An EM Based Frequency Domain Channel Estimation Algorithm for Multi-Access OFDM Systems

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Channel estimation is an important prerequisite for receiver design. In this paper the authors present a semi-blind low complexity frequency domain based channel estimation algorithm for multi-access Orthogonal Frequency Division Multiplexing (OFDM) systems. The algorithm is based on eigenvalues interpolation and makes a collective use of data and channel constraints. They exploit these constraints to derive a frequency domain Maximum A Posteriori (MAP) channel estimator. Furthermore, they develop a data aided (Expectation maximization based) estimator incorporating frequency correlation information. The estimator is further enhanced by utilizing the time correlation information through a Forward Backward (FB) Kalman filter. They also explore various implementation for the FB Kalman filter.