Performance evaluation of V2LC system using led traffic lights
Le Tung Hoa, Dang The Ngoc
PERFORMANCE EVALUATION OF V2LC
SYSTEM USING LED TRAFFIC LIGHTS
Le Tung Hoa and Dang The Ngoc
Posts and Telecommunications Institute of Technology
transferring data. Furthermore, VLC, whose wavelengths
are from 380 nm to 780 nm, offers around 1000 times
greater bandwidth compared to the RF communications.
It means that the wide available visible light spectrum
enables any VLC systems to easily reach high data rates.
Because of all above advantages, VLC has attracted lots
of studies in both indoor and outdoor applications.
Abstract— Vehicular visible light communication
(V2LC) is a promising technology that enables intelligent
transportation system (ITS). Recently, the classical light
sources have been replaced by light emitting diodes
(LEDs) on both vehicles and transportation infrastructure,
such as traffic lights and road lights. Based on that fact, it
makes easier and cheaper to apply V2LC on roads than
any other technologies. In the paper, a LED traffic light
is used to transmit data of the next road to vehicles. A
two-lane one-way road is considered in order to calculate
the values of signal-to-noise ratio (SNR), bit-error rate
(BER) and throughput of vehicles at different positions on
the road. We define a communication area where a
vehicle can receive signal from the traffic light and then
estimate the size of communication area based on BER.
The opportunity of utilizing outdoor VLC for inter-
vehicle or roadside-vehicle communication has been
highly under consideration due to the trend of the lighting
system and economical implementation of VLC on
transportation system. Recently, the lighting industry has
been replacing the classical light sources with light
emitting diodes (LEDs). LEDs have high-quality
characteristics of long-life, compact and low power
consumption that is expected to be a future energy-saving
light source. Therefore, LED-based vehicle lighting
systems are popular in vehicle production. Moreover,
most parts of the transportation infrastructure, such as
traffic lights, road lights and traffic signs, also have
changed to use LEDs. So, it is certain that LED-based
lighting will be the important part of the transportation
system, being installed in vehicles and also in the
transportation infrastructure. The VLC technology will
add LEDs more function besides lighting. In VLC, the
data is transmitted into the instantaneous switching on-off
LEDs, at speeds unperceivable by the human eye. In this
case, the same LED system provides both illumination
and data transmission [1]. The fact that a LED-based
lighting system installed through all a road makes VLC
implementation less complex and costly.
Keywords— Vehicular visible light communication
(V2LC), LED traffic light, communication area.
I. INTRODUCTION
Nowadays, road safety and traffic efficiency have
concerned everyone because people have tended to spend
more time in travelling. Consequently, a strong interest of
the public, governments, industry exits to make vehicles
safer and smarter. An intelligent transportation system
(ITS), first introduced in 1980s, has been in response to
this interest. To turn ITS into reality needs a wide variety
of innovative technologies. And visible light
communication (VLC) is the most promising key
technology that plays an important role in a reliable
component of data transmission for an ITS.
VLC is a technology that uses the visible light as a
carrier to transfer data through wireless communications.
VLC provides lots of advantages compared with the
existing radio frequency (RF) [1]. Firstly, the visible light
spectrum range doesn’t need to be registered while almost
all RFs are controlled and provided by some
organizations. Therefore, in the economy point of view, it
is better to use VLC in order to reduce the cost of a
system. Secondly, VLC is the electromagnetic spectrum
that human eye can view. Therefore, VLC can be used for
two purposes simultaneously that are lighting and
Recently, lots of papers have shown its attention to
performance analysis of vehicular VLC systems. The
authors in [2] researched a vehicular VLC system using
road illumination. The shape of LED road illumination is
introduced and then the system is evaluated by signal-to-
noise ratio (SNR). On the other hand, the researchers in
[3] implemented a vehicular VLC system using traffic
lights. In [3], the design of service area is shaped by the
decision of the vertical inclination and field of view of the
receiver located in the center of vehicle’s front panel.
Then, the service area is analyzed by SNR with different
modulation schemes like on-off keying (OOK) and
subcarrier binary shift keying (SC-BPSK). Moreover, in
[4], the visible light vehicle-to-vehicle communication is
taken into account. A 22 multiple-input multiple-output
(MIMO) configuration from two lights in front and back
Corresponding author: Dang The Ngoc
Email: [email protected]du.vn
Received: 8/2020, Revised: 9/2020, Accepted: 10/2020.
This research is funded by Ministry of Information and Communications
under grant number ĐT.05/20.
