一种相关编码正交频分复用系统的载波频偏估计算法

基于相关编码正交频分复用(OFDM)系统，提出了一种新的数据辅助载波频偏估计技术，利用相关编码OFDM系统的频域幅度特性估计载波频率偏移，增大了频偏估计的跟踪范围，同时采用改进的迭代估计剩余频偏方法，消除载波间干扰对频偏估计的影响，提高了估计精度．仿真结果表明，与传统的基于数据辅助频偏估计技术相比，该技术的跟踪估计范围增大为(-1，1)，且在较高信噪比的估计均方误差明显降低。     

Blind Carrier Frequency Offset Estimation via Power Spectrum Analysis in MIMO OFDM Systems

As a generalization of orthogonal frequency-division multiplexing (OFDM) systems,multi-input multi-output (MIMO) OFDM systems are very sensitive to carrier frequency offset (CFO).This paper proposes a blind CFO estimation method based on power spectrum analysis,which has high bandwidth efficiency and is much less complex.This method can be used to estimate the residual CFO,which is less than half of the subcarrier spacing.The method uses a cosine cost function to get a closed-form CFO estimate.Simulation results illustrate that the method is effective for MIMO OFDM systems.     

Interference-Cancellation-Based Carrier Frequency Offset Estimation for OFDMA Uplink Transmissions

A carrier frequency offset (CFO) estimator was developed based on an interference cancellation scheme for an orthogonal frequency division multiplex access uplink. An initial CFO estimate was first obtained based on the received training signals at each user’s prescribed subcarrier positions. Then, the received training signals were compensated by using the initial CFO estimates in the frequency domain and the multi-user interferences were estimated. Finally, the interference-cancelled training signals were...     

A Novel Minimum Output Variance Estimator for Carrier Frequency Offset in OFDM Systems

In orthogonal frequency-division multiplexing (OFDM) systems, the carrier frequency offset (CFO) destroys the orthogonality among subcarriers which degrades system performance. Various CFO estimation methods have been developed to compensate for the CFO at the receiver. This paper describes a novel minimum output variance method for OFDM systems with CFO in additive white Gaussian noise channels. This method utilizes the phase and the amplitude of the received signal and reduces the mean square error of the CFO by about 3 dB compared with the original minimum output variance method.     

最小平方OFDM信道估计与信号检测的联合迭代算法

提出一种基于正交频分复用(OFDM)的联合最小平方(LS)信道估计与信号检测迭代算法.与一般的LS信道估计相比,该算法可大大提高估计的精度,而且通过时域低通滤波可有效地抑制加性白高斯噪声(AWGN)和载波间干扰(ICI)的影响,使OFDM系统在移动条件下很好地工作,并能给出很精确的信号检测结果.仿真结果表明,该算法具有很好的均方误差和误比特率性能.     

A Novel Two-step Frequency Offset Estimator for OFDM

Based on an orthogonal frequency division multiplexing（OFDM） training symbol with L identical parts, a novel carrier frequency offset （CFO） estimator is proposed for OFDM systems. The CFO is estimated in two steps, fine estimate and coarse estimate. In the first step, the fine estimation is performed based on the principle of minimum variance. However, the fine estimation has ambiguity since its estimate range is limited. In the second step, the coarse estimation is obtained, which results in a larger estimate range but less precision. Using the coarse estimation, the ambiguity of fine estimation is resolved. To fully use the correlation among L identical parts, the fine estimation resolved the ambiguity and the coarse estimation are optimally combined to obtain the final estimation. Furthermore, the estimation variance of the proposed method is derived. Simulation results demonstrate that the novel two-step estimator outperforms the conventional two-step estimator in terms of estimate performance and computational complexity.     

基于TD-NLMS的航空移动通信OFDM系统载波频率偏移消除

针对航空移动通信中时变的信道环境和多普勒频移造成的子载波间干扰(ICI),提出了一种时域自适应归一化最小均方误差算法(TD-NLMS)来消除航空移动信道正交频分复用(OFDM)系统中载波频率偏移引起的干扰.该算法首先对接收的时域信号进行频偏预估计和预补偿,然后对剩余载波频移进行消除.仿真结果表明:在航空移动信道环境中,新算法可以很好的对旋转相位进行补偿,与最小二乘算法相比,误码率性能有明显提高,可以实现对载波频率偏移的消除.     

