Este trabalho trata da comparação entre os sistemas OFDM (orthogonal frequency division multiplexing) e SCCP (single carrier with cyclic prefix). Tais sistemas são analisados em função da ordem da modulação, da sensibilidade em relação à taxa de codificação de canal e do tipo de entrelaçamento utilizado. A comparação é efetuada através da adoção de um arcabouço que provê uma abordagem universal para o tratamento de ambos os sistemas. São obtidos resultados teóricos, explorando características de convexidade de funções, e resultados a partir de simulação Monte Carlo. Os sistemas são comparados, principalmente, em termos de BER (bit-error rate). Entretanto, também são realizadas comparações em termos de probabilidade de outage por cutoff rate e da SNR (signal to noise ratio) efetiva na saída do equalizador. Finalmente, os sistemas ainda são avaliados quanto à sensibilidade a erros de estimação de canal. / This work deals with the comparison between the OFDM (orthogonal frequency division multiplexing) and SCCP (single carrier with cyclic prefix). These systems are analyzed as a function of the modulation order, the sensitiveness to the channel coding rate and to the interleaver configuration. The comparison is accomplished by means of a system model that leads to an universal framework to both analyzed systems. Theoretical results are obtained exploring convexity properties of functions. In addition, some results provided by Monte Carlo simulation are also presented to complement the analysis. The systems are compared mainly in terms of the BER (bit-error rate). Moreover, comparisons in terms of outage probability obtained by cutoff rate and in terms of the effective SNR (signal to noise ratio) at the equalizer output are also provided. Finally, the systems will be compared when channel estimation error are presented at the receiver.

Esta dissertação trata da equalização no domínio do tempo de sistemas de comunicações digitais baseados em orthoghonal frequency-division multiplexing (OFDM), normalmente referida na literatura técnica como equalização pré-FFT. Tais sistemas foram originalmente projetados de modo a não necessitar de equalização, porém podem se beneficiar com seu uso, como mostrado a seguir. Foi implementado, em programa de computador, um simulador não codificado do sistema de televisão digital terrestre utilizado na Europa, o digital video broadcasting (DVB-T), que é baseado em OFDM e se encontra implantado com sucesso há alguns anos. Diversas simulações foram executadas comparando o método tradicional de recepção do sistema DVB-T com a versão equalizada proposta. Foram utilizadas várias técnicas de processamento digital de sinais para simular: a geração do sinal, sua passagem por um canal de comunicação com multipercurso, presença de ruído branco Gaussiano aditivo, equalização LMS (Least Mean Square), entre outros fenômenos importantes. Para um firme embasamento, o trabalho apresenta estudos matemáticos sobre a teoria geral do OFDM, modelos de canais de comunicação e o princípio básico do algoritmo LMS. Tendo-se utilizado o DVB-T como estudo de caso prático, não poderia deixar de constar uma descrição técnica desse sistema em que são apresentados vários dos detalhes e problemas envolvidos na geração e recepção do sinal. Com a finalidade de posicionar o leitor histórica e tecnologicamente, o texto inclui ainda uma revisão dos principais fatos que marcaram o desenvolvimento do OFDM desde os estudos iniciais até os dias de hoje. / This dissertation deals with time-domain equalization of digital communications systems based on orthoghonal frequency-division multiplexing (OFDM), usually referred as pre-FFT equalization in the technical literature. Such systems were originally designed to require no time equalization but can profit from its use, as is shown in this work. An uncoded simulator of the OFDM-based European system for terrestrial digital television transmission, the digital video broadcasting (DVB-T), was implemented in software. Many simulations were run to compare the performance of the traditional DVB-T reception method with the equalized version proposed. Several digital signal processing techniques were used to simulate as diverse fenomena as: generation of the source signal, effect of multipath communications channels, presence of additive white Gaussian noise, LMS (Least Mean Square) equalization, among others. In order to develop a solid base, the work includes mathematical studies about the general OFDM theory, models of communications channels and the basic principle of operation of the LMS algorithm. Since the DVB-T was used as a practical study case, a technical description of the system is presented, in which many problems and aspects about its generation and reception are discussed. To provide the reader with a historical and technological insight on the subject, this work also includes a summary of the landmarks in the development of the OFDM since the first experiments.

