Abstract

Wireless communication transmits and delivers data wirelessly by utilising the behaviour of electromagnetic spectrum. Radiation is classified by the wavelength. The most commonly used radiation for wireless communication technology is radio waves, which has a long wavelength and is applicable for smart phone, etc.

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

However, Visible Light Communication (VLC) as a type of wireless communication using visible light has never been popular until the recently development of White Light Emitting Diode (LED). This technology differs from traditional lighting and while combines with existing technology and more research to be done on this area, it will give a promising result for high speed wireless data transmission. In addition, it also provides extra security to data transmission.

In my final year project, a VLC system will be designed and evaluated by its data transmitting accuracy. On the other hand, the reflection property on different surfaces will also be investigated and analysed with regards of data transmission.

Results will be obtained during the second semester.

 

 

Table of Contents
1.     List of Abbreviations and Formulas. 4
2.     Introduction. 5
2.1.     Background. 5
2.2.     Objectives. 5
2.3.     Report Outline. 5
2.4.     Comparison between VLC, IR and RF. 6
2.5.     LED Characteristics. 6
2.6.     Channel Configurations. 7
2.7.     Optical Interference Noise. 8
3.     Methodology. 9
3.1.     Circuit Design and Hardware. 9
3.1.1.      Microcontroller 9
3.1.2.      Transmitter 10
3.1.3.      Receiver 11
3.2.     Reflection Property. 12
4.     Conclusion. 12
5.     References. 14
 

 

1.   List of Abbreviations and Formulas

 

IR Infrared

LED Light Emitting Diode

LOS Line-of-sight

MOSFET Metal Oxide Semiconductor Field Effect Transistor

PCB Printed Circuit Board

RF Radio Frequency

VLC Visible Light Communication

 

2.   Introduction

2.1.         Background

Visible Light Communication (VLC) can be seen as existing technology with replace of the media as visible light radiation. Visible light has the wavelength between 380nm and 780nm, which is only a small portion of the electromagnetic spectrum. Though wireless communication has a long historical background, VLC was yet never possible due to the conventional light bulbs used in the past, such as compact fluorescent lamps and incandescent bulbs, etc. The development of LED has the characteristic of high switching frequencies which allows modulation of the light for data transmission of signal. This technology is expected to be developed into a LED for illumination as well as a data transmitter simultaneously.

Some examples of VLC include underwater communication, vehicle to vehicle communication, and also for defense and security. As visible light cannot be transmitted through walls and any types of blockage, it provides a great security advantage because data can only be transmitted between transmitter and receiver within the same room.

2.2.         Objectives

The first task of this project is to build a system, with the use of a transmitter and receiver, capable of sending and receiving data by visible light. The transmitter of LED as the communication media is controlled and driven by a microcontroller to send the signal, through a transmission medium, i.e. air, and will reach the receiver of photodiode for acceptance of the signal by another microcontroller.

It has been shown by G. Pang et al. (Pang, Ho, Kwan, & Yang, 1999) that VLC can be implemented in an audio system for the audio signal transmission with 77cm transmission distance without a 50mm focusing lens. A system with similar specification will be built in my project and details of the hardware are more of the focus.

Therefore, with a reliable system, the main goal of this project is on the reflection property of VLC. Different surfaces will be investigated with respect to the link property of the two devices.

2.3.         Report Outline

In this report, the basic concepts involved in this project is discussed in the introduction, with the support by some background information of the comparison between VLC, infrared and radio frequency communication, LED characteristics, channel configuration, optical interference noise

The design mechanism of hardware, as well as the reflection method are mentioned in methodology. Experimental results with measurement parameters will be included in the final report. The conclusion of this mid-term report is a simple review of future work to be done.

 

2.4.         Comparison between VLC, IR and RF

It is useful to compare some specifications between VLC and the current existing wireless communication technologies (infrared and radio frequency) for a better understanding.

