The Research Of Channel Estimation In MIMO-OFDM Systems

The Orthogonal Frequency Division Multiplexing (OFDM) system is a multicarrier system and usually used to resist frequency selective fading and narrowband interfere. And the MIMO system could improve the capacity of the communication system and spectral utilization ratio at double in case of not increasing bandwidth. Recently, the Multiple Input Multiple Output (MIMO) system and the OFDM system are paid more attention in order to increase the systemic capacity further, raise the systemic transmission rate. Therefore MIMO-OFDM system which becomes a crucial technology of high-data-rate wireless transmission can achieve high spectral efficiency and resist interference caused by multipath and noise effectively.In this paper, channel estimation of the MIMO-OFDM system has been researched. Key points as follows:Firstly, based on the brief discussion of fading property of the wireless channel and channel model, the core principles and the composition of the OFDM and MIMO systems are discoused detailedly. The MIMO-OFDM system is researched and a simulation platform of the MIMO-OFDM system is set up. The property diagraph of Space-Time Block Coding (STBC) OFDM systems is simulated with perfect Channel State Information (CSI) .Furthermore, The paper studies deeply on Least Square (LS) time-domainestimation, LS frequency-domain estimation and Minimum Mean-Squared Error(MMSE) estimation based on the training sequence. These three methods andtheir improved methods are simulated by MATLAB. The improved methods areproved effectively.Lastly, pilot-based channel estimation methods are mainly researched. Emphatically, a new pattern of pilot-insert is proposed, that is pilots are inserted into different carriers at different time. The method can estimate the CSI of all frequencies through pilot-insert in different carriers, so it will enhance the ability to resist frequence-select. Then it regards the results of interpolation as pre-estimation, and takes different Averaged Channel Estimation in the Time-domain (ACE-T) on different channel conditions to get final channel estimation. Finally, the enhancement of channel estimation precision is proved by simulations in different Doppler-frequence-shift channel model.