共查询到20条相似文献,搜索用时 109 毫秒
1.
OFDM/OQAM系统中联合迭代信道估计和信号检测 总被引:1,自引:2,他引:1
与基于复数域空间正交条件的传统正交频分复用系统(OFDM with Cyclic Prefix, CP-OFDM)有所不同,基于交错正交调制的正交频分复用系统(OFDM/Offset QAM, OFDM/OQAM)满足实数域空间严格正交条件。因此在多径衰落信道条件下,CP-OFDM系统中的信道估计方法会导致OFDM/OQAM系统严重的字符间干扰和载波间干扰。该文结合OFDM/OQAM系统结构特点,提出了一种基于迭代信道估计和信号检测算法。该算法通过信道估计器和接收到的信号互相交换信息,消除导频序列中的字符间干扰和载波间干扰,提高信道估计和信号检测的准确度。仿真分析结果表明,经过一定次数迭代处理后,OFDM/OQAM迭代信道估计性能趋近于理想信道估计性能。 相似文献
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MIMO-OFDM快时变信道下的一种低复杂度的检测算法 总被引:1,自引:0,他引:1
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。 相似文献
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高速移动Rayleigh信道下的相位调制OFDM系统 总被引:1,自引:0,他引:1
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。 相似文献
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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。 相似文献
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OFDM(Orthogonal Frequency Division Multiplexing,正交频分复用)系统中,信道的时间选择性快衰落会破坏子载波间的正交性,导致系统中出现载波间干扰(Inter-carrier Interference,ICI),降低OFDM系统性能.论文使用信道函数泰勒展开式的前两项近似信道函数,并以此为基础分析了OFDM在时间选择性快衰落信道中的性能,给出了ICI功率及其上界与信道最大多普勒扩展的关系式.仿真分析表明论文给出的关系式和ICI功率上界能够较为准确的描述OFDM系统在快衰落信道中ICI功率及其上界与信道最大多普勒扩展的关系. 相似文献
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《Communications, IEEE Transactions on》2005,53(5):905-906
Bit Interleaved Time-Frequency Coded Modulation for OFDM Systems Over Time-Varying Channels Orthogonal frequency-division multiplexing (OFDM) is a promising technology in broadband wireless communications with its ability in transforming a frequency selective fading channel into multiple flat fading channels. However, the time-varying characteristics of wireless channels induce the loss of orthogonality among OFDM sub-carriers, which was generally considered harmful to system performance. In this paper, we propose a bit interleaved time–frequency coded modulation (BITFCM) scheme for OFDM to achieve both time and frequency diversity inherent in broadband time-varying channels. We will show that the time-varying characteristics of the channel are beneficial to system performance. Using the BITFCM scheme and for relatively low maximum normalized Doppler frequency, a reduced complexity Maximum Likelihood (ML) decoding approach is proposed to achieve good performance with low complexity as well. For high maximum normalized Doppler frequency, the inter-carrier interference (ICI) can be large and an error floor will be induced. To solve this problem, we propose two ICI mitigation schemes by taking advantage of the second order channel statistics and the complete channel information, respectively. It will be shown that both schemes can reduce the ICI significantly. 相似文献
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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。 相似文献
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Bounding performance and suppressing intercarrier interference in wireless mobile OFDM 总被引:2,自引:0,他引:2
While rapid variations of the fading channel cause intercarrier interference (ICI) in orthogonal frequency-division multiplexing (OFDM), thereby degrading its performance considerably, they also introduce temporal diversity, which can be exploited to improve performance. We first derive a matched-filter bound (MFB) for OFDM transmissions over doubly selective Rayleigh fading channels, which benchmarks the best possible performance if ICI is completely canceled without noise enhancement. We then derive universal performance bounds which show that the time-varying channel causes most of the symbol energy to be distributed over a few subcarriers, and that the ICI power on a subcarrier mainly comes from several neighboring subcarriers. Based on this fact, we develop low-complexity minimum mean-square error (MMSE) and decision-feedback equalizer (DFE) receivers for ICI suppression. Simulations show that the DFE receiver can collect significant gains of ICI-impaired OFDM with affordable complexity. In the relatively low Doppler frequency region, the bit-error rate of the DFE receiver is close to the MFB. 相似文献
