Joint Carrier Frequency Offset and Channel Estimation for OFDM Systems via the EM Algorithm in the Presence of Very High Mobility

Abstract

Abstract-In this paper, the problem of joint Carrier Frequency Offset (CFO) and channel estimation for OFDM systems over the fast time-varying frequency-selective channel is explored within the framework of the expectation-maximization (EM) algorithm and parametric channel model. Assuming that the path delays are known, a novel iterative pilot-aided algorithm for joint estimation of the multi-path Rayleigh channel Complex Gains (CG) and the Carrier Frequency Offset (CFO) is introduced. Each CG time-variation, within one OFDM symbol, is approximated by a Basis Expansion Model (BEM) representation. An auto-regressive (AR) model is built to statistically characterize the variations of the BEM coefficients across the OFDM blocks.In addition to the algorithm, the derivation of the Hybrid Cramér-Rao Bound (HCRB) for CFO and CGs estimation in our context of very high mobility is provided. We show that the proposed EM has a lower computational complexity than the optimum maximum a posteriori estimator and yet incurs only an insignificant loss in performance.

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