Non-Data-Aided Joint Carrier Frequency Offset and Channel Estimator for Uplink MC-CDMA Systems
ABSTRACT This paper addresses the problem of joint estimation of carrier frequency offset (CFO) and channel impulse response (CIR) in the uplink transmission of multicarrier code-division multiple-access (MC-CDMA) systems. A subspace-based blind estimator is proposed, which only uses the received signal and the desired user's spreading code to estimate the CFO and CIR. The CFO is estimated using a one-dimensional linear search where the objective of the search is to minimize the determinant of a low dimensional matrix and the CIR is estimated as the unit-norm eigenvector corresponding to the minimum eigenvalue of this matrix. The identifiability of the CFO and CIR estimates is investigated by imposing asymptotic constraints on the spreading codes. Although the cost function used by the proposed estimator is nonlinear and nonconvex, it is locally convex in the neighborhood of the true CFO value. This property is used to formulate a simple two-stage CFO estimator. In the first stage, a coarse search is performed to lock into the local convexity region. Then, an adaptive algorithm is used in the second stage to finetune the CFO estimate. The ldquolinearizedrdquo proposed estimator is shown to be unbiased. The simulation results show that the proposed estimator's performance is close to the Cramer-Rao lower bound (CRLB).
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ABSTRACT: 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.IEEE Transactions on Vehicular Technology 10/2012; 61(8):3790-3795. DOI:10.1109/TVT.2012.2208662 · 2.64 Impact Factor
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ABSTRACT: For uplink multi-carrier code-division multiple access (MC-CDMA) systems, we propose a multiuser detector that is robust to a small residual frequency offset existing after frequency offset estimation and compensation. In this paper, when the residual frequency offset is normalized by subcarrier spacing, it is called a normalized residual frequency offset (NRFO). In the proposed scheme, we first derive a lower bound of the signal-to-interference plus noise ratio (SINR) of the desired user when the NRFO of the desired user is bounded by a small value and the value is known to the receiver. We then design a detection filter to maximize the SINR lower bound. Simulation results show that the proposed scheme has better SINR and bit error rate (BER) performances in a high signal-to-noise ratio (SNR) region than a conventional minimum mean square error (MMSE) receiver that ignores the NRFO.IEEE Communications Letters 10/2012; 16(10):1612-1615. DOI:10.1109/LCOMM.2012.090312.121158 · 1.46 Impact Factor
Conference Paper: ICA detection for MC-CDMA systems[Show abstract] [Hide abstract]
ABSTRACT: The multicarrier code division multiple access (MC-CDMA) technique has received considerable attention due to its high data rate for future wireless communication systems. A common problem to multiuser MC-CDMA detectors under Rayleigh fading channels is that the performance is very sensitive to the signature waveform mismatch (SWM) induced by channel estimation distortion. Besides, the disturbance of colored noise could make the performance of the system worse. In this paper, the proposed multiuser detector which utilizes the modified independent component analysis (ICA) algorithm based on approximate negentropy maximization under the second-order cone programming (SOCP) constraint can provide robustness against small-to-medium SWM over colored noise environment for a synchronous MC-CDMA system.Intelligent Signal Processing and Communications Systems (ISPACS), 2012 International Symposium on; 01/2012