Plants are constantly exposed to pathogens and various environmental stresses, such as cold, salinity and drought. Plants normally respond rapidly to these biotic and abiotic stresses. Efficient perception of biotic and abiotic stresses and cell programmed signaling mechanisms for appropriate responses are important for growth and survival of plants. Calcium is an important second messenger in signaling pathways that respond to environmental stresses, pathogen attack as well as hormonal stimuli (For review, see DeFalco et al., 2010; Reddy and Reddy, 2004; Sanders et al., 2002). The transient increase of cytosolic free calcium concentration has been shown in a variety of external signals (Reddy, 2001), which in turn triggers many signal transduction pathways leading to a variety of cellular responses (Bush, 1995). Any calcium mediated signal transduction process involves generation of signal-specific calcium signature in the cytosol (Scrase-Field and Knight, 2003). These changes in cytosolic calcium level or ‘calcium signatures’ are sensed by the specific group of proteins called the ‘calcium sensors’. Different calcium sensors recognize specific calcium signatures and transduce them into downstream effects, including altered protein phosphorylation and gene expression patterns. In plants the protein kinases are a large and differentiated group of calcium sensors. After analyzing 1264 protein kinase sequences, a superfamily of protein kinase called CDPK/SnRK family of protein kinase were defined (Hrabak et al., 2003). CDPK/SnRK family of protein kinases encompasses five subfamilies viz., calcium-dependant protein kinases, (CPKs), calcium/calmodulin dependant protein kinases (CCaMKs), calmodulin-dependant protein kinases (CaMKs), CPKrelated kinases (CRKs), and SnF1 related kinase 3 (SnRK3) and are regulated by calcium directly or indirectly. Among these, in plants, calcium-dependant protein kinases (CPKs) are predominant calcium sensors, which are shown to be involved in myriads of physiological responses. They are Ser/Thr family of protein kinases typically made up of five domains with an Nterminal variable domain followed by catalytic protein kinase domain, an autoinhibitory/ junction domain, a regulatory calmodulin-like domain (CaMLD) and a Cterminal domain of variable length. The CPKs are unique due to the presence of CaMLD which couples the calcium sensor directly to its responder (kinase domain). Although CPKs are highly conserved, there are several features that distinguish different members of the plant CDPK family. In an attempt to investigate the role of a CPK isoform, in the present work we bring out the results and inferences on isolation and characterization of a novel cDNA encoding a calcium-dependant protein kinase isoform ScCPK1 from Swainsonacanescens, a pharmaceutically important Australian herb known to produce an anticancer drug, swainsonine. Initially, we have cloned an 800 bp partial CPK cDNA from S. canescens by reverse transcription polymerase chain reaction (RTPCR) using degenerate oligonucleotide primers designed based on conserved regions of the other known CPKs. A 2.1 kb full length CPK was obtained using 5` and 3` RACE which was designated as ScCPK1. An open reading frame (ORF) of 1659 bp was detected that encodes a protein of 552 amino acids with a calculated molecular mass of 61.8 kDa. Comparison of the deduced amino acid sequence of ScCPK1 with sequences of other CPKs revealed the highest identity (>90%) to Glycine max and Vigna radiate CPKs. As described for other CPKs, ScCPK1 has a long variable domain (88 aa), an auto-inhibitory domain (31 aa) and a C-terminal calmodulin domain (145 aa) containing four EF-hand calcium binding motifs, which is found in many CPKs. Phylogenetic tree analysis showed that ScCPK1 was closely related to StCPK4 , CmCPK1 and CmCPK2. The entire coding region of ScCPK1 was cloned into pRSETA expression vector and expressed as fusion protein in E.coli. The recombinant ScCPK1 protein was purified to homogeneity by NiNTA affinity chromatography. The recombinant purified ScCPK1 was catalytically active in a calcium-dependent manner. The recombinant ScCPK1 phosphorylated itself and histone IIIS as substrate only in the presence of Ca2+. Phosphoaminoacid analyses showed that ScCPK1 phosphorylates serine and threonine residues of histone IIIS and its autophosphorylation also occurs