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Turbo-Equalization for bandwith-efficient digital communications over frequency-selective channels

Abstract : This thesis deals with the problem of combining equalization with decoding for high data rate bandwidth-efficient transmissions over frequency-selective channels. Specifically, we focus on Turbo-Equalization which establishes an exchange of soft information between the equalizer and the decoder in an iterative manner. We first consider MAP turbo-equalizers which rely on trellis-based equalizers optimum in the sense of minimizing the symbol error probability. We show that these receivers achieve significant performance gains over the conventional approach where equalization and decoding are performed separately. However, the complexity of MAP turbo-equalizers becomes rapidly prohibitive for transmissions with high-order modulations over long delay spread channels. Hence, we then investigate reduced-complexity turbo-equalizers relying on filtering-based equalizers optimized according to the MMSE criterion. These equalizers share the common property of accounting explicitly for the presence of a priori information in the computation of the optimum filters coefficients and thus outperform classical MMSE equalizers. Our analysis shows that MMSE turbo-equalizers offer an attractive alternative to MAP turbo-equalizers for multilevel coded transmissions over long delay spread frequency-selective channels. We finally describe the implementation of an MMSE turbo-equalizer on the low-cost fixed-point TMS320VC5509 DSP device which is typically targeted at portable terminals. Using only C programming, a promising data rate of 42 Kbits/s has been achieved with 5 iterations. This result demonstrates the possibility of realizing such receivers in practice with current hardware capabilities.
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Contributor : Raphaël Le Bidan <>
Submitted on : Thursday, November 2, 2006 - 9:56:51 AM
Last modification on : Wednesday, January 6, 2021 - 3:33:39 PM
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  • HAL Id : tel-00110853, version 1


Raphaël Le Bidan. Turbo-Equalization for bandwith-efficient digital communications over frequency-selective channels. Signal and Image processing. INSA de Rennes, 2003. English. ⟨tel-00110853⟩



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