Performance Evaluation (performance + evaluation)

Distribution by Scientific Domains
Distribution within Engineering

Kinds of Performance Evaluation

  • relative performance evaluation

  • Selected Abstracts


    Tobias Johansson
    One of the more lasting imprints that New Public Management (NPM) has made in the public sector is an increase in the popularity of performance measurement. In Sweden, performance measurement has gained popularity in the public sector, not least at the local government level with the use of relative performance evaluation (RPE). Because utilization of RPE is a decentralized and optional mode of governance, a somewhat heterogeneous practice has evolved. The aim of this paper is to examine the causes of this differentiated practice. We jointly examine economic, political and institutional/cultural explanations in order to account for the utilization of RPE. The empirical material consists of archival data and a questionnaire sent to all Swedish municipalities in late 2005. We show that RPE adoption and use partly has different antecedents and that the institutional/cultural perspective appears to have greater explanatory power than economic and political, not least as a consequence of the potential to explain decoupling and the importance of change facilitating capabilities. The investigation contributes specifically to the literature on the utilization of RPE in local governments and more generally to the literature on why and to what extent management accounting practices are utilized. [source]

    An Agency Theory Perspective on Student Performance Evaluation

    Michael E. Smith
    ABSTRACT The emphasis in recent research on the responsibility of college and university business instructors to prepare students for future employment underscores a need to refine the evaluation of student performance. In this article, an agency theory framework is used to understand the trade-offs that may be involved in the selection of various approaches to student evaluation. Understanding these trade-offs may be particularly important as faculty members seek to balance competing obligations, such as research and service requirements, while ensuring instructional effectiveness. This article presents propositions for examining how various institutional, instructor, and student characteristics influence the selection and use of student performance evaluation techniques (i.e., exams, papers, and group assignments). In conclusion, we suggest that agency theory may serve as a foundation for understanding current evaluation practices and guiding instructors in their selection of appropriate evaluation mechanisms. [source]

    Performance Evaluation of the KEOPS Wavelength Routing Optical Packet Switch

    Philippe Cadro
    This paper presents results concerning the performance evaluation of the KEOPS wavelength routing optical transparent packetswitch. This switch solves contention using optical delay lines; these delay lines are grouped in several sets, in the first stage of the switch. Each input port has access to a few of these delay lines, and each set of delay lines has access to each output port. Non-FIFO output buffers are thus emulated using scheduling on a small number of delay lines with non-consecutive delays. Under simplifying assumptions, analytical models are derived, and checked by simulation. These models provide efficient bounds for estimating packet loss probability, under the assumption of regular, balanced input traffic. It is shown that the proposed switch architecture achieves a good performance in terms of packet loss, with a number of delay lines significantly smaller than the ones currently used in other architectures. [source]

    Split agent-based routing in interconnected networks

    Constandinos X. Mavromoustakis
    Abstract Adaptive behaviour of swarm-based agents (BT Technol. J. 1994; 12:104,113; AAMAS Conference '02, Melbourne, Australia, Month 1,2, 2002; Softcomput. J. 2001; 5(4):313,317.) is being studied in this paper with respect to network throughput for a certain amount of data traffic. Algorithmically complex problems like routing data packets in a network need to be faced with a dynamically adaptive approach such as agent-based scheme. Particularly in interconnected networks where multiple networks are participating in order to figure a large-scale network with different QoS levels and heterogeneity in the service of delay sensitive packets, routing algorithm must adopt in frequent network changes to anticipate such situations. Split agent-based routing technique (SART) is a variant of swarm-based routing (Adapt. Behav. 1997; 5:169,207; Proceedings of 2003 International Symposium on Performance Evaluation of Computer and Telecommunication Systems,SPECTS, Montreal, Canada, July 20,24, 2003; 240,247.) where agents are split after their departure to the next node on a hop-by-hop basis. Packets that are delay sensitive are marked as prioritized which agents recognize-as being a part of a packet- and try to influence the two-way routing tables. Thorough examination is made, for the performance of the proposed algorithm in the network and the QoS offered, taking into account a number of metrics. It is shown that the split agent routing scheme applied to interconnected networks offers a decentralized control in the network and an efficient way to increase overall performance and packet control reducing at the same time the packet loss concept. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    The Effect of Accuracy of Performance Evaluation on Learning From Experience: The Moderating Role of After-Event Reviews

