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Previous issue date: 2017-08-30 / Conselho Nacional de Pesquisa e Desenvolvimento Cient?fico e Tecnol?gico - CNPq / The wireless communication channel has severe signal degradation effects resulting from the usual multiplicity of propagation paths originated by reflection of the electromagnetic wave at specific points along the path of the digital transmitter-receiver link. Metallic building structures, for example, are points of reflection of the wave. This multiplicity of propagation paths, called multipath, generates signal interference on itself when multiple signals arrive at the receiver, degrading signal intelligibility, which increases the bit error rates of the link, reducing a reliability. This interference is called intersymbol interference (ISI) because, in the baseband signal at the receiver, overlapping of the digital modulation symbols occurs, resulting in a failure to detect the binary words associated with the symbols. In this context, the channel estimation and compensation process plays an important role in the wireless receiver. The increasing demand for systems with higher transmission capacities, robustness and less computational complexity, has driven several researches in the scope of the algorithms used in the channel estimation process. In recent years, data transmission technique through Orthogonal Frequency Division Multiplexing (OFDM) has been highlighted by resistance to ISI, good spectral efficiency and transmission capacity of high data rates. OFDM is a multi-carrier modulation technique that consists of dividing the total bandwidth into smaller subchannels by using orthogonal subcarriers spectrally superimposed. Despite its robustness, it is still required channel estimation techniques, in OFDM receiver, due to the multipath effect characteristic of a wireless communication channel. This work proposes the implementation of a channel estimator, based on a complex Radial Basis Function (RBF) network. The proposed network is trained from the impulse response of the channel obtained through the pilot carriers sent and known by the receiver. The simulation results show that the proposed network obtained better results than the classical estimators used for channel estimation in OFDM systems. / O canal de comunica??o sem fio (wireless) apresenta severos efeitos de degrada??o de sinal resultantes da usual multiplicidade de caminhos de propaga??o originados por reflex?o da onda eletromagn?tica em pontos espec?ficos ao longo do caminho do enlace entre transmissor e receptor digital. Estruturas met?licas de constru??es civis, por exemplo, constituem pontos de reflex?o da onda. Esta multiplicidade de caminhos de propaga??o, denominada multipercurso, gera interfer?ncia do sinal sobre ele mesmo quando os m?ltiplos sinais chegam ao receptor, degradando a inteligibilidade do sinal recebido em consequ?ncia dos m?ltiplos ecos do sinal, o que aumenta a taxa de erro de bits do enlace, reduzindo a confiabilidade. Denomina-se esta interfer?ncia de interfer?ncia intersimb?lica (ISI, do ingl?s intersymbol interference) porque, no sinal em banda-base no receptor, ocorre superposi??o dos s?mbolos da modula??o digital, resultando em falha na detec??o das palavras bin?rias associadas aos s?mbolos. Neste contexto, o processo de estima??o e compensa??o dos efeitos do canal desempenha um papel importante em um receptor de comunica??o wireless. A crescente demanda por sistemas de maiores capacidades de transmiss?o, robustez e menor complexidade computacional, tem impulsionado v?rias pesquisas no ?mbito dos algoritmos utilizados no processo de estima??o de canal. Nos ?ltimos anos a t?cnica de transmiss?o de dados atrav?s da Multiplexa??o por Divis?o Ortogonal de Frequ?ncia (OFDM) tem ganhado destaque por apresentar resist?ncia ? ISI, boa efici?ncia espectral e capacidade de transmiss?o de altas taxas de dados. OFDM ? uma t?cnica de modula??o por multiportadoras que consiste na divis?o da largura de banda total em subcanais menores, utilizando subportadoras ortogonais sobrepostas espectralmente. N?o obstante a sua robustez, faz-se ainda necess?rio aplicar t?cnicas de estima??o de canal no receptor OFDM, devido ao efeito de m?ltipercurso caracter?stico de um canal de comunica??o wireless. Neste trabalho ? proposto a implementa??o de um estimador de canal, baseado em uma rede neural com fun??o de base radial (RBF, do ingl?s Radial Basis Function) complexa. A rede proposta ? treinada a partir da resposta ao impulso do canal obtida atrav?s de portadoras piloto enviadas e conhecidas pelo receptor. Os resultados da simula??o mostram que a rede proposta obteve melhores resultados do que os estimadores cl?ssicos utilizados para estima??o de canal em sistemas OFDM.
| Identifer | oai:union.ndltd.org:IBICT/oai:tede2.pucrs.br:tede/7663 |
| Date | 30 August 2017 |
| Creators | Baloi Junior, H?lder Rob?lcio Agostinho |
| Contributors | De Castro, Maria Cristina Felippetto |
| Publisher | Pontif?cia Universidade Cat?lica do Rio Grande do Sul, Programa de P?s-Gradua??o em Engenharia El?trica, PUCRS, Brasil, Faculdade de Engenharia |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Format | application/pdf |
| Source | reponame:Biblioteca Digital de Teses e Dissertações da PUC_RS, instname:Pontifícia Universidade Católica do Rio Grande do Sul, instacron:PUC_RS |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | 207662918905964549, 500, 500, 500, 600, -655770572761439785, 4518971056484826825, -2555911436985713659 |
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