Multipath is one of the dominant causes for link loss in aeronautical telemetry. Equalizers have been studied to combat multipath interference in aeronautical telemetry. Blind equalizers are currently being used with SOQPSK-TG. The Preamble Assisted Equalization (PAQ) project studied data-aided equalizers with SOQPSK-TG. PAQ compares, side-by-side, no equalization, blind equalization, and five data-aided equalization algorithms: ZF, MMSE, MMSE-initialized CMA, and frequency domain equalization. This thesis describes the GPU implementation of data-aided equalizer algorithms. Static lab tests, performed with channel and noise emulators, showed that the MMSE, ZF, and FDE1 show the best and most consistent performance.

This dissertation presented research by the author in the development of a computer Decision Support System (DSS) for assisting in providing equal educational opportunity in a public school district. The research process consisted of five major phases: (1) The support of a local school district was obtained, and, with the assistance of the superintendent, a task group of concerned administrators was assembled to assist in defining the needs and goals for the DSS. (2) A list of key variables was developed for inclusion in the support system. Data were gathered and stored for a preliminary version of the DSS. (3) A thorough literature review was undertaken in order to reach an understanding of the concepts involved in Equality of Educational Opportunity (EEO) sufficient to provide a model to be included in the DSS. The literature review led to the development of four conceptual (subjective) EEO models. (4) Analytical techniques were undertaken to determine which model, if any, best represented reality (as defined by the data gathered in Phase 2.) The analytical techniques used were: correlation analysis, subgroup analysis, graphic analysis, and phenomena explanation. The results showed that one model, identified as the EEO Achievement Aspects Subjective Model, best fit the data examined. (5) The model was incorporated into a DSS in such a way that a single value, termed an EEO Accountability Index, was calculated for a given set of data. The potential uses of such an index and of such a DSS were then explained. The expected use of the DSS is in providing analyses based on a statistically-derived model of reality. The process of building the statistically-derived model is expected to add new insights into the concepts of EEO. Accordingly, this research is anticipated to be of particular use to (1) information specialists, (2) school district board members, superintendents, and decisionmakers, and (3) other academicians interested in developing a better understanding of the concepts of EEO and the implications those concepts have for educational decisionmaking.

The paper describes the content of the project “Tax-/Transfer-Reform and Fiscal Responsibility: Pathways to a Sustainable Fiscal Policy in Georgia”, which is supported for the period Fall 2005 to Spring 2008 by the VolkswagenStiftung. Within the project a knowledgetransfer is organized, concentrating on state theory, tax and transfer reform, revenue sharing as well as fiscal equalization. A short overview on the current situation in Georgia is presented. Then the main project components – tax reform, tax revenue estimation and microsimulation – are briefly discussed.

Under the influence of orientation towards European integration, Georgia has introduced a variety of new laws with the apparent aim to decentralize legislative and executive powers. This paper shows that the Georgian efforts of decentralization remain superficial, mainly because they are not backed by additional fiscal competences at the municipality level. Following an initial description of the pre-reform situation as of 2006 and based upon a detailed account of the structural changes since 2007, the author gives insight into the conflicts which arise from the lack of institutional congruency. Neither the extraordinary status of the capital Tbilisi nor the seeming autonomy of the Rebublic of Adjara are likely to sway the renegade territories of Abchasia and Ossetia towards a reintegration under Georgian centralized rule as it continues to exist today. Likewise, the success of the proposed and discussed fiscal equalization scheme depends on whether the President and his ruling party are willing to delegate powers to the subodinate jurisdictions.

