Direct-Sequence Code Division Multiple Access (DS-CDMA), over the last few years, has become a popular technique and finds a place in many modern communication systems. The performance of this technique is closely linked to the signature (or spreading) sequences employed in the system. In the past, there have been many successful attempts by research groups to construct families of signature sequences that offer the potential gains promised by theoretical bounds. In this thesis, we present constructions of families of signature sequences over the AM-PSK and QAM alphabet with low correlation. In this thesis, we construct a family of sequences over the 8-ary AM-PSK constella- tion, Family AOpt(16) that is asymptotically optimal with respect to the Welch bound on maximum magnitude of correlation for complex sequences. The maximum magnitude of correlation for this family, θmax, is upper bounded by √N , where N is the period of the sequences. The 8-ary AM-PSK constellation is a subset of the 16-QAM constellation. We also construct two families of sequences over 16-QAM, Family A16A, and Family A16,B , with the maximum magnitude of correlation upper bounded by √2√N . We construct a family, A(M 2), of sequences over the 2m+1-ary AM-PSK constellation of period N = 2r- 1 and family size (N + 1)/2m-1 . The 2m+1-ary AM-PSK constellation is a subset of the M 2-QAM constellation with M =2m . The maximum nontrivial normalized correlation parameter is bounded above by θmax < a √N where a ranges from 1.34 in the case of M 2 = 16 to √5 for large m. Apart from low correlation values, the family possesses several interesting and useful features. In Family A(M 2), users have the ability to transmit 2m bits of data per period of the spreading sequence. The sequences in Family A(M 2) are balanced; all points from the 2m+1-ary AM-PSK constellation occur approximately equally often in sequences of long period. The Euclidean distance between the signals assigned to a particular user in A(M 2), corresponding to different data symbols, is larger than the corresponding value for the case when 2m+1-PSK modulation and spreading is used. Perhaps most interestingly, Family A(M 2) permits users on the reverse link of a CDMA system to communicate asynchronously at varying data rates by switching between different QAM constellations. Family A(M 2) is compatible with QPSK sequence families S(p) in the sense that the maximum correlation magnitude is increased only slightly if one adds sequences from (p) S(p)\ S(0) to Family A(M 2). We also construct families of sequences over AM-PSK that tradeoff data rate per sequence period and θmax for a given family size. We have extended the construction of sequences over AM-PSK constellation to construct sequences over the M 2-QAM constellation for M =2m . The QAM sequence families, Families (AM 2), have size, data rate and minimum squared Euclidean distance same as the corresponding AM-PSK construction but have higher values of θmax. Also included in the thesis are constructions for large families of sequences over the M 2-QAM alphabet.

Multi-carrier systems based on orthogonal frequency division multiplexing (OFDM) are efficient technologies for the implementation of broadband wireless communication systems. OFDM is widely used and has been adopted for current mobile broadband wireless communication systems such as IEEE 802.a/g wireless LANs, WiMAX, 3GPP LTE, and DVB-T/H digital video broadcasting systems. Despite their many advantages, however, OFDM-based systems suffer from potentially high peak-to-average power ratio (PAR). Since communication systems typically include nonlinear devices such as RF power amplifiers (PA) and digital-to-analog converters (DAC), high PAR results in increased symbol error rates and spectral radiation. To mitigate these nonlinear effects and to avoid nonlinear saturation effects of the PA, the operating point of a signal with high peak power must be backed off into the linear region of the PA. This so-called output backoff (OBO) results in a reduced power conversion efficiency which limits the battery life for mobile applications, reduces the coverage range, and increases both the cost of the PA and power consumption in the cellular base station. With the increasing demand for high energy efficiency, low power consumption, and greenhouse gas emission reduction, PAR reduction is a key technique in the design of practical OFDM systems. Motivated by the PAR reduction problem associated with multi-carrier systems, such as OFDM, this research explores the state of the art of PAR reduction techniques and develops new signal processing techniques that can achieve a minimum PAR for given system parameters and that are compatible with the appropriate standards. The following are the three principal contributions of this dissertation research. First, we present and derive the semi-analytical results for the output of asymptotic iterative clipping and filtering. This work provides expressions and analytical techniques for estimating the attenuation factor, error vector magnitude, and bit-error-rate (BER), using a noise enhancement factor that is obtained by simulation. With these semi-analytical results, we obtain a relationship between the BER and the target clipping level for asymptotic iterative clipping and filtering. These results serve as a performance benchmark for designing PAR reduction techniques using iterative clipping and filtering in OFDM systems. Second, we analyze the impact of the selected mapping (SLM) technique on BER performance of OFDM systems in an additive white Gaussian noise channel in the presence of nonlinearity. We first derive a closed-form expression for the envelope power distribution in an OFDM system with SLM. Then, using this derived envelope power distribution, we investigate the BER performance and the total degradation (TD) of OFDM systems with SLM under the existence of nonlinearity. As a result, we obtain the TD-minimizing peak backoff (PBO) and clipping ratio as functions of the number of candidate signals in SLM. Third, we propose an adaptive clipping control algorithm and pilotaided algorithm to address a fundamental issue associated with two lowcomplexity PAR reduction techniques, namely, tone reservation (TR) and active constellation extension (ACE). Specifically, we discovered that the existing low-complexity algorithms have a low clipping ratio problem in that they can not achieve the minimum PAR when the target clipping level is set below the initially unknown optimum value. Using our proposed algorithms, we overcome this problem and demonstrate that additional PAR reduction is obtained for any low value of the initial target clipping ratio. / text

