Adaptation of Code-Domain NOMA to SC-FDE Based Overloaded mmWave Hybrid Massive MIMO

In this letter, we provide a practical framework to resolve whether code-domain NOMA (CD-NOMA) is beneficial when integrated with massive MIMO systems. In order to realize this integration, first, we develop a novel code-beamspace wideband signal model for uplink CD-NOMA in mmWave hybrid massive MIMO systems employing single-carrier (SC) transmission. Then, we apply a state-of-the-art SC frequency domain equalization (SC-FDE) based iterative receiver where the number of radio frequency (RF) chains is limited. Simulation results verify the effectiveness of the proposed architecture in overloaded scenarios. Furthermore, we show that CD-NOMA can enhance the performance of mmWave hybrid beamforming based massive MIMO systems by effectively decreasing the correlation between closely separated user channels in joint code-beamspace.