共查询到20条相似文献,搜索用时 31 毫秒
1.
Xiaoli Ma Tepedelenlioglu C. Giannakis G.B. Barbarossa S. 《Selected Areas in Communications, IEEE Journal on》2001,19(12):2504-2515
The ability of orthogonal frequency-division multiplexing systems to mitigate frequency-selective channels is impaired by the presence of carrier frequency offsets (CFOs). In this paper, we investigate identifiability issues involving high-resolution techniques that have been proposed for blind CFO estimation based on null subcarriers. We propose new approaches that do not suffer from the lack of identifiability and adopt adaptive algorithms that are computationally feasible. The performance of these techniques in relation to the location of the null subcarriers is also investigated via computer simulations and compared with the modified Cramer-Rao bound 相似文献
2.
Xiaoli Ma 《Communications, IEEE Transactions on》2005,53(12):2129-2138
Carrier frequency offset (CFO) estimation for orthogonal frequency-division multiplexing (OFDM) has caught attention as OFDM systems have become widely adopted in recent years. In this paper, we design a novel double-differential (DD) codec with low computational complexity. Our design bypasses CFO and channel estimation, and is easy to implement at both transmitter and receiver. It also guarantees full multipath diversity, and reduces the peak-to-average power ratio from the number of subcarriers to the channel order. In addition, it is robust to CFO drifting. The closed form of the performance for our design is derived for OFDM transmissions over frequency-selective channels with CFO. Thorough simulation results corroborate our claims. 相似文献
3.
Parallel interference cancellation (PIC) assisted with recursive least squares (RLS) algorithm is proposed to cancel the interference due to the carrier frequency offset (CFO) in orthogonal frequency division multiplexing (OFDM) system. The proposed algorithm is composed of two stages, which are RLS scheme and PIC scheme. RLS scheme is selected to compensate the frequency offset in the time domain in the first stage, and the interference induced by residual frequency offset is canceled by the PIC scheme in the frequency domain in the second stage. The result of bit error rate (BER) shows that its performance is robust for cancellation as comparison criteria, even though the frequency offset is 0.45. The 16QAM constellation is also simulated to observe the improvements from the proposed suppression schemes. 相似文献
4.
Bo Seok Seo Su Chang Kim Jinwoo Park 《Electronics letters》2002,38(24):1520-1521
A coarse carrier frequency offset estimation algorithm for orthogonal frequency division multiplexing (OFDM) systems is proposed. The algorithm exploits the phase difference of the adjacent subcarriers of the received signal, which is proportional to the frequency offset. The proposed scheme necessitates much lower computational load compared to the conventional correlation based methods, while it reveals similar estimation performance for practical OFDM systems. 相似文献
5.
Yugang Ma 《Communications Letters, IEEE》2003,7(4):177-179
Two modified nonlinear least square (NLS) estimators for carrier frequency offset (CFO) in orthogonal frequency-division multiplexing (OFDM) systems are proposed. In the modified NLS CFO estimators, slot elements in an OFDM block symbol are weighted in terms of their received energies. Simulation results show that the proposed new estimators outperform the original one especially in a low signal-to-noise ratio range. 相似文献
6.
In this letter, we propose a blind carrier frequency offset (CFO) estimator with high resolution and high bandwidth efficiency for orthogonal frequency-division multiplexing (OFDM) systems. The proposed estimator utilizes minimum output variance to estimate CFO. Simulation results show that the proposed estimator is highly accurate and reliable for OFDM systems. 相似文献
7.
针对正交频分复用系统频偏估计问题,提出了一种基于遗传算法的高精度盲频偏估计器。该算法首先将带载波间干扰的正交频分复用系统视为正交码分多址接入系统,将载波间干扰系数视为码分多址接入系统的扩频码,利用估计的载波频偏构造扩频码,进而重建接收信号;然后利用重建信号跟实际接收信号最小重建误差原则构造了盲频偏估计的代价函数,并设计了对应于遗传算法的适应度函数;最后利用遗传算法强大的并行搜索和全局寻优能力,通过最小化代价函数求得最佳频偏估值。仿真结果表明,所提算法具有较高的估计精度,低信噪比下性能显著,有效降低了时间复杂度,且不受频偏估计范围和信号调制类型的限制。 相似文献
8.
Cai Xuelian Li Jiandong Li Changle Chen Chen 《电子科学学刊(英文版)》2005,22(6):569-574
One of the principal disadvantages of Orthogonal Frequency Division Multiplexing (OFDM) is very sensitive to carrier frequency offset. The integer frequency offset has no effect on the orthogonality among the subcarriers, but it causes a circular shift and phase rotation of the received data symbols sequence, resulting in a Bit Error Rate(BER) of 0.5. In this paper, a novel integer frequency offset estimator for OFDM is derived based on maximum likelihood estimation technique and exploration of the differential relation between two consecutive OFDM data symbol sequences in frequency domain. Its performance is compared with the conventional method by computer simulations for the additive white Gaussian noise channel and a multipath fading channel. Simulation results show that the performance of the proposed estimator is better than the conventional estimator. 相似文献
9.
