This thesis consists of two parts addressing two different problems in fading channels. The first part deals with asynchronous cooperative relay communication. The assumption of nodes in a cooperative communication relay network operating in synchronous fashion is often unrealistic. In this work we consider two different models of asynchronous operation in cooperative-diversity networks experiencing slow fading and examine the corresponding Diversity-Multiplexing Tradeoffs (DMT). For both models, we propose protocols and distributed space-time codes that asymptotically achieve the transmit diversity bound on DMT for all multiplexing gains and for number of relays N ≥ 2. The distributed space-time codes for all the protocols considered are based on Cyclic Division Algebras (CDA). The second part of the work addresses the DMT analysis of diversity embedded codes for MIMO channels. Diversity embedded codes are high rate codes that are designed so that they have a high diversity code embedded within them. This allows a form of opportunistic communication depending on the channel conditions. The high diversity code ensures that at least a part of the information is received reliably, whereas the embedded high rate code allows additional information to be transferred if the channel is good. This can be thought of coding the data into two streams: high priority and low priority streams so that the high priority stream gets a better reliability than the lower priority stream. We show that superposition based diversity embedded codes in conjunction with naive single stream decoding is sub-optimal in terms of the DM tradeoff. We then construct explicit diversity embedded codes by the superposition of approximately universal space-time codes from CDAs. The relationship between broadcast channels and the diversity embedded setting is then utilized to provide some achievable Diversity Gain Region (DGR) for MIMO broadcast Channels.

L'environnement n'est pas un espace physique précis et stable. Sa géométrie est statique mais il est sans cesse inondé par différentes ambiances qui elles sont dynamiques. De plus sa réalité est modelée par le terrain mouvant de notre mémoire qui encode nos expériences, nos rencontres et autres complexes associations vécues à différents moments. Les ambiances olfactives plus particulièrement participent à la définition d'un espace urbain de plusieurs façons. Produites et modelées par l'environnement géographique, les conditions climatiques, les activités économiques et l'activité humaine, les odeurs appellent des repères spatio-temporels précis car se référant à des événements que l'on a personnellement vécus. Bref, les multiples flux odorants qui façonnent dans la ville un paysage olfactif mouvant sont autant de possibilités de restructurer le réel du citadin. Aussi pour permettre d'élaborer des moyens mettant en oeuvre les odeurs dans l'espace public, nous avons examiné dans quelle mesure les signaux olfactifs influencent notre perception de l'environnement en provoquant l'apparition de paysages temporels. / The smellscape participates in the definition of the environment in different ways. First, determined by the geographic environment, climate conditions, economic activities, and human activity, the reality of olfactory ambiances are also shaped by our memory. This is because odours are associated with precise spatiotemporal markers that refer to events that someone has personally experienced. Therefore, the multiple fluxes of odorants creating a mobile topography of smells in the city may become a strategic intervention tool in planning. And, with the goal of arriving at a representation of the temporal patterns provoked by odours, we have examined the influence of olfactory memory in urban space. / pour plus d'informations concernant l'auteure et sa recherche veuillez consulter le http://www.natalieb.ca

A new broadband beamformer composed of nested arrays (NAs), multi-dimensional (MD) filters, and multirate techniques is proposed for both linear and planar arrays. It is shown that this combination results in frequency-invariant response. For a given number of sensors, the advantage of using NAs is that the effective aperture for low temporal frequencies is larger than in the case of using uniform arrays. This leads to high spatial selectivity for low frequencies. For a given aperture size, the proposed beamformer can be implemented with significantly fewer sensors and less computation than uniform arrays with a slight deterioration in performance. Taking advantage of the Noble identity and polyphase structures, the proposed method can be efficiently implemented. Simulation results demonstrate the good performance of the proposed beamformer in terms of frequency-invariant response and computational requirements. The broadband beamformer requires a filter bank with a non-compatible set of sampling rates which is challenging to be designed. To address this issue, a filter bank design approach is presented. The approach is based on formulating the design problem as an optimization problem with a performance index which consists of a term depending on perfect reconstruction (PR) and a term depending on the magnitude specifications of the analysis filters. The design objectives are to achieve almost perfect reconstruction (PR) and have the analysis filters satisfying some prescribed frequency specifications. Several design examples are considered to show the satisfactory performance of the proposed method. A new blind multi-stage space-time equalizer (STE) is proposed which can separate narrowband sources from a mixed signal. Neither the direction of arrival (DOA) nor a training sequence is assumed to be available for the receiver. The beamformer and equalizer are jointly updated to combat both co-channel interference (CCI) and inter-symbol interference (ISI) effectively. Using subarray beamformers, the DOA, possibly time-varying, of the captured signal is estimated and tracked. The estimated DOA is used by the beamformer to provide strong CCI cancellation. In order to alleviate inter-stage error propagation significantly, a mean-square-error sorting algorithm is used which assigns detected sources to different stages according to the reconstruction error at different stages. Further, to speed up the convergence, a simple-yet-efficient DOA estimation algorithm is proposed which can provide good initial DOAs for the multi-stage STE. Simulation results illustrate the good performance of the proposed STE and show that it can effectively deal with changing DOAs and time variant channels. / Graduate / 0544 / imanmoaz@uvic.ca

