Joint Semiblind Frequency Offset and Channel Estimation for Multiuser MIMO–OFDM Uplink

A semiblind method is proposed for simultaneously estimating the carrier frequency offsets (CFOs) and channels of an uplink multiuser multiple-input multiple-output (MIMO)–orthogonal frequency-division multiplexing (OFDM) system. By incorporating the CFOs into the transmitted symbols and channels, the MIMO–OFDM with CFO is remodeled into MIMO–OFDM without CFO. The known blind method for channel estimation [1] is then directly used for the remodeled system to obtain the shaped channels with an ambiguity matrix. A pilot OFDM block for each user is then exploited to resolve the CFOs and the ambiguity matrix. Two dedicated pilot designs, periodical and consecutive pilots, are discussed. Based on each pilot design and the estimated shaped channels, two methods are proposed to estimate the CFOs. As a result, based on the second-order statistics of the received signal and one pilot OFDM block, the CFOs and the channels are found simultaneously. Finally, a fast equalization method is given to recover the signals corrupted by the CFOs.