Preamble Based Joint Channel and CFO Estimation for MIMO-OFDM Systems with Null Subcarriers

In this paper, challenges regarding the provision of channel state information (CSI) and carrier frequency synchronization for multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) systems with null subcarriers are addressed. We propose a novel maximum likelihood (ML) based scheme that estimates the aggregate effects of the channel and carrier frequency offset (CFO) by using two successive OFDM preambles. In the presented scheme, CFO is estimated by considering the phase rotation between two consecutive received OFDM preambles. Both channel and CFO mean squared errors (MSE) are used to evaluate the performance of our proposed scheme. Simulation results indicate that the BER performance of the proposed estimator is comparable to that of the system with known channel state information and the CFO MSE performance achieves the Cramer-Rao bound (CRB) of the fully loaded OFDM system.