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

Multi-path fading and bandwidth efficiency are two most difficult challenges in the future broadband wireless communications system. However, wireless channels have enormous limitations to reliable high data rate transmission, especially for video. Bandwidth limitations, propagation loss, noise, interference, time variance,and frequency-selective fading caused by multipath propagation can bring high symbol error ratio in high rate transmission. So it becomes a pressing problem to solve robust transmission of video over wireless channels.OFDM reduces the effect of the multi-path fading by converting a frequency-selective channel into a parallel collection of frequency flat sub-channels, and MIMO can increase transmission rate by producing independent parallel channel in the space for data streams transmission simultaneous namely, space division multiplexing of MIMO can increase frequency efficiency but do not need increase system bandwidth. MIMO-OFDM has recently received considerable attentions, which can not only effectively enhance the transmission rate and capacity of the wireless communication system, but also effectively combat multi-path fading and interfere.In order to realize the excellent transmission performance, accurate channel estimation is very necessary before demodulation. In this paper, we discuss the principle of MIMO-OFDM system based on the introduction of fading channels. Furthermore, the channel estimation technique in MIMO-OFDM system is investigated. Firstly an iterative algorithm of joint LS channel estimation and signal detection for OFDM systems is proposed. Then for MIMO-OFDM systems, a simple and efficient training sequence scheme is designed, and a maximum likelihood channel estimation algorithm and an iterative LS algorithm are proposed. Compared with the common LS channel estimation, the iterative algorithm of joint LS channel estimation and signal detection can highly promote the estimation accuracy. Moreover, the iterative LS algorithm for MIMO-OFDM systems can further promote the estimation performance, and it also work well under mobile conditions.