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

Faunas mamalógicas do sítio pós-orientalizante do Cabeço Redondo (Sobral da Adiça, Moura)

Resultados da análise dos restos faunísticos recuperados em 2011, na escavação arqueológica do sítio do Cabeço Redondo (Moura, Beja), cuja cronologia aponta para o século V a.C. A fauna mamalógica é constituída principalmente por espécies domésticas (Bos taurus, Ovis aries/Capra hircus e Sus cf. domesticus). A caça (Cervus elaphus, Lepus sp./Oryctolagus cuniculus e Sus cf. scrofa) surge com muito menor expressão. Os dados apontam para um sítio de características rurais, pelo menos em parte dedicado à exploração agropecuária dos férteis territórios em que se implanta.Results of the analysis of fauna remains recovered in 2011 during archaeological excavations at the Cabeço Redondo site (Moura, Beja), from the 5th century BC. Mamalogic fauna mainly consists of domestic species (Bos taurus, Ovis aries/Capra hircus and Sus cf. domesticus). Hunting species (Cervus elaphus, Lepus sp./Oryctolagus cuniculus and Sus cf. scrofa) are much less common. Data seem to point to a rural site dedicated - at least partially - to farming and cattle-raising on the fertile land around.Résultats de l’analyse des restes de faune récupérés en 2011, dans la fouille archéologique du site du Cabeço Redondo (Moura, Beja) dont la chronologie tend vers Vème siècle a. JC. La faune à mamelles est constituée principalement d’espèces domestiques (Bos taurus, Ovis aries/Capra hircus et Sus cf. domesticus). La chasse (Cervus elephus, Lepus sp. / Oryctolagus cuniculus et Sus cf. scrofa)apparaît de manière très faible. Les données montrent un site de caractéristiques rurales, tout du moins en partie dédié à l’exploitation agro-pécuniaire des territoires fertiles où elle s’implante

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

O Cabeço Redondo: um edifício da Idade do Ferro pós-orientalizante na herdade do Metum (Moura)

Tese de mestrado, Arqueologia, Universidade de Lisboa, Faculdade de Letras, 2013Esta dissertação analisa as evidências materiais e estratigráficas, registadas no Cabeço Redondo (Moura), obtidas através da recolha de artefactos descontextualizados após a destruição do sítio e da realização de uma escavação arqueológica. Os resultados confirmam a presença de uma ocupação rural e de um espaço edificado profundamente remodelado ao longo de várias fases construtivas. Os dados estratigráficos e a análise dos artefactos revelam uma cronologia do século V a.C., ao mesmo tempo que confirmam a presença de um edifício monumental e singular na margem esquerda do Baixo Guadiana, com paralelo nos existentes no Guadiana Médio. A análise efectuada revela, ainda, evidências de um regionalismo visível na margem esquerda do rio Ardila e, consequentemente, na margem esquerda do rio Guadiana.Abstract This dissertation analyses the material and stratigraphic evidences recorded on Cabeço Redondo (Moura), which result from decontextualized artifacts recovered after the destruction of the site and from archaeological excavations. The results confirm the presence of a rural occupation and an edified space profoundly remodeled along several constructive phases. The stratigraphic data and the analysis of the artifacts reveal a chronology which covers the whole 5th century B.C., and, at the same time, confirm the presence of a singular and monumental building on the left bank of the Low Guadiana, parallelizable with the ones existing on Medium Guadiana. This analysis also reveals evidences for a visible regionalism on the left bank of the Ardila river and, consequently, on the left bank of the Guadiana river

(Re)construção de Percursos Formativos ao Longo da Vida: O caso dos Cursos de Educação e Formação de Adultos (EFA)

Os Cursos de Educação e Formação de Adultos (adiante designados Cursos EFA), assumeme como uma das respostas formativas e de qualificação disponíveis no sistema de educação e dequalificação em Portugal. Desde a sua criação, até à data, ocorreram alterações várias, sob oponto de vista legal, metodológico e pedagógico. Procurou-se efectuar uma breve descrição daoferta EFA, apontando-se duas dimensões: (i) a sua génese e evolução; (ii) as especificidades doeu modelo de formação/ estrutura curricular, relacionando essas dimensões com a importância doprincípio de Aprendizagem ao Longo da Vida (ALV). Como palavras-chave destaque paraeducação e formação de adultos e aprendizagem ao longo da vida

Comportamento voltamétrico de perilenos bismides modificados em GCE e SPE

Uma das necessidades mais emergentes no planeta é a deteção e quantificação de diversos analitos prejudiciais aos seres vivos, presentes no meio ambiente, de uma forma rápida, com baixo custo e com elevada seletividade. Os screen printed electrodes (SPE) têm sido usados extensivamente como transdutores de sensores químicos para vários analitos importantes. A modificação da superfície dos SPEs com moléculas capazes de fazer o reconhecimento de diversos analitos traduz-se no aumento da seletividade do elétrodo, devido às interações entre as duas espécies [1]. Entre as técnicas de imobilização (covalente e não covalente) de moléculas na superfície dos SPE, destacamos a modificação não covalente, visto este ser um método rápido, com elevada reprodutibilidade, de baixo custo, e sem a necessidade de reações violentas para a superfície do sensor para formar a ligação covalente. A utilização de moléculas com estruturas capazes de formar ligações π com nanoestruturas de carbono [2] é uma vantagem, pois permite a adsorção de espécies que irão fazer o reconhecimento de analitos sem danificar a superfície da matriz principal mantendo assim as excelentes características das nanoestruras de carbono, como os nanotubos de carbono e as folhas de grafeno. (...

Electrochemical sensing using carboxylated multiwalled carbon nanotubes

Carbon nanotubes (CNTs) have demonstrated great advantages in electrochemistry. The application of CNTs most widely employed so far has been the construction of various detection devices, such as gas sensors, electrochemical detectors and biosensors [1]. The main advantage of their use is related to the increase of the electrodes surface area and of the electron transfer rates, improving sensors sensitivity. Besides, their sorption capability of different analytes can be used to improve sensors selectivity [2]. (...