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.     

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…     

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.     

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.     

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。     

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。     

Maximum-Likelihood Estimator for Coarse Carrier Frequency Offset Estimation in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) systems are more sensitive to carrier frequency offset (CFO) compared to the conventional single carrier systems. CFO destroys the orthogonality among subcarriers, resulting in inter-carrier interference (ICI) and degrading system performance. To mitigate the effect of the CFO, it has to be estimated and compensated before the demodulation. The CFO can be divided into an integer part and a fractional part. In this paper, we investigate a maximum-likelihood estimator (MLE) for estimating the integer part of the CFO in OFDM systems, which requires only one OFDM block as the pilot symbols. To reduce the computational complexity of the MLE and improve the bandwidth efficiency, a suboptimum estimator (Sub MLE) is studied. Based on the hypothesis testing method, a threshold Sub MLE (T-Sub MLE) is proposed to further reduce the computational complexity. The performance analysis of the proposed T-Sub MLE is obtained and the analytical results match the simulation results well. Numerical results show that the proposed estimators are effective and reliable in both additive white Gaussian noise (AWGN) and frequency-selective fading channels in OFDM systems.

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。     

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。     

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.     

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。     

Fast Frequency Offset Acquisition and Accurate Tracking in OFDM Systems

1　IntroductionOrthogonalFrequencyDivisionMultiplexing(OFDM )isaneffectivetransmissionschemetocombatmultipathfading[1～ 2 ,1 7] .Byinsertingaguardintervalbetweensymbolblockscalledcyclicprefix,theInter SymbolInterference (ISI)canbemitigated .OFDMisadoptedasthemodulationschemeforaDigitalAudioBroadcasting (DAB)sys tem[3] andAsymmetryDigitalSubscriberLoop(ADSL) [4] andisalso proposedastheterrestrialHDTVtransportinEurope[5] .OFDMsystemisverysensitivetocarrierfre quencyoffset.Manymet…     

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信号频率偏移盲估计算法

该算法通过联合多个正交频分复用（OFDM,Orthogonal Frequency Division Multiplexing）符号对频率偏移进行盲估计。该算法不需要数据辅助,利用接收信号循环前缀的相关性,通过计算相同子信道所传数据的相位差,来实现信号的小数倍频偏估计。利用相邻OFDM符号中频域导频的延迟相关运算来实现整数倍频偏估计。仿真结果表明该算法估计精度高,适合实际信号的应用。     

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。     

A Novel OFDM Timing Offset Estimation Algorithm

1　Introduction　OrthogonalFrequencyDivisionMultiplexing(OFDM )isamethodsuitableforhigh ratedatatransmissioninwirelesscommunications .However,thereareseverallimitingfactorsinthecommercialapplicationofOFDMforapplyingtohigh ratemo bilecommunication ,suchasDopplerfrequencyshift,synchronization ,channelestimation ,peak to averagepowerratio .　Schmidl[1 ] completedsynchronizationusingspecialPNsequence,buttheestimateisnot precise.Minn[2～ 3] andByungjoon[4] improvethealgorithmperformance,butth…     

一种OFDM剩余载波频偏估计算法的FPGA实现

分析了正交频分复用(OFDM)系统中剩余载波频偏在FFT之后对解调数据的影响,利用OFDM符号中插入的离散导频符号,对剩余频偏进行估计。在对算法进行仿真分析的基础上,提出了算法的现场可编程门阵列(FPGA)实现方案。整个设计过程在QuartusⅡ平台下进行,包括VHDL语言编程、逻辑综合和时序仿真,结果和理论分析相一致,可以用来对剩余频率偏差进行有效的纠正。     

基于导频的OFDM时钟采样频偏估计

文中分析了OFDM系统时钟采样频偏对系统性能的影响,提出了一种基于导频的OFDM时钟采样频偏最大似然估计新算法,新算法只需一个OFDM符号就能精确的估计采样频偏,理论分析和仿真表明,新算法在低信噪比条件下仍具有很好的性能.     

OFDM系统中对最大似然算法频偏估计的改进

深入研究了基于循环前缀(Cyclic-Prefix,CP)的最大似然算法(ML)算法。针对这个问题,对基于CP的ML算法做了如下改进,改进的算法同时对连续3个符号进行ML估计。符号定时同步时,当前符号同步信息能够通过前面2个符号的同步信息得到校正。在进行频偏估计时,通过使用观察窗,在窗口内进行连续频偏值的均值运算,对频偏估计值误差进行矫正。     

一种有效的OFDM载波频率偏移的盲估计

导出了具有循环前缀（CP）和虚子载波的正交频分复用（OFDM）通信系统信号的薮学模型。提出了基于PM—ESPRIT算法的0FDM系统载波频率偏移（CFO）偏移不变性的估计算法。经过粗略估计,该算法可以同时获得频率偏移和包含信道信息的矩阵,它们均有利于接收信号的偏移补偿和解调。仿真结果说明了该方法是有效的。