On the Impact of Residual Transmitter Distortions in 5G Massive MIMO Base Stations

The low-cost hardware components, commonly assumed to be used as building blocks of Massive MIMO (multiple-input multiple-output) base stations, could limit the achievable data rates. In this paper, the impact of residual transmitter distortions on downlink transmission in channels with frequency-selective fading is evaluated using link-level simulations. Nonlinear distortions, modeled here with clipping, are demonstrated to have significantly different behavior, due to directional radiation patterns, compared with additive white gaussian noise (AWGN). In a transmission with clipping distortions to a single user equipment (UE), increasing the number of antennas on the base station side leads to a negligible reduction (about 1 dB visible for 512 antennas) of the error vector magnitude (EVM) for channels with a strong line-of-sight (LoS), while for non-line-of-sight (NLoS) channels a noticeable reduction (about 4 dB for 16 antennas) can be observed. In a multi-user MIMO transmission in LoS channels, increasing the number of UEs leads to improving the EVM for clipping distortions (about 4 dB reduction visible for 8 UEs). However, for AWGN-modeled distortions sharing the transmission power between multiple UEs results in an EVM degradation, especially if the power is distributed between UEs based on their path losses to achieve comparable quality of service.