基于PSAM的OFDM系统仿真及性能分析

为了分析信道估计和循环前缀对提高正交频分复用(OFDM)系统性能的具体作用.首先简要介绍了OFDM基本原理,然后在理想同步情况下,重点分析了循环前缀(CP)和信道估计算法对OFDM系统性能的影响.在给出OFDM系统模型的基础上,用MATLAB语言实现了整个系统的计算机仿真.最后给出在不同的信道条件下,循环前缀(CP)和信道估计算法对OFDM系统误码率影响的比较曲线.从仿真曲线可以看出:高斯信道下循环前缀的作用并不显著,因为这时没有信道时延,也就不会产生ISI;但是当存在多径瑞利信道的时候cp的作用就显得很重要;MMSE估计法明显优于LS估计法.得出理想结论.     

基于LTE的OFDM导频信道估计

正交频分复用（OFDM）是LTE的关键技术之一。对LTE下行OFDM系统中基于参考信号辅助的信道估计算法进行了研究,重点介绍了各种插值算法,并通过MATLAB仿真给出了在多径信道下估计算法的性能比较。     

OFDM水声通信系统信道估计算法应用研究

信道估计的精确性和有效性是正交频分复用（OFDM）水声通信系统具有良好性能的保证。针对水声信道稀疏性的特点,在传统的LS（最小二乘）和LMMSE（线性最小均方误差）信道估计算法的基础上进行了基于压缩感知（Compressive Sensing,CS）理论的LS-MP（Matching Pursuit,匹配追踪）信道估计算法的研究。并在OFDM水声通信系统下,对传统的信道估计方法（LS和LMMSE）和基于压缩感知理论的LS-MP信道估计方法进行仿真分析,对这三种算法进行了性能比较。     

稀疏信道下OFDM信号的迭代检测方法

提出了一种适用于稀疏信道环境的OFDM信号迭代检测方法。该方法采用导频进行初始化信道估计,使用数学期望最大（EM）算法迭代检测OFDM信号。该方法需要已知信道的路径时延信息、噪声方差和信道冲击响应的协方差矩阵,因此同时给出了这些参数的估计方法。仿真结果证明了这种迭代算法的有效性,而且使用估计的信道参数时的系统性能和理想参数条件下的性能接近。     

多径衰落信道下OFDM系统的仿真性能分析

构建了正交频分复用(OFDM)系统的仿真模型,给出了具体信道的参数.在不同信道传输环境下,对不同调制方式和不同移动速度下的OFDM系统性能进行了分析比较,在仿真结果的基础上给出了OFDM系统抗多普勒频移的参考方案,采用的信道模型基于ITU-R M.1225 Channel B瑞利(Rayleigh)衰落信道.最后,在基于COST 207的信道模型下,对四种典型环境的OFDM系统进行了仿真研究,并对其结果作了讨论分析.结果表明:在多径衰落信道下,OFDM系统可以有效克服多径衰落和多普勒频移,能够应用于未来的通信系统.     

OFDM水声通信系统联合信道估计的同步算法研究

正交频分复用（OFDM）技术是目前无线通信领域的研究热点之一。本文提出了一种改进的载波频偏估计方法和信道估计方法,并将这两者与一种高精度的符号同步方法相结合,充分利用了三者的优点,提高了信道估计的精确度,改善了系统的性能。本文还在多径信道下对设计出的OFDM水声通信系统进行了仿真,对采用频偏补偿和符号同步的信道估计性能进行了分析。     

OFDM/OQAM系统中的干扰近似导频搜索算法

非合作通信背景下,针对利用干扰近似法（Interference Approximate Method,IAM）进行OFDM/OQAM系统信道估计需要导频序列位置作为先验信息的问题,提出一种IAM导频搜索算法。IAM导频符号前后时隙为全0符号,经过OFDM/OQAM虚部干扰和信道衰落后导频前后时隙符号相位相同,利用此特征可以判定IAM导频符号位置。仿真实验表明导频符号值较大,多载波符号较少时,搜索算法在低信噪比条件下具有较高的搜索正确率。     

基于小波去噪的OFDM信道估计技术研究

信道估计能够为OFDM系统提供相干解调和空时译码所必须的信道信息,是OFDM系统接收机中非常重要的一个环节,如何降低无线信道的噪声,提高信道估计精度,是关乎整个通信系统性能的重要问题.提出了一种将小波去噪应用到OFDM系统无线信道估计中的方法,利用LS算法得到导频位置频域响应后进行小波去噪,然后插值得到整个信道的频域响应,可以减少多径衰落信道中的噪声和ICI对于信道估计精度的影响,减少系统的误码率.在SISO-OFDM和MIMO-OFDM系统,无线移动信道环境下的仿真表明,与传统的信道估计方法相比,在低信噪比的情况下,提出的信道估计方法能够提供2-3dB的性能改善.     

