Sparse Space-Time-Frequency-Domain Spreading for Large-Scale Non-Orthogonal Multiple Access

Abstract

A generalised spatial modulation-aided sparse space-time-frequency spreading (GSM/SSTFS) scheme is proposed for supporting large-scale access at a high normalized user-load in next-generation systems by simultaneously exploiting the transmit diversity in the spatial- and frequency-domain. Specifically, in the GSM/SSTFS system employing two transmit antennas (TAs), each user equipment (UE) spreads its signal over two symbol durations, two active TAs, and multiple subcarriers by a unique pre-assigned sparse code, in order to attain spreading in three dimensions (3D). Furthermore, with the aid of GSM, extra information bits are embedded in the TA indices. At the receiver, a joint message passing-aided (JMPA) detector is employed for attaining near-single-user bit error rate (BER) performance, which is also compared to that of conventional multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) systems.