Turbo Equalization Based on Bi-Directional DFE

Abstract

We utilize a pair of decision feedback equalizers (DFEs) operating in opposite directions in turbo equalization setting to remove the effect of intersymbol interference (ISI) at the receiver. With a specific residual interference processing strategy proposed, the bi-directional DFE (BiDFE) are free from any significant error propagation. A diversity combining scheme is also proposed that effectively combines the extrinsic outputs of two opposite direction DFEs to minimize any correlation that may exist between them. A resulting scheme is a low-complexity equalizer that closely approaches the performance of the much more complex BCJR algorithm at the expense of an increased number of decoder-equalizer iterations. The BiDFE turbo equalizer also provides considerably better performance than the well-known soft linear minimum mean square error (MMSE) equalizer in severe ISI channels. The performance advantages are validated with bit-error-rate (BER) simulations and extrinsic information transfer (EXIT) charts analysis.