Blind Carrier Frequency Offset Estimation Research Articles

A New Cyclic-Prefix Based Algorithm for Blind CFO Estimation in OFDM Systems

In this paper, a new algorithm based on cyclic prefix (CP) is proposed for blind carrier frequency offset (CFO) estimation in orthogonal frequency division multiplexing (OFDM) transmission over multipath channels. Like other CP-based methods, the proposed method enjoys low complexity. The proposed method is very robust to the symbol timing synchronization error. Closed-form formulas for CFO estimates are derived. In addition, we also carry out the theoretical mean-square-error analysis and derive the Cramer-Rao bound. Simulation results show that the proposed method performs very well.

Blind Frequency Synchronization for Multiuser OFDM Uplink With Large Number of Receive Antennas

In this paper, we propose a new blind frequency synchronization scheme for multiuser orthogonal-frequency-division multiplexing (OFDM) uplink transmissions. The spatial multiplexing is supported in the considered model that allows the subcarriers to be simultaneously occupied by multiple users, while the orthogonal frequency division multiple access (OFDMA) can serve as a special case of our discussion. We propose to assign different null subcarriers to different users and design algorithm that can perform blind carrier frequency offset (CFO) estimation for each individual user with the aid of large number of receive antennas, which then removes the necessity of multidimensional searching. After estimating CFO for one user, the orthogonal complement space of the other users can be obtained which could be further utilized for multiuser interference cancelation. Hence, the multiuser OFDM uplink model reduces to an equivalent single user signal model, where the blind channel estimation with scalar ambiguity can be designed and the conventional single-user data detection can be peformed. To make the proposed study complete, the closed-form performance analysis for mean square error (MSE) of the CFO estimation is derived, based on which the discussion about optimal null subcarrier assignment scheme is further provided. Finally, the Cramer–Rao bound (CRB) is derived, and the numerical results are provided to corroborate the proposed studies.

Blind carrier frequency offset estimation for single carrier and orthogonal frequency division multiplexing signals using least‐order cyclic moments

A definition of least cyclostationary order (LCO) is proposed based on the inner cyclic period of single carrier and orthogonal frequency division multiplexing (OFDM) signals. The LCOs of single carrier and OFDM signals are derived. Since the LCO has a relationship with the carrier frequency offset (CFO), a blind CFO estimation scheme for single carrier and OFDM signals can be proposed. The novel scheme is entirely blind without any priori information and is proved to be the same as cumulants estimation when the LCO is known. However, the new scheme is superior to the estimation based on cumulant when the LCO is unknown. The mean-square error of M-phase shift keying signals approaches the Cramer–Rao bound in additive white Gaussian noise (AWGN) channel. Simulation results are given to verify the effectiveness of the proposed blind estimation scheme in Rician fading channel and in AWGN channel.

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.

Blind CFO estimation based on decision directed MUSIC technique for interleaved uplink OFDMA

This paper deals with blind carrier frequency offset (CFO) estimation based on the multiple signal classification (MUSIC) criterion with Taylor series expansion for interleaved orthogonal frequency division multiple access uplink systems. An efficient estimator is suggested which finds a new CFO vector based on the Taylor series expansion of the one initially given in the presence of CFO. The problem of finding the new CFO vector is formulated as the closed form of a generalized eigenvalue problem, which allows one to readily solve it. Due to more accurate residual CFO estimate, which can provide more accurate residual CFO compensation, this paper also presents a decision-directed MUSIC scheme to improve the CFO estimation performance. The proposed estimator not only can estimate CFO, but also entail less computational load. Several computer simulation results are provided for illustrating the effectiveness of the proposed blind CFO estimator.

Blind CFO Estimation for OFDM/OQAM Systems Over Doubly-Selective Fading Channels

Orthogonal Frequency Division Multiplexing based on Offset Quadrature Amplitude Modulation (OFDM/OQAM) systems are highly sensitive to Carrier Frequency Offset (CFO), especially in doubly selective fading channels. In this paper, by modeling the doubly selective channel with Basis Expansion Model (BEM), we prove the cyclostationarity of the received OFDM/OQAM signal in the presence of CFO. A blind CFO estimator is proposed based on the derived close-form second-order cyclic statistic. Analysis and simulation results demonstrate that the proposed estimator provides robust CFO estimation performance in OFDM/OQAM systems over doubly selective fading channels.

