Iterative MAP equalization and decoding in wireless mobile coded OFDM

Authors:
Daniel N. Liu;Michael P. Fitz
Affiliations:
Electrical Engineering Department, University of Southern California, Los Angeles, CA and UnWiReD Laboratory, The Department of Electrical Engineering, University of California Los Angeles, Los An ...;Northrop Grumman Corp., Redondo Beach, CA and UnWiReD Laboratory, The Department of Electrical Engineering, University of California Los Angeles, Los Angeles, CA
Venue:
IEEE Transactions on Communications
Year:
2009

Citing 2
Cited 1

Low-complexity equalization of OFDM in doubly selective channels

IEEE Transactions on Signal Processing
ICI mitigation for pilot-aided OFDM mobile systems

IEEE Transactions on Wireless Communications

On channel estimation in fast fading mobile coded MIMO OFDM

ISIT'09 Proceedings of the 2009 IEEE international conference on Symposium on Information Theory - Volume 2

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Abstract

Orthogonal frequency division multiplexing (OFDM) system suffers extra 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. Realizing that ICI channels are intrinsically ISI channels, this paper proposes a soft-in soft-out (SISO) maximum a posteriori (MAP) equalizer by extending Ungerboeck's maximum likelihood sequence estimator (MLSE) formulation to ICI channels. The SISO MAP equalizer employs BCJR algorithm and computes the bit log-likelihood ratios (LLR) for the entire received sequence by efficiently constructing a trellis that takes into account of the ICI channel structure. A reduced state (RS) formulation of the SISO MAP equalizer which provides good performance/complexity tradeoff is also described. Utilizing the fact that ICI energy is clustered in adjacent subcarriers, frequency domain equalization is made localized. This paper further proposes two computational efficient linear minimum mean square error (LMMSE) based equalization methods: recursive q-tap SIC-LMMSE equalizer and recursive Sliding-Window (SW) SIC-LMMSE equalizer respectively. Simulations results demonstrate that the iterative SISO RS-MAP equalizer achieves the performance of no ICI with normalized Doppler frequency fdTs up to 20.46% in realistic mobile WiMAX environment.