SAFETY ZONE DETERMINATION FOR WIRELESS CELLULAR TOWER - A CASE STUDY FROM TANZANIA

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IJRET: International Journal of Research in Engineering and Technology
eISSN: 2319-1163 | pISSN: 2321-7308
SAFETY ZONE DETERMINATION FOR WIRELESS CELLULAR
TOWER - A CASE STUDY FROM TANZANIA
Christina P.Nyakyi1, Salehe I. Mrutu2, Anael Sam3, Justinian Anatory4
1MSc. Student, 2 PhD. Student, 3 Senior Lecturer, The Nelson Mandela African Institute of Science and Technology,
Arusha, Tanzania.nyakyic @nm-aist.ac.tz, mrutui @nm-aist.ac.tz, [email protected]
4 Associate Professor, The University of Dodoma, Dodoma, Tanzania, anatory @ engineer.com
Abstract
Safety zone determination for wireless cellular towers has attracted attention from many researchers in the last decade. This is caused
by the rapid growth of the wireless cellular industry which has led to the installation of towers even in the residential areas. There are
many reports and ongoing researches regarding the biological and thermal effects of wireless cellular electromagnetic fields
exposures to people. Cancer, hyperthermia, neural and behaviour effects of people exposed to these electromagnetic fields have been
reported.
This motivates the research to determine safety zones from wireless cellular towers to assure safety to those living in the vicinity of
these towers. A model for safety zone determination is developed. The model takes the received power at the object, power transmitted
by the transmitter and gain of the transmitter as inputs to determine the safe distance from the radiation of a wireless cellular
transmitter. The power density received by the object and its geographical location from the radiation source are measured using the
selective radiation meter. Transmitted power and the gain of the transmitter together with the height of the tower were obtained from
the respective wireless cellular network operator. Based on the geographical location of the object, the distance from the radiation
source was calculated using the haversine formula. These inputs are then used to determine the safety zone based on the standards
and guidelines developed by WHO and ICNIRP.
Keywords - Safety zone; Power density; wireless cellular tower; Exposure limits.
----------------------------------------------------------------------***------------------------------------------------------------------------
1. INTRODUCTION
Almost all guidelines and recommended limits on human
exposure to GSM electromagnetic fields are given in terms of
The growth of the wireless cellular industry coupled with the
Specific Absorption Rate (SAR) defined by (1).
proliferation of cellular mobile applications has led to more
installation of wireless cellular transmission towers/base
2
station antennas even in residential areas, schools, markets,
E
hospitals, and other densely populated areas. This raises the
SAR
public concern regarding the safety of population exposed to
m
(1)
such networks with aggregated radiations[1].

Where
- Conductivity of body tissue,
Interaction of GSM electromagnetic fields and humans should
include all particularities of
human body which has very
E - Root mean square of intensity of electrical field at
unusual electromagnetic properties values such as electric
considered point
permittivity and electric conductivity[1].
m-mass density of tissue at that point
These properties are not well known and depend on activity of
person
SAR, the time rate of RF energy absorbed per unit mass, is

very difficult and complex to be measured in biological
This material is an active material at cell scale

tissues; standards permit the use of reference levels of power
Most cases, the problem is actually a coupled problem
flux density [W/m2] in free space. IEEE standard established
that is the thermal effect is one of the major effects and it
the limits for electric and magnetic fields, so called maximum
is affected by the blood circulation

