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     

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.     

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     

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.     

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.     

Investigations on heuristic bandwidth request mechanism with signaling analysis for BWA networks

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.     

Performance characteristics of the dual exponentially tapered slot antenna (DETSA) for wireless communications applications

The dual exponentially tapered slot antenna (DETSA) is a low-profile slot line radiator that is a modified form of a Vivaldi radiator. The DETSA is created by taking a Vivaldi radiator and tapering the outside edge of the slot line conductors. The shape of the outside edge of the slot line conductors adds additional antenna design degrees of freedom. This paper describes how the different shape parameters of the DETSA impact antenna performance.     

A technique for bandwidth extension and noise optimization of wideband low-noise amplifier with dual feedback loops

A technique for bandwidth extension and noise optimization of wideband low-noise amplifier with dual feedback loops is presented. A LC-ladder matching network has been added in front of conventional amplifier with dual feedback loops. Detailed circuit analysis and general design procedures for the modified amplifier have been provided. The technique is applied to an amplifier covering the frequency range from DC to 6 GHz in a 0.5 μm InGaAs E-mode pHEMT process. Post-layout simulation shows S ₁₁ below ?10 dB, S ₂₂ below ?10 dB, flat S ₂₁ of 16 ± 0.2 dB, and flat NF of 1.85 ± 0.35 dB across the entire band, which confirms the improvement in bandwidth and noise performance.     

A dual polarized aperture coupled circular patch antenna using a C-shaped coupling slot

The design and development of a dual linearly polarized aperture coupled circular microstrip patch antenna at C-band are presented. The antenna uses a novel configuration of symmetric and asymmetric coupling slots. Variations in isolation between orthogonal feedlines and antenna axial ratio with the position of coupling slots are studied and broadband isolation and axial ratio are achieved. The prototype antenna yields 7.6 dBi peak gain, 70/spl deg/ 3-dB beam width, 25 dB cross-polarization levels and an isolation better than 28 dB between the two ports. With an external quadrature hybrid coupler connected to the two orthogonal feedlines, the antenna yields 3-dB axial ratio bandwidth of more than 30% at 5.8 GHz.     

嵌入式Qt中信号与槽机制的研究

Qt是一个跨平台的C＋＋GUI应用构架,它提供了丰富的窗口部件集,具有面向对象、易于扩展、真正的组件编程等特点。目前Linux上最为流行的KDE桌面环境就是建立在Qt库的基础之上。伴随着KDE的快速发展和普及,Qt逐渐成为Linux窗口平台上进行软件开发时的GUI首选,而信号与槽作为Qt的核心机制在Qt编程中有着广泛的应用,本文研究了信号与槽的通信机制、元对象工具以及在实际使用过程中应注意的一些问题。     

Below-resonant-length slot radiators for traveling-wave-arrayantennas

For a frequency-scanning-radar project, a traveling-wave-array antenna was designed. It employs radiating slots in the narrow wall of a meander-rectangular waveguide, which is milled in a flat metal block. Due to the restriction of the waveguide width, the maximum slot length that could be implemented is less than a half wavelength, i.e., below the resonant length. Although such slots are commonly deemed useless, it is shown that traveling-wave-array antennas can be designed successfully. This paper describes the design and results of low-sidelobe arrays, starting from the measurement of basic slot characteristics in an array simulator. The realization of a prescribed amplitude distribution, by tapering the slot length, is shown. The creation of phase errors, due to the reactive nature of the slots, and the associated pattern-degradation effects, are discussed in detail     

A framework for bandwidth management in ATM networks-aggregateequivalent bandwidth estimation approach

A unified framework for traffic control and bandwidth management in ATM networks is proposed. It bridges algorithms for real-time and data services. The central concept of this framework is adaptive connection admission. It employs an estimation of the aggregate equivalent bandwidth required by connections carried in each output port of the ATM switches. The estimation process takes into account both the traffic source declarations and the connection superposition process measurements in the switch output ports. This is done in an optimization framework based on a linear Kalman filter. To provide a required quality of service guarantee, bandwidth is reserved for possible estimation error. The algorithm is robust and copes very well with unpredicted changes in source parameters, thereby resulting in high bandwidth utilization while providing the required quality of service. The proposed approach can also take into account the influence of the source policing mechanism. The tradeoff between strict and relaxed source policing is discussed