共查询到20条相似文献,搜索用时 140 毫秒
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为了减小超宽带通信对其它通信系统造成干扰,依据混沌码元丰富、良好的相关特性和白噪声统计特性,将混沌码引入TH-UWB系统,推导了TH-PPM超宽带信号的功率谱密度,采用matlab仿真工具分析了基于logistic混沌映射跳时码的PPM-TH超宽带信号功率谱密度.结果表明混沌跳时码可以有效平滑功率谱且增长码周期、增大码... 相似文献
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通过对跳频信号功率谱密度分析,指出经典周期图方法的不足,经过分析改进,得出跳频信号功率谱密度估计合适的方法和参数.仿真结果表明,改进方法具有良好的可行性功率谱估计性能. 相似文献
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根据直接序列扩频(DS-SS)信号的特点,将其建立为循环平稳模型。利用循环谱分析的方法估计了低信噪比下DS-SS信号的载波频率。利用时域平滑循环周期图估计了循环谱密度函数,在循环谱密度函数的数字实现过程中,研究了有限采集数据条件下数据截短点数对循环谱的时域平滑周期图估计性能的影响,分析了经过时域平滑后的DS-SS信号载频估计精度。最后,仿真实验验证了算法的有效性。 相似文献
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基于重排Gabor谱方法的跳频信号参数估计 总被引:1,自引:0,他引:1
对接收到的跳频信号进行时频分析是跳频信号参数估计的重要步骤。利用重排方法对信号的时频谱图进行重排,有效地抑制了交叉干扰项,提高了信号的时频聚集性并且改善了信号时频谱图的可读性。对跳频信号的Gabor谱进行重排,能够在低信噪比条件下估计出跳频信号的跳频周期、跳变时刻和跳频频率等参数。仿真结果表明,与Gabor谱方法比较,采用重。排Gabor谱方法对跳频信号进行分析,提高了跳频信号的跳频周期和跳变时刻估计的准确性。 相似文献
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对周期平稳随机过程的循环谱密度的估计,过去主要采用时域平均周期图法和频域平滑周期图法,但当短数据时,上述方法的分辨率很低,方差很大。本文提出了循环谱密度的两通道最大熵谱估计,该方法不仅具有很高的分辨率,而且估计的方差也很小,具有较好的估计性能。 相似文献
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该文研究了常规窄带雷达体制下利用时域回波调制周期的差异实现直升机、螺旋桨飞机和喷气式飞机3类飞机目标的分类问题。首先分析3类飞机时域回波调制周期的差异;然后针对3类飞机目标时域回波调制周期的不同,基于时域回波相关性提取了2维特征向量;最后基于仿真数据和实测数据,利用支持向量机(SupportVector Machine, SVM)分类器的分类结果证明了在脉冲重复频率较低时,多普勒谱有一定程度混叠的情况下,时域相关性特征仍能表现出相对较好的分类性能 相似文献
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Wei-Chiang Wu 《Circuits, Systems, and Signal Processing》2008,27(1):65-80
Ultra wideband impulse radio systems have attracted great attention for their promised applications in high-speed short-range
indoor wireless communication systems. Among the various modulation and multiple access schemes, this paper deals with time-hopping
(TH) antipodal pulse amplitude modulation operating in the presence of a multipath fading downlink channel. We first employ
a constrained optimization technique to design a batch mode blind (without exploiting training sequences and undesired users’
time-hopping (TH) codes) mobile station receiver. To reduce the computational complexity, we propose a blind adaptive receiver
that is based on the criterion of maximizing the receiver’s minimum possible output energy. The algorithm jointly and iteratively
optimizes the weight vector and channel impulse response to improve system performance. Simulation results show that the proposed
adaptive receiver converges to the optimum batch mode receiver. Moreover, the algorithms are shown to be robust to multi-user
interference and near-far problems. 相似文献
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不同阳极结构二维PSD的电流—位置输出特性 总被引:8,自引:1,他引:7
本文介绍了四边形电极结构,四边形电极改进结构和带电阻边框的方框形电极结构3种二维位敏器件(PSD)的结构和工作原理,导出了3种结构PSD的输出电流理论表达式和位置线性度网络图。结果表明:四边形电极结构PSD的位置偏差最大,中央60%光敏区域内最大位置误差约10.0%,与实验结果相符;四边形电极改进结构PSD在中央60%光敏区域内最大位置误差约5.0%;带电阻边框的方框形电极结构,当边框电阻很小时,位置信号与输出电流之间满足线性关系,实验测得中央79%光敏区域内的均方根位置误差小于0.3%。 相似文献
