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Analysis of Bluetooth Low Energy (BLE) based
Indoor Localization System with Multiple
Transmission Power Levels
Umair Mujtaba Qureshi, Zuneera Umair, Yaoxin Duan, and Gerhard Petrus Hancke
Department of Computer Science, City University of Hong Kong
Hong Kong, SAR, China
Email: umqureshi2-c@my.cityu.edu.hk, zaziz3-c@my.cityu.edu.hk, yxduan3-c@my.cityu.edu.hk, gp.hancke@cityu.edu.hk
Abstract—Bluetooth Low Energy (BLE) is widely considered
for wireless Indoor Localization Systems (ILS) in which BLE
Received Signal Strength (RSS) is used to derive the location
of the target. The efficacy of a BLE based ILS depends on the
localization accuracy. Whereas, localization accuracy depends on
the stability of the BLE RSS. A number of researchers have
focused on studying the impact of different parameters (such
as different type of devices, environments and deployments)
that cause the variations in BLE RSS. Today, BLE devices
are capable of operating at multiple transmission power lev-
els. Unlike previous studies, this paper focuses on evaluating
the performance of BLE based ILS at multiple transmission
power levels. Furthermore, the impact of different parameters
such as multiple advertising interval, scanning interval, device
orientation, distance, the effect of Line of Sight (LOS), Non-Line
of Sight (NLOS) and device density over BLE RSS is also studied
with multiple transmission power levels. Our main findings show
that multiple transmission power level can attain localization
accuracy with multiple precisions (i.e. from 2m to 5m) in an
indoor classroom environment.
I. INTRODUCTION
Bluetooth Low Energy (BLE) has recently attracted a num-
ber of researchers to exploit its capabilities beyond location
based services and applications [1, 2]. The ability of the BLE
to operate at multiple low transmission power levels, long
transmission range, low energy consumption, long battery
life, small size and low cost [3] have allowed BLE to be
embedded in a number of consumer electronics [4]. Due to its
ubiquitousness, BLE is now widely considered for wireless
Indoor Localization Systems (ILS) [5]. A BLE based ILS
comprises of a set of BLE devices that are deployed in an
indoor environment. The Received Signal Strength (RSS) of
the BLE devices is used to derive the unknown location(s)
of the target(s) (such as an object, a human or a robot
etc) by using a suitable localization algorithm [4]. The most
common localizations algorithms are proximity, fingerprinting
and trilateration [6]. All these algorithms are wireless signal
based localization algorithms. Different from proximity and
fingerprinting, trilateration algorithm utilizes the Received
Signal Strength (RSS) of (at least 3) BLE devices to calculate
the absolute or relative location coordinates of the target [7].
Trilateration algorithm uses a signal path loss model to derive
the distance from the corresponding RSS samples [7]. There-
fore, trilateration algorithm is preferred due to its simplicity
and ability to estimate the location coordinates through RSS
of BLE devices. The efficacy of a BLE based ILS depends on
the localization accuracy which is an important performance
metric. However, different applications and targets require dif-
ferent accuracies. For example, a localization accuracy of 5m
may be sufficient to locate a human in a shopping mall, while
it is insufficient for locating a cell phone in a bedroom. So, a
localization precision of 2m to 5m is considered as reasonable
for many applications [4]. The localization accuracy of the ILS
rely on the variations of BLE RSS. Many researchers focus on
studying the impact of different parameters (such as different
devices, deployment and environments) in order to understand
the reasons that causes the variations in BLE RSS [3, 4].
TABLE I
LIST OF TRANSMISSION POWER LEVELS AND THEIR TRANSMISSION
RANGES
Transmission Power Levels Transmission Power (dBm) Range (m)
0 10 dBm 200
1 4 dBm 70
2 0 dBm 50
3 -4 dBm 40
4 -8 dBm 30
5 -12 dBm 15
6 -16 dBm 7.0
7 -20 dBm 3.5
8 -40 dBm 1.0
The BLE RSS used for localization is a function of its
transmission power [5]. BLE devices are able to operate at
multiple low transmission power levels [5]. Table I shows ap-
proximately nine discrete transmission power levels (in dBm)
with their corresponding ranges (in m). Higher transmission
power results in strong and more stable RSS and vice versa.