on serine and threonine residues. ScCPK1 has a pH and temperature optima of 7.5 and 37 °C, respectively. It showed high affinity to histone III-S with a Km of 4.8 µM and had a Vmax of 4.700 pmoles of γ32P incorporation/min/mg at saturating substrate concentrations. The ScCPK1 is ~100fold active and showed 10fold higher affinities to histone III-S than CaCPK1 and CaCPK2, CPKs which were characterized from Cicer arietinum previously in our laboratory (Prakash and Jayabaskaran, 2006). From literature it is known that many CPKs are activated or inhibited by metal ions. (PutnamEvans etal., 1990; Anil and Rao, 2001). The influence of Na+ and Mg2+on the in vitro substrate phosphorylation activity of the recombinant ScCPK1 was tested in this work. Addition of NaCl strongly inhibited ScCPK1 activity. The inhibition of substrate phosphorylation activity by salt implies ionic interactions between the positively charged substrate and the enzyme’s active site. The optimum concentration of Mg2+ for ScCPK1 substrate phosphorylation activity was found to be 810 mM, similar to CaCPK1 and CaCPK2 (Prakash and Jayabaskaran, 2006). However, the activity was inhibited above 10 mM Mg2+suggesting the disruption of ionic interactions between the enzyme and the substrate. The kinase and autophosphorylation activities of the recombinant ScCPK1 were calmodulin independent and sensitive to CaM antagonists’ calmidazolium and W7 (N(6aminohexyl)5chloronaphthalene sulphonate). This indicates that the activation was supported by calmodulin-like domain, which is typical of CPK family. Farmer and Choi (1999), showed that DcCPK1 activity was inhibited by polyamines vizspermine and spermidine, and polylysine. We found that substrate phosphorylation activity of ScCPK1 was inhibited by polyLLysine with an IC50 of 8 M but not the polyamines, spermine and spermidine. An interesting aspect that makes CPKs attractive for research is their functional similarity to mammalian PKCs. There are no structural PKC analogues found in plant genomic data. Similar to PKCs, CPKs are regulated by intracellular Ca2+ signals. There is also experimental evidence that some of the CPKs are additionally activated by phospholipids (Farmer and Choi, 1999; Szczegielniak etal., 2000). We investigated the effects of lipid molecules on the activity of ScCPK1. Phosphorylation of histone IIIS by ScCPK1 was stimulated by phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol in the presence of Ca2+, where as lysophosphatidylcholine, phosphatidylcholine and phosphatidic acid did not increase the enzyme activity. Our data that shows interaction of ScCPK1 with phospholipids supports the idea that this protein kinase could be associated with the membrane. The work from Farmer and Choi (1999), with DcCPK1 suggested that some of the PKClike activities observed in plants may be attributed to CPKs. They also demonstrated that DcCPK1 phosphorylated PKC pseudosubstrate peptide and also was sensitive to staurosporine inhibition. However, the protein kinase inhibitor, staurosporine inhibited the substrate phosphorylation activity of ScCPK1 completely with an IC50 value of 700 nM invitro. But PKC inhibitor PMA was less effective, inhibiting the substrate phosphorylation activity of ScCPK1 to a maximum of 50%, but at a very high concentration (200 nM). Our data suggests that ScCPK1 may not have any features attributable to PKC. We investigated subcellular localization of the ScCPK1. To gain a better understanding of the subcellular localization of the ScCPK1, we generated GFP fusion protein of ScCPK1 and transiently expressed it in Agrobacterium-mediated transformed tobacco BY2 cells. Analysis of the GFP expression patterns in transformed tobacco BY2 cells revealed ScCPK1 localization in the plasma membrane of the transformed tobacco BY2 cells despite lacking consensus myristoylation and palmitoylation motifs (as per in silico analyses). Taking together, our data have demonstrated that ScCPK1 is a Ser/Thr protein kinase and its sub-cellular localization studies revealed that it is localized to plasma membrane. We propose that ScCPK1 is a key component of one or more signaling pathways and plays vital roles in plant development, responses to environmental stimuli and/ or in secondary metabolite biosynthetic gene expression. The involvement of the ScCPK1 as a component of signaling pathways warrants further studies.

