Channel estimation in two dimensions for OFDM systems with multiple transmit antennas

We address pilot-symbol aided channel estimation (PACE) for orthogonal frequency division multiplexing (OFDM) based systems, employing multiple transmit antennas. A novel approach is presented which estimates and separates N_T superimposed signals, corresponding to N_T transmit antennas, by exploiting the correlation in two dimensions of the received signal. More specifically, we apply the concept of using two one-dimensional (1D) estimators instead of a truly two dimensional (2D) estimator, by dividing the estimation as well as the separation task into two stages. The first stage separates a subset of the N_T superimposed signals, together with estimating the channel response in the first dimension. The second stage further separates the signals of each subset in the second dimension, yielding an estimate for all transmit antennas. For a space-time block coded OFDM system we demonstrate that the proposed estimator can track the channel variations even at high Doppler frequencies.