Compact wound-type slot antenna with wide bandwidth

A new type of a slot antenna in which a slot is formed in wound-type around a dielectric substrate is proposed. In comparison with a conventional meander slot antenna, the proposed antenna has a wider bandwidth and smaller size. The proposed antenna has been designed on a gallium arsenide (GaAs) substrate and fabricated by integrated circuit process for the integration of the antenna with active components. The fabricated antenna has dimensions of 6.2 /spl times/4.1 mm/sup 2/ and a 10-dB bandwidth of 300 MHz at 5.8 GHz.     

DQDB networks with and without bandwidth balancing

It is explained why long distributed queue dual bus (DQDB) networks without bandwidth balancing can have fairness problems when several nodes are performing large file transfers. The problems arise because the network control information is subject to propagation delays that are much longer than the transmission time of a data segment. Bandwidth balancing is then presented as a simple solution. By constraining each node to take only a certain fraction of the transmission opportunities offered to it by the basic DQDB protocol, bandwidth balancing gradually achieves a fair allocation of bandwidth among simultaneous file transfers. Two ways to extend this procedure effectively to multipriority traffic are proposed     

Polynomial time optimal algorithms for time slot assignment ofvariable bandwidth systems

Considers the optimal (i.e., minimum length) time slot assignment problem for variable bandwidth switching systems. Existing algorithms for this problem are known to be pseudo-polynomial. The practical question of finding a fast optimal algorithm, as well as the theoretical question of whether the above problem is NP-complete were left open. The authors present a technique to show polynomial time complexity of some time slot assignment algorithms. Such a technique applies to an algorithm proposed by Chalasani and Varma in 1991 (called the CV algorithm), as well as to a network flow based optimal algorithm, proposed in the present paper for the first time. The CV algorithm and the one proposed are slightly different. Thus, the authors give an answer to both the above questions, by establishing that the problem is in P, and by showing effective algorithms for it     

Axial-ratio bandwidth enhancement of asymmetric-CPW-fed circularly-polarised square slot antenna

A novel broadband circularly-polarised (CP) square slot antenna fed by an asymmetric coplanar waveguide (CPW) from a corner of the slot is proposed. A CP bandwidth larger than 10% can be attained simply by using an inverted-L tuning stub protruded from the signal line of the CPW. With an additional pair of grounded strips implanted in the slot, the 3 dB axial-ratio bandwidth and the VSWR ⩽ 2 impedance bandwidth can be greatly raised to be as high as 30 and 35%, respectively.     

A simple scheme for slot reuse without latency for a dual busconfiguration

A simple scheme for slot reuse without latency for the dual bus configuration is studied. The scheme relies on information read in the previous slot and will be referred to as previous slot information (PSI) slot reuse. The scheme requires a minimal addition to the station hardware and its reliability is high. The efficiency of PSI is checked over a wide range of parameters and is found to be almost as good as destination release. The scheme can be implemented with or without the addition of erasure nodes     

Comprehensive bandwidth utilization and polling mechanism for XGPON

For an efficient utilization of the upstream bandwidth in passive optical network, a dynamic bandwidth assignment mechanism is necessary as it helps the service providers in provisioning of bandwidth to users according to the service level agreements. The scheduling mechanism of existing schemes, immediate allocation with colorless grant and efficient bandwidth utilization (EBU), does not assign the surplus bandwidth to a specific traffic class and only divides it equally among the optical network units (ONUs). This results in overreporting of ONU bandwidth demand to the optical line terminal and causes wastage of bandwidth and increase in delays at high traffic loads. Moreover, the EBU also assigns the unused bandwidth of lightly loaded ONU queues to the overloaded queues through an Update operation. This Update operation has a flaw that it borrows the extra bandwidth to a queue in the current service interval, if the queue report is higher than its service level agreement and refunds in next service interval. This borrow‐refund operation causes reduced bandwidth allocation to the lower priority classes and increases their delay and frame loss. This study improves both these weaknesses. The simulation results show that the proposed scheme uses bandwidth efficiently and reduces mean upstream delay of type‐2 (T2) traffic class by 38% and type‐3 (T3) up to 150% compared to immediate allocation with colorless grant at a cost of up to 10% higher delay for T2. However, T4 performance improves by 400% compared to EBU with slight increase in delay for T2 traffic class. Overall, it shows a balanced performance for all the traffic classes and minimizes the bandwidth waste per cycle as well as the frame loss rate.     

