The Synchronization Algorithms Research On OFDM System

Orthogonal Frequency Division Multiple (OFDM) has efficient bandwidth utilization and the robustness against Multi-path delay. However, OFDM is sensitive to symbol timing offset and carrier frequency offset.The primary content of this thesis is the synchronization algorithms of the OFDM system. Firstly, the impact of symbol timing offset and carrier frequency offset in system is analyzed quantitatively. On the basis of it, the ML algorithms amending scheme of Schmidle&cox algorithms and the classic MUSIC algorithms were researched and simulated in MATLAB environment. Following is the conclusions: the maximum likelihood algorithm based on the CP using the CP to estimate timing offset and frequency offset. So the estimating accuracy is high and computing amounts is low; amending scheme of Schmidle&cox algorithms employed a training sequence to estimate timing offset and frequency offset. The estimating accuracy is high and frequency estimating range is wide but the added training sequence lower the system transmission efficiency .The classic MUSIC algorithm makes use of the inside characteristics of the OFDM system. The device of the sub-space steers the blind estimate. The algorithm operation has wide capacity and the estimate accuracy is lower.On the basis of the research, the thesis designed a scheme employing real PN sequence to realize symbol and frequency synchronization. The basic principle is inserting real training sequence. The training sequence was composed of PN sequence and zeros. The PN sequencewas inserted in 0,4, 8......4L (L=0,l,2..) Sub-carriers, the rest sub-carriers were inserted inzeros. The training symbol came from the training sequence modulated by multi-carrier. The training symbol has the character that the first half sampling datum is equal to the latter sampling datum. And the first half sampling datum conjugates summarily with the latter sampling datum. The symbol synchronization was obtained with the two characters. The fraction frequency offset was obtained with the first character .The integer frequency offset was gained by the self-correlation of PN sequence.