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改进的高效MIMO-OFDM系统EM信道估计算法 总被引:1,自引:0,他引:1
针对MIMO-OFDM系统中期望最大化(EM)信道估计算法在高信噪比(SNR)下带来的误差地板(EF)现象,且OFDM符号的数据传输效率随发射天线数的增加而明显降低,提出一种改进的高效EM信道估计算法。该算法首先引入一种准确的等效信号模型并推导出一种修正的EM算法,改善了EM算法在高SNR下的性能;在多个OFDM间利用相位正交导频序列来提高数据传输效率,同时进行联合信道估计以提高估计性能。仿真实验验证了所提算法具有更高的信道估计性能和更高的数据传输效率。 相似文献
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为了解决认知无线电或信号截获中多径信道下MIMO系统发送天线数估计问题,首先分析了现有模型在多径信道下失效的原因,将MIMO多径信道模型等效变换出一种虚拟信道矩阵,从而建立多径信道下MIMO系统发送天线数估计模型;然后,利用随机矩阵理论中协方差矩阵最小特征值分布的相关研究结果,证明了时不变瑞利信道的协方差矩阵最小特征值收敛于第二类Tracy-Widom分布,分析了该特点对发送天线数估计的影响,并提出一种改进的RMT估计算法来估计多径信道下MIMO系统发送天线数.最后对改进算法进行了仿真验证,结果表明在低信噪比和小数据条件下,改进算法的估计性能相比RMT算法有较大提升. 相似文献
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修正的MIMO-FSO信道自适应SVD估计算法 总被引:1,自引:1,他引:0
针对多入多出(MIMO)无线光通信(FSO)中传统的奇异值分解(SVD)信道估计算法由于训练序列的单极性容易导致信号能量损失,从而引起信道估计值不准确的问题,提出了一种修正的自适应SVD估计算法。该修正算法能对SVD算法中存在的估计误差进行补偿,从而能使该估计方法更好地应用于MIMO-FSO系统中。仿真结果表明,与SVD算法相比,在信噪比为15dB时,修正的算法有2个数量级的均方误差(MSE)性能提高,在信噪比为30dB时,MSE性能有3个数量级的提高。与相同条件下的均值修正SVD算法相比,平均有1dB左右的性能改善。该修正方法可移植性强,在其他信道估计方法中也可采用类似的改进方法。 相似文献
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信道编码的MIMO无线通信系统中,MIMO信号检测器需要输出编码比特的对数似然比,以获得更好的误码率性能.现有的软输出MMSE MIMO检测算法基于理想信道估计得到,在实际信道估计下会导致性能损失.本文针对MMSEMIMO信道估计,基于MMSE信道估计的统计特性,推导了考虑信道估计误差影响的新的软输出MMSE MIMO检测算法.仿真结果表明,相对于现有的软输出MMSE MIMO检测算法,所提出的算法可以显著降低由于信道估计误差导致的残留误码平层,而增加的计算复杂度可以忽略不计;同时,所提算法对信道估计误差方差的相对误差不敏感,具有实际应用的价值. 相似文献
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该文分析了瑞利平坦衰落信道下,信道估计误差对采用迫零接收的MIMO系统性能的影响,提出了一种以系统有效吞吐量最大化为目标的功率分配与自适应调制算法。为了减少信道估计误差对实际系统性能的影响,该算法对发送端估计的信噪比进行修正,并以此作为功率分配和自适应调制的依据。在系统总功率受限的条件下,对发端多天线的功率分配结合了空域注水定理和比特分配,并尽量保证调制阶数高的数据符号所在天线的功率。仿真结果表明,该算法实现较简单,获得的系统有效吞吐量接近于最优值,适用于实际系统。 相似文献
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从缩短信道时延扩展的角度出发,研究了Rake接收机的部分信道均衡能力,并推导出了Rake接收机均衡性能与Rake接收机的复杂度和信道衰减系数之间的关系;分析了信道估计误差对Rake接收机合并前后多径信道变化的影响。研究表明当存在估计误差时,Rake接收机仍然能实现均衡的作用,但是性能有所下降;由于低复杂度Rake接收机引入的估计误差较少,在低信噪比条件下其均衡性能甚至会优于高复杂度的Rake接收机。 相似文献
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空时编码是实现宽带无线数据通信的一种极有潜力的技术,随着发射天线个数的增加,对空时编码进行信道估计时,所需训练符号的个数也将增加,减少了传输数据的有效时间.本文将子空间方法同空时分组码的特性有机地结合,提出了无需训练序列,直接进行信道估计的方法.它充分利用空时分组码的特性,使得接收信号中,表示信道衰落影响的矩阵各向量间存在一定联系,利用这些联系,结合子空间方法,从接收信号中解得信道信息.Monte-Carlo仿真表明,在信噪比较低时,本文算法带来的信道估计误差对于解码性能影响较小. 相似文献
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As is known, distributed Turbo coding (DTC) performs close to the theoretic outage probability bound of a relay channel when correct decoding is assumed at the relay. However, decoding error is inevitable in practical fading channels due to the error-prone feature of radio channels, and the decoding error propagation in DTC scheme will severely degrade the error performance of the relay system. As a result, it is necessary to evaluate the error performance of the DTC scheme in multi-hop relaying wireless systems in practical fading channels. Moreover, the theoretical method of analysis provides an effective tool for obtaining the error performance besides lengthy simulations. In this article, the concept of equivalent signal-to-noise ratio (SNR) of the two-hop relay channel and the method of computing equivalent SNR are developed, and then the upper bound on the bit error probability (BEP) of DTC relay systems is analyzed by use of Turbo code's distance spectrum, the concept of uniform interleaver, the limit-before-averaging technique, and the union bound method. Both theoretical analysis and numerical simulation are implemented for relay systems with DTC scheme over quasi-static Rayleigh fading channels. The results show that the upper bound approaches the simulation results in the medium to high SNR region. 相似文献
