Research On Channel Estimation For MIMO-OFDM System

The dispersive of wireless channel and the system bandwidth efficiency are the big challenges the future broadband wireless communication facing. More and more people realize that MIMO (multiple input multiple output) and OFDM (orthogonal frequency division multiplexing) are the key techniques of the beyond 3rd generation (B3G) systems. MIMO transmit multiple data streams in parallel sub-channels in spatial, thus greatly increasing the system transmission efficiency without additional bandwidth and power requirements. Orthogonal frequency division multiplexing (OFDM) can effectively combat the multipath fading channel and convert the frequency selective channel into flat channel in frequency domain. Combing the merits of two technologies, the MIMO-OFDM system has been considered as one of the most available scheme in B3G system. To detect the transmit signal, the channel information of every subcarriers in every channels between the antennas is a precondition. Therefore, channel estimation is the key issue in MIMO-OFDM technique.The channel estimation methods for MIMO-OFDM system can be divided into three categories: the algorithm based on training sequence, the algorithm based on pilot symbols and the blind estimation algorithm. Blind estimation method has the disadvantages of large computing and poor flexibility, which limited the application in real-time systems. Therefore, in this paper, the method based on training sequences and pilot symbols based on the method are studied, and the main research work is given as follows:The frequency-domain Least Square channel estimation algorithm and Minimum Mean Square Error channel estimation algorithm based on training sequences are analysed. The LS algorithm structure is easily achieved and the computing is small, but the estimate accuracy is reduced due to the noise interference that affects the performance of the system. An improved algorithm based on adaptive noise cancellation. is presented In addtion, an improved algorithm based on Space-Time Block Codes training sequence is given, thus the complexity of MMSE algorithms is decreased. The simulation results show that the improved algorithm is better than the original algorithm and verified the effectiveness of the algorithm.The pilot symbol selection, the pilot structure and interpolation algorithm are researched, which based on the channel estimation algorithm of pilot symbol. In order to get the better effect of channel interpolation algorithm, an iterative channelestimation algorithm based on the discrete fourier transform is proposed. Theiterative algorithm restrained the noise effectively and improved the estimatedprecision.