Efficient Channel Estimation Schemes for MIMO OFDM Systems with NULL Subcarriers

In this paper, channel estimation schemes as well as low crest-factor preamble construction are presented for practical MIMO OFDM systems with NULL subcarriers. In the presence of NULL subcarriers, the performance of the channel estimator in [1] degrades considerably. Therefore, Maximum-likelihood (ML) channel estimators were proposed for MIMO OFDM systems with NULL subcarriers [2], [3]. However, they have relatively high computational complexity. Thus, more efficient schemes are proposed in our paper, with regard to two different cases of NULL subcarrier usages: only DC subcarrier is null or both DC and high frequency subcarriers are null. Simulation results show that the new schemes achieve performances near the optimum error bound.