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In this letter, the influence of temporal and spatial diversities on the performance of ultra-wideband time-hopping pulse-position modulated multiple-access impulse radio (IR) systems is analyzed. We investigate how an antenna array can be used at the receiver to improve the bit-error rate (BER) performance and can cope with the effects of multiple-access interference of IR system in dense multipath environments. Analytical and simulation results show that the BER performance of the IR systems can be improved when the number of array elements is increased. The performance can be further improved by coherently adding more multipaths at the receiver. 相似文献
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KANG Xiao-fei YANG Jia-wei MEN Shuo .State Key Laboratory of Integrated Service Networks Xidian University Xi'an China .College of Electronic Information Automation Chongqing University of Technology Chongqing China 《中国邮电高校学报(英文版)》2011,18(6):38-43
A novel receiver is proposed in this paper that uses the blind adaptive multi-user detection(MUD) technique to deal with the presence of multiple-access interference(MAI) and inter-symbol interference(ISI) in terms of high speed time-hopping ultra-wideband(TH-UWB) system.The receiver firstly adopts constrained recursive least squares constant modulus algorithm(RLS-CMA) to conduct adaptive decorrelation for eliminating MAI and ISI,and then uses projection approximation subspace tracking with deflation(PASTd)... 相似文献
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从定义出发推导了跳时调制超宽带广义高斯脉冲串(GGP)波形距离模糊函数的解析表达式,并通过仿真分析该波形模糊函数与跳时序列自相关特性、序列周期、脉冲平均重复周期、有效时间宽度、时间尺度因子及调制系数的关系.结果表明:选择良好自相关特性和较长序列周期的跳时序列可增强旁瓣抑制能力;增大时间尺度因子或减小有效时间宽度可增加距离分辨力;权衡选择适宜的调制系数不仅保持波形原有的距离分辨特性,而且有利于采用距离门技术抑制旁瓣. 相似文献
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数字超宽带信号的功率谱密度 总被引:2,自引:0,他引:2
该文根据各种超宽带(UWB)信号的调制特点,给出了统一的随机脉冲信号模型,并应用随机理论计算得出相应的功率谱密度(PSD)函数表达式,此PSD表达式应用范围广,适用于各种调制方式、多址方式、进制下的UWB信号。该文举例分析比较了几种典型调制下带有均匀分布的随机时间抖动(timing jitter)及理想情况下的信号PSD,结果表明,时抖动的存在平滑了信号功率谱,降低了对其他窄带通信系统的干扰。而且,文中给出的PSD函数表达式可以用来估计信号各参量的变化对PSD函数的影响,而不需要考虑脉冲序列的详细设计过程。 相似文献
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Multiuser detection of time-hopping PPM UWB system in the presence of multipath fading 总被引:2,自引:0,他引:2
Ultra-wideband (UWB) impulse radio (IR) systems are currently being considered for several applications due to their attractive features that include low-power carrierless and ample multipath diversity. Among the various modulation and multiple-access schemes, time-hopping (TH) pulse position modulation (PPM) is a popular technique in application. Most past works rely on strict power control and perform single-user detection (matched filtering) on the desired signal. This paper aims to apply multiuser detection techniques in binary PPM (BPPM) UWB IR multiple-access systems. Moreover, we consider frequency-selective multipath fading channels to account for the wireless cellular environment. A class of linear multiuser detectors (LMDs) is applied to extract the information bits while eliminating multiuser interference (MUI) in the presence of multipath fading. Simulation results are provided to compare the performance of different LMDs. 相似文献
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PSD空间三维非线性修正技术的研究 总被引:3,自引:0,他引:3
提出了一种长距离激光准直测量中的位置敏感探测器(PSD)空间三维非线性修正技术,研制了在三维空间内测量二维PSD非线性的自动标定系统.在长达78 m的准直测量范围内,对二维PSD的非线性特性进行了标定实验,实验结果表明,PSD与激光源距离不同时,其非线性特性具有很明显不同.利用多层前馈神经网络建立了入射光实际位置与二维PSD输出坐标以及准直距离间的空间三维映射关系,进而对PSD的空间三维非线性进行修正.非线性修正后的PSD读数误差,在整个测量范围内表现为不大于±0.012 mm的随机误差. 相似文献