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Equal educational opportunity for students with disabilities in CanadaSmith, William J., 1947- January 1993 (has links)
No description available.
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Análise comparativa de algoritmos adaptativos que usam estatísticas de alta ordem para equalização de canais esparsosFrasson, Felipe 03 July 2017 (has links)
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Atenciosamente,
Catarina Ribeiro
Bibliotecária BEE - Ramal 5992
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Felipe Frasson- Dissertação.pdf: 984658 bytes, checksum: 05ae4f112679292aefe890dc2f563010 (MD5) / Em um sistema de comunica c~oes, os sinais s~ao transmitidos atrav es de canais de comunica c~ao que, idealmente,
deveriam transportar os dados de maneira a n~ao causar distor c~ao alguma. Por em, em sistemas
reais, existem limita c~oes que interferem neste processo causando degrada c~ao nas informa c~oes transmitidas,
podendo comprometer sua recep c~ao. Tais limita c~oes ocorrem devido a presen ca de ru do aditivo, e
principalmente por interfer^encia intersimb olica, esta caracterizada pela sobreposi c~ao de s mbolos gerados
por uma mesma fonte transmissora. A equaliza c~ao de canal e uma das t ecnicas existentes que reduzem
os efeitos da interfer^encia intersimb olica, dando maior con abilidade e robustez aos sistemas de comunica
c~oes. Dentre as t ecnicas utilizadas para equaliza c~ao de canal, o uso de algoritmo adaptativos vem
sendo amplamente utilizados devido as suas propriedades de se auto-ajustarem as varia c~oes que ocorrem
ao longo do tempo.
Este trabalho tem como objetivo veri car o comportamento de diferentes tipos de algoritmos
adaptativos cegos ou semicegos, assim denominados por n~ao utilizarem sequ^encias de treinamento, aplicados
a equaliza c~ao de canais esparsos. Canais esparsos s~ao encontrados em diversos sistemas de comunica
c~oes como, por exemplo, na comunica c~ao sem o (telefonia m ovel, transmiss~ao de r adio e TV), ou,
ainda, em canais subaqu aticos. Os algoritmos foram escolhidos com base em recentes estudos desta aplica
c~ao, que operam em modo cego ou semicego e utilizam estat sticas de alta ordem, como os algoritmos
Bussgang e Matching Pursuit.
Os algoritmos foram implementados em ambiente de simula c~ao computacional no qual foram
utilizados canais esparsos simples e de resposta ao impulso conhecida, permitindo comparar o comportamento
dos diferentes algoritmos, em termos do sinal recuperado, e da inversa da resposta ao impulso do
canal original. / In communications systems, information signals are transmitted through communications channels that,
ideally, are delivered without distortions. However, on real communications channels there are limitations
that interferes on the process, reducing the probability to recover the original signal at receiver. These
distortions are basically thermal noise and Intersymbol Interference (ISI), caused by superposition on the
received symbols received from the same source. Channel Equalization acts reducing these distortions,
bringing more reliability to communications systems.
The objective of this work is to verify di erent adaptive algorithms behavior, applied to sparse
channel equalization problem. Many communications systems have sparse channels, like broadcast radio,
television, mobile telephony and underwater communications. The selected algorithms used in this work
includes high order statistics algorithms family, like Bussgang and Matching Pursuit. This kind of
algorithms are widely used, with high relevance, for blind channel equalization.
The selected algorithms were submitted to computer simulations using simple sparse channels
and knowledge about their impulse response, in order to analyze their behavior in therms of bit error
rate and the inverse impulse response of the channel.
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BLIND EQUALIZATION FOR FQPSK AND FQAM SYSTEMS IN MULTIPATH FREQUENCY SELECTIVE FADING CHANNELSGao, Wei, Wang, Shih-Ho, Feher, Kamilo 10 1900 (has links)
International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Blind adaptive equalization with application for Non-Linearly Amplified (NLA) quadrature
amplitude modulation (QAM) systems in multipath selective fading channels is presented.
With an offset sampling strategy in the receiver, the proposed blind equalization using
Constant Modulus Algorithm (CMA) exhibits a fast convergent speed for a family of
quadrature modulated systems in NLA and multipath fading channels. Feher’s patented
Quadrature Phase Shift Keying (FQPSK) and Feher’s Quadrature Amplitude Modulation
(FQAM) which correspond respectively to 4-state and 16-state QAM are used due to their
higher Radio Frequency (RF) power and spectral efficiency in NLA channel. It has been
shown that blind adaptive equalization can significantly open the eye signals in multipath
frequency selective fading channels.
