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61.
62.
A new quasi-orthogonal space-time block code (QO-STBC) based on ABBA code with lower decoding complexity and higher bit error statistics (BER) performance was proposed by U.Park recently,which can obtain full transmission rate and full diversity.In this article,the authors proposed an improved U.Park scheme based on rotational ABBA code.For eliminating the interference terms resulting from neighboring signals during signal detection,two different matrixes are used.And independent decoding can be realized when maximum-likelihood decoding at the receiver is used.Simulation results demonstrate that the BER performance is improved dramatically without increasing the decoding complexity compared with U.Park scheme. 相似文献
63.
在采用分布式发射天线的垂直贝尔实验室分层空时结构(V-BLAST)正交频分复用(OFDM)系统中,由于各发射天线与接收机之间的载波频偏(CFO)均可能不同,传统系统中针对单个频偏的简单补偿方法不再适用。不同于已有的使用高复杂度矩阵求逆运算的线性频域均衡方法,本文利用迫零(ZF)检测的固有特性,提出一种适用于低时延扩展多径信道的无需矩阵求逆运算的载波频偏补偿方法。仿真结果表明,在ITU-R M.1225信道模型的三种低时延扩展测试环境下,使用本文所提频偏补偿方法进行频偏补偿能有效改善系统误符号率(SER)性能。 相似文献
64.
针对面天线结构设计中存在的机电分离以及忽视馈源位置误差的问题,从机械电磁两场耦合的角度,将反射面天线主面误差和馈源位置误差统一到天线方向图的远场计算公式中,从而可以研究包含馈源支撑结构在内的天线结构参数对主要电性能(包括增益、副瓣、波瓣宽度、指向精度等)的影响。利用该公式建立了包含馈源支撑结构参数的天线整体机电耦合优化模型,通过某8米天线的仿真对比表明了该耦合优化模型的优点,最后将该优化模型应用于某40米大型反射面天线,取得了满意的效果。 相似文献
65.
对一起高压隔离开关投运前,例行试验发现的隔离开关绝缘套管故障进行分析。考虑实际情况和经验,找出了故障的根源所在,并进行了有效处理,重点阐述了具体处理方法,并提出预防隔离开关故障发生的措施。 相似文献
66.
Improved decoding efficiency is achieved for differential unitaryspace-time modulation across a multiple-input multiple-output(MIMO) channel. The group nature of constellations used for signaltransmission, and hence a minimised search space for maximumlikelihood (ML) decoding are utilised to give this improvement. Aprocedure using lattice reduction for fast decoding across amultiple-input single-output (MISO) channel is generalised to aMIMO channel effectively, as a modification to a previousproposal, and used to generate the ML decoder search space.Further insight into the application of this algorithm is given.The decoding technique developed is shown to have very good errorperformance for reasonably sized MIMO channels. 相似文献
67.
In this paper, we present a collision free MAC protocol for wireless networks with smart antennas that provides proportional
service differentiation to various classes of traffic based on their respective bandwidth demand. The proposed protocol works
for diverse physical parameters such as number of interfaces at each node, number of communication frequencies, and antenna
beamwidth. To the best of our knowledge, this is the first work that provides link layer differentiated services for wireless
networks with smart antennas and explores the influence of the physical parameters and network topology on the performance
of the MAC layer.
Ashish Deopura received his B.Tech degree in Electrical Engineering from the Indian Institute of Technology Delhi, India, in 2003, and he
received his M.S. degree in Computer Systems Engineering from the University of Massachusetts Amherst, in 2005. He currently
works as a Modeling Engineer for OPNET Technologies located in Bethesda, MD
Professor Aura Ganz is the director of the Multimedia Networking Laboratory at the University of Massachusetts at Amherst. She has authored more
than 170 journal and conference papers in the areas of multimedia wireless networks, ubiquitous computing, telemedicine, and
security. She is a co-author of the book: “Multimedia Wireless Networks”, Prentice Hall, 2003. Some of her recent assignments
include: general co-chair of the IEEE UWBNETS workshop, general co-chair of the IEEE BROADMED workshop, general co-chair of
the Massachusetts 3rd Annual R&D Conference, keynote speaker at the NSF sponsored workshop in Mobile Computing, and invited
speaker at Personal and Local Wireless Network Solutions conference, and Motorola’s Wireless Communications Futures Forum,
Wireless Local Area Networks Conference. She has a PhD, MSc and BSc in Computer Science from the Technion in Israel. More
details can be found at: dvd1.ecs.umass.edu/wireless. 相似文献
68.
69.
K. Rasem Qandalji 《International Journal of Theoretical Physics》2006,45(6):1158-1165
In this article, we carry out the Hamiltonization in the axial gauge,of the t’Hooft-Polyakov monopole field outside the localized region, which represents the monopole’s core. One feature of the treatment here, is using the Higgs vacuum condition as both strong and weak equation instead of using it in the degree of freedom reduction. 相似文献
70.
通过数值计算发现 ,在垂直于天线对称轴的平面内向天线对称轴平移抛物面的两个精心选定的对称部分后 ,赋形抛物面天线可产生扇形波束。馈源方向图为cosθ、抛物面口径半径为 0 .8m的抛物面经赋形后E、H平面的半功率宽度分别可达到 5.3 6°、0 .90° ,而E、H平面的副瓣电平分别为 -6.84dB、-7.86dB。 相似文献