In OFDM systems, link performance depends heavily on the estimation of symbol-timing and frequency offsets. Performance sensitivity to these estimates is a major drawback of OFDM systems. Timing errors destroy the orthogonality of OFDM signals and lead to inter-symbol interference (ISI) and inter-carrier interference (ICI). The interference due to timing errors can be exploited as a metric for symbol-timing synchronization. In this paper, we propose a novel method to extract interference components using a DFT of the upsampled OFDM signals. Mathematical analysis and formulation are given for the dependence of interference on timing errors. From a numerical analysis, the proposed interference estimation shows robustness against channel dispersion.

In this letter, a novel blind CFO estimation algorithm for the uplink of an OFDMA system is proposed. The proposed method exploits the inherent redundant information in OFDMA symbols and does not require additional pilot or preamble overhead. Since it is a post-FFT estimator, it does not use filter banks to separate the desired user's signal from the others in the time domain. Hence, the subcarriers of a certain user are not restricted to be clustered in the frequency domain. Therefore, the proposed estimator can be applied to OFDMA systems with an arbitrary subcarrier assignment over the entire bandwidth, including IEEE 802.16e, to obtain sufficient frequency diversity in a frequency selective fading channel. The proposed method can be efficiently used for continuous tracking of all active users' CFOs only with two FFT windows within a single OFDM symbol. From simulation results, the performance of the proposed scheme is shown better than that uses preamble symbols.

In this letter, a blind frequency offset estimation algorithm is proposed for OFDM systems. The proposed method exploits the intrinsic phase shift between neighboring samples in a single OFDM symbol, incurred by a frequency offset. The proposed algorithm minimizes a novel cost function, which is the squared error of the candidate frequency offset compensated signals from two different observation windows. Also, the solution of the proposed algorithm is given by an explicit equation, which does not require any iterative calculation. It is shown that the performance of the proposed method is better than those of the conventional methods, especially in the presence of multipath channels. This is due to the fact that the proposed method is insensitive to inter-symbol interference (ISI).

In this paper, we present a new all-digital carrier recovery loop for high-order quadrature amplitude modulation (QAM) signal constellations. The proposed approach is a blind phase-frequency detector structure that consists of a phase detector, a phase offset estimator, a frequency offset estimator, and a digital control oscillator. Compared to previous related approaches, the proposed algorithm provides a wider acquisition range and a more accurate estimation of frequency and phase offsets. These features are demonstrated by simulation results of the DOCSIS (Data-Over-Cable Service Interface Specifications) cable modem system.