Int. J. Communications, Network and System Sciences, 2010, 3, 330-337
doi:10.4236/ijcns.2010.33042 blished Online March 2010 (http://www.SciRP.org/journal/ijcns/).
Pu
Indoor Radio Propagation Model Based on Dominant Path
Yongxiang Zhao1, Meifang Li2, Feng Shi3
1Wuhan University, State Key Laboratory of Software Engineering, Wuhan, China
2Wuhan University of Technology, School of Management, Wuhan, China
3Wuhan Academy of Social Sciences, Wuhan, China
Received November 18, 2009; revised December 22, 2009; accepted January 12, 2010
Abstract
When there are bigger obstacles in the indoor environment such as elevator, the radio waves basically can
not penetrate it. The contribution of received signal strength by transmission and reflection will be greatly
reduced, and most of the time, the radio waves will reach the user by bypass diffraction. Therefore, the tradi-
tional path loss model is no longer applicable, and the improved model should be proposed. In this paper, we
firstly proposed an indoor radio propagation model based on dominant path in which the received signal
strength has nothing to do with the direct distance between user and access point, but is related to the length
of dominant path. Then on the basis of dominant path model, the NLOS influence is considered in order to
further improve the accuracy of dominant path model. Experimental results demonstrated that the proposed
dominant path model can improve the accuracy of traditional path loss model remarkably.
Keywords: Wireless LANs, Indoor Positioning, Radio Waves, Received Signal Strength, Path Loss Model,
Dominant Path
1. Introduction
Indoor positioning systems have become very popular in
recent years, both the research and commercial products
in this area are new, and many people in academia and
industry are currently involved in the development of
these systems.
It is possible to obtain the position location of a mo-
bile device in two ways: by using a special infrastructure
or by improving the existing communications infrastruc-
ture. GPS is not suitable for indoor areas because of the
lack of coverage. Therefore, it is preferable to employ
the existing wireless communications infrastructure to
determine the location of users. The wireless communi-
cations infrastructure is primarily based on wireless local
area networks (WLANs) [1] in indoor areas. Thus, these
indoor positioning systems mainly lie on an IEEE
802.11b or 802.11g WLAN.
Owing to the harsh multi-path environment in indoor
areas, techniques that use triangulation or direction are
not very attractive and often can yield highly erroneous
results [2]. Location fingerprinting refers to techniques
that match the fingerprint of some characteristic of the
signal that is location dependent. In WLANs, an easily
available signal characteristic is the received signal
strength (RSS) and this has been used in [3] for finger-
printing.
Due to severe multi-path fading and shadowing pre-
sent in the indoor environment, there is no accurate in-
door radio propagation model. A traditional radio propa-
gation model, named path loss model, is often used to
describe the characteristic of indoor environment.
However, when there are bigger obstacles in the in-
door environment such as elevator, the radio waves ba-
sically can not penetrate it. The contribution of received
signal strength by transmission and reflection will be
greatly reduced, and most of the time, the radio waves
will reach the user by bypass diffraction. Therefore, the
traditional path loss model is no longer applicable, and
the improved model should be pr oposed.
This paper is organized as follows. In Section 2, we
proposed three indoor radio propagation models, named
Path Loss Model, Dominant Path Model 1 and Domi-
nant Path Model 2. Section 3 described experimental
testbed which is a typical office building environment.
In Section 4, the experimental results of three models
were discussed and analyzed. Section 5 depicted field
strength simulation results of dominant path model 2
for the experimental access points. Finally, Section 6
summarized the paper and gave possible future research
directions.

Y. X. ZHAO ET AL. 331
2. Three Indoor Radio Propagation Models
2.1. Path Loss Model
In this paper, a path loss model [4] is introduced to de-
scribe the characteristic of indoor environment which is
as follows:
0
0
( )()10log() 
d
Pd Pdnd

