Spatial Multiple Access (SMA): Enhancing performances of MIMO-NOMA systems

The error performance of the Non-Orthogonal Multiple Access (NOMA) technique suffers from inter-user interference (IUI) although it is a promising technique for future wireless systems in terms of the achievable sum rate. Hence, a multiple access technique design with limited IUI and competitive to NOMA in terms of spectral efficiency is essential. In this paper, we consider so-called spatial multiple access (SMA) which is based on applying the principle of spatial modulation (SM) through the different users' data streams, as a strong alternative to multiple-input and multiple-output (MIMO)-NOMA systems. The analytical expressions of bit error probability (BEP), ergodic sum rate and outage probability are derived for the SMA. The derivations are validated via computer simulations. In addition, the comparison of the SMA system with NOMA is presented. The results reveal that SMA outperforms NOMA in terms of the all performance metrics (i.e., bit error rate (BER), outage probability and ergodic sum rate) besides it provides low implementation complexity.