Elastic properties of carbon nanotubes (CNT), boron nitride nanotubes (BNNT), double stranded DNA (dsDNA), paranemic-juxtapose crossover (PX-JX) DNA and dendrimer bound DNA are discussed in this thesis. Structural phase transitions of nucleic acids induced by external force, carbon nanotubes and graphene substrate are also studied extensively. Electrostatic interactions have a strong effect on the elastic properties of BNNTs due to large partial atomic charges on boron and nitrogen atoms. We have computed Young’s modulus (Y ) and shear modulus (G) of BNNT and CNT as a function of the nanotube radius and partial atomic charges on boron and nitrogen atoms using molecular mechanics calculation. Our calculation shows that Young’s modulus of BNNTs increases with increase in magnitude of the partial atomic charges on B and N atoms and can be larger than the Young’s modulus of CNTs of same radius. Shear modulus, on the other hand depends weakly on the magnitude of partial atomic charges and is always less than the shear modulus of the CNT. The values obtained for Young’s modulus and shear modulus are in excellent agreement with the available experimental results. We also study the elasticity of dsDNA using equilibrium fluctuation methods as well as nonequilibrium stretching simulations. The results obtained from both methods quantitatively agree with each other. The end-to-end length distribution P(ρ) and angle distribution P(θ) of the dsDNA has a Gaussian form which gives stretch modulus (γ1) to be 708 pN and persistence length (Lp) to be 42 nm, respectively. When dsDNA is stretched along its helix axis, it undergoes a large conformational change and elongates about 1.7 times its initial contour length at a critical force. Applying a force perpendicular to the DNA helix axis, dsDNA gets unzipped and separated into two single-stranded DNA (ssDNA). DNA unzipping is a fundamental process in DNA replication. As the force at one end of the DNA is increased the DNA starts melting above a critical force depending on the pulling direction. The critical force fm , at which dsDNA melts completely decreases as the temperature of the system is increased. The melting force in the case of unzipping is smaller compared to the melting force when the dsDNA is pulled along the helical axis. In the case of melting through unzipping, the double-strand separation has jumps which correspond to the different energy minima arising due to sequence of different base-pairs. Similar force-extension curve has also been observed when crossover DNA molecules are stretched along the helix axis. In the presence of mono-valent Na+ counterions, we find that the stretch modulus (γ1 ) of the paranemic crossover (PX) and its topoisomer juxtapose (JX) DNA structure is significantly higher (30 %) compared to normal B-DNA of the same sequence and length. When the DNA motif is surrounded by a solvent of divalent Mg2+ counterions, we find an enhanced rigidity compared to in Na+ environment due to the electrostatic screening effects arising from the divalent nature of Mg2+ counterions. This is the first direct determination of the mechanical strength of these crossover motifs which can be useful for the design of suitable DNA motifs for DNA based nanostructures and nanomechanical devices with improved structural rigidity. Negatively charged DNA can be compacted by positively charged dendrimer and the degree of compaction is a delicate balance between the strength of the electrostatic interaction and the elasticity of DNA. When the dsDNA is compacted by dendrimer, the stretch modulus, γ1 and persistence length, Lp decreases dramatically due to backbone charge neutralization of dsDNA by dendrimer. We also study the effect of CNT and graphene substrate on the elastic as well as adsorption properties of small interfering RNA (siRNA) and dsDNA. Our results show that siRNA strongly binds to CNT and graphene surface via unzipping its base-pairs and the propensity of unzipping increases with the increase in the diameter of the CNTs and is maximum on graphene. The unzipping and subsequent wrapping events are initiated and driven by van der Waals interactions between the aromatic rings of siRNA nucleobases and the CNT/graphene surface. However, dsDNA of the same sequence undergoes much less unzipping and wrapping on the CNT/graphene due to smaller interaction energy of thymidine of dsDNA with the CNT/graphene compared to that of uridine of siRNA. Unzipping probability distributions fitted to single exponential function give unzipping time (τ) of the order of few nanoseconds which decrease exponentially with temperature. From the temperature variation of unzipping time we estimate the free energy barrier to unzipping. We have also investigated the binding of siRNA to CNT by translocating siRNA inside CNT and find that siRNA spontaneously translocates inside CNT of various diameters and chiralities. Free en- ergy profiles show that siRNA gains free energy while translocating inside CNT and the barrier for siRNA exit from CNT ranges from 40 to 110 kcal/mol depending on CNT chirality and salt concentration. The translocation time τ decreases with the increase of CNT diameter having a critical diameter of 24 A for the translocation. After the optimal binding of siRNA to CNT/graphene, the complex is very stable which can serve as siRNA delivery agent for biomedical applications. Since siRNA has to undergo unwinding process in the presence of RNA-induced silencing complex, our proposed delivery mechanism by single wall CNT possesses potential advantages in achieving RNA interference (RNAi).

