New Integer Normalized Carrier Frequency Offset Estimators

Abstract

Carrier frequency offset (CFO) introduces spectrum misalignment of the transmit and receive filters, causing energy loss and distortion of received signal. A recent study presents an accurate signal model that incorporates these characteristics. However, CFO estimators in the existing literature were developed based on the signal models without these characteristics. This paper generalizes the accurate signal model with CFO to include timing offset and sampling offset and then studies what effects the accurate signal model bring to the CFO estimation and how to address them. We investigate different existing CFO estimators and find some of them lose their optimality under the accurate signal model. We also develop two new integer normalized CFO (ICFO) estimators under the accurate signal model using only one OFDM symbol; one of them is a pilot-aided estimator using both pilot and data and the other one is a blind estimator using data only. Compared with the existing approaches, both of the new estimators make better use of channel and energy loss information, thus yielding more accurate estimation. Furthermore, the proposed methods overcome the existing approaches' limitation to phase shift keying modulation. Simulation results corroborate the advantages of the new estimators. Analytical performance results are also provided for the proposed estimators.

Robust Blind Detection of Integer Carrier Frequency Offset for Terrestrial Broadcasting Systems Using Band Segmented Transmission

“…After FFO compensation and cyclic prefix removal, the frequency domain samples are obtained via fast Fourier transform (FFT) processing. Once the first step is completed, the IFO is estimated together with residual STO, which can usually be done in the frequency domain [12][13][14][15][16][17][18]. After frequency synchronization, there are residual CFO and SFO errors that continuously rotate the phase of the OFDM symbol.…”

“…The blind estimation method relies on the utilization of any inherent structural information in the OFDM symbol, which is preferred due to its bandwidth efficiency. In [12][13][14][15], the blind approaches were proposed utilizing the combination of data subcarriers and null subcarriers (NSCs) present at the edges of the OFDM spectrum. The main disadvantage of such a blind estimation strategy is that it requires an exhaustive search for IFO estimates.…”

“…If not correctly detected and removed, the fractional CFO (FFO) gives rise to the imperfection of the orthogonality among the subcarriers, leading to the inter-carrier interference (ICI), while the integer CFO (IFO) produces a cyclic shifting of all subcarriers in the frequency domain [8]. To address this issue, a lot of estimation methods have been studied for the estimation of the FFO and the IFO [9][10][11][12][13][14][15][16][17][18].…”

Analysis and design of joint CFO/channel estimate techniques for a cooperative STBC‐OFDM system

“…To avoid such constraints, cooperative relaying, 6,7 which is conceptually constructed from a distributed virtual multiantenna transmission system, can be considered as an alternative to MIMO. Fortunately, there are existing schemes 14,15 that have been presented to estimate an integer part of CFO. Based on the advantages of the foregoing techniques, the integration of cooperative OFDM and the space-time block coding (STBC) 8 is convinced to be a powerful scheme for the physical layer of wireless communications.…”

“…In general, the normalized CFO is defined as the ratio of CFO to the subcarrier spacing and consists of an integer part as well as a fractional part. Fortunately, there are existing schemes 14,15 that have been presented to estimate an integer part of CFO. Here, we focus on the fractional CFO estimate and assume the CFO in the proposed scheme is limited within one half of the subcarrier spacing.…”