Theoretical Research And Algorithm Realization Of Synchronization Technologies In OFDM Systems

For the good performance of high-frequency band utilization, high-speed data transmission, powerful anti-multipath fading performance and simple channel equalization, OFDM technology has been the mainly used technology in wireless and wireless-based technology. But due to the multiple orthogonal subcarriers of OFDM system, the multiple sub channels will be superstition when signal be output. Thus OFDM system is more vulnerable to the impact of synchronization deviation, so it is need to consider use synchronization technologies in OFDM system.Synchronous technology is essential to any communication system, only by precise synchronization; data transmission can be recovered reliably. In the single-carrier systems, the carrier frequency deviation of the received signal will cause some weakness and phase rotation, which can be overcome through the equalizer. However, compared to the single-carrier systems, OFDM systems are more sensitive to synchronization errors. In OFDM systems, because there are orthogonal multicarrier modulations, the spectrum is closely arranged, the frequency deviation would destroy the orthogonality of the carrier, and the signal deterioration will be much greater than single carrier systems. In addition, the symbol timing error and sampling timing error will also affect the performance of OFDM systems. Thus OFDM systems require more accurate symbol synchronization and frequency synchronization.This thesis uses OFDM system model and synchronization technology as the entry point to analyze the OFDM synchronization algorithm, describe the impacts of the carrier frequency offset, symbol timing offset and sample timing offset. Due to the drawbacks of timing estimation algorithm which based on the training sequence frame structure of SC algorithm that has a peak plateau in timing estimation, timing position ambiguity and can't make a precise time estimation, this thesis presents an improved training sequence frame structure and algorithm based on SC algorithm. This thesis improves the repetitive structure of the first part and the second part in the training sequence structure of SC algorithm and the improved training sequence frame structure uses Centro-symmetric structure of the first part and the second part. And make some improvement of algorithm, the improved algorithm doesn't use the second part of the training sequence of SC algorithm to define the energy function, while uses the whole part of the improved training sequence to define the energy function. And then establishes a timing metric function and finds the best timing synchronization point to finish timing synchronization. Both the theory analysis and the results of simulation show that timing position ambiguity and imprecise timing synchronization of SC algorithm can be solved by the improved algorithm. The improved algorithm can ensure the precision of timing synchronization.