The utilization of the basis expansion model for channel assessment is proposed for orthogonal frequency division multiple access (OFDMA) system uplink. The Basis Expansion Model (BEM) is used in a high-speed railway communication scenario for a fast time-varying channel. The channel impulse response is modeled as the sum of basis functions multiplied by various coefficients. Simulation results show that a Generalized Complex-Exponential BEM outperforms a Complex-Exponential. And BEM (CE-BEM) and a polynomial BEM in terms of Mean Squared Error (MSE). The MSE of the CEBEM diminishes as the number of basis functions increases.