Joint turbo channel estimation and data recovery in fast fading mobile coded OFDM

Abstract

Orthogonal frequency division multiplexing (OFDM) systems suffer performance degradation in fast fading channels due to intercarrier interference (ICI). Combining frequency domain equalization and bit-interleaved coded modulation (BICM), the iterative receiver is able to harvest both temporal and frequency diversity. In order to perform coherent detection and estimation, channel state information (CSI) is critical. Conventional frequency domain channel estimation (CE) methods have an irreducible error floor at high normalized Doppler frequency fdTs, since ICI corrupts the orthogonality among subcarriers. Considering that the fast time-varying channel is also a source of temporal diversity, CE ought to take place in the pre-FFT time domain. With soft a priori information about the data symbols becomes available, this paper proposes a turbo channel estimator (TCE) structure which provides a way to consistently improve the bit error rate (BER). The complexity of TCE is further reduced by completely avoiding matrix inversion. Simulation results demonstrate that the PSAM system with TCE achieves no ICI with normalized Doppler frequency fdTs up to 20.46% with realistic mobile WiMAX channel environment.