(1)
In the Equation (1), the is the received signal
strength of users when the distance between users and
access points is . And is the received signal
strength of users when the distance between users and
access points is ( is equal to 1 meter). The para-
meter is the path-loss index which depends upon the
indoor propagation environment.
()Pd
0
()Pdd
0
d0 d
n

is the shadowing
factor which is a random variable.
2.2. Dominant Path Model 1
When there are bigger obstacles in the indoor environ-
ment such as elevator, the radio waves basically can not
penetrate it. The contribution of received signal strength
by transmission and reflection will be greatly reduced,
and most of the time, the radio waves will reach the user
by bypass diffraction. Therefore, the traditional path loss
model is no longer applicable because the received signal
strength has nothing to do with the direct dis-
tance between user and access point, but is related to
the length of dominant path which is described in
Figure 1.
()Pd
L
d
Figure 1. Dominant path model 1 in indoor scenarios.
In Figure 1, AP is placed in a small room, sampling
points R1 and R2 are close to elevator. The traditional
path loss model supposes that the radio waves from AP
directly arrive at sampling points R1 and R2 by pene-
trating the elevator. However, the elevator is bigger ob-
stacle which is made up of metal and concrete materials,
and can not be penetrated by radio waves. In fact, the
radio waves from AP reach the sampling points R1 and
R2 by bypass diffraction, that is, the radio waves firstly
reach the point S1, then reach the point S2, and finally
arrive at points R1 and R2.
The proposed Dominant Path Model 1 was described
as follows:
0
0
()( )10log()
L
PL Pdnd
 (2)
In the Equation (2), the is the received signal
strength of users when the length of dominant path is .
And is the received signal strength of users when
the length of dominant path is (is equal to 1 me-
ter). The parameter is also the path-loss index which
depends upon the indoor propagatio n environment.
()PL
0
d
L
0
()Pd
0
d
n
2.3. Dominant Path Model 2
However, the received signal strength (RSS) in indoor
environment is influenced by Non-line-of-sight (NLOS)
propagation, and the attenuation level of signal strength
is different when in Line-of-sight (LOS) environment
and in Non-line-of-sight (NLOS) environment. Therefore,
the LOS propagation and NLOS propagation should be
discussed and analyzed separately in order to further
improve the accuracy of dominant path model which is
depicted in Figure 2.
Figure 2. Dominant path model 2 in indoor scenarios.
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Y. X. ZHAO ET AL. 332
In Figure 2, the whole experimental environment is
divided into two separate parts. 1) Room part. It includes
three small rooms and three big rooms, so, the Room part
is approximate LOS environment in which the path-loss
index is
L
OS
n. 2) Corridor part. All the APs are placed in
the Room part, thus, the Corridor part is typical NLOS
environment in which the path-loss index is be-
cause the radio waves from APs can not penetrate thicker
concrete wall.
NLOS
n
The proposed Dominant Path Model 2 was described
as follows:
0LOS
0
0NLOS
0
()10log(), Line-of-sight(LOS)
()
() 10log()Non-Line-of-sight(NLOS)
L
Pd nd
PL L
Pd nd
 



 


(3)
In the Equation (3), the
L
OS
n
NLO
n
is the path-loss index in
LOS environment, and the is the path-loss index
in NLOS environment. Other parameters are the same as
Dominant Path Model 1.
S
3. Experimental Testbed
The experimental testbed is located in the 11th floor of
Cherry Blossom Building. The floor has dimensions of
15 meters by 10 meters and includes 6 rooms which is
the typical indoor office environment. In this work, we
choose the TP-LINK TL-WA501G as our experimental
APs because of its low cost. The WLAN consists of four
access points, and the MAC, SSID and operating channel
of these access points are listed in Table 1.
The survey trail and AP placement of experimental
testbed is shown in Figure 3. From Figure 3, we can see
that our experimental testbed is the typical indoor office
environment. The AP placement of experimental testbed
refers to the conclusion of literature [5], that is, the ac-
cess points should be scattered asymmetrically and
should be placed around the site in a “zigzag” pattern
rather than placing several APs close together or placing
them on a straight line.
Table 1. MAC, SSID and channel of experimental access
points.
MAC SSID Channel
00:1D:0F:43:CA:7F AP1 9
00:1D:0F:43:CA:86 AP2 13
00:1D:0F:43:CB:A1 AP3 3
00:1D:0F:43:CB:A8 AP4 1
Figure 3. The survey trail and AP placement of experimen-
tal testbed.
The minimum distance between two locations or grid
spacing was fixed at 1.5 meters. At each location, we
calculated the average of 50 samples, and it would spend
25 seconds for each location when scanning frequency
was set to two times per second.
4. Experimental Results and Analysis
In our experiments, is equal to 1 meter, and
is set to –28.0 dB. The RSS estimation results and RSS
estimation error comparison for Path Loss Model, Domi-
nant Path Model 1 and Dominant Path Model 2 are listed
as follows.
0
d0 ()Pd
4.1. The RSS Estimation Results of Three
Propagation Mod el s
1) The RSS Estimation Results of Path Loss Model
The RSS Estimation Results of Path Loss Model are
shown in Figure 4, and the path-loss index of Path Loss
Model for four APs is listed in Table 2.
From the experimental results of Figure 4 and Table 2,
Table 2. The path-loss index of path loss model.
AP Name Path-loss Index n
AP1 3.45
AP2 3.73
AP3 3.20
AP4 4.20

