MWF Research Outcomes: In-Situ Measurement Methodology for 5G Base Stations

Deployment  of 5G networks is already well underway around the world and one of the areas that the MWF identified for further research work was the need for updated exposure assessment methodologies to demonstrate compliance of the base stations. 5G base stations make use of beam forming and massive MIMO (Multiple-Input Multiple-Output) to direct the signal where is needed rather than spreading the energy over a large angular beam. Beam forming and massive MIMO result in greater efficiency and better use of spectrum, but using traditional compliance assessment methodologies results in unrealistic overestimation of EMF exposure. This overestimation comes about since it assumes all the power of the base station is allocated within the same beam for several minutes.

This project therefore had two objectives:

• to develop a measurement method to assess exposure from 5G NR base stations on-site; and 
• to develop a measurement methodology applicable to assess exposure for massive MIMO products. 

Measurements being undertaken on a base station with a number of different services. The small 5G antennas are located in the middle of the head of the tower.

Measurements being undertaken on a base station with a number of different services. The small 5G antennas are located in the middle of the head of the tower. The MWF supported a research project at the University of Ghent to undertake the identified work. The results involve a five-step methodology consisting of: (1) a spectrum overview to identify the 5G NR channels; (2) the identification of the synchronization signal block (SSB) which contains the ‘always on’ signals; (3) the measurement of electric field strength per resource element of the SSB; (4) the measurement of the of the time-averaged instantaneous exposure level; and (5) the extrapolation of the resource element electric-field strength to the theoretical maximum level as well as the actual maximum level taking into account a variety of factors outlined in existing standards.

The methodology has now been presented to the International Electrotechnical Commission (IEC) standards committee overseeing work on a new standard in this area and has been published in the journal IEEE Access.

The publication details are as follows:

• In-situ Measurement Methodology for the Assessment of 5G NR Massive MIMO Base Station Exposure at Sub-6 GHz Frequencies, Aerts S, Verloock L, Van Den Bossche M, Colombi D, Martens L, Törnevik C, Joseph W, IEEE Access 2019; 7: 184658-184667