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Soft-Decision Feedback Turbo Equalization for Multilevel Modulations

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2 Author(s)
Huang Lou ; Dept. of Electr. & Comput. Eng., Missouri Univ. of Sci. & Technol., Rolla, MO, USA ; Chengshan Xiao

Error propagation phenomena is the major drawback for existing hard-decision feedback turbo equalizers. In this paper, we propose a new soft-decision feedback equalizer (SDFE) suitable for multilevel modulation systems employing turbo equalization. The proposed SDFE offers a low computational complexity growing only linearly with the number of equalizer coefficients, as opposed to the quadratic complexity of MMSE-based linear turbo equalizer with time-varying coefficients (Exact-MMSE-LE). The performance and convergence property of the proposed SDFE are analyzed using extrinsic information transfer (EXIT) chart and verified by simulations in a severe intersymbol interference channel set by Proakis. Results show that our approach performs close to Exact-MMSE-LE for BPSK/QPSK modulation. And for 8PSK/16QAM modulations, the proposed SDFE performs much better. It exhibits lower SNR threshold (SNR required for “waterfall” BER) and much faster convergence than Exact-MMSE-LE.

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Signal Processing, IEEE Transactions on  (Volume:59 ,  Issue: 1 )