Blind Frequency Offset Estimation Research Articles

Blind frequency offset estimation method based on a minimum phase correction error for a full spectrum modulated NFDM system.

To improve the spectral efficiency of a full spectrum modulated nonlinear frequency division multiplexing (FS-NFDM) system, a blind frequency offset estimation (FOE) method has been proposed. The approach based on the minimum phase correction error can achieve high estimation accuracy of sub-MHz without need of any training symbols. Furthermore, in order to reduce the computational complexity, an eigenvalue-shift method is used to get a coarse search interval of FO, and then the one-dimensional optimization algorithm based on golden section search and parabolic interpolation is used to get the optimal FOE for the coarse search interval. The feasibility and reliability of the proposed blind FOE approach have been demonstrated in both BTB and fiber transmission scenarios. Compared with the grid search method, the proposed solving scheme can save hundreds of times of the searches. The experimental results reveal that the proposed method is robust to the amplified spontaneous emission noise and phase noise and has the capabilities of a wide FOE range and a high FOE accuracy.

Blind frequency offset estimation using the optimal decision threshold-assisted QPSK-partition method for probabilistically shaped MQAM systems.

Moderate or strong shaping conditions reduce the occurrence probability of the outermost ring constellation points of probabilistically shaped (PS)-M quadrature amplitude modulation (QAM) signals, which easily causes the peaks in the 4th power periodogram of received signals be submerged, accordingly the classical frequency offset estimation (FOE) scheme using 4th power fast Fourier transform (FFT) cannot be applied in PS-MQAM system. To solve this issue, we have proposed an optimal decision threshold assisted quadrature phase shift keying (QPSK)-partition blind FOE scheme. Firstly, the proposed scheme utilizes an optimal decision threshold assisted method for the symbol decision of received symbols, then chooses the symbols on multiple specific QPSK-shape rings. Secondly, the amplitude of each symbol selected above is normalized and uniformly augmented to 18. Finally, it carries out FOE using an improved time-domain 4th power feedforward method that eliminates the time interval. The effectiveness of the proposed scheme has been verified by 28 GBaud polarization division multiplexing (PDM) PS-16/64QAM simulations and 28/8 GBaud PS-16/64QAM experiments. The results obtained by this scheme present that under moderate or strong shaping conditions, the generalized mutual information (GMI) increases with optical signal-to-noise ratio (OSNR) and eventually exceeds the corresponding GMI threshold. Besides that, the FOE range can reach [-Rs/8, Rs/8], where Rs denotes the baud rate. When OSNRs are higher than 16 dB and 19.5 dB, the NMSEs of PS-16QAM-3/3.6 are lower than 1e-7, respectively. For PS-64QAM-4.4/5, the NMSEs achieve lower than 1e-6 after OSNR increases to 20.3 dB and 23.4 dB, respectively. More importantly, the overall complexity can be reduced to O(N), which is at most as 26.5% as that of FFT FOE scheme.

Blind Frequency Offset Estimation Based on Phase Rotation For Coherent Transceiver

Conventional fast Fourier transform based frequency offset estimation (FFT-FOE) algorithm is suitable for QPSK and 8/16/64QAM signals. However, due to the non-rectangular distribution of constellation points, the conventional FFT-FOE is not suitable for 32-QAM signal. In this paper, we report a factor $\gamma $ which can indicate whether the FFT-FOE algorithm can be used for frequency offset estimation for different modulation formats. The FFT-FOE algorithm is hard to apply for frequency offset estimation if the value of $\gamma $ is low. Fortunately, the value of $\gamma $ can be increased by digital amplification and phase rotation. Based on the digital amplification and phase rotation, a modified FFT-FOE algorithm is proposed and can realize the frequency offset estimation of 32-QAM signal with only 512 symbols. The bit error ratio (BER) of a 28 Gbaud 32-QAM signal is lower than the soft-decision forward-error correction (SD-FEC) limit with the optical signal-to-noise ratio (OSNR) of 22 dB. The proposed method has better robustness to phase noise. If BER at SD-FEC limit is considered for 28Gbaud 32-QAM signal, the required OSNR is relaxed by 2 dB when the laser linewidth is greater than 5 MHz. This will make sense when the wide-linewidth laser is used in short reach optical communication system. The experimental results from 10 Gbaud 32-QAM system with 300 km fiber transmission indicate that the proposed method can be applied when OSNR is greater than 14 dB. The results demonstrate that the proposed frequency offset estimation scheme is also suitable for QPSK and 8/16/64QAM signals. Thus, the proposed algorithm can perform blind frequency offset estimation for a coherent transceiver.

