Performance of turbo codes in Rayleigh fading channels with adaptive channel estimation

For turbo-coding systems in mobile fading environments, fading amplitudes must be provided to the turbo decoder in order to exhibit the full potential of turbo codes. We investigate the performance of turbo-coding systems with adaptive channel estimation in the Rayleigh flat-fading channels. Two system models are considered for simulations. In the first model, the channel estimation is performed prior to the turbo decoder. In the second model, the decision-directed approach for refined channel estimation is considered where the fading amplitudes are re-estimated with the aid of the hard-decided turbo-decoder outputs. The least mean square (LMS) algorithm and the general optimum block adaptive (GOBA) algorithm are used for the adaptive channel estimators in the two system models. Simulation results have shown that the GOBA channel estimator with the decision-directed approach provides much better estimates of the fading amplitudes, thereby significantly improving the bit error rate (BER) performance of the turbo-coding systems