Dans cette thèse, on s'est intéressé à l'étude des canaux de diffusion avec des contraintes de transmission pratiques. Tout d'abord, on a étudié l'impact de la contrainte pratique de l'utilisation d'un alphabet fini à l'entrée du canal de diffusion Gaussien avec deux utilisateurs. Deux modèles de canaux de diffusion sont considérés lorsqu'il y a, en plus d'un message commun pour les deux utilisateurs, (i) un message privé pour l'un des deux utilisateurs sans contrainte de sécurité (ii) un message confidentiel pour l'un des deux utilisateurs qui doit être totalement caché de l'autre utilisateur. On a présenté plusieurs stratégies de diffusion distinguées par leur complexité d'implémentation. Plus précisément, on a étudié les régions des débits atteignables en utilisant le partage de temps, la superposition de modulation et le codage par superposition. Pour la superposition de modulation et le cas général du codage par superposition, les régions des débits atteignables maximales sont obtenues en maximisant par rapport aux positions des symboles dans la constellation et la distribution de probabilité jointe. On a étudié le compromis entre la complexité d'implémentation des stratégies de transmission et leurs efficacités en termes de gains en débits atteignables. On a étudié aussi l'impact de la contrainte de sécurité sur la communication en comparant les débits atteignables avec et sans cette contrainte. Enfin, on a étudié les performances du système avec des schémas d'accusés de réception hybrides (HARQ) pour un canal à écoute à évanouissement par blocs lorsque l'émetteur n'a pas une information parfaite sur l'état instantané du canal mais connait seulement les statistiques. On a considéré un schéma adaptatif pour la communication sécurisée en utilisant des canaux de retour à niveaux multiples vers l'émetteur pour changer la longueur des sous mots de code à chaque retransmission afin que le débit utile secret soit maximisé sous des contraintes d'"outages".

On-orbit servicing (OOS) of space systems provides immense benefits by extending their lifetime, by reducing overall cost of space operations, and by adding flexibility to space missions. Refueling is an important aspect of OOS operations. The problem of determining the optimal strategy of refueling multiple satellites in a constellation, by expending minimum fuel during the orbital transfers, is challenging, and requires the solution of a large-scale optimization problem. The conventional notion about a refueling mission is to have a service vehicle visit all fuel-deficient satellites one by one and deliver fuel to them. A recently emerged concept, known as the peer-to-peer (P2P) strategy, is a distributed method of replenishing satellites with fuel. P2P strategy is an integral part of a mixed refueling strategy, in which a service vehicle delivers fuel to part (perhaps half) of the satellites in the constellation, and these satellites, in turn, engage in P2P maneuvers with the remaining satellites. During a P2P maneuver between a fuel-sufficient and a fuel-deficient satellite, one of them performs an orbital transfer to rendezvous with the other, exchanges fuel, and then returns back to its original orbital position. In terms of fuel expended during the refueling process, the mixed strategy outperforms the single service vehicle strategy, particularly with increasing number of satellites in the constellation. This dissertation looks at the problem of P2P refueling problem and proposes new extensions like the Cooperative P2P and Egalitarian P2P strategies. It presents an overview of the methodologies developed to determine the optimal set of orbital transfers required for cooperative and non-cooperative P2P refueling strategies. Results demonstrate that the proposed strategies help in reducing fuel expenditure during the refueling process.

The thesis "Sibling Constellation Effects on Learning and Career Aspirations of Pupils" is aimed at the description of a relationship between birth order and personality development. It also deals with the general characteristics of sibling constellation and its historical development. It points out the importance of sibling constellation in human life and presents the personality description with regard to birth order in relation to parents, siblings, peers, education and occupation. The thesis also involves the research results of birth order effects on learning and career specialization of grammar school pupils. This main part is enriched with the information about the aspiration rate of secondary school and university students. The data were obtained through three similar questionnaires distributed on above-mentioned educational levels during February and March 2012.

