Performance of turbo frequency domain equalizer using iterative decision-directed channel estimation for DFT-precoded OFDMA

This paper proposes iterative decision-directed channel estimation (IDDCE) associated with the turbo frequency domain equalizer (FDE) for discrete Fourier transform (DFT)-precoded Orthogonal Frequency Division Multiple Access (OFDMA). By using soft-symbol estimations based on the extrinsic log-likelihood ratio (LLR) at the Max-Log-MAP decoder output and for the reference signal (RS), the accuracy of the channel response is improved in the iterative inner loop employing the feed-forward (FF)-FDE at an iteration of the outer loop for the turbo FDE. Computer simulation results show that the improvement in the required average received signal-to-noise power ratio (SNR) that satisfies the target average block error rate (BLER) is saturated with two iterations for both inner and outer loops regardless of the modulation scheme. We also show that IDDCE using the FF-FDE based on the Minimum Mean-Square Error (MMSE) criterion at an iteration of the turbo FDE is effective in improving the average BLER of the turbo FDE.