The Coding And Synchronization Algorithm Research On The COFDM System

COFDM(Coded Orthogonal Frequency Division Multiplexing)is a kind of mainstream modulation system for 3G/4G which owns the relatively high spectrum efficiency and the ability of multipath interference.In recent years,because of the characteristic in parallel transmission mechanism,internal against symbol interference and diversity of multipath channel,the COFDM is widely used in water under the land and underwater of communication.The performance of the system is very important as a solution of high-speed data transmission technology.The system performance depends on two aspects.On the one hand is the channel coding,which can ensure the accuracy of the transmission so as to improve the performance of the system,it is essential in the system.On the other hand,another important challenge is the synchronization in COFDM system.Because only a little synchronization may significantly result the reduce of the systematic performance.Therefore,the accurate synchronization is on the premise of the COFDM system with good performance.This paper mainly introduces the way to optimize the system from the two aspects of coding and synchronization.Firstly,it briefly introduces the significance,the present situation and the basic principle of COFDM system.Secondly,this paper analyzes the advantages and disadvantages of various codes,and then it constructs a new system by OFDM technology which combines RS code with QC-LDPC code based on Matlab.This paper studies on the structure of COFDM system and the ability of concatenated coding,and verifies the algorithm from code length,code rate,the mode of coding,the mode of decoding and different channels by simulation.Next it emphasizes the importance of timing estimation and frequency offset estimation in COFDM system by analyzing various synchronous technology of COFDM.At last,the algorithm is improved on two aspects of synchronous technology.One is based on adding training sequence algorithm to improve the shortcomings of Minn algorithm.The other one is based on timing and frequency deviation of Pilot and CP(Cyclic Prefix)is effective.Traditional algorithm based on Pilot and CP is effective for timing and frequency synchronism,but it has complex operation,so an improved algorithm raised.The results prove that the improved Minn algorithm and the improved method of combining CP with Pilot can improve accuracy of time-frequency estimation under multipath channels,and greatly improve the systematic transmission capacity in fast fading channel.