Enhanced Receivers for OFDM signals with super-QAM constellations

Nowadays, there is a high demand for wireless communication systems with higher through- put. One popular technique widely used in current and developing wireless technologies is Orthogonal Frequency-Division Multiplexing (OFDM) due to its robustness against fre- quency selective fading and high spectral efficiency. To further extend OFDM capacity to meet the near future’s expected demanding needs, OFDM systems with very large Quadrature Amplitude Modulation (QAM) constellations, the so-called super-QAM, are being proposed. However, OFDM signals are prone to nonlinear distortion effects due to their high envelope fluctuations which reduces the system’s performance and this issue is aggravated by the increase in the size of the constellation. For the implementation of effective super-QAM OFDM systems, it is crucial to develop receivers that expect and mitigate the nonlinear distortion on the transmitted signal. In this work, nonlinear distortion on OFDM small QAM and super-QAM constellations signals is studied, along with distortion models and methods to estimate them solely from the transmitted signal, and application of Bussgang noise cancellation receivers and analysis of their performance over a wide range of scenarios.Nos dias de hoje, há uma grande necessidade de criar sistemas de telecomunicação com maior ritmo de dados. Uma técnica popular em tecnologias de telecomunicação atuais e em desenvolvimento é Ortogonal Frequency-Devision Multiplexing (OFDM) devido à sua robustez contra atenuação seletiva na frequência e alta eficiência espectral. Para aumentar ainda mais a capacidade do OFDM de forma a preparar para ritmos ainda mais altos que são expectáveis num futuro próximo, estão a ser propostos sistemas OFDM com enormes constelações de Quadrature Amplitude Modulation (QAM), o chamado super-QAM. O problema é que sinais OFDM são suscetíveis a efeitos de distorção não linear devido às altas flutuações de envolvente e que traz pior desempenho do sistema, sendo esse problema agravado pelo aumento do tamanho da constelação. Para a implementação de sistemas super-QAM OFDM eficazes é crucial desenvolver recetores que mitiguem a distorção não linear no sinal transmitido. Neste trabalho, estuda-se a distorção não linear em sinais OFDM de pequenas cons- telações QAM e super-QAM, modelos de distorção e métodos para estimá-los a partir do sinal transmitido, aplicação de recetores de cancelamento de ruído Bussgang e análise de seu desempenho em diversos cenários

The Mississippian Toca da Moura-Cabrela Basin (SW Ossa-Morena Zone, Portugal): sedimentation and palaeoenvironments

