Analysis of nonlinear low-noise amplifiers in massive MIMO base stations

Because of the large number of antennas at the base station, the power consumption and cost of the low-noise amplifiers (LNAs) can be substantial. Therefore, we investigate the feasibility of inexpensive, power efficient LNAs, which inherently are less linear. To characterize the nonlinear distortion, we describe the LNAs using a polynomial model, which allows for the derivation of the second-order statistics of the received signal and the distortion. A massive MIMO system that serves one user in line-of-sight is studied. It is shown that the distortion from the LNAs combines coherently and that the SINR of the symbol estimates therefore is limited by the linearity of the LNAs. Furthermore, the impact of a strong transmitter in the adjacent frequency band is investigated. The second-order statistics show how the power from that transmission leaks into the main band and interferes with the symbol estimates.