相位噪声对OFDM/OQAM系统的影响

分析了相位噪声对OFDM/OQAM系统性能的影响 ,分析的结果可用于指导设计低成本的调谐器 .分析过程如下 :首先导出了离散时间的采用SRRC成型滤波器的OFDM/OQAM系统公式 ;然后将乘性相位噪声等效表示为加性白高斯噪声 ,并给出了解析的方差表达式 ,该表达式与OFDM/QAM系统类似 ;最后利用BER的下降作为性能指标 ,采用蒙特卡罗仿真验证了我们的分析结果 .     

OFDM数字调幅广播时频同步问题的研究

从OFDM系统模型入手,介绍OFDM系统信号波形特点,分析同步错误对OFDM信号的影响,简要介绍时频同步算法的优缺点,重点介绍联合估计定时和频偏的时频定时同步算法,它可以完成对采样定时和符号的同步,实现简单,准确度高,在信噪比低的情况下也能正常工作,也适用于无线多径瑞利衰落环境下的OFDM符号同步方法。     

一种OFDM符号同步改进算法的研究

针对OFDN技术对定时、频偏和相位噪声敏感,较小的同步偏差即会导致系统的误码性能恶化,甚至通信失效的缺点,主要研究了OFDM符号同步的一种改进算法,即在传统的SCA（最大相关）估计算法的基础上采用多符号同步的方法。仿真表明该方法减少了符号偏差的均方误差,改善了系统的性能。     

一种抗脉冲噪声的电力线通信系统定时同步方法

针对电力线通信系统中的脉冲噪声造成系统定时同步不准确的问题,提出了一种能够抵抗脉冲噪声且能简化定时同步计算的算法,在延时自相关阶段利用发送端前导信号峰均比与接收信号的峰均比的关系对延时自相关滑动窗设定滑动阈值过滤掉脉冲噪声,增强了同步算法抗噪声能力;在判定数据起始位置的基础上,通过缩小互相关算法的滑动范围,简化了同步过程的相关运算。仿真表明,改进的算法能够提高定时同步算法抵抗脉冲噪声的能力,进一步提高系统定时同步的正确率。     

关于混沌洛伦兹系统和陈系统中的广义投影同步

1 Introduction Since Pecora and Carroll[1]showed that it is possibleto synchronize two identical chaotic systems , chaossynchronization has been intensively and extensivelystudied due to its potential applications in secure com-munication,ecological systems ,systemidentification,etc.(see [2] and a huge volume of references citedtherein) . Among all kinds of chaos synchronizations ,projec-tive synchronization is one of the most noticeableones .This kind of synchronization was first observedin …     

OFDM的信号时域差分检测技术的应用

OFDM技术预计将成为第四代移动通信的主流技术。它的特点是各子载波相互正交,这样不但减少了子载波间的相互干扰,还大大提高了频谱利用率,而且该系统能够很好地对抗频率选择性衰落和窄带干扰。OFDM系统中二进制数据比特以PSK或QAM等调制方式调制到相应的子载波上。为了准确恢复信号,接收端需进行信号检测。时域差分检测通过比较当前OFDM符号子载波与前一个符号对应子载波的幅度和相位来实现。     

Efficient timing and frequency offset estimation scheme for OFDM systems

A new training symbol weighted by pseudo-noise(PN) sequence is designed and an efficient timing and fre quency offset estimation scheme for orthogonal frequency division multiplcxing(OFDM)systems is proposed.The timing synchronization is accomplished by using the piecewise symmetric conjugate of the primitive training symbol and the good autocorrelation of PN weighted factor.The frequency synchronization is finished by utilizing the training symbol whose PN weighted factor is removed after the timing synchronization.Compared with conventional schemes,the proposed scheme can achieve a smaller mean square error and provide a wider frequency acquisition range.     

LDPC码旋转OFDM系统误码率性能的仿真研究

将旋转技术应用于LDPC-OFDM系统中,对各部分原理进行介绍,构建系统模型。通过仿真验证,在衰落信道下,系统采用旋转技术比非旋转技术得到了更低的误码率,而且在高码率下更加明显。     

OFDM电力线通信系统抗噪性能分析

基于电力线通信（ PLC ）系统的实测噪声,分析OFDM系统的电力线通信系统性能。通过Matlab和嵌入数字信号处理（ DSP ）系统进行虚拟发送和接收,在传输信道中加入噪声（加性白高斯噪声、电力线有色背景噪声等）仿真操作来干扰发送信号,以达到系统性能分析的目的。同时,在OFDM系统中分析卷积编码的前向纠错（ FEC ）的应用。结果表明,低阶调制可使系统性能改善,前向纠错技术通过解码可以自动纠正传输误码,降低接收信号的误码率（ BER）。     

