The Research On Technique Of Channel Estimation In MIMO-OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) and multiple-input multiple-output OFDM (MIMO-OFDM) is a promising technique for broadband wireless communication recently. It can satisfy the high-data rate and large system capacity requirements of the forth generation mobile communication.The technique of OFDM changes frequency selective multi-path fading channel to flat channel and reduces the influence of multi-path fading,moreover it can greatly simplify the base band processing units at receiver and improve the data rate. MIMO can increase the channel capacity linearly,i.e.,any arbitrary high channel capacity can be achieved by increasing the number of antennas,which thus breaks through the Shannon capacity limits of SISO (single input single output) channel. Furthermore, it is crucial to estimate the channels accurately for the performance of MIMO-OFDM systems. So to research on the channel estimation becomes very important.In this dissertation, researched the channel model and channel estimation in the Mobile communication; through researched deeply on channel estimation, It improved the performance of MIMO-OFDM wirelesscommunication systems Consequently.In this thesis, the main works can be summarized as follows:1) This paper firstly analysed the characteristics of the wireless fading channel and established the fading channel model, Simply elaborated the principle of OFDM/MIMO and MIMO-OFDM.2) This thesis infers the capacity of OFDM system and the SNR with different receive antennas on the theory, Then using computer simulation to make a prove of it. Studies techniques of space-time coding in MIMO– OFDM systems, deeply researches the principle and function of two space-time coding techniques(STBC and STTC) in MIMO- OFDM systems. The virtue and disadvantage of them have concluded by theoretical analysis and computer simulation.3) Regarding the key technology of the channel estimation, thoroughly researched the method of channel estimation based on the training sequence LS in MIMO-OFDM system and the method of channel estimation based on DFT in OFDM system. Furthermore gave the corresponding channel estimateion algorithm as well as the simulation result.4) Based on the above foundation, We put forward a pilot-assisted method for estimating the frequency selective channel in MIMO-OFDM system. The pilot sequence is designed using the DFT of the Golay complementary sequences. Novel exploitation of the perfect autocorrelation property of the Golay codes, in conjunction with OSTBC based pilot waveform scheduling across multiple OFDM frames, facilitates simpleseparation of the channel mixtures at the receive antennas. NMSE between the actual and the estimated channel is used to characterize the estimation performance. Finally,the analysis and comparison of these algorithms is made by computer simulation.