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

Iterative Blind Carrier Frequency Offset Estimation Based on Orthogonal Projection Approach Under Single Data Block for Interleaved OFDMA Uplink

In this letter, an iterative approach based on the orthogonal projection (OP) criterion is presented to estimate carrier frequency offset (CFO) for interleaved orthogonal frequency division multiple access (OFDMA) uplink systems. The proposed estimator includes the center-symmetric trimmed correlation matrix and OP technique. It doesn't require eigen-decomposition and only needs single OFDMA data block. To reduce computation complexity, the proposed estimator iteratively searches for the correct CFO vector by minimizing the objective function using a first-order Taylor series approximation of the CFO vector with the one initially given. Computer simulation is also provided for illustrating the effectiveness of the proposed iterative blind CFO estimator.

One-Shot Blind CFO and Channel Estimation for OFDM With Multi-Antenna Receiver

In this paper, we design a new blind joint carrier frequency offset (CFO) and channel estimation method for orthogonal frequency-division multiplexing (OFDM) with multiantenna receiver. The proposed algorithm requires only one received OFDM block and thus belongs to the category of one-shot estimation methods. Other advantages of the proposed algorithm include 1) it supports fully loaded data carriers and is thus spectral efficient; 2) the channel from the transmitter to each receive antenna can be blindly estimated with only a scaling ambiguity; and 3) the algorithms outperforms the existing methods. Moreover, we derive the Cramer-Rao Bounds (CRB) of joint CFO and channel estimation in closed forms. Numeral results not only show the effectiveness of the proposed algorithm but also demonstrate its closed performance to CRB.

Blind carrier frequency offset mitigation in space–time block‐coded multicarrier code division multiple access uplink transmission

SummaryIn this paper, a novel blind carrier frequency offset (CFO) estimation is proposed on the basis of the linearly constrained optimization for the uplink transmission of space–time block‐coded multicarrier code division multiple access systems. First, the full‐dimensional spatial‐and‐temporal data are formed to avoid violation of the second‐order statistics in the conventional receiver design. A set of weight vectors is then provided for acquiring each multipath signal from the desired user while the others get rejected. Finally, the estimated CFO is obtained in accordance with maximizing the well‐defined measurement function, which is formulated by collecting all the output powers of the receiver. A space–time averaging technique is also proposed to enhance the robustness to the finite sample effect. Simulation study confirms that with the proposed CFO estimator used in the preceding, the receiver can successfully achieve the same performance of the optimal receiver working in the absence of CFO. Copyright © 2014 John Wiley & Sons, Ltd.

Blind carrier frequency offset estimation for tile‐based orthogonal frequency division multiple access uplink with multi‐antenna receiver

In this study, the authors propose a blind carrier frequency offset (CFO) estimation method for the tile structure orthogonal frequency division multiple access (OFDMA) uplink with multi-antenna receiver. They employ an iterative approach to extract the signal component for each user gradually and propose a carefully designed CFO estimator to update the CFO estimate during the iterative procedure. The key ingredient of the proposed method is using few subcarriers on both sides within each tile as the ‘guard subcarriers’, which can greatly mitigate the effect of multi-user interference. The proposed method supports not only fully loaded transmissions, but also the generalised assignment scheme that provides the flexibility for dynamical resource allocation. The numerical results are provided, which indicate that the proposed method can almost converge to the analytical lower bound within a few iterative cycles. It is seen that the proposed method also outperforms the existing competitor with multi-antenna receiver in terms of estimation performance, especially with few adopted blocks.

An Efficient Blind Estimation of Carrier Frequency Offset in OFDM Systems

In this paper, we propose a low-complexity blind carrier frequency offset (CFO) estimation scheme for constant modulus (CM)-signaling-based orthogonal frequency-division multiplexing (OFDM) systems. Provided that the channel can be assumed to be slowly time-varying, subcarriers having the same indexes in two consecutive OFDM symbols will experience nearly the same channel effect. This assumption enables us to derive a cost function that is determined by the sum of the products of the signal amplitudes on each pair of equivalent subcarriers from two successive OFDM symbols. The maximization process of this cost function makes it possible to find an appropriate estimate of the CFO. Over frequency-selective Rayleigh fading channels, the proposed CFO estimation method provides improved performance over existing techniques. Moreover, in the context of narrow-band noise and signal gain variations, the simulations demonstrate the robustness and immunity of our scheme.

Blind estimation of carrier frequency offset for OFDM systems with time-varying DC offset

Orthogonal frequency division multiplexing (OFDM) has been widely adopted in radar and communication systems. High sensitivity to carrier frequency offset (CFO) is one of the major drawbacks of OFDM. CFO estimation for OFDM systems had been extensively studied and various algorithms had been proposed. However, the established algorithms may be compromised by the adoption of direct-conversion architecture and multi-mode low noise amplifier in the OFDM receiver, which introduces time-varying direct current offset (TV-DCO) into the system. In our previous study, we developed an eigen-decomposition based estimation algorithm, which is robust to TV-DCO but suffers from performance degradation under low to medium signal-to-noise ratio and requires high computation efforts. To address those issues, we in this paper propose a novel blind CFO estimation algorithm. By making use of the second order differential filtering and subspace method, the proposed algorithm achieves great performance improvement with reduced complexity. The performance of the proposed algorithm is demonstrated by simulations.

