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.
['Lars Häring', 'Stefan Bieder', 'Andreas Czylwik']
Fine frequency synchronization in the uplink of multiuser OFDM systems