一种基于IEEE 802.16d的OFDM载波跟踪算法

利用OFDM符号中插入的导频信号,提出了一种基于IEEE802.16d标准的载波频率偏移跟踪的优化算法,该优化算法基于最小均方误差准则(MM SE).估计过程中,同时考虑载波频率偏移产生的2方面影响:在某个OFDM符号内,与子载波位置无关的固定相位旋转和幅度衰减;载波正交性破坏引入的载波间干扰(ICI).对于载波间干扰能量的估计则充分利用了空子载波提供的信息.仿真结果表明,基于MM SE准则的频偏跟踪算法由于减小了ICI的影响,所以比忽略ICI只考虑固定相位旋转量的跟踪算法能够更有效地减小系统的误码率和均方误差.     

相位噪声下OFDM系统中的信道估计与均衡

分析了相位噪声对正交频分复用（OFDM）系统的影响,发现相位噪声不仅产生通用相角错误（CPE）,而且还会产生载波间干扰（ICI）,这都使OFDM系统的性能急剧恶化,因此必须对CPE和ICI进行校正,文中给出了基于MSE准则的CPE校正方法,考虑到ICI干扰主要来源于相邻信道,进而提出了基于LMS法则的自适应相邻信道干扰消除方法,整个算法简单高效。仿真结果表明,所提出的算法大大改善了OFDM系统的性能。     

基于联合频分复用的水下多载波调制技术

目前水声通信的OFDM调制是一种高效率的多载波调制技术,但严格要求子载波正交,对频偏敏感.水声通信中主要采用多普勒补偿或增加子载波滤波器的方法解决多普勒频移的问题,实现复杂.本文从新的角度,即增大子载波间间隔角度研究减小子载波间干扰(ICI),提出一种联合频分复用(C-FDM)方法,将多个OFDM子载波模块联合形成一个C-FDM子载波模块,并将频率相同的子载波放在相邻位置.在C-FDM和OFDM符号长度相同情况下,C-FDM的子载波间隔更大,不需要增加复杂补偿算法,就能有效提高抗多普勒频移能力.仿真结果表明C-FDM技术在水声信道中有更优良的误码率性能.     

Precoded OFDM System for ICI Mitigation over Time-Frequency Selective Fading Channels

In orthogonal frequency-division multiplexing(OFDM)systems,the capability to support high mobility is greatly limited by the intercarrier interference(ICI)caused by time-frequency selective fading channels. This paper presents a precoded OFDM system for ICI mitigation.A precoder is introduced to relieve the ICI by transmitting N-point composite information symbols at twice the subcarrier interval.A Hadamard -matrix-like pilot pattern is used to recover the composite information symbols in a postprocessor...     

Carrier Frequency Offset Compensation for an Interleaved OFDMA Uplink

This paper reports an investigation of the carrier frequency offset （CFO） compensation in the uplink of the orthogonal frequency division multiple access （OFDMA） system with interleaved subcarrier assignment. The presence of CFOs between the transmitters and the uplink receiver will destroy the orthogonality among the different subcarriers, resulting in inter-carrier interference and multiuser interference. This paper proposes a pseudoinverse CFO compensation method based on the signal structure. The proposed method can compensate the CFOs of all users simultaneously and isolate the signals from all users at the same time. Compared with the existing CFO compensation methods, the new method provides a considerable signal-to-noise ratio gain on the bit error rate performance and has a relatively low implementation complexity.     

OFDM系统中ICI消除方法的性能比较

OFDM系统对频率偏移极为敏感,频率偏移将导致子载波之间失去正交性,于是产生子载波干扰(ICI),从而降低系统性能.针对载波间的干扰,通过对由频率偏移导致的ICI进行理论分析,对抑制ICI的3种方法（基于符号变换的自消除方法、扩展（Kalman）滤波方法（EKF）及频域编码法）进行了性能比较,比较结果表明,频率编码法在不减少频谱利用率的前提下能有效地降低系统的频间干扰.     

