Number Of Potential Users Research Articles

Large-System Analysis of Multiuser Detection With an Unknown Number of Users: A High-SNR Approach

We analyze multiuser detection under the assumption that the number of users accessing the channel is unknown by the receiver. In this environment, users' activity must be estimated along with any other parameters such as data, power, and location. Our main goal is to determine the performance loss caused by the need for estimating the identities of active users, which are not known a priori. To prevent a loss of optimality, we assume that identities and data are estimated jointly, rather than in two separate steps. We examine the performance of multiuser detectors when the number of potential users is large. Statistical-physics methodologies are used to determine the macroscopic performance of the detector in terms of its multiuser efficiency. Special attention is paid to the fixed-point equation whose solution yields the multiuser efficiency of the optimal (maximum a posteriori) detector in the large signal-to-noise ratio regime. Our analysis yields closed-form approximate bounds to the minimum mean-squared error in this regime. These illustrate the set of solutions of the fixed-point equation, and their relationship with the maximum system load. Next, we study the maximum load that the detector can support for a given quality of service specified by error probability.

A General Upper Bound on the Size of Constant-Weight Conflict-Avoiding Codes

Conflict-avoiding codes are used in the multiple-access collision channel without feedback. The number of codewords in a conflict-avoiding code is the number of potential users that can be supported in the system. In this paper, a new upper bound on the size of conflict-avoiding codes is proved. This upper bound is general in the sense that it is applicable to all code lengths and all Hamming weights. Several existing constructions for conflict-avoiding codes, which are known to be optimal for Hamming weights equal to four and five, are shown to be optimal for all Hamming weights in general.

Il valore d'uso delle aree verdi : la stima dell'universo dei fruitori di alcuni parchi urbani fiorentini

The importance of the valuation of public goods is growing. In fact, only by determining the economic value of these assets is possible to determine the efficiency of the investments and of the maintenance. The problems in estimating the total economic value relate to two fundamental aspects: the choice and implementation of the more accurate evaluation methodology and the identification of the universe of users. In literature, in fact, the issue of the universe is often resolved by considering the number of potential users (be they the inhabitants of a city, a neighborhood, a street, etc..) and not the actual visitors. This leads to an underestimation or an overestimation of the use value of public goods. The objective of this research is to focus on this issue by proposing a specific methodological approach to correctly estimate the universe of the actual users of different urban green areas of Florence.

Low-complexity receivers for multiuser detection with an unknown number of active users

Optimum multiuser detection (MUD) with an unknown number of active users requires simultaneous estimation of the active-user set, their unknown parameters and their transmitted data. Recent advances in MUD have shown that optimum receivers for this system model can be obtained using random-set theory (RST), a widely used tool in radar signal processing. Despite the capability of generalizing standard MUD to the case of unknown number of users, RST offers a way to perform detection of user log in and out by means of Bayesian recursions (BR). While previous works have concentrated on the definition of optimal detectors, design of efficient receivers was not addressed. Indeed, implementation of optimum detectors may be limited by their complexity, which grows exponentially with the number of potential users. The aim of this paper is to show that this computational burden can be drastically reduced, with little or no loss of performance, by applying a suitable version of the sphere detection (SD) algorithm. If users’ continuous parameters are known, SD algorithm allows exact implementation of the optimal detector under one-shot scenarios at polynomial complexity for moderate signal-to-noise ratio (SNR), while requiring a suitable approximation of BRs in a dynamic environment. The approach is also extended for cases wherein continuous parameters are unknown. The developed detectors are compared against their optimal counterparts and their effectiveness is shown through numerical simulations.

The GENIUS Grid Portal and robot certificates: a new tool for e-Science

BackgroundGrid technology is the computing model which allows users to share a wide pletora of distributed computational resources regardless of their geographical location. Up to now, the high security policy requested in order to access distributed computing resources has been a rather big limiting factor when trying to broaden the usage of Grids into a wide community of users. Grid security is indeed based on the Public Key Infrastructure (PKI) of X.509 certificates and the procedure to get and manage those certificates is unfortunately not straightforward. A first step to make Grids more appealing for new users has recently been achieved with the adoption of robot certificates.MethodsRobot certificates have recently been introduced to perform automated tasks on Grids on behalf of users. They are extremely useful for instance to automate grid service monitoring, data processing production, distributed data collection systems. Basically these certificates can be used to identify a person responsible for an unattended service or process acting as client and/or server. Robot certificates can be installed on a smart card and used behind a portal by everyone interested in running the related applications in a Grid environment using a user-friendly graphic interface. In this work, the GENIUS Grid Portal, powered by EnginFrame, has been extended in order to support the new authentication based on the adoption of these robot certificates.ResultsThe work carried out and reported in this manuscript is particularly relevant for all users who are not familiar with personal digital certificates and the technical aspects of the Grid Security Infrastructure (GSI). The valuable benefits introduced by robot certificates in e-Science can so be extended to users belonging to several scientific domains, providing an asset in raising Grid awareness to a wide number of potential users.ConclusionThe adoption of Grid portals extended with robot certificates, can really contribute to creating transparent access to computational resources of Grid Infrastructures, enhancing the spread of this new paradigm in researchers' working life to address new global scientific challenges. The evaluated solution can of course be extended to other portals, applications and scientific communities.

