Contrary to the common belief that the carrier frequency offset (CFO) in an orthogonal frequency division multiplexing (OFDM) system would adversely impact on system performance, this paper shows that the CFO actually has the effect of linear precoding among transmitted data symbols and hence can be exploited to improve the diversity performance over frequency-selective fading channels. With both analysis and Monte Carlo simulation, it is proved that an OFDM system with CFO equal to half of the subcarrier spacing can potentially achieve the performance of diversity order four by the maximum-likelihood detection and demonstrate a 5 dB improvement using the minimum mean squared error equalization.
X. Huang, "Making carrier frequency offset an advantage for orthogonal frequency division multiplexing," in Communications and Networking in China, 2008. Chinacom 2008. Third International Conference on, 2008, pp. 855-859.