Instrumentation & Measurement Magazine 23-9 - 11

Table 2 - Summary statistics on instantaneous electric field parameters (V/m), first week
Service

UMTS
(2100 MHz)

Day

Emin

Emax

Emean

p50

p95

σ

1

0.044

0.139

0.067

0.065

0.094

0.014

2

0.051

0.172

0.074

0.074

0.100

0.014

3

0.023

0.179

0.072

0.071

0.098

0.016

4

0.023

0.152

0.073

0.071

0.099

0.014

5

0.043

0.131

0.066

0.063

0.092

0.013

6

0.045

0.134

0.064

0.061

0.089

0.012

7

0.047

0.121

0.060

0.058

0.079

0.009

(Emean, p50, σ, ...) for different days led to the conclusion that
obtained distributions were mostly log-normal, which is generally typical in the assessments of exposure resulting from the
sources of RF emissions [12].
Other researchers, though, have reported that the environmental EMF measurements may follow normal [13] or the
log-normal distribution [14], [15]. Additionally, a clear bimodal
behavior of the measured EFSs was reported in [16], where the
possible explanations for such behavior were assumed to
be the cause of the line-of-sight (LOS) and non-line-of-sight
(NLOS) measurements mixture having the LOS responsible
for the higher median value distribution and the NLOS for the
lower median value distribution. Further, the ratio between
the maximum and minimum instantaneous EFS varied from 8
to 18 dB (mean 12 dB) over the week. When a 6-minute running
average was applied on the data set, the ratio of Emax / Emin decreased and varied from 3 to 10 dB (mean 6 dB). By increasing
the averaging time (up to 24 hours) such ratio tends to be even
much smaller comparing to those at 6-minutes (i.e., within 2.5
dB or less after 10 hours of averaging).
Based on such behavior, the averaging process cannot completely eliminate the daily variations, but it reduces them
significantly. That is why the integral-based (cumulative)
measure of the whole day is proposed. The main goal of this
approach was to find a new criterion (besides the time-averaging) that will, with the minimum deviations (under more
or less same conditions), give the results that show the total
(24 hour) level of irradiation of the measured location. The
idea was, depending on the environment, to get the results of
measurements that are stable (using the time-averaging it was
either obtained that 24 hour averaged values for all days remained within ±20% of the mean week averaged value). The
results of the integral-based measure are illustrated in Fig. 7. A
higher upslope of the curves is connected with the peak-hour
period/s of the day (increased traffic), as such instantaneous
power density (S) values add more contribution to the cumulative sum of S. However, considering the relation between the
peak-hour/s and integral-based measure, the peak-hour/s
values (in terms of traffic) have no influence on the specific
time of measurement during a day, as long as the whole day
exposure is observed. Additionally, integration of S in time
gives minor deviations in daily exposure between days of the
week which also tend to stay within approximately ±20% of
December 2020	

the mean week value obtained with the integral-based measure (against the ratio of Emax / Emin instantaneous values on a
daily level of up to 18 dB).

Discussion and Conclusions
As for measurements on 4G systems regarding compliance
with the applicable attention limits, the experimental results
have shown a significant variability (see Table 1) which can
be comparable with the measurement chain uncertainty (expanded uncertainty equal to 2.5 dB). These results suggest
that the measurement methods for the evaluation of human
exposure to EMFs generated by LTE communication systems
should be refined for reducing the measurement uncertainty
and making the comparison with applicable attention limits
more reliable.
As for measurements regarding compliance with the
exposure limits, the experimental analyses to verify the overestimation capability of the extrapolation techniques, have
demonstrated how such overestimation is generally not constant, and in some 6-minute intervals, an underestimation is
also observed. Moreover, in some cases, the extrapolated Efield could not represent the maximum value experienceable
throughout the day.
In other words, the 6-minute interval in which the measurements are performed should be carefully chosen, in opposition
to what international guidelines generally indicate. The results
of this activity research could be useful for technical committees and researchers engaged in improving the measurement
techniques and the data interpretation for assessing human exposure to 4G systems. Moreover, they also push to investigate
uncertainty modeling in such kinds of measurements.
As for measurements on 3G systems, exposure assessments
have been challenging due to high temporal variations of the
RF-EMFs, questioning how reproducible dosimetric measurements are. Issue-specific research questions have focused on
the characterization of RF-EMF exposure levels in typical everyday environments and on how the exposure changed over
time. Further, an overview of potential instabilities that could
be associated with the short-term measurements and averaging is discussed due to the high variability of the measurement
results. Even though the exposure of the general public is
known to be well below established ICNIRP guidelines, monitoring the exposure is important from an environmental

IEEE Instrumentation & Measurement Magazine	11



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