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.

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This paper analyzes the impact of inter-carrier interference (ICI) compensation on the physical layer of DVB-T2, the new digital terrestrial television standard. We compare the performance of a well-known low complexity soft demapper for different time-interleaving depths and code rates in several realistic mobile scenarios. This paper further presents an iterative receiver design that exchanges extrinsic information between the low-density parity-check (LDPC) decoder and the ICI canceller in order to improve performance. Provided simulation results show that the proposed ICI cancellation algorithms can be necessary in several DVB-T2 transmission modes when the length of the time interleaver is limited.

Recent and next-generation wireless broadcasting standards, such as DVB-T2 or DVB-NGH, are considering distributed multi-antenna transmission in order to increase bandwidth efficiency and signal quality. Full-rate full-diversity (FRFD) space-time codes (STC), such as the Golden code, have been reported to be excellent candidates, being their main drawback their detection complexity, which is enhanced when soft output is required when combined with a bitinterleaved coded modulation (BICM) scheme based on low-density parity check (LDPC) codes. We present a novel low-complexity soft detection algorithm for the reception of Golden codes in LDPCbased orthogonal frequency-division multiplexing (OFDM) systems. Complexity and simulation-based performance results are provided which show that the proposed detector performs close to the optimal detector in a variety of DVB-T2 broadcasting scenarios.

We propose a new pilot structure for inter-carrier interference (ICI) estimation and compensation in order to improve the performance of the forthcoming Digital Video Broadcasting-Next Generation Handheld (DVB-NGH) standard in mobile environments. Although classical pilot patterns and channel estimation techniques achieve good performance in fixed reception, their design can be improved for high-mobilty receivers, where the effects of ICI become more severe. For such scenarios, we propose to approximate the ICI and channel parameters using a basis expansion model (BEM). The proposed channel estimation model is assessed with new pilot designs and in combination with an ICI mitigation algorithm, showing the effectiveness of this technique by removing the error floor experienced with the ideal channel knowledge case with large Doppler frequencies.

Abstract-This paper proposes a novel framework for reducing the inter-carrier interference (ICI) caused by timevarying channels in mobile OFDM systems. The proposed ICI suppressing scheme is based on the application of the sumproduct (SP) algorithm to a factor graph (FG) representing the joint a posteriori probability (APP) of the transmitted symbols. Simulation results show that this new iterative soft-input soft-output (SISO) detection strategy achieves good performance when the ICI power is high, which can be due to high mobility or the use of large FFT sizes. We discuss its application to the reception of the new DVB-T2 broadcasting standard for a set of realistic mobile scenarios.