The Research On The Technique Of Channel Estimation In MIMO-OFDM Systems

Broadband efficiency and multi-path fading are the most attention's problems in the wireless communication systems. The new wireless communication system applies the technique of OFDM (orthogonal frequency division multiplexing) and MIMO (multiple-input multiple-output). The technique of OFDM changes frequency selective multi-path fading channel to flat channel and reduces the influence of multi-path fading. The technique of MIMO can produce independence parallel channel to transfer multi-data stream in space and increase the system's transfer's speed.The new wireless communication system adopts this two techniques to solve the problems of Broadband efficiency and multi-path fading. Furthermore, An accurate channel estimation is crucial for the performance of MIMO-OFDM systems. So to researched on the channel estimation becomes very important. This thesis put forward a well method of channel estimation, optimize design to original channel estimation algorithm through research deeply on channel estimation. Consequently improved the performance of MIMO-OFDM wireless communication systems.This thesis puts the emphases research on the technique of channel estimationin MIMO-OFDM wireless communication systems. At the same time, the combination of space-time coding(STBC\STTC and BLAST) and MIMO-OFDM systems is investigated because space-time coding is a promising technique to improve the performance of MIMO-OFDM system with transmit diversity.In this thesis, the author makes the following works and contributions:1)Simply expatiated the principle of OFDM/MIMO and MIMO-OFDM, theory ratiocinated the capacity of OFDM system with different receive antennas. Then using computer simulation to make a prove of it.2) Studied the combination of three techniques of space-time coding with MIMO-OFDM systems. Deeply researched the principle and function of three techniques of space-time coding with MIMO- OFDM systems. The virtue and disadvantage of them have concluded by theoretical analysis and computer simulation.3)Aiming at the tradition parameter channel estimation algorithm exits disadvantages which have high structure complication and large computation complexity. Bring forward optimized parameter channel estimation algorithm. Through designing optimized training sequence, which not only debased structure Complication, but also reduced computation degree. Computer simulation proved that the optimized parameter channel estimation algorithm has better performance and practice application worth.4)A novel channel estimation method for a MIMO-OFDM system is presented. Firstly, This method designs STBC(space-time block codes) pilot's to accord with the demand of transportation. Secondly, combining it with Iterative LS(least square) algorithm to improve the performance of MIMO-OFDM system's channel estimation. Theoretical analysis and computer emulation show that the new channel estimation avoids the computation of matrix inverse operation, it not only offer low computation complexity but also have a better ability to track the channels.