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Open Access Research

Factor graph based detection approach for high-mobility OFDM systems with large FFT modes

Pello Ochandiano1, Henk Wymeersch2, Mikel Mendicute1*, Lorena Martínez1 and Iker Sobrón1

Author Affiliations

1 Electronics and Computing Department, University of Mondragon, Loramendi, 4, 20500 Mondragon, Spain

2 Chalmers University of Technology, SE-412 96 Gothenburg, Sweden

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EURASIP Journal on Wireless Communications and Networking 2012, 2012:331  doi:10.1186/1687-1499-2012-331

Published: 31 October 2012

Abstract

In this article, a novel detector design is proposed for orthogonal frequency division multiplexing (OFDM) systems over frequency selective and time varying channels. Namely, we focus on systems with large OFDM symbol lengths where design and complexity constraints have to be taken into account and many of the existing ICI reduction techniques can not be applied. We propose a factor graph (FG) based approach for maximum a posteriori (MAP) symbol detection which exploits the frequency diversity introduced by the ICI in the OFDM symbol. The proposed algorithm provides high diversity orders allowing to outperform the free-ICI performance in high-mobility scenarios with an inherent parallel structure suitable for large OFDM block sizes. The performance of the mentioned near-optimal detection strategy is analyzed over a general bit-interleaved coded modulation (BICM) system applying low-density parity-check (LDPC) codes. The inclusion of pilot symbols is also considered in order to analyze how they assist the detection process.

Keywords:
Factor graph (FG); Sum-product algorithm (SPA); OFDM Doppler; Intercarrier interference (ICI)