Soft iterative channel estimation with subspace and rank tracking

This letter presents an adaptative soft-based method for channel estimation in turbo receivers. The proposed approach is based on the particular algebraic structure of multipath Rayleigh-fading channels, and it is suited for mobile systems where the multipath pattern (namely, the times of delay) changes slowly over the time. The method is implemented through a rank-and-subspace tracking algorithm that allows to adapt the estimate to the multipath variations and also to reduce the computational cost with respect to the batch implementation based on eigenvalue decomposition. A performance analysis, in terms of mean square error of the channel estimate and bit error rate, shows the advantages of the proposed technique in communications over time-varying wireless channels.