IB-DFE receiver techniques for CP-assisted block transmission within DS-CDMA and MC-CDMA systems

MC-CDMA (MultiCarrier Code Division Multiple Access), currently regarded as a promissing multiple access scheme for broadband communications, is known to combine the advantages of an OFDM-based (Orthogonal Frequency Division Multiplexing), CP-assisted (Cyclic Prefix) block transmission with those of CDMA systems. Recently, it was recognised that DS-CDMA (Direct Sequence) implementations can also take advantage of the beneficts of the CP-assisted block transmission approach, therefore enabling an efficient use of FFT-based (Fast Fourier Transform), chip level FDE (Frequency- Domain Equalisation) techniques. In this paper we consider the use of IB-DFE (Iterative Block Decision Feedback Equalisation) FDE techniques within both CP-assisted MC-CDMA systems with frequency-domain spreading and DS-CDMA systems. Our simulation results show that an IB-DFE receiver with moderate complexity is suitable in both cases, with excellent performances that can be close to the single-code matched filter bound (especially for the CP-assisted DSCDMA alternative), even with full code usage

IB-DFE receivers with space diversity for CP-assisted DS-CDMA and MC-CDMA systems

Multi-Carrier Code Division Multiple Access (MC-CDMA), currently regarded as a promising multiple access scheme for broadband communications, is known to combine the advantages of an Orthogonal Frequency Division Multiplexing (OFDM)-based, Cyclic Prefix (CP)-assisted block transmission with those of CDMA systems. Recently, it was recognised that DS-CDMA (Direct Sequence) implementations can also take advantage of the benefits of the CP-assisted block transmission approach, therefore enabling an efficient use of Fast Fourier Transform (FFT)-based, chip level Frequency-Domain Equalisation (FDE) techniques. When employing a linear FDE with both MC-CDMA and DS-CDMA, the FDE coefficients can be optimised under the Minimum Mean Squared Error (MMSE) criterion, so as to avoid significant noise enhancement. The residual interference levels can be very high, especially for fully loaded scenarios, since the FDE/MMSE does not perform a perfect channel inversion. This paper deals with CP-assisted DS-CDMA systems and MC-CDMA systems with frequency-domain spreading. We consider the use of Iterative Block Decision Feedback Equalisation (IB-DFE) FDE techniques as an alternative to conventional, linear FDE techniques, and derive the appropriate IB-DFE parameters in a receiver diversity context. Our performance results show that IB-DFE techniques with moderate complexity allow significant performance gains in both systems, with bit error rate (BER) that can be close to the single-code matched filter bound (MFB) (especially for the CP-assisted DS-CDMA alternative), even with full code usage. Copyright © 2007 John Wiley & Sons. Ltd

An iterative frequency-domain decision-feedback receiver for MC-CDMA schemes

The MC-CDMA techniques (multicarrier code division multiple access) combine a CDMA scheme with OFDM modulation (orthogonal frequency division multiplexing), so as to allow high transmission rates over severely time-dispersive channels without the need of a complex receiver implementation. We propose an iterative frequency-domain decision-feedback receiver for MC-CDMA signals. The proposed receiver has excellent performance, close to the single-code MFB (matched filter bound), even for severe time-dispersive scenarios and/or in the presence of strong interfering channels

A reduced-CP approach to SC/FDE block transmission for broadband wireless communications

For conventional cyclic prefix (CP)-assisted single-carrier/frequency-domain equalization (SC/FDE) implementations, as well as for orthogonal frequency-division multiplexing (OFDM) implementations, the CP length is known to be selected on the basis of the expected maximum delay spread. Next, the data block size can be chosen to be large enough to minimize the CP overhead, yet small enough to make the channel variation over the block negligible. This paper considers the possibility of reducing the overall CP assistance, when transmitting sequences of SC blocks, while avoiding an excessively long fast Fourier transform window for FDE purposes and keeping good FDE performances through low-complexity, noniterative receiver techniques. These techniques, which take advantage of specially designed frame structures, rely on a basic algorithm for decision-directed correction (DDC) of the FDE inputs when the CP is not long enough to cope with the time-dispersive channel effects. More specifically, we present and evaluate a novel class of reduced-CP SC/FDE schemes, which takes advantage of a special frame structure for replacing "useless" CP redundancy by fully useful channel coding redundancy, with the help of the DDC algorithm. When using the DDC-FDE technique with these especially designed frame structures, the impact of previous decisions, which are not error-free, is shown to be rather small, thereby allowing a power-efficiency advantage (in addition to the obvious bandwidth-efficiency advantage) over conventional block transmission implementations under full-length CP. Additionally, the DDC algorithm is also shown to be useful to improve the power efficiency of these conventional implementations.Fundação para a Ciencia e Tecnologia (FCT), Centro de Análise e processamento de Sinais (CAPS

A turbo FDE technique for reduced-CP SC-based block transmission systems

For conventional cyclic-prefix (CP)-assisted block transmission systems, the CP length is selected on the basis of the expected maximum delay spread. With regard to single-carrier (SC)-based block transmission implementations, a full-length CP is recommendable, since it allows good performances through the use of simple frequency-domain equalization (FDE) techniques. In this letter, a soft-decision-directed correction (SDDC)-aided turbo FDE technique is presented for reduced-CP SC-based block transmission systems using conventional frame structures. The relations with some already known iterative FDE techniques are established, and a set of performance results is reported and discussed. The advantages of the proposed approach are emphasized, namely, the possibility of approximately achieving (besides the obvious bandwidth efficiency gain) the maximum power efficiency gain that a strong CP reduction allows.Fundação para a Ciencia e Tecnologia (FCT), Centro de Análise e processamento de Sinais (CAPS

