On The Channel Estimation And Carrier Offset Estimation In Mimo-ofdm System

The combination of MIMO and OFDM (MIMO-OFDM) is an attractive mean for the next generation (Beyond 3G, B3G) wireless communication systems. The requirement for B3G systems such as high data rate, high quality and high mobility make channel estimation more challenging. OFDM is entire orthogonal system so it is easier to arouse sub-carrier offset that can cause inter-carrier interference (ICI). As a result, finding an effective carrier offset estimation technique is very important. In conclusion, the research of channel estimation and carrier offset estimation has significant alchemical meaning and practical worth.Firstly, the pilot-symbol-aided channel estimation in MIMO-OFDM systems is studied. The thesis also demonstrated the strength and weakness of these techniques. Based on it, adaptive estimation technique is further studied in MIMO-OFDM system and an Kalman based channel estimation in MIMO-OFDM system. Because the traditional Kalman channel estimation method does not fit for the characteristics of mobile channels, i.e., the mobile channels can not presuppose the channel state information, this paper proposes a channel estimation method based on extended Kalman filtering (EKF). On the basis, considering that wireless channels can show the nonlinear characteristics, this paper applies a nonlinear signal processing method which is called unscented Kalman filtering (UKF) to the channel estimation field. Thus this paper proposes a channel estimation method based on UKF. Computer simulations prove that the BER and MSE performance of UKF based channel estimation method outperforms the other channel estimation methods.High-speed data transmission in wireless communications potentially results in a sparse multipath fading channel. The significant taps approach can be used to greatly improve the performance of the channel time response. In the thesis, an adaptive significant-tap-catching method based on multipath search is proposed. Combined with based UKF channel estimation, the simulation BER and MSE performance indicates that adaptive significant-tap-catching method is better than fixed significant-tap-catching method. Meanwhile, the computation complexity decreased a lot.Then the carrier offset is researched in OFDM system and based UKF carrier offset estimation method is proposed. The simulation performance indicates the method has exacted estimation performance and the bandwidth efficiency is higher than SC method and MLE method. The thesis adapted the based UKF channel and carrier offset joint estimation in MIMO-OFDM system which has carrier offset and multipath effect. The simulation performance demonstrated the method can estimate the channel information and carrier offset at the same time.Channel estimation and carrier offset estimation are key techniques in MIMO-OFDM communication system. The thesis did some work on decreasing channel estimation computation complexity, enhancing the precision of channel estimation and increasing the bandwidth usage of carrier offset estimation. However, channel estimation is an important part of communication system. The difficulty is combination between channel estimation with other techniques, such as link adaptation and HARQ in MAC layer, which needs more and deeper research.