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1.
Range Estimation in a Time Varying Multipath Channel 总被引:2,自引:0,他引:2
In this paper, range estimation in a time varying multipath channel is investigated, on the basis of which a multicarrier (MC) signal is compared with its pseudo-random (PN) counterpart in terms of the Cramer-Rao lower bound (CRLB) and the maximum likelihood estimator (MLE). The CRLB for range estimation in a time varying multipath channel is derived for three cases: (1) known channel state information (CSI); (2) unknown CSI; and (3) a special case of unknown CSI where the channel is modeled via Doppler shift. Furthermore, the MLE is developed for range estimation for each one of the above three cases and is investigated for a multipath Doppler channel with respect to the separability of its multipath components. Besides, the condition for a multipath Doppler channel to be separable is explored for a PN signal as well as for a MC signal. Simulation results show that range estimation with a MC signal outperforms its PN counterpart in a time varying channel, similar as that in a time invariant channel. 相似文献
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现有的OFDM系统快时变信道估计方法均为时域估计方法,假定信道为整数倍采样信道,利用理想的等间隔均匀导频恢复信道时域响应函数,进而采用基扩展模型拟合并估计其时变特性。而实际的信道通常为非整数倍采样信道,频带内可用的导频也并非假定的理想模式。此时,恢复的信道时域响应出现能量泄漏,导致算法性能大大受限。本文提出一种频域快时变信道估计方法,利用信道频域时变传输函数辅助估计,从而估计得到信道频域响应矩阵。该方法在频域实现,性能不受信道时域响应能量泄露影响。仿真实验从误码率、均方误差两方面分别验证了该方法的有效性。 相似文献
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In this paper, we present computationally efficient iterative channel estimation algorithms for Turbo equalizer-based communication
receiver. Least Mean Square (LMS) and Recursive least Square (RLS) algorithms have been widely used for updating of various
filters used in communication systems. However, LMS algorithm, though very simple, suffers from a relatively slow and data
dependent convergence behaviour; while RLS algorithm, with its fast convergence rate, finds little application in practical
systems due to its computational complexity. Variants of LMS algorithm, Variable Step Size Normalized LMS (VSSNLMS) and Multiple
Variable Step Size Normalized LMS algorithms, are employed through simulation for updating of channel estimates for turbo
equalization in this paper. Results based on the combination of turbo equalizer with convolutional code as well as with turbo
codes alongside with iterative channel estimation algorithms are presented. The simulation results for different normalized
fade rates show how the proposed channel estimation based-algorithms outperformed the LMS algorithm and performed closely
to the well known Recursive least square (RLS)-based channel estimation algorithm. 相似文献
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主要研究了MIMO-OFDM系统中快速时变信道的信道估计问题,将3种自适应信道估计算法: RLS,QRD-RLS,IQRD-RLS,应用于快速时变信道进行比较研究,并对其进行计算机仿真。仿真结果表明,3种算法性能相似,其中,QRD-RLS和IQRD-RLS算法的收敛速度要快于RLS算法,对于实时系统而言,这两种算法的效率更高。因此,QRD-RLS和IQRD-RIS算法更适合于快速时变信道。 相似文献
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介绍了小尺度衰落无线信道多径成型因子理论的概念及其简洁的信道描述,同时给出经典无线信道建模的缺陷,即假设信道的多径波在各方向上均匀分布,并由此提出利用成型因子的定义基础--多径波的角度分布来建模,在此基础上利用多径成型因子来衡量所建模型的特性,并给出示例,分析发现其具有简洁且涵盖经典模型的优点,为无线信道的建模提供了一种方法. 相似文献
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从理论上分析了多径效应和多普勒效应对无线信道的影响,并分别从时域和频域给出了信号经历信道后的仿真图形,分析了典型时变多径衰落信道理论模型,并在此基础上建立了抽头延迟线(TDL)的确定性仿真模型;仿真分析表明,通过改变时延功率谱和确定性模型的参数计算方法,此模型可以进一步扩展并用于多种传播环境下的小尺度衰落仿真。 相似文献
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无线衰落信道中的正交频分复用 总被引:4,自引:2,他引:2
文中给出正交频分复用(OFDM)的产生背景、原理与系统结构。通过分析无线衰落信道的特性得知,在无线高速数据传输中OFDM对于消除符号间串扰(ISI),降低系统的复杂度等方面具有很大的优势。 相似文献
10.
