Carrier Frequency Offset Estimation in MIMO-OFDM Systems

Abstract

Orthogonal frequency division multiplexing (OFDM) is a popular method for high data rate wireless transmission. The performance of OFDM system is very sensitive to carrier frequency Offset (CFO), which introduces inter-carrier interference(ICI). Multi-input multi-output system used for increasing diversity gain and capacity of the system. Alamouti space time block code is used for MIMO transmission scheme. The basic method is used for Carrier Frequency Offset Estimation in OFDM system. In cyclic prefix (CP) based estimation, the CFO can be found from the phase angle of the product of the CP and corresponding rear part of the OFDM symbol. In CFO estimation using a training symbol, the CFO estimation range can be increased by reducing the distance between two blocks of samples for correlation. This was made possible by using training symbol that is repetitive with shorter period. An analytic expression in the form of mean square error (MSE) of frequency offset synchronization is reported, and simulation results verify theoretical analysis. Block-by-block CFO estimation is used in MIMO-OFDM system. In this algorithm we use block delay with other block and compare with the delay block. Analysis of the optimal size of block and minimization of the MSE of frequency estimator. We use S observation symbols they are grouped into two consecutive blocks with length A and S-A. The observation symbol, in each block is added sequentially and summed results are correlated block-wise.