Code-Division Multiple-Access (CDMA) is one of the leading digital wireless communication methods currently employed throughout the world. Third generation (3G) and future wireless CDMA systems are required to provide services to a large number of users where each user sends data burst only occasionally. The preferred approach is packet based CDMA so that many users share the same physical channel simultaneously. In CDMA, each user is assigned a pseudo-random (PN) code sequence. PN codephase synchronization between received signals and a locally generated replica by the receiver is one of the fundamental requirements for successful implementation of any CDMA technique. The customary approach is to start each CDMA packet with a synchronization preamble which consists of PN code without data modulation. Packets with preambles impose overheads for communications in CDMA systems especially for short packets such as mouse-clicks or ATM packets of a few hundred bits. Thus, it becomes desirable to perform PN codephase synchronization using the information-bearing signal without a preamble. This work uses a segmented matched filter (SMF) which is capable of acquiring PN codephase in the presence of data modulation. Hence the preamble can be eliminated, reducing the system overhead. Filter segmentation is also shown to increase the tolerance to Doppler shift and local carrier frequency offset. <p>Computer simulations in MATLAB® were carried out to determine various performance measures of the acquisition system. Substantial improvement in probability of correct codephase detection in the presence of multiple-access interference and data modulation is obtained by accumulating matched filter samples over several code cycles prior to making the codephase decision. Correct detection probabilities exceeding 99% are indicated from simulations with 25 co-users and 10 kHz carrier frequency offset or Doppler shift by accumulating five or more PN code cycles, using maximum selection detection criterion. Analysis and simulation also shows that cyclic accumulation can improve packet throughput by 50% and by as much as 100% under conditions of high offered traffic and Doppler shift for both fixed capacity and infinite capacity systems.

Code-Division Multiple-Access (CDMA) is one of the leading digital wireless communication methods currently employed throughout the world. Third generation (3G) and future wireless CDMA systems are required to provide services to a large number of users where each user sends data burst only occasionally. The preferred approach is packet based CDMA so that many users share the same physical channel simultaneously. In CDMA, each user is assigned a pseudo-random (PN) code sequence. PN codephase synchronization between received signals and a locally generated replica by the receiver is one of the fundamental requirements for successful implementation of any CDMA technique. The customary approach is to start each CDMA packet with a synchronization preamble which consists of PN code without data modulation. Packets with preambles impose overheads for communications in CDMA systems especially for short packets such as mouse-clicks or ATM packets of a few hundred bits. Thus, it becomes desirable to perform PN codephase synchronization using the information-bearing signal without a preamble. This work uses a segmented matched filter (SMF) which is capable of acquiring PN codephase in the presence of data modulation. Hence the preamble can be eliminated, reducing the system overhead. Filter segmentation is also shown to increase the tolerance to Doppler shift and local carrier frequency offset. <p>Computer simulations in MATLAB® were carried out to determine various performance measures of the acquisition system. Substantial improvement in probability of correct codephase detection in the presence of multiple-access interference and data modulation is obtained by accumulating matched filter samples over several code cycles prior to making the codephase decision. Correct detection probabilities exceeding 99% are indicated from simulations with 25 co-users and 10 kHz carrier frequency offset or Doppler shift by accumulating five or more PN code cycles, using maximum selection detection criterion. Analysis and simulation also shows that cyclic accumulation can improve packet throughput by 50% and by as much as 100% under conditions of high offered traffic and Doppler shift for both fixed capacity and infinite capacity systems.

The goal of this thesis is to introduce new matched field processors (MFPs) for estimating the source location and the environmental parameters of a shallow water waveguide in which the source transmits either broadband or narrowband random signals.

The goal of this thesis is to introduce new matched field processors (MFPs) for estimating the source location and the environmental parameters of a shallow water waveguide in which the source transmits either broadband or narrowband random signals.

