Enhanced Methodology to Characterize 3-D Power Monitoring and Control Features for 5G NR Systems Embedding Multi-User MIMO Antennas.

Multi-User MIMO (MU-MIMO) is widely used in the fifth generation (5G) cellular network to improve network performance at high traffic loads. When demonstrating the compliance of 5G antennas with the radio frequency (RF) electromagnetic fields standards, beamforming and MU-MIMO must be considered, since a 5G MU-MIMO antenna radiation pattern changes in both the space and time domain, adapting to changes of the user's position. To cope with the time and space variability of the power radiated by 5G systems, mobile operators can activate automatic tools to monitor and control the transmitted power (power lock (PL) systems) to ensure that a given radiated power threshold is not exceeded. This article extends and enhances the methodology introduced by the authors in previous work, by testing and verifying PL systems in an MU-MIMO and beamforming scenario (3-D PL systems, 3DPL) through field measurements, controlling the power transmitted by each beam, i.e., in each direction. Measurement results confirm that the 3DPL feature limits the average power of the traffic channels transmitted in each direction, regardless of the configured total maximum power. More specifically, it is shown that the 3DPL reduces the maximum average transmitted power by the expected 2 dB when only one user is active (i.e., in a single-user MIMO (SU-MIMO) scenario), while it does not operate any reduction when two users are active (MU-MIMO scenario) because the power transmitted toward each user is already half (i.e., -3 dB) of the maximum power that can be transmitted.