Research On The Technology Of Timming Synchronization For OFDM Systems Based On Training Sequence

Orthogonal Frequency Division Multiplexin (OFDM) technology,relying onits high spectrum efficiency, faster transmission speed and excellent features such asresistance to multipath interference ability, has become the core technology of thefourth generation (4G) mobile communication system. With the support of OFDMtechnology, not only the capacity of the communication system can be improvedgreatly, the quality of the various services it provid—such as voice, data, video,etc—will also rise to a new level.As a multi-carrier efficient modulation technique,in OFDM system, its fullbandwidth is divided into many mutually orthogonal sub-carrier,so the utilizationratio of spectrum of the system has been greatly improved,and the problem of InterSymbol Interference(ISI) and Inter Carrier Interference(ICI) has been solved by thespecial structure of Cyclic Prefix.However,the premise of existence of all theseexcellent characteristics is to keep good orthogonality between eachsub-carrier—such orthogonality will be greatly affected by frequency offset, and tocorrect the frequency offset, a good synchronization performance of the system isneeded. Based on such situation,the paper focus on the research of thesynchronization technology of OFDM system.First,the paper has introduces the relative knowledge of mobile communicationsand OFDM technology, illustrates the importance of synchronization process to thewhole OFDM system,and narrates the research status of synchronization technology.What follows is a description of the basic principles of OFDM technology,coveringthe wireless channel, modulation and demodulation, guard interval and cyclic prefix,and summarizes the advantages and disadvantages of OFDM technology. Then givesthe general synchronization scheme of OFDM system, and points out the influence ofvarious synchronization on OFDM system.Timing synchronization is the focus of the research in this paper.First it isdivided into two major categories,called data aided and non-data aided, and then thepaper introduces some typical algorithms in each classification.ML algorithm isintroduced as the representative of the first kind of algorithm,and SC algorithm，Minn algorithm and Park algorithm are introduced as the representative of the second kindof algorithm. Through the research on these algorithm of the second kind ofalgorithms，some defects are founded.For example,there is a "flat area" problem inSC algorithm,“secondary peaks” problem in Minn algorithm and Park algorithm, andthe main peak value under low SNR is close to secondary peaks values; in addition,Park algorithm needs a large amount of calculation. In view of the situation, the paperproposes an improved algorithm, by redesigning the training symbol and timingmetric,the problems above has been solved, the timing precision and performance ofthe system has been improved. Finally, the MATLAB simulation further proves theexcellent characteristics of the algorithm. At the end of the paper,an improvementidea of adaptive threshold algorithm is given,which solves the problem of falsenegatives caused by SNR changing in the OFDM system in burst mode.