Performance evaluation of v2lc system using led traffic lights

Nội dung text: Performance evaluation of v2lc system using led traffic lights

1. 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 Abstract— Vehicular visible light communication transferring data. Furthermore, VLC, whose wavelengths (V2LC) is a promising technology that enables intelligent are from 380 nm to 780 nm, offers around 1000 times transportation system (ITS). Recently, the classical light greater bandwidth compared to the RF communications. sources have been replaced by light emitting diodes It means that the wide available visible light spectrum (LEDs) on both vehicles and transportation infrastructure, enables any VLC systems to easily reach high data rates. such as traffic lights and road lights. Based on that fact, it Because of all above advantages, VLC has attracted lots makes easier and cheaper to apply V2LC on roads than of studies in both indoor and outdoor applications. any other technologies. In the paper, a LED traffic light The opportunity of utilizing outdoor VLC for inter- is used to transmit data of the next road to vehicles. A vehicle or roadside-vehicle communication has been two-lane one-way road is considered in order to calculate highly under consideration due to the trend of the lighting the values of signal-to-noise ratio (SNR), bit-error rate system and economical implementation of VLC on (BER) and throughput of vehicles at different positions on transportation system. Recently, the lighting industry has the road. We define a communication area where a been replacing the classical light sources with light vehicle can receive signal from the traffic light and then estimate the size of communication area based on BER. emitting diodes (LEDs). LEDs have high-quality characteristics of long-life, compact and low power Keywords— Vehicular visible light communication consumption that is expected to be a future energy-saving (V2LC), LED traffic light, communication area. light source. Therefore, LED-based vehicle lighting systems are popular in vehicle production. Moreover, I. INTRODUCTION most parts of the transportation infrastructure, such as traffic lights, road lights and traffic signs, also have Nowadays, road safety and traffic efficiency have changed to use LEDs. So, it is certain that LED-based concerned everyone because people have tended to spend lighting will be the important part of the transportation more time in travelling. Consequently, a strong interest of system, being installed in vehicles and also in the the public, governments, industry exits to make vehicles transportation infrastructure. The VLC technology will safer and smarter. An intelligent transportation system add LEDs more function besides lighting. In VLC, the (ITS), first introduced in 1980s, has been in response to data is transmitted into the instantaneous switching on-off this interest. To turn ITS into reality needs a wide variety LEDs, at speeds unperceivable by the human eye. In this of innovative technologies. And visible light case, the same LED system provides both illumination communication (VLC) is the most promising key and data transmission [1]. The fact that a LED-based technology that plays an important role in a reliable lighting system installed through all a road makes VLC component of data transmission for an ITS. implementation less complex and costly. VLC is a technology that uses the visible light as a Recently, lots of papers have shown its attention to carrier to transfer data through wireless communications. performance analysis of vehicular VLC systems. The VLC provides lots of advantages compared with the authors in [2] researched a vehicular VLC system using existing radio frequency (RF) [1]. Firstly, the visible light road illumination. The shape of LED road illumination is spectrum range doesn’t need to be registered while almost introduced and then the system is evaluated by signal-to- all RFs are controlled and provided by some noise ratio (SNR). On the other hand, the researchers in organizations. Therefore, in the economy point of view, it [3] implemented a vehicular VLC system using traffic is better to use VLC in order to reduce the cost of a lights. In [3], the design of service area is shaped by the system. Secondly, VLC is the electromagnetic spectrum decision of the vertical inclination and field of view of the that human eye can view. Therefore, VLC can be used for receiver located in the center of vehicle’s front panel. two purposes simultaneously that are lighting and Then, the service area is analyzed by SNR with different modulation schemes like on-off keying (OOK) and Corresponding author: Dang The Ngoc Email: ngocdt@ptit.edu.vn subcarrier binary shift keying (SC-BPSK). Moreover, in Received: 8/2020, Revised: 9/2020, Accepted: 10/2020. [4], the visible light vehicle-to-vehicle communication is This research is funded by Ministry of Information and Communications taken into account. A 2 2 multiple-input multiple-output under grant number ĐT.05/20. (MIMO) configuration from two lights in front and back