Η χωροχρονική μπλοκ κωδικοποίηση (STBC) αποτελεί μία αποδοτική και ευρέως διαδεδομένη τεχνική διαφορετικότητας μετάδοσης για την αντιμετώπιση του φαινομένου της εξασθένησης στις ασύρματες επικοινωνίες. Χαρακτηριστικό παράδειγμα είναι ο ορθογώνιος κώδικας του σχήματος Alamouti, ο οποίος με δύο κεραίες μετάδοσης επιτυγχάνει τη μέγιστη χωρική διαφορετικότητα στο μέγιστο δυνατό ρυθμό μετάδοσης, για οποιονδήποτε (πραγματικό ή μιγαδικό) αστερισμό συμβόλων. Ωστόσο, το σχήμα Alamouti έχει σχεδιαστεί για συχνοτικά επίπεδα κανάλια. Στην παρούσα εργασία μελετούμε την εφαρμογή STBC σε κανάλια συχνοτικά επιλεκτικής εξασθένησης. Εστιάζουμε κυρίως στο συνδυασμό του σχήματος Alamouti με τεχνικές εξάλειψης της διασυμβολικής παρεμβολής, εξετάζοντας τα σχήματα OFDM-STBC, FDE-STBC και TR-STBC, που έχουν προταθεί στη βιβλιογραφία. Επιπρόσθετα των συμβατικών δεκτών, για τα δύο τελευταία σχήματα περιγράφουμε και προσαρμοστικούς δέκτες, οι οποίοι παρακολουθούν τις μεταβολές του καναλιού, χωρίς να απαιτούν την ακριβή εκτίμησή του. Η έρευνα πάνω στα προηγούμενα σχήματα οδήγησε σε ορισμένα αξιόλογα αποτελέσματα. Κατ’ αρχήν, αποδεικνύουμε ότι τα σχήματα FDE-STBC και TR-STBC είναι ισοδύναμα, μολονότι καθένα εφαρμόζει διαφορετική κωδικοποίηση στα μεταδιδόμενα δεδομένα. Επίσης, σχεδιάζουμε έναν νέο δέκτη για το σχήμα TR-STBC, τον οποίο αναπτύσσουμε και σε προσαρμοστική μορφή. Βασικό πλεονέκτημα του προτεινόμενου δέκτη είναι ότι εκμεταλλεύεται τους κυκλικούς πίνακες συνέλιξης για τη μείωση της πολυπλοκότητας αποκωδικοποίησης. Τέλος, η απόδοση κάθε σχήματος και δέκτη αξιολογείται σε διάφορες συνθήκες εξασθένησης μέσω προσομοιώσεων σε υπολογιστικό περιβάλλον. / Space-time block coding (STBC) is an effective and widely used transmit diversity technique to combat multipath fading in wireless communication systems. A prominent example of STBC is the orthogonal code of Alamouti scheme, which achieves full spatial diversity at full transmission rate for two transmit antennas and any (real or complex) signal constellation. However, Alamouti scheme has been designed only for frequency-flat channels. In this thesis we study the application of STBC in frequency-selective channels. We mainly focus on combining Alamouti scheme with techniques for mitigating intersymbol interference, by studying several schemes (OFDM-STBC, FDE-STBC and TR-STBC) that have been proposed in literature. In addition to the conventional receivers, for FDE-STBC and TR-STBC we describe adaptive receivers too, which have the ability of tracking channel variations, without requiring explicit channel estimation. Research made upon the above schemes has come to some remarkable results. First, we prove that TR-STBC and FDE-STBC are equivalent, although each one encodes differently the transmitted data. Then, we design a new receiver for TR-STBC, which exploits the circulant convolution matrices, in order to reduce decoding complexity and we, also, develop an adaptive structure for the proposed receiver. At last, we evaluate the performance of all the described schemes and receivers in different fading conditions, by using computer simulations.