The classical binary error correcting codes, and subspace codes for error correction in random network coding are two different forms of error control coding. We identify common features between these two forms and study the relations between them using the aid of lattices. Lattices are partial ordered sets where every pair of elements has a least upper bound and a greatest lower bound in the lattice. We shall demonstrate that many questions that connect these forms have a natural motivation from the viewpoint of lattices. We shall show that a lattice framework captures the notion of Singleton bound where the bound is on the size of the code as a function of its parameters. For the most part, we consider a special type of a lattice which has the geometric modular property. We will use a lattice framework to combine the two different forms. And then, in order to demonstrate the utility of this binding view, we shall derive a general version of Singleton bound. We will note that the Singleton bounds behave differently in certain respects because the binary coding framework is associated with a lattice that is distributive. We shall demonstrate that lack of distributive gives rise to a weaker bound. We show that Singleton bound for classical binary codes, subspace codes, rank metric codes and Ferrers diagram rank metric codes can be derived using a common technique. In the literature, Singleton bounds are derived for Ferrers diagram rank metric codes where the rank metric codes are linear. We introduce a generalized version of Ferrers diagram rank metric codes and obtain a Singleton bound for this version. Next, we shall prove a conjecture concerning the constraints of embedding a binary coding framework into a subspace framework. We shall prove a conjecture by Braun, Etzion and Vardy, which states that any such embedding which contains the full space in its range is constrained to have a particular size. Our proof will use a theorem due to Lovasz, a subspace counting theorem for geometric modular lattices, to prove the conjecture. We shall further demonstrate that any code that achieves the conjectured size must be of a particular type. This particular type turns out to be a natural distributive sub-lattice of a given geometric modular lattice.

Limit analysis is a very powerful tool to find accurate solutions of several geotechnical stability problems. This analysis is based on the theory of the plasticity and it provides two limiting solutions within lower and upper bounds. With the advancement of the finite elements and different robust optimization techniques, the numerical limit analysis approach in association with finite elements is becoming quite popular to assess the stability of various complicated structures. The present thesis deals with the formulations and the implementation of the finite element limit analysis to obtain the solutions of different geotechnical axisymmetric stability problems. The objectives of the present thesis are twofold: (a) developing limit analysis formulations in conjunction with linear and nonlinear optimizations for solving axisymmetric stability problems related with soil and rock mechanics, and then (b) implementing these axisymmetric formulations for solving various important axisymmetric stability problems in geomechanics. Three noded linear triangular elements have been used throughout the thesis. In order to solve the different problems, the associated computer programs have been written in MATLAB. With reference to the first objective of the thesis, the existing finite element lower bound axisymmetric formulation with linear programming has been presented. A new technique has also been proposed for solving an axisymmetric geomechanics stability problem by employing an upper bound limit analysis in combination with finite elements and linear programming. The method is based on the application of the von-Karman hypothesis to fix the constraints associated with the magnitude of the circumferential stress (), and finally the method involves only the nodal velocities as the basic unknown variables. The required computational effort becomes only marginally greater than that needed for an equivalent plane strain problem. The proposed methodology has been found to be computationally quite efficient. A new lower bound axisymmetric limit analysis formulation, by using two dimensional finite elements, the three dimensional Mohr-Coulomb (MC) yield criterion, and nonlinear optimization has also been presented for solving different axisymmetric stability problems in geomechanics. The nonlinear optimization was carried out by employing an interior point method based on the logarithmic barrier function. The yield surface was smoothened (i) by removing the tip singularity at the apex of the pyramid in the meridian plane, and (ii) by eliminating the stress discontinuities at the corners of the yield hexagon in the plane. No inherent assumption concerning with the hoop stress needs to be made in this formulation. The Drucker-Prager (DP) yield criterion was also used for computing the lower bound axisymmetric collapse load. The advantage of using the DP yield criterion is that it does not exhibit any singularity in the plane. A new proposal has also been given to simulate the DP yield cone with the MC hexagonal yield pyramid. The generalized Hoek-Brown (HB) yield criterion has also been used. This criterion has been smoothened both in the meridian and  planes and a new formulation is prescribed for obtaining the lower bound axisymmetric problems in rock media in combination with finite elements and nonlinear optimization. With reference to the second objective, a few important axisymmetric stability problems in soil mechanics associated with footings and excavations have been solved in the present thesis. In all these problems, except that of a flat circular footing lying over either homogeneous soil or rock media, it is assumed that the medium is governed by the MC failure criterion and it follows an associated flow rule. For determining the collapse loads for a circular footing over homogenous soil and rock media, the problem has been solved with the usage of Drucker-Prager, Mohr-Coulomb and Hoek-Brown criteria. The bearing capacity of a circular footing lying over fully cohesive strata, with an inclusion of a sand layer is evaluated. The effects of the thickness and internal friction angle of the sand layer () on the bearing capacity have been examined for different combinations of cu/(b) and q; where (i) cu defines the undrained shear strength, (ii)  is the unit weight of sand, (iii) b corresponds to the footing radius, and (iv) q is the surcharge pressure. The results have been presented in the form of a ratio () of the bearing capacities with an insertion of the sand layer to that for a footing lying directly over clayey strata. It is noted that an introduction of a layer of medium dense to dense sand over soft clay improves considerably the bearing capacity of the foundation. The improvement in the bearing capacity increases continuously (i) with decreases in cu/(b), and (ii) increases in  and q/(b). The bearing capacity factors, Nc, Nq and N, for a conical footing are obtained in a bound form for a wide range of the values of cone apex angle () and with  = 0, 0.5 and . The bearing capacity factors for a perfectly rough ( = conical footing generally increase with a decrease in . On contrary for  = 0, the factors Nc and Nq reduce gradually with a decrease in . For  = 0, the factor N for  ≥ 35o becomes minimum for  approximately equal to 90o. For  = 0, the factor N for  ≤ 30o, like in the case of  = , generally reduces with an increase in . It has also been intended to compute the bearing capacity factors Nc, Nq and N, for smooth and rough ring footing for different combinations of ri/ro and ; where ri and ro refer to inner and outer radii of the ring, respectively. It is observed that for a smooth footing, with a given value of ro, the magnitude of the collapse load decreases continuously with an increase in ri. On the other hand, for a rough base, for a given value of ro, hardly any reduction occurs in the magnitude of collapse load up to ri/ro ≈ 0.2, whereas beyond this ri/ro, the magnitude of the collapse load, similar to that of a smooth footing, decreases continuously with an increase in ri/ro. An attempt has also been made to determine the ultimate bearing capacity of a circular footing, placed over a soil mass which is reinforced with horizontal layers of circular reinforcement sheets. For performing the analysis, three different soil media have been separately considered, namely, (i) fully granular, (ii) cohesive frictional, and (iii) fully cohesive with an additional provision to account for an increase of cohesion with depth. The reinforcement sheets are assumed to be structurally strong to