Frequency-Offset Estimation of Satellite-Based AIS Signals

Aiming at satellite-based Automatic Identification System (AIS) signals, a blind carrier frequency-offset estimation method was investigated on AWGN channels. Estimation algorithm that is based on the autocorrelation function and a suitable smoothing function was deduced to estimate the frequency-offset. Simulation results show that its accuracy is better than the earlier methods and reduced the computational complexity.

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 LCMV-Based CFO Estimation for MC-CDMA Systems Over Multipath Fading Channels

This paper proposes a blind carrier frequency offset (CFO) estimation for multi-carrier code-division multiple access systems over multipath fading channels. The scheme first determines a preliminary CFO estimate by maximizing the total output power of a set of correlators, which is constructed with the linearly constrained minimum variance optimization. A fine CFO estimate is subsequently found by solving the well-developed quadratic cost function. Finally, by using the frequency-compensated data, a subspace minimum output energy (MOE) receiver is formed to provide the maximum output signal-to-interference-plus-noise ratio. Numerical results demonstrate that, with the proposed CFO estimation as a stage proceed, the subspace MOE receiver can achieve nearly the performance of the optimal minimum mean square error receiver.

Robust MVDR Estimation via Polynomial Rooting for MC-CDMA Carrier Frequency Offset

In this letter, we present a blind carrier frequency offset (CFO) estimator by exploiting the polynomial rooting technique for multicarrier-code division multiple access (MC-CDMA) systems. Relative high accuracy and low-complexity to the CFO estimation can be achieved by rooting a polynomial. Simulation results are provided for illustrating the effectiveness of the proposed blind polynomial rooting estimator.

Blind Residual Carrier Frequency Offset and Timing Offset Estimation Using Improved Minimum Output Variance Approaches in Uplink MC-CDMA Systems

This paper deals with blind residual carrier frequency offset (CFO) and timing offset (TO) estimation based on minimum output variance (MOV) criterion without devoting training sequence and pilot symbol for uplink multicarrier-code division multiple access (MC-CDMA) systems. It has been shown that the performance of MOV estimator is degraded because the effect of noise and wideband spread-spectrum signals. In conjunction with spreading code-aided and subspace projection techniques, we present an improved code-aided MOV (ICMOV) estimator to achieve the high accuracy estimate for the noisy case. Due to more accuracy residual CFO estimate can provide more accuracy residual TO estimate, this paper also present a decision-directed ICMOV (DD-ICMOV) approach to improve the estimation performance of ICMOV estimator. Computer simulations are provided for illustrating the effectiveness of the proposed approaches.

MCMOE-Based CFO Estimator Aided With the Correlation Matrix Approach for Alamouti's STBC MC-CDMA Downlink Systems

This paper addresses the estimation problem of carrier frequency offset (CFO) in the downlink transmission of space-time block-coded multicarrier code-division multiple-access (STBC MC-CDMA) systems over multipath fading. This study proposes a multiply constrained minimum output energy (MCMOE)-based blind CFO estimator, which is simply assisted by the presented correlation matrix approach to efficiently achieve the CFO estimate. We formulate a two-level CFO estimator by optimizing the receiver output power, as well as the data correlation matrix. At the first level, all possible CFO candidates are found by evaluating the well-defined estimated merit figure. Then, exploiting multiple constraints in the design of the MCMOE receiver, a criterion is used in level two to determine the exact CFO estimate. Numerical results are presented to verify that both precise CFO estimation and reliable error performance can be achieved, even when the channel is dominated by noise because the impact of CFO on the output signal-to-interference-plus-noise ratio (SINR) and bit error rate (BER) are effectively removed by the proposed CFO estimator.

Blind Carrier Frequency Offset Estimation for Interleaved OFDMA Uplink

In this paper, we develop two novel blind carrier frequency offset (CFO) estimators for interleaved orthogonal frequency division multiple access (OFDMA) uplink transmission in a multiantenna system. The first estimator is the subspace-based one and could blindly estimate multiple CFOs from a rank reduction approach. The second estimator is based on the maximum likelihood (ML) approach and improves the performance as compared to the first one. The higher computational complexity of the ML estimator is alleviated by the alternating projection (AP) method. Both the proposed estimators support fully loaded data transmissions, i.e., all subcarriers being occupied, which provides higher bandwidth efficiency as compared to the existing schemes. The numerical results are then provided to corroborate the proposed studies.