  A novel frequency domain training sequence and the corresponding carrier
frequency offset (CFO) estimator are proposed for orthogonal frequency division
multiplexing (OFDM) systems over frequency-selective fading channels. The
proposed frequency domain training sequence comprises two types of pilot tones,
namely distinctively spaced pilot tones with high energies and uniformly spaced
ones with low energies. Based on the distinctively spaced pilot tones, integer
CFO estimation is accomplished. After the subcarriers occupied by the
distinctively spaced pilot tones and their adjacent subcarriers are nulled for
the sake of interference cancellation, fractional CFO estimation is executed
according to the uniformly spaced pilot tones. By exploiting a predefined
lookup table making the best of the structure of the distinctively spaced pilot
tones, computational complexity of the proposed CFO estimator can be decreased
considerably. With the aid of the uniformly spaced pilot tones generated from
Chu sequence with cyclically orthogonal property, the ability of the proposed
estimator to combat multipath effect is enhanced to a great extent. Simulation
results illustrate the good performance of the proposed CFO estimator.
