Optimal detection of QAM signals in fast fading channels with imperfect channel estimation

In this paper, we derive an optimal detector for pilot-assisted transmission in Rayleigh frequency-flat fast fading channels. The classical detector based on obtaining channel estimates and treating them as perfect in a minimum distance detector is called mismatched detector. The optimal detector jointly processes the received pilot and data symbols to recover the data with a minimum error. We consider spline approximation of the channel gain time variations and compare the detection performance of mismatched detectors using maximum likelihood channel estimates with the optimal one. Further, we investigate the detection performance of a receiver that iteratively improves the channel and data information in a system transmitting turbo-encoded data, where a channel estimator provides either maximum likelihood estimates or statistics for the optimal detector. Simulation results show that the optimal detector significantly outperforms the mismatched detectors.