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BER Analysis of OFDM Systems Impaired by Phase Noise in Frequency-Selective Fading Channels 总被引:1,自引:0,他引:1
Chi-Hsiao Yih 《Wireless Personal Communications》2011,59(4):667-687
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. 相似文献
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在高速移动环境下,无线信道会同时经历时间选择性和频率选择性衰落,即所谓的快速时变信道,也称之为双选择性信道。最初的发射分集Alamouti编码方案是针对时不变平坦信道提出的,不能直接应用于快速时变信道。此外,OFDM 系统在双选信道下遭受的载波间干扰(ICI)不可忽视。因此,发射分集MISO OFDM系统在双选择性信道下既节能又有效的信号恢复是有挑战的。本文基于双选择性信道的基扩展模型(BEM)表示,研究了一种有效的可动态分组的混合干扰消除(HIC)信道均衡方案。仿真结果表明,提出的方案,与传统的MMSE均衡相比,计算复杂度大大降低的同时性能显著提高,计算量的降低减少了能量消耗,达到节能的目的;与现有的关于发射分集的信道均衡方案相比,表现出性能和复杂度的较好折中;此外,在信道信息完美已知的假设下,随着移动速度的提高,误码性能没有损失。 相似文献
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在多输入多输出(MIMO)-正交频分复用(OFDM) 系统中,怎样在较高频谱利用率的情况下对快时变信道进行较为准确的估计是一个具有挑战性的课题。该文在利用压缩感知理论可提高系统频谱利用率的基础上,提出了一种适合于快时变环境下MIMO-OFDM 系统的稀疏自适应信道估计方法。该方法不再受到奈奎斯特采样频率条件约束,避免了传统导频辅助信道估计方法频谱利用率低的缺点。该文方法通过构建多天线群时频结构特征稀疏基,利用多天线间和群时变OFDM符号内信道冲激响应具有更强稀疏性的特点,对MIMO-OFDM快衰落信道进行稀疏变换。由于实际MIMO-OFDM快衰落信道往往处于频率选择性、时变性和多种干扰并存的复杂环境,受到干扰的信道参数对系统而言是未知,采用该方法克服了现有基于压缩感知理论的信道估计方法需要预先知道信道冲激响应稀疏度才能重构信道参数的不足,在信道稀疏度未知道的情况下,运用稀疏自适应的方法来对不同时频结构特征的信道参数进行估计。仿真结果表明所提估计方法具有对快时变信道参数估计的鲁棒性和较高频谱利用率,且均方误差小。 相似文献
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无线OFDM通信系统中信道的时变特性非常明显,载波间正交性遭到破坏,出现载波间相互干扰(ICI),给系统均衡带来了极大困难。基于等效数字基带模型下ICI分析,在现有的OFDM协议标准中,存在一些空闲载波。利用这些空闲子载波信息,研究了一种适用于时变信道OFDM系统的稀疏矩阵均衡器结构。该算法具有ICI消除与均衡效果良好,计算量适中,频谱利用率高的特点。 相似文献
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Kapoor S. Marchok D.J. Yih-Fang Huang 《Signal Processing, IEEE Transactions on》1999,47(12):3381-3391
This paper considers the problem of mitigating fading and interference in wireless orthogonal frequency division multiplexing (OFDM) multiple access communication systems. Applications include cellular mobile radio, wireless local loop, and wireless local area networks. The effect of interchannel interference (ICI) arising from time-selective fading and frequency offsets and co-channel interference (CCI) is analyzed. A loop-timing method that enables a synchronous uplink between multiple mobile transceivers and a base-station is described. Adaptive antenna arrays are utilized at the base for uplink reception, and optimum array combining based on the maximum SINR criterion is used for each subchannel over slowly time-varying channels. For operation over fast time-varying channels, a novel two-stage adaptive array architecture that incorporates combined spatial diversity and constraint-based beamforming is presented. While ICI alone is most effectively overcome by spatial diversity, combined beamforming and diversity are most effective to combat CCI in the presence of fading. The overall method is suitable for real-time implementation and can be used in conjunction with traditional coding schemes to increase the link-margin 相似文献
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基于并行干扰抵消的OFDM/OQAM系统中的信号检测方法 总被引:1,自引:0,他引:1
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。 相似文献
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An iterative pilot-symbol aided modulation (PSAM) channel estimation approach is proposed for vertical Bell Laboratories layered space-time (V-BLAST) orthogonal frequency division multiplexing systems operating on frequency-selective fading channels. Since the signals at the receive antennas are the superposition of signals from multiple transmit antennas, accurate channel estimates are crucial for good error performance. Furthermore, the time selectivity of the fading channels leads to inter-carrier interference (ICI). While ICI can be ignored for slow fading channels, it should be mitigated for fast fading channels. This paper proposes an ICI mitigation scheme for time-varying channels. We also propose an iterative channel estimator with low-complexity. Simulation results demonstrate the usefulness of the proposed algorithm on frequency-selective fading channels. 相似文献