XML在校园异构数据库同步系统中的应用研究

通过研究XML和异构数据库相关知识提出了一种针对校园异构系统的数据同步方法,介绍该系统的体系结构和各部分的功能,给出系统的实现。     

一个新混沌系统的自适应同步

利用自适应控制的方法，给出了一个新混沌系统的同步控制器和参数自适应律，使两个恒等系统达到了自适应同步同时识别未知参数．该控制器设计简单，易于实现，数值仿真表明所提方法具有效性．     

通用载波同步系统设计与实现

设计并实现了一种基于现场可编门陈列的通用中频载波同步系统。该系统通过控制器对载波中心频率以及低通、带通、环路滤波器的系数等参数进行设置即可实现较宽频率范围内的正交和非正交方式下的载波同步。通过软件仿真与实际测试,验证了设计的正确性和可靠性。     

关系变量中关系值属性的消除

通过分析关系值属性存在的合法性，探讨关系变量中含有关系值属性时所带来的问题，并给出消除关系值属性的理论方法．     

Robust Joint Timing and Frequency Synchronization Algorithm for IEEE802.16e OFDM System

Based on the structures of the short preamble and long preamble,which are defined for synchronization in IEEE802.16e specification,the robust synchronization algorithm for IEEE802.16e OFDM system is proposed.The correlations among the sample sequences in the preamble are investigated,especially the correlation between the first sample sequence and the last sample sequence in the long preamble.The conventional joint timing and frequency synchronization algorithm is reviewed based on the short preamble referring to the algorithm proposed by Schmidl,then a robust joint timing and frequency synchronization algorithm is proposed based on the long preamble.The simulations in the multi-path and frequency selective fading channel show that the proposed algorithm has improved the performances of timing metric plateau,timing offset and synchronization acquisition time even when signal-to-noise ratio is less than-5 dB.     

一种基于OFDM系统的子带自适应调制分组算法

分析并讨论了在不同多径衰落信道下,不同子载波分组对非精确信道信息条件下的子带自适应调制OFDM系统性能的影响;提出了一种基于信道信息误差准则的子载波分组算法,在保证系统频谱效率的同时,根据信道信息误差准则对OFDM系统的子载波进行动态分组。仿真结果表明:在典型城区信道下,OFDM系统的子载波可分为16-32个组,而农村环境下则只需分4个子载波组即可,从而大幅降低了系统的复杂度。     

A clock synchronization method based on IEEE 1588 and its implementation on Ethernet

We presented a clock synchronization method that contained a clock adjusting algorithm and a frequency compensated clock to achieve precise synchronization among distributed clocks based on IEEE 1588 protocol. Further, we presented its application on Ethernet and implementation of the frequency compensated clock in a field programmable gate array （FPGA） as experiments. The results indicate that this method can support sub-microsecond synchronization with inexpensive standard crystal oscillators.     

FDD-LTE系统中的鲁棒帧同步方法

长期演进(LTE)协议中规定的主同步信号和辅同步信号分别用来完成子帧同步和帧同步.基于频分双工长期演进( FDD-LTE)无线帧中主同步信号和辅同步信号的信道频响基本相等的假设,提出了一种帧同步方法.采用蒙特卡罗方法对该同步方法在不同信道模型下的帧同步成功概率进行了仿真.仿真结果表明:当采用线性最小均方差信道估计时,该...     

星型网络中的混沌同步

Using an example,it was analytically proved that the dynamical systems constructed on a star coupled network is more easy to be synchronized than that in coupled map lattices(CML).The result shows that the synchronization in small-world networks may be realized more easily.     

Time-domain clustered transmit power adaptation for OFDM system in fading channels

INTRODUCTION The growing demand for wireless multimedia services requires reliable and high data rate commu- nications over a wireless channel. However, the reli- ability is significantly limited by the ability of com- bating the intersymbol interference (ISI) introduced by the time dispersive nature of the wireless channel. Multicarrier transmission systems, especially OFDM systems, have aroused great interest in recent years as a potential solution to overcome ISI (Hanzo et al., 200…     

一种新的降低OFDM峰均比的子载波预留法

提出了一种基于DFT线性和循环移位性质的子载波预留方案,即利用DFT变换的线性和循环移位性质,使用非预留子载波产生削峰信号,利用预留子载波传输峰值信号的幅度、相位和位置等信息．仿真结果验证了此改进算法的有效性。