Feasibility Tests for Visible Light Communication Scheme with Various LEDs

Transcription

1 Feasibility Tests for Visible Light Communication Scheme with Various LEDs Dongsung Kim, Hoyeon Jung, Chungjo Yu, Dongjun Seo, Biao Zhou, Youngok Kim Department of Electronics Engineering, Kwangwoon University, Korea Abstract. In recent years, Visible Light Communication (VLC) has attracted amounts of researches as for energy conservation and new paradigm in the field of communication. In this paper, VLC scheme is considered for an advanced parking information system and its feasibility of implementation is simply evaluated with LEDs. According to experimental results, blue 10 Pie LED is considered as appropriate for our scheme due to its cost effectiveness as well as performance. Keyword: VLC, LED, Parking information system 1 Introduction There are many researches that focus on VLC with LED [1-3]. Current researches have more weight to communication theory or strong points of LEDs, but the practical application of VLC technique in real life or, making conception for new goods on the basis of VLC technique is still uncultivated although it can provide plentiful economic benefits. An example is parking information system. Until now, various parking information systems are introduced [4-5]. All of them are based on conventional radio communication system, which need specific industry standard. However, the VLC technique can be applied for parking information system by replacing the existing illuminating devices with the VLC devices, which can illuminate and communicate simultaneously. In this paper, the concept of VLC scheme with LEDs is briefly discussed and its feasibility for parking information system is evaluated with simple experiments. The rests of the paper are organized as follows. In Section 2, a system description is briefly provided. In Section 3, the experimental results are presented and discussed. Finally, our concluding remarks are summarized in Section 4. 2 System Description During the process of sending information, LEDs constantly turn on and off swiftly depending on data signal. The speed of LED switch can achieve as fast as AICT 2013, ASTL Vol. 26, pp , 2013 SERSC

2 Proceedings, The 1st International Conference on Advanced Information and Computer Technology nanoseconds. However, the eyes of human cannot recognize LED twinkle when the frequency reaches 100Hz, while the need of illumination can be fully satisfied because of the persistence of vision. Fig. 1 shows a simple block diagram of the VLC scheme with LEDs. As shown in the figure, the source date is modulated into digital baseband signal and sent through the visible light modulation with LEDs. At the receive side, photodiodes are integrated as a photo detector as well as demodulator in LED communication scheme, which is capable of converting light into electric signal. The signal attenuation in VLC scheme with LEDs is an urgent issue, and thus the electric signal is amplified before demodulation. In this proposed VLC scheme, operational amplifier is applied as a core of controllable amplifying circuit. The amplified electric signal is converted to digital baseband signal by the comparator. After digital baseband demodulation, the acquired bits are transferred from microcontroller to computer through serial communication. Fig. 1 VLC scheme with LEDs 2.1 Hardware description The receiver circuit (RC) is shown in Fig. 2. The proposed RC consists of three parts: photo detection part, amplifier part, and comparator part. Photo diode, BPV10, is used as a photo detector. It detects modulated signal in the form of visible light and generates current depend on intensity of light. It has average scale of μa and it is too small for demodulating process as received signal. Therefore we connect an equivalent resistance of some resistors by series connection. As a result, we can detect light signal as electrical signal of voltage and it is located in big scale enough to demodulate after amplifying process. As mentioned previously, we obtained very faint source voltage by very faint induced current. So we have to make huge voltage gain for practical use of system which has the communication range above 2 meters, which is normal distance between the ceiling and the photo detector in the parking sites. Hence, we compose two series connected amplifiers which have the same elements and voltage gain. 207

