Hybrid Precoding Scheme with Partial CSI at the Transmitter

This work proposes an Hybrid Precoding (HP) method in a Multiple-Input/Multiple-Output (MIMO) system with the objective of reducing the computational complexity inherent to nonlinear precoding methods. We show that linear precoders work better for low Signal-to- Noise Ratio (SNR) while nonlinear precoders, as in the case of the nonlinear Tomlinson-Harashima (TH) precoders, are more adequate for high SNRs. For medium scenarios, we propose a decision scheme where the transmitter decides to implement either linear or TH precoding depending on the speed of channel variations. Therefore, if the channel is bad, i.e. channel variations are significant compared to a given threshold parameter, the transmitter decides to use TH precoding for pre-equalizing channel effects. Otherwise, in case of good channel conditions, i.e. slow channel variations according to such threshold, linear precoding is enough to ensure good performance with the advantage of avoiding the complexity inherent to TH precoding. The overall performance is evaluated considering the transmission of several images.