OFDM系统中信道估计的研究

正交频分复用（OFDM）用于第四代移动通信系统,而OFDM的信道估计是一项关键技术。总结了基于导频辅助的信道估计常用算法,研究了LS、MMSE和改进的LMMSE算法的原理及其在OFDM信道估计中的应用。结合仿真对信道估计算法进行了分析与讨论。结果表明正交频分复用系统性能的提高是以系统的复杂度为代价的。     

OFDM水下通信系统信道估计插值算法性能分析

在正交频分复用(OFDM)水下通信系统中,信道估计作为一项关键技术直接影响着系统的性能.研究基于导频信息的线性插值、二阶多项式插值、三次样条插值等信道估计插值算法,应用Matlab仿真给出它们的性能比较,得出不同插值算法下OFDM系统误比特率(BER)和信噪比(SNR)之间的变化关系,以及在不同导频间隔和不同多普勒频移条件下的误比特率曲线图,从而为更好的设计导频间隔,进行水声信道估计提供有力的参考.     

Blind synchronization scheme using the conjugate characters of the OFDM BPSK-modulated symbol

Previously, Beek?s scheme for timing and frequency offset estimation in the OFDM system employs cyclic prefix (CP) has been proposed under the assumption of independent identified distributed (i.i.d.) OFDM symbols. Actually, the real data in the OFDM modulated symbol, transferred by the inverse fast Fourier transform (IFFT), has the characters of complex symmetry. With these characters, more information in the whole OFDM symbol could be used for the timing and frequency offset estimation. In this paper, two conjugate symmetry characters of the OFDM BPSK-modulated symbol are used to achieve blind timing estimation algorithm in the OFDM systems. One is symbol-based symmetry and the other is CP-based symmetry. With these two conjugate characters applied to the proposed algorithm, the timing of the OFDM BPSK-modulated symbol could be derived. Under an AWGN channel, based on the performance of lose symbol timing rate and estimator mean square error, the proposed algorithm is with a tremendous improvement compared with Beek?s estimation method. Under a multipath fading channel, the results show that performance including lose symbol timing rate and estimator MSE with the proposed algorithm is better than those algorithms with Beek?s estimation method. In practical OFDM applied system, the OFDM BPSK-modulated symbol could be used to replace the preamble or training sequences in the standard to obtain an accurate timing and frequency offset estimation and to avoid the data rate decreasing with the proposed algorithm.     

一种基于OFDM信号的多传感器测距算法研究

位置业务在未来移动通信系统中起到重要作用,引起了人们的广泛关注和研究。而正交频分复用(OFDM)技术由于其良好的抗多径衰落能力和较高的频带利用率,已被广泛应用于数字音频广播(DAB)、数字视频广播(DVB)、无线局域网等,成为下一代无线通信系统的核心技术之一。在经典的时间同步算法最大似然(ML)算法的基础上,结合一种整体相关的OFDM定时估计算法,提出了一种有效利用截短循环前缀(CP)相关来进行定时估计测距的改进算法。分别在高斯白噪声和多径衰落信道下进行仿真,结果表明:改进算法在任一信道下都有较好的性能。     

Analog study of near-field focusing and subwavelength imaging with nonlinear transmission-line metamaterial

In this paper, we report an analog study of realizing near-field focusing and near-perfect imaging at harmonic frequencies using a two-dimensional （2D） left-handed nonlinear transmission line （LH NLTL） meta- material. Firstly, we give a detailed procedure of designing LH NLTL and right-handed （RH） transmission line media that match with each other at harmonics. Then, through microwave circuit simulations, we observe strong surface waves at the boundaries between RH and LH NLTL metamaterials, which are consistent with the theoretical analysis of an LH linear superlens. Finally, we show that the LH NLTL metamaterial can act as a flat nonlinear lens that can create, with a Subwavelength resolution, an image of harmonic fields of the source which is opaque at the fundamental frequency.     

