Time, Frequency Synchronization, and Equalization for Asynchronous Multiuser MIMO Systems

An asynchronous multiuser MIMO system with multipath channels and carrier frequency offsets (CFOs) or Doppler shifts is remodeled into another system. A blind method based on second order statistics is then used for estimating the shaped channels with ambiguity. Based on the shaped channels, specially designed pilots are proposed to find the CFOs. The same pilots are also used to resolve the time delays and the ambiguity in the estimated channels. After the CFOs, time delays and ambiguity are found, an equalization method based on the minimum mean square error (MMSE) criteria is obtained to recover the transmitted symbols. Only upper bounds for the channel orders and time delays are needed for implementing the algorithms, which makes them applicable to practical multiuser MIMO systems.