SOÁ 03 (CS.01) 2020
TAÏP CHÍ KHOA HOÏC COÂNG NGHEÄ THOÂNG TIN VAØ TRUYEÀN THOÂNG
4
PERFORMANCE EVALUATION OF V2LC SYSTEM USING LED TRAFFIC LIGHTS
of vehicle is utilized to maintain communication in some m. A vehicle on the first and second lanes locates in the
particular situations. The performance of the system is position y = 0 m and y = 4.1 m, respectively. The traffic
proved by average bit-error rate (BER) in different regime is assumed to be sparse, so that all vehicles always
schemes of multiple-input single-output (MISO), single- have LOS link between receivers and the LED traffic
input single-output (SISO) and MIMO. The work in [5] is light as a transmitter. The specific road parameters are
slightly similar to [4] since, it also focused on vehicle-to- given in Table 1.
vehicle communication. However, the study in [5]
implements headlamp beam on front of vehicle to transfer
z
information through both light-of-sight (LOS) and non-
light-of-sight (NLOS) links. The system BER
performance is considered.
y
d
In summary, above-mentioned studies have taken some
kinds of visible light communications for inter-vehicle or
roadside-vehicle, but almost all are limited to calculate
x
0
SNR and BER. However, the metrics of SNR and BER
are not enough for evaluating the performance of
vehicular visible light communication (V2LC) systems.
Therefore, in this paper, we propose to determine the
overall throughput of V2LC systems using the traffic
light. Due to the fact that the traffic light cannot provide
connection to the vehicles at every location, we define a
communication area where a vehicle can receive signal
from the traffic light and then estimate the size of
communication area based on BER.
Fig 1. Road model.
TRANSMITTER
RECEIVER
Fig 2. Transmitter and receiver in the system model.
The rest of the paper is organized as follows. Section II
introduces the system model. The performances of the
given system will be analyzed in section III. Section IV
demonstrates the numerical results and discussions.
Finally, the study is summarized in Section V.
According to Fig. 1, the distance d between the LED
traffic light and the receiver at a vehicle is calculated as
2
d = x2 + y2 + h −h
(1)
(
)
l
r
The second part explains in details of a transmitter and
a receiver depicted in Fig. 2. In the system model, the
transmitter is the traffic light and the receiver is PIN
attached on each vehicle. At the LED traffic light, the
optical signals are modulated by intensity modulations
(IM) like OOK and SC-BPSK. In OOK modulation, ON-
OFF keying is used with on-off alternatively while
transferring bit “1” or “0”. Besides, SC-BPSK utilizes
subcarrier binary phase-shift keying in which the original
data is modulated by a subcarrier and converted into
optical intensity. Those IM schemes help to convey
information by on-off LED at speeds unperceivable by
the human eye. Loss of switching one color to the other
color is ignored.
II. SYSTEM MODEL
The system model is divided in two main parts: (1)
road model and transmitter-receiver model. The road
model provides the specific road information, car
position, car speed, and traffic road scheme. The
following part concentrates on transmitter-receiver in
terms of positions, modulation scheme and some
important angle parameters.
TABLE 1. ROAD PARAMETERS
Distance in lane direction
Distance in width direction
Distance in height direction
Distance
Width of vehicle (m)
Width of lane (m)
x
y
z
d
1.8
3.5
5.3
1.0
TABLE 2. TRANSMITTER AND RECEIVER PARAMETERS
Angle of irradiance
Half-power semiangle
Angle of incidence
Vertical inclination
FOV of receiver
1/2
c
Height of traffic light hl (m)
Height of receiver hr (m)
Firstly, our road model is a two-lane one-way road with
a traffic light locating at the end of the road, which is an
intersection. The width of a lane is 3.5 m. A three-
dimensional space is applied on the road as shown in Fig.
