Transmission mode switching for LTE-Advanced downlink multi-user MIMO systems

To improve the performance of LTE-Advanced downlink systems, this paper investigates adaptive transmission mode switching between statistical and instantaneous channel state information (CSI) aided, single-user (SU) and multi-user (MU) transmissions. Theoretical studies show that the system performance will have a severe degradation when instantaneous CSI (ICSI) is inaccurate, especially for the MU transmission. In this light, we investigate the switching between ICSI-aided schemes and statistical CSI (SCSI) aided schemes based on achievable rate, which is related to both the channel correlation level, and the inaccuracy level of ICSI. After that, the cell average throughput is evaluated through system-level simulations. It´s shown that the performance of SCSI-aided mode is as good as the corresponding ICSI-aided mode when the channel correlation is large enough, and SCSI varies slow and SCSI-aided schemes are more robust than ICSI-aided schemes. Therefore, SCSI-aided modes should be activated when the inaccuracy level of ICSI is high.