Blind frequency offset estimator for OFDM systems

Orthogonal Frequency Division Multiplexing (OFDM) is of great interest for the development of the fifth-generation technology. It is the cornerstone of Multiple-input multiple-output (MIMO) systems. Even though inter carrier interference (ICI) and inter symbol interference (ISI) have been processed for the fourth-generation standards, they still present a huge problem for the fifth-generation standards. This paper explores the tradeoff between the length of the cyclic prefix and the performances of the OFDM system. It also studies the effect of carrier frequency offset (CFO) on OFDM systems. A blind frequency offset estimator that uses the correlations between the remodulated sequence in the receiver side and the conventional received symbol is presented and a closed form solution is derived. The proposed estimator is derived under short interval when the correlation is high, so it has low computational complexity. Lin and Beek’s estimators are used for comparison. Simulations demonstrate the effectiveness of the proposed estimator under Rayleigh fading channel.

Blind Carrier Frequency Offset Estimation in Coherent Optical Communication Systems With Probabilistically Shaped M-QAM

We find that the conventional 4th power and circular harmonic expansion (CHE) algorithms, which are originally devised for blind frequency offset estimation (FOE) in the uniform M-quadrature amplitude modulation (MQAM) systems, cannot work properly for probabilistically shaped (PS)-MQAM under moderate or strong shaping. To solve this issue, two novel blind FOE algorithms, namely the radius directed (RD)-4th power algorithm and the generalized circular harmonic expansion (GCHE) algorithm, are proposed. The former one adopts QPSK-selection based on a radius threshold optimized for a specific constellation entropy; while the later one conducts maximum likelihood (ML) estimation with a theoretically derived nonlinear radius transfer function in the GCHE. Several issues related to the practical implementation, including the optimization of the radius threshold in the RD-4th power algorithm, the impact of SNR-mismatch in the GCHE algorithm, and the computational complexities of the proposed algorithms, are analyzed. The Monte-Carlo simulation results show that: (1) the RD-4th power algorithm works properly in most of the cases except for very weak shaping, whereas the GCHE algorithm offers robust performance regardless of the shaping strength and outperforms the RD-4th power algorithm in all cases; (2) the performance gap between the two algorithms, which have the same computational complexity, enlarges for a larger constellation entropy. These observations indicate that the GCHE algorithm is a promising blind FOE algorithm, in terms of high estimation accuracy and robust performance, for applications that leverage the rate adaptability of the PS-MQAM, such as flexible optical networks.

Blind Closed-Form Carrier Frequency Offset Estimation for OFDM With Multi-Antenna Receiver

In this paper, we propose a new blind closed-form carrier frequency offset (CFO) estimator for orthogonal frequency-division multiplexing (OFDM) with a multiantenna receiver. A cost function is carefully designed for CFO estimation by using the multiple observations from the receive antennas. We prove that this cost function can be exactly expressed as a cosine function even with the effect of noise. As a result, the CFO estimate can be then obtained in closed form without any searching procedure. The proposed estimator supports fully loaded transmissions, and thus, the spectral efficiency can be saved. As compared with the existing blind maximum-likelihood (ML) estimator for multiantenna receiver, the proposed estimator can achieve comparable estimation performance with only a significantly reduced computational burden. The numerical results are provided to corroborate the proposed studies.

