Estimation of Rapidly Time-Varying Channels for OFDM Systems

Channel estimation for OFDM systems in rapidly time-varying environments is challenging. In this paper, relying on a basis expansion channel model, we propose a scheme for estimating channel parameters varying within a transmission block. Along with the estimation scheme, we also derive the optimal pilot sequence and optimal placement of pilot tones with respect to the mean square error (MSE) of the channel estimate. It is shown that the optimal pilot sequence consists of some adjacent equipowered and equispaced subsequences that are constrained by certain phase conditions. Simulation results demonstrate the performance of the proposed scheme in rapidly time-varying scenarios