Time-Domain LMMSE Channel Estimator Based on Sliding Window for OFDM Systems in High-Mobility Situations

Recently, wideband orthogonal frequency-division multiplexing (OFDM)-based systems such as Long-Term Evolution (LTE) have been proposed for future railway communication systems. In such high-speed situations, Doppler phenomena, related to the terminal´s high speed, affects the use of OFDM systems by producing a loss of orthogonality between different carriers. Thus, the channel estimation and equalization become a challenging problem, particularly when the number of pilot carriers is limited. This paper investigates the use of time-domain channel estimation for OFDM systems in high-speed scenarios and for a sparse pilot distribution. A time-domain linear minimum mean square error (TD-LMMSE) filter is designed for channel estimation. The TD-LMMSE emulates the effect of a sliding window and takes into consideration the interference caused by the data field. The expression of the MSE of linear estimators is also developed. Furthermore, a simple technique for the estimation of the second-order channel statistics is proposed. Simulation results, showing a significant gain in terms of MSE and bit error rate, compared with other state-of-the-art algorithms, are reported over a wide signal-to-noise ratio (SNR) range.