Joint estimation of carrier frequency offsets and doubly selective channel for OFDMA uplink using line search

In this paper, we propose a novel joint estimation technique for the carrier frequency offsets (CFOs) and time-varying frequency selective (doubly selective) channels of highly mobile users in an orthogonal frequency division multiple access (OFDMA) uplink system. To avoid the identifiability problem in tracking doubly selective channels (DSCs), we incorporate the idea of basis expansion model (BEM) which uses complex exponential (CE) basis functions. With the aid of CE-BEM we need to estimate only the basis expansion coefficients instead of actual impulse responses of the channels. Our proposed scheme make use of a line search method based on minimum mean square error (MMSE) criteria. The complete set of parameters, which includes both CFO and basis coefficients for all the users, are updated in each iteration by minimizing the error between the successive iterations. Simulation studies are carried out to demonstrates that the proposed method has faster convergence rate and achieves better estimation performance even at high mobile speeds.