Efficient operation mechanism for downlink MUST
Downlink multi-user superposition transmission (MUST), being seen as a non-orthogonal multiple access technique, allows the information of multiple data layers to be superposed and delivered in the same resource. Downlink MUST is expected to improve the system spectral efficiency (SE), and has been considered as an important feature for LTE-Advanced Pro. The work item for downlink MUST was approved in March 2016, and is ongoing in 3GPP. This paper firstly gives an overview of MUST standardization work in 3GPP, and then proposes an efficient MUST operation mechanism by taking into account the practical aspects such as system complexity and receiver implementation. System level simulations validate that, compared with orthogonal multiple access system, MUST with our proposed operation mechanism achieves 11.81% and 14.82% gain in cell average SE and cell edge SE respectively. Moreover, the proposed operation mechanism can keep the scheduling flexibility for MUST UE (user equipment), significantly reduce MUST signaling overhead, and enable LTE legacy UE to be scheduled as MUST-far UE.