2. 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 y d performance is considered. 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 SNR and BER. However, the metrics of SNR and BER 0 x are not enough for evaluating the performance of Fig 1. Road model. vehicular visible light communication (V2LC) systems. TRANSMITTER RECEIVER 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 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 According to Fig. 1, the distance d between the LED given system will be analyzed in section III. Section IV traffic light and the receiver at a vehicle is calculated as demonstrates the numerical results and discussions. 22 2  (1) Finally, the study is summarized in Section V. d= x + y +( hlr − h ) II. SYSTEM MODEL The second part explains in details of a transmitter and a receiver depicted in Fig. 2. In the system model, the The system model is divided in two main parts: (1) transmitter is the traffic light and the receiver is PIN road model and transmitter-receiver model. The road attached on each vehicle. At the LED traffic light, the model provides the specific road information, car optical signals are modulated by intensity modulations position, car speed, and traffic road scheme. The (IM) like OOK and SC-BPSK. In OOK modulation, ON- following part concentrates on transmitter-receiver in OFF keying is used with on-off alternatively while terms of positions, modulation scheme and some transferring bit “1” or “0”. Besides, SC-BPSK utilizes important angle parameters. subcarrier binary phase-shift keying in which the original TABLE 1. ROAD PARAMETERS data is modulated by a subcarrier and converted into Distance in lane direction x optical intensity. Those IM schemes help to convey Distance in width direction y information by on-off LED at speeds unperceivable by Distance in height direction z the human eye. Loss of switching one color to the other Distance d color is ignored. Width of vehicle (m) 1.8 TABLE 2. TRANSMITTER AND RECEIVER PARAMETERS Width of lane (m) 3.5 Angle of irradiance  Height of traffic light hl (m) 5.3 Half-power semiangle 1/2 Height of receiver hr (m) 1.0 Angle of incidence  Firstly, our road model is a two-lane one-way road with Vertical inclination  a traffic light locating at the end of the road, which is an FOV of receiver c intersection. The width of a lane is 3.5 m. A three- dimensional space is applied on the road as shown in Fig. All the parameters of the considering transmitter and 1. In the space, the x-axis goes along the road, the y-axis receiver are given in Table 2. We assumed the light has shows the distance in the width direction and the z-axis the angle of irradiance  and half-power semiangle of points the height of attached position of transmitter or 0 receiver. We assume that the traffic light is at the origin, LED 1/2 is 15 . At a receiver, there are three angles that are the vertical inclination, the field of view (FOV) c, 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 and the instant angle of incidence. Based on the road constant velocity. A receiver is attached in the center of model, we can calculate the instant angle of irradiance  vehicle’s front panel with the height of receiver hr = 1.0 and angle of incidence, respectively, as follows
3. Le Tung Hoa, Dang The Ngoc Regarding noise power, we consider shot noise and x  = arccos circuit noise, which are denoted as  2 and 2 , y shot cir  (2) respectively. Hence, the noise power N is given by hh− 2 sin + arctan lr x2 + h − h ( lr) 22 (9) x N =+shot cir  = arccos d The shot noise depending on signal power and background current is expressed as III. PERFORMANCE ANALYSIS 2 shot=+(2qRP r 2 qI bg ) BF t  (10) This section is an in-depth introduction of LOS channel model and performance metrics such as the signal-to- where q is the electronic charge, Ibg is background light noise ratio, BER, and throughput in the considering noise current, Ft is the noise factor and B is the noise system. bandwidth. Meanwhile, mainly contains thermal A. LOS Channel Model noise and thus is calculated as The traffic regime is assumed to be sparse enough to be 4kT  2 = BF  (11) able to have LOS links between receivers attached on cirR t vehicles and the transmitter, i.e., the LED traffic light. F LEDs in traffic light are optical transmitters that follow where T is the absolute temperature and RF is the load the Lambertian model [6]. In the model, LED radiant resistance. intensity Ptr is given by We assume that SC-BPSK is used in the model. Therefore, BER is given by m+1 PP= cosm  (3) tr( ) t ( ) SNR 2 BER= Q  (12) where Pt is the transmitted optical power and the order m 2 is related to 1/2 by where Q(.) is Q function. ln 2 m =−  (4) C. Throughput ln cos12 The system throughput is calculated based on the following parameters: the packet size (L) and the Considering the VLC link, a receiver with an optical transmission data rate R. The probability of receiving an band-pass filter of transmission TS() and a nonimaging error-free packet of length L bits denoted as pc is concentrator of gain g(), the DC gain for a receiver expressed as located at a distance of d can be approximated as L pc =( 1− BER)  (13) H (0) = Throughput is therefore given by (mA+1) m (5) 2 cos()Tgs () ( ) cos(  ) = 2 d ,0  c Throughput= Rp  (14) c 0,  c An idealized nonimaging concentrator having an IV. NUMERICAL RESULTS internal refractive index n achieves a gain To prove the feasibility of our proposed system model, we have derived numerical performance results that are n2 demonstrated in this section. All the system parameters ,0   2 c  (6) are in Table 3. g ( ) = sin c TABLE 3. SYSTEM PARAMETERS 0,  c Detector physical area of PD A (cm2) 0.79 B. Bit-Error Rate Gain of optical filter Ts() 1.0 The receiver SNR is usually expressed as below Refractive index n 1.7 Absolute temperature T (K) 298 S SNR =  (7) O/E conversion efficiency  (A/W) 0.35 N Load resistance RF (k) 10 2 where S is the signal power, and N is the noise power. Noise factor Ft 10 With the transmitted optical power (Pt), the received Vertical inclination  (degree) 79.1 optical power (Pr), and LOS channel model, S can be FOV of receiver c (degree) 7.6 calculated as Transmitted power Pt (OOK) (mW) 314 2 Transmitted power Pt (SC-BPSK) (mW) 126 2 2 2  (8) SPHP=rt = (0) Packet size L (bits) 50 Transmission data rate R (Mbps) 1 where  is the responsivity of the photodetector.