permissible exposure(MPE) and similarly ICNIRP standard
The geometry is complex and generally environment of
defines reference limits for free-space incident fields as
the human body has to be taken into account
detailed in table 1 with safety limits exposure for public in
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some of the services. Getting together these limits SAR
distance from those antennas. The study based on estimated
compliance should be ensured. So as a replacement for
readings and not actual readings from the field [6].
complex SAR measurements, for compliance assessments the
above mentioned standards the simpler field measurements as
Electromagnetic radiation from mobile phone base station at
power flux density are used[2].
Gaza was the study aimed to highlight relevant international
work and develop the computer tool which can simplify
In this paper we have presented results of measurements of
estimating and measuring EMF level in the city. The tool
field strength items of power flux density in the vicinity of
developed had to store the BTS parameters and coordinates in
base station antennas
a database, and then it generates tables and maps that illustrate
EMF level estimated theoretically. It doesn't define whether
Table 1: ICNIRP Safety Limits for public exposure
the level was on safety zone or unsafe distance rather than
generate the maps and tables.[7].
Service
ICNIRP
ICNIRP
Safety
Frequency
Safety
limit
Limit
Power
The level of power density varies with the increase of gain as
E-field [V/m]
Density (W/m2)
well as the power of transmitter was shown on the study done
GSM 900
41.9
4.66
by Al-Bazzaz, 2008. In this study theoretical assessment of
GSM 1800
58.4
9.05
electric field strength and power density performed on
WCDMA
61
9.87
locations tens of meters away from mobile phone base station
antennas was presented. This study also
doesn't show the
safety zone [8].
2. RELATED WORK
The study done by Singh (2012), the exclusion zone
3. METHODOLOGY
(compliance distance) from GSM, CDMA, 3G/UMTS, and
In this study we have done a field work on measuring power
WiMAX antennas have been found at 7.30, 6.076, 7.436, and
density at discrete levels by using Selective Radiation Hazard
6.861 m, respectively are deduced. However, in this study
Meter (SRM) - Narda 3006 which has the ability to allocate
values of EIRP which is transmitted and its gain as well as at
the geographical location where the object located in terms of
what height of antenna should be installed is not defined [3].
latitude and longitude as well as to quantify the value of power
density. By having these two locations for source and object
The study titled Estimation of peak power density of
then the discrete distance was obtained by using the
electromagnetic radiation in near and far fields for 2G and 3G
`haversine' formula. This formula is more applicable in
base station in Albania done by Cela et.al (2012), this study
calculating the great-circle distance between the two points.
discussed on the safety distance from cellular base stations
The haversine formula is given by equation (2), (3) and (4).
operating at 900MHz, 1800MHz and 2100MHz has been done
by using a simplified theoretical way considering ideal
conditions for wave propagation. The study also hasn't


