Implementation of Speech Simplex Communication using Visible Light Lita Lidyawati Lucia Jambola Electrical Engineering Electrical Engineering National Institute of Technology National Institute of Technology Bandung, Indonesia Bandung, Indonesia [email protected] [email protected] Arsyad Ramadhan Darlis Electrical Engineering National Institute of Technology Bandung, Indonesia [email protected] Abstract—The visible light used by many humans as lighting wavelength. Therefore, if the infrared can be used in data only. However, in some studies have been shown that visible light communication, the same thing is likely to do with using can be used also for other needs that the communication system. visible light. Visible Light Communication (VLC) using white Light Emitting Diode (LED) is a promising technology for next generation communication for short range and high speed wireless transmission. In this paper, implementation of speech simplex communication using visible light is presented. Speech simplex communication using visible light needed in area where communication cannot be done easily using a technology that uses electromagnetic waves. Inexpensive transmitter and receiver of VLC system is designed and its performance is evaluated. Performance analysis is done with respect to color filter, photo sensitivity of photodiode at the receiver and the increase in distance between the transmitter and receiver. The result shows the system can receiving signal in speech frequency between 300 Hz until 3400 Hz. Test by transmitting the signal at a fixed distance results the voltage of the signal has increased almost two times that of the input signal, with the strengthening of 1.66 times. Experimental results show that the data transmission Fig. 1. Frequency Spectrum distance achieved up to 2,3 m and pair of red color filter mounted The communication system with light media has huge on the transmitter and the red color filter in the receiver has a potential in replacing the wireless media. This is due to human voltage received relatively good compared with most other colors. beings will not be able to work and live without their lights so that mobility and very high levels of efficiency. The Keywords— visible light communication, light emitting diode, technology utilizes visible light in a communication system photodiode, color filter pair called Visible Light Communication (VLC). I. INTRODUCTION VLC is standaridized by the Institute of Electrical and Electronics Engineers (IEEE) [5]. Visible Light Visible light is electromagnetic radiation that is visible to Communication Consortium, Japan carried out an initial the normal human eye with a wavelength of 380 to 780 nm. research on Visible Light Communication. Now Asia, Europe, Infrared is electromagnetic radiation with wavelengths longer Wireless World Research Forum are also working in VLC than visible light, but shorter than radio wave radiation. This research. infrared has a wavelength between 1 µm to 700 mm. This technology will be very useful to remember that in Visible light produced by lighting lamps have the same place - a particular place, communication cannot be done easily properties as the infrared. Today, the visible light used by using a technology that uses electromagnetic waves, for humans for lighting, both indoors and outdoors. This is due to example in water, tunnel or in a place that cannot receive both an electromagnetic radiation, just has a different electromagnetic waves (blank spot). In addition, in these places, conversation (speech) between people simultaneously (full duplex) using cellular technology cannot do. Full Duplex communication system is a form of communication between two parties which transmit and receive information at the same time. In this paper, we are only examining speech simplex communication using Visible Light Communication. II. SYSTEM DESIGN OF SPEECH SIMPLEX COMMUNICATION USING VISIBLE LIGHT COMMUNICATION VLC system consists of: (a) transmitter using white LEDs as a light source, (b) free space (air) as the transmission medium, and (c) photodiode at the receivers. VLC communication has the advantages of bandwidth, low power consumption, visibility, free from Electro Magnetic Interference and radiation hazards. Fig. 2 shows the block diagram of the proposed VLC system. Fig. 4. Schematic design of VLC Receiver C. Integration of VLC Transmitter and Receiver Circuit Fig. 2. Block Diagram of speech simplex Visible Light Communication A. VLC Transmitter In this work, the input frequency of 2 kHz and voltage of 5 V is given using signal generator. Light emitting source is of phosphor based White LED of 1 Watt with the viewing angle as 180. Fig. 3 shows the schematic circuits design of the proposed VLC Transmitter. Fig. 5. Integration of VLC Transmitter and