  The error performance of the Non-Orthogonal Multiple Access (NOMA) technique
suffers from the inter-user interference (IUI) although it is a promising
technique for the 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 letter, 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 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 to the 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.
