A low complexity residual frequency offset compensation algorithm for coherent QPSK/16QAM OFDM systems

In this paper, the effects of residual frequency offset on OFDM systems are analyzed, and incorrect decision will be made due to the introduced signal constellation rotation. Kobayashi and Nikitopoulos present a method of estimating the phase rotation caused by residual frequency offset. In their work, phase error is obtained by comparing signals after frequency equalization with signals after decision, then compensates the following signals by using the estimated value of the phase rotation. The method involves two decision operations and the calculation of the quantity of every signal´s phase rotation, consequently its computational complexity is high. Considering that in estimation what we need is only the phase information, we propose a method which obtains the phase rotation information from data directly by using such operations as sign inversion, real and imaginary part exchanging, accumulation and avoids two decision operations. The proposed method reduce the computational complexity without degrading the performance of the original algorithm, which is more suitable for hardware implementation. Simulation results show that the degradation of SNR caused by the residual frequency offset is not more than 0.2 dB after employing the proposed algorithm on the AWGN or SUI-2 channel.