A Blind Carrier Frequency Offset Estimation Scheme for OFDM Systems via Hybrid-ICA Algorithm

This paper addresses a new iterative blind carrier frequency offset (CFO) estimator in orthogonal frequency-division multiplexing (OFDM) systems. In our scenario, relying on a hybrid independent component analysis (ICA) scheme, a blind frequency offset estimator is proposed for OFDM systems employing single antenna. The proposed estimator is a combination of the fast fixed-point ICA (FastICA) algorithm and the natural-gradient ICA algorithm, which inherits the fast convergence and high accuracy of theses algorithms, respectively. As a major advantage, the proposed estimator works in an efficient way in practical high-data-rate OFDM systems especially with large number of subcarriers. To demonstrate the efficiency of our proposed algorithm, numerical results are provided from computer simulations and comparisons are made with other existing CFO estimators in the literature. It is shown that by applying our proposed algorithm, the normalized mean-square error of the CFO estimator is decreased to a high extent. DOI: http://dx.doi.org/10.11591/ijece.v4i5.6533

Blind Maximum Likelihood Carrier Frequency Offset Estimation for OFDM With Multi-Antenna Receiver

In this paper, based on the maximum likelihood (ML) criterion, we propose a blind carrier frequency offset (CFO) estimation method for orthogonal frequency division multiplexing (OFDM) with multi-antenna receiver. We find that the blind ML solution in this situation is quite different from the case of single antenna receiver. As compared to the conventional MUSIC-like CFO searching algorithm, our proposed method not only has the advantage of being applicable to fully loaded systems, but also can achieve much better performance in the presence of null subcarriers. It is demonstrated that the proposed method also outperforms several existing estimators designed for multi-antenna receivers. The theoretical performance analysis and numerical results are provided, both of which demonstrate that the proposed method can achieve the Cramer-Rao bound (CRB) under the high signal-to-noise ratio (SNR) region.

A Blind Frequency Offset Estimator for Coherent M-PSK System in Autonomous Radio

This paper presents a novel blind frequency offset estimator for coherent M-PSK systems in an autonomous radio. The proposed estimator is based on the spectrum of the signal's argument. A data remo...

Frequency Offset Estimation for Unknown QAM Constellations

We introduce a novel, both gain and signal-to-noise ratio independent, constellation unaware, blind frequency offset estimation procedure for QAM signals. Asymptotic performance analysis and numerical simulations show that the herein presented method outperforms a selected state of the art blind constellation unaware estimator, especially for cross constellations.

An Efficient Blind Deterministic Frequency Offset Estimator for OFDM Systems

This paper proposes an efficient blind deterministic carrier frequency offset (CFO) estimation method for orthogonal frequency division multiplexing (OFDM) systems. In the proposed method, two OFDM symbols with time difference are generated by exploiting both the oversampled OFDM signal and the cyclic prefix, and a cost function is introduced for CFO estimation. It is shown that the cost function can be expressed as a cosine function. Using a property of the cosine function, a formula for estimating the CFO is derived. The estimator of the CFO requires three independent cost function values calculated at three different frequency offsets. Using the formula, the CFO can be estimated without searching all the frequency offset range. The proposed method is very suitable for real wireless environments since it requires only one OFDM symbol for blind reliable estimation of CFO. The computer simulations show that the performance of the proposed method is superior to those of the MUSIC method and the oversampling method . Unlike the conventional methods such as MUSIC method and the oversampling method, the accuracy of the proposed method is independent of the searching step.

Blind frequency offset estimation based on cyclic prefix and virtual subcarriers in CO-OFDM system

A new blind frequency offset estimation method based on cyclic prefix and virtual subcarriers in coherent optical orthogonal frequency division multiplexing (CO-OFDM) system is presented. It is able to estimate the fractional part and integral part of frequency offset at the same time. Its estimation range is about [?3.5 GHz, 3.5 GHz]. The influence of the integral frequency offset is comprehensively analyzed in COOFDM system. Its performances in the additive white Gaussian noise (AWGN) channel and the dispersive channel are investigated, respectively. Simulation results indicate that even in the dispersive channel, when the optical signal-to-noise ratio (OSNR) is low, it can still work very well.

