A Simplified NLS Frequency Offset Estimator for OFDM Systems

A simplified nonlinear least square (NLS) carrier frequency offset (CFO) estimation scheme is proposed based on an OFDM training symbol with L identical parts. Since the NLS CFO estimate scheme has no close-solution, the estimate process is divided into two steps of fine and coarse estimations. The fine estimation is obtained by the correlation of two identical halves in the training symbol. After compensating the fine estimation, the coarse estimation is easily obtained based on NLS by searching the peak on the L-point frequency grids.Moreover, to reduce the computational complexity of coarse CFO estimation, a strategy of adaptive adjusting the number of used sub-symbols based on estimate reliability evaluation is devised. Computer simulations demonstrate that the proposed CFO estimator has a satisfying estimate performance, while maintaining a low computer complexity.