However, at each discrete transmission power level, BLE RSS
is different. This indicates that, each discrete transmission
power level setting, can result in different localization preci-
sion. Unlike previous studies, this paper focuses on evaluating
the performance of BLE based ILS at multiple transmission
power levels to achieve multiple localization precision (i.e
2m to 5m). Along with multiple transmission power levels,
there are a number of other parameters that also have a
significant effect over the BLE RSS. These parameters include
the ability of BLE device to operate at multiple advertising
interval, scanning interval, the effects of device orientation,
Line of Sight (LOS) and Non-Line of Sight (NLOS) over
l-)))
BLE RSS. After analysing their effect over BLE RSS, we
then focus on investigating the effect of number of devices at
each discrete transmission power level to achieve a localization
precision of 2m to 5m in an indoor environment. Thus, the
main contribution of the this paper is to analyze the effect of
multiple signal advertising interval, scanning interval, device
orientation, distance, the effect of LOS and NLOS and device
density at multiple transmission power levels.
The rest of the paper is structured as: Section II presents
the relevant literature. Section III explains BLE based ILS in
detail. Section IV explains the experimental setup along with a
detail discussion over the set of experiments and their results.
Finally, Section V concludes the paper.
II. LITERATURE REVIEW
There are many works and approaches on localization in
literature, including uses in non-consumer applications, e.g.
target localization [8, 9], simulation methods [10] and data
selection [11, 12]. This section presents only a subset of review
of the most relevant works that are present in the literature.
Contreras et al. [7] studied the impact different parameters
such as scanning window, transmission interval and number of
frequency channels over BLE RSS for localization. All devices
operated at default transmission power level (i.e. 0 dBm).
The authors proposed to increase the transmission interval to
increase the localization accuracy. However, the authors did
not provide comprehensive analysis and their work was mainly
focused to the suitability of BLE technology for ILS. The
authors in [13], evaluated BLE based ILS by using trilateration
algorithm. The authors studied the behaviour of BLE RSS with
different kinds of BLE devices that operated at default trans-
mission power level (i.e. 0 dBm) in different environments
such as such as living room, office and workshop.
In [14], Faragher et al. presented a comparative analysis
of the BLE based ILS and WiFi based ILS. The authors
analyzed the effect of human body as an obstacle to BLE and
WiFi RSS . The authors used signal advertising interval and
number of access points as variables to analyze the impact
over localization accuracy. The authors in paper [15], also
evaluated the performance of BLE and WiFi based ILSs in
different conditions such as indoor/outdoor and LOS/NLOS.
They compared the propagation characteristics of the two ILSs
and estimated the localization accuracies.
In [16], the authors evaluated BLE radio for indoor localiza-
tion to achieve localization accuracy with different precisions
(i.e. <2m,<3m,<4m,<5mand >5m). The
authors tested BLE devices of different vendors in different
environments (such as offices, corridors and rooms etc).The
authors in [17] studied the performance of BLE based ILS
in empty and cluttered indoor environments in which they
compared the BLE RSS of different device vendors.
In [18], Golestanian et al. exploited multiple transmis-
sion power level feature of BLE in which they analyzed
the variation of BLE RSS at 4 dBm, -8 dBm, -12 dBm
and -20 dBm. The authors analyzed and proposed moving
average filter to the smooth BLE RSS operating at different
transmission power levels. In [19], Cara et al. presents an
empirical study for the transmission power setting for BLE
based indoor localization. The authors demonstrated that the
effects of the multipaths can be mitigated by using different set
of transmission powers levels. Recently, the authors in [20],
explored different transmission power levels (i.e. 4 dBm, 0
dBm, -4 dBm and -8 dBm) and studied their effect on BLE
RSS with distance. The authors used K-Nearest Neighbour
(KNN) based fingerprinting technique and four different filters
to smooth the BLE RSS. Lastly, the authors evaluated the
performance with 4 different transmission power levels and
concluded with the best possible localization accuracy of 2m
when all devices operate at transmission power level of 4 dBm.
