Research On Time-varying Fading Channel Estimation Algorithm For MIMO-OFDM Systmes

MIMO-OFDM (Multiple Input Multiple Output and Orthogonal Frequency Division Multiplexing) technique which combined with MIMO (Multiple Input and Multiple Output, multiple-input multiple-output) technology and OFDM (Orthogonal Frequency Division Multiplexing, orthogonal frequency division multiplexing) technology has increasingly become the focus of attention. It can obtain time diversity spatial diversity and frequency diversity at the same time. So it not only can improve the wireless channel capacity and spectral efficiency, but also can effectively resist the frequency selective fading and suppress the interference and noise in the course of spread.In the idea of Superimposed Pilot, additional periodic training sequence that it is arithmetically added to information sequence in time-or frequency-domain on the transmitter. The advantage of Superimposed Pilot is that there is no loss in transmission rate, and thus enables higher bandwidth efficiency, and it can real-time track the channel state of the time-varying.Start from the basic principle of MIMO-OFDM, this paper focuses on the research of Time-varying channel estimation based on superimposed pilots and the channel modeling for MIMO-OFDM system. The major works of this paper can be summarized as follows:(1)On the basis of time-invariant modeling for OFDM, an improved algorithm based on Superimposed Pilot that suit to time-invariant channel estimation has been proposed. In the algorithm, the data are assumed to be transmitted in a data frame while the pilot sequences and data sequences are combined by superimposing. After getting the channel impulse responses corresponding to each symbol of OFDM signals in a data frame, they are weighted averaged over the frame. In such a way the accuracy of channel estimation is improved. Finally, the MATLAB simulation results shows that the efficiency of the improved algorithm.(2)This papers design the superimposed pilot in the time and frequency domain which is suitable for the slowly time-varying channel for MIMO-OFDM. On the receiver, we study the interence from the signal of the residual pilots. In addition aided reconstruction scheme is adopted to enhance the bit error rate.(3)Research on the fast time-varying channel model for MIMO-OFDM system based on piece-wise linear model when the relative Doppler shift is less than or close to 0.1. On the basis of a new piece-wise liner model based on a rectangular window function in time domain. On this basis, it is given an optimal pilot for the model. In the end, the MATLAB simulation shows that the performance of MSE.