Joint estimation and data detection in ofdm systems with very high mobilityWe consider frequency selective and very rapidly time varying channels. H were we compare he estimation performance of three algorithms mainly VBLAST EM and SAGE.It is found that in fast fading channels the orthogonality between subcarriers is destroyed by the time variation of a fading channel over an ofdm symbol duration which causes severe Inter Carrier interference(ICI) and conventional frequency domain approaches result in irreducible error flows.The algorithm we use based on sage technique which is well suited o multi carrier signal formats,leading a receiver structure that incorporates ICI cancellation.A computational study of the algorithm shows that using discrete cosine orthogonal basis functions o represent he rapidly time varying fading channels depending on normalized Doppler frequencies only a small number of expansion coefficients is sufficient o approximate the channel perfectly even without knowledge of the correlation of the input signals.An extension o the algorithm using maximum aposteriori probability technique is also studied which enables one o use the Gaussian approximation of transmitted ofdm samples.The extended Algorithm makes possible the averaging of the non pilot data symbols resulting in a feasible and computationally efficient channel estimation algorithm.We also derive he Bayesian CRLB and convergence rate of the algorithm analytically.