无线移动信道特性分析 总被引:1,自引:0,他引:1
为了更快捷方便地搭建无线通信网络,对由多径效应和多普勒频移引起的大尺度衰落和小尺度衰落等信道特性进行了分析,总结其一般的传播规律,并利用Matlab软件对路径损耗模型及平坦衰落模型进行了仿真分析,为无线通信研究人员分析和仿真信道提供基础。 相似文献
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Based on superimposed training methods, a novel time‐varying multipath channel estimation scheme is proposed for orthogonal frequency division multiplexing systems. We first develop a linear least square channel estimator, and meanwhile find the optimal superimposed sequences with respect to the channel estimates’ mean square error. Next, a low‐rank approximated channel estimator is obtained by using the singular value decomposition. As demonstrated in simulations, the proposed scheme achieves not only better performance but also higher bandwidth efficiency than the conventional pilot‐aided approach. 相似文献
13.
为应对无线通信中的未知非法检测威胁,该文提出一种随机跳径隐蔽通信方案,实现了信号能量在多径上随机动态打散。首先,基于我方多径信道信息设计了隐蔽传输策略,并构建了敌方检测模型。接着,通过引入相关性纠偏因子,分别推导了所提方案、选最强径方案和经典最大比发送方案的敌方平均接收信噪比(SNR)闭式表达式,并基于曲线拟合的方法计算了我方最小平均隐蔽概率,完成了隐蔽性能定性和定量评估。然后,推导了我方平均接收信噪比闭式解,分析了系统速率性能。仿真实验表明,所提方案不仅在未知敌方任何信息的一般情形下具有隐蔽性能优势,而且在敌方抵近我方的极端情形下可以最大程度地解决隐蔽通信失效问题。 相似文献
14.
Xian Wang Pingzhi Fan 《Communications Letters, IEEE》2007,11(2):158-160
Channel holding time is fundamental to teletraffic analysis of wireless cellular networks. This quantity depends on user's mobility which can be characterized by the dwell time, and the traffic model which is associated with the unencumbered session time. In this paper, under a general assumption on the distributions of unencumbered session time and dwell time, the characteristics of new call channel holding time and handoff call channel holding time are investigated. Analytical formulae for the distributions of new call channel holding time and handoff call channel holding time are derived 相似文献
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Frequency Selective Characteristics of a Plasma Layer with Sinusoidally Varying Electron Density Profile 总被引:1,自引:0,他引:1
Çiğdem Seçkin Gürel Emrah Öncü 《Journal of Infrared, Millimeter and Terahertz Waves》2009,30(6):589-597
In this study reflection, absorbtion and transmission characteristics of a plasma layer having sinusoidally varying electron
number density are analysed. In the analysis, plasma layer is divided into thin subslabs with constant electron number densities.
The general frequency selective behavior of the plasma is investigated by varying the plasma parameters, external magnetic
field excitation and sinusoidal electron distribution in order to be used in recent plasma applications. 相似文献
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In many mobile satellite communication systems specular multipath exists and acts as a distortion to the transmitted message stream. In most cases there is a singular specular return which can be characterized by a delay and reflection coefficient. If this return is viewed as intersymbol interference on the channel, then it is possible to consider the resulting channel as modeled by a finite state machine and process the received data stream optimally using the Viterbi algorithm. This paper develops such a scheme and derives a performance bound. A suboptimum scheme is also developed which is less sensitive to inaccurate knowledge of the multipath parameters. Performance bounds for the suboptimum scheme are also developed. 相似文献
19.
Jian Zhang Yahong Rosa Zheng 《International Journal of Wireless Information Networks》2009,16(1-2):12-21
This paper introduces an improved frequency domain channel estimation method based on interpolation vectors for single carrier frequency domain equalization (SC-FDE) with the multiple-input multiple-output (MIMO) scheme. The proposed algorithm is derived by employing the least squares (LS) criterion, and a specified application for the wide sense stationary uncorrelated scattering (WSSUS) Rayleigh fading channel is presented. The channel frequency domain responses estimated at two adjacent pilot blocks are used to track the time-variant channel information, which can effectively improve the accuracy of channel estimation without significantly increasing complexity. Maximum mean square error (MMSE) frequency domain equalization based on the estimated channel is employed in the receiver to recover transmitted signals. This paper also investigates a training sequence design method for multiple transmit antennas and a noise variance estimation method. Numerical simulation results show that the proposed methods can perform very well for fading channels with long multipath delay and high Doppler spread. 相似文献
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