resist axial tension but without having any resistance to bending; such an approximation usually holds good for geogrid sheets. The shear failure between the reinforcement sheet and adjoining soil mass has been considered. The increase in the magnitudes of the bearing capacity factors (Nc and N) with an inclusion of the reinforcement has been computed in terms of the efficiency factors c and . The critical positions and corresponding optimum diameter of the reinforcement sheets, for achieving the maximum bearing capacity, have also been established. The increase in the bearing capacity with an employment of the reinforcement increases continuously with an increase in . The improvement in the bearing capacity becomes quite extensive for two layers of the reinforcements as compared to the single layer of the reinforcement. The stability of an unsupported vertical cylindrical excavation has been assessed. For the purpose of design, stability numbers (Sn) have been generated for both (i) cohesive frictional soils, and (ii) pure cohesive soils with an additional provision to account for linearly increasing cohesion with depth by using a non-dimensional factor m. The variation of Sn with H/b has been established for different values of m and ; where H and b refer to height and radius of the cylindrical excavation. A number of useful observations have been drawn about the variation of the stability number and nodal velocity patterns with changes in H/b,  and m. In the last, by using the smoothened generalized HB yield criterion, the ultimate bearing capacity of a circular footing placed over a rock mass is evaluated in a non-dimensional form for different values of GSI, mi, ci/(b) and q/ci. For validating the results, computations were exclusively performed for a strip footing as well. For the various problems selected in the present thesis, the failure and nodal velocity patterns have been examined. The results obtained from the analysis have been thoroughly compared with that reported from literature. It is expected that the various design charts presented here will be useful for the practicing engineers. The formulations given in the thesis can also be further used for solving various axisymmetric stability problems in geomechanics.

This diploma thesis focuses on the use of inflation targeting as monetary policy regime in a situation of imminent deflation. The thesis is divided into three main parts. The first part introduces the basic mechanism of inflation targeting with its basic elements and describes its possible failure. The second part focuses mainly on the analysis of the economic factors which contributed to achieving the zero lower bound for the repo rate of CNB. The third part presents an alternative (unconventional) monetary policy instruments in case of achieving zero lower bound, in particular the use of the exchange rate. The end of the last part of this thesis analyzes the development of key macroeconomic indicators in the Czech Republic.

This diploma thesis is focused on unconventional monetary policy tools that individual central banks introduced into practise as a response to the global financial crisis. It is about quantitative easing policy, foreign exchange interventions with exchange rate commitment and negative interest rates. This thesis also deals with classical tools of monetary policy such as open market operations, discount tools, minimum requirement reserve or foreign exchange interventions. The aim of the thesis is to document the development of central banks policy and then to examine relationship of selected assets in comparison with balance sheet of Federal reserve systems with help of correlation coefficient. The thesis also deals with the thought how should behave in the zero lower bound environment and what are the pitfalls of unconventional monetary policy.

This thesis concerns the interaction of monetary and fiscal policy. Using New Keynesian model, we show the impact of fiscal expansion under different specifications of monetary policy rules. The analysis of the transmission of fiscal expansion focuses on the situation in which central bank's nominal interest rate reaches zero lower bound. We verify the economic model using vector autoregression based on data of the United States. The results of the theoretical and empirical research suggest that the influence of government spending on the product is greater at the zero lower bound.

