移动WIMAX下OFDM载波间干扰消除

高速移动WIMAX下的信道变化使得OFDM的正交性遭到破坏，从而产生载波间干扰，导致系统估计性能明显降低，为了降低ICI的影响，文中提出了一种基于泰勒级数逼近的ICI消除算法，并以此进行了时域迭代消除信道估计，仿真结果表面估计算法在高速移动环境具有良好的估计性能，ICI消除效果好，计算复杂度低。     

OFDM系统中载波间干扰自消除算法研究

OFDM系统对频率偏移极为敏感,频率偏移将致使各个子载波之间失去正交性,导致子载波干扰（ICI）,从而降低系统性能。通过对有效抑制ICI的方法—ICI自消除算法进行研究,分析了ICI自消除算法对OFDM系统的影响。研究结果表明：与标准OFDM系统相比,ICI自消除算法使OFDM系统改善了系统误码率。     

OFDM系统中载波间干扰自消除算法研究

OFDM系统对频率偏移极为敏感,频率偏移将致使各个子载波之间失去正交性,导致子载波干扰(ICI),从而降低系统性能。通过对有效抑制ICI的方法—ICI自消除算法进行研究,分析了ICI自消除算法对OFDM系统的影响。研究结果表明:与标准OFDM系统相比,ICI自消除算法使OFDM系统改善了系统误码率。     

OFDM系统中载波间干扰抑制方法

在高速移动通信环境下,OFDM系统在传输过程中出现的多普勒频移和收发两端本地振荡器之间的频率偏差,形成子载波间干扰(ICI)并造成系统性能降低。在分析子载波间干扰机制的基础上,讨论了自消除方法和分段均衡方法,并提出一种利用加窗技术改进的分段均衡方法。仿真结果表明,采用该改进的分段均衡方法能更好地改善系统的性能,有约2 dB的信道估计增益。     

基于电力线信道的OFDM盲同步算法

在Takahashi提出的盲同步算法的基础上,提出了一种正交频分复用（OFDM）多符号联合的差分盲同步算法。同Takahashi的算法一样,该算法利用OFDM符号的循环前缀内不被多径时延扩展所影响的那部分码元提取定时信息,但是为了避免电力线信道中随机的脉冲噪声对符号同步产生的影响,在每个定时时刻,取差值的前后移动平均,并采用多个OFDM符号的联合,以增强同步效果。仿真结果表明,在第一径为最强径或是非最强径的电力线多径衰落信道中,该算法取得了更好的符号同步性能。     

基于电力线信道的OFDM盲同步算法

在Takahashi提出的盲同步算法的基础上,提出了一种OFDM多符号联合的差分盲同步算法。同Takahashi的算法一样,该算法利用OFDM符号的循环前缀内不被多径时延扩展所影响的那部分码元提取定时信息,但是为了避免电力线信道中随机的脉冲噪声对符号同步产生的影响,在每个定时时刻,取差值的前后移动平均,并采用多个OFDM符号的联合,以增强同步效果。仿真结果表明,在第一径为最强径或是非最强径的电力线多径衰落信道中,该算法取得了很好的符号同步效果。     

基于载波间干扰自抵消的OFDM频率同步

载波间干扰自抵消(ICISC)方案在频率域引入了冗余信息,提高了OFDM系统对频偏的稳健性.基于最大似然原理,针对ICISC方案提出了两种OFDM最大似然同步新算法.分析了算法的估计范围、方差性能以及Cramer-Rao下界.两种方法具有估计频偏范围大、估计精度高以及实现简单等优点,计算机仿真结果表明了方法的优越性.     

地面数字电视广播OFDM系统中子载波间干扰的消除

提出了一种基于差分调制消除地面数字电视广播OFDM系统子载波间干扰的新方法.仿真结果表明:差分调制能够有效消除频率偏移造成的OFDM系统子载波间的干扰,并且计算简单,不牺牲系统的带宽利用效率,具有很好的实用性.     

OFDM系统中联合信道估计的载波同步算法的研究

针对采用正交频分复用（OFDM）调制的欧洲数字电视地面广播系统（DVB—T），详细分析了剩余载波频偏对信道估计的影响，并根据DVB—T特有的信道估计方式提出了与信道估计相结合的频域相位调整和时域补偿两种同步方案，仿真结果表明，在多径信道条件下，这两种同步方案能完全消除剩余载波频偏对信道估计的影响，且具有令人满意的性能。     

OFDM系统中帧同步和载波同步的ML算法

文中给出一种应用于正交频分复用系统中帧同步和载波同步的最大似然估计算法,它是基于循环前缀和脉冲成形推出的。本文详细阐述了算法推导过程,并给出了计算机仿真结果分析了其性能,最后由此算法提出一种估计器的设计方案。     

Inter-Carrier Interference Cancellation for OFDM Systems with Macrodiversity and Multiple Frequency Offsets

Macrodiversity provides improved coverage in wireless communications. It isused in single frequency networks (SFN), and in some cellular systems, whena mobile is in a soft handoff. The combination of OFDM and macrodiversity isvery attractive for the ability of OFDM to cope with delay spread resultingfrom macrodiversity. However, such system is very sensitive to poor frequencysynchronization among transmitters, which results in multiple frequencyoffsets. These cause inter-carrier interference (ICI), which severely degradesperformance. In this paper we quantify the degradation, providing expressionsfor the receiver SINR, and find the optimum receiver frequencysynchronization. Furthermore, we propose to mitigate ICI degradation usinglinear and decision feedback interference cancellation. In each case, weprovide a solution using both the decorrelating and the MMSE criteria.Simulation results show that, for macrodiversity OFDM, our approach resultsin significantly improved performance and robustness to frequency offsets.     

