| At the end of the twentieth century, information technology begun to enter people's lives, gradually, with the advancement of science and technology in the twenty-first century, people's demand for information technology is bound to increase. Information technology, is increasingly changing people's lives. Visible light communication technology is developing with the advancement of information technology and the development will make people's lives more comfortable.Visible light indoor wireless communications technology is a wireless optical communication technology with white LED lighting technology. LED lamps are high-brightness, long life, stable performance, energy-saving, high reliability, it will be the next generation of lighting methods. LED-based high-sensitivity and free-space optical communication modulation characteristics, LED lighting system also has the ability to transmit signals which can be lighting and composition of the visible light indoor wireless communications systems at the same time.Compared with traditional infrared and radio communication, LED visible light communication systems have launched a high-power, non-electromagnetic interference, no need to apply for spectrum resources and data will not be leaked indoor. Therefore, LED visible light communications system has prominence meaning on study and good prospects on the development, It has been recognized as an emerging short-range high-speed wireless communication systems.This article is mainly based on white LED visible light communication technology, establishing and analysis of visible light communication technology in practical applications in the field of system and structure based on white LED lighting source. and also studying on the key issue for achieving. The research of LED-based white light-emitting characteristics and physical properties studied and designed the circuit of a white LED driving and the modulation of visible light receiving, and studied the establishment of a wireless transmission channel visible light, made a detailed analysis of design of the visible light and communication system as a whole, had a discussion of the overall design of the visible light communication technology in a number of key issues, This article is divided into several sections:1 the system of visible light communication indoor used white LED light source as communications lamp-house, so the LED white light of the characteristics will affect the construction of the system. This article introduces the special white LED light-emitting principle, I-V characteristics, modulation characteristics, spectral characteristics and the characteristics of white LED to get ready for a good theory of the high-speed modulation and communications system of white LED.2 Achieving from the physical level of the white LED lighting source communication technologies, research and design of the high-speed modulation of the white LED driver circuit, and how to achieve the best light of the carrier signal reception at the receiving end of the circuit , and summed up what Should be pay attention to in the transmitting and receiving optical circuit design.3 Building the model of the white LED light distribution in space , given the degree of distribution of indoor light, and using theoretical analysis and mathematical simulation, in the given judge set conditions, to get the best lighting layout.4 To establish and research white interior LED lighting source of the communication transmission channel model based on the white LED light source radiation characteristic . Focus on the visible channel of the DC gain characteristics, To analyze the way to raise channel gain by the point of view of the receiver optical system design ,and discuss the key issue of crosstalk of optical transmission of signals between the communication channel, as well as the performance of background light on the communication.5 By optimizing circuit design, which has been commercialization used for the purpose of the white LED lighting can be used as a source of communication, and it can be to achieve 10MHz of signal modulation, the white LED lighting provide stability lighting indoor at the same time ,in the expected future, it may be the signal lamp-house which broadband data access into.6 By analysis of the transmission channel model, it calculated the white LED lighting source communication channel parameters, designed the Lambert distribution of the optical power of the LED light source, and increased the refractive index of optical lens, reduced the receiver perspective that can increase the effective photodetector Reception area, so as to enhance the transmission channel gain.7 Choosing and designng reasonably the circuit of photoelectric detector, as well as pre-amplifier circuit, designing the suitable optical loop system, it has achieved the best receive for the modulation signal of the white LED lighting8 the low-loss optical path does't exist in the wireless optical communication system, so the modulation fashion of wireless optical communication must be taken into account wireless optical channel of the absorption,scattering as well as the infection of background noise, at the same time the infection which caused by the spread of crosstalk between the code. The safety for human eye limits the average optical transmission power ,then it sets higher requirements on the modulation. Wireless communication is commonly adhibited laser intensity modulation / direct detection (IM / DD) system, the modulation includes switches keying (OOK),pulse position modulation (PPM),differential pulse position modulation (DPPM),digital pulse interval modulation (DPIM),As well as the double-headed pulse interval modulation (DH-PIM), and so on。variety of modulation methods have advantages and disadvantages, this section carried out a detailed analysis for a variety of modulation on the symbolic structure,average transmission power,bandwidth efficiency,error rate and so on..The visible light communication technology based on the white LED is still in the primary step. Its real mature and wide use depend on the improve of the frequency modulation of the white LED and the research of the visible light network..At present, the research of the wireless communications system based on the white LED is aimed at downlink. The study of uplink and perfect visible light network is not in-depth. Similar to radio-frequency communications and infrared communications, the future visible light communications network still need to resolve the technology which channel can be sub-multiplexed and the user can automatically switch, to develop and constitute regulatory networking protocol. With the mature of this technology, its applications and forms will be diverse. Hence, in terms of different signal transmitter from different application areas, portable terminals general physical specifications need further constitute. |
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