This work concentrates on the application of diversity techniques and space time block coding for future high speed mobile wireless communications on multicarrier systems. At first, alternative multicarrier kernels robust for high speed doubly-selective fading channel are sought. They include the comparisons of discrete Fourier transform (DFT), fractional Fourier transform (FrFT) and wavelet transform (WT) multicarrier kernels. Different wavelet types, including the raised-cosine spectrum wavelets are implemented, evaluated and compared. From different wavelet families, orthogonal wavelets are isolated from detailed evaluations and comparisons as suitable for multicarrier applications. The three transforms are compared over a doubly-selective channel with the WT significantly outperforming all for high speed conditions up to 300 km/hr. Then, a new wavelet is constructed from an ideal filter approximation using established wavelet design algorithms to match any signal of interest; in this case under bandlimited criteria. The new wavelet showed better performance than other traditional orthogonal wavelets. To achieve MIMO communication, orthogonal space-time block coding, OSTBC, is evaluated next. First, the OSTBC is extended to assess the performance of the scheme over extended receiver diversity order. Again, with the extended diversity conditions, the OSTBC is implemented for a multicarrier system over a doubly-selective fading channel. The MIMO-OFDM systems (implemented using DFT and WT kernels) are evaluated for different operating frequencies, typical of LTE standard, with Doppler effects. It was found that, during high mobile speed, it is better to transmit OFDM signals using lower operating frequencies. The information theory for the 2-transmit antenna OSTBC does not support higher order implementation of multi-antenna systems, which is required for the future generation wireless communications systems. Instead of the OSTBC, the QO-STBC is usually deployed to support the design of higher order multi-antenna systems other than the 2-transmit antenna scheme. The performances of traditional QO-STBC methods are diminished by some off-diagonal (interference) terms such that the resulting system does not attain full diversity. Some methods for eliminating the interference terms have earlier been discussed. This work follows the construction of cyclic matrices with Hadamard matrix to derive QO-STBC codes construction which are N-times better than interference free QO-STBC, where N is the number of transmit antenna branches.

Fitting of parametric models to spatial and space-time point patterns has been a very active research area in the last few years. Concerning clustered patterns, the Cox point process is the model of choice. To avoid the computationally demanding maximum likelihood estimation or Bayesian inference, several estimation methods based on the moment properties of the processes in question were proposed in the literature. We give overview of the state-of-the-art moment estimation methods for stationary spatial Cox point processes and compare their performance in a simulation study. We also discuss generalization of such methods for inhomogeneous spatial point processes. In the core part of the thesis we focus on minimum contrast estimation for inhomogeneous space-time shot-noise Cox point processes and investigate the possibility to use projections to the spatial and temporal domain to estimate different parts of the model separately. We propose a step-wise estimation procedure based on projection processes and also a refined method which remedies the problem of possible cluster overlapping. We establish consistency and asymptotic normality of the estimators for both methods under the increasing window asymptotics and compare their performance on middle-sized observation windows by means of a simulation study....

