Study On The Uplink And Downlink Of Indoor Optical Wireless Communication Based On White LED

With the rise and rapid development of the LED(light emitting diode) industry,it is imperative that conventional lighting is to be replaced by semiconductor lighting.The advantages such as energy-saving,long life,high reliability and good modulation performance enalble the white LED to be the communication equipment while lighting. Since the palmtops and PDA(personal digital assistant) have been used more and more widely,the wireless optical communication technology of large information,flexible deployment,easy maintainance and security is demanded urgently,to provide a flexible solution to the rapid deployment of wireless broadband access,which provides a great opportunity for the development of white-light LED-based indoor visible light communication technology.Based on the physical properties of the LED lights,this paper studied the impact brought by the layout of two types of typical indoor LED lights on the lighting and communication,and the impact of signal's 1th reflection on the optical power.The perfomance of a varienty of modulation modes in indoor wireless optical communications, RMS(root-mean-square) delay produced by multi-path channel in high-speed transmission,and the resulted ISI(intersymbol interference) were also studied.In order to solve the ISI under the high-speed communications situation,a diversity receive was used to improve the performance.At last,the visible light indoor communications uplink was established,and the length of the OOC(optical orthogonal code),the impact of the number of the user on the performance were analysed.Multi-user detection method was used to reduce interference between users.The major research results are showed as follow.(1) Taking a typical indoor room model as the subject,from the layout of two types of typical indoor lighting,the impact of the two layouts on the indoor lighting were compared and analysed.Besides,in conjunction with the requirements of communication,a reasonable layout was chosen.Combined with the choice of the lighting layout,the pulse signal strength and DC gain reflectance from wall were simulated and compared,and the impact of reflected signals on received performance was analysed.(2) The BER(bit error ratio) performance at the transmit speed of 10M to 100M with modulaiton schemes of OOK(on off key),PPM(pulse pusition motulation) and MPPM(multiple PPM) was analysed.According to the layout of the light source,the RMS delay distribution inside the room,the BER of the three representabibe point under the different transfer rate,the optical power loss with different modulation were analysed as well.(3) In response to the fact that when under high-speed transmission,the performance of the wide-angle receiver is not satisfactory,a kind of angle diversity receiver was proposed to be used and the angle of the receiver branch was calculated.By changing the angle of the receiver,the impact of multi-path on the communication was reduced. The channel model of the diversity receiver was analysed,and the receiverd BER was simulated.(4) The uplink was designed and the OCDMA was used to achieve multi-user access in oredr to establish a duplex communication.In this paper,the impact of the OOC length,weight and the receiver decision threshold on the receptivity was analysed.The BER of single-user detection and multi-user detection were simulated,and the results show that under premised BER,the user number is increased by using multi-user detection.