A Web-based Application to Estimate the Total Exposure Ratio Due
to Base Stations
Um Aplicativo Web para Estima a Taxa de
Exposição Total Devido a Estações Base
Leandro Carísio Fernandes1 orcid.org/0000-0002-4114-2334
1 Universidade de Brasília, Brasília, Brasil
E-mail: carisio@gmail.com
ABSTRACT
There is a global concern about radiation from telecommunications base
stations. Although there is no evidence that this radiation cause adverse
health effects if its level is below some reference level, people continue to
fear its effects. In a recent survey in Europe, 70% of the respondents believe
that this radiation have some effects on health. This can impact the country-s
legislation, setting unnecessary rules to deploy new base stations.To shed
light on this subject, this paper proposes a web-based application to estimate
the amount of radiation emitted by base stations. With this tool, the general
public can easily check an upper limit for the total exposure ratio in any
location with just a click on a map. The software can also be used by public
authorities to find locations where measurements are necessary.
KEY-WORDS: Total
exposure ratio; Radiation; Base stations.
RESUMO
Existe
uma fonte de preocupação global em relação à radiação emitida por estações
radiobase. Embora não haja evidências de que esta radiação cause efeitos
adversos à saúde se o seu nível estiver abaixo de determinados limites de
referências, as pessoas continuam temendo seus efeitos. Em uma recente pesquisa
realizada na Europa, aproximadamente 70% dos respondentes disseram acreditar
que esta radiação causa algum efeito na saúde. Esse tipo de receio da opinião
pública pode ter impacto inclusive na legislação do país, definindo regras
desnecessárias para a implantação de novas estações radiobase. Como uma forma
de lançar luz a este tema, este artigo propõe uma aplicação web para estimar o
total de radiação emitida por estações radiobase. Com essa ferramenta, o
público em geral pode verificar, com apenas um clique em um mapa, um limite
superior para a exposição a campos eletromagnéticos em qualquer localidade,
informando se determinada localidade adere aos limites ou não. O software
também pode ser utilizado por entes reguladores para encontrar locais onde
medições são necessárias.
PALAVRAS-CHAVE: Radiação; Estações rádio base.
1
INTRODUCTION
Human
exposure to radiation emitted by telecommunications base stations still
concerns the public. In a survey on electromagnetic fields (EMF) conducted by
the European Commission, 70% of the respondents believe that mobile phone masts
have at least some effects on health [1]. This concern has also
been reported in different countries [1-5].
Nevertheless,
up to date, there is no evidence that the radiation emitted by mobile telephony
base stations cause adverse health effects [6]. Due to their characteristics
(antennas with narrow beam not pointing to the ground, usually deployed in
rooftops or with some height, power level decreasing quickly with distance, etc
[3]), the exposure ratio from
base stations usually range from 0.002% to 2% of the international reference
levels [6]. The same occurs in inhabited areas near broadcasting
facilities: measurements from the Federal Communications Commission (FCC) show
that the exposure is well below the limits [7].
On
the one hand, there are no health effects due to the exposure from base station
radiation. On the other hand, citizens still fear EMF radiation emitted by
them. Since the public opinion influences legislators, these concerns can
affect the deployment of new base stations [8]. For instance, in Brazil
there is a Federal Law that enforces the regulatory agency to measure the
exposure level around base stations located in critical areas (defined as those
up to 50 m from hospitals, schools, etc.) [9], which can increase the
cost to deploy a base station without any reasonable reason [10].
There
is a need to better inform citizens. Special Eurobarometer 347 concludes that
“regardless of whether or not EMF do actually damage public health, the average
EU citizen believes that public authorities do not do enough to protect them
from their potential health risks” [1]. The issue is with the perception of
the risk.
It
is necessary to be transparent about this topic. To assist the dissemination of
data relating to non-ionizing radiation due to telecommunications base station,
this paper reviews a methodology to estimate the total exposure ratio from the
telecommunications base stations. Then, a web-based application to estimate an
upper limit for the total exposure ratio is proposed [11]. This tool can be used in
two ways: by the general public, to check if any location is considered safe;
and by the regulators, to simultaneously check critical areas, which can
support some decisions (e.g. select specific location to measure the total
exposure ratio). The source code is available to the public [12].
2 REVIEW
In this paper,
a base station is considered as a physical structure with one or more radio
sources, each of them transmitting at some frequency. Our intention is to
calculate the exposure ratio due to all radio sources of the base stations at
some probe and check if it complies with the international reference limits.
The total
exposure ratio (TER) at some location is defined as [13]:
(1)
Where
ERi is the exposure ratio due to the radio source i
and, in the far-field, is defined as [13]:
(2)
Where E
(V/m) is the electric field at that probe location and Elim
(V/m) is the electric field limit, both at the same frequency of the radio
source. The International Commission on Non-Ionizing Radiation (ICNIRP) has a
guideline establishing safety levels for EMF. Table 1 shows the reference level
for the electric field for general public exposure.
