Investigation of Control Signaling and Reference Signal Design for Downlink MU-MIMO in LTE-Advanced

3rd Generation Partnership Project (3GPP) is specifying Long Term Evolution Advanced (LTE-A) targeting for higher average cell and cell-edge spectrum efficiency over LTE, and multi-user MIMO (MU-MIMO) is identified as a key technique to reach the International Mobile Telecommunication Advanced (IMT-A) performance requirements. In this paper, we present the investigation on the MU-MIMO enhancement issues in LTE-A mainly from the viewpoint of MU-MIMO transparency, i.e., necessity of indication of co-scheduled UEs in the same resource block, and demodulation reference signal (DM-RS) configuration. Besides qualitative analysis from various system impacts, e.g., signaling overhead, scheduling flexibility and channel estimation accuracy, extensive numerical results are provided by both link-level and system-level simulations. In addition, we further propose an adaptive data mapping scheme for transparent MU-MIMO to improve the channel estimation accuracy. Moreover, a novel system-level simulation methodology taking into account dynamic change of channel estimation error is provided in this paper. Finally, based on the investigation results, we propose transparent MU-MIMO with quasi-orthogonal DM-RS configuration in LTE-A.