A combined channel estimation in time-frequency domain for OFDM system in mobile channel

As a consequence of the time-varying channel, the orthogonality between subcarriers is destroyed in conventional frequency-domain approaches for orthogonal frequency-division multiplexing (OFDM), resulting in interchannel interference, which increases an irreducible error floor in proportion to the normalized Doppler frequency. In this paper, we propose a combined channel estimation in time domain and frequency domain. In time domain, the channel statistics like the channel correlation matrix can be achieved by PN sequence, which may be used for frame synchronization in MIMO system. In frequency domain, in order to reduce the complexity of the estimator, we still apply theory of optimal rank-reduction to linear minimum mean-squared error(LMMSE) estimators. This enables us to achieve performance superior to any other structure without increasing bandwidth or incorporating redundancy. The performance is presented in terms of BER and MSE, and confirms that the estimator is robust to changes in channel characteristics.