Rapid identification of Aspergillus fumigatus within the section Fumigati

<p>Abstract</p> <p>Background</p> <p>New fungal species that are morphologically similar to <it>Aspergillus fumigatus </it>were recently described and included in section <it>Fumigati</it>. Misidentification of such fungal species, particularly of the human pathogens, <it>Aspergillus lentulus</it>, <it>Neosartorya fischeri</it>, <it>Neosartorya hiratsukae</it>, <it>Neosartorya pseudofischeri </it>and <it>Neosartorya udagawae</it>, has been increasingly reported by numerous clinical labs. Nevertheless, <it>A. fumigatus </it>still accounts for more than 90% of all invasive aspergillosis cases. The purpose of the present study was to develop a rapid method for the molecular identification of <it>A. fumigatus </it>to distinguish it from other species within the section <it>Fumigati</it>.</p> <p>Results</p> <p>A multiplex PCR was developed using prior information based on β-tubulin (βtub) and rodlet A (rodA) partial gene sequences. PCR amplification of βtub and rodA fragments resulted in a distinctive electrophoretic pattern in <it>A. fumigatus </it>and <it>N. udagawae</it>. The polymorphisms found in the smallest amplified sequence of βtub (153 bp) and rodA (103 bp) genes were then compared among and within species of this taxonomic section. βtub was able to differentiate among 13 individual species and two groups of species that included the pathogenic fungus <it>A. lentulus</it>. A more limited number of sequences were available for rodA; nevertheless, we were able to distinguish <it>Aspergillus viridinutans, N. hiratsukae </it>and <it>N. udagawae</it>.</p> <p>Conclusions</p> <p>The assay described in the present study proved to be specific and highly reproducible, representing a fast and economic way of targeting molecular identification of the relevant mould, <it>A. fumigatus</it>, in clinical laboratories.</p

Estudo experimental da limitação de contaminantes através de jatos planos combinados com exaustão de ar

Com o objetivo de melhorar a qualidade de ar no interior dos espaços, cada vez mais se recorre à utilização de cortinas de ar, que consistem num dispositivo mecânico que gera um jato de ar no plano da porta, funcionando com uma barreira aerodinâmica capaz de minimizar as trocas de energia e massa entre dois espaços contíguos. Neste trabalho apresenta-se o estudo experimental sobre a aplicação de cortinas de ar de jato plano vertical e descendente com o objetivo de assegurar a estanquidade a contaminantes (neste caso, fumo). Para o efeito, foram realizados ensaios em regime isotérmico, à escala real, em que a cortina de ar está situada entre duas zonas diferentes, uma limpa e outra contaminada. Foram testados e avaliados diferentes parâmetros geométricos e dinâmicos, tais como a velocidade, espessura e ângulo no bocal do jato, associados a um caudal mínimo de exaustão no interior do compartimento contaminado, capaz de assegurar a estanquidade da cortina de ar, na tentativa de encontrar uma relação entre a velocidade média de admissão de ar na porta e a velocidade do jato. Através dos resultados experimentais obtidos demonstrou-se que, quando corretamente implementadas, as cortinas de ar proporcionam uma vedação aerodinâmica adequada para baixos números de Reynolds do jato plano de ar. Foi, ainda, obtida uma expressão que relaciona os parâmetros do jato (velocidade, espessura e ângulo do bocal) com a velocidade média de admissão na porta

New sequence variants detected at DXS10148, DXS10074 and DXS10134 loci

A great amount of population and forensic genetic data are available for X-STRs supporting the need for having a common and accurate nomenclature among laboratories allowing for better communication, data exchange, and data comparison. DXS10148, DXS10074 and DXS10134 are commonly used X-STRs particularly due to their inclusion in the commercial kit Investigator Argus X-12 (Qiagen). Samples from West Africa and Iraq were sequenced for all three X-STRs allowing the detection of new DNA sequence variants. At DXS10148, variation was detected at four bases downstream from the flanking region from the repeat motif. The sequence AAGG-AAAG has been detected for the first time as a varying (AAGGAAAG)1–3 motif, in the present work. One additional string when compared to the common one (AAGGAAAG)2 adds eight bases to the fragment size of the tetranucleotide STR. This means that 2 repeats are added in these cases to the fragment size of the allele, while the presence of only one copy will reduce the expected allele size by 2 repeats. At DXS10074 two varying stretches consisting of AC and AG dinucleotide repeats were observed in the upstream flanking region, six bases from the main repeat core that also influence the expected allele size. DXS10134 revealed a simpler nomenclature in the Guinea-Bissau sample set when compared to the previously described allele nomenclature. This detected new hidden variation also has impact on the actual allele nomenclature at this locus as it contributes to a new class of short alleles so far undetected in other studies.info:eu-repo/semantics/publishedVersio

Differentiation of candida albicans strains by microsatellite multiplex PCR genotyping

Resumo da comunicação apresentado na conferência Candida and Candidiasis realizada em Março de 2004 em Austin, Texas EUA