Channel estimation for OFDM systems with transmitter diversity in mobile wireless channels

This paper describes a channel estimation and tracking scheme for OFDM MIMO systems based on pilot tones. The mean square error of the proposed scheme is derived, and through this we derive optimal training sequences and placement of the pilot tones. It is shown in this paper that minimum mean square (MMSE) channel estimation is obtained with equipowered, equispaced, orthogonal and phase shift orthogonal training sequences. Through simulations it is shown that the optimal pilot-tone based training sequences as derived in this paper significantly outperform full-block training sequences in rapidly time varying channels. Additionally, we show that by satisfying all conditions of optimality, our training sequences outperform orthogonal and random sequences, which both appear to be sub-optimal for channel identification.