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Bulletin of Electrical Engineering and Informatics
Vol. 7, No. 2, June 2018, pp. 264~271
ISSN: 2302-9285, DOI: 10.11591/eei.v7i2.871 264
Journal homepage: http://journal.portalgaruda.org/index.php/EEI/index
WiFi-Friendly Building to Enable WiFi Signal Indoor
Suherman
Electrical Engineering Department, Universitas Sumatera Utara, Indonesia
Article Info
ABSTRACT
Article history:
Received Jan 01, 2018
Revised Feb 02, 2018
Accepted Feb 16, 2018
The 802.11 networks (wireless fidelity (WiFi) networks) have been the main
wireless internet access infrastructure within houses and buildings. Besides
access point placement, building architectures contribute to the WiFi signal
spreading. Even dough WiFi installation in buildings becomes prevalent; the
building architectures still do not take WiFi-friendliness into considerations.
Current research on building and WiFi are on access point location, location
based service and home automation. In fact, the more friendly the building to
WiFi signal, the more efficient the 802.11 based wireless infrastructure. This
paper introduces the term of WiFi-friendly building by considering signal
propagations, the obstacle impact, as well as proposing an ornament-attaced
reflector and a hole-in-the-wall structure to improve WiFi signal distribution.
Experiment results show that obstacle materials made of concrete reducing
WiFi signal the most, followed by metal and wood. Reflecting materials are
able to improve the received signal level, for instance, the implemented
ornament-attached reflector is able improving the received signal up to 6.56
dBm. Further, the hole-in-the-wall structure is successfully increasing WiFi
signal up to 2.3 dBm.
Keywords:
802.11
Hole-in-the-wall structure
Ornament-attached reflector
WiFi-friendly building
Copyright © 2018 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Suherman,
Electrical Engineering Department,
Universitas Sumatera Utara, Indonesia
Email: suherman@usu.ac.id
1. INTRODUCTION
Internet access has been available in houses and offices as the access network technologies
advanced. The internet networks within buildings are shared among cable and wireless networks. The 802.11
wireless local area network (WLAN) or Wireless Fidelity (WiFi) is the common technologies providing
wireless internet access within buildings. This is due to its sufficient mobility and the connection speed
compared to the existing cable and mobile networks. Moreover, its standard development allows speed up to
135 Mbps [1]. As mobile computer and mobile phone application are becoming popular, users in houses and
offices tend to choose WLAN when available.
Even dough WLAN demands in buildings are parts of building necesities; the integration of wireless
network requirement is not yet included in building design. The consideration is just limited on how the
cabling infrastructure provided. In fact, wireless signal propagation always faces indoor propagation
problems [2].
On the other hand, there is an empty gap on scientific publications in discussing how to design
buildings that are friendly to WiFi signal. The WLAN and building relationship generally are shared in the
following topics:
a. How to locate the access point optimally within the buildings to cover are as much as possible. The
access point placement can either based on propagation analysis and model [3], user density traces [4],
the overall Euclidian distance [5] or interferences possibilities [6].
b. Location based services that are talking about how to find a terminal by analyzing the received access
point signals. This is often referred to as indoor localization [7-10].
BEEI ISSN: 2302-9285
WiFi-Friendly Building to Enable WiFi Signal Indoor (Suherman)
265
c. Home automation services using internet connections [11].
Meanwhile, materials used in buildings mostly absorb WiFi signal that make the access point
placement inefficient as the transmitted signal blocked, absorbed, dispersed or reflected back by the wall and
building structures. Isolative materials, such as concrete absorb and disperse the WiFi signal, while
conductive materials such as metal reflect WiFi signal. The characteristics of those materials are
approximated by using conductivity and complex permittivity parameter. The more conductive materials, the
more reflective to radio signals. The more permittive a material, the more absorbing to radio signals. Table 1
shows the examples of permittivity and conductivity of some materials exist on buildings.
Table 1. Permittivity and Conductivity of Some Material [12]
Material.
Relative Permittivity
Conductivity (S/m)
Frequency (GHz)
Concrete
5.31
0.0326
1-100
Brick
3.75
0.038
1-10
Plaster board
2.94
0.0116
1-100
Wood
1.99
0.0047
0.001-100
Glass
6.27
0.0043
0.1-100
Ceiling board
1.50
0.0005
1-100
Metal
1
10
1-100
Indoor propagations as the main problems for WiFi networks have been studied and modeled in
some mathematical expressions. Deterministic model relies only on mathematical expressions, such as free
space loss model, log distance path loss model, and log normal shadowing model. A more sophisticated
model uses a complex approach such as impulse response [13] and statistic dispersion [14]. The modeling is
performed only for a specific frequency band.
This paper introduces the term of WiFi-friendly building by reminding that the building structure is
the major challenge on indoor signal propagation, mainly about signal losses caused by the obstacles. This
paper also introduces that the properties within the buildings may assist signal spreadings so that building is
friendlier to WiFi signal. At the end of this paper, a simple though-hole application on the wall is examined
to increase WiFi signal in other wall side.
