Rapid changing channel estimation and equalisation based on hyperbolic modelling for OFDM systems

Recently, OFDM systems have been proposed as a solution to solve broadband railway communication problems. Channel estimation and equalisation for OFDM system become challenging when the mobile terminal is moving at high speed as the OFDM subcarriers lose their orthogonality in such situations. In this paper we present a novel channel estimation algorithm based on the hyperbolic modelling of rapidly varying channels. The hyperbolic model is based on the observation of the OFDM frequency domain channel matrix provided by rapid channel simulator, and on mathematical analysis of the off-diagonal elements of the channel matrix. The hyperbolic model can be combined with an FFT interpolation technique and then used to perform an iterative least square estimation of the channel matrix even when sparse pilot distribution is used. Furthermore, a sliding window discrete optimisation procedure is introduced to improve the performance of the suboptimal Linear Minimum Mean Square (LMMSE) channel equalisation technique. Numerical results for a mobile moving at 280 km/h and under the Wide Sense Stationary Uncorrelated Scattering (WSSUS) channel assumption are reported. The provided results prove the efficiency and effectiveness of the suggested algorithms.