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In this study, the authors consider a multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing system operating over unknown frequency-selective fading channels. Based on two different signal models, two maximum-likelihood schemes for joint carrier frequency offset (CFO) and MIMO channel estimation under timing ambiguity have been derived. The first estimator jointly estimates the timing offset, CFO and channel coefficients, but the complexity is high owing to the need of two-dimensional searches. The second estimator has a reduced complexity, but its performance slightly degrades compared with the first one. The performance of proposed estimators was benchmarked with Cramer-Rao bounds (CRB), and investigated by computer simulations. The simulation results show that the proposed estimators achieve almost ideal performances compared with the CRB.