NOMA-Aided Precoded Spatial Modulation for Downlink MIMO Transmissions

In this paper, a novel multi-user multiple-input multiple-output (MIMO) transmission scheme, called non-orthogonal multiple access (NOMA) aided precoded spatial modulation (PSM) (NOMA-PSM) is proposed for overloaded downlink transmissions. NOMA-PSM beneficially amalgamates the concept of index modulation (IM) and NOMA techniques, and therefore it inherits both the merits of IM with low-complexity transceiver and the advantages of NOMA with high bandwidth efficiency. For the proposed scheme, we develop a pair of low-complexity yet effective detection algorithms by combining the spatial index demodulation and successive interference cancellation. The spectral efficiency (SE), implementation cost, and multi-user interference of NOMA-PSM are evaluated and compared with conventional designs. Furthermore, we derive the mutual information (MI) of the proposed NOMA-PSM to characterize its achievable SE and also obtain a lower bound for simplifying the measurement of MI. Our simulation results show that the proposed NOMA-PSM scheme is capable of achieving considerable performance gains over conventional orthogonal multiple access aid PSM and antenna-grouping-based PSM in wireless MIMO fading channels.