| Visible Light Communication(VLC)uses the white-light LED as its source,which can use enormous bandwidth resources without authorization.VLC is widely accepted as one of the promising solutions for indoor short distance wireless access enviroments,while it is a suitble solution for RF sensitive environments.VLC realizes the data transmission in an effective and energy-saving way,but the uplink transmission scheme still faces many problems simultaneously.The wireless LAN(WiFi)can provide comparatively large coverage range,which can be an effective complement issue for VLC.This thesis presents a comprehensive and indepth research on VLC+WiFi combination system in the typical application scene of indoor wireless access network.Firstly,the fundamental principle and key technologies of VLC are presented,including white-light LED working characteristic and indoor channel transmission characteristic.Then,the indoor wireless access network based on VLC+WiFi is analyzed in detail.The bi-directional link transmission scheme,networking way and the handover strategy are deeply researched,respectively.The handover strategy and layout scheme of VLC+WiFi heterogeneous access network are discussed by theoreotical analysis and numerical calculation.An equivalent SNR handover algorithm is also proposed which introduces a trigger handover mechanism according to the comparison result of the set handover threshold and the difference between WiFi SNR and VLC equivalent SNR.The improved algorithm can accurately perceive and compare the performance of different transmission scheme.Meanwhile,in order to guarantee the accuracy of judgment,the network parking timer mechanism is introduced to briefly keep the handover judgment.Finally,a design of transceiver in both light source terminal and mobile terminal based on the combination of VLC and WiFi technology is proposed.A demo system is also realized and the relevant experiment verifies the feasibility of the design plan. |
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