Research On Channel Estimation Techniques For Mimo-Ofdm System In Wireless Mobile Channel

A multiple-input and multiple-output MIMO-OFDM system is a system that employs multiple transmit and receive antennas in an Orthogonal frequency division multiplexing (OFDM) communication system. Using multiple transmit and receive antennas can enhance system capacity, While Using Orthogonal frequency division multiplexing technique can combat the multi-path delay spread and mitigate inter-symbol interference.However, for the wireless mobile communication systems, the radio channel is frequency selective and time-varying. A dynamic estimation of channel is necessary for diversity combining, coherent detection, and decoding. So, to improve the performance of MIMO-OFDM systems by accurate channel estimation, we will mostly investigate the channel estimation techniques of MIMO-OFDM system. At the same time, the combination of space-time coding and MIMO-OFDM system is investigated because space-time coding is a promising technique to improve the performance of MIMO-OFDM system with transmit diversity. By carefully investigating MIMO-OFDM system, we obtain the following results:By the investigations of the decision directed channel estimation method and pilot-symbol-aided channel estimation method of SISO-OFDM system, we propose the improved method and simplified method to solve their problems. We also demonstrate the their performance by computer simulation.Starting with the superposition problem of multiple antennas, we investigate many channel estimation methods of MIMO-OFDM system. By computer simulation, we demonstrate the tracking performance of simplified channel estimation based DFT technique and decision feedback FIR filtering; analyze the robustness of robust two dimensional pilot-symbol-aided channel estimator for the time-varying channel statistics; and compare the performance degradation of the simplified two dimensional pilot-symbol-aided channel estimator with the optimum MMSE channel estimator.Employing space-time coding in the MIMO-OFDM system using decision directed channel estimation method and pilot-symbol-aided channel estimation method is proposed. The performance of MIMO-OFDM system can be significantly improved for the diversity gain and coding gain of space-time coding.