1. In the space, the x-axis goes along the road, the y-axis
shows the distance in the width direction and the z-axis
points the height of attached position of transmitter or
receiver. We assume that the traffic light is at the origin,
the height of traffic hl is 5.3 m. In the road, vehicles are
the same in shape with 1.8 m width and they move at a
constant velocity. A receiver is attached in the center of
vehicle’s front panel with the height of receiver hr = 1.0
All the parameters of the considering transmitter and
receiver are given in Table 2. We assumed the light has
the angle of irradiance and half-power semiangle of
LED 1/2 is 150. At a receiver, there are three angles that
are the vertical inclination, the field of view (FOV) c,
and the instant angle of incidence. Based on the road
model, we can calculate the instant angle of irradiance
and angle of incidence, respectively, as follows
SOÁ 03 (CS.01) 2020
TAÏP CHÍ KHOA HOÏC COÂNG NGHEÄ THOÂNG TIN VAØ TRUYEÀN THOÂNG
5
Le Tung Hoa, Dang The Ngoc
Regarding noise power, we consider shot noise and
x
y
2
2
= arccos
circuit noise, which are denoted as
and
,
shot
cir
respectively. Hence, the noise power N is given by
(2)
h −h
x
2
x2 + h −h
l
r
sin +arctan
(
)
2
2
l
r
(9)
N =shot +cir
= arccos
d
s2hot
The shot noise
depending on signal power and
background current is expressed as
III. PERFORMANCE ANALYSIS
2
t
(10)
shot = (2qRP +2qIbg )BF
r
This section is an in-depth introduction of LOS channel
model and performance metrics such as the signal-to-
noise ratio, BER, and throughput in the considering
system.
where q is the electronic charge, Ibg is background light
noise current, Ft is the noise factor and B is the noise
bandwidth. Meanwhile,
2
mainly contains thermal
cir
noise and thus is calculated as
A. LOS Channel Model
The traffic regime is assumed to be sparse enough to be
able to have LOS links between receivers attached on
vehicles and the transmitter, i.e., the LED traffic light.
LEDs in traffic light are optical transmitters that follow
the Lambertian model [6]. In the model, LED radiant
intensity Ptr is given by
4kT
RF
c2ir
=
BF
t
(11)
where T is the absolute temperature and RF is the load
resistance.
We assume that SC-BPSK is used in the model.
Therefore, BER is given by
m+1
2
(3)
P =
tr ( )
P cosm
( )
t
SNR
(12)
BER = Q
where Q(.) is Q function.
C. Throughput
2
where Pt is the transmitted optical power and the order m
is related to 1/2 by
ln2
(4)
m = −
lncos1 2
The system throughput is calculated based on the
following parameters: the packet size (L) and the
transmission data rate R. The probability of receiving an
error-free packet of length L bits denoted as pc is
expressed as
Considering the VLC link, a receiver with an optical
band-pass filter of transmission TS() and a nonimaging
concentrator of gain g(), the DC gain for a receiver
located at a distance of d can be approximated as
L
(13)
p = 1−BER
(
)
c
H 0 =
( )
Throughput is therefore given by
m+1 A
(5)
(
)
cosm T g cos
s ( ) ( ) ( )
(
)
2
=
,0 c
(14)
2d
Throughput=Rpc
0, c
IV. NUMERICAL RESULTS
An idealized nonimaging concentrator having an
To prove the feasibility of our proposed system model,
we have derived numerical performance results that are
demonstrated in this section. All the system parameters
are in Table 3.
internal refractive index n achieves a gain
n2
,
0 c
g = sin2
(6)
( )
c
TABLE 3. SYSTEM PARAMETERS
0, c
Detector physical area of PD A (cm2)
Gain of optical filter Ts()
Refractive index n
Absolute temperature T (K)
O/E conversion efficiency (A/W)
Load resistance RF (k)
0.79
1.0
1.7
298
0.35
10
B. Bit-Error Rate
The receiver SNR is usually expressed as below
S
N
(7)
SNR =
Noise factor Ft
102
79.1
7.6
314
126
50
where S is the signal power, and N is the noise power.
With the transmitted optical power (Pt), the received
optical power (Pr), and LOS channel model, S can be
calculated as
Vertical inclination (degree)
FOV of receiver c (degree)
Transmitted power Pt (OOK) (mW)
Transmitted power Pt (SC-BPSK) (mW)
Packet size L (bits)
2
(8)
2
2
2
S = P = H 0 P
( )
r
t
Transmission data rate R (Mbps)
1
where is the responsivity of the photodetector.
SOÁ 03 (CS.01) 2020
TAÏP CHÍ KHOA HOÏC COÂNG NGHEÄ THOÂNG TIN VAØ TRUYEÀN THOÂNG
6
PERFORMANCE EVALUATION OF V2LC SYSTEM USING LED TRAFFIC LIGHTS
1
55
1st lane
2nd lane
OOK, 1st lane
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
50
45
40
35
30
25
20
15
10
5
OOK, 2nd lane
SC-BPSK, 1st lane
SC-BPSK, 2nd lane
0
0
10
20
30
40
50
60
70
80
0
10
20
30
40
50
60
70
80
Distance in Lane Direction x [m]
Distance in Lane Direction x [m]
Fig 3. SRN in different modulation schemes and lanes.
