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In single frequency network (SFN), there exist some special long delay spread channels as well as conventional multipath channels.
For pilot-aided orthogonal frequency division multiplex (OFDM) systems, channel estimation is usually accomplished by interpolation
with pilots. However, few pilot sub-carriers exist within the coherent bandwidth of the long delay spread channels in SFN.
In this case, conventional frequency domain interpolation methods cannot work properly. In a narrowband channel, this paper
indicates that both the real and the imaginary parts of channel frequency response can be accurately approximated as a sine-wave
with DC offset. For many practical pilot-aided OFDM systems, the bandwidth of the narrowband channel mentioned before is comparable
with the interval between several adjacent pilot sub-carriers. Then this paper proposes a sine-wave based frequency domain
interpolation method for the channel estimation of pilot-aided OFDM systems in SFN. As simulation results show, the proposed
method performs well in the long delay spread channel, whereas the mismatched Wiener interpolation filter (WIF) estimates
channel response inaccurately. Moreover, the proposed method gives accurate channel estimation in conventional multipath channels,
especially for the systems which adopt high order modulations. 相似文献
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In this paper we consider the design of a robust timing synchronization algorithm for pilot-aided OFDM systems in high-mobility fading environments. We first analyze the impact of both mobility and timing errors on the performance of a pilot-aided OFDM system for frequency selective fading channels, by deriving an expression for channel estimation error variance. The analysis will show that, even for high levels of mobility, a pilot-aided channel estimator is considerably sensitive to timing errors, due to the impact of rotations in different bases. We then show how this sensitivity can be utilized to design a robust timing synchronization algorithm for mobile OFDM systems, without relying on synchronization training information. Theoretical results are then confirmed by simulating the performance of an OFDM system in high delay and Doppler spread fading environments. Finally, we show how the proposed mathematical framework and algorithm can be used to address timing synchronization in the presence of a frequency offset as well. The analysis of this paper is the extension of the derivations of Part I [8], the accompanying paper on the design of a robust timing synchronizer for low-mobility OFDM systems. 相似文献
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Chuan-Wang Chang Ho-Lung Hung Shu-Hong Lee Jyh-Horng Wen 《Wireless Personal Communications》2011,59(2):345-360
Pilot-aided channel estimation in orthogonal frequency division multiplexing (OFDM) systems often needs an interpolation technique
to construct the channel frequency response on nonpilot subcarriers. Many studies on interpolations have been published; however,
the performance of interpolations such as cubic spline interpolation and linear interpolation is limited by either the number
or the position of the pilot subcarriers. This paper proposes an analytic interpolator developed using a linear least square
criterion to replace conventional interpolation techniques for comb-type pilot-added channel estimation in OFDM systems without
inter-carrier interference. The performance evaluation of the analytic interpolator is performed both on the basis of theory
and through simulation, and the results from both the analyses are found to be in good agreement. The simulation results show
that the proposed method can effectively mitigate the ill-influences of limitations on the number and position of the pilot
subcarriers and that it also outperforms the cubic spline interpolation and linear interpolation, especially for short or
nonequidistant pilot patterns. 相似文献
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In this paper we are interested in designing a robust timing synchronization algorithm for OFDM systems that utilize pilot-aided channel estimation. We first characterize the impact of timing errors on the performance of a pilot-aided OFDM system. We derive analytical expressions for average channel estimation error variance in the presence of timing errors in high delay spread fading environments. The derived expressions show that pilot-aided channel estimators are considerably sensitive to timing synchronization errors due to the impact of rotations in different bases. We then show how to utilize this sensitivity to design a robust timing synchronization algorithm, without training overhead. The proposed algorithm is a cross-block design that uses channel estimation information to improve timing synchronization. We confirm our analytical results by simulating the proposed algorithm in high delay spread fading environments. In this paper, i.e. part I, we focus on timing synchronization for low-mobility cases. The analysis and results are then extended to high-mobility applications in part II. 相似文献
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OFDM同步跟踪阶段的频偏估计算法 总被引:1,自引:0,他引:1
OFDM对栽频偏差是很敏感的,因此不仅在同步的捕获阶段,而且在同步的跟踪阶段,精确的频偏估计是很重要的。文献[3]提出了一种简化的相干判决反馈的迭代算法来估计同步跟踪阶段的载频偏差,对于128个子载波、QPSK调制的OFDM系统,在多径衰落信道下,当频偏小于子载波间隔的15%时,频偏估计的标准方差小于1%,但是这个结果是在假设信道频率响应、定时偏差、载波相位等参数已知的条件下取得的,而当这些参数的估计存在误差时,由仿真结果可看出,频偏估计性能恶化了,因此,提出了采用差分判决反馈的频偏估计算法,虽然只能估计小于子载波间隔 8%的频偏,但差分判决反馈算法不需要知道信道的参数,由于在同步跟踪阶段,频偏一般都较小,因此采用差分判决反馈算法可以很好地估计出同步跟踪阶段的频率偏差。 相似文献
