一种OFDM系统强窄带干扰消除方法

OFDM系统由于具有子载波的正交性从而可以充分利用频谱资源,鉴于当OFDM受到窄带干扰而影响较多的子载波时,会出现系统误码率性能严重恶化的现状。文中提出了一种OFDM系统窄带干扰消除技术,该技术在接收端检测出受干扰子载波,利用反馈信道告知发送端,并在发送端将受干扰的子载波不加调制的信息发送到信道中,而在信道中该部分子载波只受干扰信号的影响,接收端将干扰信息重构并储存,从而完成干扰消除确保正常通信。仿真和分析结果表明,该方法在不浪费频谱资源的情况下,能有效抑制OFDM系统的窄带干扰。     

空频联合干扰对齐中的子载波分组处理方案

干扰对齐是解决下一代移动通信系统信号传输时用户间相互干扰问题的技术之一.为了弥补传统干扰对齐在空间上波束成形方案的不足,提出一种空频联合干扰对齐中的子载波分组处理方案.对信号在频域上进行子载波分组处理,然后在每个分组上进行预编码,使各组间的干扰为零,然后信号在多个天线上发送,接收端运用干扰抑制方法实现接收端的干扰对齐.仿真结果表明,在相同的信道条件下该方案能更进一步地提高系统容量和传输速率.     

MIMO-OFDM快时变信道下的一种低复杂度的检测算法

OFDM系统中信道的快速变化会破坏载波间的正交性,产生载波间干扰(ICI)。该文基于快变信道的统计特性,分析了载波间干扰的频域表达式,设计了一种针对快时变OFDM系统载波间干扰的载波间干扰对消检测方案。它可以有效地补偿由于信道快速变化所产生的载波间干扰,从而提高系统性能。实验表明,该文提出的检测方案可以在计算复杂度很小的情况下,有效地抑制由于载波间干扰所产生的误码率性能的下降,并利用载波间分集提高系统性能。     

高速移动Rayleigh信道下的相位调制OFDM系统

高速移动的Rayleigh信道会使得传输信号的频谱发生Doppler扩展。本文对存在Doppler扩展的OFDM系统进行子载波干扰的理论分析，并针对高速Rayleigh信道对误码率造成的影响进行了基带仿真。仿真结果证实，相位调制OFDM系统在存在Doppler扩展的Rayleigh信道条件下的性能可以用单载波相位调制系统在慢衰落条件下的误码率理论值来近似；即使在移动台高速移动的情况下，实际中的Doppler扩展并不会使相位调制OFDM系统的误码率出现地板效应，所以相位调制OFDM系统比较适合高速移动的Ravleigh信道条件下的高速数据传输。     

无线信道中OFDM技术和QAM技术传输的性能差异

本文介绍了OFDM技术。OFDM是一种多载波调制技术，能够把有符号间干扰的信道转换成无符号间干扰的并行子信道，所以，OFDM技术能够有效的对抗信道的频率选择性衰落．它已经得到了广泛的应用。本文比较了语音文件在OFDM系统和QAM系统中的传输效果，得出在相同条件下OFDM调制要优于QAM调制的结论。     

基于相位调制技术的可见光通信系统码间干扰识别研究

室内可见光通信系统的传输信道易受到多径效应产生严重码间干扰,降低通信质量,为此提出了相位调制技术的可见光通信系统码间干扰识别方法.通过构建可见光通信系统信道模型,针对信道光源之间在时域和频域上形成的重叠光信号在多径效应作用下,产生的码间干扰,利用位调制技术对系统信道展开均衡设计,并依照多径扩展统计限定码元速率均值,实现...     

存在多个载波频率偏移的分布式STBC-OFDM系统的均衡技术

本文研究了存在载波频率偏移的分布式空时分组编码(DSTBC)正交频分复用(OFDM)系统(DSTBC-OFDM)的性能。首先给出存在多个载波频率偏移的DSTBC-OFDM系统的接收信号模型,然后提出一种频域均衡技术来抑制符号检测时的载波间干扰(IC I)以及符号间干扰(ISI)。仿真结果表明这种均衡技术在各分布式发送端间的载波频率之差较小时具有优异的性能,同时,通过把接收端的频率设置为各发送端频率的平均值可以获得更好的性能。     

一种基于预处理的OFDM低复杂度频域线性均衡算法

针对高频段OFDM无线传输系统中严重的载波间干扰（Inter-Carrier Interference,ICI）,提出了一种基于预处理的低复杂度频域线性均衡算法.在接收端先对各时刻的信道响应提取时变因子,进行一维时域滤波预处理;再用带状结构去近似提取时变因子后信道的频域矩阵,进行频域线性均衡.仿真结果表明,相对于MMS...     