In the light of the relevant literature, the novelty of the work
presented in this paper is that it comprehensively analyzes
the effects of multiple transmission power levels over BLE
RSS. Additionally, it also examines the effects of multiple
parameters such as multiple signal advertising interval, scan-
ning interval, device orientation, distance, effects of LOS and
NLOS and device density at each discrete transmission power
level without applying any preprocessing techniques to the
BLE RSS. In the next section, we briefly discuss the BLE
based ILS that is used in our experiments.
III. BLE BASED INDOOR LOCALIZATION SYSTEM
The BLE based ILS in our experiments consists of a
set of BLE devices, called as Anchors, denoted by AkA,
where krepresent the kth anchor that is deployed in an
indoor environment. Whereas, another BLE enabled device
is attached to the target, called as a Tag, denoted by TtT ,
where trepresents the index of the tag. It is assumed that the
location of all anchors, denoted by (xAk,y
Ak), is fixed. While
the location of the target, denoted by (xTt,y
Tt) needs to be
estimated. Each BLE device (i.e. anchor and tag) is identified
by its Universal Unique Identifier (UUID). The UUID is
advertised in small data packets, called as beacons. The rate
at which the beacons are advertised is called as Advertising
Interval, denoted by Tadv. Each anchor is allowed to transmit
the beacons at a fixed transmission power level, denoted by
P. The transmission power level Pof each anchor defines
its transmission range. Large transmission power corresponds
to large transmission range. A target within the transmission
range of an anchor, is able to receive its beacons. It is assumed
that target is within the transmission range of the at least 3
tags at all times. The tag attached to the target, scans for
the beacons at regular intervals. The rate at which the tag
scans for the beacons is called as Scanning Interval, denoted
by Tscan. If the beacon is received, the tag estimates its
Received Signal Strength (RSS). The RSS of the beacon
signal decreases with distance i.e. distance between an anchor
and a tag [19]. This relation between RSS and distance is
modelled by using a signal path loss model, called as Log-
Distance Path Loss model (LDPL). In the next subsection, we
give a brief overview of the LDPL model.
A. Log-Distance Path Loss (LDPL) Model
Log-Distance Path Loss (LDPL) model is one of the most
common method that is used to map the relation between RSS
samples with their corresponding distances. Mathematically it
can be represented by Eq. 1[21]:
RSS(d)=RSS(d0)−10 ×n×log(d
d0
)(1)
where, RSS(d)(in dBm) represents the strength of the beacon
signal when the tag is at a distance d(in m) from the
anchor, RSS(d0)(in dBm) represents the beacon strength at
default distance (d0)=1m and nis the attenuation factor that
characterizes an indoor environment (typically ranges in 2 to
4) [19]. The distance dis calculated for each anchor by the
tag through LDPL model by using Eq. 2:
d=10
RSS(d0)−RSSd
10×n.(2)
When dis calculated, the tag initiates the localization
algorithm i.e. trilateration algorithm (defined in the next sub-
section), to estimate the location of the target.
B. Trilateration Algorithm
Trilateration algorithm is used to determine absolute or
relative locations of a target with reference to locations of at
least 3 BLE devices [21]. In BLE based ILS, we assume the
locations of all the deployed anchors are reference locations
and known to the ILS. The estimated location, denoted by
(ˆxTt,ˆyTt) of the target is calculated with reference to the
set of reference locations by using trilateration algorithm.
Mathematically, it is represented by Eq. 3 [22]:
⎧
⎪
⎪
⎪
⎪
⎪
⎪
⎨
⎪
⎪
⎪
⎪
⎪
⎪
⎩
dA1,Tt=(xA1−ˆxTt)2+(yA1−ˆyTt)2
dA2,Tt=(xA2−ˆxTt)2+(yA2−ˆyTt)2
.
