Handling PA Nonlinearity in Massive MIMO: What are the Tradeoffs Between System Capacity and Power Consumption

Massive MIMO enables a very high spectral efficiency by spatial multiplexing and opens opportunities to reduce transmit power per antenna. On the other side, it also introduces new challenges in tackling the power amplifier nonlinearity due to the increased number of antennas. The behavior of Out-of-Band radiation from PAs in Massive MIMO is non-trivial depending upon the applied precoding scheme, propagation environment, and how the users are distributed spatially. In this paper, we analyze the in-band and Out-of-Band power distribution in space for a Massive MIMO base station with nonlinear power amplifiers. We also study the tradeoff between amplifier power consumption and system performance (in terms of error vector magnitude at intended receivers) for PAs with different backoff operating levels. The spatial analysis of Out-of-Band under more realistic channel conditions is more reflective of the situation, to determine system emission requirements. The tradeoff between performance and power consumption will provide a basis for future investigations into the design of efficient Massive MIMO systems, taking nonlinearities into account.