共查询到20条相似文献,搜索用时 15 毫秒
1.
We consider the problem of estimating the frequency offset between the transmitter and receiver in flat-fading communication channels using a training sequence. Kuo and Fitz (1997) and Morelli, Mengali and Vitetta (see IEEE Commun. Lett., vol.2, p.327-30, 1998), proposed two frequency estimators to solve the aforementioned problem. They rely on weighted linear regression for the phases of the correlation sequence or their differences. The method of Kuo et al. needs phase unwrapping and both methods require knowledge of the correlation of the fading process. In this paper, two simple methods which do not require any of these assumptions are proposed. The first is the unweighted version of the method of Morelli et al. The second is drawn from the array processing framework. It is based on a nonlinear least-squares approach that assumes an unstructured correlation of the fading process. The performance of the proposed methods is as good as that of the methods of Kuo et al. and Morelli et al., but the robustness of our methods to modeling errors is much enhanced 相似文献
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This paper addresses an optimal periodic training signal design for frequency offset estimation in frequency-selective multipath Rayleigh fading channels. For a fixed transmitted training signal energy within a fixed-length block, the optimal periodic training signal structure (the optimal locations of identical training subblocks) and the optimal training subblock signal are presented. The optimality is based on the minimum Cramer-Rao bound (CRB) criterion. Based on the CRB for joint estimation of frequency offset and channel, the optimal periodic training structure (optimality only in frequency offset estimation, not necessarily in joint frequency offset and channel estimation) is derived. The optimal training subblock signal is obtained by using the average CRB (averaged over the channel fading) and the received training signal statistics. A robust training structure design is also presented in order to reduce the occurrence of outliers at low signal-to-noise ratio values. The proposed training structures and subblock signals achieve substantial performance improvement. 相似文献
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Fang Zhi Xiao Wan'ang Shi Yin 《电子科学学刊(英文版)》2008,25(1):1-6
A new fine carrier frequency offset estimation algorithm in Orthogonal Frequency Division Multiplexing (OFDM) system is proposed. The correlation item is the training sequence instead of the received signal in the new algorithm. Simulation results show that the performance of the new algorithm is 4dB-9dB better than that of Schmidl's algorithm. Coarse frequency offset estimation is also discussed in this paper, which is the improvement of Zhang's method. The estimation range using the improvement method is twice as that using the Zhang's method. Based on the hardware of the receiver and the improved algorithm, a method using Fast Fourier Transform (FFT) is proposed to implement the coarse frequency estimation. The chip area of OFDM system can be reduced by using the proposed method. 相似文献
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OFDM在对抗多径方面是一种有效的宽带数字通信技术,但是由于频率误差的存在,使得OFDM(正交频分复用)子载波之间的正交性遭到破坏,系统在频率选择性衰落信道中的传输能力大大下降。本文提出了一种精确的频率误差估计法,可以很好地恢复频率同步。该方法的主要特点是以FFT为界分别在时域和频域内进行频率误差估计,并在时域中进行频率误差校正。 相似文献
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This paper discusses the effects of frequency offset on the performance of orthogonal frequency division multiplexing (OFDM) digital communications. The main problem with frequency offset is that it introduces interference among the multiplicity of carriers in the OFDM signal. It is shown, and confirmed by simulation, that to maintain signal-to-interference ratios of 20 dB or greater for the OFDM carriers, offset is limited to 4% or less of the intercarrier spacing. Next, the paper describes a technique to estimate frequency offset using a repeated data symbol. A maximum likelihood estimation (MLE) algorithm is derived and its performance computed and compared with simulation results. Since the intercarrier interference energy and signal energy both contribute coherently to the estimate, the algorithm generates extremely accurate estimates even when the offset is far too great to demodulate the data values. Also, the estimation error depends only on total symbol energy so it is insensitive to channel spreading and frequency selective fading. A strategy is described for initial acquisition in the event of uncertainty in the initial offset that exceeds 1/2 the carrier spacing, the limit of the MLE algorithm 相似文献
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A novel frequency offset estimation method for OFDM systems with large estimation range 总被引:4,自引:0,他引:4
Chunlin Yan Shaoqian Li Youxi Tang Xiao Luo Jiayi Fang 《Broadcasting, IEEE Transactions on》2006,52(1):58-61
In this paper, we proposed a novel frequency synchronization method which has larger estimation range than conventional method proposed by Tufvesson. A two steps frequency offset estimation method is performed in the new method. In the first step the received signal is correlated with local training sequence to eliminate the influence of training sequence which makes the estimation range of frequency offset is independent of period of the repeated data in the training sequence. The received signal is correlated with its delay in the second step to obtain the fine estimation of frequency offset. Precise estimation can be achieved in the proposed method than Tufvesson's method. The period of the repeated data in the training sequence determines the estimation range of the frequency offset in the conventional method, while in the new method they are irrelevant. Tens of subcarriers spacing can be estimated by the new method. The new method can be used in other cases as long as a known sequence is transmitted, which will introduce valuable flexibility in training sequence design. The validity of the algorithm is verified in AWGN channel and multipath fading channel. 相似文献
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针对正交频分复用(OFDM)系统,提出了一种低复杂度、高性能的载波频偏盲估计
方法。该方法充分利用载波频偏估计代价函数在一定区间内的单谷特性,采用黄金分割法搜
索载波频偏估计代价函数极值,从而大大降低其计算复杂度。最后对该方法和Tureli′s MU
SIC-like(TML)载波频偏估计方法在加性高斯白噪声信道和多径信道环境下进行了仿真,结
