Energy efficient OFDMA networks maintaining statistical QoS guarantees for delay-sensitive traffic

An energy-efficient design is proposed under specific statistical quality-of-service (QoS) guarantees for delay-sensitive traffic in the downlink orthogonal frequency-division multiple access (OFDMA) networks. This design is based on Wu’s effective capacity (EC) concept [1], which characterizes the maximum throughput of a system subject to statistical delay-QoS requirements at the data-link layer. In the particular context considered, our main contributions consist of quantifying the effective energy-efficiency (EEE)-versus-EC tradeoff and characterizing the delay sensitive traffic as a function of the QoS-exponent ?, which expresses the exponential decay rate of the delay-QoS violation probabilities. Upon exploiting the properties of fractional programming, the originally quasi-concave EEE optimization problem having a fractional form is transformed into a subtractive optimization problem by applying Dinkelbach’s method. As a result, an iterative inner-outer loop based resource allocation algorithm is conceived for efficiently solving the transformed EEE optimization problem. Our simulation results demonstrate that the proposed scheme converges within a few Dinkelbach iterations to the desired solution accuracy. Furthermore, the impact of the circuitry power, of the QoS-exponent and of the power amplifier inefficiency is characterized numerically. These results reveal that the optimally allocated power maximizing the EEE decays exponentially with respect to both the circuitry power and the QoS-exponent, whilst decaying linearly with respect to the power amplifier inefficiency

Comparison of multiple-input single-output single-user ultra-wideband systems with pre-distortion

This paper presents a performance analysis of a baseband multiple-input single-output ultra-wideband system over scenarios CM1 and CM3 of the IEEE 802.15.3a channel model, incorporating four different schemes of pre-distortion: time reversal, zero-forcing pre-equaliser, constrained least squares pre-equaliser, and minimum mean square error pre-equaliser. For the third case, a simple solution based on the steepest-descent (gradient) algorithm is adopted and compared with theoretical results. The channel estimations at the transmitter are assumed to be truncated and noisy. Results show that the constrained least squares algorithm has a good trade-off between intersymbol interference reduction and signal-to-noise ratio preservation, providing a performance comparable to the minimum mean square error method but with lower computational complexity. Copyright (C) 2011 John Wiley & Sons, Ltd.Brazilian agency National Council for Scientific Technological Development (CNPq)Brazilian agency National Council for Scientific Technological Development (CNPq) [303426/2009-8

Telemetria hidrometeorológica sobre linhas de alta-tensão

Pages: 322-33

Compatibilização das redes de telemetria hidrometeorológica do DAEE e DNAEE, na região do Rio Ribeira de Iguape (SP)

Pages: 447-45

Sistemas DS/CDMA Multitaxa com Detector Heurístico-Genético em Canais Multipercurso

Este trabalho analisa uma técnica de otimização combinatória baseada em algoritmo genético (GA) aplicada ao problema da detecção ao multiusuário (MuD) em sistemas DS/CDMA multitaxa por códigos múltiplos (MC) em canais com desvanecimento multipercurso. Resultados de desempenho via simulação ao Monte Carlo (MCS), em duas situações de carregamento multitaxa, indicaram convergência próxima ao limite do detector multiusuário ótimo (OMuD). A complexidade computacional do algoritmo genético, em termos do número de operações necessárias para se atingir a convergência, é encontrada e comparada à do OMuD, indicando um expressivo ganho em termos de compromisso complexidade-desempenho em relação ao ao receptor convencional (Rake)

Modelo populacional de Verhulst aplicado ao controle de potência distribuído DS/CDMA

Neste artigo, utiliza-se o modelo dinâmico contínuo de Verhulst, elaborado inicialmente para descrever o crescimento populacional de espécies biológicas com restrição de alimento e espaço físico, na síntese de um novo algoritmo de controle de potência distribuído (DPCA, Distributed Power Control Algorithm),aplicável em sistemas de múltiplo acesso por divisão de código (DS-CDMA, Direct Sequence-Code Division Multiple Access). Realiza-se a discretização da equação diferencial correspondente por meio do método de Euler de integração numérica (NIE, Numerical Integration Euler Method). São investigadas via simulações computacionais as propriedades do algoritmo recursivo assim obtido, como distância Euclidiana do vetor ótimo em regime, velocidade de convergência, erro quadrático médio normalizado (NSE, Mean Normalized Squared Error) na condição de regime, consumo médio de potência por usuário e complexidade de implementação. Os resultados são confrontados com resultados de simulações análogas para o algoritmo clássico de Foschini e Miljanic e o sigmoidal de Uykan e Koivo. Na presença de erros de estimação, o DPCA proposto apresentou menor discrepância em regime em relação ao vetor ótimo e maior velocidade de convergência. Adicionalmente, aplica-se a teoria dos Círculos de Gerschgorin (GC) na determinação de condições suficientes para que o problema de alocação de potência seja factível