Y. X. ZHAO ET AL. 333
(a) The RSS estimation results of AP1
(b) The RSS estimation results of AP2
(c) The RSS estimation results of AP3
(d) The RSS estimation results of AP4
Figure 4. The RSS estimation results of path loss model.
we can see that the RSS estimation result of AP3 is better,
and its path-loss index is 3.20. However, the RSS esti-
mation results of AP1, AP2 and AP4 are worse, and the
path-loss index are 3.45, 3.73 and 4.20.
The reason is that, the AP3 is placed at the entrance of
Room part, thus, the propagation environment of radio
waves in Corridor part is close to the propagation envi-
ronment in Room part which is approximate LOS envi-
ronment. But the AP1, AP2 and AP4 are placed in the
inside room which are farther away from the corridor and
elevator, thus, the attenuation level of signal strength in
Corridor part is more serious than in Room part.
The most serious situation is that, from Figure 4(b)
and Figure 4(d), we can see that the radio waves propa-
gation does not match with th e Path Loss Model at all in
Corridor part because the received signal strength is
weaker and weaker when the direct distance between
user and AP is closer and closer. Therefore, the tradi-
tional path loss mode l is no longer applicable because the
received signal strength has nothing to do with the direct
distance between user and access point, but is related to
the length of dominant path.
2) The RSS Estimation Results of Dominant Path
Model 1
The RSS Estimation Results of Dominant Path Model
1 are shown in Figure 5, and the path-loss index of
Dominant Path Model 1 for four APs is listed in Table 3.
From the experimental results of Figure 5 and Table 3,
we can see that the RSS estimation results of AP1, AP2,
AP3 and AP4 are all better, and the path-loss index are
3.26, 3.48 , 3. 10 and 3.43.
Compared with the result of Path Loss Model, the
Dominant Path Model 1 achieves remarkable improve-
ment because the path-loss index of four APs are all de-
creased, for example, the path-loss index of AP1 de-
creases to 3.26 from 3.45, the path-loss index of AP2
decreases to 3.48 from 3.73, the path-loss index of AP3
decreases to 3.10 from 3.20, and the path-loss index of
AP4 decreases to 3.43 from 4.20. Therefore, the Domi-
nant Path Model 1 is more rational and accurate th an the
traditional Path Loss Model.
3) The RSS Estimation Results of Dominant Path
Model 2
The RSS Estimation Results of Dominant Path Model
2 are shown in Figure 6, and the path-loss index of
Dominant Path Model 2 for four APs is listed in Table 4.
Table 3. The path-loss index of dominant path model 1.
AP Name Path-loss Index n
AP1 3.26
AP2 3.48
AP3 3.10
AP4 3.43
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Y. X. ZHAO ET AL. 334
(a) The RSS estimation results of AP1
(b) The RSS estimation results of AP2
(c) The RSS estimation results of AP3
(d) The RSS estimation results of AP4
Figure 5. The RSS estimation results of dominant path
model 1.
(a) The RSS estimation results of AP1
(b) The RSS estimation results of AP2
(c) The RSS estimation results of AP3
(d) The RSS estimation results of AP4
Figure 6. The RSS estimation results of dominant path
model 2.

