Maximum-Likelihood Estimator for Coarse Carrier Frequency Offset Estimation in OFDM Systems

Abstract

Orthogonal frequency division multiplexing (OFDM) systems are more sensitive to carrier frequency offset (CFO) compared to the conventional single carrier systems. CFO destroys the orthogonality among subcarriers, resulting in inter-carrier interference (ICI) and degrading system performance. To mitigate the effect of the CFO, it has to be estimated and compensated before the demodulation. The CFO can be divided into an integer part and a fractional part. In this paper, we investigate a maximum-likelihood estimator (MLE) for estimating the integer part of the CFO in OFDM systems, which requires only one OFDM block as the pilot symbols. To reduce the computational complexity of the MLE and improve the bandwidth efficiency, a suboptimum estimator (Sub MLE) is studied. Based on the hypothesis testing method, a threshold Sub MLE (T-Sub MLE) is proposed to further reduce the computational complexity. The performance analysis of the proposed T-Sub MLE is obtained and the analytical results match the simulation results well. Numerical results show that the proposed estimators are effective and reliable in both additive white Gaussian noise (AWGN) and frequency-selective fading channels in OFDM systems.

Efficient Joint Carrier Frequency Offset and Phase Noise Compensation Scheme for High-Speed Coherent Optical OFDM Systems

“…However, in the conventional FOE algorithms [12]- [14], the IFO calculation cannot work correctly due to the high power effect induced by RF-pilot tone. In order to cope with the contradiction, a novel FOE algorithm (i.e., RAFOE) is proposed, in which the high power characteristic of RF-pilot, as a positive factor, is further exploited.…”

“…is the index of the maximum timing metric , [14]. In the conventional algorithm, exhaustive search of a large amount of integer candidates is required to get the optimal integer by the merit function.…”

“…Therefore, frequency offset estimation (FOE) is necessarily required and implemented before RAPR. However, for conventional FOE algorithms [12]- [14], two challenges arise in the integral part of frequency offset (IFO) calculation: 1) it causes high computational complexity by the use of a merit function, and 2) it cannot work coordinately with RAPR. Because in order to obtain a good phase compensation performance, RF-pilot is required with large power in RAPR so as to suppress the interferences from OFDM signal and ASE noise, but the correlation between training symbols of IFO estimation will be seriously disturbed by the high-power RF-pilot.…”

Blind Integer Carrier Frequency Offset Estimation for OFDM Systems with Constant Modulus Signaling

“…Data-aided estimators, which are mainly suited for packet-oriented applications, rely on periodically transmitted training symbols [3][4][5][6]. This idea was first introduced in [3] where two identical OFDM blocks were observed to estimate the IFO.…”