Research On Synchronization Algorithm In OFDM System

Synchronization technique is one of the key technologies in the Orthogonal Frequency Division Multiplexing (OFDM) systems. In this paper, based on the OFDM system model, we analyze the system performance degradation caused by the offset of timing, carrier frequency and sampling clock, which cause Inter-Symbol Interference and Inter-Carrier Interference in OFDM systems.We study the typical timing and frequency synchronization algorithms in the acquisition phase and simulate the performance of these algorithms, and a modified method of timing estimation is proposed, the new timing method is based on the cross-correlation algorithm, which not only reduces the estimation variance through windowing and averaging, but also has the characteristics of lower computation complexity and easy to be implemented in hardware.We study the timing and frequency synchronization algorithms in tracking phase, the effect of Residual Frequency Offset (RFO) on OFDM systems is analyzed, and we present some frequency tracking algorithms and compare the two typical algorithms' performance based on phase rotation calculation and cyclic prefix (CP). Simulations show that the performance of frequency tracking algorithm based on phase rotation calculation is more accurate than the other, and more adaptable to the channel, the frequency estimation errors can be ignored. When the length of channel-impulse response is as much as that of cyclic prefix, the standard deviation of the RFO estimation based on cyclic prefix exceeds 1% sub-carrier spacing, which causes an obvious SNR lost. In addition, the algorithm based on cyclic prefix is a low complexity scheme which can be easily implemented and has the ability to track the symbol timing drift caused by sampling clock frequency offsets simultaneously.