2. RESEARCH METHOD
In order to introduce the needs of WiFi-friendly building, research methods are designed to show
that:
a. obstacles reduce WiFi signal
b. reflector on certain positions increases the received signal
c. reflector can be inserted in building properties or ornaments
d. A small hole-in-the-wall structure may reduce the impact of signal blocking.
2.1. The Obstacle Impact
In order to show the obstacle impact to WiFi signal propagation, a measurement device is
assemblied by using ESP8266. ESP8266 is a system on a chip (SOC) integrated circuit that can work as an
access point as well as a client of the 802.11 network. ESP8266 can work either with microcontroller or stand
alone. In order to examine the impact of obstacle to WiFi signal, an experiement is set up as shown in Figure
1a. Figure 1b is for assessing the impact of the reflector on the received signal.
(a) Obstacle experiment (b) Reflector Experiment
Figure 1. Experiment set up for obstacle and reflector impact
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A smart phone is turned on to broadcast WiFi signal that will be blocked by an obstacle, separated
by 2.5 m to 15 m from a smart phone and 20 cm from the receiver. WEMOS D1 ESP8266-E12 is applied as a
WiFi signal receptor. Obstacles are made of concrete, wood and metal, while reflector is metal. Samples of
the obstacles are shown in Figure 2.
(a) Concrete
(b) Metal
(c) Wood
Figure 2. Sample of the obstacle materials
2.2. An Ornament-attaced Reflector
Properties within the building such as painting, foto frames and statue can be used as signal
spreaders, rather than obstacles. As an example, this paper utilizes a painting frame mounted in the wall as
the reflector. An aluminium sheet is attached behind the painting. This ornament-attached reflector is
employed to increase WiFi signal on the second floor. The access point is placed on the first floor. Figure 3
shows the sketch of the experiment. There are three points for the reflector positioning: position 1, position 2
and position 3.
Figure 3. Sample of the obstacle materials
2.3. A hole-in-the-wall Structure
Building wall is the main obstacle within the building. Some rooms are isolated from WiFi signal as
there is no way signal getting trhough. In this case, a hole-in-the-wall structure is designed to help signal
passing through the wall. Figure 4 shows the designed structure.
Figure 4. A hole-in-the-wall structure
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The hole is made of an aluminium tube with diameter d and length l, attached to two aluminium
sheets. This structure is embedded to the wall so that concrete filled the area between the two aluminium
sheets. The hole is expected to pass WiFi signal. An experiment is set to measure the impact of the hole-in-
the-wall structure as shown in Figure 5.
Figure 5. A hole-in-the-wall experiment
3. RESULTS AND ANALYSIS
3.1. Obstacle Impact to WiFi Signal
The results of experiment on Figure 1 are shown in Figure 6. Data shown in Figure 6 is based on the
average of 30 times measurements. The average signal level decreases as distance between transmitter and
receiver increases. The concrete obstacle absorbs signal the most which lead to the average received signal
level of - 66.27 dBm. Metal is following by producing received signal level of -64.23 dBm. Wood is the less
absorbing material, the average received signal is - 58.9 dBm.
Figure 6. Signal reductions due to propagation and obstacles
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3.2. Reflector Impact to WiFi Signal
A metal reflector placement as depicted in Figure 1b has been successfully reduce the signal
absorption and increase received signal level. Signal level increases 1.14 dBm in average. The received
signal for concrete obstacle is -64.74 dBm, metal obstacle is -63.27 dBm and wood obstacle is -58.17 dBm.
The plots are also shown in Figure 6.
3.3. Impact of Ornament-attached Reflector
Figure 7 shows the exact locations of the ornament-attached reflector and the results are plotted in
Figure 8.
Position 1
Position 2
Position 3
Figure 7. Reflector position
The concrete wall blocks the received signal on the second floor. The only way signal gets through
is by reflection through the door. Without additional reflector, the average received signal on the second floor
is -68.69 dBm. By transforming the painting frame on the wall to be a reflector causes increments of received
signals. There are 4.03 dBm increments in average. Reflector in position 1 increases 3.39 dBm, position 2
increases 6.56 dBm and position 3 increases 2.14 dBm. Position 2 results the best increment. These
increments are plotted in Figure 8.
Figure 8.Signal reductions due to propagation and obstacle
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The increment on received signal can be approximated by using the propagation model, for instant,
the ITU-R model, where the losses occurred between the access point and the receiver can be calculated
directly by using Equation 1, with d be distance, n is number of floor and Lf is losses factor, and Lf is floor
losses [12].
(1)
If the transmitted power of access point known, then the effective isotropic radiated power (EIRP)
is:
= ()– + (2)
And the received signal strength indication (RSSI) in receiver is:
no-reflector = – + − (3)
This RSSI no-reflector is the received power without reflector. In order to calculated the RSSI with-reflector
the power increment should be calculated by considering losses from transmitter to reflector. The losses as
the link is direct can be calculated using free space loss formula:
(4)
The reflected power,
is calculated by using the following formula
(5)
Since the first medium is air and the second one is aluminium, then:
If it is assumed that the reflected power directed to the receiver, then the power increment or
RSSIincrement is:
RSSIincrement = Prec=
-Lossref-rec (6)
the total received power with reflector is:
with-reflector = no-reflector+ increment (7)
The with-reflector may vary depending on the reflected power by the reflector. with-reflector could
be smaller than no-reflector if reflection causes the opposite phase signal.
