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41.
Queue Analysis and Multiplexing of Heavy-tailed Traffic in Wireless Packet Data Networks 总被引:1,自引:0,他引:1
Recent research based on traffic measurements shows that Internet traffic flows have a fractal nature (i.e., self-similarity
property), which causes an underestimation of network engineering parameters when using the conventional Poisson model. Preliminary
field measurements demonstrate that packet data traffic in wireless communications also exhibits self-similarity. In this
paper, we investigate the queuing behavior of self-similar traffic flows for data applications in a packet-switching single-server
wireless network. The traffic is generated by an on–off source with heavy-tailed on periods and exponentially distributed
off periods. We extend previous analysis of a relation among the asymptotic distribution of loss probability, traffic specifications,
and transmission rate for a wireline system to a wireless system, taking into account wireless propagation channel characteristics.
We also investigate the multiplexing of heavy-tailed traffic flows with a finite buffer for the downlink transmission of a
wireless network. Computer simulation results demonstrate that assumptions made in the theoretical analysis are reasonable
and the derived relationships are accurate. 相似文献
42.
Research in multi-robot pursuit-evasion demonstrates that three pursuers are sufficient to capture an intruder in a polygonal environment. However, this result requires the confined of the initial location of the intruder within the convex hull of the locations of the pursuers. In this study, we extend this result to alleviate this convexity through the application of a set of virtual goals that are independent of the locations of the pursuers. These virtual goals are solely calculated using the location information of the intruder such that whose locations confine the intruder within their convex hull at every execution cycle. We propose two strategies to coordinate the pursuers. They are the agents votes maximization and the profile matrix permutations strategies. We consider the time, the energy expended, and the distance traveled by the pursuers as metrics to analyze the performance of these strategies in contrast to three different allocation strategies. They are the probabilistic, the leader-follower, and the prioritization coordination strategies. 相似文献
43.
AbstractFault localization is an important part in communication networks. Faults are unwanted and unavoidable in communication systems, and hence, their quick detection and localization is essential for sustaining the health of the network. This paper proposes an end-to-end approach that uses passive measurements for fault localization in communication networks. We formulate the fault localisation issue as an optimisation problem and then employ the genetic algorithm technique to solve it. Extensive simulation results show that although our algorithm needs to test only a small set of network components to localise all faults, it can infer the faulty nodes in at least 97% of cases. This simulation shows that the proposed algorithm, called genetic algorithm-based fault localisation is superior to the other approaches to localise all faults in a network. 相似文献
44.
This paper describes a methodology for measuring rheological flow properties in-line, in real-time, based on simultaneous measurements of velocity profiles using an ultrasound velocity profiling (UVP) technique with pressure difference (PD) technology. The methodology allows measurements that are rapid, non-destructive and non-invasive and has several advantages over methods presented previously. The set-up used here allows direct access to demodulated echo amplitude data, thus providing an option to switch between time domain algorithms and algorithms based on FFT for estimating velocities, depending on the signal-to-noise ratio (SNR) and time resolution required. Software based on the MATLAB® graphical user interface (GUI) has been developed and provides a powerful and rapid tool for visualizing and processing the data acquired, giving rheological information in real-time and in excellent agreement with conventional methods. This paper further focuses on crucial aspects of the methodology: implementation of low-pass filter and singular value decomposition (SVD) methods, non-invasive measurements and determination of the wall positions using channel correlation and methods based on SVD. Measurements of sound velocity and attenuation of ultrasound in-line were introduced to increase measurement accuracy and provide an interesting approach to determine particle concentration in-line. The UVP-PD methodology presented may serve as an in-line tool for non-invasive, real-time monitoring and process control. 相似文献
45.
In this study, we present a new topology for realizing a grounded inductor employing only a single current conveyor, called a negative‐type modified inverting second‐generation current conveyor (MICCII‐), and a minimum number of passive components, two resistors, and one capacitor. The non‐ideality effects of the MICCII‐on a simulated inductor are investigated. To demonstrate the performance of the presented inductance simulator, we use it to construct a third order Butterworth high‐pass filter and a parallel resonant circuit. Simulation results are given to confirm the theoretical analysis. 相似文献
46.
Removal of hydrogen sulfide from methane using commercial polyphenylene oxide and Cardo-type polyimide hollow fiber membranes 总被引:1,自引:0,他引:1
Mahdi Pourafshari Chenar Houman Savoji Mohammad Soltanieh Takeshi Matsuura Shahram Tabe 《Korean Journal of Chemical Engineering》2011,28(3):902-913
The performance of commercially available poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) and Cardotype polyimide (PI) hollow
fiber membranes was investigated in removing hydrogen sulfide from methane in a series of bench-scale experiments. It was
observed that in the concentration range of hydrogen sulfide in methane from 101 to 401 ppm, the methane permeability decreased
in the presence of hydrogen sulfide for Cardo-type polyimide hollow fiber membranes, whereas the PPO membrane performance
was not affected. The separation coefficients of hydrogen sulfide/methane were 6 and 4 for PI and PPO membranes, respectively.
Effects of temperature on the performance of PI and PPO membranes were investigated. It was observed that the permeabilities
of both components of the mixture increased by increasing temperature, whereas the selectivities remained constant. 相似文献
47.
48.
Shahram Esmaeilsabzali Nancy A. Day Joanne M. Atlee Jianwei Niu 《Requirements Engineering》2010,15(2):235-265
With the popularity of model-driven methodologies and the abundance of modelling languages, a major question for a requirements engineer is: which language is suitable for modelling a system under study? We address this question from a semantic point-of-view for big-step modelling languages (BSMLs). BSMLs are a class of popular behavioural modelling languages in which a model can respond to an input by executing multiple transitions, possibly concurrently. We deconstruct the operational semantics of a large class of BSMLs into eight high-level, mostly orthogonal semantic aspects and their common semantic options. We analyse the characteristics of each semantic option. We use feature diagrams to present the design space of BSML semantics that arises from our deconstruction, as well as to taxonomize the syntactic features of BSMLs that exhibit semantic variations. We enumerate the dependencies between syntactic and semantic features. We also discuss the effects of certain combinations of semantic options when used together in a BSML semantics. Our goal is to empower a requirements engineer to compare and choose an appropriate BSML from the plethora of existing BSMLs, or to articulate the semantic features of a new desired BSML when such a BSML does not exist. 相似文献
49.
In this paper, a novel design for realizing a voltage-mode (VM) all-pass filter utilizing two differential voltage current conveyors (DVCCs) is proposed. Also, the suggested filter uses a canonical number of passive elements (one grounded capacitor and one resistor) without requiring any element matching condition. The proposed filter has high input and low output impedances, which make it suitable for cascading. The effects of the nonidealities of the DVCCs on the proposed design are investigated. As an application, a quadrature oscillator is designed using the proposed VM all-pass filter and an integrator. The proposed filter and oscillator circuits are simulated using the SPICE simulation program to confirm the theory. 相似文献
50.
Over 100 fatigue tests were conducted on high strength welded steel (HSLA-80) cruciforms of different thickness. Tests were conducted under both constant and random amplitude axial loads to characterize thickness effects on fatigue strength. Specimens were similar in size, except for the thickness which was varied between four nominal values. Examination of both experimental and analytical results (obtained using linear cumulative damage and Rayleigh approximation) indicates thicker specimens exhibit lower fatigue lives under both constant and random amplitude loadings. These results, when compared with the commonly used ‘fourth root rule' thickness correction formula, indicate the latter to be generally conservative, particularly at low stress levels. 相似文献