ADAPTIVE COMBINED DFE MLSE TECHNIQUES FOR ISI CHANNELS/

By embedding a decision-feedback equalizer (DFE) into the structure of a maximum-likelihood sequence estimator (MLSE), an adaptive combined DFE/MLSE scheme is proposed. In this combined DFE/MLSE, the embedded D FE has three functions: i) prefiltering the received signals and trunc ating the equivalent channel response into the desired one, ii) compen sating for channel distortions, and iii) providing the MLSE detector w ith predicted values of input signals, Since the embedded MLSE detecto r operates on the predicted signals the detected symbols at the output of the DFE/MLSE do not suffer arty delay and can be directly fed back into the embedded DFE so that the error propagation, which usually ta kes place in conventional DFE, can be greatly reduced, Analytical and simulation results indicate that the performance is significantly impr oved by the DFE/MLSE compared to conventional DFE while its computatio n complexity is much less than that of conventional MLSE receiver, The combined DFE/MLSE can use different adaptive structures (block-updati ng, sliding window updating or symbol-by-symbol updating) to meet diff erent performance objectives. Moreover, the proposed DFE/MLSE provides a trade-off between performance and complexity with a parameter m rep resenting the MLSE detection depth as well as the number of predicting steps of the embedded DFE, For some particular values of m, this sche me is capable of emulating the conventional DFE, MLSE-VA, adaptive LE- MLSE equalizer, adaptive DDFSE, and adaptive BDFE without detection de lay.