visible light communication using rgb led for …...visible light communication (vlc) uses visible...

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 13, December 2018, pp. 951–958, Article ID: IJMET_09_13_100

Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=9&IType=13

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

VISIBLE LIGHT COMMUNICATION USING RGB

LED FOR MACHINE-TO-MACHINE

COMMUNICATION

Tae-Kook Kim

Department of Information and Communications Engineering, Tongmyong University, Busan,

Republic of Korea

ABSTRACT

Visible light communication (VLC) is a communication technology that sends digital

signals comprising “0” and “1.” VLC uses light emitting diodes (LEDs) for both lighting

and communication functions. This study aims to investigate the wavelength

characteristics in VLC using red, green, and blue (RGB) LEDs. Furthermore, a method

for transmitting and detecting RGB signals was proposed and verified. The proposed VLC

technology can be applied to machine-to-machine communication.

Keywords: Visible Light Communication (VLC), Machine to Machine (M2M), Light

Emitting Diode (LED), Near Field Communication (NFC).

Cite this Article: Tae-Kook Kim, Visible Light Communication Using Rgb Led for

Machine-to-Machine Communication, Journal of Mechanical Engineering and

Technology, 9(13), 2018, pp. 951–958

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=9&IType=13

1. INTRODUCTION

Visible light communication (VLC) uses visible light spectrum for transmitting information. In

VLC, an incandescent light bulb or a fluorescent lamp is replaced by a LED, which is a digital

semiconductor. The visible light spectrum is a region that is visible to the human eye with a

wavelength ranging between approximately 380 and 740 nm. The principle of VLC lays in

displaying digital signals “0” and “1” by blinking the LED that has an output wavelength in the

visible light spectrum. In this case, when the number of blinks per second is 100 or more, the

blinking of LED cannot be recognized by the human eye due to the limited perception of the

human optic nerve, allowing users to perceive that LED is continuously on, and thus, serving

both lighting and communication functions [1-5].

There are 2 types of LEDs that are used in VLC: RGB (Red, Green, Blue) LEDs that emit

white light by combining diodes that emit RGB lights and other LEDs that emit white light by

coating blue LED with a fluorescent agent. Among these LEDs, RGB LEDs have a higher

bandwidth [6], [7].

Tae-Kook Kim


Herein, a method for transmitting signals from RGB LEDs and detecting the respective RGB

signals at the receiver is proposed and verified. This method can be applied to machine-to-

machine (M2M) communication.

2. BACKGROUND

2.1. Visible light communication

VLC is a convergence technology of digital lighting and communication that employs LED,

which is a semiconductor device. The ON/OFF function of a LED can be digitally controlled,

allowing it to blink for several million times per second [1-5].

First, VLC functions as digital lighting. When the LED is turned on, it functions as a source

of light due to the emission of light. Furthermore, the brightness of the LED can be adjusted by

changing its ON/OFF cycle. Second, VLC functions the means of communication. “High” and

“low” signals can be transmitted through the ON/OFF function of the LED. The photodetector

detects the ON/OFF function of the LED and communication can be performed by detecting high

and low signals. If the ON/OFF signal of the LED changes to 100 times or more per second,

humans do not perceive the blinking of the LED, thus recognizing that the LED is continuously

on. Therefore, the LED performs the lighting and communication functions simultaneously [8],

[9].

Figure 1 shows the visible light spectrum. Since the spectrum belongs to the visible light

band, the LED can perform both lighting and communication functions [10].

Figure 1 Visible light spectrum

2.2. Machine-to-Machine communication

M2M communication means direct communication between devices using all communication

channels, including wired and wireless channels. M2M communication can transmit sensor data

and content data between the devices without passing through infrastructure such as a base station

[11-14].

There are various communication technologies for M2M communication. A typical example

is radio frequency (RF) communication. RF wave is an electromagnetic wave with a wavelength

ranging from 1 mm to 100 km, i.e., a frequency of 3 KHz–300 GHz. Table 1 compares the VLC

Visible Light Communication Using Rgb Led for Machine-to-Machine Communication


and RF communication. VLC has fewer compliance issues in comparison with RF

communication, as well as advantages in terms of security and electromagnetic hazards [15-18].

Table 1 Comparison between VLC and RF communication

Features VLC RF VLC advantages

Regulations on spectrum

assignment No Yes

No compatibility issues

between countries

Obstacle crossing by

signals Impossible Possible Secured

Electromagnetic hazards No Yes Ecofriendly technology

Multipath dispersion

phenomenon Yes Yes

Troubles in high speed

communication

3. VISIBLE LIGHT COMMUNICATION USING LED

Since LEDs that emit white light have a single channel, only 1 datum is transmitted at a time.

However, RGB LEDs can transmit 3 data at one time because RGB LEDs have 3 channels, i.e.,

red (R), green (G), and blue (B). In this case, if the widths of RGB channels are same during one

cycle, the colors of RGB are combined to emit white light. Herein, the wavelength band

characteristics of RGB LEDs were investigated, and a transmitter for transmitting signals

independent of RGB signals and a wavelength filter for detecting signals at the receiver were

proposed.

