Pilot symbol design for channel estimation in MIMO-OFDM systems with null subcarriers

In this paper, pilot design for channel estimation in multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) systems with null subcarriers is considered, where the mean square error (MSE) is chosen as our optimization criterion. We design the placement of pilot symbols and their powers for multiple transmit antennas to minimize the MSE of the least square (LS) channel estimates. To reduce the interference of pilot symbols from other transmit antennas, an algorithm that ensures that the pilot symbols are disjoint from the ones of any other antenna is proposed. Simulation results based on IEEE 802.16e are presented to illustrate the superior performance of our proposed method over the existing standard and the partially equi-spaced pilot symbols.