Reduced-Overhead Channel Estimation for OFDM Systems in Multipath Fast Time-Varying Channels

Abstract

Orthogonal frequency division multiplexing (OFDM) is the core technology in new generation cellular networks, which can compete the last mile broadband wireless access solution. Accurate OFDM channel estimation with low pilot overheads in high mobility communication environments is one of the key issues to be resolved in broadband wireless access. Unfortunately, the Doppler frequency resulted from high mobility will cause inter-carrier interference (ICI) and degrade the performance of the OFDM systems. Due to the severe ICI, channel estimation becomes a difficult task in higher mobility scenarios. This paper proposes a computationally efficient channel estimation method for OFDM systems that is robust to high Doppler frequency with low pilot overheads. In this method, the time durations of each channel path corresponding to the transmitted consecutive OFDM systems, which are considered a 'window', are interpolated using polynomial functions. To improve interpolation accuracy, the training symbol and pilot symbol are allocated at the two ends of the windows, and the data symbols are allocated between the training symbol and the pilot symbol. The proposed two-step method is initialized to the least squares (LS) estimates of the channels corresponding to the time interval of the training symbol and pilot symbol within the window. Then, the channel interpolation is performed in the entire window. Compared with the state-of-the-art method, the computational complexity and pilot overhead of this method can be markedly reduced for each estimate. Simulation results show that the proposed method is robust to high Doppler frequencies and enhances transmission efficiency.