A hierarchical, agent-based service oriented architecture for smart environments

Service Oriented Architectures, which allow for the integration of different subsystems and of applications running on different devices and platforms, may be very suitable to solve the problem of service personalization in large smart environments like cities, where the number of potential users and potentially available services is rapidly growing. Taking this into account, we have designed an agent-based service oriented architecture for smart spaces. Two of the greatest challenges in the design of such a solution are providing effective device, service and context federation and composition mechanisms and handling user mobility. For the first challenge, we have designed a hierarchical architecture and developed a set of inheritance, aggregation and access mechanisms for devices, services and context. To handle user mobility, we have followed three different strategies, using stationary, mobile or nomadic agents. In this paper, we describe the main aspects of our architecture and perform an experimental evaluation to determine the advantages and drawbacks of the different strategies.

Some aspects in photogrammetry education at the department of geodesy and cadastre of the VGTU

Abstract The education in photogrammetry is very important when applying photogrammetric methods for the terrain mapping purposes, for spatial data modelling, solving engineering tasks, measuring of architectural monuments etc. During the time the traditional photogrammetric technologies have been changing to modern fully digital photogrammetric workflow. The number of potential users of the photogrammetric methods tends to increase, because of high‐degree automation in photographs (images) processing. The main subjects in Photogrammetry (particularly in Digital Photogrammetry) educational process are discussed. Different methods and digital systems are demonstrated with the examples of aerial photogrammetry products. The main objective is to search the possibilities for training in the photogrammetric measurements. Special attention is paid to the stereo plotting from aerial photography applying modified for teaching analytical technology. The integration of functionality of Digital Photogrammetric Syste...

Collusion-Resistant Video Fingerprinting for Large User Group

Digital fingerprinting protects multimedia content from illegal redistribution by uniquely marking copies of the content distributed to users. Most existing multimedia fingerprinting schemes consider a user set on the scale of thousands. However, in such real-world applications as video-on-demand distribution, the number of potential users can be as many as 10-100 million. This large user size demands not only strong collusion resistance but also high efficiency in fingerprint construction, and detection, which makes most existing schemes incapable of being applied to these applications. A recently proposed joint coding and embedding fingerprinting framework provides a promising balance between collusion resistance, efficient construction, and detection, but several issues remain unsolved for applications involving a large group of users. In this paper, we explore how to employ the joint coding and embedding framework and develop practical algorithms to fingerprint video in such challenging settings as to accommodate more than ten million users and resist hundreds of users' collusion. We investigate the proper code structure for large-scale fingerprinting and propose a trimming detection technique that can reduce the decoding computational complexity by more than three orders of magnitude at the cost of less than 0.5% loss in detection probability under moderate to high watermark-to-noise ratios. Both analytic and experimental results show a high potential of joint coding and embedding to meet the needs of real-world large-scale fingerprinting applications.

Lightweight autonomic dissemination of entertainment services in widescale wireless environments

The spread of wireless portable devices is opening new market opportunities to provide entertainment services to a growing number of potential users. A notable deployment scenario is represented by limited spatial regions, such as stadiums, railway stations, and airports, with a high number of simultaneously present mobile wireless peers (dense MANETs). The provisioning of entertainment services (e.g., the distribution of news, movie trailers, songs, and game components) in dense MANETs is a challenging task, hard to achieve in a scalable way with traditional static network infrastructures. We propose lightweight autonomic dissemination of entertainment services that exploits impromptu collaborations among mobile wireless peers to replicate resources in an efficient and lazily consistent way. In particular, we have developed the REDMAN middleware to manage, retrieve, and disseminate replicas of data/service components transparently from the point of view of service developers, thus facilitating the realization of widescale entertainment services. REDMAN implements novel lightweight solutions to identify dense MANETs, maintain the desired resource replication degree, and efficiently perform resource retrieval, by exploiting the assumptions of relatively high and almost constant node density to achieve scalability and limited network overhead.