 

VLC

IR

RF

Carrier wavelength

380-780nm visible light
(multiple wavelength)

850nm infrared

1mm to 100 km radio wave

Distance

Short

Short to long (outdoor)

Short to long (outdoor)

Line of sight

Yes

Yes

No

Services

Illumination + communication

Communication

Communication

Noise sources

Sun light, ambient lights

Sun light, ambient lights containing IR

All electrical / electronic appliances

Standards

In progress (IEEE)

Standardization (IrDA)

Matured

Security

Good

Good

Poor

Hazard

No
Daily usage, eye safe (visible)

No
Eye safe for low power (invisible)

Yes

Application

Indoor, vehicle to vehicle communication

Remote control

Mobile communication, broadcasting

 

2.5.         LED Characteristics

LED has been proven to have many advantages in comparison with the conventional light bulbs, such as high energy efficiency, extended lifespan, compatibility with controls, etc. As mentioned previously, the use of LED is due to its ability to act as the lighting device and also the data transmission media.

The first property of visible light that is worth paying attention to is that it cannot penetrate through objects. This means that walls, ceilings and floors will block light from passing through and the signal cannot be transmitted. Therefore, the transmitter and receiver have to be placed in the same room. There are a few types of channel configurations that can be explained later on.

The second property and also the most important property that makes VLC possible is its switching properties. LED are able to be switched on and off according to the logic levels high and low at high frequency. Data can therefore be modulated and transmitted without being sensed by human eyes. It is shown that human eyes can detect flickering of visual images at 500Hz. (Davis, Hsieh, & Lee, 2015)

 

2.6.         Channel Configurations

Directed Line-of-sight (LOS) link

Non-directed LOS link

Directed non-LOS link

Non-directed non-LOS link

(Ramirez-Iniguez, Idrus, & Sun, 2008, April 3)

The four basic types of configuration are shown in above. Directed and non-directed of source refers to the direction of the transmitter and receiver. As LED is an illumination source with a diffusion property, it is considered to be a non-directed source unless a focusing lens is used. LOS and non-LOS of source is determined by whether a barrier exists between the transmitter and receiver. This also means that reflection is needed for non-LOS data transmission.

In this project, non-directed LOS link is considered for testing of a reliable VLC system and non-directed non-LOS link is investigated for surface reflection property.

2.7.         Optical Interference Noise

This figure above shows the experimental set-up of the investigation of optical interference noise conducted by T. Adiono et al. (Adiono & Fuada, 2017) The results show that fluorescent and incandescent lamps emit both DC signal and interference signal as ambient light at the noise frequency of 100 – 150 Hz, while the decrease of distance between the LED lamp and the receiver will create a larger DC offset voltage.

It is not easy to filter out all of the ambient light during the experiment. Therefore, it is important to identify all of the possible ambient light and take measures into account.

3.   Methodology

 

Block diagram of the VLC system

3.1.         Circuit Design and Hardware

3.1.1.     Microcontroller

A microcontroller acts as a small and less sophisticated computer in a system or device. It has the processor cores (CPUs), memory, and input/output pins. It is usually used for applications with automatic controls programed and embedded. The parameters of choosing a microcontroller includes the operating frequency and programming environments.

Two separated Arduino DUE boards are used as the microcontrollers of both transmitter and receiver. The operating frequency also known as the clock speed is 84MHz. The higher the clock speed, the faster and more instructions can be executed per second. Arduino DUE also supports this high-level programming language C++.

A great detail to pay attention to when using an Arduino DUE board is its operating voltage of 3.3V. This means that the output voltage from the circuit towards the I/O pins cannot exceed this maximum voltage, or else it will damage the board. 

 

3.1.2.     Transmitter

In the transmitter circuit, it consists of the LEDs, the MOSFET and the Arduino DUE.

In consideration of the LED, the relative spectral emission range is taken into account to be compared with the relative spectral sensitivity of photodiode of the receiver. As the peak of the relative spectral emission range of this LED LCW W5SM is around 580nm, a suitable photodiode SFH 2701 is chosen with its relative spectral sensitivity range covering the emission range of the LED. The most ideal LED and photodiode pair is where the peaks overlap. The graphs show below is taken from the data sheets.

