What Role Can NOMA Play in Massive MIMO?

TL;DR

This paper compares NOMA and multi-user beamforming in massive MIMO systems, finding that beamforming generally outperforms NOMA, but hybrid schemes can offer superior performance in certain scenarios.

Contribution

The paper provides a comparative analysis of NOMA and beamforming in massive MIMO, highlighting scenarios where NOMA is advantageous and proposing a hybrid approach that outperforms standalone schemes.

Findings

Beamforming achieves higher average sum rate in massive MIMO.

NOMA can be preferable in specific cases within massive MIMO.

Hybrid NOMA-beamforming schemes outperform individual methods.

Abstract

This paper seeks to answer a simple but fundamental question: What role can NOMA play in massive MIMO? It is well-established that power-domain non-orthogonal multiple access (NOMA) schemes can outperform conventional orthogonal multiple access (OMA) schemes in cellular networks. However, this fact does not imply that NOMA is the most efficient way to communicate in massive MIMO setups, where the base stations have many more antennas than there are users in the cell. These setups are becoming the norm in future networks and are usually studied by assuming spatial multiplexing of the users using linear multi-user beamforming. To answer the above question, we analyze and compare the performance achieved by NOMA and multi-user beamforming in both NLOS and LOS scenarios. We reveal that the latter scheme gives the highest average sum rate in massive MIMO setups. We also identify specific cases where NOMA is the better choice in massive MIMO and explain how NOMA plays an essential role in creating a hybrid of NOMA and multi-user beamforming that is shown to perform better than two standalone schemes do.