A compact wide slot antenna with dual band-notch characteristic for ultra-wideband applications

A new type of ultra-wideband (UWB) antenna with a dual-notched frequency band, compact size of 21?×?28?mm² and a coplanar waveguide (CPW) fed is proposed in this article. Two notched frequency bands are obtained by embedding two U-shaped slots in the radiation patch and a rectangle slot in the ground plane, which can be controlled by adjusting the length of the responding slots. The frequency domain characteristics are investigated and measured. Both the experimental and numerical results show that the proposed antenna has an impedance bandwidth ranging from 3.1?GHz to more than 11.0?GHz in which voltage standing wave ratio is less than 2, expect two notch frequency band, 5–6?GHz (WLAN) and 7.7–8.5?GHz (X-band for satellite communications in China).     

SIW cavity-backed circularly polarized square ring slot antenna with wide axial-ratio bandwidth

In the proposed work, Substrate Integrated Waveguide (SIW) cavity-backed circularly polarized slot antenna for wideband operation is proposed. A square-ring-slot is etched on the top of the SIW cavity, used for radiation To generate the circularly polarized (CP) wave, the slot is placed slightly offset from the centroid of the cavity. By finely optimizing the antenna dimensions, it exhibits a wide axial-ratio (AR) bandwidth of 789 MHz (7.1%) ranging from 10.64 to 11.45 GHz. Moreover, the radiating slot is excited by an SIW based feed by an inductive window, which lead to a wide impedance matching over 1.74 GHz ranging from 9.92 to 11.67 GHz. Due to the SIW cavity-backing structure, the antenna offers unidirectional radiation patterns while maintaining a low-profile and planar compatibility. To validate the proposed design, the antenna is fabricated and experimentally tested in terms of reflection coefficients, AR, gain, and radiation patterns. The simulated and measured results reveal good mutual agreement. Moreover, the proposed antenna is very useful for wideband applications operating in X-band (8–12 GHz)     

基于可延展带宽分配的卫星网络高可用性方案

随着IPTV等网络服务的蓬勃发展,以及地面互联网的接入与融合,针对空间信息网络的资源规划势在必行.同时,为了有效抵抗分布式拒绝服务(DDoS)攻击,可用性设计成为卫星正常运转的重要前提.提出了基于网络带宽资源分配的DDoS攻击防御体系,建立了有效的卫星网络拓扑结构模型,并引入了路由状态数据包的概念,设计了相应的卫星网络路由协议.在此基础上,阐述了具有延展性的网络带宽分配机理及其实现方式.根据安全性分析与实验评估结果,提出方案可在有效防范敌手攻击的同时,保障带宽资源的可延展分配,同时方案具备良好的实现性能.     

一种均衡物理资源和网络带宽的虚拟机部署方法研究

随着互联网的发展,云计算的发展越来越快,云资源管理平台也受到了越来越多的关注。云计算资源管理系统是云计算体系的大脑,具有重要的研究价值。针对目前虚拟机部署未能均衡考虑能耗与网络流量的问题,文章设计了一种结合能耗和网络均衡优化的虚拟机部署算法。该算法采用K-均值聚类,利用改进的皮尔逊相关系数进行相似度计算,最终为虚拟机在所有的候选宿主机中选择合适的宿主机。     

A bandwidth request reiteration mechanism for IEEE 802.16 wireless networks

The IEEE 802.16 is a leading technology for Broadband Wireless Access (BWA), where a Base Station (BS) provides a set of Subscriber Stations (SSs) with first-mile network access. Each SS has multiple connections directed to the BS, which are assigned bandwidth on a demand basis. Specifically, the BS allocates part of the channel as request slots, which are accessed by best-effort connections in a random access manner to transmit bandwidth requests. Although bandwidth requests sent by different SSs may collide the standard does not specify an explicit acknowledgment mechanism. This, and the bandwidth being assigned by the BS to each SS as a whole, may lead to critical inconsistencies between the perception of the SSs’ requirements at the BS and the actual SSs’ requirements, which in turn may entail SS service disruption. While the standard suggests that an SS should regularly update the BS about the backlog of its connections, the algorithm to do so is left unspecified. In this paper we propose a simple, yet effective, mechanism to be employed by the SSs, called Bandwidth Request Reiteration (BR²), which prevents deadlock from occurring. Using detailed packet-level simulation, we compare BR² to an alternative approach based on timeout, and show that BR² achieves better performance, in terms of the average transfer delay, while it does not incur a significant additional overhead, in terms of MAC signaling.     

