Research On Synchronization Technology In VLC-OFDM System

The thesis studies the visible light communication (VLC) system based on LEDs, and the research focuses on the first step of the DCO-OFDM receiver, that is synchronization.Firstly, the thesis analyzes the impacts of timing error in the system. Analysis shows that the symbol timing offset may cause phase rotation, or inter symbol interference, or inter carrier interference, and the sampling clock deviation will cause the amplitude attenuation, phase rotation and inter carrier interference.Secondly, to solve symbol timing problem, the thesis proposes two novel timing synchronization methods. Considered the mirror symmetric structure of DCO-OFDM symbol, we do auto correlation of received sequence and use the same decision metric of Park’s, a sharper peak is achieved and two side peaks are eliminated, this is adapted Park’s algorithm. The other one is enhanced timing algorithm based on repeated sequences cross correlation, its preamble has D repeated training sequences of length L. Do cross correlation firstly and then multiply the current correlation values with that L symbols before, by detecting D-1 peaks we can find the correct timing position. Simulation results show that both of them can reduce FER, and have a low timing offset MSE. Besides, the latter is more suitable for hardware realization because of its low complexity.Thirdly, sampling clock synchronization is another key problem in the thesis, two methods are presented and they both need pilots aided. The first one is to detect sampling clock error by 3 different LS algorithms, recover correct sampling values by polynomial interpolation, and then re-demodulate. The other one is to compensate in frequency domain after estimating phase rotation in every subcarriers. Simulation results show that two methods have good performance in VLC system. The thesis proposes an adapted simplified architecture that is easy for hardware realization.At last, the thesis designs and accomplishes a complete indoor VLC DCO-OFDM baseband processing system on the platform developed by our lab. The baseband transceiver system design and hardware architecture are given. The thesis describes how to implement the two synchronization methods proposed above on FPGA in details. The transmission link is finally successfully accomplished in FPGA, so the whole system is confirmed to be right and the synchronization methods proposed are effective.