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超宽带系统通常使用纳秒级的超宽带脉冲,系统内所有用户实现同步是非常困难的。本文提出了一种时分多路复用(TDM)网型超宽带系统,根据系统内同步基准站提供的同步信息和每个用户分配的发送时间,实现系统内所有用户间信息交换。计算机仿真和理论计算结果表明:同步帧中使用的同步脉冲越多,同步概率越高。 相似文献
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提出了利用低频超宽带(UWB)脉冲信号实现穿墙探测的设想,研究了超宽带穿墙探测雷达(UWB—TWDR)的运动目标回波信号模型,并基于运动目标回波信号的相关性,利用相干叠加原理对多次观测的结果实现运动目标的检测。最后通过具体的穿透混凝土砖块墙壁实测实验验证了上述设想和算法。 相似文献
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提出了一种基于认知无线电的自适应超宽带(UWB)窄带干扰抑制方法。为了使UWB对变化的
干扰环境具有自适应调节能力,引入了认知无线电技术。通过频谱感知和认知引擎技术提取
窄带干扰频谱特征作为陷波器的设计依据。以高斯脉冲为例,对陷波器的陷波性能进行检验
。最后,就陷波前、后脉冲的通信性能进行比较。仿真结果表明:认知陷波脉冲具有良
好的窄带干扰抑制能力,能够自适应的随着感知结果而动态地规避授权用户,从而实现UWB
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统与其它通信系统的共存,且此方法不需要在整个频段范围内降低UWB脉冲功率,实现简单
灵活,为提高UWB脉冲发射功率、增大UWB系统的通信距离提供了一种可行的方案。 相似文献
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超宽带天线是与UWB技术共同发展的,是UWB系统的重要组成部分,超宽带天线的性能好坏直接影响UWB系统的功能.本文对超宽带应用天线深入研究,探讨了对新型3G系统超宽带天线系统和网络需考虑的事项. 相似文献
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对直扩超宽带(DS UWB)信号分别于时域和频域进行描述,并对其功率谱密度进行了
详细研究。在干扰功率计算中,选择现有3G移动标准宽带码分多址(WCDMA)、码分多址200
0(CDMA2000)和时分同步码分多址(TD SCDMA)作为被干扰系统。与UWB信号带宽相比,
被干扰系统的带宽相对较窄,因此假设在接收端频谱是平坦的。研究结果表明,可以通过调
整DS UWB脉冲波形和脉冲成形因子α来减少干扰功率。通过权衡和比较,脉冲成形因
子小于0.3 ns的三阶高斯脉冲是一个最优选择。 相似文献
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针对当前航天测控系统安全性不足的问题,将脉冲超宽带技术应用于航天测控系统中,构建了一种新的脉冲超宽带测控体制。建立了基本的脉冲超宽带测控信号模型,对脉冲超宽带测控系统的性能和传输链路进行了分析。给出了脉冲超宽带测控系统结构框图,介绍了系统工作过程。针对并行信号捕获方法资源消耗大的不足,提出了两步并行捕获方法。分析表明,脉冲超宽带技术可用于航天测控系统中,完成测距测速和数据传输任务。脉冲超宽带测控系统可有效提高测控系统的隐蔽性和抗干扰能力,同时提高测距精度。在信号捕获方面,与并行捕获方法相比,两步并行捕获方法的硬件资源消耗得到大大降低,同时还可保证较快的捕获速度,但会产生一定的信噪比损失。 相似文献
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Utpal M. Dholakia 《心理学和销售学》2000,17(11):955-982
Research pertaining to the consumption impulse is sparse in the literature. To address this lacuna, the author presents and validates a detailed theoretical framework explicating the consumption impulse formation process, and examining the role played by cognitive and volitional processes in its resistance or enactment. The model makes the distinction between consonant (harmonious) impulses and dissonant (conflicting) impulses and elaborates on the role of the impulsivity trait, situational variables, and constraining factors in enactment or resistance of the consumption impulse. The results of two studies provide support to the general working of this theoretical framework. This research has the potential to inform many critical issues surrounding consumer behavior, such as regulating consumption impulses in retail and on‐line shopping environments, and developing interventions for prevention of harmful consumer behaviors such as addictions. © 2000 John Wiley & Sons, Inc. 相似文献
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为了解决实际OFDM通信系统中信道稀疏度未知的不足,提出将弱选择正则化正交匹配追踪算法用于估计稀疏信道。算法在不知晓信道稀疏度的情况下,对不同迭代残差与测量矩阵中原子的相关系数进行判定后,根据原子的弱选择准则灵活地确定出表示信道冲激响应的原子候选集,进而利用正则化原则从候选集中挑选出表示信道冲激响应的最优原子组,逐步实现精确重建。仿真结果和理论分析表明:与正则化正交匹配追踪算法相比,相同条件下改进算法可以获得更低的均方误差和误比特率;另外,算法无需将信道稀疏度作为先验信息,实用性更强。 相似文献
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基于超宽带采集存储技术构建了测量与监视系统,实现了对无线电监测系统试验场中的模拟无线电监测目标信号群的测量与监视。重点研究了基于并行交替采样的超宽带信号高速采集技术、基于固态磁盘(Solid-State Disk,SSD)阵列流水拼接的海量数据实时存储技术和基于统一计算设备架构(Compute Unified Device Architecture,CUDA)的超宽带信号频谱分析技术等关键技术。测量与监视系统工作频率范围为1.5 MHz~22 GHz,单通道采集速率可达5 GB/s,三通道实时带宽达到6 GHz,最大存储容量达到48 TB,满足对无线电监测系统试验场中通信、导航、雷达等多路模拟无线电监测目标信号进行测量与监视的使用需求。 相似文献
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PurposeEnvironmental changes, specifically the economic crisis and the growing penetration of digital technologies, have produced significant changes in shopping habits designed to create new paradigms for impulse buying behaviour. A new scenario seems to be opening up where customers enter the store much more prepared than in the past searching for products they had planned to buy. The purpose of this paper is to explore the determinants of impulse buying in a context of more planning and preparation for shopping.Design /methodology/approachThe data were obtained using a structured questionnaire from 316 respondents interviewed instore thanks to the cooperation of a leading Italian retail chain. We conducted a two-stage approach mall-intercept survey method to collect data. Firstly, we interviewed customers before entering the store, enquiring them about the pre-shopping preparation and shopping enjoyment tendency. Secondly, we interviewed the same customers at the end of their shopping trips, asking them to indicate which purchases were unplanned. Then, shoppers answered to questions regarding their general tendency to engage in impulse buying, the urges experienced to make impulse purchases, the level of positive and negative affect experienced during the shopping trip.FindingsIn the structural model tested with LISREL 8, we found that pre-shopping tendency influences directly impulse buying: confirming our hypotheses, a higher pre-shopping preparation lead to lower levels of impulse buying. Results also showed that the personality variables (shopping enjoyment tendency and impulse buying tendency) influenced impulse buying through positive affect and urge to purchase. Our research did not find support for the relationship between negative affect and urge. Finally, higher levels of urge to buy impulsively lead to higher levels of impulse buyingOriginality/valueFrom the review of past and recent literature, we have not found a model that considers the influence of pre-shopping tendency on impulse buying behaviour. This paper addresses this major gap in extant literature by including pre-shopping tendency among the individual characteristics (impulse buying tendency and shopping enjoyment tendency) taken into consideration by past contributions. 相似文献