Double Krylov subspace approximation for low complexity iterative multi-user decoding and time-variant channel estimation

Iterative multi-user detection and time-variant channel estimation in a multi-carrier (MC) code division multiple access (CDMA) uplink requires high computational complexity. This is mainly due to the linear minimum mean square error (MMSE) filters for data detection and time-variant channel estimation. We develop an algorithm based on the Krylov subspace method to solve a linear system with low complexity, trading accuracy for efficiency. This approach enables drastic reduction of computational complexity for time-variant channel estimation as well as storage reduction and parallelization of the computations for multi-user detection. The performance of the low-complexity iterative Krylov subspace receiver is validated by simulations.