Research On Channel Estimation For OFDM System With Multiple Antennas In Wireless Communications

Orthogonal Freqency Division Multiplex (OFDM) and Multiple Input Multiple Output (MIMO) are widely recognized as a revolutionary technology for providing higher data rate in the future broadband wireless communication system. This dissertation mainly concerns some key techniques for OFDM and MIMO, including channel estimation, PAPR, and etc.The first part of this thesis deals with pilot-aided channel estimation methods for OFDM system. In this part, pilot arrangement, channel estimation criterion and interpolation method are discussed and DFT-based channel estimation algorithm is introduced. In the flowing, an iterative channel estimation method using discrete cosine transform is proposed. The proposed iterative algorithm of DCT-based channel estimation mitigates the aliasing effect of conventional DFT method and reduces the additive while Gaussian noise (AWGN) and inter-carrier interference (ICI) significantly by the iteration.Next, channel stimation methods for MIMO-OFDM system are investigated. We discussed two different pilot arrangement schemes: frequency-multiplexed pilot and phase shifted pilot. For frequency-multiplexed pilot arrangement, the proposed iterative algorithm of DCT-based channel estimation for SISO-OFDM system is extended into MIMO-OFDM system for better channel estimation result. Then, we propose a DCT-based channel estimation method using phase shifted pilot sequences. By exploiting the properties of DCT, the proposed method mitigates the aliasing effect introduced in DFT-based channel estimation method. With reasonable design and phase shifted pilot sequences for each transmitter antenna, the DCT-based channel estimation method can achieve highly efficient and accurate estimation without sacrificing much system overhead. Further more, no matrix reverse is required for channel estimation, so the computation complexity is largely simplified.At last, we focus the research on MIMO-OFDM via carrier interferometry. In this part, carrier interferometry (CI) technique is combined with MIMO-OFDM architechure, resulting in the so called MIMO-CI/OFDM system. It is shown that the novel system can achieve dramatic performance gains by taking advantage of large frequency diversity inherent in the CI/OFDM technique. Further more, the proposed MIMO-CI/OFDM system has a more stable envelope and, ultimately, an average PAPR far smaller than that of MIMO-OFDM. The simulation results show that the BER performance and the PAPR performance of the proposed MIMO-CI/OFDM system are better than those of MIMO-OFDM system.