High-speed Downhole Transmission System and Its Synchronization Algorithm Based on Optical OFDM

To overcome the shortcomings of low transmission rate due to limited bandwidth in traditional wired transmission, this paper proposes a wireless downhole transmission system based on optical OFDM technique. This system is advantageous in both optical communications technique and OFDM technique. It has higher transmission rate. Furthermore, in order to overcome the defects of being sensitive to synchronization of OFDM systems, a frame synchronization algorithm based on superimposed training sequence is proposed. The mirror symmetry property of training sequence is used to shift intercept the received signals. The intercepted signals are mirror symmetrically superimposed, which cause frame synchronization objective function to accumulate more energy to synchronize. At the same time, it effectively avoids complex multiplication of long sequence. The simulation results show that good synchronization performance with low SNR is obtained and the proposed frame synchronization algorithm has lower mean square error. 