We can associate an incidence graph with any CNF formula. It's a bipartite graph, in which he first part corresponds to variables and the second one to clauses. We can define matched formulas and biclique satisfiable formulas, based on this incidence graph. Both of these classes share an interesting property: Given a formula F which is matched or biclique satisfiable, F remains satisfiable even after we switch polarity of any occurrence of any literal. Class of formulas with this property is called var-satisfiable. In this thesis, we consider a parameterized algorithm introduced by Stefan Szeider for deciding satisfiability of formulas with small deficiency. Here deficiency of a formula is defined as a difference between the number of clauses and the number of variables in the formula. We explain why this algorithm cannot be simply generalized for the case of biclique satisfiable formulas. Since the problem of determining whether a formula is biclique satisfiable is NP-complete, we introduce a heuristic, which tries to find some biclique cover in time O(n2 e), where n denotes the number of variables and e denotes the length of the input formula. We performed experiments testing this heuristic on random formulas. The results of these experiments suggest, that there is a phase transition in the behaviour of the heuristic....

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Nous nous intéressons à des problèmes de transmission entre diélectriques et métamatériaux, milieux présentant des propriétés électromagnétiques inhabituelles comme des caractéristiques effectives négatives à certaines fréquences. Par exemple, ces milieux peuvent être construits comme des assemblages périodiques de microstructures résonantes et dans ce cas la théorie de l'homogénéisation permet de justifier mathématiquement ces propriétés effectives. En régime harmonique et dans des géométries à variables séparables, des calculs analytiques peuvent être menés. Ils révèlent dans des cas dits critiques des difficultés mathématiques: les solutions n'ont pas la régularité standard, voire le problème peut être mal posé.La première partie étudie ces problèmes de transmission en régime temporel pour lequel les métamatériaux sont modélisés par des modèles dispersifs (modèle de Drude ou de Lorentz). Les difficultés résident dans le choix d'un schéma de discrétisation mais surtout dans la construction de conditions absorbantes. La méthode retenue ici est celle des Perfectly Matched Layers (PMLs). Comme les PMLs classiques sont instables pour ces modèles du fait de la présence d'ondes inverses, nous proposons une nouvelle classe de PMLs pour lesquelles nous menons une analyse de stabilité. Cette dernière permet de construire des PMLs stables. Elles sont ensuite utilisées pour simuler le comportement en temps long d'un problème de transmission; nous illustrons alors le fait que le principe d'amplitude limite peut être mis en défaut en raison de résonances d'interface.La deuxième partie vise à pallier ces phénomènes d'interface en régime harmonique en revenant sur le processus d'homogénéisation classique, pour un milieu dissipatif. Pour des problèmes de transmission, il est connu que les modèles issus de cette méthode perdent en précision du fait de la présence de couches limites à l'interface. Nous proposons un modèle enrichi au niveau de l'interface. En combinant la méthode d'homogénéisation double-échelle et celle des développements asymptotiques raccordés, nous construisons des conditions de transmission non standards faisant intervenir des opérateurs différentiels le long de l'interface. Le calcul de ces conditions nécessite la résolution de problèmes de cellule et de problèmes non standards posés dans des bandes périodiques infinies. Une analyse d'erreur confirme l'amélioration de la précision du modèle. Des simulations numériques illustrent l'efficacité de ces nouvelles conditions. Enfin, cette démarche est reproduite formellement dans le cas des matériaux à fort contraste se comportant comme des métamatériaux. Nous montrons alors que ces nouvelles conditions permettent de régulariser le problème de transmission dans les cas critiques. / We are interested in transmission problems between dielectrics and metamaterials, that is to say media with unusual electromagnetic properties such as negative constants at some frequencies. These media are often made of periodic assemblies of resonant micro-structures and in this case the homogenization theory can justify mathematically these effective properties. A preliminary part deals with these problems in the harmonic domain and in geometry with separation of variables.Analytical computations are done and reveal in the so-called critical cases some mathematical diffculties: the solutions do not have the standard regularity and the problem can even be ill-posed.The first part examines these transmission problems in the time domain for which metamaterials are modelled by dispersive models (Drude model or Lorentz model for instance). The diffculties reside in the choice of a discretization scheme but especially in the construction of absorbing conditions. The method used here is the use of Perfectly Matched Layers (PMLs). Since classical PMLs are unstable for these models due to the presence of backward waves, we propose a new class of PMLs for which we conduct a stability analysis. The latter allows us to build stable PMLs. They are then used to simulate the long-time behaviour of a transmission problem; we illustrate the fact that the limit amplitude principle can be faulted because of interface resonances.The second part aims to overcome these phenomena by coming back to the classical homogenization in the harmonic domain, for dissipative media. For transmission problems, it is known that models resulting from this method lose accuracy due to the presence of boundary layers at the interface. We propose an enriched model at the interface: by combining the method of two-scale homogenization and that of matched asymptotic expansions, we build non-standard transmission conditions involving tangential derivatives along the interface (Laplace-Beltrami operators). This requires to solve cell problems and non-standardproblems in infinite periodic bands. An error analysis confirms the improvement of the accuracy of the model and numerical simulations show the effectiveness of these new conditions. Finally, this approach is formally reproduced in the case of high contrast materials which behave like metamaterials. We show that these new conditions regularise the transmission problem in the critical cases.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / In this paper, we extended the matched filter bound (MFB) of time-discrete multipath Rayleigh fading channels derived in [1,2] for multiscale wavelet signaling communication.

