VLC

Outdoor Visible Light Communication For Inter-Vehicle Communication Using Controller AreaNetworkDeok-Rae Kim, Se-Hoon Yang, Hyun-Seung Kim, Yong-Hwan Son and Sang-Kook HanDept. of Electrical and Electronics EngineeringYonsei University Seoul, South Korea lantiz@yonsei.ac.krAbstract —In this paper, we implemented the outdoor Visible Light Communication (VLC) system based on Controller Area Network (CAN) which is normally used in a car, plane, ship, product line control system, medical device and industrial device. For vehicle to vehicle (V2V) or indoor vehicle communication, we used common use device such as head light and back light. We made an application circuit and explained the principle. Also, we found an outdoor VLC problem which is sun light noise and photo detector (PD) saturation problem. Circuit's pulse features were demonstrated by signal. Total communication distance was 20 m in the daytime outdoor condition and its experimental transmission performance is presentedKeywords-component; VLC; CAN, Vehicle communication; Sunlight noise; PD saturationI.I NTRODUCTIONLight Emitting Diode (LED)’s price has been dropped and has been improved luminous efficiency rapidly. Special lighting market and general light market has been extended. Especially, LED has in compact size, longevity, and low power consumption.[1] And also nowadays many new application in which combine LED light and communication are developing.[2][3][4]. Thus, many countries which are South Korea, the United States, Japan, Europe, etc. recognize the benefit of LED. VLC is the communication method using LED. It uses a visible wavelength (380～780 nm). So VLC can use a communication and lamp simultaneously. [5][6] Recently car’s head light, back light, indoor light, directional light, and etc. are installed by high power LED. And these days V2V communication using VLC LED has not been started yet. So when we use VLC in vehicle, Intelligent Transportation System (ITS), drivers should be more convenience and get more driving safety than before.[7]Here, we investigated that the outdoor main issue which is sun light noise, PD saturation problem, the method of improving distance and etc. So we made filter design, optical design and effective signal correction circuit for our transmitter, receiver module. We performed simulation and experiment about outdoor VLC using CAN. In hardware, to transmit CAN signal, we made CAN transceiver and application circuit. Afterthat we installed this device to common use device such as head and rear light. And then we tried to communicate between transmitter and receiver module. For communication, we choose an ON-OFF Keying modulation format and 500 kBaud transmission rate. Total communication distance was 20 m in the daytime outdoor condition and its transmission performance less than Q-factor of 10 has been verified.Figure 1. Concept of vehicle VLC using CANII. SYSTEM CONFIGURATIONA. Concept of vehicle VLC communicationThe concept of experiment is shown in Figure 1. Almost every car’s control signals are made by CAN such as a light, engine control, air bag control, car speed, engine RPM signal and etc. Thus, if drivers receive a CAN signal, they can get information of near vehicle. For example, drivers can know how fast near vehicle, which direction they want to go, even they get some simple text message from other driver. So drivers should be more convenience and get more safety driving. As you can see in Figure1, head and rear LED light of center car transmits signal to near car’s receiver module. Transmitted signal is received from receiver module. And it signal is processed by processing module. That processed signal is sent to display panel or dash board for driver.B.Circuit configuration and applicationFor experiment, we made transmitter and receiver. It is shown in Figure 2, 3. We used a commercial head and rear light. On the right side is transmitter part and on the left side is receiver part. To generate a digital signal, we used CAN signal generation device (PEAK, NI). It generates CAN low (1.5V~2.5V) and CAN high (2.5V~3.5V) signal. These signals are changed by CAN transceiver. And CAN transceiver make differential signal using CAN high and CAN low signal. As we know, LED can modulate digital signal ‘1’,’0’. When current is supplied LED, it modulate digital signal ‘1’ and current isn’t supplied LED, it modulate digital signal ‘0’.In our transmitter, when digital signal ‘1’ of transceiver was passed to switch IC, switch IC was changed open state and at the same time LED was off. In another case, LED was on. We already said that VLC can use a communication and lamp simultaneously. This is the reason why we used this way. In our receiver, PD detected the luminance change. At this time, PD converted photon to current. This current was passed to Transimpedance Amp (TIA). TIA converted current to voltage. Because almost every ICs are voltage driving. After that, we used limiting amplifier. Because the received signal power was changed by distance, light power and input current power.limiting amplifier had a constant output value regardless of input signal power (V PP). This means when received signal was high, it was decreased by limiting amplifier. In another case, when received signal was low, received signal was increased by limiting amplifier. So it maintains almost the same value. This output of limiting amplifier was passed to bias control circuit. For using CAN transceiver, we used bias control circuit. This circuit controlled input DC level of CAN transceiver. CAN transceiver can divide into CAN high and CAN low signal. We detected this CAN signal using Digital Phosphor Oscilloscope (DPO). It can measure Q-Factor. Thus, we can get a reliability of our system.Figure 2. Transmitter circuit design and transmitted signalFigure 3. Receiver circuit design and received signalIII.O UTDOOR VLC ISSUES AND OVERCOMEA.PD saturationVLC generally uses the Intensity Modulated Direct Detection (IM/DD). However, it causes PD saturation problem in the day time outdoor condition. To overcome this saturation problem, we used a light shield and filter. In case of our experimental setup, sun light luminance was tens of thousands of lux. However, LED generates just tens of lux. In addition to, PD is working properly in LED luminance area. So, if PD wants to detect the LED light signal in the daytime outdoor condition, PD operates in saturation area. In this case, the LED light signal is too hard to detect. To overcome sun light noise and PD saturation, we tried to experimental confirmation which is shown in Figure 4. The transmitted signal which is a 500 KHz frequency carrier was generated by signal generator. And this signal was received and analyzed by RF spectrum device.In Figure 4, (A) was an outdoor experimental enviroment.