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Theses

Etude et amélioration d'une technique de réception numérique itérative : turbo-égalisation

Abstract : The aim of this thesis is to study and to improve a digital receiver which is called a turbo-equalizer and is based on the turbo principle. This system consists of several functions that treat iteratively different disturbances created by the propagation channel. A special equalizer called the Interference Canceller (IC) build with filters optimized according to the Minimum Mean Square Error (MMSE) criterion combats the InterSymbol Interference (ISI). Then a channel decoder processes the additive noise and the residual ISI. Each function generates soft information about the emitted data that are improved at each treatment. Consequently ISI is progressively cancelled during the iterations.

Thanks to an analogy with the coded modulations, we can explain the influence of the interleaving scheme, which can be performed on the bits or on the symbols of modulation, on the performance of the turbo-equalization for different time selectivity characteristics of the propagation channel. In order to obtain satisfactory performance on the ionospheric channel, whose characteristics are well-known to be difficult, we study different structures and algorithms of the equalizers of the turbo-equalization. We then present the improvements of the demapping without a priori information. A mapping optimization for the demapping function with a priori information is proposed and leads to a gain in Bit Error Rate performance. Finally, we compare the turbo-equalization to three alternative techniques : a system with a turbo-decoder, the COFDM scheme and a turbo-detector with reduced-state trellis, called turbo-DDFSE.
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https://tel.archives-ouvertes.fr/tel-00008945
Contributor : Charlotte Langlais <>
Submitted on : Monday, April 4, 2005 - 3:58:17 PM
Last modification on : Thursday, November 7, 2019 - 1:19:17 AM
Long-term archiving on: : Friday, April 2, 2010 - 9:22:42 PM

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  • HAL Id : tel-00008945, version 1

Citation

Charlotte Langlais. Etude et amélioration d'une technique de réception numérique itérative : turbo-égalisation. Traitement du signal et de l'image [eess.SP]. INSA de Rennes, 2002. Français. ⟨tel-00008945⟩

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