## 2 Materials and Methods
### Measurement Method  
The measurement method for the assessment of 5G NR base station exposure was described in detail in [13]. A short summary is given below:  
* **Step 1 'Spectrum overview'**--A spectrum overview measurement in the frequency range between 700 MHz and 6 GHz to identify the RF environment in general and the NR signals in particular at the measurement site.
* **Step 2 'Identification of the Synchronization Signal Block (SSB) (or Synchronization Signal (SS) burst)'**--For each present NR signal, an in-band measurement to detect the bandwidth (and therefore the numerology or subcarrier spacing (SCS)) and frequency position (\(SS_{REF}\)) of the channel's SSB or SS burst, as well as the channel bandwidth.
* **Step 3 'Assessment of the electric-field level per resource element (RE) of the (dominant) SSB and PDSCH'**--For each present NR signal, a measurement of the electric field strength per resource element \(E_{RE}\) of the (dominant) SSB (of the SS burst) as well as of the PDSCH was taken.
* **Step 4 'Assessment of the time-averaged electric-field level'--**For each present NR signal, the time-averaged electric-field strength \(E_{avg}\) over the channel bandwidth was measured. The applicable averaging time is specified by the exposure standards (e.g., 6 min or 30 min for localized and whole-body exposure, respectively, according to [3]). However, for convenience, in this work, an averaging time in the order of 30 s was used since it was found that this provided an accurate estimate of exposure when time-averaged over 6 min or 30 min. Time averaging over periods different than what was given by the relevant exposure standards can be used provided that this results in a reliable estimate of exposure [3,18].
* **Step 5 'Post-processing'--**Post-processing of data and calculation of the maximum theoretical electric-field level \(E_{max}\), using either \[E_{max}=\sqrt{12N_{RB}}\,\sqrt{\frac{G_{PDSCH}}{G_{SSB}}}E_{RE,SSB}\ \ [\frac{V}{m}],\] (1) with \[N_{RB}\] the maximum number of resource blocks used in the channel bandwidth (depends on the bandwidth and the numerology), \[E_{RE,SSB}\] the electric-field level per RE in the _dominant_ SSB of the SS burst, i.e., the SS beam with the highest gain in the direction of the evaluation point (hence resulting in the maximum \[E_{RE,SSB}\] ), \[G_{PDSCH}\] the (maximum) gain of the PDSCH-allocated resources transmitted by the BS radio in the direction of the evaluation point, \[G_{SSB}\] the gain of the SS beam in the direction of the evaluation point, or \[E_{max}=\sqrt{12N_{RB}}\ E_{RE,PDSCH}\ \ [\frac{V}{m}].\] (2)  
Equation (1) represents the theoretical extrapolation, useful when only \(E_{RE,SSB}\) can be measured and the antenna patterns of the SSB and PDSCH signals have been provided to calculate the factor \(\frac{G_{PDSCH}}{G_{SSB}}\) at the point of evaluation. Equation (2), on the other hand, is the experimental extrapolation and is based on the direct measurement of \(E_{RE,PDSCH}\) at the point of evaluation.  
Finally, in the case of time division duplexing (TDD), an additional factor \(f_{TDD}\) < 1 is added to Equations (1) and (2) that takes into account the resource division between uplink (UL) and downlink (DL) signals.