.
dAk,Tt=(xAk−ˆxTt)2+(yAk−ˆyTt)2
(3)
Here, dA1,Tt,dA2,Ttand dAk,Ttrepresents the distance be-
tween set of the anchor nodes and the target which is calcu-
lated by Eq. 2. The estimated location coordinates of the tag
are given by Eq. 4 [22]:
ˆxTt=|k|
k=1
xAk
dAk,Tt
|k|
k=1
1
dAk,Tt
,ˆyTt=|k|
k=1
yAk
dAk,Tt
|k|
k=1
1
dAk,Tt
.(4)
Here, 1/dAk,Ttis the weight assigned to the coordinates of
the tag. Localization accuracy is computed by estimating the
error that is the difference between the real coordinates of
the tag i.e. (xTt,y
Tt) and estimated coordinates of the tag i.e.
(ˆxTt,ˆyTt).
The localization accuracy depends on correctness of the
distance value which is derived from the BLE RSS samples.
That means, if the RSS changes, the localization accuracy
will also change. As, BLE devices can operate at multiple
transmission power levels with multiple signal advertising in-
terval and scanning interval. Each of these parameter have their
own effect over RSS. The orientation of the devices, effect
of LOS and NLOS can further vary the RSS. The effect of
number of devices that participate in localization and operate
at multiple transmission power levels, is also an important
factor in influencing localization accuracy. Therefore, it is
important to investigate the effects of these parameters with
respect to distance and at discrete transmission power levels.
In the next Section, we describe our experimental setup and
conduct experiments to analyze the effects of all the above
mentioned parameters over RSS.
Table
Table
Table
Table
Table
Table
Table
Door
Door
Screen
15m
12m
ૠ
ૡ
ૢ
ࢀ
ࢀ
ࢀ
Fig. 1. Indoor classroom environment with nine BLE estimotes that are
randomly deployed
IV. EXPERIMENTAL SETUP AND RESULTS
In this section, we present our experimental setup and
analyze the results in detail. The setup is deployed in an indoor
classroom environment as shown in Fig. 1. The dimensions of
the classroom are 12m ×15m. Estimotes [23] BLE beacons
are used as BLE anchors. Whereas, a BLE capable smart
phone is used as a tag which is attached to the target. BLE
anchors (A1through A9) are randomly deployed at fixed
locations in the classroom as shown in Fig. 1. There are three
tags T1,T2and T3that are deployed at different locations.
The location of these tags needs to be estimated. From the
nine deployed anchors, there are six anchors that are at LOS
with all three tag locations while the remaining three anchors
are at NLOS. All BLE anchors have the capability to transmit
beacons with multiple advertising interval, denoted by Tadv.
Typically, Tadv ranges from 100ms to 2000ms [24]. Each BLE
device is capable to operate at nine discrete transmission power
levels as shown in Table I. The tag is also capable to scanning
beacons with multiple scanning interval, denoted by Tscan.
Typically, Tscan ranges from 1000ms to 5000ms [24]. All
smart phones use a default scanning interval i.e. Tscan=1s [24].
Therefore, the default scanning interval in our experiments is
1s. It is to be noted that the RSS shown in the results of the
experiments is mean RSS (in dBm) which is an average of the
RSS samples collected over a period of 60s . In the subsequent
sections, we shall discuss the set of performed experiments and
their results.
A. Effect of Multiple Transmission Power Levels
To analyze the effect of multiple transmission power levels
over RSS to achieve the high localization accuracy, the anchors
are configured to operate at nine discrete transmission power
levels as listed in Table I. The anchors advertise beacons at
Tadv=200ms fixed interval, which indicates 5 beacons per
Tscan. The BLE RSS is recorded at different distances i.e.
from 1m to 8m with step size of 1m. A total of 300 RSS
samples are collected. The observations are shown in Fig. 2.