3 Feasibility Tests for Visible Light Communication Scheme with Various LEDs Fig. 2 The receiver circuit consisting of three parts: photo detection, amplifier and comparator. For a comparator, a threshold is set to compare voltages. We can employ this voltage threshold for noise filtering and enhancing the output performance of receiving circuit. Meanwhile, the voltage comparison has influence on communicating range because it is related with distinguishing higher intensity of light and making saturated signal of light, which has lower intensity than former one. Therefore, we should choose suitable value of compare voltage according to received illumination intensity and value of noise. 2.2 Software description Generally, software consists three parts: the programming for demodulating the digital baseband signal, i.e., the output of RC to binary data and programming for serial communication between a micro-controller and a computer, which performs as a server for the parking information system. During the process of digital signal transceiving, channel coding can be adopted for ensuring the transmission quality, With error-correcting code (ECC) or forward error correction (FEC) code, it can be recovered by a receiver even when a number of errors, which is up to the capability of the code being used, were introduced. 3 Experimental Results During the process of experiment, we tested the light source with various types of LED and the fixed measure voltage threshold, which is according to resistor. The 208

4 Proceedings, The 1st International Conference on Advanced Information and Computer Technology induced voltages of various LEDs are summarized in Table 1. Table 1. Performance comparison of various LEDs Color LED Style Red Blue Yellow White Green Power LED 532 mv 563 mv 469 mv 514 mv 493 mv 10 PIE LED 352 mv 413 mv 312 mv 400 mv 390 mv As shown in the Table, the blue LED outperforms other colors of LEDs. Moreover, when we use power LED and 10 Pie LED as the transmitter, induced voltages on the resistor at the receiver are not significantly different, although the former one costs about 5~6 times than the later one. Therefore, we choose blue 10 Pie LED as the transmitter for testing. When the distance between transmitter and receiver is set as 15cm and the provided voltage on LED is 5V, we get the results presented in Table1. Obviously, it has a gap with practical implementation. Therefore, to mitigate this gap, we need greater voltage gain of in the RC as well as stronger illumination intensity at the transmitter. Table 2 shows the effective distance between transceivers as RC gains and the number of LEDs are increased. Since the distance in the practical implement is above 2 meters, it is convinced that the RC gain should be set at least above 400 and two LEDS are recommended. Table 2. Effective distance variation with different gains and number of LEDs No. of LEDs Gain cm 50cm 110cm 170cm 200cm 2 50cm 100cm 160cm 200cm 250cm 4 Conclusions and Future Works In this paper, VLC scheme for an advanced parking information system is considered and its feasibility of implementation is simply evaluated with LEDs. During the experiment progress, 10 PIE LED and power LED with various colors are 209

5 Feasibility Tests for Visible Light Communication Scheme with Various LEDs evaluated and it is revealed that blue 10 PIE LED is appropriate for our scheme due to its cost effectiveness as well as performance. According to the experimental results, the effective distance increase nonlinearly as the number of LEDs and voltage gains are increased. This paper is mainly focusing on theoretical basis of VLC with LEDs and a feasibility test for parking information system. For future works, we will evaluate the performance of our scheme by increasing the number of LEDs, while decreasing RC gains. We also expand the effective distance between transceivers up to 5 meters to confirm the possibility of the application in parking area system. In addition, the framework of parking information system based on the proposed VLC scheme will be designed and implemented. Acknowledgment. This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (NRF-2013R1A1A ). Reference 1. T. Komine, M. Nakagawa, Fundamental analysis for visible light communications using LED lights, IEEE transactions on Consumer Electronics, Vol. 50, Number1, pp , February T. Komine, M. Nakagawa, Integrated system of white LED visiblelight communication and power-line communication, IEEE Trans. Consumer Electron., vol. 49, no. 1, Feb F. J. Lopez Hernandez, E. Poves, R. Perez-Jimenez, and J. Rabadan, Lowcost diffuse wireless optical communication system based on white LED, 2006 IEEE Tent h International Symposium on Consumer Electronics (ISCE 06). 4. G. Yan, W. Yang, D. B. Rawat and S. Olariu, "Smart Parking: A Secure and Intell igent Parking System," in Intelligent Transportation Systems Magazine, IEEE, vol. 3, pp , M. F. Ismail, M. O. Reza, A. A. Rokoni, M. A. R. Sarkar, "Design and development of an advanced vehicle parking system", Informatics, Electronics & Vision (ICIEV), International Conference on, pp