一种新的基于前导的定时和频偏联合估计方法

提出了一种基于前导的OFDM的定时和频偏的联合估计算法,该算法仅使用了一个具有共轭对称的特点的训练序列完成了定时恢复和频偏估计,通过仿真分析了提出方法的均值和标准方差,表明该方法是有效的.     

A Data-Aided Symbol Timing and Frequency Offset Estimation Algorithm for OFDM Systems

In this paper the problem of data-aided symbol timing and frequency offset estimation in OFDM systems is considered. A synchronization scheme based on a pilot symbol containing two identical parts obtained by transmitting BPSK data symbols on the even subcarriers and setting zero on the remaining subcarriers is proposed. In this case, if the number of subcarriers is sufficiently large, the pilot symbol can be modeled as a noncircular (NC) complex Gaussian random vector (CGRV). By exploiting the joint probability density function of NC-CGRVs, the joint maximum likelihood estimator for the parameters of interest is derived. Since its implementation complexity is high, a simpler synchronization scheme is obtained. Moreover, refined symbol timing and frequency offset estimators, that assure relevant performance in multipath channels, are proposed. T. Fusco was born in Naples, Italy, on March 22, 1977. She received the Dr. Eng. degree (summa cum laude) in electronic engineering from the Second University of Napoli in 2002. Since November 2002 she has been a Ph.D. student at the Department of Electronic and Telecommunication Engineering of the University of Napoli Federico II. Her current research and study interests lie in the area of statistical signal processing, with emphasis on parameter estimation problems in the context of OFDM communications. M. Tanda was born in Aversa, Italy, on July 15, 1963. He received the Dr. Eng. degree (summa cum laude) in electronic engineering in 1987 and the Ph.D. degree in electronic and computer engineering in 1992, both from the University of Napoli Federico II. Since 1995, he has been an Appointed Professor of Signal Theory an the University of Napoli Fe-de-ri-co II. Moreover, he has been an Appointed Professor of Electrical Communications (from 1996 until 1997) and Telecommunication Systems (from 1997) at the Second University of Napoli. He is currently Associate Professor of Signal Theory at the University of Napoli Federico II. His research activity is in the area of signal detection and estimation, multicarrier, and multiple access communication systems.     

一种新的定时和频偏联合估计算法

提出了一种新的正交频分复用(OFDM)系统定时和频率同步联合算法.该算法仅需要一个训练符号就可以完成定时和频偏估计,额外开销量小,定时和频率同步的实现均在时域进行,简化了同步实现的复杂度.由于使用自相关处理,定时同步对频率偏差具有较强的鲁棒性.与以往的定时同步算法相比,该算法避免了定时平台和多峰值的出现,即使在非常低的信噪比下,其定时测度都是一个尖脉冲.仿真结果表明,该算法能快速地实现定时和频率同步.     

一种新的OFDM系统载波频偏估计算法

在正交频分复用(OFDM)系统中,频率偏移会破坏子载波间的正交性,降低整个系统的性能。在研究传统频偏估计算法的基础上,利用简单的实数训练序列,进行OFDM系统的载波频偏估计,只需要一个训练序列,就可以有效地在时域内同时对小数倍和整数倍的频率偏移进行估计。仿真结果表明,基于实数训练序列的载波频偏估计算法不仅方法简单,易于实现,而且可提高频偏估计精度。     

OFDM系统中定时偏移的估计技术

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。     

一种新的OFDM系统载波频率偏移估计和跟踪方案

针对载波偏移使OFDM系统出现严重的子载波干扰和性能的下降,该文提出一种OFDM频偏估计和跟踪方案,载频捕获阶段频偏估计采用时域内插入等值导频的方法,载频跟踪阶段不需要导频,而是利用循环前缀来估计频率偏移并进行校正。仿真结果证实,该方案中导频辅助的频率偏移估计和载频跟踪不仅估计范围大,而且估计值准确,频偏校正后系统的性能能达到信道理想估计条件下的误比特率。     

一种基于二倍钟采样的OFDM载波偏差估计算法

本文从OFDM信号的二倍钟采样出发,给出了一种载波偏差估计算法,该算法直接利用时域信号的采样来估计载波偏差,克服了频域实现算法受载波偏差影响大的缺点,使得算法在不同的载波偏移下具有相同的估计精度,载波偏差估计范围大,同时该算法充分利用信号的有效能量,估计精度高,优于采用循环前缀的算法;论文同时给出了算法性能的理论分析和计算机仿真结果.     

OFDM分数倍频偏与码元定时的联合估计

Smidle和Cox（SC）算法是OFDM系统中频偏和码元定时估计的经典算法。基于SC的导频设置,利用最大似然（ML）准则,提出一种分数倍频偏（FFO）和码元定时联合估计算法,通过计算机仿真比较可以看出,文中提出的联合估计算法的FFO估计性能与SC算法相同,而码元定时估计方法的性能明显优于SC算法。     

OFDM系统上行链路的一种载波偏差估计算法

通过分析OFDM信号的特点,该文给出了OFDM系统上行链路的一种基于高倍钟采样的载波偏差估计算法.与采用循环前缀的载波偏差估计算法相比,该算法实现复杂度低,算法精度高,受用户子载波数目影响较小,适宜于多用户OFDM系统.计箅机仿真表明该算法具有优良的性能,优于采用循环前缀的载波偏差估计算法.     