    Shmuel Ellis
    Two studies (one field, one experimental) found that the more accurately individuals evaluated their performance, the better they performed on a subsequent task. The first study also found that the more individuals overestimated their previous performance, the lower was their performance on the next task. In contrast, the evaluation accuracy of the underestimators was unrelated to their subsequent performance. The second study found that when participants received feedback from an external authority, the effect of the inaccuracy of self-performance evaluation on subsequent performance was reduced. The results of the 2 studies are explained in motivational and cognitive terms. [source]

    Relative Performance Evaluation of Mutual Funds: A Non-Parametric Approach

    Yoon K. Choi
    We propose an alternative mutual fund performance index which addresses the benchmark problem and controls for economies of scale in managing mutual funds. We advance a new concept of ,return-cost' efficiency as another important element in evaluating portfolio management, in addition to the mean-variance efficiency concept. Our index based on a non-parametric estimation is shown to be similar to the Sharpe index with multiple slopes (or factors). We have shown that all fund categories, except income funds, have similar average efficiency scores after controlling for economies of scale. Most funds operate in increasing returns to scale and seem to be successful in holding mean-variance efficient portfolios, but unsuccessful in allocating transaction costs efficiently, evidenced by excessive turnovers and loads. [source]

    Single Laboratory Method Performance Evaluation for the Analysis of Total Food Folate by Trienzyme Extraction and Microplate Assay

    L. Chen
    ABSTRACT:, Single laboratory method performance parameters, including the calibration curve, accuracy, recovery, precision, limit of detection (LOD), and limit of quantification (LOQ), were evaluated for the analysis of total food folate by the trienzyme extraction and microplate assay with Lactobacillus casei subsp. rhamnosus. Standard Reference Material (SRM) 1546 (meat homogenate), SRM 2383 (baby food composite), SRM 1846 (infant formula), Certified Reference Material (CRM) 121 (wholemeal flour), and CRM 485 (mixed vegetables), representing a broad selection of food matrices, were used to evaluate the performance of the method. A generated 4-parameter logistic equation of the calibration curve was y= (0.0705 , 1.0396)/(1 + (x/0.0165) 1.3072) + 1.0396 (P < 0.0001). The test of parallelism demonstrated that matrix components in the food extracts did not affect the accuracy. Measured values of the SRMs and CRMs were within their certified or reference values. Recoveries for all reference materials met the requirements of the AOAC guidelines for single laboratory validation. Precision measured as repeatability, including simultaneous and consecutive replicates for each SRM and CRM, met the Horwitz criterion. LOD and LOQ values were 0.3 and 0.6 ,g/100 g, respectively. The results showed that trienzyme digestion using ,-amylase, PronaseR, and conjugase from chicken pancreas coupled with a 96-well microplate assay provided a highly accurate, reproducible, and sensitive method for the determination of folate in a variety of foods. [source]

    Performance Evaluation of the Scent Transfer UnitÔ (STU-100) for Organic Compound Collection and Release

    Brian A. Eckenrode Ph.D.
    ABSTRACT: The Scent Transfer UnitÔ (STU-100) is a portable vacuum that uses airflow through a sterile gauze pad to capture a volatiles profile over evidentiary items for subsequent canine presentation to assist law enforcement personnel. This device was evaluated to determine its ability to trap and release organic compounds at ambient temperature under controlled laboratory conditions. Gas chromatography-mass spectrometry (GC-MS) analyses using a five-component volatiles mixture in methanol injected directly into a capture pad indicated that compound release could be detected initially and 3 days after the time of collection. Additionally, 15 compounds of a 39-component toxic organic gaseous mixture (10,1000 parts per billion by volume [p.p.b.v]) were trapped, released, and detected in the headspace of a volatiles capture pad after being exposed to this mixture using the STU-100 with analysis via GC-MS. Component release efficiencies at ambient temperature varied with the analyte; however, typical values of c. 10% were obtained. Desorption at elevated temperatures of reported human odor/scent chemicals and colognes trapped by the STU-100 pads was measured and indicated that the STU-100 has a significant trapping efficiency at ambient temperature. Multivariate statistical analysis of subsequent mass spectral patterns was also performed. [source]

