Modified clustered comb pilot-aided fast time-varying channel estimation for OFDM system

As high-speed railway is booming worldwide, the communication system with fast-time varying channel has drawn great attention. The comb pilot based linear minimum mean square error (LMMSE) channel estimator is proved to be an effective method for fast time-varying channel estimation. In this paper, the clustered comb pilot-aided channel estimation for orthogonal frequency-division multiplexing (OFDM) system is discussed, where the time varying channel is approximated by a basis expansion model (BEM). A modified clustered comb pilot structure is proposed and justified to improve the estimation performance compared with the clustered comb pilot proposed by Tang. Based on the complex-exponential BEM (CE-BEM) model, a suboptimal-pilot structure is proposed. In addition, optimal pilot length is analyzed and simulated with a predefined total number of pilots. The simulation results show that the modified clustered comb pilot can greatly reduce the estimation error especially with high Doppler spread. The suboptimalpilot structure with guard pilot approximation is proven to be competitive. Optimal nonzero pilot lengths for different Doppler spread are obtained by simulation with a predefined channel order and fixed pilot subcarriers.