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移动自组网中大多采用冲突避免协议,广播时存在大量的冗余数据及信道冲突,在复杂的信道环境下会降低系统的通信效率。结合协同通信与动态时隙分配技术,提出了一种基于协同通信的移动自组网广播方案。该方案分成竞争、控制报文和数据传输3个阶段。竞争阶段利用基于载波侦听多址访问(Carrier Sense Multiple Access,CSMA)的广播网络洪泛少量竞争报文,分配广播权限;控制报文阶段结合协同通信,利用时隙分配算法完成节点的时隙分配;数据传输阶段,利用协同通信结合时分多址(Time Division Multiple Access,TDMA)动态时隙分配算法,使得节点能够充分利用信道资源进行数据发送,避免节点间的相互竞争,提高数据传输效率。 相似文献
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Ad Hoc网络组网效率提升的一个重要方面就是研究高效的时隙分配算法,动态TDMA时隙分配机制已经成为提高组网效率的一个热门研究点。这里基于动态优先级表提出一种新颖的动态时隙分配算法,该算法能在时间维上保证各节点对空闲时隙资源竞争使用的公平性。仿真结果表明基于动态优先级表的时隙分配算法能高效利用时隙资源,提高信道利用率。 相似文献
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协作通信可以有效地降低衰落信道中数据传输的中断概率,从而提高数据的传输速率。但是在TDMA系统中采用协作通信必然引入额外的带宽开销,为了提高传输速率而采用协作通信,是否能克服因此而产生的不利因素并不明确。在提出的CD-TDMA时隙算法中,在传统TDMA帧的前部增加了一个侦听和动态分配时隙的预约阶段。所有节点在每个数据帧的开始如果没有新产生的数据,则有义务协作转发其他节点在上个时隙帧中发送失败的数据。该算法提高了数据重传的成功概率,提高了整个网络的吞吐量。仿真结果表明,尽管该算法引入了额外的时隙开销,和传统的TDMA接入方式相比,该算法可以有效地提高整个网络的吞吐量。 相似文献
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一种基于固定TDMA的无冲突动态时隙分配算法 总被引:1,自引:0,他引:1
本文提出了一种适用于Adhoc网络的动态时隙分配TDMA算法——IP-TDMA算法,该算法以一种新颖的方式在固定TDMA的基础上叠加了优先级竞争机制,既有最差性能保障,又有较高信道利用率。通过采用一种特殊的帧结构,P-TDMA算法还可以避免信令分组的碰撞,是一种有效而又可靠的广播动态时隙分配TDMA算法。仿真结果表明,无论在吞吐量还是迟延方面,P-TDMA算法都比固定TDMA表现出更好的性能。 相似文献
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传统的移动自组网大多采用全向天线组网,为提高传输距离、减少时隙冲突、提高时隙利用率,因此在组网过程中引入定向天线。为解决移动自组网中因引入定向天线带来的时隙冲突问题,论文从研究较为成熟的DTRA协议出发,通过在帧结构中增加随机微时隙的方式来减少时隙冲突。为给网络中各节点提供高效、公平的时隙分配策略,论文改进了DTRA协议中的时隙预留过程,提出了基于节点自身缓存队列数分配不同优先级时隙数目的动态时隙分配算法。通过提出的DTDMA协议与DTRA协议进行的对比仿真,验证了提出的DTDMA协议能够有效减少时隙冲突,且协议在保证高优先级节点可多申请数据时隙的前提下,改善了节点接入信道的公平性。 相似文献
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传统的移动自组网大多采用全向天线组网,为提高传输距离、减少时隙冲突、提高时隙利用率,因此在组网过程中引入定向天线。为解决移动自组网中因引入定向天线带来的时隙冲突问题,论文从研究较为成熟的DTRA协议出发,通过在帧结构中增加随机微时隙的方式来减少时隙冲突。为给网络中各节点提供高效、公平的时隙分配策略,论文改进了DTRA协议中的时隙预留过程,提出了基于节点自身缓存队列数分配不同优先级时隙数目的动态时隙分配算法。通过提出的DTDMA协议与DTRA协议进行的对比仿真,验证了提出的DTDMA协议能够有效减少时隙冲突,且协议在保证高优先级节点可多申请数据时隙的前提下,改善了节点接入信道的公平性。 相似文献
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Meihua Shen Wilfred Pau Nicolas Gani Jianping Wen Shashank Deshmukh Thorsten Lill Jian Zhang Hanming Wu Guqing Xing 《半导体技术》2004,29(8)
This paper presents a brief overview of the Applied Centura(R)DPS(R)system,configured with silicon etch DPS Ⅱ chamber, with emphasis on discussing tuning capability for CD uniformity control. It also presents the studies of etch process chemistry and film integration impact for an overall successful gate patterning development. Discussions will focus on resolutions to key issues, such as CD uniformity, line-edge roughness, and multilayer film etching integration. 相似文献
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White organic light-emitting devices based on fac tris(2- phenylpyridine) iridium sensitized 5,6,11,12-tetraphenylnap -hthacene 总被引:1,自引:0,他引:1
We have fabricated the white organic light-emitting devices (WOLEDs) based on 4,4' -bis(2,2 -diphenyl vinyl)-1,1' - biphenyl (DPVBi) and phosphorescence sensitized 5,6,11,12,-tetraphenylnaphthacene (rubrene). The device structure is ITO/2T-NATA (20 nm)/NPBX (20 nm)/CBP: x%Ir(ppy)3:0.5% rubrene (8 nm)/NPBX (5 nm)/DPVBi (30 nm)/Alq(30 nm)/LiF(0.5 nm)/A1. In the devices, DPVBi acts as a blue light-emitting layer, the rubrene is sensitized by a phosphorescent material, fac tris (2-phenylpyridine) iridium [Ir(ppy)3], acts as a yellow light-emitting layer, and N,N' -bis- (1-naphthyl)- N,N' -diphenyl -1, 1' -biphenyl-4,4' -diamine (NPBX) acts as a hole transporting and exciton blocker layer, respectively. When the concentration of Ir (PPY)3 is 6wt%, the maximum luminance is 24960 cd/m^2 at an applied voltage of 15 V, and the maximum luminous efficiency is 5.17 cd/A at an applied voltage of 8 V. 相似文献
