A Novel Subspace Based Method for Compensation of Multiple CFOs in Uplink MIMO OFDM Systems

The tri-linear data model for an arbitrary multi-user uplink multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) system comprising orthogonal frequency division multiplexing access users and co-channel (CC) users is formulated in this letter. A novel subspace-based method for multi-access interference cancellation and CC data separation in multi-user MIMO OFDM systems, utilizing the independent manifolds spanned by user's carrier frequency offset matrix, is proposed in this letter. The system constraints under which the proposed subspace nulling method works are derived, which includes the under-determined cases, where minimum mean square error/zero forcing methods fail.