Cette thèse est dédié à l’étude de la problématique des interférences multi utilisateurs dans le système Argos et à la proposition des diverses techniques pour réduire les effets de ces interférences. Le système Argos est un système mondial de localisation et de collecte de données géo positionnées par satellite. Il permet à l’échelle mondiale de collecter et de traiter les données émises par des émetteurs installés sur la surface de terre. Ces émetteurs sont connus sous le nom de balises. Ces balises sont installées sur des voiliers, des stations météo, des bouées, ainsi que sur quelques animaux (phoques, penguins, etc.…). Le système Argos a été créé en 1978 par le Centre National des Études spatiales (CNES), l’agence spatiale américaine (NASA) et l’agence américaine d’étude de l’atmosphère et de l’océan (NOAA). Depuis sa création, le nombre de balises Argos n’a cessé d’augmenter afin de couvrir au mieux la couverture mondiale. Nous sommes orientés ainsi à la saturation de la bande d’émission et à la présence des interférences multi utilisateurs (MUI) provenant de la réception simultanée de plusieurs signaux émis par les balises. Cette MUI limite la capacité du système Argos et dégrade les performances en termes de Taux Erreur Bit (TEB). Actuellement, le système Argos n’est capable de traiter qu’un seul signal reçu à un instant donné. D’où, l’intérêt d’implanter des techniques au niveau du récepteur capable de réduire les effets des interférences et de traiter les signaux émis par toutes les balises. Plusieurs techniques de détection multi utilisateurs (MUD) ont été développées dans le cadre de cette problématique. Ces techniques sont principalement implantées dans les systèmes CDMA où des codes d’étalement sont utilisés afin de différencier entre les différents signaux. Ceci n’est pas le cas du système Argos où les signaux ne présentent pas des séquences d’étalement et que les bandes de fréquences pour ces différents signaux ne sont pas disjointes à cause de l’effet Doppler et donc, un recouvrement spectral au niveau du récepteur est très probable. Dans ce contexte, l’objectif du travail présenté dans cette thèse est d’étudier différentes techniques MUD appliquées au système Argos et d’évaluer ces techniques au niveau des performances en termes de TEB et de complexité d’implantation. Dans ce travail, nous présentons les différentes composantes du système Argos ainsi que son mode de fonctionnement. Ensuite, nous présentons la problématique dans le système Argos ainsi que les différentes solutions proposées. Parmi ces solutions, nous montrons celle basant sur l’implantation des techniques MUD au niveau du récepteur. Ces différentes techniques MUD sont alors présentées ainsi que les avantages et les inconvénients de chacune d’elles. Parmi les techniques possédant un bon compromis entre les performances d’une part et la complexité d’autre part, nous notons la technique d’annulation par série d’interférence (SIC). Dans cette technique, les signaux sont démodulés successivement suivant l’ordre décroissant des puissances. Cette technique nécessite une étape d’estimation des paramètres des signaux à chaque étape. L’impact d’une estimation imparfaite des différents paramètres est aussi étudié. Après l’étude des impacts des erreurs d’estimation, nous proposons des estimateurs adaptables au système Argos. Les performances de ces estimateurs sont obtenues en comparant les variances de leurs erreurs aux bornes de Cramer Rao (CRB). Enfin, nous terminons le travail par une conclusion générale des résultats obtenus et nous envisageons les perspectives des prochains travaux. / In our thesis, we investigate the application of multi user detection techniques to a Low Polar Orbit (LPO) satellite used in the Argos system. Argos is a global satellite-based location and data collection system dedicated for studying and protecting the environment. User platforms, each equipped with a Platform Transmitter Terminal (PTT), transmit data messages to a 850 km LPO satellite. An ARGOS satellite receives, decodes, and forwards the signals to ground stations. All PTTs transmit at random times in a 100 kHz bandwidth using different carrier frequencies. The central carrier frequency f0 is 401.65 MHz. Due to the relative motion between the satellite and the platforms, signals transmitted by PTTs are affected by both a different Doppler shift and a different propagation delay. Thus, the Argos satellite receives overlapping signals in both frequency and time domains inducing Multiple Access Interference (MAI). One common approach to mitigate the MAI problem is to implement Multi User Detection (MUD) techniques at the receiver. To tackle this problem, several MUD techniques have been proposed for the reception of synchronous and asynchronous users. In particular, the Successive Interference Cancelation (SIC) detector has been shown to offer a good optimality-complexity trade-off compared to other common approaches such as the Maximum Likelihood (ML) receiver. In an Argos SIC receiver, users are decoded in a successive manner, and the signals of successfully decoded users are subtracted from the waveform before decoding the next user. This procedure involves a parameter estimation step and the impact of erroneous parameter estimates on the performance of Argos SIC receiver has been studied. Argos SIC receiver has been shown to be both robust to imperfect amplitude and phase estimation and sensitive to imperfect time delay estimation. The last part of our work focuses on the implementation of digital estimators for the Argos system. In particular, we propose a time delay estimator, a frequency estimator, a phase estimator and an amplitude estimator. These estimators are derived from the ML principle and they have been already derived for the single user transmission. In our work, we adapt successfully these estimators for the multi user detector case. These estimators use the Non Data Aided (NDA) cases in which no a priori information for the transmitted bits is required. The performance of these different estimators are compared to the Cramer Rao Bound (CRB) values. Finally, we conclude in our work by showing the different results obtained during this dissertation. Also, we give some perspectives for future work on Argos system.

