Low-bit rate feedback strategies for iterative IA-precoded MIMO-OFDM-based systems

Interference alignment (IA) is a promising technique that allows high-capacity gains in interference channels, but which requires the knowledge of the channel state information (CSI) for all the system links. We design low-complexity and low-bit rate feedback strategies where a quantized version of some CSI parameters is fed back from the user terminal (UT) to the base station (BS), which shares it with the other BSs through a limited-capacity backhaul network. This information is then used by BSs to perform the overall IA design. With the proposed strategies, we only need to send part of the CSI information, and this can even be sent only once for a set of data blocks transmitted over time-varying channels. These strategies are applied to iterative MMSE-based IA techniques for the downlink of broadband wireless OFDM systems with limited feedback. A new robust iterative IA technique, where channel quantization errors are taken into account in IA design, is also proposed and evaluated. With our proposed strategies, we need a small number of quantization bits to transmit and share the CSI, when comparing with the techniques used in previous works, while allowing performance close to the one obtained with perfect channel knowledge

Phytotoxic metabolites produced by Botryosphaeriaceae involved in grapevine trunk diseases

Fungi belonging to the Botryosphaeriaceae family are well known as cosmopolitan pathogens, saprophytes and endophytes and occur on a wide range of hosts including grapevine. More recently, a new species of Lasiodiplodia was isolated from declining grapevines in Sardinia (Italy). This still undescribed species showed to produce in liquid culture several phytotoxic secondary metabolites. In this communication the chemical and biological characterization of these bioactive secondary metabolites is discussed together with their role in the pathogenesis process

Efficient Uniform Channel Quantization of Sparse CIR for Downlink OFDM Systems

Channel state information at the transmitter side is an important issue for wireless communications systems, namely when precoding techniques are employed. Recent works explored random vector quantization (RVQ) as a solution for limited feedback for multi-user systems equipped with multiple antennas. Despite of being a good option for narrowband channels, this method requires large complexity and is not efficient for sparse channels. To overcome these drawbacks we consider a strategy based on uniform quantization, denoted partial uniform quantization (P-UQ), where just part of channel frequency response is quantized. This allows an efficient feedback of channel frequency response from the receivers to the transmitter, by using a reduced number of quantization bits. The comparison between the proposed P-UQ-based method and RVQ performed in this paper leads to the conclusion that the most advantageous method for sparse channels is the P-UQ

Novel precoded relay-assisted algorithm for cellular systems

Cooperative schemes are promising solutions for cellular wireless systems to improve system fairness, extend coverage and increase capacity. The use of relays is of significant interest to allow radio access in situations where a direct path is not available or has poor quality. A data precoded relay-assisted scheme is proposed for a system cooperating with 2 relays, each equipped with either a single antenna or 2-antenna array. However, because of the half-duplex constraint at the relays, relaying-assisted transmission would require the use of a higher order constellation than in the case when a continuous link is available from the BS to the UT. This would imply a penalty in the power efficiency. The simple precoding scheme proposed exploits the relation between QPSK and 16-QAM, by alternately transmitting through the 2 relays, achieving full diversity, while significantly reducing power penalty. Analysis of the pairwise error probability of the proposed algorithm with a single antenna in each relay is derived and confirmed with numerical results. We show the performance improvements of the precoded scheme, relatively to equivalent distributed SFBC scheme employing 16-QAM, for several channel quality scenarios. Copyright © 2010 Sara Teodoro, et al.European project CODIVPortuguese project CADWINPortuguese project AGILEFC

Codificação distribuída em sistemas com diversidade cooperativa

Doutoramento em Engenharia ElectrotécnicaO presente trabalho propõe-se a divulgar as mais significativas técnicas de esquemas cooperativos, de forma a ultrapassar alguns dos problemas dos sistemas móveis sem fios da próxima geração, estendendo a área de cobertura destes sistemas, assim como a sua capacidade e fiabilidade. O estudo de diversos esquemas cooperativos é efetuado em termos de capacidade e de taxa de erros, fazendo variar o número de relays e de antenas em cada elemento do sistema. Diversos algoritmos com aplicação em sistemas cooperativos são desenvolvidos e propostos ao longo desta tese, como códigos espaço-frequência aplicados de forma distribuída nos relays, para sistemas baseados na tecnologia OFDM e sob diversos cenários próximos da realidade. Os sistemas cooperativos são particularmente úteis em situações em que o caminho direto entre dois terminais não está acessível ou tem uma fraca qualidade de transmissão. Tendo este aspeto em consideração, e pretendendo ter a máxima eficiência espetral e máxima diversidade, um algoritmo com precodificação é também proposto para múltiplos relays, cada um equipado com uma ou duas antenas. A formulação matemática associada aos algoritmos propostos é apresentada, assim como a derivação da probabilidade de erro teórica. O desempenho dos sistemas assistidos por relays usando os algoritmos propostos é comparado em relação a outros esquemas cooperativos equivalentes e a esquemas não-cooperativos, considerando cenários com diferentes qualidades de canal, daí advindo importantes conclusões em relação a estes sistemas.Cooperative schemes are promising solutions for cellular wireless networks aiming to improve system fairness, extend coverage and increase capacity. Measurements of these system performances are made in terms of BER and capacity for different configurations, by varying the number of relays and of antennas equipping each node. In this work we propose and evaluate distributed space-frequency codes applied to cooperative systems in a distributed way, with application in OFDM systems and considering realistic scenarios. Moreover, the use of relays is of significant interest to allow radio access in situations where a direct path is not available or has poor quality. Thus, a data precoded relay-assisted scheme is also proposed for a system cooperating with multiple relays, each equipped with either a single antenna or two-antenna array. Mathematical formulation of the proposed algorithms is derived as well as the pairwise error probability. We further present the performances of the proposed algorithms apllied in relay-assisted schemes, and compare them with equivalent cooperative and non-cooperative schemes, for several channel quality scenarios, through which important conclusions are achieved.FCT/FS