actual
Givenby a
2
;
Sin
Co
s .Co
s
2
Sin

1
2
readings from the field as well as identify physical dimension
2
2 ,
(2)
for the surface even the time taken for capture the entire
readings [4].
c
a
2
.
2 tan a, 1 a,
(3)
The study done by Kaur et.al, 2012 on the effect of
permittivity
and
conductivity
of
tissue
on
SAR
of
d R c
.
electromagnetic radiations shows, how the Voltage Standing
,
(4)
Wave
Ratio
(VSWR)
and
return loss
from 900MHz
communication frequency on simulated antenna for analyzing
Where; is latitude, is longitude, R is Earth's radius (mean
its effect in terms of variation in specific absorption rate
radius = 6,371km). All angles are in radians
(SAR) of EMF radiation in human tissue at different
permittivity and conductivity has different effects accordingly.
3.1 Measurement of Power Density from Cellular
this study does not indicate whether the permittivity and
Towers
conductivity are affected by distance variation from the source
[5].
Undertaking the measurements by SRM, the operating
The study done by Kamo et al.(2011) shows; the relationship
procedure is followed. The equipment was installed with
between theoretical values with exposure limits for both public
software which has the ability of downloading the data as well
and occupational from cellular base stations, FM, UHF and
as to identify the geographical location in terms of latitude and
WiMAX antennas as well as suggest the possible safety
longitude with the help of building GPS. On setting the
frequency span GSM 900MHz was on the range of 890MHz to
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960MHz, where GSM 1800MHz was on the span of 1790MHz
up to 1880MHz the Resolution Bandwidth (RBW) was 17.5
and 450 respectively according to the manufacturer guidelines.
The standard was observed for the Europe as per setting on the
equipment.
On measuring technique the very high lobe should be detected
so that the maximum power density can be obtained as shown
on the figure 1.The detection of main lobe is done by visual
and sweeping the measuring tool to detect the appropriate
direction of the very high lobe.[9]
Figure 1: Radiation Pattern of Cell Tower Antennas
Table 2 and 3 shows the measurements obtained for GSM900
and GSM1800 antenna at the field area
Table 2: Mbauda Cellular tower, Tanzania - Actual data readings on 05/29/2013 at 10hrs
Power Density [W/m]
Latitude[S]
Longitude[E]
Distance[m]
900MHz
1800MHz
322'50.5'
3639'34.0'
974.30
054.01
00.00
322'50.8'
3639'34.0'
936.52
281.43
09.27
322'51.3'
3639'34.0'
445 .00
267.25
24.71
322'51.6'
3639'34.0'
004.06
049.59
33.98
322'52.1'
3639'34.0'
012.01
053.35
49.42
Table 3: Mrombo Cellular tower, Tanzania - Actual data readings on 05/29/2013 at 14hrs
Power Density [W/m]
Latitude [S]
Longitude [E]
Distance [m]
900MHz
1800MHz
325'09.2'
3639'25.0'
41.30
259.90
00.00
325'09.5'
3639'24.8'
64.00
148.60
09.27
325'09.7'
3639'24.6'
35.80
198.20
15.44
325'10.0'
3639'24.4'
59.30
146.50
24.71
325'10.2'
3639'24.1'
46.01
118.90
30.89
The values in table 2 and 3 are very small compared to the
CASE 1: Single Tower
limit exposure provided by the ICNIRP as shown on table 1
above. The measured value readings vary with respect to
Consider the case of single tower in a free space, a case
distance and time, which lead to stochastic readings.
common in rural/remote area.
3.2 Derivation of Model Equations
In this study we derive the power density received at
destination in free space path loss for one and two antenna and
generalize with n-antenna and consider the case when the
height of object h0 is defined. We study the effect when the
distance of object increases and the height changes.
Figure 2: Single tower with an object.
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The power density at point on the ground at a distance, x
If the equation (5) is modified to consider the height, h0, of an
metres from the tower is given by the equation:
object (like a house or human), then power density at the top
of the house is given by:
Pt Gt
Pd
Pt Gt
R2
4

(5)
Pd
r 2
4
(8)
P
Where;
d means power density from cellular tower in
W/m2.
2
2
2

(h
r
x
h )
But
o
(9)
pt
G
and
t are power and gain from transmitters in dBm and
Then equation (8) become;
dB respectively and R the distance from transmission tower to
object at ground level in metre. When the height of the tower h
P G
t
t
in metre and the distance of the point x in metre from the
P
d
tower are known, then we have;
4
2
2
x h ho
(10)
R2 x2 h2
(6)
Figure 4. Shows the variation of power density at the top of an
object of 3 metres height for antenna with Pt = 16dBm,
Thus, we have;
20dBm, and 25dBm. Field data for GSM900 and GSM1800
has been plotted together to enable comparison with
theoretical values. The graph shows that power densities from
Pd PtGt
the field were less than the theoretical power densities
x2
4
h2
(7)
produced by an antenna of Pt = 25dBm.
Figure 4.3 shows the power density of Pt = 16dBm and
-3
x 10
20dBm with a gain Gt = 17dB. These values were used
1.8
Pt = 16dBm
because many service providers of cellular network use Pt in a
1.6
Pt = 20dBm
range of 16dBm to 20dBm
Pt = 25dBm
1.4
GSM900
GSM1800
-4
2
x 10
1.2
4.5
m/
W
Pt = 16dBm
ni
1
4
Pt = 20dBm
ytisne 0.8
3.5
Drew
2
o
3
0.6
m/
P
Wni 2.5
0.4
ytisne 2
0.2
Drewo 1.5
0
P
0
50
100
150
Distance from base to object in metres (m)
1
0.5
Figure 3: Power Density with fixed height of object ho=3m in
0
various Pt
0
20
40
60
80
100
120
140
160
180
200
Distance from base to object in metres (m)
To compute the total power density absorbed by an object of
height h0, we use the idea of calculus, and show that the total
Figure 2: Power density versus distance of a point for Pt =
power density is given by
16dBm, 20dBm and a gain Gt = 17dB
Total Power Density =
The graph shows that power density decrease with the increase
ho
P G
t
t
h
h h
0
in distance of a point from the tower, and at some point the
P
d
arctan arctan

