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分析了无人机测控信道模型以及由小规模衰落带来的非频率选择性衰落、频率选择性
衰落与时间选择性衰落的产生机理及特性,并针对这3种衰落进行了抑制方法分析,指出O
FDM、交织与编码以及空间分集是无人机测控中值得重点研究的抗衰落技术。 相似文献
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针对直升机卫星通信系统中直升机旋翼对通信信道造成的周期性衰落问题,采用射频收发器AD9361模拟了信道周期性衰落模型,基于此模型在现场可编程门阵列(Field Programmable Gate Array,FPGA)上优化并实现了缝隙检测算法。根据信道衰落模型和缝隙检测算法及数据链路速率和带宽的要求,提出了一套直升机卫星通信系统可靠通信方案,即前向链路采用重发和分集接收及短码LDPC编码技术,返向链路根据前向链路缝隙检测的结果在无遮挡缝隙采用突发通信和长码低密度奇偶校验(Low Density Parity Check,LDPC)编码技术,实现可靠通信。系统测试结果表明,该方案不受直升机机型限制,系统可在40%遮挡率下实现前向链路25.6 kb/s和返向链路4 Mb/s速率下的可靠通信。 相似文献
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Hilary L. Seal 《Scandinavian actuarial journal》2013,2013(2):114-117
Abstract It was the Swiss actuary Chr. Moser who, in lectures at Bern University at the turn of the century, gave the name “self-renewing aggregate” to what Vajda (1947) has called the “unstationary community” of lives, namely where deaths at any epoch are immediately replaced by an equivalent number of births. It was Moser too (1926) who coined the expression “steady state” for the stationary community in which the age distribution at any time follows the life table (King, 1887). With such a distinguished actuarial history, excellently summarized by Saxer (1958, Ch. IV), it behoves every actuary to know at least the definitions and modus operandi of today's so-called renewal (point), or recurrent event, processes. 相似文献
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我国加入WTO以后,对于上海的发展是一个千栽难逢的机遇,同时也给上海的发展带来新的挑战。本文通过详实的资料分析了上海经济发展的现状和制约上海进一步发展的问题,并运用市场营销新理论,提出构建上海现代化大都市的营销战略。 相似文献
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针对规则LDPC码,采用了行列都均匀的(evenboth)随机构造H的方式,在瑞利平坦衰落信道下和卷积码的性能进行了对比,证明了规则LDPC码在中短帧传输下在瑞利平坦衰落信道的优异性能。这对LDPC码应用于实际无线通信系统具有重要参考价值。 相似文献
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Heiner Evanschitzky B. Ramaseshan Michael K. Brady Fazlul K. Rabbanee Christian Brock Joanna Pokorska-Zare 《心理学和销售学》2020,37(6):815-836
This paper explores the phenomenon of consumer relationship fading with a series of three adjacent studies. Analyzing two longitudinal behavioral datasets, Study 1 shows that about one-third of the relationships could be described as fading. Drawing on prior work in the marriage disaffection literature, Study 2 defines relationship fading for the consumer marketing context as a process of gradual decline in consumers' intention to continue their relationship with a brand, generally manifested in negative feelings toward the brand, diminishing frequency and/or volume of transactions with it, and initiation of switching intentions. It further identifies disillusion, disaffection, and crossroads as three distinct fading stages, and outlines boundary conditions. Study 3 observes relationship fading through a diary study approach and finds attitude movement in both positive and negative directions between the stages. Further, while positive attitudes generally decline over the course of the fading trajectory, negative emotions peak at the penultimate fading stage and then level off at the final, crossroads stage. By defining and analyzing consumer relationship fading, we improve understanding of an under-researched, large segment of consumers. 相似文献
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为设计频谱性能优良的有限冲激响应(FIR)数字带通滤波器,从窗函数的性质及选择指标出发,分析了椭圆球面波函数(PSWF)作为窗函数的优势;在此基础上根据数字滤波器设计的原理和要求,选择0阶基带椭圆球面波函数作为窗函数设计数字带通滤波器,并利用微分方程状态转移矩阵逼近的PSWF求解算法,给出了基于PSWF的FIR数字带通滤波器设计方法。理论分析和仿真结果表明:PSWF数字带通滤波器具有较低的设计复杂度,与Kaiser滤波器和Blackman滤波器相比,其旁瓣衰减有超过7 dB的优势,且具有与两种滤波器相当的通带波纹波动和过渡带宽。 相似文献