Y. X. ZHAO ET AL. 335
Table 4. The path-loss index of dominant path model 2.
AP Name Path-loss Index nLOS Path-loss Index nNLOS
AP1 2.49 4.62
AP2 2.87 4.56
AP3 2.86 3.52
AP4 2.81 4.52
From the experimental results of Figure 6 and Table 4,
we can see that the RSS estimation results of AP1, AP2,
AP3 and AP4 achieve further improvement after the
LOS propagation and NLOS propagation are analyzed
separately.
The path-loss index nLOS of four APs are 2.49, 2.87,
2.86 and 2.81 which are all less than 3, and the path-loss
index nNLOS of four APs are 4.62, 4.56, 3.52 and 4.52.
Therefore, the Dominant Path Model 2 is more rational
and accurate than the Dominant Path Model 1.
4.2. The RSS Estimation Error Comparison of
Three Propagation Model
The RSS estimation error comparison of three propaga-
tion model, named Path Loss Model, Dominant Path
Model 1 and Dominant Path Model 2 , are shown in Fig-
ure 7, and the RSS estimation error values of three
propagation model are listed in Table 5.
Experimental results of Figure 7 and Table 5 demon-
strated that the accuracy of Path Loss Mode is worst, and
its average mean value for four APs is 9.32, its average
Table 5. The RSS estimation error values of three propaga-
tion model.
Path Loss
Model (dB) Dominant Path Model 1 (dB) Dominant Path Model 2 (dB)
AP
Name Mean
Value Std. Dev. Mean value Std. Dev. Mean value Std. Dev.
AP1 11.06 7.78 10.256.76 5.64 4.03
AP2 9.57 8.15 8.12 6.68 5.61 4.33
AP3 4.46 3.79 4.19 3.62 3.51 3.22
AP4 12.20 8.77 8.25 5.55 4.76 3.58
Average 9.32 7.12 7.70 5.65 4.88 3.79
(a) The RSS error comparison of AP1
(b) The RSS error comparison of AP2
(c) The RSS error comparison of AP3
(d) The RSS error comparison of AP4
Figure 7. The RSS estimation error comparison of three
propagation model.
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Y. X. ZHAO ET AL. 336
standard deviation is 7.12. The accuracy of Dominant
Path Model 1 is better, and its average mean value for
four APs is 7.70, its average standard deviation is 5.65.
Finally, the accuracy of Dominant Path Model 2 is best,
and its average mean value for four APs is only 4.88, its
average standard deviation is only 3.79.
results of dominant path model 2 for the experimental
access points which is shown in Figure 8. In this paper,
the color indication of received signal strength is as fol-
lows:
Therefore, the proposed dominant path model in this
paper can improve the accuracy of traditional path loss
model remarkably. When the NLOS influence is further
considered, the dominant path model is more rational and
accurate, and its average estimation error of received
signal strength is only 4.88 dB in the typical indoor of-
fice environment.
The field strength simulation of Figure 8 demon-
strated that when there are bigger obstacles in the indoor
environment such as elevator, the radio waves basically
can not penetrate it. The contribution of received signal
strength by transmission and reflection will be greatly
reduced, and most of the time, the radio waves will reach
the user by bypass diffraction.
5. The Field Strength Simulation of
Dominant Path Model In dominant path model 2, the received signal strength
has nothing to do with the direct distance between user
and access point, but is related to the length of dominant
path. Therefore, the proposed dominant path model in
Finally, we depicted the whole field strength simulation
(a) Field strength simulation of AP1 (b) Field strength simulation of AP2
(c) Field strength simulation of AP3 (d) Field strength simulation of AP4
Figure 8. The field strength simulation of dominant path model 2.

Y. X. ZHAO ET AL.
337
is paper can improve the
. Conclusions and Future Work
this paper, we firstly proposed an indoor radio propa-
s: h model
in
his work wa s supported by Nationa l 863 project (Grant
. References
] IEEE P802.11 Working Group, “Changes and additions
location
awala, A. U. Shankar, and S. H.
s
. F. Li, “Indoor access points
th accuracy of traditional path 7. Acknowledgment
loss model remarkably.
6
In
gation model based on dominant path in which the re-
ceived signal strength has nothing to do with the direct
distance between user and access point, but is related to
the length of dominant path. Then on the basis of domi-
nant path model, the NLOS influence is considered in
order to further improve the accuracy of dominant path
model. Experimental results demonstrated that the pro-
posed dominant path model can improve the accuracy of
traditional path loss model remarkably.
Future research directions are as follow
1) Further improve the proposed dominant pat
Noh
this paper, for example, the influence factor of wall
should be further considered.
2) Study and design intelligent algorithm to automati-
cally search and determine the dominant path of radio
propagation in bigger office building environment in
order to further improve the applicability and scalability
of the proposed dominant path mode l in this paper.
T
Nos. 2007AA12Z324, 2009AA12Z324).
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C opyright © 2010 SciRes. IJCNS