Table 1:Reference levels for general public exposure to
time-varying electric fields [14, 15].
|
Frequency range
|
E-field strength (V/m)
|
|
3 kHz – 10 MHz
|
83
|
|
10 – 400 MHz
|
28
|
|
400 – 2,000 MHz
|
1.375 
|
|
2 – 300 GHz
|
61
|
f is the frequency of the radio source,
in MHz.
If
the TER ≤ 100% in some location, its radiation level complies with the limits
of Table 1 [16]. Measure the electric field at all possible locations is an
impossible task. An alternative is estimate its value. Since we are dealing
with estimates of the exposure from base station radiation, it is necessary to
get a conservative value of TER. One possible estimate for the electric
field is [16]:
(3)
Where
λ (m) is the wavelength of the radio source and Pr;watt
is the power received by the probe, in Watt. In dBm, the power is given by:
(4-a)
(4-b)
(4-c)
(4d)
(4-e)
(4-f)
Table
2 describes all the symbols used in the set of equation (4).
Table 2:Description of the symbols
in equation (4).
|
Symbol
|
Description
|
|
θ
|
Angle between the horizon and a virtual line
connecting the radio source and the probe.
|
|
eirp (dBm)
|
Equivalent isotropically radiated power (eirp) in the
probe direction.
|
|
L
(dB)
|
Propagation loss between the radio source and the
probe. For a conservative estimate, the free space path loss was considered.
|
|
d
(km)
|
Distance between the radio source and the probe.
|
|
f (MHz)
|
Frequency of the radio source.
|
|
eirpmax(dBm)
|
Equivalent isotropically radiated power in the
direction of the main lobe.
|
|
F (dB)
|
Antenna pattern in the probe direction. Equation
(4-d) considers the model for broad coverage antennas used for wireless
communications or broadcasting [16, 17].
|
|
a(radian)
|
Tilt of the antenna.
|
|
Asl(dB)
|
Side-lobe envelope level.
|
|
θbw(radian)
|
Vertical half-power beamwidth.
|
|
θfirst_null
|
First null of the antenna. In equation (4-d), it is necessary
to know if the probe is radiated by the main lobe or by some side lobes,
which is done checking if θ is within the first null of the antenna lobe.
|
Equation
(4-b) uses the free space path loss model. Although it is not suitable for
assessing some aspects of the propagation environment (e.g. coverage), we are
interested in estimating an upper limit of the TER. Therefore, equation (4-b)
should be used to keep our estimate conservative [16]. With equations (1)-(4),
it is possible to estimate an upper limit for the TER at any location. It is
important to calculate it for three heights (1.1 m, 1.5 m, and 1.7 m) and
report the largest value [13].
3 EMF EXPOSURE
WEB
To
consider a real environment with thousands of base stations, the calculation
using the previous approach needs to be done by a computer. For an urban
region, there are hundreds or even thousands of base stations, each of them
with one or more radio sources. This section proposes a software to estimate
the TER using the previous set of equations.
Since
the end user of this software might be the general public, it should be
user-friendly, intuitive, with just one feature: show if the location complies
the limit or not. Besides, it should be easily available, without the need to
install it. These characteristics point to a web-based software. In the
perspective of the end-user, the software can be described with only one user
story: “As a user, I want to view a map with the base stations, click anywhere
and check if that location is considered safe”.
To
implement this application, equations (1)-(4) were coded in TypeScript. Then, a
Single Page Application (SPA) was built using the Angular framework. The
software, EMF Exposure Web, is shown in Figure 1 and its source code is
available in [12]. The user selects a city to analyze and clicks the “Load”
button. The base stations of that city will be loaded on the map. Depending on
the zoom and the position of the base stations, they will be shown as a cluster
or with a single icon indicating the base station. If the user clicks at some
location, the exposure is estimated, and the result is shown – Figure 1.
Furthermore,
there is also a more advanced type of user. Although the end-user is the
citizens, some organization should be responsible to provide it. In this case,
it should have access to the base station database and can be regulatory
bodies, network operators or, if the country has a public base station
database, even a person with some programming knowledge.
To them, an advanced mode is welcome.
In this mode, the application allows to estimate the TER in several locations,
which allows an in-depth analysis of the data. Figure 2 shows this mode, with
some colored circles representing the TER estimated in several locations, using
a pre-defined color scale recommended in [18].
Figure 1: In the left panel, the user chose a city. The map in
the right panel shows its base stations. If the user clicks on it, an estimate
for the TER is shown in the box.
Source:Author (2018).
Figure 2: Advanced mode. In this mode, the user can estimate the
TER for a specific probe height. Besides, using the icon <> in the
top-right size of the title bar, the user can view the TER for several
locations using a pre-defined color map.
Source: Author (2018).
4 RESULTS
To
validate the software, the data of all cellular base stations in crowed regions
of four of the most populated Brazilian cities was loaded into the software
(Belo Horizonte, Brasília, Rio de Janeiro, and São Paulo). The software with
this data is available in [11].
