Research On Synchronization Based On Energy Difference Set Correlation And Quaternion Sequence

Orthogonal frequency division multiplexing (OFDM) has become a new generation of mobile communication systems (B3G or B4G) widely used technology with the advantages of anti-multipath fading and high spectrum efficiency. However, OFDM system is very sensitive to carrier frequency offset and symbol timing error. So the good synchronization is a prerequisite for normal operation of OFDM system. This paper makes an in-depth study of symbol timing synchronization and carrier frequency estimation in OFDM systems. The following is the work done:First of all, this paper describes the effect of the symbol timing and frequency offset to the system in detail, presents some classic frequency and symbol timing synchronization methods and analyses the ML algorithm based on CP by simulation.Secondly, a combination symbol timing method based on difference and set correlation is researched in-depth. Simulation results show that the accuracy based on CP set correlation is better than CP difference when the SNR is low, for that the noise immunity of CP set correlation is better; but when the SNR is higher, the accuracy based on CP difference is better,this is due to good multipath immunity of CP difference. On this basis, this paper proposed a more suitable weighting factor. The purpose is to make the CP set correlation gain greater weight when the SNR is low, using its advantages of anti-noise,and make the CP difference gain greater weight when the SNR is high, using its advantages of anti-multipath. The research of this method is simulated in matlab software, and the simulation results show that the measures taken are effective.Finally, a preliminary study of quaternary sequence based on the carrier frequency offset estimation method has done. Since the quaternary sequence inserted in cyclic prefix carry rich information of phase, so this feature can be used to complete the carrier frequency offset estimate. The method is simple. It doesn't limit the special modulation. Therefore, the system can be completed with slightly improve on the original, reducing the complexity of system implementation. Simulation results show that this method can fulfill the estimation of frequency offset when SNR is higher than 16 dB and the sequence is short enough.