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LDPC码应用于OFDM系统能够得到非常好的性能,然而当信道估计信息发生错误将直接影响译码性能.为此,研究了信道估计误差对LDPC-OFDM系统性能的影响.理论和仿真得出了以下结论:信道估计误差可带来译码过程外部信息信噪比的提高或降低,由此加速成功译码或者导致译码失败. 相似文献
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We study the effect of imperfect channel estimation (ICE) on the error probability performance of M-level quadrature amplitude modulation ( M-QAM) with maximal-ratio combining and equal-gain combining diversity formats in Nakagami fading channels. We provide a novel formulation of the bit-error rate (BER) of M-QAM with ICE in terms of the signal constellation-dependent effective signal-to-noise ratios (SNRs) or amplitudes, which allows us to derive the general, accurate, and easy-to-evaluate BER formulas for square and rectangular diversity M-QAM with channel estimation errors. Our result shows that the performance loss caused by ICE may be manifested by the signal decision space distortion and a scaling of the effective SNR. Using our analytical result, we evaluate the performance of M-QAM with pilot-symbol assisted modulation and present some insightful findings 相似文献
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In order to attain near-single user performance in uplink multicarrier code- division multiple-access (MC-CDMA) systems, multiuser
detection (MUD) methods may be employed which rely on simultaneous estimation of the channel frequency responses of multiple
users. Pilot symbol assisted (PSA) channel estimation is needed in fast fading channels and it can be performed either by
applying maximum likelihood (ML) criterion or minimum mean-squared error (MMSE) criterion. The performance of ML estimation
technique degrades significantly in the case of fractionally spaced (FS) multipath channels where dominant paths are closely
spaced with respect to the time resolution of the system. In such situation, the number of effective paths (which contribute
more towards signal power) becomes considerably less than the actual number of multipaths at low and moderate SNR values.
We propose an improved ML estimation method which considers only effective paths during the estimation process. The proposed
method performs nearly identical to the MMSE estimation method and it can also provide significant reduction in the computational
complexity when a large number of users are accommodated in the system. 相似文献
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为了提高空间相关信道估计的精度,提出了一种适用于空间相关信道的MIMO-OFDM系统的空域LMMSE信道估计算法及其改进算法,从理论上分析了MSE误差。仿真结果表明,空域LMMSE算法能有效地提高信道估计的精度,尤其是在低信噪比的情况下,所提出的算法获得的效果更为明显。 相似文献
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In orthogonal frequency-division multiplexing(OFDM)amplify-and-forward(AF)relay networks,in order to exploit diversity gains over frequency-selective fading channels,the receiver needs to acquire the knowledge of channel state information(CSI).In this article,based on the recent methodology of distributed compressed sensing(DCS),a novel channel estimation scheme is proposed.The joint sparsity model 2(JSM-2)in DCS theory and simultaneous orthogonal matching pursuit(SOMP)are both introduced to improve the estimation performance and increase the spectral efficiency.Simulation results show that compared with current compressed sensing(CS)methods,the estimation error of our scheme is reduced dramatically in high SNR region while the pilot number is still kept small. 相似文献
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信道估计技术作为获得信道衰落信息的方法,是提高无线信道传输接收性能的关键技术。本文针对放大转发双向中继系统的时间选择性平坦衰落信道,利用信道在多普勒域的稀疏性进行压缩信道估计。相比于传统的线性估计方法,压缩信道估计考虑了信道的固有稀疏性,降低了导频的开销,改善了信道估计性能,提高了频谱利用率及系统吞吐量。文中通过对双向中继信道进行多普勒域的稀疏建模,仿真分析了信道估计性能随着导频数量增加、信噪比增加,得到不断改善;而不同的导频分布将影响观测矩阵的相关度,从而对信道估计产生影响。仿真表明,当导频随机分布时,信道估计效果最佳。同时,文中还仿真分析了最大多普勒频移对信道估计性能的影响。 相似文献