4. PERFORMANCE EVALUATION OF V2LC SYSTEM USING LED TRAFFIC LIGHTS 55 1 OOK, 1st lane 1st lane 50 0.9 OOK, 2nd lane 2nd lane 45 SC-BPSK, 1st lane 0.8 SC-BPSK, 2nd lane 40 0.7 35 0.6 30 0.5 25 SNR [dB]SNR Throughtput 0.4 20 0.3 15 10 0.2 5 0.1 0 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 The system throughput is investigate versus the direction x with two types of modulation scheme distance in lane direction x in Fig. 5. The figure shows including OOK and SC-BPSK. According to the figure, that the system throughput reaches the maximum value of SNR depends mostly on the lane of a vehicle in which the 1 Mbps when the vehicles are at the communication area. vehicle runs. Vehicles in the first lane always have better This is due to the fact that the system provides error-free SRN than those in the second lane at the same lane in communication. direction x. The reason is that the angles of irradiance  The vertical inclination 휃 shows the angle of sensor and incidence  of the second lane, described in attached on front of a vehicle to receive information from Equations (1) and (2), are narrower than that in the first the LED traffic light. Different vertical inclinations will lane if both have the same x. When a vehicle runs closer affect angle of incidence  and consequently change to the traffic light, the SNR increases. However, when the communication areas. As shown in Fig. 6, at the same vehicle is at the position too close to the traffic light, the first lane, communication areas achieve three different transmitter is not in the FOV of the receiver and thus SNR values where we use three different vertical inclinations. becomes zero. In addition, the different modulation 1 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 0.8 due to its higher transmitted power allowed according to the standard. 0.6 Figure 4 demonstrates the relation between BER and Vertical inclination: 75° Vertical inclination: 79.1° the distance in lane direction x for the case of SC-BPSK. Vertical inclination: 80° 0.4 The communication area is defined as the range of Throughtput distances, where BER is lower than 10-6. In the first lane, the communication area extends from 10 m to 74 m on 0.2 the x-axis. Meanwhile, in the second lane, the communication area is within 36 m to 51 m on the x-axis. 0 It is clear that the communication area in the first lane is 0 10 20 30 40 50 60 70 80 larger than the second lane. It means that the vehicles in Distance in Lane Direction x [m] the first lane can receive more information than the Fig 6. Throughput in 1st lane with different vertical inclinations. vehicles the second lane with the condition that these When we increase the value of vertical inclination , the vehicles move at the same velocity. start points and end points of the communication areas are 0 10 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 -10 10 estimate the best vertical inclination 휃 which satisfies our desired communication area and avoids inter-section interference. BER -20 10 V. CONCLUSION In the paper, the simple system model of two-lane one- way road for V2LC is considered. In different lanes, the 1st lane first and the second lanes, the values of SNR, BER, and -30 2nd lane 10 throughput are calculated. These values prove that 0 10 20 30 40 50 60 70 80 vehicles in the first lane always have better performance Distance in Lane Direction x [m] Fig 4. BER in different lanes. metrics than those in the second lane due to the fact that
