# RF-EMF Exposure near 5G NR Small Cells
## 2 Materials and Methods
### Measurement Method  
The followed measurement procedure was presented in [10] and adopted in the revised IEC 62232 standard [2]. The different steps are summarized below, while the specific measurement settings can be found in [13]:  
**Step 1. ** A spectrum overview measurement of the frequency range between 700 MHz and 6 GHz was performed at one position in the environment of the assessed 5G NR base stations (in this study, at about 5 m horizontal distance) using the aforementioned FSV setup. This measurement identified the RF environment at the specific location, and more specifically the frequency band of the considered NR signal. **Step 2. ** An in-band measurement of the considered NR signal was performed at the same position as Step 1, using the same FSV setup (to the authors' knowledge, this measurement cannot easily be performed with the SRM setup without the aforementioned 5G NR option). The measurement data (i.e., the received-power samples) were post-processed to retain only those signals (i.e., samples above the noise floor) that are roughly four Orthogonal Frequency-Division Multiplexing (OFDM) symbols long, which is the size of one NR Synchronization Signal Block (SSB) in the time domain. For example, in the case of a subcarrier spacing (SCS) of 30 kHz, the SSB is about 4 \(\times\) 35.7 \(\upmu\)s = 142.8 \(\upmu\)s long. Plotting just samples of these four-symbol long signals reveals the specific frequencies used by the SSB, and thus its center frequency (SSREF) and its bandwidth (which, in the case of an SCS of 30 kHz, is 7 MHz). In the case SSREF is known, this step can be skipped. **Step 3. ** In this study, at several positions in the near vicinity of the base station as well as at distances of up to 100 m, a scope or zero-span measurement was performed with a resolution bandwidth (RBW) of 1 MHz around SSREF. The sample time is set approximately equal to the OFDM symbol duration (e.g., -36 \(\upmu\)s for 30 kHz SCS), such that the obtained samples constituted the root-mean-squared (rms) power \(P_{r}\) received during one OFDM symbol and within 1 MHz, which contains about 33 resource elements in the case of a 30 kHz SCS. Figure 2: Second type of equipment used in this study to measure the exposure to 5G new radio base stations, consisting of a Narda SRM-3006 field strength analyzer (SRM) and a tri-axial isotropic antenna (“probe”). With these measurement settings and for an SCS of 30 kHz, it is known that during the transmission of SSB(s) (at frequencies below 6 GHz there can be up to 8 SSBs transmitted consecutively), the measured 1 MHz bandwidth contained 33 REs that were effectively used, so each SSB's power per resource element \(P_{RE,SSB}\) can be directly derived from the \(P_{r}\) measured during the SSB transmission [10; 18]. However, for other signal types, such as the Physical Downlink Shared Channel (PDSCH), i.e., the downlink transmission of data from the base station to a user equipment (UE), the allocation of the REs is not known. At any given time, the number of allocated REs within the measured bandwidth can vary between 0 and 33 (with SCS = 30 kHz). These different allocations result in different Gaussian distributions making up the total received-power sample distribution [10]. Hence, to obtain the correct \(P_{RE,PDSCH}\), it is essential that the number of resources allocated to PDSCH is maximized during this measurement, forcing at least sometimes 33 active REs within the measured bandwidth. This is performed by maximizing the downlink traffic load, e.g., by using iPerf, a speed test, or by downloading a very large file (of several GBs) on a UE in the near vicinity of the measurement probe [13]. Then, the'maximum' \(P_{r}\) (actually, the peak of the highest-valued Gaussian distributions) measured during PDSCH transmission is used to calculate \(P_{RE,PDSCH}\)[10]. Since the FSV setup's probe was put on a telescopic pole, measurements with an active UE involved placing the UE on a plastic cart (\(\sim\)0.8 m above ground level) at a 2 m distance from the SRM setup's probe.