一种自适应群组交互的网络带宽管理机制

本文在分析现有的基于集中式MCU实现群组交互的基础上，提出了一种能够自适应群组交互规模变化和QoS要求的网络带宽动态管理和分配机制，给出了实现算法，并在实际中得到测试和应用，取得良好的效果。     

Swastika shaped slot embedded two port dual frequency band MIMO antenna for wireless applications

Analog Integrated Circuits and Signal Processing - A compact dual band 2?×?2 multiple-input-multiple-output (MIMO) antenna with dimension...     

A study of slot reuse in dual bus multiple access networks

In dual unidirectional bus networks, packets usually occupy fixed-length slots form the sending station to the end of the network. An erasure node is a specialized station which recognizes packets which have passed their destination stations and releases the slots for subsequent use. The authors derive the optimal locations for erasure nodes and show analytically, for uniform traffic, that only several erasure nodes are needed to achieve throughput close to twice the nominal network bandwidth. The results are tested by simulation of the DQDB (distributed queue dual bus) protocol, which demonstrates a realistic improvement of 40% with only three erasure nodes. Fair access among the stations is improved as well. The authors generalize the analytic results by providing an algorithm for determining the optimal erasure node locations and the throughput improvement, given any arbitrary traffic pattern. The application of this methodology to the related problem of bridged subnetworks is briefly discussed     

一种双扼流槽双极化低旁瓣阵列天线

设计了一种新型低副瓣双极化阵列天线,阵列单元采用角锥喇叭,利用探针分层正交馈电实现双极化辐射,利用双扼流槽解决了宽波束降旁瓣的难题.在阵列馈电设计中,利用空气同轴线网络实现泰勒加权降旁瓣设计,同时,利用反相馈电技术改善了极化隔离度和交叉极化.实测结果表明：在工作频带9.5 GHz±500 MHz,回波损耗小于-10 dB,俯仰面、方位面方向图旁瓣电平小于-16 dB,极化端口隔离度小于-30 dB,交叉极化电平小于-35 dB.     

On the efficiency of slot reuse in the dual bus configuration

Slot reuse is a simple method to improve the efficiency of MACs designed for the slotted, dual bus configuration. The authors propose several schemes for the assignment of throughput to stations in this configuration, taking into account slot reuse and assuming uniform source destination distribution. The criteria for comparison of the schemes are throughput gain, worst averages of message queueing and access delays at stations and the fraction of blocked messages. On the average, it turns out that the scheme in which every station receives the same throughput is very attractive     

A new bandwidth allocation mechanism for next generation wireless cellular networks

In this paper we design and study the performance of a Medium Access Control (MAC) scheme for the multiplexing and the integrated delivery of voice, mobile messaging, IP, gaming and H.264 videoconference traffic over a high-speed cellular TDMA channel with errors and capture. To the best of our knowledge, this is one of the first papers in the literature investigating the integration of actual H.264 video traces and gaming traffic with other types of traffic over wireless networks. Our results show that the proposed scheme achieves high throughput results while preserving the strict Quality of Service (QoS) requirements of each traffic type, and outperforms two efficient schemes previously proposed in the literature.     

Miniaturized wideband dual linearly and circularly polarized printed square slot antenna for multiradio wireless systems

A dual symmetrical coplanar waveguide (CPW)-fed small size wideband printed square slot antenna (SSA) with dual linearly and circularly polarized radiation capability is presented. The antenna is composed using a square slot, two symmetrical orthogonal CPW feed lines connected to horizontal and vertical arm of L-shaped radiator, an embedded parasitic inverted-L strip at the lower left corner of the square ground slot and engraving slots in the ground plane. Circular polarization (CP) is achieved due to two orthogonal CPW feed lines and a common L-shaped radiator. Isolation between ports is improved by engraving slots at the lower left corner of ground plane and embedded parasitic inverted-L strip. The sense of dual-polarization can be changed in pass-band by changing the port excitation. Measured antenna reveals that an 84.4% (4.6 GHz, 3.15–7.75 GHz) −10 dB impedance bandwidth (IBW) and about 33% (2.03 GHz, 5.12–7.15 GHz) 3-dB axial ratio bandwidth (ARBW). Isolation between ports <−16 dB is achieved over usable CP band.     

Power amplifier bandwidth expansion via dual fulfillment of class E conditions

The calculation procedure and experimental investigation of class E power amplifier with broadening of the working frequency bandwidth have been considered. The specified broadening was achieved via double fulfillment of switching conditions at zero voltage (class E conditions) in the working frequency range. The dependence of amplifier characteristics on the parameters of output matching network were also analyzed.