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Coupled applications on distributed resources  [PDF]
P. V. Coveney,G. De Fabritiis,M. J. Harvey,S. M. Pickles,A. R. Porter
Physics , 2006, DOI: 10.1016/j.cpc.2006.05.008
Abstract: Coupled models are set to become increasingly important in all aspects of science and engineering as tools with which to study complex systems in an integrated manner. Such coupled, hybrid simulations typically communicate data between the component models of which they are comprised relatively infrequently, and so a Grid is expected to present an ideal architecture on which to run them. In the present paper, we describe a simple, flexible and extensible architecture for a two-component hybrid molecular-continuum coupled model (hybrid MD). We discuss its deployment on distributed resources and the extensions to the RealityGrid computational-steering system to handle coupled models.
Escape of resources in distributed clustering processes  [PDF]
J. van den Berg,M. R. Hilário,Alexander E. Holroyd
Mathematics , 2010,
Abstract: In a distributed clustering algorithm introduced by Coffman, Courtois, Gilbert and Piret \cite{coffman91}, each vertex of $\mathbb{Z}^d$ receives an initial amount of a resource, and, at each iteration, transfers all of its resource to the neighboring vertex which currently holds the maximum amount of resource. In \cite{hlrnss} it was shown that, if the distribution of the initial quantities of resource is invariant under lattice translations, then the flow of resource at each vertex eventually stops almost surely, thus solving a problem posed in \cite{berg91}. In this article we prove the existence of translation-invariant initial distributions for which resources nevertheless escape to infinity, in the sense that the the final amount of resource at a given vertex is strictly smaller in expectation than the initial amount. This answers a question posed in \cite{hlrnss}.
Probabilistic Modeling of IEEE 802.11 Distributed Coordination Functions  [PDF]
Rui Fang,Zequn Huang,Louis F. Rossi,Chien-Chung Shen
Computer Science , 2014,
Abstract: We introduce and analyze a new Markov model of the IEEE 802.11 Distributed Coordination Function (DCF) for wireless networks. The new model is derived from a detailed DCF description where transition probabilities are determined by precise estimates of collision probabilities based on network topology and node states. For steady state calculations, we approximate joint probabilities from marginal probabilities using product approximations. To assess the quality of the model, we compare detailed equilibrium node states with results from realistic simulations of wireless networks. We find very close correspondence between the model and the simulations in a variety of representative network topologies.
IEEE 802.11 Distributed Coordination Function:Enhancement and Analysis
IEEE 802.11 Distributed Coordination Function: Enhancement and Analysis

WU HaiTao LIN Yu CHENG ShiDuan PENG Yong and LONG KePing National Key Lab of Switching Technology,Telecommunication Networks Beijing University of Posts,Telecommunications,Beijing,PR China,

计算机科学技术学报 , 2003,
Abstract: IEEE 802.11 Medium Access Control (MAC) is proposed to support asynchronous and time bounded delivery of radio packets. Distributed Coordination Function (DCF), which uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) and binary slotted exponential backoff, is the basis of the 802.11 MAC. This paper proposes a throughput enhancement for DCF by adjusting the Contention Window (CW) setting scheme. Moreover, an analytical model based on Markov chain is introduced to compute the enhanced throughput. The accuracy of the model and the enhancement of the proposed scheme are verified by elaborate simulations.
Adaptive Distributed Inter Frame Space for IEEE 802.11 MAC Protocol  [PDF]
Ja’afer AL-Saraireh, Saleh Saraireh, Mohammad Saraireh, Mohammed Bani Younis
Communications and Network (CN) , 2014, DOI: 10.4236/cn.2014.63018

In this research, an Adaptive Distributed Inter Frame Space (ADIFS) has been proposed for IEEE 802.11 Medium Access Control (MAC) protocol. The aim of this approach is to improve Quality of Services (QoS) for IEEE 802.11 MAC protocol in single-hop wireless network. The proposed approach is based on traffic type, Collision Rate (CR), Collision Rate Variation (CRV) and Packet Loss Rate. These parameters are used to adjust the DIFS at runtime. The adjusted DIFS is employed to enhance service differentiation at the MAC layer in single-hop wireless networks. The proposed approach contributes to the enhancement of the average QoS for high priority traffic by 32.9% and 33.4% for the 5 and 10 connections, respectively. While the average QoS for the low priority traffic is improved by 14.3% and 18.2% for the 5 and 10 connections, respectively. The results indicate that, the proposed approach contributes in the enhancement of the QoS in wireless network.

