Instrumentation & Measurement Magazine 23-9 - 6

Nevertheless, the hypothesis of having an almost constant
value of the control and/or signaling channels is not always
true, thus worsening the overall reliability of the results (i.e.,
the comparison with limits). Moreover, the technical standards leave to the operator some degrees of freedom about the
measurement procedures to be adopted, as well as instrument
settings and averaging times, which can introduce further errors and uncertainty components.
As for dosimeter measurements, they offer us information about non-self-induced or involuntary exposure [7].
Monitoring with a dosimeter or Personal Exposure Meter
(PEM) is a suitable approach when targeting to get a general impression of RF-EMF continuous daily life exposure
and to differentiate between sources. The PEM measures
the EFS for different frequency bands, including downlink
and uplink bands of various Radio Access Technologies
(RATs) such as 2G (900 MHz to1800 MHz), 3G, and 4G.
Samples in every frequency band are taken at regular time
intervals, which can be tuned depending on the acquisition time.
Current dosimeters cannot distinguish between different service providers. For instance, they cannot separate, for
the 900 MHz band, the E-field caused by 2G and 3G technologies, but they will provide the overall value. This property
would be useful in case one wishes to determine the exposure
from a specific service provider in a given area. Also, the frequency- or channel-specific information is not available. In
contrast, PEMs allow collecting numerous measurements with
relatively little effort and include a large variety of different environments [8]. Such devices have been successfully applied
in a few previous studies discussed in [9]. Having in mind
the stochastic nature of RF signals and the fact that optimal
conditions to measure RF-EMF exposure hardly exist when
planning exposure assessments, arising questions are: how to
characterize the short-term variations, reduce the variability
of the results and increase the repeatability of measurements
at the same time? Such issues are crucially important to have
reliable measurements, enabling a consistent comparison over
time. Since the RF bands are active 24 hours a day, the monitoring process should cover the same period, as well, to answer
such questions.
In this framework, the main aim of the article is to highlight
how, for both narrowband measurements (based on spectrum
analyzers) and dosimeter measurements (based on PEM), in
2G, 3G, and 4G systems, several issues are still open. In particular, a suitable refinement of measurement methods and data
processing is needed to improve the reliability of the measurement results and the level of confidence in when compared to
the applicable emission limits.
These issues are also significant when considering incoming 5G‑connectivity. Indeed, there will be massive diffusion
and usage of low and very high frequencies in several ranges
of the spectrum, which will increase human exposure to RF
fields. All of these concerns push the industry to improve all
measurement procedures to be applied for compliance with
applicable limits for each kind of source.
6

In this paper, measurements related to 3G and 4G systems will be shown. In particular, the discussion focuses on
measurements on 4G systems that have been carried out in
Italy by applying the extrapolation techniques [4] and on
the measurements on 3G systems that have been performed
in Bosnia and Herzegovina by applying the dosimetric approach [11].

Standard Measurement Techniques
Measurement Equipment and Narrowband
Evaluation Techniques for 4G Systems
Each country has fixed specific exposure limits to RF-EMFs
within the frequency range of 100 kHz to 3 GHz. In general,
a time interval of six minutes is adopted for the evaluation of
all RF fields emitted by different sources. All of these contributions must be summed up and compared with the limits.
According to [4], it is possible to use two possible instruments: spectrum analyzers (SA) and vector signal analyzers
(VSA). Each defines extrapolation techniques to predict the
maximum electric field (Emax) which is used for the limits' compliance evaluation. Because nowadays, in Europe, the most
common technologies for cellular communications are GSM
(2G), UMTS (3G) and LTE (4G), an extrapolation technique has
been defined in [4] for each of them. Since we are specifically
interested in narrowband measurements, in this paper, we focus our attention on LTE emissions adopting an SA.
An LTE signal is characterized by the presence of a Physical
Broadcast Channel (PBCH) located exactly at the center of the
LTE signal spectrum, occupying around 1 MHz bandwidth,
that is used as a signaling tool. It should exhibit a constant and
high power, at least higher than the traffic channels during the
day, and always be active. Considering this characteristic, the
extrapolation technique in [4] suggests to set: the center frequency equal to the carrier frequency of the LTE signal to be
monitored, a resolution bandwidth (RBW) equal to 1 MHz, a
sweep time equal to 70 μs times the number of trace points, a
RMS detector with Max-Hold functionality to stabilize with at
least 20 seconds waiting time, and it is recommended to perform the analysis in zero-span mode.
In this way, only the PBCH is considered and it is possible
to evaluate its electric field (EPBCH). The maximum electric field
(Emax) is then evaluated by scaling this value with a coefficient
(nPBCH), applying (1):

Emax  nPBCH EPBCH (1)

The value of nPBCH is the ratio between the maximum power
the cell is able to irradiate and the PBCH power. This implies
that (1) ensures that the obtained Emax is surely greater than an
integral measurement on the whole signal bandwidth under
real load traffic conditions.
Some countries also define another limit, the so-called attention limit. It is usually considered as the mean value of the
measurements carried out during a time interval equal to 24
hours.

IEEE Instrumentation & Measurement Magazine

December 2020

Instrumentation & Measurement Magazine 23-9

Table of Contents for the Digital Edition of Instrumentation & Measurement Magazine 23-9