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Complete approach to automatic identification and sub-pixel center location for ellipse feature 总被引:1,自引:0,他引:1
XUE Ting WU Bin SUN Mei YE Sheng-hua 《光电子快报》2008,4(1):51-54
To meet the need of automatic image features extraction with high precision in visual inspection, a complete approach to automatic identification and sub-pixel center location for similar-ellipse feature is proposed. In the method, the feature area is identified automatically based on the edge attribute, and the sub-pixel center location is accomplished with the leastsquare algorithm. It shows that the method is valid, practical, and has high precision by experiment. Meanwhile this method can meet the need of instrumentation of visual inspection because of easy realization and without man-machine interaction. 相似文献
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Credence Systems Corporation 《半导体技术》2004,29(9)
Integrated circuits (ICs) intended for increasingly sophisticated automotive applications bring unique test demands. Advanced ICs for applications such as highly integrated automatic braking system (ABS) and airbag controllers combine high voltage digital channels, significant VI demands and precise timing capability. Along with continued missioncritical reliability concerns, the trend toward higher voltage operation and increased device integration requires specialized test capabilities able to extend across the wide operating ranges found in automotive applications. Among these capabilities, automotive test requirements increasingly dictate a need for a cost-effective versatile mixed-signal pin electronics with very high data rates reaching up to 50MHz with a voltage swing of-2 V to +28 V. 相似文献
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It is of interest to get appropriate information about the dynamic behaviour of rotating machinery parts in service. This paper presents an approach of optical vibration and deviation measurement of such parts. Essential of this method is an image derotator combined with a high speed camera or a laser doppler vibrometer (LDV). 相似文献
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正For a long time,optical and wireless systems/net-works are developed in separate communities witha few attempts for in-depth convergence.In fact,it prom-ises many advantages to combine the optical and wire-less technologies in the levels of systems and networks.Recently,both academia and industry have made manyefforts to enter a new phase of development to take op-tical and wireless systems as fully integrated networks.To provide high bandwidth and reliable service for bothfixed and mobile users,a well-designed network must 相似文献
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Zhang Xinsheng 《中国通信》2014,(1)
正Happy New Year!As we step into a new year,we take a look back at the key feature topics covered in China Communications over the past 12 months and set out our expecta- 相似文献
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正Cloud computing is a novel computing paradigm that utilizes remote cloud resources to achieve a high-performance computation.Cloud provides infrastructure,platform and software as different on-demand services.China has made remarkable progress in cloudbased products and operating system technology.The government,enterprises and research institutions are all active in the development of cloud computing-related projects.Despite the progress,many important problems 相似文献
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