CO-OFDM系统中基于维纳滤波的相位噪声ICI抑制算法

针对相干光正交频分复用(CO-OFDM)通信系统中相位噪声引起的载波间干扰(ICI)问题,提出一种基于维纳滤波的相位噪声ICI抑制算法。算法不需要改变OFDM符号原有的结构,只需要利用相位噪声预先得到的统计数据,通过相关计算,得到ICI的修正项。由于没有在OFDM符号中添加额外的辅助数据,所以与ICI自消除算法相比,所提出的ICI抑制算法具有较高的频谱利用率。仿真结果表明,在相位噪声比率为10-4级别时,基于迭代检测的ICI消除算法的误码率(BER)趋于10-4,出现错误平层;而本文所提出的ICI抑制算法能够有效地降低错误平层,改善BER性能。     

一种适用于快衰落信道的ICI抑制方案

针对高速移动环境下多普勒频偏造成信道的快衰落和正交频分复用(OFDM)系统中子载波间干扰(ICI)的问题,提出了一种适合快衰落环境的OFDM系统子载波间干扰抑制算法。此算法用线性变化模型来近似一个OFDM符号周期内的信道冲激响应,并以此为基础采用迭代MMSE均衡方法抑制载波间干扰。分析和仿真结果表明,此方法能有效地保证载波间的正交性,从而改善了OFDM系统的误码率(BER)性能。     

一种针对双衰落信道OFDM的新均衡算法

在OFDM系统中，子载波间的正交性是保证OFDM性能的重要保障。针对双选择性衰落信道下的OFDM系统，该文在分析载波间干扰（ICI）的基础上，提出了一种采用频域迭代消除ICI的均衡算法。分析和仿真结果表明此方法能有效地保证载波间的正交性和改善了OFDM系统的误码率（BER）性能。     

基于IT＋＋的MIMO—OFDM非线性预编码仿真研究

预编码技术能够有效的抑制MIMO信道中的多用户干扰,能显著提高系统容量,同时也能大大简化接收机的算法。主要对MIMO—OFDM系统的非线性预编码技术进行了深入研究,通过搭建出的MIM0-OFDM仿真平台对DPC（DirtyPaperCoding,脏纸编码）和THP（TomlinsonHarashimaPre—coding,模代数TH编码）两种非线性预编码算法进行了性能仿真,比较了这两种算法的BER（误码率）,同时也比较了它们与线性zv（ZeroForcing,迫零）预编码算法的BER差异,并指出了不同算法的适用性。     

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系统在时变多径信道中的干扰抑制方法

本文主要就OFDM系统在时变多径信道中由信道时变特性产生的ICI进行分析,给出进行ICI抑制的一种算法和性能分析。首先简单介绍OFDM系统的基本模型并阐述OFDM系统在时变信道中ICI产生的基本原因,接着针对ICI的生成原因,提出一种在时变多径信道条件下梳状导频放置方式下进行的ICI干扰抑制方法,并指出相对于传统的信道估计方法该方法能显著地降低系统误码率。摘要     

双选择性信道条件下OFDM系统的频域Turbo均衡

未来OFDM系统将工作在高载频、高容量、高移动速率的条件下,传统的单抽头频域均衡器将不再适用。该文基于双选择性信道的ICI分析,提出了一种用于OFDM系统的频域Turbo均衡(Frequency-domain Turbo Equalization, FTE)算法。仿真表明该算法具有BER性能好,计算复杂度低的优点,能够很好地抑制ICI。     

基于LDPC-TCM OFDM的60GHz光载毫米波传输性能实验研究

提出采用低密度奇偶校验码-网络编码调制(LDPC-TCM)提高正交频分复用(OFDM)信号在60GHz光载无线通信(ROF)系统中的传输性能。研制了60GHz LDPC-TCM OFDM-RoF系统,实验比较LDPC-OFDM信号和LDPC-TCM OFDM信号在60GHz光载毫米波的性能,当误码率(BER)为10-3时,经过光纤传输20km后,LDPC-OFDM信号的接收机灵敏度比原始OFDM信息提高了15dB,而LDPC-TCM OFDM信号比LDPC OFDM信号提高1dB。结果说明,LDPC-TCMOFDM信号比LDPC OFDM信号在光链路传输系统中具有更佳的纠错能力和更能降低光链路中色散的影响。     

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ICI消除方法分析

多径时变信道产生的多普勒频展会引起OFDM系统中的子载波间干扰(ICI),从而影响系统的误码率性能。针对无线移动通信环境,通过对多径时变信道的频率响应分析,从而进一步分析了子载波间干扰的原理。并对相邻数据取反自消除算法、SSC-ASIZ算法和扩展卡尔曼滤波(EKF)算法这三种抑制ICI的方法进行了比较分析,由仿真结果表明,SSC-ASIZ算法的系统误码率性能优于其他两个系统。     