Fig 5. Throughput in different lanes.
Figure 3 investigates SNR versus the distance in lane
direction x with two types of modulation scheme
including OOK and SC-BPSK. According to the figure,
SNR depends mostly on the lane of a vehicle in which the
vehicle runs. Vehicles in the first lane always have better
SRN than those in the second lane at the same lane
direction x. The reason is that the angles of irradiance
and incidence of the second lane, described in
Equations (1) and (2), are narrower than that in the first
lane if both have the same x. When a vehicle runs closer
to the traffic light, the SNR increases. However, when the
vehicle is at the position too close to the traffic light, the
transmitter is not in the FOV of the receiver and thus SNR
becomes zero. In addition, the different modulation
schemes, OOK and SC-BPSK, show fairly difference in
the value of SNR. In the same lane and at the same lane
direction x, using OOK performs better than SC-BPSK
due to its higher transmitted power allowed according to
the standard.
The system throughput is investigate versus the
distance in lane direction x in Fig. 5. The figure shows
that the system throughput reaches the maximum value of
1 Mbps when the vehicles are at the communication area.
This is due to the fact that the system provides error-free
in communication.
The vertical inclination 휃 shows the angle of sensor
attached on front of a vehicle to receive information from
the LED traffic light. Different vertical inclinations will
affect angle of incidence and consequently change
communication areas. As shown in Fig. 6, at the same
first lane, communication areas achieve three different
values where we use three different vertical inclinations.
1
0.8
0.6
Vertical inclination: 75°
Figure 4 demonstrates the relation between BER and
the distance in lane direction x for the case of SC-BPSK.
The communication area is defined as the range of
distances, where BER is lower than 10-6. In the first lane,
the communication area extends from 10 m to 74 m on
the x-axis. Meanwhile, in the second lane, the
communication area is within 36 m to 51 m on the x-axis.
It is clear that the communication area in the first lane is
larger than the second lane. It means that the vehicles in
the first lane can receive more information than the
vehicles the second lane with the condition that these
vehicles move at the same velocity.
Vertical inclination: 79.1°
Vertical inclination: 80°
0.4
0.2
0
0
10
20
30
40
50
60
70
80
Distance in Lane Direction x [m]
Fig 6. Throughput in 1st lane with different vertical inclinations.
When we increase the value of vertical inclination , the
start points and end points of the communication areas are
further to the LED traffic light and communication areas
consequently are wider. However, if we consider more
traffic light sections, the overlapping of communication
areas will create inter-section interference. So, we need to
estimate the best vertical inclination 휃 which satisfies our
desired communication area and avoids inter-section
interference.
100
10-10
10-20
V. CONCLUSION
In the paper, the simple system model of two-lane one-
way road for V2LC is considered. In different lanes, the
first and the second lanes, the values of SNR, BER, and
throughput are calculated. These values prove that
vehicles in the first lane always have better performance
metrics than those in the second lane due to the fact that
1st lane
2nd lane
10-30
0
10
20
30
40
50
60
70
80
Distance in Lane Direction x [m]
Fig 4. BER in different lanes.
SOÁ 03 (CS.01) 2020
TAÏP CHÍ KHOA HOÏC COÂNG NGHEÄ THOÂNG TIN VAØ TRUYEÀN THOÂNG
7
Le Tung Hoa, Dang The Ngoc
giao thông. Mô hình đường một chiều hai làn được khảo
sát nhằm tính toán các giá trị của tỷ số tín hiệu trên tạp
âm (SNR), tỷ lệ lỗi bit (BER) và thông lượng của các
phương tiện giao thông tại các vị trí khác nhau trên
đường. Bên cạnh đó, chúng tôi cũng định nghĩa vùng
truyền thông nơi một phương tiện giao thông có thể nhận
tín hiệu từ đèn giao thông và sau đó tính toán kích thước
của vùng truyền thông này dựa trên tham số BER.
the angles of irradiance and incidence of the second
lane are narrower than that in the first lane if both have
the same position on 푥-asix. A communication area is
defined as a range of road where vehicles can receive
successfully signal from the traffic light. Then, this area is
identified based on BER.
