The Research On Timing And Carrier Offset Estimate Algorithm In OFDM System

Orthogonal Frequency Division Multiplexing (OFDM), has become the core physical layer technology of the next generation wireless communication. Having the merits of anti-multipath fading, high frequency efficiency, simple system structure and much higher capability, OFDM is especially suitable for the high-speed data transmission in wireless environment.Meanwhile, OFDM system is sensitive to carrier offset and timing offset. Timing synchronization is the base of data transmission. Timing offset of symbols could bring ISI to system and add phase noise to carriers. It also could impact the tolerance of time domain delay and extension, especially in multipath channel. It is much sensitive than traditional single carrier system. The offset of carriers could break up the orthogonal property of OFDM system and damage the performance. Just a little carrier offset could lead to great damage. So synchronization technology of OFDM system becomes the hotspot of research and application.This paper mostly focuses on the timing synchronization and carrier synchronization estimate algorithms. First I introduce the characteristics of wireless fading channel and the basic principle of OFDM technique and so on. Then I analyses the influence of timing offset and carrier offset to the OFDM system, using simulation to show the importance of synchronization. After reading lots of paper, I classified and analyzed the status in synchronization research. I also choose two typical algorithms, MLE algorithm and T&D algorithm, to expatiate the trend in synchronization algorithm research field.After that I improved the typical algorithms of T&D, which uses asymmetrical short training sequence and specially designed estimator to make the precision synchronization of timing and carrier offset estimate. We make use of the mean and variance to analyze the performance of new algorithm. The results with the compare between typical algorithm and new method shows that it has much better performance either in AWGN channel or multipath fading channel, consuming less source of OFDM system.With the phase offset of symbols at the receiver, I designed a new practical timing synchronization algorithm for VDSL (very high speed digital service link) application. This algorithm has been simulated with Matlab, showing the capability and performance. This method has been used in compatible segment of firmware in a VDSL2 chip project and work well.