Many communications signal formats are not power efficient because of their large peak-to-average power ratios (PARs). Moreover, in the presence of nonlinear devices such as power amplifiers (PAs) or mixers, the non-constant-modulus signals may generate both in-band distortion and out-of-band interference. Backing off the signal to the linear region of the device further reduces the system power efficiency. To improve the power efficiency of the communication system, one can pursue two approaches: i) linearize the PA; ii) reduce the high PAR of the input signal. In this dissertation, we first explore the optimal nonlinearity under the peak power constraint. We show that the optimal nonlinearity is a soft limiter with a specific gain calculated based on the peak power limit, noise variance, and the probability density function of the input amplitude. The result is also extended to the fading channel case. Next, we focus on digital baseband predistortion linearization for power amplifiers with memory effects. We build a high-speed wireless test-bed and carry out digital baseband predistortion linearization experiments. To implement adaptive PA linearization in wireless handsets, we propose an adaptive digital predistortion linearization architecture that utilizes existing components of the wireless transceiver to fulfill the adaptive predistorter training functionality. We then investigate the topic of PAR reduction for OFDM signals and forward link CDMA signals. To reduce the PAR of the OFDM signal, we propose a dynamic selected mapping (DSLM) algorithm with a two-buffer structure to reduce the computational requirement of the SLM method without sacrificing the PAR reduction capability. To reduce the PAR of the forward link CDMA signal, we propose a new PAR reduction algorithm by introducing a relative offset between the in-phase branch and the quadrature branch of the transmission system.

Selected mapping (SLM) schemes are commonly employed to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. It has been shown that the computational complexity of the traditional SLM scheme can be substantially reduced by adopting conversion vectors obtained by using the inverse fast Fourier transform (IFFT) of the phase rotation vectors in place of the conventional IFFT operations. To ensure that the elements of these phase rotation vectors have an equal magnitude, conversion vectors should have the form of a perfect sequence. This study firstly presents three novel classes of perfect sequence, each of which comprises certain base vectors and their cyclically shifted versions. Three novel low-complexity SLM schemes are then proposed based upon the unique structures of these perfect sequences. It is shown that while the PAPR reduction performances of the proposed schemes are marginally poorer than that of the traditional SLM scheme, the three schemes achieve a substantially lower computational complexity. Since the three proposed PAPR reduction schemes cannot be utilized in the orthogonal frequency division multiple access (OFDMA) system. A low-complexity scheme for PAPR reduction in OFDMA uplink systems using either an interleaved or a sub-band sub-carrier assignment strategy is also proposed in the second part of this study. The proposed scheme requires just one IFFT operation. The PAPR reduction performance of the proposed scheme is only marginally poorer than that of the traditional SLM scheme. However, the proposed schemes have significantly lower computational complexities. Besides, multiple-input multiple-output (MIMO) OFDM systems with space-frequency block coding (SFBC) are well-known for their robust performance in time selective fading channels. However, SFBC MIMO-OFDM systems have a high computational complexity since the number of IFFTs required scales in direct proportion to the number of antennas at the transmitter. Furthermore, SFBC MIMO-OFDM systems have a high PAPR. Accordingly, a low-complexity PAPR reduction scheme for SFBC MIMO OFDM systems with the Alamouti encoding scheme is proposed in this study. Extending this scheme obtains two low-complexity transmitter architectures for SFBC MIMO-OFDM systems with a general encoding matrix and an arbitrary number of transmitter antennas. The proposed schemes achieve a significant reduction in computational complexity by fully exploiting the time-domain signal properties of the transmitted signal. In addition, a PAPR reduction scheme is presented based on the proposed transmitter schemes. It is shown that the PAPR reduction performance of the proposed scheme is almost as good as that of the traditional SLM scheme, but is achieved with a substantially lower computational complexity.

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

In this work are presented results of the experimental study of state selected reactions of H+ and N+(3PJa) ions with molecular hydrogen H2(J = 0, 1) at temperatures in the range 10 - 100 K using 22-pole rf ion trap apparatus. These reactions are important for the formation of interstellar trihydrogen cations and ammonia. To determine the temperature of ions, calibration measurements of the Doppler broadening of spectral lines using N2+ + Ar  Ar+ + N2 laser induced reaction and rate of the ternary association He+ + 2He  He2+ + He were performed. Both ternary and radiative channels of the H+ + H2(J) association reaction were observed at hydrogen number densities in the range 1012 - 1014 cm-3 and 1011 - 1012 cm-3 respectively. Obtained temperature dependences at 11 - 33 K demonstrate substantial role of the H2 rotational energy, results cannot be explained with the existed theories of the stabilization of collisional complexes. Measurements of the rate coefficient of N+(3PJa) + H2(J) reaction at different ortho fractions of H2 show dependence on internal energy of both reactants. State specific rate coefficients of the reaction of nitrogen and hydrogen ions were derived. The adiabatic model and collisional relaxations of N+(3PJa) fine structure levels were considered. Powered by TCPDF (www.tcpdf.org)