A knowledge‐based expert system for dyeing of cotton. Part 2: Testing and evaluation

The diagnosis of a number of faulty dyed samples and faults obtained from case studies was carried out by both human experts and the expert system developed in this study, and their performance was compared. An evaluation copy of the software was provided to a number of potential users to obtain feedback on the utility and the helpfulness of the system. The results show highly satisfactory performance when compared to human experts as well as considerable utility potential, providing further impetus for further improvements in the system.

Commons with increasing marginal costs: random priority versus average cost*

Indivisible units are produced with increasing marginal costs. Under average cost, each user pays average cost. Under random priority, users are randomly ordered (without bias) and successively offered to buy at the true marginal cost. Both average cost (AC) and random priority (RP) inefficiently overproduce. RP tends to overproduce less, but which game collects more surplus depends much on the demand configuration. We show that a key to compare the welfare properties of the two mechanisms is the crowding factor, i.e., the number of potential users over the number of units of output users can afford: The more crowded the commons, the more RP outperforms AC. In the quadratic cost case, beyond the threshold value of 2.4 for the crowding factor, RP strongly outperforms AC; beneath it AC only mildly outperforms RP. Thus the RP mechanism manages crowded commons better than AC.

Intelligent Simulation of Multibody Dynamics: Space-State and Descriptor Methods in Sequential and Parallel Computing Environments

Real-time dynamic simulation of large, realistic and complexmultibody systems is essential in developing modern technologies such asvirtual prototyping, man-in-the-loop simulators and intelligent vehiclecontrol systems. In order to achieve real-time performance, currentcommercial codes require the use of large costly computers, thuslimiting the number of potential users. This paper shows thatreal-time can be achieved on medium-size workstations if, on the onehand, an adequate combination of modeling, dynamic formulation, andnumerical integration scheme is selected and, on the other hand,advantage is taken of sparse matrix technology and parallel computing. Astudy of space-state and descriptor methods involving the dynamics of awhole vehicle model is carried out and in conclusion, two methods areproposed as the best candidates for real-time simulation.

Free Access to the Commons: Random Priority versus Average Cost

A technology with increasing marginal costs produces indivisible units of service. Each agent wants at most one unit of service. We compare two natural mechanisms where users have free access to the technology. In one mechanism, Average Cost, each user pays the same average cost, in the other, Random Priority, users are randomly ordered (without bias) and successively offered to buy at the true marginal cost. Both mechanisms, AC and RP, lead to inefficient overproductions. Which one leads to a less severe tragedy ? We show that RP tends to overproduce less but that which game collects more social surplus depends much on the configuration of the demand (namely the social value of the goods produced). We give general results as well as canonical examples, describing demand and cost profiles for which one mechanism outperforms the other. We find that the key element for the comparison is the crowding ratio, i.e., the number of potential users over the number of units of output users can afford: (1) we prove that the more crowded the commons, the more RP outperforms AC, and (2) we exhibit a threshold value of 2.4 for the crowding ratio beyond which RP strongly outperforms AC, and beneath which AC only mildly outperforms RP. Thus the Random Priority mechanism offers a (partial) probabilistic resolution of the tragedy of crowded commons.

Electronic money and the network externalities theory: lessons for real life

The aim of this paper is to show that the network externalities theory provides a useful framework to analyse the introduction and further development of the new electronic payment instruments currently being launched. To that end the paper presents a pragmatic (and selective) reading of the network externalities literatures i.e., it screens the literature in search of both theoretical insights and empirical results which can be transposed to the case of electronic payment instruments. In so doing, the paper concentrates on the so-called electronic money products and, especially, on electronic purses. Specifically the paper shows that the network externalities literature provides a number of useful insights concerning consumer reactions to the introduction of electronic purses (and the ways in which card issuers can anticipate these reactions) and concerning the strategies card issuers may follow in a competitive market with incompatible electronic purses. All this is substantiated by multiple references to real-life situations. The first section of the paper defines the concept of network externalities. The third section demonstrates that payment cards in general are indeed network goods. It also points out which kind(s) of network effects apply to the electronic purses currently available. The paper then goes on to answer five questions in depth. Firstly, what can we learn from the network externalities literature as far as the ‘chicken-and-egg’ problem is concerned? – the problem being: merchants will not invest in terminals without a sufficient number of potential users, while the general public will not use electronic purses unless there is sufficient acceptance. Secondly, is there room for more than one incompatible electronic purse, or is the electronic purse market prone to ‘tipping’ and ‘lock-in’? Thirdly, can an electronic purse issuer gain a (decisive) first-mover advantage by entering the market before others do? Fourthly, under which conditions will card issuers be inclined to make their electronic purses compatible? And finally, what is the optimum pricing strategy for an electronic purse issuer?