L'étude des espaces-temps plats singuliers munis d'une surface de Cauchy polyédrale est motivée par leur rôle de model jouet de gravité quantique proposé par Deser, Jackiw et 'T Hooft. Cette thèse porte sur les paramétrisations de certaines classes d'espaces-temps plat singuliers : les espaces-temps plats avec particules massives et BTZ Cauchy-compacts maximaux. Deux paramétrisations sont proposées, l'une reposant sur une extension du théorème de Mess aux espaces-temps plats avec BTZ et la surface de Penner-Epstein, l'autre reposant sur une généralisation du théorème d'Alexandrov aux espaces-temps plats avec particules massives et BTZ. Ce travail propose également une amorce de cadre théorique permettant de considérer des espaces-temps singuliers plus généraux. / The study of singular flat spacetimes with polyhedral Cauchy-surfaces is motivated by the quantum gravity toy model role they play in the seminal work of Deser, Jackiw and 'T Hooft. This thesis study parametrisations of classes of singular flat spacetimes : Cauchy-compact maximal flat spacetimes with massive and BTZ-like singularities. Two parametrisations are constructed. The first is based on an extension of Mess theorem to flat spacetimes with BTZ and Penner-Epstein convex hull construction. The second is based on a generalisation of Alexandrov polyhedron theorem to radiant Cauchy-compact flat spacetimes with massive and BTZ-like singularities. This work also initiate a wider theoretical background that encompass singular spacetimes.

[pt] O objetivo do presente trabalho é discutir as propostas estéticas dos modernismos de Mário de Andrade e de Almada Negreiros como respostas específicas a uma experiência de crise civilizacional. Este entendimento do seu tempo como período de viragem histórica suscitou diferentes propostas baseadas em expectativas diversas de futuro. Esta abordagem parte do pressuposto de que a representação artística se apresenta de forma intimamente relacionada à percepção do espaço e sua relação com os corpos. O modernismo, como forma simbólica, está intimamente relacionado com uma alteração significativa da percepção espaço temporal. Entretanto, essa dialética entre movimento artístico (modernismo) e experiência de espaço (modernidade) produziu na crítica literária uma avaliação do modernismo como uma resposta cultural à experiência da modernidade. Essa leitura relaciona-se com uma visão da modernidade como uma linha contínua de avanços tecnológicos, sociais, econômicos, etc., que surgem em centros e se espalham em direção à periferia. A partir desta interpretação produziram-se conceitos como modernismo tardio, modernismo periférico ou atraso cultural. A análise se propõe a situar as doutrinas e práticas estéticas agrupadas sob o conceito de modernismo em relação a conjunturas internas de cada país e a conjunturas internacionais num complexo mapa de coordenadas geopolíticas. Para isso, a Tese se estrutura em quatro pilares fundamentais de sustentação: Modernos, modernidades e modernismos; Futurista?! Em busca de uma expressão moderna de nacionalidade; Modernismos em modernidades incipientes: a insuficiência de invenções características da segunda revolução industrial nas narrativas romanescas de Mário de Andrade e Almada Negreiros; Modernismos e Estados Novos: os projetos de transformação cultural na esfera política do Salazarismo e do Varguismo. A partir destes pontos, o trabalho se pretende a associar o modernismo, não como uma dinâmica que surgiu no centro e se espalhou pela periferia como aplicação de um discurso estrangeiro, mas antes como a constituição de uma problemática impulsionadora de questionamentos diversos nas instâncias de entrecruzamento da cultura, da política e da arte. / [en] Modernisms in incipient modernities: Mário de Andrade and Almada Negreiros. The objective of the present work is to discuss the modernist aesthetical proposals from Mário de Andrade and Almada Negreiros as specific responses to an experience of civilizational crisis. This understanding of the time as a period of historical shift produced different proposals based on diverse expectations of future. This approach is based on the prerogative that the artistic representation presents itself intimately related to the perception of space-time and its relations with the bodies. The modernism, as symbolic form, is intimately related to a significant change in space-time perception. However, the dialetic between artistic movement (modernism) and experience of space (modernity) produced in the literary critique an evaluation of modernism as a cultural response to the experience of modernity. This reading in related to a understanding of modernity as a continuous line of technological, social and economical advances that occurred in centers and spread to the peripheries. From this interpretation concept such as late modernism, peripheral modernism and cultural delay were produced. The present analysis intend to situate the doctrines and aesthetical practices grouped under the concept of modernism in relation to the internal conjunctures of each country and the international conjunctures in a complex map of geopolitical coordinates. Thereunto, the Thesis structure itself in four fundamental supporting pillars: Moderns, modernities and modernisms; Futurist?! Searching for a modern expression of nationality; Modernisms in incipient modernities: the insufficiency of characteristic inventions from the second industrial revolution in the prosaic narratives from Mário de Andrade and Almada Negreiros; Modernism and New States: the projects of cultural transformation in the political field of Salazarism and Varguism. From these topics the work intends to associate modernism, not with a dynamic that rise in the centers and spread to the peripheries as application of a foreign speech, but rather as the constitution of a problematic that produced e diverse investigations in the lathing among culture, politics and arts.

