Combined Variable Active Antenna Spatial Modulation and NOMA to Enhance Spectral Efficiency for Multiple Users MIMO Systems

In multi-user multiple input multiple output (MIMO) systems, the non-orthogonal multiple access (NOMA) method based spatial modulation (SM) and generalized spatial modulation (GSM) can mitigate inter-user interference. However, the spectral efficiency of these methods is restricted because of antenna configuration. In this paper, a combination of the variable active antenna spatial modulation (VASM) scheme with the downlink power domain NOMA system, so-called NOMA-VASM, is proposed to improve spectral efficiency while main-taining mitigation of inter-user interference. In the novel NOMA-VASM, the antenna configuration is arbitrary and the number of enabled transmitting antennas (TAs) can be altered, so it is easier to increase spectral efficiency compared to NOMA-SM and NOMA-GSM. Monte Carlo simulations were performed under various scenarios, and the results showed that NOMA-VASM outperformed conventional NOMA-SM and NOMA-GSM in terms of spectral efficiency, average bit-error-rate (ABER) performance, and required number of TAs.