    The Impact of Same-Sex LMX Dyads on Performance Evaluations

    Arup Varma
    Numerous studies have found that supervisors rate women lower than men for similar levels of performance, suggesting that for female employees, performance alone may not be able to guarantee fair ratings. What is not clear is whether this disparity is a function of the gender composition of the supervisor,subordinate dyad or simply a case of male supervisor rating behavior. Based on data from supervisor,subordinate dyads in four organizations, we found that after controlling for performance, both male and female supervisors exhibit a positive bias toward subordinates of the same sex and rate members of the same gender higher. © 2001 John Wiley & Sons, Inc. [source]

    The Effects of Race and Worker Productivity on Performance Evaluations

    Marta Elvira
    Using personnel data from a large firm, we examine the role of race, supervisor's race, and worker productivity on performance ratings for a diverse employee population. Controlling for worker productivity and other demographic variables, black employees receive lower ratings than whites. These differences in performance evaluations are associated with the racial composition of the subordinate-supervisor pair. Racial differences between subordinate and supervisor lead to lower ratings for both black and white subordinates. [source]

    Performance evaluation of an autonomic network-aware metascheduler for Grids

    A. Caminero
    Abstract Grid technologies have enabled the aggregation of geographically distributed resources in the context of a particular application. The network remains an important requirement for any Grid application, as entities involved in a Grid system (such as users, services, and data) need to communicate with each other over a network. The performance of the network must therefore be considered when carrying out tasks such as scheduling, migration or monitoring of jobs. Surprisingly, many existing quality of service efforts ignore the network and focus instead on processor workload and disk access time. Making use of the network in an efficient and fault-tolerant manner is challenging. In a previous contribution, we proposed an autonomic network-aware scheduling architecture that is capable of adapting its behavior to the current status of the environment. Now, we present a performance evaluation in which our proposal is compared with a conventional scheduling strategy. We present simulation results that show the benefits of our approach. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Performance evaluation of the SX-6 vector architecture for scientific computations

    Leonid Oliker
    Abstract The growing gap between sustained and peak performance for scientific applications is a well-known problem in high-performance computing. The recent development of parallel vector systems offers the potential to reduce this gap for many computational science codes and deliver a substantial increase in computing capabilities. This paper examines the intranode performance of the NEC SX-6 vector processor, and compares it against the cache-based IBM Power3 and Power4 superscalar architectures, across a number of key scientific computing areas. First, we present the performance of a microbenchmark suite that examines many low-level machine characteristics. Next, we study the behavior of the NAS Parallel Benchmarks. Finally, we evaluate the performance of several scientific computing codes. Overall results demonstrate that the SX-6 achieves high performance on a large fraction of our application suite and often significantly outperforms the cache-based architectures. However, certain classes of applications are not easily amenable to vectorization and would require extensive algorithm and implementation reengineering to utilize the SX-6 effectively. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Performance evaluation of steel reduced flange plate moment connections

    Chung-Che Chou
    Abstract This study details a new moment connection that overcomes difficulties in achieving field-weld quality and eliminates steel beam buckling encountered in steel moment connections. This study presents cyclic test and finite element analysis results of full-scale subassemblies using steel reduced flange plates (RFPs) to connect steel beam flanges and the column without any other direct connection. Since the RFP connection is designed as strong column-strong beam-weak RFPs, the RFP functions as a structural fuse that eliminates weld fractures and beam buckling. Test and analytical results show that (1) the connections transferred the entire beam flexural strength to the column and reached an interstorey drift of 4% with minor strength degradation, (2) failure of the connections was owing to buckling or fracturing of the RFP and not of the beam, and (3) the RFP connection subassembly, modelled using the nonlinear finite element computer program ABAQUS, exhibited hysteretic behaviour similar to that of the flange plate (FP) moment connection subassembly. The inelastic buckling force of the RFP was also evaluated by nonlinear regression analyses performed on a nonlinear model that relates buckling force to RFP geometries. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Cover Picture: Electrophoresis 8'2010