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Combining a Reed-Solomon Block Code with a Blind Equalizer: Synchronization and Bit Error Rate PerformanceSkrzypczak, Alexandre, Blanc, Grégory, Le Bournault, Tangi 10 1900 (has links)
ITC/USA 2015 Conference Proceedings / The Fifty-First Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2015 / Bally's Hotel & Convention Center, Las Vegas, NV / The performance of telemetry systems may be strongly affected by diverse sources of perturbations. Among them, multipath channels and transmission noise are the most critical. While the effects due to the multipath channels can be attenuated thanks to equalization, the effects of the noise are limited if forward error correction is used. This paper first proves that the combination of blind equalization and forward error correction can strongly improve bit error rates. The other objective of the paper is to show that reasonably powerful codes like Reed-Solomon codes are sufficient to enable quasi-error free transmissions in a large majority of propagation channel scenarios.
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Can Space Time Encoding and Adaptive Equalization Benefit Rotary-Wing Missions at the Yuma Proving Ground?Diehl, Michael, Swain, Jason, Wilcox, Tab 10 1900 (has links)
ITC/USA 2015 Conference Proceedings / The Fifty-First Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2015 / Bally's Hotel & Convention Center, Las Vegas, NV / The US Army Yuma Proving Ground (YPG) utilizes telemetry in several critical ways. Data, video, and voice from test aircraft provides YPG the information necessary to effectively execute missions. This information must be displayed real-time for efficient use of available flight time, making a robust telemetry link vital. In seeking an increased telemetry downlink capability, YPG considered three new technologies: Space Time Coding (STC), Adaptive Equalization (EQ), and Low Density Parity Check (LDPC). These technologies have shown reduced multipath and increased datalink reliability on fixed-wing aircraft; however, YPG's concern was the technology's benefits on rotary wing aircraft tested here. To assess potential benefits of these technologies, YPG conducted flight tests using representative flight profiles and vendor-supplied equipment to collect quantitative and qualitative data.
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QAM Multi-path Characterization Due to Ocean ScatteringSwanson, Richard, Dimsdle, Jeff, Petersen, Tom, Pasquale, Regina, Bracht, Roger 10 1900 (has links)
International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California / A series of RF channel flight characterization tests were recently run to benchmark multi-path
performance of high-speed quadrature amplitude modulation (QAM) over the ocean surface. The
modulation format was differential-phase/absolute-amplitude two level polar 16 QAM. The bit rate
was 100 Megabits per second with a symbol period of 40nS. An aircraft radiated the test signal at 5
different altitudes. It made two inward flights, on two different days, at each altitude with vertical
and horizontal polarization, respectively. Receivers, using circular antenna polarization, were in two
different locations. Analysis of the resulting data shows flat fading and frequency selective fading
effects.
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A COMPARISON OF ADAPTIVELY EQUALIZED PCM/FM, SOQPSK, AND MULTI-H CPM IN A MULTIPATH CHANNELHill, Terrance, Geoghegan, Mark 10 1900 (has links)
International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California / It is widely recognized that telemetry channels, particularly airborne channels, are
afflicted by multipath propagation effects. It has also been shown that adaptive
equalization can be highly effective in mitigating these effects. However, numerous
other factors influence the behavior of adaptive equalization, and the type of modulation
employed is certainly one of these factors. This is particularly true on modulations which
exhibit different operating bandwidths. In this paper, we will examine the effect
multipath and adaptive equalization for three modulation techniques which are either
already in use, or have been proposed, for airborne telemetry.
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Simulation of wireless communications in underground tunnelsHe, Shabai January 2012 (has links)
The new released 4G standard wireless communication reminds us that higher transmission data rate and more reliable service are required urgently. However, to fulfill the demand can face problems in a complex environment like mines. In this thesis, characterization of underground tunnel mines with the idea of combating intersymbol interference effect is presented. Ray tracing simulation method is applied to characterize channel impulse response in different positions of an underground tunnel. From this channel impulse response, we can obtain how intersymbol interference affects different wireless systems. Intersymbol interference occurs due to multipath propagation of time dispersion channel. Adaptive Equalization is the most effective way to compensate intersymbol interference. Adaptive filter adapts filter coefficients to compensate the channel so that the combination of the filter and channel offers a flat frequency response and linear phase. The bit error rate performance without using adaptive equalization is compared with using equalizer. Moreover, adaptive equalization approaches using RLS and LMS algorithms are compared with each other. The tradeoff between convergence rate, computation cost instability and ensemble averaged minimum squared errors are analyzed to determine how to select the optimum adaptive equalizer.
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DEMOCRACY AND THE EDUCATION OF THE DISADVANTAGED: A PRAGMATIC INQUIRYWashburn, David E., Washburn, David E. January 1970 (has links)
No description available.
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Equalização pré-FFT de sistemas baseados em orthogonal frequency-division multiplexing. / Pre-FFT equalization of systems based on orthogonal frequency-division multiplexing.Acácio, Luís Carlos Lorenzo 19 October 2004 (has links)
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.
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