Modeling the influence of fading channel estimation errors on turbo code performance

In this paper, we address the issue of imperfect fading channel estimation in turbo-coded systems. Since turbo codes are influenced in different ways by different components of channel estimation errors, we develop a simplified model which separates the estimation errors of a Wiener-filtered fading channel into the amplitude error and the phase error. The derivations show that the classical Wiener filtering results in a biased estimate of the channel amplitude. We also show that the probability of having a phase estimation error large enough to cause decision error in the receiver is significant. Based on the model we derive an upper limit on the optimum pilot symbol spacing and propose a simple method to evaluate the performance of turbo codes with a given pilot symbol separation. The proposed model and derivations are confirmed by extensive simulations.