It is well known that multiple antennas at the transmitter and receiver are imperative for reliable and high data-rate communication over wireless channels. However, these systems essentially need multiple radio frequency (RF) chains owing to multiple antennas, and hence pose challenges for applications with limited form-factor. Antenna Selection (AS) techniques alleviate this problem by using only a subset of the total available antennas and hence require only a few RF chains compared to the number of antennas. These systems operate in a closed-loop scenario, where the information fed back from the receiver is used for the transmit antenna subset selection. In contrast to this, a novel open-loop technique known as spatial modulation (SM) was recently proposed that uses a single RF-chain at the transmitter and achieves a higher spectral efficiency compared to single-input and AS based systems. The work in the thesis mainly focuses on the following aspects of SM system: Study of Mutual Information in SM systems operating in open-loop and closed-loop scenarios: We study the achievable mutual information in the SM system operating with finite and Gaussian input alphabet, and compare the results with that of the SIMO and AS based systems. Reduced-complexity maximum-likelihood (ML) decoding algorithms for SM systems: We propose ML-optimal sphere decoders for SM systems with arbitrary number of transmit antennas. Furthermore, a reduced-complexity ML detector is also proposed whose computational complexity is lowest among the known existing detectors in the literature. Transmit diversity techniques for SM systems: The conventional SM system achieves a transmit diversity order of one. We propose a complex interleaved orthogonal design baaed SM scheme that achieves a transit diversity order of two, while offering symbol-by- symbol ML decodability. Transmit antenna subset selection algorithms for SM systems: The SM system is considered in the closed-loop scenario, where only a subset of the total number of transmit antennas is chosen based on the information fed back by the receiver. Specifically, the Euclidean distance and capacity optimized antenna selection algorithms are studied in comparison with the conventional AS based systems. SM system operating in dispersive channels: The SM system operating in a dispersive channel with the aid of zero-padding is studied. It is shown that the SM system achieves full receive-diversity and multipath-diversity with ML decoding, but offers a decoding complexity that is exponential in the number of multipaths. Furthermore, a reduced complexity linear receiver is proposed that achieves achieves full multipath as well as receive-diversity, while offering a decoding complexity order same as that of the SM system operating in a frequency-flat channel.

Submitted by Vasti Diniz (vastijpa@hotmail.com) on 2017-09-18T11:49:17Z No. of bitstreams: 1 arquivototal.pdf: 2571485 bytes, checksum: 176b4eb5f639864aaef387d41330b286 (MD5) / Made available in DSpace on 2017-09-18T11:49:17Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2571485 bytes, checksum: 176b4eb5f639864aaef387d41330b286 (MD5) Previous issue date: 2016-03-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / After the formulation of general relativity differential geometry has become an increasing important tool in theoretical physics. This is even more clear in the investigation of the so-called embedding space-time theories. In this work we focus our attention in the Cauchy problem. These have played a crucial role in our understanding of the mathematical struc­ture of general relativity and embedding theories. We investigate the similarities and diffe­rences between the two approaches. We also study an extension of the Campbell-Magaard theorem and give two examples of both formalisms. / A geometria diferencial passou a ser uma ferramenta fundamental na fisica com o surgi­mento da relatividade geral. Em particular, destacamos sua importância na investigado das chamadas teorias de imersdo do espaco-tempo. Neste trabalho analisamos dois grandes for­malismos fundamentados de forma direta ou indireta na teoria de imersões: o teorema de Campbell-Magaard e o problema de Cauchy para a relatividade geral. Tendo como princi­pal objetivo tracar um paralelo entre esses dois formalismos, estudamos, nesta dissertacdo, o problema de valor inicial (pvi) para a relatividade geral mostrando que alem de admitir a formulae-do de pvi, a mesma é bem posta. Ademais, aplicamos este formalismo para o caso de uma metrica do tipo Friedmann-Robertson-Walker em (3+1). Estudamos tambem o teorema de Campbell-Magaard e sua extensdo para o espaco-tempo de Einstein e aplicamos este teorema para uma metrica do tipo de Sitter em (2+1).