Periodogram-based carrier frequency offset estimation for orthogonal frequency division multiplexing applications

Abstract

In this paper, a novel carrier frequency offset (CFO) estimation algorithm is proposed for OFDM applications. The maximum likelihood estimator (MLE) for the CFO is derived, which reveals the relationship between the CFO and the periodogram of the received signal. Theoretical analysis shows that the proposed MLE is statistically efficient. To realize this MLE in practice, a sub-optimal estimator is also introduced in which zero-padded FFT is invoked for implementation. For the objectives of reducing the implementation complexity and broadening the estimation range, a preamble structure comprising nonuniformly-spaced pilot tones is presented. Based on this preamble, the CFO estimation is split into two phases: the coarse estimation is obtained through the correlation between the received spectrum and the original pattern of the preamble; whereas the fine estimation is obtained by comparing the relative magnitude attenuation in the vicinities of those CFO-shifted pilot tones. Both analytical investigations and computer simulations indicate that the accuracy of this simplified sub-optimal estimator is proportional to the oversize ratio of zero-padded FFT, and its estimation range is equal to the bandwidth of OFDM signal. When the oversize ratio is sufficiently high, the performance of the proposed sub-optimal estimator approaches that of the proposed MLE.