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1.
We present the dispersive characteristics of an electronically tunable optical filter, with application toward delaying high speed digital and analog signals. Square waves can be dynamically delayed and reshaped through a change in injection current to the filter. Since the filter is of an all-pass nature, its usable bandwidth is limited primarily by the phase response (dispersion). We show that for 2-GHz square waves, dispersion is not a limiting factor and the filter can be operated over the full range of delays. At 5 GHz, the pulses can still be delayed, however the range of operation is dispersion limited. Additionally, at 5 GHz this dispersion can be harnessed for pulse reshaping applications. The filter is studied both experimentally and theoretically, demonstrating good agreement. 相似文献
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《AEUE-International Journal of Electronics and Communications》2014,68(6):504-514
Best effort services in next generation broadband wireless access (BWA) networks would be more interactive and bandwidth demanding. This attracted a substantial amount of researches to focus on contention bandwidth request mechanisms for best effort services. The contention resolution with code division multiple access (CDMA) based mobile assisted truncated binary exponential backoff (C-MAB) suffers low contention efficiency and high access delay due to the nature of accessing mechanism in worldwide interoperability for microwave access (WiMAX) network that confines the mobile station in estimating the optimum contention window. Further, these performances decrease when transmission failure is modeled with unavailability of bandwidth, collision due to contention, transmission code failure, and channel error. To improve the performances, in this paper, we suggest a contention resolution with CDMA based base station assisted backoff (C-BAB) for orthogonal frequency division multiple access (OFDMA) based WiMAX networks. With C-BAB, the base station computes an optimum contention window by accounting average contention window and probability of failure. With a 2.69% additional overhead at the BS, the proposed C-BAB shows a 32.82% increase in contention efficiency and 24.21% decrease in access delay (25% error rate, q = 0.60 and ranging slot = 64) compared to C-MAB. 相似文献
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Xiaohui Li Junfeng Wang Li Han Yingjie Zhou Sunyoung Han 《Wireless Communications and Mobile Computing》2016,16(17):3056-3069
As the exponential growth of the Internet, there is an increasing need to provide different types of services for numerous applications. Among these services, low‐priority data transfer across wide area network has attracted much attention and has been used in a number of applications, such as data backup and system updating. Although the design of low‐priority data transfer has been investigated adequately in low speed networks at transport layer, it becomes more challenging for the design of low‐priority data transfer with the adaptation to high bandwidth delay product networks than the previous ones. This paper proposes an adaptive low‐priority protocol to achieve high utilization and fair sharing of links in high bandwidth delay product networks, which is implemented at transport layer with an end‐to‐end approach. The designed protocol implements an adaptive congestion control mechanism to adjust the congestion window size by appropriate amount of spare bandwidth. The improved congestion mechanism is intent to make as much use of the available bandwidth without disturbing the regular transfer as possible. Experiments demonstrate that the adaptive low‐priority protocol achieve efficient and fair bandwidth utilization, and remain non‐intrusive to high priority traffic. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Rajesh Anbazhagan Nakkeeran Rangaswamy 《AEUE-International Journal of Electronics and Communications》2013,67(1):40-44
In this letter, we suggest contention resolution with exponential increase and exponential decrease (EIED) backoff for bandwidth request in worldwide interoperability for microwave access (WiMAX) networks. In EIED, setting of backoff factor to overcome collision due to contention is very challenging and hence we suggest a method to compute backoff factor with average contention window. Further, to reduce access delay, we estimate the response time based on probability of failure and average contention window. Simulations validate the proposed EIED backoff in terms of contention efficiency, capacity and access delay. The contention efficiency and capacity is improved by 47.50% (for q value of 0.25) and 28.57% (for 25 numbers of transmission opportunity), respectively, when bandwidth request is made with the proposed EIED backoff mechanism. 相似文献
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Jianhua He Zuoyin Tang Hsiao-Hwa Chen 《Communications Letters, IEEE》2008,12(4):283-285