An Enhanced Inter-carrier Interference Reduction Scheme for OFDM System with Phase Noise

Inter-carrier interference (ICI) reduction techniques achieve a better carrier-to-interference ratio (CIR) in OFDM system in the presence of synchronisation errors. However, the frequency diversity available on the frequency-selective channel has not been utilised by conventional ICI reduction techniques. In this paper, the frequency diversity of ICI reduction methods in the presence of phase noise over frequency-selective fading channels is analysed. Based on the analysis, an ICI reduction technique is proposed, enhanced symmetric data-conjugate (ESDC) technique, to enhance the frequency diversity in multipath fading channel. The carrier-to-interference ratio (CIR) and common phase error (CPE) of the proposed ICI reduction scheme are derived and the BER performance of the proposed system is compared with the conventional ICI reduction methods such as adjacent data-conjugate (ADC) and symmetric data-conjugate (SDC) methods. Simulation results reveal that the proposed ICI reduction scheme provides an improvement in BER performance over a fading channel and it is also better than conventional ICI reduction techniques in the presence of ICI due to phase noise.     

An Improved ICI Reduction Method in OFDM Communication System

Orthogonal frequency division multiplexing (OFDM) is a promising technique for the broadband wireless communication system. However, the inter-sub-carrier-interference (ICI) produced by the phase noise of transceiver local oscillator is a serious problem. Bit error rate (BER) performance is degraded because the orthogonal properties between the sub-carriers are broken down. In this paper, ICI self-cancellation of data-conjugate method is studied to reduce ICI effectively. CPE (common phase error), ICI and CIR (carrier to interference power ratio) are derived and discussed by the linear approximation of the phase noise. Then, the system performance of the data-conjugate method is compared with those of the original OFDM and the conventional data-conversion method. As results, it can be shown that CPE becomes zero in the OFDM of the data-conjugate method. Besides, in the OFDM system with phase noise, the data-conjugate method can make remarkable improvement of the BER performance and it is better than the data-conversion method and the original OFDM with or without convolution coding.     

BER Analysis of OFDM Systems Impaired by Phase Noise in Frequency-Selective Fading Channels

In this paper, we study the effect of finite-power, phase-locked loop based phase noise on the bit-error-rate (BER) performance of orthogonal frequency division multiplexing (OFDM) systems in frequency-selective fading channels. It is well known the impact of phase noise on the performance of an OFDM system can be divided into a multiplicative term called common phase error (CPE) and an additive term called intercarrier interference (ICI). Based on the conditional Gaussian approximation technique, we first derive the BER formulas for BPSK, QPSK, 16-QAM, and 64-QAM modulated OFDM signals in frequency-selective Rayleigh fading channels. To further quantify the individual influence of the CPE and the ICI on system performance for different phase noise spectra, we derive the BER expressions for perfect CPE compensation cases. The analytical results obtained for frequency-selective Rayleigh fading channels are then generalized to frequency-selective Rician fading channels. Simulation results not only validate the accuracy of our analysis but also show the dependency of BERs on the shapes of phase noise spectra.     

Probability of error calculation of OFDM systems with frequencyoffset

Orthogonal frequency-division multiplexing (OFDM) is sensitive to the carrier frequency offset (CFO), which destroys orthogonality and causes intercarrier interference (ICI), Previously, two methods were available for the analysis of the resultant degradation in performance. Firstly, the statistical average of the ICI could be used as a performance measure. Secondly, the bit error rate (BER) caused by CFO could be approximated by assuming the ICI to be Gaussian. However, a more precise analysis of the performance (i.e., BER or SER) degradation is desirable. In this letter, we propose a precise numerical technique for calculating the effect of the CFO on the BER or symbol error in an OFDM system. The subcarriers can be modulated with binary phase shift keying (BPSK), quaternary phase shift keying (QPSK), or 16-ary quadrature amplitude modulation (16-QAM), used in many OFDM applications. The BPSK case is solved using a series due to Beaulieu (1990). For the QPSK and 16-QAM cases, we use an infinite series expression for the error function in order to express the average probability of error in terms of the two-dimensional characteristic function of the ICI     