power density attains a constant minimum value.
4
0

x
x (11)
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Remember that this formula is applicable only when h0 is
R2 h2 x2
defined otherwise the total power for h0 = 0 is computed from
1
1
1
(12)
equation (5).
2
2
2


Figure 5. Shows the total power density at the top of various
R
h
x
2
2
2
(13)
object heights from 3m to 10m. It can be seen that total power
density increases with the height of an object
The power density for each antenna from the two towers is
given by
P1G
0.7
1
P

d 1
,
2
Pt = 16dBm
4 R1
(14)
Pt = 20dBm
2
0.6
m/
W
P2 G
ni
2

0.5
P
y
d ,2
ti
2
4
s
R2
n
(15)
eDr 0.4
ewo
By substituting equation (12) and (13) into equation (14) and
P
de 0.3
(15) then it becomes
talu
P G
1 1
m

u
Pd 1
,
4 h2 x2
c 0.2
cA
1
1
l
(16)
atoT 0.1
2
2
Pd ,2 4 P G
h2 x2
03
4
5
6
7
8
9
10
2
2
(17)
Height of object in metres (m)
.
The average power density at a point from the two antennas is
Figure 4: Total Power Density for object with height from
given by
h0=3m to 10m



1
1 1
2
2
P
P
P

P G P G


d
d 1
,
d ,2
4 2
2
2
2
h
x
h


CASE 2: Two Towers
1
1

x
2
2 (18)
Consider two towers that generate and transmit power at P1
Figure 7. Shows that power density depends on the distance of
and P2. Let the respective height of towers be h1 and h2 and
an object from the antenna. That is, power density decreases as
x1 and x2 be the horizontal distance of the object from the two
the density increases
towers respectively. The power density at a particular point on
the ground will be the sum of the power densities from the two
antennas.
.
Figure 6: Graph of Power Density at a object from two
Figure 5: Power Density to an object from two towersFrom
antennaWhen the height of object is considered then the
Pythagoras theorem, we have
expression (18) is derived as shown on equation (19) and its
relation is illustrated in the graph figure 8.
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n
1
P G
i i
1


P1G1
P2G2

P


d, i
P
d P

d 1
,
P

d,2


(19)
4
2
i 1 2
x h h
i
i
0

4



2
2
h
1 h0 2
x
h
2 h0

2
x

1
2
(24)
Note: The equation (24) is a general expression which can be
Figure 8 shows the variation of power density at the top of an
used to determine the power density at any point for an object
object of height 3m situated at a distance x1 and x2 from the
with height 0 to h0 provided that power transmitted and the
two antennas of height h1 and h2 respectively.
gains of antenna as well as the distance from the transmitter
are known.
3.3 Computation and Validation of safety zone
There are a number of national and international regulations
standards and recommendations dealing with electromagnetic
exposure in the radio frequency range. The limits are generally
very similar and usually based on recommendation from the
World Health Organization (WHO) and the International
Commission on Non-Ionizing Radiation Protection (ICNIRP)
guidelines. It is shows that the limits have been set with a wide
margin in order to protect people from any known negative
health effects of both short and long term exposure to
electromagnetic field. Basic restrictions on exposure are
provided for both occupational exposure and public exposure.
The standard posed by ICNIRP guidance for public exposure
limits is 9.2W/m2 for GSM 1800MHz and 4.7 W/m2 for GSM
900MHz. However, these limits can be tolerable if the person
is exposed for few seconds and not for permanent exposure
[10].
Consider a case of a human lying on the bed of 2m2 the hip or
height made by the body taken to be negligible. Then, the
Figure 7: Power Density from two towers for an object at a
power absorbed is given by exposure limits times the surface
height ho=3m
area.
CASE 3: For n towers
For GSM 1800 power density;
2
2
2

