This paper considers the combination of two promising technologies: Spatial Modulation (SM) and Non-Orthogonal Multiple Access (NOMA). In contrast to the conventional Multi-Radio Frequency (M-RF) NOMA-SM model, we propose a generalized Single-Radio Frequency (S-RF) model. This model splits each NOMA user data between the spatial bits and modulation bits in a flexible manner. Hence, the S-RF models in the literature are special cases of our proposed model. Besides, our model preserves the energy efficiency property of SM and strikes a compromise between the M-RF and existing S-RF models in terms of Spectrum Efficiency (SE). The SE of the proposed model is evaluated through mutual information analysis with Monte Carlo integration. Moreover, we propose a fair power allocation algorithm based on Equal Signal to Interference plus Noise Ratio (ESINR) for the NOMA-SM users. Besides, we evaluate the Bit Error Rate (BER) performance of the M-RF and S-RF NOMA-SM models and show considerable advantages of the proposed S-RF system.