This paper discusses the problems regarding the decentralisation of a formerly communist country. In Georgia, the first steps towards decentralisation failed, since the transition process led to a power vacuum that escalated in bloody conflicts and secessionist movements. The status of Abkhazia and South Ossetia is still unclear and the intra-state tensions remain unsolved. This may be one of the reasons why the most recent attempts of decentralisation are rather hesitant. It is far from clear whether decentralisation in response to regional tensions would increase instability or political stability. We identify the limited autonomy at the local and regional levels as a major obstacle and challenge for the further reform process.

In recent years, ultra-wideband (UWB) communications has gained tremendous popularity in both research community and industry. The large bandwidth of UWB systems raises new wireless channel effects and consequently unique advantages as well as challenges to be dealt with, compared to conventional wireless systems. One of these advantages is the ability to resolve dense multipath components and use Rake combining at the receiver in order to significantly reduce the negative effects of fading. However, implementing a Rake receiver with a sufficiently large number of fingers to make use of this advantage is an evident challenge for most UWB devices with limited signal processing capabilities. A possible approach to overcome this problem is to move computational complexity from the receiver to the more powerful transmitter, which is the main focus of the present work. In this thesis, we propose two novel pre-equalization schemes for multiple- input single-output (MISO) direct-sequence ultra-wideband (DS-UWB) systems with pre-Rake combining and symbol-by-symbol detection. The first pre-equalization filter (PEF) scheme employs one PEF per transmit antenna, whereas in the second, simplified PEF (S-PEF) scheme all transmit antennas share the same PEF. For both schemes the optimum finite impulse response (FIR) and infinite impulse response (IIR) PEFs are calculated based on the minimum mean squared error (MMSE) criterion. We show that in contrast to previously proposed schemes for DS-UWB, both our proposed PEF schemes efficiently exploit the channel shortening properties of the pre-Rake filter. In particular, our proposed PEF schemes operate at the symbol level. We also show that under certain conditions the S-PEF scheme achieves the same performance as the more complex PEF scheme. Finally, we demonstrate that a single-input multiple-output (SIMO) DS-UWB system with post-Rake combining and MMSE post-equalization is the dual system to the considered MISO DS–UWB system with pre-Rake combining and MMSE pre-equalization. This uplink-downlink duality can be exploited for efficient calculation of the PEFs and for complexity reduction. Our simulation results show that the proposed PEF schemes achieve significant performance gains over pre-Rake combining without equalization even if only short PEFs are employed, and this is the case even for long UWB channel impulse responses.

A 4-PAM/2-PAM receiver analog front-end (AFE) targeting 20GSymbol/s for use with coaxial cable channels is presented. Behavioral simulations incorporate a transmitter, scalable coaxial cable model, and the proposed receiver architecture, targeting cable loss of 32dB at 10GHz. To accommodate links of varying lengths, the AFE includes a variable-gain amplifier (VGA) and analog peaking equalizer. The input preamplifier is important for achieving the required input sensitivity. A DC bias current is introduced through the feedback resistor in a conventional shunt-shunt feedback nMOS transimpedance amplifier (TIA) to level-shift the output, obviating a following level-shifting stage. The fabricated AFE occupies 0.89mm2 in a 90-nm CMOS process and dissipates 138mW from a 1.3V supply. The AFE amplifies and opens the eye pattern of a 20-Gb/s 2-PAM data stream transmitted over coaxial cable with 7.5dB loss at 10GHz.

This thesis presents the design, implementation, and fabrication of a pattern-guided equalizer in a 65nm CMOS process. By counting the occurrence of 6 out of 16 4-bit patterns in the received data and utilizing their spectral content, the signal is equalized separately at fN and fN/2, where fN is half the bit rate. The design was packaged using a 64 pin Quad Flat No leads (QFN) package. Two different channels were used and the equalizer was able to open the eye for both 13dB and 17dB of attenuation at the Nyquist frequency. The adaptation performance was determined by measuring the vertical and horizontal eye openings for all possible equalizer coefficients. Measured results at 6Gb/s confirm that the adaptation engine opens a closed eye to within 2.6% of optimal vertical opening and 7% of optimal horizontal eye opening while consuming 16.8mW from a 1.2V supply.