Study Of Channel Estimation Technique In MIMO-OFDM System

OFDM technology and MIMO technology is the key technology of future communication system. Firstly we use OFDM technology to divide broadband channel into several narrowband channel, these sub-channel are flat and mutually orthogonal channel. Then we can make full use of channel capacity by multiple antenna technology. MIMO-OFDM can improve the capacity in communication system. At the same time, it can against the fading and noise.MIMO-OFDM system's complexity and wireless communication channel's diversity makes the channel estimation techniques faces great challenges. Based on these problems, we will research and analysis the MIMO-OFDM system and its channel estimation techniques in this paper:(1) Firstly we study the general decline channel characteristics, and establish the basic channel model. Secondly we study the composed principle and technical features about the MIMO technology and OFDM technology, and use the Matlab to simulate the system capacity of the MIMO, then summarizes the basic principle and structure of MIMO-OFDM system.(2) Analysis of the important function and meaning about channel estimation technology in MIMO-OFDM system, make a depth study of basic channel estimation algorithm, then simulate and compare the LS and MMSE traditional algorithm respectively.(3) On the basis of the above details, this paper puts emphasis on the expectation maximization algorithm of channel estimation method in MIMO-OFDM system. Although the complexity about EM algorithm relatively higher, its occupancy resources relatively less, it can make up the shortage of the traditional channel estimation. Through the study of EM algorithm, firstly we use it in an uncoded MIMO-OFDM system. Combined with the traditional pilot-aided channel estimation method, we can obtain the received signal information and channel statistical properties by EM algorithm, and then compared with the traditional wiener interpolation method. The simulation result shows good performance.(4) Though the simulation analysis of STBC coding system, we proposed an EM algorithm in STBC MIMO-OFDM system, and then compared with the traditional adaptive channel estimation algorithm--RLS method. From the simulation results we learned that the EM has better properties in the high SNR area, at the same time it also reduces the complexity.