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光突发交换网络(OBS)是一种IP over WDM的光交换技术,能很好地支持突发业务。OBS系统采用单向波长资源预留方式为突发数据分组预留前向数据波长通道,这样提高了传输交换效率、减少了建链时间,但同时因路由连接的非确定性而引起突发分组的易丢失性。所以QoS戍为OBS网络中的最亟需解决的问题。对OBS网络所采取的多种改善其QoS的策略进行了研究。 相似文献
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文章首先讨论了与光突发交换(OBS)相关的一些问题。接着讨论了OBS如何应用于下一代光互联网中,特别是偏置时间和延迟预留协议有助于避免使用光缓存,能在波分复用(WDM)层支持服务质量(QoS)服务。 相似文献
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光突发交换集合了光电路交换和光分组交换的优点。资源预留过程对OBS至关重要。本文讨论分析了OBS资派预留的重要参数以及它们对资源预留性能的影响,并用排队论的模型详细研究了资源预留过程。 相似文献
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基于保护资源的混合光交换网络 总被引:1,自引:1,他引:0
提出一种基于保护资源的混合光交换方案P_HyLABS。该方案利用光电路交换(OCS)网络中的保护资源(波长信道),构建光突发交换(OBS)网络层,与OCS工作光路组成的OCS网络层一起,组成OCS/OBS混合交换网络。仿真结果表明,由于将OCS传送的电路交换的优势与OBS传送的统计复用能力进行了较好的结合,与单一的OCS网络和OBS网络相比,P_HyLABS混合交换在保证数据高效传输的同时,可应对呈高突发性的数据传送,在多失效的网络环境下也能部分恢复数据传送。 相似文献
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光互联网络的典型特征是高速宽带、灵活可控、资源高效利用。光突发交换(OBS)结合了光电路交换和光分组交换的优点,又克服了二者的不足,将成为下一代光互联网的一种典型的核心支撑技术。文章分析和讨论了OBS网络增强型通用多协议标记交换(GMPLS)控制面技术、多粒度光交换技术,以及光网络节点结构模型、波长资源预留与调度机制、竞争解决机制、OBS网络故障监测技术等关键技术;还分析和讨论了下一代光互联网络的光虚拟专用网(OVPN)关键技术问题。文章指出为了增强目前光网络在资源分配、服务发现、服务质量保障等方面缺乏与上层IP网络的协同支持,需要对网络控制面体系结构、流量工程和业务管理等方面加强研究。 相似文献
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光突发交换(OBS)是构造下一代光互联网最有前途的解决方案之一.首先简单介绍了在OBS网络中实现QoS的几种传统机制,接着对波长分组预留策略提出了一种改进方案,并分析了其优越性和可行性. 相似文献
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《Vehicular Technology, IEEE Transactions on》2009,58(6):2783-2792
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Accurate and Simple Time Synchronization and Frequency Offset Correction in OFDM System 总被引:1,自引:1,他引:0
LIU Xiao-ming JIANG Wei-yu LIU Yuan-an Wireless Communication Center Beijing University of Posts Telecommunications Beijing P.R. China 《中国邮电高校学报(英文版)》2004,11(3)
1 Introduction OFDMisaneffectivetransmissionschemetocopewithmultipathfading[1] .Byinsertingaguardintervalbetweensymbolsblockscalledcyclicprefix ,theInterSymbolInterference (ISI)canbemitigated .OFDMwasadoptedasthemodulationschemeforaDigitalAu dioBroadcasting (DAB)system[2 ] andisalsoproposedastheterrestrialHDTVtransportinEurope[3] . SymboltimingoffsetsinOFDMreceiversnotonlyin troduceISIbutalsocauselinearphaserotationsofthesignalconstellationofthereceiverFastFourierTrans form (F… 相似文献
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主要研究AWGN信道下,残余频偏对重叠时分复用(OvTDM)信号接收的性能影响;同传统的QAM技术相比,OvTDM是一种可以获得高频谱效率的传输技术,它通过引入符号码间串扰,并利用符号间互扰的约束特性来实现更高传输速率。在一个实际通信系统中,接收信号不可避免的会受到系统载波频偏的影响,从而影响信号的接收性能。因此,分析了系统残余频偏对OvTDM的性能影响,对比了相同条件下QAM信号性能,研究结果表明,在相同的信噪比和残余频偏条件下,OvTDM信号具有更好的误码性能。 相似文献
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In this research paper, demonstrates, the logic performance of n and p channel complementary metal oxide semiconductor (CMOS) circuits implemented with dual material gate silicon on insulator junctionless transistor (DMG SOI JLT). The logic performance of a CMOS circuit is evaluated in terms of static power dissipation, voltage transfer characteristic, propagation delay and noise margin. The gate capacitance is less as compared to gate capacitance of DMG SOI transistor in saturation. The power dissipation for CMOS inverter of DMG SOI JLT is improved by 25% as compared to DMG SOI transistor. The DMG SOI JLT common source amplifier has 1.25 times amplification as that of DMG SOI transistor. The noise margin of DMG SOI JLT CMOS inverter is improved by 23% as compared to the DMG SOI transistor CMOS inverter. The NAND gate static power dissipation of DMG SOI JLT is found improved imperically as compared to DMG SOI transistor for various channel length. The improvement obtained is 53% for 20nm, 46% for 30nm and 34% for 40nm respectively. Static power dissipation of DMG SOI JLT inverter is reduced by 3% as compared to junction transistor inverter at channel length of 30nm. 相似文献
