Research On MIMO System Spatial Correlation And Channel Estimation

Recent research has shown that MIMO system can be used to improve the system capacity and spectral efficiency significant. Adaptive sub-carrier allocation technique is employed in multi-user OFDM applications. In frequency selective channels, adaptive MIMO-OFDM systems are able to support high reliable and high spectral efficiency communication with low complexity. MIMO and OFDM are key technologies for the fourth generation wireless communications system.MIMO channel test and model setting up are key techniques of MIMO. One is receiver & transmitter correlation setting up. It is well known that it evident channel content. The other key technique is channel characterization. Direction of arrival is discussed in this paper.There three parts in this paper: One is about the system model, one is about the direction of arrival estimation, the others is about MIMO-OFDM channel estimation and algorithm realization.The first part, the performance of multiple input multiple output (MIMO) - orthogonal frequency division multiplexing (OFDM) systems is analyzed with the existence of spatial correlation and the exploitation of adaptive techniques. For the spatial correlation analysis, the antenna arrays are liner antenna array, plane circular antenna array and the general antenna array. The general antenna array is based on three-dimension. At the same time, the signal distribution of angle of arrival is extended from one-dimension to two-dimension. Correlation analysis is performed for uniform, cosine, Gaussian and Laplacian distribution. By then using the MIMO capacity, the performance of the system is analyzed. It is observed that environment richness is the key factor for obtaining signals. The analysis points out the differences between the existing models. The study concludes that for future high data rate oriented MIMO-OFDM system, the effect of spatial correlation needs to be taken into account.The second part, the signal direction of arrival estimation is studied. Previous showed that correlation increases substantially with less angle spread, which then leads to very low capacity. Since angle spread is environment dependent, it is a long term channel parameter, meaning its estimation can be performed based on average channel information. By estimating angle spread, a MIMO system can re-execute its adaptive algorithms like antenna selection. In this part, the estimation focus is on the accuracy of estimation. The estimation accuracy formula based on three antenna arrays is deduced. At the same time, the multiple signal classification (MUSIC) algorithm is introduced briefly. Algorithms are developed in which the array manifold is modified with a spatial correlation function that includes the angle spread.Third part presents a channel estimation technique applicable to MIMO-OFDM system. MIMO-OFDM channel estimation is introduced. The time region and frequency region channel estimation algorithm are presents. Then the hardware to realization the algorithm is showed. The core chip is TMS32C6416. It is a digital signal processor produced (DSP) by TI company. DSP and FPGA are work together to complete the channel estimation algorithm.