Studies On The Key Techniques Of MIMO-OFDM Systems In The Fast-moving Environment

Future wireless communications are supposed to provide data rate of over 1OOMbps to satisfy the multi-media services. To achieve this goal, there are two main challenges: multi-path fading channel and bandwidth efficiency. OFDM (Orthogonal Frequency Division Multiplexing) technology can eliminate the inter-symbol interference and significantly simplify the equalizers'complexity at the receiver. MIMO(Multi-Input Multi-Output) technology takes advantages of space diversity by spatially separated antennas in a multi-path environment to boost the system capacity. MIMO-OFDM, which contains the advantages of MIMO and OFDM technology, is regarded as a most promising wireless access scheme for the fourth generation mobile communications and has been adopted by some standardization organizations. In the fast-moving environment, this paper does extensive research on the keytechniques of MIMO-OFDM systems and mainly focuses on its coding techniques, synchronization techniques and channel estimation techniques, and then the critical technologies of MIMO-OFDM systems have been deeply studied in three chapters.Firstly, in the fast-moving environment, this paper explores the new encoding and decoding algorithm of differentia STBC. A lot of simulations have been done corresponsively, and then draw a conclusion that D-STBC is more suitable for the situation of high-speed mobile and fast-changing channel fading. Secondly, this paper adopts the new time and frequency synchronization algorithm which is fit for the distributed MIMO-OFDM systems, which considers the different delay of all the transmitting antennas'arrival. Thirdly, an optimal pilot strategy in the transmitter diversity based on the MMSE principle is deduced. Combining with this pilot strategy, an improved robust Frequency domain Diversity Time Combining (FDTC) channel estimation algorithm which can improve the accuracy of channel estimation is proposed. The analysis and comparison of these algorithms'validity and feasibility is made by System View communication simulation tool.