Multiuser Superposition Transmission (MUST) for LTE-A Systems

A new study item termed downlink Multiuser Superposition Transmission (MUST) has been established in 3GPP Release 13 [1]. As the name suggests, MUST utilizes the concept of superposition coding for a multiuser transmission in LTE-Advanced (LTE-A) systems. While superposition coding can be applied at symbol level, the symbol-domain superposition coding not only increases network signaling overhead and implementation difficulty, but also causes performance degradation due to non-Gray mapping resulting from the symbol-domain superposition. In this paper, we propose a bit-domain multiuser superposition technique by exploiting the intrinsic properties of bit-interleaved coded modulation (BICM) which is one of key technologies for LTE systems. Simulation results show that the bit-domain MUST can increase both the cell-average and cell-edge user spectral efficiency by more than 20% compared to single-user MIMO (SU-MIMO).