Closed-Form Estimators of Carrier Frequency Offsets and Channels in the Uplink of Multiuser OFDM Systems

This contribution proposes a new joint estimation method of multiple carrier frequency offsets (CFOs) and channels in the uplink of multiuser orthogonal frequency division multiplexing (OFDM) systems. The estimators are derived from the optimal maximum-likelihood (ML) principle. Complexity reductions are achieved by exploiting the correlation properties of the training-sequence. The grid search algorithm is converted into a polynomial root finding procedure which leads to closed-form estimators for moderate CFOs. Numerical results confirm that the performance degradation due the approximations compared to the Cramer-Rao bound (CRB) is small and may be negligible in practice