Análise do cortisol salivar livre em atletas fisiculturistas brasilienses

O estudo dos níveis do hormônio cortisol como preditor de estresse, vem ganhando interesse em aprofundar as investigações sobre o efeito do exercício no organismo e formas de controlar o efeitos adversos deste hormônio.O presente estudo teve como finalidade analisar os níveis de cortisol salivar, em atletas fisiculturistas brasilienses, antes de um treino resistido e após o mesmo treino, associando estas concentrações com os níveis de estresse fisiológico, verificar o consumo de suplementos alimentares por estes atletas e por quem foi indicado a suplementação. Foi realizado um estudo transversal quantitativo e qualitativo a partir da análise do Cortisol Salivar em fisiculturistas e o preenchimento de um questionário com perguntas fechadas. Foram avaliados 10 atletas de fisiculturismo, do sexo masculino com idade média de 29,6 anos ±3,027 anos, sendo que a maioria compete há 1,7 anos ±1,505 anos. Foram realizadas duas coletas de saliva, uma imediatamente antes do treino resistido (1° coleta) e outra imediatamente após a realização do mesmo treino (2° coleta). Após a coleta cada voluntário respondeu a um questionário a respeito do consumo de suplementos. Os dados foram tabulados no programa excel versão 2007 e no programa R onde foi feito o teste t-student (com 9 graus de liberdade) calculados a média, o teste de Shapiro-Wilk, a variância e o teste F. A análise do hormônio cortisol salivar livre no período pré-treino encontravase em média, dentro dos valores de referência (inferior a 19.7 nmol/l) e no pós-treino manteve-se dentro da referência para todos os atletas, contudo houve uma redução nos valores do pós-treino em 80% da amostra analisada. A análise dos dados demonstrou que 100% (n=10) dos atletas faziam uso de suplementos alimentares sendo o suplemento mais utilizados o whey protein, consumido por 100% (n=10) dos atletas, em segundo lugar o BCAA com 90% (n=9) e, em terceiro lugar, a glutamina com 70% (n =7). Quanto à indicação de uso dos suplementos, a maioria dos participantes relatou ter sido orientados a consumirem tais produtos por indicação de um nutricionista (40%; n=4), (30% n= 3) do professor da academia e com 30 % (n=3) tiveram indicações de outros profissionais. Conclui-se que a análise dos níveis médios do hormônio cortisol pré-treino foram maiores do que os níveis pós-treino sugerindo uma espécie de adaptação às situações agressivas impostas pelo exercício físico. Outros estudos devem ser realizados afim de que possíveis fatores confundidores possam ser analisados

Single and multiple antenna relay-assisted techniques for uplink and downlink OFDM systems

In this paper we propose and assess the performance of relay-assisted schemes designed for both the uplink and downlink OFDM based systems, using efficient distributed space-frequency block coding protocols. We consider the use of an antenna array at the base station and a single antenna at the user terminal. At the relay node we consider either single antenna or an antenna array. 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 optimal maximum ratio combining coefficients are derived for the proposed relay-assisted schemes. The performance of these cooperative schemes is evaluated under realistic scenarios, considering typical pedestrian scenarios based on WiMAX specifications and using channel convolutional turbo code. The proposed schemes are also compared against the non-cooperative OFDM based systems. +umerical results show that the availability of antenna arrays at the relays significantly improves the cooperative systems performance, which outperform the non-cooperative ones in most studied scenarios

New robust iterative minimum mean squared error-based interference alignment algorithm

Interference alignment (IA) is a promising technique for multiple input multiple output interference channels based systems, achieving the theoretical bound on degrees of freedom. However, these gains are reduced in the presence of imperfect channel state informa- tion (CSI), because of quantisation or channel estimation errors. In this Letter, the authors propose a new robust iterative IA minimum mean squared error-based algorithm, which includes these channel errors in the IA design. The results show that the proposed robust IA algorithm outperforms the known IA-MMSE algorithms, for low-to-moderate variance of CSI errors