IEEE 802.16 standard specifies two contention based bandwidth request schemes working with OFDM physical layer specification in point-to-multipoint (PMP) architecture, the mandatory one used in region-full and the optional one used in region-focused. This letter presents a unified analytical model to study the bandwidth efficiency and channel access delay performance of the two schemes. The impacts of access parameters, available bandwidth and subchannelization have been taken into account. The model is validated by simulations. The mandatory scheme is observed to perform closely to the optional one when subchannelization is active for both schemes. 相似文献
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《Lightwave Technology, Journal of》2006,24(6):2276-2286
In this paper, a novel method to expand the compensation bandwidth of a tunable dispersion compensator (TDC) based on ring resonators utilizing a negative group-delay peak is presented. The operation conditions of the ring resonator, where the negative group-delay peak appeared, are theoretically analyzed and then experimentally verified. The ratio of the usable bandwidth to the channel spacing (25 GHz) was increased from 75% to 86%, employing the proposed scheme of the expansion method. The improved dispersion-compensation characteristic was confirmed in a 10-Gb/s experiment. 相似文献
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We consider the problem of allocating bandwidth fairly to each node in a shared, unidirectional bus network. We focus on the pi persistent protocol, since these are open loop policies designed to operate well in high speed networks, which have a very large bandwidth-delay product and feedback in the upstream direction is not available in a timely manner. First, we introduce an improvement to the basic pi persistent protocol, in which we replace random coin tosses with a deterministic counting algorithm, and thereby reduce the delays for all nodes for any given choice of {pi}. We then describe an exact method for calculating average packet delays and queue lengths in both the pi persistent and our new deterministic n out of m protocols, based on the regenerative approach of Georgiades et al. (1987). These delay results, together with simulation measurements, show that both of these protocols still waste some bandwidth. After presenting a lower bounding argument to show that some wasted bandwidth is inevitable in all such distributed access control schemes, assuming a passive bus without feedback in the upstream direction, we show that changing the bus to unidirectional point-to-point links between (very simple) active interfaces at each node allows us to construct distributed access schemes that require no upstream feedback and are both work conserving and fair. To illustrate how this can be done, we introduce the pi preemptive protocol, in which each node randomly inserts its own packets into the traffic arriving from upstream. We derive a simple and effective heuristic for calculating the preemption probability for each node, and use simulation to show how well it equalizes the delays at each node 相似文献
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为了降低光突发交换网络中突发包的丢失率、减小网络延时、提高网络信道的利用率,采用了一种新型考虑优先级的基于冗余合并的突发包冲突解决机制。算法增加了回退信道作为保护信道,根据业务的优先级对冲突的突发包进行分段,使无法顺利传送的突发包碎片进入到回退信道;同时,考虑到网络中存在着很多短小而难以利用的信道资源,算法将回退信道里的突发包碎片进行多次克隆,多个克隆碎片和由上游节点到来的突发包合并成粒度可变的虚拟突发包发送,克隆碎片的优先级定义为最低,以保证不抢占正常突发包的信道资源。结果表明,相比以往的冲突解决算法,此算法具有较低的丢包率、相对小的延时率和优越的信道利用率。 相似文献
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《Digital Communications & Networks》2016,2(1):15-23
One of the important aspects of seamless communication for ubiquitous computing is the dynamic selection of the best access network for a multimodal device in a heterogeneous wireless environment. In this paper, we consider available bandwidth as a dynamic parameter to select the network in heterogeneous environments. A bootstrap approximation based technique is firstly utilized to estimate the available bandwidth and compare it with hidden Markov model based estimation to check its accuracy. It is then used for the selection of the best suitable network in the heterogeneous environment consisting of 2G and 3G standards based wireless networks. The proposed algorithm is implemented in temporal and spatial domains to check its robustness. The numerical results show that the proposed algorithm gives improved performance in terms of estimation error (less than 15%), overhead (varies from 0.45% to 72.91%) and reliability (approx. 99%)as compared to the existing algorithm. 相似文献
11.
In future BISDN networks, significant burdens will be placed on the processing elements in the network since call routing and admission policies will be more computationally intensive than those in present day networks. Thus, the bottleneck in future networks is likely to shift from the communication links to the processing elements. The delays at these elements are influenced by their processing capacity and factors such as; routing algorithms, propagation delays, admission control functions, and network topology. The goal of this paper is to characterize the behavior of these factors on the call setup time and accepted call throughput. This behavior is examined for three sequential routing schemes and two flooding routing schemes under various network parameters and different forms of admission control. The results of our study indicate that processing capacity and the admission control function can affect the call setup time and accepted call throughput significantly while propagation delay does not affect these performance measures significantly 相似文献
12.
