This paper introduces new joint estimation methods of multiple carrier frequency offsets (CFOs) and channel impulse responses (CIR) in application to 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 (TS). The grid search algorithm is converted into a polynomial root finding procedure which leads to low-complexity closed-form estimators for moderate CFOs. Furthermore, iterative estimators for larger CFOs are proposed. Numerical results confirm that the performance degradation due to the approximations compared to the Cramer-Rao bound (CRB) is small and may be negligible in practice.

This contribution considers the estimation and compensation of residual multiple carrier frequency offsets (CFOs) and sampling frequency offsets (SFOs) in the uplink of multiuser OFDM systems. Based on the observation of a user-dependent phase rotation, an approximate maximum-likelihood (ML) estimator is proposed in order to estimate the CFOs and SFOs and to track the phase in a post-synchronization step. By using a Taylor approximation, the estimation complexity is reduced. Bit error-ratio (BER) simulations show that the system performance degradation due to (small) frequency mismatches is negligible if the proposed method is applied.

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

This contribution considers the estimation and compensation of residual multiple carrier frequency offsets (CFOs) and sampling frequency offsets (SFOs) in the uplink of a multiuser OFDM system. Based on the observation of a user-dependent phase rotation, an approximate maximum-likelihood (ML) estimator is proposed in order to estimate the CFOs and SFOs to track the phase in a post-synchronization step. Bit-error-ratio (BER) simulations show that the system performance degradation due to (small) frequency mismatches is negligible if the proposed method is applied