交织多址技术在BRadio系统上行链路中的应用

基于BRadio系统上行采用的时频域联合单载波调制时分多址（TFu—SCM—TDMA）技术,将交织多址接入（IDMA）技术引入其中,同一时隙中可以支持多用户同时通信。该方式用不同的交织器区分不同用户,并在发送端插入训练序列以分别获得用户到基站的信道信息,在接收端采用多用户迭代译码消除其他用户的干扰。在AWGN和瑞利衰落信道下进行仿真,验证了所提方法的可行性。     

压缩ICI的延迟分集算法

针对在正交频分复用(OFDM)系统中,时变信道引起符号内子载波间传输的数据出现ICI,引起系统性能下降[1]。提出在时域延迟分集即循环延迟发送、分集接收的算法来压缩子载波间干扰(ICI)。其思想是:将OFDM符号时域循环延迟,再以正常的发送方式发送这些符号,经空中信道后,这些经历不同衰落,在接收端通过分集接收能压缩ICI,增强系统性能。通过性能分析和仿真表明,时域自干扰删除(TDSIC-OFDM)系统和其他系统如PCC-OFDM系统相比,能有效对抗时变信道,并且能获得极大的系统性能增益。     

OFDM系统中相位噪声的影响及ICI自消除方案

相位噪声也能引起信道间干扰( ICI) ,本文系统的分析了采用ICI自消除方案前后相位噪声对OFDM系统的影响,得出了载波干扰比和信噪比的近似计算公式,在AWGN信道上仿真了系统的误码性能。从仿真结果看,ICI自消除的方案能够显著提高系统的载波干扰比和误码率     

分组衰落信道下OFDM系统载波干扰线性均衡技术研究

多普勒频移和接收载波频差使OFDM系统中各个子载波的正交性得到破坏,产生载波间干扰(IC I)。本文分析了分组衰落信道下OFDM系统各个子载波的信干比(SIR),得出载波间干扰主要集中在相邻的几个子载波上,由此提出了一种估计部分干扰系数来线性均衡OFDM符号中子信号的方法,从而改善接收信号的信干比,提高系统性能。仿真结果表明,使用相邻2个和4个子载波的干扰系数时,接收信号的信干比增益为6dB和10dB,较有效地克服了OFDM系统中载波间干扰。     

A Novel Bit Error Rate Analysis and Improved ICI Reduction Method in OFDM Communication Systems

In this paper, we have proposed a novel method for the bit error rate (BER) analysis with frequency offset and improved inter-carrier-interference (ICI) reduction in the OFDM digital communication system. We also analyze the sub-carrier index before and after cancellation of the frequency offset and discuss the carrier-to-interference ratio (CIR). The results of the present analysis are compared with the others reported literatures.     

ICI problem and compensation in MIMO SC‐FDMA system with SC‐SFBC scheme

In this paper, we address the ICI (intercarrier interference) problem and compensation in MIMO (multiple input multiple output) SC‐FDMA (single carrier frequency division multiple access) system that exploits SC‐SFBC (single carrier‐space frequency block coding) scheme. Recently, SC‐FDMA technique has received more attention due to the low PAPR (peak to average power ratio) property. However, SC‐FDMA system is sensitive to phase noise and CFO (carrier frequency offset) which is unavoidable in wireless communication systems. Phase noise and CFO introduce CPE (common phase error) as well as ICI into the received signal and seriously degrade the system performance. Therefore, analysis and suppression of these interferences are of great importance. In this paper, we analyze the interferences in MIMO SC‐FDMA system with SC‐SFBC. Then a new ICI estimation and suppression method is proposed to suppress the interferences. Instead of directly estimating the CFO and phase noise, which is pretty difficult and complex, this algorithm exploits block‐type pilots, which is a common pilot pattern in wireless communication systems, such as LTE standard, to estimate the interferences. After that the interferences are suppressed by the inverse matrix method. Simulation results show that the system performance is significantly improved. Copyright © 2010 John Wiley & Sons, Ltd.     

改进的基于多倍频的单边带调制ROF全双工系统

利用单边带调制技术,设计了一种改进的毫米波光纤传输系统,进行了系统色散分析及仿真实验.该系统在中心站通过设置相位调制器的偏置电压,使调制器产生的奇数边带被抑制,采用滤波器滤出其中的一个二阶边带.基带信号经过中频调制形成副载波,再将此副载波通过单边带调制到二阶边带上;在基站,通过带通滤波器滤出上行链路所需的光载波.用该单...     