5. Le Tung Hoa, Dang The Ngoc the angles of irradiance  and incidence  of the second giao thông. Mô hình đường một chiều hai làn được khảo lane are narrower than that in the first lane if both have sát nhằm tính toán các giá trị của tỷ số tín hiệu trên tạp the same position on -asix. A communication area is âm (SNR), tỷ lệ lỗi bit (BER) và thông lượng của các defined as a range of road where vehicles can receive phương tiện giao thông tại các vị trí khác nhau trên successfully signal from the traffic light. Then, this area is đường. Bên cạnh đó, chúng tôi cũng định nghĩa vùng identified based on BER. truyền thông nơi một phương tiện giao thông có thể nhận This research will be easily extended if we consider tín hiệu từ đèn giao thông và sau đó tính toán kích thước more complex road models which involve two-way của vùng truyền thông này dựa trên tham số BER. directions and a real cross road with more than one traffic lights. This paper is limited to use only VLC between a Từ khóa- Truyền thông bằng ánh sáng nhìn thấy (V2LC), traffic light to vehicles, but in fact, V2LC can be applied đèn giao thông LED, vùng truyền thông. on both inter-vehicle and roadside-vehicle communications. The traffic regime is mostly ignored by Le Tung Hoa received B.E. from assumption of low-density traffic which always enables Posts and Telecommunications LOS channel. Therefore, researchers can develope the Institute of Technology (PTIT), research to fulfill the real traffic situation. Vietnam, in 2007, and M.E. degree from University of Electro- REFERENCES communication, Japan, in 2010, both in telecommunication engineering. [1] Alin-Mihai Cawilean and Mihai Dimian, Now, she is a lecturer at Faculty “Current Challenges for Visible Light Communications Us age in Vehicle Applications: A Survey,” IEEE Telecommunication 1 of PTIT. Her Communications Surveys & Tutorials, Vol. 19 , Issue: 4 , research interests include wireless communications, pp. 2681 - 2703, Fourthquarter 2017. VANET, Vehicular VLC and cognitive radio. [2] S. Kitano, S. Haruyama and M. Nakagawa, “LED road illumination communication system,” in 2003 IEEE 58th Dang The Ngoc received the B.E. Vehicular Technology Conference. VTC 2003-Fall, 2003. degree from the Hanoi University of [3] M. Akanegawa, Y. Tanaka and M. Nakagawa, “Basic study Science and Technology, Hanoi, on traffic information system using LED traffic lights,” Vietnam in 1999, and the M.E. IEEE Transactions on Intelligent Transportation Systems, degree from the Posts and Vol. 2, Issue: 4, pp. 197- 203, Dec. 2001. [4] Vima Gupta and Rahul Singhal, “Performance analysis of a Telecommunications Institute of visible light vehicle-to-vehicle wireless communication Technology (PTIT), Hanoi, Vietnam system,” 2019 TEQIP III Sponsored International in 2005, both in electronics and Conference on Microwave Integrated Circuits, Photonics telecommunications; and received and Wireless Networks (IMICPW), May 2019. the Ph.D. degree in computer science and engineering [5] Pengfei Luo, Zabih Ghassemlooy, Hoa Le Minh, Edward from the University of Aizu, Aizu-wakamatsu, Japan in Bentley, Andrew Burton and Xuan Tang, “Fundamental 2010. He is currently an Associate Professor/Head with analysis the Department of Wireless Communications at PTIT. He of a car to car visible light communication system,” 2014 was also an invited/visiting researcher at FOTON- 9th International Symposium on Communication Systems, Networks & Digital Sign (CSNDSP), July 2014. ENSSAT Lab., Universite de Rennes 1, France, in 2011 [6] J.M. Kahn and J.R. Barry, “Wireless infrared and Computer Communications Lab., The University of communications,” Proceedings of the IEEE, Vol. 85, Issue: Aizu, Japan in 2012, 2013, 2015, and 2017. His current 2, pp. 265-298, Feb. 1997. research interests include the area of communication [7] Taniya Shafique, Osama Amin, Mohamed Abdallah, Imran theory with a particular emphasis on modeling, design, Shafique Ansari, Mohamed-Slim Alouini and Khalid and performance evaluation of optical CDMA, RoF/FSO, Qaraqe, “Performance Analysis of Single-Photon optical wireless communication, and QKD systems. He is Avalanche Diode Underwater VLC System Using ARQ,” a member of IEEE. IEEE Photonics Journal, Vol. 9, Issue: 5, Oct. 2017. 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