Research On Synchronization Technology Of OFDM System Based On Training Sequence

With the advent of the Internet era and the rapid development of wireless communication technology,people's demand for communication systems is not only high speed and convenience,but also strict low time ductility and high reliability.The orthogonal frequency division multiplexing technology(OFDM)is still the key technology in waveform transmission according to the fifth generation mobile communication technology(5G)standard developed in IEEE 802.11 protocol,and it is also one of the core technologies in military communication system.OFDM technology can be integrated with a variety of technologies,widely used,and the performance of the system can not be improved without synchronization technology.This paper mainly studies the synchronization technology of OFDM system,improves the calculation method of training sequence and normalization factor,improves the timing synchronization algorithm,inserts the improved training sequence structure into the pilot,and combines the pilot and cyclic prefix to improve the frequency synchronization algorithm.The main contents are as follows.Firstly,the working principle of the OFDM system is analyzed,the working model of the OFDM system is combed through the flow chart,the signal model is deduced by formulas and its advantages and disadvantages are analyzed.OFDM system has strong anti-interference ability and can be integrated with many technologies,but it is easy to be affected by synchronization deviation.Therefore,for sampling,symbol timing and carrier frequency offset three kinds of synchronization errors,mechanism analysis,example verification and simulation are carried out.It is concluded that timing and frequency offset will cause signal distortion,which will have a worse impact on the system,so this paper will mainly focus on the symbol timing and carrier frequency offset two aspects of the technology to improve.Secondly,the data-assisted synchronization technology is studied,the characteristics of classical synchronization algorithms are analyzed,and the problem of sub-peak interference in classical algorithm is improved.Constant envelope zero autocorrelation(CAZAC)sequence is used as the training sequence,and its arrangement structure and normalization factor are improved.Based on theoretical analysis,the timing measurement curve of the improved algorithm is simulated,and simulated in Gaussian channel and Rayleigh fading channel.The accuracy of timing synchronization and mean square error(MSE)are verified.The performance of the improved algorithm is better than that of the classical algorithm.Finally,in view of the limited range of frequency offset estimation in the classical frequency offset synchronization algorithm,the pilot structure of the classical algorithm is improved by analyzing the principle,and the improved training sequence structure is inserted into the pilot.Combined pilot and cyclic prefix(CP)improved frequency offset synchronization algorithm.In the aspect of fractional frequency doubling bias estimation,the CP data correlation is used for coarse estimation,and then the CAZAC sequence is used for fine estimation.With the signal demodulation,the integer frequency offset is calculated in the frequency domain by using the cyclic shift characteristic of the sequence.In Rayleigh fading channel simulation,the MSE under different frequency offset is verified,which proves that the improved algorithm is optimized in frequency offset estimation range and accuracy.