3.4. Impact of the Hole-in-the-wall Structure
Figure 5 shows the exact locations of the ornament-attached reflector and the results are plotted in
Figure 9. The hole-in-the-wall structure is able to improve signal level about 2.3 dBm in average.
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Figure 9. Impact of the hole-in-the-wall structure
When radio signal propagates through a small hole, the transmitted signal combined with the
induced surface signal diffracted toward the hole as shown in Figure 10. This is occurred if the hole is sub
wavelength or much smaller then λ [15].
Figure 10. Small hole signal diffraction [15]
The forwarded signal power is [15]:
(8)
Where a is radius of the hole, k is propagation parameter (2*π/λ) and Si is the flux given by:
(9)
Since the hole-in-the-wall structure is isolated by the concrete and the hole is not smaller then λ,
then output electric field transmitted through the hole is not E0=Et+Esi [13], but E0= Esi. In order to increase
higher signal level, size of l in Figure 4 should be as thin as possible. But it will reduce the objective of the
wall exists for.
4. CONCLUSION
This paper has introduced the WiFi-friendly building idea that enables the 802.11 signal propagating
indoor efficiently. The study has proven concrete materials that dominate the building materials absorb WiFi
signal the most. However, reflectors in certain positions are able to increase WiFi signal. For instance,
ornament-attached reflector is able to improve WiFi signal up to 6.56 dBm. Further, a small hole-in-the-wall
structure within the wall is able to increase signal in other side by 2.3 dBm in average.
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WiFi-Friendly Building to Enable WiFi Signal Indoor (Suherman)
271
By transforming the building properties as well as building structure, WiFi signal indoor can be
boosted in certain level. Future works may explore more on building properties that may help its friendliness
to WiFi signal.
ACKNOWLEDGEMENT
This research has been supported and funded by Applied TALENTA Research Grant of Universitas
Sumatera Utara, 2017.
REFERENCES
[1] Shidik G F, bin Muhamad Noh Z. A. Performance Evaluation of Bonding Techniques at Wireless 802.11n.
TELKOMNIKA (Telecommunication Computing Electronics and Control), 2013; 11(1), 181-190.
[2] Bahaweres R B, Karya O T, and Alaydrus M. Transmission of Real-time Video Signal with Interference Density
and Human Traffic. TELKOMNIKA (Telecommunication Computing Electronics and Control), 2015; 13(4), 1352-
1360.
[3] Gu Y, Ren F, and Li J. PAWS: Passive Human Activity Recognition Based on WiFi Ambient Signals. IEEE
Internet of Things Journal. 2016; 3(5), 796-805.
[4] Bulut E, Szymanski B K. WiFi access point deployment for efficient mobile data offloading. ACM SIGMOBILE
Mobile Computing and Communications Review. 2013; 17(1), 71-78.
[5] Lee G. 3D coverage location modeling of Wi-Fi access point placement in indoor environment. Computers,
Environment and Urban Systems. 2015; 54, 326-335.
[6] Farsi A, Achir N, Boussetta, K. WLAN planning: Separate and joint optimization of both access point placement
and channel assignment. Annuals of telecommunications-annales des telecommunications. 2015; 70(5-6), 263-274.
[7] Varzandian S, Zakeri H, Ozgoli S. Locating WiFi access points in indoor environments using non-monotonic signal
propagation model. IEEE Asian Control Conference (ASCC). 2013; pp. 1-5.
[8] Ma R, Guo Q, Hu C, Xue J. An improved WiFi indoor positioning algorithm by weighted fusion. Sensors. 2015;
15(9), 21824-21843.
[9] Retscher G, Moser E, Vredeveld D, Heberling D, Pamp J. Performance and accuracy test of a WiFi indoor
positioning system. Journal of Applied Geodesy jag. 2007; 1(2), 103-110.
[10] Barcelo-Arroyo F, Martin-Escalona I, Ciurana-Adell M. Positioning Terminals in Mobile Computing
Networks.Mobile Computing. 2013; 11.
[11] Sangogboye F C, Droegehorn O, Porras J. Analyzing the Payback Time of Investments in Building Automation. In
Sustainable Ecological Engineering Design. 2016; pp. 367-381.
[12] Rec. ITU-R P.2040-1, ITU-R Recommendation, Vol.1, P Series, ITU, Geneva, 2015.
[13] Rappaport T S, Seidel S Y, Takamizawa K. Statistical channel impulse response models for factory and open plan
building radio communication system design. IEEE Trans. Communication. 1999; 39(5), pp.794-807.
[14] Hashemi H. The indoor radio propagation channel. Proceedings of the IEEE. 1993; 81(7), 943-968.
[15] Weiner J. The physics of light transmission through subwavelength apertures and aperture arrays. Reports on
progress in physics. 2009; 72(6), 064401.k