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Time synchronization is critical in distributed environments. A variety of network protocols, middleware and business applications rely on proper time synchronization across the computational infrastructure and depend on the clock accuracy. The Network Time Protocol (NTP) is the current widely accepted standard for synchronizing clocks over the Internet. NTP uses a hierarchical scheme in order to synchronize the clocks in the network. In this paper we present a novel non-hierarchical peer-to-peer approach for time synchronization termed CTP-Classless Time Protocol. This approach exploits convex optimization theory in order to evaluate the impact of each clock offset on the overall objective function. We define the clock offset problem as an optimization problem and derive its optimal solution. Based on the solution we develop a distributed protocol that can be implemented over a communication network, prove its convergence to the optimal clock offsets and show its properties. For compatibility, CTP may use the packet format and number of measurements used by NTP. We also present methodology and numerical results for evaluating and comparing the accuracy of time synchronization schemes. We show that the CTP outperforms hierarchical schemes such as NTP in the sense of clock accuracy with respect to a universal clock. 相似文献
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一种采用干扰抑制技术的Chirp超宽带同步算法 总被引:2,自引:1,他引:1
时间同步是Chirp超宽带通信系统的主要挑战之一。文章通过对直接调制方式下同步误差对系统误码率的影响进行分析,证明随着时间带宽积的增大,对同步算法的精度提出了更高的要求。而常用同步算法对噪声很敏感,文章利用干扰抑制的思想提出了一种新的同步算法。由于利用干扰抑制提高了信噪比,文章算法跟常用算法相比,可以使系统性能有较大提高。 相似文献
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文章把信道分组和PPJET(Preemptive Prioritized Just Enough Time)协议以及光纤延时线三者结合使用,提出了一种新的QoS调度方案D-PPJET(Developed-PPJET)协议.在该协议下,高优先级数据包可以被动态地调度到任何可用的信道上去,而低优先级数据包只能在规定的部分信道上调度,并利用光纤延时线(FDL)缓存机制为未成功调度的突发包提供二次调度的机会,这样高优先级业务包调度成功的机会就大大增加,为高优先级业务提供了保证,同时还使得低优先级突发分组丢失率下降.结果表明它能够大大地改善整个网络突发包的丢失率、信道吞吐量及信道利用率. 相似文献
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Inamori M. Bostamam A.M. Sanada Y. Minami H. 《Wireless Communications, IEEE Transactions on》2009,8(5):2214-2220
A direct conversion architecture reduces the cost and power consumption of a receiver. However, a direct conversion receiver may suffer from direct current (DC) offset, frequency offset, and IQ imbalance. This paper presents an IQ imbalance estimation scheme for orthogonal frequency division multiplexing (OFDM) direct conversion receivers. The proposed IQ imbalance estimation scheme operates in the presence of dynamic DC offset and frequency offset. The proposed scheme calculates IQ imbalance from a simple equation. It employs the knowledge of the preamble symbols of the IEEE 802.11 a/g standards, while it does not require the impulse response of the channel. Numerical results obtained through computer simulation show that the bit error rate (BER) performance for the proposed IQ imbalance estimation scheme has a degradation of about 4dB with a large DC offset, frequency offset, and IQ imbalance. 相似文献