无线网络MAC协议中RTS/CTS机制的研究

从无线信道利用率的角度对无线局域网络的RTS/CTS机制进行性能仿真研究,发现数据包负荷较大时,机制对网络性能有正面影响,数据包负荷较小时;机制对网络性能有负面影响.在评判RTS/CTS机制在无线网络接入协议中的影响作用时,应将能量有效性作为系统主要性能指标.此外,还要考虑网络多跳的结构对机制的限制作用,从跨层优化的角度分析无线信道接入机制.     

平行板波导CTS 天线的设计与分析

采用传输线理论的方法分析设计了平行板波导CTS 天线。建立平行板波导天线的等效电路模型,利用传输线方 程计算天线上的电压分布、电流分布以及辐射阻抗,进而分析远场的辐射特性。最后用Ansoft HFSS 软件仿真验证了该 方法的正确性。     

Design and experimental realization of a robust decentralized PI controller for a coupled tank system

This paper presents design and realization of a robust decentralized PI controller for regulating the level of a coupled tank system. The proposed controller is designed based on a predefined reference transfer function model in which we adopt a frequency matching of actual and reference models. Realization of control algorithms for a multivariable system is often complicated owing to uncertainties in the process dynamics. In this paper, initially a frequency response fitting model reduction technique is adopted to obtain a First Order Plus Dead Time (FOPDT) model of each higher order decoupled subsystem. Further, using the obtained reduced order model, the proposed robust decentralized PI controller is designed. The stability and performance of the proposed controller are verified by considering multiplicative input and output uncertainties. The performance of the proposed robust decentralized controller has been compared with that of a decentralized PI controller. To validate the performance of the proposed control approach, real-time experimentation is pursed on a Feedback Instrument manufactured coupled tank system.     

The mixed-mode fracture behavior of epoxy by the compact tension shear test

In this study, pure mode I, pure mode II and mixed mode fracture behavior of an epoxy were investigated. Specifically, the mixed mode values of fracture toughness and critical strain energy release rate (CSERR) were measured. Specimens were subjected to mixed mode loading using compact tension shear (CTS) test. Some experimental modifications were found to be necessary to eliminate rotation and ensure crack propagation at the notch when testing epoxy specimens at high mode II loading. A failure criterion for the mixed mode loading of polymer is developed and its predictions are compared with the experimental results. The crack propagation direction in epoxy was investigated in this research as well. A detailed study of failure mechanisms on the fracture surface was performed. The results indicate that the increase in the value of toughness can be directly related to the fracture morphology.     

多时钟源分割方法在时钟树综合中的应用

本文以sha256算法模块的数字后端物理设计为例,提出了将多时钟源分割技术应用在传统时钟树综合中的方法。应用该方法后,利用有效时钟偏移,仅通过少量时钟缓冲器的插入就解决了该模块设计中的建立时间违例问题,大大降低了后续时序收敛工作的复杂度,将时序修复耗时缩短为采用传统方法的20%。     

基于Jaguar CTS的企业多层分布式应用架构

文章建立在Jaguar CTS的基础之上,详细研究了一种全新的企业多层分布式应用架构,首先对Jaguar CTS实际应用中的主要优势、以及使用特性进行了简要分析。进而提出了在Jaguar CTS支持下,整个企业多层分布式应用架构的作业流程,对于信息服务需求庞大、数据处理复杂的电力企业而言,此种分布式应用架构有着良好的发展潜力,值得进一步关注与应用。     

IEEE802.11g协议中一些问题的分析与研究

本文简要介绍了IEEE80 2 .11协议族标准的发展过程 ,重点分析了IEEE80 2 .11g协议标准。对IEEE80 2 .11g协议中可能出现的一些问题进行分析和研究 ,并针对这些问题给出了相应的解决方法     

Analytical modeling of MAC protocol in ad hoc networks

In ad hoc networks, CSMA/CA is a widely used MAC layer protocol. There has been considerable work on the performance evaluation of this protocol. But most work is confined to saturation performance of single‐hop ad hoc networks. In this paper, we employ a linear feedback model to evaluate the performance for CSMA/CA according to the Poisson distributed traffic in both single‐hop and multi‐hop ad hoc networks. To the best of our knowledge, this is the first attempt to analytically evaluate the performance for CSMA/CA protocol under a general assumption about the traffic. This paper also gives analytical results, showing the impact of RTS/CTS. Although RTS/CTS do add the overhead to the system, they become essential when either the hidden terminal problem is dominant, or the traffic is heavy, or the packet length is very large. This paper also shows that the performance degrades dramatically in multi‐hop ad hoc networks when the number of competing nodes increases, which implies that the scalability is still a major problem in ad hoc networks. To validate our analytical results, we have done extensive simulations, and it is observed that the simulation results match the analytical results very well. Copyright © 2006 John Wiley & Sons, Ltd.     

T-GCTS磁选机在密地选矿厂的工业试验

攀钢密地选矿厂为了提高粗选作业的选别指标和单机处理量,应用T-GCTS1230型中磁场磁选机与生产中使用的CTS1030型磁选机进行了对比工业试验,结果表明：在给矿品位相近的情况下,试验系列比生产系列粗精矿品位提高1.11个百分点、粗选尾矿品位降低0.54百分点、粗选作业回收率提高0.92个百分点,单机处理量可满足130 t/h的要求。根据试验结果,T-GCTS1230型中磁场磁选机已经在密地选矿厂16个系列全面推广,据估算,其经济效益为1 077万元/a。     

A refined MAC protocol with multipacket reception for wireless networks

Medium access control (MAC) protocols making use of multipacket reception (MPR) capability achieve better throughput than conventional MAC protocols. When a wireless network operates with MPR capable nodes and non‐MPR nodes, the MAC protocols must not only utilise the MPR capability to maximise throughput, but must also enable the co‐existence with these two types of nodes. We propose a new MPR MAC protocol to achieve the co‐existence requirement by adopting a request‐to‐send (RTS)/clear‐to‐send (CTS) mechanism in IEEE 802.11 MAC standards. This MPR MAC protocol also improves throughput by allowing additional data transmissions to use the MPR capability fully. We analyse the system throughput of the co‐existence of different link characteristics of nodes, and optimise its throughput by adjusting contention window sizes with respect to certain throughput requirements of the nodes. Copyright © 2010 John Wiley & Sons, Ltd.