Time domain channel estimation schemes for OFDM systems with multiple antenna transmissions

In this report, time domain channel estimation schemes for OFDM systems are studied. It is known that the time domain maximum likelihood estimation (MLE) scheme out-performs the conventional frequency domain channel estimation; however, the performance degradation becomes noticeable at low SNRs. Although we proposed a singular-value truncation approach for the MLE to improve the performance, we have been required more performance improvement in noisy environment. A minimum mean square error (MMSE) estimation is a promising technique to improve the performance in the low SNRs. However, we need considerable efforts to carry out the time domain MMSE channel estimation because it requires statistical information such as power delay profiles of MIMO channels in advance. Concerning this issue, we propose to construct the covariance matrix of the channels by using the estimated power delay profiles given by the MLE in every frames, and solve a normal equation by using the conjugate gradient method (CGM). Simulation results will show some packet error rate performances of an MIMO-OFDM system when we apply these channel estimation schemes.