Robust Precoding With Bayesian Error Modeling for Limited Feedback MU-MISO Systems
IEEE Transactions on Signal Processing
We consider the robust precoder design for Multi-User Multiple Input Single Output (MU-MISO) systems, where the Channel State Information (CSI) is fed back from the single antenna receivers to the centralized transmitter equipped with multiple antennas. We propose to compress the feedback data by projecting the channel estimates onto a vector basis, known at the receivers and the transmitter, and quantizing the resulting coefficients. The channel estimator and the basis for the rank reduction
... he rank reduction are jointly optimized by minimizing the Mean Square Error (MSE). Expressions for the conditional mean and the conditional covariance of the channel are derived which are necessary for the robust precoder design. These expressions take into account the following sources of error: channel estimation, truncation for rank reduction, quantization, and feedback channel delay. Three well-known precoder types, namely Linear Precoding (LP), Vector Precoding (VP), and Tomlinson-Harashima Precoding (THP), are designed based on the expectation of the MSE conditioned on the fed-back CSI. Our results show that robust precoding based on fedback CSI clearly outperforms conventional precoding designs which do not take into account the errors in the CSI. Additionally, we observe that a robust design is especially crucial for systems employing non-linear precoding with scarce feedback rate.