Study Of Coding And Modulating Techniques Under MIMO Wireless System

Through MIMO (Multiple Input Multiple Output) antennas technology, space-time block code (STBC) can take advantage of multi-path to improve the transmission rate and reduce the symbol error rate. STBC can be designed simply, and can be decoded by using ML(maximum likelihood) algorithm, which applies the linear combination method to the received signal. OFDM (Orthogonal frequency division multiplexing) is a multi-carrier technology, by which the wireless channel is divided into some orthogonal sub-channels in the frequency domain, the data can be modulated and transmitted on every sub-carrier in parallel.The receiver only use the coherent demodulation to separate the sub-channel, so, it is important to estimate the wireless channel information.In this paper, we mainly research the STBC coding and decoding algorithms under MIMO-OFDM system. Firstly,the space-time coding model and design criteria are detailed analyzed. In addition we compare and analyze the performance of Alamouti code, orthogonal STBC code and quasi-orthogonal STBC code, by using QPSK,8PSK,16QAM,64QAM modulation under the circumstances of different transmitting and receiving antennas. The simulations show that in the case of the same coding method and numbers of the transmitting and receiving antennas, the BER performance improves gradually with the modulation order increasing. Secongdly, this paper introduces the OFDM principle, and deeply researches some channel estimation algorithms based on the block pilot, comb pilot, cyclic prefix. The simulation shows that the SER and MSE of MMSE and LMMSE algorithm are less than the LS algorithm; In addition, the simulation compares the performance between the second order linear interpolation algorithm and the linear interpolation algorithm;The performance of cyclic prefix iteration channel estimation is better than the second order interpolation algorithm and linear interpolation algorithm, so, this method can reduce the pilot symbols and can improve the channel utilization rate.