FMT和OFDM在频偏影响下的可达比特率性能比较

滤波多音（filtered multi-tone,FMT）和正交频分复用（orthogonal frequency division multiplexing,OFDM）同属于多载波调制技术,FMT子信道频谱不重叠,OFDM子信道频谱正交．频谱特性的差异导致对各种干扰的敏感性不同．FMT技术的频谱特性使其可以有效克服信道间干扰（ICI）,但需要在接收端加入有效均衡器以消除符号间干扰（ISI）．OFDM的频谱正交性容易受到ICI的影响被破坏．分析AWGN环境中,频偏对FMT和OFDM系统造成的干扰,通过计算机仿真比较频偏对两种系统的可达比特率性能的影响．     

基于干扰子空间估计的跳频多址信号检测

通过对跳频多址信号的时频图案分析,建立了基于信号子空间的系统模型和跳频多址信号的解相关检测算法.该算法采用子空间跟踪的思想,将干扰子空间从检测信号空间上予以消除,克服了传统检测器需要知道系统中所有用户跳频图案的约束和串行干扰消除中的干扰扩散问题.与传统检测器相比,该算法具有更好的系统误码性能、较低的计算复杂度和很好的系统稳健性.MonteCarlo仿真结果表明,在同一个误码率条件下,基于子空间的盲多用户检测器比传统检测器的信噪比提高了2～4dB.     

一种基于PN序列的上行多用户OFDM系统载波频偏估计算法

针对多用户正交频分复用(OFDM) 系统上行链路中的载波频偏估计问题, 提出一种基于伪噪声(PN)序列的载波频偏(CFO)估计算法。该算法将不同相位的PN序列作为各个用户的训练序列, 利用训练序列良好的自相关性估计出存在CFO 情形下不同用户的信道参数, 再根据两个训练周期内信道参数的相位变化获得各用户的CFO估值。理论分析和仿真结果表明本算法具有优 良的估计性能。     

基于TD-LMS算法的OFDMA上行链路载波频偏补偿

针对OFDMA上行链路的通信系统,各用户存在不同的子载波频偏,导致子载波正交性的破坏,本文提出一种基于最小均方误差(MMSE)的时域自适应算法(TD-LMS)来补偿子载波频偏引起的干扰。该算对OFDMA系统接收端的时域信号进行无偏估计,然后利用估计量来调整频偏值,最后利用TD-LMS算法进行自适应消除。与传统的算法相比,此算法无需获得子载波频偏范围的先验知识。仿真结果表明,该算法对各用户的子载波频偏的估计精度较高,而且补偿的效果更明显。     

CDMA系统中多用户检测算法的研究

在DS-CDMA系统中,多用户检测技术是抗多址干扰和“远近效应”的有效方法,因此也成为了第三代移动通信的关键技术之一。文中通过仿真比较分析了传统检测器、最优检测器、解相关检测器、MMSE检测器、串行干扰抵消检测器、并行干扰抵消检测器和解相关判决反馈检测器等经典多用户检测器的误码率、渐近多用户有效性和抗远近能力,并从计算复杂度和所需的假定知识两个方面讨论了这些检测器的实现复杂度。     

OFDM系统中干扰消除技术的分析

正交频分复用（OFDM）技术已被越来越多的人所关注,并且在IEEE802．11无线局域网中得到实际应用．在OFDM系统中为了消除符号间干扰（ISI）和子载波间干扰（ICI）,一般要采用加入循环前缀（CP）的技术．从信道对信号作用方面分析了循环前缀技术消除干扰的过程,并给出了仿真结果．结果表明,循环前缀的加入可以有效地消除符号间干扰（ISI）和子载波间干扰（ICI）．     

基于循环延迟分集的空时频编码策略

结合空时编码和正交频分复用(OFDM)技术，将循环延迟分集引入到传统的空时OFDM编码系统中，提出了一种新的空时频编码策略．在该策略中，对OFDM帧间相同载波上的符号进行空时编码，实现空时分集；OFDM帧内各子载波上的符号则使用循环延迟引入频率分集，实现空频编码．接收端综合利用空时、空频编码的结构信息实现联合译码，获得空时频分集增益．仿真结果表明，该策略具有结构简单、差错性能改善明显等优势．在频率选择性信道中，新编码策略可以获得空时频全分集增益．在相同信干比条件下，差错性能明显优于传统空时或空频OFDM系统的差错性能．