On Timing Offset Estimation of OFDM

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一种用于OFDM符号定时跟踪的盲估计算法

利用具有循环前缀和循环后缀的OFDM帧结构,该文提出了一种新的符号定时跟踪盲估计算法。理论分析及仿真表明,无论在AWGN还是多径衰落信道条件下,该定时算法估计的均方差都小于ML算法。     

Improved Carrier Frequency Offset Estimation in OFDM Systems

1　Introduction　OrthogonalFrequencyDivisionMultiplexing(OFDM )isaneffectivetransmissionschemetocombatmultipathfading[1 ] .Byinsertingaguardin tervalbetweensymbolblockscalledcyclicprefix ,theInterSymbolInterference (ISI)canbemitigat ed.OFDMwasadoptedasthemodulationschemeforaDigitalAudioBroadcasting(DAB)system[2 ]andADSL (AsymmetryDigitalSubscriberLoop) [3]andwasalsoproposedastheterrestrialHDTVtransportinEurope[4] .　OFDMsystemsareverysensitivetocarrierfre quencyoffset,andcarrie…     

M-CPFSK信号的定时与频偏联合估算分析

目前已有的定时频偏联合估计方法仅仅解决了正交高阶连续相位频移键控(M-CPFSK)信号的同步问题,但仍无法直接应用于非正交信号的解调中。针对这一问题,通过对非正交M-CPFSK的基带采样信号进行幂变换,修正了信号的调制指数,使其满足了联合估计算法中的信号正交性。新方法实现了非正交情况下M-CPFSK信号的精确同步,并在加性高斯白噪声信道条件下对估计性能进行了理论分析和试验仿真。仿真结果及性能分析均验证了新算法的有效性和可行性。     

OFDM系统中一种新型联合时频同步算法

OFDM同步技术是OFDM系统中的关键技术。针对OFDM系统面对的大范围频偏问题,提出了一种新的基于单个训练符号进行OFDM同步的算法,构造了新的训练序列以及新的频偏估计函数,该算法能在最大范围内对载波频率偏移做出有效的估计,并且不需要特定结构的训练符号。基于高斯白噪声信道的仿真比较表明了该算法具有较强的优点。     

Frequency and Timing Offset Estimation Using Single Reference Symbol

In this paper we will investigate the performance of an estimator employing single OFDM reference symbol for timing and frequency offset estimation. We will show how both coarse and fine frequency offset estimation can be performed with this single OFDM reference symbol. The performance of this estimator will be compared with the ML estimator employing OFDM reference symbols of different length for coarse and fine frequency offset estimation. It will be shown that, unlike ML estimator, the estimation range of the analyzed estimator is not constrained.     

A Novel Carrier Frequency Offset Estimation for OFDM Systems Over Time-Varying Multipath Channels

This paper introduces a novel method to estimate fractional carrier frequency offset (CFO) under time-varying multipath channels in OFDM systems based on the approximation of Basis Expansion Model (BEM). Due to the symmetrical character of the BEM basis, we propose a new design of training sequence with trailing zeros. This training sequence can be used at the receiver to estimate the frequency offset without channel estimation only in one OFDM symbol. We also compare our method with Beek’s ML estimator and Lv’s fine synchronization estimator. The numerical results demonstrate that the proposed method provides an improved performance when the training sequence has a short length.

OFDM系统的对数似然比最大化盲频偏估计算法

为了消除短波OFDM通信中的频率偏移问题,对差分OFDM信号进行了分析,并对最大 后验概率（MAP）译码的性质进行了研究,提出了一种似然比最大化的迭代盲频偏估计 算法。由于该算法充分利用了软译码得到的似然比信息,因此可以实现最优信号检测。计算 机仿真证明了该算法的有效性。进行了短波OFDM信号通信实验,得到了实测数据。实测数据 检测结果表明,该算法的误码率性能随着迭代次数的增加而提高,且一发两收系统性能要比 单发单收系统性能至少提高2 dB。     

基于DVB-T的OFDM频偏估计算法及DSP实现

由于OFDM调制是基于载波间正交的调制方式,频偏存在会使载波间正交性破坏,进而影响解调和性能。基于DVB-T提出了一种基于时域和频域相结合的频偏估计算法并对性能进行了仿真分析,并结合项目实际给出了DSP实现方法,最后对DSP实现后的数据进行了星座图验证和项目最后ARM接收端接收数据的验证。结果表明此算法对解决DVB-T物理层的频偏非常有效。     

一种新的OFDM采样频偏盲估计算法

针对OFDM技术对系统的时钟同步要求非常高的问题,提出了一种新的采样频偏盲估计算法,该算法可较好地解决估计精度和估计复杂度的折中问题。通过仿真结果表明,在高斯白噪声信道下,与同类算法相比,该算法不仅估计精度高,而且估计复杂度低,符合实际工程应用。     

一种基于Kalman滤波的OFDM系统频偏估计方法

文章基于正交频分复用（OFDM）系统对频偏的敏感性特点,介绍和分析了在OFDM接收机中的一种快速采样和精确跟踪技术。这种技术基于Kalman滤波算法和它快速的收敛速度,通过改变OFDM系统和接收端的设计参数来研究载波频率及估计器在接收端错误率中的影响。通过研究将得到一个最佳的频率偏移估计。该方法应用良好,有快速收敛能力,能在极短信号间歇中获取频偏,并拥有良好的跟踪能力。