Mimo-ofdm System Semi-blind Channel Estimation Methods

Utilizing the spacial diversity obtained by spatially separated antennas in a dense multi-path scattering environment ,multi-input multi-output communication can increase significantly the channel capacity without the band-width increasing.OFDM is robust against the frequency-selective fading channels.Thus,it is a challenge to research on MIMO-OFDM system to achieve high data rate and high channel capacity.Accurate channel estimation is just crucial for high data rate and high reliability of multi-input multi-output orthogonal frequency division multiplexing(MIMO-OFDM) wireless system.The usual channel estimation, which is by sending training data or pilot tones,seriously limits the utilization of system bandwidth. The blind channel estimation completely uses the received signals'related characteristics,increases spectrum efficiency,but has high level of computation and estimation of uncertainty.Semi-blind estimation is an algorithm that adding few pilot tones in the blind channel estimation,solves uncertainty in blind channel estimation and increases spectrum efficiency.It discusses the principle of MIMO-OFDM system,and points out that the channel is one of the most import element for the performance of the system,summrises and compares the three sorts of channel estimation methods,channel estimation by training data or pilot tones,blind and semi-blind channel estimation. In which two kinds of blind channel estimation algorithms are introduced in detail: direct extraction correlation blind channel estimation and subspace-based blind channel estimation.Finally the subspace-based semi-blind channel estimation has been investigated,in order to propose the method for tracking subspace in semi-blind channel estimation algorithm based on the decomposition of subspace,a fall-order orthogonal iteration noise subspace tracking algorithm is advanced,the MIMO-OFDM semi-blind channel estimation algorithm based on subspace tracking is proposed to reduce the high computational complexity of the singular value decomposition. Finally the subspace tracking algorithm based on FRANS noise is used in MIMO-OFDM semi-blind channel estimation. With MATLAB simulation results,compares to the original algorithm,the improved algorithm while reduces the complexity of computing and has better convergence effect .