Figure 2 RGB signals at transmitter and receiver

3.1. Transmitter

As shown in Figure 2, the transmitter has the same widths for RGB signals during one cycle.

Thus, LEDs function as lighting by emitting white color obtained by combining the RGB colors.

Subsequently, RGB channels transmit signals independently, and the transmission is performed

by avoiding any overlapping among RGB signals, as shown in Figure 2. Each signal in the T

Tae-Kook Kim


cycle can use Manchester coding or pulse position modulation techniques to represent “0” and

“1” signals.

3.2. Wavelength filter

RGB lights have different wavelengths. This study used IWS-S83D6-FC RGB LED

manufactured by ITSWELL to measure the wavelength. Typical RGB LEDs exhibit similar

wavelength band characteristics. ITSWELL RGB LED used in this experiment has a center

wavelength for red, green, and blue LEDs from 615 to 630 nm, 515 to 535 nm, and 455 to 475

nm, respectively, as shown in Figure 3. The filter transmits the light selectively according to the

wavelength. Thus, using a red filter that passes the red wavelength band can attenuate the green

and blue wavelengths and detect only red signal. Equation 1 represents the output voltage

according to the wavelength filter.

Vo = α VRED + β VGREEN + γ VBLUE (1)

Here, α, β, γ refer to the wavelength filter values. VRED, VGREEN, and VBLUE refer to the output

voltages of the RGB LEDs, respectively. If the red wavelength filter is used, α has a value close

to 1, and β and γ have values close to 0. This is because RGB colors have different wavelength

bands. Figure 4 shows an example of a wavelength filter.

Figure 3 RGB LED characteristics of ITSWELL product



Figure 4 Wavelength filter

3.3. Dimming Controls for Lighting

To control the brightness of the light, the brightness can be adjusted by changing the ratio of the

on time of the LED to its OFF time, i.e., the brightness of the lighting is controlled by fixing one

cycle, and adjusting the widths of RGB within a fixed cycle. Equation 2 shows the output voltage

according to the width of the RGB signals.

Vo = dRED·VRED + dGREEN·VGREEN + dBLUE·VBLUE (2)

Here, dRED refers to the on duration of the red LED. VRED, VGREEN, and VBLUE refer to the

output voltages of the RGB LEDs, respectively. If the ON duration of RGB LEDs is long, dRED,

dGREEN, and dBLUE values are close to 1 and the light is bright.

4. PERFORMANCE EVALUATION

The proposed method was verified by conducting experiments. For the performance evaluation,

a transmitter and a receiver were used, and the waveform was measured using an oscilloscope.

Figure 5 shows the implemented VLC transceiver. Furthermore, Table 2 shows lists the

component used. Figure 2 shows the transmitter using RGB LED. The transmitter (TX) in Figure

5 uses the RGB signals shown in Figure 2, where only R signal is visualized, and G and B signals

in TX are not shown in the figure. The receiver (RX) used to detect the signal is a Newport 818-

BB-22 Silicon PIN Detector. The transmitter and receiver were tested at a distance of 15 cm.

Figure 6 shows the signal detection of RGB lights. The RGB signals could be detected at the

receiver, and the RGB voltage values of RX were different because the intensities of the PIN

detector and RGB LED at the receiver are different. The intensity of the Newport 818-BB-22

Silicon PIN Detector used in this experiment is shown in Figure 3.

Table 2 Experimental environment

Features Description

Transmitter RGB LED

Receiver Newport 818-BB-22 Silicon PIN Detector

Distance between

transmitter and receiver 15 cm

Tae-Kook Kim


Figure 5 Implemented transceiver for VLC

Figure 6 Red, green, blue signal detection



Figure 7 Red signal detection using red wavelength filter

Figure 7 shows red signal detection using a wavelength filter. As shown in Figure 7, it can be

seen that green and blue signals were attenuated using the red filter, and only the red signal was

detected. This experiment confirmed that RGB signals can be separately detected using a

wavelength filter which passes these signals only when they have different wavelength bands at

specific wavelengths.

5. CONCLUSION

This study investigated the wavelength characteristics of RGB LEDs. Since RGB LEDs have

different wavelengths, a filter that passes only a specific wavelength can be used to detect a signal

in each wavelength band. Moreover, the data transmission rate can be enhanced using the

proposed transmission and reception method.

The proposed VLC using the RGB LED for the M2M communication can transmit 3 signals

simultaneously and can adjust the brightness of the light. In other words, the LED can perform

the functions of lighting, brightness control of light, and communication.

The proposed VLC can be applied to data transmission and content delivery in M2M

communication.

ACKNOWLEDGMENTS

This work was supported by the National Research Foundation of Korea(NRF) grant funded by

the Korea government(MSIP : Ministry of Science, ICT & Future Planning) (No.

2017R1C1B2011285).

Tae-Kook Kim


REFERENCES

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