Research On Channel Estimation And Adaptive Modulation Algorithms Of MIMO-OFDM Systems

Channel state information is required in OFDM systems for correlation detection and in MIMO-OFDM systems for space-time decoding. Meanwhile, it is also the required information to the transmitter in closed-loop systems. Therefore, channel estimation is very important, especially, its accuracy affects the overall performance directly in MIMO-OFDM systems. On the other hand, adaptive modulation technique can enhance data rate, spectrum efficiency and transmission reliability in MIMO-OFDM systems. This paper is concerned with channel estimation in both OFDM and MIMO-OFDM wireless communication systems and adaptive modulation in MIMO-OFDM systems.Firstly, in view of OFDM system channel estimate, this paper present one kind of LRMMSE Channel Estimation based on SVD analysis. By simulation and analysis. Compared with the LMMSE and LRMMSE , The result indicates that they are the same in the performance. When the SNR is rising , LMMSE is the better than LRMMSE, But in view of estimation algorithm's complexity and performance ,LRMMSE and MMSE have no large difference .but LRMMSE algorithm complexity is greatly decreasing.Secondly, this paper propose an adaptive modulation scheme in order to minimize the total transmission power subject to given BER and transmitting data rate in single-user MIMO-OFDM wireless communication systems ,which is based on the pre-coding design. The key algorithm of the scheme is Chow algorithm and Campellos algorithm which are used widely, meanwhile, it is improved by various-step adaptive bit loading. The simulation results show that the presented improved algorithm has a similar system's BER performance to original algorithm, and less complexity and time than it.