-120
-100
-80
-60
-40
-20
0
12345678
RSS (dBm)
Distance (m)
10 (dBm) 4 (dBm) 0 (dBm) -4 (dBm) -8 (dBm) -12 (dBm) -16 (dBm) -20 (dBm)
-40 (dBm)
Fig. 2. Effect of Multiple Transmission Power Levels on RSS (dBm) with
Distance (m)
It can be observed that the RSS decreases with distance for
each discrete transmission power level. The RSS of the first
6 transmission power levels is reasonably strong from 1m to
8m compared to the RSS of the last 3 transmission power
levels. The reason is that a strong RSS is able to withhold the
multipath effects that are created by clutter that is present in
the environment. Whereas a weak RSS is more effected by
multi-paths. Therefore, it can be concluded that in order to
achieve the location precision up to 5m, the RSS of anchors
operating at 10 dBm, 4 dBm, 0dBm, -4 dBm, -8 dBm and
-12 dBm transmission power levels will result in significantly
strong RSS and better localization accuracy in comparison to
the RSS of anchors that operate at -16 dBm, -20 dBm and -40
dBm transmission power levels.
B. Effect of Multiple Advertising Interval
Advertising interval Tadv defines the rate of beacon trans-
mission [24] per Tscan. Small Tadv indicates that a large
number of beacons are transmitted. To analyze the effect of
Tadv for high location accuracy, each anchor is configured to
operate at different discrete Tadv interval i.e. 100ms, 200ms
and 500ms beacons per Tscan. Each anchor operates at multi-
ple transmission power levels as listed in Table I. The beacons
were recorded by the tag over distance from 1m to 8m with
the step size of the 1m. The results are shown in Fig. 3.
The results in Fig. 3 shows a significant difference in
the RSS for anchors operating with Tadv=500ms interval in
comparison to the anchors that operate with Tadv=100ms
and Tadv=200ms intervals. The reason is that Tadv =500ms
indicates 2 beacons/Tscan which is much lower as compared
to 5 beacons/Tscan and 10 beacons/Tscan of Tadv=100ms and
Tadv=200ms. When beacons are transmitted, some samples
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
100
200
500
100
200
500
100
200
500
100
200
500
100
200
500
100
200
500
100
200
500
100
200
500
12345678
RSS (dBm)
Advertising Interval (100ms, 200ms and 500 ms) at each Distance (m)
10 (dBm) 4 (dBm) 0 (dBm) -4 (dBm) -8 (dBm) -12 (dBm) -16 (dBm) -20 (dBm) -40 (dBm)
Fig. 3. Effect of Multiple Advertising Interval that Transmit at Multiple
Transmission Power Levels on RSS (dBm) with Distance (m)
loose their strength and some samples are lost completely
before they are received by the tag. This difference in RSS for
Tadv=500ms further increases for anchors operating at lower
transmission power levels with distance. One important point
to note here is the Tscan=1s. If tag operates at interval lower
than the default Tscan, the RSS will be more weak because the
number of beacon received are reduced. Based on the results,
we select the intermediate transmission interval Tadv=200ms
for the rest of our experiments.
C. Effect of Multiple Device Orientations
Device orientation represents the angle of an anchor. To
analyze the effect of the anchor orientation with respect to the
tag, four different orientations are selected i.e. 0◦,90◦,180◦
and 270◦as shown in Fig. 4. The anchor was fixed at one
location and was configured to operate at multiple transmission
power levels with a constant advertising interval Tadv=200ms.
The results are shown in Fig. 4.
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
Beacon 0°
Beacon 90°
Beacon 180°
Beacon 270°
Beacon 0°
Beacon 90°
Beacon 180°
Beacon 270°
Beacon 0°
Beacon 90°
Beacon 180°
Beacon 270°
135
RSS (dBm)
Anchor Orientation at each Distance (m)
10 (dBm) 4 (dBm) 0 (dBm) -4 (dBm) -8 (dBm) -12 (dBm) -16 (dBm) -20 (dBm)
-40 (dBm)
Fig. 4. Effect of Anchor Orientation that Transmit at Multiple Transmission
Power Levels on RSS (dBm) with Distance (m)
Since the Estimote anchors used in our experiments are
small in size (i.e. 5.5cm to 4cm) [23], their orientation has very
less effect over the RSS. It can be observed from results shown
in Fig. 4, that an average RSS difference of 1 dBm is observed
for all the anchors that transmit at large transmission power
levels. Anchors operating at lower transmission power levels
are effected with RSS difference of approximately 3 dBm up
to 5m. Thus, it is concluded that orientation of the anchors
is less likely to effect the anchors that operate specifically at
first 6 transmission power levels.