多径衰落信道下OFDM系统的符号同步方法研究

由于在正交频分复用(OFDM)的系统中存在符号时间同步误差,为了消除这种误差,提出了工作在多径衰落信道的符号时间频移(STO)估计方法,即基于CP的符号时间偏移估计和基于训练符号的符号时间偏移估计,通过仿真对基于循环序列(CP)估计技术的最大似然法(ML)和基于训练符号的最小均方差异法(Classen)两类性能比较分析,在无载波频移条件下,ML算法精确度更高,当存在载波频移时,Classen算法精确度更高。     

Blind symbol timing synchronization scheme for real-time industrial wireless control network using high-speed preambleless OFDM systems over multipath fading channels

An accurate estimation of symbol timing is crucial for orthogonal frequency division multiplexing (OFDM) demodulation, since synchronization errors might destroy the orthogonality among all subcarriers and have greater impact on the system performance than single carrier systems. The symbol timing offset (STO) that leads to inter-symbol interference (ISI) and inter-channel interference (ICI) must be avoided as much as possible. In this paper, a novel symbol timing synchronization algorithm is proposed for OFDM systems on the basis of cyclic prefix (CP). A metric function and a positioning function have been designed by taking advantage of the correlation properties of OFDM signals. Computer simulations demonstrate that the schemes are superior because they achieve accurate timing offset estimation with smaller standard deviation (SD) and relatively lower computational complexity compared with the existing methods based on CP under high signal–noise ratio (SNR) assumption over frequency-selective channels, which can meet the real-time requirements in wireless local area network (WLAN) environments for factory automation (FA).     

基于Matlab的OFDM系统仿真与性能分析

正交频分复用技术(Orthogonal Frequency Division Multiplexing)是第四代移动通信技术的关键技术。文章首先简要介绍了OFDM的基本原理和主要结构,建立了系统仿真模型,对系统的载波同步和信道估计进行了分析。通过训练符号结构和频偏判决函数来完成频偏估计,给出了具体的算法并基于所建模型,给出了系统的星座图和短训练和长训练相关值曲线。仿真结果表明,所建模型能够很好地验证理论分析结果。     

OFDM系统信道估计的研究

OFDM(正交频分复用)系统以其抗多径衰落和较高的频带利用率,得到了众多领域的广泛应用。本文就OFDM系统中关键技术之一的信道估计技术进行了介绍。并分别叙述了OFDM系统和信道估计的意义,归纳了信道估计的分类,最后介绍了各种信道估计算法。     

OFDM系统中同步偏差的联合估计算法

研究基于IEEE 802.11a的正交频分复用(OFDM)系统,分析同步偏差对该系统的影响,提出一种联合估计算法。利用导频序列估计频域中OFDM系统的同步偏差,包括符号定时偏差、载波频率偏差和采样时钟频率偏差。仿真结果证明,该算法的误包率较低,能较好地应用于OFDM系统。     

A novel energy-efficient ICI cancellation technique for bandwidth improvements through cyclic prefix reuse in an OFDM system

Orthogonal frequency division multiplexing (OFDM), a very promising technique that is leading the evolution in wireless mobile communication to sideline the bandwidth scarcity issue in spectrum allocation, is severely affected by the undesirable effects of the frequency offset error, which generates inter carrier interference (ICI) due to the Doppler shift and local oscillator frequency synchronization errors. There are many ICI cancellation techniques available in the literature, such as self-cancellation (SC), maximum likelihood estimation (MLE), and windowing, but they present a tradeoff between bandwidth redundancy and system complexity. In this study, a new energy-efficient, bandwidth-effective technique is proposed to mitigate ICI through cyclic prefix (CP) reuse at the receiver end. Unlike SC and MLE where the whole OFDM symbol data is transmitted in duplicate to create redundancy at the transmitter end, the proposed technique uses the CP data (which is only 20% of the total symbol bandwidth) to estimate the channel, and it produces similar results with a huge bandwidth saving. The simulation results show that the proposed technique has a significant improvement in error performance, and a comparative analysis demonstrates the substantial improvement in energy efficiency with high bandwidth gain. Therefore, it outperforms the legacy ICI cancellation schemes under consideration.