Quantized CDI Based Tomlinson Harashima Precoding for Broadcast Channels

For the Multiuser Multiple-Input Single-Output (MUMISO) system in a downlink (DL) scenario, we design a non-linear precoding scheme, namely the spatial Tomlinson-Harashima precoder (S-THP) based on the total mean squared error (MSE) criterion. The channel state information (CSI) available at the transmitter for the precoding is the quantized channel direction information (CDI) relayed back in a frequency division duplex (FDD) system from each receiver using B feedback bits received erroneously and quasi-instantaneous. The proposed MMSE-STHP with a suboptimum precoding order clearly outperforms the linear precoding scheme given in starting from a certain Signal-to-Noise Ratio (SNR) and a number of feedback bits in terms of Bit Error Ratio (BER).