Spectral-efficiency of multicarrier sparse-mapping non-orthogonal multiple-access systems: Downlink

In this paper, we propose a non-orthogonal multiple-access (NOMA) scheme, namely the multicarrier sparse-mapping NOMA (MC/SM-NOMA), for supporting downlink data transmission in the scenarios where user load might be very heavy. Our MC/SM-NOMA scheme allows information to one user to be conveyed by multiple subcarrier channels, and each subcarrier channel to be shared by multiple (two or more) users. We consider two subcarrier-allocation schemes and the subcarrier-by-subcarrier optimum power-allocation. The performance of the MC/SM-NOMA systems employing the proposed subcarrier- and power-allocation schemes is investigated in terms of spectral-efficiency based on simulations. Our studies demonstrate that the MC/SM-NOMA scheme is beneficial to high-flexibility implementation of NOMA for various purposes. Furthermore, allowing more users to share one subcarrier channel is capable of significantly increasing the achievable spectral-efficiency.