Made available in DSpace on 2009-11-18T19:01:40Z (GMT). No. of bitstreams: 1 ACF184.pdf: 384059 bytes, checksum: a31414177b45e3233caa19e06b1294ee (MD5) Previous issue date: 2007 / The main purpose of this exploratory work is to investigate the attributes that motivate customers to choose services within beauty and aesthetic centers. Everyday, we are taking by surprise due to the discovery of new procedures that will make many dreams come true regarding youth¿s prolong. Customers are much more demanding now, so the beauty industry must emphasize the importance of beauty in our day lives. The old age fears, the need of men and women in getting close to the perfect beauty and looking great explaining the reason many customer looking for beauty and aesthetic centers to ¿postpone¿ the inevitable old age.This work focus on the increase of beauty and aesthetic industry market position, the quality of service provide by these centers, emphasize the concepts of service quoted by different authors, for instance, Lovelock (2006), Las Casas (2002), Kotler (1998), the characteristics of services, the behaviour of customers, the conceptualized models of service quality from Albrecht and Zemke (1998), moments of truth according to Carlzon (1994).This work presents a summary of beauty along the years; shows the methodology used and the interviews results showing the main quality service attributes in beauty and aesthetic centers; the difficulty faced and suggestion for future research. / O objetivo deste estudo exploratório é investigar quais os atributos que motivam os consumidores na escolha de serviços em ambientes de Estética e Beleza. Todos os dias somos surpreendidos por descobertas que possibilitarão a concretização do sonho tão cobiçado de prolongar a juventude. Com o mercado cada vez mais exigente, a indústria da beleza enfatiza a influência da ¿beleza¿. O medo da velhice, a necessidade que o homem e a mulher têm de parecer cada vez mais perfeitos e de se manter cada vez mais atuantes são alguns dos fatores que os induzem a adotar estratégias para retardar o inevitável envelhecimento. O trabalho aborda o crescimento do setor de Beleza e Estética; discute os aspectos relativos à qualidade do atendimento nos ambientes de Beleza e Estética; evidencia os fundamentos básicos dos conceitos de serviços citados por diferentes autores, a exemplo de Lovelock (2006), Las Casas (2002), Kotler (2000); as características dos serviços; o comportamento do consumidor; os modelos conceituais de qualidade em serviços de Albrecht e Zemke (1998); Momentos de verdade, segundo Carlzon (1994). Apresenta uma síntese da beleza através dos tempos; mostra a metodologia utilizada e o resultado das entrevistas que elegeram os principais atributos da qualidade de serviço nos ambientes de estética e beleza; as limitações do trabalho e sugestões para pesquisas futuras.

Performance in Lesotho at senior level (COSC) has been poor. One of the subjects which is performed poorly is Biology 5090. This prompted the researcher to examine factors responsible for the poor performance in Biology 5090. The study also aimed at finding ways in which teachers envisage to improve Biology 5090 performance. Data was collected from three schools through semi-structured interviews and document analysis. The study also adopted the General System Theory (GST) as the theoretical framework. Data was analyzed in line with qualitative content analysis, and from the perspective of the GST. The data analysis scheme was developed and presented (appendix P). The results of the study showed that Biology 5090 performance was affected by factors such as human resources, and the transformation process. The study also suggested ways in which Biology 5090 performance could be improved in Lesotho. These include: in-serving training, team work and others. / Science and Technology Education / M. Ed. (Natural Science Education)

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The diploma thesis is devoted to presentation of risks in the financial statements of the public sector entities, where the main objective is to evaluate the degree of presentation of risks in the financial statements and to assess of the current legislation and its possible amendments. The first chapter deals with the definition of the public sector and defines the term "selected accounting entity". The following chapter describes the general concept of risks, focusing on the public sector and on generally accepted principles and guidelines of accounting, in particular the conservatism. The third chapter discusses the accounting law for selected accounting entities and selected instruments of the accounting presentation of risks, including the comparison with the IAS/IFRS, IPSAS and US GAAP. The last chapter is divided to the practical parts, which the first one is based on data analysis of Central System of Accounting Information of the State (CSUIS) and the second one on the evaluation of the questionnaire survey for addressed accounting entities.

This thesis deals with risks threatening agricultural activity, with agricultural insurance and with state aid to agricultural insurance in the Czech Republic. Furthermore, it describes history and development of agricultural insurance in the Czech Republic. Under this chapter is explored dependence of the premium on selected factors. The attention is also paid to agricultural insurance schemes in 16 selected countries of the world. Consequently, there are proposed possible suggestions of improvement of current agricultural insurance system in the Czech Republic with regard to foreign practice. The supply of crop insurance including a practical example of farmer using crop insurance in his risk management is concisely described in the end of the thesis.

The diploma thesis is focused on comparison of selected differences in accounting and reporting of items in statutory financial statements which arise between Czech accounting legislation and International Financial Reporting Standards. Based on the selected differences, the effect of applying IAS / IFRS requirements on assets, liabilities and company's financial statements is described there. At the end of the thesis, the selected indicators of financial analysis are calculated, showing the performance of the company and its financial position.