Research Of Channel Estimation Method Based On Training Sequence In MIMO-OFDM Systems

OFDM (orthogonal frequency division modulation) has gained more and more attraction in recent years due to its high bandwidth efficiency and robustness against frequency selective fading channels. MIMO(Multi-InPut and Multi-OutPut)makes use of multi-antennae at transmitting and receiving side to transmit signals, and the multi-paths spreading characters of wireless channel to improve the performance of the system and the capability of the channel. Therefore unite MIMO technique and OFDM’s these two techniques the consideration becomes a kind of very natural view point. Channel estimation is one of the key technologies in MIMO-OFDM system. Channel estimate of accurate or not is the quality for relating to system function directly, so looking for quickly,accurate and dependable channel estimate algorithm is an important research topic by raising channel estimate accuracy. This text mainly launches the discussion now.Firstly, based on the analysis of the main features of wireless channel and the channel model this text discusses MIMO,OFDM system’s main principles and key technologies, in-depth study based on the training sequence channel estimation, the text Introduce LS channel estimation algorithm and MMSE channel estimation algorithm.Secondly, on the channel estimation of MIMO-OFDM system, the thesis mainly research on the LS and the MMSE algorithms, and gave both the simulation of the LS, the MMSE algorithms and their improved algorithms and analysis their performance. Aim at LS algorithm, put forward a method can reducing time-domain algorithm LS matrix inverse operation of the complex, at the same time gives its optimization training sequence; then proposes a new channel estimation algorithm based on LS algorithm and discrete Fourier transform. The initial estimated value of the channel response is attained through LS algorithm, and then the time-domain response outside the length of cyclic prefix is cleared(CP), and third important path during the length of CP is chosen, with eventually the channel response value is obtained by calculating phrase offset of reference pilot to compensate. The algorithm can meet a certain need for accuracy, and is easy to be realized. With regard to MMSE, the improving system performance through the design of appropriate training sequence estimation method MMSE antenna into a single channel estimation, in order to further simplify the algorithm in this LMMSE introduced on the basis of estimation algorithm is proposed to use a single value decomposition method to reduce the complexity of the algorithm.Lastly, this essay research on an iterative method of channel estimation which based on the EM algorithm and applied it to the space-time coded MIMO-OFDM system. This channel estimation can reduce the complexity of computing. And the simulation shows that the performance of MIMO-OFDM system which use iteratived EM algorithm for channel estimation is better than the one which uses simplified LS channel estimation algorithm.