D. Effect of LOS/NLOS
In the experimental setup shown in Fig. 1, there are 3
anchors (A7,A
8and A9) that are deployed outside of the
classroom boundary which is a glass wall. The glass wall
acts as an obstruction and it creates a NLOS between the
tag locations and these three anchors. To analyze the effect of
LOS and NLOS to achieve the location precision of 2m to 5m,
all anchors are configured to operate at multiple transmission
powers as listed in Table I with constant Tadv=200ms interval.
The results are shown in Fig. 5.
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
LOS NLOS (Glass) LOS NLOS (Glass) LOS
NLOS (Glass)
135
RSS dBm
Effect of LOS and NLOS at each Distance (m)
10 (dBm) 4 (dBm) 0 (dBm) -4 (dBm) -8 (dBm) -12 (dBm) -16 (dBm) -20 (dBm)
-40 (dBm)
Fig. 5. Effect of Anchor that Transmit at Multiple Transmission Power Levels
in Presence of Line of Sight and Non Line of Sight (Glass) on RSS (dBm)
with Distance (m)
From the results shown in Fig. 5, it can be observed that
the RSS is significantly attenuated due to NLOS compared the
RSS at LOS at 1m at all transmission power levels. The lowest
attenuation is approximately 4 dBm for anchor that operates
at transmission power of 10 dBm. Whereas, a severe signal
distortion is observed for the anchors that operates at -40 dBm.
The effect of NLOS tends to vary between 6 dBm to 8 dBm
for anchors that operate at high transmission power level at
distances from 3m to 5m. For anchors that operate at low
transmission power level, the attenuation in RSS increase to
20 dBm for a precision of 3m to 5m. The effect will be severe
if RSS is weak. Thus, it is concluded that the NLOS severely
effect the RSS of BLE anchors. All anchors that are NLOS
with tag locations will lead to large localization errors in an
un-calibrated environment (i.e. without any pre-processing).
In summary, it is observed that BLE anchors that operate
at higher transmission power levels (roughly 10 dBm, 4 dBm,
0 dBm, -4 dBm, -8 dBm and -12 dBm) results in reasonable
RSS to achieve the high localization accuracy in an indoor
classroom environment. All BLE anchors result in strong RSS
with advertising interval Tadv=200ms. The orientation of the
Estimote anchors is allowed to be random as its effect is not
significant. All anchors that are at NLOS with respect to the
target locations are most likely to create large localization
errors. Based on the above findings, we now analyze the effect
of device density to estimate the target location coordinates.
E. Effect of Device Density on Localization Error
We now analyze the effect of increasing device density
over the localization error. Localization error is computed by
estimating the difference between real and estimated coordi-
nates. In Fig. 1, there are 3 tag locations, whose coordinates
are estimated with all nine anchors operating at each discrete
transmission power level. Initially, three anchors with strongest
RSS are used to estimate the coordinates of each target
location. Then, the number of anchors are increased (i.e. up
to 9 anchors) for localization in order to see their effect over
localization accuracy. At each iteration of localization, the
anchors are selected on the basis of strongest RSS. Once the
coordinates of the location are estimated, the localization error
is determined. Fig. 6 shows the results.