MIMO-OFDM系统ICI自消除改进算法

现有的ICI自消除算法在提高系统载干比(CIR)的同时会降低系统的抗噪声性能。针对这一问题,提出一种在发送端对数据进行复数加权共轭运算的ICI自消除改进算法,这种算法造成的相位旋转最小,可以有效减少接收信号因相位旋转而导致的相位误差,从而提高系统的抗噪声性能。仿真结果表明,所提算法具有与已有算法相近的ICI抑制能力,但比现有算法具有更好的抗噪声性能。     

Decision Feedback Frequency Offset Estimation and Tracking for General ICI Self-Cancellation Based OFDM Systems

Inter-carrier interference (ICI) self-cancellation schemes were often employed in many OFDM systems as a simple and effective approach to suppress ICI caused by carrier frequency errors. The same procedure, however, can not perform very well at high frequency offsets. We propose a simple decision feedback scheme based on the general ICI self-cancellation scheme to perform estimation and tracking of the carrier frequency offsets. A system with the scheme does not consume additional bandwidth since it used the same data symbols employed for ICI cancellation for the estimation. After an initial estimation is completed, the scheme switches to the tracking mode to carry out the estimation of deviations in the frequency offsets. Finally this fine-tuned estimate is applied to the ICI self-cancellation scheme concurrently for frequency offset correction and hence improved the system performance greatly. Simulation results showed that our scheme allowed up to 9% of random variations in the frequency offset. The effectiveness of our scheme is further verified by calculating the bit error rate performance of various OFDM receivers.     

Pilot-free dynamic phase and amplitude estimations for wireless ICI self-cancellation coded OFDM systems

OFDM has the advantage over the conventional single-carrier modulation schemes in the presence of frequency-selective fadings. Nevertheless, intercarrier-interference (ICI) due to Doppler frequency drift, phase offset, local oscillator frequency drift, and sampling clock offset will be a severe problem in the wireless OFDM systems. Previous ICI self-cancellation coding schemes can greatly reduce the ICI, but they are very sensitive to the phase ambiguity, which is due to the composite effect of the phase offset, the multipath fading and the local oscillator frequency drift. In this paper, a novel receiver which combines the current ICI self-cancellation coding techniques with a new pilot-free joint phase/amplitude estimation and symbol detection scheme is proposed. Based on the energy modulation or the irregular symbol constellation, our new technique does not have any requirement of pilot symbols and it can operate on all kinds of phase error ranges. The proposed scheme is promising in comparison with other existing methods at different noise levels through OFDM simulations.     

Theoretical analysis of ICI self-cancellation in OFDM systems over Rayleigh flat-fading channels

Orthogonal frequency division multiplexing (OFDM) has been widely used for its robustness against multipath fading and low-complexity implementation. However, OFDM system, especially with large number of subcarriers and high modulation order, is severely affected by the phase noise of oscillators and carrier frequency offset (CFO). On the other hand, self-cancellation schemes have received a lot of attention due to their simple implementation and high efficiency to suppress inter-carrier interference (ICI) in OFDM systems. Among those ICI self-cancellation methods, symmetric conjugate symbol repetition (SCSR) has been proven to have the best bit error ratio (BER) performance for phase noise suppression. In this paper, the performance of OFDM systems with SCSR ICI self-cancellation in the presence of both phase noise (PHN) and CFO are investigated, and analytical expressions are derived to calculate error probability evaluated by symbol error ratio (SER) over additive white Gaussian noise (AWGN) and Rayleigh flat fading channels. An approach of second order approximation of PHN/CFO has been performed to estimate the residual ICI, which could provide more accurate results. Simulation results show perfect agreement with those obtained by theoretical analysis, which could be used to estimate OFDM system error probability, facilitating the design of the overall system.     

MIMO-OFDM with insufficient cyclic prefix

For orthogonal frequency division multiplexing (OFDM), cyclic prefix (CP) should be longer than the length of channel impulse response, resulting in a loss of bandwidth efficiency. In this letter, the CP reconstruction (CPR) technique is first applied to a multi-input multi-output (MIMO)-OFDM system with insufficient CP. The intercarrier interference (ICI) from multiple transmit antennas is so large for MIMO system that it can not be sufficiently suppressed with the conventional CPR procedure used in single-input single-output (SISO) system. A new minimum mean-square error (MMSE) equalization and ordering process is proposed for MIMO system to suppress the ICI during the CPR procedure. By applying the proposed CPR algorithm to MIMO-OFDM system, we can obtain both the benefits of multiplexing gain and spectral efficiency gain.