Receptores Multiusuários DS/CDMA Baseados na Projeção de Sinais em Subespaços Vetoriais

Neste trabalho são analisados detectores multiusuários (MuD) cegos e grupo-cegos (Bld-MuD e SBld-MuD, respectivamente) do ponto de vista do compromisso desempenho versus complexidade; especificamente, são caracterizados os detectores cegos e grupo-cegos baseados na inversão direta de matriz de correlação (DMI), no erro médio quadrático mínimo (MMSE) e os SBld-MuD híbridos nas formas I e II propostos em (H.-MADSEN; WANG, 2002). Simulações Monte Carlo (MCS) foram realizadas tendo em vista comprovar os resultados analíticos de desempenho, evidenciando-se a superioridade de desempenho do detector SBld-MuD. A contribuição deste trabalho consiste na análise comparada da degradação de desempenho dos três detectores, considerando erros nas estimativas dos parâmetros fase de portadora e coeficientes de canal Rayleigh (módulo e fase). Resultados MCS indicaram a superioridade de desempenho do detector SBld-MuD híbrido I na presença de erros nas estimativas dos três parâmetros

Power Allocation based on Certain Equivalent Margin Applicable to Wireless Communication Systems Limited by Interference

This paper analyzes the method of power allocation for wireless communication networks, limited by multiple access interference under fading Rayleigh channels. The method takes into account the statistical variation of the desired and interfering signals power and optimally and dynamically allocates the power resources in the system. This allocation is made being taken into account the restrictions imposed by the outage probability for each receiver/transmitter pair. Based on the Perron-Frobenius eigenvalue and geometric programming (GP) theories, some interesting results were found for the optimization problem analyzed. A GP is a special type of optimization problem that can be transformed in a non-linear convex optimization problem simply by the change of variables, and then to be globally solved. Also, an iterative method for fast convergence was shown to find the optimally power allocation seeking to minimize the outage probability in the communication

Distributed power control algorithm for multiple access systems based on Verhulst model

In this paper the continuous Verhulst dynamic model is used to synthesize a new distributed power control algorithm (DPCA) for use in direct sequence code division multiple access (DS-CDMA) systems. The Verhulst model was initially designed to describe the population growth of biological species under food and physical space restrictions. The discretization of the corresponding differential equation is accomplished via the Euler numeric integration (ENI) method. Analytical convergence conditions for the proposed DPCA are also established. Several properties of the proposed recursive algorithm, such as Euclidean distance from optimum vector after convergence, convergence speed, normalized mean squared error (NSE), average power consumption per user, performance under dynamics channels, and implementation complexity aspects, are analyzed through simulations. The simulation results are compared with two other DPCAs: the classic algorithm derived by Foschini and Miljanic and the sigmoidal of Uykan and Koivo. Under estimated errors conditions, the proposed DPCA exhibits smaller discrepancy from the optimum power vector solution and better convergence (under fixed and adaptive convergence factor) than the classic and sigmoidal DPCAs. (C) 2010 Elsevier GmbH. All rights reserved

Constrained least square pre-distortion scheme for multiuser ultra-wideband

The study proposes a constrained least square (CLS) pre-distortion scheme for multiple-input single-output (MISO) multiple access ultra-wideband (UWB) systems. In such a scheme, a simple objective function is defined, which can be efficiently solved by a gradient-based algorithm. For the performance evaluation, scenarios CM1 and CM3 of the IEEE 802.15.3a channel model are considered. Results show that the CLS algorithm has a fast convergence and a good trade-off between intersymbol interference (ISI) and multiple access interference (MAI) reduction and signal-to-noise ratio (SNR) preservation, performing better than time-reversal (TR) pre-distortion