果表明,
在同等条件下该方法的计算复杂度大大低于TML载波频偏估计方法。 相似文献
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Guenach M. Simoens F. Wymeersch H. Moeneclaey M. 《Selected Areas in Communications, IEEE Journal on》2006,24(1):181-189
This paper deals with joint data detection, synchronization and channel parameter estimation for direct-sequence code-division multiple-access systems over frequency-selective channels. In low-signal-to-noise ratio environments, conventional data-aided (DA) estimation algorithms may require an unacceptably large number of pilot symbols in order to obtain sufficiently accurate estimates of the channel and synchronization parameters. Especially, frequency offset estimation results in a significant loss in spectral efficiency. In this contribution, we consider several code-aided estimation schemes which can be incorporated in an iterative turbo detection scheme. We consider the expectation maximization algorithm, as well as the space alternating generalized expectation maximization algorithm as tools to develop code-aided estimation algorithms for a variety of scenarios. We pay special attention to the issue of computational complexity, and propose some complexity-reducing approximations. We show through computer simulations that the proposed code-aided estimation techniques considerably outperform their conventional DA counterparts. 相似文献
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Carrier frequency offset (CFO) in orthogonal frequency-division multiplexing(OFDM) systems, which can induce the loss of orthogonality among subcarriersand result in significant performance degradation, is critical to be estimatedand compensated for. In this paper, a suboptimal scheme is proposed to estimatethe CFO using subcarriers. In the proposed scheme, the CFO is dividedinto the fractional part and the integer part, with the fractional CFO estimatedfollowed by the integer CFO estimation. Compared with previous work using subcarriers and exhaustive search, the implementation complexity of theproposed scheme is significantly lower due to the fact that the main componentrequired is a simple correlator. Furthermore, with only one trainingOFDM symbol and proper subcarrier allocation, the estimation range ofthe proposed scheme can be the inverse of the sampling duration. In contrast,conventional schemes with the same estimation range and complexity require two OFDM symbols. To achieve good performance,it will be shown that the subcarrier allocation should be based uponsome specific binary sequences such as the proposed extended m-sequences. It willalso be shown by simulations that the same subcarrier allocation criterionshould be employed for optimal maximum-likelihood CFO estimation. 相似文献
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《Optical Fiber Technology》2014,20(3):268-273
To improve the outage performance of an optical orthogonal frequency-division multiplexing (OFDM) system under the frequency offset between the sampling clocks in the transmitter and receiver, a pilot-aided sampling frequency offset (SFO) estimation and compensation scheme for the optical OFDM system with intensity-modulation and direct-detection (DD-OOFDM) is experimentally demonstrated. The experimental and simulated results show that the scheme can work effectively even with large sampling frequency offsets. In addition, it can achieve a good bit error rate (BER) performance without the sampling clock frequency synchronization in the receiver. 相似文献
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Blind carrier frequency offset estimation for noncircular constellation-based transmissions 总被引:1,自引:0,他引:1
We address the problem of nondata aided frequency offset estimation for noncircular transmissions over frequency-selective channels in a linear precoder-based communications context. Linear precoding is representative of a downlink direct-sequence code division multiple access (DS-CDMA) system or of an orthogonal frequency division multiplexing (OFDM) system. We observe that twice the frequency offset is a cyclic frequency of the received signal. We thus introduce an estimator relying on the maximization of the empirical cyclocorrelations. We analyze its asymptotic behavior and obtain a closed-form expression for the asymptotic covariance. This enables us to design relevant system parameters. Numerical illustrations are provided and confirm our theoretical assertions. Comparisons with existing methods are also reported. 相似文献
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提出了一种改进的基于训练符号的频偏估计方法.该方法通过综合利用训练符号和循环前缀的信息得到时域的细频偏估计,通过峰值检测得到频域的粗频偏估计.仿真结果表明,在多径衰落信道下,在频偏估计范围达到整个信号带宽的同时,本算法的估计精度也有了明显的提高,并且当信噪比达到12dB时,可以使剩余频偏限制在子载波间隔的2%以内. 相似文献
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Residual frequency offsets may often result in poor functioning of a digital receiver. This is particularly true in a frequency selective environment where an adaptive equalizer may be required. In this paper, a frequency offset estimation algorithm is presented which is based on applying a nonlinear operation on the received sampled baseband signal. Tones at multiples of the clock frequency are produced and the phases of these tones provide both the desired frequency offset and clock phase information. This algorithm is intended to operate without knowledge of the pulse shape and therefore may be suitable for frequency selective environments. Additionally, the clock phase may be estimated with very little overhead. Simulations with AWGN, flat and frequency selective fading channels are included 相似文献
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针对通信接收中的载波同步问题,提出一种基于Fitz算法的改进载波频偏估计算法.分析了Fitz算法频偏估计方法中估计范围受限的原因,针对性地提出了改进方法,利用离散傅里叶变换(DFT)算法得到基准频偏,以此修正大间隔自相关函数估计频偏,保持了Fitz算法的估计精度优势,极大地扩展频偏估计范围,同时具有低的信噪比门限.最后给出了改进算法的实现步骤,并通过MATLAB仿真实验证明了算法的有效性. 相似文献
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In ho Hwang Hwang soo Lee Keon woo Kang 《Electronics letters》1998,34(6):520-521
The authors propose a frequency and timing period offset estimation technique for orthogonal frequency division multiplexing (OFDM) systems, which estimates both frequency and timing period offsets at the same time by using the line-fitting method. The performance of the proposed scheme is confirmed by computer simulation for QPSK and 16-QAM signals 相似文献