(B) was a receiver part shape using light shield. (C) was RF spectrum view when receiver part used only RED filter. (D) was RF spectrum view when receiver nonused of light shield and filter. (E) was RF spectrum view when receiver used only a light shield. (F) was RF spectrum view when receiver used a light shield and RED filter. In case of (C), measured RF power was a –87.61 dBm at 500 KHz. And measured RF power of (D) was a –85.47 dBm. It’s almost similar. However, in case of (E), we saw significant improvements of RF power. Measured RF power of (E) was a –24.20 dBm. Because of (E) case using light shield. Final case of (F), It used a light shield and RED filter. Measured RF power of (F) was almost the same as (E), however, overall sun light noise is reduced. So case of (E) had higher Carrier to Noise Ratio better than other cases. We could see a reduced sun light noise and Carrier to Noise Ratioimproving. So, when we use the light shield and filter, we could reduce the outdoor sunlight noise. Thus, we applied this experimental result to our transmitter and receiver.Figure 4.Outdoor communication channel environment analysisFigure 5. Optical lens design for improving distanceB.Transmit distanceEven though we solve many outdoor VLC problems, if thesignal doesn’t reach the receiver, this signal couldn’t recognize.To solve this recognize problem, we tried to design an opticallens. So we designed transmitter and receiver’s optical lenswhich is shown in Figure 5. In case of transmitter lens which isshown in Figure 5’s (A), (B) was attached in head oftransmitter. And to find a proper lens position for receiver, wetried to change distance between lens and PD. This experimentis shown in Figure 5’s (E), (F). After that we applied this lensdesign to our transmitter and receiver module which is shownin Figure 5’s (C), (D). Because of this lens design, weimproved communication distance to 20 m in the daytimeoutdoor situation.Figure 6. Outdoor VLC experimental setupIV.T HE EXPERIMENTAL SETUP AND ANALYSIS OF RESULTSA.The experimental setupFigure 6 is my outdoor VLC experimental setup. It was inthe daytime outdoor condition. Direct sun light luminance wasalmost 20000 lux. The other case of sun light was about 3000lux. CAN signal was generated from CAN signal generationdevices (PEAK, NI). These devices were connected tocomputer using USB. Transmitter module was supplied by18~20 voltage. And 245mA was applied to LED from switchIC output. Receiver module was supplied by 5V and biascontrol voltage was 1.4V at that time driving current was260mA. Transmitter and receiver height was 20 cm from theground. And communication distance was 20 m betweentransmitter and receiver.B.Measure of changing performance according toexperimantal setupFor performance evaluation, we tried to measure of oursystem. Transmitter was fixed in our experimental setup. Andwe changed distance between transmitter and receiver. Wechecked four cases. First, we used head light module with lensand second, head light module without lens and third, rear lightmodule with lens and last, rear light module without lens.Performance evaluation was measured by Q-Factor of DPOdevice. We got a different performance from our experimental cases. It is shown in Figure 7. In case of head light and back light with lens, its transmission performance has been verified Q-factor of 10 in 20 m. Q-factor of 6 is almost the same as BER 10-9.[8] In case of head light and back light without lens, it transmission performance has been verified Q-factorFigure 7. Changing performance according to experimental setupV.C ONCLUSIONIn summary, we implemented the Visible Light Communication system based on CAN communication which is usually used in a car, plane, ship, product line control system, medical device and industrial device. And we also investigated the outdoor VLC issues which are sun light noise, PD saturation and the method of improving distance. To solve these issues, we applied optical filter and lens design to our transmitter and receiver module. It was made by commercial head and rear light. For effective signal correction, we made a application circuit and we combined this application circuit and CAN devices. As a result, total communication distance was 20 m in the daytime outdoor condition and its system performance has been verified Q-factor of 6 which is the same as BER 10-9. From this research, we investigated the possibility of integration between CAN and outdoor VLC. So we are expecting to contribute to the research of ITS and outdoor VLC.A CKNOWLEDGMENTThis work has been supported by the Broadcasting-Communications R&D Program of Korea Communications Commission/Korea Communications Agency (No. 11911-01111) and the IT R&D program of MKE/KEIT [10035362, Development of Home Network Technology based on LED-ID].R EFERENCES[1]Gu. Y., N. Narendran, and J. P. Freyssinier, "White LED Performance",4th International Conference on Solid State Lighting, Proceedings of SPIE 5530, pp. 119-124, 2004.[2]Shogo Kitano, Shinichiro Haruyama and Masao Nakagawa, “LED RoadIllumination Communications System”, Vehicular Technology Conference, pp. 3346 – 3350, 2003. [3]Lubin Zeng; Hoa Le Minh; O'Brien, D.; Faulkner, G.; KyungwooLee; Daekwang Jung; YunJe Oh; , “Equalisation for high-speed Visible Light Communications using white-LEDs” , Communication Systems, Networks and Digital Signal Processing, 2008. 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