Improved iterative channel estimation and turbo decoding over flat-fading channels

In this paper, we discuss the influence of imperfect Wiener channel estimation on performance and dynamics of a turbo decoder using nonlinear soft data feedback. We show that the correlation between the channel estimates and soft bits produced in subsequent iterations can lock the turbo decoder in a wrong minimum and create a high error floor. This problem can be circumvented by a different way of estimating code symbols used to improve the synchronization of the signal. An enhanced version of the channel estimator using Wiener filtering of the initial pilot symbols, followed by a modified Viterbi decoder and turbo decoder is shown to improve the system´s performance by around 0.5 dB in the waterfall region and to considerably lower the error floor.