OBS网络中基于优先级的先分割后缓存冲突解决方法 总被引:2,自引:2,他引:2
为了有效地降低突发包的丢失率和保证OBS网络中不同优先级业务的服务质量,提出了一种基于优先级的先分割后缓存冲突解决方法。该方法通过在多波长信道系统的输出数据信道上设置光纤延迟线组来缓存被分割的冲突突发包。当冲突发生时,首先基于突发包的优先级和处理完毕时间进行"竞争突发包头部分割或者原突发包尾部分割"处理;无冲突部分进行交换或者直接在事先预留的输出数据信道上处理,冲突部分的分割突发包进行光缓存。仿真结果表明,多波长信道系统中,高优先级突发包的丢失率低于低优先级突发包的丢失率。同时该方法在一定程度上可以有效地减少端到端的传输时延和整个网络的丢包率,从而提高整个OBS网络的性能。 相似文献
13.
The utilisation of a CSMA/CD LAN as an inter-radio-port transmission medium and an autonomous macroscopic diversity, based on bus contention selective control, are proposed for a local area radio network. The diversity selection performance was analysed, and it is shown that satisfactory performance was obtained with the proposed scheme 相似文献
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LIN Qun ZHAO Yong-li CAO Xu-ping YU Xiao-song TANG Ting-ting ZHANG Jie 《中国邮电高校学报(英文版)》2012,19(6):105-112
The granularity of the flexible bandwidth optical network is the spectral slots,which is much smaller than that of the wavelength switch optical network.For the dynamic clients’ connections setup and tear down processes,it will give rise to fragmentation of spectral resources.It is the decline in the probability of finding sufficient contiguous spectrum for new connections that result in the fragmentation of spectral resource.To be more specific,these spectra may be unavailable and waste.In this case,the severe waste of the spectrum will lead to low efficiency in spectral utilization and will not adapt to large capacity requirements of transmission in the future.Because path computation element(PCE) framework has the characteristics of the central disposal and deployment of the spectrum resource,we construct the spectral resource allocation scenario based on PCE framework in the flexible bandwidth optical network to use spectrum resource effectively.Based on the principle of the generation of the fragmentation,we put forward a spectrum resource defragmentation algorithm to consolidate the available spectrum for clients’ connections.The simulation results indicate that this algorithm is able to reduce fragmentation of network,improve the continuity of spectral resource,reduce the blocking rate of services in the network and improve the spectral efficiency significantly. 相似文献
17.
为了促使无线网络中的"自私"节点参与合作,提出了谈判解协作带宽分配(CBA)策略,解决了节点间采用交换带宽资源协作传输,彼此以多大带宽中继对方数据的问题.首先,将两个节点的协作带宽分配问题建模为合作博弈中的谈判过程;之后,采用拉格朗日乘数法得到两个用户的纳什谈判解(NBS)协作带宽分配;其次,提出了一种新的Kalai-Smorodinsky谈判解(KSBS)协作带宽分配策略;最后,对两种谈判解协作带宽分配策略的公平性进行了研究.仿真表明,KSBS协作带宽分配策略和NBS协作带宽分配策略对提升用户效用的作用基本相同,但KSBS策略比NBS策略更为公平. 相似文献
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A fundamental issue in optical burst switching (OBS) networks is to solve the burst contention for the core node. In this
paper, a novel priority-based contention solution strategy for OBS networks is proposed. When the contention occurs, the burst
priority is considered firstly, and then the burst segmentation method is used for the low priority bursts in this strategy.
Ensuring the integrity of high priority bursts, part of the segmented bursts can be transmitted to the destination node via
combining wavelength conversion and optical buffer method. Simulation results show that the proposed scheme not only ensures
the integrity of high priority bursts, but also reduces the packet loss rate of the low priority bursts maximally, so that
it can support good quality of service (QoS) for the network. 相似文献