基于并行干扰抵消的OFDM/OQAM系统中的信号检测方法

在多径衰落信道中,基于交错正交幅度调制的正交频分复用(OFDM with Offset QAM,OFDM/OQAM)系统使用迫零均衡器进行信号检测时,不能完全消除信道复数特性和滤波器实数正交特性引入的时域符号间干扰和频域子载波间干扰,及信道估计误差导致的误码率性能损失。该文利用对数据初始判决并重构相邻载波及符号间干扰的思想,通过分析采用迫零均衡信号检测时的残余干扰与信道估计误差干扰,提出了一种基于并行干扰抵消和迫零均衡器结合的OFDM/OQAM信号检测方法,并在IEEE 802.22技术标准的两种典型多径衰落信道中进行了计算机仿真与比较研究。仿真结果表明,与基于迫零均衡的检测方法相比,基于并行干扰抵消的迭代信号检测方法在误码率为1%时,可获得1 dB至2 dB的性能提升。     

OFDM快时变信道下的相位旋转调制技术

由于发射端和接收端振荡器之间的频率偏差以及无线信道的时变性,OFDM系统各个子载波之间的正交性将会被破坏,从而产生载波间干扰(ICI)。该文利用发送端的多天线分集,提出了一种新型的相位旋转调制技术。它通过在频域对不同发送天线上的发送信号进行不同角度的旋转,使接收端等效信道频域响应产生的载波间干扰最小,达到抑制载波间干扰的作用。实验证明,这种新型的相位旋转调制技术不会改变OFDM系统的发送功率,能够在不占用额外系统带宽的情况下有效地消除快时变信道环境下系统的载波间干扰,达到较好的误码率性能。     

KLT-CRKCN: Hyperspectral Image Classification via Karhunen Loeve Transformation and Collaborative Representation-Based K Closest Neighbor

Nowadays, there is a great demand for ultra-high data rate (UHDR) transmission on most 5th generation wireless networks. In this concern, the multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) scheme is used on a large scale to achieve UHDR transmission with reduced inter-symbol interference (ISI) and inter-carrier interference (ICI). Discrete wavelet transform-based OFDM (DWT-OFDM) provides better orthogonality due to presence of orthogonal wavelets, which mitigates the effects caused by ISI and ICI. Also, it has extended bandwidth than the traditional OFDM systems. But a major drawback in this system is that it suffers from down sampling. The down-sampling effect reduces the actual size of the input bit streams. As a result, the system performance is degraded. For solving this problem, a multilevel redundant discrete wavelet transform (ML-RDWT) is used instead of DWT to achieve improved spectral performance. Here, complex down-sampling operation is eliminated. From the simulation outcomes, it is clearly viewed that effects caused by ICI, ISI and BER are mitigated by improving the performance of CIR. The proposed method employs optimal red deer algorithm (ORDA) to locate the optimized weights for the ICI cancellation system. This algorithm enhances the spectral efficiency by achieving high CIR with reduced BER, ISI and ICI. The BER in the proposed MIMO-ML-RDWT-OFDM-ORDA method is 68%, 76%, 38% and 75%, which is very low when compared to the BER in the existing techniques like MIMO-DWT-OFDM-RDA, MIMO-RNS-OFDM-PNMA, MIMO-OFDM-BMA and MIMO-OFDM-ICIMA. The ISI in the proposed method is 94%, 91%, 95% low when compared to the ISI in the existing techniques. The ICI in the proposed work is 71%, 57%, 73% and 86% low when compared to the ICI in the existing techniques. Therefore, the general performance of the proposed MIMO-ML-RDWT-OFDM-ORDA method is improved in an efficient way with less complexity, error rate and processing delay.

     

基于MMSE准则的改进型并行迭代ICI消除算法

无线信道的时变性破坏了OFDM系统各子载波间的正交性,造成子载波间功率泄漏,从而产生子载波间干扰(ICI).ICI的产生严重影响了OFDM系统的性能.本文首先从ICI的特性出发,对MMSE准则进行了修正,在此基础上,提出一种改进的并行迭代(PIC)均衡算法消除ICI的影响.Jakes谱瑞利衰落信道上的仿真结果表明,该方...     

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。     

An equalization technique for orthogonal frequency-divisionmultiplexing systems in time-variant multipath channels

A loss of subchannel orthogonality due to time-variant multipath channels in orthogonal frequency division multiplexing (OFDM) systems leads to interchannel interference (ICI) which increases the error floor in proportion to the Doppler frequency. A simple frequency-domain equalization technique which can compensate for the effect of ICI in a multipath fading channel is proposed. In this technique, the equalization of the received OFDM signal is achieved by using the assumption that the channel impulse response (CIR) varies in a linear fashion during a block period and by compensating for the ICI terms that significantly affect the bit-error rate (BER) performance