Carrier Frequency Offset Estimation for Multiuser MIMO OFDM Uplink Using CAZAC Sequences: Performance and Sequence Optimization

This paper studies Carrier Frequency Offset (CFO) estimation in the uplink of multi-user Multiple-Input Multiple-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) systems. Conventional maximum likelihood estimator requires computational complexity that increases exponentially with the number of users. To reduce the complexity, the authors propose a suboptimal estimation algorithm using Constant Amplitude Zero AutoCorrelation (CAZAC) training sequences. The complexity of the proposed algorithm increases only linearly with the number of users. In this algorithm, the different CFOs from different users destroy the orthogonality among training sequences and introduce Multiple Access Interference (MAI), which causes an irreducible error floor in the CFO estimation.