Unified view of channel estimation in MIMO-OFDM systems

This paper provides a unified view of time-domain and frequency-domain least square (LS) channel estimation in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. Time-domain and frequency-domain LS channel estimation are formulated under the same framework and their average mean square error (MSE) lower bounds for arbitrary number of transmit antennas and arbitrary number of pilot symbols are derived. Moreover, general optimum pilot design rules are developed to achieve average MSE lower bounds for time-domain and frequency-domain LS channel estimation, respectively. Their applicable conditions and computational complexity are also investigated and compared. It can be shown by theory and simulation that time-domain LS channel estimation is equivalent to frequency-domain LS channel estimation with discrete-time Fourier transform (DFT) improvement, but time-domain LS channel estimation has boarder applicable condition.