Channel Estimation Technique In MIMO-OFDM System

Future broadband wireless communication system needs higher spectral efficiency and higher data rate. MIMO-OFDM technique can improve the tolerance limit to noise, interference and multi-path effect by introducing array antennas to OFDM communication system and utilizing space-time-frequency three dimensional signal processing technique. MIMO-OFDM is an important developing direction of future broadband wireless communication system.In this thesis, the history of mobile communication system is first introduced. After that, it describes the background and characteristic of MIMO-OFDM as well as the principle and key technology of MIMO-OFDM. And the channel characterizes, channel capacity of MIMO system and channel estimation techniques are introduced.Then it mainly studies the channel estimation algorithms respective based on frequency-domain pilot-symbol-aided and training-sequence in MIMO- OFDM system especially under multi-path time-varying environment.The channel estimation algorithm based on frequency-domain PSAM method firstly estimates the channel frequency response (CFR) in pilot position and then estimates CFR in data position by filter processing. Filter processing can be based on interpolation method, wiener filtering and transform domain method. Different interpolation methods are proposed to implement the channel estimation, after which their performance is studied. Then the MMSE Wiener filter is proposed for channel estimation, and thereout bring up a new algorithm :two dimensional adaptive channel estimation. At last according to the transform domain based channel estimation method, the thesis proposes significant tap catching method to improve channel estimation performance.The channel estimation algorithm based on training-sequence method firstly introduces the definition of the training sequence and discusses the optimum training-sequence in MIMO-OFDM system. Then proposes two training-sequence schemes: diagonal orthogonal pilot and phase-shift orthogonal pilot, analyzes the channel estimation method based on each scheme. Finally, we introduce the channel estimation algorithm on decision-feedback method, according to the optimum training-sequence, we get the initial value of the channel impulse response, then estimates accurate impulse response through decision-feedback and Wiener filter methods.