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Abstract-In this paper, we present a novel approach based on compressive sensing theory to estimate and mitigate asynchronous narrow-band interference (NBI) in orthogonal frequency division multiplexing systems with multiple transmit and/or multiple receive antennas. We consider the practical scenarios where one or multiple asynchronous NBI signals experience fast fading and/or frequency-selective fading channels. Furthermore, we propose a novel technique for estimating the desired signal's channel in the presence of unknown NBI. Our approach does not require any prior information about the NBI. Simulation results demonstrate the effectiveness of our proposed techniques in mitigating NBI and approaching the interferencefree performance limit over practical ranges of NBI power levels, spectral widths, and mobility levels.Index Terms-Narrow-band interference (NBI), OFDM, compressive sensing, sparsity, MIMO.

In this paper, we design MMSE-optimal training sequences for multi-user MIMO-OFDM systems with an arbitrary number of transmit antennas and an arbitrary number of training symbols. It addresses spectrally-efficient uplink transmission scenarios where the users overlap in time and frequency and are separated using spatial processing at the base station. The robustness of the proposed training sequences to residual carrier frequency offset and phase noise is evaluated. This analysis reveals an interesting design tradeoff between the peakto-average power ratio of a training sequence and the increase in channel estimation mean squared error over the ideal case when these two impairments are not present.Index Terms-Training sequences design, pilot design, MIMO-OFDM, multi-user systems, carrier frequency offset, phase noise, RF impairments.

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