The
Brazilian base station database is available to the public [19] and contains
the necessary information to estimate the TER using equations (1)-(4). When
converting the database, eirpmax was set equals to 61 dBm for
all radio sources, which is a typical value for the maximum eirp of a LTE 5 MHz
carrier [20]. Although cellular base stations do not operate with its
maximum power the whole time, we are interested in an upper limit for the TER.
Note that only the cellular base stations were loaded, so the estimated TER
will not consider the contributions of other telecommunications stations.
Using a Monte Carlo method, 20,000
random probes were uniformly distributed over circle with 2 km around a
reference location. Figure 3 shows the cumulative distribution function
(c.d.f.) of these data for TER ≤ 10%. Table 3 shows more details of the c.d.f.
Figure 3:Cumulative distribution function of the TER.
Source: Author (2018).
Table 3: Cumulative distribution function of the TER.
|
|
Belo Horizonte
|
Brasília
|
Rio de Janeiro
|
São Paulo
|
|
Reference location (latitude,
longitude)
|
(-19.9119126º,
-43.938385º)
|
(-15.7966675º,
-47.8915836º)
|
(-22.930369º,
-43.2407815º)
|
(-23.5632103º,
-46.6547975º)
|
|
Number of probes
|
20.000
|
20.000
|
20.000
|
20.000
|
|
cdf (TER ≤ 10%)
|
99.88%
|
99.93%
|
99.89%
|
99.27%
|
|
cdf (TER ≤ 25%)
|
99.98%
|
99.97%
|
99.75%
|
99.88%
|
|
cdf (TER ≤ 50%)
|
99.99%
|
100%
|
100%
|
99.98%
|
|
cdf (TER ≤ 75%)
|
100%
|
100%
|
100%
|
99.99%
|
|
cdf (TER ≤ 100%)
|
100%
|
100%
|
100%
|
100%
|
Except in São Paulo, EMF Exposure Web
estimates that at least 90% of the area has TER ≤ 5%. In all cities, more than
99.88% of the area around the reference location has TER ≤ 10%. This is an
upper boundary for the real exposure value due to cellular base stations and is
consistent with measure data all over the world. For example, in [21], the measured exposure
ratio due to second and third generation cellular base stations was less than
1%. In [22], a similar result was found. The exposure ratio from base
stations usually range from 0.002% to 2% [6].
A
fine grain test can be done comparing estimates with measures in some
locations. Anatel, the Brazilian telecommunications regulatory agency, has an
online map with some measures [23] that can be used to test the proposed
software. The available values for TER corresponds to measures from 100 kHz to
3 GHz. So, to make better comparisons, it is necessary to choose points far
from broadcasting stations, because their transmitted power is higher than the
one of cellular base stations. In some places, the exposure ratio due to
broadcasting stations is responsible for 90% of the total exposure ratio [21].
Figure 4 shows some measures (left)
and estimates (right) of the TER at the same location in two different cities
(Brasília and Belo Horizonte). The estimated value is higher than the measured
value, which is desired, since we are interested in an upper limit for the
total exposure ratio.
(a)
(b)
Figure 4: Measured (left) and estimated (right) TER in the same
location. Measured values are public available in [23]. The boxes in the left images show, respectively, the
timestamp of the measured, the average of the electric field intensity, the
measured TER divided by its reference limits (in percentage), the measured
bandwidth, and the city. EMF Exposure Web was used to calculate the estimated
values. (a) Brasília; (b) Belo Horizonte.
Source: Author (2018).
A
software like EMF Exposure Web can also assist in some decisions. For example,
in São Paulo, five locations have TER ≥ 50%. This is an unexpected result,
because we are considering only radiation from cellular base stations. So, the
public authority can analyze what occurred. In these cases, the height of the
base stations near these locations is extremely low (lower than 5 m), which can
be an error in Anatel’s database (they are usually deployed in top of
buildings). Besides, in these five locations, the vertical beamwidth of the
base stations near them has values that are not compatible with other base
stations operating at the same frequency, which perhaps is also an error in the
public database.
In
the case of the Brazilian data used in this paper, the operators register the
base station information in the regulators database [24]. Thus, the regulator can
check the consistency of its database. If the information is correct,
measurements can be done specifically at these locations to assess their TER
value. This allows the regulator to measure the TER in places where it is more
likely to have a high total exposure ratio from telecommunications base
stations.
5
CONCLUSIONS
This
paper reviewed how to estimate an upper limit for the total exposure ratio
(TER) from telecommunications base stations. Then, it proposes a software (EMF
Exposure Web) that implements this procedure. The source code and a reference
implementation are available in [11, 12].
To
validate EMF Exposure Web, data of all cellular base stations in four crowed
Brazilian regions were loaded into the software. The results were consistent
with measurements in the same location, i.e., the estimated TER represents an
upper limit for the measured TER.
Therefore,
the proposed software can be used by the general public to check if the
exposure level from base stations in any location is below the reference
limits, which assists in the dissemination of information.
The
software also allows more in-depth analysis. In this case, it may be useful for
public authorities to find critical areas requiring on-site measurements.
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