 
 
 
 

Relative spectral emission range

Relative spectral sensitivity

 

The MOSFET drives the LED on and off by high frequency switching. 2N7000 is chosen with the consideration of the following parameters, VGS(on) and the turn-on and off delay time. The former has the value of maximum 3.0V. This value has to be lower than 3.3V, which is the output voltage of the I/O pins of the Arduino DUE that can tolerate. The latter has the value of 10ns. This affects the frequency of LED and therefore, should aim for a shortest time possible.

The value of Vdd depends on the number of LEDs used during the project. The general addition formula of it is Vdd = (VLED (on) x number of LEDs) + VDS(on). VLED(on) has the value of maximum 3.2V forward voltage and VDS (on) is 2.5V. This value gives the control of brightness, yet it should not over load the LEDs or else they will be damaged.

3.1.3.     Receiver

In receiver circuit, it consists of the photodiodes, the operational amplifier and the Arduino DUE.

As mentioned in the transmitter part, the photodiode is chosen according to the relative spectral emission range of LED and the relative spectral sensitivity of photodiode. It has to have fast response with respect to the brightness. It also has a rise and fall time of around 2ns.

The Op-amp chosen is OPA380. It responds to small changes of current generated by the photodiodes and converts it to digital signal. There are a few factors followed by the configuration of OPA380 according to the data sheet. Firstly, a 1u bypass capacitor is used for electrical noise filtering. Seconding, with the Cdiode of 3pF from the photodiode, the resistor and capacitor values are chosen accordingly to the transimpedance amp characteristic graph shown below. It shows the relationship between the transimpedance gain and frequency. The higher the frequency, the fast the data transmission. While the greater transimpedance gain is always desirable. However, it is not possible to have both high frequency as well as high transimpedance gain at the same time in the circuit, therefore, a balance is needed to be obtained by taking the middle value and the most suitable ranges for the project design. Thirdly, V(bias) is achieved due to the presence of ambient light. The main light source that is desired to be detect by op-amp is only the transmitter LED, yet it is impossible for the photodiode to do the work of differentiating the two light sources. It is essential for the op-amp to do the adjustment, as a result a potentiometer is inserted.

3.2.         Reflection Property

Previously LOS link configuration is described. However, in the real indoor environment, reflections of light can be experienced from multiple paths. Comparison of different reflectors between the power spectral distribution (PSD) and the spectral reflectance against wavelength is shown as below for reference (Lee, Park, & Barry, 2011). PSD is the radiant power per unit wavelength and the spectral reflectance is the reflectivity. It indicates that different reflectors with different properties will give the distinct spectral reflectance. The properties include colours, texture and patterns.

4.   Conclusion

In this first semester, most hardware design has been done, including the choice of components and the PCB drawings. However, more about the transmission methods and signal processing needs to be looked into, as well as the decision on the parameters for the data taking is yet to be made.

I am hoping to be able to complete a successful research on this topic in the near future.

5.   References
Adiono, T., & Fuada, S. (2017, December 4-7). Investigation of Optical Interference Noise Characteristics in Visible Light Communication System. 2017 Interational Symposium on Nonlinear Theory and Its Applications.
Davis, J., Hsieh, Y.-H., & Lee, H.-C. (2015, February 3). Humans perceive flicker artifacts at 500 Hz. Sci Rep, 5(7861). doi:10.1038/srep07861
Lee, K., Park, H., & Barry, J. (2011). Indoor Channel Characteristics for Visible Light Communication. IEEE Communications Letters, 15, 217-219.
Pang, G., Ho, K.-L., Kwan, T., & Yang, E. (1999, November). Visible Light Communication For Audio Systems. IEEE Transactions on Consumer Electronics, 45(4).
Ramirez-Iniguez, R., Idrus, S., & Sun, Z. (2008, April 3). Optical Wireless Communications: IR for Wireless Connectivity. Auerbach Publications.
 

 

Author