Introduction and Geological context The Iberian Massif is the most southwestern domain of European Variscides, displaying an internal organization that allows to identify several palaeogeographic zones, among which the Ossa-Morena Zone (OMZ) that is included in the hinterland domains of this Massif. The Carboniferous sedimentation in the hinterland is restricted to small basins, controlled by the tectonic setting. During early Mississippian, the transitional subduction-collision process seems to be responsible for the genesis of syn-orogenic basins in the OMZ, such as the Toca da Moura-Cabrela Basin (TMCB) along the southwest boundary of the OMZ. The TMCB is characterized by a volcano-sedimentary complex with a Late Tournaisian-Late Visean age, which is the object of this study. Sedimentation ages Samples from several sections of the TMCB were taken, processed for palynology and analysed under transmitted light microscopes. The observed organic particles were invariably dark grey to black, indicative of a very high thermal maturation. From the 4 oxidized samples, only 2 provided recognizable palynomorphs. The two samples derived from carbonate-bearing shale/siltstone outcrops in the northern part of the Cabrela sub-basin, thus far unstudied. One provided a fairly diversified late Tournaisian spore assemblage. The poor preservation frequently hampered the identification to species level, but several stratigraphically relevant taxa were observed. The other productive sample allowed only to determine a general Tournaisian-Visean age. Several thin sections were produced from the 3 samples taken for micropaleontological purposes, from the rare non-remobilized carbonates in the TMCB (interbedded in the turbidite succession). The occurrence of foraminifera, such as the rare Paraarchaediscus, Pojarkovella, Hemiarchaediscus? stilus together with widespread Uralodiscus spp. in this association indicates the subzone MFZ11B (mid Visean). Sedimentology and palaeoenvironments Along the edges of the Cabrela sub-basin, conglomerate beds outcrop at the bottom of succession. In the northern edge, the conglomerate lithoclasts derived from early Palaeozoic units of the OMZ, currently outcropping to the East and North (and partially to the South) of the basin. Clasts from the South Portuguese Zone are notably absent. In the southern edge, several carbonate clasts are present, frequently dolomitized. The remainder of the sedimentary rocks are dominated by grey to black shales interbedded with siltstones and fine sandstones (rarely coarser-grained), which are interpreted as low-density turbidite deposits. Locally the coarser-grained intervals are dominated by volcanic-derived clasts. Palaeocurrent study on turbidite deposits from TMCB indicates: (1) the dominance of palaeocurrents to the SW quadrant in the Cabrela sub-basin (northern part); (2) great dispersion in the northern domains of Toca da Moura sub-basin (central area), although with dominance to the western quadrant; and (3) transport to the N quadrant in the southern part. The palynofacies analysis showed varying amounts of organic particle types, with AOM and phytoclasts as dominants types – up to 73% and 89% respectively. Phytoclasts are in most instances black and opaque, of several sizes. Palynomorphs were present in all samples, but always subordinate, up to 11%. These were composed of essentially sporomorphs and extremely rare acritarchs. The TMCB samples plot in fields I, VI, VII and IX of the Tyson diagram, with a greater prevalence in fields corresponding to suboxic to anoxic settings (shelf to basin). Ichnology and ecological traits Bioturbation was found in simple tiering profiles in three of the studied sections, namely Corte Pereiro, Monte Novo and “Buraco”. In Corte Pereiro, the upper 9 m of the succession show thin-bedded turbidites composed mainly by Td-Te Bouma intervals, dominated by dark pelites with rare, cm-thick intercalations of fine-to-very fine sandstones and siltstones with convolute, oblique and parallel lamination, sole marks including flute casts and, occasionally, hypichnial bioturbation. Slumps are also visible at the outcrop-to-bedding scales. Bioturbational tiering is condensed and divided in post- and pre-depositional suites: horizontal, slightly curving, unlined, evenly-sized meniscate burrows (Taenidium satanassi), sub-horizontal to oblique winding, lined burrows (Palaeophycus isp.) and the millimetric sub-horizontal winding burrow with levees Helminthoidichnites isp. (post-depositional); rare wide spiral, single-whorled Spirodesmos archimedeus and the irregular burrow network Megagrapton irregulare graphoglyptids, besides bowl-shaped vertical burrows of Bergaueria isp. (pre-depositional). Both tiers are intersected by 3D tunnel branching systems (Chondrites isp.) extending downwards to the organic-rich shales and filled by pyrite. Diversity of behaviours in deep sea deposits reached a relative maximum by the Mississippian. This is not the case in the TMCB. Diluted turbidite events in a succession otherwise dominated by black shales, showing simple shallow tiers and low ichnodiversity, with the presence of opportunistic bioturbation events dominated by simple, mobile deposit-feeding strategies and the rare presence of pre-depositional graphoglyptid-bearing suites and the deeper activity of a non-vagile organism below the redox boundary, reveal a hostile, unstable, quickly oxygen-depleting environment with high sedimentation rates. Turbidites were responsible for the short-term colonization windows, episodically increasing in oxygen the bottom and interstitial waters of these organic-resourceful substrates, but where oxygen-depletion was faster than the bioturbation rate during the quiescent deposition. Moreover, the post-depositional suite is dominated by only three facies crossing, simple deposit-feeding ethologies in low ichnofabric indices, indicative of a low-energy slope environment and being closer to shelfal expressions of the Zoophycos Ichnofacies