Multiple users compete for a common resource like bandwidth to communicate data in interference networks. Existing approaches in dealing with interference limit the rate of communication due to paucity of shared resources. This limitation in the rate gets more glaring as the number of users in the network increases. For example, existing wireless systems either choose to orthogonalize the users (for example, Frequency Division Multiple Access (FDMA) systems or Code Division Multiple Access (CDMA) systems) or treat interference as Gaussian noise at the receivers. It is well known that these approaches are sub-optimal in general. Orthogonalization of users limit the number of available interference-free channels (known as degrees of freedom, abbreviated as DoF) and treating interference as noise means that the receiver cannot make use of the structure in the interfering signals. This motivates the need to analyze alternate transmit and decoding schemes in interference networks. This thesis mainly analyzes transmit schemes that use linear precoding for various configurations of interference networks with some practical constraints imposed by the use of finite input constellations, propagation delays, and channel state availability at the transmitters. The main contributions of this thesis are listed below. Achievable rates using precoding with finite constellation inputs in Gaussian Interference Channels (GIC) is analyzed. A metric for finding the approximate angle of rotation to maximally enlarge the Constellation Constrained (CC) capacity of two-user Gaussian Strong Interference Channel (GSIC) is proposed. Even as the Gaussian alphabet FDMA rate curve touches the capacity curve of the GSIC, with both the users using the same finite constellation, we show that the CC FDMA rate curve lies strictly inside the CC capacity curve at high powers. For a K-user MIMO GIC, a set of necessary and sufficient conditions on the precoders under which the mutual information between between relevant transmit-receive pairs saturate like in the single user case is derived. Gradient-ascent based algorithms to optimize the sum-rate achieved by precoding with finite constellation inputs and treating interference as noise are proposed. For a class of Gaussian interference networks with general message demands, identified as symmetrically connected interference networks, the expected sumspectral efficiency (in bits/sec/Hz) is shown to grow linearly with the number of transmitters at finite SNR, using a time-domain Interference Alignment (IA) scheme in the presence of line of sight (LOS) channels. For a 2×2 MIMO X-Network with M antennas at each node, we identify spacetime block codes that could be coupled with an appropriate precoding scheme to achieve the maximum possible sum-DoF of 4M 3 , for M = 3, 4. The proposed schemes are shown to achieve a diversity gain of M with SNR-independent finite constellation inputs. The proposed schemes have lower CSIT requirements compared to existing schemes. This thesis also makes an attempt to guarantee a minimum throughput when the zero-interference conditions cannot be satisfied in a wireline network with three unicast sessions with delays, using Precoding Based Network Alignment (PBNA). Three different PBNA schemes namely PBNA with time-varying local encoding coefficients (LECs), PBNA using transform approach and time-invariant LECs, and PBNA using transform approach and block time-varying LECs are proposed and their feasibility conditions analyzed.

Tato práce se zaměřuje na klasifikaci vysokofrekvenčních vysílačů v závislosti na nedokonalostech jejich komponent pomocí algoritmu strojového učení. Práce je rozdělena na dvě části - teoretickou a praktickou.V teoretické části je nejprve popsána základní struktura vysílače s přímou konverzí a jsou uvedeny nedokonalosti rádiového front-endu, které mohou být využity ke klasifikaci. Dále jsou vysvětleny vybrané metody strojového učení s učitelem, zejména metoda support vector machines a neuronové sítě. Praktická část se zabývá implementací a dosaženými výsledky těchto dvou metod v prostředí MATLAB na problému klasifikace rádiových front-endů.

Space debris growth and an influx in space traffic will create a need for increased space traffic management. Due to orbital population density and likely future growth, the implementation of a slot architecture to Sun-synchronous orbit is considered in order to mitigate conjunctions among active satellites. This paper furthers work done in Sun-synchronous orbit slot architecture design and focuses on two main aspects. First, an in-depth relative motion analysis of satellites with respect to their assigned slots is presented. Then, a method for developing a slot architecture from a specific set of user defined inputs is derived.

Digital Video Broadcasting (standard DVB) is a system for transmission of the television signals in the digital form. There are used a various types of modulations in this system as QPSK modulation is used in the systems of satellite video broadcasting DVB-S (Satellite) and M-QAM modulations in the cable transmitting DVB-C (Cable). This paper mainly deals with system of the terrestrial digital video broadcasting DVB-T (Terrestrial), where OFDM modulation is used. This type of signal processing is more resistant to the distortions caused by multipath transmitting, which is main problem in the DVB-T. Matlab application, which can simulate digital modulation and demodulation of the transmission signals in the DVB-T, is created in this thesis. The models of the transmission channel is inserted between structures of modulator and demodulator. The user of this application can set the parameters of the broadcasting (e.g. constellation, OFDM mode, guard interval insertion) and the type of distortions (additive noise, reflected and delayed signals). By calculation of the channel bit error rate (BER) user can study influences of broadcasting parameters to the quality of transmission.

In its theoretical part, the thesis "Sibling rivalry as reflected in primary school success" provils a description of the primary school pupil and definitions of sibling rivalry and scholastic success. Further attention in giwen to parenting practices which foster sibling rivalry. The aim of the practical part of the thesis is to decode the tokens of sibling rivalry and to covvelate it with scholastic success in the kontext of parent - pupiů - teacher relationships. Both qualitative and quantitative approaches were employed and thein results compared. The results of this thesis can serve as the basis for further research and be used by parents to better understand thein children's interactions.