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《Broadcasting, IEEE Transactions on》2009,55(1):84-94
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In orthogonal frequency division multiplexing (OFDM) systems, most of the conventional sampling frequency offset (SFO) estimation
methods work under the assumption of time-invariant or slow time-variant channels. In mobile environment, the time-variant
channel significantly degrades the accuracy of SFO estimation. To solve the problem, we first analyze the properties of time-variant
channels. If terminal moves within some tens of the wavelength of radio frequency (RF) signal, channel path delay almost remains
unchanged. For most practical OFDM systems, our analysis indicates that channel path delay can be regarded as unchanged during
the interval of some tens of OFDM symbols in time-variant channels. Based on the analysis, we propose a novel SFO estimation
method for pilot-aided OFDM systems. Different from the conventional methods, the proposed method estimates SFO by detecting
the variation of the symbol timing error caused by SFO. The detection is finished by implementing correlation between the
channel impulse responses (CIRs) estimated by different OFDM symbols. Performance of the proposed method is simulated and
compared with that of two conventional post-FFT methods. Numerical results show that, the proposed SFO estimation method performs
better than the conventional methods not only in time-variant channels, but also at low SNRs and large residual carrier frequency
offsets (CFOs). 相似文献
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符号定时和载波频率偏差将严重影响OFDM系统的性能。基于具有重复结构的CAZAC序列,提出了一种仅利用一个CAZAC符号实现符号定时、整数倍频偏与小数倍频偏估计的同步算法。首先,所提算法在完成粗定时同步的同时得到整数倍频偏估计。然后根据整数倍频偏估计值对定时估计进行修正,最后完成小数倍频偏估计。分析与仿真结果表明,该算法相比于传统PARK算法,不仅完成了定时估计,而且得到了频偏估计;相对于经典SC算法,不但提高了传输效率,还显著改善了OFDM系统的定时与频偏估计性能;相比于利用CAZAC序列的同步算法,提高了算法的估计精度以及对多径信道的适应性。 相似文献
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在时变信道下正交频分复用(OFDM)系统中,通过导频辅助,提出基于可变遗忘因子RLS(VFF-RLS)的载波频偏(CFO)估计改进算法。针对传统RLS(CFF-RLS)算法中遗忘因子无法同时满足CFO估计收敛速度和收敛精度的缺陷,本文设计了线性变化遗忘因子(LFF)和非线性变化遗忘因子(NLFF) 两种可变遗忘因子方案来提升CFO估计性能。仿真结果显示:在低信噪比的情形下,基于VFF-RLS算法的CFO估计性能明显优于基于CFF-RLS算法的CFO估计性能。 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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OFDM系统中定时偏移的估计技术 总被引:1,自引:0,他引:1
在T.M.Schmidl和D.C.Cox提出的解决正交频分多路复用(OFDM)系统定时同步的基础上,给出了两种改进算法。在加性高斯白噪声信道(AWGN)和存在符号间干扰(ISI)的两种信道中,分别对估值进行比较,这两种改进算法得到估值的方差要小得多。 相似文献
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Jing Zheng Suping Peng Guowei Zhu Huaixiu Wang 《Wireless Personal Communications》2013,69(4):1207-1222
A joint synchronization and channel estimation scheme is proposed for orthogonal frequency division multiplexing (OFDM) system. In the proposed scheme, the integer frequency offset, fine timing offset and channel estimation are estimated based on the characteristics of the chirp signals. The main contributions of the paper are: the more robust ability to find the actual first path instead of the strongest path on the assumption of repeated chirp waveforms in the timing synchronization approach, and the lower computational complexity with high performance in the channel estimation approach. Moreover, we analyze the performance of the proposed method and check it via Monte Carlo simulations. The simulation results show that the proposed method can achieve good performance for both synchronization and channel estimation in frequency selective channels. 相似文献
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Serafin Salido F. Javier Lopez-Martinez Eduardo Martos-Naya J. Tomas Entrambasaguas 《Wireless Personal Communications》2014,78(2):1129-1141
In orthogonal frequency division multiplexing (OFDM) systems, since the cyclic prefix (CP) is designed to be longer than the channel impulse response, there exists a certain range within the CP where symbol timing synchronization can be accomplished avoiding adjacent inter symbol interference. However, the appearance of a linear phase term across subcarriers in the frequency-domain due to symbol timing offset (STO) is known to affect the performance of channel interpolation. In this paper, we analyze the performance degradation due to the interaction between STO and channel interpolation in OFDM systems affected by multipath Rayleigh fading. Particularly, simple closed-form expressions for the bit error rate (BER) are obtained for different quadrature amplitude modulation constellations. Results show that there exists an irreducible BER floor due to STO and channel interpolation, which depends on the STO, the subcarrier index, the pilot spacing and the correlation between pilot subcarriers. 相似文献
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本文研究了基于变换域处理的OFDM系统信道估计的基本原理和变换域滤波处理方法,提出了一种变换域导频插值信道估计的改进迭代算法,同时,采用具有更好滤波效果的“带阻滤波器”优化了其中的变换域滤波器的设计,通过接收端检测到的信噪比调整能量参数。仿真结果表明,提出的采用优化变换域滤波器的信道估计算法具有较好的性能,在一定程度上可以接近于理想信道估计的性能。 相似文献
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CAO Xue-hong Department of Information Engineering Nanjing University of Posts Telecommunications Nanjing P.R. China 《中国邮电高校学报(英文版)》2005,12(2)
1Introduction Orthogonal Frequency Division Multiplexing(OFDM) has become a popular technique for transmis-sion of signals over wireless channels . OFDMhas beenadoptedinseveral wireless standards such as Digital Au-dio Broadcasting ( DAB) , Digital Video Broadcasting(DVB-T) ,the IEEE 802 .11a[1]Local Area Network(LAN) standard and high performance LAN type 2(HIPERLAN/2)[2]standard. OFDMis also being pur-sued for Dedicated Short-Range Communications(DSRC) for road side to … 相似文献