| LED indoor visible light communication(VLC)technology is one of the effective solutions for data access and transmission at the end of wireless communication.It is necessary to improve the transmission distance and capacity of the VLC system based on published international and domestic standards.Based on the main protocol standards,the structure and functions of LED indoor VLC network are proposed.The performance of indoor transmission channel and the influence of front optical path on the performance of communication system are studied in details.First of all,the international VLC protocols are summarized,in which IEEE802.15.7,IEEE802.15.7rl and domestic VLC standard white are mainly included.The structure and functions of LED VLC network are presented,and optical transceiver module as well as modulation coding/decoding technologies in the physical layer are discussed in details.Then,the transmission channels of the front subsystem in the LED indoor VLC system are analyzed,and the mathematical model of channel transmission is established.The power distribution and signal noise ratio(SNR)of directional,non-directional links for single LED,four LEDs lighting subsystems are simulated,respectively.It is found that four LEDs illumination subsystem is covering the whole room and evenly distributed.The non-directional link that reflects the signal transmitted many times makes the power increase,but the SNR decreases.The relationships between multipath interference,receiving angle and transmission rate are found.The higher the receiving angle,the higher the transmission rate,but the more serious multipath interference is.Finally,the front subsystem of LED indoor VLC is designed.The optical transceiver module and the transmission light path are developed,and the experimental platform is built.Test LED volt ampere curve and modulation bandwidth of 42.26MHz are tested.Bandwidth of 30MHz and SNR of 50dB are obtained when the communication distance is 6m for the subsystem. |
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