| Summary: | 博士 === 國立交通大學 === 電子研究所 === 100 === Orthogonal frequency-division multiplexing (OFDM) is a popular broadband wireless transmission technique, but its performance can suffer severely from the intercarrier interference (ICI) induced by fast channel variation arising from high-speed motion. Existing ICI countermeasures usually address a few dominant ICI terms only and treat the residual similar to white noise.
We show that the residual ICI has high normalized autocorrelation and that this normalized autocorrelation is insensitive to the maximum Doppler frequency and the multipath channel profile, the OFDM sample period, the discrete Fourier transform (DFT) size, the OFDM symbol time, the transmitted symbol energy. Consequently, the residual ICI plus noise can be whitened in a nearly channel-independent manner,
leading to significantly improved detection performance. Simulation results confirm the theoretical analysis. As a result, a whitening transform for the residual ICI plus noise can be obtained based solely on the ICI-to-noise ratio. Such a transform can be used in association with many different signal detection schemes to significantly improve the detection performance.
In particular, they show that the proposed technique can significantly lower the ICI-induced error floor by several orders of magnitude in maximum-likelihood sequence estimation (MLSE) designed to address a few dominant ICI terms. For QPSK, the proposed method can lower the error floor induced by ICI to under 10^−6 with MLSE that takes into account two nearest-neighbor ICI terms with perfect channel state information (CSI).
Furthermore, we consider linear minimum mean-square error (LMMSE) and
iterative LMMSE detection with the above partial whitening of additive disturbance, together with soft decision feedback. The method is shown to provide good performance-complexity tradeoff compared to other ICI countermeasures.
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