Out-of-Band Radiation Measure for MIMO Arrays with Beamformed Transmission

TL;DR

This paper analyzes the out-of-band radiation characteristics of multiuser MIMO systems with beamforming, showing that massive MIMO systems emit less problematic out-of-band radiation overall, allowing relaxed spectral regrowth requirements.

Contribution

It provides an analytical expression for out-of-band radiation in MIMO systems and demonstrates that massive MIMO reduces out-of-band radiation deviations compared to single-user systems.

Findings

Out-of-band radiation deviations are small in multiuser MIMO.

Massive MIMO systems radiate less total out-of-band power.

Spectral regrowth requirements can be relaxed in massive MIMO.

Abstract

The spatial characteristics of the out-of-band radiation that a multiuser MIMO system emits in the environment, due to its power amplifiers (modeled by a polynomial model) are nonlinear, is studied by deriving an analytical expression for the continuous-time cross-correlation of the transmit signals. At a random spatial point, the same power is received at any frequency on average with a MIMO base station as with a SISO base station when the two radiate the same amount of power. For a specific channel realization however, the received power depends on the channel. We show that the power received out-of-band only deviates little from the average in a MIMO system with multiple users and that the deviation can be significant with only one user. Using an ergodicity argument, we conclude that out-of-band radiation is less of a problem in massive MIMO, where total radiated power is lower compared to SISO systems and that requirements on spectral regrowth can be relaxed in MIMO systems without causing more total out-of-band radiation.