A hp-finite element method is implemented to numerically study the modes of waveguides with two dimensional cross-section and to compute electromagnetic scattering from three dimensional objects. A method to control the chromatic dispersion properties of photonic crystal fibers using the selective hole filling technique is proposed. The method is based on a single hole-size fiber geometry, and uses an appropriate index-matching liquid to modify the effective size of the filled holes. The dependence of dispersion properties of the fiber on the design parameters such as the refractive index of the liquid, lattice constant and hole diameter are studied numerically. It is shown that very small dispersion values between 0±0.5ps/nm-km can be achieved over a bandwidth of 430-510nm in the communication wavelength region of 1300-1900nm. Three such designs are proposed with air hole diameters in the range 1.5-2.0μm. A novel multi-core fiber design strategy for obtaining a at in-phase supermode that optimizes utilization of the active medium inversion in the multiple cores is proposed. The spatially at supermode is achieved by engineering the fiber so that the total mutual coupling between neighboring active cores is equal. Different designs suitable for different fabrication processes such as stack-and-draw and drilling are proposed. An important improvement over previous methods is the design simplicity and better tolerance to perturbations. The optimal implementation of perfectly matched layer (PML) in terms of minimizing the computational overhead it introduces is studied. In one dimension it is shown that PML implementation with a single cell and a high order finite element produces minimal overhead. Estimates of optimal cell size and optimal finite element degree are given. Based on the single cell implementation of PML in three dimensions, field enhancement in metallic bowties is computed.

This thesis presents results obtained during 2007/08 in the course of doctoral research into attitudes towards linguistic variation in England and Austria and is based in part on a study by Lees (2000). In this project attitudes amongst British and Austrian informants towards low-prestige ('dialect') and high-prestige varieties are investigated on the basis of assumptions made about speakers of these varieties. The data are collected by means of the 'matched-guise technique', whereby informants listen to a number of recordings of low and high-prestige varieties and note their reactions on the basis of a selection of traits using a semantic differential. In this way the research aims to ascertain whether a pattern emerges, where the informants' perception of the guises is influenced by the prestige of the spoken variety. The results in England and in Austria are compared in order to determine similarities and differences in language attitudes towards low and high-prestige varieties in the two countries. Some results presented here correspond to certain social expectations, with high-prestige speakers being associated with better-paid employment and a better education. Other results, though, are less predictable, as where, for example, the female informants in England and in Austria judge the speakers more positively than the male informants, regardless of the prestige of the speaker's variety. In any case, there is evidence from both countries of the informants' evaluations of the speaker being influenced by their associations of the speaker's variety with that speaker's social status. The data also indicate that the social status of speakers in England is judged to a greater extent on the basis of their spoken variety than is the case in Austria, where speakers are more used to switching freely between points on the standard-dialect continuum and are consequently less judgemental in their perception of a speaker based purely on the evidence of their spoken variety.