    ELECTROPHORESIS, Issue 8 2010
    Article first published online: 20 APR 2010
    Issue no. 8 is a regular issue comprising19 manuscripts distributed over four distinct parts. Part I is on proteins and proteomics and has 5 articles; Part II is on nucleic acids with 5 articles on DNA purification, sequencing, genotyping and differential gene expression; Part III has 4 articles on droplet dispensing and particle separation; Part IV is on various methodologies and applications assembling 5 articles on improved sample preparation method for glycan analysis by CE, measurement of intracellular accumulation chemotherapeutic drugs in cancerous cells, metabolic monitoring in microfluidic cell arrays, microchip electrophoresis for continuous monitoring of microdialysis samples, and determination of glyphosate and its metabolites in plant materials by CE. Featured articles include: Delta2D and Proteomweaver: Performance evaluation of two different approaches for two-dimensional electrophoresis analysis. ((10.1002/elps.200900766)) A Multidimensional Electrophoretic System of Separation for the Analysis of Gene Expression (MESSAGE). ((10.1002/elps.200900624)) Particle trapping using dielectrophoretically patterned carbon nanotubes. ((10.1002/elps.200900717)) [source]

    Gallager bounds on the performance of maximum-likelihood decoded linear binary block codes in AWGN interference

    Shahram Yousefi
    Performance evaluation of maximum-likelihood (ML) soft-decision-decoded binary block codes is usually carried out using bounding techniques. Many tight upper bounds on the error probability of binary codes are based on the so-called Gallager's first bounding technique (GFBT). In this method, Gallager bisects the error probability to the joint probability of error and noise residing in a region , (here referred to as the Gallager region) plus joint probability of error and noise residing in the complement of , (also referred to as regions of many and few errors, respectively); where , is a volume around the transmitted codeword. In this tutorial review, a comprehensive study of a number of upper bounds on the error probability of ML decoding of binary codes based on GFBT is provided. For some bounds, their applicability to other schemes is also pointed out and argued. We also provide an overview of bounds based on Gallager's second bounding technique (GSBT) and discuss some of their relations and interconnections. Copyright © 2006 AEIT [source]

    Performance evaluation of heat exchanger using alternative refrigerant R407C

    Masayuki Nonaka
    Abstract R22 (HCFC22) has been widely used as the refrigerant in air conditioners. According to the Montreal protocol for ozone layer protection, the total production of HCFCs has been capped since the beginning of 1996. Zeotropic refrigerant mixture R407C and nearly azeotropic refrigerant mixture R410A have been selected as alternatives to R22. We examined refrigerant passages in heat exchangers used in heat pump-type room air conditioners using zeotropic refrigerant R407C through simulation, and obtained the following conclusions. In an indoor heat exchanger, a counter flow configuration when operating as a condenser has higher temperature efficiency. When an outdoor heat exchanger operates as an evaporator, a configuration that suppresses the temperature glide by partially reducing the refrigerant passage not only produces high efficiency, but also reduces the frost formation on fins. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(8): 626,638, 2002; Published online in Wiley InterScience ( DOI 10.1002/htj.10064 [source]

    Performance evaluation for asynchronous MC-CDMA systems with a symbol timing offset

    Myonghee Park
    Abstract This paper models a symbol timing offset (STO) with respect to the guard period and the maximum access delay time for asynchronous multicarrier-code division multiple access systems over frequency-selective multipath fading channels. Analytical derivation shows that STO causes desired signal power degradation and generates self-interferences. This effect of the STO on the average bit error rate (BER) and the effective signal-to-noise ratio (SNR) is evaluated using the semi-analytical method, and the approximated BER and the SNR loss caused by STO are then obtained as closed-form expressions. The tightness between the semi-analytical result and the approximated one is verified for the different STOs and SNRs. Furthermore, the derived analytical results are verified via Monte Carlo simulations. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Performance evaluation of GPON vs EPON for multi-service access

