Study On PHY Layer Of Indoor Visible-Light Wireless Communications System

Expected to serve in the next generation of lamps, LED offersadvantageous properties such as high brightness, reliability, lower powerconsumption and long lifetime. The LED lighting system , based on thefast switching of light emitting diodes and the modulation of thevisible-light waves for the free space communication, is capable of the(?) signal transmission. Compared with the traditional infrared and radiocommunication system, LED visible light communication system hashigh transmission power, no electr-magnetic interference, no need forspectrum resources and indoor no data leakage, and other advantages.Therefore, LED visible light communications system possess greatersignificance and development prospects, and it has also become anemerging transmission scheme for short-range and high-data-ratewireless communication. In this paper, an algorithm is described for thetypical LED indoor visible-light channel model, and the physical (PHY)characters such as signal modulation, multiplexing, receptionperformance optimization, etc, are investigated. Furthermore, we obtainthe simulation data results by mathematics formula or computerprogrammer, and the objective analysis and evaluation for thiscommunication system are presented.Considering the transmission character of the LED visible-light communication system, a more advanced algorithm for expressing the communication channel is proposed based on the theories of LOS mode in visible light and multi-reflect mode in infrared transfer links proposed by Nakagawa and John.Barry respectively. Based on the expression and the formula of the multi-path indoor LED communication on the physical channel, different kinds of signal modulation schemes, anti-multi-path RACK receiver and multiple access technology performance are mathematical modeled and simulated.The research and simulation data show the following results: The simple OOK and 2PPM schemes can be used in the indoor data communication at the data speed lower than 10Mbps, while more complicated modulation schemes may be used at the data speed higher than 50Mbps. The anti-multi-path receiver performance is greatly improved by PRACK receiver with 8 fingers , but the cost will rise with the increase of fingers while the performance can not be further improved significantly. The balance between the reuse distance and the signal-to-co-channel interference is reached when the cell radius is 2m and the sending power requirement by the multi-user is least in the TDMA/FDMA indoor LED wireless communication system.