Blind iterative frequency offset estimator for orthogonal frequency division multiplexing systems

This study presents an iterative carrier frequency offset estimator for orthogonal frequency division multiplexing (OFDM) systems. The proposed estimator is based on the efficient Viterbi-and-Viterbi (VAV) algorithm. The proposed estimator is blind and can be used with non-constant modulus subcarrier modulations such as quadrature amplitude modulation (QAM). The performance of the proposed estimator is assessed theoretically and via Monte Carlo simulations over various channel models and compared to the performance of other well established blind techniques in addition to the Cramer–Rao lower bound. The comparison results demonstrate that the proposed estimator outperforms other well-established blind estimators by more than 12 dB at moderate and high signal-to-noise ratios (SNRs).

Gain-Control-Free Blind Carrier Frequency Offset Acquisition for QAM Constellations

This paper introduces a novel blind frequency offset estimator for quadrature amplitude modulated (QAM) signals. Specifically, after a preliminary frequency compensation, the estimator is based on the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">¿/2</i> -folded phase histogram of the received data. Then, the frequency offset estimate is taken as the frequency compensation value that minimizes the mean square error between the phase histogram measured on the received samples and the reference phase probability density function analytically calculated in the case of zero frequency offset. The ¿/2 -folded phase histogram of the received data is here called Constellation Phase Signature, since it definitively characterizes the phase distribution of signal samples belonging to a particular QAM constellation, and it has already been employed to develop a gain-control-free phase estimator that well performs both for square and cross constellations. Also the here described frequency offset estimator has the remarkable property to be gain-control-free and, thus, it can be fruitfully employed in frequency acquisition stages. The asymptotic performance of the estimator has been analytically evaluated and assessed by numerical simulations. Theoretical analysis and numerical results show that the novel frequency offset estimator outperforms state-of-the art estimators in a wide range of signal-to-noise ratio (SNR) values.

Blind frequency-offset estimator for OFDM with general symbol constellation

An efficient feedforward blind carrier frequency offset (CFO) estimator for orthogonal frequency division multiplexing (OFDM) systems with general symbol constellation is presented. The proposed estimator requires only one OFDM symbol period to blindly and accurately estimate the CFO in Gaussian and multipath fading channels.

A Novel Frequency Offset Estimation for OFDM Systems

SUMMARY 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).

Blind Estimation of MC-CDMA Carrier Frequency Offset

In this letter, two types of blind adaptive frequency offset estimator for multicarrier code division multiple access systems are proposed that do not need any specific training sequence. It can not only accurately estimate the frequency offset, but also improve the revision capability and convergence rate. Several computer simulations confirm the effectiveness of the blind estimate approaches.

New blind frequency offset estimator for OFDM systems over frequency selective fading channels

In this paper, a blind frequency offset estimator for orthogonal frequency division multiplexing (OFDM) systems over frequency selective fading channels based on modeling the unknown channel fading gains as deterministic variables is proposed. In this estimator, the received time domain OFDM samples are first partitioned into subsets, in which neighboring samples are uncorrelated, leading to a tri-diagonal signal correlation matrix for each subset. The ML cost functions from each of the subsets are combined to perform frequency offset estimation. Simulation results show that the proposed frequency offset estimator achieves better performance than the estimators reported in [J.-J. Van De Beek, M. Sandell, P.O. Borjesson, ML estimation of time and frequency offset in OFDM systems, IEEE Trans. Signal Process. 45 (July 1997) 1800–1805] and [X. Ma, G.B. Giannakis, S. Barbarossa, Non-data-aided frequency-offset and channel estimation in OFDM: and related block transmission, IEEE ICC’01, June 2001, pp. 1866–1870]. Moreover, although the power delay profile needs to be known in deriving the proposed estimator, simulation and analytical results show that the performance of the proposed estimator is not sensitive to variation in the power delay profile.

Analysis of ESPRIT-Based Algorithms for Blind Frequency Offset Estimation on MC-CDMA Downlink

In this letter, we investigate ESPRIT-based approaches for blind frequency offset estimation on MC-CDMA downlink. By analyzing the signal subspace structures of the MC-CDMA signals, the natures of the spreading codes and the number of users determine the feasibility of the ESPRIT-based approaches for the blind estimation task.

Blind frequency offset estimation for overlap PCC-OFDM systems in presence of phase noise

Blind frequency offset estimation for overlap PCC-OFDM systems in presence of phase noise