    T. Orphanoudakis
    Abstract Recently both ITU and IEEE have standardized solutions for passive optical networks (PONs) operating at gigabit per second line rates and optimized for the transport of packet-based traffic to improve the efficiency of previously standardized broadband PONs, which used the ATM cell as the data transport unit. The efficiency and performance of PON systems depend on the transmission convergence layer and mainly on the implemented medium access protocol. Although the latter is not part of the standards and left to the implementer, the standards describe a set of control fields that constitute the tool-set for the media access control (MAC) operation. Though starting from a common and quite obvious basis, the two standards present significant differences with the legacy of Ethernet marking the IEEE approach, while the emphasis of ITU is on demanding services. In this paper we compare the efficiency and performance of the two systems assuming the implementation of as close as possible MAC protocols. The target is twofold: assess and compare the traffic handling potential of each of the two standards and identify the range of applications they can support. Useful insight can also be gained to the MAC tools that could be designed into the next generation extra large WDM PONs. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Performance evaluation of CSMA/ID MAC protocol for IP over WDM ring networks

    Jih-Hsin Ho
    Abstract In this paper, a packet pre-classification media access control protocol based on a carrier sense multiple access with idle detection (CSMA/ID) scheme is investigated for supporting IP packets over all-optical WDM ring networks. The purpose of the protocol is to increase throughput and to decrease the packet transmission delay of IP packets over optical networks in a metropolitan area network. This protocol avoids both packet collision and packet fragmentation. In order to improve the utilization of the network, the packets transmitted from a local area network are first pre-classified into various class queues of an access point (AP) according to their length. After checking the available space based on the wavelength received by the receivers of the AP, the packets in the queues are transmitted. An analytical model is developed to evaluate the performance of the protocol, with simulation results showing good network efficiency. The proposed network has short-term variations that introduce unfairness conditions. This problem could be overcome by assigning a quota on individual queues to allow all queues fair access. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Delay aware reliable transport in wireless sensor networks

    Vehbi C. Gungor
    Abstract Wireless sensor networks (WSN) are event-based systems that rely on the collective effort of several sensor nodes. Reliable event detection at the sink is based on collective information provided by the sensor nodes and not on any individual sensor data. Hence, conventional end-to-end reliability definitions and solutions are inapplicable in the WSN regime and would only lead to a waste of scarce sensor resources. Moreover, the reliability objective of WSN must be achieved within a certain real-time delay bound posed by the application. Therefore, the WSN paradigm necessitates a collective delay-constrained event-to-sink reliability notion rather than the traditional end-to-end reliability approaches. To the best of our knowledge, there is no transport protocol solution which addresses both reliability and real-time delay bound requirements of WSN simultaneously. In this paper, the delay aware reliable transport (DART) protocol is presented for WSN. The objective of the DART protocol is to timely and reliably transport event features from the sensor field to the sink with minimum energy consumption. In this regard, the DART protocol simultaneously addresses congestion control and timely event transport reliability objectives in WSN. In addition to its efficient congestion detection and control algorithms, it incorporates the time critical event first (TCEF) scheduling mechanism to meet the application-specific delay bounds at the sink node. Importantly, the algorithms of the DART protocol mainly run on resource rich sink node, with minimal functionality required at resource constrained sensor nodes. Furthermore, the DART protocol can accommodate multiple concurrent event occurrences in a wireless sensor field. Performance evaluation via simulation experiments show that the DART protocol achieves high performance in terms of real-time communication requirements, reliable event detection and energy consumption in WSN. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Adaptive zone routing protocol for ad hoc network nodes with non-uniform mobilities

    Xiaofeng Zhang
    Abstract In recent years, a variety of new routing protocols for mobile ad hoc wireless NETworks (MANETs) have been developed. Performance evaluation and comparison of many of these routing protocols have been performed using detailed simulation models. Zone routing protocol (ZRP) is one of these routing protocols, which is a hybrid routing protocol that proactively maintains routing information for a local neighbourhood (routing zone), while reactively acquiring routes to destinations beyond the routing zone. The studies on ZRP have assumed homogeneous scenarios where all mobile nodes have uniform mobility and are statistically identical, lacking the studies on heterogeneous scenarios where mobile nodes move with non-uniform mobilities in the same network. In this paper, we study the performance of ZRP in such scenarios. We propose an efficient scheme for ZRP to adapt to the non-uniform mobilities scenario and study its performance for different mobility scenarios, network loads and network sizes. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Performance evaluation of LIBTA/hybrid time-slot selection algorithm for cellular systems,