Resource Management Techniques for OFDM Systems with the Presence of Inter-Carrier Interference

The aim of the paper is to study the problems of resource management in the presence of inter-carrier interference (ICI) and multipath fading channel for orthogonal frequency division multiplexing (OFDM) systems. OFDM is a promising technique for the broadband wireless communication systems. However, the OFDM communication system is sensitive to ICI which arises because of Doppler spread and carrier frequency offset (CFO). To solve these problems, an optimization method has been exploited, and a computationally efficient method using numerical optimization techniques is proposed. The simulation results show that these derived optimal solutions and proposed suboptimal algorithms as compared with the uniform power allocation algorithm or conventional water-filling algorithm can significantly improve the performance of the OFDM systems.     

OFDM系统同步问题研究

首先介绍了OFDM系统同步问题的研究背景,然后分别说明了传统的OFDM和MIMO-OFDM的系统模型,接着重点介绍了这两个系统近年来具有代表性的同步算法,并对算法的优缺点进行了分析,最后总结并对以后工作进行展望。     

一种改进的OFDM盲同步算法

研究了OFDM系统中的最大似然估计(ML)算法,并使用数据循环移位以及多符号联合估计等技术对ML算法进行了改进,随后提出了一个综合性的新方案。仿真结果显示,在AWGN和瑞利多径衰落信道中,该方案可以有效提高符号定时偏差(STO)和载波频率偏移(CFO)的估计性能。     

Blind Symbol Synchronization Based on Cyclic Prefix for OFDM Systems

In this paper, a blind symbol synchronization algorithm is presented for orthogonal frequency-division multiplexing (OFDM) systems, and a new timing function based on the redundancy of the cyclic prefix (CP) is introduced. It proves that the maximum of this function necessarily points to the correct timing offset, irrespective of channel conditions when the signal-to-noise ratio is high. Using the timing function, the timing offset is estimated through a searching algorithm. Channel power profile and channel length information are unnecessary. Simulation results show that the proposed algorithm is robust and outperforms the existing CP-based algorithms, particularly in frequency-selective fading channels.     

An HαFilter Based Approach to Combat Inter-Carrier Interference for OFDM Systems

In this paper, an extended H_infin filter-based carrier frequency offset (CFO) estimator is proposed for orthogonal frequency division multiplexing (OFDM) systems. The design criterion of the proposed estimator is to minimize the effect of worst-case disturbances (noise and model error) on the CFO estimation errors. This data-aided CFO estimator does not require any statistical knowledge of the disturbances. Moreover, its computational complexity is similar to that of the extended Kalman filter (EKF) method. Simulation results show that the proposed method can combat ICI effectively and obtain better bit error rate (BER) performance in the unknown noise for OFDM systems.     

OFDM系统中载波间干扰消除方法性能分析

OFDM系统面临的一个主要问题是对频率偏移的敏感性,频率偏移将导致载波闻干扰(ICI)的产生,从而大大 降低系统性能。对由频率偏移而导致的ICI进行了理论分析,并对抑止ICI的三种方法:自消除方法(SC)、最大似然估计方法 (MLE)及扩展Kalman滤波方法(EKF)进行了仿真和性能比较。     

Interference avoidance and cancellation in automotive OFDM radar networks

With increasing use of millimeter-wave radars in driving safety applications, interference between vehicles becomes a significant issue. Moreover, oscillator imperfections and relative velocity effects induce inter-carrier interference (ICI) owing to frequency offset, leading to degradation of target detection. In this paper, time-frequency resources are divided into several orthogonal logical channels according to the time-frequency division (TFD) scheme. We propose a two-stage interference mitigation method. First, an interference avoidance technique is designed for each piece of radar equipment (RE) to select logical channels with the least ICI. Then, each RE reconstructs and cancels interference according to estimated parameters based on the proposed interference cancellation technique. Computer simulations reveal that the proposed interference avoidance technique can approximately achieve the performance of ground truth, especially when the number of interferers is small. In addition, noise enhancement effects can be effectively mitigated through the proposed cancellation technique.

     

OFDM传输系统同步方案简介

本文研究数字地面电视DVB-T的OFDM传输系统接收端的同步。根据OFDM的原理特点和DVB-T标准,设计同步方案。该方案采用多载波(OFDM)系统时域插在循环保护间隔携带的冗余信息进行粗符号和分数频率偏移估计。该方案利用OFDM系统时域插入的保护间隔前缀所携带的冗余信息,进行粗符号同步和分数频率偏移估计。FFT后,再利用频域插入的连续导频进行整数频偏估计,及利用分散导频通过估计信道冲击响应,实现精符号同步。仿真表明,同步设计在加性高斯白噪声信道能达到最佳性能,在慢衰落Rayleigh信道下也有较好的性能。     

基于电力线信道的一类OFDM盲同步算法的改进

针对电力线通信中多普勒频移为零以及具有一定拓扑结构的电力线信道中由多径反射所产生的时延扩展较移动信道而言相对稳定的特点,这里在最大似然（ML）类算法的基础上,实现了基于电力线信道的改进的正交频分复用技术（OFDM）同步算法。该方法有效的弥补了ML类算法不适合具有多径效应的电力线信道的不足。理论分析和仿真结果表明,该算法在电力线信道中具有良好的定时估计和频率偏移估计性能,而且计算量减少。