The concept of a joint optimization of multiuser (MU) operation from both transmitter and receiver's perspective has the potential to further improve MU system capacity even if the transmission/precoding is non-orthogonal which could come from, for example but not limited to, the simultaneous transmission of a large number of non-orthogonal beams/layers with the possibility of more than one layer of data transmission in a beam. Such non-orthogonal transmission could allow multiple users to share the same resource elements without spatial separation, and allow improving the MU system capacity for networks. An example of such joint Tx/Rx optimization associated with adaptive Tx power allocation and CW-IC receiver is recently a remarkable technical trend, including schemes based on superposition coding. Joint Tx/Rx optimization might require standardization effort. Hence it is important to study the trade-off, in terms of system performance, complexity, and signalling overhead. A study item, "Study on Downlink Multiuser Superposition Transmission," was approved at 3GPP TSG RAN #67 [2]. This study is to evaluate the system performance of potential LTE enhancements enabling downlink multiuser superposition transmission (MUST). The objectives of the study include the definition of target deployment scenarios and an evaluation methodology for MUST, identification of potential MUST schemes and corresponding LTE enhancements, an assessment of feasibility and system-level performance of the potential MUST schemes. The results and findings of the study are documented in this technical report.

The present document captures the results and findings of the study item "Study on Downlink Multiuser Superposition Transmission" [2][3]. The purpose of this TR is to document the identified LTE enhancements to enable downlink multiuser superposition transmission and corresponding evaluation results in the target deployment scenarios. This activity involves the Radio Access work area of the 3GPP studies and has potential impacts both on the Mobile Equipment and Access Network of the 3GPP systems. This document defines evaluation methodology and target deployment scenarios for the study on downlink multiuser superposition transmission. This document identifies LTE enhancements and potential specification impacts to enable downlink multiuser superposition transmission. This document contains an assessment of feasibility and performance of the identified LTE enhancements to enable downlink multiuser superposition transmission. This document is a 'living' document, i.e. it is permanently updated and presented to TSG-RAN meetings.