    Jyh-Horng Wen
    Abstract This paper studies the performance of radio assignment algorithms for portable access in cellular systems. Several channel access procedures are proposed and simulated using block oriented network simulator (BONeS) simulation of a model 36-port system. Simulation results exhibit that load-sharing system with LIBTA algorithm is better than directed retry system with the same algorithm by around 0.9 erlangs while better than quasi-fixed channel assignment (QFCA) system by around 2 erlangs if the grade of service (GOS) is constrained to less than 10 per cent. Plus, a hybrid time-slot selection procedure is proposed to enhance the system performance. It is observed that systems with hybrid time-slot selection perform better than those with LIBTA algorithm in GOS under heavy load. It is also observed that load sharing system with hybrid time-slot selection algorithm is better than directed retry system with the same algorithm by around 0.7 erlangs and better than QFCA system by around 2 erlangs. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    Performance evaluation of an electricity base load engine cogeneration system

    Denilson Boschiero do Espirito Santo
    Abstract Decentralized electricity production by cogeneration can result in primary energy economy, as these systems operate with a high-energy utilization factor (EUF), producing electricity and recovering energy rejected by the prime mover to meet site thermal demands. Because energy demands in buildings vary with such factors as the hour of the day, level of activity and climatic conditions, cogeneration case studies should consider different system configurations, energy demand profiles and climatic profiles. This paper analyzes an engine cogeneration system as an integrated thermal system by means of a computational simulation program. The simulation takes into account characteristics of the system, characteristics of the pieces of equipment, design choices and parameters, the variability of operating conditions, site energy demand profiles and climatic data to evaluate the performance of the cogeneration plant. Performance evaluation is based on: (i) the EUF, (ii) the exergy efficiency and (iii) primary energy savings analysis. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Performance evaluation of the PENTRA 60C+ automated hematology analyzer and comparison with the ADVIA 2120

    Summary The PENTRA 60C+ hematology analyzer provides a complete blood cell (CBC) count, including a five-part differential (5-DIFF) count and two leukocyte subpopulations, i.e. large immature cells (LIC's) and atypical lymphocytes (ALY's). We evaluated its analytical performance and assessed agreement with the ADVIA 2120, in order to install the analyzer in a small satellite hematology laboratory. First we assessed repeatability, reproducibility and carry-over to evaluate the analytical performance. Then we used Pearson correlation coefficients, Passing and Bablok regression analysis and a graphical approach (n = 209) to evaluate agreement with the ADVIA 2120. Repeatability and reproducibility were excellent for the majority of CBC and 5-DIFF count parameters. Carry-over was negligible. Our data showed very good correlation for most CBC count parameters. Lower correlation coefficients were observed for red cell distribution width, mean corpuscular volume and mean platelet volume. As compared to the ADVIA 2120, the 5-DIFF count performed very well. Agreement was poorer for low-level eosinophils and basophils. Furthermore, the PENTRA 60C+ was equally able to identify pathological blood samples through the determination of LIC's and ALY's. Therefore, the PENTRA 60C+ is an eligible blood cell counter to be operational in a satellite laboratory setting. [source]

    Performance evaluation of distributed multiple home agents with HAHA protocol

    Jong-Hyouk Lee
    Mobile IPv6 (MIPv6) is a protocol that supports mobility of mobile nodes (MNs) within the IPv6 environment. However, the current MIPv6 supports insufficient mobility of MNs. If an MN is moved away from the home link, it takes time for the MN to make a registration and binding update at the home agent (HA). Moreover, the Dynamic Home Agent Address Discovery (DHAAD) mechanism in MIPv6 is too slow for the MN to recover when its HA fails. To solve these two problems, we propose a Distributed Multiple Home Agents (DMHA) scheme. This scheme allows an MN to perform a binding update with the nearest HA, so that the delay in the binding update process can be reduced. It also reduces the fault rate of handoff up to about 55.5% based on the same network parameters. Numerical results presented in this paper show that our scheme has superior performance compared to the standard scheme. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Performance evaluation of TCP-based applications over DVB-RCS DAMA schemes

