Research On Synchronization Of OFDM For Indoor Visible Light Communication

Visible light communication is a new type of wireless optical communication technology, because of its own advantages and wide application prospects attention. We introduce OFDM technology into the visible light communication, which can further improve the system transmission rate and the ability of anti-multipath interference, and to solve the synchronization of visible light OFDM system is very important for the realization of the system.This thesis mainly focuses on indoor visible-light OFDM communication system. First, we analysis the indoor optical channel, given the channel model; then gives the principle of visible light OFDM system model and discuss the system in a number of practical issues, such as the cyclic prefix length, the impact of Doppler frequency shift and the LED non-linear distortion; for visible light communication can only use the characteristics of a unipolar OFDM signals, we introduce the Asymmetrically Clipped OFDM, and compare the error-rate performance and bandwidth utilization for difference modulation.Finally, the thesis focuses on the synchronization issues of OFDM for indoor visible light communication system. Analyzes difference between the RF-OFDM and VLC-OFDM on synchronization, which is the system requires timing synchronization and sampling clock synchronization, but no need for carrier frequency synchronization. Based on the Park algorithm, we improved a new algorithm as the system timing synchronization solution; and use of a simple the maximum likelihood sequence estimation method based on pilot for the sampling clock frequency offset estimation, using interpolation loop as the frequency deviation compensation circuitry to achieve the sampling clock synchronization. The simulation results show that, the synchronization algorithm we proposed can accurately achieve timing synchronization and sampling clock synchronization for indoor visible light communication system.