Time And Frequency Synchronization Algorithm Of OFDM And MIMO In LTE Communication System

Orthogonal Frequency Division Multiplexing technology, has the lowest complexity carrier technology. The channel is divided into multiple sub-channels, high speed of data tranferred to slow parallel data flow and assigned to each sub-channel. Orthogonal sub-channels can not only reduce the interference between the channel and each sub-bandwidth are far less than the bandwidth of channel, therefore each one can be treated as flat fading sub-channels.The principle of Multiple-Input Multiple-Output technology is that using multiple antenna to send and receive signals. It could improve the load of communication system without adding transmission power and frequency spectrum, at the same time MIMO also can correct signal to reduce the rate of error in the process of transmission.OFDM and MIMO combine more antennas with orthogonal frequency division multiplexing technology. under the condition of limited frequency width and transmitted powerusing, using multi-antenna to improve communnication capacity; using OFDM to minimize the disturbance from transferring process. OFDM and MIMO, learning from other's strong points to offset one's weakness, which has high spectrum efficiency and reliable data transmission, is a major breakthrough in the wireless communication technology research.Time and frequency synchronization algorithm as the key technology of OFDM and MIMO system, Only strictly keeping orthogonality between multicarrier, could OFDM pay out the advantages. Under mutipath fading channel, multipath time delay would cause migration of valid data symbol. Therefore, there is no efficient and accurate time and frequency synchronization algorithm, the advantages of OFDM and MIMO technology will be become nothing.At present time, the applicable scenarion of existing synchronization technology having lagre caculation is ideal and single, lack of compatibility of multiple scenarios. At the same time, the burden of building training sequence is heavy, even ignoring the impact of integer frequency offset on timing synbol. To solve these problems, under keeping the performance of synchronization, we have optimized and streanlined the traditional algorithm, also considing the impact of integer frequency offset on the orientation of symbol time.Orthogonal subcarrier signals are more likely to frequency offset under the effect of mobile's Doppler. At the end of sending and receiving, the difference of oscillation frequency also can produce frequency offset. these will destroy the orthogonality between each subcarrier even cause carrier interference(ICI). According to the present research, we found that relative frequency estimation have large complexity, time consuming and big error, still need to optimize computational process and improve its accuracy of synchronization.Due to multipath time delay during transmission, the integer frequency offset will generate random delay, which could change the original postion of valid data, resulting in symbol interference(ISI). The present scheme has heavier burden to build training sequence, even missing the integer frequency offset. Thus, a lightweight and thoughtful algorithm research is indispensable.Current synchronization algorithm is only suitable for AWGN channel or only suitable for multipath fading channel, lack of a superior and general algorithm. The latest algorithm based on WPS also has a lot problems. for example, the error of integer frequency offset is out of acceptable range at the same time, the scheme has huge computation and complex caculation. In order to optimize the coplexity, shorten processing and fix integer frequency offset estimation, this paper need to make a deep analysis and thoretical caculation, assumptions and simulation for mang times.Through the study of current and traditional synchronization algorithm, it concluded that the most optimal time and frequency synchronization algorithm is adaptable for various communications, mastered the structture and construction method of training sequences, which can not only be convenient to continue depth study for other scholars, but also improve the integrity and availablity of algorithm. some of synchronization algorithm with a large amount of caculation and complex operation need to be optimized and streamlined. After calculation merge and simulation, this paper reduce the complexity and improve the processing speed of algorithm, under the condition of keeping its performance; some algorithm considering insufficiently and has big error, for which we increase processing program and repeated experiment to propose corresponding correction scheme. Finally we use MATLAB to finish channel simulations, algorithm implementation and simulation verification. This measure improve its accuracy and reliability significantly. The paper not only enrich and perfect the research of synchronization algorithm in wireless communication, but provide a strong reference for the next 5G communication system. However, the environment of MATLAB simulation still be much too different from real scene of communication. The improved time and frequency synchronization need to be tested and verified in the actual communication scenarios.