Spectral Efficiency for Massive MIMO Multi-Relay NOMA Systems with CSI errors

We consider a multiple-relay-aided massive multi-input multi-output (MIMO) non-orthogonal multiple access (NOMA) system. We practically model this system by considering channel estimation error, and the consequent imperfect successive interference cancellation, which the existing literature has ignored. We derive a novel lower bound for the ergodic spectral efficiency of this multi-relay NOMA system, and characterize its degradation with respect to orthogonal multiple access (OMA), due to the aforementioned artifacts. We crucially show that a multi-relay massive MIMO NOMA system requires accurate channel information to outperform OMA.