Investigation of Two-Dimensional Orthogonal Sequence Mapping to Multi-Layer Reference Signal for LTE-Advanced Downlink
In the LTE-Advanced downlink, to satisfy high-level performance requirements, advanced multi-antenna transmission techniques such as higher-order Single-User (SU)- MIMO, Multi-User (MU)-MIMO, and Coordinated Multi-Point transmission/reception (CoMP) are key. At the 3GPP RAN WG1 meeting, the De-Modulation Reference Signal (DM-RS) was defined to support channel estimation and data demodulation for up to eight transmission layers. A hybrid Code Division Multiplexing (CDM) and Frequency Division Multiplexing (FDM) scheme was adopted as a DM-RS multiplexing scheme. The time-domain Orthogonal Cover Code (OCC) is used for CDM since time domain orthogonality among OCCs is relatively robust against channel variation.