RF Impairments Compensation and Channel Estimation in MIMO-OFDM Systems

The application of multi-input-multi-output (MIMO) technology in orthogonal frequency division multiplexing (OFDM) systems provides better spectral efficiency with high capacity gain. It also introduces significant complexity at the transceivers which can be partially reduced using homodyne or zero-IF receivers. However, those transceivers are very sensitive to imperfections of analog components at the RF front end and suffer severe performance degradation in the presence of RF impairments. Two of the most common impairments that significantly limit the performance of MIMO-OFDM transceivers are IQ-Imbalance and phase noise. In this paper, we propose a joint estimation and compensation technique to estimate channel, phase noise and IQ-Imbalance parameters in MIMO-OFDM systems under multipath slow fading channels. A subcarrier multiplexed preamble structure to estimate the channel and impairment parameters with minimum overhead is introduced and used in the estimation of IQ-Imbalance parameters as well as the initial estimation of effective channel matrix including common phase error (CPE). We then use a novel tracking method using pilot subcarriers to update the effective channel matrix throughout an OFDM frame. Simulation results for a variety of scenarios indicate that the proposed estimation and compensation technique efficiently improves the performance of MIMO-OFDM systems in terms of bit- error-rate (BER) as compared with the non- compensated case.