W
2
.
9

W
P
4
.
18
d
m
m
n
P
PiGi
d,i
2
For GSM 900 power density;
i 1 4 Ri
(20)
2
2
2
7
.
4
W

W
P
4
.
9
d
m
m
R2 x2 h2
If time is considered then power absorbed
For
i
i
i
(21)
For 30min. exposure in GSM 1800;

W
4
.
18
30
(
)
60 sec
120
,
33
Joule
n
Pd
P

P G
i
i
d , i
2
2
i 1 4 x h
i
i
Then,
(22)
For 30min. exposure in GSM 900;

W
4
.
9
30
(
)
60 sec
920
,
16
Joule
Pd
If height of object h0 is considered
Therefore;
If the exposure provided is compared with the exposure from
n
the microwave cooker of 500W then;
P

Pi Gi
d , i
2
i 1 x2
4
h
i
i
h0 (23)
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For GSM 1800 the exposure will be =
This exposure time is high for a person who is exposed for the
33120W.sec 500W 670sec
long time. We need to look for the minimum distance for
tolerable exposure. To do this we apply the standard given by
EMF-Exposure-Guidelines-For-Sleeping-Areas[11]which
While the exposure for GSM 900 will be =
recommend the maximum exposure of 10 W/m to be of less
16920W.sec 500W
84
.
33
sec
concern as shown on the table below.
Table 4: Exposure guidelines for sleeping area
Power
density
in
No Concern
Slight Concern
Severe Concern
Extreme
microwatt
Concern
per square meter W/m
< 0.1
0.1-10
10 - 1000
> 1000
per square cm W/cm
< 0.000,01
0.000,01 - 0.001
0.001 - 0.1
> 0.1
Figure 9; shows the minimum distance where an object can
geographical limitations, geographical locations were taken
live with less concern of exposure. The distance is obtained by
and later converted to distances as it has been explained in
the point at which the graph for power densities meets the line
Section 3 subsection A. The results show that the power
Pd = 10 W/m shown by black line above zero power density.
densities depend on the distance from the antenna. That is, the
This distance is the safety distance to live. The safety zone
longer the distance the smaller the power density and that the
depends on the power transmitted by the antenna [11].
power density is maximum at the tower. The results also show
that the power density at a point from an antenna depended on
P
dBm
the application. That it, the power density from a GSM900
Thus for the power transmitted;
t
16
is 120m
application was different from the GSM1800 application.
P
dBm
And for power transmitted;
t
20
is 190m as shown
on the figure 9.
Numerical analysis reveals that the power received by the
object varies directly proportional with the power transmitted
Therefore more the power of transmitter the far the safety zone
by the source and inversely proportional with its square
occur.
distance from the source. The greater the power transmitted,
the longer the distance to the safety zone, and hence it
-4
x 10
4.5
becomes severe to live near the source.
4
Pt = 16dBm
3.5
Pt = 20dBm
4.2 Findings Regard the Safety Zone
2 m/
Min
3
W
To develop a model for cellular tower radiations several
ni 2.5
y
parameters were considered including the power transmitted
tisne
by an antenna, the gain of an antenna, the allowable exposure
2
Dre
for both GSM900 and GSM1800 and the surface area
1.5
woP
occupied by an object. The results show that the safety zone
1
will much depend on the power transmitted by the antenna
0.5
given the same antenna gain. From our study the safety zone
0
for transmitted power of 16dBm was 120m and for 20dBm
0
20
40
60
80
100
120
140
160
180
200
Distance from base to object in metres (m)
was 190m for a gain of antenna of 17dB,
Figure 8: Graph of Power densities versus distance with
To validate the model measurement taken from the field were
safety zone defined.
plotted together with the theoretical values. The data for