Locating Consumer Health Information on U.S. Federal Agency Web Sites

Abstract In the continuing tradition of the Federal Depository Library program, many federal agencies are increasing the number of potential users by providing their publications on the Internet. As the number of Internet sites continues to grow exponentially, users find it difficult to locate Web sites that are information sources rather than lists of links. Librarians can educate their users about evaluating information from the Internet for validity. This article will examine several of the richest consumer health information sites from the U.S. federal government and will suggest search strategies to help the user find what he's looking for within them.

NICU-Net: An Electronic Forum for Neonatology

The neonatology list server NICU-Net was created over a year ago at the University of Washington as an international forum for neonatologists and other neonatal health care providers. The stated purpose was discussion of neonatal issues such as: recently published trials and recommendations, proposed or ongoing multicenter trials, dilemmas in diagnosis, management and ethics, and the effects of health care reform on neonatology. Much like the forums of Rome, NICU-Net was intended to be a "place" of public assembly for discussion and debate. To allow access to the greatest number of potential users, it was set up as a mailing list server that allows anybody with Internet electronic mail (E-mail) access to participate.

Empirical studies and intelligent language tutoring

The research described in this paper addresses how a language tutoring system tackles a practical problem in learning a language — negative transfer (mother tongue influence). The empirical studies we have undertaken indicate that negative transfer is the most obvious explanation for most of the errors committed by first-year students in their study of Chinese grammar at the University of Durham. The results of our empirical studies accord with the views of experts on both negative transfer and the Chinese language. A language tutoring prototype (the Chinese Tutor) has been designed on the basis of the results of the empirical studies. The Chinese Tutor contains five models: the expert model, the student model, the diagnoser, the tutor model and the interface module. The five models work effectively together in order to ensure a successful tutorial session. A number of potential users from the Department of East Asian Studies at the University of Durham have used the Chinese Tutor with positive results. In this paper, we will first address issues in relation to empirical studies: the significance of empirical studies and the results of the empirical studies. We will then move on to some of the important design issues, i.e., how the problem of negative transfer is tackled by the Chinese Tutor, which includes discussions on how the rules in the mixed grammar are used for detecting arbitrary transfer errors; how the types of error made by the student are inferred; and how an appropriate tutorial strategy is selected. Finally, a tutorial session run by one of the students who has used the Chinese Tutor is presented and what the Chinese Tutor can offer to the students will also be addressed.

Logiciel sans frontieres

In general terms, nations that have taken the step of introducing computing into the curriculum, in whatever form, will identify the shortage of educational software as one of the reasons why development is slow, children and teachers are not motivated and the technology is being under-exploited. The cost of developing new educational software is rising rapidly and even in the English or Spanish speaking worlds, where the numbers of potential users are large, the economies of scale are not sufficient to encourage developmental growth. The last 2 or 3 yr have seen the implementation of a number of projects aimed at increasing the access to software in a variety of languages and cultures. The authors review a number of these projects, particularly the European Community initiative EPES (European Pool of Educational Software), involving 12 nations and 15 languages. A number of barriers such as machine configuration and language, cultural and curriculum issues, graphics, written language and character sets, documentation and machine capacity are addressed. None are found to be insurmountable. The ownership and copyright issues in the European and world-wide context are considered together with the publishing opportunities. In conclusion, the authors argue for a wider network of educational software exchange both within Eastern and Western Europe and the other five continents. To achieve this ideal, some standards need to be agreed and these are considered in the conclusions.

A model for forecasting public transit

This study develops a model that explains public transit ridership in Orange Country, California over quarterly periods during the 1974–1988 period. The model uses a Cobb-Douglas functional form and a Cochrane-Orcutt iterative procedure to measure the association between public transit ridership and the potential number of users, relative level of public transit service, relative price of public transit, seasonality, and external shocks. Relative measures of the explanatory variables are used to reduce the potential for multicollinearity and give greater confidence in the reliability of the estimated elasticities. The model is then used to prepare conditional quarterly forecasts for ridership in 1988 and unconditional quarterly forecasts during the 1989–1993 period.

Questions of liability in the provision of information services

Today the total number of databanks is still increasing and online information providers are facing quasi‐unlimited opportunities to expand their services both on a national and an international level. Unfortunately for databank producers this also means increasing the risk of liability as the number of potential users and kind of uses of the information is growing. This risk of liability is not a fiction. The user expects the information he receives to be reliable and accurate. In case of unreliability or inaccuracy, he will blame the person who provided him with the information.