An improved frequency offset estimator for OFDM applications 总被引:3,自引:0,他引:3
An efficient algorithm has been proposed by Schmidl and Cox (see IEEE Trans. Commun., vol.45, p.1613-21, 1997) for carrier frequency estimation in orthogonal frequency-division multiplexing systems. The scheme is based on the transmission of a training symbol composed of two identical halves in the time domain. We extend this algorithm by considering a training symbol composed of L>2 identical parts. This makes it possible to achieve a better accuracy at the cost of some increase in computational load. The estimation range can be made as large as desired without the need of a second training symbol, as required by the Schmidl and Cox method 相似文献
10.
OFDM blind carrier offset estimation: ESPRIT 总被引:4,自引:0,他引:4
In orthogonal frequency-division multiplex (OFDM) communications, the loss of orthogonality due to the carrier-frequency offset must be compensated before discrete Fourier transform-based demodulation can be performed. This paper proposes a new carrier offset estimation technique for OFDM communications over a frequency-selective fading channel. We exploit the intrinsic structure information of OFDM signals to derive a carrier offset estimator that offers the accuracy of a super resolution subspace method, ESPRIT 相似文献
11.
A high-efficiency carrier estimator for OFDM communications 总被引:1,自引:0,他引:1
While multipath induced phase rotations can be dealt with by differential encoding in orthogonal frequency division multiplexing (OFDM) communications, the loss of orthogonality due to the carrier offset must be compensated before discrete Fourier transform (DFT)-based demodulation can be performed. In this letter, we present a high-performance/low-complexity blind carrier offset estimation algorithm by exploiting intrinsic structure information of OFDM signals. The algorithm offers the accuracy of a super resolution subspace method, viz. MUSIC, without involving computationally intensive subspace decompositions 相似文献
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14.
Two important, to scientists and engineers, sphere fitting procedures, namely the linear least squares (LLS) and the non-linear least squares (NLLS) methods and their general random-error analysis are described. The first-order random errors of the center coordinates and the radius of the fitted sphere using the above mentioned procedures are derived in detail under the assumption that the variance-covariance matrix exists for the random error vector. With the additional trivariate normal error distribution assumption, the Maximum Likelihood (ML) estimators and their standard deviations are also derived. The effectiveness of these procedures are studied through computer stimulation. 相似文献
15.
Low-complexity pilot-aided compensation for carrier frequency offset and I/Q imbalance 总被引:1,自引:0,他引:1
We propose a novel pilot-aided compensation scheme for carrier frequency offset (CFO) and I/Q imbalance. The proposed scheme comprises a generalized periodic pilot and a low-complexity acquisition algorithm, where the CFO and the coefficients for I/Q imbalance compensation can be obtained in explicit closed-form. 相似文献
16.
Yun Hee Kim Iickho Song Seokho Yoon So Ryoung Park 《Vehicular Technology, IEEE Transactions on》2001,50(5):1307-1312
In this paper, we propose a new frequency synchronization algorithm for orthogonal frequency division multiplexing (OFDM) systems requiring only one training symbol, based on a conventional method which requires two training symbols. While the timing synchronization is obtained by using the conventional method, the carrier frequency offset is efficiently estimated by the proposed method. It is shown that the proposed method not only reduces the number of the training symbols but also possesses better performance than the conventional method without increase in complexity 相似文献
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18.
Sanguinetti L. Morelli M. Imbarlina G. 《Wireless Communications, IEEE Transactions on》2009,8(9):4470-4475
We consider an orthogonal frequency-division multiplexing (OFDM) system and address the problem of carrier frequency estimation in the presence of narrowband interference (NBI) with unknown power. This scenario is encountered in emerging spectrum sharing systems, where coexistence of different wireless services over the same frequency band may result into a remarkable co-channel interference, and also in digital subscriber line transmissions as a consequence of the cross-talk phenomenon. A possible solution for frequency recovery in OFDM systems plagued by NBI has recently been derived using the maximum-likelihood criterion. Such scheme exhibits good accuracy, but involves a computationally demanding grid-search over the uncertainty frequency range. In the present work, we derive an alternative method that provides frequency estimates in closed-form by resorting to the expectation-maximization algorithm. This makes it possible to achieve some computational saving while maintaining a remarkable robustness against NBI. 相似文献
19.
Kaufman L 《IEEE transactions on medical imaging》1993,12(2):200-214
The EM algorithm is the basic approach used to maximize the log likelihood objective function for the reconstruction problem in positron emission tomography (PET). The EM algorithm is a scaled steepest ascent algorithm that elegantly handles the nonnegativity constraints of the problem. It is shown that the same scaled steepest descent algorithm can be applied to the least squares merit function, and that it can be accelerated using the conjugate gradient approach. The experiments suggest that one can cut the computation by about a factor of 3 by using this technique. The results are applied to various penalized least squares functions which might be used to produce a smoother image. 相似文献
20.
Orthogonal frequency division multiplexing (OFDM) systems with direct-conversion receiver (DCR) are vulnerable to carrier frequency offset (CFO), dc offset (DCO) and in-phase/quadrature (I/Q) imbalance. In this paper, we propose blind estimator for joint estimation of CFO, DCO and I/Q imbalance in OFDM systems with DCR. Simulation results show that performance of proposed estimator approaches Cramér-Rao lower bound (CRLB) asymptotically, which demonstrates its effectiveness. 相似文献