GSM900 were below the graph corresponding to Pt = 25dBm
4. FINDINGS, RESULTS AND CONCLUSIONS
and
those
from
GSM1800
were
below
the
graph
corresponding to Pt = 20dBm.
4.1 Findings Regard the Measurements
Furthermore, the results show that all the measurements taken
To gain understanding of the power densities at different point
within 50m from the antenna in the field were above the
from the antenna, measurement of power density were made at
discrete distances from the transmission towers. Due to
minimum exposure of 10 W/m for sleeping areas.
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The results obtained in this study for safety zone are far
[6] R. M. Bexhet Kamo, Vladi Kolici,Sanie Cela, Algenti
greater than those obtained by Kamo et al (2012) which were
Lala, "Estimation of peak power density in the vicinity of
between 12.9 to 46.3 meters from antenna for GSM900,
cellular base stations, FM,UHF and WiMAX antennas,"
1800.respectively, the difference is due to exposure limits used
International Journal of Engineering & Technology
IJET-
where Kamo used 9W/m2 and 4.5W/m2 exposure limits from
IJENS, vol. Vol:11, 2011.
ICNIRP guidelines recommendation [6].
[7] M. Abdelati, "Electromagnetic Radiation from Mobile
Phone Base Stations at Gaza," At Islamic University of Gaza
4.3 Results and Conclusions
(Natural Sciences Series), vol. Vol.13, pp. p129-146, 2005.
[8] S. H. S. Al-Bazzaz, "Theoretical Estimation of Power
The results regarding the safety zone shows that the safety
Density Levels around Mobile Telephone Base Stations,"
zone depend on the power transmitted by the antenna for the
Journal of Science & Technology, vol. 13, 2008.
same antenna gain. The safety zone for transmitted power of
[9] M. K. T. S. A. Kumar, "Effects of Mobile Tower
16dBm was 120m and for 20dBm was 190m for a gain of
Radiations & Case Studies from different Countries Pertaining
antenna of 17dB with the fixed height of antenna 30m above
the Issue," International Journal of Applied Engineering
the ground. All field measurements taken within 50m from the
Research, vol. 7, 2012
antenna in the field were above the minimum exposure of
[10] ICNIRP, "Guidelines for limiting exposure to time-
10 W/m for sleeping areas.
varying electric, magnetic fields (up to 300GHz)," ed. Health
Physics Society, 1998, pp. 494-522.
The measurements of power densities at the field and the
[11] G. Abdel-Rassoul, et al., "Neurobehavioral effects among
model has been presented to give an estimate of the safety
inhabitants
around
mobile
phone
base
stations,"
zone for people living in close vicinity to wireless cellular
Neurotoxicology, vol. 28, pp. 434-440, 2007.
towers. Different analyses have been carried out before
estimating the safety zone. Results have shown that safety
zone depends on the power transmitted by the antenna.
However, for a power of 16dBm taken to be the smallest, the
safety zone was 120m from the tower. This call for a concern
for people living in the close vicinity and respective
authorities should ensure that people reside far from the tower
by 120m or more depending on the power transmitted to avoid
severe health effect.
REFERENCES
[1] L. Nicolas, et al., "Interactions between electromagnetic
field and biological tissues: Questions, some answers and
future trends," International Compumag Society Newsletter,
vol. 10, pp. 4-9, 2003.
[2] L. A. Mimoza Ibrani, Enver Hamiti,Ruzhdi Sefa,
"Exposure assessment in the vicinity of 900 MHz GSM base
station antenna," in The 11th WSEAS International Conference
on
COMMUNICATIONS,
Agios
Nikolaos,Crete
Island
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