0
1
2
3
4
5
6
7
8
9
10
10 (dBm) 4 (dBm) 0 (dBm) -4 (dBm) -8 (dBm) -12 (dBm)
Localization Error (m)
Number of Anchors (k) at Multiple Transmission Power Levels
|k|=3 |k|=4 |k|=5 |k|=6 |k|=7 |k|=8 |k|=9
5m
4m
3m
2m
Fig. 6. Effect of Number of Anchors that Transmit with Multiple Transmission
Power Levels over Localization Accuracy
It is observed that there are 5 transmission power levels
(i.e 10 dBm, 4 dBm, 0 dBm, -4 dBm and -8 dBm) that are
able to achieve a localization precision of 5m with minimum
3 anchors. There are 4 transmission power levels (i.e 10
dBm, 4 dBm, 0 dBm and -4 dBm) that are able to achieve
localization precision of 4m with minimum 3 anchors. And
there are 3 transmission power levels (i.e 10 dBm, 4 dBm
and 0 dBm) that are able to achieve localization precision of
3m with minimum 3 anchors. The best localization accuracy
achieved is approximately is 2.2m with 4 anchors that operate
at transmission power level of 10 dBm. The reason is at high
transmission power level, the RSS is strong. Similarly, the best
possible localization accuracy is 2.95m with 4 anchors, 3.5m
with 3 anchors, 3.8m with 4 anchors and 4.5m with 3 anchors
at transmission power level from 4 dBm to -8 dBm. For all the
anchors that operate at transmission power level of -12 dBm
or below, the localization accuracy is low as the localization
error is greater than 5m. From the results shown in Fig. 6 it can
be observed that by merely increasing the number of anchors,
localization accuracy may not necessarily be increased. The
reason is that the anchors which are located far from the target
or operate at low transmission power levels, their RSS gets
erroneous and weak which deviates the estimation and causes
high localization errors.
In summary, it is observed that anchors with multiple
transmission power levels can achieve localization accuracy
with multiple precision (i.e. 2m to 5m). This interesting finding
allow anchors to operate at relatively low transmission power
levels in order to save energy and maintain a reasonable local-
ization accuracy required to locate the target. By using suitable
preprocessing techniques and filters, the performance of ILS
can be further improved to achieve even better localization
accuracy.
V. C ONCLUSION
The paper presents an analysis of the BLE based ILS and
exploits the feature of multiple transmission power levels to
achieve localization accuracy with multiple precisions (i.e.
from 2m to 5m). A total of 9 transmission powers were
selected and tested by using Estimote BLE devices that
were randomly deployed in an indoor classroom environment.
Initially, effects of parameters such as multiple transmission
power levels, advertising interval, scanning interval, device
orientation, distance, LOS and NLOS over BLE RSS were
analyzed. It is concluded that the anchors that operate at 10
dBm, 4 dBm, 0 dBm, -4 dBm, -8 dBm, -12 dBm and -
16 dBm transmission power levels results in stable RSS up
to distance 5m. An advertising interval of 200ms, results in
strong RSS compared to an advertising interval of 500ms
at multiple transmission power levels. Due to the small size
of the Estimote BLE anchors, the orientation had very less
effect at each discrete transmission power level over the BLE
RSS. Anchors that were at NLOS with reference to the target
locations lead to large localization errors. Analyzing the effects
of device density that operate at multiple transmission power
levels, it is concluded that increasing the number of devices
do not improve the localization accuracy of the system. The
reason is random variations in BLE RSS that significantly
increases with increase in distance. However, localization
accuracy with multiple precisions can be achieved with devices
operating at multiple transmission power levels. To achieve
the localization accuracy with precisions (i.e. 2m to 5m),
it is concluded that out of 9 transmission power levels, 5
transmission power levels (i.e 10 dBm, 4 dBm, 0 dBm, -4
dBm and -8 dBm) achieved a localization precision of 5m
with minimum 3 anchors. Similarly, 4 transmission power
levels (i.e 10 dBm, 4 dBm, 0 dBm and -4 dBm) achieved
localization precision of 4m with minimum 3 anchors and
at 3 transmission power levels (i.e 10 dBm, 4 dBm and 0
dBm) achieved localization precision of 3m with minimum 3
anchors. The final conclusion leverages the use of multiple
transmission power levels such that BLE based ILS is able
to extend its battery life by saving energy and maintain a
reasonable localization accuracy required to locate the target.
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