The Channel Estimation Of MIMO-OFDM Systems

Orthogonal frequency division multiplexing (OFDM) is a parallel multi-carrier modulation technique, which uses multiple orthogonal subcarriers to transmit information, with good resistance to multipath interference and high bandwidth efficiency. It can provide high data transfer rate when combined with Multiple Input Multiple Output (MIMO). And this has become one of the key technologies in the fourth generation mobile communication system. The OFDM systems need coherent demodulation which requires channel information. So the channel estimation is significant for OFDM systems.The first part of this paper describes the principle and background of the techniques involved in the channel estimation. In this part, the basic principles and the advantages, and disadvantages of OFDM technology is introduced first. Then the basic principles and the application, which contains spatial multiplexing and spatial diversity, is introduced. Finally, the basic characteristics of the wireless channel are introduced, including wireless channel fading, multipath effect and time variability.In the second part of this paper, the channel estimation algorithm of the OFDM system and the channel estimation method for MIMO-OFDM system are investigated. First, the purpose and the basic processes of channel estimation are introduced, and the structure of the pilot for channel estimation is analyzed. Then it is focus on the channel estimation algorithm and the channel estimation method for MIMO-OFDM system. In the study of the channel estimation algorithm, the algorithms are analysis and simulated, which contains LS estimation, LMMSE estimation and DFT-based estimation. In the study of the channel estimation method for MIMO-OFDM system, the two channel estimation methods are shown based on the different structure of pilot, which are the overlapping pilot channel estimation and the staggered pilot channel estimation. Then the impact of the pilot quantity is analyzed based on the simulation result.In the third part of this paper, pilot design and channel estimation for the IMT-Advanced TDD system are investigated. First, the basic background, frame structure and main parameters of the IMT-Advanced TDD system are introduced. Then, four pilot programs are designed for the low speed or static environment, and one of the four pilot programs is selected by the simulation results and theoretical analysis. Later, the channel estimation algorithms are researched, including the LS estimation, DFT-based channel estimation and regularization LS estimation. Finally, an improved DFT-based channel estimation algorithm is proposed, which can eliminate the effect of the virtual carrier by restore the channel impulse response.