A novel joint estimation technique for doubly selective channel and carrier frequency offset in high mobility OFDMA uplink

In this paper, we propose a novel pilot-aided joint estimation technique for carrier frequency offset (CFO) and doubly selective channel coefficient in high mobility orthogonal frequency division multiple access (OFDMA) uplink systems. The time variations of the channel within the OFDMA symbol is modelled by complex exponential basis expansion model (CE-BEM). By representing channels in terms of basis functions we need to track only the slowly varying basis expansion coefficients instead of actual channel impulse response. Our proposed method makes use of variable projection (VP) method based on least squares (LS) criterion for the joint estimation of CFO and basis expansion coefficients. The CFO and basis coefficients are updated separately in each iteration of the VP method. The proposed method has faster convergence rate and achieves better CFO and channel estimation performance even at high mobile velocities and thus an attractive solution for low complexity practical implementation.