Selective Fading
Mostrando 1-12 de 15 artigos, teses e dissertações.
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1. Desempenho de codigo turbo quaternario em sistemas de multiplexação por divisão de frequencias ortogonais / Performance of quaternary turbo codes in orthogonal frequency division multiplex systems
This study evaluates the performance of quaternary turbo codes, with generator matrix G = [7, 5] for the constituent convolutional codes and s-random interleaving , in an OFDM transmission system. This performance is measured in terms of bit error rate versus energy per bit to unilateral noise power spectral density ratio. The results obtained are analyzed c
Publicado em: 2010
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2. Códigos LDPC quaternários aplicados à técnica de transmissão OFDM / Quaternary LDPC codes applied to OFDM transmission technique
This dissertation addresses the study of error correcting codes based on sparse non-binary matrices. The LDPC (Low Density Parity Check) codes constitute a efficient family of codes generated by sparse parity check matrices and it is considered as one of the classes of codes that presents the best performance in digital communications systems. LDPC codes ove
Publicado em: 2010
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3. Evaluation of the spread sequences selection algorithm over frequency selective fading channels with error correcting codes / Avaliação do algoritmo de busca de sequencias de espalhamento em canais com desvanecimento seletivo em frequencia com codigos corretores de erros
The performance of wireless communication systems that use the multiple access code division technique, CDMA, is interference-limited. A sequence selection algorithm allows a reduction in the mean interference of the system. In the standards like CDMA2000 and WCDMA no algorithm is defined for choosing the sequences. For this reason, in this dissertation we e
Publicado em: 2008
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4. EstratÃgias de EstimaÃÃo para Canais Variantes no Tempo em Sistemas OFDM / Strategies of estimation for channels variantions in the time in OFDM systems
Nesta dissertaÃÃo à abordado o problema de estimaÃÃo de canais variantes no tempo em sistemas de modulaÃÃo OFDM (Orthogonal Frequency Division Multiplexing). Foi escolhido o modelo de canal WSS-US (Wide Sense StationaryâUncorrelated Scattering) com um nÃmero de percursos bem definido. Mostrou-se que, quando o canal à seletivo no tempo, as sub-porta
IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia. Publicado em: 31/08/2006
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5. Selection algorithm of spreading sequences for CDMA systems with space-time coding and antenna array / Algoritmo de escolha de sequencias de espalhamento em sistemas CDMA com codificação espaço-temporal e arranjo de antenas
The performance of mobile communication systems based on the CDMA technique is limited by interference. In this thesis, we propose a selection algorithm of spreading sequences with fixed length for interference mitigation on CDMA systems over frequency-selective fading channels, that is based on the minimization of the overall mean bit error probability of t
Publicado em: 2005
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6. EFFECTS OF ATMOSPHERIC MULTIPATH IN LINE-OF -SIGHT MICROWAVE SYSTEMS / EFEITOS DE MULTIPERCURSOS ATMOSFÉRICOS EM ENLACES DE MICROONDAS EM VISIBILIDADE
The variations which happen in the troposphere layers throughout the time in relation to the median condition of the signal cause various phenomena that change the received signal level at digital radio relay systems randomly. The random changes are named fading. Fading is normally classified as fast or slow. The former is normally associated with the atmosp
Publicado em: 2004
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7. Modulação Multiportadora M-QAM Não-Quadrada Codificada por Blocos para Canais com Modelo de Rummler
Um dos principais fatores que provocam a degradação da qualidade dos sistemas digitais de longo alcance em linha de visada com taxas de transmissão na ordem de algumas dezenas de Mb/s, são os desvanecimentos seletivos em freqüência. Uma das alternativas para diminuir o efeito provocado pelos desvanecimentos seletivos em freqüência é a utilização d
Publicado em: 2004
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8. Modulação multiportadora codificada por bloco para radioenlaces digitais em microondas com linha de visada
The availability of line-of-sight (LOS) microwave digital systems which work at high transmission rates such as 155 Mb/s, may be strongly limited by frequency-selective fading effects. The main countermeasure techniques against the fading are equalizations, diversity and error control coding. Under adverse geoclimatic conditions, the path length and/or the t
Publicado em: 2002
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9. Desempenho de sistemas CDMA com detector multi-usuario descorrelacionador
: ln this study, simpIe and precise expressions for the mean asymptotic multiuser efficiency of synchronous and asynchronous CDMA systems using multiuser decorrelating detection (MUD-D) are obtained. Expressions for the signal-interference plus noise ratio (SlNR) gain of MUD-D in relation to the conventional detection on AWGN and frequency-selective and non
Publicado em: 2002
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10. Um sistema FH-CDMA com cancelamento de interferencia e codigos corretores de erro
This work presents a study of interference cancellation for a FH-CDMA system. At first, the performances of two interference cancellation algorithms proposed by Timor and Fiebig are compared for a channel with noise and frequency selective fading. Timor s algorithm, which makes use of the algebraic structure of the users addresses, showed a better tradeoff b
Publicado em: 1999
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11. Desempenho de codigos TCM sobre aneis em canais com desvanecimento
This thesis presents the performance of coded modulation with convolutional codes over rings of integers modulo-8 on fadinf channels. The performance is obtained by computer simulation and it is given by curves of Bit Error Rate (BER) versus Signal to Noise Ratio (SNR). Basic concepts related with codes modulation, characterization of digital modulations, co
Publicado em: 1998
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12. DETECTION OF TRELLIS-COBE MODULATED SIGNAL IN FREQUENCY NON-SELECTIVE FADING CHANNELS / DETEÇÃO DE SINAIS COM MODULAÇÃO CODIFICADA EM TRELIÇA EM CANAIS COM DESVANECIMENTO NÃO-SELETIVO EM FREQÜÊNCIA
Este trabalho examina uma nova estratégia para detenção de Sinais TCM em presença de desvanecimento não-seletivo em freqüência. Esta estratégia faz uso de um conjunto de estimativas da distorção do canal, cada uma associada a um estado da treliça de decodificação, que são utilizadas simultaneamente no processo de decodificação. No método pro
Publicado em: 1997