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An EM-based joint maximum likelihood estimation of carrier frequency offset and channel for uplink OFDMA systems

A maximum likelihood estimator (MLE) based on expectation maximization (EM) method is presented to jointly estimate the carrier frequency offset (CFO) and the channel of each user in uplink OFDMA systems. The proposed MLE distinguishes itself from existing methods by its applicability to any arbitrary carrier assignment schemes. The proposed MLE achieves high computational efficiency by transforming a multidimensional maximization problem into a number of substantially smaller separate maximization problems. Computer experiments have been conducted to confirm the effectiveness of the proposed estimators in estimation accuracy and robustness against the near-far effect.