Receive Circuit III. EXPERIMENT AND RESULT Performance is measured from the output system that includes some testings. A. Tests by transmitting a signal at a fixed distance Fig. 6. Block Diagram Testing VLC system with the source of signal generator and a distance of 50 cm Figure-6 shows the test block of the system that has been Fig. 3. Schematic design of VLC Transmitter implemented. In this test signal generator generates a signal sinusoid with a frequency of 20 Hz to 20,000 Hz which is a B. VLC Receiver frequency signal that can be heard by humans. The distance In general, the receiving circuit consisting of a series of between the transmitter and the receiver made fixed by 50 cm. photo sensor (photo diode), amplifier circuit, and signal The ouput of the system is measured by the oscilloscope are conditioner shows in Fig. 4. compared with the characteristics of the input signal. The test condition can be seen in Fig. 7. frequency is the frequency of the signal that can be heard by humans. Meanwhile, if the frequency conversation (speech) has a magnitude of 300 up to 3400 Hz, so if the first test is to have good results, it means that the sound signal in the form of a conversation (speech) has a good performance. From the test results are obtained that signals can be passed to the system at a frequency of 20 Hz to 20000 Hz with the average gain was 1.41 times. This can be interpreted speech signal (300 - 3400 Hz) can be passed using this system as well. Fig.7. System Testing Condition B. Tests by transmitting a signal at a changing distance Fig. 8 shows the input and output signals are measured with an oscilloscope system. Fig. 10. Block Diagram Testing VLC System with the source of the function generator and within a changing distance Fig. 8. Input (top) and output (bottom) Signal Fig. 10 shows the block of the second testing of the system The signal output system (bottom) experiencing a phase has been implemented. This test is similar to the first test, but shift of 180 degrees of the input signal (top). This is caused by with a changing distance until the signal cannot be received the influence of the channel transmission system is used. The by the Rx on a system that has been implemented. The results phase shift can be addressed by a series of phase shifter (phase of these tests can be seen in Fig. 11 below: shifter) to restore the output signal to a form which should be the same as the input signal. Nevertheless, designed and implemented a system that has worked well as evidenced by the frequency of the input signal is the same as the frequency of the output signal of the system. The voltage of the signal has increased almost two times that of the input signal, with the strengthening of 1.66 time where the sample images shown in Fig. 8. The strengthening of each signal is different in each measurement and the frequency of the input signal. This is caused by environmental and measurement conditions change at any time. Results of tests performed on the system by making the input signal has a changing frequency is shown in Fig. 9. Fig. 11. Comparison chart system based on the output changing voltage range The greater the distance between the light source or LED with receiver circuit voltage reduction occurs this proves that the greater the distance, the smaller the signal received by a receiver capable. The maximum distance that has been able to be tested by the system is 2.3 m. Distance is limited due to the need to carry on a conversation between two people about less than 2 meters. Therefore, testing is only done at a distance only. C. Tests by transmitting a signal that is using a color filter (Red to color) Fig. 9. Comparison chart the frequency of the output signal to the output In this third test, the transmitter and receiver on the system voltage system with a fixed distance will use a color filter on each side. This test was conducted to In this test signal generator generates a signal sinusoid with analyze a couple of colors to match the performance yielding a 5 V and a frequency changed from 20 Hz to 20,000 Hz. The pair of color is best. Block diagram of the test is shown in Fig. 12. Fig. 12. Block Diagram Testing VLC system using color filters The information signal generated from the signal generator Fig. 14. Graph output voltage system with a red filter on the transmitter with a frequency of conversations (300 Hz to 3400 Hz) with a voltage of 5 volts. In this test the red color filter used at the The frequency of speech signal is similar to audio transmitter and multiple colors on a receiver. Table 1 shows frequency and the system should transmit and receive the the position of the color filter. signal with a good performance. The performance represented by the received voltage. Seen in Fig. 14, that the voltage Table I.