Joint channel estimation and turbo decoding for OFDM-based systems

In this paper, we propose a joint channel estimation and decoding scheme using soft bit output information in OFDM-based systems. In order to estimate the complex OFDM channel amplitudes, the estimation algorithms usually rely on the pilot signal assisted modulation (PSAM). We enhanced this method by using the soft code bits after each turbo decoding iteration in a feedback loop. This way, the quality of the initial channel estimation can be significantly increased without the need of using additional pilot symbols. The proposed algorithm is tested on a selection of different time and frequency selective fading channels based on Rayleigh fading discrete taps of an exponentially decaying average power delay profile. We compare the performance of our algorithm with other channel estimation techniques for two different sizes of the data frame and demonstrate gains in order of 1-2 dB. We also show that our algorithm is better suited for fast changing, highly frequency-selective channels.