    M. Luglio
    Abstract Transmission Control Protocol (TCP) performance over Digital Video Broadcasting,Return Channel via Satellite (DVB-RCS) standard is greatly affected by the total delay, which is mainly due to two components, propagation delay and access delay. Both are significant because they are dependent on the long propagation path of the satellite link. The former is intrinsic and due to radio wave propagation over the satellite channel for both TCP packets and acknowledgements. It is regulated by the control loop that governs TCP. The latter is due to the control loop that governs the demand assignment multiple access (DAMA) signalling exchange between satellite terminals and the network control center, necessary to manage return link resources. DAMA is adopted in DVB-RCS standard to achieve flexible and efficient use of the shared resources. Therefore, performance of TCP over DVB-RCS may degrade due to the exploitation of two nested control loops also depending on both the selected DAMA algorithm and the traffic profile. This paper analyses the impact of basic DAMA implementation on TCP-based applications over a DVB-RCS link for a large set of study cases. To provide a detailed overview of TCP performance in DVB-RCS environment, the analysis includes both theoretical approach and simulation campaign. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Performance evaluation on a double-layered satellite network

    Feng-Ge Wu
    Abstract How to evaluate the performance of satellite networks is a prerequisite to the construction of satellite networks, and is also one of challenges in the researches on satellite networks. In this paper, generalized stochastic Petri net (GSPN) models are presented to carry out the performance analysis of a double-layered satellite network. Firstly, the GSPN model of a double-layered satellite network is simplified by proper analysis. Then, two sets of experiments are conducted to analyse the performance of the satellite networks, and show that the double-layered satellite network outperforms single-layered ones on the heavy traffic load. Finally, the feasibility and effectiveness of the proposed approach is verified by simulation experiments. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Intersegment handover performance in integrated terrestrial satellite systems

    M. Leo
    Abstract To achieve a global cellular network, integration among segments offering different coverage (indoor, outdoor and global) must be pursued. Of course, the possibility to hold the call switching among different segments must be guaranteed. Hence, efficient algorithms to perform intersegment handover (ISHO) must be implemented. The paper aims at analysing some ISHO procedures developed in the frame of some European projects and other proposed in the literature, in a scenario with satellite and terrestrial segments interworking to achieve a worldwide cellular coverage. Performance evaluation will be carried out for different system configurations utilizing a dynamic satellite constellation simulator in the time domain. The impact of the distance user-gateway on performance will be addressed. For each procedure, the execution delay and its complementary cumulative distribution have been evaluated for different constellation geometries at different distances from the gateway. Copyright © 2002 John Wiley & Sons, Ltd. [source]

    Performance evaluation of adaptive routing algorithms in packet-switched intersatellite link networks

    Mihael Mohor
    Abstract This paper addresses the performance evaluation of adaptive routing algorithms in non-geostationary packet-switched satellite communication systems. The dynamic topology of satellite networks and variable traffic load in satellite coverage areas, due to the motion of satellites in their orbit planes, pose stringent requirements to routing algorithms. We have limited the scope of our interest to routing in the intersatellite link (ISL) segment. In order to analyse the applicability of different routing algorithms used in terrestrial networks, and to evaluate the performance of new algorithms designed for satellite networks, we have built a simulation model of a satellite communication system with intersatellite links. In the paper, we present simulation results considering a network-uniform source/destination distribution model and a uniform source,destination traffic flow, thus showing the inherent routing characteristics of a selected Celestri-like LEO satellite constellation. The updates of the routing tables are centrally calculated according to the Dijkstra shortest path algorithm. Copyright © 2002 John Wiley & Sons, Ltd. [source]

    Performance evaluation of decision making strategies for an embedded lane departure warning system

    Woong Kwon
    An on-board lane departure warning system embedded in a vehicle is composed of a localization module and a decision making module. The decision making module detects unintended lane departure so as to warn the driver of the danger. The performance of a decision making module is crucial to the performance of the total embedded system. This article proposes two heuristic decision making strategies: a lateral offset (LO) based strategy and a time-to-lane crossing (TLC) based strategy. The performance criteria of decision making strategies are proposed as: (1) false alarm rate, and (2) alarm triggering time (ATT). Numerical parameters of both strategies are optimized through numerical simulation, taking the performance criteria into consideration. The proposed strategies are incorporated into the prototype system and evaluated in real expressway experiments. The comparative study of both methods with experimental results shows the applicability of the on-board lane departure warning system. © 2002 Wiley Periodicals, Inc. [source]