This thesis presents a predictive energy management controller for long-haul hybrid trucks. In a receding horizon control framework, the vehicle speed reference, battery energy reference, and engine on/off decision are optimized over a prediction horizon. A mixed-integer quadratic program (MIQP) is formulated by performing modelling approximations and by including the binary engine on/off decision in the optimal control problem. The branch-and-bound algorithm is applied to solve this problem. Simulation results show fuel consumption reductions between 10-15%, depending on driving cycle, compared to a conventional truck. The hybrid truck without the predictive control saves significantly less. Fuel consumption is reduced by 3-8% in this case. A sensitivity analysis studies the effects on branch-and-bound iterations and fuel consumption when varying parameters related to the binary engine on/off decision. In addition, it is shown that the control strategy can maintain a safe time gap to a leading vehicle. Also, the introduction of the battery temperature state makes it possible to approximately model the dynamic battery power limitations over the prediction horizon. The main contributions of the thesis are the MIQP control problem formulation, the strategy to solve this with the branch-and-bound method, and the sensitivity analysis.

With the increasing demand for faster communication systems, soon data rates in the terabit regime (100 Gbit/s and beyond) are required, which yields new challenges for the design of analog-to-digital converters (ADCs) since high bandwidths imply high sampling rates. For sampling rates larger than 300MHz, which we now achieve with 5G, the ADC power consumption per conversion step scales quadratically with the sampling rate. Thus, ADCs become a major energy consumption bottleneck. To circumvent this problem, we consider digital receivers based on 1-bit quantization and oversampling. We motivate this concept by a brief comparison of the energy efficiency of a recently proposed system employing 1-bit quantization and oversampling to the conventional approach using high resolution quantization and Nyquist rate sampling. Our numerical results show that the energy efficiency can be improved significantly by employing 1-bit quantization and oversampling at the receiver at the cost of increased bandwidth. The main part of this work is concerned with the synchronization of fully digital receivers using 1-bit quantization and oversampling. As a first step, we derive performance bounds for phase, timing, and frequency estimation in order to gain a deeper insight into the impact of 1-bit quantization and oversampling. We identify uniform phase and sample dithering as crucial to combat the non-linear behavior introduced by 1-bit quantization. This dithering can be implemented by sampling at an irrational intermediate frequency and with an oversampling factor with respect to the symbol rate that is irrational, respectively. Since oversampling results in noise correlation, a closed form expression of the likelihood function is not available. To enable an analytical treatment we thus study a system model with white noise by adapting the receive filter bandwidth to the sampling rate. Considering the aforementioned dithering, we obtain very tight closed form lower bounds on the Cramér-Rao lower bound (CRLB) in the large sample regime. We show that with uniform phase and sample dithering, all large sample properties of the CRLB of the unquantized receiver are preserved under 1-bit quantization, except for a signal-to-noise ratio (SNR) dependent performance loss that can be decreased by oversampling. For the more realistic colored noise case, we discuss a numerically computable upper bound of the CRLB and show that the properties of the CRLB for white noise still hold for colored noise except that the performance loss due to 1-bit quantization is reduced. Assuming a neglectable frequency offset, we use the least squares objective function to derive a typical digital matched filter receiver with a data-and timing-aided phase estimator and a timing estimator that is based on square time recovery. We show that both estimators are consistent under very general assumptions, e.g., arbitrary colored noise and stationary ergodic transmit symbols. Performance evaluations are done via simulations and are compared against the numerically computable upper bound of the CRLB. For low SNR the estimators perform well but for high SNR they converge to an error floor. The performance loss of the phase estimator due to decision-directed operation or estimated timing information is marginal. In summary, we have derived practical solutions for the design of fully digital receivers using 1-bit quantization and oversampling and presented a mathematical analysis of the proposed receiver structure. This is an important step towards enabling energy efficient future wireless communication systems with data rates of 100 Gbit/s and beyond.