call each function block in the MRE and execute the entire decomposition processes is required. In this thesis, an algorithm is developed based on the construction pattern of the MRE to enable its realization. An LTE standard-compliant turbo code is simulated to evaluate the practical performance gains of the MRE concept. MATLAB is selected as the simulation environment. According to the simulation results, the channel throughput can be increased by employing the MRE together with LTE turbo code indeed. One time-invariant and one time-varying channel model are employed. Three kinds of MRE with binary modulation are considered. Those are the MRE with two, four and eight sub-channels. The increase in throughput is at least 25% and can reach 80% in highly frequency selective scenarios.

Emergence of dramatic increase in applications provided by smart devices, such as smart phones, is no longer supported by traditional telecommunications systems such as wireless cellular systems. Arising challenges are ever increasing traffic demand, shortage of available spectrum and congestion over wireless systems. On the other hand, network resources such as spectrum and computational capability, are severely under-utilized. With regard to efficient use the available resources, promising trend is to develop heterogeneous networks (HetNets) such that different operators can share their excess capacities among themselves with the previous agreement. The most research done in spectrum sharing is focused only on the network access point. In this thesis work we extend the modelling of the spectrum sharing problem to include all links on the route for a given session. While this problem might have been analyzed from the point of view of route availability our control system is focused on queue management across the network that maintains predetermined spectra sharing rules at the session level of each operator. Addressing an issue of congestion over wireless system different congestion control mechanisms are presented and analyzed enabling a variety of options for managing traffic across the spectra sharing network. These models are generalized to include different pricing mechanisms. Two approaches are taken for analyzing pricing models with congestion control mechanism. First, network nodes are modeled as two-dimensional Markov processes. Since memoryless nature of Markov process imposes restrictions on analyzed system, in order to generalize analysis, averaged non-Markov models are introduced. Performance metric used for assessing different models is average packet dropping rate.

This thesis investigates the power allocation scheme and essential design constraints to be considered in multicarrier systems particularly in the case of orthogonal frequency division multiple access (OFDMA) system in multiuser (MU) scenario. The compatibility between multicarrier system and multiple input multiple output (MIMO) system is exploited in designing the power allocation algorithm for a cellular network with multiusers. The multicarrier MIMO system facilitates dynamic resource allocation due to the decomposition of physical resources into multiple domains. The energy efficiency and interference management are the crucial aspects especially in uplink (UL) transmission. Limiting the power consumption of mobile terminals (MT) in uplink (UL) is inevitable due to the limited amount of available energy. Furthermore, the traditional multicarrier system introduces a dynamic peak power variation with respect to average power causing erroneous circuit behavior. This phenomenon is usually quantified as peak to average power ratio (PAPR). High PAPR drives the high power amplifier (HPA) into non-linear region to result in significant degradation in the system performance in terms of power efficiency. In this thesis an iterative power allocation algorithm is proposed to minimize the sum power and PAPR. This thesis presents the power allocation strategy such that the PAPR is controlled during the power allocation (minimization) stage in frequency domain. The optimal power allocation is achieved by joint optimization of transmit power and receive beamformers (TX-RX) using convex optimization technique. The original problem is not jointly convex with respect to TX-RX. Therefore an iterative algorithm is proposed to optimize TX and RX alternatingly such that by calculating TX for given fixed set of RX and vice versa until convergence. The statistical approach is adopted to reduce the PAPR by actually minimizing the signal power variance (SPV) due to the fact that the large number of independent and identically distributed complex OFDMA symbols tends to follow Gaussian probability density function characterized by certain mean and variance. The non-convex constraints in the formulation are transformed into convex form using the successive convex approximation (SCA) with required change of variable (COV). The algorithm guarantees to maintain the user-specific quality of service (QoS) defined by the rate constraint. Hence, equipped with the potentials of future generation technologies and using convex optimization as a tool, this thesis offers a sum power and PAPR minimization scheme for MU SIMO-OFDMA UL transmission.