CSI-Adaptive Encoded Pilot-Symbols for Iterative OFDM Receiver with IRA Coding

This paper proposes a novel orthogonal frequency- division multiplexing (OFDM)-based iterative channel estimation and irregular repeat-accumulate (IRA) decoding scheme where the pilot symbols are encoded along with the input data and are used for both channel estimation and decoding. To achieve the objective of minimizing the bit error rate, this paper employs systematic IRA codes so that pilot symbols can be encoded as part of the data. In this way, initial channel estimation can be performed using the systematic encoded pilot symbols before channel decoding. In addition, the known pilot symbol positions have higher reliability than data and can significantly improve the initial decoding. The availability of channel state information (CSI) at the transmitter via feedback from the receiver is also exploited by introducing a second pilot permutation that adapts to the receiver channel conditions, which is shown to outperform the conventional uniform pilot spacing within the OFDM symbol. Simulation results verify the improvement in performance compared to iterative OFDM receivers with either un-encoded or encoded uniformly-spaced pilot symbols without CSI feedback.