A tracking based BEM algorithm for joint channel and CFO estimation in OFDMA uplink

This paper investigates joint channel and Carrier Frequency Offset (CFO) estimation for Orthogonal Frequency Division Multiple Access (OFDMA) uplink system in doubly selective channel. We develop a Basis Expansion Model (BEM) based signal model for the OFDMA system in a doubly selective channel and, then we analyze the Inter-carrier Interference (ICI) introduced by rotation due to CFO. After formulating a Maximum Likelihood (ML) based CFO compensation method in time domain, a tracking based BEM algorithm is developed to estimate the BEM coefficients in frequency domain. By introducing a tracking term in the BEM coefficients, giving the rate of change in the coefficients, the algorithm is particularly suitable for high mobility applications. Specifically, the algorithm estimates the BEM coefficients for each OFDMA block in an iterative manner based on using a new objective function that takes into consideration first order variations in the coefficients in the current and adjacent blocks.