An Improved Analytical Model for IEEE 802.11 Distributed Coordination Function under Finite Load  [PDF]
Rama Krishna CHALLA, Saswat CHAKRABARTI, Debasish DATTA
Int'l J. of Communications, Network and System Sciences (IJCNS) , 2009, DOI: 10.4236/ijcns.2009.23026
Abstract: In this paper, an improved analytical model for IEEE 802.11 distributed coordination function (DCF) under finite load is proposed by closely following the specifications given in IEEE 802.11 standard. The model is investigated in terms of channel throughput under perfect and slow Rayleigh fading channels. It is shown that the proposed model gives better insight into the operation of DCF.
Coordinated Collaboration between Heterogeneous Distributed Energy Resources  [PDF]
Shahin Abdollahy,Olga Lavrova,Andrea Mammoli
Journal of Solar Energy , 2014, DOI: 10.1155/2014/135106
Abstract: A power distribution feeder, where a heterogeneous set of distributed energy resources is deployed, is examined by simulation. The energy resources include PV, battery storage, natural gas GenSet, fuel cells, and active thermal storage for commercial buildings. The resource scenario considered is one that may exist in a not too distant future. Two cases of interaction between different resources are examined. One interaction involves a GenSet used to partially offset the duty cycle of a smoothing battery connected to a large PV system. The other example involves the coordination of twenty thermal storage devices, each associated with a commercial building. Storage devices are intended to provide maximum benefit to the building, but it is shown that this can have a deleterious effect on the overall system, unless the action of the individual storage devices is coordinated. A network based approach is also introduced to calculate some type of effectiveness metric to all available resources which take part in coordinated operation. The main finding is that it is possible to achieve synergy between DERs on a system; however this required a unified strategy to coordinate the action of all devices in a decentralized way. 1. Introduction As the electric utility industry enters an increasingly competitive environment, utilities must concern themselves with the market value of the services they provide and the cost of providing those services. At the same time utilities are still burdened with the obligation to serve their customers with adequate reliability. Utilities must undertake new investments in demand-side resources to meet this obligation [1]. Distributed energy resources (DERs) have demonstrated potential advantages to address the challenges utilities are facing. Photovoltaic generation (PV), fuel cell (FC), battery energy storage (BES), natural gas powered GenSet (NGPG), wind turbine, thermal storage (TS), and micro-CHP (combined heat and power) are exemplary DERs technologies successfully deployed at power distribution level. On the other hand, in light of increased needs for both energy efficiency and high reliability the microgrids are gaining increasing interest. A microgrid is a collection of DERs that from the viewpoint of the utility is controllable, acts as a single load, and is able to function in both grid-tied and islanded modes [2]. Recent trends in small-scale distributed generation particularly drastic price reductions of PV and small wind turbines will soon result in high penetration levels of variable generation, some of which are not
Improved Stability Design of Interconnected Distributed Generation Resources  [PDF]
Mahmood Saadeh,Roy McCann
Computer Science , 2013,
Abstract: This work provides a design method for achieving a specified level of stability for inverter-based interconnected distributed generation. The stability of parallel connected distributed energy resources determined from a linearized state-space model of the inverter dynamics that includes the admittance matrix of the interconnecting distribution lines. Each inverter uses a localized droop control scheme with the associated voltage and frequency measurements obtained through the application of an enhanced phase locked loop. Previous work on this topic has focused on single inverters connected to an infinite bus without modeling of delays from a phase locked loop implementation. This proposed method overcomes both of these limitations of previous research. A detailed large-signal simulation of a three-bus interconnected power system is analyzed under two different network admittance values. Results confirm the effectiveness of the proposed stability design method.
Journal of Engineering Science and Technology , 2006,
Abstract: IEEE 802.11a is one of the latest standards to be released by the IEEE Project 802 for wireless LANs. It has specified an additional physical layer (PHY) to support higher data rates, and is termed as the orthogonal frequency division multiplexing (OFDM). In order to exploit its benefits, one of the medium access control (MAC) protocols specified in the IEEE 802.11 specification is called distributed coordination function (DCF). DCF is a carrier sense multiple access with collision avoidance (CSMA/CA) scheme with slotted binary exponential backoff. The frames can be transmitted using the basic access scheme or the RTS/CTS scheme in DCF. It was demonstrated previously that the RTS/CTS mechanism works well in most scenarios for the previously specified PHYs. In this work, a simple simulator is developed to verify the scalability of the RTS/CTS mechanism over OFDM PHY, which supports much higher data rates.
Modelling and Analysis of the Distributed Coordination Function of IEEE 802.11 with Multirate Capability  [PDF]
F. Daneshgaran,M. Laddomada,F. Mesiti,M. Mondin
Computer Science , 2008,
Abstract: The aim of this paper is twofold. On one hand, it presents a multi-dimensional Markovian state transition model characterizing the behavior at the Medium Access Control (MAC) layer by including transmission states that account for packet transmission failures due to errors caused by propagation through the channel, along with a state characterizing the system when there are no packets to be transmitted in the queue of a station (to model non-saturated traffic conditions). On the other hand, it provides a throughput analysis of the IEEE 802.11 protocol at the data link layer in both saturated and non-saturated traffic conditions taking into account the impact of both transmission channel and multirate transmission in Rayleigh fading environment. Simulation results closely match the theoretical derivations confirming the effectiveness of the proposed model.
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