Research On Omni-directional Visible Light Communication Transceiver And Channel Characteristics

As the development of solid state lighting,LED is playing a more important role in indoor illumination.LED is replacing the traditional incandescent and fluorescent light sources.LED has a lot of advantages such as long life expectancy,high tolerance to humidity,low power consumption,and minimal heat generation lighting.With the extensive use of LED,Visible Light Communication(VLC)using LED as the transmitter has been studied well.VLC was firstly employed to achieve indoor communication while providing enough illumination.As research continues,VLC under many other application contexts has been researched,such as secret service,hospital,industrial control,which are sensitive to RF.VLC can also be applied in Underwater Communication and Underground Communication.In such applications,communication devices are assembled on operation staffs or machines which have high mobility,therefore VLC is supposed to be an omnidirectional duplex Communication.To achieve the mobility and Omni-direction,this paper measures and analyses the channel characteristic of VLC and proposes a Omni-directional VLC(OVLC)model according to the channel characteristic and the property of VLC.On this basis,this article makes innovation which mainly includes two items:·propose a OVLC system applying Adaptive Noise Cancelling(ANC)to eliminate the noise and interference.ANC is a technology which can restore the interfered signal.The major method is to extract reference signal which is related to the interference,and achieve cancelling through minus the interference with the reference after adjusting the reference.The extraction of the reference is achieved by utilizing the difference between the isotropy of the interference and the directivity of the transmission signal.The experiment result shows that ANC has a well cancelling performance while dealing with the interference caused by uniform background light sources and local transmitter in OVLC.·propose a OLVC Time-Space Division Multiplex(TSDM)model based on L+R-Pulse Position Modulation(L+R-PPM),aiming at improving the effective transmission distance while keep a low transmission power.The SDM based on L+R-PPM eliminates the interference of multi overlap signal through adding recognition bits.In many application scenes of OVLC,the transmission distance is supposed to be long enough.In this system,the diffuse of the light is the main factor that influence the transmission distance.Through assembling optical lens the distance can be enlarged,but the transmission angel will be reduced.Thus more LEDs are needed to achieve Omni-directional communication.Moreover,more LEDs means more transmission power which is hard to obtain in portable device.In the TSDM model based on L+R-PPM,LEDs are divided into different LED sets in terms of different illumination positon.Different LED transmits signal in different time slots.By empowering LEDs in different time slots,the total power keeps in low level.On this basis,this paper discusses the dimming,switch-over,multiplex problems in this model,then gives the solution to the problems.