This research will be easily extended if we consider
more complex road models which involve two-way
directions and a real cross road with more than one traffic
lights. This paper is limited to use only VLC between a
traffic light to vehicles, but in fact, V2LC can be applied
Từ khóa- Truyền thông bằng ánh sáng nhìn thấy (V2LC),
đèn giao thông LED, vùng truyền thông.
on
both
inter-vehicle
and
roadside-vehicle
Le Tung Hoa received B.E. from
Posts and Telecommunications
Institute of Technology (PTIT),
Vietnam, in 2007, and M.E. degree
communications. The traffic regime is mostly ignored by
assumption of low-density traffic which always enables
LOS channel. Therefore, researchers can develope the
research to fulfill the real traffic situation.
from
University
of
Electro-
communication, Japan, in 2010, both
in telecommunication engineering.
Now, she is a lecturer at Faculty
REFERENCES
[1] Alin-Mihai
Cawilean
and
Mihai
Dimian,
Telecommunication 1 of PTIT. Her
research interests include wireless communications,
VANET, Vehicular VLC and cognitive radio.
pp. 2681 - 2703, Fourthquarter 2017.
[2] S. Kitano, S. Haruyama and M. Nakagawa, “LED road
illumination communication system,” in 2003 IEEE 58th
Vehicular Technology Conference. VTC 2003-Fall, 2003.
[3] M. Akanegawa, Y. Tanaka and M. Nakagawa, “Basic study
on traffic information system using LED traffic lights,”
Vol. 2, Issue: 4, pp. 197- 203, Dec. 2001.
[4] Vima Gupta and Rahul Singhal, “Performance analysis of a
visible light vehicle-to-vehicle wireless communication
Dang The Ngoc received the B.E.
degree from the Hanoi University of
Science and Technology, Hanoi,
Vietnam in 1999, and the M.E.
degree from the Posts and
Telecommunications Institute of
Technology (PTIT), Hanoi, Vietnam
in 2005, both in electronics and
telecommunications; and received
the Ph.D. degree in computer science and engineering
from the University of Aizu, Aizu-wakamatsu, Japan in
2010. He is currently an Associate Professor/Head with
the Department of Wireless Communications at PTIT. He
was also an invited/visiting researcher at FOTON-
ENSSAT Lab., Universite de Rennes 1, France, in 2011
and Computer Communications Lab., The University of
Aizu, Japan in 2012, 2013, 2015, and 2017. His current
research interests include the area of communication
theory with a particular emphasis on modeling, design,
and performance evaluation of optical CDMA, RoF/FSO,
optical wireless communication, and QKD systems. He is
a member of IEEE.
[5] Pengfei Luo, Zabih Ghassemlooy, Hoa Le Minh, Edward
Bentley, Andrew Burton and Xuan Tang, “Fundamental
analysis
of a car to car visible light communication system,” 2014
9th International Symposium on Communication Systems,
Networks & Digital Sign (CSNDSP), July 2014.
communications,” Proceedings of the IEEE, Vol. 85, Issue:
2, pp. 265-298, Feb. 1997.
[7] Taniya Shafique, Osama Amin, Mohamed Abdallah, Imran
Shafique Ansari, Mohamed-Slim Alouini and Khalid
Qaraqe, “Performance Analysis of Single-Photon
Avalanche Diode Underwater VLC System Using ARQ,”
ĐÁNH GIÁ HIỆU NĂNG CỦA HỆ THỐNG V2LC
SỬ DỤNG ĐÈN GIAO THÔNG LED
Tóm tắt- Truyền thông bằng ánh sáng nhìn thấy
(V2LC) là một công nghệ tiềm năng nhằm hiện thực hóa
hệ thống giao thông thông minh (ITS). Ngày nay, các
nguồn sáng truyền thống đang dần được thay thế bởi điốt
phát quang (LEDs) trên cả phương tiện giao thông và cơ
sở hạ tầng giao thông như là hệ thống đèn giao thông và
đèn đường chiếu sáng. Dựa trên thực tế này, việc triển
khai sử dụng V2LC trên đường trở nên dễ dàng và kinh tế
hơn nhiều so với bất kì công nghệ nào khác. Trong bài
báo này, đèn giao thông LED được sử dụng để truyền tải
thông tin của tuyến đường tiếp theo đến các phương tiện
SOÁ 03 (CS.01) 2020
TAÏP CHÍ KHOA HOÏC COÂNG NGHEÄ THOÂNG TIN VAØ TRUYEÀN THOÂNG
8
5 trang
16260
Free
Bạn đang xem tài liệu "Performance evaluation of V2LC system using led traffic lights", để tải tài liệu gốc về máy hãy click vào nút Download ở trên
File đính kèm:
- performance_evaluation_of_v2lc_system_using_led_traffic_ligh.pdf
