Research On Frequency And Symbol Joint Synchronization In MIMO-OFDM System

With the rapid development of wireless mobile communication systems,people's requirements for the accuracy and stability of communication transmission rate are gradually improved.The 802.11 n protocol standards in IEEE is formulated on the basis of the works in the 5 GHZ band 802.11 ac protocol standard,in which multiple input multiple output(MIMO)technology is added 802.11 ac protocol standard,and combining the orthogonal frequency division multiplexing(OFDM)system.The formation of MIMO-OFDM system is a key technology of 5G.MIMO-OFDM system enhances the anti-multipath jamming capability of MIMO technology,as well as the channel capacity of OFDM system increases many times with the transmission rate,making the system more security and stability.Thus optimized MIMO-OFDM system performance into research becomes popular in recent years.The joint synchronization problem of MIMO-OFDM symbol and frequency is studied in this paper.The synchronization algorithm is improved by using training sequence and cyclic prefix(CP)and implemented on the simulation software.The main contents include:Firstly,the basic working principle and technical classification of MIMO technology,the orthogonality principle and working principle of OFDM system,as well as the working principle and channel model of MIMO-OFDM are analyzed in detail.At the same time,the advantages and disadvantages of MIMO technology,OFDM system and MIMO-OFDM system are discussed.It can be concluded that MIMO technique and OFDM system make the channel capacity of MIMO-OFDM system with transmission rate many times and the ability of resisting to multipath interference and resisting frequency decline are enhanced.However,the MIMO-OFDM system is still affected by synchronous deviation and peak power ratio.Secondly,the causes of sample value synchronization deviation,sampling timing deviation,symbol synchronization deviation(STO)and carrier frequency deviation(CTO)in MIMO-OFDM system and their effects on the system were analyzed.Then,simulation software was used to simulate the effects of symbol synchronization deviation and carrier frequency deviation.It is proved that the signal synchronization deviation and carrier frequency deviation have great influence on the system.Therefore,this paper focuses on the synchronization problem.Then,the traditional synchronization algorithm is improved,and the structure and data information of training sequence and cyclic prefix are improved.The Zadoff-Chu(ZC)sequence with high autocorrelation,low cross correlation and constant amplitude is used.The partial loop of the effective OFDM data and the partial data loop of the loop sequence are realized.The interference of the data of the upstream and downstream links is effectively prevented,and the symbol and frequency synchronization performance of the MIMO-OFDM system is availably improved.Finally,based on the theoretical analysis of the improved algorithm,simulation was carried out for the number of different transceiver antennas in Rayleigh fading channel,with the subcarrier number 256 and SNR range-15db?25d B under 16 QAM modulation and demodulation.It is proved that the improved algorithm optimizes the accuracy of timing position estimation and the compensation accuracy of frequency deviation under certain conditions.