Research And Implementation Of Near Field Communication Protocol Based On Visible Light

In recent years,with the rapid development of mobile networks,the mobile devices provide people with convenient communications.Near-field communication as one of short-range wireless communication technologies can be applied in several scenarios,such as the mobile payment,identification,advertising and other areas of information exchange.In nowadays networks,some state-of-the-art short-range communication technologies are adopted,such as Wi-Fi,Bluetooth,NFC communication.However,these wireless technologies need the broadcast of electromagnetic wave,which leads to the security issues,such as eavesdrop or intercept.For this,the visible light communication technology has been proposed as a promising solution to guarantee the communication security in recent years.Due to the directionality and fast attenuation of visible light communication,the unauthorized device is difficult to receive the signal from transmitter,and thus it can effectively avoid eavesdropping or intercepting.However,the existing visible light communication methods require special expensive hardware,such as Li-Fi which is a novel technology with high-speed wireless combination and need lighting equipment using special lighting-chip.Recently,visible light communication method has not been applied in smartphones or other mobile terminals.After studying the existing visible light communication methods,this thesis proposed a near-range field communication method based on the visible light using ordinary smart phone,and we also design a suitable protocol for improving performance of our method.In this method,we employ the camera and light sensor of smart phone as the receivers,and the phone screen and LED as transmitters.In this thesis,we first study the possibility of information transmission using LED and light sensor.Then,we design a State Transaction Modulation(STM)modulation of the visible modulation method.Comparing with OOK,PWM,PIM modulations,this method can effectively improve the signal transmission throughput with the same bit error rate(BER).Finally,we conduct as serial experiments,in order to test the influence of transmission rate,transmission distance and visible angle under three modulation methods.On the basis of realizing one-way communication,this thesis adopts the two-dimensional code method to complete reverse communication.Because the Quick Response(QR)coding scheme is simple and enough for ordinary information carrying,it is widely used in daily life.However,scanning this QR code displayed on the smart phone needs a certain background intensity.The existing approach is to maximize the screen brightness adjustment and energy-hungry.In this thesis,we propose an advanced QR coding method to adjust the brightness of the screen on demand to reduce the energy consumption.When the scanning smartphone can't get the two-dimensional code,it will send a control message to the display smartphone by visible light communication.Once the display smart phone receives the message,it will gradually adjust the background brightness of the display until the scanning smart phone can read QR code.Finally,we use off-the-shelf smart phone to design and implementation of a near-field communication system based on visible light.This system uses visible light as the information carrier and achieves the following functions:(1)Text transmission,identification and message verification;(2)A new method to achieve payment or unlocking;(3)It reducing the energy consumption of displaying code.At the same time,this paper explore probability of the visible light communication applied in the smart phone and other mobile terminals.