Out-of-band radiation measure for MIMO arrays with beamformed transmission

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 outof-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.Index Terms-ACLR, massive MIMO, MIMO, nonlinearity, outof-band radiation, power amplifier, spectral regrowth.

On out-of-band emissions of quantized precoding in massive MU-MIMO-OFDM

“…This demonstrates that by increasing the number of antennas at the BS, OOB emissions due to low-resolution DACs can be significantly reduced. Similar findings have been reported for PAs in [14].…”

Spatial Characteristics of Distortion Radiated From Antenna Arrays With Transceiver Nonlinearities

“…In other directions, however, barely any distortion is received from the array, which stands in contrast to the single-antenna array that radiates distortion in all directions. This point was not correctly described in [1], where it was claimed that the distortion always has an array gain smaller than the desired signal. Figure 6 shows how the maximum beamforming gain at the out-of-band frequency f = B is changing as the number of users increases.…”

“…Part of this work was presented at IEEE International Conference on Communications in 2016 [1]. paper is to give a rigorous description of the distortion created by nonlinear hardware in multi-antenna transmitters, and to quantify to which degree the distortion combines coherently.…”

Digital Predistortion for Hybrid MIMO Transmitters

“…Based on the nonlinear distortion analysis in the previous section, we formulate the proposed DPD structure and learning philosophy in this section keeping in mind that the main objective is to primarily minimize the harmful emissions in the intended RX direction, i.e., the in-band and OOB nonlinear distortion products in the effective combined signal y(n) expressed in (5).…”

“…These studies show that the spectral efficiency and the energy efficiency, both of which are fundamental objectives of massive MIMO, are compromised. In [5], the out-of-band radiation due to PA nonlinearity was analyzed in both single antenna and massive MIMO transmitter scenarios, assuming a memoryless polynomial model for each PA unit. It was shown that the adjacent channel leakage ratio (ACLR) due to PA nonlinearity in the massive MIMO scenario is, on average, equal to the single antenna scenario when transmitting with the same total sum-power.…”